In recent decades, the adoption of industrial robots in various manufacturing finishing processes such as sanding, deburring, and polishing has been on the rise. Robotic finishing processes require very close interaction with the workpiece, and forces are exerted by the robot’s end-effector on the workpiece during this interaction. The contact forces play a major role in the surface quality of the finished product and therefore need to be regulated to achieve the desired finish. However, when dealing with complex parts with free-form surfaces, such as the composite panel used in this thesis, controlling the contact forces would require more advanced force control methods. The aim of this research is to develop a hybrid force/position control methodology to enhance the quality and efficiency of the sanding process and control the forces applied on the workpiece.

The first aim of this thesis is to develop a simulation model for the KUKA KR6 R700 used in this study. The model is developed in MATLAB Simulink using the forward and inverse kinematic model of the robot. The sanding motion is simulated with a visual representation, and the response and efficiency of the designed hybrid controller are tested. The forces and torques at the end-effector during the sanding motion are estimated. The estimated forces/torques are validated and used as feedback to the force control loop. The designed model can successfully estimate the forces at the end-effector using the Jacobian, and also control the contact forces and torques applied on the workpiece based on a defined setpoint.

In the second part of this thesis, the designed hybrid force/position controller is experimentally implemented on a 6-axis robot. A 6-axis force/torque sensor is mounted at the end effector to measure the forces and torques applied on the workpiece when the robot performs the sanding motion. A PI controller is used for the force control loop, and a PD controller is used for closing the position loop. The sanding process is also performed using the KUKA ForceTorqueControl software package, and the results and limitations are discussed.

It is shown that the designed controller effectively maintains a constant contact pressure between the sanding tool and workpiece, which is crucial for achieving a uniform surface finish.