Positioning and trajectory following tasks in microsystems using model free visual servoing

In this paper, we explore model free visual servoing algorithms by experimentally evaluating their performances for various tasks performed on a microassembly workstation developed in our lab. Model free or so called uncalibrated visual servoing does not need the system calibration (microscope-camera-micromanipulator) and the model of the observed scene. It is robust to parameter changes and disturbances. We tested its performance in point-to-point positioning and various trajectory following tasks. Experimental results validate the utility of model free visual servoing in microassembly tasks

A versatile and reconfigurable microassembly workstation

In this paper, a versatile and reconfigurable microassembly workstation designed and realized as a research tool for investigation of the problems in microassembly and micromanipulation processes and recent developments on mechanical and control structure of the system with respect to the previous workstation are presented. These developments include: (i) addition of a manipulator system to realize more complicated assembly and manipulation tasks, (ii) addition of extra DOF for the vision system and sample holder stages in order to make the system more versatile (iii) a new optical microscope as the vision system in order to visualize the microworld and determine the position and orientation of micro components to be assembled or manipulated, (iv) a modular control system hardware which allows handling more DOF. In addition several experiments using the workstation are presented in different modes of operation like tele-operated, semiautomated and fully automated by means of visual based schemes

The effects of cold arm width and metal deposition on the performance of a U-Beam electrothermal MEMS microgripper for biomedical applications

Microelectromechanical systems (MEMS) have established themselves within various fields dominated by high-precision micromanipulation, with the most distinguished sectors being the microassembly, micromanufacturing and biomedical ones. This paper presents a horizontal electrothermally actuated 'hot and cold arm' microgripper design to be used for the deformability study of human red blood cells (RBCs). In this study, the width and layer composition of the cold arm are varied to investigate the effects of dimensional and material variation of the cold arm on the resulting temperature distribution, and ultimately on the achieved lateral displacement at the microgripper arm tips. The cold arm widths investigated are 14 μm, 30 μm, 55 μm, 70 μm and 100 μm. A gold layer with a thin chromium adhesion promoter layer is deposited on the top surface of each of these cold arms to study its effect on the performance of the microgripper. The resultant ten microgripper design variants are fabricated using a commercially available MEMS fabrication technology known as a silicon-on-insulator multi-user MEMS process (SOIMUMPs)TM. This process results in an overhanging 25 μm thick single crystal silicon microgripper structure having a low aspect ratio (width:thickness) value compared to surface micromachined structures where structural thicknesses are of the order of 2 μm. Finite element analysis was used to numerically model the microgripper structures and coupled electrothermomechanical simulations were implemented in CoventorWare ®. The numerical simulations took into account the temperature dependency of the coefficient of thermal expansion, the thermal conductivity and the electrical conductivity properties in order to achieve more reliable results. The fabricated microgrippers were actuated under atmospheric pressure and the experimental results achieved through optical microscopy studies conformed with those predicted by the numerical models. The gap opening and the temperature rise at the cell gripping zone were also compared for the different microgripper structures in this work, with the aim of identifying an optimal microgripper design for the deformability characterisation of RBCs.peer-reviewe

Potentialities of optimal design methods and associated numerical tools for the development of new micro- and nanointelligent systems based on structural compliance - An example -

11 pagesInternational audienceThis paper deals with the interest and potential use of intelligent structures mainly based on compliant mechanisms (and optionally including smart materials), for the development of new micro- and nano-robotics devices. The state of the art in optimal design methods for the synthesis of intelligent compliant structures is briefly done. Then, we present the optimal method developed at CEA LIST, called FlexIn, and its new and still in development functionalities, which will be illustrated by a few simple design examples. An opening will be given about the possibility to address the field of Nanorobotics, while adding functionalities to the optimal design method

Modeling and optimal force control of a nonlinear electrostatic microgripper.

