Electro-optical scanner having stationary, multi-surface mirror having surfaces with aplanar profiles

REFERENCES TO RELATED APPLICATION

0001This application is a division of U.S. patent application Ser. No. 09/009,231, filed Jan. 20, 1998, now U.S. Pat. No. 5,988,502 which, in turn, is a continuation-<i>in</i>-<i>part of application No. <b>08</b>/<b>912</b>,<b>147</b>, filed on Aug. <b>15</b>, <b>1997</b>, now U.S. Pat. No. <b>5</b>,<b>859</b>,<b>417</b>, which </i>is a continuation-in-part of U.S. patent application Ser. No. 08/405,585, filed Mar. 17, 1995, now abandoned, which is a continuation-in-part of U.S. patent application Ser. No. 08/268,982, filed Jun. 30, 1994, now U.S. Pat. No. 5,742,038, which is a continuation-in-part of U.S. patent application Ser. No. 08/314,519, filed Sep. 28, 1994, now U.S. Pat. No. 5,506,392, which is a divisional of U.S. patent application Ser. No. 08/109,021, filed Aug. 19, 1993, now U.S. Pat. No. 5,352,922, which is a divisional of U.S. patent application Ser. No. 07/735,573, filed Jul. 25, 1991, now U.S. Pat. No. 5,278,397, and is related to U.S. patent application Ser. No. 08/864,452, filed May 28, 1997,now allowed.

BACKGROUND OF THE INVENTION

00021. Field of the Invention

0003The invention relates generally to optical scanners, and in particular to scanners having dual or multiple working ranges.

0004Most optical scanners such as bar code scanners are adapted for use at a particular distance, or a range of distances, from an indicia to be scanned. If the user holds the scanner too close to the indicia, or too far away, the indicia and/or the flying spot beam will not be in focus, and decoding will not be possible.

0005Such scanners may not be particularly convenient in environments where a series of indicia to be read are presented to the scanner at various distances, and where it is difficult or impossible for the user to alter the distance between the scanner and the indicia. To deal with such situations, attempts have been made to expand the acceptable working range of conventional scanners, to give the user as much leeway as possible, and also to provide multi-distance scanners which can operate, for example, at a first working range or at a second working range according to the user's preference or requirements. One possibility is for the provision of a two-position switch on the scanner, with the scanner operating at a first working distance in a first position of the switch and at a second working distance in a second position. A disadvantage of such scanners is that they require additional moving parts to provide for operation at the two separate working ranges. Such systems are also not “automatic” in the sense that the user has manually to select the correct working range, according to the distance of the current indicia to be read; if the incorrect working range is chosen, a decode will not result.

0006One or the difficulties that bar code reader designers face when attempting to produce increased working ranges is that the greater the working range, and the greater the range of possible indicia that might be read, the lower tends to be the resultant signal to noise ratio in light that is reflected from the indicia. One approach for dealing with this involves the provision of non-conventional optics, in which the optics associated with either the laser or with the photodetector have two distinct focal points. An example of this is shown in U.S. Pat. No. 5,332,892, which is commonly assigned with the present application. In the device shown in that document, the two focal points are associated with corresponding circuitry to provide two separate channels of data derived from the scanned bar code. The two channels have differing resolutions. As the working angle and density vary, at least one of the resolutions is likely to be appropriate for sensing all or most of the bar coded data, regardless of the distance of the bar code with respect to the scanner and/or the size or density of the code. The scanning beams of bar code readers are typically derived from laser diodes. Such diodes are robust and relatively inexpensive, but they do suffer from the disadvantages that the beam emerging from a laser diode is astigmatic. The astigmatic laser diode can be characterized as having two apparent light sources spaced apart from each other along the optical path. One of the light sources lies in a horizontal plane, appears to be coming from inside the laser diode chip, and has a low angular divergence. The other apparent light source lies in a vertical plane, appears to be coming from a facet of the chip, and has a high angular divergence. The two apparent light sources, which are spaced apart from each other by typically about 20 micrometers, form two beam waists in different planes and in different directions, as measured relative to the planar junction of the chip.

0007The resultant relatively complex beam profile may need selective shaping before it can efficiently be used in an optical scanner. Some methods of providing such beam shaping are described in our co-pending U.S. patent application Ser. No. 08/268,982, filed Jun. 30, 1994, the teachings of which are incorporated herein by reference.

0008A simpler option is simply to provide separate long and short range visible laser diodes, as is suggested in our earlier patent U.S. Pat. No. 5,420,411.

0009A further problem associated with known arrangements is that of distinguishing the respective images received corresponding to objects in each working range.

0010The present invention, in various other embodiments, further relates to optical scanning stations having a conveyor for moving articles carrying indicia to be read past an optical scanner, and to optical scanners having means for manually or automatically selecting one of a plurality of desired scan patterns.

