Design of a new passive end-effector based on constant-force mechanism for robotic polishing

Polishing is an important final machining process in manufacturing. For robotic polishing, active compliance control is the most frequently used approach to control the contact force between the end-effector and workpiece. However, it usually exhibits the problem of force overshoot at the start of contact, with poor force accuracy normally larger than 1 N. This paper proposes the concept design of a novel end-effector based on constant-force mechanism for robotic polishing. This design is the first constant-force mechanism based robotic end-effector for use in polishing experiment. An industrial robot is used to position the end-effector and the end-effector regulates the contact force passively. The constant-force motion range acts as a buffer to counteract the excessive displacement caused by inertia. As a result, there is no force overshoot, producing the consistency for the workpiece's surface quality. Moreover, the property of the constant force ensures more accurate contact force without using a complex controller. Design, modeling, and simulation study have been performed to demonstrate the proposed idea. A prototype is fabricated for experimental testing. The end effector is adopted to polish rusty steel, and the recorded contact force signal during polishing demonstrates the effectiveness of the constant-force mechanism in counteracting the force overshoot and improving the force accuracy. Results indicate that the polished surface is extremely uniform with steady contact force regulated by the constant-force mechanism.