Force Tracking Impedance Control with Unknown Environment at the Microscale.

International audienceA new method to estimate the environment parameters is proposed in order to perform force tracking in impedance control despite the presence of an unknown environment. In impedance force tracking, the location of the environment relative to the robot and the stiffness of the environment should be known. The proposed method estimates the environment location and stiffness using only force and position measurements. The study is done for microscale taking into consideration microscale specificities, especially pull-off force. The impedance control formulation is tested experimentally in a contact transition scenario consisting of a compliant microforce sensor mounted on a microrobotic positioner, and three compliant microstructures with different stiffness. A traditional double mass-spring-damper model of the overall robot is employed to develop the closed-loop impedance control

Dynamic Force/Position Modeling of a one-DOF Smart Piezoelectric Micro-Finger with Sensorized End-Effector.

International audienceIn this paper, a generic microscale system is studied where a smart microsystem composed of an active based material actuator, sensorized structure and transformation system is studied. This problem is important at the microscale because it offers a force measurement of the applied force by the actuator to a flexible environment which enables to understand the interaction between the complete smart microsystem and the environment and to design and control the interaction between the system and the environment. A special case where a sensorized end-effector is fixed on the tip of a piezoelectric actuator is detailed. Integrating a sensorized end-effector influences the behavior of the smart microfinger and is not studied in recent works. The complete finger, which is called in this paper smart finger, consists of a piezoelectric actuator, an end-effector and a novel piezoresistive force sensor. A complete model is developed for generating both force and displacement at the finger's tip while interaction with a flexible environment. A nonlinear model of the piezoelectric actuator is considered and a complete model is developed taking into account the frequency dependent hysteresis of the piezoelectric actuator. The model of the hysteresis is based on the Bouc-Wen method which simplifies the parameter estimation. The complete dynamic force/position model of the finger is validated experimentally with small errors (less than 10%)

Prototyping of a highly performant and integrated piezoresistive force sensor for microscale applications

International audienceIn 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 700mm in length, 100mm in width and 12mm 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

Automated Guiding Task of a Flexible Micropart Using a Two-Sensing-Finger Microgripper.

International audienceThis 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

Explicit force control V.S. impedance control for micromanipulation.

International audienceThis paper presents a study of different force control schemes for controlling contact during manipulation tasks at the microscale. Explicit force control and impedance control are compared in a contact transition scenario consisting of a compliant microforce sensor mounted on a microrobotic positioner, and a compliant microstructure fabricated using Silicon MEMS. A traditional double mass-spring-damper model of the overall robot is employed to develop the closed-loop force controllers. Specific differences between the two control schemes due to the microscale nature of contact are highlighted in this paper from the experimental results obtained. The limitations and tradeoffs of the two control laws at the microscale due to the presence of backlash are discussed. A simple method to deal with the pull-off force effects specific to the microscale is proposed. Future improvements of the impedance control schemes to include adaptation are discussed in order to handle objects with unknown stiffness

Piston Motion Performance Analysis of a 3DOF Electrothermal MEMS Scanner for Medical Applications.

International audienceMEMS scanners are useful for medical applications as optical coherence tomography, and laser microsurgery. Although widespread design of MEMS scanners have been presented, their behaviour is not well known and thus their motions are not easily and efficiently controlled. This lack induces several difficulties (limited resolution, accuracy, cycle time, etc.) and to tackle this problem, the paper presents the modeling of an ISCelectrothermally actuated MEMS mirror and the experimental characterization for the piston motion. Modeling and characterization are important to implement the control.A multiphysic model is proposed and an experimental validation is performed with a good correspondence for a voltage range from 0V to 3.5V with a maximum displacement up to 200_m and with a relative tilting difference of 0.1°. The paper also presents a simple and efficient experimental setup to measure a displacement in dynamic and static mode or a mirror plane tilting in static mode

Micro-assemblage à l'aide d'une pince instrumentée en force et d'une commande hybride force / position.

