Rotary reflecting devices for use in optical scanning apparatus

Abstract: A rotary reflecting device (18; 32), for use in optical scanning apparatus, of the type being rotatable about an axis of rotation therethrough and having a plurality of reflectors (20; 38) positioned at respective different angular locations around that axis, is characterised in that each of the said reflectors (20; 38) has two mutually-adjacent substantially planar reflecting faces (20a, 20b; 38a, 38b) which meet in a line (21) of intersection that is inclined with respect to the said axis of rotation, and in that the respective said lines (21) of intersection of adjacent reflectors (20; 38) of the device are inclined respectively at different angles (ϑ₁) with respect to the said axis of rotation. The use of such a rotary reflecting device in optical scanning apparatus, for reading bar codes for example, can enable a satisfactory scanning pattern to be produced without the need for additional, and/or comparatively large, components such as are required in prior art optical scanning apparatus, thereby permitting a reduction in the overall size and cost of the apparatus.

Description: This invention relates to rotary reflecting devices for use in optical scanning apparatus, for example apparatus for scanning coded bars by means of a laser beam to read a bar code of the coded bars. POS (point of sales) systems have been introduced in many department stores and supermarkets in order to improve the efficiency in management of commodities and checking out operations. In such systems, a bar code reader, including an optical scanner is used, which scans coded bars attached to a commodity by means of a laser beam, detects diffused signal light from the coded bars by means of a photodetector and converts it into a signal having a form of information suitable for subsequent calculation processing. Such a bar code reader commonly comprises a laser beam generating source, a laser beam shaping optical system, a scanning optical system, a signal light detecting optical system, a wave form shaping circuit and a bar code demodulating circuit. Typically, a laser beam emitted from a He-laser is shaped into a laser beam of a suitable size by the beam shaping optical system, and a scanning pattern for the universal reading is formed with the thus shaped laser beam by the scanning optical system and the laser beam is caused to irradiate the coded bars with the scanning pattern. Diffused light reflected from the coded bars is condensed by the signal light detecting optical system and the signal light is converted into an electric signal by the photodetector. The electric signal is shaped by the signal waveform shaping circuit and then converted into a numerical value by the bar code demodulating circuit, and the numerical value thus obtained is transmitted to a POS terminal. While various types of optical scanners for use with such bar code readers have been proposed and put into practical use, they can be roughly divided into two types, one of which employs a rotary reflecting device, such as a polygon(al) mirror, and the other of which employs a hologram disk. Conventional optical scanners of either of the two types are commonly disadvantageous in that, since a scanning pattern generating mirror device including a plurality of reflecting mirrors must be provided in order to obtain a scanning pattern which is composed of a plurality of scanning lines of various directions, the number of components is increased, and the cost is high, and in addition miniaturization of the device cannot be achieved. Further, in order to obtain a long or large beam pattern, the reflecting mirrors must necessarily be large in size, which also causes a rise in cost and an obstacle to miniaturization of the device. Accordingly, it is desirable to provide optical scanning apparatus which can be reduced in size and in production cost as compared with prior art optical scanners. EP-A-0283717 discloses a rotary reflecting device which is rotatable about an axis of rotation therethrough and has a plurality of reflectors positioned at respective different angular locations around that axis, each of the said reflectors having two or more substantially planar reflecting faces, two mutually-adjacent such faces meeting in a line of intersection that is inclined with respect to the said axis of rotation. However, an appropriate scanning pattern could not be obtained using this device. In accordance with a first aspect of the present invention, there is provided a rotary reflecting device for use in an optical scanning apparatus, which device is rotatable about an axis of rotation therethrough and has a plurality of reflectors positioned at respective different angular locations around that axis, each of the said reflectors having two or more substantially planar reflecting faces, two mutually-adjacent such faces meeting in a line of intersection that is inclined with respect to the said axis of rotation; characterised in