International audienceMicrogrippers with integrated force sensors are very efficient tools for dexterous manipulation of objects in the microworld (size less than 100 µm). In this paper, we first propose a modeling approach of a nonlinear electrostatic microgripper with integrated force sensor while handling calibrated micro-glass balls of 80 µm diameter. Limit of the linear operating range of the microgripper is investigated and a nonlinear model is proposed and validated experimentally for large displacements. We then propose the design of an optimal force feedback controller to ensure reliable handling operations with appropriate gripping forces. To overcome the limitation caused by the low signal to noise ratio provided by the sensor, a Kalman filter is used to estimate the states of the process from noise measurements. The control law is implemented and validated using real time experiments for 10 µN gripping force reference with a noise level (peak-to-peak magnitude of the noise) reaching 8 µN in the worst case. The effectiveness of the optimal filter is proven by comparison with external interferometric measurements

Design and analysis of a MEMS-based electrothermal microgripper

Microelectromechanical systems (MEMS) have established themselves in various science and engineering domains. MEMS-based microgrippers provide several advantages in terms of compact size and low cost, and they play vital roles in microassembly and micromanipulation fields within both micromanufacturing and biological sectors. Microactuators based on different actuation principles have been devised to drive MEMS microgrippers. This paper presents a finite element model of a MEMS-based electrothermally actuated microgripper performed using CoventorWare ®. The microgripper design follows standard micromachining processes that make use of reactive ion etching where polysilicon acts as the main structural material while a chromium and gold layer is deposited on the structure for thermal actuation. The simulations are used to assess the performance of the microgripper and to optimise its operating parameters.peer-reviewe

Redesign of the MMOC microgripper piezoactuator using a new topological optimization method.

International audienceThis paper presents a new method developed for the optimal design of piezoactive compliant mechanisms. It is based on a flexible building blocks method, called FlexIn, which uses an evolutionary approach, to optimize a truss-like structure made of passive and active piezoelectric building blocks. An electromechanical approach, based on a mixed finite element method, is used to establish the model of the piezoelectric blocks. A planar monolithic compliant microactuator is synthetized by the optimization method, based on the specifications drawn from a piezoelectric microgripper prototype (MMOC). Finally, some performances comparisons between the optimally FlexIn synthetized gripper and the previous gripping system demonstrate the interests of the proposed optimization method for the design of microactuators, microrobots, and more generally for adaptronic structrures

Hybrid Design of a Polymeric Electrothermal Actuator for Microgripper

Thermal micro actuators are widely used for large displacement, high accuracy and repeatability. The applications of these devices are in the fields of micro assembly, micro surgery and manipulation of micro particles. In this paper, the development of electro thermal micro actuator based on PMMA (Poly Meta Methyl Acrylate) is described. The paper presents the development of a new micro actuator for a microgripper which has a combination of asymmetric arm and bi-layer structure to completely eliminate the undesirable out of plane movement. Three models of electro thermally actuated polymeric micro actuators using low voltage of 0.1 V are designed and analyzed using COMSOL Multiphysics software. The results are discussed and compared to show the efficiency of the hybrid design. The hybrid design gives 2.5 μm of in plane gripping displacement and 0.02 μm out of plane displacement at 0.1 V

Submerged freeze gripper to manipulate Micro-objects.

International audienceManipulating microscopic objects with the necessary dexterity still remains a very challenging task. In this paper, we propose a freeze gripper able to manipulate micro-objects in an innovative way, i.e. in submerged surroundings. We first review the influences of dry and liquid media on contact forces and non contact forces. This comparative analyse clearly shows the interest of the liquid medium. A survey of different microhandling systems based on the use of ice is also given. Then submerged microgripper with frozen water as an active end-effector is porposed as a promising new approach for manipulating low thermal conductive micro-objects. A prototype using the Peltier effect has been numerically modeled and developed. It is described in the paper. Experimental results validate the cooling and warming of the freeze gripper. A generic micromanipulation task is the purpose of further work

Dynamic modelling for a submerged freeze microgripper using thermal networks.

International audienceThe growing interest for micromanipulation systems requires efficient, reliable and flexible handling strategies. Recent studies have demonstrated that performing manipulations and assembly in liquid surroundings is more advantageous than in dry conditions, especially when objects are under 100 μm in size. The thermally actuated ice microgripper proposed and analysed in this paper is designed to operate in a completely submerged manner in an aqueous medium. The handling principle which benefits from adhesive properties of ice, its thermal control principle based on Peltier effect, some features of the prototype, and the first micromanipulation tests are summarized. This paper is focused on the modelling of the thermal microhandling system using electrical analogy. The submerged microgripper is split into different subsystems which are studied in order to identify their thermal network. Then they are interconnected to build the whole thermal network of the submerged microgripper. This model is validated by comparison with experimental measurements. Controlling the temperatures involved in our device will be the purpose of further works