Note: Descriptions are shown in the official language in which they were submitted.
~058~57
-EJD ,
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1 METHOD AND ~P~ARATUS FOR R~ADING BAR CODED DATA ~5
10 Disclosure '.
This invention relates to a data collection system ',
and more particularly to a method and apparatus for reading ',~
bar coded data for entry into a~data collection system. ,~
Prior Art - ,~,
At the present time there ~ in use data collection ;',' ~''
- systems for inventory control or electronic o,rdering in ,' ~,
retail outlets such as supermarkets, and the like. These ~, '
systems are generally portable devices and the entry of the ~ ;
data into the system is'accomplished by the operator reading ~,l'' ;'
20 ~ the data from an item or product on a sheI~ and operating a
keyboard to enter~the data~read. ~One~;such portable data
~collection,system~is~ described in U. S~. Patent 3,771,132. ~ , -
; ~ Portable~devices~of the type~disclosed,in the aforementioned , ''
patent, in order~to be commercially easible must be battery
~5 (D.C.) powered. The system described in the above reerenced , ' '
patent is a battery~powered data coll'ection system wherein ' ,~`
the informa~ion is entered in~o the system by means o~ an ', ~'
operator actuating a hand-held keyboard. As in all human ' 'p'~
operated devices, the opportunity for errors arise and ,' '~
errors have been introduced into the data collection sys~em
~ ~ r
0 5 87 5 7 !~i
'``''i ' ` "' ""
l ns a result o the operator's improper actuation of the
keyboard, In addition, a ~inite amount of time is required ~-
for the operator to effect ~he necessary entry into the
system. To reduce or eliminate these operator errors, ;;
S codes have been proposed to be printed on the products or ~ :
~he shelves storing the products subject to the inventory
control, Labels having coded data recorded thereon have
been proposed for the shel~es storing the products to be
inventoried so tha~t they may be read automatically by means of
lO a portable optical sensor. These types o~ codes are ;
characterized as~bar codes and are adapted to be read
optically by passing an optical sensing wand over the bar
coded item or upon the production of relative motion between ~(
the bar coded item and a sensor. The bar codes are arranged
lS with a unique pattern ~or identiying an item or product.
A bar code consists of a series of dark and light bars ~`~
~;~: of varying widths and with the information encoded in terms
of~the sequence of light and;dark bars. When this bar code
:: i6 read by an optical scanner, for example, the time required
and the error rate experienced by the keyboard entry are
greatly reduced. ~ j
There are two problems with op~ical scanners as they ~;
are presently constructed for use in a portable data collection `;
system. First, a truly~portable data coilecting device ~`~
must be battery powered. An op~ical scanner requires a
source o~ radiation to illuminate the bar coded data and ~-
~his would place~ a significant drain on the battery. A
. ~. .
second problem is that photo detectors or sensors, such as
photo diodes, photo transistors, or PIN diodes, exhibit
leakage (or dark) current~ that vary signi~icantly between
unlts and with tcmperature changes. Re~ardless o~ the
. . .
.~ . . ,.,. ~
- - ~ 2 ~ ~ -
1~587S7
manner in which the photo detector is incorporated in a
circuit, the result is that an unknown D.C. offset voltage
:, .
is produced that may be on the order of a magnitude or more
greater than a data signal. This D.C. offset could be
blocked by a series capacitor so that only an information
containing alternating current (A.C.) signal is passed.
This would be satisfactory if there is no Ao (D.C.) term
in the Fourier series computed for the signal produced when
the bar coded datà~is scanned. A D.C. component might be `
inherent in the code itself if, for example, the area of
light bars and dark bars were not equal. More significant
with hand-held scanners is the manner in which the scanner ,!~
is employed. An operator would position the scanner on the
light surface (reflective) ahead of the bar code and then ,
sweep across the coded area relatively quickly. llhe result `
is a relatively long period of a light signal before
. .
alternating dark and light signals are received. This will -
~ , , .
produce~an initlaL ~slgnal level of i~ndefinite duration that i ;~
cannot be supported by a blocking capacitor. To use this
~20 méthod, complex circuits~that detect peaks and establish
. .
~ varyLng slicing~leve}s must be employed. ~
.:,
Summary of the_Invention
The prese~t~invention provides an impr~ved method and
apparatus for reading bar coded data that may be readily
incorporated into prlor art data collection systems and ;~
allows the coded data to be read in microseconds. In particular,
the apparatus for reading bar coded data into a data collection
system in accordance with the present invention is applicable
to battery powe~ed~systems and reduces the problem of battery
drain due to the requirement of a light source in the
.,
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.~.
~ '`' .:
058757
: .
optical scanner to a minimum~ In addition, the problcm o~ :
varying direct current (D.C.~ offset ~oltages which are
produced by a pho~o detector is solved by simple signal ~: :
processing circuitry ~nd enhances ~heir margins. Specificaf
the problem of exces~ive power consumption, or battery drain,
is solved by the p-eriodic pulsing of a light source for a ~ :
scanner at a relatively high rate to minimize the power
requirements and then interrogate the output o~ the optical. :
. scanner to determine the reflective chaxacteristic of the
lo . sur~ace undergoing:senging. The results of the interrogation
~; control the energization or de-energization o~ the light .
souxce to reduce power drain to an absolu~e minimun and
yet allows reliable, high speed reading of ~he bar coded
~:~ ` information. This technique allows a simple solution to : :
~; l5 the problem of D.C. offset voltages by maintaining D.C.
