Voltage based linearization of a reluctance actuator for high-precision applications

A single-phase C-core reluctance actuator is linearized using a combined analog and digital control, and magnetic field measurements. The analog stage contains a high-bandwidth sensing coil voltage tracking controller which rejects the electric and magnetic circuit disturbances and makes the plant behave as an idealized transformer between the driving coil and the sensing coil on a wide frequency range. Since this is the natural high frequent behavior of the actuator, very low sensing coil voltage tracking errors are achieved. Furthermore, in combination with flux feedforward and drift stabilizing low bandwidth Hall probe feedback, this circuitry achieves very low reluctance force tracking errors, i.e. very small linearization errors and low stiffness inherent to voltage-based control schemes. The performance is experimentally verified on a 1DoF measurement rig with 1 nm position and less than 50 mN force resolution, where linearization errors smaller than 0.05 N for challenging 200 N second order force profiles are measured.