Development Of Linearity Measuring And Trimming System For Carbon-film Potentiometer

As position feedback devices, precise carbon-film potentiometers are widely usedin the servo system in aerospace industry. With the development of the new processtechnology in carbon-film coating and trimming, the traditional carbonpotentiometer production efficiency and yield face significant challenges. The mostimportant factor which affects the qualified rate of the potentiometers is thepotentiometer linearity trimming process. Based on this, the paper analyzes thetechnical problems of two different models of the existing potentiometers throughresearch studies aiming at the development of new measuring and trimming modeand improving the production efficiency and the linearity to the fullest according tothe existing potentiometer trimming process.Firstly, this paper conducts an in-depth analysis on the existing producing processof the potentiometers and established the conceptual design of the measuring andtrimming system which includes measuring module, the trimming module and theupper computer module.Secondly, we developed a potentiometer automatic measuring and trimmingsystem by building a measuring and trimming platform and developing the operatingsoftware interface system. The platform includes the mechanical structure, thecircuit part and PC control section. Among them, the mechanical structure serve ashardware foundation which consists of the system sets, the layout of thepotentiometer fixture design, measuring brush mechanism design, the trimmingstation selection and design. The circuit module which focuses on potentiometervoltage signal acquisition and motor control includes the test circuit design, A/Dconverter module design and the trimming station control circuits. The uppercomputer ensures the regular data communication between the software andhardware with the data acquisition card and the motor control card. Softwarecomponents used LabVIEW as a development platform, using the unique Ggraphical programming language to realize the potentiometer voltage signalacquisition, displacement signal acquisition, electronic switch and the trimmingsystem motion control. While the software is equipped with measuring curvereal-time display, data storage, query and report printing function.Finally, we optimized process options which include measuring step, collectingvoltage stabilization time, trimming tool parameters through some measurementsand experiments. Then we analyzed the errors of measuring and the trimmingprocess and finally got the functional performance of the measuring and trimmingsystem. Meanwhile, we developed a number of error compensation measures to ensure the overall accuracy. Experiments show that the automation system has astable and reliable measuring accuracy and precision motion control onpotentiometer and has reached the technical requirements of the final index.