An integrated electromagnetic actuator with adaptable zero-power gravity compensation

Abstract

Lorentz actuators are frequently used for electro-magnetic levitation and actuation. Especially in robot-based inline measurement applications, Lorentz actuators can be used for actuation of a vibration compensating measurement platform. However, a purely Lorentz-based actuation system comes with the drawback of a permanent offset current to compensate a mover for gravity, limiting the overall system performance. Facing the undesirable offset power consumption of such magnetically levitating systems, a integrated actuator with integrated zero-power gravity compensation is designed and implemented in the course of this thesis. The mover is able to remain in a constant position while the gravity compensation is adapted to the effective load, which depends on the mass and the orientation of the measurement system. An electropermanent magnet (EPM) is used to achieve a tunable zero-power gravity compensation for arbitrary direction and an integrated two degrees of freedom (DoFs) Lorentz actuator stabilizes the mover at a constant operating point. The position of the mover is determined with two integrated proximity sensors and the force of the EPM is tuned by a capacitor discharge pulse magnetizer. The decoupled design of the reluctance and Lorentz actuation justifies a single-input single-output proportional-integral-derivative control of each DoF to stabilize the mover. The optimized Lorentz actuator design shows a motor-constant of 19.3N/A. The prototype achieves sub-micrometer resolution in a translational range of 4mm and a rotational range of 3.27°. The mass-dependent position control bandwidth exceeds 100Hz with no payload and still achieves 28Hz for an additional 1.5kg load. The cascaded gravity compensation control minimizes the current of the Lorentz actuators by tuning the EPM with a robust, heuristic algorithm, while the mover is kept in a free floating position. The tunable gravity compensation handles additional payloads up to 1.5kg and reduces the power consumption at least by a factor of 7800 with an actuator weight of 828.3g. Experimental results demonstrate a compensation rate of 9.61N/s.