Scan pattern generator for bar code symbol readers.

BACKGROUND OF THE INVENTION

1. Field of the Invention

0001This invention generally relates to laser scan­ning systems for reading bar code symbols and, more parti­cularly, to scan pattern generators for generating scan patterns which extend across the symbols to be read.

2. Description of the Related Art

0002Laser 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; 4,460,120 and 4,607,156, as well as U.S. Application Ser. Nos. 519,523; 831,415; 706,502 and 883,923 -- all of said patents and patent applications 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 spot being scanned over each symbol to trace a scan line.

0003It has previously been proposed to generate scan patterns of mutually parallel scan lines extending along one or two directions, as well as omni-directional scan patters of intersecting scan lines, and even curvi­linear scan patterns, for superposition over the symbol to be read to insure that, no matter what the angular orientation of a respective symbol might be within pre­determined limits, at least one of the scan lines or part of the pattern will be scanned over the entire length of the respective symbol. Yet, the known patterns are gen­erated by highly complex and expensive systems.

0004Also, quite apart from the angular orientation of the symbols to be read, one symbol might be located close-in to the scanner, whereas another symbol might be located far-out from the scanner and, in short, successive symbols may be located at different working distances from the scanner. In the case of a scanner which has been designed to read symbols within a certain range of working distances, should it occur that a particular symbol falls outside this range, then the distance between the scanner and the symbol must be adjusted, and usually within a short time interval, for, otherwise, the symbol will not be read. In the case of a hand-held scanner, the scanner is usually manually moved toward or away from the symbol to adjust the distance between the scanner and the symbol. This can be a tiring procedure and require multiple read­ing attempts. It would be desirable, therefore, if the scan pattern generators also incorporated a so-called "zoom" characteristic in which the working distance is automatic­ally changed during scanning.

SUMMARY OF THE INVENTION

1. Objects of the Invention

0005It is a general object of this invention to advance the state of the art of laser scanning systems for reading bar code symbols.

0006It is another object of this invention to gen­erate scan patterns of mutually parallel lines or of inter­secting lines over the symbol with a relatively simple pattern generator system, with the option of simultaneously changing the working distance of the outgoing laser beam.

0007It is a further object of this invention to generate a bidirectional scan pattern of mutually parallel scan lines, at least one scan line scanning in one direc­tion, and at least another scan line scanning in an oppo­site direction.

2. Features of the Invention

0008In 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 semi­ conductor 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.

0009More particularly, this invention is embodied in pattern means for generating a scan pattern of mutu­ally parallel scan lines extending linearly across each symbol. The scan lines are arranged over the height of the symbol. At least one of the scan lines sweeps across each symbol along one sweep direction, whereas, at least another of the scan lines sweeps across each symbol along an opposite sweep direction countercurrent to said one sweep direction, thereby forming a bidirectional scan in which a respective symbol can be read by the first avail­able scan line no matter what its sweep direction. This improves reading speed.

0010In one advantageous embodiment, the pattern generating means includes a planar rotary mirror consti­tuted of a light-refractive material having an index of refraction and having opposite major mirror surfaces spaced apart by a mirror thickness. The mirror surfaces extend generally parallel to a shaft axis of an output shaft of a scanning drive. One of the mirror surfaces has a light-­reflecting coating thereon. The mirror is impinged at an angle of incidence by the laser beam, and a pair of fold­ing mirrors are arranged for reflecting the light reflec­ted off the mirror through the exit port of the housing. The scan lines are spaced apart from one another in a di­rection parallel to the shaft axis due to the index of refraction, the thickness of the rotary mirror, and the angle of incidence of the impinging laser beam on the rotary mirror.

0011In another embodiment of the pattern generating means, both opposite major mirror surfaces of the rotary mirror are provided with light-reflecting coatings. The mirror surfaces extend at an acute angle relative to the shaft axis. During rotation of the output shaft during scanning, the laser beam impinges on both mirror surfaces to generate the scan lines positioned across the height of each symbol.

0012Yet another feature resides in generating an omni-directional scan pattern of intersecting scan lines over each symbol. A rotary mirror is mounted on a shaft for rotation about the shaft axis during scanning. This mirror has a light-reflecting coating on a surface which extends at an angle to the shaft axis. A plurality of folding mirrors are equiangularly arranged about the rotary mirror to generate the omnidirectional pattern. One of the folding mirrors may be movable so as to change the length of the optical path of the outgoing laser beam. By changing the length of the optical path, the predeter­mined working distance of the beam spot is changed during scanning. This so-called "zoom" feature enables the scan pattern to read close-in and far-out symbols.

