Abstract:
The present invention comprises a device for reading a code on an article, comprising: a housing provided with at least two windows for passage of radiation which are disposed at a relative mutual angle; radiation source means for transmitting radiation to the article, which radiation source means are arranged in the housing and comprise at least two separate radiation sources; a rotatable polygonal mirror for reflecting radiation coming from the radiation source means; a number of fixedly disposed mirrors for reflecting through the respective windows the radiation coming from the polygonal mirror; and detection means for detecting the radiation scattered by the code.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a device and method ergonomically suitable for users for reading a code, such as a bar code, on, or scanning of, an article, wherein radiation is projected onto the article, from two sides, thereby preventing the person holding the article from having to turn it with awkward wrist movements. 
     Such devices are per se known, and the present invention has for its object to improve this invention, particularly in the sense that interruption of the reading process at the end of the lifespan of the laser is precluded and/or further possibilities are created by making wavelengths and/or focus points of both radiation sources mutually different. 
     SUMMARY OF THE INVENTION 
     The present invention comprises a device for reading a code on an article, comprising: 
     a housing provided with at least two windows for passage of radiation which are disposed at a relative mutual angle; 
     radiation source means for transmitting radiation to the article, which radiation source means are arranged in the housing and comprise at least two separate radiation sources; 
     a rotatable polygonal mirror for reflecting radiation coming from the radiation source means; 
     a number of fixedly disposed mirrors for reflecting through the respective windows the radiation coming from the polygonal mirror; and 
     detection means for detecting the radiation scattered by the code. 
     In the preferred embodiment wherein the radiation sources each transmit radiation of a different wavelength, it is possible in the case that one of the two wavelengths has difficulty in distinguishing the bar code from the background that the code can still be recognized using other wavelengths. 
     As a result of the preferred embodiment wherein each of the radiation sources is focussed at a different distance relative to the window, the area within which bar codes can be effectively scanned is enlarged. 
     The present invention further provides a method wherein the device according to the present invention is applied. 
     In each of the two above stated preferred embodiments the scanning potential is increased, whereby the movement of the article during the scanning movement by for instance a check-out operator requires the least possible adjustment, whereby the ergonomics are improved further. 
     In a further preferred embodiment the radiation sources each have a different polarization direction. In many cases the material of the bar code is sensitive to the polarization of the incident laser light such that a stronger reflection is obtained for one of the two radiation sources. It is then possible to take into account in the microprocessor for which polarization direction the best score of bar code recognition is obtained so that this can be switched ON more often than the other radiation source. 
     As much use as possible is preferably made of symmetrical scan patterns since, from a statistical viewpoint, there is no preference for the direction of the bar code. The scan lines are projected alternately whenever possible through each of the two windows. This further enables the use of the same components for a horizontal and a vertical window with fixed mirrors. It is however possible to suffice with a single polygonal mirror and sensor with associated analog electronics. 
     Finally, the present invention provides a number of co-acting devices according to the present invention, whereby a passage is obtained for scanning articles on all sides, for instance articles supplied on a conveyor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further advantages, features and details of the present invention will be elucidated on the basis of the following description of preferred embodiments thereof with reference to the annexed drawing, in which: 
     FIG. 1 shows a view in perspective of a preferred embodiment of a device according to the present invention; 
     FIG. 2 shows a schematic view in perspective of a device of FIG. 1; 
     FIGS. 3A,  3 B show respectively a top view and a view in cross-section of the device shown in FIGS. 1 and 2 to illustrate a first scan line; 
     FIGS. 4A,  4 B show respectively a top view and a view in cross-section of the device shown in FIGS. 1 and 2 to illustrate a second scan line; 
     FIGS. 5A,  5 B show respectively a top view and a view in cross-section of the device shown in FIGS. 1 and 2 to illustrate a third scan line; 
     FIGS. 6A,  6 B show respectively a top view and a view in cross-section of the device shown in FIGS. 1 and 2 to illustrate a fourth scan line; 
     FIGS. 7A,  7 B show respectively a top view and a view in cross-section of the device shown in FIGS. 1 and 2 to illustrate a fifth scan line; 
     FIG. 8 is a view in perspective of detail VIII in FIG. 2; 
     FIG. 9 is a schematic view in perspective of four devices according to the present invention wherein a tunnel is formed for scanning of an article on all sides; and 
     FIG. 10 shows a diagram of a preferred embodiment of the device according to the present invention; 
     FIGS. 11A and 11B show signals in the arrangement of FIG. 10; and 
     FIG. 12 is a view elucidating the increase in the scanning area in a preferred embodiment of the device according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A device  1  (FIG. 1) comprises a housing which is preferably constructed from identically shaped injection moulded components  3 ,  4  respectively  3 ′,  4 ′, wherein in components  4 ,  4 ′ are arranged windows  5 ,  5 ′ for passage of scanning scan lines a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, s respectively t. 
     The moving parts and the electronic components are arranged as far as possible in a corner par  6  of the housing. For rapid assembly, in addition to several screw connections between the parts  3 ,  3 ′ respectively  4 ,  4 ′ and the corner part  8 , slide elements  7 ,  8 ,  9 ,  10  are arranged for quick sliding together of the different components. Assembly is speeded up by omitting screw connections; the slide elements can likewise be injection moulded. 
