Research On A Stylus Sensing System For Measuring Displacement Based On Interferometry

The measurement and evaluation of surface topography is the research hotspot intoday's nano-metrology. However, a nano-scale displacement probe system is requiredin all of the high-precision surface topography measuring instruments. The probesystem can use the contact or non-contact measurements, but the stylus probe systemhas been widely used with reliable result, high resolution, good reproducibility, etc.Therefore, the design of a stylus probe micro-displacement measurement system issignificant in the field of surface engineering.Firstly, a stylus leveraged micro-displacement conversion system is designed,which converts the micro-displacement probed by the stylus to the mechanicaldisplacement inside the instrument. In order to obtain good dynamic characteristics,optimal design of the lever structure and the connected part in the two ends is completed.Choosing high-quality optics and compensation devices, a laser interferometer systemhas been constructed to measure the internal mechanical displacement. The relationshipbetween the measuring and the optical path difference has been established by thecoordinate analysis method, and non-linearity error when measured in a wide range hasbeen analyzed. A grating angle sensing system with compensation strategy has beenmade. As for the problem that the stylus probing force change with the rotation angle ofthe lever, a constant force probing technique is proposed based on force of a voice coilmotor, and the flat rectangular voice coil motor is designed.Finally, the experimental platform was built. The current-thrust characteristiccurve of the voice coil motor is obtained. In combined with the relationship of thestylus probing force changes with the rotation angle of the lever, the rotation angle-control current curve is obtained. By measuring the contour line of a lenticular lens, theconstant probe force is verified, and the quadrature signals obtained by grating anglesensing system and the laser interferometry measuring system is verified in themeasurement process.