This invention relates to a device for driving a placing stand on which an aperture card is placed.
In a placing stand driving device driven by a step motor, a vibration inherent in the step motor is caused when the step operation of the step motor is suspended. The vibration is transmitted to the placing stand, to cause the latter to vibrate slightly back and forth. As a result, the resolution is decreased or the resultant image is staggered; that is, the resultant copy is of low quality.
In order to overcome the above-described difficulties, a variety of methods have been proposed in the art. In one of these methods, a spring is employed to push a flywheel against the shaft of a step motor, so that the frictional contact between the motor shaft and the flywheel applies a load to the motor. In another method, oil is provided between a flywheel mounted through a bearing on the motor shaft and an external shell member secured to the motor in a manner such as to cover the flywheel, to apply a load to the motor. In another method, the flywheel is made of a permanent magnet, so that the magnetic flux formed between the permanent magnet and the motor shaft loads the motor. In each of these conventional methods, a flywheel effect is utilized to apply a load to the motor so that the step operation is made smooth at the start and end points.
In all of the conventional methods of damping the inherent vibration of a step motor, the load of the motor is increased so that the inherent vibration of the motor may be eliminated when the original is scanned. However, the conventional methods are disadvantageous in that the placing stand cannot be quickly returned to its original position because of the increased load.