Classifications

• • G—PHYSICS
  • G06—COMPUTING OR CALCULATING; COUNTING
  • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
  • G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
  • G06K7/10—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation
  • G06K7/10544—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation by scanning of the records by radiation in the optical part of the electromagnetic spectrum
  • G06K7/10821—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation by scanning of the records by radiation in the optical part of the electromagnetic spectrum further details of bar or optical code scanning devices
  • G06K7/10851—Circuits for pulse shaping, amplifying, eliminating noise signals, checking the function of the sensing device
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03G—CONTROL OF AMPLIFICATION
  • H03G3/00—Gain control in amplifiers or frequency changers
  • H03G3/20—Automatic control
  • H03G3/30—Automatic control in amplifiers having semiconductor devices
  • H03G3/3084—Automatic control in amplifiers having semiconductor devices in receivers or transmitters for electromagnetic waves other than radiowaves, e.g. lightwaves

Definitions

• the present invention relates generally to signal processing and, more particularly, concerns a method and filter for processing a light beam that has been encoded with data so as to improve the signal-to-noise ratio of the signal that is extracted after the light beam is processed.
• Data communication utilizing light as a transmission medium is gaining widespread acceptance.
• One application in which data encoded light has long been in use is optical code scanners, such as barcode scanners.
• barcode scanners typically use laser light to illuminate a remote barcode.
• FIG. 1 is a schematic block diagram illustrating the operation of a typical barcode scanner.
• Laser light L reflected from the barcode is modulated by the dark and light portions of the barcode and is sensed by a photodiode PD, which produces a current representing the modulated light. That current signal is applied to a preamplifier 10, which converts it to a voltage signal.
• the voltage signal is provided to a differentiation circuit 12, which generates pulses corresponding to each transition in the preamplifier output, and an automatic gain control (AGC) circuit 14 maintains the signal amplitude relatively constant, regardless of variations in the received signal.
• AGC automatic gain control
• the gain controlled signal is then applied to a low pass filter (LPF) 16, which removes extraneous high-frequency variations, and then to an analog-to- digital converter (ADC) 18.
• LPF low pass filter
• ADC analog-to- digital converter
• the resulting digital signal is then applied to a processor 20, which decodes and extracts the barcode from the signal.
• an adjustable bandwidth filter replaces the low pass filter.
• the distance of the optical code is detected, and the filter bandwidth is increased in relationship to the distance of the bar code.
• the input signal to the filter is applied to a shift register and the output at each stage of the register is multiplied by a predetermined coefficient calculated to achieve a particular waveshape, preferably a Gaussian waveshape, via the entire set of coefficients.
• the register stage outputs, multiplied by the coefficients are then added together to produce a filtered output signal applied to the processor.
• the clock rate of the register is adjusted.
• the detected bar code distance is used to control the frequency of a voltage controlled oscillator (VCO), which serves as the clock for the shift register.
• VCO voltage controlled oscillator
• Figure 1 is a schematic block diagram illustrating the operation of a typical barcode scanner
• Figure 2 is a schematic block diagram illustrating the operation of a barcode scanner embodying the present invention
• Figure 3 shows Gaussian waveforms representing filters with different standard deviations (bandwidths);
• Figure 4 is a schematic block diagram illustrating a preferred embodiment of a digital filter
• Figure 5 presents waveforms useful in further understanding the operation of digital filter.
• FIG. 2 is a schematic block diagram illustrating the operation of a barcode scanner embodying the present invention.
• Laser light L reflected from the barcode is modulated by the dark and light portions of the barcode and is sensed by a Photodiode PD, which produces the current representing the modulated light. That current signal is applied to a preamplifier 10, which converts it to a voltage signal.
• the voltage signal is provided to a differentiation circuit 12, which generates pulses corresponding to each transition in the preamplifier output, and an automatic gain control (AGC) circuit 14 maintains the signal amplitude relatively constant, regardless of variations in the received signal.
• the gain controlled signal is then applied to analog-to-digital converter (ADC) 18.
• ADC analog-to-digital converter
• the resulting digital signal is then applied through a digital filter 30 and a digitizer 22 to a processor 20, which decodes or extracts the barcode from the signal.
• digital filter 30 is a variable filter, of which the bandwidth may be controlled.
• a distance detector senses the distance of the barcode, and the bandwidth of digital filter 30 is controlled in direct relationship to that distance.
• Pulses received by digital filter 30 have an approximately Gaussian waveshape.
• Figure 3 shows Gaussian waveforms representing filters with different standard deviations (bandwidths). On one of the waveforms, points are marked K sub zero, K sub one... K sub three. These represent coefficient values that will be used for a purpose to be described below, in order to characterize the Gaussian or normal curve.
• FIG. 4 is a schematic block diagram illustrating a preferred embodiment of filter 30.
• the signal from (ADC) 18 is applied as an input to a shift register 32, in which the outputs at each stage are tapped and, in multiplier of 34 , multiplied by a respective 1 of the coefficients K sub 0, K sub 1, ... K sub 3.
• the shift register outputs, so multipled, are then summed in adder 36 to produce an output signal which is applied to the processor 20.
• This operation is performed continuously, in real time, to, effectively, convolve the input signal from the ADC 18 with the characteristic of the digital filter 30.
• VCO voltage controlled oscillator
• the voltage controlled oscillator is driven by a distance detector 50.
• the detector 50 produces a voltage signal which increases with the distance of the bar code and causes the output frequency of the VCO 40 to increase accordingly. This, effectively, causes the bandwidth of filter 30 to increase, while still maintaining the same characteristic shape.
• Waveform cap A represents the input waveform to the filter.
• Waveform B represents the Gaussian characteristic of the filter 30, and waveform C and D represent convolutions between waveforms A and B when different frequencies are applied by VCO 40. In this instance, the frequency was increased from waveform C to waveform D, resulting in an improvement in signal-2 -noise.
• waveforms C and D correspond to differentiated versions of the signal received from preamplifier 10. A signal corresponding to the detected bar code would then be obtained by integrating these waveforms.

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• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Engineering & Computer Science (AREA)
• Health & Medical Sciences (AREA)
• General Health & Medical Sciences (AREA)
• Toxicology (AREA)
• Artificial Intelligence (AREA)
• Computer Vision & Pattern Recognition (AREA)
• General Physics & Mathematics (AREA)
• Theoretical Computer Science (AREA)
• Optical Radar Systems And Details Thereof (AREA)

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• 2007
  • 2007-11-08 EP EP07864101A patent/EP2218034A4/en not_active Withdrawn
  • 2007-11-08 CN CN200780101463A patent/CN101855638A/zh active Pending
  • 2007-11-08 JP JP2010533056A patent/JP2011503712A/ja active Pending
  • 2007-11-08 WO PCT/US2007/084071 patent/WO2009061319A1/en not_active Ceased

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