Note: Descriptions are shown in the official language in which they were submitted.
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PORTABLE LASER SCA~NING SYSTEM AND SCANNING METHOD
BACKGRO~ND OF T~l~ INVENTION
1 Field of the Invention
. .. I
The present invention generally relates to laser scanning
systems for, and methods of, scanning, reading and/or analyzing
bar code symbols~~nd, more particularly, to a miniature laser
scanning system which is completely field-portable due to its
light-~eight and small-size and small-volume characteristics.
Still more particularly, this invention relates to a hand-held
laser scanning head in which the laser source, power component,
optics, scanning elements, sensors, and signal processing circui- !
try are all moun~ed therein. Yet more particularly, this inven-
tion relates to new high-speed scanning elements and their meth-
ods of scanning.
2. Description of the Prior Art
_
Many industries, particularly the grocery and food processing
industry, have begun to designate their products with a uni~ue
bar code symbol consisting of a series of lines and spaces of
varying widths. Various bar code readers and laser scanning
systems have been developed to decode the symbol pattern to a
multiple digit representation for check-out and inventory purposes.
For example, the contact-type wand or pen bar code readers
were manually positioned on the symbol, and then manually dragged
across-the svmbol, with the pen tip always remaining in contact
with 'he symbol. Skilied personnel were generally required to
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effect the movement, because, among other factors, the angle
and pressure of the pen on the symbol was somewhat critical,
and the speed of the pen during its manual movement, as well
as the uniformity of the pen speed, were also critical.
These contact-type pens were disadvantageous not
only because of the requirement for skilled personnel, but
also because the pen tip tended to scar the symbol i-tself.
Repetitive manual sweeps were often necessary, because success-
ful decoding may not have occurred on the first attempt.
Also, in some applications, a product may need to be scanned
several times a day, or repetitively over the years. To
protect the symbols, mylar protective coatings were used,
however, the mylar coating is not only expensive, but also
diffuses the light, thereby resulting in reading problems.
The lack of uniformity of the pen speed also means
that the pen readers could not be reliably used as scanners,
and particularly not for accurately measuring line widths in
symbol analyzers, which measurement requires a uniform scan-
ning speed.
Contact-type pen readers cannot be used with wax-
coated products, such as milk cartons, because the wax
diffuses the light and alsG adheres to the pen tip, thereby
necessitating constant cleaning of the tip.
Nor can contact-type readers be used on soft products,
such as soft-packaged potato chips, cheese, or blood bags.
The user would have to follow the wrinkles with the pen over
these soft packages, and might even rip the package itself.
Nor can contact-type readers be used where the bar
code symbol is located on the outer surface of reflective
aluminum cans, also, contact-type readers cannot be used
where the symbol is not located at the outer surface of the
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pacXaging. For example, cassette tapes are coded, but the
plastic container for the cassette spaces the symbol at a
small, but non-negligible, distance from the outer plastic
surface of the container across which the pen is drayged.
This small distance can cause light diffusion and non-read-
ing
Some wand or pen readers are of the non-contact
type, i.e., the pen tip need not be in physical contact with
the symbol. Nevertheless, the depth of focus is not large,
and the pen must be positioned in the immediate vicinity
of the symbol. For all practical purposes, the non-contact
pens are usually manually dragged across the symbol, thereby
resulting in the scarring and cleaning problems discussed
above.
Moreover, non-contact pens still require criticality
in the manipulation of the angle of the pen on the symbol,
the pen speed, the pen pressure and the uniformity of pen
speed. Most importantly, just like the contact-type pens,
the user, at best, gets one scan per manual movement. If
the symbol was not successfully read on the first attempt,
then the user must repeat the manual scan again and again
until a successful decode has been performed. This is time-
and labor-consurning.
True laser scanners, not manual readers, are built-
into supermarket counters. These point-of-sale or "deck"
scanners may be of the moving beam or fixed beam type.
However, these are large, massive, stationary installations.
Some objects are too heavy, or too big, or too inconvenient
to be brought to the stationary scanning installation.
Some objects may be stationary themselves.
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More modern scanners have recently been designed to have
hand-held, portable laser scanning heads. However, the known
portable heads weigh over three pounds and are too heavy for those
assembly-line aPplications where a user is reading codes all dav
long. The known ~ortable heads are also somewhat difficult to
manipulate easily due to their size, as well as due to the fact
that a rather thick and somewhat unwieldy cable interconnects the
portable head to-~7desk-top cQnsole which houses the decode cir-
cuitry. The cable contains relatively thick, shielded wires and
a relatively thic~-power wire which do not permil a relatively
easy freedom of movement as the portable head is manipulated.
SUMMARY OF THl~: INVENTI ON
1. Objects of Ihe Invention
Accordingly, it is the general object of the present invention
to overcome the aforementioned drawbacks of the prior art.
Another object of the invention is to eiiminate the require-
ment of using skilled personnel to effect a carefully practiced
manual scanning movement across a bar code s~mbol.
Still another object of the invention is to eliminate scarring
or tearing of the symbol during scanning.
Yet another object of the invention is to accurately scan a
symbol with a high degree of reliability on the first attempt
without requiring subsequentscanning attempts. I
An additional object of this invention is to provide a complete-
y field-portable and mobile las~r scanninq system.
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A Eurther object of this inver-ltion is -to provide an
entirely ~ield-por-table and light-weight laser scanning sys-
tem in which some of the components thereof are mounted in
a hand-held head, and others of the components thereof are
mounted in a body harness.
Still another object of this invention is to provide
a light-weight laser scanning head of small volume and low
weight such that it can be mounted at any desired location
on an assembly line without requiring extensive modification
to the assembly line.
Another object of this invention is to provide a
laser scanning head which is so light-in-weight and small-
in-volume that it can be easily held in a user's hand.
Yet another object of this invention is to provide
a hand-held, gun-shaped housing which has good balance and
a low center of gravity, and is easy to manipulate.
A further object of this invention is to provide a
laser scanning head which is shock-resistant.
Still another object of this invention is to reliably
scan a symbol using either a generally circular beam spot
or a generally rectangular or oval beam spot.
An additional object of this invention is to provide
novel high-speed miniature scanning elements and novel scan-
ning methods of operation.
Yet another object of this invention is to conven-
iently generate single line, multi-line or omni-directional
scan patterns with the same scanning elements.
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Still another object of this invention is to sense objects
bearing the bar code sy~bols, each in their respective turn.
A further object of this invention is to repetitively scan a
symbol a sufficient number of times before attemvting to scan
another symbol.
¦ An additional object of this invention is to sense the reflec-
ted light off the~symbol over an expanded field of view.-
Yet another ob~ect of this invention is to interconnect thelaser scanning head and the rest of the scanning system with a
flexible, non-bulky cable which is easy to manipulate.
Still another object of this invention is to shut-down the
laser source of the laser scanning system after a predetermined
time interval has elapsed in which no symbol has been scanned. I
Yet another ob~ect of this invention is to eliminate frequent ¦
shut-down of the laser source of the laser scanning system immed-
iately after a symbol has been scanned.
2. Features of the Invention
In keeping with these objects and others which will become
apparent hereinafter, one feature of the invention resides, brief-
ly stated, in a light-weight laser scanning head comprising a
housing having wall portions which bound anoutlet port and an in-
terior s?ace. A miniature light source means, preferably a laser I
tube or a semi-conductor laser diode, are mounted within the hous-j
ing, for-generating a laser light beam. Miniature optic means
are also mounted within the housing fordirecting the laser light
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beam along a light path through the outlet port and towards a
bar code symbol which is located in the vicinity of a reference
plane that is located exteriorly of the housing. Miniature
scanning means, preferablv a high-speed scanning motor and/or a
penta-bimorph scanning elemen'" are mounted in the light path
within the housing for cyclically sweeping the laser beam across
the symbol for reflection therefrom. Miniature sensor means,
preferably a ~air of photodiodes, are mounted within the housing
for detecting the intensity of light reflected from the symbol,
and for generating an electrical analog sisnal indicative of the
detected intensity of the reflected light. Miniature signal pro- ¦
cessing means, e.g. analog-to-digital circuitry and envelope de-
tection circuitry, are mounted within the housing for processing I
the electrical analog signal to generate therefrom data descriptiv,e
of the bar code svmbol.