0011The invention further relates, in yet further embodiments, to scanners having an extended working range using two lasers, each focused to cover a different portion of the scan distance. Present systems turn on one laser for a full scan, and then the second laser for the next scan, alternating on a scan-by-scan basis. Since, in general, only one of the lasers is capable of reading a bar pattern at any given distance, this technique typically doubles the length of time that it takes to generate a successful decode over single-laser embodiments. There is a need to regain the aggressiveness of a one-laser scanner, while maintaining the range benefits of the two-laser system. One device making use of two lasers is disclosed in our application Ser. No. 08/405,585, filed Mar. 17, 1995, now abandoned, the disclosure of which is incorporated herein by reference.

SUMMARY OF THE INVENTION

0012Objects of the Invention

0013It is an object of the present invention at least to alleviate the problems of the prior art.

0014It is a further object to provide a multiple working range optical system, for example for a scanner arrangement capable of distinguishing between respective images corresponding to images in different working ranges.

0015It is yet a further object of the invention to provide a multiple working range optical scanner arrangement having a minimum of imaging and image-recording elements.

0016It is yet a further object of the invention to provide an optical scanner capable of being easily and conveniently mounted for optimum operation and user comfort.

0017It is yet a further object of the invention to provide a convenient and easily-operable optical scanning station, for example for use at a point of sale.

0018It is a further object to provide an optical scanner capable of generating different scan patterns using a single scanning mechanism.

0019It is yet a further object to provide an optical scanner which maintains the range benefits of a two-laser system, while providing the rapid decoding typical of a one-laser system.

0020According to the present invention there is provided a multi scan-pattern optical scanner including a laser assembly for producing a plurality of laser beams of differing wavelengths and a scanning mechanism including a wavelength selector for selectively passing a beam of predefined wavelength, thereby producing at least a first scan pattern from a beam which is passed by the selector and a second scan pattern from a beam which is stopped by the selector.

0021A device of this type allows for the creation of multiple scan patterns without the need to have individual scanning mechanisms for each pattern. In a preferred embodiment, parts of the scanning mechanism are coated or otherwise provided with filters to absorb, or to prevent the reflection of, at least one of the beams. Alternatively, parts of the mechanism may be coated so that only those coated parts reflect one of the beams. Preferably, the coatings may be thin coatings which achieve their reflective/absorptive effect by optical interferences.

0022It would also be possible to provide holographic optical elements and/or diffraction gratings to separate two laser beams of differing wavelengths, and thereby allow them to be deflected differently by a single scanning mechanism.

0023Preferably, each laser is provided with its own optical assembly, providing individual focusing and allowing each laser to scan efficiently at a given working distance. To extend the overall working range even further, more than two lasers could be used, each having its own working distance.

0024The invention extends to any individual feature described above or set out in the specific description, and to any compatible combination of features. It is to be understood, in particular, that features shown in relation to one figure may be combined, where compatible, with features shown in connection with any other figure.

BRIEF DESCRIPTION OF THE DRAWINGS

0025The invention may be carried into practice in a number of ways and several specific embodiments will now be described, by way of example, with reference to the accompanying drawings, in which:

0026<figref idref="DRAWINGS">FIG. 1a</figref> shows a multiple range optical system according to an embodiment of the present invention;

0027<figref idref="DRAWINGS">FIG. 1b</figref> is an end view of the multi-focus lens used in the arrangement of <figref idref="DRAWINGS">FIG. 2a</figref>;

0028<figref idref="DRAWINGS">FIG. 2</figref> shows a typical bar code scanner in conjunction with which the present invention may be implemented;

0029<figref idref="DRAWINGS">FIG. 3a</figref> shows a mounting option for an optical scanner;

0030<figref idref="DRAWINGS">FIG. 3b</figref> shows a user carrying the optical scanner in the mounting option of <figref idref="DRAWINGS">FIG. 3a</figref>;

0031<figref idref="DRAWINGS">FIG. 4a</figref> shows an alternative mounting option for an optical scanner;

0032<figref idref="DRAWINGS">FIG. 4b</figref> shows the optical scanner of <figref idref="DRAWINGS">FIG. 4a</figref> being used in dismounted mode;

0033<figref idref="DRAWINGS">FIG. 5</figref> shows the internal arrangement of the scanner of <figref idref="DRAWINGS">FIG. 3a</figref> incorporating the multiple range optical system of <figref idref="DRAWINGS">FIG. 1</figref>; and

0034<figref idref="DRAWINGS">FIGS. 6a-6c</figref> show an exemplary housing for a bar code scanner for use with any of the embodiments of the present invention;

0035<figref idref="DRAWINGS">FIG. 7</figref> schematically illustrates an embodiment of a scanner having two pulse-mode operated lasers;

0036<figref idref="DRAWINGS">FIG. 8</figref> shows a variation on the embodiment of <figref idref="DRAWINGS">FIG. 7</figref>;

0037<figref idref="DRAWINGS">FIG. 9</figref> illustrates the use of filtered optics to implement multi-scan pattern generation; and

