Bar code scanner system and scanner circuitry therefor

• US 4,970,379 A
• Filed: 10/12/1988
• Issued: 11/13/1990
• Est. Priority Date: 04/30/1987
• Status: Expired due to Fees

• Current Assignee: Intermec IP Corporation (Honeywell International Inc.)
• Original Assignee: Norand Corporation (Baker Hughes Company)
• Inventors: Danstrom, Eric J.
• Primary Examiner(s): Westin, Edward P.
• Application Number:
  US07/257,106
• Time in Patent Office: 762 Days
• Field of Search: 250/205, 250/566, 250/568, 235/455, 235/462, 235/472
• US Class Current: 250/205
• CPC Class Codes: G06K 2207/1018 Source control
• 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
• CPC Class Codes: G06K 7/10881 constructional details of hand-held scanners

Abstract

In an exemplary wand type bar code scanner the scanner circuit includes a first control loop for reducing the LED driving current as the D.C. voltage level supplied to the digitizer tends to exceed a selected D.C. reference value; a second control loop becomes active when the LED is shut off by the first control loop, e.g. in the presence of sunlight. The second control loop controls the gain of the scanner amplifier so that the D.C. reference level at the input to the digitizer circuit is maintained as the scanner scans bar codes in the presence of sunlight but with the LED de-energized.

Claims

1. In an optical scanner system,

scanner means having controllable light source means for illuminating a surface containing optical information to be scanned during a scanning operation, and controllable for emitting light of adjustable intensity,

optical sensor means for supplying an information signal varying in accordance with input optical information as it is scanned during a scanning operation, and

a scanner circuit comprising:

information signal translating means coupled with said optical sensor means and supplying an output signal as a function of the intensity of the input optical information, and

control loop means coupled with said information signal translating means and controlling said light source means such that the light output from the light source means is reduced with increased average illumination of the optical sensor means, but said control loop means having a response time such that the information content of the optical information being scanned is reliably transmitted,

said information signal translating means comprising variable gain signal amplifier means, and further control loop means coupled with said optical sensor means and responsive to intensities of the input optical information exceeding an effective operating range of the first mentioned control loop means for progressively reducing the gain of the signal amplifier means.

2. In an optical scanner system,

scanner means having controllable light source means for illuminating a surface containing optical information to be scanned during a scanning operation, and controllable for emitting light of adjustable intensity,

optical sensor means for supplying an information signal varying in accordance with input optical information as it is scanned during a scanning operation, and

a scanner circuit comprising:

information signal translating means coupled with said optical sensor means and supplying an output signal as a function of the intensity of the input optical information, and

control loop means coupled with said information signal translating means and controlling said light source means such that the light output from the light source means is reduced with increased average illumination of the optical sensor means, but said control loop means having a response time such that the information content of the optical information being scanned is reliably transmitted,

further control loop means for essentially shutting off said light source means in the presence of ambient light sufficient to provide for maintaining a desired dynamic range of the information signal supplied by the optical sensor means, said information signal translating means comprising variable gain signal amplifier means, and said further control loop means being coupled with said optical sensor means and responsive to intensities of the input optical information exceeding an effective operating range of the first mentioned control loop means for progessively reducing the gain of the signal amplifier means such that the system is reliably operative in the presence of sunlight.

3. In a system according to claim 2, said optical sensor means being solid state photodiode means.

4. In a system according to claim 3, said light source means being light emitting diode means receiving an energizing current of not more than thirty-five milliamperes.

5. In an optical scanner system,

scanner means having controllable light source means for illuminating a surface containing optical information to be scanned during a scanning operation, and controllable for emitting light of adjustable intensity,

optical sensor means for supplying an information signal varying in accordance with input optical information as it is scanned during a scanning operation, and

a scanner circuit comprising:

information signal translating means coupled with said optical sensor means and supplying an output signal as a function of the intensity of the input optical information, and

control loop means coupled with said information signal translating means and controlling said light source means such that the light output from the light source means is reduced with increased average illumination of the optical sensor means, but said control loop means having a response time such that the information content of the optical information being scanned is reliably transmitted,

said control loop means having reference circuit means for defining a reference signal level for determining a desired output signal level from the scanner circuit for the case of scanning a black region of a bar code and reference signal adjusting means for automatically adjusting the reference signal level to compensate for optical offset due to optical leakage between said light source means and said optical sensor means, said reference signal adjusting means comprising further control loop means coupled between the output of the scanner circuit and said reference circuit means for adjusting the reference signal level in accordance with an output signal from the scanner circuit during an active mode of the light source means.

6. In a system according to claim 5, said further control loop means having a time of response to black to white transitions which is long in comparison to a maximum interval between black and white signal levels due to scanning of a bar code.

7. In a system according to claim 6, said reference circuit means comprising reference capacitor means whose potential controls said reference signal level, said further control loop means adjusting the charge on said capacitance means to compensate for optical offset at each turn on of said light source means.

8. In a system according to claim 7, means operable at turn on of the light source means to pre-charge the reference capacitor means to a selected value prior to build-up of light output from said light source means to an initial operating value.

