ANALYSIS OF MECHANICAL ERRORS OF PLANAR CAPACITIVE SENSOR FOR TWO DIMENSIONAL DISPLACEMENT MEASUREMENT

摘要

A new non-contact planar capacitive sensor was proposed for two dimensional displacement measurement, influences of possible mechanical errors of which was then mainly discussed. Based on the results, improved design was approached to decrease measuring errors.rnTwo dimensional displacement interpretation of this new PCS depends basically and independently on measuring the periodic variation in capacitance caused by the change of overlapped area of sensing electrodes on a moving plate and electrodes on a fixed plate. Accumulating the number of quarters in each direction and the specific position in the final quarter, large scale measurement is fulfilled. Mathematical model of planar capacitive sensor under rotational disturbances is then constructed. FEA simulation revealed errors derived from mathematical model and that from FEA had a cohesive result. Approach was proposed and analyzed to decouple errors from rotational disturbances, sensing electrodes on the moving plate are symmetrically positioned, then influences of rotational disturbances and tilting errors on each sensing electrode can be decoupled using the classical trigonometric formulas. FEA simulaiton results demonstrate the feasibility of these approaches.rnThe following work would focus on fabricating a planar capacitive sensor prototype to verify all the analyses.