0038<figref idref="DRAWINGS">FIGS. 10a</figref> to <b>10</b>c show scan patterns generated by the embodiment of <figref idref="DRAWINGS">FIG. 9</figref>;

0039<figref idref="DRAWINGS">FIG. 11</figref> shows yet another embodiment, namely a dual-range scanner using dual laser beams;

0040<figref idref="DRAWINGS">FIG. 12</figref> shows in more detail a segmented scan mirror used in the embodiment of <figref idref="DRAWINGS">FIG. 11</figref>;

0041<figref idref="DRAWINGS">FIG. 13</figref> shows a laser scanner according to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

0042Referring first to <figref idref="DRAWINGS">FIG. 1</figref>, there is shown a multiple working range optical system according to one embodiment of the present invention, forming effectively an imaging auto-focusing device. The arrangement comprises a lens system L₁,L₂and a narrow band filter system NBF₁,NBF₂. Although any number of lenses and filters can be included allowing, as will become clear from the following discussion, a corresponding number of working ranges, in the present embodiment for the purposes of simplicity a system including two lenses and associated filters is shown, providing two working ranges.

0043The lens system shown in <figref idref="DRAWINGS">FIGS. 1a and 1b</figref> comprises two semi-circular convex lens elements L₁, L₂with respective focal lengths F₁,F₂. Two working ranges W₁, W₂are selected and the lens power of the respective lens element is selected such that the conjugate image planes corresponding to the object planes defined by working ranges W₁, W₂coincide at plane P. Accordingly a first object S₁at working range W₁is focused onto plane P by lens element L₁. Additionally a second object S₂at working range W₂is focused by lens element L₂at plane P. Thus the system is able automatically to focus objects at different ranges. It will be understood that, in the case of a bar code reader, the objects S₁,S₂would be bar code symbols to be read. Because the conjugate image planes coincide for the working ranges, only a single detector D is required; this could, for example, be a charge coupled device array, or conventional film. Furthermore complex beam propagation or mirror assemblies are not required. In order to increase the number of working ranges the lens system is simply enhanced by including further lens elements and associated filters arranged to image objects in additional working ranges onto the plane F. In such a case, each lens element would form a segment of a circular multi-focus lens.

0044Associated with each lens element L₁, L₂is a respective spectral narrow band filter NBF₁, NBF₂. The filters NBF₁, NBF₂are arranged to pass different wavebands of light received from the objects S₁,S₂. As a result the images of the objects S₁, S₂at plane P are composed of light of different wavelengths and can be resolved from one another. In order to do this, the system is provided with additional movable, filters NBF₁′, NBF₂′. Each filter can be moved into position in front of the detector D to allow light of the relevant wavelength to pass dependent on which working range is selected. If the working range W₁is selected, light from the object S₁passes through the lens element L₁, is filtered at NBF₁, and then passes through the movable filter NBF₁′ (now in position in front of the detector D); light which may have passed through NBF₂and lens element L₂is blocked at NBF₁′ and so cannot form an image at D. If the working range W₂is selected, NBF₂′ is moved into position, and S₂is imaged; light from S₁passing through L₁and NBF₁is then blocked at NBF₂′.

0045<figref idref="DRAWINGS">FIG. 2</figref> illustrates an exemplary hand-held laser scanner suitable for use with the embodiment of <figref idref="DRAWINGS">FIG. 1</figref>, or indeed suitable for use with any other compatible embodiments to be subsequently described.

0046The scanner of <figref idref="DRAWINGS">FIG. 2</figref> comprises a main body <b>1</b> having a graspable hand portion <b>2</b> which carries a trigger <b>3</b>. Within the body <b>1</b> is a laser module <b>4</b>. Light from the laser module <b>4</b> is arranged to shine onto an oscillating mirror <b>5</b>. The resulting beam <b>6</b> passes out of the housing via a window <b>7</b>. The mirror <b>5</b> is arranged to oscillate in such a way that the beam <b>6</b> traces out a scan line <b>8</b> across an indicia <b>9</b> to be recorded. Light reflected back from the indicia passes through the window <b>7</b>, is collected by a collecting mirror <b>10</b>, and is reflected to a photodetector <b>11</b>. The optical signal is then converted into an electrical signal and the features of the indicia <b>9</b> determined.

0047In order to modify the bar code scanner a multiple working range optical system described in detail below is included in the system. The system can be inserted at an appropriate point in the path of the light beam reflected from the indicia <b>9</b>, for example between the window <b>7</b> and the collecting mirror <b>10</b> or between the collecting mirror <b>10</b> and the photodetector <b>11</b>. Indeed components of the standard bar code scanner such as the collecting mirror can be removed and replaced by the optical system according to the present invention.

