Optical based Precision Measurement System and Its Application on Dynamic Force Measurement

Abstract

Force is one of the basic quantities of mechanics, which is usually measured using a force transducer. However, the force transducer is usually calibrated by a static method. While the dynamic calibration for the force transducer is not sufficient. Dynamic calibration and measurement are needed to measure and evaluate mechanical parameters of materials in industry and research applications such as material testing, measurement of friction of a material, motion control, and crash testing. Dynamic measurement of force is also very necessary to produce and evaluate force with micro-Newton levels. However, there are difficulties in dynamic measurement, namely: there are difficulties in evaluating the inaccuracies in the measurement of varying forces, then there is difficulty in evaluating the inaccuracy in the time when measuring force. To overcome this problem, an optical-based precision measurement system was developed. This system can measure the force with high accuracy without using a force transducer. In the developed system, a levitated load (moving part) is used as a reference force imposed on the material to be measured for mechanical parameters. The inertial force of the levitated load is calculated accurately as a result of the multiplication between the load mass and its acceleration. In systems that are developed, speed, acceleration, force, and position are calculated accurately from the shift in the laser beam Doppler frequency reflected by the load. So that the measurement accuracy is strongly influenced by the accuracy of frequency calculations. In this system, a special program for zero-crossing-based frequency estimation is also very accurate. The developed system has proven to be able to perform mechanical/dynamic measurements and can evaluate the style with newton-level micro very accurately.