domain: phys sdv

text:
B , M.D Camille A Apamon
email: camille.apamon@insa-rennes.fr

Frédéric Marie
email: frederic.marie@insa-rennes.fr

Mathieu Miroir
email: mathieu.miroir@univ-rennes1.fr

Ronan Le Breton
email: ronan.le-breton@insa-rennes.fr

Eric A Courteille
email: eric.courteille@insa-rennes.fr

Dr Bruno B Fournier
email: bruno.fournier@robocath.com

Marie Frédéric

Miroir Mathieu

Assoc Prof
email: .prof@insa-rennes.fr

Eng

Screening of factors influencing catheter rotation of a vascular interventional surgical robot using design of experiment approach

ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Cardiovascular diseases, including ischaemic heart diseases and strokes remain the leading cause of death worldwide [START_REF] Katan | Global burden of stroke[END_REF]. Coronary angioplasty, coiling and mechanical thrombectomy are the gold standard procedures to treat these diseases and involve inserting guidewires and catheters into the patient's vascular system. To see the devices progressing through the body, physicians need to inject a contrast agent (iodine) and use X-rays-based techniques such as fluoroscopy. Thus, radiation exposure and musculoskeletal disorders justify the use of Vascular Interventional Surgery Robots (VISRs) [START_REF] Benjamin | Ergonomics in the development and prevention of musculoskeletal injury in interventional radiologists[END_REF] , which also increase positioning accuracy and improve patient care.

In this paper, the patented manipulation principle of the R-One™ robot, designed by Robocath and which has already been shown to be safe and effective on Human [START_REF] Robocath | Robocath demonstrates safety and efficacy of R-One[END_REF], is investigated. This method mimics the movements of the physician pushing and rolling the catheter by squeezing it between his or her thumb and forefinger. The physician's fingers are replaced by two planar surfaces called "pads" to perform millimetric tasks with high accuracy and repeatability. Each pad has three translational degrees of freedom (DOF), one of which manages the clamping and unclamping of the device along the 𝑦 ⃗ axis of Figure 1.

Figure 1 -The studied method for the rotational manipulation of catheters, from the Robocath patent [START_REF] Deboeuf | Robotic method for driving a catheter and a catheter guide[END_REF] The translation is simply achieved by moving the two clamped pads along the axis of the device (𝑥 ⃗ axis of Figure 1). The rotation of the device is achieved by rolling it between the two pads moving vertically in an asymmetrical way along the 𝑧 ⃗ axis, as explained in Figure 1. The force applied by the robot pads on the device along the 𝑦 ⃗ axis is called "clamping force" while the force applied along the 𝑧 ⃗ axis is called "transverse force".

To successfully perform the procedure, the robot will need to transmit sufficient axial force and torque to the catheter. The quantification of the required torque on the device is the subject of the first paragraph of this article. Then, to determine the specifications of the robot, these forces expressed at the catheter level will have to be translated to the pads level to determine the forces required on each of the 𝑥 ⃗, 𝑦 ⃗ and 𝑧 ⃗ axis. Assuming that there is no slippage between the pads and the catheter, the force required on the 𝑥 ⃗ axis will be directly equal to the axial force required on the catheter. On the other hand, the rotation of the catheter induces a multifactorial phenomenon which is the rolling, and which will be specifically studied in this article.

The objective of this paper is to provide a generic approach to optimise the gripping and manipulation performance of a VIRS, as well as to determine its technical specifications in terms of the forces required on the end effector, that is the pads, with a particular focus on the most complex movement which is the rotation of the catheter. Since the overall goal is to miniaturise the robot, these forces must also be minimised.

Beyond the numerical results and observations, the contribution of this paper is to provide a standard process for characterising the forces involved in the rolling of a medical device between two planar surfaces. The key steps of this proposed process are the following:

1-Identification of the parameters to be studied. In the first part of this article, the physician's gestures are under study, and the torque required to manipulate a catheter in rotation is quantified. The first step of the proposed process is also addressed in this first part, by studying the rolling phenomenon in order to deduce the gripping parameters to be studied. These parameters will be the factors of the DOE developed in this paper, the objective of which is to find an optimal combination of these factors in order to maximise the torque applied to the catheter and minimise the forces developed at the end effector.

The second and third steps are dealt within the second part of this article, through the description of the developed test bench, as well as its characterisation in terms of reproducibility of measurements. The test protocol will also be described in this part.

The third part of this article will be devoted to the fourth and fifth steps of the process, by presenting general trends of the DOE results and by verifying the obtained models.

Finally, in the fourth part, the response surface graphs will be used to determine the optimal combination of factors, and the results and limitations of this study will be discussed.

Context of the study

Operating torques for catheters manipulation

The required forces to handle rotating catheters are complex to quantify, due to the large number of factors impacting their values [START_REF] Du | Exploration of Interventionists' Technical Manipulation Skills for Robot-Assisted Intravascular PCI Catheterization[END_REF]. Indeed, between the physician's hands and the distal end of the catheter located into the patient's body, the catheter is subjected to resistive forces that can be classified into four categories [START_REF] Yang | Operation and Force Analysis of the Guide Wire in a Minimally Invasive Vascular Interventional Surgery Robot System[END_REF], [START_REF] Guo | A novel robot-assisted endovascular catheterization system with haptic force feedback[END_REF], [START_REF] Sankaran | Design and development of surgeon augmented endovascular robotic system[END_REF]: the frictional forces between the manipulated device and others devices (introducer sheath, haemostasis valve…), the contact and collision forces between the distal end of the catheter and the vessel walls, the frictional forces between the surfaces of the catheter (along its length) and the vessel walls and the viscous resistance forces caused by the viscosity of the blood.

As the robot is located at the proximal end of the catheter and it must reproduce the movements the physician's hands, the values retained correspond to the measurements made on the physician's hands in the literature [START_REF] Rafii-Tari | Assessment of navigation cues with proximal force sensing during endovascular catheterization[END_REF]- [START_REF] Wang | Toward In-Vivo Force and Motion Measurement for Vascular Surgery[END_REF]. The average of the maximum values presented in these studies is 5.5 mN.m. This value will be considered as the torque that should be applied to the catheter by the VISR end effector. The torque required on the catheter will determine the forces required at the VISR end effector, that is the forces required on the 𝑦 ⃗ clamping axis and the 𝑧 ⃗ rotation axis of the pads.

A review of the literature presented in the following section has contributed to identify the gripping parameters that are essential to work on, to allow both minimization of these forces and maximization of the operating torque on catheter.

Factors influencing catheter handling and rotation

The rotation of the catheters between two pads induces a multifactorial phenomenon which is rolling. This phenomenon can be characterized by the rolling resistance, which is due to the deformation of both the rolling object and the surface on which it rolls near the contact area [START_REF] Zegelaar | The dynamic response of tyres to brake torque variations and road unevennesses[END_REF]. To ensure sufficient torque on the catheter, the dynamic friction coefficient between the two surfaces must be high enough to prevent sliding. However, the greater the rolling resistance, the greater the forces required for rotation. Since the overall goal is to miniaturise the robot, these forces must be minimised. Hence, a literature review is required to identify the gripping parameters that are essential to work on to enable this optimisation.

Research has been conducted to model the rolling of a cylinder on a surface [START_REF] Zegelaar | The dynamic response of tyres to brake torque variations and road unevennesses[END_REF]- [START_REF] Nakajima | Rolling Resistance of Tires[END_REF]. However, due to the many factors and their interactions, the chosen approach, for example in the automotive sector, is the DOE method. Several studies in this area [START_REF] Taghavifar | Investigating the effect of velocity, inflation pressure, and vertical load on rolling resistance of a radial ply tire[END_REF]- [START_REF] Pexa | Experimental verification of small diameter rollers utilization in construction of roller test stand in evaluation of energy loss due to rolling resistance[END_REF] have shown the importance of vertical load, diameter and pressure of the tyre, rotational speed and contact width, on the overall performance of the system.

In the case of the present study, and following preliminary tests, it therefore appears essential to study the hardness of the material of the pads, the width of the pads and the rotational speed.

These 3 parameters are the 3 factors of the DOE.

In order to study the impact of these 3 factors on the required forces at the end effector (clamping force and transverse force) and on the torque applied to the catheter, an experimental set-up was developed.

Material and methods

For the sake of confidentiality, the numerical values, including the axis of the graphs, and the nature of the material (apart from the fact that it is a biocompatible polymer) will be omitted, but this will allow the scientific approach detailed in this article to be presented, and the results to be compared.

Experimental set-up

The 3 factors and 3 responses studied are the following:

-𝑋 1 : The pads width, which is the dimension along the 𝑥 ⃗ axis of Figure 1.

-𝑋 2 : The hardness of the biocompatible polymer of the pads.

-𝑋 3 : The rotational speed of the catheter.

-𝑌 1 : The minimum required clamping force.

-𝑌 2𝑖 : The maximum torque applied to the catheter, corresponding to a given clamping force.

-𝑌 3𝑖 : The minimum required transverse force, corresponding to a given clamping force and to obtain a given torque on the catheter.

Each of the factors will take three values in the experimental design, coded -1, 0 and 1, and the formula that gives the coded variable value as a function of the physical variable value is as follows:

𝑥 𝑐𝑜𝑑𝑒𝑑 = 2𝑥 𝑝ℎ𝑦𝑠𝑖𝑐𝑎𝑙 -𝑙𝑒𝑣𝑒𝑙 ℎ𝑖𝑔ℎ -𝑙𝑒𝑣𝑒𝑙 𝑙𝑜𝑤 𝑙𝑒𝑣𝑒𝑙 ℎ𝑖𝑔ℎ -𝑙𝑒𝑣𝑒𝑙 𝑙𝑜𝑤

Equation 1 -Coded variable according to physical variable

The experimental set-up detailed in Figure 2 was developed to study these 3 factors and 3

responses.

