Abstract:
An optoelectronic device for detecting labels with defined contrast patterns includes a transmitter for emitting light rays, a receiver for receiving light rays, as well as a deflection unit with a motor-driven polygonal mirror wheel. The transmitted light rays and the received light rays are guided over the polygonal mirror wheel in order to scan the labels and reassemble the label-reflected received light rays, respectively. The device furthermore is provided with an evaluation unit for evaluating electrical receiving signals converted from received light rays at the receiver. The motor for driving the polygonal mirror wheel has a drive shaft and is provided with a magnet that is an injection-molded part, which is formed onto the shaft and operates jointly with at least one coil.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
         [0001]    This application claims the priority of European Patent Application No. 01 116 015.7 filed Jul. 2, 2001, the disclosure of which is being incorporated herein by reference.  
         FIELD OF THE INVENTION  
         [0002]    The invention relates to an optoelectronic device for detecting labels with defined contrast patterns. In particular, the optoelectronic device can be embodied as a barcode reader.  
         BACKGROUND OF THE INVENTION  
         [0003]    Optoelectronic devices of this type comprise a transmitter for emitting light rays, a receiver for received light rays, as well as a deflection unit with a motor-driven polygonal mirror wheel. The transmitted light rays and the received light rays are guided over the polygonal mirror wheel. As a result of the rotational movement of the polygonal mirror wheel, the transmitted light rays are deflected such that they periodically sweep across an area where the labels are located.  
           [0004]    The transmitted light rays are guided across the labels in order to scan the patterns thereon. The received light rays, which are reflected back by the labels, are amplitude modulated in accordance with the label contrast pattern. The correspondingly modulated receiving light signals at the receiver output are evaluated in an evaluation unit for detecting the labels.  
           [0005]    The polygonal mirror wheel is motor-driven, so that the polygonal mirror wheel performs a rotational movement with a predetermined speed. Commercially available motors with an integrated motor control are normally used for this. The motor is additionally provided with a shaft. A mechanical holding fixture is attached to this shaft and the polygonal mirror wheel is mounted on the top of this fixture. For this, the polygonal mirror wheel preferably is provided with a mounting support for screwing on the holding fixture. The shaft itself is inserted into a bearing and is secured there with fastening means. The motor control is connected via cable to the evaluation unit, which is arranged on a separate printed circuit board. The cable end is provided with a contacting plug that is plugged into a corresponding socket on the evaluation unit.  
           [0006]    The disadvantage of a deflection unit with this type of design is that it comprises a plurality of electrical and mechanical components. The assembly of these components is time-consuming and thus represents an undesirably high cost factor when producing the optoelectronic device. In addition, the tolerances of the individually produced components lead to problems with the accuracy of the deflection units produced in this way. Finally, deflection units with this type of design have an undesirably large structural size.  
         SUMMARY OF THE INVENTION  
         [0007]    It is the object of the invention to develop a deflection unit for an optoelectronic device of the aforementioned type, which has the smallest possible structural size at the lowest possible production cost, and with a smaller number of production parts than known optoelectronic devices.  
           [0008]    The features of the optoelectronic device according to the invention are designed to solve this problem. Advantageous embodiments and useful modifications of the invention are described in the claims.  
           [0009]    The optoelectronic device according to the invention is used to detect labels with defined contrast patterns and comprises a transmitter for emitting light rays, a receiver for receiving light rays from a label and for generating receiving signals and a deflection unit with a motor-driven polygonal mirror wheel. The transmitted light rays are guided over the polygonal mirror wheel in order to scan the labels and the reflected, received light rays are also guided across the polygonal mirror wheel. The optoelectronic device according to the invention furthermore comprises an evaluation unit for evaluating the receiving signals present at the receiver. The motor for driving the polygonal mirror wheel has a drive shaft and is provided with a magnet, which is embodied as an injection-molded part. The magnet is molded onto the shaft and operates jointly with at least one coil.  
           [0010]    One essential advantage of the device according to the invention is that the shaft with molded-on magnet forms an extremely compact structural unit that can be produced inexpensively. In particular, no additional adapters or the like are required to connect the drive shaft to the magnet. As a result, the motor for driving the polygonal mirror wheel can be produced efficiently with a small number of individual parts and with extremely small dimensions.  
           [0011]    An additional advantage is that the shape of the magnet can be specified freely due to the injection-molding procedure, which forms the magnet. In particular, the outside contour of the magnet can be designed such that the polygonal mirror wheel is fitted directly onto the magnet and can be secured, for example, by gluing it on.  
