Claire Aubron

Sébastien Bainville

Olivier Philippon

Bruno Dorin

Thinking the future of work in

Keywords: patronal farming, family farming, hired labour, India, comparative agriculture

come

Introduction

Following the collapse of most of the socialist regimes that extolled State farms and production cooperatives, the diversity of agricultural holdings in the world seemed to have been reduced to a simple dichotomy: family farming on the one hand and corporate farming on the other [START_REF] Purseigle | Les agricultures de firme[END_REF]. There is a wide consensus on the latter category of farms, both in terms of the definition and the risks it provokes. While they are marginal in the agricultural sector, these companies are predominant in other sectors: investors tie up their capital to rent or buy land, equipment and inputs, and employ workers to make a profit from these investments. While it remained limited to South America for a long time, this corporate form of agriculture has recently spread to other continents, attracting media attention to what is sometimes described as "land grabbing" [START_REF] Cochet | Capital-labour separation and unequal value-added distribution: repositioning land grabbing in the general movement of contemporary agricultural transformations[END_REF]. Family farming, on the contrary, has been largely celebrated in recent years. The year 2014 was declared the international year of family farming, and was marked by numerous seminars and academic articles dedicated to this type of farm. The multiple benefits of this type of farm (particularly in terms of employment and food security) are widely recognized, and the United Nations General Assembly declared the period 2019-2028 "the decade of family farming". This wide academic and political consensus is paradoxical as, while we are capable of demonstrating the benefits of family farming, we have few tools to actually define it today. There is a range of definitions and all of them are not unanimously accepted. Thus, [START_REF] Garner | Identifying the Family Farm. An Informal Discussion of the Concepts and Definitions[END_REF] have recorded and compared 36 definitions taken from the academic, political or associative worlds. The authors show that despite the great diversity of forms, the family continues to be involved in the working and management of the farm. Nonetheless, this family labour is generally described in a vague or arbitrary manner. Thus, in Brazil or Mexico, to be classified as a family farm, the majority of the work has to be done by the family. This is WS 5 Wage-earners 2 also the definition accepted by the High Level Panel of Experts on Food Security and Nutrition [START_REF] Hlpe | Investing in smallholder agriculture for food security, A report by the High Level Panel of Experts on Food Security and Nutrition of the Committee on World Food Security[END_REF]. In Argentina, a family farm can employ temporary workers, but no permanent staff. In Uruguay, there can be no more than two permanent employees [START_REF] Graeub | The State of Family Farms in the World[END_REF]. Beyond the definitions, the national agricultural censuses are problematic: the type of labour is rarely recorded and even more rarely measured [START_REF] Lowder | The Number, Size, and Distribution of Farms, Smallholder Farms, and Family Farms Worldwide[END_REF]. As a result -and although the type of labour involved is central to the definition -most studies seeking to assess the numerical importance of family farms are based on the physical size of the farm. This criterion raises a certain number of issues. Firstly, because this changes the object of study, as the farms in this category are no longer family farms, but small farms. Then, because this criterion varies from one country to another. Thus, according to the definition applicable in Chile, family farms have less than 12 hectares, while in Uruguay the threshold is set at 500 hectares. In Brazil, the threshold is based on modules, fiscal units whose surface varies from one state in the federation to another. It is hence difficult to carry out international comparisons and researchers are obliged to make choices: 2 hectares is now seen as the most commonly accepted threshold (World Bank, 2003;[START_REF] Hazell | The future of small farms: trajectories and policy priorities[END_REF][START_REF] Salami | Smallholder Agriculture in East Africa: Trends, Constraints and Opportunities[END_REF]Conway, 2011;[START_REF] Lowder | The Number, Size, and Distribution of Farms, Smallholder Farms, and Family Farms Worldwide[END_REF]. Such an approach is far from satisfying. Indeed the quantity and nature of the work invested in a farm does not depend solely on the cultivated area, but also on the way in which it is cultivated, and the production system implemented, which can be more or less labour intensive [START_REF] Mazoyer | A history of world agriculture: from the neolithic age to the current crisis[END_REF][START_REF] Dorin | India and Africa in the Global Agricultural System (1960-2050): Towards a New Sociotechnical Regime?[END_REF]. These semantic and statistical issues are particularly pertinent in India. Not only because of the demographic scale of the country, which is home to 24% of the world's farms [START_REF] Lowder | Farms, family farms, farmland distribution and farm labour: What do we know today?[END_REF]), but also because, in 2015, 86% of the farms in the country occupied less than 2 hectares. As a result, on the maps created by Graeub et al. (2015), the Indian territory seems to be covered with family farms. This conclusion may be somewhat hasty. Indeed, the number of agricultural labourers has steadily increased since the 1950s, and today their numbers surpass those of the farmers themselves [START_REF] Dorin | Croissance et revenu du travail agricole en Inde : une économie politique de la divergence (1950-2014[END_REF]. On the other hand, although the national agricultural policy has been encouraging corporate farming for the last few years, this form of agriculture remains the exception in India [START_REF] Singh | Corporate Farming in India: Is it Must for Agricultural Development[END_REF]. Indian farm holdings hence seem to evade the usual nomenclature. Their size, and the family labour invested, could lead them to be included in the "family farm" category. Howewer, since they employ numerous labourers, we could also place them in the "corporate farm" category, but yet again, their size and the family labour invested prevents this. A third category, more rarely considered, seems better adapted to this situation: the "patronal farm", in which a family works, but also employs labourers. Based on research carried out in the UK [START_REF] Gasson | The farm as a family business: a review[END_REF], Australia (Pritchard et al., 2006;[START_REF] Weller | Family or Enterprise? What shapes the business structures of Australian farming?[END_REF]), Brazil (de Souza et al., 2018) or Argentina [START_REF] Chaxel | Family-Run Farm Enterprises, Territories and Policies in Argentina[END_REF], various authors come to a similar conclusion about the inadequacy of the "family farming" and "corporate farming" categories to refer to some of the farms they study. To name this in-between, we prefer the term "patronal" to the sometimes used "family business farming" [START_REF] Gasson | The farm as a family business: a review[END_REF][START_REF] Sourisseau | On the Boundaries of Family Farming: Examples of Family Business Farming[END_REF], because "patronal" better reflects the focus on labour relations we adopt in the study of these farms. The works cited are indeed more concerned with the specificities of the management of farms by a family entity, in terms of intrafamily working relationships, investment planning and attitude to risk, articulation with off-farm activities, intergenerational transfer of assets or evolution of the farm over the family's life cycle. Based on the Indian case and labour focused, this article aims to analyse the way this type of farm holding functions, in order to understand what fundamentally distinguishes it from family farming, without making it any more similar to corporate farming. Clermont-Ferrand (France)