0048The arrangement of <figref idref="DRAWINGS">FIG. 1</figref> may, in the preferred embodiment, be used in association with the housing shown in <figref idref="DRAWINGS">FIGS. 3a-3d</figref>. <figref idref="DRAWINGS">FIGS. 3a-3c</figref> show from left to right, a front, side and perspective view of a pendant-held scanner <b>20</b>. As discussed below in more detail with reference to <figref idref="DRAWINGS">FIG. 5</figref> the scanner <b>20</b> includes a housing <b>21</b> in which are included a light beam generating means such as a laser or light emitting diode, a light-beam-directing means such as a lens system, a scanner window <b>22</b> and a detecting means such as a CCD array. The light beam passes through the scanner window, is reflected by a printed indicia such as a bar code symbol and returns to be detected by the detecting means.

0049It will be seen that the scanner <b>20</b> is mounted on a strap <b>23</b> and, as shown in <figref idref="DRAWINGS">FIG. 3d</figref>, is carried by a user <b>24</b> with the strap <b>23</b> around the neck of the user <b>24</b>. Accordingly, if the user wishes to read a bar code symbol <b>25</b> on an item <b>26</b> the item <b>26</b> is simply positioned with the bar code symbol <b>25</b> pointing generally towards the user and the bar code symbol <b>25</b> is read automatically by the pendant scanner <b>20</b>. It will be seen that the scanner window <b>22</b> is preferably located on the pendant scanner so as to face outwardly.

0050It will be seen that this arrangement can be advantageously used in association with the multiple range optical scanner system described above; the working ranges of the scanner can be determined to correspond with parameters determined ergonomically by the user; for example a first working range can correspond to the arrangement shown in <figref idref="DRAWINGS">FIG. 3d</figref> in which the item <b>26</b> is held at the user's waist level, and a second working range can correspond to an item being held at arms length. The scan area of the scanner <b>20</b> is shown in <figref idref="DRAWINGS">FIG. 3d</figref> at <b>27</b>.

0051<figref idref="DRAWINGS">FIGS. 4a and 4b</figref> show alternative mountings for an optical reader. <figref idref="DRAWINGS">FIG. 4a</figref> shows a point of sale application which could be applied equally in other applications whether the operator remains stationary and it is appropriate to move items to be scanned past the scanner rather than vice versa. A scanner <b>30</b> is shown mounted over a conveyor <b>31</b> at a point of sale <b>32</b>. The scanner <b>30</b> is mounted on a support such as an arch <b>33</b> over a conveyor <b>31</b>. As items <b>34</b> on the conveyor <b>31</b> pass under the arch <b>33</b> bar code symbols <b>35</b> on the items <b>34</b> are read by the scanner <b>30</b>. In the embodiment shown the scanner <b>30</b> is roughly the shape of a quadrant of an ovoid with two substantially planar faces, a side face extending in the direction of the long axis of the ovoid and an end face extending in the direction of the short axis to the ovoid. The end face carries a scanning window <b>37</b> as shown in FIG. <b>4</b>b. When mounted on the arch <b>33</b> the scanner <b>30</b> is oriented with its end face and scanning window <b>37</b> pointing downwards towards the bar code symbol <b>35</b> to be read.

0052In a further preferred option the scanner <b>30</b> can be detechably mounted on the arch <b>33</b> for example by including resilient gripping means on the arch <b>33</b>. Accordingly the scanner <b>30</b> can be removed from the arch <b>33</b> and held in the user's hand <b>38</b> as shown in FIG. <b>4</b>b. The end face and scanning window point outwardly away from the user's body and a control button <b>39</b> is placed on the planar side face so as to be easily operable by the user's thumb. The curved surface of the scanner <b>30</b> then fits snugly and comfortably into the user's hand <b>38</b>. The scanner <b>30</b> can be simply aimed at an article to be scanned and operated by actuating button <b>39</b>. As a result the scanner <b>30</b> can be used in a wide variety of applications and in particular, for example, applications where items are too bulky or heavy or inappropriately positioned to be passed under the arch <b>31</b> and scanned.

0053<figref idref="DRAWINGS">FIG. 5</figref> shows in more detail the pendant scanner of <figref idref="DRAWINGS">FIGS. 3a-3d</figref> incorporating the multiple working range optical arrangement of FIG. <b>1</b>a. The scanner <b>20</b> is shown in partial cross section and partly from one side. The scanner comprises an elongate body having a long broad face <b>40</b> for resting against the user's chest when used as a pendant and an opposing face <b>41</b> in which is positioned a scanning window <b>42</b>. The opposing face <b>41</b> is preferably slightly curved or otherwise inclined such that the scanning window points at a shallow downwards angle as ergonomically appropriate when the user is holding an item to be scanned at waist level.

