| 摘要 |
A mirror is oscillated through an angular arc defined by arc terminal points. Springs absorb the kinetic energy of halt at the terminal points, the springs returning the energy to the mirror thereby reversing the direction of oscillation thereof. Magnetic means coupled to the mirror provides a source of force to induce oscillation of the mirror and to bias the mirror to a position off the center point of the arc of oscillation when operative. The magnetic means is so driven by a square wave signal, having twice the frequency of oscillation, to create an intermittent force on the mirror that one portion of the square wave force aids movement of the mirror from its center point of oscillation towards one of the terminal points and another portion of the square wave force acts against movement (and spring energy) of the mirror from the terminal point towards the center point. Too slow or too fast movement of the mirror is compensated for by the square wave force. The mirror therefore moves at a substantially constant angular velocity between the terminal points.
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