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Data and method

To tackle this subject, we first looked at the available secondary data. The secondary data used in this article are taken from the national censuses, ten-yearly for the population, and five-yearly for agriculture, as well as major national surveys carried out occasionally on smaller samples: the NSS (National Sample Survey) and the IHDS (India Human Development Survey). As in most countries, the statistics available in India have certain limitations when it comes to a subtle analysis of agricultural work, hence here we sought to combine this secondary data with fieldwork. The aim of the fieldwork was to go beyond the farmers' cultivated areas and to understand the production systems implemented and the work they involve. It also sought to measure the latter, to assess the proportion of work entrusted to labourers and the proportion the family itself carries out, depending on the seasons. We also attempted to assess the economic results of the different production systems, in order to understand why labourers are hired and to evaluate the impact of this. Surveys of this type take time, and can only be envisaged for a limited number of farms, which implies being capable of building a purposive sample. To do this, we carried out what is call an "agrarian diagnosis", using the conceptual framework of comparative agriculture [START_REF] Cochet | Comparative Agriculture[END_REF], in thirteen small study regions in India (Figure 1). The thirteen small regions were gradually selected in the framework of a research project dealing with the role of livestock farming in Indian agriculture (IndiaMilk project) so as to cover a range of contrasting situations in terms of biophysical environment, land tenure and historical development of irrigated agriculture and dairy farming. Thanks to a characterisation of the biophysical milieu and a reconstitution of the recent agrarian history based on interviews, the agrarian diagnoses allowed us to grasp the diversity of the cultivated land in each small study region, within a limited time period, and also to capture the historical circumstances that led to the way land is divided between the farmers in each area [START_REF] Cochet | Fonctionnement et performances économiques des systèmes de production agricole : une démarche à l'échelle régionale[END_REF][START_REF] Lacoste | Assessing regional farming system diversity using a mixed methods typology: The value of comparative agriculture tested in broadacre Australia[END_REF]. This led to a first typology of farms. In a second series of interviews with a purposive sample comprising 30 to 60 farmers in each of the small regions, we were able to carry out an in-depth study of the work on these farms. The farmers surveyed were selected so as to cover the diversity of farms identified during the first phase of the fieldwork, which was gradually refined. We thus recreated work calendars for the different crop and livestock activities, by identifying the operations and tasks carried out, and the workload associated with each operation (in days or hours, with a day representing eight hours of work), and the type of labour used (family or employee). We also assessed the daily (or hourly) labour productivity: this is equal to the added value divided by the number of days (or hours) of total work required to create it [START_REF] Aubron | Labor and its Productivity in Andean Dairy Farming Systems: A Comparative Approach[END_REF]. It can then be usefully compared to a local labourer's daily or hourly wage. For farms that employ hired labour, we used another supplementary indicator: the gross margin (equal to the added value, minus the salaries paid to the labourers) per day of family work. Finally, we assessed the agricultural income obtained per farm. When the family running the farm also works as labourer on other farms, the income from wage work is included in the total income. The aim of this article is not to describe Indian agriculture in general, but to understand its diversity from a work perspective. The agrarian diagnosis data presented in this article are chosen from different regions in order to illustrate this diversity, but in no way seek to be representative of Indian agriculture at a national level. Rainfed agriculture, for example, is underrepresented, because the "patronal" agriculture we seek to understand is mainly present in irrigated zones.

Farming marked by land inequality and high labour intensity

The size of farms clearly plays a role in structuring their labour requirements. With an average size of 1.08 ha in 2015, Indian farms are extremely small in size (Figure 2). This is a well-known feature of Indian agriculture, which is reinforced over time due to land division as a result of inheritance and division between generations. The other key characteristic of the Indian land structure, which is less often highlighted, is a result of the unequal distribution of land between agricultural workers. While the agrarian reforms introduced in the decades following India's independence undoubtedly ended the taxation system that existed earlier and allowed farmers and former tenants to formally own private property, there was no large-scale distribution of land, and numerous families remained landless. Cultivated land is hence very unequally distributed between cultivators (Figure 2) and landless households represent a considerable weight in Indian rural society: on the basis of NSS data the proportion of landless households in Indian rural areas is estimated at 40% [START_REF] Rawal | Ownership Holdings of Land in Rural India: Putting the Record Straight[END_REF], and in the 2011 Census, for the first time, the number of agricultural labourers (144 million) with no, or very limited, access to land surpassed the number of cultivators (111 million) (Dorin and Aubron, 2016: Figure 3). (1953,1970,1990,2015). Source: B. Dorin, based on [START_REF] Dorin | Agriculture and Food in India. A Half-Century Review, from Independence to Globalization[END_REF], [START_REF] Bhattacharjee | Tax on Agricultural Income. Holy Cow of the Indian Economy[END_REF]. In the case of crop production, following the introduction of a series of proactive public policies in 1967 [START_REF] Dorin | Agriculture and Food in India. A Half-Century Review, from Independence to Globalization[END_REF], the Green Revolution, implemented in a large part of the country, had a profound effect on agricultural work. Irrigated areas, most of which now use groundwater lifted with pumps, have more than doubled since 1970 (Dorin, "Agribiom-India" model, 2020 version). Irrigation, and the selection of shorter crop cycle varieties, enabled an increase in the number of crop cycles per year on the same plot, which rose from one to two or even three, with an average crop intensity, at the scale of India, of about 140% in 2017 (Figure 4). The multiplication of crop cycles and the increase in yields translated into an increase in the time dedicated to harvest and post-harvest activities, which are still little mechanised (see Konduru et al., 2013 for cotton). The tractor, introduced in the 1990s, has become a common sight on the largest farms in irrigated zones (that rent its services to the neighbouring farms) [START_REF] Gulati | Farm Mechanization in Indian Agriculture with Focus on Tractors[END_REF]. But its usage is often limited to soil preparation and transportation operations. On certain irrigated farms, cereals, sugar cane or even cotton were replaced in the 2000s by vegetable crops, combining at the same time and successively producing cycles that are highly labour intensive in terms of manual work. While it required inputs (seeds, fertilizer) and irrigation equipment, the Green Revolution also represents a vast process of labour intensification. According to the data collected in three study regions, the number of work days per hectare per year required to cultivate irrigated crops is between 176 and 940, as compared to only 112 to 269 for rainfed crops (Table 1). The role of livestock in this type of farming and the work associated with it, have also been greatly transformed over the last decades. In irrigated zones, livestock has to face the challenge of reduced spaces and grazing periods as a result of the development of irrigated crops and the replacement of its two historical roles (draught and manure) by equipment or inputs [START_REF] Aubron | Livestock farming in Indian agrarian change through 13 agrarian diagnoses, Presented at the International seminar "Milk and Dairy in India's Development Path. Lessons, challenges and perspectives[END_REF]. This situation has led certain irrigated farms to abandon livestock and to specialise in crop production. On the contrary, smaller farms, or farms that do not have access to water, maintain or even develop their livestock activity: they thus seek to take advantage of its traditional roles (draught and manure) as well as to produce milk, for which a market now exists, particularly via the dairy cooperatives created by the Indian White Revolution introduced in 1970 [START_REF] Dorin | Agriculture and Food in India. A Half-Century Review, from Independence to Globalization[END_REF][START_REF] Scholten | India's White Revolution: Operation Flood, Food Aid and Development[END_REF]. In some regions, this dairy farming even involves agricultural labourers with no access to cultivated land, who thus develop landless livestock farms. According to estimates, 40 to 90 million families are involved in dairy farming at the scale of India, with very low average sizes in this case too. The size of the herds is on average 3 cows or buffaloes for farms that possess them, including 1 to 1.3 milk producing females, respectively cows or female buffaloes (GoI, 2012;[START_REF] Dorin | The Indian Dairy Households through the IHDS surveys (2005 and 2012), International seminar "Milk and Dairy in India's Development Path. Lessons, challenges and perspectives[END_REF]; 70% of India's cows and female buffaloes are bred on farms with access to less than one hectare of cultivated land (NSSO, 2013). The work time associated with raising these herds depends on the fodder resources used to feed them. A large amount of time is required on farms that have limited access to land and water and thus little access to straws and cultivated fodder: they are largely dependent on spontaneous vegetation, and both gathering fodder and grazing are time consuming, even for small herds [START_REF] Aubron | Livestock farming in Indian agrarian change through 13 agrarian diagnoses, Presented at the International seminar "Milk and Dairy in India's Development Path. Lessons, challenges and perspectives[END_REF].