In accordance with one feature of this invention,the light
source means, optic means, scanning means, sensor means and signal
processing means are all mounted within the housing whose volume
is less than about 100 cubic inches. .~oreover, all the afore-
mentioned means together with the housing weigh less than abouttwo and one-half pounds. The small volume and low weight charac- i
teristics of the laser scanning head permit it to be readily
mounted at an inspection station of an assembl~ line ~ithout re-
quiring éxtensive modification to the latter.
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Another feature of the invention is embodied in providing a
handlebar-type grip on the housing so that the user can convenient'-
ly grip the rear end of the housing in his hand and hold the head ¦
in the palm of his hand.
In accordance with another feature of this invention, the
housing may be shaped in a gun-like configuration having a handle
portion mounted below a barrel portion. This feature provides
for convenient m.~ual support of the head bv the user.
Another feature of the invention resides in mountina the
10 ; heaviest component~within the handle portion so as to provide
for a low center of gravity and for an optimum balance design
for the head.
Still another feature of the invention is to utilize a multi-
mode laser tube which generates a laser beam characterized by a
non-uniform brightness characteristic which varies with time,
and to optically modify the latter to produce a beam where the
non-uniform brightness effects are much less pronounced over a
considerable wor};ing distance in the vicinitv of the reference
plane.
Another feature of the invention is embodied in providing a
semiconductor laser diode having a rectangular laser-emitting
cavity for generating a laser beam having a rectangular or oval-
shàped cross-sectional beam spot. By sweeping the rectanaular or I
oval-shaped spot such that its longer dimension is aligned with the
height of the sv~bol, the laser scanning head possesses better
symbol resolution capability.
In accordance with yet another feature of this invention, a
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new 1ight-weight~ high-speed, miniature light beam scanning device
is disclosed. This device comprises a scanning motor having an
output shaft, and motor control means for driving the scanning
motor to reciprocally oscillate the output shaft in alternate cir
cumferential directions over arc lengths which are less than 360
and typically over arc lengths of about 5. Light-reflecting means
are mounted on the shaft for joint oscillating movement therewith.
The light beam ~h~ ch impinges on the light-reflecting means wiil
be rapidly swept across a symbol to be scanned in predetermined
cyclical manner. ~
Still another high-speed, miniature light beam scanning device
proposed by this invention, is a penta-bimorph. The penta-bimorph
comprises a pair of spaced-apart bimorph elements, and light-re-
flecting surfaces mounted on each bimorph element and oriented
at a 45 angle relative to each other. An incoming light beam
which impinges on one of the light-reflecting surfaces will be
reflected off the other of the light-reflecting surfaces at a
right angle relative to the incoming beam for any undesired motionl
of the entire penta-bimorph even as the bimorph elements resonate i
and create the output scan pattern.
Both the scanning motor and the penta-bimorph are high-speed
scanners which do not utilize any springs, as is common with
galvanometer-type optical scanners. Such springs generally con-
tribute to the large size of the galvanometer-type scanners and,
of course, the scanning elements of this invention do not comprise
any such springs, nor are they faced with the possibility of any
such springs wearing out through prolonged use.
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Another eatllre of the invention rec3ides in a com-
pletely field-portable and mobile laser scanning system which
comprises a hand-held laser scanning head, a body-support
harness, and a non-bulky connecting cable connected between
the harness and the head. The connecting cable readily accommo-
dates itself to span the ever-changing distance between -the
harness and the head as the latter is moved from one symbol
to another. Inasmuch as the signal processing means converts
the generated analog signal to the digital signal in the head,
only digital signals are required to be conducted along the
connecting cable. Such digital signals do not require radio
frequency shielding and hence, the individual wires are much
thinner and more flexible as compared to the prior art con-
necting cables. Furthermore, it is no longer necessary to
bring high voltage to the head by means of a thick power
wire. This likewise contributes to the bendability of the
connecting cable.
Another important feature of this invention is the
capability of sensing objects, each in their respective turn.
It is critical to distinguish between whether many scans
have been performed for one object, or whether one scan has
been performed for many objects. When a user approaches an
object bearing a symbol, he manually actuates a trigger to
initiate repetitive scanning of the symbol. Once the de-
code circuitry has determined that a sufficient number of
scans have been performed to successfully decode the symbol,
then the user is alerted, typically by an indicator, such
as a light-emitting diode and/or a beeper, that the repetitive
scanning of the object has been terminated. The trigger can be
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released either prior to, or after, the indicator is actuated.
The actuation of the trigger and the indicator are separate
definable events in which only a single object has been
repetitively scanned for a determinate number of times.
Another feature of the invention is based on safety
considerations. In some prior art systems, the laser tube
itself is shut down after each scanning of a symbol in order
to prolong the laser working lifetime. In other applications,
a mechanical shutter is placed in the path of the laser beam.
Those mechani~al shutters are generally run by solenoids which
wear out over time, and which require a lot of drive power.
In contradistinction to those prior art safety
techniques, the present invention proposes to place a laser-
reflecting means associated with the scanning means in the
light path of the laser beam, and thereupon to move the laser-
reflecting means to a shutter position. In accordance with
this feature, transmission of the laser beam through the outlet
port is prevented without separately deactuating the laser tube
and without using a solenoid-operated mechanical shutter
assembly.
The invention, in accordance with the present
divisional application, is a lightweight, high-speed, miniature
light beam scanning device for scanning bar code symbols in
laser scanning systems. The device comprises a scanning motor
having an output shaft and motor control means for driving the
scanning motor to reciprocally oscillate the output shaft in
alternate circumferential directions over arc lengths which are
less than 360. Light-reflecting means are mounted on the
output shaft for joint oscillating movement therewith, whereby
a light beam impinging on the light-reflecting means is rapidly
swept across a bar code symbol in a predetermined cyclical
manner.
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t)73~3
A method i.9 also described wherein the output shaft
of the scanning motor is driven in one circumferential direc-
tion over an arc length which is less than 360 and then
driving the output shaft in the opposite circumferential
direction over an arc length which is less than 360, and
alternately, repeating these steps in a predetermined cyclical
manner. Further, a light-reflecting means is mounted on the
output shaft for joint oscillating movement therewith, whereby
a laser light beam impinging on the light-reflecting means is
repetitively swept across a bar code symbol.
The novel features which are considered as charac-
teristic of the invention are set forth in particular in the
appended claims. The invention it~elf, however, both as to
its construction and its method of operation, together with
additional objects and advantages thereof, will be best
understood from the following description of specific embodi-
ments when read in connection with the accompanying drawings.
