Abstract:
A point of sale (POS) device, such as an optical scanner, reduces the beam diameters of two light beam components having been emitted from a common light source and split by an optical beam splitter. The optical scanner includes a light source emitting a light beam, a light beam splitter splitting the emitted light beam, a polygon mirror reflecting the split light beam components into mutually different directions, and groups of mirrors. The groups of mirrors are provided for each reading window, allowing the light beam components to be emitted therefrom. The emitted light beam components can then impinge on an object, whereupon the optical scanner detects by detectors and reads a bar code located on the object. The optical scanner also includes beam shaping devices, one of which is placed between the light source and light splitting device and the other of which is placed in one of the optical paths followed by one of the light beam components. Since the beam diameter of the light beam components are reduced, and since the light beams are emitted from multiple reading windows, bar codes with narrow spaces between the bars can be read more easily, even with varying orientations of the bar code on the object.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on, and claims priority to Japanese Patent Application 9-208137, filed Aug. 1, 1997 in Japan, and which is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates in general to an optical scanner, and in particular, to a method of and device for reducing the beam diameter of separate light beam components emitted from a common light source for optical scanner. 
     BACKGROUND OF THE INVENTION 
     Point of Sale (POS) systems, such as optical scanners, capable of detecting and reading light reflected from a bar code attached to a commodity are widely used. For example, optical scanners, which are also referred to as bar code readers, are used at “check-out” counters in grocery stores to scan a bar code attached to a commodity such as a food product. By manipulating the commodity, these optical scanner systems provide an operator, such as a cashier, using the system to reduce the amount of time it takes to “scan” information about the commodity, reducing the burden on the operator and increasing the operator&#39;s efficiency. 
     In recent years, optical scanners with two reading windows have been developed. The two windows are provided, for example, in the bottom and front portions of the optical scanner, forming an “L” shape. The two windows enable the optical scanner to read and scan from multiple directions bar codes attached to commodities. Hence, a bar code attached to a commodity may be detected and read from light sources emitting from both windows, despite differing orientations of the bar code on the commodity. This feature further lightens the burden imposed on the operator. However, conventional optical scanners with multiple windows require separate optical scanners for each window. The result is a costly, complex optical scanner with numerous parts and which is large in size. 
     For example, optical scanners which have reading windows respectively provided in both the bottom and front portions thereof require optical scanning systems for each of the reading windows. Each of the optical scanning systems includes a light source, scanning means such as a polygon mirror, and other mirrors. Thus, the scanner is complex and requires a large number of components or parts, which increases the manufacturing costs. However, if a common light source is used for both of the optical scanning systems, the required number of parts and the costs associated therewith decrease. 
     The use of a common light source  1  in an optical scanner  100  is shown in FIG.  27 . FIG. 27 is an exemplary prior art diagram illustrating a conventional optical scanner  100  with a common light source  1  and used, for example, to scan a bar code attached to an object. To use a common light source  1  in the optical scanner  100  shown in FIG. 27, a light splitting device  2 , such as a half mirror (semi-transparent mirror), is used to split a common light source  1  into a first light beam component X and a second light beam component Y. The first and second light beam components X and Y, respectively, are then directed to a common polygon mirror  3 , either directly or through another mirror. Light beam component X is then emitted through a group of mirrors M 1  from reading window  4  (provided in the bottom portion of the optical scanner  100 ), and light beam component Y is emitted through a group of mirrors M 2  from reading window  5  (provided in the front portion of the optical scanner  100 ). The emitted light beam components X and Y then impinge on, for example, a bar code attached to an object passing through the emitted light, which reflects back to the optical scanner  100 . The bar code is read by the optical scanner  100  by detecting the reflected light by detectors  6  and  7 . 
     In order to more accurately read a bar code, and in particular, a bar code having narrow spaces between adjacent bars, the beam width of the light beam scanning the bar code must be sufficiently reduced. To reduce the beam width of the light beam scanning the bar code, for example, light beam components X and Y (shown in FIG.  27 ), a beam shaping device  8  is placed between the common light source  1  and the light splitting device  2 . Moreover, it is also necessary not only to reduce the diameter of the light beam components X and Y, but to reduce the diameter at a desired position. That is, the diameter of the beam size must be sufficiently reduced at the desired position, particularly the position where the object is being scanned. 
     As the width of the bars in the bar code narrows, it becomes increasingly difficult for an emitted light source to read the bar code. A desirable solution to reading bar codes having narrow spaces between bars would be to use a common light source  1  having a smaller diameter. As discussed above, it is desirable to “split” the common light source  1  (i.e., laser beam) into first and second laser beam components X and Y, such that the bar code may be read or scanned from multiple directions (from a bottom portion and a front portion of the optical scanning device). Using the first and second laser beam components X and Y, respectively, an “optimum reading zone” is established by defining first and second focal points of the first and second laser beam components X and Y, respectively. It is desirable that the focal point (a point at which the laser beam has the smallest diameter) of the laser beam is established near the reading center the optimum reading zone. In this regard, the common light source  1  is able to read and scan the bar code with increasing efficiency when the two focal points are directed towards the same location. To accomplish this, it is desirable that the distance from the light source from which the scanning light (light beam component X in FIG. 27) emitted from the bottom reading window  4  to the reading center is equal to the distance from the light source from which the scanning light (light beam component Y in FIG. 27) emitted from the side reading window  5  to the reading center. 