;coupling throughout,~thereby:circumventing the varying thres ;
holds that are encountered:when alternating:current (A.C.) :
coupling is employed. ~
n accordance with the present inyention there is
~:20; provided an appara~s ~or optically reading bar coded data .~ `
where~n the binary bits are encoded in terms ~ bars o ~ `.
d~fferent widths~of the s:ame optical charac~eristic separated ~: x
by areas o~ the opposite optical characteristic comprising
::~ . . optical sensing means for producing electrical` .
~25 signals representative ~f the optical characteristic of a
sur~ace presented thereto upon the production o* relative;
~ovemen~between the sur*ace and-the sensing means, said
sensing means having~a normaliy de-energiæed light source
and a light sensor for:~receiving the light rays~from the
.light source xeflec ed from the surface being sensed~ and
.
1058757
control circuit means including means for automatically
and periodically energizing the light source coupled to be ~:~
responsive to the sensor signals and mainta.ining the energiz-
ation of the light source in response to a sensor signal of one
kind and automatically de-energizing the light source in response
to a sensor signal of the other kind.
Also in accordance with the present invention there is ~-
p ~ ided an apparatus for optically reading bar coded data ,~
:- wherein the binary bits are encoded in terms o bars of ~ ; ,'
.10 differen.t widths o~ ~the same optical characteristic separated
by areas of the opposite optical characteristic compris~ng ; ~'~ ,..' ':
optical sensing means ~or producing electr~cal , , ;'
signals representative o the optical characteristic of ~' . .'.
.~ ~ sur~ace presented there~o~upon the production o rela~ve ,~
: ~15 ' movement between the'surface and the sensing means, said : ~ ', ", ' '.
': sensing means having a norm~lly de-energized light source and : ~`
a light sensor or receiving the light rays.rom the ligh~
eource reflected from the sur~ace being:sensed~
the e~eneor.electrical signals include~ an ... .''`
20~ 'unknown'D.C. ofset vPltage, , . :
~ f~rst smplifying circuit means coupled ~o be ..: .':.'~''.: :responsive to the signals from the light sensor includin~ ...... ,;,.
~:. the offset voltages, . ' ' ` "','.'.': '
econd amplifying means nonmaliy coupled to ~:.. .`~ . "~
~25 - receive the outpue~signals rom ~he irst ampliying means~` ,.;.~`,'
and providing an outpu~'signal,corresponding thereto or .: ' .'.''"~.
- ' :' preselected periods,; :.~
differential.amplifying circuit means coupled :.'.' '. ,.
to be responsive to the output signals from the irst and . ' .- .,
30~ second amplifying ci~cui~t ~eane and providing output 6ignals
S87s7
representative of the re~lective characteristics of the : .
.:
sensed surface, and :
swltching circuit means coupled to the light source :
for automatically and periodically energizing the light source for
preselected intervals and decoupling the first and second
ampli~ying means during the intervals the light sourae is ~ .energized.
Further in accordance with the present invention~e is
provided an apparatus ~or optically reading bar coded data
~,:
where~n the b~naxy bits are encoded in ~erms of barg of
~ di~exent widths of the same optical characteristic : .
;~ ~ ; separated by areas of the opposite opt~cai characteristics
comprising
~`: op~ical sensing me~ns for producing electrical
~15 signals representative:of the reflec~ive characteristic of
; a surface upon ~he production o re~at~v~ movement between
the t~o,~ . .. ~.
:said:sensing~means having a Dormally de-energized
light source and a~ ht sensor, the electric~l signals .
-~ 20~;~produced including an unknown D.C. offse~t voltage, :`~-
amplifying means coupled to be responsive. to the
gnals~rom the sens~ng means.~ncluding ~h~.o~ee~ voltages,
diS~erential amplifying means for receiving the signals from
the;amplif~ying means, : ~
~ample and hold ampliying circui~ means normally
coupled to receive the'cutpu~: signals ~rom said amplifying .:
means and for~coupling:the output signals to sa~d differentiai
smplifying means, :
~ controller means coupled:to~be responsive to the
: 30 :output slgnals from~said diferen~ial amplifying means ~or~
~0587~7 ;
controlling the energization of the light source, said controller
means providing a series of pulses adapted for automatically and .
periodically energizing the light source, and
switching means coupled to be responsive to the $ ~: ~
series of pulses for switchably energizing the light source ~ :
in response to the~operation of the switching means and
coupled between the output of said amplifying means and 1 :
. .
the input to said~sample hold amplifying circuit to
switchably de-couple said sample and hold circuit in
: 10 response to the operation of the switching means
;.
said controller means being effective or main `
: taining the switching means energized in response to a
sensed reflective surface and for de-energizing the light
source i.n response to a sensed absorptive surace.
also in accordance with the present invention there is
,
provided an apparatus for optically reading bar coded data
.. . . . . .. . .
wherein the binary bits are encoded in terms of bars of
different widths of the same opt:ical characteristic~
: separated by areas~of: the opposite optical characteristic ~.
comprislng
optical sensing means for producing electical
signals representative of the optiaal characteristic of
a surface presented thereto upon the production of relative
;~ movement between the~surface and the sensing means, said sensing ~ :
means having a normally de-energized light source and a light
sensor for receiving the light rays from the light source ;
reflected from the surface being sensed, ::
differentially D.C. amplifying circuit means coupled
: to be responsive to the signals from the light sensor and pro-
viding binary coded signals representative of the optical ;. ~ :
characteristics .
k~ 4 c -- !, . . .
~.,., :' .