that the angle between the said two mutually-adjacent reflecting faces of each reflector is different from the angle between the said two mutually-adjacent reflecting faces of an adjacent reflector of the device. In accordance with a second aspect of the present invention, there is provided optical scanning apparatus as claimed in claim 4. Reference will now be made, by way of example, to the accompanying drawings, in which:- Fig. 1 shows a schematic view of an optical scanner embodying the first aspect of the present invention; Fig. 2 shows a perspective view of a rotary polygonal mirror embodying the second aspect of the present invention; FIG. 3 shows a front elevational view of a portion of the rotary polygonal mirror shown in FIG. 2; FIG. 4 shows a side elevational view of the portion shown in FIG. 3; FIG. 5 is a diagrammatic representation of a scanning pattern; FIG. 6 is a diagrammatic representation of another scanning pattern; FIG. 7 is a diagrammatic representation of a further scanning pattern; FIG. 8 shows a schematic view of another optical scanner embodying the first aspect of the present invention; and FIG. 9 shows a schematic view of a portion of another rotary polygonal mirror embodying the second aspect of the present invention together with part of an optical scanner. Optical scanning apparatus embodying the first aspect of the present invention will now be described with reference to FIGS. 1 to 7. Referring first to FIG. 1, a reading window 12 is provided at the top of a casing 10. A light source 14 for generating a laser beam, such as a He-Ne laser or the like, is provided in the casing 10, and a laser beam LB emitted from the light source 14 is reflected by a mirror 16 and onto a rotary reflecting device, comprising a polygon mirror 18 which embodies the second aspect of the present invention. The rotary polygon mirror 18 has a plurality of reflecting portions (reflectors) 20 on an outer periphery thereof and is rotated around an axis of rotation thereof by a motor 22. The laser beam LB reflected by a reflecting portion 20 of the rotary polygon mirror 18 scans coded bars 26 attached to a commodity 24. Since the reflecting portions 20 of the rotary polygon mirror 18 have different reflecting directions for a beam as hereinafter described, the rotary polygon mirror 18 produces a scanning pattern which is composed of a plurality of scanning lines of different directions so that the laser beam may scan the entire coded bars 26 attached to the commodity 24 irrespective of the orientation of the coded bars 26. Diffused signal light diffused by the coded bars 26 is once reflected by the reflecting portion 20 of the polygon mirror 18 and condensed to or focused upon a photodetector 30 by a condenser or focussing lens 28 as indicated by broken lines in FIG. 1. Construction of the rotary polygon mirror 18 will be described with reference to FIGS. 2 to 4. The rotary polygon mirror 18 has a plurality (6 in the present embodiment) of reflecting portions 20 disposed around the rotational axis thereof, and each of the reflecting portions 20 includes a pair of reflecting faces 20a and 20b. Referring particularly to FIG. 3, where an angle defined by a line 21 of intersection between the reflecting faces 20a and 20b of each of the reflecting portions 20 and the axis 18a of rotation of the rotary polygon mirror 18 is represented by ϑ₁ , the rotary polygon mirror 18 is formed such that the value of the angle ϑ₁ of each of the reflecting portions 20 thereof may be different from those angles ϑ₁ of adjacent reflecting portions 20 on the opposite sides of the reflecting portion 20. Meanwhile, referring to FIG. 4, where an included angle between the reflecting faces 20a and 20b of each of the reflecting portions 20 of the rotary polygon mirror 18 is represented by ϑ₂, the rotary polygon mirror 18 is formed also such that the value of the angle ϑ₂ of each reflecting portion 20 thereof may be different from the included angles ϑ₂ of adjacent reflecting portions 20. In particular, in the present embodiment shown in the drawings, the rotary polygon mirror 18 is formed such that it has six reflecting faces 20 and the values of ϑ₁ and ϑ₂ of each of the reflecting portions 20 are different from the values of ϑ₁ and ϑ₂ of adjacent reflecting portions 20 on the opposite sides of the reflecting portion 20, respectively. Each pair of those of the reflecting portions 20 which are positioned on the opposite sides with respect to the axis 18a of rotation are equal in inclination angle ϑ₁ and included angle ϑ₂ to each other. In operation, a laser beam LB emitted from the light source 14 is reflected by the mirror 16 onto the rotary polygon mirror 18. The laser beam LB reflected by the reflecting face 20a of a reflecting portion 20 of the rotary polygon mirror 18, which is rotating at a high speed, is reflected again by the other, opposing reflecting face 20b and scans coded bars 26 of a commodity 24 through the reading window 12. Here, if the angle ϑ₁ is otherwise