     However, due to the complexity of the optical components in the optical scanner for prior art, it is difficult to equalize these distances and may result in the focal point of the first light beam component X being set at the center of the optical reading zone, and the focal point of the second light beam component Y being set off-center of the optimal reading zone. In that case, the bar code cannot be read using the second scanning light. Hence, achieving optimal first and second focal points is hindered, resulting in the failure of one of the laser beam components from reading or scanning the bar code as it passes through the “optimum reading zone”. 
     Thus, there exits a need for a cost effective optical scanner having multiple windows which reduces the overall size of the scanner by reducing the number of components required therein. Additionally, there exists a need for an optical scanner having multiple windows capable of reading and scanning a bar code using a common light source. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an optical scanner which reduces the beam diameters of two light beam components into which a light beam emitted from a common light source is split by an optical beam splitter. 
     Another object of the present invention is to provide an optical scanner which is provided with a common light source and two reading windows, and which can read a bar code with good sensitivity by using light beams respectively emitted from the reading windows. 
     In accordance with one embodiment of the present invention, an optical scanner includes a body, at least one reading window provided in the body, a light source, light splitting means for splitting a light beam emitted from the light source into a first light beam component traveling along a first optical path, and a second light beam component traveling along a second optical path. Also provided in the optical scanner of the present invention are light scan means allowing the first light beam component and the second light beam component to be emitted from the reading window, first beam shaping means placed between the light source and the light splitting means, and second beam shaping means placed in one of the first and second optical paths. 
     In accordance with another embodiment of the present invention, an optical scanner includes a body, a first reading window provided in the body, a second reading window provided in the body at an angle with the first reading window, a light source, and light splitting means splitting a light beam emitted from the light source into a first light beam component traveling along a first optical path and a second light beam component traveling along a second optical path. Also provided are scan means allowing the first light beam component and the second light beam component split by the light splitting means to be emitted from the first reading window and the second reading window, at least one detector detecting the light beam which is emitted from the reading windows and impinges on and is reflected by an object, first beam shaping means placed between the light source and the light splitting means, and second beam shaping means placed in one of the first and second optical paths. 
     In the above-mentioned embodiments of the present invention, a light beam emitted from the light source is shaped by the first beam shaping means in such a manner as to have a reduced beam diameter at a desired position. However, in some cases, each of the two light beam components split by the light splitting means does not have a minimum beam diameter at a desirable position. To solve this problem, the first beam shaping means reduces one of the two light beam components at a desired position, and the second beam shaping means is placed in the optical path of the other light beam component, correcting the position of the light beam to a desired position. Hence, each of the two light beam components split by the light splitting means has a minimum beam diameter at a desired position. 
     In accordance with another embodiment of the present invention, the scan means comprises a polygon mirror reflecting the first and second light beam components split by the light splitting means, at least one mirror placed between the light splitting means and the polygon mirror, a first group of mirrors causing the first light beam component reflected by the polygon mirror to be emitted from the first reading window, and a second group of mirrors causing the second light beam component reflected by the polygon mirror to be emitted from the second reading window. 
     In accordance with still another embodiment of the present invention, there is provided an apparatus for scanning an object having a bar code attached thereto. The apparatus comprises a body including first and second reading windows emitting and receiving a light beam, a light splitting device splitting the beam of light emitted from a light source into first and second beam components, a light scan device for directing the first beam component and second beam component through the respective first and second reading windows, a first beam shaping device, a second beam shaping device, and a first and second detector for detecting the first and second beam components, respectively. 
     In accordance with yet another embodiment of the present invention, there is provided a light source module. The light source module comprises a light source, first and second beam shaping means, a light splitter splitting a light beam which is emitted from the light source. The first beam shaping means shapes a cross-sectional shape of the light beam and the second beam shaping means changes a focal distance of the light beam. 
     In accordance with another embodiment of the present invention, there is provided a light source module. The light source module comprises a light source, a beam shaping device, a light splitter splitting a light beam which is emitted from the light source into first and second light beams. The beam shaping device changes a focal position of one of the first and second light beams to a position in from of or beyond a focal position of the other one of the first and second light beams. 
     In one aspect of the present invention, the first beam shaping means reduces the light beam diameter at a first distance from the light source, and the second beam shaping means reduces the beam diameter of the light beam traveling along an optical path at a second distance from the light source which is different from the first distance. 
     In another aspect of the present invention, the first beam shaping means includes a collimator lens and an aperture. 
     In still another aspect of the present invention, the second beam shaping means comprises a convex lens whose focal length is greater than the collimator lens. Alternatively, the second beam shaping means comprises a concave lens, or a concave mirror. 
     In a further aspect of the present invention, the light source, the light splitting means and the first beam shaping means are formed as one unit. 
     In yet another aspect of the present invention, the light source, the light splitting means, the first beam shaping means and the second beam shaping means are formed as one unit. 
