Abstract: Precise and efficient thickness on-machine measurement is a challenging problem for complex thin-walled parts. A shape adaptive thickness on-machine measurement method using ultrasonic is developed. A multi-function integrated ultrasonic thickness on-machine measuring device is innovatively designed, and a basic measurement motion control model is further established. The best measuring posture of ultrasonic sensor in dynamic adjustment can be determined, through the position and pose calculation based on static force equilibrium and the posture angle error automatic identification based on first echo energy attenuation. For echo signals with fixed time delays, a variable step size adaptive algorithm for ultrasonic time of flight(TOF) calculation is designed using a novel step control function, which can improve the convergence rate and reduce the steady-state error effectively. Taking the arc-and S-thin-walled parts as typical objects, the experimental study is conducted using the proposed method. It shows that the ultrasonic thickness on-machine measurement accuracy with posture angle error compensation can be controlled within 0.02 mm by comparing with coordinate measuring machine(CMM) calibration, which could meet the requirements of thickness on-machine measurement of complexed thin-wall parts.

Key words: on-machine thickness measurement, posture angle, shape adaptive, thin-walled part, TOF calculation, ultrasonic