1058~S7 :
of the sensed surface,, and
control circuit means including means for automatic-
ally and periodically energizlng the,light source coupled to be
responsive to the binary code signals and maintaining the ',~
energization of the light source in response to a binary signal '~,.' ,.
of one kind and de-energizing the light source'in response to a
binary signal of the other kind. ; ~ ,
In accordance with the present invention thqre is ...
provided a method of optically reading bar coded data '.i:~
.:~ . . .
wherein the binary bits are encoded in terms of bars of .~
different widths of the same optical characteristics and ', ' '
separated by areas of.the opposite optical characteristic ~:~
including the steps of ,.,, ''
providing an optical.wand having a light source and ;
a light sensor for reading bar,coded data, ';'
moving the wand over a surface having bar coded data, ,., ;,'
recorded thereon,.
; automatically and periodically energizing the light ".
~. .
source.in the wand, ,'
electrically determining the reflective aharacteristic
.of the surface sensed by the wand and producing electrical signals ..
corresponding to the sensed reflective characteristics,
and utilizing the electrical signals or de-energizing '""
the light source if no reflective surace is sensed by the wand. ~`' -
Further in accordance with the present invention there
is provided a method of optically reading a bar coded data , :
wherein binary bits are encoded in terms o bars of different `' :
;. , !
widths of the same optlcal.characteristics separated by areas of ~,
the opposite optical.characteristic comprising the steps of
'.~: :
',,,:
''''' ' ' ' '
~ ~ 4d _ ~
1058~57
,, .
producing relative movement between the bar coded
data and an optical bar coded sensor for producing electrical
signals representative of the sensed binary bits, .
the sensor including a light source and a light
sensor for receiving the light rays reflected from the bar
coded data,
maintaining the light source normally dark,
automatically and periodically energizing the light
source at a preselected rate,
determining`the reflective characteristic of the -.
surface -exposed to the sensor,
if no reflective surface is sensed, automatically .
de-energizing the light source,
if a reflective surface is sensed, maintaining the
light source energized,
and generating the electrical signals representative
of the bar coded data while the light source is energized. `
Also in accordance with the present invention there is :~
.-.
provided a:method of optically reading bar coded data wherein .
the binary bits are~encoded in terms of bars of different widths .
....
: of the same optical cparacteristics and separated by areas of ~:
the opposite characteristic including the steps of :;:
providing an optical wand having a light source and
a light sensor responsive to the light rays from said source `j
25 re~c~te-~ from a surface the wand is passed over, ~.
arranging the light source to be normally de-energized, ,
peridoically energizing the light source in the wand, ~^
generating electrical signals by means of the light .`
sensor when the light source is energized representative of .
j
: .
- 4e -
'~,~'
:10~87S7
the light reflective or light: absorptive characteristics
of the surface the wand is passed.over, ..
processing the thus generated electrical signals to '~
produce binary coded signals representative of the light i .~ ~.
characteristic of the surface the wand is passed over, andinterrogating the binary signals representative of
the sensed light characteristic to determine the surface ! ~,
characteristic sensed and controlling the light source by . .
either de-energizing.the light source in response to a binary A''. '
coded signal representative of an absorptive light surface or
mal~ntaining the light source energized in response to a binary -~ -
: coded signal representative of a reflective light source to .
allow the bar coded data to be read by the energized wand.
Further ln accordance with the present invention there
: L:5 is provided a method of optically reading bar coded data com-
prising the steps of .. `
providing an optical sensor having a normally
de-energized light:source and light sensor adapted to receive ;~
the light~rays reflected from a surface,
~20: : producing relative.movement between a surface having
bar coded.data and the optical sensor for reading the bar ~i~
coded data, ~ `
. .
automatically and period~ally energizing the light ~.
source to generate signals at the sensor representative of the
reflective characteristic of the:surface sensed~
; amplifying the sensor signals, .
rejecting any D.C. offset voltage introduced into the
amplified sensor signal, : :
and producing binary coded signals representative of
the reflective characteristic of the sensed surface including
the sensed bar coded data. ~ :
.
~ . :
'' .. .
lOS~7S7 ~
.. .. ..
'Descri~tion of_the Draw ngs ~
:,:
These and other features o the present invention '
may be more fully appreciated when considered in the light .~'
.. .
of the following specification and drawings, in which:
Fig. 1 is a diagrammatlc illustration of a shelf in ~'~
a retail outlet storing a number of brands of a particular `
product wherein the shelves include a label having bar coded ''~
data recorded thereon for identifying the product. '
Flg. 2 is a diagrammatlc view of an optical wand -
employed with a data collection system for reading the shelf '
arranged with bar coded data as illustrated in Fig. l; and
Fig. 3 is a schematic-block diagram of a data collection
system including the bar coded data reading circuitry for '`
interacing with the syste~ and entering the sensed bar coded
data into the data collection system. '
I5 Now referring to the drawin~s, the present invention "`:
will be described Ln detail. The present invention will i~
be described as lt may be incorporated into a portable, ;
~dlrect current (D.C.) powered data collection~system of the ;
type disclosed in Dnited States Patent No. 3,771,132. It
~20 ~ should be understood that the;invention does not comprehend '
the structure of the optical scanning device that is employed
for sensing the bar coded data. Such optLcal sensing apparatus ,!,~
., ~ . .. .
is pxesently commercially available. One source for a portable ;'-' '`
~ optical wand that may~be used for reading bar coded data is
available from Welch Allyn Co~ through its Industrial Products !~,. . . . .
Division of Skaneatelas Falls, New York. It should also be ''.
'!,
noted that apparatus of this type is disclosed in the patent
'Iiterature and one such disclosure is found in United States ~''';''
Pàtent 3,417,234. For the purposes of the present invention,
;.~ :''. .