Family work combined with wide use of hired labour

In the thirteen study regions, the use of paid workers is noteworthy (see Figure 5 for five small regions).

The vast majority of farms employ workers, most often day labourers, to carry out a part of the agricultural work, alongside family work. In some farms, more than half the work is thus entrusted to labourers. Production systems where all the work is carried out by family labour are actually quite rare, and while a few cases correspond to farms that function solely on the basis of hired labour, with the family making no contribution in terms of work, such cases are even rarer in our sample.

The results obtained in all the study regions reveal the following trends: (i) The use of hired labour increases with the size of the farm. Landless livestock farmers do not employ paid labour, and farms smaller than a certain area (0.3 to 0.4 ha in the cases shown in Figure 5), mainly or even exclusively make use of family labour to carry out the agricultural work. The households surveyed across the country by the IHDS in 2011-12 (IHDS, 2011), largely confirm these results. Among the 16,409 households shown in figure 6, we note that with a few exceptions, the intensity of hired labour remains high, even on farms smaller than 1 ha. The general (unweighted) average is 30 days/year, or 32 days/ha (for 1.15 ha/household on average). However, on holdings smaller than 0.4 ha, this average falls to 7 days/year (37 days/ha for 0.19 ha/ household on average), while with 5 ha or more, it rises to 182 days/year (less than 21 days/ha for 9.27 ha/household on average).

"Patronal" agriculture: a specific rationale

Between landless farmers, small family farms and corporate farming, a wide range of combinations of family and hired labour

The regions studied here reveal a wide range of situations when it comes to making use of paid labour. The different types of farms identified in Gundlupet in Karnataka (Figure 5) clearly show the gradient that runs from farms where the members of the family hire out their labour for part of the year, to companies where work is exclusively provided by hired workers.

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In the case of landless families that nonetheless have a dairy herd, the work is done exclusively by the family and represents 470 days per year (Figure 5). The relatively homogenous distribution of the work over the year, allows one of the two active members of the family to engage in off-farm agricultural day labour for about sixty days a year. The family thus supplements the income it earns from dairy farming (20 000 Rupees per active worker) to obtain a total income of 30 000 Rupees per active worker, a sum slightly higher than the poverty threshold, which is estimated at 25 000 Rupees for an active worker with a dependent child (Planning Commission, 2014). Access to a few hectares of unirrigated land is sufficient to change this work organisation. Thus, for a farm that has 1 hectare per family worker, cultivated with cereals and sunflower, raising 2 milk cows continues to occupy more than one family worker throughout the year, but the work required for rainfed crop farming is more seasonal. During the monsoon, family labour is rapidly insufficient to carry out all the crop operations. Sowing and harvesting that cannot be delayed, are not only periods of intense work, with a day being longer than 8 hours of work, they also involve hiring day labourers (Figure 7). On the contrary, in the dry season, part of the workforce can dedicate a few days to working on neighbouring farms that cultivate irrigated crops. The salary thus earned usefully supplements the low agricultural income from rainfed crops, allowing families to earn more than the poverty threshold, with a total income of 30 000 Rupees per active family worker per year. Here, employing day labourers, and working as labourers outside their farm, are means of ensuring full time employment for the family workforce, despite the irregularity of the crop calendar (Table 2). Thanks to irrigation, it is possible to grow several crop cycles, or crops with longer crop cycles. The period when it is necessary to employ paid labour is hence longer. Thus, another farm, in Gondal in Gujarat, illustrates this situation (Figure 7). Cotton cultivation that has become widespread in this region, thanks to irrigation, also implies making use of a large number of workers from July to January or February. In addition, the income from irrigated crops is higher and earnings from off-farm work are far less essential. Nonetheless, balancing the work required and the available family labour is not always sufficient to explain the use of hired labour. Thus, in Vinukonda in Andhra Pradesh, a farm with 2 family workers, occupying 2.4 hectares, producing a combination of partially irrigated tobacco, gram, castor oil plants, chilli and cotton, and raising 2 traction animals, employs day labourers including during periods when family labour is available to carry out the work (periods when the work requirement is less than 50 days per month for the two family workers, Figure 7). The same can be said for the farm in Ekangarsarai in Bihar (Figure 7). In such a situation, the importance of paid labour goes beyond a mere supplement to family work. Far from the result of calendar constraints, using paid labour is a deliberate choice here. This situation exists not only on large farms: it is, for example, very frequent in West Bengal, a very densely populated region, where the agrarian reforms were the most effective [START_REF] Bardhan | Evolution of land distribution in West Bengal 1967-2004: Role of land reform and demographic changes[END_REF].

Hiring to ensure that family labour is fully employed or to increase its income?

