Bar code symbol readers with variable spot size and/or working distance

Systems for changing the working distance and/or the beam spot size of an outgoing laser beam scanned across symbols to be read by a bar code symbol reader use different optical assemblies, or a single optical assembly having changeable light-transmissive portions of a plate, or changeable pupils, or a movable laser light source.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention generally relates to laser scanning systems for reading bar 
code symbols and, more particularly, to various optical systems for 
changing the working distance and/or the reading spot size of an outgoing 
laser beam scanned across the symbols to be read. This invention also 
relates to systems for turning oval-shaped outgoing laser beams. 
2. Description of the Related Art 
Laser scanning systems and components of the type exemplified by U.S. Pat. 
Nos. 4,251,798; 4,360,798; 4,369,361; 4,387,297; 4,593,186; 4,496,831; 
4,409,470; 4,673,805; 4,758,717; 4,760,248; 4,736,095; 4,460,120 and 
4,607,156--all of said patents being owned by the assignee of the instant 
invention and being incorporated by reference herein--have generally been 
designed to read bar code symbols, particularly of the Universal Product 
Code (UPC) type, at a certain working or reading distance from a hand-held 
or stationary scanner, and with a reading spot of a certain size. The 
particular spot size and working distance are typically optimized in 
dependence upon the particular application and, in effect, the system 
tends to be custom-made for each intended use. 
For example, UPC symbols are typically affixed on objects in at least three 
different densities or sizes, depending to a great extent on the size of 
the object itself. So-called "high-density" (HI-D) symbols are typically 
characterized by very thin bars separated by very thin spaces and, hence, 
are typically affixed to small objects. So-called "low-density" (LO-D) 
symbols are generally characterized by very broad bars separated by very 
broad spaces and, hence, are typically affixed to large objects. So-called 
"medium-density" (MED-D) symbols are generally characterized by bars and 
spaces whose respective widths along the scanning direction lie somewhere 
between those of HI-D and LO-D symbols, and are affixed to medium-sized 
objects. The definitions of HI-D, LO-D and MED-D symbols in terms of 
numerical values may be different for different applications, bu for any 
one particular application, e.g. the inventorying and check-out of 
supermarket goods, these relative definitions and their numerical values 
are readily understood by those skilled in the art. 
To read HI-D symbols with accuracy, a very fine reading spot, e.g. a six 
mil diameter circular spot, is desired. The known optical systems for 
forming such a very fine spot produce a very highly divergent laser beam 
and, as a result, the working distance is correspondingly very short. To 
read LO-D symbols with accuracy, a very large reading spot, e.g. a forty 
mil diameter circular spot, is desired. The known optical systems for 
forming such a very large spot produce a laser beam with very low 
divergence and, as a result, the working distance is correspondingly very 
long. 
Hence, it will be appreciated that no single known laser scanning system 
can read both LO-D and HI-D symbols, because the known optical systems 
designed to read LO-D symbols cannot read HI-D symbols, and vice versa. An 
optical system designed to read LO-D symbols will have a very long working 
distance--which is very desirable to read close-in and far-out 
symbols--but the very large spot size will simultaneously overlap at least 
one bar and its adjacent space, thereby obscuring a HI-D symbol. On the 
other hand, an optical system designed to read HI-D symbols has a very 
short working distance which is very disadvantageous to read far-out 
symbols. It would be desirable to combine the very long working distance 
characteristic of LO-D reading systems with the very fine spot size 
characteristic of HI-D reading systems in a single instrument. 
SUMMARY OF THE INVENTION 
1. Objects of the Invention 
It is a general object of this invention to advance the state of the art of 
laser scanning systems for reading bar code symbols. 
It is another object to combine the best features of HI-D and LO-D reading 
systems in a single instrument. 
Another object of the invention is to provide a hand-held scanner having 
the capability of reading both LO-D symbols and HI-D symbols. 
An additional object of the invention is to read either LO-D symbols alone, 
or HI-D symbols alone, at an increased range of working distance. 
A further object of the invention is to read far-out LO-D symbols with a 
larger reading spot, and to read close-in HI-D symbols with a smaller 
reading spot, with the same instrument. 
Yet another object of the invention is to change the reading spot size 
and/or the working distance of an outgoing laser beam during scanning, and 
preferably during each scan of a symbol, or after each scan. 
Still another object of the invention is to simultaneously change the 
reading spot size and/or the working distance of an outgoing laser beam 
during scanning. 
2. Features of the Invention 
In keeping with these objects, and others which will become apparent 
hereinafter, one feature of this invention resides, briefly stated, in an 
optical arrangement for use in a laser scanning system for reading 
symbols, particularly bar code symbols having alternate bars and spaces 
arranged in a pattern which, when decoded, identify an object on which the 
symbol is affixed. The scanning system comprises a housing having an exit 
port, a laser source, e.g. a gas laser tube or a semiconductor laser 
diode, for generating a laser beam, and scanning means in the housing for 
scanning the laser beam in scans across successive symbols located 
exteriorly of the housing. The optical arrangement comprises optical means 
in the housing for directing the scanning beam along an optical path 
through the exit port, and for optically forming the scanning beam with a 
cross-sectional beam spot of a predetermined waist size and at a 
predetermined distance from the exit port of the housing. 