; ., ~:
6 ''
~ .
- 1 ~0 587 57 `
1 ¦ it i~ su~icicnt that such wands are known ln ~he art and are
¦ commercially available. These wan~s generally comprise a
¦ light source and a light sensor ~rranged within the wand
¦ housing with a cable coupling the light sensor signals to the !'
5 ¦ data collection system. One such sensing wand 10 is illustra~ed
¦ in ~ig. 2 and may have a light source and a ligh~ sensor ;~
¦ mounted in one ext~emity of the wand housing adjacent to the
I cable end thereo~, The ligh~ rays ~`rom the ligh~ source
¦ are concen~rated and g~ided by suitable optical elements
10 ¦ to exit ~rom the opposite end o the housing to illuminate
¦ the bar coded data on a label, such as the label 11. Any
light from the light source that is re~lected Prom the label
¦ 11 is also guided through the inside o the wand housing so
¦ as to impinge upon the light sensor. The signals generated
15¦ by the light sen~or are then coupled by means oP the cable 12 - `;
to the data collection system, generally identiPied by the
reference numeral 13 nnd in particular a~digital controller
13A therefor.
At this point, it should be noted that the light source
0 that is utiIized for the purposes o the present invention r,` '~
must have a ast~response time so that it precludes the use
o a light source~having incandescent ilaments. L~ght
emitting diodes that have the required response time or use -`
in wand 10 are readily availnble commercially and are well
25 known. It should be noted, however, that whenever the ``
terms "light source" or "light rays" are employed in con-
junction with the description and claims of the present
~invention that the term ie not restricted to visible light -
as the radiation ~rom the light source may be in ~he
in~rared region.
. ' '' ' ~,,",.
i 7
`I 1 0 5 87 ~ 7
1 ¦ It is impor~ant to keep in mind ~hat the present '~
¦ invention is directcd to the circuits that inter~ace and '.'
process the light wand 10 si~nals with the data collection
¦ system 13 ~or ~llowing the necessary data signals to be '
s¦ entered and processed by the system 13. Before describing
the particular interfacing circ~i~s, it is well to briefly "~.
examine the bar coded data and the method of using the .
wand 10 or sensing~ At this point it should be recognized ,'
¦ that the use of the wand lO is only one e~ample o~ sensing
10¦ such bar coded data or portable applications. It is xeadily
apparent that bar coded da~a may be sensed through the "j'~
production of relative movement between the optical sensor .i ' .
and the object carrying the bar coded data, The bar coded ' '
data as employed for the present portable data collection '~
system is of tbe ~eneral type tha~ is identiied in the art
as the "UnLversal Product Code" which can be applied to most ".`':',.
products sold in 'the grocery industry. The bar coded data "',`.. ',~.
: ~illustrated in Figs.;~l and 2 is a simplified ~orm of thë bar .
coded information comprising the universal products code.
The bar coded data illustrated in Figs. 1 and 2 comprises a . .,; .
series o~ dark and light bars:o~ varying widths and the ~`,',;, ,
in~ormation is encoded in terms of the sequencing o~ ~hese '~
bars. One pair o~.~these bars may represent the binary
characters o~ one.kind whiIe a pair o~ different width ra~ios
25 will represent a binary character o~ the o~her kind. For ' '..... ` .:~
example, a narrow dark bar followed by a wide whi~e space ` ~
will represent the binary character ~'O" while a wide ~ '
dark bar ~ollowed by a narrow white space will repr~sent
~he opposite binary character or a binary character "1". '.
30 The sensing o~ such a bar coded label 11 by the wand lO will ~.',.' :
. .....
. .' `,.... .
:
~ ~ 1 0 587 57
¦ produce a series of electrical s~gna~s reading from ~he let
¦ to the right in accordance with the sensed light and dark
¦ bars so as to produce a train o~ binary coded pulses in ~-
I response to the production of the relative movement between
51 the label 11 ~nd the wand 10.
For the purposes of sensing or determining the information
that is recorded on the label 11 as ~he data collection
¦ system 13 may be employed or inventory control purposes in ;;
l supermarkets, reerence to Figs. 1 and 2 is convenient. In
10¦ Fig. 1, a portion of the shelving in a conv ~tional supermarket
¦ is illustrated storing cereal o~ differént brands that are ,~;
offered for sale by the supermarket. As illustrated in Fig. 1,
cereals of the same brand are stored on the same shelf.
For this purpose, brand No. 1 is illustrated on the topmost
15 shelf, while brand Nos. 2, 3 and 4 are sequentially stored on ~;
the shelves below the top shelf. Eac~ shelf is provided with
a label 11 which has the bar coded information recorded x -
; thereon~ The label 11 is placed on the edge of the shelf
immedLately below the product or cereal that is stored on
20 the shelf. Each label ll is data coded thereon in terms o~
the bar code and identifies the product such as the particular
brand o~ cereal stored on that shelf~ I~, in examinin~ the
products stored on the shelves, the data system operator
notes that there is a shortage of a particular brand of cereal
Z5 on the shel~, or the cereal has been exhausted, for the
purposes o~ recordin~ this ~act he can move the wand 10 over
the label 11 to record the brands which are in short supply
or exhausted and require reordering. To properly employ ` j ;~
the wand 10 to read the bar coded data on~the label 11, the ~ -
30 operator should place ~he wand 10 ngainst the white portion
' ; ,.