The economic assessment of crop and livestock systems, and a comparison of labour productivity with day labourers' wages, is extremely enlightening when it comes to understanding why these farms employ hired labour (Figure 8). In all the regions studied, the gross added value created per day of total work (labour productivity) in irrigated cropping systems is far higher than the daily wage agricultural labourers earn. In the three study areas presented in figure 8, it varies between 340 and 3200 Rs per day of total work, and is between 2.3 and up to 10 times higher than the local daily wage. When it comes to rainfed crops, their productivity is similar to, or lower than, the daily labourer's wage. Livestock systems do not make it possible to achieve a level of labour productivity higher than a salary, except when the number of animals is more than 3 to 10 heads. The difference in labour productivity between rainfed and irrigated crops, leads us to clearly distinguish between two types of situation where agricultural labourers are employed: the first is imposed by work peaks; the second is economically justified. Employing labourers to work on rainfed crops is not, so to say, economically "profitable". The labour productivity they generate is generally close to the daily wage. Employing workers is hence equivalent to paying them all the added value they produce. But this employment that represents neither a gain nor a loss for an employer, allows them to exploit the total land surface available. Without this additional labour a part of the land would not be cultivated and, outside peak periods, family labour would be largely under employed. In these circumstances, hiring paradoxically contributes to full employment of the family workforce. In the Indian context, this is the type of farming we would specifically call family farming. This is not the case of irrigated crops or dairy farming with above 3 to 4 heads of bovines. In these cases, the labour productivity is far higher than a daily labourer's daily wage. Independently of any calendar constraints, it is profitable to hire labourers, as the wage paid remains lower than the added value generated (Table 2). With this, the employer keeps an appreciable gross margin (added value, from which the cost of the salary is deducted). On these farms, on which the family works, hiring labourers is a means of increasing family earnings to levels above its actual productivity. This can be measured by dividing the gross margin by the number of days of family work. This is particularly visible on vegetable farms in Bangaon in West Bengal (Figure 9). It seems to be necessary to clearly distinguish this type of farm from family farming and to specifically identify it as "patronal faming". Corporate farms (the final case presented in Gundlupet in Figure 5) differ from family and patronal farms. When investors tie up their capital in farming, all the work is provided by employees. Paid labour is a cost that has to be reduced and the production systems implemented demand relatively little labour per unit of land or per animal (Table 2). Thus, in Gundlupet, coconut groves covering 4 to 40 ha are planted with rotating crops alternating irrigated ginger and banana trees. Once they are established, banana and coconut trees require little care. Ginger cultivation is more labour intensive, but as it is sensitive to fungal diseases, it requires long fallow periods and is only grown one year out of ten. The absentee owner entrusts the plantation to a part-time manager. The sowing, weeding and harvesting of ginger, and the banana plantation, is left to day labourers. The bananas and coconuts are harvested by the buyer. The whole process requires far less work per hectare than the production systems followed on family or patronal farms. However, the larger surface area makes it necessary to multiply the lower work requirement per hectare by the total number of hectares.

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Discussion and conclusion

The Indian countryside is hence filled with lessons that allow us to understand the role of paid agricultural labour. Numerous farms are clearly family farms. They correspond to families who invest their labour to earn an income, but wage-labour is nonetheless present. This allows them to supplement their income and to ensure that the family workforce is fully occupied, either by hiring out their labour when the means of production are lacking (land, animals, irrigation) or during fallow periods in their farm calendar, or by employing labourers when family labour is insufficient during certain periods. But there are also numerous patronal farms. As they have greater means available to them, particularly good access to irrigation, they can follow cropping systems that are very productive, despite being labour intensive. They hire labourers, not only to cope with work peaks, but also to increase the income the members of the family earn. While they are clearly different to family farms, these patronal farms are still a far cry from "corporate farms". In the latter case, the investors are motivated by the relationship between the profit and the capital invested, and not by the payment for work they do not provide [START_REF] Cochet | Capital-labour separation and unequal value-added distribution: repositioning land grabbing in the general movement of contemporary agricultural transformations[END_REF]. Indian agriculture cannot be reduced to a homogenous series of family farms, and it shows a large diversity of agricultural enterprises. The latter differ more in terms of the role they attribute to hired labour, than in terms of their surface area. While it is common to employ labourers on most farms, the reasons for this cover a range of contrasting realities. While it complements family labour on family farms, it is a means of increasing the earnings of the family workforce on patronal farms.

The latter category is probably the most typical in Indian agriculture and the most original in world agriculture. In the family business farms studied in different parts of the world [START_REF] Gasson | The farm as a family business: a review[END_REF]Pritchard et al., 2006;[START_REF] Weller | Family or Enterprise? What shapes the business structures of Australian farming?[END_REF][START_REF] De Souza | Family Farming in Brazil: Modernized and Integrated[END_REF][START_REF] Chaxel | Family-Run Farm Enterprises, Territories and Policies in Argentina[END_REF], the use of hired labour is not systematic and does not have the same intensity. Patronal farms with similar functioning to those identified in India are described in Indonesian palm oil production, but they find their place in a dynamic linking agro-industries and small family farms set up temporarily by the labourers [START_REF] Barral | Between Agro-industries and Family Business Farms: Ephemeral Smallholder Family Plantations in Indonesia[END_REF] which has no equivalent in India. The structural importance of patronal farms in India is linked to the country's agrarian history. It is the result of an incomplete agrarian reform, which left landless large part of the rural workforce, and a Green Revolution, which beyond inputs, was largely based on an intensification of the use of labour, thereby partly provided by hired workers. While this model has not allowed a large part of the rural Indian population to shift out of poverty, it created more jobs than corporate farming and made it possible to retain a large proportion of the active population in the countryside.

According to the International Labour Office, the agricultural sector still provides over 40% of jobs in India, while this proportion is 30% in China for example. This patronal agriculture has thus contributed to limiting unemployment and the expansion of slums, in an economy that is still little industrialised, and marked by secondary and tertiary sectors that generate few jobs. The Indian State developed a coherent agricultural policy, stabilising agricultural prices for patronal producers, while subsidising food for the poorest [START_REF] Dorin | Formation et répartition des gains de productivité agricole en Inde. 1980-1996[END_REF], often working for them. The Public Distribution System (PDS) has thus made it possible to keep agricultural salaries low. The White Revolution that gave the poorest access to a supplementary income through milk, has reinforced this edifice [START_REF] Aubron | Livestock farming in Indian agrarian change through 13 agrarian diagnoses, Presented at the International seminar "Milk and Dairy in India's Development Path. Lessons, challenges and perspectives[END_REF].

