Design, Fabrication And Performance Testinging Of Micro Tactile Probe Based On MEMS Capacitive Sensing

With the rapid development of MEMS technique, the feature size and tolerance of device decreases continuously down to the level of millimeter even micron, which puts forward higher requirements of devices’ high precision measurement. Micro/nano Coordinate Measuring Machine is widely used in the field of high precision metrology. Cooperated with Micro/nano Coordinate Measuring Machine, micro tactile probe is a sensing component which acquires surface information of measured sample, its performance influence the measuring precision directly. Developing novel and low uncertainty micro tactile probe has recently become a research focus. To meet the demands of high precision and resolution, this paper developed a micro tactile probe based on MEMS capacitive sensing. Then relative performance testing was made and the main work is as follows.Firstly, based on capacitive sensing, a micro tactile probe composed of micro probe and micro capacitive sensor was proposed and its measuring principle and sensitivity were analyzed, through researching how the gravity of micro probe and measuring force influence on the sensitivity and measurement range, the relationship between sensitivity, measurement range and vertical stiffness of micro tactile probe was acquired. Besides, the optimum vertical stiffness of micro tactile probe was also acquired. Then we researched the how structure parameters change the stiffness of “S” type spring and movable plate, combining with MEMS process, we designed the structure and dimension of micro capacitive sensor and validate the feasibility by finite-element analysis.Based on current process of laboratory, a fabrication process scheme of micro capacitive sensor was proposed and proper structural material was selected. Then a lot of experiments were made and the failure devices and the cause of each defect are analyzed, we found the main problem is the buckling of movable plate caused by residual compressive stress, Then we changed the material and designed the “Ni-Cu-Ni” sandwich structure of movable plate. By a large number of experiments, we fabricated the micro capacitive sensor whose movable plate is flat. At last, an initial micro tactile probe is configured by combining the micro capacitive sensor with the micro probe.After fabricating micro tactile probe, cooperated with Shanghai Institute of Measurement and Testing Technology, we designed the signal detection circuit based on single chip C8051 and AD7747 capacitance to digital converter. To make the circuit work, the procedure and relative software are configured. Then based on the standard and requirement of calibration system, then the framework of calibration testing platform was designed and the calibration testing platform was configured.Based on configured calibration testing platform, lots of experiments are made aim at the static and dynamic characteristics of micro tactile probe. By processing and analysis experimental datas, we achieved the main static and dynamic characteristics including sensitivity, linearity, hysteresis, repeatability, resolution, coupling, dynamic response, etc. A conclusion whether the micro tactile probe can be used for high precision measurement was discussed.Finally, defect and the limitations of micro tactile probe was presented, and some specific improvement methods and measures for the tactile probe have been suggested.