.. : . , ,`~`. ~''',:,
1 10 5~7 57
I
l ¦ of ~he label ll, at the left hand extremLty thoreo~ as
1 illustrated in Figs. l and 2. He would then sweep the
¦ .wand lO across the bar code rapidly until he l~s read the .~
1 entire label. Since the data collection system circuitry .~
51 is operating at electronic speed, or uery hi8h speed, this .`-
reading or sampling routine can be repeated every few .
l milliseconds assuring that when the wand lO is against the
¦ label ll it will always be detected. For the purpose o
utilizing the wan~ lO in a por~able D.C. powered data
collection system wherein the power drain on the battery
is an impor~ant consideration, the sampling process or
~:reading may be accomplished in a period measured in micro-
seconds, thus substantially reducing the standby power
required for the light source in the wand to a small .~
lS percentage and thereby effectively employ the D.C. power .;
.~ for energizing the ligh~ source only when necessary.
The above description comprises the general characteristics -
of the signals derived from the wand lO:relative to the genera- :.
:~tLon o the binary coded signals as a result of detecting the
reflective and nonreflective characteristics of the bars
coded.on the label ll. The interfacing circuitry for process~
. , .;,
ing the signals from the light sensor i8 arranged to provide
:the correct binary si~nal 8S a result of the production o~ ..
. relative movement~between the coded data and the sensor ~`
~5 without reference to the rate at which the relative motion
:is produced or the rate that the wand lO is moved over the .
label ll. ~The binary slgnals generated are based on the
ratio of the width of a black bar to the width of a white bar.
In this respect the slgnal level representing the average .
30 o~ the ratLo o~ black to white ba~s is cmployed to si~nal a
, ,,,
' ,' ' ':
,' 10 .
. ~ - ,,, ; :, ,: ~ . -. .
l ~ S ~7 57 ; ;
1 binary character since the ~enerated sign~l has a subs~antially
trapezoidal wave sha~e. For this purpose it will be recognized
that the re~erence signal level ~or the generated signal is
5 an important consideration and a variable reference level
may be in~roduced by the production of an unknown D~ Co offset ,
voltage that is inherent in most light sensors. In accordance
with the present invention any unknown D.C. offset voltages
generated are rejected or compensated for in the signal
processing circuits so as to provide the correct binary coded
output signals to the~digital controller 13a. In accordance
with the present invention and as will be made more evident -~
hereinafter~ these binary coded signals are generated in
terms o~ signals o~ differen~ polarity for processing by
the digital con~roller l3a o the d~ta collection system 13.
For this purpose direct current (D.C.) coupling is maintained
through the signal processing circuits thereby circumventing ~`
any varying thresholds;or re~erence levels encountered with
alternating~current (A.C.) coupled circuits.
~The method that i9 comprehended by the present inven~ion
2 ~or the purposes o~ minimizing the power drain on the power
source includes the steps of maintaining the light source de-
energized or dark and periodically energizing the light source
to determine the reflective character oP the surface to which
the scanner or wand lO is presented. With the energi~ation '~;
of the light source, a binary eignal is generated by the
signal processin~ circuit interfacing the wand 10 with the
data collection system 13. If~a signal is generated that ,~
indicates that a non~reflective surface is presented to ~he ~ `' ;
wand 10, the light source is de-encrgized. The digital ~-
3 controller i9 constructed and deined to maintain this
de-ener~ized condition o a light source ~or a predetermincd
' ' ' ' ' : , ' ';
. 11 ', '.
`: :
;
587 57
'`,':". '
l period aftcr which the light is re-energi~ed and tha process `.
is repeated. I~ the b~nary signal, however, represents the
fact that the wand 10 has sensed a reflective surface, the
light source will be main~ained in energization as this is
S a signal that the bar coded information is immin~n~. This
will occur, for example, when the wand 10 is placed adjacent
the left hand extremity o~ the label ll and since the source ~.i; ~-
is maintained energized, the continued passing of the wand 10
over the label ll will produce the required output signals
10 representative of the bar coded data. When ~e wand 10 is ~ :
moved off o~ the label 11 on the righthand extremity as . `
illustrated in Fig.~2, the light source will be de-energiæed
in response to the nonreflective or light absorbent
characteristic of the ad~acent surface o the shelf.
From the above Lt should be e~ident that a digital
controller 13a is req~lired for interrogating the binary `~
characteristic of the:signals coupled rom the wand 10.
One such digital controller in which the signal processing
circuLts of the present invention may be coupled to is the
~ype of controller described in United States Patent No.
3,771,132. alsO, there is at the present time digital :~
controllers that are constructed as micro-processors having `.
a programmable read only memory. These micro-processors
are constructed o~ miniature integrated circuits, or "chips",
~5 that can be readily programmed to perorm the necessary .
routine for controlling the energization and de-energization
o~ the light source. These mlcro-processors are presently ii~
in use and one such micro-processor is incorporated in a
porta~ie data collcction system commercially available from `~
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; ~0 587 S7
1 ¦ MSI Data Corporatlon, o~ Co~ta Mesa, California. This data
I collection system is identi~ied as the MSI Model 2100 sys~em.
¦ This da~;a collection system is also a D.C operated system.
¦ The micro-processor in this MSI 2100 series data collection
S¦ sys~-em can readily be programmed by one skilled in the art to
recognize the difference bet~een valid and invalid data and
when to provide the necessary signal for energizing or de- ;
I energiæing the light source. For example, invalid da~a may be
¦ generated when the sensing end of the wand 10 is placed at a
101 point on the labe~ 11 wherein the coded data appears rather
than to the lethand extremity o the label 11 for proper
operat;on; see Fig. 2. m e micro-processor system will be
programmed to determine that this data is invalid or incomplete
and upon th subse~uent passing o the wand 10 over the label 11,
the correct data will be recognized by the system 13 and processed
~ccordingly. In our particular implementation, the label may
be read in either direction, but that is not essential to the ;~
invention.