The recent history of Indian agriculture nonetheless questions the durability of this model. The question of rural salaries is a key issue today, and changes, however timid, seem to be taking place in agricultural production systems. The Mahatma Gandhi National Rural Employment Guarantee Act (MNREGA), voted in August 2005, follows on from numerous programmes that, since 1970, have sought to create employment for the poor by developing rural infrastructure. But for the first time, this is a legally binding law: the State commits to providing at least 100 days of paid employment to every rural household engaged in unqualified manual labour. The candidates are entitled to unemployment benefits if the local administration does not provide them work within 15 days of their application. This particularly restrictive context seems to have borne fruit, and may even have led to raising real salaries, which have stagnated for over twenty years [START_REF] Das | Wage Rates in Rural India, 1998-99 to 2016-17[END_REF][START_REF] Berg | Can public works increase equilibrium wages? Evidence from India's National Rural Employment Guarantee[END_REF]. These changes in salaries are probably not unrelated to the more frequent use of moto-mechanisation.

In the regions studied here, apart from irrigation equipment, moto-mechanisation has long remained marginal. Tractors nonetheless appeared in the countryside in the 1990s, and moto-mechanised cereal harvesting is increasingly common in certain regions. Less pronounced, but more problematic, is the growing use of chemical herbicides. The Indian consumption level had remained exceptionally low until present. Manual weeding was done by labourers, for whom it was a precious source of fodder. However, over recent years there has been a clear increase in the use of herbicides [START_REF] Gupta | The Rapid Diffusion of Herbicides in Farming in India: Patterns, Determinants, and Effects on Labor Productivity[END_REF]. Soil preparation that is increasingly mechanised is not a very time consuming activity, but this is not true of weeding and harvesting, which mobilise numerous workers. In parallel, in several states, land regulations have recently been modified to facilitate the introduction of large capitalist holdings and numerous authors question the effects of such measures on rural employment [START_REF] Singh | Corporate Farming in India: Is it Must for Agricultural Development[END_REF][START_REF] Swain | Corporate farming vis-a-vis contract farming in India: a critical perspective[END_REF]. More recently, three farm bills question in the long term the system of cereals public purchases and the price guarantees for producers in the concerned regions. These producers, often at the head of patronal farms where moto-mechanization is underway, have in fact strongly contested these farm bills during demonstrations in Delhi at the end of 2020. The question which arises is whether the Indian patronal farming model, which creates employment without being nonetheless able to reduce poverty, is compatible with a further liberalization of the Indian economy. If that is not the case and these transformations continue, the Indian subcontinent would change both its type of farm and its model of economic development.

India's weight in the world's agriculture and the originality of this farming model make the study of these transformations a major issue, and the methods used in this study (field research investigating in detail agricultural labour, both in technical and socio-economic terms) particularly valuable. These questions also call for a much more in-depth consideration of agricultural labour in national statistics, by quantifying within farms: the number of work days provided by family members and by labourers, as well as agricultural labour productivities and wages for different crop and livestock activities. As we have shown here, these indicators are as important as the size of the farms in characterizing and understanding the Indian farming model.

Figure 1 .

 1 Figure 1. Location and year of the field studies. Source: O. Philippon 2020.

Figure 2 .

 2 Figure 2. Agricultural land distribution according to farm size(1953, 1970, 1990, 2015). Source: B. Dorin, based on[START_REF] Dorin | Agriculture and Food in India. A Half-Century Review, from Independence to Globalization[END_REF],[START_REF] Bhattacharjee | Tax on Agricultural Income. Holy Cow of the Indian Economy[END_REF].

Figure 3 .

 3 Figure 3. Population and composition of the workforce: Census of India and NSS (1971-2018). Note: (1) NSS rounds 1977-78 to 2011-12: "agriculture" = "Primary sector"; (2) Value for the NSS round 2017-18 to be confirmed; (3) 2018 and 2021 population based on K.C. et al., (2018). Source: B. Dorin, based on various reports (Population censuses of India, National Sample Surveys).

  sown area (cumulative percentage) Operational holdings (cumulative percentage) 1953-54 (2.88 ha/farm)

Figure 4 .

 4 Figure 4. Crop intensity(India, 1961(India, -2017)). Source: Dorin 2020, "Agribiom-India" model, mostly based here on EPWRF (2020).

Figure 5 .

 5 Figure 5. Use of paid work in the production systems present in five study regions. Source: C. Aubron, S. Bainville and O. Philippon 2020, based on agrarian diagnoses IndiaMilk project.

Figure 6 .

 6 Figure 6. Relationships between farm size and salaried work. Note: Of the 42,152 households surveyed by the India Human Development Survey II (IHDS survey 2011-12), 16,475 have a net sown area greater than zero, those shown in the graph after removing few outliers (66 households). Source: B. Dorin, based on IHDS-II and Dorin et al. (2019).

Figure 7 .

 7 Figure 7. Work calendar for four contrasting types of farm. Source: C. Aubron, S. Bainville and O. Philippon 2020, based on agrarian diagnoses IndiaMilk project.

Figure 8 .

 8 Figure 8. Comparison of daily labour productivity in the main cropping and livestock farming systems with the agricultural daily wage in three study areas. Source: C. Aubron, S. Bainville and O. Philippon 2020, based on agrarian diagnoses IndiaMilk project

Figure 9 .

 9 Figure 9. Labour productivity, work time and gross margin per day of family labour in Bangaon, West Bengal 1 .

Table 1 . Labour requirements for the main cropping systems in three study areas (Number of work days/ha/year

 1

			Finger millet/horsegram	180
			Sunflower/horsegram	112
		Rainfed cropping systems	Sorghum/horsegram	137
			Maize/horsegram	143
	Gundlupet		Marigold/horsegram Associated turmeric	269 716
			Vegetables (3 cycles a year)	736
		Irrigated cropping systems	Vegetables and bananas on a two-year cycle	308
			Ginger associated with chilli	777
			Bananas	200
			Tobacco	299
			Tobacco/Millet	398
			Tobacco/Rice	437
	Petlad	Irrigated cropping systems	Wheat/Rice	225
			Mustard/Millet	176
			Chilli	466
			Tobacco//Banana	417
		Rainfed cropping systems	Aman rice	179
			Aman rice/boro rice	326
	Debra	Irrigated cropping systems	Cabbage+cucumber+chili Mulberry	845 940
			Aman rice/marigold	875

). Source: C. Aubron, S. Bainville and O. Philippon 2020, based on agrarian diagnoses IndiaMilk project.

Table 2 . Main features of family, patronal and corporate Indian farming models.