In accordance with one feature of this invention, the optical means 
includes means for changing the predetermined waist size of the beam spot 
during scanning. This feature enables the scanning system to read LO-D and 
HI-D symbols. It is further advantageous if the changing means is 
operative for changing the predetermined distance of the beam spot during 
scanning, and preferably simultaneously with the changing of the waist 
size. This so-called "zoom" feature enables the scanning system to read 
close-in and far-out symbols. 
In a first advantageous embodiment of the optical arrangement, the optical 
means includes a first optical sub-assembly for directing the scanning 
beam through the exit port during a part of each scan, and for optically 
forming the scanning beam with a beam spot of a predetermined first waist 
size and at a predetermined first distance, as well as a second optical 
assembly which directs the scanning beam through the exit port during 
another part of each scan and optically forms the scanning beam with a 
beam spot of a predetermined second waist size and at a predetermined 
second distance from the exit port. 
In one modification of this invention, the first and second optical 
sub-assemblies form their respective beam spots of the same waist size bu 
at different predetermined distances. This feature increases the range at 
which symbols of the same predetermined density can be read. Thus, LO-D 
symbols can be read with a large spot size both close-in and far-out from 
the housing. Similarly, HI-D symbols can be read with a fine spot size for 
both close-in and far-out symbols. Thus, the invention has an increased 
working distance range. 
In another modification, the first and second optical sub-assemblies form 
their respective beam spots of different predetermined waist sizes and at 
different predetermined distances. This feature advantageously enables the 
system to read symbols of one density to be read at close range and 
symbols of another density to be read at far range. For example, LO-D 
symbols having a larger spot size can be read at far range, while HI-D 
symbols having a finer spot size can be read at close range--all in the 
same instrument without sacrificing reading accuracy for either HI-D or 
LO-D symbols. In effect, the best features of optical spot forming systems 
for both HI-D and LO-D symbols have been integrated in the same 
instrument. 
Another advantageous feature in connection with the use of two optical 
sub-assemblies is related to automatic gain control. Close-in symbols, due 
to their proximity to the scanner, have a higher signal-to-noise ratio 
than far-out symbols. It would be advantageous to reduce the amplitude of 
laser light reflected off close-in symbols for detection by photosensor 
means in the housing while, at the same time, increasing the amplitude of 
the laser light reflected from far-out symbols. This may advantageously be 
accomplished by the use of a common beam splitter shared by both 
sub-assemblies. The beam splitter may be designed to send a larger 
fraction of the laser beam emitted by the laser source to one optical 
assembly, and a smaller fraction to the other optical sub-assembly. Thus, 
the optical assembly which is to be used for forming a beam spot at a 
relatively further distance from the exit port will be provided with the 
higher fraction of the laser beam. 
Another optical arrangement for changing the waist size of the beam spot 
and/or the working distance thereof comprises the use of a focusing means 
having a high magnification factor, e.g. on the order of twenty, an 
entrance pupil, and a light-transmissive plate having plate portions of 
different optical distance characteristics. The changing means is 
operative for moving the plate between a close position in which one plate 
portion is positioned adjacent the entrance pupil to enable close-in 
symbols to be read, and a far position in which another plate portion is 
positioned adjacent the entrance pupil to enable far-out symbols to be 
read. The different optical distance characteristics move the beam spot 
through a working distance which is proportional to the square of the 
magnification factor. 
In another modification, the changing means is operative for changing the 
size of the pupil which, in turn, changes the waist size of the beam spot. 
The change of the working distance and the change of the beam spot waist 
size can be independently controlled, or can be simultaneously controlled 
by the use of a single optical component. 
In still another optical arrangement of this invention, which is of 
particular benefit when the laser source is embodied by a diode, the 
change in working distance may advantageously be effected by moving the 
diode in a reciprocal manner upstream and downstream of the optical path 
along which the outgoing laser beam is directed. An 
electrically-controlled position transducer is mounted in the housing, and 
the laser diode is mounted on the transducer. A high magnification factor 
focusing means is mounted downstream of the diode. When the diode is moved 
back and forth over a small distance, this motion is translated by the 
square of the magnification factor to generate a zoom-acting system in 
which the working distance is continuously increased and decreased. 
Yet another way of changing the waist size of the beam spot is to use an 
electrical circuit operative for changing the waist size of the spot by 
changing the electrical characteristics of the electrical circuit which 
senses the light of variable intensity reflected from the symbols to be 
read, and which processes the sensed light into data descriptive of the 
symbols. 
The beam spot of the laser beam emitted by a gas laser generally has a 
circular cross-section, whereas, by contrast, the cross-section of the 
beam spot of the laser beam emitted by a laser diode is generally 
non-circular and, in fact, is oval in shape. In this case, it will be 
recognized that: the oval spot has a longer and a shorter waist dimension 
in two mutually perpendicular directions. This can be used to advantage to 
read both HI-D and LO-D symbols by turning the scanning beam between a low 
density and a high density orientation. In the low density orientation, 
the longer waist dimension of the spot is positioned to extend along the 
scanning direction and is used for reading LO-D symbols since the spot has 
an "effective" larger size. In the high density orientation, the shorter 
waist dimension of the spot extends along the scanning direction for 
reading HI-D symbols since the spot has an "effective" smaller size. The 
turning of the scanning beam may advantageously be combined with means for 
changing the working distance of the beam spot during scanning so that the 
beam spot can be not only turned, but also zoomed. 
