Development of a compact displacement accumulation actuator device for both large force and large displacement J. Park, S. Keller, G.P. Carman * , H.T. Hahn 1 Mechanical and Aerospace Engineering Department, University of California, Los Angeles, 48-121, Eng. IV, Los Angeles, CA 90095-1597, USA Received 6 July 2000; received in revised form 23 January 2001; accepted 24 January 2001 Abstract The design, fabrication, and testing of a compact displacement accumulation device is presented in this paper. The piezoelectric device provides both large displacement mm) and large force 100 N). The device is based on conventional inchworm motor design that produces large displacement. The device integrates piezoelectric stacks for large force output and high-speed operation with MEMS ridges as a new clamping system. The device should be able to push and pull 450 N at 11 mm/s in a relatively compact size. FEM analysis is used for the design, EDM is used for the fabrication of a prototype, and conventional test techniques are used to evaluate performance. Stress and modal analysis are used to con®rm that the device has an in®nite fatigue life and a ®rst modal frequency at 1309 Hz. Experimental data for clamping strength of the ridges and blocking force of the device validate that the device transfers the required load of 450 N. The device is successfullytestedoverawiderangeofoperatingconditionsatspeedsupto11mm/susingopenloopcontrol.Thestallloadofthedeviceis measured to be exceeding 2250 N. For the dynamic loading test, the device pushes test weights up to 50 N with the open loop control approach. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Displacement accumulation; Inchworm motor; Piezoelectric stacks; MEMS ridges 1. Introduction Recentresearchonthedevelopmentofthemotorempha- sizes increasing power density while reducing size. In an attempttoimprovepowerdensity,differentactivematerials are being considered based on the advantages associated with each material. For example, shape memory materials provide large displacement with moderate response time while piezoelectric materials provide high speed operation with moderate displacement. In addition to different active materials, various methods or concepts such as displace- ment ampli®cation [1±6] and displacement accumulation also called frequency recti®cation) are being considered. Therefore,selectionofactivematerialswithsuitableampli- ®cation or accumulation methods represents important issues necessary to develop a compact high power density motor. Inchworm motors [7±12] represent a class of displace- ment accumulation motors. These motors have virtually unlimited displacements at relatively high speeds. Although displacement accumulation ideally increases displacements while retaining high force output, current displacement accumulation devices including inchworm motors have limited force outputs. In general, inchworm motors use static friction to clamp and are limited to force outputs less than5kgf.Otherclampingmechanismssuchaselectrostatic clamping [13] and electrorheological ER) clamping [14] havebeenattempted,buttheforceoutputsfromthesemotors were less than 1 kgf. Recently, Park et al. [15] designed the ®rst detailed displacement accumulation device that transfers a mechan- ical load up to 450 N at 1 kHz 11 mm/s). The device integrated piezoelectric stacks with MEMS ridges [16±18] toformanewclampingsystem.Analuminumprototypewas fabricated and tested successfully. Successful operation of the device with the MEMS ridges validated the operational concepts. However, the speed of the aluminum prototype was limited to 0.88 mm/s due to power supply limitation, andtheprototypecouldnottransfermechanicalloadsdueto low stiffness housing. Therefore, an improved system is necessary. Sensors and Actuators A 90 2001) 191±202 * Corresponding author.Tel.: 1-310-825-6030; fax: 1-310-206-2302. E-mail addresses: carman@seas.ucla.edu G.P. Carman), thomas.hahn@afosr.af.mil, hahn@seas.ucla.edu H.T. Hahn). 1 Present address: AFOSR/NA, 801 N. Randolph Street, Rm 947, Arlington, VA 22203, USA. Tel.: 1-703-696-8483 AFOSR/NA); 1-310-825-2383 UCLA). http://ime.ucla.edu/hahn. 0924-4247/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII:S0924-424701)00521-0