Lahcen Oubahssi
email: lahcen.oubahssi@univ-lemans.fr

Claudine Piau-Toffolon
email: claudine.piau-toffolon@univ-lemans.fr

Virtual Learning Environment Design in the Context of Orientation Skills Acquisition for LUSI Class

Keywords: Virtual Learning Environments, Pedagogical Scenario, Educational simulation, Orientation skills

Virtual Reality (VR) is an interesting technology in the context of learning especially for learners with learning disabilities. The design of virtual learning environments (VLEs) is a complex task due to the interdisciplinarity intrinsic to VR and its cognitive aspects. This research work identifies some limitations with existing solutions and studies the design and operationalization of learning situations in the form of scenario models. It takes place in the context of LUSI (Learning Units for School Inclusion) classes and involves a specific learning situation of acquisition of orientation skills. We propose a solution based on virtual reality technology to enhance traditional learning and provide trainers with an educational toolkit, thus allowing them to recreate virtual reality scenarios and assess the learners' progress for learning orientation skills.

INTRODUCTION

We present in this article a research work that took part of the ARVAD project [START_REF] Arvad | Troubles des fonctions cognitives -pistes pédagogiques. Enseigner -Aux élèves en situation de handicap -En unité d'enseignement[END_REF]. The aim of this project is to propose a solution based on virtual reality to enhance the traditional learning to acquire orientation skills in the LUSI (Local Units for School Inclusion) classes. These units accommodate pupils with cognitive or mental health difficulties, with the main objective of schooling, the development of adult autonomy and a sustainable socio-professional integration in society. The daily activity of orientation skills presents a real obstacle for these learners. Different pedagogical approaches are used: from learning how to read a map in class to real orientation skills in an urban environment. As part of this research project, we worked with the LUSI class of twelve learners aged 16-18 (only nine could participate to the experiment). Their major difficulty is managing their stress, which can be caused by several factors, including the crowd, the noise, the delay of the bus, their own delay or the forgetting of the transport card. Our objective is to provide solutions to this problem of autonomy of the orientation skills by using the techniques of virtual reality.

For the learners of LUSI class, we distinguish two types of disorders, cognitive [START_REF] Lahav | Multisensory virtual environment for supporting blind persons' acquisition of spatial cognitive mapping, orientation, and mobility skills[END_REF] and psychosocial (ASH02, 2011) [START_REF] De Gasparo | L'ergonomie face aux nouveaux troubles du travail: le retour du sujet dans l'intervention[END_REF]. From the point of view of behaviour, they succeed in adapting to places; to the people they meet by having the proper attitude. On the other hand, they have no introspection activity and they have major difficulty explaining why they are doing this or that action. The identified cognitive problems are located on four domains: memory, sense of time, reasoning and the space notion. The identified psychosocial problems are located on three domains: attention, motivation and self-esteem.

Several research studies have studied the issues related to the assessment and rehabilitation of these disorders. [START_REF] Sehaba | Adaptive serious game for the re-education of cognitive disorders[END_REF] cited some examples that are based on clinical tests, and deal with different cognitive functions, such as working memory [START_REF] Diamond | Comparison of human infants and rhesus monkeys on Piagets AB task: Evidence for dependence on dorsolateral prefrontal cortex[END_REF], attention [START_REF] Manly | The differential assessment of children attention: The Test of Everyday Attention for Children (TEA-Ch), normative sample and ADHD performance[END_REF], auditory perception [START_REF] Mody | Speech perception deficits in poor readers: auditory processing or phonological coding?[END_REF], oral and written language [START_REF] Broomfield | Children with speech and language disability: caseload characteristics[END_REF].

The evolution of computer science has led to the development of several digital solutions for cognitive and linguistic remediation. [START_REF] Botella | Virtual reality in the treatment of claustrophobic fear: A controlled, multiple-baseline design[END_REF] [START_REF] Campos | Tutor Informatico: Increasing the Selfteaching in Down Syndrome People, Computers Helping People with Special Needs[END_REF] [START_REF] Conde | LAGUNTXO: a rule-based intelligent tutoring system oriented to people with intellectual disabilities[END_REF]) [START_REF] Parfitt | Multimedia in Distance Learning for Tertiary Students With Special Needs[END_REF] [START_REF] Sehaba | Interactive Educational Games for Autistic Children with Agent-Based System[END_REF]) [START_REF] Sehaba | Adaptive serious game for the re-education of cognitive disorders[END_REF] noted that these systems have the advantage of being more flexible and easily accessible. However, most of these systems do not adapt to the specificities and needs of each user. The emergence of virtual reality in computer sciences offers new experiences to users along with more powerful interaction and immersion possibilities. These possibilities are of great interest in the learning domain because they allow the creation of original and dynamic learning situations detached from the constraints that can exist during real training (danger, cost, uncertainty) and bringing specific advantages (enrichment of situations, replay, etc.) (Barot et al., 2013) (Barot et al., 2013) (Carpentier and Lourdeau, 2014) [START_REF] Lourdeaux | Relevance of an intelligent tutorial agent for virtual reality training systems[END_REF] [START_REF] Mikropoulos | Educational virtual environments: A ten-year review of empirical research (1999-2009[END_REF]. All these learning systems using virtual reality techniques can be grouped under the acronym 3D-VLEs (Virtual Learning Environments) [START_REF] Fowler | Virtual Reality and Learning: Where is the Pedagogy?[END_REF].

The research trends towards this type of environment have an influence on the teachers' practices and responsibilities in defining new pedagogical strategies within this type of training units. In our work, we address the issues of designing and operationalizing pedagogical situations enhanced by VR environments in an engineering approach based on scenario models. We aim at giving teachers the opportunity to freely design computational scenarios by providing them with tools dedicated to the design, reuse and adaptation of each scenario to new pedagogical situation if needed. The initial proposal of this research effort has been discussed in [START_REF] Chaabouni | Indexing learning scenarios by the most adapted contexts : An approach based on the observation of scenario progress in session[END_REF] [START_REF] Oubahssi | Design and operationalization of patterns: Case of a training situation of personal assistance for public in professional integration[END_REF] [START_REF] Tadjine | A process using ontology to automate the operationalization of pattern-based learning scenarios[END_REF].

This paper is structured as follows: the next section will present related research works on virtual reality and instructional design, we focus on educational scenario model design. We present in section 2 the context and objectives of our project and the main stages of the design of the orientation skills process. Our proposal is presented in section 3. A discussion is made in section 4 on results of the pilot study we carried out to verify the usability of the developed environment [START_REF] Nielsen | Usability Engineering[END_REF]. We draw a conclusion and present our research perspectives in the last section.

VIRTUAL REALITY AND LEARNING SCENARIOS

The 3D-VLEs (Virtual Learning Environments) are used in many domains including educational settings. The VLEs design is a task that poses new technical difficulties, induced by the interdisciplinary intrinsic to the VR (graphic computer, haptic devices, distribution, etc.) and cognitive aspects (respect of the learned task characteristics, transfer of learning to the real world, etc.) [START_REF] Bossard | Transfer of learning in virtual environments : a new challenge ?[END_REF] [START_REF] Marion | Integrating knowledge from virtual reality environments to learning scenario models-A meta-modeling approach[END_REF]) [START_REF] Sehaba | Adaptive serious game for the re-education of cognitive disorders[END_REF]. Therefore, the design and integration of VLEs into learning are complex and costly process. The description of the pedagogical simulations must take into account the specificities of this environment (its structure and its dynamics) in order to describe precisely the operationalization and the control of the activities in the environment. We also note that the simple fact of using virtual reality is not enough to motivate the learners, just as aesthetic fidelity is not a guarantee of pedagogical effectiveness. Tools by themselves do not teach; appropriate theories and/or models to guide the design and development of this technology are needed [START_REF] Chen | The design, development and evaluation of a virtual reality based learning environment[END_REF]. We might consider both didactic situations and scenario model.