The novel features which are considered as characteristic of the invention 
are set forth in particular in the appended claims. The invention itself, 
however, both as to its construction and its method of operation, together 
with additional objects and advantages thereof, best will be understood 
from the following description of specific embodiments when read in 
connection with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings, reference numeral 10 in FIGS. 1A and 1B 
generally identifies an optical arrangement in a laser scanning system of 
the type generally described in the above-identified patents, the entire 
contents of all of which are hereby incorporated by reference herein, for 
reading symbols, particularly UPC bar code symbols. As used in this 
specification and the following claims, the term "symbol" is intended to 
be broadly construed and to cover not only symbol patterns composed of 
alternating bars and spaces, but also other patterns, as well as 
alpha-numeric characters. 
The arrangement 10 includes a housing 12, shown in broken-away view, and 
intended to represent either hand-held, desk-top workstation, or 
stationary scanner, housings having an exit port 14 through which an 
outgoing laser light beam is directed to impinge on, and to be scanned 
across, symbols located exteriorly of the housing, each symbol to be 
scanned and read in its respective turn. A laser source, e.g. a gas laser 
tube 16 or a semiconductor laser diode, is mounted in the housing and, 
when energized, the source 16 generates a laser beam. 
The arrangement 10 also includes a transmitter means, e.g. a beam splitter 
18 operative for transmitting a first fractional magnitude of the laser 
beam emitted by source 16 through the splitter and to a first assembly 20, 
and for transmitting a second fractional magnitude of the laser beam 
emitted by source 16 by reflection from the splitter and to a second 
optical assembly 22. For ease of understanding the drawings, the first 
fractional magnitude has been designated by reference character L1, and 
its optical path is shown by single-headed arrows. The second fractional 
magnitude has been designated by reference character L2, and its optical 
path is shown by twin-headed arrows. Although the fractional magnitudes 
could be equal to one-half each, there are circumstances, as explained 
below, in which the fractional amplitudes could and will be different. 
Each optical assembly 20, 22 includes a beam expanding negative lens 20a, 
22a, respectively, and an objective positive lens 20b, 22b, respectively. 
The optical assemblies are operative to optically modify the fractional 
beams L1, L2 to be focused at predetermined working or reading distances 
Z1, Z2, respectively, outside the housing, and with reading beam spots, 
preferably, but not necessarily, of circular cross-section, having 
predetermined waist sizes w1, w2, respectively. 
Folding mirror 24 directs the fractional beam L2 reflected from the 
splitter 18 to the second optical assembly 22. Additional folding mirrors 
26, 28 direct the L1, L2 beams, after respective passage through 
assemblies 20, 22, to a scanning mirror 30 for reflection therefrom. As 
described in detail in U.S. Pat. No. 4,496,831, the scanning mirror 30 is 
mounted on an output shaft 32 of a scanning motor which is operative to 
reciprocally turn the scanning mirror 30 in opposite circumferential 
directions, as indicated by curved twin-headed arrow 34, through a limited 
angular extent in order to direct any laser beam impinging thereon to be 
reflected therefrom and moved along repetitive linear sweeps. In a 
preferred embodiment, as many as forty linear sweeps per second may be 
generated. 
The reflected beams L1, L2 reflected off the scanning mirror 30 may or may 
not be directed through the exit port 14 and, in fact, in the preferred 
embodiment, the beams L1, L2 take turns exiting the housing during each 
scan. Thus, as shown in FIG. 1, during a part of each scan, after beam L1 
has passed through optical assembly 20 and reflected off folding mirror 
26, the scanning mirror 30 directs beam L1 out through the exit port 14 
where the beam L1 is focused with a spot size w1 at a distance Z1 from the 
housing. At the same time, the beam L2 is directed by the scanning mirror 
30 into the interior of the housing where the beam L2 is permitted to 
harmlessly "bounce around". 
As shown in FIG. 2, during another part of each scan, after beam L2 has 
passed through optical assembly 22 and reflected off folding mirror 28, 
the scanning mirror 30 directs beam L2 out through the exit port where the 
beam L2 is focused with spot size w2 at a distance Z2 from the housing. At 
the same time, the beam L1 is directed by the scanning mirror 30 into the 
interior of the housing where it is allowed to harmlessly "bounce around". 
It will thus be seen that during each sweep of the scanning mirror, both 
beams L1 and L2 exit the housing, albeit at different times. 
In the event that a symbol is located at such predetermined distances Z1 or 
Z2, or anywhere within the respective depth of fields DOF1, DOF2 of the 
beams L1, L2, then the respective beam will repetitively sweep across the 
symbol until the system successfully decodes the symbol. Although the 
cross-sectional size of the beam spot varies within the depth of field, 
the symbol can nevertheless be successfully decoded and read so long as it 
is located within the respective depth of field. 
In accordance with this invention, provision of an auxiliary optical 
assembly and a beam splitter shared by the two optical assemblies enables 
the system to be designed to be much more versatile than heretofore. For 
example, the first and second optical assemblies 20, 22 may be designed to 
form their respective beam spots with the same waist size, i.e. w1=w2, but 
at different distances, e.g. Z1&gt;Z2. By way of non-limiting numerical 
example, assembly 22 can be designed as described in U.S. Pat. No. 