9. In a system according to claim 8, means for intermittently turning on said light source means at intervals such that the charge on the reference capacitance means is adjusted to compensate for optical offset prior to a scanning operation.

10. In a system according to claim 9, said further control loop means having further reference circuit means providing a further reference signal level for defining a fixed black responsive signal level from said scanner circuit during a scanning operation.

11. In a system according to claim 5, and means for changing a signal level at the control loop means to suppress a spurious output signal from the scanner circuit during turn on of the light source means.

12. In an optical scanner system,

scanner means having controllable light source means for illuminating a surface containing optical information to be scanned during a manual scanning operation, and controllable for emitting light of adjustable intensity,

optical sensor means for supplying an information signal varying in accordance with input optical information as it is scanned during a manual scanning operation, and

a scanner circuit comprising:

information signal translating means coupled with said optical sensor means and supplying an output signal as a function of the intensity of the input optical information, and

control loop means coupled with said information signal translating means and controlling said light source means such that the light output from the light source means is reduced with increased average illumination of the optical sensor means, but said control loop means having a response time such that the information content of the optical information being scanned is reliably transmitted,

said information signal translating means having a bandwidth in the kilohertz range and at least in the order of a hundred times that required for transmission of the manually scanned optical information in order to also transmit information received by the optical sensor means from a host computer.

13. In a system according to claim 12, said control loop means having illumination reference means for establishing an illumination reference signal and controlling said light source means to increase the intensity of illumination of a bar code when the average value of the output signal of the information signal translating means tends to fall off relative to the illumination reference signal, thereby to maintain the dynamic range of the output signal with decreasing bar code contrast without requiring an increase in power supply voltage applied to the information signal translating means.

14. In a system according to claim 13, said control loop means automatically compensating for a decreasing optical transfer function of the scanner means by correspondingly increasing the intensity of illumination of a bar code by the light source means.

15. In a system according to claim 13, said control loop means automatically reducing power consumption during scanning of relatively high contrast bar codes.

16. In a system according to claim 13, said control loop means automatically increasing the intensity of illumination of a bar code as produced by the light source means for a less favorable read angle, thereby to maintain the dynamic range of the output signal.

17. In an optical scanner system according to claim 12, said information signal translating means comprising variable gain signal amplifier means, and further control loop means coupled with said optical sensor means and responsive to intensities of the input optical information exceeding an effective operating range of the first mentioned control loop means for progressively reducing the gain of the signal amplifier means.

18. In an optical scanner system according to claim 12, further control loop means for essentially shutting off said light source means in the presence of ambient light sufficient to provide for maintaining a desired dynamic range of the information signal supplied by the optical sensor means.

19. In a system according to claim 18, said information signal translating means comprising variable gain signal amplifier means, and said further control loop means being coupled with said optical sensor means and responsive to intensities of the input optical information exceeding an effective operating range of the first mentioned control loop means for progressively reducing the gain of the signal amplifier means such that the system is reliably operative in the presence of sunlight.

20. In an optical scanner system according to claim 12, said system being operated with a supply voltage of not more than five volts and providing a dynamic range in response to bar code scanning of at least one hundred millivolts at the output of said information signal translating means over a range of bar code contrasts of at least two to one.

21. In a system according to claim 20, said optical sensor means being solid state photodiode means.

22. In a system according to claim 21, said light source means being light emitting diode means receiving an energizing current of not more than thirty-five milliamperes.

23. In an optical scanner system according to claim 12, said control loop means having reference circuit means for defining a reference signal level for determining a desired output signal level from the scanner circuit for the case of scanning a black region of a bar code and reference signal adjusting means for automatically adjusting the reference signal level to compensate for optical offset due to optical leakage between said light source means and said optical sensor means.

24. In a system according to claim 23, said reference signal adjusting means comprising further control loop means coupled between the output of the scanner circuit and said reference circuit means for adjusting the reference signal level in accordance with an output signal from the scanner circuit during an active mode of the light source means.

25. In a system according to claim 24, said further control loop means having a time of response to black to white transitions which is long in comparison to a maximum interval between black and white signal levels due to scanning of a bar code.

26. In a system according to claim 25, said reference circuit means comprising reference capacitor means whose potential controls said reference signal level, said further control loop means adjusting the charge on said capacitance means to compensate for optical offset at each turn on of said light source means.

27. In a system according to claim 26, means operable at turn on of the light source means to pre-charge the reference capacitor means to a selected value prior to build-up of light output from said light source means to an initial operating value.

28. In a system according to claim 27, means for intermittently turning on said light source means at intervals such that the charge on the reference capacitance means is adjusted to compensate for optical offset prior to a scanning operation.

29. In a system according to claim 28, said further control loop means having further reference circuit means providing a further reference signal level for defining a fixed black responsive signal level from said scanner circuit during a scanning operation.

30. In a system according to claim 23, and means for changing a signal level at the control loop means to suppress a spurious output signal from the scanner circuit during turn on of the light source means.