     In accordance with another embodiment of the present invention, a method for scanning an object using an optical scanner splits a light beam emitted from a light source, emits first and second beams respectively through first and second reading windows, scans the first and second beam components through the first and second reading windows such that the emitted light cross paths at an optical reading position, shapes the light beam and first or second beam components to minimize the diameter of the both the first and second beam components at the optical reading position, and detects the object. 
     These together with other objects and advantages which will be subsequently apparent, reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective diagram showing an optical scanner embodying the present invention; 
     FIG. 2 is a cross-sectional diagram schematically illustrating the internal structure of the optical scanner embodying the present invention; 
     FIG. 3 is an enlarged diagram showing the first beam shaping device of FIG. 2; 
     FIG. 4 is an exemplary graph illustrating the relationship between the beam diameter of a light beam passing through the first beam shaping device and the distance from a light source; 
     FIG. 5 is an exemplary graph illustrating beam shaping performed by the first and second beam shaping device of FIG. 2; 
     FIG. 6 is an exemplary diagram showing a modification of the first beam shaping device; 
     FIG. 7 is an exemplary diagram illustrating the divergence angle in the vertical direction of a light beam emitted from the light source different from the divergence angle in the transverse direction; 
     FIG. 8 is an exemplary diagram showing a modification of the first beam shaping device in another embodiment of the present invention; 
     FIG. 9 is an exemplary diagram showing a modification of the first beam shaping device in another embodiment of the present invention; 
     FIG. 10 is an exploded diagram showing the lower and upper frames of the body of the optical scanner, illustrating mirrors of a bottom mirror group; 
     FIG. 11 is an enlarged diagram showing the lower frame of FIG. 7; 
     FIG. 12 is an exemplary diagram showing light beams emitted from the bottom reading window; 
     FIG. 13 is a partially cross-sectional diagram showing the lower and upper frames of the body of the optical scanner, illustrating mirrors of a side mirror group; 
     FIG. 14 is a perspective diagram showing mirrors mounted in a mirror frame placed in a cover; 
     FIG. 15 is an exemplary diagram showing light beams emitted from the side reading window; 
     FIG. 16 is a cross-sectional diagram schematically illustrating the internal structure of the optical scanner or another embodiment of the present invention; 
     FIGS.  17 (A) and (B) are exemplary diagrams showing a reflecting mirror which includes the second beam shaping device of FIG. 16; 
     FIG. 18 is an exemplary diagram showing another example of a modification of the reflecting mirror of FIG. 17; 
     FIG. 19 is a cross-sectional diagram schematically illustrating the internal structure of another embodiment of the optical scanner embodying the present invention; 
     FIG. 20 is an exemplary graph illustrating the beam shaping performed by the first and second beam shaping device of FIG. 19; 
     FIG. 21 is a cross-sectional diagram schematically illustrating the internal structure of another embodiment of the optical scanner embodying the present invention; 
     FIG. 22 is a cross-sectional diagram schematically illustrating the internal structure of another embodiment of the optical scanner embodying the present invention; 
     FIG. 23 is a cross-sectional diagram schematically illustrating the internal structure of another embodiment of the optical scanner embodying the present invention; 
     FIG. 24 is a cross-sectional diagram schematically illustrating the internal structure of another embodiment of the optical scanner embodying the present invention; 
     FIG. 25 is a cross-sectional diagram schematically showing another embodiment of the optical scanner embodying the present invention; 
     FIGS.  26 (A)-(D) are exemplary diagrams showing a light source module; and 
     FIG. 27 is a diagram showing a prior art optical scanner. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 and 2 are exemplary diagrams illustrating an optical scanner, such as a bar code reader, according to one embodiment of the present invention. The optical scanner  10  includes a body  12 , a base portion  14  and a cover portion  16 . 
     A bottom reading window  18  is provided in the surface of the base portion  14 , and a side reading window  20  is provided in the surface of the cover portion  16 . The bottom reading window  18  and the side reading window  20  are placed at an angle with respect to each other, forming essentially an “L” shape. 
     As shown in FIG. 2, a light beam emitted from the bottom reading window  18  is designated by an arrow X, and another light beam emitted from the side reading window  20  is designated by an arrow Y. An optimum reading zone (region P) extends over the bottom reading window  18  and has a center at a predetermined distance from the side reading window  20 . Hence, when an object is in the optimum reading zone (region P), a commodity with a bar code attached can be read optimally. In addition, even if the commodity, or object, is outside of the optimum reading zone P, a bar code attached thereto can be read, but may not be read successfully. 
     Referring to FIG. 2, the optical scanner  10  includes a light source (such as a laser diode)  22 , a first beam shaping device  24 , a light splitting member  26 , and a second beam shaping device  28 . These members are attached to a common frame and comprise a single unit designated as light source module  30 . 
     The optical scanner  10  further includes a polygon mirror  32 , which is rotated by a motor  32 a, and two mirrors  34  and  36 . The light source module  30  is located near a lower end of the base portion  14  towards the rightmost end portion of the main body  12  as viewed in FIG.  2 . The mirror  34  is located above the light source module  30  which is at one end of the base portion  14 , and the mirror  36  is located near the other end of the base portion  14 . The polygon mirror  32  is located in the vicinity of the leftmost portion of the main body  12 , between the reading windows  18  and  20 . 