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BRIEF DESCRIPTION OF THE DRA~INGS
FIG. 1 is a side sectional view of a gun-shaped
embodiment of a laser tube-based laser scanning head in accord-
ance with this invention'
FIG~ 2 is a top sectional view of the gun-shaped em-
bodiment of FIG. 1,
FIG. 3 is a front view of the gun-shaped embodim~nt
of FIG. 1,
FIG. 4 is a side sectional view of a miniature high-
speed scanning motor with schematically-illustrated control
circuitry in accordance with this invention,
FIG. 5 is a diagrammatic view of the motor of FIG. 4
with the rotor in its equilibrium position'
FIG. 6 is analogous to FIG. 5, but showing the rotor
in one of its sweep-limiting positions in solid lines, and
its shutter position in dashed lines,
FIG. 7 is analogous to FIG. 5, but showing the rotor
in the other of its sweep-limiting positions'
FIG. 8 is a feedback circuit for modifying the output
shaft speed motor of FIG. 4,
FIG. 9 is a closed loop scanning motor control cir-
cuit for the motor of FIG. 4 in accordance with this invention
FIG. 10 is an electrical schematic of the motor
control circuit o FIG. 9,
FIG. 11, which is on the same sheet of drawings as
FIG. 1, is a schematic view of a completely field-portable
and mobile laser scanning system utilizing the FIG. 1 gun-
shaped embodiment of a laser scanning head in accordance
with this invention'
1 ~7~3
FIG. 12, which is on the same sheet of clrawings as
FIG. 2, is a schematic view of a semiconductor laser diode-
based embodiment of the portable laser gun scanning heacl in
accordance with this invention,
FIG. 13, which is on the same sheet of drawings as
FIG. 2, iS a diagrammatic view of an assembly line equipped
with a box-shaped, bracket-mounted embodiment of a laser
scanner head serving as an inspection station in accordance
with this invention'
FIG. 14, which is on the same sheet of drawings as
FIG. 4, is a schematic view of another hand-held embodiment
of a laser scanning head in accordance with this invention,
FIG. 15, which is on the same sheet of drawings as
FIG. 4, is a diagrammatic view of a penta-bimorph scanning
element with schematically-illustrated drive circuitry in
a_cordance with this invention' and
FIG. 16, which is on the same sheet of drawings as
FIG. 1, is an electrical circuit diagram of the control cir-
cuitry in accordance with this invention.
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DETA~LED DESCRIPTION OF THE PREFERRED EMBOD~MENTS
I. LASER TUBE SCANNER
Referring now to FIGS. 1-3 and 11 of the drawings, ref
erence numeral 10 generally identifies a light-weight, hand-held,¦
portable laser scanning head for use in a laser scanning system
operative for reading and/or analyzing bar code symbols. Such
symbols comprise a series of lines and spaces of varying widths,
which pattern decodes to a multiple digit representation charac-
teristic of the product bearing the symbol. Typical symbol bar
10 " codes in current use are the Universal Product Code (~PC), EA~,
Codabar and Code 39.
Turning again to ~IG. 1, the portable laser scanning head
10 includes a generally gun-shaped housing having a handle portion
12 and a barrel portion 14. The handle portion 12 has a cross-
sectional dimension and overall size such that it can conveniently
fit in the palm of a user's hand. The barrel ~ortion 1~ is connec-
ted to the handle portion 14 at detachable connectors 16,18.
Both the handle and barrel portions are constituted of
a light-weight, resilient, shock-resistant, self-supporting mater-
ial, such as a synthetic plastic material. The plastic housing ispreferably injection-molded, but can be vacuum-formed or blow-
molded to form a thin shell which is hollow and bounds an interior
space whose volume measures less than a value which is on the
order of 100 cubic inches. The specific value of 100 cubic inches
is not intended to be self-limiting; it has been provided merely
to give an approximation of the overall maximum volume and size
of the head 10. The overall.volume can be much lower than 100
cubic inches, and indeed, in some applications, interior volumes -
~on the order of 50 cubic inches are obtainable.
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The barrel portion 14 is generally horizontally elongateq
and has opposite end regions 20,22. The handle portion 12 is
elongated and is connected to the barrel portion'such that the
handle portion forms an angle with the latter. The detachable
connectors 16,18 mount the handle portion below the barrel portion
and intermediate the opposite end regions 20,22 of the latter. 1,
This feature vermits the user to conveniently manually support the
head 10 from below the barrel portion and at a location for optim-
um manual manipulation and balance of the head.
Miniature-light source means for generating a laser light
beam is mounted in the interior space of the barrel portion 14.
In one preferred embodiment, the light source is a co-axial helium-
neon laser tube 24 which generates a red-light beam at a wavelength
of 632.8 nanometers. The laser tube is a hard-sealed, unpackaged
tube. The laser tube is of light-weight (i.e., less than six
ounces; typlcally on the order of three ounces); is of short lengtlh
(i.e., less than eight inches; typically on the order of five in- ¦
ches); ~as a low input DC power requirement (i.e., anode voltage 1i
less than 1100 volts, typically about 650 volts; anode current
less than 4.5 milliam?s, typicall,y about 4 milliamps); has a low
firing voltage (i.e., less than six kilovolts, t~pically about 3.4
kilovolts maximum); has a low output power (i.e., on the order of
0.5 milliwatts); and is long lasting (i.e., on the order of 15,000
hours).
The laser tube 24 produces a light beam in the TEMnm~
mode. ~ This multi-mode tube generates a laser light beam havi~g an
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axial cross-sectional, generally circular, beam spot in the immedi-
ate vicinity of the anode 26 which is about 35 mlls in diameter.
It will be understood that the laser light beam diverges in direc
tion away from the anode 26 at an angle of divergence at about
3.5 to ~ milliradians. In contrast to conventional single mode
laser tubes whose output beam circular spots are characterized bv~
a gaussian brightness distribution characteristic which does not
vary over time,-~e circular beam spot of the multi-mode laser 1,
tube 24 is characterized by a non-uniform brightness characteris-¦
10 ' tic which varies with time. Visual observation of the output
beam spot of the multi-mode tube is characterized by darker zones
within the output beam spot, which darker zones move ran
domly within the output beam spot in a manner roughly analogous
to sunspot activitv.
Straps 32,34 having springs at their respective ends are
wrapped around the tube 24 for mounting the latter on a mother-
board or support plate 30. Rubber bumpers 36,38 are used to mount
the support plate in shock-resistant relationship with the barrel
portion. Specifically, bumper 36 is mounted bet~een the housing
and a front vertical flange portion 40 of the plate 30 in order to
minimize to-and-fro horizontal movement of the plate and its assoc-
iated components mounted thereon. Bumper 38 is mounted between
the housing and a rearward horizontal portion of the plate 30 in
order to minimize up-and-down vertical movement of the plate and
its associated components.
The underside of the laser tube 24 which faces the plate
30 is received in a pair of soaced-apart grooved supports 42,44.
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I 1 73103
Each support 42,44 has a threaded adjustment ele~ent which is
threadedly mounted on the support plate 30. The threaded elements
46,48 are independently turnable to adjust the position of the
laser tube relative to the support and, in p2rticular, to properly
align the laser light beam with respect to the miniature optic
means, as described below. I
The DC power supply 50 for supplying DC power to the laser
tube 24 is mount~ within the interior space of the handle portion
12. The DC power component 50 occupies a volume of about four
cubic inches and weighs about six ounces. This power component I
is the heaviest component from among all the other components moun-
ted within the housing, and therefore, the placement of this heav-
iest component within the handle portion provides the head with a
low center of gravity and better balance for ease of manipulation.l
As best shown in FIG. 16, the power supply 50 has an in-j
put terminal 52 to which low DC voltage, e.g. 12 VDC, is applied.¦
The 12 volts DC is suDplied by a separate non-shielded wire con-
ductor which is located within connecting cable 58. The supply
50 also has an out~ut terminal 54 which supplies the appropriate ¦
anode voltage and anode current to the anode 26 of the laser tube !
24 via a ballast resistor 55. The ballast resistor 55 is about
100 kilohms, 2 watts. The cathode 28 of the tube 24 is grounded.,
The supply 50 further includes a control terminal 56
which is operatively connected to a trigger switch 60 and to a
control circuit, as described in detail below. The presence or
absence of a control signal at the control terminal 56 determines
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~-73103
whether or not the anode voltage is generated at the output term-
inal 54. The electrical connections for the varlous terminals 52,
54,56 have been o~itted from FIG. 1 for the sake of clarity.
Turning again to FIG. 1, the laser light beam is directedl
to miniature optic means which is also mounted in the barrel por- ¦
tion. The optic means includes an optical train operative for
optically modifying the laser light beam, and for directing the
modified beam along a light path through the housing. The beam
exits the housing through an outlet port 62 located at end region j
10 ~ 20, and impinges on a bar code symbol which is located in the vic-
inity of a reference plane that is located exteriorly of the hous-
ing. -
The optical train includes a beam expanding negative lens
64 and an objective positive lens 66 each having individual f num-
bers which are typically in the range from f/6 to f/7. The f num-
ber for the beam exiting the optical train is typically in the
f/50 to f/60 range. ~ther choices of lens parameters can lead to '
larger numbers for the depth of focus in the range from 1" or
more for the multi-mode laser.