4,409,470 to have a fine spot size w2=6 mils suitable for reading HI-D 
symbols, at a working distance Z2 equal to 3.5", and a DOF2 ranging from 
1" up to 5" relative to the exit port 14 of the housing; the other optical 
assembly 20 can be designed to have the same spot size w2 equal to 6 mils, 
but at a working distance Z1 of 7.5" and a DOF1 which ranges from 4" up to 
11". In this example, a HI-D scanning system has been provided which can 
read symbols anywhere from 1" up to 11" --a much more increased range than 
if an auxiliary optical assembly were not employed. It is not necessary 
that DOF1 and DOF2 overlap each other. Indeed, in some applications, it 
may be desired that they do not so overlap. It does not matter to the 
system whether the symbol is read by the L1 or L2 beam. The system itself 
detects when a successful decode has occurred. 
By the same analysis, both optical assemblies 20, 22 can be designed to 
form spot sizes on the order of 40 mils and at different distances from 
the housing, for reading LO-D symbols at an increased range by employing 
the L1 beam to read symbols at close range and the L2 beam for reading 
symbols at far range. Again, there need not be any overlap between the 
depth of fields of the beams. 
In another variation, the optical assemblies could also be designed to form 
beam spots of different waist sizes, at different or at the same 
predetermined distances. In many applications, it typically happens that 
LO-D symbols which are affixed to large objects are generally located far 
from the housing and, concomitantly, HI-D symbols which are affixed to 
smaller objects are generally located closer to the housing. In such 
event, optical assembly 20 can form beam L1 with a large beam spot, e.g. 
on the order of 40 mils, at a far distance, e.g. 6', and optical assembly 
22 can form beam L2 with a small beam spot, e.g. on the order of 6 mils, 
at a close distance, e.g. 31/2" relative to the housing. This latter 
system has the best of both worlds in that the optical system 20 can read 
far-out LO-D symbols with accuracy and, at the same time, the same system 
can read close-in HI-D symbols, all without sacrificing reading accuracies 
or being disadvantaged with short working distances. 
As noted above, the beam splitter 18 need not divide the beam issuing from 
the laser source 16 in equal amounts, and can be used to obtain at least 
some measure of power equalization. Thus, it is known that the laser light 
reflected off the symbol is detected by photosensor means operative for 
generating an electrical signal proportional to the magnitude of the 
reflected light. The electrical signal is thereupon processed by 
electronic circuitry to obtain data descriptive of the symbol. The closer 
the symbol is to the photosensor means, the higher the magnitude of the 
reflected laser light, and the larger the amplitude of the electrical 
signal generated by the photosensor means and presented to the electronic 
processing circuitry. In certain cases, the amplitude variation of said 
electrical signal can vary as much as 1000:1 (60 dB) between close-in and 
far-out symbols. Hence, it would be desirable to increase the electrical 
signal amplitude associated with far-out symbols and/or decrease the 
electrical signal amplitude of close-in symbols and, for that purpose, the 
beam splitter can be designed to send more than 50% of the beam issuing 
from the laser source 16 to the optical assembly responsible for reading 
far-out symbols. Thus, because the system needs more power to detect 
far-out symbols, the optical coatings on the beam splitter can be so 
designed as to direct more than 50%, e.g. 75%, of the light entering the 
splitter to the optical assembly 20 responsible for reading far-out 
symbols. The remaining 25% of the laser beam, of course, is directed to 
the other optical assembly because all that power is simply not needed for 
reading close-in symbols. 
As discussed above, fine beam spots of generally circular cross-section are 
most suitable for reading HI-D symbols, whereas, large circular beam spots 
are most suitable for reading LO-D symbols. Since a single optical 
assembly will focus a gas laser beam to a circular beam spot of a certain 
diameter within a certain depth of field, the single optical assembly of 
the prior art cannot simultaneously satisfy the requirement to read HI-D 
and LO-D symbols with a single instrument. The invention, as shown by 
optical arrangement 40 of FIGS. 2-5, proposes to satisfy this requirement 
by making use of a non-circular beam spot having a longer and a shorter 
waist dimension in two mutually perpendicular directions. When a symbol is 
being scanned in a linear sweep over its length along a scanning direction 
by a beam spot, it is the waist dimension of the beam spot, as considered 
along the scanning direction, which determines whether the beam spot is to 
be considered fine or large, which, in turn, determines whether the spot 
will successfully read the particular density of the symbol being scanned. 
Hence, in the case of a non-circular beam spot, which can be elliptical, 
rectangular, oval or the like, in cross-section, the optical arrangement 
40 proposes to orient the longer waist dimension along the scanning 
direction to read LO-D symbols, and to orient the shorter waist dimension 
along the scanning direction to read HI-D symbols. Since it may not be 
known whether the next symbol to be read is of low density or high 
density, the arrangement 40, in an advantageous embodiment, alternately 
orients the longer, and then the shorter, waist dimension along the 
scanning direction. Preferably, this alternate orientation will occur 
during each scan and, more preferably, more than once during each scan. At 
the same time, as explained below, the optical arrangement 40 changes the 
predetermined working distance at least more than once during each scan. 
In order to obtain a non-circular spot, the diffraction optics theory of 
spot formation can be utilized, wherein a diaphragm 42 having a 
non-circular aperture or exit pupil 44 can be positioned in the path of a 
laser beam having a circular cross-section, i.e. a gas laser tube. 