0054The scanner <b>20</b> includes a light source <b>43</b> such as a laser or LED and a scanning mirror <b>44</b> which is rotated in a known manner to oscillate about an axis A. The light beam <b>45</b> generated by the laser <b>43</b> is reflected by the mirror <b>44</b> through the scanning window <b>42</b> onto a printed indicia such as a bar code symbol <b>46</b> to be read. Light reflected from the bar code symbol <b>46</b> passes back through the window <b>42</b> and is reflected once more by the mirror <b>44</b> via the lens system L₁, L₂onto a detector <b>47</b> such as a CCD array aligned with the image conjugate plane P. As discussed above, narrow band filters NBF₁′, NBF₂′ are associated with the lenses L₁, L₂respectively and can be moved in the direction implicated by the double-headed arrows in and out of position in order to select a desired working range. The filters are mounted for reciprocal movement by means of a rack <b>48</b> which is driven back and forth by a toothed wheel <b>49</b> driven by a motor and controller (not shown). Of course, any suitable method can be used.

0055It will be appreciated that the lens elements L₁, L₂can be replaced by any suitable optical arrangements such as holographic elements, prisms or gratings. The narrow hand filters may be of any known type.

0056The desired working range can be selected manually by user input, or automatically by identifying for which working range an object is focused, for example by introducing each of the filters in turn and ascertaining which of the narrow band images is in focus.

0057An alternative scanner housing is illustrated schematically in <figref idref="DRAWINGS">FIGS. 6a-6c</figref>. This is suitable for use with the embodiment of <figref idref="DRAWINGS">FIG. 1</figref>, and/or for the embodiments of <figref idref="DRAWINGS">FIG. 7</figref> onwards.

0058The scanner housing of <figref idref="DRAWINGS">FIGS. 6a</figref> to <b>6</b>c comprises an integrally molded and shaped head portion <b>100</b> and manually-graspable handle portion <b>102</b>. Within the head portion <b>100</b> are the scanning optics, for example those shown schematically in FIG. <b>2</b>. At the front end of the head portion <b>100</b> is a window <b>104</b> through which the scanning laser beam (not shown) exits the housing, when scanning is initiated by the user pressing the trigger <b>106</b>. Information on the detected bar code symbol or other indicia is passed out of the scanner along a lead <b>108</b> to a base unit (not shown). Strain relief is provided by a flexible strain-relief element <b>109</b>.

0059The housing incorporates front and rear feet <b>110</b>,<b>112</b>, enabling the scanner to be laid down in the position shown on a flat desk top or other surface <b>114</b> (FIG. <b>6</b>a).

0060One method of achieving multiple working distances, for example within a bar code scanner, has already been described with reference to FIG. <b>1</b>a. Reference should now be made to <figref idref="DRAWINGS">FIG. 11</figref> which shows an alternative approach.

0061This embodiment incorporates dual laser assemblies <b>1310</b>, <b>1311</b> emitting parallel beams. The laser assembly <b>1310</b> is focused for short-range operation. This will be referred to, for shorthand, as the “short-range laser”. Similarly, the laser assembly <b>1311</b> is focused for long-range operation. This will be referred to, for shorthand, as the “long-range laser”. Appropriate optics <b>1312</b>, <b>1314</b> define the working range and different beam profile characteristics of the lasers. Alternatively, the short-range laser, and its optics, may be identical with the lone-range laser and its optics.

0062The beam from the long-range laser <b>1311</b> is reflected by a pair of parallel angled mirrors (or by an appropriately shaped prism) so that the two resultant laser beams are closely parallel to each other. The beams impinge upon a scanning mirror <b>1322</b> from which they are reflected onto an indicia to be read (not shown, but off to the left of the drawing in FIG. <b>11</b>).

0063Instead of there being separate long range and short range lasers, a single laser could be used instead with appropriate optics (for example a beam splitter).

0064Light reflected back from the indicia is collected by the mirror <b>1322</b> (which acts as a collection mirror as well as a scanning mirror) and is directed to a photodetector <b>1324</b>).

0065Details of the mirror <b>1322</b> are shown in FIG. <b>12</b>. As will be seen, the mirror is generally curved, and includes a large area of collecting surface <b>1323</b> with a central section which is split into two. The left side of the central section <b>1325</b> has a cylindrical profile, and the right hand section <b>1327</b> a flat profile. The light beam from the short-range laser <b>1310</b> impinges upon the portion <b>1325</b>, and the light from the long-range laser <b>1311</b> impinges upon the portion <b>1327</b>.

0066In use, a laser control <b>1326</b> operates the lasers so that they are switched on and off alternatively. The system is controlled so that two scans (left to right, then right to left) are performed with the long-range laser on, and then two scans with the short-range laser on. The alternation continues until a successful decode has been achieved.

0067The system also provides for an aiming mode which is initiated by a user selecting a first position of a trigger <b>1328</b> on the scanner housing <b>1330</b>. In this mode, the controller <b>1326</b> causes the long-range laser <b>1311</b> to blink on and off while moving the mirror <b>1322</b>. In this mode the user can easily see the scanning beam and he can align the indicia accordingly. As soon as the indicia has been properly aligned with respect to the scanner, the user moves the trigger <b>1328</b> to a second position to commence scanning proper.