0013The 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.

BRIEF DESCRIPTION OF THE DRAWINGS

0014<ul id="ul0001" list-style="none"><li>FIG. 1 is a diagrammatic view of a scan pat­tern generator for generating multiple scan lines in a laser scanning system in accordance with this invention;</li><li>FIG. 2A is a top plan, diagrammatic view of the scan pattern generator of FIG. 1 during one stage of scanning;</li><li>FIG. 2B is a view analogous to FIG. 2A, but at another stage of scanning;</li><li>FIG. 2C is a view analogous to FIG. 2B, but at still another stage of scanning;</li><li>FIG. 2D is a view analogous to FIG. 2C, but at yet another stage of scanning;</li><li>FIG. 2E is a view analogous to FIG. 2D, but at an additional stage of scanning;</li><li>FIG. 2F is a view analogous to FIG. 2E, but at a further stage of scanning;</li><li>FIG. 3A is a diagrammatic view of another scan pattern generator during one stage of scanning;</li><li>FIG. 3B is a diagrammatic view of the scan pattern generator of FIG. 3A during another stage of scanning.</li><li>FIG. 4 is a perspective view of still another scan pattern generator;</li><li>FIG. 5 is a front view of the scan pattern generator of FIG. 4 during one stage of scanning;</li><li>FIG. 6 is a view analogous to FIG. 5, but during another stage of scanning;</li><li>FIG. 7 is a perspective view of yet another scan pattern generator in accordance with this invention, and diagrammatically illustrating one scan pattern;</li><li>FIG. 7A is a diagrammatic illustration of another scan pattern;</li><li>FIG. 7B is a diagrammatic illustration of yet another scan pattern;</li><li>FIG. 7C is a diagrammatic illustration of still another scan pattern;</li><li>FIG. 7D is a diagrammatic illustration of a further scan pattern;</li><li>FIG. 8 is a perspective view of a further scan pattern generator in accordance with this invention; and</li><li>FIG. 9 is a sectional view of the further scan pattern generator of FIG. 8.</li></ul>

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

0015Referring now to the drawings, reference numer­al 10 in FIG. 1 generally identifies an arrangement in a laser scanning system of the type generally described in the above-identified patents and patent applications, 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.

0016The arrangement 10 includes a housing 12, shown in dashed lines, 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.

0017A multiple line scan pattern generator 120 is illustrated in FIGs. 1 and 2A-F, and is operative for generating not only multiple scan lines or traces across a symbol to be read, but also for positioning at least some of the scan lines at different working distances from the housing 12 in which the generator 120 is housed. Another feature of generator 120 resides in the bidirec­tional nature of the resulting scan pattern.

0018Laser source 16 directs a laser beam through optical lens 122 for directing the beam onto rotary main mirror 124 which is mounted on a vertical shaft 126 which is rotated by a motor drive 128 about a vertical axis. As shown in enlarged view of FIG. 3B, mirror 124 has op­posite major planar surfaces 130 and 132 which are separ­ated by a mirror thickness dimension T₃. A light-reflect­ing coating 134 is applied over one of the surfaces, e.g. 132.

0019The generator 120 also includes a pair of sta­tionary first surface side mirrors 136, 138 inclined at angles relative to the vertical axis of the shaft 126, and also including an angle with each other. Side mirrors 136, 138 have front surfaces on which light-reflecting coatings 140, 142 are respectively applied. Inclined side mirrors 136, 138 are so positioned relative to main mirror 124 that, during rotation of mirror 124, laser light impinging on mirror 124 will, at certain times, during each revolution of mirror 124, be directed toward one of the side mirrors for reflection therefrom forward­ly to an exterior symbol.

0020The bidirectional multiple scan line pattern 144 depicted in FIG. 1 is generated as follows: Assume that mirror 124 is initially positioned as shown in FIG. 2A with its coated surface 134 directly facing laser source 16. The laser beam emitted by source 16 is re­turned along the same optical path (shown slightly sep­arated for ease of illustration) for impingement on a symbol located at distance Z9. During rotation of mirror 124 about the FIG. 2A position, scan line 150 is generated. Eventually, after movement of mirror 124 in the circum­ferential direction of arrow 146, the mirror 124 will be oriented as shown in FIG. 2B, wherein the mirror 124 di­rects the laser beam incident thereon to side mirror 136 for reflection by coated surface 140 forwardly for impinge­ment on a symbol located at distance Z10. Z10 is shorter than Z9 due to the diversion of the beam to side mirror 136. During rotation of mirror 124 about the FIG. 2B position, scan line 152 is generated. Scan line 152 is swept in the opposite direction to that of scan line 150.

