Smooth Surface-to-Surface Contact Control for Rope-Base Soft-Tip Manipulator

A new control pipeline has been proposed for the Rope-Base Soft-tip Manipulator (RBSM) to execute the surface contact task to prevent the jamming and slipping problems. The control pipeline enables smooth surface-to-surface contact for the RBSM using only force sensors, eliminating the dependence on additional pose measurement of the window surface plane and soft-tip deformation information. The pipeline consists of three steps: free contact step implemented by an exponential force shape controller to avoid force overshoot to the window surface; orientation refinement step implemented by a force and torque combined controller to make the RBSM cleaning head surface stable adapt to the smooth window surface; and finally, a release normal force step to reduce head jamming and region covering with a pre-defined vibration-less cleaning trajectory for smooth cleaning on the slippery window surface. The proposed pipeline has been validated in a Rope base Cleaning Manipulator prototype to clean a common window surface. The force and velocity curves during the cleaning experiment show that the proposed method achieves smooth scraping and cleaning under unknown initial significant errors in surface orientation. Note to Practitioners—The current robotic rope base high-rise exterior work, especially cleaning, is not efficient due to the instability of the base and the influence of the soft-tip on the window and end-effector contact. A new control pipeline has been proposed for the Rope-Base Soft-tip Manipulator (RBSM) to clean the window surface smoothly to avoid jamming, slipping, and leaving problems in the contact process. The control pipeline realizes smooth surface-to-surface contact of RBSM with only force sensors without additional pose measurement of the window surface plane. The pipeline consists of three steps: free contact step implemented by an exponential force shape controller to avoid force overshoot to the window surface; orientation refinement step implemented by a force and torque combined controller to make the RBSM cleaning head surface stable adapt to the smooth window surface; and finally, a release normal force step to reduce head jamming and region covering with a pre-defined vibration-less cleaning trajectory for smooth cleaning on the slippery window surface. This setting can effectively guarantee the RBSM contact process and can also avoid physical damage to the window. Therefore, it lays the foundation for autonomous robotic rope base manipulation.