Registers – Coded record sensors – Particular sensor structure
Patent
1991-11-04
1994-02-15
Nelms, David C.
Registers
Coded record sensors
Particular sensor structure
235472, G06K 710
Patent
active
052869601
ABSTRACT:
A method and apparatus are provided for detecting bar-space and space-bar transitions in a bar code symbol. A sequence of sparsely sampled analog signals from a photodetector in a bar code scanner is representative of the reflectance pattern of a symbol.
Following initialization, a threshold, representing the value of the analog signal at a transition point, is derived from observed samples of the bars and spaces in the bar code symbol. Sampled reflectance information is accumulated as the symbol is scanned, and a program driven microprocessor calculates and repeatedly updates this threshold, using observed maxima and minima in the analog samples, and also referencing a binary output to determine whether a bar or space is currently being viewed.
When the values of two successive analog samples bracket this threshold, then a bar-space or space-bar transition has occurred. Linear interpolation is performed on the two samples to determine the transition point and an offset from the first of the two samples. After a delay corresponding to this offset, the level of a binary output is changed. A bit serial binary output is thus produced, representative of the relative widths of bars and spaces.
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Hammond, Jr. Charles M.
Havens William H.
Longacre Jr. Andrew
Pidhirny John M.
Nelms David C.
Shami K.
Welch Allyn Inc.
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