0021Eventually, the mirror 124, during further rotation in direction of arrow 146, is oriented in the FIG. 2C position, wherein the coated surface 134 faces away from the laser source 16 so that the laser beam must initially pass through non-coated surface 130 of mirror 124 prior to reaching the rear coated surface 134. As shown in enlarged view in FIG. 3B, this incident beam impinges at an angle of incidence ϑ, whereupon the beam is refracted at an angle ϑʹ to the extent determined by the index of refraction nʹ of mirror 124. The refracted beam reflects off coated surface 134 until it is again refracted at the mirror/air surface 130. A comparison of FIGs. 3A and 3B reveals that the positional shift ΔD between the beam reflected solely off coated surface 134 in the FIG. 2B situation and the beam leaving the mirror 124 after having been refracted therein is:<maths id="math0001"><img file="EP0273554A2_D0001.tif" /></maths>

0022Returning to FIG. 2C, the refracted beam exit­ing mirror 124 is directed to coated surface 142 of the side mirror 138 for reflection forwardly to a symbol lo­cated at working distance Z10. Rotation of mirror 124 about the FIG. 2C position generates scan line 154 which is swept in the same direction as scan line 152.

0023In analogous manner to that described earlier in connection with FIG. 2A, further rotation of the mirror 124 eventually orients the mirror 124 to the FIG. 2D posi­tion, wherein the coated surface 134 converts the mirror 124 into a second surface mirror. In this case, the in­coming beam must pass through the mirror thickness T₃ before being forwardly reflected by coated surface 134 to working distance Z9. Scan line 156 generated by rota­tion of mirror 124 about the FIG. 2D position is swept in the same direction as scan line 150.

0024Scan line 158 is generated by rotation of mirror 124 about the FIG. 2E position in a manner ana­logous to that described earlier in connection with FIG. 2C, except that the beam exiting mirror 124 is directed instead to the other side mirror 136 prior to forward reflection to a symbol located at working distance Z10.

0025Scan line 160 is generated by rotation of mirror 124 about the FIG. 2F position in a manner analo­gous to that described earlier in connection with FIG. 2B, except that the beam leaving mirror 124 is directed to the other side mirror 138 prior to reflection forwardly to a symbol located at working distance Z10. Scan line 160, as well as scan line 158, are swept in the same di­rection as scan line 152.

0026As best shown in FIG. 1, it will be noted that the scan pattern 144 comprises a plurality of scan lines in mutual parallelism, with scan lines 150, 156 swept from left to right, and with the remaining scan lines 152, 154, 158 and 160 swept from right to left. All the scan lines are spread apart over the height of the symbol. This spread can be controlled by, and is a function of, the thickness T3 of mirror 124, the angle ϑ of incidence of the laser beam on mirror 124, and the index of refrac­tion nʹ of mirror 124, the latter being preferably con­stituted of glass. Also, as shown in FIGs. 2A through 2F, the beam spot is focused and alternately located at either working distance Z9 or Z10, thereby obtaining a zooming function.

0027Another way of spreading multiple scan lines apart from one another is to replace the vertically ex­tending mirror 124 having a single coated surface with a tilted mirror 162, as shown in FIGs. 4-6, which has two light-reflecting coated surfaces 164, 166 on opposite sides thereof. The tilted mirror 162 is mounted on a shaft 126 of a motor drive 128 at an angle relative to the vertical. When impinged by a light beam emitted by laser source 16, either the coated surface 164 which is oriented at angle φ, or the coated surface 166 which is oriented at an angle supplementary to φ will face the source 16. The different angles of inclination of the coated surfaces of mirror 162 results in the desired angu­lar spread between the scan lines.

0028An omni-directional scan line pattern generator 170 is illustrated in FIG. 7, and is operative for gener­ating intersecting line patterns. The generator 170 is simple in construction and comprises a drive motor 172 having a vertical output shaft 174 on which a front sur­face planar mirror 176 is fixedly mounted for rotation in the circumferential direction of arrow 178. A plural­ity of inclined reflecting side mirrors 180, 182, 184 are equiangularly distributed about the vertical shaft 174. The side mirrors are positioned in the light path of a laser beam emitted from source 16 and directed by over­head folding mirror 186 to the center mirror 176.

0029Upon rotation of center mirror 176, the laser beam is successively directed to mirrors 180, 182, 184 each in its turn, for reflection toward a symbol to be read. The resulting multiple line pattern 188 covers the symbol in the FIG. 7 embodiment with three intersecting lines. If four, eight, six, or five mirrors were equi­angularly distributed about vertical shaft 174, then the patterns depicted in FIGs. 7A, 7B, 7C and 7D, respectively, would be generated during each revolution of the center mirror 176.

