Machine Design

Sensor Technology SAW Sensor is Key to Nonlinear Testbed for Actuators and Motors

Robotics Research Group,

Sensor Technologies Ltd.,

The University of Texas,

A universal test bed for motors uses a surface acoustic-wave (SAW) sensor for gauging torque. The Nonlinear Test Bed for Actuators (NBTA), developed by Robotics Research Group and the University of Texas, measures an array of properties during dynamic and nonlinear load testing. The torque sensor from Sensor Technologies Ltd., Raleigh, N.C., uses a pair of SAW transducers embedded on a shaft to form part of a high-frequency oscillator circuit. When the shaft twists, deformation of the substrates creates a frequency difference between the two transducers. The frequencies are combined and mixed to create difference and sum signals. The difference signal is a measure of induced strain from the twisting moment, and it can be used to calculate torque.

The NBTA design also includes a load motor, a four-bar linkage, and a brake/clutch. Bellows coupling link the components together. Steel rails hold all components rigidly in place to resist horizontal and vertical forces. Keeping the components still leads to accurate picture of the motor performance. The NBTA motor generates various types of loads, while the linkage creates nonlinear periodic loads mimicking real-world conditions. An encoder connected to the motor measures position, velocity, and acceleration, while the torque senor measures torque between the load and test motors.

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