Low-Backlash Worm Gears with NiTi Shape Memory Alloys

Abstract
This paper investigates the use of martensitic Nickel-Titanium within worm gear transmissions in order to reduce the backlash of the gearwheels. In drive technology low-backlash transmissions are demanded. The backlash, adjusted at room temperature, decreases with increasing temperature as a consequence of different thermal expansions of the gear wheels and the housing. This can result in clamping of the teeth and leads to failure of the whole transmission. With NiTi-actuators, working in the extrinsic two-way effect, it is possible to realize two conditions of low-backlash and to avoid clamping of the gear wheels. The actuators induce a radial movement of the worm wheel depending on the increasing temperature within the gearbox. The decreasing backlash, as a result of different thermal expansions, is compensated by the expansion of the martensitic NiTi actuators while transforming to the austenite. The adjustment travel of the actuators has to correspond to the thermal change of the centre distance. By measuring the change of backlash on the test bench, the theoretical dimensioning of the actuator system can be verified. The variation of the main parameters like torque, the speed and different temperature levels as a result of the input power should demonstrate the effectiveness of the NiTi actuators.