Barcode reading device

The invention relates to a bar code reading device for scanning a Barcodes along a scan direction with a laser light source for generating a transmitted light beam and a diaphragm for limiting the Cross-section of the transmitted light beam, wherein the aperture an aperture possesses whose outline comprises four contiguous portions, of which two sections facing each other and substantially transverse to the scanning direction run (cross-sections) and two of which Portions facing each other and substantially along the Scanning direction run (longitudinal sections).

Such bar code reading devices are used for scanning barcodes. The scanning direction corresponds to the direction of relative movement between the transmitted light beam and barcode. Such relative movement can for example be achieved by the bar code reading device having a deflection unit, through which the transmitted light beam at a stationary bar code along the scan direction deflected periodically is, or by a bar code along the scan direction by a stationary Transmitted light beam is guided.

The bar code acts on transmitted light beam appears at this as a light spot for the correct identification of the bars of the bar code should have a sufficiently small extent. In many applications, the bar code reader is the greatest possible depth of field desirable that the light spot is sufficiently small extension along the largest possible reading area in front of and behind the Barcode maintained. To this end, in addition to the use of imaging Optics using diaphragms with apertures known which limit the cross-section of the transmitted light beam and its Border to the above-mentioned manner with respect to the scanning direction in two opposite cross sections and two can today divide opposing longitudinal sections.

Limiting the expansion of the light spot by such aperture with correspondingly small openings, however, due to diffraction effects limited: The diffraction of the transmitted light beam at the border the aperture causes the progression of the intensity of the different light spot from an initially uniform flow significantly can. These diffraction phenomena on barcode interfere but the correct identification of strokes or their width disadvantageously Wise. Due to this effect the apertures, and thus can the cross section of the transmitted light beam are thus not reduced as desired, and the depth of field of the known bar code reading devices limited to an undesirable extent.

It is an object of the invention to provide a bar code reading device of the initially to provide said type which has an improved depth of field.

This object is achieved firstly by the fact that for the compensation of Diffraction phenomena of the transmitted light beam, the boundary of the diaphragm aperture on at least one cross-section at least one compensatory projection which, in relation to this cross-section direction the opposite transverse section as in Zwischenextremität the aperture protrudes.

By the compensatory projection invention in the direction of each opposite cross section of the aperture has, he runs at least approximately parallel to the scanning direction.

The formation of the compensatory projection as Zwischenextremität is characterized defined such that the border of the aperture in question to the Transverse portion opposite on both sides of the compensatory projection this is set back. Mathematically forms of compensation protrusion with its extension along the scanning direction so a maximum with respect to the relevant cross-section. The maximum can in this sense relative to the two ends of the corresponding cross section or regarding possible another compensatory projections local or constitute an absolute maximum.

The outline of the respective aperture, for example, a having substantially rectangular shape, either the two shorter or the two longer sides of the rectangle transverse to the extend scanning direction and therefore by definition the projection with a balance form provided cross section. In a similar way , the boundary of the diaphragm aperture also have an oval or round possess basic form.

The compensatory projection invention causes desirably an at least partial smoothing or superimposing those diffraction phenomena, by the dimming of the transmission light beam at the border the apertures to be created and attached to a barcode Fluctuations of the intensity distribution of the resulting light spot cause. A desirable balance created by the compensatory projection even cause diffraction phenomena unwanted the counteract diffraction phenomena at least partially and this slur or smear each other.

The compensatory projection thus causing an approximately continuous and smooth transition of the intensity from the center of the transmitted light beam to its edge region. It will not necessarily canceled all diffraction phenomena, however, are its negative Effects substantially reduced, so that an advantageously achieve greater inclusion and bundling the transmitted light beam leaves. Thereby, in bar code reading device of the present invention achieves a greater depth of field.

Particularly advantageously, the aperture invention proves if by the cross-section according to the invention, such a part of the transmitted light beam to be dimmed in comparison to the center the cross section of the transmitted light beam has a relatively high or even similar Intensity has, which ultimately leads to strong diffraction phenomena leads. This can occur, for example, when a transmitted light beam with an elliptical cross-section in such a way by means of an aperture of rectangular shape is to be limited so that the cross-sections of the Boundary of the diaphragm aperture a significantly larger part of the elliptical Cross-section of the transmitted light beam to dim as the longitudinal sections.