Prior to examining the signal processing circuits for ;-
processing the signals from the light sensor, it is necessary
to consider the ofset voltages introduced into the signals
by the light sensor. The ligh~ sensor is generally iden~if~ed 't,'.,~
in Fig. 2 by a bloak identiied as lOLS as i~ ~ay be arranged
within the housin~ ~or the wand 10. Similarly srranged ;~
2 within the wand 10 and adjacent to the light sensor lOLS
there is illustrated a block or xepresenting the light
source that is identiEied as lO Lite. The light sensor lOLS ;~
may be a phototransistor that is positioned at the ocus of
reflective optics to receive the light ray~ rom the source 10
3 Lite that are reElected from a surace such as the label 11
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13 `
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1 The blocks lOLS and 10 Lite are 'schcmatically illustrated ,~
in the circuits o Fig. 3. The light source 10 Lite is ,,;~
illustrated as a light emitting diode having its anode "'-
electrode connected to a source o~ positive potential and
S its cathode electrode connected to the signal processing -,
circuits by means of a dropping resistor lOR. The light
sensor lOLS is illustrated as a phototransistor having its ,-,
collector electrode connected to a source of positive
potential. The emitter electrode is coupled to the signal
` 10 processing circuits proper. In addition, a dropping resistor '~ lOLSR is coupled between the emitter elec~rode and-ground
and is also included within the wand 10. The light rays '~
that are reflected from a surace undergoing sensing by ,the ~''
wa~d 10 impinge upon the base electrode o~ the ph~ototransistor '``
15 lQLS. When there is no radiation or li~ht impinging upon "~
the base of the sensor lOLS, the transistor will pass only ,'
a leakage or dark current. When radiation or light strikes
the base region of the transistor lOLS, it will cause hole-
electron pairs to be generated which will cause a current to
20 flow across the base of transistor lOLS. This will result ;
in a more positive voltage appearing at the emitter electrode ,
than when no radiation strikes the base electrode. The '~;
transistor 10 LSR has to be proportioned with respect to '
the signaI processing circuits relative to the offset Yoltage
~5 produced by the dark currents in,'the pho~otransistor. It ",'
would be desirable to proportion the resis~or lOLSR so that 'x
Lt has a small resistance value to minimiæe the o~set by ',~"' `
the dark currents produced at the transistor lOLS. ,,~
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~! 10 587 57
1 ~lternatively, a large reslstive value ~or resistor lOLSR '~ -
is deslrable to maximize the signal derived from the sensor
lOLSR. The value o the resistance selected for lOLSR
therefore is a compromise between the two'value's. In the ~`
5 elementary conigura~ion shown in Fig. 3, only positive ''
ofsets can be realized but it will be recognized by those
skilled in the ar~ that more elaborate circuits can be ''
provided that exhibit bipolar offsets.
It should also be noted that the o~set voltages may
10 be produced as a result o the inherent characteristics of ''
the bar code i~self during the ~ntervals when the areas o '''
the light bars or reflective areas and the dark or absorbing ;
areas are not equal. Furthermore, of~set voltages are
produced by the amplifiers employed in the signal processing ';
15 circuits. ~ ' ' ''
With the above structure in mind, then, the detailed -'~
circuit organizatlon~of the interfacLng circuits for ; ' ';'
`processLng the siglals from the wand 10 to control the '''
; ~energiæation and de-ehergization of the light source 10 Lite '~';;'
20 will be examined in more detail. Basically, the signal '';
processing circuits are handled by means of three operational
amplifiers identified by a dotted outline as amplifiers Al, '!~ `,
~A2 and A3. The operational amplifiers'are~well known in the 'i
art and are commercially available in the form of an integrated '
Z5 c~rcuit or micro-chip. The amplifiers are all arranged in ''`
a D.C. coupling circuit and are each provided with two input
terminals, identified~as a plus (~) and minus (-) input ~ '
terminal in Fig. 3.~ For this purpose, an integrated circuit ~ ;
device Type 72741 may be employed as the amplifiers Al and A3'. ;i'
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~ I ~)5~3757
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Tl~e ampli~icr ~2 may be an LM3G8 type of integrated circuit ::
dcvice. . :
. The emit~er electrode o~ the light sensor lOLS is
coupled to the positive terminal of the Al amplifier by means :~.
o a series input resistance of relative high value that is
identified by the reference numeral 20 while a capacitor 21 ;;
is coupled bet~een the positive terminal to ground. The
amplifier Al is further arrang~d as providing a preselected
amount o~ the amplification of the signals from the sensor
lOLS including the-unknown D.C. offset signais that are .~
generated by the light sensor lOLS. In particular, the ~. :
ampli~ier Al is further characterized as a potentiometric
amplifier having a high input impedan~e and a known gain .
that is related to the feedback network associated the~ewith.
The gain o the amplifier Al is determined by the ratio of :.
the feedback resistor 22 connected between the output terminal
of the amplifier Al~and the negative input terminal of the ~: .
amplifier Al an~ the resistors 23 and 24 connected between
:the negative input terminal of the amplifier Al in series ..
circuit relationship to ground or a reference potential. ...
Stated mathematically, the gain~o~ the Al ampli~ier is ~`
represented by the fo~mula
~ `' ~`, .
