Full Closed-loop Position Control of the Surgical Cable-driven Micromanipulator Based on Joint Angle Estimator

As the micromanipulator of surgical robots works in a narrow space, it is difficult to install any angle sensor at the end, and therefore the closed-loop position control can't be achieved. For this problem, a closed-loop control method based on joint angle estimator is presented. Firstly, a 4-DOF (degree of freedom) driving scheme for micromanipulator is designed, an experiment system is established on the single-joint principle prototype of the surgical robot micromanipulator, and the joint angle estimator is designed based on the dynamics analysis of the cable-driven system. Then, the parameters of joint angle estimator are given through the method of dynamic parameter identification. What's more, the simplified and modified model of the angle estimator is achieved by experimental data analysis. The experiment results show that the output precision of the joint angle estimator can reach 0.38°. Finally, the closed-loop control experiment of the micromanipulator joint angle is carried out by taking the output of the angle estimator as the feedback signal. Results show that the maximum following error of the micromanipulator joint angle is about 0.734° when the system moves freely. The precision of the joint angle estimator is 0.59° and the maximum following error is about 1.112°, when an external force of 1.5N is exerted on the micromanipulator end. These results indicate that the proposed closed-loop joint angle control method has a relatively high control accuracy.