 2

March 29 th -April 1 rst , 2021Clermont-Ferrand (France)

1 bigha=0,1350 ha


Kanty Rabenorosoa

Cédric Clévy
email: cclevy@femto-st.fr

Philippe Lutz
email: plutz@femto-st.fr

Sylwester Bargiel
email: sbargiel@femto-st.fr

Christophe Gorecki
email: cgorecki@femto-st.fr

A micro-assembly station used for 3D reconfigurable hybrid MOEMS assembly

Micro-assembly has been identified to be a critical technology in the microsystems technology and nanotechnology. The increasing needs of MOEMS (Micro-Opto-Electro-Mechanical Systems) for the microsystems conducts to development of new concepts and skilled micro-assembly stations. This paper presents a 3D micro-assembly station used for the reconfigurable free space micro-optical benches (RFS-MOB) which are a promising type of MOEMS. The designed parts of RFS-MOB are assembled by using the developped microassembly station. Experimental results are shown and validate the effectiveness of the micro-assembly station and the microassembly strategies.

I. INTRODUCTION

Over the last few years the request for miniature objects and devices has continuously increased. So the need for MEMS (Micro Electro Mechanical Systems) and MOEMS (Micro Opto Electro Mechanical Systems) in the field of telecommunication and sensor technology [START_REF] Tolfree | Commercializing Micro-Nanotechnology Products[END_REF] has become more and more important. Miniaturization of optical components and the assembly of various components constitute the principal challenge in hybrid MOEMS manufacture. For fabricating MOEMS, Free-Space Micro-Optical Benches (FS-MOB) represent a very promising solution. They consist in the mounting of several different micro-optical components coming from various sectors of manufacturing on a same substrate. The relative position of these components with the alignment of optical path enables the fabrication of complex hybrid products. Indeed, optical components (lenses, mirrors, fiber holders, detectors, beam splitters) are microfabricated using "simple", well known and reliable processes [START_REF] Motamedi | Micro-opto-electromechanical devices and on-chip optical processing[END_REF], [START_REF] Wu | Micromachined free-space integrated micro-optics[END_REF]. These components are then assembled together permitting the fabrication of complex 3D microstructures [START_REF] Rathmann | Concepts for Hybrid Micro Assembly Using Hot Melt Joining[END_REF], [START_REF] Descour | Toward the development of miniaturized imaging systems for detection of pre-cancer[END_REF], [START_REF] Nolan | Apparatus and methods of manufacturing and assembling microscale and nanoscale components and assemblies[END_REF], [START_REF] Kim | A flexible microassembly system based on hybrid manipulation scheme for manufacturing photonics components[END_REF]. The understanding of the microworld phenomena [START_REF] Gauthier | Forces analysis for micromanipulations in dry and liquid media[END_REF] and the automation of the micro-assembly tasks are currently under investigation. Recent results in the field of multiscale assembly, especially serial precise assembly demonstrate the validity of a new approach for fabricating complex 3D MOEMS based on micro-assembly [START_REF] Das | µ 3 : Multiscale, deterministic micro-nano assembly system for construction of on-wafer microrobots[END_REF], [START_REF] Dechev | Microassembly of 3-d microstructures using a compliant, passive microgripper[END_REF]. These results are accompagnied by the development of micro-assembly stations which integrate flexibility, modularity, precision and repeatability. High yield assembly of micro-objects depends on the compatibility of tolerances between micro-assembly station and micro-object dimensions. The micro-assembly station bring an interesting solution for fabricating 3D MOEMS which integrate some RFS-MOB and enable the design of 3D complex optical path. Due to the microfabrication tolerances and the inaccuracy of optical parameters coming from technological processes, the development of new micro-assembly station able to compensate them through the assembly of reconfigurable free space micro-optical benches (RFS-MOB) is proposed. This station enables the manipulation of generic components of RFS-MOB using active microgripper associated to a robotic microassembly system. Active gripping ensures reversible locking systems (which are not possible with passive gripping) and a fine control of tasks like [START_REF] Rabenorosoa | Precise motion control of a piezoelectric microgripper for microspectrometer assembly[END_REF]. For the precise control of position and the alignment of optical path, the 3D micro-assembly station comprises of 8 degrees of freedom (DOF) arranged into 2 manipulators with a vision system. In this paper we propose an original micro-assembly station equiped with an active microgripper. In the following, the concept of RFS-MOB is detailled in Section I. Section II describes the robotic micro-assembly system. Section III presents the experimental results. Finally, Section IV provides some conclusions.

II. THE CONCEPT OF RFS-MOB

The concept of RFS-MOB is composed of two bulkmicromachined silicon parts: a non-movable substrate (base), and a removable MOEMS chip (holder) with desired optical component (see Figure 1,2). The hybrid free-space optical system can be built on the substrate by the assembly of the individual holders equipped with optical function on the precisely formed rails using an active microgripper . The substrate is a reference part for the others parts of the optical system and allows their alignment on micromachined rails, along the optical axis. The substrate can be designed for the simplest configuration with one straight rail or the complex form (two or three perpendicular rails). It is composed of two anisotropically etched V-grooves (guiding of movement) and a central runner with two vertical V-grooves (see Figure 4). Such a construction of the rail ensures the well defined surfaces of reference for the other parts of MOB. This surface permits the optical path alignement in Z direction which improve the performance of the optical bench (reduction of optical loss). The holder with appropriate optical component can be assembled on such a rail using a microgripper, accurately positioned by a 3D micro-assembly station. In such a configuration, the holder contacts with the rail by two protruding grooves with triangular cross-section, compatible to the guiding V-grooves. In order to fasten the holder in a chosen position onto the rail, it contains a mechanical snap connector with two folded springs, which shape is adjusted at the end to the shape of the vertical V-grooves (see Figure 1). Once the springs are pressed by the microgripper (see Figure 3), the holder can be inserted directly into the rail, adjusted to the optical setup, and then fastened by the release of the springs. The mechanical contact of the holder with the substrate occurs between its two protruding rails and the V-grooves on the base. The snap connector is also in contact to a rhomboidshaped runner formed on the carrier's back side and they ensures the lock in Z direction (see Figure 2). Hence, once the adjustment of the all holders is finished, UV-curable glue can be used to definetely preserve their positions on the rail.

The dimensions of the bench is 2.5 cm x 1 cm. The dimensions of the holder is 800 µ m x 1350 µ m x 50 µ m, and the cross section of the spring is 10 µ m x 50 µ m.

The results of fabricated rails are shown in At the end of the process, the holders are maintained by a tether designed in [START_REF] Hériban | A mechanical detethering technique for silicon mems etched with a drie process[END_REF]. The lens holder receives a special design for integrating a lens grip. A lens grip is two flexible cantilever equipped at the end by doble hooks (see Figure 5). From a micro-assembly point of view, the RFS-MOB concept helps to reduce adhesion effects during releasing the holder. When the holder is locked into the rail, protruding rail and V-grooves are in contact, like the leg and the vertical V-grooves. These contacts are blocking the lateral movement of the holder during the releasing which occurs when the adhesion force is not dominated by another forces.

