Identify a Surface with Robot Force Control

Abstract: The topic of this thesis is to identify a surface with robot force control. To achieve this a robot performing contact force control on a surface while it also follows a trajectory is needed. All experiments were performed in the robot laboratory at the Department of Automatic Control at Lund Institute of Technology. The robot used was an ABB Irb-2000 robot, equipped with a wrist mounted force and torque sensor of type JR3.

In the master thesis the robot kinematics is treated. Kinematics describes the geometric relationship between the motion of the robot in joint space and the motion of the tool in the task space. Furthermore a compensation for the gravitational force acting on the end-effector was implemented.

Direct force control has been used throughout this thesis. Direct force control operates on a force error between the desired and the measured values and aims to have a constant value of the contact force. When only controlling on three joints a PI force controller with variable proportional part is to be preferred. This because it can be tuned to be very fast, when in contact and thereby it can apply a constant force on an object without large force errors. The simulated result did not completely agree with the result achieved when the experiment was done in the reality. The reason is probably the assumption in the simulation that the force signal was without noise.

The result from the three-dimensional experiments was applied to the six joint controller structures. All the simulations using six joints worked successfully, both reorienting and reorienting while following a trajectory. In the simulations it was possible to identify parts of simpler surfaces such as planes, cylinders, and spheres.