We analyzed the various research works that studying the question of scenario model design in VLEs. [START_REF] Carpentier | Generation of learning situations according to the learner's profile within a virtual environment[END_REF] and (Barot et al. 2013) propose a model based on a centralized and indirect control of an emergent simulation from learning scenario content model. In this model, the environment is populated with autonomous virtual characters and the user is free from his/her actions. Learning scenario design is realized in two steps: dynamic objectives are determined from the user activity, and then a learning scenario is generated by these objectives and implemented through simulation adjustments. [START_REF] Trinh | Ensuring semantic spatial constraints in virtual environments using UML/OCL[END_REF] proposed models allowing the explicitation of knowledge for agents that populate virtual environments. This knowledge relates to the structure and the dynamic of the environment as well as the procedures that teams can perform. [START_REF] Sehaba | Adaptive serious game for the re-education of cognitive disorders[END_REF] propose a serious adaptive game for the evaluation and rehabilitation of cognitive disorders; their system makes it possible to personalize the course of games to each patient according to their capacities and competences. The architecture of the system organizes the knowledge in three layers: domain concepts, pedagogical resources and game resources. The main objective of this work is to reuse this architecture in different fields of applications and different serious games. [START_REF] Marion | Integrating knowledge from virtual reality environments to learning scenario models-A meta-modeling approach[END_REF] propose a learning scenario model that describes machine-readable educational activities in a virtual environment, in a generic way in terms of learning domain, type of task to carry out and learning strategy. The author uses a virtual environment meta-model that provides an abstract representation of virtual environments to allow its model to be both generic and machine-readable. [START_REF] Chen | Enhancing an instructional design model for virtual reality based learning[END_REF] propose an analysis that focuses on the improvement of a pedagogical design model of virtual environments using formative research. This later model initially proposed by [START_REF] Chen | The theoretical framework for designing desktop virtual reality-based learning environments[END_REF], allows to formatively develop and to evaluate simulations on a non-immersive virtual system. The analysis produced a five-level model to improve the pedagogical design of virtual environment. These research works overcome some limits identified in [START_REF] Carpentier | Generation of learning situations according to the learner's profile within a virtual environment[END_REF] that are related to the limited reactivity of the system or pedagogical control of the adaptation approaches. The models proposed improve the way to explicit knowledge [START_REF] Carpentier | Generation of learning situations according to the learner's profile within a virtual environment[END_REF] [START_REF] Trinh | Ensuring semantic spatial constraints in virtual environments using UML/OCL[END_REF] or the pedagogical design of virtual environment [START_REF] Chen | Enhancing an instructional design model for virtual reality based learning[END_REF] or permit the personalization of the course [START_REF] Sehaba | Adaptive serious game for the re-education of cognitive disorders[END_REF]. To overcome the lack of dynamic of the pedagogical scenario design, some works [START_REF] Carpentier | Generation of learning situations according to the learner's profile within a virtual environment[END_REF] [START_REF] Trinh | Ensuring semantic spatial constraints in virtual environments using UML/OCL[END_REF] embed virtual agents in the virtual environment. But these works still limit the use of the virtual environment to predefined knowledge and learning activities. In [START_REF] Carpentier | Generation of learning situations according to the learner's profile within a virtual environment[END_REF], experts can enter their own model in a graphical editor that relies on a formal representation directly interpretable by computer systems. The meta-model approach developed by [START_REF] Marion | Integrating knowledge from virtual reality environments to learning scenario models-A meta-modeling approach[END_REF]) also permits to experts to generate their virtual environment. But, despite these interesting approaches, they do not address in particular, the problem of the definition and adaptation of scenario models directly by the trainers according to the pedagogical situations they might encounter. Trainers can still not adapt by themselves the pedagogical scenario according to the learner profiles and enable a gradual learning process. Our main concern is to propose solutions to trainers to help representing scenario according to their own pedagogical needs in new environments such as those dedicated to virtual reality. As part of this research, we study the design and operationalization of several learning situations in a virtual reality environment. We are particularly interested in learning design activities by means of scenarios models, by the teachers themselves, to enable them to design learning situations in virtual reality environments to ensure the achievement of their educational objectives. Last but not least, it is important to take note that the implementation of these scenarios always requires an extra effort in order to meet different technical and pedagogical constraints required by this type of environment.

THE ARVAD PROJECT

Proposition of a Learning Scenario Model

Financed by Agglomeration of Laval, the ARVAD project was conducted in collaboration with the INSH laboratory, the IEIAH (Technology Enhanced Learning (TEL) Engineering research team) of the LIUM laboratory and the Robert Buron High School in Laval (France).

The aim of this research project is to propose a solution implemented in virtual reality environment to enhance the traditional learning to acquire orientation skills in the LUSI classes. Our goal is to facilitate this learning through digital, and to provide trainers of the LUSI classes with an educational toolkit, allowing them to recreate virtual reality scenarios and to assess the learner's progress. We used a constructivist teaching approach based on problem situations, and a virtual reality environment to develop automation that can be latter exploited in a context of orientation skill acquisition. The challenge of this research project relies on the interest of digital technologies in the learning for young people with cognitive disabilities. As stated by (Martin-Guttiérrez et al., 2017) younger students have always lived surrounded with technologies and are digital natives [START_REF] Prensky | Digital Natives, Digital Immigrants[END_REF] but relationships between technology and learning are not evident and virtual technologies are not an exception to this. But an investigation by [START_REF] Mikropoulos | Students'attitudes towards educational virtual environments[END_REF] found that students had a favourable attitude towards these technologies in the educational process. Studies in the scientific literature linking virtual technologies with improvements in particular in students' social and collaborative skills (Kaufman et al., 2005) and students' psychomotor and cognitive skills [START_REF] Feng | Trends in augmented reality tracking, interaction and display: A review of ten years of ISMAR[END_REF] permit us to suppose that the use of tablets, smartphones or video games in their daily life, and the attraction they show for all these devices suggest that virtual technologies can be beneficial for both learning and autonomy development.

In order to achieve our objectives, we adopt an iterative and participative approach: analysing and modelling existing learning situations, developing a functional demonstrator and testing the usability and relevance of the demonstrator in real situations.

Users took part of the design process and allowed the design of the prototype to evolve at each iteration. During the analysis phase, we tested the technical acceptance of virtual reality environments through the manipulation by the LUSI class learners of two well-known 3D video games based on displacement situations using a joystick. This test proved that learners were very comfortable with these environments and associated peripherals. In order to define the practices and put them into perspective with the theories and methods of learning adapted to the target audience, we observed for a period of three months in the LUSI class the different pedagogical situations. Based on this study, we proposed pedagogical models to be implemented in the future virtual environment.

These models may offer the possibility to trainers to define their own scenarios according to the learner's profile and the pedagogical situation.

Figure 1: High School Category -Progress of activity 1 (Table 1)

Example of a Learning Scenario

The learners of the LUSI class are asked to carry out various educational activities related to orientation skills so that they could develop more autonomy in their personal and professional lives. While doing so, an observation is being made on a number of activities, as illustrated in Table 1. The activities being carried out can be characterized with different variables and parameters characterising in accordance with the needs of the teaching staff of the LUSI class. For instance, an activity "work stress management" can be adjusted with the variation of the level of stress by adding "noise" as parameter (Table 2). Thanks to the observation process, we are able to propose a version of a model of scenarios (as illustrated in Fig. 1), which leads us to propose a conceptual model of different pedagogical scenarios based on the needs of the referring teacher. Fig. 1 illustrates the course of the learning situation related to Activity 1, beginning with Activity 0 (Table 1).

