超声在机测厚接触力控制方法研究

Research on the Contact Force Control Method of Ultrasonic On-machine Thickness Measurement

摘要:

针对接触式超声在机自动测厚中可靠接触难题，提出了超声探头与被测工件之间接触力控制方法，制定了基于接触力实时反馈的闭环控制策略，建立法向接触力计算模型，设计了接触力调控量向机床位移校正量转化的阻抗模型与接触力滑模变结构控制器，在Simulink环境下对控制模型进行了数值仿真，验证了算法有效性，可实现超声在机测厚中恒定接触力精确跟踪控制。在所研制的测量系统中进行了测量实验，结果表明超声在机扫描测厚接触力控制误差在4N以内，实现了超声在机自动扫描测量过程中的接触状态保持，保证超声传感器输出信号稳定，测厚误差明显减小。

Abstract:

In view of the reliable contact problem of contact ultrasonic on-machine thickness measurement automatically, the contact force control method between the ultrasonic probe and the measured workpiece is proposed. The closed loop control strategy based on the real-time feedback of contact force is formulated. The calculation model of the normal contact force is set up. Impedance model for converting the contact force to the displacement correction of the machine and the contact force sliding mode variable structure controller are designe. The numerical simulation of the control model is carried out in the Simulink environment, the effectiveness of the proposed algorithm is verified. The accurate tracking control of the constant contact force in the ultrasonic thickness can be realized. The measurement experiments have been carried out in the developed measuring system. The results show that the control error of the ultrasonic measuring thickness is within 4N, and the contact state in the automatic scanning measurement process is maintained. Output signal of the ultrasonic sensor is stable and the thickness error of the measurement is reduced obviously.