Dynamic calibration for high accuracy flux control of reluctance actuators

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Abstract

In the semiconductor industry, the demand for a continuously higher throughput puts tough requirements on the force capacity and accuracy of actuators. Reluctance actuators, as a promising alternative to the present state-of-the-art Lorentz actuators, are capable of achieving much higher force densities. On the other hand, reluctance actuators suffer from strong intrinsic nonlinearity, such as the quadratic and position-dependent current-force relation, negative stiffness, and magnetic hysteresis, making accurate control challenging. These nonlinear effects can be much suppressed if, instead of controlling the current through the driving coil, the magnetic flux in the actuator core is controlled. As a preparation step for implementing the flux control experimentally on reluctance actuators, this project aims to design and realise the necessary hardware for flux control implementation, including a reluctance actuator prototype and a test setup, and then dynamically calibrate the actuator for flux measurement and control. More specifically, a hybrid reluctance actuator prototype that is suitable for flux control, as well as a test setup for measuring the position and dynamic force output of the actuator, are designed and realised. Using this setup, relations between key variables of the actuator are measured to enable nonlinear compensation in the current and flux control, and a hybrid flux measuring scheme using a Hall sensor and a sense coil is proposed and experimentally implemented. Although noise in the flux measurement is effectively minimised, the result shows a mismatch in the frequency domain between the outputs of the Hall sensor and the sense coil, where further investigation is needed to improve the feasibility of this approach. Furthermore, a hybrid force measuring scheme is proposed and implemented where errors of the load cell due to high-frequency dynamics of the setup can be compensated using acceleration measurements, leading to a wider frequency range for the force measurement. With the realised hardware and the obtained measurements from this project, the next step in future works would be to experimentally implement the flux control on a reluctance actuator and compare its performance with the standard current control.