Sensing chuck for thin-walled workpieces

During turning processes of thin-walled workpieces, e.g., bearing rings and sleeves, dimensional and shape deviations are a challenging problem. The main cause of these deviations is the clamping force applied by the turning chuck to hold the workpiece in place. Due to the low stiffness of thin-walled workpieces, high workpiece deformations can occur even when clamping forces are low. For this reason, the clamping force needs to be precisely adjustable. However, conventional chucks usually are actuated by an external clamping cylinder. This limits the achievable accuracy of the clamping force caused by mechanical interfaces and the long force transmission path. Thus, this paper presents an innovative chuck with four integrated electric drives. As a result of the more direct power transmission, the chuck has a potentially higher sensitivity compared to external actuation. For the first time, inherent sensors of electric drives are used to draw quantita tive conclusions about the precise clamping force. Based on the measured drive signals (motor current and angular p osition), a clamping force measurement accuracy of 98.6% is achieved.