Variable-sweep bar code reader

• US 5,115,121 A
• Filed: 01/05/1990
• Issued: 05/19/1992
• Est. Priority Date: 01/05/1990
• Status: Expired due to Fees

• Current Assignee: Control Module, Inc.
• Original Assignee: Control Module, Inc.
• Inventors: Drummond, Bernard, Bianco, James S.
• Primary Examiner(s): Levy, Stuart S.
• Assistant Examiner(s): Glembocki, Christopher R.
• Application Number:
  US07/461,936
• Time in Patent Office: 865 Days
• Field of Search: 235/462, 235/463, 235/466, 235/467, 235/472, 235/470, 235/454, 350/6.6, 350/6.5
• US Class Current: 235/462.25
• CPC Class Codes: G06K 2207/1016 Motor control or optical moving unit control
• CPC Class Codes: G06K 7/016 Synchronisation of sensing process
• CPC Class Codes: G06K 7/10861 sensing of data fields affixed to objects or articles, e.g. coded labels postal sorting B07C3/14, conveying articles B65G47/48

Abstract

There is provided, in one preferred embodiment, a bar code reader which has a variable scan angle, with the amplitude of the scan angle initially being relatively small and then increasing in magnitude until a bar code is read. As the amplitude of the scan angle increases, the scan frequency is decreased, thereby keeping the scan rate across the bar code relatively constant. Consequently, for example, a high-density bar code may be read at either a close distance or a far distance without sacrificing resolution. Additionally, the reading of a selected bar code in the presence of other, closely-spaced bar codes is facilitated. In another preferred embodiment, the scan frequency is held constant and the clock rate in the bar code reader is increased with increasing amplitude of the scanning angle. In yet another preferred embodiment, scan angle and frequency are held constant, while a microprocessor varies the length of the bar code decoded and increases/decreases resolution to compensate for the distance of the bar code from the reader head.

Claims

1. A reader, comprising:

a) a light source to produce a beam of light;

b) scanning means to cause said beam of light to travel through an angle of selected amplitude and to sweep across, in a continuous series of sweeps, at a selected scan rate, coded indicia consisting of a pattern of relatively more and less reflective regions;

c) photodetector means to detect light reflected from the relatively more reflective regions of said coded indicia and thereby discriminate between said more and less reflective regions; and

d) means, connected to said scanning means, to selectively vary said selected amplitude for successive sweeps of said beam of light and to cause said scan rate to remain relatively constant as said selected amplitude is increased, by decreasing the frequency of said scan as said amplitude is increased.

2. A reader, comprising:

a) a light source to produce a beam of light;

b) scanning means to cause said beam of light to travel through an angle of selected amplitude and to sweep across, in a continuous series of sweeps, at a selected scan rate, coded indicia consisting of a pattern of relatively more and less reflective regions;

c) oscillator means connected to drive said scanning means;

d) photodetector means to detect light reflected from the relatively more reflective regions of said coded indicia and thereby discriminate between said more and less reflective regions;

e) means, connected to said scanning means, to selectively vary said selected amplitude for successive sweeps of said beam of light, said means including waveform generating means having an output signal to which said oscillator means is responsive and in response to which signal said oscillator causes said amplitude to vary in a selected manner;

f) gate means to receive as one input the output of said photodetector and as the other input a clock signal, such that said gate means will output a pulse train comprising groups of pulses corresponding to the widths of said nonreflective regions; and

g) frequency generator means the input of which is the output of said waveform generator and the output of which is said clock signal, such that the frequency of said clock signal increases directly in proportion to the increase in said amplitude to compensate for the resulting increase in said scan rate in proportion to said increase in said amplitude.

3. A reader comprising:

a) a light source to produce a beam of light;

b) scanning means to cause said beam of light to travel through an angle of selected constant magnitude and to sweep across, at a selected scan rate, coded indicia consisting of a pattern of relatively more and less reflective regions;

c) photodetector means to detect light reflected from the relatively more reflective regions of said coded indicia and thereby discriminate between said more and less reflective regions;

d) pulse-generating means connected to receive an output signal from said photodetector means and to produce a pulse train representative of said pattern during a selected portion of said angle of constant magnitude of the swept beam of light; and

e) means, connected to said pulse generating means, to vary the selected portion of said angle of constant magnitude of the swept beam of light during which said pulse-generating means produces said pulse train.

4. A reader, as defined in claim 3, wherein:

(a) said pulse-generating means comprises gate means to receive as one input the output of said photodetector and as the other input a clock signal, such that said gate means will output a pulse train comprising groups of pulses

corresponding to the widths of said nonreflective regions; and

(b) said means to vary said selected portion of said angle of constant magnitude of the swept beam of light provides said clock signal and decreases the rate of said clock signal as said selected portion increases.

5. A reader, as defined in claim 3, wherein said means to vary said selected portion of said amplitude additionally samples said pulse train and varies, as necessary, the rate of said clock signal to enhance the resolution of said pulse train for succeeding sweeps of said angle.