Calibrating initial position of manipulator via ultrasound transducer

Before a manipulator begins operation, its initial position needs to be confirmed. The manipulator will work more accurately after eliminating offsets in the initial position. Though some measuring devices have been widely used to calibrate the initial position, they are generally used to measure absolute position and featured with high cost and complex operation. Considering that ultrasonic testing system has measurement capability, we proposed a calibration method based on ultrasonic theory. This method employs relative position to calibrate the initial position of the manipulator, which can avoid complex process in measuring absolute position. According to reflection characteristics existing in ultrasonic theory, we find that the initial position of the manipulator can be calculated according to the relative position and posture between an ultrasonic transducer and a reflective surface. Firstly, D-H parameters are introduced to build kinematic model. Then, the model is rewritten according to Taylor series. The first order of Taylor series is retained to estimate relative relationship between joint angle and spatial position of the end-effector. The positioning error in X, Y and Z direction is increased by 85.8%, 69.2% and 81.4% respectively, demonstrating that this method can calibrate initial position effectively.