As noted above, the beam spot diameterimmediately outside
the laser tube is about 35 mils. The beam expanding lens 64 in- ,
creases the beam spot diameter to about 250 mils at the objective !
lens 66. The optical train will focus the beam such that the beam
spot will have a diameter on the order of from 5 to 7 mils at the
reference plane which is about 260 mm away from the objective lens
66. The 6 mil spot size at the reference plane is maintained on
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1 173103
both sides of the latter over a working distance. In a preferredi
embodiment, the reference plane is spaced about 1 inch away from ¦
the end region 22 of the barrel portion 14, and the working dis- ¦
tance is about 2 inches. Hence, the 6 mil spot size is generally¦
maintained from the end region 22 for a distance of 1 inch to the !
reference plane, and also beyond the latter for an additional l
inch. A bar code symbol placed anywhere in this region will be
accurately decoded and/or analyzed.
The focal lengths and distances of the positive and nega
tive lenses of the optical train are specially designed to mo~ify
the multi-mode laser beam. The beam spot at the reference plane
still contains dark zones, but the uneven brightness characteris-
tic is less pronounced.
The optics for a single mode laser tube are more conven-
tional then for the multi-mode case, and f numbers for the lenses
would typically lie in the range from f/120 to f/200 to obtain
depths of focus in the range from 2" to 3". For the multi-mode
case, the f numbers for the lenses are lower, thereby mandating a¦
smaller depth of focus on the order of 1". However, we have foundj
that the working distance can be greater than 1", and typically
in the neighborhood of 2".
The preferred embodiment of the positive lens 66 for mini-
mum spot size is an infinity-corrected achrometric doublet, where-
in the spot size will be increased only about 5~ over the diffracl
tion concition. If a single plano-convex single~ is used, as illus-
trated, the spot size will be increased by about on the order of
90%.
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Miniature scanning means are mounted in the light
path in the interior space of the barrel portion for cyclic-
ally sweeping the laser beam across the bar code symbol for
reflection therefrom. The scanning means comprises at least
one miniature scan means 68 for sweeping the symbol along a
predetermined direction (X-axis scanning) lengthwise thereof.
The scanning means may, but not necessarily, comprise another
miniature scan means 70 for sweeping the symbol along a
transverse direction (Y-axis scanning) which is substantially
orthogonal to the predetermined direction.
Many types of scan elements can be utilized for
either scan means 68, 70. For example, miniature polygons
driven by motors can be used, or the various bimorph scan-
ning oscillating elements described in U. S. Patent No.
4,251,798, issued February 17, 1981.
Nevertheless, the X-axis scan means 68 and the Y-
axis scan means 70, as described in detail below, are par-
ticularly compatible in terms of their size and weight to
be mounted within the barrel portion 14. The operation of
these scan means 68, 70 will be discussed below in con-
nection with FIGS. 4-10. At this stage of the discussion,
it is sufficient to understand that both scan means 68, 70
are scanning motors which have reciprocally oscillating out-
put shafts 72, 74. Light-reflecting means or mirrors 76, 78
are respectively mounted on shafts 72, 74 and positioned in
the light path. Motor control means are operative for driv-
ing each motor to reciprocally turn each shaft in a pre-
determined cyclical manner in alternate circumferential
directions over arc lengths which are
- 20 -
~ ~73~03
less than 360. Typically the arc lengths will be about 5
relative to the vertical. Of course, other arc lengths
could also be utilized. Any light beam impinging on the
mirrors will be moved at a very rapid rate of speed which
is at least on the order of five oscillations per second,
and typically about 100 oscillations per second~
The miniature scanning means includes a stationary
light-reflecting mirror 80 which is fixedly mounted on the
support plate and which is positioned at a 45 angle rela-
tive to the axis about which the output shaft 72 turns.The light beam leaving the objective lens 66 impinges on
the stationary mirror 80, and is thereupon reflected in
a horizontal plane to impinge on the mirror 76 which, in
turn, is mounted on the shaft 72 and is positioned at a
45 angle relative to the turning axes of shafts 72, 74.
The light impinging on mirror 76 is reflected upwardly to
mirror 78 which is mounted on the shaft 74 at a 45
angle. The light impinging on mirror 78 is thereupon
reflected forwardly in lengthwise direction along the
barrel portion 14. The light beam passes through the
laser beam-transmissive exit window 62.
The reciprocal oscillation of the shaft 72 causes
the light beam to be moved lengthwise along the bar code
symbol to thereby obtain X-axis scanning. If desired, the
reciprocal oscillation of the shaft 74 causes the light beam
to be moved along the height of the symbol to thereby obtain
Y-axis scanning.
If only the X-axis scanning motor 68 is
driven such that mirror 76 is driven at a uniform
rate of speed, then the laser beam will be linearly
displaced in horizontal direction, and a
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1 173103
generally linear scan line will be generated at the reference
plane. If the Y-axis scanning motor 70 is likewise driven such
that mirror 78 is driven at a uniform rate of speed, then the laser
beam will be linearly displaced in vertical direction, and a ras- ¦
ter-type scan pattern will be generated at the reference plane.
The scan pattern comprises a set of generally parallel, equidis-
tantly spaced-apart scan lines which are stacked one about another
along the vertical direction.
~ Other types of s~an patterns are also available. For
example, if the X- and Y-axis scanning motors are both driven such
that mirrors 76,78 are driven at a sinusoidally-varying rate of
speed, then the scan pattern at the reference plane will be a
Lissajous-type pattern for omni-directional scanning of UPC sym- I
bols. , -
The barrel portion 14 has an upper wall portion 82 and alower tapered wall portion 84 respectively located above and below;
the output port at the end region 20. The upper wall portion 82
is generally planar and has no upstanding projections mounted
thereon in the vicinity of the end region 20. The outlet port
is dimensioned to be wide and narrow. The laser beam exits the
outlet port at a location just below the upper wall portion.
~ence, the upper wall portion 82 serves as a convenient sighting
guide in which to accurately aim the laser light beam towards the i
target symbol. It will be recognized that a user generally si~hts
the target symbol from a position generally behind the head 10,
and that therefore, an upper-wall portion 82 having projections
- 22 -
~1
Il
~173103
would block his view. The smooth upper wall portion 82 described I
above avoids visual interference between the housing and the laser
beam itself. , I
Miniature sensor means are likewise mounted on the front j
upright flange 40 of the support plate 30 in the interior space
of-the housing. The miniature sensor means includes a photo-sen-
sor device such as a photomultiplier tube or a semiconductor photo-
diode, for detec'.;-ng the intensity of the light reflected from the
symbol, and for generating an analog electrical signal indicative ¦
of the detected intensit~ of the reflected light.
As shown in FI5. 1, the reflected light first passes
through the exit window 62, and thereupon passes through the red-
light laser beam-transmissive filter 90, whereupon it impinges on
a pair of photodiodes 86,88. The photodiodes are mounted in
spaced-apart relationship on the flange 40, and generate an analog
electrical signal. Two diodes are used, rather than one, in o,rder,
to increase the field of view. The two diodes are spaced apart
such that their individual zones of covera~e overlap each other.
If the field of view of the scanning means is on the order of four
inches, then the photodiodes are spaced about two inches apart for
complete zone coverage.
Miniature signal processing means 92 (see FIC.. 2) are
also mounted in the interior space of the barrel portion 14 for
processing the electrical signal generated from the sensor means. ,
The processing means is fixedly mounted on the support plate 30
at one side of the laser tube 24. The processing means is prefer-,
ably fabricated as an integrated circuit which processes the elec-
- 23 -
I ~73103
trical analog signal ~nd digitiæes it to generate data des-
criptive of the bar code symbol. Reference may be had to
United States Patent 4,251,798, for details of one preferred
type of signal processing means.
