The amount of the external impulse exerted on the object being sawn has been treated one of important control parameters. At the same time, the internal impulses experienced in the joints should be taken into account to avoid serious damage or injury at the joints of robot. This paper discusses the impulse models in a straight sawing task. And, a motion planning algorithm is proposed, which employs the external and internal impulses as performance indices. For this, the gradient projection method is employed to exploit the kinematic redundancy of the robot structure. Finally, through both simulation and experimentation for the sawing task, the effectiveness of the proposed motion planning algorithm could be verified.