The design, fabrication, and characterization of millimeter scale motors for miniature direct drive robots

Abstract

Absrroct -This paper reports on research into miniature, direct drive, high force/torque motors to support insect-sized mobile robotic platforms. The primary focus is on scalable motors based on piezoelectric transducers. The contributions of this work include:(1.) the design, analysis, and characterization of a miniature mode conversion rotary ultrasonic motor based on a piezoelectric stack transducer; this produced a static torque density of 037 Nrnkg, (2.) a millimeter scale Linear piezomotor, constructed with a parallel arrangement of annular stressed unimorph piezoelectric transducers and passive latches, exhibited 0.23 N of blocked force, and (3.) Simulation data is presented that compares these motor concepts to commercial systems in the context of scalability. Results suggest that smaller versions of the rotary ultrasonic motor would possess a static torque density seven times that of a commercial 3-mm electromagnetic system. This technology shows promise for driving the platform.

Dynamometer power output measurements of piezoelectric actuators

“…This yields a power density of 476W/kg, easily beating the estimate for Dipteran muscle power density in Table IV. This also compares favorably to other available millimeter scale actuators such as the rotary piezoelectric motor of [20] with a power density of 81W/kg.…”

Drive circuit for a mode conversion rotary ultrasonic motor

“…Shown in Fig. 1 is a prototype of a mode conversion USM, developed at North Carolina State University, which includes a stator assembly and a rotor assembly [3]. The resonator and the L/T coupler comprise the stator assembly.…”

“…The resonator produces longitudinal resonant vibrations which are converted to elliptical displacements at the tips of the L/T coupler. Then the rotor is driven by the elliptical displacements and coupling friction; thereby, producing useful torque [3]. USMs are expected to be used in mobile devices such as miniature robotics.…”

“…This prototype of a mode conversion USM used a multilayer Lead-Zirconate-Titanate (PZT) ceramic stack transducer [3]. Compared with a cylinder or disk ceramic transducer, the multilayer ceramic stack transducer has much larger electrode area and is much thinner; hence, it has much larger static capacitance (~40nF).…”