The upper pad, which is linked to a load cell [Micro Load Cell (0-5kg) -CZL635, Phidget], is driven in translation. along the 𝑧 ⃗ axis by a stepper motor and a ball screw transmission (AM2224R3025086 with M3x100T and PE22-120, Faulhaber). This rotates the catheter placed between the two pads on which the tested material is placed. The clamping force can be varied by placing weights on this support, and the counter-weight mechanism is used to compensate for gravity.

Figure 2 -Experimental set-up

The torque applied to the catheter is determined statically. The tip of the catheter is bent at 90° so that its rotation causes a beam to be lifted, on which weights are positioned. By increasing the weights until the catheter slips, the maximum permissible torque is determined.

Experimental protocol

The test procedure can be stated as follows:

1 -The clamping force is increased until the catheter rolls continuously (without sliding). This value corresponds to 𝑌 1 .

2 Thus, the impact of clamping force can also be studied.

In addition, the pads will be continuously humidified with a saline solution, to get closer to the real conditions, and the used catheter has a diameter of 1.33 mm, which corresponds to the diameter mainly used in interventional cardiology (angiographic and guiding catheters) [START_REF]European Device Guide', Cardiac Interventions Today[END_REF].

The arrangement of factors levels for the Box-Behnken DOE for three factors is described in Table 1.

The total number of required experiments is 15 and the total number of different factor combinations is 13, as the last three experiments correspond to the same factor levels. In addition, a repeatability and reproducibility (R&R) study was conducted to ensure that the variability of the observed results are due to the studied factors. This study determined the variability of the measurements by calculating a confidence interval for each response, which is expressed as detailed in Equation 2.

Experiment

𝜇 𝑅 = 𝑦 𝑖𝑗.. ̅̅̅̅ ± 𝑡𝛼 These confidence intervals will be used as safety margins.

Results

Trends in clamping force, transverse force, and torque evolutions

The torque and transverse force evolutions with clamping force are respectively given in Figure 6a and Figure 6b, and the torque evolution with transverse force is given in Thus, Figure 3 demonstrates the non-linear impact of polymer hardness on forces and torque.

Increasing the clamping force does not indefinitely increase the torque applied to the catheter. This means that in order to both maximise the torque and minimise the required forces, it is unnecessary to increase the clamping force beyond the minimum value 𝑌 1 with an additional force of 2𝐹 𝑑 . Thus, the models of transverse force and torque corresponding to this minimum clamping force with an additional force of 2𝐹 𝑑 (𝑌 33 and 𝑌 23 ) will be determined and analysed.

Models

The determined models are polynomial functions of the 3 factors, their second-order interactions, and quadratic effects. The model of a response n°i is denoted by 𝑌 𝑖 ̂ and is detailed in Equation 3.

𝑌 𝑖 ̂= 𝛽 0 𝑖 + 𝛽 With 𝑋 the design matrix described in Table 1.

The p-values associated with the models for the three responses 𝑌 1 ̂, 𝑌 23 ̂ and 𝑌 33 ̂ are 0.11, 0.097 and 0.007 respectively. With the confidence level set at 0.1, this means that the models are globally relevant.

The analysis of the coefficients of each of the models showed that the width of pads 𝑥 1 is the most influential factor. Moreover, the interaction between the width of the pads 𝑥 1 and the polymer hardness 𝑥 2 has a great influence on transverse force. Indeed, for a constant clamping force and torque, these two parameters will determine the relative deformation of both pads and catheter and will therefore determine the force required to rotate the catheter on the pads.

On the contrary, the rotational speed 𝑥 3 has a negligible impact on all three responses. This may be due to the fact that the viscosity of the saline solution is very low (about 1,9. 10 -3 Pa.s [23, pp. 8-77]) , making the dynamic viscous friction force negligible.

Thus, in order to maximise the torque and minimise the required forces, the two factors that need to be optimised are the width of the pads and the hardness of the material of the pads, so the rotational speed will be set at its 0 level (300 °/s).

Discussion

Optimum levels of factors for torque maximization and forces minimization

The response surface methodology (RSM) is an effective tool when studying the impact of factors and their interactions on responses [24, p. 568], [25, p. 414]. Hence, this method is used and the response surfaces for all three models as functions of the hardness of the polymer and the width of pads are given in Figure 4. It can be seen that the interaction of these two factors is non-negligible on the transverse force.

Hence, as Figure 8c shows, for low polymer hardness, the transverse force increases as the width of the pads decreases, which is not the case for high polymer hardness. This can be explained by the fact that a small pad width concentrates the clamping pressure on both catheter (which can become oval) and material of the pads (which becomes more compressed as its hardness decreases), and lead to an increase in the transverse force.

The optimum value for the width of the pads is therefore set at 0.5 (coded level), and Figure 5 shows the models of the three responses as a function of polymer hardness, for this level of width. The sum of the required clamping force and the required transverse force (which is 𝑌 33 2 per pad if the two pads are movable along the 𝑧 ⃗ axis) is also shown. The sum of the forces required on the 𝑦 ⃗ and 𝑧 ⃗ axis of the end effector robot is almost constant but seems to be minimised for low hardness values. It is also observed that the torque is minimised for polymer hardness at its coded value of 0.1, and it is maximised for low hardness values. This could be explained by a higher deformation of the soft polymer and thus a better holding of the catheter.

However, compared to a hard polymer, a soft polymer leads to the concentration of the saline solution on the areas of high deformation, which increases catheter sliding. This explains the good performances also obtained with very hard silicones. However, when the hardness is at its 0 level, neither of these advantages apply, and the performance decreases.

The optimal configuration is therefore a width of pads of 0.5 and a polymer hardness of -1.

Under these conditions, a torque of 3 mN.m and 5.5 mN.m were measured respectively on a 1.33 mm and 1.67 mm diameter catheter, which falls precisely within the required torque range defined in the introduction.

Moreover, further testing has shown that the optimum hardness of the polymer decreases as the diameter of the catheter being handled increases. In the case of a large diameter catheter, this may be due to the fact that the material must deform strongly to optimise its grip. Conversely, when handling a small diameter catheter, using a material that is too soft could cause the two pads on either side of the catheter to come into contact with each other, thus increasing friction and decreasing performances.

Conclusion

In this paper, the rotation of catheters by a VISR whose end-effector consists in two planar surfaces that mimics the movements of the physician's thumb and forefinger is studied. During the manipulation in rotation, the catheter is rolled between these two planar surfaces. This paper presents a general method for optimising gripping performance and determining the forces required for this handling kinematics.

A test bench was developed to determine the optimum value of the rotational speed and the width and hardness of the pads. A DOE approach was used to determine the models of each of the three responses (clamping force, transverse force, and torque applied to the catheter) through a minimum of experiments. These models were then verified by the statistical method ANOVA, and the RSM was finally applied to find the combination of factors that minimised the clamping and transverse forces while maximising the torque applied to the catheter. Further tests were then carried out to validate the results.

Thus, the optimal parameters are a relatively large width of pads (coded level of 0.5) and a very soft polymer (coded level -1). Under these conditions, the required forces to achieve sufficient torque on the catheter were determined. The results of this study were used to develop an industrial prototype of VISR which was successfully tested on pigs. However, the information about these tests is confidential.

This study provides a promising methodology for the optimisation of grasping parameters for robotic manipulation of over-the-wire catheters and the design of appropriate actuation. However, the limitations of the study (including the method of torque measurement or the exclusive use of a 1.33 mm diameter catheter) should be considered and further investigated in future works.

Funding statement

This work was supported by a grant from an industrial research training agreement (cifre program, agreement n°2018/00480), between the Civil and Mechanical Engineering Laboratory (LGCGM, INSA rennes) and Robocath.

Declaration of Competing Interest

None.

Ethical approval

2 -

 2 Development of a dedicated test bench. 3-Characterisation of this test bench in terms of reproducibility of measurements. 4-Setting up a design of experiment. 5-Verification of the response models thus obtained. 6-Analysis of the results with regard to the objectives pursued.

Equation 2 - 2 ;

 22 Reproducibility standard deviationN is the total number of experiments during R&R study, and n = 3, as the considered value for each response for each combination of factors during the DOE will be the average of 3 measurements.Hence, the 95% confidence intervals (for which the Student variable 𝑡𝛼 𝑛-1 is equal to 4.30) are the following:-Clamping force: +/-1.3 N, -Torque: +/-0.7 mN.m, -Transverse force: +/-2.2 N.

  Figure 6c. Each line corresponds to one combination of factors and each point of these lines corresponds to one value of clamping force (it means 𝑌 1 , 𝑌 1 + 𝐹 𝑑 or 𝑌 1 + 2 𝐹 𝑑 ). The colours of the lines indicate the hardness of the polymer.

Figure 3 -

 3 Figure 3 -(a) Clamping force effect on torque, (b) Transverse force effect on torque and (c) Clamping force effect on transverse force, for each combination of factors.

Figure 4 -

 4 Figure 4 -Response surface showing the effect of pad width and polymer hardness on (a) the minimum required clamping force 𝑌 ̂1, (b) the torque 𝑌 ̂23 𝑎𝑛𝑑 (c) the required transverse force 𝑌 ̂33

Figure 5 -

 5 Figure 5 -The effect of polymer hardness on minimum clamping force with additional force of 2𝐹 𝑑 (large dotted green line), transverse force (thin dotted blue line) and torque (wide red line) with a pad width of coded level equal to 0.5. The thin black line corresponds to the sum of the clamping and transverse forces

  .1 -With this clamping force 𝑌 1 , the load 𝑃 on the catheter is increased until the catheter slips, thus determining 𝑌 21 .