An attractive feature of the presented MOB technology is the ability to adjust the position of every optical part by active way. Thus, the inaccuracy of the optical parameters coming from technological processes, e.g. shift in a focal length of microlens, can be compensated. This feature makes the MOB an reconfigurable tool to build the optical systems at different level of complexity.

III. MICRO-ASSEMBLY CHALLENGE AND MICRO-ASSEMBLY SYSTEM

A. Micro-assembly Challenge

The micro-assembly of micro-optical benches needs a precise and an adapted micro-assembly station. In addition, the features of this station must match the required DOF for micro-optical bench assembly. For these reasons, the developped micro-assembly station integrates:

1) coarse and fine postionning stages. The ability of the micro-assembly station for positioning the holder along the rail depends on the range of the stage. The fine positioning is used for compensating positioning errors from of the coarse manipulator, 2) two rotation stages (pitch and yaw) for micro-object orientation on the bench (rolling is not necessary because of the design of the components), 3) views of assembly sequence (top view and side view) to enable teleoperated assembly, 4) adapted end-effector of the microgripper which have a suitable dimension for the holder and ball lens gripping, 5) reduction of the effects of adhesion forces during micro-assembly.

B. Micro-assembly system 1) Description of the workcell:

In order to perform serial assembly, the workcell comprises a robotic structure, vision system, and a microgripper. The proposed 3D microrobotic assembly system is a structure with eight DOF motorized stages arranged into two robotic manipulators. The kinetic scheme of this robotic structure is presented in Figure 6. The resolution of the piezo actuator can attain 1.6 µ m/V consequently submicrometric accurate motions are achievable. In reference to [START_REF] Clévy | Flexible micro-assembly system equiped with an automated tool changer[END_REF], [START_REF] Hériban | Robotic micro-assembly of microparts using a piezogripper[END_REF], the modularity of this microgripper is largely proved. Appropriate finger tips (tools) are chosen and installed on the MMOC. The microgripper is mounted at the end of manipulator M1 (see Figure 7). The grasping is done on the flexible part of the holder shown in Figure 3. This microgripper has to provide enough gripping forces during micro-assembly. The blocking forces is up to 100 mN in Y direction and 15 mN in Z direction for 100 V .

3) Control system of the micro-assembly station: The micro-assembly station is also equipped with a visualization system. It helps the alignment for entering in the groove, guiding, and supervising the whole assembly process (teleoperated mode in these works). This micro-assembly station is controlled via AP2M (French acronym of "Application for Controlling the MicroManipulation"), a home made software based on Borland C++ Bulder 6.0. AP2M is a software which makes a link between human (operator) and movable parts of the station. The modularity of this software enables the rapid development of the station. An AP2M module is developped for each constituant of the micro-assembly station (stage, gripper,...). It enables teleoperated assembly by a joystick and automated pick and place tasks. Due to the flexibility of the AP2M, the integration of new devices (force sensor, position sensor, camera) is simplified.

C. Micro-assembly sequence 1) General assembly sequence:

The general assembly sequence gives a global view of the tasks done after microfabrication of the parts. For the holders, there are made by using a 4 Inches SOI wafer and at the end of the microfabrication process, each holder is maintained by the theter on the wafer. Substrates are done on 4 Inches wafer and separated by dicing. The substrate is firstly brought on the M2 robot and is used like a workplane during the holder assembly (Figure 8-1). The tethers are broken and the holder is picked and put on the holder storage (Figure 8-2). After that, the holder storage is put on the substrate and the assembly of the holder on the substrate is following (Figure 8-3).

2) Detailled assembly sequence: Micro-assembly process is the sequence of tasks to operate for obtaining complexe heteregenous devices. The sequence of tasks takes into account the specifities of the parts. The substrate is the reference part during assembly process of RFS-MOB. Holders are sequentially assembled on it and a precise position control is very important for ensuring the optical features of the assembled systems. Each holder assembled to the substrate goes through six steps, which are: (1) the holder is picked by a microgripper, (2) the holder is removed from the chip wafer, (3) the holder is moved and rotated, (4) the holder is aligned to the groove and inserted on input port of the guiding rail, (5) the holder is guided on the rail, and (6) the holder is released. During the guiding, two strategies can be employed: -The contact between the protruding rails and the V-grooves is maintained. The overshoot of the contact force has to be controlled to avoid the sliding of the micro-parts between the microgripper and the breaking of the flexible part.

-The contact is avoided and control laws which take into account the forces in micromanipulation are developing. In this sense, force feedback during the guiding task is investigating. For the teleoperated mode, the operator manages the guiding task by the views of the cameras.

IV. EXPERIMENTAL RESULTS

A. Holder assembly

The assembly sequence is tested on the micro-assembly station. This experiment is done by teleoperated mode by using the joystick. The assembly sequence is followed and first results of assembly are shown in the Figure 9. During the releasing of the holder, the effectiveness of the blocking force for reducing the adhesion force is observed. The Z-lock rail and two folded springs ensure the fastening of the assembled holder.

B. Ball lens assembly

The ball lens has to be inserted on the lens holder designed with the ball lens grip. The diameter of the ball lens is 254 µ m. Two strategies can be used for the ball lens assembly: -the ball lens is previously put on the lens holder and after that the lens holder is assembled on the substrate -the ball lens is put on the lens holder when this one is assembled on the substrate.

This second strategy is choosen because the right position of the holder in the substrate enables a good accessibility on the lens grip. For assembling the ball lens in the lens holder, the ball lens is picked by the microgripper and inserted into the lens grip. The ball lens is correctly maintained when it is gripped on the center. The sequence of pictures during the insertion of the ball lens in the lens grip is shown in Figure 10.

C. Assembled demonstrator

First results conduct to the fabrication of a demonstrator. The assembled demonstrator is composed of a mirror and a lens holder. The ball lens is put on the lens holder after the assembly of the holder on the substrate. This demonstrator can be used for testing the focal length of the ball lens by changing the distance between the mirror and the lens holder. The distance which minimizes the spot size form the fiber laser source corresponds to the focal length. The complete view of the RFS-MOB demonstrator is shown in Figure 11.

D. Positioning accuracy

Positioning accuracy of components is an important criteria which influences optical microbenches. The developed microassembly station enables 1 nm resolution along x, y, and z and 3 µ • in α and β. Fine positioning of components can be done by active positioning, in other words, optimized position corresponds to a minimal optical loss. The reversible locking enables to perform this step.