That the compensating projection at least at one cross section of the Aperture is provided, ie, at such a portion, the cross- and thus essentially is perpendicular to the scanning direction, harbors the following special feature: With such countervailing projection can in particular those from the boundary of the diaphragm aperture caused diffraction maxima and minima of the light spot on Barcode can be reduced, as in appearance intensity pattern substantially parallel to the extension direction of the barcode bars run, making it difficult especially strong their correct identification. Such diffraction maxima and minima are of the compensatory projection caused diffraction spikes pierced.

Another advantage of the diaphragm according to the invention is that they can be produced in a simple manner. The openings of conventional Aperture, for example by laser cutting, etching, stamping produced or drilling. This means no substantial or only little additional effort, in the boundary of the diaphragm aperture provide one or more compensatory projections.

In preferred embodiments of the inventive compensating projection this is designed as a wave or as a tongue in the example two straight or curved borders the outline form of Augleichsvorsprungs. These two boundaries can a acute or an obtuse angle with one another. Of the Compensatory projection can also be uniformly round shaped or be formed rectangular tongue. Furthermore, it is possible, the course the outline of the compensatory projection a stochastic pattern to give that to the desired purpose of compensating for diffraction phenomena deliberately chaotic diffraction pattern causes.

Finally, it is also possible to compensate with additional projection to provide lateral indentations or protrusions to the desired Effect of mutual compensation of the induced diffraction effects to further strengthen.

The boundary of the diaphragm aperture may at its two cross-sections possess a balance projection, so that the desired balance by diffraction phenomena selected both in and counter to the Scan direction. Furthermore, it is preferable if the question Cross-section and the two cross-sections of several compensatory projections exhibit. In addition, one or more compensatory projections of the aforementioned type also on a longitudinal portion or the two formed along portions of the boundary of the diaphragm aperture be.

By a plurality of balancing protrusions, the balance of Diffraction phenomena by their mutual blending and smoothing be particularly effectively caused. These multiple compensatory projections form along the cross section in question preferably a stochastic arrangement, ie, a non-periodic, especially targeted chaotic arrangement. Thereby, the occurrence of be avoided by periodic diffraction or interference patterns. However, even a periodic arrangement of a plurality of balancing protrusions the desired balance of the diffraction phenomena cause.

The object of the invention is for a bar code reading device of the kind mentioned secondly also achieved in that at least at a cross-section or longitudinal section of the boundary of the diaphragm aperture to compensate for diffraction effects of the transmitted light beam a filter is arranged, which for the transmission of the transmitted light beam a continuous or a stepped through the aperture Transition from essentially 100% in the center of the aperture effected to 0% outside the boundary of the diaphragm aperture. Thus, this approach aims of the border the aperture diffraction phenomena caused by attenuation equalize the light intensity.

The course of the transmittance of the filter, for example, a follow continuous history, in particular a linear or a gaußkurvenförmigen history. The transmittance can, however, also a discontinuous, in particular a stepped curve have, for example, individual diffraction maxima, which in itself a light spot on a barcode would manifest as intensity maxima, selectively attenuate. Alternatively, the filter can at least locally be formed as a neutral density filter so that it in these areas in substantially a constant transmittance has.

Preferably, the two transverse portions of the boundary of the Aperture, a filter of the type described is provided. It is also possible that each portion of the edge has such a filter. In particular, the along the filter can be formed as a round filter, the entire boundary of the diaphragm aperture is arranged.

The invention also extends to a diaphragm with an aperture, are limited by the cross-section of a light beam to and their border two longitudinal sections and two cross sections having provided that such aperture features that Aperture has, as in described connection with bar code reading device of the present invention is. Such orifice can be in a versatile manner in devices other than the bar code reading device according to the invention Insert.

Another preferred invention of the invention are in the dependent claims described. The invention will be referred by Embodiments described with reference to the drawings; in which:<dl tsize="16"><dt>figure 1</dt><dd>is a schematic perspective view of parts of a bar code reading device according to the invention,</dd><dt>figure 2a</dt><dd>the superposition of the elliptical cross-section of a Transmitted light beam over a rectangular outline an aperture,</dd><dt>figure 2b</dt><dd>the intensity curve is one of the transmitted light beam caused according 2A light spot along the Scanning direction,</dd><dt>2c</dt><dd>the intensity curve is one of the transmitted light beam caused according to Figure 1 the light spot along the Scanning direction, </dd><dt>Figures 3a - 3h</dt><dd>different apertures with different inventive Balancing protrusions, and</dd><dt>Figures 4a, 4b</dt><dd>Aperture invention with gray filters or graduated filters.</dd></dl>