           [0012]    Separate mechanical means for attaching the polygonal mirror wheel to the magnet are not required according to the invention, which results in a further reduction of the individual parts and thus a further lowering of the assembly and material costs when producing the deflection unit. The size of the deflection unit is additionally reduced further with this type of design.  
           [0013]    In one particularly advantageous embodiment of the invention, the motor is mounted directly on a printed circuit board with an integrated evaluation unit. As a result, the motor, which operates jointly with the coil, is thus actuated directly via this evaluation unit. Consequently, a separate motor control, as well as an electrical cable and plug connection between a motor control of this type and the evaluation unit may be dispensed with.  
           [0014]    The drive shaft according to the invention rotates inside a bearing. The bearing is positioned inside a tube. In an embodiment of this type, the tube with the bearing for guiding the motor shaft and the coil, which operates jointly with the magnet, rest on the printed circuit board.  
           [0015]    According to this embodiment, the motor shaft is inserted with its lower end into a bearing bore that opens up at the tube top. The motor shaft does not need to be secured inside the bearing, which is particularly advantageous as it is possible to dispense with additional means for securing.  
           [0016]    As a result of this structure, the shaft can be moved in a longitudinal direction; but this movement is limited by an end stop, formed by a housing ceiling of the optoelectronic device. The housing ceiling is located close to the upper edge of the shaft, provided the shaft is in the desired position. If the shaft with magnet is moved upward inside the bearing bore, for example as a result of impact on the device, the end stop will push the shaft back to its desired position without this hindering the rotational movement of the deflection unit.  
           [0017]    A device according to the invention of this type requires only a small number of mechanical and electronic individual components and as a result, can be produced inexpensively. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    These and other features and advantages will be further understood from the following detailed description of the preferred embodiment with reference to the accompanying drawings in which:  
         [0019]    [0019]FIG. 1 illustrates, in schematic form, the basic layout of an optoelectronic device designed as barcode reader.  
         [0020]    [0020]FIG. 2 is an exemplary embodiment of a deflection unit for the device according to FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]    [0021]FIG. 1 shows the basic layout of an optoelectronic device  1  for detecting labels provided with defined contrast patterns. In principle, the labels can have optional sequences and shapes for adjoining light/dark areas, preferably black and white areas. Barcodes  2  form the labels for the present exemplary embodiment. The barcodes  2  essentially consist of a series of black and white line elements  2   a ,  2   b  with a defined length and width. The optoelectronic device  1  consequently is a barcode reader.  
         [0022]    The optoelectronic device  1  comprises a transmitting element  3 , a receiving element  4 , as well as an evaluation unit  5 . The transmitting element  3  consists of a transmitter  6 , preferably a laser diode, as well as a transmitting optic  7  that is installed in front of the transmitter  6  and is designed to focus the transmitted light rays  8 . The focused transmitted light rays  8  are deflected via a rotating polygonal mirror wheel  9  and are guided across the barcode symbol  2  to be detected. The rotational axis for the polygonal mirror wheel  9  is arranged perpendicular to the equatorial plane, shown in FIG. 2, of the polygonal mirror wheel  9 . As a result of the rotational movement of the polygonal mirror wheel  9 , the transmitted light rays  8  are periodically guided inside a predetermined angular range in the equatorial plane that forms the scanning plane. In the process, barcodes  2  can be read within a predetermined distance range, corresponding to the focusing of the transmitted light rays  8 .  
         [0023]    The polygonal mirror wheel  9  for the exemplary embodiment shown in FIG. 1 is provided with eight mirror surfaces  9   a  in the form of facets on which the transmitted light rays  8  are deflected. Corresponding to the number of facets of the polygonal mirror wheel  9 , the transmitted light rays  8  periodically sweep across an angular range of Δα=90°. With the arrangement shown in FIG. 1, the scanning plane in which the transmitted light rays  8  are guided is positioned in the equatorial plane of the polygonal mirror wheel  9 .  
         [0024]    The received light rays  10  that are reflected by the barcode  2  are guided over the polygonal mirror wheel  9  to the receiving element  4 . The receiving element  4  consists of a receiver  11 , which is designed as a photodiode and converts the received light rays  10  to an electrical receiving signal. An amplifier  12  is connected behind the receiver  11 . A receiving optic  13  is connected in front of the receiving element  4  to improve the detection sensitivity. The receiving signal present at the output of receiver  4  is supplied to the evaluation unit  5 .  
