A Double Path Laser Interferometric Length Measuring Instrument And Its Application In 3D Coordinate Measuring Machines

In scientific research and industrial production, along with the need of high accuratedimension measurement and precise positioning and tracking, laser interferometer is widely usedin more and more domains because of its prominent performance and characteristics.This thesis studies a new double path laser interferometric length-measuring instrumentbased on the work of Dr. Zang Yanfen and Liu Haining. It aims at its product development andmaking it more convenient in practical applications.The research work covered by this thesis includes:1. The principle and characteristics of the interferometric length-measuring instrument areanalyzed. In measurement, the probe can move from one end of the measurand to another endwithout losing count. Compensation for the Abbe error caused by pitch of the probe isintroduced in the optical diagram.2. All optical components have been designed and manufactured. The difficulties in systemadjustment and their influences on measured results are discussed and studied.3. The mechanism for installing all the optical components is designed and manufactured. Thismechanism has a reliable and concise structure. In this structure, each optical component thatmust be adjusted has its independent trimming system. It facilitates three-degree freedomangle adjustment of the corresponding optical component. After all the components arealigned, they are assembled together as a body. Only whole adjustment is needed in the laterusage of the probe, and no individual adjustment for each internal optical component isneeded. The entire mechanism is small and light. The probe triggers when it comes intocontact with the piece. The measuring stylus, ball tip and measuring mirror are suspended byparallel springs. An Eddy current sensor is used to trigger the signal.4. The application of the laser interferometric length-measuring instrument in 3D coordinatemeasuring machines is studied. A special triggering circuit is designed and implemented todetect the contact between the probe and the work piece while the 3D coordinate measuringmachine is running. Once the contact signal is detected, this circuit samples the reading of thelaser interferometer to record the displacement and stops the 3D coordinate measuringmachine to avoid damages of probe or workpiece by collision.By using the Eddy current sensor minimum contact forces in measurement is realized, and inturn the deformations of measuring ball and measuring stylus are minimized.5. Some comparison experiments on a 3D coordinate measuring machine were conducted. Thelaser interferometric length-measuring instrument was mounted on a 3D coordinate measuringmachine and a reference 8-mm quartz block was measured. The uncertainty of measurementwas tested.6. The possible errors in measurement are analyzed qualitatively. Some suggestions forimproving the accuracy of the probe are given.