Gripping and holding of objects are key tasks for robotic manipulators. The development of universal grippers able to pick up unfamiliar objects of widely varying shape and surface properties remains, however, challenging. Most current designs are based on the multifingered hand, but this approach introduces hardware and software complexities. These include large numbers of controllable joints, the need for force sensing if objects are to be handled securely without crushing them, and the computational overhead to decide how much stress each finger should apply and where. Here we demonstrate a completely different approach to a universal gripper. Individual fingers are replaced by a single mass of granular material that, when pressed onto a target object, flows around it and conforms to its shape. Upon application of a vacuum the granular material contracts and hardens quickly to pinch and hold the object without requiring sensory feedback. We find that volume changes of less than 0.5% suffice to grip objects reliably and hold them with forces exceeding many times their weight. We show that the operating principle is the ability of granular materials to transition between an unjammed, deformable state and a jammed state with solid-like rigidity. We delineate three separate mechanisms, friction, suction, and interlocking, that contribute to the gripping force. Using a simple model we relate each of them to the mechanical strength of the jammed state. This advance opens up new possibilities for the design of simple, yet highly adaptive systems that excel at fast gripping of complex objects.

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Universal robotic gripper based on the jamming of granular material

This paper reports on a novel piezo-driven, parallel-kinematic, micropositioning XY stage. This monolithic design is comprised of parallelogram four-bar linkages, flexure hinges, and piezoelectric actuators. Kinematic and dynamic analysis shows that the mechanical structure of the stage has a large work space, high bandwidth and good linearity. The stage system was run in open-loop mode to measure the step response and frequency response. The results show that the resonation frequencies of the two vibration modes are 563 and 536 Hz and the damping ratios are 0.049 and 0.0228. Two fiber optic sensors were added to the system to build a closed-loop positioning system. Linear and circular contouring performance in closed-loop mode suggests high scanning performance for such parallel-kinematic stages. The positioning resolution of the stage, limited only by the feedback sensors used, is about 20 nm.

Design analysis, fabrication and testing of a parallel-kinematic micropositioning XY stage

In this paper we review the world-wide study on micro-motion systems both from an academic and an industrial perspective. The objective of the review is to answer the following questions: (1) What are the limitations of technologies to develop a micro-motion device in terms of function, motion range, accuracy, and speed it can achieve? (2) What is any economic implication of these technologies? (3) What are future research directions? The micro-motion systems considered in this paper are classified into four kinds in terms of their motion ranges: (a) 1000 μm. This review concludes that the PZT actuation element integrated with the compliant mechanism is the most promising technology which can achieve high accuracy (sub-nanometer) of all four kinds of motion ranges. This promise is further based on the amplification technology using the compliant mechanism concept. The amplification mechanism is used to com- pensate the problem with a limited stroke of the PZT actuation element. The compliant amplification mecha- nism allows one to achieve a high resolution and high stiffness motion which does not compromise the loss of accuracy due to motion amplification. The PZT actuation element and the compliant mechanism are both econom- ically viable. Future research direction should generally focus on the interface between the PZT actuation element and compliant mechanism and the reliability of the compliant mechanism under cyclic deformation of com- pliant materials.

Micro-motion devices technology: The state of arts review

Delicate interaction control is a crucial issue for automated microsystems dedicated to microobjects handling. This paper proposes a new approach to regulate both position and contact force of a piezoelectric-bimorph microgripper for micromanipulation and microassembly applications. The methodology is developed based on the framework of a discrete-time sliding mode generalized impedance control with adaptive switching gain. One unique feature lies in its easy implementation based on a second-order dynamic model, whereas neither a state observer nor a hysteresis/creep model of the system is required. The stability of the control system is proved in theory, which ensures the tracking performance in the presence of model uncertainties and disturbances. The effectiveness of the scheme is validated by experimental investigations on grasp operation of a microgear. Results show that the approach is capable of accomplishing precision position/force control simultaneously. Moreover, the influences of control gains and target impedance parameters on the tracking performance are addressed, and the achievement of balance between the position and force control accuracy is discussed.

Adaptive Discrete-Time Sliding Mode Impedance Control of a Piezoelectric Microgripper

http://www.lmm.jussieu.fr/~fernande/resources/2003-ijss.pdf

Analytical and numerical approaches to piezoelectric bimorph

This paper is a study on the hybrid position/force control of a two-fingered miniature gripper driven by piezoelectric bimoph cells. The system is composed of the flexible cantilevers and a compact force sensor attached to the tip of one finger. Control action is applied by two piezoelectric bimorph strips placed at the base of each finger. The theoretical model of the electro-mechanical system is developed and applied to the study of a control problem where the gripper is commanded to grasp its object with a time-constant force 0.01 N at a prescribed commanded fingertip position. The PID control algorithm is introduced to drive the gripper.The system control behaviour is examined both theoretically and experimentally.

http://petit.lib.yamaguchi-u.ac.jp/G0000006y2j2/file/16323/20110721164516/2009010409.pdf

Soft-handling gripper driven by piezoceramic bimorph strips

http://iopscience.iop.org/article/10.1088/0964-1726/5/4/004/pdf

M. Koseki

Papers

Soft-handling gripper driven by piezoceramic bimorph strips

Soft-handling gripper driven by piezoceramic bimorph strips

Force Holding Control of a Finger Using Piezoelectric Actuators