0068In another embodiment, the laser assemblies <b>1310</b>, <b>1311</b> have lasers of different frequencies. Visible laser diodes are now available in two different wavelengths, 635 mm and 670 mm. The shorter wavelength device (635 mm) is more visible to the eye, and may preferably be used in high ambient light conditions or for aiming. Thus, in the preferred implementation, the 670 mm laser diode could be focused as the “short range laser” and the 635 mm laser diode focused as the “long range laser” since at long range the brightest beam is desirable for visibility and aiming. In high ambient light conditions, it is possible to use both lasers on, rather than alternate between the lasers. Although there will be two beams, if the beams are properly focused at the target plane so the spots are overlapping or very closely adjacent, the bar code symbol can be effectively read.

0069In still another embodiment, one of the laser assemblies <b>1310</b>, <b>1311</b> is a visible laser and the other assembly an IR laser, whose beam is generally not visible to the eye. IR lasers are suitable for use in applications such as reading security badges that require an IR reading beam, reading direct thermal printed bar codes; and reading certain colored bar codes. The same arrangement as shown in <figref idref="DRAWINGS">FIG. 11</figref> may be used, except there is no limitation that the optics be “short range” or “long range”. As in the previous embodiment, one can alternate scans between lasers or use both lasers on.

0070Yet another embodiment is shown in FIG. <b>7</b>. Here lasers <b>201</b>,<b>202</b> are used, each having its own separate focusing optics <b>203</b>,<b>204</b>. The optics differ in focal length, giving the two laser beams <b>205</b>,<b>206</b> differing points of focus and hence differing working ranges. Both beams are scanned by a scanning mechanism such as an oscillating mirror <b>207</b>, and are directed towards an indicia <b>208</b> to be read. It will be understood that because of the differing focus lengths of the optics <b>203</b>,<b>204</b>, only one of the two scanning beams will properly be in focus at the indicia <b>208</b>. If the distance to the indicia is small, the beam corresponding to the optics of shorter focal length will be in focus; if the diameter is large, the other beam will be in focus.

0071Light <b>210</b> which has been reflected from the indicia <b>208</b> is collected by a collecting mirror <b>211</b>, and passed to a photodetector <b>212</b>. This produces an electrical output signal on a line <b>213</b> which is representative of the changes in intensity within the reflected light.

0072The lasers <b>201</b>,<b>202</b> are repeatedly pulsed by a controller <b>260</b>, at the same rate but out of phase so that one laser is on while the other is off. The controller also sends a signal along a line <b>261</b> to a time divisional sampler and demultiplexer <b>214</b> which accepts as input the signals on the line <b>213</b>, and separates them out into a first pulse stream on a line <b>215</b> representing pulses from the first laser <b>201</b>, and a second pulse stream on a second line <b>216</b> representing pulses from the second laser <b>202</b>. In order to ensure that the sampling is accurate, the time division demultiplexer <b>214</b> samples at a rate greater than the Nyquist limit (twice the highest frequency contained in the signal on the line <b>213</b>).

0073The individual pulse streams on the lines <b>215</b>,<b>216</b> are each individually processed by respective decoders <b>217</b>,<b>218</b> to provide respective high level outputs <b>219</b>,<b>220</b>. The simultaneous processing/decoding allows for the indicia <b>208</b> to be decoded without delay, regardless of whether it is positioned at a distance suitable for scanning by the laser <b>201</b>, or at a distance suitable for scanning by the laser <b>202</b>. It will be understood, of course, that typically only one of the decoders <b>217</b>,<b>218</b> will produce a “valid decode” output for a given indicia at a given distance from the scanner.

0074<figref idref="DRAWINGS">FIG. 8</figref> shows a variant of the embodiment of <figref idref="DRAWINGS">FIG. 7</figref>, with identical elements being given identical reference numerals. In this variant, the lasers are pulsed by the controller <b>260</b> at two different and unrelated frequencies. For the sake of discussion it will be assumed that the laser <b>201</b> is pulsed at a frequency f₁, and the laser <b>202</b> at a frequency f₂; it will further be assumed that the signal bandwidth is f_s.

0075The output signal on the line <b>213</b> is then sampled at <b>229</b>, and the sampled signal is passed through the two bandpass filters <b>230</b>,<b>231</b>. The filter <b>230</b> has a passband of f₁plus or minus f_s, whereas the second filter <b>231</b> has a passband of f₂plus or minus f_s. This filtering separates the output of the two lasers in the frequency domain, so that the output of the filter <b>230</b> on the line <b>232</b> represents the signal just from the laser <b>201</b>, and the output from the filter <b>231</b> on the line <b>233</b> represents just the other laser <b>202</b>. The two signals are processed/decoded simultaneously by respective decoders <b>234</b>,<b>235</b> to produce individual outputs <b>236</b>,<b>237</b>. As before, this simultaneous decoding eliminates delay.