     Examples of light splitting member  26  include a half mirror, a half-cube beam splitter, or a polarization beam splitter. Light splitting member  26  splits a light beam emitted from the light source  22  into a first light beam component traveling along a first optical path L 1 , and a second light beam component traveling along a second optical path L 2 . In the example of FIG. 2, the first light beam component L 1  is transmitted through the light splitting member  26 , and travels in a straight line to one side of the polygon mirror  32 . The second light beam component L 2  is reflected by the light splitting member  26  and transmitted first to mirror  34  and then reflected to mirror  36  so that the optical path from light splitting member  26  to the other side of polygon mirror  32  is bent. Mirror  36  reflects the second light beam component L 2  to the other side of polygon mirror  32 . The second light beam component L 2 , when reflected between mirrors  34  and  36 , travels along a path located under the polygon mirror  32 . 
     The first light beam component L 1  reflected by the polygon mirror  32  is emitted from the bottom reading window  18  through a group of bottom mirrors  38  as, for example, a light beam X which scans an object. The second light beam component L 2  is emitted from the side reading window  20  through a group of mirrors  40  as, for example, a light beam Y which then scans the object. In order for an object to be scanned by the light beams X and Y, the object must pass through a space zone referred to as an optimum reading zone. This optimum reading zone, which extends over the bottom reading window  18 , and has a center at a predetermined distance from the side reading window  20 , is defined in FIG. 2 as region P. An object to be scanned, including, for example, a bar code, passing through region P can then be optimally read. If the object passes outside the optimum region P, bar code can still be read, however, the accuracy is substantially reduced. 
     More specifically, when an object is present in (or around) the optimum reading zone P, the light beams X and Y are scanned and reflected off of the object in scattered directions. The reflected, scattered light re-enters the bottom reading window  18  and the side reading window  20 . The reflected, scattered light re-entering the reading window  18  is then reflected by one side of polygon mirror  32 , as illustrated by L 3 . Similarly, the reflected, scattered light re-entering the side window  20  is then reflected by the other side of polygon mirror  32 , as illustrated by L 4 . 
     To detect the reflected light, a reflecting mirror  42  is placed near the light source module  30  in the optical path of the first light beam component L 1 . The reflecting mirror  42  is formed as a concave mirror, having a hole  42   a  bored in the central portion. The hole  42   a  permits the first light beam component L 1 , which is transmitted to the polygon mirror  32  from the light splitting member  26 , to pass therethrough. A first detector  44  is placed at the focal point of the reflecting mirror  42 . The reflected light beam L 3  upon re-entering the reading window  18 , impinges upon reflecting mirror  42 , and is condensed and incident to the first detector  44 . The first detector  44 , for example a pin photodiode, operates to convert the quantity of detected light into an electric signal. This electric signal is sent to an electric circuit (not shown), in which demodulation or the like is performed thereon. Thus, for example, a bar code attached to an object is read. 
     A collector  46 , larger in size than the mirror  36 , is placed on the rear side of the mirror  36 . The collector  46  comprises, for example, a convex lens or Fresnel lens. A second detector  48  is placed at the focal point of the collector  46  to detect the reflected light beam L 4  which passes through and is condensed by the collector  46 . The second detector  48  comprises, for example, a pin photodiode, and operates to convert the quantity of detected light into an electric signal. The electric signal is sent to an electric circuit (not shown), whereupon an object having, for example, a bar code attached thereto can be read. 
     FIG. 3 illustrates an example of the first beam shaping device  24 . The first beam shaping device  24  comprises a collimator lens  50  and an aperture  52 , which are formed as a single unit serving as a module. The collimator lens  50  condenses divergent light beams emitted from the light source (for example, a laser light source)  22  so that the light beams are made to be slightly convergent in comparison with parallel beams. The aperture  52  operates to cut off any extra part of the light beam passing through the collimator lens  50 , further reducing the beam diameter. In this regard, the diameter of the light beam emitted from the aperture  52  gradually decreases, until passing through a section S in which the light beam has a minimum beam diameter. After passing through section S, the beam diameter gradually begins to increase. 
     FIG. 4 is an exemplary graph illustrating the relationship between the beam diameter of a light beam, having passed through the beam shaping device  24 , and the distance from the light source  22 . The distances a, b, c and d correspond to the positions A, B, C and D found in FIG.  2 . Namely, the distance a corresponds to the distance between the light source  22  and position A on the bottom reading window  18 , the distance b corresponds to the distance from the light source  22  to position B on the optimum reading zone (region P) through the bottom reading window  18 , the distance c corresponds to the position C on the side reading window  20 , and the distance d corresponds to the distance between the light source  22  and the position D located across from the optimum reading zone (region P) through the side reading window  20 . 
     Referring to FIG. 4, a bottom reading zone E is a region in which an object having a bar code attached thereto can be read by a light beam emitted from the bottom reading window  18 . A side reading zone F is a region in which an object having a bar code attached thereto can be read by using a light beam emitted from the side reading window  20 . The optimum reading zone (region P) is narrower than either the bottom reading zone E or the side reading zone F. The point PB corresponds to the distance between the light source  22  and the center of the optimum reading zone (region P) of FIG. 2 in the direction along line AB. Additionally, the point PS corresponds to the distance between the light source  22  and the center of the optimum reading zone (region P) of FIG. 2 in the direction along line CD. 