E. Observed difficulties during micro-assembly

During the micro-assembly of the demonstrator, the principal diffulties concern the control of the guiding task. Indeed the contact appears between V-grooves of the substrate and protruding grooves of the holder. During the contact, the overtaking friction can break the flexible part of the holder. The use of force control can reduce the risk of breaking. In this case, the integration of force sensors in the micro-assembly station constitutes a future works. Additionnaly, the microscale forces like electrostatic, and pull-off force (included van de Waals, and capillary force) have to be taken into account and conducts to the developpment of microscale hybrid force position control for precise control of the contact (or the interaction).

V. CONCLUSION

In this paper, we have proposed a micro-assembly station which permits the assembly of 3D MOEMS. The RFS-MOB is introduced to bring a response to a new generation of complex assembled MOEMS. Indeed the microfabrication of elementary optical components uses "simple", well known and reliable processes. This station enables the assembly of new micro-optical systems based on the micro-assembly of holders with optical features and the substrate. The use of actuated microgripper is a proposed solution for ensuring the reconfigurability of the micro-benches. The micro-assembly system is developed and an eight DOF robotic configuration with nanometric resolution ensures the precise positioning of the components. The principle is validated through successful assembly sequence of holders on the substrate in teleoperated mode. A demonstrator MOEMS with a mirror and a lens holder is assembled. Other type of optical components can be designed like diffractive lens, beam splitter, and others,which can also be assembled with the same micro-asssembly station. At the end, complete MOEMS like microspectrometer, 3D confocal miniaturized microscope, and miniaturized goniometer can be obtained. The main advantages of the RFS-MOB concept is the reconfigurability and the use of generic optical components for obtaining rapidly complexe and new hybrid microsystems. According to the reconfigurability of RFS-MOB, it can also be used like a tool for characterizing new optical components. Due to the compliance of the micro-objects, the use of the force sensor constitutes a promising solution for automated pick and place or guiding. The integration of force sensor in the workcell and hybrid force/position control law are in current investigation. The characterization of the assembled microbench should complete the project and future work will focus on this.

Fig. 1 .

 1 Fig. 1. RFS-MOB concept: general view.

Fig. 2 .

 2 Fig. 2. RFS-MOB concept: Holder assembled on the substrate.

Fig. 3 .

 3 Fig. 3. (1) Gripping principle of the holder by the microgripper and (2) releasing in the groove.

Figure 4 .

 4 The substrate is obtained after the following microfabrication process: 1) thermal oxydation of the double side wafer with 1.4 µ m, 2) photolitography 1 of the back side and SiO 2 etching in BHF, 3) KOH etching in back side for forming 100 µ m membrane, 4) thermal oxydation of the back side with 1.0 µ m, 5) photolitography 2 of the top side and SiO 2 etching in BHF, 6) photolitography 3 of the top side and DRIE etching of 100 µ m membrane, 7) after stripping and cleaning, silicon etching in KOH, 8) SiO 2 stripping in HF.

Fig. 4 . 6 )

 46 Fig. 4. Microfabricated substrate using DRIE and KOH etching: (1) general view of the wafer, (2) bench with straight rail after dicing, (3) the rail with a ruler, and (4) view of V-groove and the vertical V-groove. The results of fabricated holders are shown in the Figure 5. The available components are mirror, lens holder, and circular aperture. The substrate is obtained after the following microfabrication process: 1) thermal oxydation of the double side wafer with 1.2 µ m, 2) photolitography 1 of the back side and photolitography 2 of the top side, 3) SiO 2 etching in BHF and photoresist stripping, 4) DRIE etching of the top side, 5) silicon etching in KOH by protected the top side by a chuck,

Fig. 5 .

 5 Fig. 5. SEM pictures of the designed lens holder

Fig. 6 .

 6 Fig. 6. The kinematic sheme of the microrobotic structure. The manipulator M1 is a large space positioning robot with four DOF. It is composed of linear coarse positioning stages from Physik Instrumente -M112.1 DG (with 25 mm of travel range) and a rotation stage SmarAct -SR-3610-S (with 1.1 µ • of resolution). This robot permits to manipulate holder (break tether, pick, move, align to the groove and guide the holder) and other optical components. The manipulator M2 constitutes a support of the substrate and is composed of fine positioning robot with four DOF based on P-611.3 NanoCube XYZ Piezo Stage with nanometric resolution (with 100 µ m of travel range) and a rotation stage SmarAct -SR-3610-S. This robot carries the substrate during the assembly process and corrects the trajectory during the guiding operation. All of these stages are closed loop controlled. The robotic configuration is shown in Figure 7. 2) High voltage piezogripper: For gripping holders, ball lenses,.. and ensuring reconfigurability, actuated microgripper which is the MMOC (Micromanipulator-Microrobot-On-Chip) piezogripper developed in FEMTO-ST Institute [13] was chosen. It has two active fingers and two DOF for each finger. Both fingers of the microgripper can independently move along Y and Z. It permits a stroke of 320 µ m in open-close motion(Y) and 400 µ m in up-down motion (Z).The resolution of the piezo actuator can attain 1.6 µ m/V consequently submicrometric accurate motions are achievable. In reference to[START_REF] Clévy | Flexible micro-assembly system equiped with an automated tool changer[END_REF],[START_REF] Hériban | Robotic micro-assembly of microparts using a piezogripper[END_REF], the modularity of this microgripper is largely proved. Appropriate finger tips (tools) are chosen and installed on the MMOC. The microgripper is mounted at the end of manipulator M1 (see Figure7). The grasping is done on the flexible part of the holder shown in Figure3. This microgripper has to provide enough gripping forces during micro-assembly. The blocking forces is up to 100 mN in Y direction and 15 mN in Z direction for 100 V .3) Control system of the micro-assembly station: The micro-assembly station is also equipped with a visualization system. It helps the alignment for entering in the groove,

Fig. 7 .

 7 Fig. 7. Developed micro-assembly station for micro-optical benches.

Fig. 8 .

 8 Fig. 8. Description of the general assembly sequence.

Fig. 9 .

 9 Fig. 9. Assembly sequence for holder micro-assembly: (1) Pick of the mirror on the flexible part (springs), (2) Move on space after rotation, (3) Guide in the groove, (4) Release.

Fig. 10 .

 10 Fig. 10. Assembly sequence of ball lens using a microgripper: (1) the ball lens is gripped by the microgriiper ann align to the lens grip, (2) the ball lens is inserted to the lens grip, and (3) the ball lens is released and maintained into the lens grip.

Fig. 11 .

 11 Fig. 11. SEM pictures of the assembled demonstrator.

VI. ACKNOWLEDGEMENT

This work has partially been supported by the Franche-Comté region under the MIAAMI Project and NEMO/Marie-Curie. The authors would like to thank David Hériban for discussions and his help.