Combined Luenberger state and disturbance observer for semi-dual loop control of two-mass actuator system

The semi-dual loop control of two-mass actuator system, proposed in the previous work, requires the motor velocity estimation based on the load-side sensing. In this paper, we elaborate a combined Luenberger state and disturbance observer so as to reduce the spurious non-zero velocity observation at idle state of the controlled plant. The observation bias arises due to the impact of nonlinearities between the motor and load and consecutive non-zero control action at actually zero motion. The necessity of an auxiliary disturbance observation, in particularly at positioning steady-state, is analyzed and proved with experiments. The proposed observer is incorporated in the (inner) velocity control loop without motor sensing and evaluated on a laboratory setup. The designed controller brings efficiently the actuator load in vicinity to the positioning reference and that without direct load-side feedback. This allows, in the next stage, designing an auxiliary load-side position feedback control to meet the required positioning accuracy.