The control circuitry 94 (see FIG. 2) for the scan~
ning means 68, 70 is likewise preferably fabricated as an
integrated circuit and is mounted on the other side of the
laser tube. A11 of the electrical connections for the photo-
diodes 86, 88, the processing means 92, and the control
circuitry 94 for the scanning means 68, 70 have been omitted
from FIGS. 1-3 for the sake of clarity. A detailed descrip-
tion of the control circuitry is set forth below in connec-
tion with FIG. 16.
All of the above components, including, among others,
the laser tube 24, the power supply component 50, the lenses
64, 66, the scanning motors 68, 70, the photodiodes 86, 88,
the processing circuitry 92, the control circuitry 94, and
the support plate 30 together with the handle portion 12 and
the barrel portion 14 of the housing comprise a light-weight
~0 scanning head whose total weight measures less than a value
which is on the order of two and one-half pounds. The specific
two and one-half pound weight figure is only exemplary, and
is not intended to be self-limiting. Typically, weights on
the order of one to two pounds are readily obtainable,and, in
the semiconductor laser diode embodiment described below,
weights on the order of less than one pound are realized.
The portable head 10 depicted in FIGS. 1-3 and 11 is a
hand-held unit, and flexible non-bulky cable 58 interconnects
the head 10 to the remaining components of the laser scan-
ning system.
- 24 -
1 173103
These remaining components include, among others, the digital sig-
nal decode computer clrcuitry, the data storage circuitry, and, in
some applications, the control voltayes for the power supply 50
and for the control circuitry 94. These additional circuitry com-
ponents can be mounted in a desk-top console for AC uall power
operation, or in the preferred embodiment of ~IG. 11, they can be
incorporated into a body harness 100 to be worn by the user. ~n
: this latter case; a rechargeable batterv pack is mounted on the
harness for complete field-portability of the entire sysiem.
The body harness 100 can be a back-pack or preferably a
belt-pack ~see FIG. 11) which is worn about the user's waist. he
decode computer circuitry 102 is mounted on .he belt-pack, and
is oyerative t.o decode the digitized signals generated by the si~-
nal processing means 92. The data storage circuitry 104 is also
mounted on the belt-pack, and is onerative to store the decoded
signals. Essentia~ly, the data storage circuitry 104 is a self- ¦
contained memory device, such as non-volatile bubble memory means,l
or magnetic cassette, or volatile semiconductor read/write memory ¦
means. The low voltage rechargeable battery supplv 106 is like-
wise mounted on the belt-pack. The decode circuitry 102, data
storage circuitry 104 and battery 106 can be separately mounted on
the belt 100, or can all be mounted within a single housing roughly
measuring about 2" x 4" x 10". The entire laser scanning system
is completely field-portable and self-contained.
It is also within the spirit of this invention to minia-
turize the additional components mounted on the belt-pack 100,
~ , . '
. I
- 25 - I
tl73103
particularly by large scale integration of the decode computer
circuitry into from one to three chips, and to mount these addi-
tional components into the housing of the portable head 10 itself.
In that case, the entire laser scanning system can be held in the
user's hand.
The cable 58 comprises a plurality of radio-frequency non-
shielded wires therein. Some of these wires conduct the input
voltage to the input terminal 52 of the power supply 50, as well
~ as biasing voltages for the control circuitry. Another wire con-
ducts the digitized signals from the processing circuitry 92 to
the belt-pack 100. Still another wire conducts an indicator signal
to the light-emitting diode 99 and/or the auditory beeper 98 to
indicate, either visually or by sound, that the symbol has been
successfully decoded.
All of the aforementioned non-illustrated individual wire's
are unshielded. This me~ns that the cable 5, is relatively small
in cross-section, light~in-weight, non-bulky, and flexible, and
therefore is easily moved when the head 10 is aimed at different
target symbols. The cable 58 is characterized by multiple free-
doms of movement and does not require excessive strength on theuser's part for manipulation purposes.
The head 10 need not have the gun-shaped configuration as
¦ depicted in FIGS. 1-3 and 11. Other configurations such as stream-
lined or box-like configurations are also contemplated. For exam-i
ple, another hand-held configuration for the head 1OA is shown in
FIG. 14. The streamlined head 10a is basically identical to the
- 26 -
1 173103
gun-shaped head, except that the handle portion 12 is co-
linear with the barrel portion, and that the rear end of
the barrel portion 14 has finger-receiving grooves 101
resembling a handlebar-type grip. The user can thus grip
the head and hold it in the palm of his hand.
Another feature of the streamlined head lOa is an
external rubber bumper 103 which could be utilized for any
of the housings disclosed herein. As noted above, like any
hand-held equipment, a hand-held laser scanner head must be
strong enough to withstand some physical abuse, such as
being unintentionally pushed off a table onto the floor.
Hence, the rubber shock mounts 36, 38 are used to support
the rigid plate 30 within the housing in such a way as to
allow the plate and the components mounted thereon to
momentarily shift within the housing under shock loading.
Sufficient clearance is provided around the plate 30 to
allow it to move without hitting the inside wall of the
housing. After the shock has passed, the rubber shock
mounts will return the inner structure to its original
position within the housing.
Shock absorbtion is also performed by flexing of
the resilient outer housing wall itself. Constructing the
outer housing out of suitable material such as vacuum-
formed ABS can permit this flexing with no damage occurring
to the housing.
Still further shock absorbtion is obtained by the
rubber bumper or ridge 103 running around the outside of
the housing and positioned so as to absorb the most common
shocks such as dropping the scanner on its side on a table.
The housing is molded in two parts, and the ridge 103 is
placed between the two housing parts.
- 27 -
;, ~1731lo3
As another exa~ple, the miniature size, small volume,
and light-weight characteristic of the head 10 ma]~e it suitable
not only for hand-held applications, but also for conveniently
converting any~designated location on a production line to an in- ¦
spection station or to any on-line symbol affixing station. As
best shown in FIG. 13, the box-shaped head 10b is ?rovided with a'
bracket 11 for stationarily mounting the head 10b at any designated
location on the-a~,sembly line 13. A ~lurality of objects 15 are
conveyed past the head 10 for inspection purposes. The head 10b
10 ~ can also be conveniently ~ounted on a sup~ort stand.
The miniature size and light weight parameters insure
that extensive modification to the production line facilitv 13 is
not required. In view of the fact that the ins~ection station is
stationary, it is not necessary to mount the DC power supply com-
ponent 50 within the head 10. Instead, the DC power supply com-
ponent 50 can be mounted at another location remote from the in-
terior space of the housing, thereby obviating the need for pro-
viding a handle as in the gun-shaped version.
II. HIGH-SPEED SCANNING ~OTOR
The structural and functional details of the X-axis
scanning motor 68 are illustrated in FIGS. ~-10. These details
are identical for Y-axis scanning motor 70, and hence will not
be repeated for the sake of brevity.
The scanning motor 68 is a light-weight, miniature laser
light beam scanning device for the high-speed scanning of bar code
symbols in laser scanning systems. The motor 68 includes an os-
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1~73103
cillatory output shaft 72 which is journalled in bearing 108; and
a mirror 76 fi~edly mounted on theshaft 72 for participating in
the joint oscillatory movement therewith. I
The motor 68 includes an upper cup-shaped statox housing¦
110 and a lower cup-shaped stator housing 112. Stator coil wind-
ings 11~, 116 are respectively mounted in stator housings 110,
112. A permanent magnet rotor 120 is ]ournalled on stu~ shaft ll~
which is co-linearly arranged with shaft 72. The rotor 120 is
surrounded by the--stator coils, and is operatively connected to
the output shaft 72 for joint oscillatorr movement therewith.
The upper stator housing 110 has a pair of poles 122,124
mechanically displaced by 180. The lower stator housing 112 has
a pair of poles 126,128 mechanically displaced by 180. The upper
poles 122,124 are spaced 90 apart from the lower poles 126,128.
The permanent magnet rotor 120 is magnetized with the same number
of pole pairs (i.e., one pair) as contained by each stator coil
winding.