     As indicated from FIGS. 2 and 4, the distance between the light source  22  and the point PB is shorter than the distance between the light source  22  and the point PS. In such a case, the conventional scanner is set such that the point PS is the point at which light beam X has a minimum beam diameter. Hence, as described above, the position at which the light beam Y has a minimum beam diameter is not the point PS. As a result, the beam diameter at the point PS is slightly larger than the minimum beam diameter. When the pitch of the bars of a bar code is further reduced, it is preferable that scanning is performed using a light beam with a diameter further reduced. Hence, the second beam shaping device  28 , provided in the present invention, reduces the beam diameter of the light beam Y in the vicinity of the point PS. 
     FIG. 5 is an exemplary graph illustrating the characteristics of the first beam shaping device  24  and the second beam shaping device  28  of the present invention. Curve G represents the graph illustrated in FIG.  4 . Curve H represents the beam diameter when the setting of the first beam shaping device  24  is changed to decrease the beam diameter at the point PS, as described below. Thus, the beam diameter corresponding to the point PS on curve G is transferred to the beam diameter corresponding to the point PS′ on curve H. In particular, the beam diameter of the light beam Y, emitted from the side reading window  20 , is reduced at the point PS. As a result, the beam diameter represented by curve H between points c and d is further reduced over that of curve G. Similarly, the curve I represents the beam diameter when the setting of the second beam shaping device  28  is changed to decrease the beam diameter of the light beam X at the point PB. The beam diameter represented by curve I between points a and b is further reduced over that of curves G and H. Therefore, the beam diameter is decreased over the entire reading zone, allowing bar codes having a small width to be read using any of the light beams. 
     To change the characteristics shown in curve G to those shown in curve H, and hence improve the performance of the optical scanner, the setting of the first beam shaping device  24  is changed to increase the distance between the light source  22  and the position of the focal point S at which the light beam has the minimum beam diameter. This is accomplished by increasing the focal length of the collimator lens  50  of the first beam shaping device  24  to a length greater than the length shown in FIG.  4 . For example, curve G represents the case when the focal length of the collimator  50  is 3.6 mm, and the curve H represents the case when the focal length of the collimator  50  is 14 mm. The change in characteristics of the curve G to that represented by the curve H is attained by changing the diameter of the aperture  52 , or by changing the distance between the light source  22  and the collimator lens  50 . 
     However, a problem arises in that the point PB on curve G moves to the point PB′ on curve H indicating that the beam diameter of the light beam emitted from the bottom reading window  18  is increased. To solve this problem, the second beam shaping device  28  is placed in the optical path of the first light beam component L 1  as shown in FIG. 2, and the point PB on curve G moves to the point PB′ on curve H, as represented on the graph illustrated in FIG.  5 . As a result, the diameter of light beam X emitted from bottom reading window  18  is decreased. Hence, beam shaping is performed by second beam shaping device  28  only on the light beam X, and the beam diameter of the light beam emitted from the bottom reading window  18  is decreased. That is, when light beam X is emitted from reading window  18 , the characteristics corresponding to the position of the focus is changed from that represented by curve H to that represented by curve I. Moreover, the beam diameter at the point PB′ on the curve H is reduced to that at the point PB″ on the curve I. 
     When the second beam shaping device  28  is placed after the beam splitter  26 , the focal length f of the plano-convex lens of the second beam shaping device  28  is 3000 mm. Since the focal length of the collimator lens  50  is 14 mm, the plano-convex lens of the second beam shaping device  28  for reducing the beam diameter of the light beam X at the point PS has a focal length which is hundreds of times as long as the focal length of the collimator lens  50 . 
     As a result, the beam diameters of the light beams X and Y emitted from the bottom reading window  18  and the side reading window  20 , respectively, are decreased. Scanning of an object can, therefore, be performed using the light beam with the smaller beam diameter. In the module of the embodiment of the present invention, the focal point of the light beam component Y is adjusted to the optimum reading position. The focal point of the light beam component X, which is collimated by the collimator lens  50 , is set at a position whose distance from the light source is slightly shorter, by using the plano-convex lens. 
     FIG. 6 is an exemplary diagram illustrating modification of the first beam shaping device  24 . In this example, the first beam shaping device  24  further includes a right-angle prism  54  between the collimator lens  50  and the aperture  52 . The right-angle prism  54  is placed so that the oblique side of the right-angle prism  54  faces the aperture  52 . However, the right-angle prism  54  may be placed so that the oblique side of the right-angle prism  54  faces the light source  22 . Moreover, instead of the right-angle prism  54 , other prisms may be employed. 
     As illustrated in FIG. 7, when a light beam is emitted from the laser diode  22 , the divergence angle of one of the first and second light beam components, which are orthogonal to each other, is generally larger than the divergence angle of the other light beam component. The light beam is shaped by the right-angle prism  54  which reduces the larger divergence angle of the one of the light beam diameters to a value equal to the divergence angle of the other light beam diameter. For example, the right-angle prism  54  reduces the beam diameter of the longitudinal light beam having a large divergence angle, but does not reduce the beam diameter of the transverse light beam having a small divergence angle. 
