Wiping Strategy for Soft Contact in Disinfection Robot

Abstract

The use of robots in disinfection tasks has been developed to prevent the exposure of human workers to viruses and reduce workload. Unlike conventional methods that involve spraying disinfectants or using UV lamps for space disinfection, the disinfection robot project has been developed focusing on surface disinfection through wiping and organic matter removal. Soft contact in wiping refers to the contact between the robot and soft objects, achieved using tools or wiping soft surfaces. During soft contact, stick-slip, which indicates jerky motions occur due to friction, decreases force control performance. A decrease in force control performance indicates a decrease in the performance of disinfection tasks because force control is linked to the evaluation metric of disinfection tasks obtained through sterilization rate experiments.

This thesis proposes a robust wiping strategy to attenuate oscillation caused by soft contact. Experiments were conducted by adjusting robot operation variables using a low-stiffness tool that exhibits significant oscillation due to friction and verifying contact force errors and friction patterns. The decrease in force error was measured at low contact forces and high task velocities. Observing the tilting strategy of tools during human wiping motions showed that tilting the tool during robot wiping tasks reduces force errors and improves friction patterns. Specifically, an optimal value for tilting velocity was identified based on force errors, and a method for generating tilting trajectories was proposed. The proposed wiping strategy added an observer to the existing hybrid controller to observe the onset of oscillation through contact force direction error and a trajectory generator to create trajectories for tilting the tool. Experimental results using the proposed wiping strategy showed a decrease in the root mean square error of force from 4.5020 to 1.5181 compared to the existing controller, indicating improved force control performance.