0076In either the embodiment of <figref idref="DRAWINGS">FIG. 11</figref>, or the embodiments of <figref idref="DRAWINGS">FIGS. 7 and 8</figref>, the laser beams may if desired be directed onto two separate regions within the field of view. This could be achieved either by providing an appropriate spacing between the parallel laser beams, or by arranging for the laser beams to be slightly out of parallel alignment. The light which has been reflected from the two respective regions in the field of view may then be sensed simultaneously to produce two data streams which are related to the detected light intensity in the respective two regions. From those two data streams, a single decoded representation may be derived.

0077Depending on the set-up of the lasers, the reflected light from the two regions may differ either in intensity, frequency, or pulsing frequency. Such differences provide a convenient way of discriminating between light which has been reflected from the individual regions, thereby enabling the two data streams to be conveniently separated. This applies whether the two regions are entirely separate from each other within the field of view, or whether they overlap.

0078It will be understood that both the embodiment of FIG. <b>7</b> and the variation of <figref idref="DRAWINGS">FIG. 8</figref> is not restricted to the use of exactly two lasers. As many lasers may be used as is required, with different working ranges for each.

0079In some implementations it may be desirable not only to change the working distance, but also to change the scan pattern generated by an optical scanner. This may be achieved by means of the embodiment of FIG. <b>9</b>.

0080A laser <b>300</b> generates a beam <b>302</b> which is focused and shaped by beam optics <b>304</b> and directed to a stationary flat mirror <b>306</b>. The beam is reflected from the mirror and onto a rotating polygon <b>308</b>, which is driven for rotation about an axis <b>309</b>. The reflections from the polygon produce a scanning laser beam <b>310</b>.

0081The scanning beam next impinges upon an arrangement of fixed mirrors <b>312</b> in a crown configuration, with the various reflection <b>314</b> from the individual mirrors making up the crown, as the scanning beam <b>310</b> moves across, resulting in the omni-directional scan pattern shown in FIG. <b>10</b>a. In order to achieve this pattern, all of the reflecting surfaces are appropriately coated to provide a high level of reflectivity at the wavelength of the laser <b>300</b> (preferably 670 nm).

0082The scanning mechanism shown in <figref idref="DRAWINGS">FIG. 9</figref> further includes an additional laser <b>300</b>′ having its own optics array <b>304</b>′. This laser operates at a different wavelength than the laser <b>300</b>, and preferably at a wavelength of about 630 nm. By coating only some of the relevant surfaces for reflection at 630 nm, other scan patterns may be generated. For example, if only the central mirror element <b>314</b> of the crown is coated for reflection at 630 nm, the scan pattern of <figref idref="DRAWINGS">FIG. 10b</figref> may be generated. Other scan patterns could be created by selectively coating one or more of the other mirror elements <b>316</b>, <b>318</b>, <b>320</b>, <b>322</b>. In addition, further permutations may be obtained by coating only some of the surfaces of the rotating polygon <b>308</b> for reflection at 630 nm. For example, if only one surface <b>324</b> of the polygon is coated, along with the central mirror element <b>314</b> of the crown, one can obtain the single line scan pattern shown in FIG. <b>10</b>c.

0083By coating all of the relevant surfaces for reflection at 670 nm, and only some of the surfaces for reflection at 630 nm, two different scan patterns may be generated by user selection or automatic selection of the appropriate laser. Manual selection could be achieved by means of a user-operable trigger, such as the trigger <b>3</b> shown in <figref idref="DRAWINGS">FIG. 2</figref>; automatic control could be achieved by arranging for the scanner to detect the type of bar code symbol being scanned, and automatically selecting the scan pattern accordingly.

0084A further benefit of the method is that the 630 nm beam may be focused differently from the 670 nm beam.

0085It will be understood of course that more than two lasers could be used, each having a different wavelength. The described wavelengths of 670 and 630 nm, while preferred, could be varied if necessary accordingly to the particular application.

0086It will be appreciated, in connection with <figref idref="DRAWINGS">FIG. 9</figref>, that a variety of other methods could be used to achieve the same effect. In <figref idref="DRAWINGS">FIG. 9</figref>, the beams of differing wavelengths are selected by means of coatings, but of course it would also be possible to select the beams by conventional filters attached to or positioned in front of the mirrors. It would also be possible to separate the wavelengths using holographic elements and/or diffraction gratings. Where coatings are used they may be applied, as a thick layer, to a conventional mirror, thereby acting as a conventional filter to block light of a certain wavelength. Alternatively, the coatings may be a thin layer, arranged to reinforce or to cancel out the incident waveform by optical interference techniques.

0087While the optical system of <figref idref="DRAWINGS">FIG. 1</figref> has been described in relation to a bar code reader it will be appreciated that it could equally be used in any optical arrangement requiring differing worldng ranges. For example the invention could be used in conjunction with a CD ROM pick-up, a camera, a telescope or other optical systems.

0088While the invention has been illustrated and described with reference to a number of particular embodiments, it is not intended to be limited to any of the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

0089Without 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 stand point of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention. Accordingly, such adaptations should be and are intended to be comprehended within the meaning and range of equivalence of the following claims.