     FIG. 8 is an exemplary diagram illustrating a cylindrical convex lens  54   a  and a cylindrical concave lens  54   b , in place of the right-angle prism  54 . In this example, the divergence angle of the longitudinal light beam, which is indicated by solid lines and initially has a large divergence angle, can be made to be equal to the divergence angle of the transverse light beam which initially has a small divergence angle and is indicated by the dashed lines. 
     A light source module  30  which includes the right-angle prism is shown and described with reference to FIGS.  26 (A)- 26 (D) herein below. 
     FIG. 9 is an exemplary diagram showing a modification of the first beam shaping device  24  in another embodiment of the present invention. Referring to FIG. 9, an example is provided with a cylindrical concave lens  54   c  and a cylindrical convex lens  54   d , similar to the above example. In this case, the divergence angle of the transverse light beam, which is indicated by the solid line and initially has a small divergence angle, is made to be equal with the divergence angle of the longitudinal light beam which initially has a large divergence angle and is indicated by dashed lines. 
     FIGS. 10 and 11 are exemplary diagrams illustrating the placement of a group of the bottom mirrors  38  of FIG.  2 . In FIGS. 10 and 11, the mirrors are illustrated so that the mirrors of FIG. 2 are reversed from left to right. Although the group of the bottom mirrors  38  depicted in FIG. 2 are placed just under the bottom reading window  18  of the base portion  14 , the group of bottom mirrors  38  may be placed in other locations, such as in a lower part or a peripheral part of the base portion  14 . 
     More specifically, FIG. 10 illustrates that the base portion  14  of FIG. 2 comprises of a lower frame  14   a  and an upper frame  14   b . FIG. 11 shows only the lower frame  14   a  of the base portion  14 , but the upper frame  14   b  is mounted to the left-side part of the lower frame  14   a . The cover portion  16  of FIG. 2 is mounted to the right-side part of FIG.  11 . 
     The polygon mirror  32  is shown in the central part of the lower frame  14  of FIG. 10. A support base  32   b  is shown in the central part of the lower frame  14   a  of FIG.  11 . The polygon mirror  32  (not shown in FIG. 11) is mounted to this support base  32   b . Additionally, the mirror  34  which receives a light beam reflected by the light splitting member  26  of FIG. 2 is illustrated in the left end part of FIG.  11 . The light source module  30  of FIG. 2 is placed below this mirror  34 . The mirror  36  receiving a light beam reflected by the mirror  34  is shown in a right end part of FIG.  11 . The collector  46  of FIG. 2 is shown in the rear of this mirror  36  as a Fresnel lens. The second detector  48  receiving reflected light condensed by the collector  46  is mounted on a printed circuit board  56 . The first detector  44  is also mounted on the printed circuit board (not shown) which is placed in a “V-zone” of the left-end bottom portion of FIG.  11 . 
     As shown in FIGS. 10 and 11, the lower frame  14   a  is also provided with mirrors ZB 2 , VBRR, VBLL, HBR 2 , HBL 2 , ZML 2  and ZMR 2 . These mirrors comprise a part of the group of bottom mirrors  38 . The lower frame  14   a  is also provided with the mirrors VSR 1  and VSL 1 . FIG. 10 depicts mirrors ZL and ZR attached to a cover (not shown). These mirrors comprise a part of the group of side mirrors  40 . These mirrors are placed such that the reflecting faces thereof are directed nearly obliquely upwardly. 
     The upper frame  14   b  is provided with mirrors ZBR 1 , ZBL 1 , HBR 1 , HBL 1 , VBR 1 , VBL 1 , VBR 2 , VBL 2 , ZMR 1  and ZML 1 . These mirrors comprise a part of the group of bottom mirrors  38 . These mirrors are placed such that the reflecting faces thereof are directed nearly obliquely downwardly. 
     A light beam emitted from the light source  22 , transmitted by the light splitting member  26 , is reflected by the polygon mirror  32 , and is incident to the mirrors of the upper frame  14 . When, however, the polygon mirror  32  is rotated clockwise, scanning is performed on the mirrors ZMR 1 , VBR 2 , VBR 1 , HBR 1 , ZBR 1 , ZBL 1 , HBL 1 , VBL 1 , VBL 2  and ZML 1 , in this order. The light beam reflected by the mirrors of the upper frame  14   b  go to the mirrors of the lower frame  14   a . For example, the light beam reflected by the mirror ZMR 1  is further reflected upwardly by the mirror ZMR 2 , and is then emitted from the bottom reading window  18 . The light beam reflected by the mirrors VBR 2  and VBR 1  is further reflected by the mirror VBRR upwardly, and is then emitted from the bottom reading window  18 , and so on. 
     As a result, as illustrated in FIG. 12, light beams are emitted from the bottom reading window  18  in various directions and angles. Thus, an object can be scanned in various directions, angles, and orientations. An arrow X in FIG. 2 indicates a light beam emitted from the bottom reading window  18  of the optical scanner  10  of the present invention, which, after impinging upon an object, is detected by first detector  44 . Additionally, as shown in FIGS. 13 and 14, the cover portion includes a mirror holder  17 , in which the mirrors VSL 2 , ZLL, ZHL, ZHR, ZRR, and VSR 2  are mounted. These mirrors comprise a group of side mirrors  40 . 
