Electrostatic Microgripper Research Articles

Identification and Robust Controllers for an Electrostatic Microgripper

In this paper, it is presented system identification and design of robust force controllers for an electrostatic microgripper grabbing a microparticle. Firstly, it is analysed the most common models in the literature and then the identification process is performed. It is identified a family of models of Box–Jenkins type. Linear controllers of increasing complexity are designed, which are of low order aiming to reduce the computational burden in real-time. The controllers must have robustness of stability and performance. Simulations are performed in order to validate the controllers, which have robustness of stability and performance. Suggestions of future work are presented.

Gain Scheduling Control of a Nonlinear Electrostatic Microgripper: Design by an Eigenstructure Assignment With an Observer-Based Structure

This paper deals with the modeling and the robust control of a nonlinear electrostatic microgripper dedicated to embedded microrobotics applications. We first propose a polynomial linear parameter varying model of the system, where the varying parameter is the mean position of the microgripper that is used for the linearization. The controller is then derived using a multimodel and scheduled observer-based control strategy. The structure and the order of the controller are defined a priori allowing the derivation of a robust low-order controller suitable for a real-time implementation in embedded on-chip environments. Results show that a very wide (several tens of micrometers) and fast positioning of the gripping arm can be achieved using the control strategy. A robustness analysis and experimental implementation results show the efficiency of the controller and the relevance of the theoretical approach.

An output feedback LPV control strategy of a nonlinear electrostatic microgripper through a singular implicit modeling

The aim of the paper is the design and the analysis of a gain scheduled controller for an accurate and fast positioning with nanometer resolution of a nonlinear electrostatic microgripper. The controller is designed to achieve a positioning of the gripping arm from few hundred nanometers to several tens of micrometers with some performance criteria. This very large operating range is crucial for a range of microrobotics applications and has never been addressed in existing control techniques of microgrippers. The controller is designed considering noises that are relevant at the nanometer scale and nonlinearities that become significant at the micrometer scale. Therefore, a nonlinear model of the system is proposed and is reformulated into a polynomial LPV (Linear Parameter Varying) model. The most relevant source of noise to be considered for the controller synthesis is defined taking into account results from previous works. Considering the particular polynomial parametric dependence of the LPV model, a multivariable controller is designed using an affine LPV descriptor representation of the system and specific linear matrix inequalities. The efficiency of the controller and the relevance of the theoretical approach is demonstrated through experimental implementation results.

Overview of flexure-based compliant microgrippers

Microgripper is an essential device in the micro-operation system. It can convert other types of energy into mechanical energy and produce clamp movement with required chucking force, which enables it a broad application prospect in the domain of tiny components' processing and assembly, biomedicine and optics, etc. The performance of a microgripper is dependent on its power supply, type of drive, mechanism structure, sensing components, and controller. This paper presents a state-of-the-art survey of recent development on flexure-based microgrippers. According to the drive type, the existing microgrippers can be mainly classified as electrostatic microgripper, electrothermal microgripper, electromagnetic microgripper, piezoelectric microgripper, and shape memory alloy microgripper. Additionally, some different mechanisms, sensors, and control methods that are used in microgripper system are reviewed. The key issue of how to choose those components in microgripper system design is also addressed.

Modeling and Optimal Force Control of a Nonlinear Electrostatic Microgripper

Microgrippers 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 microglass 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.

Performance Enhancement of Electrostatically Actuated Microgripper with Modified Fingers for Microassembly

The application of microgrippers for handling and assembling micro parts in the field of robotics attracts more attention by the growth in micro electro mechanical systems. In this paper an electrostatic microgripper using comb drive is designed and analyzed using IntelliSuite. The use of modified fingers in the combdrive amplifies the output displacement of microgripper for given supply voltage. It also provides a linear force displacement behavior over a range of displacement. To show this amplification, finite element simulations are performed on the proposed design of microgripper models. It was found that displacement of about 7 µm has been obtained at a voltage of 14 volts with 28 fingers only with one of the proposed designs of microgripper against 25 volts for rectangular finger microgripper with 28 fingers. The simulation results have been verified by analytical results. The results of analytical and simulation are found to be in good agreement.

Simulation and experimental investigation of a novel electrostatic microgripper system

Microgrippers are amongst the preferred tools for microassembly applications and have drawn extensive attention of the researches on their mechanism and actuation principles. One of key parameters is efficiency of microgripping systems in handling more than one part at a time. Multi-part-gripping mechanism is one of the least investigated subjects in the published literature. In this paper, an electrostatic microgripping system using comb drive mechanism is designed with the capability of gripping two micro components simultaneously. S-type springs are utilized to amplify the displacement range of microgripper arms. The objects gripped with this microgripping system are diverse from biomedical (e.g. arrow shaped microshuttles); MEMS and microelectronic field with the dimensions from 145 to 100@mm for the operating voltage of 20-80V. A mathematical model with derived formulas is developed showing displacement of the tool versus applied voltage. Estimation of the performance of comb-drive is done through considering five capacitors all around a comb finger. The designed model predicts the displacement of the rotor more accurately compared to dominant method of calculating the equivalent capacity of only two lateral capacitors. Furthermore a multi-field simulation of the electrostatic comb finger of the comb drive is performed using finite element method. The FEA results show good agreement with the prediction obtained from analytical model. Microgripper function is enhanced through introducing a suspension system with optimum stiffness values. It helps the microgripper work under lower levels of actuating voltage. Finally, to verify analytical results, the microgripper is fabricated and the displacements are measured that compare well with analytical results and numerical simulation.

