Abstract-This paper studies automated tasks based on hybrid force/position control of a flexible object at the microscale. A guiding task of a flexible micropart is the case of the study and is achieved by a two-sensing-finger microgripper. An experimental model of the behavior of the microgripper is given and the interaction forces are studied. Based on grasp stability, a guiding strategy taking into account the pull off forces is proposed. A specific control strategy using an external hybrid force/position control and taking into account microscale specificities is proposed. The experimental results of automated guiding task are presented.Note to Practitioners -This article's motivation is the need of very precise positioning in micromanipulation and microassembly tasks. The guiding tasks are a part of the microassembly process. Such guiding tasks are rarely automated. This is mainly due to the fact that automation in the microworld is a new issue and the literature only concerns the local control of microactuators and microrobots for the moment. Hybrid force/position control is a promising approach to achieve an automated guiding task of the micropart. To detect the contact between the micropart and the rail, a two-sensing-finger microgripper is used. The controller aims to release the contact and to continue going forward within the guiding axis. The proposed controller is very accurate, with high speed (low rejection time) and easy to implement. It is noticed that the proposed control scheme can also be applied to other microassembly tasks (pick-and-place, insertion, etc).

In this paper, the prototyping of a new piezoresistive microforce sensor is presented. An original design taking advantage on both mechanical and bulk piezoresistive properties of silicon is presented and enables to easily fabricate a very small, large range, high sensitivity with high integration potential sensor. The sensor is made of two silicon strain gages for which widespread and known microfabrication processes are used. The strain gages present a high gage factor which allow a good sensitivity of this force sensor. The dimensions of this sensor are 700µm in length, 100µm in width and 12µm in thickness. These dimensions make its use convenient with many microscale applications notably its integration in a microgripper. The fabricated sensor is calibrated using an industrial force sensor. The design, microfabrication process, and performances of the fabricated piezoresistive force sensor are innovative thanks to its resolution of 100nN and its measurement range of 2mN. This force sensor presents also a high signal to noise ratio, typically 50dB when a 2mN force is applied at the tip of the force sensor.