A Human-Guided Spherical Robot for the Compliant Grinding of Delicate Workpieces

A robotic grinding system requires a force-controlled grinding module to provide a consistent surface roughness and a robot arm to position the grinding module to reach a wide range of surface area on a workpiece. Existing pneumatic grinding modules are bulky and energy-inefficient. Existing 6-axis robot arms are often used for grinding positioning, but they require a large accommodation space and have limited access to the surface of a workpiece. This paper proposes a compact 3-axis spherical robot with no grinding surface limitations. The robot has back-drivable actuators and hence can be guided by a human operator to facilitate the path planning of a grinding surface. The proposed grinding module has low reflected inertia and hence can be used to control the grinding force accurately. The proposed grinding module also has a small size, low noise, and minimum energy consumption. Experiments are presented to verify the accuracy of grinding force control. Through an illustration of removing the parting line of a helmet hardshell, the spherical robot is shown to be able to effectively provide grinding treatments on a delicate surface with a wide range of roughness. It is expected that the proposed robot can be widely used in automatic grinding operations.