Research On A4-DOF Piezoelectric Micro-gripper

To improve the flexibility of the piezoelectric micro-gripper, decrease the difficulty in designingthe front actuators and reduce the system cost, a new kind of micro-gripper of four degrees of freedomwas designed based on the structure of piezoelectric bimorph. Both the static and dynamiccharacteristics were analyzed and tested. The details researches were as follows.Firstly, the structure of the4-DOF piezoelectric micro-gripper was explored and the staticcharacteristics were analyzed. The electrodes of piezoelectric bimorphs were divided; meanwhile, twogroups of opposite lateral inverse piezoelectric effect were generated on the piezoelectric bimorphs.Therefore, each finger of the micro-gripper can generate movements both in gripping direction andvertical of gripping direction, so the4-DOF movements of the micro-gripper can be achieved throughthe co-operation of the two fingers. Then, based on the first type of piezoelectric equations andcantilever beam bending deformation theory, the relationships between the displacement of the fingerand input voltage in the two directions was attained, so as to the relationships between the grippingforce and input voltage. And the results indicated: with the driving voltage of90V, the maximumdisplacements in gripping direction and vertical of gripping direction were32.2μm,46.8μm,respectively. And the gripping forces were137.0mN,199.3mN, respectively.Secondly, the static and the dynamic characteristics of the micro-gripper were analyzed byANSYS. And the geometry size of the micro-gripper was optimized based on piezoelectriccoupled-field. The optimized results indicated that the displacement of the finger in the two directionswas proportional to the square of the length, decreased with the increasing of the width, and inverselyproportional to the thickness. Meanwhile，Displacement of one finger in gripping direction increasedwith the width of electrode, and displacement of finger in vertical of gripping direction wasproportional to the width of electrode. Finally, the geometry size of finger was confirmed: the length,width and thickness of micro-gripper were18mm,1.6mm and0.4mm, respectively. The widthof electrode and the gap between the electrodes were0.5mm,0.05mm respectively. Next, the staticand dynamic characteristic of micro-gripper with the above geometry size was simulated by ANSYS.The results show that: the maximum displacements in the two directions were37μm,51.4μm,respectively, still with driving voltage of90V. The first natural frequencies of the micro-gripperin gripping direction and vertical of gripping direction were2120Hz,532Hz, respectively. Underthe step voltage of10V, the steady-state displacement and response time of the micro-gripper ingripping direction were3.66μm,0.1s respectively; the same parameters in the vertical of gripping direction were4.72μm,0.1s, respectively. Based on the above work, a prototype of the micro-gripperwas fabricated.Finally, the static and the dynamic characteristics of the prototype were measured throughexperiment. An experiment system was set up. And the displacement of the micro-gripper was gottenthrough a laser displacement sensor. The results were as follows: under the triangular wave of30Vthe maximum displacements in the gripping direction and vertical of gripping direction were10.8μm,17.6μm, respectively. Under the same voltage the maximum interference displacements in twodirections were4μm,17.7μm, respectively. And the reason which caused interference was theelectrodes of the clamp up and down two piezoelectric bimorphs were distributed inconformity. Underthe18V step voltage, the response times in the two directions were0.25s,0.45s, respectively.