equal among all of the reflecting faces 20 of the rotary polygon mirror 18 while only the angle ϑ₂ varies between each adjacent ones of the reflecting faces 20, then a pattern with which the laser beam LB is to scan the coded bars 26 is constituted from a plurality of such parallel scanning lines of the same direction as seen in FIG. 5. On the other hand, if the angle ϑ₂ is equal among all of the reflecting faces of the rotary polygon mirror 18 while only the angle ϑ₁ varies between each adjacent ones of the reflecting faces 20, then a pattern with which the laser beam LB is to scan the coded bars 26 is constituted from such a plurality of scanning lines which intersect each other at a particular point as seen in FIG. 6. Accordingly, where both of the angles ϑ₁ and ϑ₂ vary between each adjacent ones of the reflecting portions 20 of the rotary polygon mirror 18 as in the embodiment described above, such a scanning pattern is produced which is constituted from a plurality of scanning lines of various directions as seen in FIG. 7. If the coded bars 26 on the commodity 24 are scanned with such a scanning pattern as described just above, the entire coded bars 26 can be scanned by at least one of such scanning lines irrespective of an orientation of the coded bars 26. Diffused signal light from the coded bars 26 advances reversely along the passage of the scanning beam and is thus reflected by the rotary polygon mirror 18 and then focused upon the photodetector 30 by the condenser lens 28. The photodetector 30 converts the received diffused signal light into an electric signal, which is then converted into a digital signal by an analog to digital converter not shown and decoded by a bar code demodulating circuit. With the optical scanner of the construction described above, a scanning pattern which is composed of a plurality of scanning lines of various directions can be produced using only the rotary polygon for 18. Accordingly, a hologram disk or a set of reflecting mirrors such as are used in a conventional optical scanner can be eliminated, which enables miniaturization and reduction in cost of the arrangement. Further, if the rotary polygon mirror 18 is formed by molding a body from a resin material and applying an aluminum film on the resin body by vapor deposition to form reflecting faces, it can be produced at even lower cost. Further, since a laser beam is reflected a comparatively small number of times, the amount of light required can be minimized, and hence the output power of the light source 14 can be reduced. Another optical scanner embodying the first aspect of the present invention will now be described with reference to FIG. 8. It is to be noted that, since the optical scanner of the present embodiment has somewhat similar construction to that of the optical scanner of the preceding embodiment, substantially like components are denoted by like reference numerals and overlapping description thereof is omitted herein to avoid redundancy. The optical scanner of the present embodiment includes a mirror 36 for changing the advancing direction of diffused signal light condensed by a condenser lens 28 and adopts a hollow rotary polygon mirror 32 comprising a substantially hexagonal tube which is open at the top thereof. A plurality (six in the present embodiment) of reflecting portions 34 are provided on an inner periphery of the rotary polygon mirror 32 and are each constituted from a pair of opposing reflecting faces 34a and 34b. The reflecting faces 34a and 34b of the reflecting portions 34 are disposed such that such a scanning pattern which is composed of a plurality of scanning lines of various directions as seen in FIG. 7 may be obtained similarly as in the embodiment described above. Since the optical scanner of the present embodiment has such construction as described just above, a scanning pattern constituted from a plurality of scanning lines of various directions can be obtained using only the rotary polygon mirror 32 similarly as in the optical scanner of the preceding embodiment. Accordingly, such a hologram disk or a set of reflecting mirrors as is required in a conventional optical scanner is eliminated, which enables miniaturization and reduction in cost of the arrangement. The optical scanner of the present embodiment further has such advantages as those of the optical scanner of the embodiment described hereinabove. It is to be noted that, while the optical scanners of both the embodiments described above are constituted such that each of the reflecting portions of the rotary polygon mirror has a pair of reflecting faces having different inclination angles with respect to the axis of rotation of the rotary polygon mirror, the number of such reflecting faces of each reflection portion is not limited to two. For example, as shown in FIG. 9, each reflecting portion 38 may include three reflecting faces 38a, 38b and 38c having different inclination angles with respect to the axis of rotation of the rotary polygon mirror.