The objective of this activity is to locate different places on a map. The pedagogical strategy being used in this example is to work individually, and afterwards collectively for the correction. Thus far, we note that, the main characteristic of the given scenarios is that they are adaptable to the learners' progress (suggesting an itinerary to be followed first with visual and / or audible indications or without indication, adding noises from environments, etc.). In the suggested scenarios, the general objective of having learners move independently while managing stress with a map and benchmarks in the environment is fulfilled. In the meantime, we have identified several intermediate objectives that allow for a gradual learning towards this general objective (Fig. 2). Each intermediate objective is composed of a pedagogical sequence, which is divided into activities. The sequences are independent of one another because they do not respond to the same intermediate objectives. The set of these sequences constitutes a group of activities. The teacher assigns a specific sequence to one or more learners depending on their competency levels on orientation skills. In our study, we distinguish two groupings of learners according to two competence levels:

• Group 1: is the grouping of learners with a low level of competence on orientation skills. For example, group 1 always starts activities with a simplified map because they have difficulty moving on a complex map (with a lot of path choices).

• Group 2: is the grouping of learners with an average level of competence on orientation skills. For example, group 2 always begins activities with a complex map because we consider that they are able to move with a simple map.

We found that for the same objective, the teacher does not evaluate the same competency. For the same objective, the same activity may be used, but with lower or higher level of requirements according to the handicap and education level. For the same objective, activities of different (gradual) levels may be used. To evaluate the learner progress, a scale is used by the teacher according to the academic evaluation system (acquired, being acquired, almost acquired, not acquired). This makes it possible to locate them in relation to their competence booklet. Fig. 3 illustrates an example of a learner's pedagogical path with the different adaptations (change of activities, adaptation of objectives, etc.). Table 1) Figure 3: The progression of a learning path with a complex map

The 3D Environment

Following this analysis and modelling of existing pedagogical situations, we proposed a set of specifications summarizing the main one of a virtual reality environment to adapt specified needs and scenarios. This allowed the development of a virtual environment enabling the pedagogical team to define orientation skills scenarios and learners to carry out the activities related to the objectives set. For these activities, the learner has a joystick, a synchronized tablet displaying a 2D map, and visual indices (images or texts) (Fig. 4). We developed a non-immersive virtual reality environment in the form of a window into a virtual world displayed on a computer monitor and the interaction made via a mouse or a joystick.

To set up the orientation skills activities, the teacher uses a configuration interface communicating with the ARVAD execution environment. This interface permits:

• Management and configuration of the travel plans; • Management of learners or group of learners, set up of activities according to learning profile and pedagogical progression;

• Analysis of the results of the activities achieved;

• Management of the learner's accounts. As shown in Fig. 5, the ARVAD execution environment uses a model of orientation skills scenario and the 3D environment (a labyrinth). A server is dedicated to the management of data and resources. An instance of the 3D orientation skills scenario model is generated through the setting up of the activities generating a scenario for a learner or a group of learners.

The environment includes two main parts. The first one is dedicated to the learner, playing the scenario defined by the trainers. The second part (not developed at this time) will allow the teacher to set pedagogical scenarios according to the learner's profiles and their pedagogical progression and save the results to track the progress of these learners.

The virtual environment has been developed with the cross-platform game engine Unity as a desktop version, where the user navigates using a joystick, related to a tablet. The design of the scenes did not try to provide authentic situations but only one close to the reality. Data of the various games play by each learner are recorded in databases. • Pause/Exit: Permits to the learner to take a break at any moment. This pause is not taken into account when the activity is timed.

Figure 6: The two main parts of the ARVAD Environment

PILOT STUDY

User Story

This pilot study was realized with nine learners (aged between 15 and 18) from the LUSI class at the Laval Robert Buron high school, France. With the pedagogical team, we organized the learners into two groups according to the abilities and skills of each one. Table 3 shows an overview of the profiles of each group. We conducted the pilot study in order to assess the feasibility and the usability of the proposed system. We defined a set of objectives to evaluate if the functionalities and modalities of interactions (Table 4):

• Are well adapted to the LUSI classes learners; • Allow one or more skills to be easily worked; • Allow one or more skills to be easily evaluated.

The scope of the experiment does not still permit to evaluate the effectiveness of the pedagogical approach.

Table 4: List of the pilot study objectives

O1

The learner gets to locate easily on the map (tablet) O2

The learner is able to move easily in the virtual environment O3

The learner can easily visualize the indices (image, pictogram) O4

The learner manages to make the global link between the tablet and the virtual environment 05

The learner is able to move with visual aid in the virtual environment O6

The learner is able to make the link between the positioning in the 3D environment and the positioning on the tablet (know how to implement)

Method and Protocol

The aim of the pilot study is to evaluate qualitatively the feasibility of the pedagogical approach and some aspects of the usability of the virtual environment. We empirically verify usability criteria of the environment such as learnability, efficiency, memorability, errors or satisfaction [START_REF] Nielsen | Usability Engineering[END_REF]. According to the model of [START_REF] Dillon | User acceptance of information technology : theories and models[END_REF] we evaluate the concept of attitude, mainly the concept of perception of the user. To do so, we observed how the perception of content on the screen (visibility, display, texture) was perceptible, the perception of the contents on the shelf and the link between the tablet and the main screen. We defined a protocol based on two learning groups (Group 1 and 2) and four steps: pretest, test, post-test and results analysis. Fig. 7 proposes an activity diagram of the pilot study process. During the first step, the pedagogical team organized learners in two groups (Table 3), prepared an orientation map (on paper), the activities to be realized (duration, objective) and defined evaluation criteria (according to the skills to be tested for each group). The teacher then worked the orientation activity with the learners of the two groups (paper based map). For the post-test phase, an evaluation grid has been developed by researchers and a questionnaire for learners according to the experiment objectives to evaluate the virtual environment during the learner's activities (Table 4). The map and the learning game scenario model were operationalized on the tablet and in the prototype of the virtual environment. In the second step (test), each group of learners plays their learning game scenario in the virtual environment. During each game session, the research team observes the learners' activities and notes their observations on the evaluation grid. For each objective (Table 4) we evaluate if the learner was able to achieve it. In the third step, the researchers submit a questionnaire to the two groups of learners. The objective of this questionnaire is to have a learner's feedback on the realised activities. The questionnaire was submitted by oral and the research team recorded answers. Finally, in a last step, the researchers conducted an analysis of the results and defined the improvements elements to the virtual environment. During the test step, each group realized 3 sets of scenarios of the same activity (moving from point A to point B) but with a different variant depending on the group (with visual aid for Group 1 and with textual indications in Group 2). The skills to be evaluated were not the same for the two groups. For example, among the skills to be assessed for Group 1, we can cite:

• I know how to go from a point A to a point B on the tablet map without indices.

• I know how to go from a point A to a point B using the visual aid in the virtual environment. Each learner was asked individually to study the map on a tablet, which is the reproduction of the one that was played in class. Then he/she explains what he/she should do, before realizing his/her activities in the virtual environment. At any moment they could get help (by asking directly to the project team members conducting the experiment) or by clicking with the joystick to spot on the map of the tablet where they were located in the environment. The time (in seconds) and distance covered (in meters) were recorded in order to evaluate the efficiency according to the mode of use.