	𝑌 32 .
	2.3 -The step 2.1 is performed again with an increased clamping force of 2𝐹 𝑑 , thus determining
	𝑌 23 .
	3.3 -The step 3.1 is performed again with an increased clamping force of 2𝐹 𝑑 , thus determining
	𝑌 33 .

3.1 -With this clamping force 𝑌 1 and a load 𝑃 corresponding to a torque 𝑌 21 , the transverse force 𝑌 31 is measured. 2.2 -The step 2.1 is performed again with an increased clamping force of 𝐹 𝑑 , thus determining 𝑌 22 . 3.2 -The step 3.1 is performed again with an increased clamping force of 𝐹 𝑑 , thus determining

Table 1 -

 1 Box-Behnken experimental design matrix of three variables

		𝑥 1	𝑥 2	𝑥 3
	no.
	1 → 4	±1	±1	0
	5 → 8	±1	0	±1
	9 → 12	0	±1	±1
	13 → 15	0	0	0

  1 𝑖 𝑥 1 + 𝛽 2 𝑖 𝑥 2 + 𝛽 3 𝑖 𝑥 3 + 𝛽 12 𝑖 𝑥 1 𝑥 2 + 𝛽 13 𝑖 𝑥 1 𝑥 3 + 𝛽 23 𝑖 𝑥 2 𝑥 3 + 𝛽 11 𝑖 𝑥 1 2 + 𝛽 22 𝑖 𝑥 2 2 + 𝛽 33 𝑖 𝑥 3

		𝛽 0 𝑖
		𝛽 1 𝑖
		𝛽 2 𝑖
		𝛽 3 𝑖
	𝛽 𝑖 =	𝛽 12 𝑖 𝛽 13 𝑖	= (𝑋 𝑇 𝑋) -1 𝑋 𝑇 𝑌 𝑖
		𝛽 23 𝑖
		𝛽 11 𝑖
		𝛽 22 𝑖
		[ 𝛽 33 𝑖 ]
	Equation 4 -Calculation of the coefficients of the models

2 Equation 3 -Model for a response n°i

A coefficient 𝛽 𝑗 𝑖 corresponds to the response n°i and the factor or interaction of factors n°j and is determined as described in Equation

4

.

Not required.

Acknowledgements

This work was supported by a grant from an industrial research training agreement (cifre program, agreement n°2018/00480), between the Civil and Mechanical Engineering Laboratory (LGCGM, INSA rennes) and Robocath.


Sonika Gogineni
email: sonika.gogineni@ipk.fraunhofer.de

Kai Lindow

Jonas Nickel

Rainer Stark

Applying contextualization for data-driven transformation in manufacturing

Keywords: Contextualization, manufacturing planning, semantics

Manufacturing is highly distributed and involves a multitude of heterogeneous information sources. In addition, Production systems are increasingly interconnected, hence leading to an increase in heterogeneous data sources. At present, data available from these new type of systems are growing faster than the ability to productively integrate them into engineering and production value chains of companies. Known applications such as predictive maintenance and manufacturing equipment management are currently being continuously optimized. While these applications are designed to help companies manage their manufacturing and engineering data, they only use a fraction of the total potential that can be realized by linking manufacturing and engineering data with other enterprise data. In the future, the context in which the data can be set will play an essential role. A meaningful added value in manufacturing can be achieved only with context specific data. Against this background, this paper presents three main areas of application for contextualizing data (semantics, sensitivity and visualization) and explains these applications with the help of a contextualization architecture. The concept is also evaluated using an industrial example. Furthermore, the paper describes the theoretical background of contextualization and its application in industry. The major challenges of the ability of engineers to adapt their activities and the integration of process knowledge for semantic linking are addressed as well.

Introduction

An increasing number of data sources is leading to larger pools of data being collected in manufacturing for diverse applications (scheduling, quality monitoring, maintenance, new design assumption etc.). The data is then being converted into information that helps users perform their activities. Increasing information implies that users need to find, understand, process and act on additional information. Which leads to increasing efforts and perhaps to frustration, especially for the information discovery and usage (e.g. searching relevant information across various tools and databases against the unclear background of responsibilities and rights). At this point, the context of data becomes relevant. Until now, various domains have already largely defined the context [START_REF] Zimmermann | An Operational Definition of Context in Modeling and Using Context[END_REF]. In the information technology (IT) environment context means any kind of information that can be used to characterize the situation of an entity in interaction with other entities. Context can be a single piece of information or a combination of many pieces of information from different sources or at different points in time. For example, a CPS (Cyber-Physical System) interacts with a CPPS (Cyber-Physical Production System). Examples of such contextual information could be location, product identification number, machine identification number, time, energy consumption, etc. From the manufacturing user's point of view, the appropriate situational context must be established (e.g. "I want to know why my bearing is not available at work station three."). From a data processing point of view, the interaction between the entities has to take place (e.g. work station three reports that the bearing is not available and an automated search finds possible solutions based on historical data, the worker has to make a solution respectively "I decide to take the bearing from workstation one, because there is still one available and the station is currently in maintenance mode."). Eventually, a decision can be made on the basis of the respective situation and the data. Hence, contextualization contributes to saving time and efforts involved in carrying out an activity and making decisions. A connection to Industry 4.0 as well as data allocation and contextualization of this data is an ongoing challenge: research gaps are becoming apparent [START_REF] Roy | Continuous maintenance and the future -Foundations and technological challenges[END_REF]. So far, there are only partial solutions in individual technology domains, but no general industrial approach is apparent [START_REF] Erkoyuncu | Improving efficiency of industrial maintenance with context aware adaptive authoring in augmented reality[END_REF]. To fill this gap, the research methodology followed is to identify the main aspects of contextualization, develop a suitable architecture to integrate them and evaluate the same with an industrial application. The effective evaluation of the contextualization concept and its future scope are further detailed in this paper.

Technological approach

Contextualization consists of three major aspects which have to be combined: context sensitivity, semantics and visualization. These three aspects are described in detail below: Context sensitivity is becoming increasingly important to ensure that systems are situation-dependent. By using a knowledge base and linking it with context data, information can be provided to the right user at the right time. According to [START_REF] Augusto | Co-creation of Smart Technology with (and for) People with Special Needs[END_REF], contextsensitive systems can be divided into four levels of interactivity: active execution, active configuration, passive execution and passive configuration. Active executing systems make independent decisions based on the current context and execute the necessary measures to implement the decision independently. Active configuring systems get to know the user over time and adapt accordingly. Passive executing systems understand the context and, based on this, develop proposals of action for the user, who then decides on the next steps. Passive configuring systems offer the user configuration options depending on the context, allowing the user to influence the system configuration.

Semantics: Production and production planning are highly distributed and involve a multitude of heterogeneous data. Necessary distributed systems and their heterogeneous databases require adequate technical possibilities to present (e.g. production and planning) information in a semantic context, otherwise the interpretation of the information is difficult or impossible. Ontologies have proven to be suitable technologies for modelling these semantic relationships in application and research. In the industrial environment, semantics modelled by ontologies are currently mainly used for semantic searches. Ontologies can be created automatically and manually. Automated ontologies can be created efficiently without human intervention and are thus suitable for large amounts of data, but do not represent the implicit knowledge of engineers. Therefore, the literature recommends creating semi-automated ontologies according to templates such as ISO 15926 "Industrial automation systems and integration -Integration of life cycle data for process plants including oil and gas production facilities". Technically, the trend is towards cloud-based applications based on Semantic Web technologies. Semantic Web offers a good basis for doing this in an enterprise context: [START_REF] Khilwani | Managing corporate memory on the semantic web[END_REF] for example, presents a concept for the automated creation of an enterprise-wide, semantically linked knowledge base.

Visualization of primary abstract data and the interaction with it is important for the development of modern user interfaces. A widely accepted definition of information visualisation is "The use of computer-supported, interactive, visual representations of abstract data in order to amplify cognition" [START_REF] Card | Readings in information visualization: Using vision to think[END_REF]. Information visualization should help to prepare and visualize abstract data accordingly. Therefore, information visualization also supports the cognitive processes of the user, i.e. all processes related to perception and recognition. The aim is to understand semantically analysed and sensitive data more quickly. This forms the basis for human-centred decision making or at least decision support. In the understanding of manufacturing, the development and planning of complex systems requires visualizations that provide an overview of the complex and extensive models. Visual validation can be performed in immersive (virtual) environments where data / information can be experienced [START_REF] Card | Readings in information visualization: Using vision to think[END_REF].

Contextualization approach

Contextualization of data can be seen as a valuable input for various applications along the lifecycle of products. Figure 1 shows how the data can be exchanged across the different phases of product lifecycle by using a contextualization architecture as a backbone. The contextualization architecture, which consists of semantics interconnection, context sensitivity and visualization elements supports the users with relevant data from various phases. For example, a designer can benefit from contextual information about market research. This helps the designer to design a product closer to the market needs. Another example is contextualization of production information with regards to the machines available and their capabilities, which helps production planners to plan future production better.

Fig. 1. Contextualization across product lifecycle

To illustrate the above approach, a real case from the production of aero engines is presented here: in terms of manufacturing, the efficiency of execution of processes, such as production, assembly, maintenance or quality assurance, is directly related to the availability of up-to date product data. The product data has to be updated, available, manageable and traceable throughout the lifecycle. Increasing product variance leads to complexities in production. Complexities in turn cause difficulties in flexible production management, as resources have to be rescheduled and managed across various production programs. This increased complexity creates a challenge for employees who have to be informed and qualified to run the different production programs. In order to support the future of flexible production, it is important to provide the production employees with the workplace of the future equipped with contextualized information.

