| 摘要 |
A reflective deflector of a light beam which scans in opposite directions across a bar code is controlled in scan angle by monitoring the AC component of a current passing through a winding of a scanning motor which oscillates the deflector to scan the beam across the code over a scan angle. The inductance of the winding corresponds to the length of the scan angle and is measured in terms of the peak to peak value of the AC component during a scan period or frame which occurs over an interval corresponding to the reciprocal of the scan rate. During successive periods, successive trains of pulses are generated. The number of pulses or their duty cycle during each period is changed in accordance with an error signal corresponding to the difference between the desired scan angle and the peak to peak value of the AC component. The pulse trains are translated into trains of current pulses which are passed through another winding of the motor in opposite directions so as to drive the rotor of the motor which reciprocates the reflector in opposite directions over the desired scan angle. By modifying the desired scan angle in accordance with changes in temperature affecting the system, the system can be compensated for temperature changes. By modifying the error signal by processing it with a filter, the response of the system to changes in scan angle can be controlled.
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