The structural aspects of the scanning motor 68 are anal-
ogous to a simplified stepper motor, which is a device which is
used to convert electrical pulses into discrete mechanical angular
movements every time the polarity of a stator winding is changed.
~y alternately energizing and de-energizing the two stator coils
of a stepper motor, the magnetic interaction between the rotor
poles and the stator poles causes the rotor to turn in discrete
angular steps over the entire 360 circumference of the output
shaft. -
.
. 1~
- 29 -
. I
~173103
In contradistinction to stepper motors, the motor contro~
means 94 is operative to oscillate the shaft 72, first in one
circumferential direction over an arc length less than 36n~, and
secondly in the opposite circumferential direction over an arc
length less than 360, and thereupon to repeat the aforementioned
cycle at a high rate of speed. Each arc length is tv~ically abou~
5 relative to the vertical, although other angular displacementsi
.,
are possible. The rate of oscillation is typically on the order
~ of one hundredcycles per second.
The motor control means 94 includes reference means 140
for applying a generallv constant low level DC voltage to one of
the stator windings. For example, a 12v DC signal is applied to
stator winding 114 via conductor 132~ The motor control means also
includes variable means 142 for applying a periodic voltage of
time-varying amplitude to the other of the stator windings. For
example, a triangular voltage waveform is applied to stator winding
116 via conductor 134.
In FIGS. 5,6 and 7, the reference means applies a con-
stant positive DC voltage to stator coil 114, therebv energizing
stator poles 122,124 as north and south, respectively. In FIG. 5,
the variable means apvlies a zero voltage to stator coil 1~6,
thereby permitting the permanent north and south poles of the
rotor to align themselves with stator poles 12?,124, as shown. In
FIG. 6, the variable means applies a positive DC voltage to coii
116, thereby energizing stator poles 126 and 128 as north and south,
respectively, and concomitantly causing the rotor to turn in
clockwise direction to an angular position which is dependent up-
on the positive amplitude of the voltage applied to coil 116. In
- 30 -
~73103
FIG. 7, the variable means applies a negative DC voltage to coil
116,thereby energizing stator poles 126 and 12~ as south and north,
respectively, and concomitantly causing the rotor to turn in
counterclockwise direction to an angular position which is depend-l
ent upon the negative amplitude of the voltage applied to coil 116.
In summary, the shaft 72 is moved in an analos manner to
an angular position which corresponds to the amplitude of the
periodic voltage. The number of degrees of angular move~ent is
proportional to the voltage amplitude. The speed of movement of
the shaft 72 corresponds to the rate of change of the periodic
voltage. The direction of movement, i.e. clockwise or counter-
clockwise, is dependent upon the slope, i.e. positive or negative,
of the periodic voltage. The oscillation rate is proportional to
the periodicity of the periodic waveform. The xate of oscillation
is at least five oscillationsper-second, and in a preferred embodi-
ment, the rate is on the order of one hundred cycles per second~.
The periodic voltage waveform can be any time-varying
voltage, such as a sawtooth, sinusoidal or triangular waveform.
For periodic drive waveforms, the speed of the shaft is non-linear,
and in fact, is sinusoidal-like in the sense that the shaft speed
slows down when the shaft approaches the sweep-limiting positions
of FIGS. 6 and 7, and speeds uP when the shaft approaches the
e~uilibrium position of FIG. 5.
In order to obtain more linear tracking of the shaft posi-
tion with respect to the amplitude of the periodic drive voltage,
one adjustment is to pre-set the amplitude of the constant DC vol-
: I
~173103
tage which is applied to stator coil 114 by adjusting the referenjemeans 140 to a predetermined value. All oscillatory components
can be characterized by a resonant frequency. For the scanning
mobor 68, the ,resonant frequency is determined, among other things,
by the mass of the moving structure and by the fixed magnetic
field (i.e., spring constant) which is established by the stator !
windings. Hence, by changing the DC voltage level applied to
stator coil 114,-^ne adjus~s the frequency of movement of the
shaft to any desired value.
If the reference means 1~0 is adjusted such that the fre-
quency of movement is at or near the inherent resonant frequency,
then a large amplitude of ~otion for the shaft is obtained for a
relatively small input power. This adjustmen~ is used for those li
applications where a minimum power drain is desired, typically ini
battery-powered operation. I
On the other hand, if the reference means 140 is ad~usted
such that the frequency of movement is remote from the resonant
frequency, then more linear tracking of shaft position versus driv!e
voltage amplitude is obtained at the expense of input power. This,
adjustment is useful for those applications where a more linear
sweep is desired; for example, for measuring bar code widths.
Anothe'r method of obtaininq more linear tracking is to
widen the sweep by over-driving the shaft 72 to s~eep-limiting
positions which are more angularly spaced apart to sweep a field o,f
view which is more than necessary to scan the symbol. I~e have
recognized that the shaft undergoing a sinusoidal-like movement
. ' '''.'~
- 32 - '
1173103
undergoes a somehwat linear movement over a central portion of
its overall movement. Analysis of the harmonieally-varying angu-
lar velocity reveals that the linear spot velocity of the beam
spot on the scan surface is relatively constant over a much larger
portion than normally expected. Perhaps twice as much of the duty
cycle portion of the harmonic motion is useable. The linear s~ot,
velocity of the harmonically-varying angular velocity ean be des-
cribed as a comp'ix transcendental function, and has a velocity
which is uniform to within a few per-cent over a + 25 to 30
range.
Hence, in the vicinity of the equilibrium position, the
shaft undergoes a somewhat linear movement. By over-driving the
shaft 72 to generate a sweep having a field of view on the orcler
of eight inches, in a situation where only a four inch sweep is
reguired to adec!uately scan a symbol, the speed of the shaft 72 is
essentially linear over the central three and one-half to four
inches of sweep.
Still another method of obtaining more linear tracking
is to utilize the feedback circuitry depicted in FIG. 8. The
drive waveform VD is applied to the positive input terminal of the
differential amplifier 144. The amplifier output is connected to
one end of the stator coil winding 116. The voltage at the oppos-
ite end of the coil 116 is connected to ground via resistor 146,
and is fed back to the negative input terminal of the amplifier
149 via feedback conductor 148. The voltage in the feedback con-
ductor 148 is the attenuatecl drive voltage which is superimposed
_ 33 -
. .
1173103
with the voltage generated b~ the stator coil due to shaft motion.
The voltage in the feedback conductor 148 attem~s to follow the
drive voltage, thereb~ making the output shaft speed more uniform.!
Any laser light impinging on the mirror 76 will there- ~
fore be linearly swept across the target symbol. If two scanning !
motors are used, then the laser beam can be swept over two mutually
orthogonal directions to generate raster-ty~e scan patterns. Of
course, if omni-directional scan patterns, such as Lissajous-type ¦
pat~erns, are required for some applications, then the above-
described linear tracking techniues are not utilized. The un-
modified sinusoidal--like movement of the output shaft then repre-
sents a significant feature of the scanning motor element.
The miniature scanning motor weighs about one ounce, and
occupies a volume on the order of one inch x 0.~ inches. The
scanning motor also has a long working-lifetime on the order of
10,000 hours, because it is frequently shut down, as described
below.
Yet another method of obtaining more linear tracking is
illustrated by the closed loop scanning motor control circuit de- I
picted in FIGS. 9 and 10. The scanning motor control circuit in-l
cludes the scanning motor 68 operative for reciprocally oscilla-
ting the shaft 72 first in one direction, and then the other, with
angular motion of always less than 360, as described above. The !
mirror 76 is mounted at the end of the shaft 72 to reflect a light
beam in a desired predetermined manner.
- The control circuit comprises a ~rimarv coil 160, two or
more secondary coils 162 and 164, and a movable shield 166. The
- 34 -
` ~ ~73103
primary coil 160 is energized by a raclio frequency oscillator
168. The secondary coils 162, 164 are juxtaposed physically
close to the primary coil 160. The shield 166 is fixedly
mounted on motor shaft 72 for joint oscillatory movement
therewith, and is located between the primary coil 160 and
the two secondary coils 162, 164.