0090According to another aspect of the present invention there is provided an optical scanner for scanning indicia having areas of different light reflectivity, comprising: <ul id="ul0001" list-style="none"><li id="ul0001-0001" num="0000"><ul id="ul0002" list-style="none"><li id="ul0002-0001" num="0091">a light source for producing a light beam;</li><li id="ul0002-0002" num="0092">a scanning optical element for receiving the light beam and producing a scanning light beam therefrom; and</li><li id="ul0002-0003" num="0093">a beam-shaping reflector comprising an aplanar mirror for shaping the beam.</li></ul></li></ul>

0094By reflecting from an aplanar surface, any desirable beam shape may be achieved. If the reflector is shaped both in the X direction and in the Y direction, beam shaping in both dimensions may be achieved. Alternatively, if a cylindrical mirror is used, the beam may be shaped only in one dimension. The aplanar surface may comprise the scanning mirror, or alternatively a stationary fold mirror.

0095Proper beam shaping using a cylindrical mirror in this way can enable the designer to reduce the spot size in the vertical (Y) direction at large scanning distances. This improves visibility. In addition, spot size for near distances (0-30 inches) is increased, thereby improving dot matrix performance.

0096In addition, the shaping may be carried out by reflecting the light beam from one or more stationary mirrors either after or before the light has impinged upon a scanning element. In its most general form, beam shaping is carried out by reflecting the beam from one or more aplanar surfaces.

0097<figref idref="DRAWINGS">FIG. 13</figref> shows a multiple-range laser scanner, for example for a bar code reader, comprising a first embodiment of the present invention. In the embodiment shown, a laser diode <b>400</b> produces a light beam which is directed to a scanning mirror <b>412</b> via a small central hole <b>413</b> in a fold mirror <b>414</b>. The fold mirror <b>414</b> is a segmented or multiple mirror comprising three separate mirror portions <b>416</b>, <b>418</b>, <b>420</b>. The mirror portion <b>416</b> is convex, the mirror portion <b>418</b> is planar and the mirror portion <b>420</b> is concave. As the scanning light beam produced by the scanning mirror <b>412</b> moves across the fold mirror <b>414</b> it strikes each of the mirror portions <b>416</b>, <b>418</b>, <b>420</b> in turn. The light reflected from the fold mirror passes out of the scanner housing <b>422</b> through a window or aperture <b>424</b> to impinge upon an indicia <b>426</b> to be read.

0098The indicia <b>426</b> is shown at three possible positions, a near position <b>428</b> corresponding to the working distance of the mirror portion <b>420</b>, a middle distance <b>430</b> corresponding to the working distance of the mirror portion <b>418</b>, and a far distance <b>432</b> corresponding to the working portion of the mirror portion <b>416</b>. It will be appreciated, of course, that in a practical embodiment there will be considerably greater spacing between the positions <b>428</b>, <b>430</b> and <b>432</b>: in the drawing the spacings are shown closer than they would be in reality, merely for the sake of clarity.

0099The result of the three separate mirror portions is that three separate scan lines are produced, the first at the position <b>428</b>, the second at the position <b>430</b> and the third at the position <b>432</b>. The intention is, accordingly, that whatever the distance of the indicia <b>426</b> from the scanner, it has a very good chance of being read by at least one of the scan lines. It will be appreciated of course that the indicia does not need to be exactly at one of the distances <b>428</b>, <b>430</b>, <b>432</b> in order to be decodable; there is in each case a substantial depth of field, and depending upon the actual distances these depths of field may even overlap so that they effectively merge into one complete “working region” within which the bar code symbol will almost certainly be decodable.

0100The mirror portions are suitably angled so that the respective scan lines lie on top of one another, but are merely focused at different distances.

0101It is not essential that there are exactly three mirror portions; there could be two, or more than three, according to the requirements of the particular application. The exact mirror profiles may also be chosen according to the particular application (e.g., cylindrical). The profiles chosen will depend upon the required working ranges and also upon the profile of the scanning mirror <b>412</b>. The scanning mirror <b>412</b> may preferably be flat, but may in some circumstances be aplanar, for example cylindrical or spherical. The mirror <b>412</b> could also be replaced by a rotating prism, polygon, hologram, lens, zone plate, or any other convenient optical scanning element. If the scanning element comprises a polygon, each facet of the polygon may have a different curvature. In that case, the mirror portions <b>416</b>, <b>418</b>, <b>420</b> may (but need not) all have the same profile since the curvature of the polygon facets. An exemplary polygon suitable for use with three planar fold mirror portions is shown at <b>436</b>.

0102Further spacing of the beam may be achieved by the use of optics <b>438</b> in front of the laser <b>410</b>.

0103In the embodiment of <figref idref="DRAWINGS">FIG. 13</figref>, light reflected back from the indicia <b>426</b> may either follow substantially the same path, in the reverse direction, to a photodetector (not shown) or alternatively there may be separate light collector optics (not shown) for that purpose.