Figure 1 shows a schematic perspective view of parts of an inventive Bar code reading device. This has a laser light source 11, emitting a transmitted light beam 13, with only the in figure 1 represented by the center of the transmitted light beam 13 extending beam axis is. Along the transmitted light beam 13 are connected in an inventive Diaphragm 15, a trained as a partially transparent mirror 17 Beam splitter and acting as a deflecting unit, in the direction 18 rotating polygon mirror 19. The polygon mirror reflects 19 in varying deflection angles the emission light beam 13 in the direction a barcode element 21st

The transmitted light beam 13 appears on the barcode element 21 as an in Scan direction 43 migratory light spot 23, and he is among other things from there as Reception light beam 25 reflected toward the polygon mirror 19th This reception light beam 25 is from the polygon mirror 19 in the direction the partially transparent mirror 17 and from this to a receiver element 27 diverted.

The diaphragm according to the invention 15 has an aperture 31 of rectangular shape. The border 33 of the aperture 31 has two opposite cross-sections 35 as well as two mutually opposed, rectilinear formed longitudinal sections 37. Each the two cross sections 35 has three shaped than sharp spikes Compensatory projections. 39

While caused by the rotating polygonal mirror 19 periodic Deflecting the transmitted light beam 13 due to the uniform Rotation 18 of the polygon mirror 19 only in a single direction takes place, is the scan direction 43 in Figure 1 and in the other Figures shown as a double arrow, as it in known bar code reading devices is irrelevant in which of the two by the illustrated Scan direction 43 predetermined directions of the barcode from the transmitted light beam 13 is covered. In addition, instead of the polygon mirror be 19 provided as a deflection unit, a vibrating mirror, through which the transmitted light beam 13 oscillating along the two by the scanning direction 43 predetermined directions is deflected.

In the area of ​​the aperture 15 of the transmitted light beam 13 undergoes Although no periodic Redirection. Since the transmitted light beam 13 at the polygon mirror 19, however, undergoes a purely geometrical reflection, is also in the field of Lens 15 is a scanning direction 43 at the barcode element 21 corresponding Scanning direction 43 'clearly defined. The position of the two cross-sections 35 of the aperture 31 and the projections formed thereon compensation 39 correspond to the invention of this scanning direction 43 ' abhähgig. Purpose and advantage of this function will now be based of Figures 2a to 2c explained.

2a shows a known aperture 45 with an opening whose border in the sense of the definition mentioned above with respect to the scanning direction 43 'two respective mutually opposed and linearly formed Cross sections 47 and having longitudinal sections 49th The aperture 45 is in the border of their opening of a transmitted light beam elliptical cross-section acted upon in such a way that the cross-sections 47 and the longitudinal sections 49 each in the representation according to Figure 2A shown shaded edge area 51 of the transmitted light beam Dim.

The cross sections 47 and longitudinal sections 49 cause diffraction of the aperture of the stop 45 passing through the transmitted light beam so that The intensity profile of the remaining cross-section of the transmitted light beam Diffraction maxima and minima having. Figure 2b shows schematically the profile of the light intensity I of the transmitted light beam after This aperture 45 has happened according to 2a, and indeed for a sufficient Distance from the aperture 45 and for different positions X along an axis 53, within the cross section of the transmitted light beam through the center thereof and parallel to the scanning direction 43 'and 43 runs.

If the cross section of the respective transmitted light beam before it passes through the aperture 45 a substantially gaußkurvenförmiger History its intensity is believed shows the intensity profile I of the by Passing through the aperture 45 remaining transmitted light beam - as in Fig. 2b - deviations from this Gaußkurvenform effect that at both the respective edge portion of the remaining transmission beam corresponding flanks significant intensity maxima and minima can be seen. Just this 2b in Figure apparent diffraction phenomena along the axis 53 and thus along the scan direction 43 may particularly complicate the scanning of a barcode.

These undesirable diffraction phenomena can at least partially be compensated by the fact that instead of the aperture 45 of rectangular Opening a shutter of the invention is used 15 as above with reference to Figure 1 and in the following figures 3a - 3h is explained. If again by a transversely elliptical cross section and a gaußkurvenförmigen intensity profile of the original is the transmitted light beam is considered as follows, after passing through a Inventive diaphragm 15 an intensity curve I along Scanning direction 43, further approximate a Gaußkurvenform follows and schematically for a sufficient distance from the aperture 15 is shown in Fig. 2c. The diaphragm 15 according to the invention can therefore, the undesirable diffraction phenomena largely suppress. This can be 15 used to this aperture, the transmitted light beam 13 even more laterally limit what ultimately beneficial may allow an extended depth of field.