~5 wherein R represents the resistance value o~ the resistors
R22, R23 and R24 in ohms. In a typical example, R~2 is
10,000 ohmsj R23 is l,000 ohms and R24 is 100 ohms. ;
The outpu~signal from the ampliier Al is coupled
30 as an input si~nal to the negative terminal as the amplifier
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~058757
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1 ~3. The ~mplifier ~3 is arran~cd as a di~ferential amplifier.
The posit~ve inpu~ terminal for the amplifier a3 is coupled
to receive ~he output signals rom ampliier A2. As will
be eviden~ from examining Fig. 3, amplifier A2 is arranged '!,' .
as a unity gain amplifier to receive the signal excursions
coupled thereto from the output of the amplifier Al. It
will be noted ~hat for this purpose there is a direct j;
connection between the output ter~inal of the amplifier A2 ~ ?
to the negative input terminal of the amplifier. The output
signal from the amplifier Al is coupled to the positLve
terminal of the amplifier A2 by means of resistor 25 and
through a switch identified as the switch S2. The switch
S2 may be an electronLc switch that is a commercially ~i;
available integrated circuit device. One such in~egrated
circuit device iæ Ldentified as Model No. CD4016AE~ This
Al output signal Ls also coupled in parallel circuit
~; relatLonship with a storage device illustrated aæ a storage
capacitor 26 connected between the positive terminal of the
~amplifLer~A2 and ground. In the normal circuit relationship ~;
20 ~there is a signal coupling path for the si&nal from the
amplifier Al~to the input of the amplLfier A2. The operation
o the switch S2 is e~ectLve to decouple or open the circuit
between amplifiers~Al and A2 aæ will be made evLdent
immediately hereinafter. The arrangement of the ampliier A2 ;~
X in a unity gain configura~ionJ along with the provision of
capacitor 26, ren~eræ thLs circuitry a simple sample and
hold circuit. ThLs cLrcuit organization will produce an
output æignal from the ampli~ier A2 that corresponds identi~
cally to the output æignal from the ampli~ier ~1. In this
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~ 10 587 57
l ¦ respcc~ it will be notcd that when the output sl~nal rom
tl~e amplifi.er Al represents a dark sensor lOLS that this
¦ output volta~e will represen~ the unlcnown D.C. offset
~ introduced into the circuit by means o the sensor lOLS and
51 the amplifier ~1. This Al output signal from the amplifier
A2 will then, in the normal operation o the circuitry (when
the source 10 Lite is de-energized) will appear as the -~
equivalent signal at the output of the amplifier A2. ~:
l There is coupled to the o~tput terminal of the ampli~er
10¦ A2 and in parallel circuit relationship to the positive `.
input terminal to the ampliier A3 a current source identiied
by the reference numeral 27. The current source 27 is .
provided to assure that the amplifier A3 output signal has ~ i
a preselected polarity when the source lO Lite is de-energized.
15 In the circuit configuration illustrated, the poIarity o~ the `;
output signals from the amplifier A3 will be posîtive when ~
the light source is de-energiæed as a result of the provision ~;
~: of the current source 27. The current source 27 comprises
a transistor which may be o the 2N4125 type and is identified
~as the transistor 27T. The emitter electrode of the
transistor 27T is connected to a positive source o potential ~i
shown as ~12 through a resi9tor 28. The base electrode o ;.:
the transistor 27T is coupled to ground through a relatively ;;i
high resistor 29. A resistor 30 is also coupled to the
~5 base electrode and to the source o posi~ive potential (~12V.).
The collector electrode for the transistor 27T is coupled -
to the positive input tenmLnal ~or the amplifier A3.
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¦ 1 0 587 57
l ¦ At this point, lt should be recognized that the di~erential
¦ amplifier A3 will ampli~y the di~erence between the signals `-
¦ appearing at its two input tenminals. With the light source ` -
¦ lO Lite de-energi~ed and in view o~ the above discussion, it
S ¦ wlll be recognized that the signals nonmally passed to the ~ ;
¦ differen~ial amplifier A3 will be equal and under these con- .,!',., ,".,,
¦ ditions its output signal would be zero, however, certain '/ ;~
¦ offset voltages are produced as a result of th2 amplifiers ~-
I . .,~ .
A2 and A3 themselves and the tolerances of the resistors
32 and 33 ~or the amplifier A3 arranged therewith. The
resistor ~2 is a ~eedback resisbor coupled between the output
and the negative input terminals of the amplifier A3 while
the resistor 33 is coupled to the positive input terminal
of the amplifier A3 and grou~d. It will also be noted that
the gain of the amplifier A3 is proportiOned by the ratio o the
resistance values for the resistor R32 relative to the
resistor R33. Under these conditions, then, the current
s~ource 27 assures that the output signal ~rom the amplifier `~
A3 is at a positive voLtage level so as to be readily
2~ recognizable to the digital controller l3a. The magnitude
o the current provided by the source 27 or this purpose
will be considered immediately hereinater.