This work proposes the use of an active microgripper with sensorized end-effectors for the automationof the microassembly of 3D hybrid MOEMS. Each of the two fingers of the microgripper is composedof a piezoelectric actuator with an integrated piezoresistive force sensor. The integrated force sensorpresents innovative performances compared to the existing force sensors in literature. The forcesensors provide the ability to measure the gripping forces applied by the microgripper to grasp a microcomponentand estimated the contact forces between the microcomponent and the substrate ofmicroassembly. A dynamic nonlinear model of the microgripper is developed. A hybrid force/positioncontrol is used for the automation of the microassembly. In the hybrid force/position control formulation,some axes are controlled in position and others are controlled in force. For the force controlledaxes, a new nonlinear force control scheme based on force tracking sliding mode impedance controlis proposed with parameter estimation. Using the proposed hybrid force/position control scheme, fullautomation of the microassembly is performed, notably for the guiding of a flexible component in arail.La thèse propose l’utilisation d’une pince active instrumentée en force pour automatiser l’assemblage des MOEMS 3D hybrides. Chacun des doigts de la pince instrumentée est composé d’un actionneur piézo-électrique et d’un capteur de force piézorésistif intégré. Le capteur de force intégré présente des performances innovantes par rapport aux capteurs existants dans l’ état de l’art. Cette pince offre la possibilité de mesurer les forces de serrage appliquées par la pince pour saisir un micro composant et d’estimer les forces de contact entre le micro composant et le substrat de micro-assemblage.Un modèle dynamique et non linéaire est développé pour la pince instrumentée. Une commande hybride force/position est utilisée pour automatiser le micro-assemblage. Dans cette commande, certains axes sont commandés en position et les autres sont commandés en force. Pour les axes commandés en force, une nouvelle commande fondée sur une commande en impédance avec suivi de référence est proposée selon un principe de commande non linéaire par mode glissant avec estimation des paramétres en lignes. En utilisant le schéma de commande hybride force/position proposé, une automatisation de toutes les tâches de micro-assemblage est réalisée avec succès, notamment sur un composant flexible à guider dans un rail

High Bandwidth Microgripper with Integrated Force Sensors and Position Estimation for the Grasp of Multi-stiffness Microcomponents.

International audienceAt the microscale, small inertia and high dynamics of microparts increase the complexity of grasping, releasing and positioning tasks. The difficulty increases especially because the position, the dimensions and the stiffness of the micropart are unknown. In this paper, the use of a microgripper with integrated sensorized end-effectors with high dynamic capabilities is proposed to perform stable and accurate grasps of multistiffness microcomponents. A dynamic nonlinear force/position model of the complete microgripper while manipulating a microcomponent is developed. The model takes into consideration not only free motion and constrained motion, but also, contact transitions which is a key issue at the microscale due to the predominance of surface forces. It enables to estimate the position of the microgripper’s end-effectors, the contact position of the microcomponent and the force applied on the microcomponent. Using the proposed microgripper and its model, both of the gripping forces are measured and the position of each of the microgripper’s endeffectors is estimated. This enables to perform a stable grasp of the micropart by providing force and position feedback. Moreover, using the developed microgripper and its model, the characterization of the microcomponent can be performed by estimating its dimensions and its stiffness

Microrobotic Station for Nano-Optical Component Assembly

Compact photonic structures have strategic importance in several fields. In order to fabricate more complex structures with optimized optical function, robotic nano-assembly is a promising solution because it enables to integrate several types of materials from different fabrication processes into the same structure. This paper presents a microrobotic station which is designed for the assembly of nano-optical components. The robotic station has 8-DOF for positioning and 4-DOF microgripper with integrated force sensors to perform dexterous and accurate manipulation of components by considering both position and contact force to achieve precise alignment and parallelism of structures

Microrobotic Station for Nano-Optical Component Assembly

Compact photonic structures have strategic importance in several fields. In order to fabricate more complex structures with optimized optical function, robotic nano-assembly is a promising solution because it enables to integrate several types of materials from different fabrication processes into the same structure. This paper presents a microrobotic station which is designed for the assembly of nano-optical components. The robotic station has 8-DOF for positioning and 4-DOF microgripper with integrated force sensors to perform dexterous and accurate manipulation of components by considering both position and contact force to achieve precise alignment and parallelism of structures