Development of Trajectory/Pressure Control System of Robotic Manipulator for NDT by Using AMFC Technique and Pressure Sensor

Abstract

Microcomputer-based A. M. F. C (Adaptive Model Following Control) for a robotic manipulator that is equipped with a UT (Ultrasonic Testing) transducer as well as a pressure sensor is developed. The transducer must be scanned smoothly with a moderate contact pressure on the surface of structural components such as pipes and pressure vessels for a successful NDT (Non-Destructive Testing) . To avoid instability of surface contact, springs have been used between the transducer and the surface. However, they are not enough to control contact pressure precisely. Then the authors have developed a new pressure sensor having a function of spring, and developed a trajectory/pressure control system based on the A. M. F. C. technique.
Since 6 D. O. F. (Degrees Of Freedom) are required for the perfect trajectory control, one more D. O. F. must be added for the trajectory/pressure control. In the present study, the authors have reduced from 7 D. O. F. to 6 D. O. F. by using the pressure sensor, and constructed an efficient trajectory/ pressure control system.
The A. M. F. C. technique, which was applied to robotic manipulator by Balestrino, is suitable for the trajectory/pressure control system because it can adjust robotic parameters automatically. However, it requires fine parameter choice and shorter sampling time for the perfect control. In the present study, the A. M. F. C. technique has been applied to a practical robotic manipulator controlled by a 16 bits microcomputer with a slower computing speed.
The developed system was applied to experiments of trajectory/pressure control of a robotic manipulator. In non-scanning mode where no perturbation occurs, controlled pressure was demonstrated to follow model pressure precisely. In scanning mode where some perturbation can be seen, the hybrid control of A. M. F. C. and feedback control was successfully used.