Design and fabrication of miniature combination lock

Design and fabrication of a miniature combination lock is reported. The prototype's outline size is less than 15mm × 20mm × 25mm, with the function of 24 steps single-try discrimination. Two miniature application-specific electromagnetic motors are used to drive a counter meshing gears (CMG) mechanism. Ratchet-pawl mechanism is respectively attached to each CMG gears assembly, to insure it step forward at accurate angles in company with motor driving circuit. Main functional components of the lock are fabricated by UV-LIGA micromachining process, including the motor's stator with 4-level planar coils. Handcraft assembling process and control circuit design are also briefly introduced. The prototype had already endured more than 1000 times of unlocking and 100 times of manually unlocking. It is proved that micro-motor and micromachining technologies are very useful in miniaturization of such a surety device.