Development of a contextualization architecture

The basis for the development of a contextualization architecture is formed by the three essential components "context of origin", "context of processing" and "context of use" (cp. [START_REF] Weichselbraun | Enriching semantic knowledge bases for opinion mining in big data applications[END_REF]). The "context of origin" is the information about origin of the data. This is linked to the question of "who organized and performed the actions; what were the objects; which features have been measured; what were the reasons or motives for collecting the data; when and where the data were collected; who were the owners; what were the licences used, etc." [START_REF] Weichselbraun | Enriching semantic knowledge bases for opinion mining in big data applications[END_REF]. The "context of processing" is on a technological level and describes "formats, encryption keys, used pre-processing tools, predicted performance of algorithms etc." [START_REF] Weichselbraun | Enriching semantic knowledge bases for opinion mining in big data applications[END_REF] Eventually, the "context of use" describes the "potential domains, potential or known applications, which may use the data or the knowledge extracted from it, potential customers, etc." [START_REF] Weichselbraun | Enriching semantic knowledge bases for opinion mining in big data applications[END_REF]. The three components are shown on the left hand side in Figure 2. Furthermore, Figure 2 shows the application of the components to a general contextualization architecture. Since the processing component is the technological advanced one, it has to be divided into several sub-components to be made applicable. That way, four layers describe the architecture, namely: data layer, semantic middleware layer, context-algorithm layer and the application layer. The application layers host the user interface with which the user interacts with and has contextual information using suitable visualization techniques. Based on the users tasks or request context algorithms pull or push requests to adjacent layers. The request to pull the relevant data is interfaced with the semantic middleware which can be any form of a semantic network which connects various data sources present in the data layer. For example, an ontology web language (OWL) ontology can be used to connect data and generate triples which can be stored and accessed from the triple stores [START_REF]Mapping to RDF Graphs for OWL[END_REF]. It is important to note that heterogeneous data sources can be connected using this method, but structuring of the data sources is required.

Fig. 2. Contextualization architecture

Evaluation of contextualization in manufacturing

The evaluation of contextualization is conducted as part of a project called Cockpit 4.0 (funded by the Berlin Senate, the State of Brandenburg and the European Regional Development Fund -ERDF 1.8/03) in which a consortium of Rolls-Royce Germany, Fraunhofer IPK and the BTU Cottbus are working together to address different challenges in the context of digitalization [START_REF] Gogineni | Semantic Assistance System for Providing Smart Services and Reasoning in Aero-Engine Manufacturing[END_REF]. The aim of the project is to address industrial challenges by assisting in making process data available and interconnected across various processes such as production, assembly, maintenance or quality assurance. Hence, users can work with contextual information to obtain a big picture of the entire lifecycle, track changes, manage, collaborate and interoperate across processes. This helps in improving efficiency of processes, therefore, leading to time and cost savings.

Goal of the research

The goal of the project is to develop and study concepts that support the navigation and data analysis in heterogeneous information ecosystems by providing relevant data in context to the current use case activity.

Methodological approach

The research approach was based on the Design Science Research Methodology (DSRM) for Information Systems Research [START_REF] Peffers | A Design Science Research Methodology for Information Systems Research[END_REF]. Initially the needs or requirements from the company were derived through a series of workshops with various stakeholders. The needs were then converted to user stories and further grouped and detailed to form use cases. The use cases enabled capturing of the features that needed to be developed. One suitable use case was then selected and developed into a demonstrator with a contextualization architecture. The demonstrator and its user interface were then evaluated by the users.

Concept

The concept of the demonstrator that was developed together with Rolls-Royce was an assistance system for the assembly of aero engines. The purpose of this demonstrator was to assist a team, called Voice of the Fitter (VoF), in their daily tasks to solve issues faced by the fitters during assembly processes. Examples for the problems occurring are part shortages, tool related issues, non-conformances identified during the assembly and others. As the team had to often search for causes of the problem and solve the problem by searching through various data sources, the assistance system was equipped with contextualization fields to address this situation. The aim was to provide useful information and suggestions, to help speeding up finding and solving problems which occur on the assembly line.

Implementation

The architecture for the assistance system is based on the contextualization architecture discussed in section 3. It provides context sensitive information to the VoF team from various data sources. The data sources comprise information about the parts of the aero engine, current and historic problems recorded by the team called VoF-cases and reported non-conformances (concessions) associated with a specific engine type. These data sources are generated by different processes along the product lifecycle of the engine. Data from these various sources were connected using an ontology, this represents the connection of data layer with the semantic middleware layer. The ontology is mined for context relevant data through contextualization algorithms. The contextualization algorithms used data fields such as part number and engine type to identify associated information relevant to the user. The algorithms also relied on natural language processing (NLP) to identify datasets with contextually similar and relevant information.

Fig. 3.

Front end of assistance system [START_REF] Gogineni | Semantic Assistance System for Providing Smart Services and Reasoning in Aero-Engine Manufacturing[END_REF] (numbers 1 to 4 are explained in the text below)

The assistance system's front end is shown in Figure 3. This is a part of the application layer where the user interacts with the system. The first field, indicates the selection and filter field which was designed to provide the team with options to obtain relevant problem information on the part having the problem. The part is displayed in the 3D viewer (2 nd pane) this helps the team to visualize the part on which they are planning to solve a problem. The problem identification field (3 rd pane) provides information about the problem. The fourth field, is an information field which provides additional context sensitive information (including deep links) from various data sources such as nonconformances, historic problems, similar problems and their solutions, hence, saving research time for the team. This helps in avoiding delays which are extremely critical on the assembly line. The assistance system was evaluated twice with a gap of six months. A VoF team member was briefed about the features available and then was interviewed to receive qualitative feedback and suggestions for improvement. The user then filled the questionnaire presented by F.D Davis to measure perceived usefulness, perceived ease of use, and user acceptance [START_REF] Davis | Perceived Usefulness, Perceived Ease of Use, and User Acceptance of In-formation Technology[END_REF]. The results indicated that the user acknowledged the advantages of the system to support daily work. However, highlights scope for improvement with respect to the user interface and additional features to integrate it into the work environment.

Conclusion and potentials for the future

Data contextualization becomes a base foundation for the design and operation of manufacturing systems. In this paper, the authors have introduced the foundation for data contextualization in the heterogeneous field of data sources in the product and assembly context. The main potentials of data contextualization can be realized in the processes of decision making, knowledge reuse, knowledge transfer and user (planer, fitter, and maintenance personnel) experience. It became clear throughout the execution of this research that new capabilities in designing, planning and executing manufacturing with respect to the collection, identification, interpretation and digital composition of the right or decisive data sets will form a new discipline in manufacturing. This discipline will need competence in manufacturing/ engineering process know-how, data analytics, data contextualization, human-machine interaction and IT knowledge. Data contextualization will be a competence that process planners and manufacturing engineers can take on in their professional skill profile, if the digital assistant system configurations offer the appropriate manufacturing problem configurations.


Danijela Ciric
email: danijela.ciric@uns.ac.rs

Teodora Lolic

Danijela Gracanin

Stefanovic

Bojan Lalic

The Application of ICT Solutions in Manufacturing Companies in Serbia

Keywords: ICT Software Solution, Manufacturing Sector, Industry 4.0, SEM

Information and Communications Technology (ICT) integration in the entire process of manufacturing management is necessary and obliging from the perspective of efficient resource allocation, time-saving, broadening the variety of products, reducing waste, and increasing the productivity and economy of production. Delivering competitive advantage needed for being successful in the new digital era is of crucial importance for the Serbian manufacturing industry. This research, in the first instance, seeks to examine the empirical link between the ICT software solutions importance and the actual software application, and in the second instance, to explore the empirical link between ICT software solutions application and the company's competitive position, as perceived by the respondents from 74 Serbian manufacturing companies included in the study. Research results have shown that if the managers in manufacturing companies believe that the usage of the specific software solution is vital for their business, the usage of that software will be empowered and, therefore, will positively impact the company's competitive position.

Introduction

The business environment today has been undergoing unprecedented changes, and constant technological advancement is keeping manufacturing companies in a continuous state of disruption, in order to be competent to handle huge amount of extrinsic data, and rejoinder to vibrant and dynamic worldwide markets [START_REF] Prasad | A QFD-Based Decision Making Model for Computer-Aided Design Software Selection[END_REF]. Many manufacturing companies are seeking new ways to stand out from the competition by transforming their traditional business processes and sustaining their competitive advantage through the application of ICT software solutions in a wide range and operations areas. Nowadays, ICT integration in the entire process of manufacturing management is necessary and obliging from the perspective of efficient resource allocation, time-saving in production, broadening the variety of products, reducing waste, and increasing the productivity and economy of production. The application of advanced digital technologies and software solutions has become the focus of the research related to Industry 4.0, as they are considered as one of the main enablers of this new paradigm [START_REF] Droege | Innovation in Services: Present Findings, and Future Pathways[END_REF]. Taking into account that manufacturing is destined to play the most significant role in the reindustrialization of Serbia [START_REF] Jovanovic | Prioritization of Manufacturing Sectors in Serbia for Energy Management Improvement -AHP Method[END_REF], delivering competitive advantage needed for being successful in the new digital era is of crucial importance for the Serbian manufacturing industry. This research, in the first instance, seeks to examine the empirical link between the ICT software solutions importance and the actual software application, and in the second instance, to explore the empirical link between ICT software solutions application and the company's competitive position, as perceived by the respondents, from 74 Serbian manufacturing companies, included in the study.