     Regarding the group  40  of side mirrors, a light beam which is emitted from the light source  22  and is reflected by the light splitting member  26 , travels toward the polygon mirror  32 . Then, the light beam reflected by the polygon mirror  32  is incident on the mirrors VSR 1 , VSL 1 , ZL and ZR of the lower frame  14   a . Scanning is performed on the mirrors VSL 1 , ZL, ZR and VSR 1 , in this order. The light beam reflected by these mirrors then travels to the mirrors of the mirror holder  17 . Subsequently, the light beam reflected by the mirrors of the mirror holder  17  is emitted from the side reading window  20 . As shown in FIG. 13, a mirror  47  is also placed between the collector  46  and the second detector  48 . Thus, a light beam having passed through the collector  46  is reflected to the mirror  47 , and is then incident on the second detector  48 . 
     As illustrated in FIG. 15, light beams, emitted from the side reading window  20  in various directions and at diverse angles, scan an object. An arrow Y shown in FIG. 2 indicates a typical one of these light beam. After having impinged on an object, the reflected light beam is detected by second detector  48 . Therefore, unless a bar code is attached to an object directly upward, most bar codes can be read by using the light beams emitted from the bottom reading window  18  and the side reading window  20 . 
     FIG. 16 is an exemplary diagram illustrating another embodiment of the present invention. The embodiment shown in FIG. 16 is similar to the embodiment of the present invention described herein above. However, in the embodiment of FIG. 16, the second beam shaping device  28  is located in a different place than the second beam shaping device  28  in the above-described first embodiment. In the embodiment of FIG. 16, the second beam shaping device  28  is formed as a plano-convex lens inserted in a hole  42   a  bored in the reflecting mirror  42 . The hole  42   a  bored in the reflecting mirror  42  permits a first light beam component, which travels from the light splitting member  26  to the polygon mirror  32 , to pass therethrough. Additionally, the second beam shaping device  28  provided therein performs “beam-shaping”. The second beam shaping device  28  formed in the hole  42   a  of the reflecting mirror  42  can be formed by a plano-convex lens which is similar to that of FIG.  2 . Therefore, the operation and advantageous effects of this second embodiment shown in FIG. 16 are similar to those of the above-described first embodiment shown in FIG.  2 . 
     FIG.  17 (A) is a perspective diagram showing the reflecting mirror  42 , which is formed as a concave mirror as described with respect to FIG.  2 . FIG.  17 (B) is an exemplary plan diagram illustrating a modification of the reflecting mirror  42 . In a hole  42   a  bored in the reflecting mirror  42 , a transmission type of hologram  43  having a concentric circular pattern is provided. A transmission type of hologram  43  condenses transmitted light. Thus, the hologram serves as the second beam shaping device  28 , similar to the plano-convex lens in the first embodiment. The plano-convex lens and/or a hologram may be formed in such a manner as to be integral with the concave mirror  42  (not shown in FIG.  17 (B)). Further, the plano-convex lens and/or a hologram may be formed (or molded) separately from the concave mirror  42 , and then fit into the scanner  10 . 
     FIG. 18 is an exemplary diagram showing a modification of the reflecting mirror  42 . In the example of FIG. 18, the reflecting mirror  42  is formed as a plane mirror, and as a reflection type hologram having a concentric circular pattern. Thus, a light beam coming from the polygon mirror  32  is reflected toward the first detector  42  (see FIG.  2 ). A transmission hologram having a concentric circular pattern is provided in the hole  42   a  bored in the reflecting mirror  42 . Therefore, the operation and advantageous effects of the example shown in FIG. 18 are similar to the aforementioned embodiments of the present invention. 
     FIG. 19 is an exemplary diagram illustrating another embodiment of the present invention. The embodiment shown in FIG. 19 has a configuration similar to the aforementioned embodiment of the present invention, except that the second beam shaping device  28  is located in a different place than in the first embodiment. In the embodiment of FIG. 19, the second beam shaping device  28  is formed as a concave lens  29 . The concave lens  29  is placed between the mirrors  34  and  36  and reflects a light beam emitted from the light source  22  and reflected by the light splitting member  26  before reaching the polygon mirror  32 . 
     FIG. 20 is an exemplary graph illustrating the effects of the first beam shaping device  24  and the second beam shaping device  28  depicted in FIG.  19 . As in the example shown in FIG. 5, curve G represents characteristics which are the same as FIG.  4 . Curve J represents the first beam shaping device  24  changed to decrease the beam diameter at the point PB. In order to change the characteristics represented by the curve G to those represented by the curve H, the distance between the light source  22  and the point S (at which the beam has a minimum beam diameter) must be decreased by changing the setting of the first beam shaping device  24  to reduce the focal length f of the collimator lens  50 . 
