Prototype micromanipulator for space robotics applications

University of Houston • University of Houston-Clear Lake • ISSO Annual Report Y2007• 83-84

FOLLOW-UP REPORT — INNOVATIONS AND NEW DEVELOPMENTS

James B. Dabney

Abstract—Piezoelectric actuators offer dramatic improvements to a variety of space-based robotics applications. Bending piezoelectric actuators offer a simple, lightweight, and reliable means for actuating end effectors. This research produced a single degree-of-freedom micromanipulator prototype that can be used to solve open issues in bending actuator control, particularly hysteresis modeling and control.

Premise of the Project
Piezoelectric actuation is ideal for space-based robotics applications because of its light weight, its inherent simplicity, and its immunity to magnetic fields. End effectors for miniature space-based robots must also be simple and lightweight, and can also benefit from immunity to magnetic fields. Therefore, a piezoelectric actuator is an ideal candidate for an end effector.

A piezoelectric bending actuator consists of two layers of piezoelectric material bonded together with opposite polarity in the form of a cantilever beam. The application of an electric field to the actuator causes one layer to extend slightly and the other layer to contract slightly.¹ The differential length causes the beam to bend toward the contracting layer. By controlling the applied electric field precisely, it is possible to control the movement of the beam tip. The tip of this particular actuator has a range of motion of ±0.5 millimeters. LabVIEW 6.0 is used to generate voltages in the range +5V to –5V which are in turn supplied to a piezo-linear amplifier. The piezo-linear amplifier is used as a high-voltage drive source for the piezoelectric actuating device. The capacitive sensor² senses the motion and produces an analog voltage proportional to the distance between the capacitive probe and the piezoelectric actuator. LabVIEW 6.0 is used to record the capacitive sensor output.

Laboratory Apparatus
The UHCL micromanipulator system facilitates research in dynamics and control of micromanipulators. The device uses a piezoelectric bending actuator that has a range of motion of approximately ±0.5mm. The apparatus consists of the piezoelectric bending actuator mounted on a mechanical breadboard and driven by a linear amplifier. The manipulator position is measured using a commercial high-resolution capacitive position sensor (Series 4000 Capacitec amplifier) mounted on the mechanical breadboard. LabVIEW 6.0 is used to generate drive voltages to the piezo driver and measure capacitive sensor output. The experimental laboratory setup is shown in Figure 1.

Figure 1. Micromanipulator experimental set-up

Results
The actuator, capacitive position sensor, actuator driver, and sensor amplifier were assembled as shown in Figure 1. LabVIEW 6.0 software was developed to control the actuator driver and capture the sensor amplifier output. Using the LabVIEW software, open-loop control was implemented to characterize the input-output behavior, particularly hysteresis. Based on these results, a preliminary design for a piezoelectric bending parallel micromanipulator was developed (Figure 2). This system will demonstrate the viability of a large range-of-motion, high-precision micromanipulator suitable for medical and space applications.

Figure 2. Piezoelectric bending parallel micromanipulator layout

Acknowledgments
This work was supported by an ISSO mini-grant for the summer of 2006. The assistance of the University of Houston Smart Materials Laboratory is gratefully acknowledged.

References
1. Novotny, M. and Ronkanen, P. Piezoelectric actuators. <http://www.ad.tut.fi/aci/courses/ACI-51106/pdf/Piezo/PiezoelectricActuators.pdf>
2. Ayer, M.A. Operation/maintenance manual: Series 4000 Capacitec amplifiers and rack accessories (Ayer, MA, Capacitec, Inc., 1998).

Proposals
Dabney, J.B. and Harman, T.L. Piezoelectric bending parallel micromanipulator prototype, Texas Advanced Research Program, $145,000 (2008) (not funded).

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