Optical code reading device with autofocussing

• US 5,122,644 A
• Filed: 07/16/1991
• Issued: 06/16/1992
• Est. Priority Date: 11/17/1988
• Status: Expired due to Term

• Current Assignee: ALPS Electric Company Limited (Alps Alpine Co., Ltd.)
• Original Assignee: ALPS Electric Company Limited (Alps Alpine Co., Ltd.)
• Inventors: Ouchi, Ikuo, Hasegawa, Kazuo, Ouchi, Junichi
• Primary Examiner(s): PITTS, HAROLD I
• Application Number:
  US07/731,295
• Time in Patent Office: 336 Days
• Field of Search: 235/462, 235/467, 235/470, 235/472, 235/455, 307/258, 307/302, 307/560, 372/38
• US Class Current: 235/462.26
• CPC Class Codes: G06K 2207/1013 Multi-focal
• CPC Class Codes: G06K 7/10831 Arrangement of optical elements, e.g. lenses, mirrors, prisms optical elements per se G02B
• CPC Class Codes: G06K 7/10851 Circuits for pulse shaping, amplifying, eliminating noise signals, checking the function of the sensing device basic electronic circuitry H03

Abstract

In a code reading device, which receives reflected light obtained by scanning a code represented on a recording medium with a laser light beam and decodes it to obtain the code, the reading probability is improved by varying the focusing position for every scanning period with the laser light beam.

Claims

1. A code reading device having circuit for protecting a laser diode comprising:

a laser diode for outputting a laser beam and connected to a power source;

driving means connected in series therewith for controlling current flowing through said laser diode;

control means for supplying a signal for controlling said driving means; and

means for detecting a voltage of said power source and outputting a signal to said control means preventing surge of current through the laser diode during a predetermined time after switching on of said power source, said means for detecting including a capacitor connected to said power source and charged by said voltage of said power source and a transistor having its control terminal connected to said capacitor and a second terminal connected to said power source, wherein said signal to said control means increases as a current at said second terminal increases in response to the charge on said capacitor.

2. A code reading device including a circuit for detecting light levels comprising:

a comparator having a reference input terminal to which a reference voltage is applied, having a comparison input terminal to which a voltage to be compared is applied, and having an output terminal for outputting a comparison output voltage;

positive feedback means for supplying positive feedback current from the output terminal to the comparison input terminal;

voltage dividing means for dividing the voltage to be compared and to which said positive feedback means is connected; and

means connected to the reference input terminal for preventing feedback current from flowing through the positive feedback means and resetting the comparator when the value of the voltage supplied through said voltage dividing means equals the reference voltage, said means for preventing including a reset switch connecting said reference terminal to said reference voltage when said voltage is being compared, and connecting said reference terminal to a reset voltage differing from said reference voltage when said feedback is to be prevented;

wherein both the positive feedback means and the voltage dividing means include a diode for regulating the direction of current therethrough.

3. A code reader comprising:

a scanner for scanning with light a medium on which a code is recorded;

a photodetector for detecting a level of light reflected by the medium;

a preamplifier for comparing the level of light detected by the photodetector to a reference value and providing an output signal in response thereto;

an amplifier for amplifying the output signal of the preamplifier and for providing the reference value, the amplifier having a reference terminal;

a decoder for converting the amplified output signal to a digital value;

a deflection control for causing the scanner to scan the code and for providing an amplification factor by which the amplifier amplifies the output signal of the preamplifier, wherein the deflection control includes means for keeping the amplification factor constant during each scan of the code, and changing the amplification factor prior to a subsequent scan of the code when the decoder indicates the code has not been read by the previous scan;

a plurality of resistors each switchably connected to the reference terminal of the amplifier; and

a counter for switching the resistors and actuated by a signal indicating the duration of the scanning;

wherein operation of the counter by the signal indicating scanning also determines the amplification factor.