Surgical robots are usually controlled by the method of independent PD or the PD model based on gravity compensation.However

after both of the control models imported

the equation of the closed-loop error is linear.The two models cannot use the dynamics effectively.According to this problem

a control model based on Input-Output stability theory is proposed.The closed-loop error of this model is non-linear

accord with the essence of the robot.Then the position tolerance of PD control based on gravity compensation and that of control based on Input-Output stability theory are compared by Matlab software.The maximal tolerance of the robot end-effector is 0.15 mm.