No abstract

No abstract

Abstract-Piezocantilevers are commonly used for the actuation of micromechatronic systems. These systems are generally used to perform micromanipulation tasks which require high positioning accuracy. However, the nonlinearities, i.e. the hysteresis and the creep, of piezoelectric materials and the influence of the environment (vibrations, temperature change, etc.) create difficulties for such a performance to be achieved. Various models have been used to take into account the nonlinearities but they are often complex. In this paper, we study a one degree of freedom piezoelectric cantilever. For that, we propose a simple new model where the hysteresis curve is approximated by a quadrilateral and the creep is considered to be a disturbance. To facilitate the modelling, we first demonstrate that the dynamic hysteresis of the piezocantilever is equivalent to a static hysteresis, i.e. a varying gain, in series with a linear dynamic part. The obtained model is used to synthesize a linear robust controller, making it possible to achieve the performances required in micromanipulation tasks. The experimental results show the relevance of the combination of the developed model and the synthesized robust H∞ controller.Index Terms-Piezoelectric devices, hysteresis and creep, quadrilateral approximate model, robust control, micromanipulation.

Piezoelectric meso- and microactuator systems required for manipulation or assembly of microscale objects demand reliable force and/or displacement information. Available sensors are prone to dimension restrictions or precision limitation. Self-sensing method, based on the electric charge measurement, may represent a solution in terms of cost-effectiveness and integration, the actuator performing simultaneously as its own sensor. This paper presents a self-sensing method dedicated to free uni- and bimorph piezocantilevers but can also be adapted to other piezoactuator types. The integrated electric current, used to convert the charge, can be compensated against piezoelectric material nonlinearities to provide accurate displacement information. The advantages relative to existing self-sensing methods consist in the ability to keep this displacement information for long-term periods (more than a thousand seconds) and in the reduction in signal noise. After introductive issues related to the method the base principle allowing the estimation of tip displacement is presented. Then, the identification procedure of the estimator parameters is depicted and representative experimental results are shown. Finally, a series of aspects related to electronic circuits are discussed, useful for successful system implementation.

The works presented in this article are motivated by the high performances required in micromanipulation/microassembly tasks. For that, this paper presents the developement, the modelling and the control of a 2 degrees of freedom (in linear and angular motion) micropositioning device. Based on the stick-slip motion principle, the device is characterized by unlimited strokes and submicrometric resolutions. First, experiments were carried out to characterize the performances of the micropositioning device in resolution and in speed. After that, a state-space model was developed for the sub-step functioning. Such functioning is interesting for a highly accurate task like nanopositioning. The model is validated experimentally. Finally, a controller was designed and applied to the micropositioning device. The results show good robustness margins and a response time of the closed-loop system.

Self-sensing technique consists in using an actuator as a sensor at the same time. This is possible for most of actuators with physically reversible principle such as piezoelectric materials. The main advantages of self-sensing are: 1) the embeddability of the measurement technique, and 2) its low cost as no additional sensor is required. This paper presents a self-sensing technique for piezoelectric actuators used in precise positioning applications like micromanipulation and microassembly. The main novelty is that both displacement and force signals can be simultaneously estimated. This allows a feedback control using one of these two signals with a display of the other signal. To demonstrate this advantage, a robust H∞ feedback control on displacement with real-time display of the force is used as an application of the proposed selfsensing technique. Along the paper, experimental results obtained with a piezoelectric cantilever actuator validate and demonstrate the efficiency of the proposed self-sensing.

This paper deals with a historical overview of the activities of the French FEMTO-ST institute in the field of microrobotic manipulation and assembly. It firstly shows tools developed for fine and coarse positioning: 4 DOF microgrippers, 2 DOF modules and smart surfaces. The paper then goes on the automation of tridimensional microassembly of objects measuring between 10 and 400 microns. We are especially focusing on several principles. Closed loop control based on micro-vision has been studied and applied on the fully automatic assembly of several 400 microns objects. Force control has been also analyzed and is proposed for optical Microsystems assembly. At least, open loop trajectories of 40 microns objects with a throughput of 1,800 unit per hour have been achieved. Scientific and technological aspects and industrial relevance will be presented. Keywords Microgrippers • Microassembly • Micromanipulation • Microrobotic automation • MEMS assembly 1 Introduction Until now, miniaturization was driven by a general diminution of the volume of the product (e.g. cell phones). Currently, the major objective of the miniaturization is to

Size reduction is a constant objective in new technologies, for which very accurate devices are needed when manipulating sub-millimetric objects. A new kind of microfabricated microrobot based on the use of bistable modules is designed to perform open-loop controlled micropositioning tasks. The DiMiBot (Digital MicroroBot) opens a new paradigm in the design of microrobots by using mechanical stability instead of complex control strategies. We propose a new architecture of digital microrobot for which forward and inverse kinematics models are easy to use. These kinematic models are validated with FEA simulations before the fabrication of a real DiMiBot prototype. Tests and characterization of the prototype are made and compared to the desired behavior. Thanks to its submicrometric resolution and to its small dimensions (∼ 400 µm thickness), it is able to manipulate micro-objects in confined environments, where no other robot can be used.