As best shown in FIG. 10, the tuning capacitors
170, 172 tune the secondary coils to resonate at the
frequency at which the primary coil is excited. When the
primary coil is excited, the secondary coils are inductively
coupled to it to establish an oscillating magnetic field,
and an AC voltage of the same high oscillating frequency
as the primary coil appears across the secondary coils,
and is detected by the sensing circuitry 174.
The shield 166 modifies the radio frequency
signal at the primary coil which is coupled to the secondary
coils by an amount proportional to the area of the latter
covered by the shield. As the shaft 72 oscillates, the
shield moves relative to the magnetic field, the voltage
across one secondary coil increases as that secondary coil
becomes unshielded, and concomitantly the voltage across
the other secondary coil decreases as it becomes more
shielded.
The voltage sensing circuitry 174 comprises peak
diode detector sub-circuits which include diodes 176, 178 and
resistor-capacitor parallel-combinations 180, 182. Each
detector sub-circuit detects the voltage on its respectively
associated secondary coil, and feeds the voltages to a
differential amplifier 184 for generating a difference
signal which is proportional to the angular displacement
of the shaft 72. This difference signal is, in turn, fed
~ ~3~03
to one input of another differential amplifier 186~ whose
other input is supplied with a control voltage. The output
drive signal is fed to the stator coil.
In a preferred embodiment, the primary coil with
its oscillator is printed on a printed circuit board. The
primary coil is printed with a circular pattern, and the
shaft 72 extends through the center of the primary coil.
The secondary coils are printed with their sensing circuitry
on another printed circuit board. The secondary coils are
printed as generally triangular patterns with the apex
located on the shaft axis.
Referring now to FIG. 16, each miniature scanning
motor 68, 70 is provided with a reference means 140 and a
variable voltage means 142. In addition 7 shutter means 150
are provided in the control circuitry 94 for generating a
shutter voltage which moves either or both output shafts
of the motors 68, 70 to a shutter position in which the
associated mirrors are moved such that the laser beam is
prevented from passing through the outlet port 62 towards
the symbol.
The shutter means 150 is electrically connected to
the variable voltage means. In one embodiment, the shutter
means 150 generates a voltage having an amplitude greater
than the amplitude of the drive voltage. In FIG. 6, the
dashed line representation of the rotor 120' depicts the
shutter position. The large amplitude voltage displaces
the output shaft to a greater angular extent than that
required by the sweep-limiting position shown in solid
lines. In this case, the associated mirror is moved out
of the light path, to thereby interrupt laser beam trans-
mission.
t ~73~3
In another preferred embodiment, the shutter rneans
is not operative to move the mirror out of the sweep range,
as described above. Instead, the shutter means is operative
to move the mirror to a position within the sweep range
such that the reflected light will not pass through the
outlet port. The reflected light can be contained within
the housing itself, or preferably can be diverted to a
light absorber, such as a black body, mounted within the
housing.
In the preferred embodiment, the variable voltage
means moves the mirror such that the reflected laser light
beam is swept across a field of view which is longer than
the length of the exit window at the outlet port 62. In
effect, the housing walls at opposite sides of the exit
window intercept the laser light beam and block its trans-
mission when the beam is swept through its entire sweep
range beyond the length dimension of the exit window. In
this case, the shutter position can be any position of the
mirror which results in its reflected light being directed
beyond the length dimension of the exit window. It will
be noted that the shutter position in this case is within
the entire sweep range but is still such that the laser
light beam is prevented from reaching the symbol.
The shutter position represents a motor shut-off
condition. The frequent motor shut-downs described below
means a very low duty cycle.
III. OBJECT SENSING
As described above, the scanning means is operative
to rapidly and repetitively scan the target symbol. For
proper operation, it is necessary to distinguish between
whether many scans have been performed for one object, or
- 37 -
~ 17~103
whether one scan has been performed for many objects. l~e
capability of sensing each object to be scanned in its turn
is critical for successful decoding.
Trigger means 60 (see FIGS. 1 and 10) is operative
for actuating the scanning means 68, 70 to repetitively
sweep the bar code symbol a number of times each time the
trigger means 60 is actuated. Trigger means 60 is preferably
a manually-depressable switch mounted on the housing in the
vicinity of the interconnection of the barrel and handle
portions of the housing. The trigger switch 60 is located
on the handle portion such that the forefinger of the user's
hand can be used to manually depress the switch. Each time
the switch is depressed, the scanning means sweeps the
symbol many times, on the order of two hundred times.
When the decode circuitry 102 successfully decodes
the symbol, which may occur on the first scan or at any scan
up to and including the two hundredth scan, the decode
circuitry generates a successful decode signal and conducts
the latter through a conductor in the cable 58 to actuate
the indicator means located in the head. The indicator
means comprises an auditory-type beeper 98 and/or a light-
emitting diode 99. When the beeper 98 sounds and/or when
the diode 99 lights up, then the user knows that the scan-
ning for that particular symbol has been terminated. The
actuation of the switch 60 and the actuation of the indicator
means are definable events which advises the laser scanning
system when scanning begins and ends. The trigger 60 may
be released either before or after actuation of the indicator
means.
When scanning ends, upon indication of the indicator
means, the mechanical shutter circuitry 150 moves the output
- 38 -
1 ~731~0~
shafts to their shutter positions, thereby preventing further
laser beam transmission out through the outlet port. The
laser tube 24 is not shut off at this time, only the scanning
motor is shut down. This not only represents a safety
feature, but also lengthens the working-lifetime of the
laser tube and of the scanning motors.
Actuation of the trigger means 60 concomitantly
turns the laser tube 24 on, provided that the laser tube
was previously shut-down. Moreover, actuation of the
10 trigger means 60 simultaneously turns timer means 152 on.
The timer means 152 remains operative for a predetermined
time period, on the order of five minutes. If the trigger
switch 60 is not actuated during the five minute timing
period, then the laser tube is automatically shut down by
sending a control signal to the control terminal 56 of the
power supply component 50. This conserves power. If the
trigger switch is pulled during the timing period~ then
the timing period is reactivated, and the laser tube has
another five minutes to wait before it is automatically
shut-down in the event that the trigger switch is not
depressed again in the next five minutes. Another light-
emitting diode 97 (see FIG. 1) is mounted on the head to
indicate the on-off status of the laser at all times.
- 38a -
~ ~731D3
As noted above, each actuation of the trigger means 60
initiates a plurality of scans until the decode cireuitry has de- ¦
termined that a successful decode measurement has taken place, atj
which time a successful decode signal is conducted to either the
beeper 98 and/or the light-emitting diode 99. The sound and/or
the light indication advises the user that the repetitive scannina
has been terminated, and that another symbol can now be scanned.
The repetitive scanning for each object results in high-
er reliability as compared to the prior art readers and scanners
lO , where only one manual or automatic scan is performed. In some
instances, the printing of the symbol on the product is poor in
terms of the contrast of the color of the lines of the symbol as
compared to the color of the spaces of the symbol. In these
eases, the probability of getting a successful decode on any
given scan attempt for a given object (i.e., percenL decode) is
very low, and thus poor printing also contributes to low reliabil-
ity.
It can be shown that the probability of getting at least ~
one deeode after N scans is determined by Lhe following e~uation: ¦
~O P = 1 - (1 - P.D.)
wherein P = probability of getting at least one success-
ful decode after N scans (%);
N = Number of scans per attempt; and
P.D.= Percent decode, i.e. the probability of
getting a successful decode on any given scan
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If we assume that the percent decode Oc a given symbol is
~ about 10~ because of its poor printing, and that the laser scann-
I ing system of this invention performs about 200 scans a second,
¦I then:
P = 1 ~ .10)200
= 1 - ( 9)200
. = 1 - (~0)
= 1 or 100~ probability of success
' By contrast, for prior art readers and scanners which only scan
10 ' once for an object, then:
P = 1 - ~1 - . 10)
, = 1 - ( 9)
= .1 or 10% probability of success.
