Optimal Design and Sensorless Position Control of a Piezoelectric Motor Integrated into a Mechatronic Cylinder Lock
Electronic door lock cylinders need some sort of mechanical actuator to toggle the locking state between open and closed. The main requirements are high security standards, low power consumption, reasonable production costs, and facile integration of the actuator into the mechatronic system. Existing mechatronic locking devices are actuated by DC motors. Complex security setups are necessary to prevent the motor to be moved when not supplied or to impede magnetic picking. Piezoelectric ultrasonic motors (PUM) respond better to these challenges. The presented work adresses a design methodology whose goal is to optimally integrate a PUM into an existing mechatronic system. By doing so, we optimise the motor, the drive electronics and the position control method, while the interdependency of all three subsystems is the gist of the optimisation approach. With respect to the drive electronics, resonance matching is realised with a LLCC resonant converter and a resonance frequency tracking controller. A direct digital synthesis based drive signal regulator allows for reducing the overall size of drive and control electronics. The locking position is detected indirectly by motional admittance modulation, obviating the need for a position sensor.