Planar Rotational Magnetic Micromotors With Integrated Shaft Encoder and Magnetic Rotor Levitation

Deep x-ray lithography and electroplating may be combined to form a fabrication tool for micromechanical devices with large structural heights, to 500 _tm, and extreme edge acuities, less than 0.1 ktm run-out per 100 I.tm of height. This process concept which originated in Germany as LIGA[ 1] may be further extended by adding surface micromachining[2]. This extension permits the fabrication of precision metal and plastic parts which may be assembled into three-dimensional micromechanical components and systems. The processing tool may be used to fabricate devices from ferromagnetic material such as nickel and nickel-iron alloys. These materials when properly heat treated exhibit acceptable magnetic behavior for current to flux conversion and marginal behavior for permanent magnet applications. The tool and materials have been tested via planar, magnetic, rotational micromotor fabrication. Three phase reluctance machines of the 6:4 configuration with 280 lam diameter rotors have been tested and analyzed[3,4]. Stable rotational speeds to 34,000 rpm with output torques above 10 x 10 -9 N-m have been obtained. The behavior is monitored with integrated shaft encoders which are photodiodes which measure the rotor response. Magnetic levitation of the rotor via reluctance forces has been achieved and has reduced frictional torque losses to less than 1% of the available torque. The results indicate that high speed limits of these actuators are related to torque ripple. Hysteresis motors with magnetic bearings are under consideration and will produce high speed rotational machines with excellent sensor application potential.