The virtual certainty (100%) of getting a successful de- ;
code using repetitive scanning even for poorlv printed symbols
which have only a 1 in 10 chance of being successfully decoded; as
compared to the very lo~ certainty (10%) for the prior art devices
illustrates the high reliability of our invention.
, In the event that no successful decode measurement has
been made, then the trigger means is operative to terminate the re
petitive scanning upon elapse of a ~redetermined time period as
measureA from actuation of the trigger. The predetermined time
period, typically on the order of three seconds, is selected to
provide the user with sufficient time to sisht the object.
Scanning will also be automatically ter~inated i' the
trigger is released before the aforementioned three second time
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¦ period has lapsed and before a successful decode measurement has
been obtained.
. Another or the same visual and/or auditory indicator
can be used to indicate that the scanner system has not success-
fully dccoded the symbol. to be xead.
', I
;
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IV. LASER DIODE SCANNE~
The means for generating a laser beam need not be the
laser tube 24, as described above, but may be a semiconductor
laser diode 200, as shown in FIG. 12. The laser diode may be of
the continuous wave-or ?ulse-type. Such laser diodes are commer-
cially available from many sources, such as the General Optronics I
Corporation, Laser Diode, Inc., and OPtical Information Systems, Inc~ ¦
¦ The laser diode 200 is mounted in the head 10. In one
l preferred mounting arrangement, the diode 200 is mounted on a heat
~ sink 202 which is threadedly mounted to the head 10. The diode
200 is much smaller in size and lighter in weight as com~ared to
the laser tube 24. Hence, the use of a laser diode is particular-
ly desirable for applications where weight requirements, on the
order of less than one pound, and size requirments, on the order
of less than fifty cubic inches, are to be kept to a bare minimum.'
Moreover, in contrast to the laser tube 24 which requires
a high voltage (i.e. 650v DC) power supply and a low voltage (i.e.
12v DC) power supply, the laser diode 200 only requires a low
voltage (i.e. 12v DC) power supply. The elimination of the high
voltage power supply 50 conserves even more space and weight.
The laser diode 200 is formed with a generally rectangu- !
lar cavity or laser-emitting aperture 204 which measures about
one micron x ten microns. The emitted laser beam diverges outward-
ly from the aperture 204 and has an asymmetrical angular splay
which measures about 10-20 x 40-50. The lens system 206 is
. ' '' . i
~ 173lO3
designed with a numerical aperture on the order of 0.25, a net
magnification from about lOX to about 15X, and an f number on
the order of about f/2~ The scanning means and signal pro-
cessing means have been omitted from FIG. 12 for the sake of
clarity.
Due to the rectangular exit aperture 204, the axial
cross-section of the beam spot is likewise generally rectangu-
lar or oval in shape. The elongated beam spot at the reference
plane is on the order of 6 mils X 1 mil. The longer dimension
of the elongated spot is aligned along the height of the symbo
to be scanned. The shorter dimension of the elongated spot
is aligned along the length of the symbol to be scanned.
Scanning with a rectangular or oval beam spot is more
desirable than scanning with a circular beam spot, because the
elongated spot generates electrical signals having more abrupt
amplitude changes as the elongated spot moves across a dark-
light transition on the symbol. When an elongated spot is
juxtaposed with a dark line on the symbol, variations in line
width over the entire height of the line are averaged out.
When the elongated spot thereupon moves into the next space,
the transition is more abrupt for an elongated spot as com-
pared to a circular spot. This greater resolution capability
reduces decoding errors, particularly for symbols where the
contrast between the printed lines and spaces is poor.
The lens system 206 is designed to allow for a small
angular tilt of about 10 to about 15 in the alignment of the
elongated spot relative to the lines of the symbol.
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~ ~173103
. ~ ~
V. PEI~TA-BIMORPH SC~ t~ING ELEMEll~T
~ urning now to FIG. 15, a penta-bimorph scanning element !
is generally identifie~ bS~ reference numeral 250. The penta-bi-
morph 250 is a miniature, high-speed scanning element which can re-
place either the X-axis scanning element 6~, or the Y-axis scann- !
ing element 70, or both.
The penta-bimorph 250 comprises a pair of bimorphs 252, i
254 which are ferro-electric-type oscillating elements which re-
ciprocall~y oscillate when voltages are applied thereto. At their
~ lower ends, the bimorphs are mounted on a grounded sup?ort struc-
ture 256. At their upper ends, light-reflecting mirrors 262,264
are mounted on the bimorphs such that they include a 45 angle
between their reflecting surfaces. Wedge-shaped blocks 258,260
are mounted between the mirrors and the bimorphs to properly posi-,
tion the mirrors at the aforementioned angle.
Before describing the drive circuitry, it should be noted
that the incoming light beam Li and the outgoing light beam Lo
include a right angle therebetween. The incoming beam impinges
on mirror 264, thereupon is reflected to mirror 262, and then is
reflected at a 90~ angle relative to the incoming beam. More
importantly, as described below, even if the entire penta-bimorph
is subjec-ted to mechanical shock, the ri~ht angle relationship
between the incoming and outgoing beams is maintained throughout
the scanning movement.
The bimorphs 252,254 are driven in a manner resembling
the movement of the tines of a tuning fork. For exam~le, a vol-
tage is applied to bimorph 252 to drive the same in an oscillatorv
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, I
~ ~73~03
manner in the direction of the double headed arrow. Re-
generative feedback is provided to drive the other bimorph
254. An operational amplifier 266 has its positive input
terminal connected to the sensing bimorph 254. The negative
terminal is connected through a capacitor 268 to the wiper
arm of a gain-adjust potentiometer 270. The amplifier output
is connected to the driven bimorph 252.
The drive circuitry is operative to oscillate the
two bimorphs in anti-phase relationship. In other words, the
two bimorphs either simultaneously move towards each other,
or simultaneously move apart of each other.
Throughout the entire oscillating scanning movement,
the incoming and outgoing beams always define a right angle
therebetween. This is analogous to the penta-prism effect,
wherein the beam exiting from one face always defines a 90
angle with the beam entering from another face. The establish-
ment of a constant angular relationship between the incoming
and outgoing beams is advantageous in making the penta-
bimorph scanning element 250 insensitive to vibration- or
shock-effects. Even if the housing in which the penta-
bimorph is mounted is subjected to undesirable mechanical
forces, the scanning will not be effected, because the
effects of the mechanical forces are completely cancelled.
Moreover, the penta-bimorph is self-compensating due to
temperature, because both bimorphs will be affected in
the same manner.
By adjusting the gain-adjust control of the
potentiometer to a value just over the threshold for
oscillation, the penta-bi-
~173103
morph should closely approach a harmonic oscillator. I
~ 50reover, the penta-bimorph greatly amplifies the scanning
movement. The mirror 264 doubles the ampli,fication; the mirror
2S~ doubles the amplification again; and the anti-phase movement
of the two mirrors doubles the amplification still again. The
outgoing beam scans over a rela,ively long range as com~ared to
the range over which the incoming beam is moved. '~
. .,
.~ , ,i
~ 173103
lll
It will be understood that each of the elements described
above, or two or more to~ether, may also find a useful application
in other types of constructions differing from the types described
above.
l~hile the invention has been illustrated and described as- em-
bodiec in.a portable~laser scanning system and scanning methods, it is
not intended to h~. limited to the details shown, since various
modifications and structural changes may be made without departing
in any way from the spirit of the present invention.
Without further analysis, the foregoins will so fully reveal
the gist of the present invention that others can by applying
current knowledge readily adapt it for various applications with-
out omitting features that, fro~ the standpoint of prior art,
fairly constitute essential characteristics o' the generic or
specific aspects of this invention and, therefore, such adaptati~ns
should and are intended to be comprehended within the meaning and
range of equivalence of the following claims.
What is claimed as new and desired to be protected bv Letters
Patent is set forth in the appended claims.
This application is a divisional of application Serial No.
371,938, filed February 27, 1981.