Starting with a rectangular or any other basic shape is for the inventive aperture 15 a multitude of possible configurations with at least one compensatory projection at at least 39 a cross section 35 of the rim 33 of their opening 31 possible. Examples are in Figures 3a - 3h shown.

As shown in FIGS 3a and 3c each having a diaphragm 15 in which both Cross sections 35 of the edge 33 two trained than sharp spikes have compensation projections. 39 3b shows three Balancing protrusions 39 at each cross section 35. In the figures 3d and 3e is provided at each cross-section 35 each have a projection 39 compensation formed as acute wave. The border 33 of the aperture 31 shown in FIG 3f starts from a basic square shape, wherein both on the two transverse portions 35 as well at the two Longitudinal sections 37 each have two rectangular tongues as compensatory projections 39 are provided. Figure 3g shows compensatory projections 39 are designed as round tongues. are cross sections from FIG 3h 35 seen that in each case several as stochastic pattern formed Balancing projections 39 comprise respective cross-section of which along the 35 also form a stochastic arrangement.

Figures 4a and 4b, finally, show aperture 61 with apertures 63 whose respective border at least in sections according to the invention is provided with a filter.

The aperture 63 of the aperture 61 of FIG 4a has a rectangular Basic shape, with a cross along the two portions 65 each first gray filter 67 and thereafter each a second neutral density filter positioned 69th To create a discontinuous transition of Transmittance of the aperture 61 from the center of its opening 63 in Direction of the respective cross-section 65 has the first gray filter 67 a lower transmittance than the second neutral density filter 69. As part of the invention may also further filter areas of a particular Transmittance at the transverse portions 65 or the Longitudinal sections 73 can be provided, and the gradation of the transmittances the different gray filters 67, 69 may also be in an alternating Order or related to the aforementioned order carried out in the reverse sequence.

4b shows a diaphragm 61 with a round aperture 63. Along the the entire border of this orifice 63, that is along both the Transverse portions 65 and along the longitudinal portions 73, is an annular Graduated Filter placed 71, which, starting from its in Toward the center of the aperture 63 side pointing radially outwardly having an ever lower transmittance.

The filter shown in Figures 4a and 4b 67, 69, 71 are used to compensate of diffraction phenomena similar to that of those portions 65, 73 Boundary of the diaphragm aperture 63 are caused, at which the respective Filters 67, 69, is arranged 71st This is to limit the Cross section of a light beam relatively small expansions or diameter of the orifice 63 is possible without the diaphragm 61 diffraction phenomena causes in the light beam, which provided the Use of the light beam, for example, scanning a barcode, would interfere significantly.

<b>LIST OF REFERENCE NUMBERS</b>

<dl tsize="4" compact="compact"><dt>11</dt><dd>Laser light source</dd><dt>13</dt><dd>Transmitted light beam</dd><dt>15</dt><dd>aperture</dd><dt>17</dt><dd>partially transparent mirror</dd><dt>18</dt><dd>direction of rotation</dd><dt>19</dt><dd>polygon mirror</dd><dt>21</dt><dd>Barcode element</dd><dt>23</dt><dd>light spot</dd><dt>25</dt><dd>Reception light beam</dd><dt>27</dt><dd>receiving element</dd><dt>31</dt><dd>aperture</dd><dt>33</dt><dd>border</dd><dt>35</dt><dd>cross section</dd><dt>37</dt><dd>longitudinal section</dd><dt>39</dt><dd>compensatory projection</dd><dt>43</dt><dd>scanning direction</dd><dt>43 '</dt><dd>scanning direction</dd><dt>45</dt><dd>aperture</dd><dt>47</dt><dd>cross section</dd><dt>49</dt><dd>longitudinal section</dd><dt>51</dt><dd>Edge region truncated</dd><dt>53</dt><dd>axis</dd><dt>61</dt><dd>aperture</dd><dt>63</dt><dd>aperture</dd><dt>65</dt><dd>cross section</dd><dt>67</dt><dd>First Graufilter </dd><dt>69</dt><dd>second Graufilter</dd><dt>71</dt><dd>Graduated filter</dd><dt>73</dt><dd>longitudinal section</dd><dt>I</dt><dd>Intenstität the transmitted light</dd><dt>X</dt><dd>position</dd></dl>