HE Shun-feng, ZHU Ming-chao, LI Zhong-can, ZHOU Yu-fei, CUI Jing-kai
Accurate force/position control in the presence of modeling uncertainty in robots is a challenging task. This article is based on improved integral sliding mode control for hybrid visual & force control. To perform visual servoing, an optimized visual feature is adopted to avoid the ill-condition visual Jacobian matrix. An improved super-twisting algorithm is proposed based on time delay estimation for integral sliding mode control, and an improved sliding surface and convergence law is used for the positive definite part of integral sliding mode control. Correspondingly, visual control method and force control method are proposed to apply to the hybrid visual & force control framework. To avoid the impact of noise from the force control part on the control output, a visual admittance framework is used for hybrid control. To optimize the solidification impedance characteristics caused by fixed admittance parameters, a fuzzy adaptive admittance framework is proposed to inherit the advantages of admittance while adaptively adjusting parameters in real-time. Finally, a 6-degree-of-freedom deviation model is used for simulation to verify that the proposed scheme can accurately track visual trajectories and expected forces under relatively small chatting. The performance of the three with different focuses is compared based on direct visual perception hybrid control, visual admittance control framework, and fuzzy adaptive admittance framework. Under the deviation model, the proposed i-CISMC algorithm is validated by surface force tracking to have better tracking accuracy while ensuring smaller control chattering; the proposed algorithm is combined with the fuzzy adaptive admittance framework, and the results of tracking under noise have proved that the framework inherites the suppleness of the admittance framework to the disturbance of the force loop, and at the same time, can adaptively change the parameters of the admittance to obtain better tracking speed and tracking accuracy.