Theoretical Background

The advent of digitalization and ICT is reshaping the manufacturing sector to highly interconnected but, at the same time, increasingly complex and dynamic [START_REF] Jaewon | Impacts of the Digital Economy on Manufacturing in Emerging Asia[END_REF]. The strategic role of ICT highlights the importance of ICT usage in developing products, services, and capabilities that help a company gain a competitive advantage or meet other strategic objectives [START_REF] Seev | Strategic Information Systems: Competition through Information Technologies[END_REF]. Today's successful companies are deploying ICT to enhance performance and continually renew their ability to manage their interfaces with the environment dynamically [START_REF] Olamade | Strategic ICT-Use Intensity of Manufacturing Companies in Nigeria[END_REF]. The accelerated development of communication technologies driven by computer hardware and and system software solutions has conditioned the overcoming the application of manual systems for production control and enabled the adoption of new processes and operations [START_REF] Berić | The Implementation of ERP and MES Systems as a Support to Industrial Management Systems[END_REF]. This has led to sustainable gains in productivity, quality, and responsiveness [START_REF] Brynjolfsson | Beyond Computation Informational Technology, Organizational Transformation and Business Performance[END_REF] today, there is a large number of commercial ICT software solutions that are available for manufacturing management. Software solutions are used to automate a business process, streamline and improve operations, make the supply chain more transparent, or improve the enterprise asset management. The emergence of change in the manufacturing sector to ensure the pathway to Industry 4.0 is evident. For example, enterprise-resource-planning (ERP) systems, as one of the modern ICT solutions are being used in the majority of companies. In the manufacturing sector, ERP system implementation benefits are concentrated in quickly providing high-quality information within a company [START_REF] Hasan | Implementation of ERP of the Australian Manufacturing Companies[END_REF]. Other authors [START_REF] Mabert | The Impact of Organization Size on Enterprise Resource Planning (ERP) Implementations in the US Manufacturing Sector[END_REF] pointed out that the benefits of ERP systems differ by company size, so larger companies emphasize improvements in financial measures. In contrast, smaller companies report better performance in manufacturing and logistics. On the other side, there are social media, as one of the most widely used IT application [START_REF] Annisa | Impact of Alignment between Social Media and Business Processes on SMEs' Business Process Performance: A Conceptual Model[END_REF], which contains valuable information collected from the customers. Companies can use data not only for the prediction of customer behavior but also for making decisions on product and process design [START_REF] Chan | The Role of Social Media Data in Operations and Production Management[END_REF]. Still, there is no evidence in the literature about the connection between social media and its impact on business process performing [START_REF] Annisa | Impact of Alignment between Social Media and Business Processes on SMEs' Business Process Performance: A Conceptual Model[END_REF]. One of the major developments in business has been the emergence of the Internet as a channel for commerce [START_REF] Weber | Digital Customer Experience: The Risk of Ignoring the Non-Digital Experience[END_REF]. Cyber-physical system (CPS), Internet of Things (IoT), digital twins, and other available ICT solutions should be used for design or redesign of the production landscape, and these technologies are being cultivated around large multinational companies [START_REF] Hansen | Generic Challenges and Automation Solutions in Manufacturing SMEs[END_REF]. Currently, in Serbia, there is little interest and very modest results in the development of Industry 4.0. However, orientation to Industry 4.0 could provide a chance for its revitalization. Industry 4.0 is based on rapidly evolving ICT capacities starting already from the production planning process using ICT solutions for operational planning and manufacturing resource planning [START_REF] Dakic | Production Planning Busi-Ness Process Modelling Using UML Class Diagram[END_REF].

Research Methodology

Research Instrument

The questionnaire was used as a research instrument. In the first section, respondents gave their background information. In the second section, respondents were asked to rank the importance of different ICT software solutions in their business. In the third section, the actual software application was assessed, and the fourth section was dedicated to the company's competitive position. This research used a self-reporting (subjective) assessment of software importance and usage and the company's competitive position, as perceived by respondents. The importance and actual application of various software solutions in manufacturing were operationalized with 26 questions. The variables were classified into seven groups, representing different software products (office, email, enterprise resource planning, production, marketing, calculation, and simulation software, business processes). To capture respondents' subjective perception of software importance, a continuum of five-point, unipolar, Likert type scale was used (1 = not important at all; 2 = of little importance; 2 = of average importance; 3 = very important; 4 = absolutely essential). To capture respondents' subjective perception of actual software application, a continuum of five-point, unipolar, Likert type scale was used (1 = not using at all; 2 = of little usage; 2 = of average usage; 3 = very important; 4 = absolutely using it). The company's competitive position, as the dependent variable, was operationalized with 11 questions. The variables were classified into five groups (1) quality, (2) delivery, (3) price, (4) flexibility, and (5) innovativeness. To capture respondents' subjective perception of the company's competitive position, a continuum of four-point, unipolar, Likert type scale was used (1 = behind the competitors; 2 = the same as competitors; 3 = better than competitors; 4 = much better than competitors).

ICT Software Solutions Used in This Research

In this research, we included those software solutions that are most commonly found in manufacturing companies. The list of software, divided into seven groups, is given in the following section.

Research Model and Hypotheses

The questionnaire has been structured into three sections forming three factors. Fist independent factor -ICT software usage importance described the importance of different ICT software solutions in respondents' business. Second, the dependant factor -ICT software actual application showed the actual application of different types of software solutions. The third dependant factor addressed the respondents' subjective perception of the company's competitive position compared to competitors. To assess if the perceived importance of ICT software solutions influences the actual software usage, the authors proposed the first hypothesis. H1 -ICT Software Usage Importance has a positive influence on the ICT Software Actual Application. However, if the company applies a particular software solution, believing it will gain a competitive advantage, it is essential to know if that influence exists. Thus, the second hypothesis is proposed.

H2 -ICT Software Actual Application has a positive influence on the Company's

Competitive Position.

Results and Discussion

Based on the collected data, a measurement instrument consisted of 26 indicators was tested. Exploratory factor analyses (EFA) was conducted in an iterative procedure until an adequate model, and factor structure satisfied the criteria [START_REF] Tabachnick | Using Multivariate Statistics[END_REF]: validity of variance higher than 1(applying the Keizer-Guttman's rules), visual representation of variance value using scree plot, elimination of the variables that have been creating other, not relevant factors, and suitability of the Chi-square index and usage of the suitability index.

Reliability and validity assessment

By calculating the Cronbach's alpha coefficient for each factor, the reliability of the measurement instrument has been determined. All factors Cronbach's alpha values are higher than the minimum criteria (0.70 or more), as it is suggested by the authors [18] . The reliability and convergent validity of the factors were estimated, and the results are presented in Table 2. Ultimately, the measurement model had adequate reliability, convergent, and discriminant validity.

Structural model

To test the proposed research hypotheses, the structural model has been created (see Fig. 1). The model had adequate suitability indexes with the values shown in Table 3.

Observed indexes' values are in the acceptable range, which presents a proper fitting of models. All obtained values for part coefficients were above-recommended values of 0.20 [19] . Results of the Structural equation modeling (SEM) reveal that both explored hypotheses are confirmed and accepted. the Serbian manufacturing sector also showed the most significant software solutions for the enterprises are the ones for the production planning and scheduling, near realtime production control systems, as well as the systems for the automation of the logistics [20] . On the other side, factor ICT software actual application shows a significantly lower effect on the assumed factor company's competitive position, with 4.3%. The respondents addressed that ICT software solution application will make the most significant influence on their flexibility and innovativenessas the key indicators of their competitiveness.

Conclusion

What is quite certain is that almost all companies in the world use some kind of ICT solutions in their business. The manufacturing companies are not lagging behind either. Still, the question is whether they use narrowly specialized software intended solely for direct use in the production or whether they use a spectrum of various ICT solutions to support their business. The choice of ICT solutions to be applied depends primarily on the activity of the company, then the goals to be achieved, but most of all, the company's financial capacity and the level of management's awareness about the importance of implementing different ICT software solutions. This study aimed to investigate the relationship between ICT software importance and its actual application, and a relationship between ICT software actual application and the company's competitive position, accordingly. Research results have shown that if the managers in manufacturing companies believe that the usage of the specific software solution is vital for their business, the usage of that software will be empowered and, therefore, will positively impact the company's competitive position. ERP systems are shown to be the most important ones. Moreover, the actual application positively affects companies' competitiveness with the most significant influence on their flexibility and innovativeness. Taking into account that H2 with the competitiveness implication is very tightly on the border of significance, the conclusions drawn in this work can also be observed as partly interpreted assumptions. It is of massive importance for the companies to carefully choose and invest in new ICT software solutions, which they find as ones potentially improving business processes, having in mind that investment will increase their competitiveness. For Serbian manufacturing companies to embark on this reindustrialization and keep up with current trends, it is necessary to implement at least some or all of the elements of Industry 4.0, including the application of various ICT software solutions. This study has potential limitations. The first is the respondents' subjective perception of the research constructs. The second limitation concerns the use of unipolar scales to measure the ICT software solutions application level and the company's competitive position. What has undoubtedly not been sufficiently explored is the impact that the application of ICT software solutions has directly on profitability and cost-effectiveness. Also, the insights are focused on Serbia with no comparison to some other referential economies. Future research should overcome these limitations, and also take into consideration the influence of the company's size on ICT software application.

Fig. 1 .

 1 Fig. 1. Structural model

Table 1 .

