In the natural environment, animals grasp and bite foods or transport objects mostly by means of their skilful hands or their mouths with sharp teeth. If you hope that your robot have such functions, it is the best choice to give it a machine clamp which opens and closes neatly. However, the precise processing devices and processing skills are necessary to make a neat machine clamp and it is difficult to make by hand. So the making of machine clamp is a problem to the robot makers.