     Additionally, a change in the characteristics from those represented by the curve G to those represented by the curve J can be achieved by changing the hole size of the aperture  52  or the distance between the light source  22  and the collimator lens  50 . Consequently, the point PS on the curve G moves to the point PS′ on the curve J. Thus the beam diameter of the light beam at the point PS is increased. 
     On the other hand, as a result of using concave lens  29 , the beam diameter of the light beam at the point PS′ is reduced to the beam diameter at the point PS″. As shown in FIG. 20, the characteristics are changed from those represented by the curve J to those represented by the curve K. The concave lens  29  has the effect of increasing the distance from the light source  22  to the point S at which the light beam emitted from the light source  22  has a minimum beam diameter. Consequently, this (third) embodiment of the present invention obtains advantageous effects similar to those of the embodiment of the present invention illustrated in FIG.  2 . 
     FIG. 21 is an exemplary diagram illustrating another embodiment of the present invention. The embodiment shown in FIG. 21 has a configuration similar to the aforementioned embodiment, except that the second beam shaping device  28  is located in a different place than that of the previously discussed embodiment. In this (fourth) embodiment of the present invention, shown in FIG. 21, the second beam shaping device  28  is formed as a mirror  34  reflecting a light beam emitted from the light source  22  and reflected by the light splitting member  26  to the mirror  34 . Mirror  34  is formed as a concave mirror. Consequently, advantageous effects similar to those of FIG. 19 are attained by the present invention. 
     FIG. 22 is an exemplary diagram showing an embodiment of the present invention similar to the embodiment illustrated in FIG.  21 . In the embodiment of the present invention shown in FIG. 22, the second beam shaping device  28  is formed as a mirror  36  reflecting a light beam emitted from the light source  22  then reflected by the light splitting member  26  to the polygon mirror  32  through the mirror  34 . Consequently, advantageous effects similar to those of the embodiment of the present invention illustrated in FIG. 19 are obtained. 
     FIG. 23 is an exemplary diagram showing another embodiment of the present invention similar to that shown in FIG.  22 . In the embodiment of the present invention shown in FIG. 23, the second beam shaping device  28  comprises the mirrors  34  and  36 . One of the mirrors  34  and  36  is formed as a concave mirror, and the other is formed as a cylindrical lens. The mirror formed as a cylindrical lens, as described above with reference to FIGS. 8 and 9 are adapted to control the divergence angle of one of the light beams emitted from the laser light source  22 , the divergence angles of which are different from one another. 
     FIG. 24 is an exemplary diagram showing an embodiment of the present invention similar to the embodiment illustrated in FIG.  2 . In the embodiment shown in FIG. 24, the second beam shaping device  28  is formed as a plano-convex lens  33 , placed between the light splitting member  26  and the mirror  34 . The operation and advantageous effects of this plano-convex lens  33  are the same as the plano-convex lens of FIG. 2, serving as the second beam shaping device  28 . In contrast with the embodiment of FIG. 2, the embodiment of FIG. 24 is effective when the distance between the light source  22  and the bottom reading zone E is greater than the distance between the light source  22  and the side reading zone E. 
     FIG. 25 is an exemplary diagram showing another embodiment of the present invention. In the case of the aforementioned embodiments of the present invention, the optical scanner  10  includes the bottom reading window  18 , the side reading window  20 , and the common light source  22  used for these reading windows. In contrast, in the embodiment of the present invention of FIG. 25, the optical scanner  10  includes a single reading window  180 . Additionally, a light beam emitted from the common light source  22  is split into two light beam components by the light splitting member  26 . An object is then scanned by the scanner  10  emitting the two light beam components from the reading window  180 . The first beam shaping device  24  is located between the light source  22  and the light splitting member  26 . The second beam shaping device  28  is located in one of the optical paths of the light beam components formed when the light beam is split by the light splitting device  26 . The operation and advantageous effects of the first and second beam shaping devices  24  and  28  are similar to those of the aforementioned embodiments. 
     FIGS.  26 (A) and  26 (B) are exemplary diagrams illustrating a light source module  30  including a right-angle prism. FIG.  26 (A) is a plan view of the light source module  30 , and FIG.  26 (B) is a vertical cross-sectional diagram schematically illustrating the light source module  30 . The light source module  30  includes a body  30 a to which the light source  22  is attached. The collimator lens  50  of the first beam shaping device  24 , the right-angle prism  54 , the aperture  52  of the first beam shaping device  24 , the light splitting means (half mirror)  26 , and the second beam shaping device  28  are located in the body  30   a  of the light source module  30 . The collimator lens  50  is attached to an aluminum block  50   a  and is then inserted into a hole bored in an end part of the body  30   a , as shown in FIG.  26 (D). A lens serving as the second beam shaping device  28  is inserted into a hole bored in the other end part of the body  30   a , as shown in FIG.  26 (C). The lens acting as the second beam shaping device  28  is shaped nearly like a semi-circle. The shape of a mounting hole  28   a , which is a groove having a U-shaped section, is matched with that of the same lens. 
     As described above, in accordance with the present invention, the beam diameters of the two light beam components which are emitted from a common light source and split by an optical beam splitter are minimized. 
     The many features and advantages of the invention are apparent from the detailed specification and, thus, it is intended by the appended claims to cover all such features and advantages of the invention which fall within the true spirit and scope of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.