 1 Respondents from 74 Serbian manufacturing companies were included in the study. The sample consisted of companies across different manufacturing industries and companies sizes. To present the determined fundamental indicators of statistical series, authors have used descriptive statistical analysis. Sample demographics are shown in Table 1. The demographic composition

	1. Office	5. Marketing
	-Text editing (MS Word, OpenOffice...)	-Company website
	-Spreadsheets (MS Excel, OpenOffice	-Social network accounts (Facebook,
	Calc...)	Instagram...)
	-Communication	-Survey and market research tools
	2. Email	(Mailchimp, SurveyMonkey...)
	-Project and team management software	-E-commerce
	(Trello, Slack, Jira...)	6. Calculation and simulation software
	-Conference and messaging (Zoom,	(Matlab, Simul, Solid Works...)
	Skype, Messenger...)	7. Business processes (Visio, Mind Jet,
	3. Enterprise Resource Planning (ERP)	Org Plus...)

Table 2 .

 2 Reliability, convergent validity and construct correlation

	Factor	α	CR	AVE MSV ASV SwApp SwImp Comp
	SwApp	0.950 0.952 0.665 0.160 0.101 0.816 a
	SwImp	0.924 0.925 0.674 0.160 0.097 0.400	0.821 a
	Comp	0.860 0.861 0.556 0.042 0.038 0.204	0.187	0.746 a
	a Indicates the square root of AVE construct; SwImp -ICT Software Usage Importance,
	SwApp -ICT Software Actual Application, Comp -Company's Competitive Position

Table 3 .

 3 Suitability indexes for Confirmatory factor analyses (CFA) and SEM

	Model	χ 2 /df	NFI	CFI	RMSEA
	Measurement model	1.497	0.802	0.923	0.080
	Structural model	1.493	0.802	0.923	0.080
	Recommended value	< 3	> 0.80 ~0.95	0.05 -0.10


Ioan Turcin
email: ioan.turcin@campus02.at

Ali Abdallah

Manfred Pauritsch

Cosmin Cosma

Nicolae Balc

Integrating electronic components into 3D printed parts to develop a digital manufacturing approach

Keywords: Digital manufacturing, stereolithography, sensors, conductive ink

Digital manufacturing (DM) processes such as additive manufacturing (AM) technology, allow a high degree of integrability and functionality of printed parts. In this work, we present a proof of the DM concept focused on the integration approach where a product is developed and embedded with sensors. We also take this example one step further and introduce a method that allows 3D printing of heating elements into the specimens. The thermal characteristics of the developed heaters are investigated, and the results detailed. The novelty relates to a heater prototype injected and solidified into a curved 3D printed channel, which can produce a temperature between 23-46°C on the printed surface of the sample both in a dry and wet environment. This research demonstrates that it is possible to construct parts with embedded electrical structures using the described method.

Introduction

This work uses complex methods, tools, and processes to demonstrate the possibilities of digital manufacturing (DM). The proposed approach combines the design and manufacturing information with the concept of functionalizing additively manufactured parts in various aspects. As a practical case study, we present an anatomical sweat glands module, which was developed with DM instruments, starting from design and conception to the direct fabrication by additive manufacturing (AM). This prototype will be further developed to optimize textile materials and to elaborate specific analysis of this industry.

The sweating glands are all over the human body surface within the first 3 mm of the skin. Their density is between 80 to 100 glands/cm 2 and they have 40 μm diameter. These reduced characteristics of sweat glands are not possible to be fabricated with standard AM machines. Due to AM limitations, we concentrated on considering the surface and the sweat rate. Thus, an anatomical module was designed that offer the possibility to bring the same amount of liquid to the required surface. The armpit area was selected to develop a complex sweat glands module [START_REF] Turcin | Sweat glands module with integrated sensors designed for Additive Manufacturing[END_REF]. Regarding the AM possibilities, various scientific papers shown that 3D printing technologies can produce complex prototypes for different applications under the "layer by layer" principle [START_REF] Ispas | Influence of Ti-Ceramic or Ti-Composite crown on stress distribution: finite element study and additive manufacturing[END_REF][START_REF] Popescu | Effect of temperature on the mechanical properties of extrusion glass fibre reinforced polyamide 6.6 composites (GFRPA 6.6)[END_REF][START_REF] Gowda | Studies on the Process Parameters of Rapid Prototyping Technique (Stereolithography) for the Betterment of Part Quality[END_REF][START_REF] Pacurar | Research on the durability of injection molding tools made by selective laser sintering technology[END_REF][START_REF] Kocisko | Postprocess Options for Home 3D Printers[END_REF][START_REF] Molnar | Medical Applications of Biomaterials: The Case of Design and Manufacture of Orthopedic Corsets Made of Polylactic Acid by Additive Manufacturing[END_REF][START_REF] Monkova | Some Aspects Influencing Production of Porous Structures with Complex Shapes of Cells[END_REF][START_REF] Grobelny | Investigations of Surface Topography of Hot Working Tool Steel Manufactured with the Use of 3D Print[END_REF][START_REF] Miron-Borzan | Custom Implants: Manufacturing Principles and Determination of Psychological Price[END_REF][START_REF] Loginov | Finite Element Simulation of Cellular Structure Built from Orthogonal Cylindrical Struts[END_REF]. Comparing with conventional manufacturing methods [START_REF] Sobotova | The Analysis of Chosen Material Properties at Thermal Drilling[END_REF][START_REF] Harnicarova | Comparison of non-traditional technologies for material cutting from the point of view of surface roughness[END_REF][START_REF] Popan | Study on chip fragmentation and hole quality in drilling of aluminium 6061 alloy with high pressure internal cooling[END_REF], 3D printing provides reduced time to market, lower product development costs, and improved design process [START_REF] Chua | Rapid Prototyping: Principles and Applications[END_REF]. Emerging technologies such as 3D printing and robotics [START_REF] Pisla | Risk Management for the Reliability of Robotic Assisted Treatment of Non-resectable Liver Tumors[END_REF] accelerates a sustainable developing of Industry 4.0 with DM. Analyzing the literature recommendations, the actual sweat glands module can be manufactured by stereolithography (SLA) technology. This AM process can produce directly accurate parts with good surface quality. A sweat glands module was designed according to AM requirements. To design the sweat glands module, boolean and CAD operations were developed using Creo Parametric and Meshmixer software. Boolean operations offer a versatile tool for editing or modifying the STL format, adding artificial constructions [START_REF] Guo | Boolean operations of STL models based on loop detection[END_REF][START_REF] Herle | Simulation-Based Stress Analysis for a 3D Modeled Humerus-Prosthesis Assembly[END_REF]. With the design freedom afforded by the SLA process, atypically channels networks were developed for liquid flow. The designed and printed part is illustrated in Fig. 1. This module contains more than 600 outlet glands on the anatomical shape of the armpit. All the parts from this study were fabricated using a Form2 SLA system and a standard photo-polymer (Clear Resin-Formlabs). To add functional requirements to the actual sweat glands module, the study was focused on embedding electronic components into the 3D printed parts. This work combines additive polymer printing with liquid metal infiltration for use in potential practical applications. The novelty of this study relates to a heater prototype developed by injecting a silver conductive ink into a curved channel, which can produce a temperature between 23-60°C on the printed surface of the sample.

Integrating electronics in SLA parts

AM technologies offer the possibility to integrate electric components and sensors in complex parts. Various applications of 3D printed sensors were reported for measuring the following: strain, pressure, ultrasounds, gas detection, food quality, biosensor, or even brain activity [START_REF] Xu | The Boom in 3D-Printed Sensor Technology[END_REF]. This paper describes two practical examples of how electronic components could be integrated into a sweat glands module. The first method is a straightforward one, where traditionally manufactured electronic components and sensors are integrated into pre-designed holes in the printed part. After the part was SLA manufactured, additional sensors were integrated into the pre-designed holes. The concept is presented in Fig. 2, where humidity and a temperature sensor are connected. The humidity sensor is Honeywell HIH-4000-003 and has the following features: near linear voltage output versus relative humidity, laser-trimmed interchangeability, low power design, enhanced accuracy, fast response, and low drift performance and chemical resistant. The temperature sensor is a PTF type produced by TE Connectivity. It combines a resistance temperature detector using a platinum resistor in the thin film as a sensing element. This sensor contains a structured platinum film on a ceramic substrate, passivated by glass coating [START_REF]PTF temperature sensor, Data sheet[END_REF]. The main features of it are the following: resistance tolerance ±0.12%, application temperature ±200°C, and silver wire. As shown in Fig. 2, a specially printed circuit board (PCB) was designed, equipped with an ARM controller (STM32C476), which controls the electronics. This board enables the connection of various sensors and actuators and controls the integration of the components. After setting up the controller via an ST-Link (Nucleo-F103RB), the first data from the sensors (temperature and humidity) were read (Fig. 2b). Furthermore, this sweat glands module, and electronics will be implemented in a mechatronic system, which will allow us to simulate the sweating process in various conditions. The second example is based on a previous report focused on 3D printed microelectronics for integrated circuitry and passive wireless sensors [START_REF] Wu | 3D-printed microelectronics for integrated circuitry and passive wireless sensors[END_REF]. In this method, some channels are left intentionally hollow in the part, and after manufacturing, they are filled with conductive ink. In this manner, interesting components such as micro-electro-mechanical-systems (MEMS) could be developed [START_REF] Birleanu | Humidity influence on the adhesion of SU-8 polymer from MEMS applications[END_REF]. Using this technique, we produce integrated paths in the 3D printed sample, which can be used for actuating, in this case, thermal regulation, or even sensing purposes. Several samples were SLA manufactured with "U" channels (Fig. 3b). Each sample has three channels with a 1.00 mm diameter and 26 mm length. The SLA parts were post-cured with 1.25 mW/cm 2 of 405 nm LED for 60 minutes at 60°C. For these conditions, the heat deflection of SLA parts is approx. 58.4°C for 1.80 MPa load value (according to ASTM D 648-07). Using a normal syringe, all the channels were injected with a conductive liquid (Fig. 3a). The material used is based on silver conductive element and has a volume resistivity of 0.001 Ω cm (product code RS PRO 186-3600). According to the material data sheet, this conductive ink contains 50-75% silver, 10-25% 2-methoxy-1-methyl ethyl acetate, and 10-24% nbutyl acetate. In general, this conductive ink is used to repair circuits on printed circuit boards or to make electrical connections to non-solderable surfaces. Fig. 3b shows a sample developed using this procedure, which contains three resistive elements. To investigate the heating behavior of these elements integrated into the SLA part, they were characterized for temperature sensitivity. In this step, we analyzed their suitability as heating elements. To undertake this work, a programmable DC power supply from Instek PSS-3203, and an infrared thermal camera from Flir i7 was used (Fig. 3c). The power was varied from 0 to 300 mW and the surface temperature of SLA parts was recorded. Typical temperature maps at different power values are shown in Fig. 4. Moreover, Fig. 5 shows the temperatures measured in air and with the elements immersed in a liquid with respect to increasing power. The results presented are the mean values recorded on the surface. All the measurements were made until the part was no longer conductive. The interruption appears at maximum resistance, where a voltage supply of 1.15 V was applied (power of ~ 298 mW). The resistance of samples varied between 3.278 and 3.727 Ω. These results show that temperature from 31°C to 42°C can be achieved using a power input from 40 to 107 mW in a dry environment (Fig. 5a). To investigate this system in a sweating environment, other samples were tested in water at room temperature (18°C). The results are exposed in Fig. 5b. In this case, the power was increased up to 420 mW. In a wet environment, temperature from 32°C to 44°C can be archived using an input between 310 and 390 mW.