Three series of displacement (scenarios) per learner were proposed (Table 5). The project team monitored the process, observed the learner's activities and questioned the learner at the end of the session on the basis of the planned questionnaire and noted observations on the evaluation grid.

Results and Discussions

The analysis of the results from the post-test questionnaire submitted to the learners and the evaluation grid completed during the test (results presented for Group 1 in Table 6, Table 7 and Fig. 8, Fig. 9), made it possible to verify some of the usability criteria. The feasibility of the approach was validated as learners of the two groups were able to move in the virtual environment and achieved a series of activities (no abandonment). Only one learner (learner 4) unfamiliar with the joystick had some difficulties during the series (can be observed through the travel time recorded). They were all able to easily locate themselves on the map in the tablet (tracing the requested itinerary). Objectives O1 to O3 in Table 4 were satisfied. Some of them had more difficulties to understand and use the link between the tablet and the virtual environment (O4, O6 in Table 4, Table 7). Those who did not use the link with the tablet and the help proposed (by clicking with the joystick), randomly explored the environment for the first attempt in search of the arrival point. Then they used their memory to locate objects to achieve the series of displacement, thus the time taken to complete the activity or the covered distance in the two first series was greater, in a ratio of 1 to 3 for the time in the case of learner 4 of the Group 1.

The time taken to complete the activity and the covered distance was variable according to the learners without being directly linked to the different types of help proposed. Objective O5 seems more difficult to achieve. We still noted in series 3 (changed start and arrival points -no indices provided in the virtual environment) that time and covered distance was greater for the two groups (see results Table 6, Fig. 8, Fig. 9 for Group 1-except for learner 2 and 4). We observed that Learner 2 used systematically the aid provided in the environment but the results (in terms of distance and time) were not better than the others (except for the last series). The first two series permit to verify the usability of the prototype and the skill (I know how to go from a point A to a point B using the visual aid in the virtual environment). In the last series, despite change with the points of departure and arrival, the indices permit the learners to locate themselves in the environment. Learners used more internal skills instead of exploiting the link between the map on the tablet and the environment. Group 2 presented results rather similar as Group 1.

CONCLUSION AND PERSPECTIVES

VLEs based on virtual reality techniques proved to be efficient in learning but some limits have been identified, as they do not always permit teachers to adapt the learning situation to the learner's paths. The aim of this work was to propose a learning environment exploiting virtual reality and scenariobased models that could be adapted by teachers to learning situations in the context of learners with cognitive disabilities. We have developed our own environment rather than reusing existing environments that would have provided better visual feedback but would not have allowed us to develop our adaptable scenario models. The solution produced is authentic but in a simplified reality that can be complicated according to the learner's learning profile and promotes repetition which is an important learning spring for this learner audience. The effort to provide operationalization (machinereadable model) still remains semi-automatic to deploy a new scenario, the teacher having to parameterize variables in text files. The experimentation based on qualitative evaluation validated the feasibility and usability of the pedagogical approach implemented in the virtual environment. The main improvements relate to the teacher part, to permit the adaptation of learning scenario to the learners and enable their monitoring. It remains to develop an editor that will facilitate the design or simple parameterization of scenarios in different environments (simple labyrinths or city in 3D) and the follow-up of the different paths by the teachers and in a reflexive way by the learners (applicable to several environments, regardless of the domain or type of simulation to be played). Future experiments should evaluate interfaces and usability on the part of the teacher and the effectiveness of pedagogical approach. We will also need to address the follow-up of learners and the adaptation of scenarios by teachers according to profiles and learning situations.

Figure 2 :

 2 Figure 2: Progress of Activity 1 (Table 1)

Figure 4 :

 4 Figure 4: 3D Environment Screenshot

Figure 5 :

 5 Figure 5: ARVAD Software Architecture Fig. 6 depicts the software architecture of the ARVAD environment. It is composed of two functionalities modules, a teacher's module and a learner's module. The teacher module is composed of the following functionalities: • Mapping map: Permits to set up or to associate a map to an orientation skills activity. • Managing orientation skills activities: Permits to create to set or to delete an orientation skills activity. Teacher can generate new orientation skills scenario. • Managing tracks/indicators: Permits to visualize the different activities achieved by learners or group of learners for a period of time selected. Some indicators may be: date, learner code, number of activities achieved by a learner, distance travelled (by activity), success or not of an activity. The teacher can export the results. • Managing learner sessions: Permits to create, to modify or to remove a learner

Figure 7 :

 7 Figure 7: Activity Diagram of the Pilot Study Process

Figure 8 :Figure 9 :

 89 Figure 8: Results of Group 1: Distance travelled (in meters)

Table 1 :

 1 Extract of the various orientation skills activities achieved in LUSI class

	Activities Objectives	Variables
	High School Category
	Act.1	Locate places in	Type of maps
		high school
	Act.2	Identify places in	No variable, only
		high school (with	the map with
		colours)		many indices is
				used
	City Category
	Act.1	Locate on a city	No variable
		map
	Act.2	Locate	important	Search strategy
		places with a grid	with	imposed
				grid

Table 2 :

 2 Example of variables in orientation skills activities

	Noise	Timer	Obstacle
	With/	Display (Yes/No)	Present/Absent
	Without	Duration
		(Limited/Unlimited)

Table 3 :

 3 Learner's group profile of the pilot study

	Group	Size	Capacities and Skills
	1	4	Difficult access to reading or very
			difficult	understanding	of
			instructions. Use of pictograms.
	2	5	Easy access to write and
			understand a simple instruction

Table 5 :

 5 Displacement series for the two groups of learners

	Series	Description
	1	Same departure and arrival point of the
		paper map
	2	A new departure and arrival point with
		indications
	3	A new departure and arrival point without
		indications

Table 6 :

 6 Results of Group 1

	Learner Activity	Distance	Time	Help
	1	1	31.2	51	0
		2	25.9	47	0
		3	51.5	133	2
	2	1	30.8	66	5
		2	25.8	58	5
		3	21.3	34	6
	3	1	36.1	82	0
		2	21.7	51	0
		3	53.9	122	1
	4	1	32.1	143	0
		2	24.9	103	0
		3	28.4	127	0

Table 7 :

 7 Results of Group 1 by objectives for each series of activities

	Lea	Seri	O1	O2	O3	O4/O6 O7
	rner	es
	1	1	Ok	Ok	Ok	Ok	Ok
		2	Ok	Ok	Ok	No	Ok
		3	Ok	Ok	A few	Ok	-
	2	1	Ok	Ok	Ok	Ok	Ok
		2	Ok	Ok	Ok	Ok	Ok
		3	Ok	Ok	Ok	Ok	-
	3	1	Ok	Ok	Ok	No	Ok
		2	Ok	Ok	Ok	No	Ok
		3	Ok	Ok	No	A few	-
	4	1	Ok	Ok	Ok	No	Ok
		2	Ok	Ok	Ok	A few	Ok
		3	Ok	Ok	Ok	A few	-

ACKNOWLEDGEMENTS

This work was funded by Agglomeration-Laval (France). We want to thank all partners of this project. We would also like to thank especially the learners and teachers for their full support and key contributions: the Laval Robert Buron high school, France.


