Registers – Coded record sensors – Particular sensor structure
Reexamination Certificate
1999-05-12
2001-03-06
Pitts, Harold I. (Department: 2876)
Registers
Coded record sensors
Particular sensor structure
C235S462160
Reexamination Certificate
active
06196462
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an optical device for reading and decoding bars of different reflectivity arranged in accordance with a barcode and adjoining one another, comprising an optical scanning device for scanning the bars by means of a light beam, a sensor for receiving the reflected light beam and the conversion thereof into an electrical sensor output signal, a transition detector for detecting the level tansitions in the sensor output signal and a decoding device which decodes the scanned barcode on the basis of the output signals from the transition detector.
A device of this type, in which the path from sensor to transition detector has been designed in analogue electronics, is generally known.
In practice the optical readers for reading and decoding barcodes are frequently confronted by a problematically low signal-to-noise ratio, in particular in the case of poorly printed barcodes and in the case of reading close to the edge of the read area. It is then not easy accurately to determine the transitions. These transitions are frequently determined by determining the peaks of the first derivative of the sensor output signal.
OBJECTS OF THE INVENTION
The aim of the invention is to provide a device of the type mentioned in the preamble, with which, despite a poor signal-to-noise ratio of the sensor output signal, the reliability of the determination of the transitions can be improved in a simple manner and with which the costs of the device are restricted to a minimum.
A step in the right direction would be digitising using an analogue-to-digital converter, for example a fast ADC (analogue-to-digital converter). However, a component of this type also comes at a price because of the required speed, as a result of which dissipation is also a problem.
SUMMARY OF THE INVENTION
The stated objective is achieved according to the invention in that the transition detector is provided with a comparator and a flipflop connected to the output thereof, the sensor output signal being fed to one of the inputs of the comparator and the output of the flipflop being coupled via one or more first integrators to the other input of the comparator, one or more second integrators connected to the output of the flipflop and a device, connected to said second integrators, for determining the positions of the transitions in the barcode.
In principle, with this device use is made of a so-called bit stream converter which consists of the abovementioned comparator, flipflop and first integrators. Second integrators. preferably digital integrators, are connected to the output of the bit stream converter (of the flipflop).
In one embodiment the sensor output signal is fed to the comparator and the number of first integrators is equal to the number of second integrators, so that the sensor output signal is produced at the output of the last of the second integrators. A first derivative signal can be generated from said sensor output signal, it being possible to determine the positions of the transitions in the barcode from the maxima and minima of said first derivative signal.
In another embodiment two first integrators and one second integrator are used, it then no longer being necessary to use a device which generates a first derivative signal. The first derivative signal can be taken off at the output of the second integrator, the positions of the transitions in the barcode being determined from the maxima and the minima of said first derivative signal.
Preferably, the sensor output signal is fed to the comparator via a first derivative device, which generates a first derivative signal from the sensor output signal. If the number of first integrators is equal to the number of second integrators a first derivative signal is thus produced at the output of the second integrators. This arrangement has the advantage that the large dynamic range of the sensor signal as a consequence of ambient light is much less troublesome.
Further embodiments of the invention are described in the dependent claims.
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Greenblum & Bernstein P.L.C.
Pitts Harold I.
Scantech B.V.
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