Claims: A rotary reflecting device (18; 32) for use in an optical scanning apparatus, which device (18; 32) is rotatable about an axis of rotation therethrough and has a plurality of reflectors (20; 38) positioned at respective different angular locations around that axis, each of the said reflectors (20; 38) having two or more substantially planar reflecting faces (20a, 20b; 38a, 38b, 38c), two mutually-adjacent such faces (20a, 20b; 38a, 38b, 38c) meeting in a line (21) of intersection that is inclined with respect to the said axis of rotation; characterised in that the angle (ϑ₂) between the said two mutually-adjacent reflecting faces (20a, 20b; 38a, 38b) of each reflector is different from the angle (ϑ₂) between the said two mutually-adjacent reflecting faces of an adjacent reflector of the device. A device as claimed in claim 1, wherein the respective said lines (21) of intersection of adjacent reflectors (20;38) of the device are inclined respectively at different angles (ϑ₁) with respect to the said axis of rotation. A device as claimed in claim 1 or 2, wherein each of the said reflectors (38) has three substantially planar reflecting faces (38a, 38b, 38c), two (38a, 38b) of which faces are the faces of claim 1 and the other (38c) of which faces meets one of those two faces (38a, 38b) at a further line of intersection that is inclined with respect to the said axis of rotation. Optical scanning apparatus for scanning coded bars (26) by means of a laser beam (LB) to read a bar code of the coded bars (26), comprising: a light source (14) for generating a laser beam (LB); a rotary reflecting device (18; 32) as claimed in claim 2, or in claim 3 when read as appended to claim 2, for reflecting the laser beam (LB) from said light source (14) towards the coded bars (26); and a photodetector (30) for detecting diffused signal light reflected by the coded bars (26). Optical scanning apparatus as claimed in claim 4, wherein said rotary reflecting device (18; 32) has six reflectors (20; 38), arranged in three pairs, the reflectors (20; 38) of each pair of said reflectors (20; 38) being positioned respectively on opposite sides of said device (18; 32) with respect to the axis of rotation and having a mutually-identical arrangement of reflecting faces (20a, 20b; 38a, 38b, 38c). Optical scanning apparatus as claimed in claim 4 or 5, wherein said reflectors (20; 38) are provided on an outer periphery of the said rotary reflecting device (18). Optical scanning apparatus as claimed in claim 4 or 5, wherein the said rotary reflecting device (32) has a tubular configuration which is open at the top thereof, and said reflectors (34) are provided on an inner periphery of said tubular rotary reflecting device (32).

Inventors: KATOH HIROAKI, KITAMURA NOBUYUKI, MIYAZAKI TOSHIMASA, MURAKAWA YOSHITAKA, KATOH, HIROAKI, KITAMURA, NOBUYUKI, MIYAZAKI, TOSHIMASA, MURAKAWA, YOSHITAKA
Applicants: FUJITSU LTD, FUJITSU LIMITED
Application year: 1990
Main classification: G02B26
IPC codes: G02B26, G06K7, G02B5