Mandy Tawalbeh
email: mandy.tawalbeh@mb.tu-chemnitz.de

Ralph Riedel
email: ralph.riedel@mb.tu-chemnitz.de

Samuel Horler

Egon Müller

Case Studies of Participatory Design

Keywords: Open Innovation, Participatory Design, Prototyping, LEGO® SERIOUS PLAY®, LEGO® MINDSTORMS®, Factory Planning, Merging Technology, Digitalization, Education

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

Introduction and motivation

The increasing significance of innovations [START_REF] Franke | The frequency of end-user innovation: A reestimation of extant findings[END_REF] results either from the rising market demands [START_REF] Reguia | PRODUCT INNOVATION AND THE COMPETITIVE ADVANTAGE[END_REF] or the need to improve products and processes by consideration of new technologies and digital approaches [START_REF] Radziwon | The smart factory: exploring adaptive and flexible manufacturing solutions[END_REF][START_REF] Lasi | Industry 4.0[END_REF]. Innovations are only successful when the provided products and services sate the wants of the end users by gaining an additional value [START_REF] Cavaye | User participation in system development revisited[END_REF]. Hence, user-integrated innovation is a key competitive factor for the design of innovative products, services and processes [START_REF] Reguia | PRODUCT INNOVATION AND THE COMPETITIVE ADVANTAGE[END_REF] supporting the implementation of new technologies in a working factory and their consideration in the planning process. Hence, methods of open innovationespecially of participatory designare investigated to identify their application fields in the context of factory planning and management.

Currently, there is a big variety of methods whose applications are not concerted with the innovation process. Different procedures should be selected by focusing the targeted objectives of the innovation process. Three case studies are used to represent the characteristics of different applications and demands for appropriate methods. LEGO® SERIOUS PLAY®, LEGO® MINDSTORMS® and an interactive workshop are investigated related to their suitability and conditions of use. The findings lead to the design process for dealing with new technologies by varying initial situations.

This article starts with a literature review referring to the disciplines of open innovation and describes the diversity of methods of participatory design with focus on process innovation. Product innovation will be neglected. Subsequently, three case studies represent the potentials of different methodological approaches in comparison.

Open Innovation

Innovations are the driver of the national economics [START_REF] Bauer | Innovation als Treiber der Wirtschaft[END_REF] by generating new ideas as basis for the creation of new products, processes and services. The importance of a product innovation is its impact on the competitive strategy of the enterprise. Process innovations increase the economic efficiency of the production by improving business and production processes. New ideas for innovations result either from user or customer needs or from new production procedures and technologies. [START_REF] Gakkai | Innovation and Management: International Comparisons[END_REF] Hence, it is necessary to study demands across the enterprise with open innovation approaches considering internal as well as external ideas in the development of innovative processes. [START_REF] Gassmann | Open Innovation: Externe Hebeleffekte in der Innovation erzielen[END_REF] The phases of an innovation process are shown in Fig. 1.

Fig. 1. Innovation circle (related to [9])

Participatory Design is a discipline of open innovation during the ideation phase of the innovation process and describes the involvement of different stakeholders in the design process to increase the degree of need satisfaction of the end users. [START_REF] Colin | User's Typology for Designing[END_REF] In the field of factory planning, it is necessary to integrate stakeholders directly representing their actual needs of functional and designing features. Hence, the methods of Participatory Design have to be investigated in detail. Muller and Kuhn [START_REF] Muller | Participatory design[END_REF] provide an overview of methodological approaches of Participatory Design related to their utilization point along the product life cycle and their stakeholder participation (shown in Fig. 2). Fig. 2. Overview on methodological approaches of participatory design (related to [START_REF] Muller | Participatory design[END_REF])

The diversity of methods in Participatory Design can be divided in five categories: gamification, prototyping, creativity techniques, dynagrams and image schemes.

Gamification is used to understand the context playfully [START_REF] Riedel | Measuring the Commercial Outcomes of Serious Games in Companies -A Review[END_REF]. Examples of methods are LEGO® SERIOUS PLAY® or scenario analysis. LEGO® SERIOUS PLAY® is an innovative hands-on and minds-on method based on metaphorical thinking to improve the understanding of processes. This is achieved by interpretation of alternatives and significances, and discussions in the group. [START_REF] Carpenter | Metaphors in qualitative research: shedding light or casting shadows?[END_REF] Scenario Analysis describes the investigation of future developments based either on varying ways to reach desired situations or on varying expectations of progressing. [START_REF] Hassani | Scenario Analysis in Risk Management: Theory and Practice in Finance[END_REF] LEGO® MINDSTORMS® rebuilds the production structure in a scaled Lego model representing processes with the aid of programming, and technical components. [START_REF] Biermann | Lego EV3: Lego Mindstorms ist kein Kinderspielzeug[END_REF] Prototyping describes the creation of the first of its manner with reduced demands related to design, function and quality compared with the end product / process to identify weaknesses. Prototypes are physical or virtual models of products or processes. Physical product prototypes are realized by rough or rapid prototyping, while virtual product prototypes are done by CAD modelling and drawing. [START_REF] Geuer | Rapid Prototyping in der Produktentwicklung[END_REF][START_REF] Trossin | Nutzung der Ähnlichkeitstheorie zur Modellbildung in der Produktionstechnik[END_REF] A process prototype represents the main activities of a process considering their interdependencies. The level of detail is geared to the original process. Hence, the complexity increases. [START_REF]DIN 66201 Prozessrechensysteme[END_REF] Process prototypes can be implemented physically by using LEGO® MINDSTORMS® or Cardboard Engineering for example [START_REF] Biermann | Lego EV3: Lego Mindstorms ist kein Kinderspielzeug[END_REF] and virtually by simulating. Simulation is the key method of systems dynamics used to investigate the characteristics of a social, economic, biological and ecological system. Such a system is defined by dynamic and temporary interdependencies between system components and their environment. [START_REF] Forrester | Industrial Dynamics -After the First Decade[END_REF] Creativity techniques are well-known methodological approaches to gather ideas by open-minded and unlimited thinking. Typical methods are Mind Mapping, Morphological Box and Brainwriting. [START_REF] Mesquita | Technology for Creativity and Innovation: Tools, Techniques and Applications: Tools, Techniques and Applications[END_REF] Dynagrams are defined as interactive visualizations based on a diagram. They allow users to create, change and extend collaboratively products or processes. The analysis and investigation of scenarios, the yield of conclusions, the preparation of experiences as well as the evaluation and decision-making are enabled. Common dynagrams are the Roger Dynagram, the Sankey Diagram and the Confluence Diagram. [START_REF] Eppler | Dynagrams: Enhancing design thinking through dynamic diagrams[END_REF] Image schemes are abstract representations of recurring dynamic patterns of interactions to structure people's view on the world. The basis are abstractions being more tangible than symbols but less realistic than pictures. They represent sensorimotor contours consisting of information which can be visual, haptic, kinesthetic or acoustical. Hence, image schemes are a metaphorical approach originating from linguistic contexts that is now extended into non-linguistic fields like cognitive psychology. [START_REF] Hurtienne | DESIGN FOR INTUITIVE USE -TESTING IMAGE SCHEMA[END_REF] 3

Methodological investigation and case studies

All the different methods of Participatory Design are suitable for varying use cases in factory planning to tap their full potential. Hence, it was necessary to classify them on their objectives. Three main objectives of participatory design methods result from the knowledge basis of the single participants. (1) Acquisition of knowledge, i.e. participants don't know the technologies yet and get to know them by acquiring knowledge related to these new technologies. (2) Identification and analysis of potentials i.e. participants know the new technologies, but neither did they consider their implementation nor any analysis of potentials in their enterprises. (3) Prototypical realization i.e. participants develop a prototype for the identified application fields.

For these categories, based on design objectives, three case studies are investigated varying in their application fields and selected methods of participatory design. The suitability of these methods is analyzed by additional influences resulting from the innovation context and the integrated participants. After the workshop, the fit of the methods was assessed by analyzing the initial situation, while considering the quality of the results, too. The comparison of the methods is based on deduced criteria. The three used approachesthe interactive workshop, LEGO® SERIOUS PLAY® and LEGO® MINDSTORMS®are evaluated and possible application fields are deduced.

