Force feedback keyboard: self sensing

Within the framework of a project consisting in developing a haptic keyboard, each key is aimed to be controlled individually in position and force. Small sized actuators has already been designed and integrated in a 64 keys force feedback keyboard. The project goal is to develop a new self-sensing method to determine the key position without adding any extra sensor. Sensorless techniques are already used in motor control but still represent a challenge in actuators drives. The method could be applied to numerous force feedback systems developed nowadays. Based on studies previously run within the laboratory, the aim is to take advantage of the variation of inductance seen by the coil during its travel to measure the position and identify other parasitic effects. The number of actuators constituting a multi-fingered device like the Haptic Keyboard avoids using heavy algorithms. It is thus proposed to take advantage of the pulse width modulation (PWM) used for power by modifying its resonance frequency using an additional capacitor. Efficient force and position controls are aimed to be implemented in the end. A single key demonstrator with its own electronics will be designed and mounted.