Serial robot arm is designed as a series of links connected by motor-actuated joints that extend from a base to an end-effector. It has a large workspace with respect to the size of the robot and the floor space it occupies. However, as Serial robot arm is an open kinematic structure, it has the low stiffness. And its errors are accumulated and amplified from link to link. It also needs a perfect counterbalance design to carry and move the large weight of most of the actuators.