Case study 1: Merged technologies to produce hybrid components

The German Federal Cluster of Excellence MERGE studies the combination of different technologies like plastics injection molding and metal die casting to produce resource efficiently hybrid components for lightweight conveyor systems in a large-scale manner. Hence, factory planning deals with the upcoming challenge of space-concentration requiring optimization of logistics processes. A modified logistics concept and a logistics planning procedure have been created which bring up changing conditions.

A workshop (described in [START_REF] Wagner | Planning of Logistics of Large-scale-Production of Metal-plastic-hybrid Components[END_REF][START_REF] Merkel | Logistikplanung im Bereich fusionierter Produktionsprozesse von Hybridbauteilen[END_REF]) was used to validate the new approaches and to offer a frame for educational contexts. It consists of two parts: (1) challenges of merged production processes and (2) knowledge transfer for dimensioning a load carrier.

In the first workshop part "challenges of merged production processes", the participants present, analyze and investigate synergy effects of merged production processes. This is based in the previous introduction of plastic injection molding and metal die casting. Subsequently, synergy effects of production and logistics processes can be identified and investigated. The results of this first part concentrate on technological aspects. The identified synergy effects are:

Material flows on a modular constructed tool as well as on several clamping units and robots for handling facilitates a faster change of cavities to deal with small production batches. Whereas, the transportation complexity decreases. The big differences of melting temperatures of metal and plastics can be reduced by using zinc alloy instead of aluminum alloy. Thereby, the energy demand decreases.

The second part "knowledge transfer for dimensioning a load carrier" is based on the definition of needs and attributes resulting from the chosen material which has to be conveyed. These needs and attributes include handling geometries, work flows, operations and premises of logistics. Afterwards, workshop participants design a load carrier and define its demands on transportation and material supply. They create different variants of load carriers with the aid of a load carrier morphology being evaluated by a cross-impact matrix and an efficiency analysis. One result is the identification of the best variant dimensioned afterwards related to technical or structural parameters, type and size in conjunction with the existing setting restrictions.

Case study 2: Transfer of digitalization knowledge

The German promotion initiative "Mittelstand 4.0 -Agentur Prozesse" is focused on the digitalization of resource and process management. The main objective is the qualification of information multipliers who are enabled to assist SMEs as well as handicraft enterprises. Hereby, the LEGO® SERIOUS PLAY® method is used. [START_REF] Schneider | Mittelstand 4.0 -Agentur Prozesse[END_REF] In this context, LEGO® SERIOUS PLAY® aims at the establishment of a shared comprehension of digitalization. A fictive enterprise builds the frame where each participant puts oneself in the position of a certain role. After a short theoretical introduction and warm up with Lego, each participant designs a future vision of the enterprise as most digitalized SME in the year 2020 from his point of view. They accentuate special features in comparison to the rival businesses. Concrete realization actions are carved out for the working area of his role in the enterprise. Additionally, possibilities to integrate users and colleagues into the digitalization of the processes are reflected. The resulting single models are presented to the other participants by storytelling.

Subsequently, a collective model is created in the group by combing the single models. It is important that every participant is represented in his role. The design has to be accepted by everyone and new ideas are also considered. Finally, this collective model is presented by one or more participants via storytelling. This presentation is filmed.

Additionally, the systems environment has to be analyzed to identify external influences considered as small single Lego models. Their relations to the main system and its components are rebuilt with their positions on the table. The participants are supposed to move around the table to be inspired by different perspectives on the system.

The analysis of potential future events with positive or negative effects follows. Therefore, the creativity technique approach of issue cards is used. The most important scenario has to be identified in a group discussion which will be investigated concerning its influences and consequences for the system. That's the finishing point to work with the Lego model.

Finally, each participant changes his role from the fictive enterprise to the multiplier role and all findings of the design process being relevant for the work of multipliers are collected. Possible recommended actions and starting points for digitalization are assembled creating the foundation for the support of centers of excellence and enterprises. The five most important approaches are highlighted.

Case study 3: Professional education in factory planning

The professorship factory planning and management at Chemnitz University of Technology offers several subjects to students for specialized knowledge transfer based on theoretical learning procedures which don't represent the actual key competence of interdisciplinary thinking and working with the entire factory. Therefore, the course "Methods of Systems Engineering" combines different disciplines and the students get the chance to connect abstract theoretical knowledge within a practical context.

In this practical context, a connection between an intermediate store and two machines for laser cutting has to be analyzed, optimized, planned and realized prototypically by minimizing the work in progress of semi-finished goods.

Students create a technical solution in a team under consideration of given and arising restrictions. This task improves the ability to solve problems in a creative and innovative procedures by using group synergies.

At the beginning, the students have to analyze different given process variants to select their favorite one by applying queuing theory. Additionally, the project has to be planned by focusing on team building with different competencies and planning the project organization, structuring of the context and defining demands.

In the execution phase, the main task is to generate a model of the entire production system with LEGO® MINDSTORMS®. The sub systems are solved step by step in different variants. Their tests and evaluations are done continuously to identify the favorite solution by using predefined criteria. Besides the model building tasks, the project has to be controlled related to the achievement of the objectivestime and progress. The procedure as well as the results are documented continuously.

Comparison of the Methods

The three case studies access different methodological approaches to integrate users in the innovation process. Case study 1 uses creativity techniques to collect ideas and acquire knowledge. In contrast, a combination of methods builds the basis for case study 2 where the open-minded idea generation is realized by LEGO® SERIOUS PLAY® and results are collected and prioritized by creativity techniques like storytelling. In case study 3, the participants are supposed to design a realistic prototype with LEGO® MINDSTORMS®.

The main differences of the used methodological approaches are identified in innovation need as well as the abstraction and design level.

The interactive workshop with creativity techniques is suitable for case study 1 to acquire knowledge because it serves as tool for further education regarding merged production processes, the new logistics concept and general methods of factory and logistics planning. The workshop is accepted as suitable tool for further education.

In case study 2, the participants with varying knowledge background aim at the creation of a shared understanding of digitalization and investigation of technological potentials. The basis is an open-minded team working progress achievable with LEGO® SERIOUS PLAY® which allows creative thinking and interpreting of common structures. During discussions and storytelling of the participants, everybody is able to share knowledge and experiences. Hence, LEGO® SERIOUS PLAY® supports successfully the open-minded innovation process whose results are prepared by additional using of creativity techniques.

In case study 3, students work in a creative but realistic way to design a prototype of a factory by using project management and synergies from team work. Idea generation refers to finding new realization approaches to solve problems during the modeling process. Technological possibilities are known. The realistic representation of a factory system supports the understanding of the theoretical knowledge from lectures. Students can integrate their own ideas into the model under consideration of restrictions. Hence, LEGO® MINDSTORMS® is an applicable method in the professional education.

More detailed characteristics of each designing process are shown in table 1. All three case studies achieve the targeted objectives with the aid of the pre-selected methods of participatory design what their suitability affirm.

Summary

The significance of Participatory Design methods increases in the process innovation. Hence, three case studies were investigated in the application field of factory planning. Every case study has its own characteristics and demands towards user-integrated innovation processes improving the quality of the results. The affirmation of the suitability of the preselected user-integrated methods was successfully for all case studies. In summary, the interactive workshop with creativity techniques supports the acquisition of knowledge. In contrast, LEGO® SERIOUS PLAY® combined with creativity techniques is used to design innovative and open-minded ideas or solutions while getting a shared knowledge base in the team. Finally, prototyping improves the professional education at university because theoretical knowledge is transferred into a practical context. As conclusion, the results can be used as data base for the development of a systematical approach to select a suitable method of participatory design for different use cases. The systematical approach should be based on the consideration of targeted effects, characteristics of content and participants. Hence, a suitable approach of participatory design has to be selected to tap its full potential.

