Study On The Influence Caused By Thermal To Structure Of Piezoelectric Dynamometer

With the development of measure and automatic control technology, piezoelectric dynamometer is widely applied in fields such as cutting force, engine thrust and heavy equipment automatic control etc, for the good performance in static/dynamic characteristics. Reduce the impact of the environment disturbance, especially thermal influence, can improve piezoelectric dynamometer test accuracy. The influence of thermal to piezoelectric dynamometer is manifested as the deviation of output signal. And the deviation will affect the accuracy of measurement. Thus, it’s meaningful to study the thermal influence to the outputs of piezoelectric dynamometer.This paper studies the output signal deviation of piezoelectric dynamometer effected by thermal. Expounds the influence of thermal stress to dynamometer output. The corresponding improvement is put forward. And develop a dynamometer which output signal is steady under the influence of thermal.Firstly, this paper analyze the thermal strain and thermal stress of pre-tightening structure under the hypothesis that the temperature is uniform. Analyze the change of thermal stress by FEA software. The result shows that thermal stress of the piezoelectric quartz on the pre-tightening exerted direction changes obviously. The thermal strain and the elicited thermal stress is the main reason that the dynamometer output signal has a offset under the influence of thermal.Secondly, design the dynamometer structure basing on thermal influence principle. Develop the pre-tightening structure. Pre-tighten two piezoelectric sensors by a screw. The developed structure change the parallel rigid relationship between preload element and piezoelectric sensor. And thermal stress becomes internal force between sensors. Combine with appropriate adjustment the influence of the thermal stress to dynamometer output can be eliminated theoretically. The result FEA method analyze and heating experiment also indicate that the developed pre-tightening structure can reduce the influence caused by thermal stress obviously.Finally, assemble the piezoelectric dynamometer, adjust and calibrate. Design heating and loading experiment. The calibrate result shows the dynamometer has good static performance in 600N loading range. Nonlinearities of each direction output is 0.15%,0.37% and 0.99%. And cross-interference errors are less than 5%. The performance indicates the dynamometer is high-precision and can be used in force measurement. The heating and loading experiment shows the output of dynamometer is steady. The change rate is less than 4mV/min. The phenomenon of the experiment fits the design principle, indicating the developed pre-tightening structure can reduce the output offset caused by thermal.