Development Of MEMS Capacitive Encoder

Micro Electro Mechanical System(MEMS)has broad applications in both civilian and military fields due to its small size,low power consumption,and stable performance.Micro actuator,as the driving component of MEMS,is used to generate mechanical motion,force,and torque,and is one of the most important structures in MEMS.The micro-ultrasonic motor is a new type of micro actuator that has advantages such as high torque and fast dynamic response,but it is difficult to control.To achieve precise control of the micro-ultrasonic motor,high-precision angle feedback is required,but there is currently a lack of sensors on the market that can meet the motor’s angle detection requirements.This article focuses on the detection needs of the micro-ultrasonic motor and proposes a design of a micro capacitive encoder based on MEMS technology.This encoder can achieve absolute angle position detection within a given angular detection range.The main content of this article is divided into the following parts:1.The structure of the encoder was designed targeting the detection requirement of the micro-ultrasonic motor.This paper analyzed the impact of the shape of the capacitor electrode on the output signal from a principle point of view,determined suitable electrode patterns,and then simulated the encoder using finite element methods.The structure of the encoder was optimized by adjusting the size parameters.2.The encoder circuit design,angle calculation scheme design,and error analysis were carried out.The paper designed a signal detection circuit for detecting encoder output signals and analyzed its error.This circuit consisted of carrier waves,differential amplification,synchronous detection,filtering as well as power supply sections.The detected output signal of the encoder was filtered and smoothed using MATLAB,and then angle calculation was performed using the arctangent formula.The errors occurring during the process of detecting the encoder were classified into structural errors and signal errors,and corresponding compensation measures or suppression methods were provided after analyzing them.3.Encoder manufacturing and experimental testing were conducted.The paper used MEMS technology to manufacture encoder structures,set up an experimental platform,and used a high-precision photoelectric encoder carried by the turntable as the angle calibration reference.Several different groups of angle stepping tests were performed,and the accuracy of the designed MEMS encoder was determined by comparing the capacitive encoder test results with the angle reference.Then the platform and experimental devices were adjusted to test the application effect of the encoder on miniature traveling wave motors,and the experimental data was analyzed.The results showed that the designed MEMS encoder had an accuracy of ±0.1°,which met the expected target.