Position control of a bidirectional moving magnet actuator based on contactless hall-effect transducer

Abstract

In this paper it is studied an open loop command method for controlling the position of a bidirectional moving magnet actuator with elastic magnetic forces (MMAEMF). This type of actuator has, due to its design, an equilibrium position that allows displacement of the actuator's rod in both directions. To energize and drive the actuator it is used a method of adjusting the duty-cycle of a PWM signal and MOSFET transistors. As a feedback non-contact displacement transducer it is used an arrangement of two linear ratiometric Hall sensors and a small permanent magnet disc attached to the mobile actuator's rod that moves between the two fixed sensors. Both input data, acquired from the sensors, and output PWM signal is processed through the pins of an open-source electronics prototyping platform based on Atmel microcontroller. Analog data acquired from the sensor is converted to distance after a calibration method through a lookup table. The setup allows measurements to be taken with 0.1 mm precision of the actuator's rod position and to plot the static characteristic of displacement for a range up to ±5mm.