Non-Linear Observer-Based Control of Flexible-Joint Manipulators Used in Machine Processing

This paper proposes to use a non-linear observer to build the state and the external force of flexible manipulator robots during their machining (composite materials) processes or Friction Stir Welding (FSW) processes. These two different processes have a problem in common: the flexibility of the robot can not be neglected, that is to say, the errors due to the deformation of the links should be taken into account. However, in most industrial robots, the real positions and velocities of each link are not measured, so in this study, an observer is proposed to reconstruct the real angular positions and velocities of links by using the measured angular positions and the velocities of actuators. A simulation by Matlab/Simulink has been carried out with a 2 axis Robot during its machining processes: the proposed observer showed great performances in estimating the state of the robot (position and velocity). Then, in order to improve the tracking accuracy in the tool frame, the state of the external force along the forward direction (x) and its normal direction (y) are required, while they are also not measured by our robot. A disturbance observer has been added to reconstruct the processing force. A good precision during the proposed processes have been obtained using the latter. This study contributes to solve the problem from the point of view of accuracies during the machining processes.