Adaptive control for lift-off effect of EMAT based on IF-THEN rules and ultrasound RMS value

Abstract

In the manufacturing industry, the detection of discontinuities on or below the surface of a test object is important for quality control. Also, in many instances when the object's surface cannot be in physical contact with the sensor (i.e. high temperature or surface conditions) a scan using non contact technique is required. In this work, the use of electromagnetic acoustic transducer (EMAT) to detect discontinuities without contact is proposed. To optimize the EMAT performance a constant lift-off distance between the sensor and the surface is needed. Here, we propose to use the signal gathered by the EMAT sensor as the position feedback of the end-effector of a linear system with one degree of freedom. A novel adaptive scheme for accurate positioning of an EMAT sensor based on RMS value of signal's amplitude and IF-THEN rules is proposed. This incorporates human knowledge about the manipulator and signal behavior into the artificial controller. An experimental system to validate the proposed controller was developed.