Omnidirectional Optical Scanning Apparatus

The invention disclosed herein parallels that merchandizing optical omnidirectional scanning system disclosed in the copending U.S. Patent application Ser. No. 382,783 of Arlen J. Bowen et al filed on the 26th day of July 1973 for "An Omnidirectional Optical Scanner" and thereafter issued on the 11th day of November 1975 as U.S. Pat. No. 3,919,527.

The invention relates to optical scanning systems and more particularly to omnidirectional optical scanning systems.

The invention finds particular application for scanning randomly oriented bar coded labels, which for example, are attached to consumer items being checked out at a counter. The check out clerk, or checker, merely passes the item across the scan window insuring that the label is within the scanning window as the item is being placed into a box or bag. Except for some relatively small items, little attention need be paid to the orientation of the items as they are moved across the scanning window.

Omnidirectional scanning systems have been suggested as particularly suitable for scanning systems where the checker passes the items across a scanning window. The prior art also discloses optical systems and components which those skilled in the art will consider in the design and development of a point-of-sale item scanning system.

The more pertinent arrangements in the prior art are to be found in the following U.S. Pat. Nos. 3,414,731 12/1968 Sperry 250/219 3,456,997 7/1969 Stites et al 350/7 3,553,437 1/1971 Boothroyd 235/61.11 3,600,556 8/1971 Acker 235/61.11 3,684,867 8/1972 Acker 235/61.11 3,701,098 10/1972 Acker 340/146.3 3,718,761 2/1973 Meyer 178/7.6 3,728,677 4/1973 Munson 340/146.3P

The patents to Sperry and U.S. Pat. No. 3,600,556 to Acker are directed to circular labels which are readable without orientation; the arrangements shown are for the centering of the label before the scanning is begun. The U.S. Pat. No. 3,701,098 to Acker is directed to an arrangement for orienting the item by rotation of optical system components to coincide with each other after which scanning is begun. The patents to Stites, Boothroyd and the U.S. Pat. No. 3,684,867 to Acker are directed to arrangements for accommodating skew, which is a relatively slight misalignment in orientation, and the arrangements are not readily applicable to the solution of the problem with which the invention is concerned.

The patents to Meyer and Munson are more pertinent but they are directed to systems limited to a square scanning window rather than a narrow rectangular scanning window of the invention. The square scanning window for a given width requires a greater reach on the part of the checker and is not as desirable from a human factors point of view as is a narrow rectangular scanning window. The narrow rectangular scanning window; however, does require multiple trace scanning patterns for insuring that the coded label will be properly scanned. The multiple trace scanning patterns are produced according to the invention by deflected light beam patterns, which have a subtle safety advantage in that the average laser power entering a fixed aperture (laser power times aperture diameter divided by length of scan) is less. The desired light patterns according to the invention are generated by relatively simple and inexpensive optical apparatus.

The objects of the invention indirectly expressed hereinbefore and those that will appear as the specification progresses are attained in an optomechanical system having an intense, substantially non-divergent light source, such as a laser, and fixed and rotating mirrors that deflect the beam from that source to a narrow rectangular scanning window. The rotating mirror is arranged with respect to fixed beam-forming mirrors so that the beams trace out an overlapping and crossing pattern. Beam splitting apparatus is interposed to provide an interlaced pattern.

In order that all the advantageous aspects of the invention obtain in practice, a specific embodiment, given by way of example only, is described in the remainder of this text with reference to the accompanying drawing, also forming a part of the specification, and in which:

FIG. 1 is a schematic diagram of omnidirectional optical scanning apparatus according to the invention;

FIG. 2 is a perspective view illustrating a setting for the omnidirectional scanning apparatus of the invention;

FIG. 3 depicts a typical label for which the omnidirectional scanning apparatus of the invention is arranged;

FIG. 4 is a diagram illustrating one complete scanning pattern;

FIG. 5 is a schematic diagram illustrating the layout of light scanning segments for omnidirectional scanning;

FIGS. 6a and 6b are plan and evaluation views of optical scanning segment dividing apparatus according to the invention;

FIG. 7 is another diagram showing scan segments reflected for producing crossed scanning segments;

FIG. 8 is a diagram illustrating optical scanning beam splitting apparatus for producing an interlaced scan according to the invention;

FIG. 9 is a diagram of a mirror arrangement according to the invention;

FIG. 10 is a schematic diagram illustrating an alternate displacement of scan segments according to the invention; and

FIG. 11 is a diagram illustrating another complete scanning pattern.

