Experiments on semi-closed loop oscillatory control for cantilevered electromagnetic actuators using gradient force model

Micro electro-mechanical systems (MEMS) are fabricated by applying semiconductor manufacturing technology. MEMS which integrate sensors and actuators are prospective in a wide field like automotives and medicines. The actuator integrated in MEMS often employs nonlinear forces like electromagnetic force and electrostatic force. For the gap closing actuators, it is known that pull-in instability due to nonlinear forces strictly limits mobility range. We have proposed the open loop oscillatory stabilization control as a solution for this problem, however, model error on nonlinear electromagnetic force causes steady state deviation. To resolve this problem, in this paper, we propose a closed loop feedback oscillatory control of the position of the cantilevered electromagnetic actuators. The actuator is oscillatory controlled but the amplitude and the bias current are adaptively tuned using the gradient of the electromagnetic force model. Thus we reduce the steady state deviation due to identification error of electromagnetic force. The advantage of the proposed method is shown through the experiments where inevitable modeling error exists.