| 摘要 |
<p>An improved control circuit for an electromagnetic actuator of the type having an armature mounted for movement in a magnetic field, and means connected to the armature for urging the armature toward a rest position. The circuit applies an electrical pulse of a first polarity, magnitude and duration to the armature to quickly move the armature to a programmed position determined by the magnitude and duration of said pulse, the programmed position lying within a range of positions between said rest position, and an extreme position achievable by the armature. The control circuit then applies a pulse of opposite polarity and of magnitude and duration effective to stop the armature at the programmed position. The control circuit applies a periodic train of pulses of said first polarity, of fixed magnitude and of duration, effective to hold the actuator in the programmed position, the period of said train of pulses being above the natural cutoff frequency of the actuator. To quickly return the armature to the rest position, the control circuit applies a pulse of opposite polarity and of duration and magnitude effective to the armature to move the armature in cooperation with the urging means, to the rest position. The circuit then applies a braking pulse of said first polarity and of duration and magnitude effective to stop the armature at the rest position. In a preferred embodiment, the actuator controls a shutter/aperture in a camera, the duty cycle (i.e. pulse duration) of the train of pulses determines the aperture size, and the number of pulses in the pulse train determines the shutter time. The control circuit also includes means for boosting the voltage of the moving and braking pulses to achieve extremely short shutter times.</p> |
