A Hybrid Actuator .

Venkataraman, Prof. P.S. Krishnaprasad and Prof. W.P. Dayawansa

PROJECT BACKGROUND AND GOALS

An electromagnetic d.c motor has a high efficiency but a low torque at a high speed. For low speed, high torque applications, speed reduction gears have to be used which make the system bulky and lower efficiency. Precise positioning would be difficult because of the backlash caused by the gears. Since most high performance electromagnetic motors today are servo type and not steppers, they must use brakes or must keep the power in the hold position. A SMART rotary motor on the other hand, is good for low speed, high torque applications and direct drive is possible because of the high torque. The motors can be made inherently self braking with the power off. Previous research has focused on actuators with magnetostrictive or piezoelectric materials, but never using a combination of both. The main idea of this project is to build a `hybrid' actuator taking advantage of the properties of both SMART materials.

METHODOLOGY

Electrically, as piezoelectric actuators are essentially capacitive in nature while magnetostrictive actuators are inductive, an electrical resonance can be created which would reduce the reactive power load on the power source. As the strains obtainable from both types of actuators is in the order of 1000 ppm, we decided to run the hybrid actuator at a sufficiently high frequency (of about 1KHz), inorder to get significant motion. Inorder to keep costs low, we also decided to build the actuator with as many commercial components as possible, without worrying about the size. With this in mind, a detailed computer simulation of the system was done, even taking into account impact effects. Due to the high frequency of operation, the nonzero time of impact cannot be ignored in the system study. Satisfactory results from the simulations encouraged us to build a prototype hybrid actuator.

PROJECT RESULTS

The prototype actuator is still undergoing tests, and is expected to behave as the simulations suggested.

SIGNIFICANCE

It is known that a trailing edge flap or a `flaperon' can provide an active vibration reduction for helicopters. Currently the flaperons are actuated hydraulically. If the actuation can be made electrical, the significant weight reduction can reduce costs. Other types of actuators that are being studied, for example, bimorph actuators, piezoelectric and electrostrictive stack actuators, magnetostrictive actuators are feasible but donot produce the required torque. It is conceived that a miniature version of the hybrid actuator can be used instead. Due to the inherent small motions of the hybrid actuator, precision positioning can be another application.

FUTURE DIRECTIONS

The testing of the prototype hybrid actuator will provide proof of concept. The development of a control strategy for precision positioning can be a direction for future research. Another direction can be a study of a series of such actuators.