A schematic overall view of an optical scanning system according to the invention is given in FIG. 1. A laser 20 is employed as a light source for generating an intense narrow beam of light. This beam of light is directed through optical apparatus 22 which includes lenses for expanding the laser beam onto a beam splitting arrangement 24 which in turn directs a multiple of beams onto a multifaceted rotating mirror 26 driven by an electric motor 28. The beam splitting arrangement 24 is provided for effecting an interlaced pattern where desired and otherwise may be omitted. Each beam swept out by the rotating mirror 26 is divided into a multiple of beam scanning segments, each parallel to the other scan segments by a fixed mirror assembly 30 composed of a multiplicity of mirrors disposed in slightly different angular orientations about a common imaginary straight line 31 in the plane of each mirror in response to the infringing "fan" of light translated by a lens 32. The line 31 is parallel to the plane of the window 35 and each mirror is arranged at an angle of approximately 45.degree. to the longitudinal axis of the window 35. A pair of end mirrors 34 are arranged to reflect some of the beam scan segments so that there will be scan segments at right angles to the first (non-reflected) scan segments. Thus, a series of X-shaped or crossed scans will be produced in the aperture of a scanning window 35. Photoelectric devices 36 and 38 are arranged below the scanning window 35 and in such positions that light from the scanning beams as reflected by the label will impinge upon the photosensitive devices 36 and 38 which are connected to video signal processing circuitry 40 for analyzing the electric signal to identify the information presented at the scanning window 35. An output electric signal is delivered at output terminal 42 for application to the utilization circuitry.

A setting for the invention is shown in FIG. 2. The scanning window 35 is located at the top of an enclosure 50 forming a market checkout stand housing the previously described components. The scanning window 35 is a narrow rectangular aperture ideally about 2.5 by 25 centimeters, formed in the housing 50 and covered by glass or other suitable material transparent to the light generated by the laser 20.

An item of merchandise 70 bearing a bar coded label 71 is transported by a conveyor belt 15 to the scanning area. The checkout clerk passes the item 70 with the label 71 face down over the scanning window 35 just prior to placing the item 70 into a paper bag 55 which is supported on a shelf 56.

The label 71 is a bar coded label of the type shown in FIG. 3. The label 71 is printed with a plurality of bars 72 which have a reflectance less than the background area 73. Thus, as the light beam scans across the label 71, it is modulated by the difference in reflectance between the background 73 and the printed ink bar 72. The modulated reflected light is collected by the photosensitive devices 36 and 38 (FIG. 1) which deliver an electric signal to the video signal processing circuitry 40 where it is analyzed to identify the information represented by the bars 72 on the label 71. The scanning pattern at the window 35 is arranged to interpret the bars of the label 71 so that the data will be recovered irrespective of the orientation of the label 71 to the scanning window 35.

In order to make the operation of the optomechanical scanning system according to the invention clear and to enable those skilled in the art to practice the invention, the system will be described hereinafter in a step-by-step progression.