According to diffraction theory, the spot size is proportional to the 
focal number of the optical system, which, in turn, equals the ratio of 
the image distance (Z) of the spot to the size of the pupil 44. Hence, the 
larger the open dimension of the pupil 44, the smaller the waist dimension 
of the beam spot at the focal plane, and vice versa. Thus, by varying the 
dimensions of the pupil 44, the degree of non-circularity of the beam spot 
can be controlled. 
Another way of obtaining a non-circular spot is to make use of the 
diffraction property of the laser diode 46 itself which has different 
sizes of emitting area in two mutually perpendicular directions, as a 
result of which, the focused beam spot already has a non-circular 
cross-section without having to use a non-circular exit pupil on an 
external diaphragm. Nevertheless, to obtain more precise control over the 
non-circularity of the laser diode beam, it is recommended that an 
external diaphragm having a non-circular exit pupil be mounted in the path 
of the laser diode beam. 
In order to orient the non-circular beam with either its longer or its 
shorter waist dimension along the scanning direction, the diaphragm 42 can 
be rotated, and/or a rotary mirror 50, as shown in FIGS. 2-5, can be 
located in the optical path of the non-circular beam and rotated. The 
mirror 50 is mounted at a tilt angle .alpha. on a vertical shaft 48 for 
joint rotation therewith about the vertical axis along which the shaft 48 
extends. Preferably, the tilt angle is on the order of 45.degree.. 
As shown in an initial stage illustrated in FIG. 2, the laser diode beam 
emitted from diode 46 passes through exit pupil 44 having longer dimension 
A1-A2 and shorter dimension B1-B2 and, thereupon, impinges upon rotary 
mirror 50 with a cross-sectional beam spot thereon having dimensions 
A1'-A2' and B1'-B2', respectively. The beam is then reflected forwardly 
through the exit port 14 on housing 12 to impinge on a LO-D symbol 52 
located exteriorly of the housing. The beam spot focused on symbol 52 has 
a longer waist dimension B1"-B2" along the scanning direction, as 
indicated by arrows 54, and a shorter waist dimension A1"-A2". In this 
initial stage, the longer waist dimension is oriented along the scanning 
direction so that the beam has an "effective" larger spot size adapted to 
read LO-D symbols. 
As shown in a partially rotated stage illustrated in FIG. 3, the mirror 50 
has been rotated 90.degree. about the vertical axis as compared to the 
initial stage of FIG. 2. As before, the laser diode beam impinges on 
mirror 50 with a cross-sectional spot having dimensions A1'-A2' and 
B1'-B2'. The beam is then reflected off to one side to inclined side 
mirror 56 which is oriented to reflect the beam forwardly through the exit 
port 14. The beam on side mirror 56 has dimensions A1"-A2" and B1"-B2", 
and the resulting beam spot focused on a HI-D symbol 58 has a longer waist 
dimension B1'"-B2'" and a shorter waist dimension A1'"-A2'", the latter 
being oriented along the scanning direction, as indicated by arrows 60. In 
this 90.degree. rotated stage, the beam has an "effective" fine spot size 
more suited to read HI-D symbols. 
As shown in a further rotated stage, illustrated in FIG. 4, the mirror 50 
has been rotated 180.degree. about the vertical axis relative to the 
aforementioned initial stage. The laser beam passing through pupil 44 
impinges on mirror 50 with a cross-sectional spot having dimensions 
A1'-A2' and B1'-B2'. Thereupon, the laser beam is reflected rearwardly to 
inclined top mirror 62 where the beam spot has dimensions A1"-A2" and 
B1"-B2". The top mirror 62 reflects the laser beam downwardly toward 
inclined bottom mirror 64 upon which the laser beam has dimensions 
A1'"-A2'" and B1'"-B2'". The bottom mirror is arranged to forwardly 
reflect the beam through the exit port 14 of the housing to impinge on a 
non-illustrated LO-D symbol analogous to symbol 52. The beam spot focused 
on such symbol has a longer waist dimension B1.sup.IV -B2.sup.IV along the 
scanning direction, as indicated by arrows 66, and a shorter waist 
dimension A1.sup.IV -A2.sup.IV. In this further rotated stage, the longer 
waist dimension B1.sup.IV -B2.sup.IV is more suited to read LO-D symbols. 
A further 90.degree. rotation of the rotary mirror 50 from the stage 
illustrated in FIG. 4 has not been separately illustrated, but is 
completely analogous to the stage shown in FIG. 3, except that the beam 
reflected off mirror 50 is not reflected toward inclined side mirror 56, 
but, instead, is reflected to inclined side mirror 68. As before, the 
laser beam reflected off side mirror 68 is directed forwardly through the 
exit port 14 and results in a focused beam spot at the symbol whose 
shorter waist dimension is oriented along the scanning direction for the 
purpose of reading HI-D symbols. 
