| 摘要 |
<p>PROBLEM TO BE SOLVED: To detect the external light that is optimum to the change of the ambient external light by varying the constant which decides the detection level of a detection signal to reduce the sensitivity against the external light as the time when no state shift occurs is increased. SOLUTION: When a power supply is applied to a bar code reader 1, a CPU 16 first initializes the constant value to decide a detection range of the external light. The constant value is set in every state. If a bar code label 7 is not detected for 10 seconds in a state A where a laser beam is turned on in 100% and a motor 4 is driven to revolve a polygon 3, the state A is shifted to a state B where the turn-on/off ratio is reduced down to 50% compared with the state A. If the label 7 is not detected either and the external light is reduced less than the value decided by multiplying the mean value by the constant value (b) in the state B, the wrong detection is judged and 0.1 is subtracted from the value (b). Thus the detection level of the external light is reduced and the detection sensitivity of the external light is also reduced.</p> |