0030A drive, such as a piston rod 181, reciprocally movable relative to a cylinder 183 along the directions of double-headed arrow 185, is connected to any one of the side mirrors, e.g. 180. As the side mirror 180 is moved radially toward and away from the axis of rotation of the center mirror 176, the focused scan line associated with the side mirror 180 is located at different working distances, thereby achieving a zooming function.

0031Another omni-directional scan line pattern generator 190 is illustrated in FIGs. 8 and 9, and gener­ates not only intersecting scan line patterns, but also individual scan lines which are located at different work­ing distances from the housing, thereby. achieving a zoom­ing function. As before, a drive motor 172 rotates a vertically oriented output shaft 174. A plurality of inclined side reflecting mirrors 180, 182, 184 are equi­ angularly arranged about the shaft 174. A housing 12 having exit aperture 14 also supports an overhead folding mirror 186 to which a laser beam from source 16 is di­rected.

0032Rather than rotating a single mirror on shaft 174, as proposed by the previous embodiment, this embodi­ment proposes mounting a mirror assembly on the shaft 174. This mirror assembly includes elongated upper and lower bars 192, 194 whose inner ends are fixed to shaft 174 and rotatable therewith in mutual parallelism. The bars 192, 194 are axially spaced apart by spacer 196. At the outer ends of bars 192, 194 are respectively supported mirrors 198, 200. Mirror 198 is stationarily mounted at the outer end of bar 192. Mirror 200 is mounted for rotation about axis 202 which is parallel to vertical axis 204 of the shaft 174. Mirror 200 is mounted at the outer end of bar 194 on a central shaft of a planetary gear 206 having ex­terior gear teeth which meshingly engage with exterior gear teeth of a stationary sun gear 208. Sun gear 208 coaxially surrounds the shaft 174 and is stationarily mounted on the housing of motor 172. Gears 206, 208 are circular, and sun gear 208 has a much larger diameter than that of planetary gear 206, so that mirror 200 is rotated at a high angular speed about its axis 202.

0033Another mirror 210 is fixedly mounted at the inner end of bar 192, and is located in the optical path of light reflected from overhead mirror 186. The light reflected from mirror 210 is directed to stationary mirror 198, whereupon the reflected light is directed through a hole 212 in bar 192 to the rotary mirror 200 located underneath hole 212.

0034In operation, light from source 16 is directed along an optical path by successive reflections off mir­rors 186, 210, 198 and 200 prior to being directed to side mirrors 180, 182, 184. The relative positions of mirrors 210 and 198 are fixed relative to each other dur­ing rotation of the mirror assembly. At the same time that shaft 174 rotates, the mirror 200 experiences a dual move­ment. First, the mirror 200 rotates about its axis 202 with an angular speed proportional to the ratio of the diameters of gears 206, 208. Second, the mirror 200 is moved along a circular annulus concentric with axis 204. Hence, the light reflected off mirror 200 will, for each revolution of mirror 200 about axis 202, sequentially im­pinge on side mirrors 180, 182, 184 which are inclined to direct successive scan beams out through port 14. Due to the diversion of light and the different optical paths between the rotary mirror 200 and the side mirrors 180, 182, 184 at any one moment, at least some of the scan lines are positioned closer in to the housing 12 than other scan lines, thereby achieving a zooming action. Also, as the mirror 200 is also orbiting about the axis 204, the work­ing distance generated by reflection from any one side mirror is always changing.

0035A three-dimensional coverage of a symbol can thus be achieved with a very sophisticated pattern to­gether with a zooming action. Of course, more than three side mirrors could have been used to obtain even more coverage. The exit port 14 need not be located above the generator 190, as shown in FIGs. 8 and 9 for use in a so-called "scan-above" system. Alternately, the port 14 could have been located so as to form a "scan-below" system or even a "scan-out" system.

0036Although the preceding description has been rendered in terms of laser scanning systems and arrange­ments for optically modifying laser beams, it will be ex­pressly understood that this invention is not intended to be so limited and, in fact, is intended to include non-­laser light sources and beams, including non-coherent and coherent light sources such as light-emitting diode sources, incandescent light sources, gas discharge sources, etc.

0037It 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.

0038While the invention has been illustrated and described as embodied in scan pattern generators for bar code symbol readers, 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.

0039Without 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.

0040What is claimed as new and desired to be pro­tected by Letters Patent is set forth in the appended claims.