Table 1 .

 1 Characteristics of the different case studies

		Criteria	Case study 1	Case study 2	Case study 3
	Objectives	Innovation need Innovation level Planning level	Knowledge acquisition new creation strategic	shared under-standing & potential analysis new creation / changing strategic	idea generation & prototypical realization new creation / changing tactical
	People	Knowledge basis Professional background	homogeneous homogeneous	heterogeneous homogeneous	heterogeneous homogeneous
	Method	Abstraction level Design level	realistic traditional	metaphoric creative	realistic creative


Jan Hrdina
email: jan.hrdina@continental-corporation.com

Gert Zülch
email: gert.zuelch@gefora-beratung.de

Simulation-Supported Verification of Methods for Controlling Disassembly Lines

Keywords: Disassembly Line, Flow Principle, Disassembly Control, Staff Deployment, Simulation

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

Requirements for an Economical Disassembly Process

Due to legal requirements, in particular due to the European Waste Framework Directive 2008/98/EG [1] and the principle of producer responsibility that goes along with the basis of changing values towards greater environmental awareness ( [START_REF] Huber | Demontageplanung und -steuerung[END_REF], p. 7), an increase in the amount of end-of-life products to be disassembled can be expected in the future. At the same time disassembly processes are characterized by generally low value creation compared to industrial production. Disassembly inefficient operations often prevail, exacerbating the situation further. Moreover, disassembly is often characterized by poor working conditions (e.g. noise, dirt, muscular stress etc.). Therefore it is firstly necessary to reduce disassembly costs through systematic planning and control of the related processes. Secondly, the cost-effectiveness of disassembling improves when it is of an increasingly industrial character. However, to a greater extent automation is only technically and economically feasible with special end-of-life products. Nevertheless, a combination of manual operations with automated sub-processes -featuring so-called hybrid and flexible automated systems -is seen as especially economical (e.g. [START_REF] Seliger | Hybrid Disassembly System[END_REF], pp. 290).

During disassembly, however, due to the uncertainty with respect to the properties of the end-of-life products, the operations to be performed are not fixed and therefore not deterministic (e.g. [START_REF] Grochowski | A machine learning approach for optimal disassembly planning[END_REF], p. 374). The selected disassembly methods must be chosen depending on the condition of the individual end-of-life product, from which the necessary processing times can possibly then be derived [START_REF] Heinz | Zeitermittlung für die manuelle Demontage[END_REF].

The scope of the used parts or sub-assemblies to be disassembled, i.e. the degree of disassembly, is also not necessarily specified. Instead, depending on the respective state of each end-of-life product this must be re-determined from an economic point of view ([6], pp. 31). For this reason it is logical that the degree of disassembly should not be equated with the degree of assembly, because it is operation-based, not product-based.

2

State of the Art for Control of Disassembly Systems

According to Zülch ([7], pp. 56) there are basically three possible measures by which the processes of a given production order program can be controlled appropriately. These are: changing the order size (for example, by combining orders A and B), changing of order sequences (bringing forward order B to before order A) as well as the initialization logic (e.g. splitting an operation or order). In principle, these control measures have been developed for parts manufacture and assembly. However, such control measures are only conditionally suitable for disassembly orders, since they do not account sufficiently for their specific characteristics. In division of labor-based systems such as disassembly lines, the control problem is complicated by the diversity of end-of-life product types and by the various usage states of the individual product. The latter in particular must be considered during disassembly control. Especially in manual systems compared to conventional production systems advanced or more detailed control measures are needed in manual systems in order to achieve efficient processes for disassembly.

As early as 1996 Geiger, Zussmann and Lenz [START_REF] Geiger | Probabilistic reactive disassembly planning[END_REF] recognized that disassembly must be reactively controlled. The reason for this is that extraction of certain end-of-life components depends on the success of the disassembly of its previous components. Moreover, the state of these components determines the likelihood of successful disassembly (cf. ibid., p. 49).

Many literature sources regard the assignment of disassembly operations to stations, thus regarding the planning problem of line balancing (e.g. [START_REF] Paksoy | Mixed model disassembly line balancing problem with fuzzy goals[END_REF]). As a control task, the planning of the order sequence is considered. Some authors try to solve this problem analytically using methods of operations research ( [START_REF] Lambert | Methods for optimum and near optimum disassembly sequencing[END_REF]; [START_REF] Elsayed | A Genetic Algorithm Approach to End-Of-Life Disassembly Sequencing for Robotic Disassembly[END_REF]). But these procedures solve only problems without any disassembly-typical disturbances.

Lee and Bailey-Van Kuren [START_REF] Lee | Modeling and Supervisory Control of a Disassembly Automation Workcell Based on Blocking Technology[END_REF] investigate disassembly strategies with the help of the simulation using two end-of-life products as examples. The strategies are materi-al-oriented and are carried out in robotic cells. Their contribution focuses on the mutual blocking of components; other disassembling difficulties are not considered.

As part of the planning of a hybrid disassembly system, Kim, Harms and Seliger [START_REF] Kim | Automatic Control Sequence Generation for a Hybrid Disassembly System[END_REF] developed reactive control measures. Their application, however, also involves a robotic automated disassembly system, but not the manual systems considered in this paper. There is no evidence of the effectiveness of the developed method, as it is the case here using simulation. In a further study of this procedure, Kim, Kernbaum and Seliger [START_REF] Kim | Emulation-based control of a disassembly system for LCD monitors[END_REF] use the simulation of another hybrid system to select from the possibilities of alternative disassembly operations a feasible one. Whether this procedure is also valid for an entire order program, as it is the case in our paper, is not checked with the aid of the simulation.

As a result, the control concepts proposed in the literature do not take into account disassembly specific difficulties, or if so then only partially -that is if such a concept considering a disassembly order program consisting of different end-of-life products exists at all. A dynamic, reactive control that takes into account available human and technical resources has not been carried out with any of the previously presented methods.

Development of a Novel Disassembly Control Procedure

In order to respond to difficulties or disturbances during disassembly it is not enough to manage these short-term changes to the order sequence with so-called re-sequencing or re-scheduling measures. Rather, the novel disassembly control procedure must be capable of much more, namely a re-configuration of the existing flow principle. In the sense of reactive control short-term scheduling should be feasible (e.g. a reassignment of individual disassembly operations to line stations). Moreover, the control procedure must allow for a re-distribution of operations in conjunction with an adaptive-dynamic work plan ( [START_REF] Schiller | Ein Beitrag zur adaptiv-dynamischen Arbeitsplanung in der Demontage[END_REF], pp. 29). Consequently, what is sought is a shortterm work schedule taking the given additional constraints into account (e.g. limited resources, cycle time) and as much compliance with the objectives as possible (e.g. high utilization of disassembly stations).

The following assumptions determine the initial situation that is the basis for the novel disassembly control procedure: It is assumed that there is a pre-existing balanced disassembly line with one worker at each station and an order program whose end-of-life products initially shall be disassembled in a pre-defined sequence. This order program can consist of different variants of an end-of-life product type with individual product states.

In terms of economics, the objective of the procedure developed here is, on the one hand, to ensure a high and most uniform utilization of the existing disassembly stations. On the other hand, the proceeds or contribution margin of the initialized disassembly order program for a defined planning period is to be maximized.