Turning now to FIG. 5, the optical arrangement 40 is shown in top plan 
view. Quite apart from the turning of the laser beam to read HI-D or LO-D 
symbols during each rotation of the rotary mirror 50, the arrangement also 
simultaneously focuses the beam spot at different distances from the 
housing and, thus, performs a zooming function. The outgoing beam which is 
reflected forwardly solely by mirror 50 in the initial stage of FIG. 2 
extends along a path denoted by a single-headed arrow, and is focused on 
LO-D symbol 52 located at a far-out distance Z3 from the housing. The 
outgoing beam which is reflected forwardly by mirror 50 and side mirror 56 
extends along a path denoted by twin-headed arrows, and is focused on HI-D 
symbol 58 at an intermediate distance Z4 from the housing. The outgoing 
beam which is reflected forwardly by mirror 50, top mirror 62 and bottom 
mirror 64 extends along a path denoted by triple-headed arrows, and is 
focused on a LO-D symbol 52' at a close-in distance Z5 from the housing. 
The outgoing beam which is reflected forwardly by mirror 50 and side 
mirror 68 extends along a path denoted by quadruple-headed arrows, and is 
focused on a HI-D symbol 58' located at an intermediate distance Z6 from 
the housing. It will be appreciated that the total length of the various 
optical paths from the mirror to the focal plane at which the focused beam 
spot intercepts the symbol is the same in all cases. The different 
distances of the focal plane relative to the housing is due to the 
diversion of the beam to either side mirror 56 or 58, or to both top and 
bottom mirrors 62, 64. Hence, during each rotation of mirror 50, four 
sweeps of the symbol are performed: a far-out and a close-in sweep of LO-D 
symbols, and two intermediate range sweeps of HI-D symbols. Other 
variations are, of course, possible. 
Turning now to FIGS. 6A and 6B, optical arrangement 70 is operative for 
adjusting the working distance between distances Z7 and Z8 and/or for 
adjusting the waist dimension of the beam spot along the scanning 
direction. A laser source is positioned at site S1. A light-transmissive 
rotary plate 72 has a first plate portion 74 of small thickness T1, and a 
second plate portion 76 of larger thickness T2. Plate 72 is rotatable 
about axis 73 which is offset from and parallel to optical axis 78. Each 
plate portion is preferably made of glass and has a different optical 
distance characteristic which is the product of the respective index of 
refraction (n) and the thickness of the respective plate portion. Either 
plate portion 74 or 76 is located downstream of the source. A diaphragm 80 
having a vertical stop or entrance pupil 82 is located downstream of plate 
72. A focusing lens 84 having a high magnification factor M on the order 
of twenty or twenty-five is located downstream of diaphragm 80. 
It can be shown that the value of the thickness dimension T1 of the plate 
portion 74 will cause an apparent shift .DELTA. S1 in the position S1 of 
the source to position S2 in FIG. 6A, and also that the value of the 
thickness dimension T2 of plate portion 76 will cause an apparent shift 
.DELTA. S2 in the position S1 of the source to position S3 in FIG. 6B. It 
can further be shown that the shift in the actual and apparent positions 
of the source, when multiplied by the square of the magnification factor, 
is proportional to the shift in the focal plane positions of the focused 
beam spot, i.e. from Z7 to Z8. Hence, due to the high magnification 
factor, a relatively small shift in the actual and apparent positions of 
the source can cause a very large and major shift in the position of the 
focused beam spot. By way of numerical example, assume that the index of 
refraction of the glass plage 72 is 1.6, and that the source is located 7 
mm away from the upstream side of the plate 72, then the following 
position shifts are obtained: 
TABLE I 
______________________________________ 
Source Magnification 
Beam Spot 
Thickness 
Shift Factor Shift 
(T) (.DELTA.S) (M) (.DELTA.Z) 
______________________________________ 
0.25 mm 0.1 mm 20 40 mm 
25 62.5 mm 
0.50 mm 0.2 mm 20 80 mm 
25 125 mm 
0.75 mm 0.288 mm 20 115.2 mm 
25 180.0 mm 
______________________________________ 
Hence, by positioning, e.g. by rotating, either plate portion 72 or 74 in 
the optical path, the laser beam can be focused at two different distances 
Z7 or Z8 which are spaced relatively far apart. By incorporating the 
optical arrangement 70 in a scanner housing, symbols can be scanned over 
an increased range. Of course, the plate 72 need not be limited to having 
two plate portions of different optical distance characteristics, 
different indices of refraction, or different thicknesses, but equally can 
be provided with multiple plate thicknesses for generating multiple beam 
spot shifts. 
It can also be shown that by making the entrance pupil 82 smaller, the 
divergence of the laser beam increases, and the spot size on the focal 
plane is larger. Conversely, by making the entrance pupil 82 larger, the 
focused spot size is smaller. Hence, by opening or closing the size of the 
entrance pupil, the waist dimension of the focused beam spot, particularly 
along the scanning direction, can be controlled, either in a digital or 
analogue manner. 
FIG. 7 illustrates a one-piece disc-like component 90 which conveniently 
combines the functions of the glass plate 72 and the diaphragm entrance 
pupil 82. Component 90 is mounted between focusing lens 84 and the laser 
source, and has a circular shape. The upper half of component 90 
corresponds to plate portion 74, and has a relatively thin thickness T1. 
The lower half of component 90 corresponds to plate portion 76, and has a 
relatively thick thickness T2. The downstream surface of component 90 is 
coated with an opaque coating, shown by stippling, which blocks the 
passage of light therethrough, except through small semi-circular pupil 
region 92 and large semi-circular pupil region 94, the pupil regions being 
small or large as considered along the scan direction. When laser light 
passes through pupil region 92, a large spot size is created on the focal 
plane. When laser light passes through pupil region 94, a fine spot size 
is created on the focal plane. 