For better mechanical and electrical properties, the conductive ink could be cured at 121-148°C for 5 to 10 minutes. To achieve this, another resin must be used for the printing process (e.g. High Temp Resin from FormLabs). The measurements conducted above allow the determination of the thermal resistance (Rth) using the following equation:

𝑅𝑅𝑅𝑅ℎ = 𝛥𝛥𝛥𝛥 𝑃𝑃 = (𝛥𝛥𝑇𝑇 -𝛥𝛥𝑇𝑇) 𝑃𝑃 [°𝐶𝐶/𝑊𝑊] ( 1
)
where Td is the device temperature (°C), Ta is the ambient temperature (°C) and P is the electrical power through the device (W).

The results of thermal resistance are shown in Fig. 6. Depending on the power supply, the thermal resistance varies from 34 to 142 °C/W. The presented results showed that this concept of resistive elements can be used as a heater. Future studies will integrate this heater concept into the anatomical shape of the sweat glands module, allowing us to simulate the sweating process at various temperatures in a dry or wet environment. To create an instrument, which combines both fluidic channels and sensing elements, the actual study shows a possible method to integrate electronic components into a 3D printed part.

The results reported brings a valuable contribution and useful reference for future applications of DM. The work was focused on functional design and the high levels of integration enabled by DM. In this study, the SLA process has been utilized to develop a sweat glands module with integrated electronic components such as temperature and humidity sensors, and a heating component made of silver conductive ink. Combining the 3D printing process and liquid metal paste filling method, a heater prototype was developed. The heating results show that it is possible to obtain a temperature from 36°C to 46°C both in a dry or wet environment using this heater. This preliminary study demonstrates that it is possible to develop an embedded heater into the SLA parts. From the manufacturing point of view, these findings suggest that a future heater can be constructed into the anatomical shape of the sweat glands module.

Conclusion

With the increase in the quantity and quality of computer systems in production facilities, the transition to a DM approach has become popular. DM concept refers to smart, networked methods, techniques, and tools that enable more flexible and customized manufacturing, increasing productivity and strengthening competitiveness [23]. In this study, a practical implementation of DM was developed which explores the benefits of 3D printing. Due to enabling to produce prototypes, tools, and final parts directly from virtual models, DM fosters dramatic reductions in delivery times and production costs while improving overall product quality. From our perspective, the technique described can be used to produce various electrical components with an atypical structure such as resistors, capacitors, inductors, circuits, and wireless sensors.

Fig. 1 .

 1 Fig. 1. Sweat glands module of armpit: a) Virtual model, b) SLA manufactured

Fig. 2 .

 2 Fig. 2. Sweat glands module with integrated sensors: a) setting up the controller b) sensors data

Fig. 3 .

 3 Fig. 3. a) Silver conductive ink used, b) 3D printed heater: SLA sample where the "U" channels injected with silver conductive ink, c) Instruments used for temperature sensitivity experiment

Fig. 4 .

 4 Temperature maps at different values of power: a) 0.002 W, b) 0.107 W, c) 0.226 W

Fig. 5 .

 5 Chart with surface temperature versus power: a) Dry environment, b) Wet environment

Fig. 6 .

 6 Fig. 6. Thermal resistance (Rth) versus power consumption

Acknowledgments. This paper was supported by the Project "Entrepreneurial competences and excellence research in doctoral and postdoctoral programs -ANTREDOC", project co-funded by the European Social Fund, and by a grant of the Romanian Ministry of Research and Innovation, project number 77PCCDI/2018 within PNCDI III (acronym DigiTech).


Srdjan Tegeltija

Vule Reljić

Ivana Šenk

Laslo Tarjan

Improving the Safety of Using Didactic Setups by Applying Augmented Reality

Keywords: didactic setup, remote control, augmented reality

The application of didactic setups is one of the commonly used teaching methods at schools and universities nowadays. By using the didactic setups, students are introduced to real components and real processes that take place in the industry. However, the students often need to use the didactic setups outside of regular teaching activities and at times when teaching staff is unavailable. This paper presents a solution for improving the safety of using the didactic setups by applying an augmented reality solution. The presented solution was implemented on a didactic setup for control of a three-phase asynchronous motor. In addition to improving the safety, the proposed solution allows the students to autonomously use the didactic setups beyond regular teaching hours.

Introduction

In order to provide training for the use of various equipment, there are numerous different solutions aiming to provide simple, fast and safe training for people. One of the possible ways is that the trainees learn solely from literature [START_REF] Bhutkar | Usability issues of user manuals provided with medical devices[END_REF][START_REF] Møller | Usability Testing of User Manuals[END_REF]. In such a setting, the users are introduced to the equipment and its use through printed literature (textbooks, books, operating instructions, etc.) or through literature in a digital format (PDF, audio and video, etc). By following the descriptions and instructions, the users are introduced to the equipment and its operation. The obvious advantage of this type of training is simplicity. However, its main disadvantage is that it is completely theoretical, and lacks hands-on trainings which are essential for real acquisition of knowledge and skills. After such a training, the trainees need some time to become familiar with the real equipment, which might additionaly pose a potential safety risk. Another disadvantage of this type of training is that certain instructions may be difficult to read and incomprehensible to the trainees without experimenting with the actual equipment. Also, there may be errors in the text that may lead the users to the wrong conclusions, which also poses a safety risk (for example, electric shock, injuries due to contact with actuators, etc). Another training possibility is to apply didactic setups [START_REF] Cunha | DidacTronic: A low-cost and portable didactic lab for electronics: Kit for digital and analog electronic circuits[END_REF][START_REF] Ostojic | Development and implementation of didactic sets in mechatronics and industrial engineering courses[END_REF][START_REF] Stankovski | Using a didactic manipulator in mechatronics and industrial engineering courses[END_REF]. The didactic setups serve as system models with actual parts of equipment, which are used to simulate the systems and processes that are executed in real industrial and non-industrial systems under controlled and laboratory conditions. The main advantage of this type of training is the hands-on experience of working with real components of the system. The didactic setups are often created by the producers of the equipment to make it easier and faster for the users to familiarize themselves with the equipment, or by companies in order to train new employees as quickly as possible. After such a training, the trainees can apply the acquired knowledge directly in real systems because they have the hands-on experience with working with real components during the training. A disadvantage of this type of training is that there are some, althought minimal, safety risks. Even though the didactic setups simulate the operating processes in the controlled laboratory conditions, there is a possibility of electric shock if the trainees would accidentally touch metal parts which could get connected to the power supply, as well as injuries from physical contact with actuators, or burns from handling high temperature fluids (hot water or steam), etc. Consequently, in order to minimize the safety risks, at least one responsible person must be present to supervise the training process (instructor, laboratory assistant, etc). Thus, the availability of didactic setups for the users depends on the availability of the responsible personel for supervising the training as well as on the availability of the laboratories in which the didactic setups are located. Further disadvantage of this type of training is that didactic setups cannot be used by a large number of users at the same time, i.e. there is a limit on the number of the trainees per training. In recent years, following the development and popularization of virtual and augmented reality technologies, training systems which utilize these technologies have been developped [START_REF] Van Wyk | Virtual reality training applications for the mining industry[END_REF][START_REF] Gavish | Evaluating virtual reality and augmented reality training for industrial maintenance and assembly tasks[END_REF][START_REF] Hasan | Virtual reality as an industrial training tool: A review[END_REF]. The advantage of this type of training is that, similarly to hands-on trainings, the users are introduced to a model of the system with real system components, but in a virtual environment, so there is no possibility of physical injury. In addition, a large number of trainees can attend the training at the same time, and there is a possibility of conducting the trainings from remote locations. The disadvantage of this type of training is that the virtual reality systems can cause side effects on the user such as a headache, blurred vision and nausea, so planned breaks are recommended during the training at regular time intervals. Another disadvantage of this type of training is that it employs emerging technologies whose cost is still relatively high, and many organizations may not have the resources to make the initial investment, although the costs are usually justified in the long run. To overcome the disadvantages of the individual training types, the trainings for users who will work in more complex industrial and non-industrial environments often utilize a combination of multiple training methods. Educational institutions such as schools and universities commonly use dedicated didactic setups as a training method in order to provide hands-on experience to the students. By using the didactic setups, students are introduced to real components as well as to the models of real systems and processes under controlled laboratory conditions. A disadvantage of using such didactic setups at schools and universities is that they are available to pupils and students only during regular teaching activities with the presence of teaching staff (professors, assistants, laboratory assistants). However, the students often need to use the didactic setups outside of regular teaching hours, including times when the teaching staff is not available for them. This paper presents a concept for a solution that increases safety of using the didactic setups as well as enables autonomous use of didactic models by pupils and students beyond regular teaching hours by applying augmented reality technology.