A schematic diagram of the desired scanning pattern to appear in the window 35 is shown in FIG. 4. In this embodiment, the window 35 was 2.8 by 25.4 centimeters. The scanning lines were developed as follows. One beam from the laser 20 is deflected by the rotating mirror 26 through the lens 32 that focuses the beam in the scan area. Referring to FIG. 5, a line 76 produced by the rotating mirror 26 is divided into eight segments 81 . . . 88 laterally displaced with respect to the line 76, as shown in FIGS. 6a and 6b by an assembly 30 of fixed mirrors 91 . . . 98 that fold the fan of light produced by the rotating mirror 26. Each mirror 91 . . . 98 is set at its own unique angle in order to reflect light from the laser 20 as directed by the rotating mirror 26 through the lens 32 to its respective line segment in order to produce scanning line segments. A pair of end mirrors 110 and 112 are placed to reflect four of the eight segments back onto the other four as shown in FIG. 7. The mirror images 102, 101, 108, 107 of line segments 81, 82, 87, 88 then form scan segments intersecting scan segments 83, 84, 85 and 86 to form four X's. The end mirrors must be long in the direction normal to the plane of the drawing in order to intercept the beams directed to what, in the absence of the end mirrors 110 and 112, would be the outer two scan segments 81, 82, and 87, 88 at each end.

Thus far four crossed scanning line segments have been produced. Three additional sets of cross line scanning segments are interlaced between each of the existing pairs of cross scanning line segments 83, 102; 84, 101; 85, 108 and 86, 107. Three additional scanning beams from the laser 20 are generated by the arrangement shown in FIG. 8. Three beam splitting mirrors 114, 116, and 118 are interposed between the laser 20 and a " reflecting mirror 120 all of which mirrors are arranged to direct the component beams produced thereby onto the rotating mirror 26. Each of the four beams is incident upon the rotating mirror 26 at a different angle such that only one of the beams, when reflected by the rotating mirror 26 is operable in the field of view of the remainder of the optical system for a given angular position of mirror 26. Thus, one beam is scaanning while the other three are 37 flying back". Thus, the angular field of view of mirror assembly 30 as seen in the space between lens 32 and mirror 26 should be less than, or just equal to 720/(nxm), where n is the number of facets on mirror 26 and m is the total number of beams generated by the beam splitter assembly 24. From the diagram, it is apparent that each of the beams reflected from a given segment of the segmented mirror assembly 30 will produce an image somewhat displaced from that produced by the other beams. If the direction of the beams out of the plane of diagram is different, there will also be an image displacement in the direction normal to the plane of the drawing. Hence, the interlaced cross scan line segments can be positioned relative to each other as desired, by adjusting the position (relative to each other) at which the beams are reflected from the rotating mirror 26. This is done in the proper orientation of laser 20 and the beam splitting mirrors 114, 116, and 118 and the reflecting mirror 120 that give rise to the four separate scanning beams.

Since the optical path length from the segmented mirror assembly 30 to the image surface at the scanning window is greater for the outer segments 81 and 88, it may be desirable to use slightly convex mirrors for the segments near the end of the array in order to increase the focal length of the system slightly for these segments.

With a a line of segmented mirrors 81 . . . 88 set at different angles to produce the displaced scanning line segments as described above, the exact relative position of the scanning line segment will be somewhat the function of the longitudinal position of the scanning window 35. If a slight change in relative positions of the scanning line segments produced by moving the observing screen longitudinally is objectionable, the assembly 30 of segmented mirrors 91 . . . 98 are replaced by a series of mirrors that each reflect the scanning beam 90.degree. and where the mirrors are staggered in order to produce the scanning line segments. This arrangement will greatly reduce, but will not eliminate, the change in relative scanning line segments positions as the window is moved.

FIG. 9 is a geometric diagram of the system as described useful to those skilled in the art in designing the optical system described.

The number of scanning beams necessary in the system as described can be reduced to three with a significantly greater overlap in the scanning line segments by reducing the off-set or lateral displacement of the scanning line segments as shown in the diagram of FIG. 10. The amount of interlace is less than that described before because the scanning lines form angles of 35.degree. with the side of the scanning window 35 rather than the angle of 45.degree. shown before. With the lower angle, the scanning lines overlap more and thus less interlace is necessary.

FIG. 11 shows a scanning window 35 approximately 22 .times. 2.4 centimeters having such 35.degree. scanning line segments.

While the invention has been shown and described particularly to reference to a preferred embodiment thereof, and alternatives have been described, it should be understood that those skilled in the art will make further changes without departing from the spirit and scope of the invention as defined in the apended claims.