In operation, when component 90 is rotated about axis 73, the small and 
large pupil regions 92, 94 take turns being situated in front of the laser 
beam. At the same time, the thin and thick portions of the component 90 
take turns being situated in front of the laser beam. When the thin plate 
portion 74 and the small pupil region 92 are together positioned along the 
optical light path, then a beam spot having a relatively large spot size 
and located at a distance close-in to the housing is generated. When the 
thicker plate portion 76 and the larger pupil region 94 are situated along 
the optical path, then a beam spot having a relatively small spot size and 
located at a distance further out from the housing is generated. Further 
half-turning of the component 90 causes the outgoing beam to be moved 
between positions Z7 and Z8 and, concomitantly, the beam spot is changed 
in size. 
Other variations are, of course, within the spirit of this invention. For 
example, the small pupil region 92 could be located on thicker plate 
portion 76, and large pupil region 94 could be located on thinner plate 
portion 74. 
FIG. 8 shows an optical disc-like component 96 analogous to component 90 of 
FIG. 7, except that, rather than providing two disc pupil openings, a 
single pupil opening 98 of continuously changing size is formed. The scan 
direction is horizontal in FIG. 8. The opening 98 tapers along the scan 
direction from a large size to a small size. When rotated, the opening 98 
causes the resulting beam spot size to be continuously variable on the 
focal plane. Assuming that the scanning component 96 rotates very fast, 
e.g. on the order of forty revolutions per second, then for each 
revolution of the component 96, at least one scan across the bar code 
symbol will have the optimum beam waist. 
It should further be noted that more laser output power will be transmitted 
through a larger pupil opening, and vice versa. Since more power will be 
transmitted through larger pupil opening 94, as compared to the power 
transmitted through smaller pupil opening 92, this power difference can be 
used to achieve at least a limited measure of power equalization, wherein 
more power is transmitted to far-out symbols, and less power is 
transmitted to close-in symbols. 
It is known that, under some circumstances, the actual waist position of a 
focused Gaussian laser beam will be closer to the focusing lens than the 
image position given by conventional geometric optics. It has been found 
that not only Gaussian beams, but also any beam, can exhibit so-called 
focal shift if the Fresnel number which describes the beam over the exit 
aperture of the focusing lens is on the order of unity or smaller. 
The Fresnel number (N) is defined as: 
##EQU1## 
wherein: a is the radius of the exit aperture of the focusing lens; 
.lambda. is the wavelength of the laser beam; and 
R is the distance between the image position and the focusing lens. 
Hence, in order to obtain the aforementioned focal plane shift using laser 
diode beam aperturing, i.e. by changing "a" in the Fresnel number 
equation, the various parameters of the system must be chosen so that the 
Fresnel number will be close to unity. Thus, the laser diode beam has a 
wavelength .lambda.=780 mm; the aperture radius a is selected to be 
variable about 0.5 mm; and the focusing distance R is selected to be about 
300 mm. With such parameter values, the Fresnel number N=1.07 at the exit 
aperture of the focusing lens. 
Since, in the above numerical example, the Fresnel number is close to 
unity, the variation of the aperture radius of the focusing lens, e.g. 
lens 84, can therefore be used as the basis for a zooming system. For 
example, in the case where the aperture radius is changed from 0.3 mm to 
0.8 mm, the focused beam spot is shifted from about 90 mm to about 270 mm. 
The change in the aperture radius of the focusing lens can be achieved, 
e.g. by positioning the diaphragm 80 having pupil 82 of varying width 
either directly in front or in back of the focusing lens 84, and 
preferably in close proximity therewith in order to convert the pupil 82 
to the aforementioned exit aperture having radius "a". Either optical 
component 90 or 98 in FIGS. 7 and 8 can advantageously be employed to 
change the aperture radius of a focusing lens and, in turn, to shift the 
predetermined distance at which the laser beam is focused at the focal 
plane. 
Optical arrangement 100 in FIG. 9 is also operative for changing the 
predetermined working distance, but in this embodiment, this function is 
achieved by moving the laser source itself. As stated previously, a shift 
.DELTA.S in the position of a source, when multiplied by the square of the 
magnification factor M of a focusing lens, equals a corresponding shift 
.DELTA.Z in the working distance. If the magnification factor is high 
enough, then a relatively small shift in the position of the laser source 
will result in a major shift in the working distance. 
Thus, in FIG. 9, the magnification factor or focusing lens 84 is assumed to 
be on the order of 100. Also, since it is the source which is to be moved, 
practical and energy considerations dictate that it would be more 
efficient to move a compact laser diode 46 rather than the very bulky gas 
laser tube. Hence, diode 46 is mounted on a voltage-to-position 
transducer, e.g. a unimorph substrate 102. Transducer 102 is electrically 
connected to a unimorph drive 101 which is connected to an AC electrical 
supply. The drive 101 reciprocally drives the transducer 102 back and 
forth in the direction of arrows 112. Transducer 102 is mounted on a 
stationary support 104 in the housing 14. 
When the drive 101 applies an alternating voltage to the transducer 102, 
the transducer is moved along the optical axis 78, and the diode 46 
participates in this movement. Due to the high magnification factor of 
lens 84, the working distance shift .DELTA.Z is M.sup.2 times larger than 
the source position shift .DELTA.S. 
