Performance Analysis for Direct Drive Motor Built in a Lens Barrel for Zoomlens

Abstract

Zoomlenses are adjusted by driving motors outside of lens barrels and reduction gear trains in a majority of camcorders. If built-in direct driving motors housed in the lens barrels with no protrusion were invented, more compact, lighter and lower-cost camcoders than coventional ones would be developed. A new motor satisfying such a tough requirements is proposed in this paper. A stator (lens barrel) and a rotor (variator lens) function as a female screw and a male screw, respectively. Then, switching currents of armature windings buried in the lens barrel sequentially, the rotor rotates and the lens is shifted to an optical axis direction. This motor is a kind of a permanent magnet synchronous motor driven by an inverter, but the stator is in screwed engagement with the rotor and a torque is directly converted to an axial force without gear trains. Such a principle has not yet been presented. Although the motor was developed only for camcorders, it would also be used for other apparatuses. Performance analysis of this motor is reported in the paper.