A novel robust, continuous, PID-assisted control for precision tracking of flexible systems a case study on timing belts

Low-cost, indirect-drive actuators, like timing belts are widely used in many industrial applications requiring linear translational motion. However, the timing belt faces greater control challenges as newer technological processes necessitate an increased tracking accuracy, precision and a need for minimal vibration all in the presence of rapid payload changes. Firstly, it is widely known that belt dynamics contribute higher order modes to the system. This causes a non-collocated control problem where the encoder position on the motor side does not provide a good estimate of the end-effector position. Second, these higher order modes coupled with Coulomb friction associated with the end-effector makes system identification tedious and inviable. In addition, this makes control tricky as standard discontinuous robust techniques have a tendency to excite those higher frequency dynamics. Furthermore, they are used to carry payloads of varying mass and are loaded and unloaded in quick succession adding to model uncertainty. In order to achieve higher position tracking accuracy, the authors propose a continuous robust controller that compensates for higher order disturbance while having a DOB that handles lower frequency, friction-related dynamics of the timing belt. In this paper, the details of this control scheme, simulation results justifying our approach and relevant stability proofs are presented.