2

The Proposed Solution

The proposed solution is based on a combination of using didactic setups and the augmented reality concept. The augmented reality is a concept that expands a user's view of the world with computer-generated text, images and sound. The idea behind the augmented reality concept is not new. The concept was created in the 1960s, and its foundations were laid by Ivan Sutherland through the development of a system with a head mounted display which was used to show a simple wireframe cube overlaid onto the real world [START_REF] Billinghurst | others: Tangible augmented reality[END_REF]. This technology has long been neglected due to the limitations of hardware and software resources (large computers with low performances, cameras and displays with large dimensions but low resolutions, etc.) [START_REF] Ostojic | Development and implementation of didactic sets in mechatronics and industrial engineering courses[END_REF]. With the emergence and widespread use of smartphones with built-in high-speed processors, high-resolution displays and cameras, the augmented reality concept has gained in popularity and became implemented in a number of fields, such as industry, medicine, education, and other areas [START_REF] Marescaux | Augmented-reality-assisted laparoscopic adrenalectomy[END_REF][START_REF] Fraga-Lamas | A review on industrial augmented reality systems for the industry 4.0 shipyard[END_REF][START_REF] Yuen | Augmented reality: An overview and five directions for AR in education[END_REF][START_REF] Kounavis | Enhancing the tourism experience through mobile augmented reality: Challenges and prospects[END_REF][START_REF] Fischer | Medical Augmented Reality based on Commercial Image Guided Surgery[END_REF][START_REF] Yovcheva | Smartphone augmented reality applications for tourism[END_REF][START_REF] Pettersen | Augmented reality for programming industrial robots[END_REF][START_REF] Peng | Personalised Virtual Fitting for Fashion[END_REF]. In the meantime, a variety of glasses that allow augmented reality to be displayed have been developed [START_REF] Cherdo | The 8 best augmented reality smartglasses in[END_REF]. All this leads to new possibilities of implementing the augmented reality concept in various areas.

In this paper we propose a solution for using the augmented reality concept in order to enhance the existing didactic setups used for teaching students through handson experiences with a model of a system that includes real industrial equipment. The proposed solution is based on using a server application, a smartphone with a dedicated user application providing the augmented reality features and the remotely controlled didactic setup. The concept diagram of the proposed solution is shown in Fig. 1. The server application is designed to store the user profiles and the didactic setup data. When creating the user profile, each user is assigned adequate access rights for the didactic setup along with dedicated timeslots when they can access it. The didactic setup data includes the 3D model of the setup as well as the descriptions of its functions required for using the augmented reality options in the smartphone application. The smartphone application allows the user to log on to the system, and based on their defined access rights it grants or denies the user control of the didactic setup. After the user has logged on, a connection between the smartphone application and the didactic setup is established, in order to establish communication and enable sending commands to the didactic setup, as well as downloading data from the didactic setup to display them on the smartphone through augmented reality. Communication between the smartphone application and the didactic setup can be established either via Bluetooth or via Wi-Fi communication, depending on the actual equipment of the didactic setup.

The Realized Solution

As a proof of concept, an experimental system was developed and realized for use in hands-on teaching activities. This experimental system serves as an upgrade of a didactic setup for control of a three-phase asynchronous motor, previously developed at the Faculty of Technical Sciences in Novi Sad. The didactic setup consists of a programmable logic controller (PLC), type Siemens Simatic S7-1200, frequency converter type Danfoss FC51, a three-phase asynchronous motor, command buttons and switches, signal lamps and auxiliary components (fuses, power supply, etc) [START_REF] Ostojic | Development and implementation of didactic sets in mechatronics and industrial engineering courses[END_REF]. The command butons are connected to the PLC, and allow executing basic commands such as starting or stopping the three-phase asynchronous motor, changing the direction of rotation of the motor, or changing (reducing or incerasing) its speed. Following the user commands, the PLC sends commands to the frequency converter, which controls the direction and speed of rotation of the three-phase asynchronous motor. In addition, the PLC controls the signal lamps that show the current operation state of the didactic setup to the users. The used didactic setup is shown in Fig. 2.

In order to provide remote control of the didactic setup, a dedicated Android smartphone application was developed and implemented by using the Vuforia augmented reality library and Unity development environment [START_REF] Cherdo | The 8 best augmented reality smartglasses in[END_REF]. By starting the smartphone application, the user logs on to the system with their credentials, which were previously assigned to them by an authorized person. This allows the control of the didactic setup only to the users having the adequate access rights for the specific time slot. When the user selects the didactic setup, the communication between the smartphone application and the didactic setup is established. The server computer, the didactic setup, and the smartphone are all connected to a local computer network via a WiFi access point. In the next step, the didactic setup data (its 3D model and the descriptions of its functions) become visible to the user. By directing the camera of the smartphone towards the didactic setup, the image processing algorithms implemented in the Vuforia library recognize the didactic setup and, implementing the concept of augmented reality, the information on the didactic setup and commands for its control are displayed on the screen of the smartphone. Fig. 3 shows the flow diagram for the user side of the developed solution. The control of the didactic setup by using a smartphone and augmented reality was realized through the use of virtual buttons. Fig. 4 shows the smartphone application with virtual command buttons "S", "R", "-" and "+". The virtual control button "S" is used to start and stop the three-phase asynchronous motor. The virtual control button "R" is used to change the direction of rotation of the three-phase asynchronous motor. Virtual command buttons "-" and "+" are used to reduce or incerase the speed of the three-phase asynchronous motor. Virtual buttons do not physically exist but are displayed to the user's smartphone screen as augmented reality. By activating the virtual control buttons, the smartphone sends adequate commands to the didactic setup. This way, the control of the didactic setup (starting and stopping the motor rotation, changing the motor rotation direction, changing the motor rotation speed) without physically touching the control buttons on the didactic setup is enabled. In order to allow sending commands to the didactic setup, the existing PLC program of the didactic setup for controlling the three-phase asynchronous motor has been modified. The server application was implemented in C# programming language in Microsoft Visual Studio development environment [START_REF]Microsoft: Visual Studio tutorials | C#[END_REF]. The server application allows easy creation and modification of user profiles, as well as transfering the data about the didactic setup upon request. For further improvement of the concept as well as increase of general security, the implementation of a system for identification of didactic setups (for example 2D barcodes [START_REF] Tarjan | Automatic identification based on 2D barcodes[END_REF]) and a more advanced system for identification of users (for example access control as a service for software security [START_REF] Dašić | Applications of access control as a service for software security[END_REF]) is planned.

Conclusion

This paper presents a solution for improving the safety of using didactic setups by applying the concept of augmented reality. This system enables the control of the didactic setup from a dedicated smartphone application through augmented reality, which enables the control without physical contact of the user and the didactic setup. Such a solution improves safety as during its intended use there is no possibility of injury due to electric shock or contact with actuators. The advantage of the proposed and realized solution is that students can control the didactic setup without supervision of the teaching staff with minimal risks, assuming that they follow the safety regulations for handling the machines in the laboratory. In such a setting, the physical buttons on the didactic setup can be completely disabled, or the access to the buttons or even to the whole didactic setup can be physically disabled (e.g. by locking the control cabinet or putting the safety barrier between the students and the didactic setup), as the solution allows control of the didactic setup by using only the smartphone application and the virtual command buttons. It is important to note that even if full control of the didactic setup is available through the smartphone application, a physical emergency stop button has to be available to the students at all times for unexpected situations. A preliminary assessment and validation of the developed solution was conducted in collaboration with five students. All five students gave a positive assessment of the realized solution regarding the safety aspect, with only a single comment that it is not always easy to simultaneously keep a phone directed at the didactic setup and command virtual buttons. To confirm this preliminary assessment, an extensive user study is planned, which would include a larger number of students, in order to assess the applicability and usability of the presented solution. The study would also extend the developed solution to include additional didactic setups located at the Faculty of Technical Sciences in Novi Sad. As further development of the system it is planned to include the use of augmented reality smartglasses to facilitate the manipulation of the setup by the users and improve usability (instead of holding the smartphone directed toward the didactic setup, the students could control the setup simply by looking through the smartglasses).

Fig. 1 .

 1 Fig. 1. The concept diagram of the proposed solution for improving the safety of using the didactic setups by applying augmented reality: server, smartphone and the didactic setup.

Fig. 2 .Fig. 3 .

 23 Fig. 2. The didactic setup for control of a three-phase asynchronous motor

Fig. 4 .

 4 Fig. 4. User smartphone application with virtual command buttons.

Acknowledgment

This research has been supported by the Ministry of Education, Science and Technological Development, Government of the Republic of Serbia, through the project: "Innovative scientific and artistic research from the FTN activity domain".