When a robot hits an object by a hammer, the robot manipulator has to absorb a impulsive reaction with the motor of a joint or a link.
This paper deals with a flexible link for a hammering robot. When the root of the link is driven by a motor, the head of a hammer vibrates complicatedly because the litik is a distributed parameter system. The first mode of the vibration is of great use for increasing a hitting velocity and for absorbing a reaction from the object easily. The second mode or more, however, disturbs the hitting velocity and direction which is specified by an operator. In order to suppress the higher modes of the vibration, a hammer driving system is equipped with a feedback loop which is composed of a strain meter and a high pass filter. It is shown that the hammer system can hit an object from a normal direction with a specified velocity.