| 摘要 |
Apparatus for synchronizing rotational speed of a color filter wheel to a video field rate using a stepping motor drive. The derivation of the stepping rate is taken directly from the video system's master clock through dividers and a phase locked loop which provide the required fractional rate division. An integrating capacitor in the phase locked loop controls the output of a voltage control oscillator so that at power up the capacitor is charged at a relatively slow rate thus ramping up the stepping rate of the motor until phase locking is achieved. A pair of optical switches monitor the rotation of the filter wheel. If the switches are not made within a predetermined number of steps, the integrating capacitor is discharged and the ramping procedure reinitiated. Final synchronization of the wheel in correct orientation with the video field is obtained by thorough use of a coincidence detector circuit that causes the motor to be stepped at a slower than normal rate until coincidence between a video system generated field index signal and an optically derived wheel rotational index signal is detected at which time the stepping rate is brought up to the desired rate.
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