If it i9 assumed that the source lO Lite is energized, ` ~ ,
the circuit is arranged so that the switch control network
~5 34 controls the energization o~ the source lO Lite and
simultaneously operates the switch S2 to decouple the
amplifiers Al and A2 during the intervals that the source
lO Lite is energized. Under these operating conditions, the
output voltage from the amplifier A2 will remain equal to the
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1 outpu~ volta~e ~1 tha~ exlsted beore the source lO Lite
was energizcd. If the wand 10 is placed opposite a
re~lec~ive sur~ace, the output voltage from the amplifler
Al will go positive and thereby cause the output of the
differential ampll~ier A3 to go negative for signalling
to the digital controller l3a that the wand is in a position
to present the bar coded da~a ro the data collection system
13. In response, then, to the presence of a negative signal
at the output of the amplifier A3, the source 10 Li~e will
lO be maintained energized so that the bar coded data on the -;
label 11 may be r~ad. This condition prevails until the
wand 10 is moved beyond the bar coded data on the label 11
onto a non-reflec~ive surface thereby causing the switch
control network 34 to de-energize the source 10 Lite and
15 operate the switch S2 ~o once again couple the amplifiers ``
Al and A2. ;
At this point it should be noted that the change in j `
the output level o~the signa1 from the amplifier Al in ;`
response to the reflected light signal will be known. i
20 Accordingly, the current source 27 can be proportioned to ;~
provide a bias equivalent to one-hal~ o~ the minimum change. ;~
This will assure that the alternating dark and light bars on
the bar coded label 11 will be transmitted as positive and -;
negative voltages from the output o~ the amplifier a3~ The ; ;~
Z5 DC coupling provided throughout the signal amplifier
processing circuits is maintained and thereby avoids the
variations in thresholds that would be encountered when A.C.
coupling is employed. ` `
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. 1 ~0 587 57 ; .~.
¦ To control the energization and de-energization of i;
¦ the source 10 Lite the switching control network 34 energizes ..
¦ and de-energizes à.switching transistor 40. For this purpose .r:~
¦ the switching transistor 40 has its emi~ter electrode -
5 I connected directly to ground and i~s collector electrode
¦ connected to the light resistor lOR. The base electrode is ....
¦ coupled to receive the swi~chi~g signals through the swi~ching
: ¦ .control network 34. The switching network is responsive to ~-~
¦ the pulses from the digital controller 1~ for simultaneously ~Yi. ;
10 ¦ controlling the switching or conductive conditions of the .
¦ switch S2 and the transistor 40~. For this purpose, the `
~: ¦. pulses from the digital controller 1~ are directly coupled
to a pair of transistors arranged with the input ~or the
I switch S2 identified as "13". The transistors axe identified r'
~ 15¦ as the transistor 41 which is responsive to the pulses ;~. .
: : delivered by the digital controller 13a and its output is
;~ connected to the transistor 42~which is co~pled to control ~ .
the switch S2. To:this end the emitter electrode of the ~: -
~transistor 41 is connected through a resistor 43 to the
source of pulses and with its base electrode connected to
ground. The collector electrode of the transistor 41 is ..
connected directly to the base electrode for ~he transistor
42. The emitter electrode for the transistor 42 is .
;~ : connected:to the~source of negative potential shown as -10.
~5 ~ resistor 44 is coupled between the negative potential
source L-10 and the base electrode of the transistor 42.
: The collector electrode for the transistor 42 is connected
directIy . to the "13" terminal o~ the switch S2,
aS illustrated. The pulses from the controller 13a are
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~ 1058757
l also coupled to a pair of reverse oriented diodes 45 and 46.
The anode electrode for the diodes 45 and 46 are connected
in common wi~h a resistor 47 having its opposite terminal
coupled to a source of positive potential. The cathode
electrode for the diode 45 is coupled in common witll the
input end of the resistor 43. The cathode electrode for
the diode 46 is coupled to the base electrode for the
switching transistor 40. A resistor 47 is also coupled
between the base electrode for the transistor 40 and ground.
lO It should be recognized that in the normal circuit operation j;
no pulses are received from the digita1 controller 13a and
the switching transistor 40 maintains the source lO Li~e
de-energized. Upon the receipt of a pulse at the base o~
the transistor 40, its conductive condition is changed so
lS as to cause it tP conduct and thereby energize the light
èmitting diode lO Lite. At the same time the conductive
condition o transLstors 41 and 42 are reversed so as to
operate the switch S2 to decouple the amplifiers Al and A2.
The structure for the digital controller 13a was briefly
20 ~described~hereil~above. It will be recognized that the i
signals rom the amplifier A3 are processed by the digital ,;
controller l3a or periodically applying pulse~s to the swi~ch `,~
control network 34 to energiæe and de-energize the source
lO Lite. In particular, the signals received from the output
2S of the amplifier a3 are coupled into the digital controller
a by means o a logic circuit 48. The logic circuit
includes a switching transistor 49 having its base electrode
connected directly to the output of the amplifier ~3. The -`
collector electrode is connec~ed into an isolating ~te
~ 22
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l ~l
~ 10 587 5~
1 ¦ tllat i9 illllStrated ~S a N~ND elemen~ 50 but is not employed
¦ ~or that ~urpose. The emitter electrode for the transistor
49 is connected directly to ground and the output from the
~ logic network 4~ is applied to the digital controller 13a. ~-
51 At this point, it will be recognized that the sign~ls applied
l to the digital controller 13 are the binary ooded signals
¦ that have opposite polarities. The signals can be considered
as being applied to a "light switch~ which is effective for
¦ controlling the energization or de-energization of ~he -
10¦ source of puLses that are derived from the controller and
applied to the switching network 34. As indicated hereinabove, i~
the sensing of a dark surface or nonreflective surface will
de-energize the source 10 Lite while the light switch of the
controller will be effective for maintaining the light
energized in response to the sensing of a reflectlve surface.
It should now be evident that the present invention -;
has advanced the state of the art through the provision of
simple interfacin~g circuits for an optical wand adapted to
read bar coded data for entry into a portable, bat~ery
operated data collection system. The interfacing circuit
controls the energization o~ the light source to minimize
battery drain and compensates with simple D.C. coupled ;i;
circuits for any offset vol~ages generated in the system.
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