Self-Timed Bar Code Reader
Original Publication Date: 1990-Aug-01
Included in the Prior Art Database: 2005-Mar-16
Barenboim, MM: AUTHOR [+4]
A technique is described whereby bar code information can be accurately read, despite variations in the scanning speed of the reading mechanism, by using a self-timed bar code reader. The concept is particularly adaptable to applications where it is desirable to reduce bar code reading time, such as reading the bar code before a scanning mechanism is brought up to speed.
Self-Timed Bar Code Reader
is described whereby bar code information can
be accurately read, despite variations in the scanning speed of the
reading mechanism, by using a self-timed bar code reader. The
concept is particularly adaptable to applications where it is
desirable to reduce bar code reading time, such as reading the bar
code before a scanning mechanism is brought up to speed.
In prior art,
self-timed bar code readers designed to
accurately read the code, despite speed variations, required a second
time- referenced bar code to be inscribed adjacent to the code being
read. The positional, or phase, relationship between the code lines
was required to be known in order for the system to operate properly.
The concept described
herein allows the bar code to be read
accurately at variable scanning speeds, without requiring the
application of an additional referenced bar code. Time-reference
pulses are provided from an emitter, and the scanning of the bar code
and the emitter are synchronized so that they are similarly affected
by changes in scanning speed.
relationship between pulses produced by the emitter
and the width of the bars in a bar code are shown in the timing
chart of Fig. 1. The bar code width will vary in accordance with the
pulse count. Bars 1 through 5 have a width which is an even multiple
of that of the narrowest bar 1. Fig. 2 shows the hardware circuitry
used in the concept. Transducer 6 and bar code reader sensor 7 are
arranged to produce a time-varying output as the bar code is scanned.
Emitter sensor 8 is similarly arranged to produce a time-varying
output as the emitter wheel is scanned. The scanning motions are
achieved by moving the bar code and emitter pattern past stationary
sensors, or by moving the sensors past stationary bar code and
emitter patterns, or by scanning the optical path by using a moving
mirror, or by employing a combination of these methods. The scanning
methods are tied together so that the bar code pattern and the
emitter pattern are scanned at the same time. In this way, any
variations in the speed of the scanning motion will affect the
scanning of the bar code pattern and the emitter, similarly. Sensors
7 and 8 may include pulse-shaping circuitry to assure that a binary
output is achieved.
width of the narrowest bar (bar 1) is known, a
pattern is sensed by emitter sensor 8 so that two complete cycles are
sensed as the width of the narrowest bar is scanned. Because the
phase relationship between the emitter pattern and the bar code
pattern is not known, either two complete pulses, or one complete
pulse and two partial pulses, will be produced by the emitter as the
narrowest code bar is scanned. Switching circuitry that can switch
rapidly will recognize the latter situation as three pulses.
Therefore, two or three pulses from the emitter will be recognized by
the circuitry as the narrow...