In the following, control measures are discussed that can react to disassembly specific difficulties or disturbances in an adaptive-dynamic manner (cf. also e.g. [START_REF] Zülch | Development of a Computer Aided Procedure to Control Division of Labour Based Disassembly Systems[END_REF]; [START_REF] Zülch | Control of Disassembly Systems Based on the Division of Labour by Means of Dynamically Adapting Routing Plans[END_REF]). In this approach, priority is given to a manual disassembly system ( [START_REF] Hrdina | Beitrag zur Steuerung von arbeitsteiligen Demontagesystemen[END_REF], pp. 101): ─ Variation of disassembly operation sequences ─ Variation of disassembly operations ─ Variation of disassembly tools ─ Variation of the disassembly order sequence ─ Variation of the disassembly depth ─ Re-assignment of disassembly operations to stations Figure 1 illustrates the general flow of the newly developed disassembly control procedure: For each disassembly station the remaining time for the current order program is determined. Taking into account the available control measures the one is then selected, that on the one hand maximizes the disassembly proceeds and on the other hand maximizes the utilization of the disassembly stations, but also considering the uniformity of their utilization. Below the effectiveness of the developed algorithm and control measures is shown with the aid of the simulation using an application study: In a disassembly line an order program that consists of three different variants of an end-of-life product is executed in a defined order period. The end-of-life products are disassembled at four stations in a line with one employee at each station. Three variants of an end-of-life product type with beta distributed activity times with respect to the applicable tools are available as well as the associated potential proceeds. Furthermore, the feasibility probability, the damage probabilities and the probability of depreciation due to damage associated with the respective tool are considered. Of the examined different control scenarios, only two are presented here, the initial solution as well as the most favorable improvement solution.

The following scenarios were conducted with a simulation period of 8 hours. Included here were end-of-life products to be disassembled with the order sequence Variant A, Variant B, Variant C, Variant A etc. with the setting batch size 1.

The simulation results are shown in the following. The presented Figures illustrate the Gantt chart representations, stating the workload of staff (and thus implicitly of stations). In addition, the Tables contain the disassembly proceeds generated (shown here simply as 1 currency unit -CU -each per disassembly operation). To reduce the randomness of the results obtained, 10 simulation runs were carried out with different seeds for random numbers. Both, the respective results of the simulation runs as well as the average over all runs are listed.

Situation of the Initial System

The initial situation in modelled with the following assumptions: In the case of workflow disturbances, the workers select randomly a control measure or an alternative disassembly operation. The disassembly stations have an average workload of 83.0% (Figure 2 and Table 1). Disassembly Station 4 is particularly poor with 77.2%; Disassembly Station 1 on the other hand has already achieved relatively high workload at Resources Workers Time scale Workflow through stations 89.4%. The aim of the disassembly control procedure is to achieve high proceeds as well as a uniform utilization of all disassembly stations. In the initial situation, the difference between the busiest and least busy disassembly station is 12.2%. The disassembly proceeds amount to 7,854 CU.

Possible Control Improvements

The improvement solution is run under the following assumptions: Through buffers, staff can access the operations of the previous disassembly stations, and thereby help each other during processing. Determination of the disassembly proceeds is achieved by the developed control algorithm, whereby a re-assignment of disassembly operations to stations can be carried out if this is appropriate. Thus, those disassembly operations are selected which promise the highest possible proceeds. Through a re-assignment of disassembly operations to stations in conjunction with the instruction which end-of-life product is to choose those alternatives that promise the highest proceeds, the following results can be obtained: The proceeds now achieve 8,411 CU. The difference between the busiest (91.6%) and least busy disassembly station (82.4%) stands at 9.2%, while the average workload is 87.2% (Figure 3 and Table 2).

Conclusion of the Application Study

With the help of the application study performed here, it has been demonstrated that the disassembly processes can be improved with the help of the developed control procedure. Although the disassembly line is already highly utilized in the initial situation, as the static workload across all disassembly stations shows with an average of 83.0%, and relatively high disassembly proceeds, the system can still be improved. Through the use of the developed disassembly control procedure in the improvement solution, utilization of all disassembly stations can be further increased. The proceeds will improve by 557 CU or 7.1%. Thus, the effectiveness of the disassembly control procedure is verified. In particular, the combination of the developed control measures can improve processes for division of labor-based disassembly systems.

Summary and Outlook

In this paper, a reactive control procedure has been developed that allows division of labor based disassembly systems to be controlled so that an existing order program can be as economically performed as possible. For this purpose, adequate disassembly-specific control measures have been developed and brought together in an overall concept. In addition, the effectiveness of the procedure has been demonstrated. For further improvements of the developed control procedure, the control measures must be communicated to staff in an appropriate form. In order to respond to specific situations, interaction between staff and control management should be facilitated by means of staff communicating current disassembly difficulties or disturbances to a control management system (e.g. using an earlier approach suggested by Schiller [START_REF] Schiller | Ein Beitrag zur adaptiv-dynamischen Arbeitsplanung in der Demontage[END_REF], pp. 231). Staff then receives new operating procedures for the purpose of an updated selection of the end-of-life products and their components to be disassembled, as well as an updated work plan.

Fig. 1 .

 1 Fig. 1. Disassembly control procedure by re-assignment and operation-related measures for a disassembly station. (according to [16], p. 404)

Fig. 2 .

 2 Fig. 2. Gantt chart representation of the initial situation. (following [17], p. 146)

Fig. 3 .

 3 Fig. 3. Gantt chart illustration of the improvement solution. (following [17], p. 151)

Table 1 .

 1 Proceeds and utilization of the initial situation. (cf.[START_REF] Hrdina | Beitrag zur Steuerung von arbeitsteiligen Demontagesystemen[END_REF], p. 147)

	Simulation Proceeds		Workload in %		Average
	run	in CU	s=1	s=2	s=3	s=3	s
	1	7.982	90,3	83,1	82,9	79,7	84,0
	2	7.805	89,3	84,1	82,2	75,2	82,7
	3	7.810	89,6	80,5	77,2	78,6	81,5
	4	7.682	88,5	83,9	81,4	74,1	82,0
	5	8.010	89,9	84,8	85,4	77,4	84,4
	6	7.924	89,0	87,2	82,5	77,9	84,1
	7	7.718	89,0	82,5	82,6	74,7	82,2
	8	8.022	89,0	83,1	79,8	80,7	83,2
	9	7.982	89,1	84,7	85,0	77,5	84,1
	10	7.606	89,8	85,9	75,3	76,5	81,9
	Average	7.854	89,4	84,0	81,4	77,2	83,0

Table 2 .

 2 Proceeds and utilization of the improvement solution. (cf.[START_REF] Hrdina | Beitrag zur Steuerung von arbeitsteiligen Demontagesystemen[END_REF], p. 151)

	Simulation Proceeds		Workload in %		Average
	run	in CU	s=1	s=2	s=3	s=3	s
	1	8.218	91,7	86,2	87,4	79,3	86,1
	2	8.233	91,0	87,5	88,5	83,2	87,6
	3	8.344	91,0	86,5	89,6	84,1	87,8
	4	8.667	92,2	85,1	88,9	81,4	86,9
	5	8.430	91,4	86,0	89,5	83,5	87,6
	6	8.487	90,4	85,5	89,6	81,0	86,6
	7	8.348	92,2	85,2	89,4	81,5	87,1
	8	8.460	91,0	86,2	87,5	83,5	87,0
	9	8.559	92,8	87,0	89,6	82,7	88,0
	10	8.369	92,2	85,0	86,9	83,4	86,9
	Average	8.411	91,6	86,0	88,7	82,4	87,2