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

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.