A type of material handling units useful for transferring workpieces from a chucking position to a loading position for a machine has a swinging arm or manipulator provided at its outer end with means for gripping the workpiece. In a material handling unit of this kind relatively high positioning accuracy is required at the chucking position where the swing motion starts and at the loading position where it ends.
Such positioning is commonly carried out by engagement of a striking face of the swinger arm against a fixed abutment mounted on the frame of the material handling unit. In this manner high positioning accuracy is attained in comparison with a mechanical cam or electric positioning device and moreover repeatable accuracy and reliability are extremely high.
However when positioning the swinger arm by engagement with an abutment especially when the speed of the swinging motion of the swing arm is increased and the cycle time is reduced the swing arm may bounce or vibrate by reason of the impact shock in accordance with the weight of the payload. When such bouncing or vibration occurs the desired high positional accuracy and reliable motion cannot be attained.