The optical arrangement 100 is mounted within housing 12 having exit port 
14 through which outgoing laser beam is directed to a symbol. The laser 
beam reflected off the symbol is detected by photosensors mounted in the 
housing. In the FIG. 9 embodiment, it is advantageous if a Fresnel 
condenser lens 106 surrounds the diode-transducer sub-assembly. The 
condenser lens 106 collects the reflected light and focuses the latter on 
photosensor 108 which is operative to convert the collected light to an 
electrical signal which, in turn, is processed by electronic circuitry to 
data descriptive of the symbol. The electrical symbol generated by the 
photosensor 108 could simultaneously be supplied to an open-loop or a 
closed-loop feedback circuit 110 which is electrically connected to the 
transducer drive 101. The feedback circuit generates a feedback signal 
.beta. which controls the drive 101 and moves the diode 46 to the optimum 
position required for reading the symbol, wherever it may be located 
within the zoom range of the system. 
Before considering FIG. 10, it must be recognized that the overall 
performance of a scanning system for reading symbols is a function not 
only of the optical, but also of the electronic, sub-system. The optical 
subsystem will focus the beam to have a certain measurable spot size, but 
the electronic sub-system, and particularly the analogue signal processing 
circuitry, also has a role to play in contributing to the detection and 
spot size. The concept of effective spot size was introduced by Mr. Eric 
Barkan and Dr. Jerome Swartz in the following two articles: 
"Advances in Laser Scanning Technology", Proceedings of The International 
Society For Optical Engineering, Volume 299, Aug. 27-28, 1981. 
"SYSTEM DESIGN CONSIDERATIONS IN BAR-CODE LASER SCANNING", Optical 
Engineering, Volume 23, No. 4, Pages 413-420, July/August, 1981. 
The concept of effective spot size was defined by the following equation: 
##EQU2## 
wherein: w.sub.opt is the spot size of the focused beam at the focal plane 
due solely to the optical system; and 
w.sub.el is the addition to the spot size caused by the electrical system. 
The w.sub.el parameter is a function of the frequency bandwidth or the time 
constant of the analog system processing circuitry, as well as a function 
of the laser beam spot velocity at the focal or scanning plane. 
Now, as noted previously, it is an object of this invention to increase the 
working distance at which symbols can be read. However, with increasing 
distance from the housing, the contribution of w.sub.el results in an 
increase in the value of w.sub.eff, thereby degrading overall system 
performance at such far-out distances. At too long a far-out distance, the 
symbol can no longer be read. Hence, to compensate for the increasing 
contribution caused by the electronic circuitry with increasing distance 
of the symbol relative to the housing, this invention proposes decreasing 
the time constant of the electronic circuitry with increasing symbol 
distances. This decreasing the time constant will compensate for 
concomitant spot speed velocity increases so that w.sub.el will be kept 
more or less constant over an increased working distance. 
As shown on the left side of FIG. 10, an operational transconductance 
amplifier 114 having a very high output impedance is connected upstream of 
the analog electronic processing circuitry. The positive input of 
amplifier 114 is connected to ground. A resistive R1-R2 network is 
connected to the negative input of amplifier 114. The amplifier output is 
connected through a capacitor C to the analog electronic circuitry. An 
amplifier 116 has its negative input and output connected across capacitor 
C. The positive input of amplifier 116 is grounded. A control current 
I.sub.c is supplied to a gate of amplifier 114, and varies the gain 
thereof. 
A simplified equivalent circuit to the one just described is shown on the 
right side of FIG. 10. The time constant of the equivalent circuit is 
proportional to R.sub.eq and C. The time constant depends on the input 
voltage V.sub.in and the output current of the transconductance amplifier. 
In order to provide power equalization for far-out and close-in symbols, 
the output current should be maintained constant. This can be achieved by 
a corresponding change in the magnitude of the control current I.sub.c. 
Assuming such- constant- output current, then R.sub.eq which is equal to 
##EQU3## 
is determined only by the input voltage. Since the input voltage decreases 
with an increase in the distance between the scanner housing and the 
symbol, a decrease in the time constant is achieved because of the 
corresponding decrease in the value of R.sub.eq. 
Therefore, the circuitry of FIG. 10 provides not only gain control and 
power equalization, but also simultaneously changes the time constant of 
the electronic circuitry in such a way as to compensate for spot speed 
increase with increase of the working distance. Depending upon the 
relationship between spot speed and signal amplitude, w.sub.el can be made 
independent of the working distance, or at least the contribution of 
w.sub.el can be less and less noticeable with an increase of the working 
distance. 
The transconductance amplifier 114 may advantageously be integrated circuit 
chip Model No. CA 3080 made by RCA Corp. 
It will be understood that each of the elements described above, or two or 
more together, also may find a useful application in other types of 
constructions differing from the types described above. 
While the invention has been illustrated and described as embodied in a bar 
code symbol reader with variable spot size and/or working distance, it is 
not intended to be 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 foregoing will so fully reveal the gist of 
the present invention that others can, by applying current knowledge, 
readily adapt it for various applications without omitting features that, 
from the standpoint of prior art, fairly constitute essential 
characteristics of the generic or specific aspects of this invention and, 
therefore, such adaptations should and are intended to be comprehended 
within the meaning and range of equivalence of the following claims.