Displacement Amplification of Electrostatically-Driven Microgripper in a Hybrid Design with Electrothermal Actuation

By the growing development of micro electromechanical systems, the application of microgrippers for handling and assembling of microparts attracts more attention. In this paper, an electrostatic microgripper using comb drive mechanism is designed and a formulation is presented to predict the critical voltage for pull-in instability threshold. Then the advantages of a modified model of electrothermal U-shape actuator with large forces and bilateral displacement are utilized to amplify the output displacement range of microgripper prongs. To show this amplification, finite element simulations are performed on the primary and modified microgripper proposed models.

Design of a Hybrid-Type Electrostatically Driven Microgripper Integrated Vacuum Tool

This work is focused on design and fabrication of a hybrid-type electrostatic silicon microgripper integrated vacuum tool. Vacuum tools are integrated in this novel microgripper in order to improve its pick and place capability. Surface and bulk micromachining technology is employed to fabricate the microgripper from single crystal silicon wafer (i.e., no silicon on insulator wafer is used). And the bonding technology is used to form the gas pipes for the vacuum tool. The linear motion of the microactuator is converted into a rotational gripping motion by a system of spring beams. At a driving voltage of 80V, a deflection of 25μm at the arm tip of the gripper is achieved.

A self-centering electrostatic microgripper

Automated microassembly of micro hybrid devices is one fundamental step to reduce their high cost. Often, microassembly deals with fragile and wear-sensitive microparts that must be accurately grasped, positioned, and released or fastened in stable positions. The requirements of reliable, flexible, and fast assembly devices are other important characteristics to be achieved. This paper deals with the design of an electrostatic gripper that can grasp standard microcomponents and delicate mini and micro parts alike. The aim of this work is to theoretically and experimentally demonstrate the good performance of a self-centering gripper based on electrostatic forces. This paper extends previous works concerning electrostatic handling by adding new theoretical and FEM models, further tests, and new interpretations of the gripper’s grasping and centering capabilities. The design of the gripper is justified and supported by theoretical considerations. To better evaluate the generated force and the influences of the component on the gripper performance, FEM models are presented. Experiments concerning both grasping and releasing of mini and micro parts of different material shapes (spheres, cylinders, etc.) and dimensions (between 0.3 and 1 mm) have been performed, and quantitative measurements are reported. For industrial applications, the reliability of the grasping phase is close to 100%, the centering capability in grasping is appealing, and even if some centering errors remain, the transparency of the gripper allows the use of an eye-on-hand camera that could eliminate them during the releasing phase.

An optically transparent gripper for micro-assembly

This paper describes the development of a novel optically transparent electrostatic microgripper for assembly of micro-electromechanical systems (MEMS). The principle of operation, design and tests of the new device are described. Fabrication sequence and the materials used are also provided. The resulting gripping force is measured as a function of the applied voltage and compared with a parallel pate capacitor model. The frictional (in-plane) force was also determined for two common materials, silicon and nickel. As expected, a small amount of trapped interfacial charge was observed and characterized via scanning potential microscopy (SPM). The present work provides experimental data on the magnitude of the residual charge, the corresponding force, as well as charge decay data. Although undesirable, in the assembly of high-aspect-ratio interconnects, the part release can be achieved via path planning, since the parts are inserted into micro-machined slots. A simple demonstration assembly cell with image- and laser-based position-sensing modalities has also been described.

Fabrication of an Electrothermally Actuated Electrostatic Microgripper

A novel electrostatic microgripper, which can handle micro objects with the electrostatic force, is designed and fabricated. It consists of gripping part with one inner and two outer electrodes, and releasing part with an electrothermal actuator. It grips micro objects using electric field generated between the electrodes, and releases them using the backward motion of inner electrode with electrothermal actuation. The backward motion of inner electrode breaks the electric field and rapidly reduces the remaining charges of objects. The graspless work shows the safe object handling method and also suggests the solution for the releasing problem. The microgrippers are fabricated with 20 /spl mu/m and 40 /spl mu/m thick SOI wafers, and they successfully grip glass beads with 170 /spl mu/m diameter at 250 V and 100 V, respectively.

Polysilicon microgripper

A polysilicon electrostatic comb-drive microgripper has been designed and fabricated using surface micromachining on a silicon wafer. It features flexible cantilever comb-drive arms with a bidirectional actuation scheme and over-range protectors. Three different electromechanical models are developed and, along with fabrication constraints, are employed to design the microgripper and to simulate its performance. Experiments demonstrate that a gripping range of 10 μm can be effected with an applied potential variation of less than 20 V. The motion dependence on drive voltage is measured and compared with predictions from models; it is observed to be smooth, stable, and controllable. Experimental behavior (voltage versus displacement) is characterized for voltages up to 50 V.