     As can be seen particularly in FIG. 2, a number of fixedly disposed mirrors  21 ,  22 ,  23 ,  24 ,  25 ,  26 ,  27 ,  28 ,  29 ,  30 ,  31 ,  33 ,  34 ,  35 ,  36 ,  37 ,  38  are situated in the interior of housing  1 . Further arranged in corner part  6  are two laser sources  41  respectively  42 , the radiation of which is projected onto a fixed mirror  45  via further fixed mirrors  43 ,  44  (to the greatest possible extent reflective for the one laser and transparent for the other). The optical axes of both laser sources thus coincide as much as possible. The radiation from source  41  is projected via fixed mirrors  46 ,  47  and  44  onto mirror  45 . The radiation from both laser beams is projected onto the rotating mirror  50  which, depending on the position of the side surfaces thereof, projects radiation onto the fixed mirrors  21 - 28  or onto the fixed mirrors  30 - 38 . 
     The radiation scattered by the bar code on the article (not shown) reaches detector  53  via the same optical paths via focussing mirror  51  and fixed mirror  52 . 
     In the present preferred embodiment the radiation from laser source  41  has a wavelength of about 820 nm, while the wavelength of the laser light from laser source  42  amounts to about 670 nm. The focus points preferably also differ mutually, for instance with a difference of about 7 cm, so that the area of maximum detection of bar codes differs slightly for each of the two laser beams. 
     The different wavelength is of particular importance in cases wherein for a determined wavelength the distinction between bar code and background is insufficient. It is possible in a manner not shown to switch between the laser sources, for instance it is possible to switch between the laser sources at a fixed location during rotation of the mirror. 
     FIGS. 3A and 3B show in top view and side view how a line, for instance e, is projected from laser source  41  via mirrors  46 ,  47 ,  44 ,  45  and  29  onto polygonal rotatable mirror  50 , from where the line e is written using mirrors  28  and  25 . The radiation scattered by a bar code is received via the same optical path by a focussing mirror  51  and detected on detector  53  via fixed mirror  52 . 
     Line c (FIGS. 4A,  4 B) is written in similar manner from rotating mirror  50  via mirrors  23  and  24 . 
     A line such as h (FIGS. 5A,  5 B) is written from mirror  50  via mirrors  22  and  25 . 
     FIGS. 6A,  6 B shows a line such as q which is written from the housing part  3  from rotatable mirror  50  using fixed mirrors  33  and  31 . 
     In similar manner FIG. 7A shows a line such as m which is written from rotatable mirror  50  via mirror  36 . 
     FIG. 8 shows the rotatable mirror  50  which is preferably manufactured from plastic with vapour-deposited mirror surfaces and with which the diverse lines are written alternatingly per mirror surface  61 ,  62 ,  63 ,  64  from the lower window and the upper window. 
     In FIG. 9 is shown an arrangement wherein four devices according to the present invention  1 ,  1 ′,  1 ″,  1 ′″ are placed in a compact arrangement whereby an internal tunnel  60  is formed, inside which an article is transported in and out as according to arrow A or therethrough, so that an article can be scanned from all sides. 
     The preferred embodiment described in FIGS. 1 and 2 further preferably comprises a drive motor  61  for driving the polygon, the output signal A of which is connected to a means for dividing by two  62  since in this preferred embodiment a pulse is generated by motor  61  at each half-rotation, as indicated in FIG. 11A in which a time period t R  is shown. Multiplication by the signal from the means for dividing by two  62  (FIG. 113) results in the signal C as according to FIG. 11B, which is fed to a microprocessor  63  which is connected to a so-called host computer  64 . Sensor  53  detects the radiation and generates an analog signal which is converted in converter part  65  into a digital decoding signal which is likewise fed to microprocessor  63 . This latter further generates control signals to drive elements  66  and  67  for driving of lasers  41  and  42 . 
     In a manner not shown, the quadrangular polygon and the motor are both provided with a marking which are placed one above the other during assembly. The position of the polygon is hereby calibrated relative to the motor pulse as shown in FIG.  11 A. 
     A great number of options are thus possible for ON/OFF switching of the two laser sources. In a first preferred embodiment the polygon is for instance switched alternatingly at each half-rotation so that, as the surfaces of the polygon have a differing position at each quarter-turn, two lines are written in each case by one laser, one of these through the horizontal window and one through the vertical window. Thus ensured continuously to the best possible extent is that all pattern lines are present in the space to be scanned. 
     As noted earlier, laser sources  41  and  42  can have radiation with differing polarization direction, differing wavelengths and/or different focus points. In determined conditions one of the two laser sources will hereby achieve a better score in recognition of a bar code or bar code half. It is also quite conceivable for a first bar code half to be detected by radiation from the first laser source while a second bar code half is scanned by the other laser source. 
     By now recording in the microprocessor which of the two laser sources achieves the best “score” in recognizing a bar code, the switching of the laser sources can be changed, for instance to a ratio of 1:3 or 1:5, so that the laser source with the highest score is switched ON more often.