         [0025]    In accordance with the contrast pattern for barcode  2 , the received light rays  10  that are reflected on this barcode are amplitude modulated. The output electrical receiving signal indicating the received light rays  10  at the receiver  11  shows a corresponding amplitude modulation. Based on this amplitude modulation, the contrast pattern for the barcode  2  is reconstructed in the evaluation unit  5  with the aid of the receiving signals.  
         [0026]    [0026]FIG. 2 shows an exemplary embodiment of a deflection unit  14 , of which the polygonal mirror wheel  9  according to FIG. 1 is a component. In addition, the deflection unit  14  comprises a motor for driving the polygonal mirror wheel  9 , so that this wheel performs a rotational movement with a predetermined speed. This motor comprises a shaft  15 , on which the polygonal mirror wheel  9  is rotationally positioned, as well as a coil  16  and a magnet  17  that operates jointly with this coil.  
         [0027]    The motor is arranged on a printed circuit board  18  with an integrated evaluation unit  5 . The motor is actuated directly via the evaluation unit  5 , which is directly connected to the motor via printed circuit board  18 . As a result, it is possible to dispense with separate electronic components and adapters for the motor control.  
         [0028]    The printed circuit board  18  contains a bore  19 . A tube  20 , which projects perpendicularly from printed circuit board  18 , is positioned inside bore  19 . Tube  20  preferably is a hollow-cylindrical plastic part that is open on the top and the bottom. Alternatively, tube  20  may be made of metal.  
         [0029]    A bearing  21  is secured inside tube  20 , at the inside wall of tube  20 . Bearing  21  is designed to accommodate shaft  15  and extends in a longitudinal direction of tube  20 , along its symmetry axis S. Bearing  21  is preferably designed as a sliding bearing, ball bearing or roller bearing and is provided with a central bearing bore  22  that extends in the longitudinal direction of tube  20 , symmetrical to the symmetry axis S of tube  20 . An upper end of bearing bore  22  is adjacent the open top of tube  20 . The bottom of tube  20  is closed off with a bottom part  23 , which extends in a horizontal plane that is parallel to the plane of printed circuit board  18 .  
         [0030]    Magnet  17  is designed as injection-molded part and is molded onto shaft  15 . For the injection-molded part, magnetic materials such as iron or the like are mixed into a molding material that can be poured, e.g. a plastic material, such that the magnetic materials are finely distributed with the molding material.  
         [0031]    [0031]FIG. 2 shows magnet  17  molded onto the upper portion of shaft  15 . To secure magnet  17  safely on shaft  15 , the shaft is provided with a groove  24  extending in circumferential direction. The molding material that forms magnet  17  is injected into this groove.  
         [0032]    Magnet  17  is a symmetrical molded part that encircles shaft  15 . Polygonal mirror wheel  9  is fitted on top of and against the side surface of magnet  17 . The top surface of magnet  17  is essentially a flat, circular-disk shaped area while the side surface of magnet  17  has a cylindrical shell surface.  
         [0033]    One component of magnet  17  is an essentially hollow-cylindrical guide segment  25 , which projects from the top surface of the molded part. Preferably, guide segment  25  may have a conical shell surface, wherein the outside diameter of guide segment  25  is tapered toward its upper edge. Guide segment  25  is arranged in the center of magnet  17  and is arranged symmetrical to the symmetry axis S of symmetrical magnet  17 . The guide segment  25  encompasses the upper portion of shaft  15  and thus improves the support of magnet  17  on shaft  15 . The top of guide segment  25  is level with the top of shaft  15 .  
         [0034]    Polygonal mirror wheel  9  may be an injection-molded plastic part with mirror surfaces  9   a  applied to its outer shell surface. Mirror surfaces  9   a  are applied, preferably by evaporating and depositing a light-reflecting layer thereon.  
         [0035]    Polygonal mirror wheel  9  essentially is basically made from a circular disk segment and side walls of which project downward from edges of the disk segment to form a single unit together with the disk segment. The underside of the disk segment is mounted to the top surface of magnet  17 . The insides of the side walls of polygonal mirror wheel  9  enclose a cylindrical hollow space, which is adapted to the outside contour of magnet  17 .  
         [0036]    The circular disk segment of the polygonal mirror wheel  9  is provided with a central, circular bore  26 , the diameter of which is adapted to the outside diameter of the hollow-cylindrical guide segment  25  of magnet  17 . The polygonal mirror wheel  9  is fitted onto magnet  17  for mounting the deflection unit  14  and is secured thereon with adhesive.  
         [0037]    The underside of the circular disk segment of polygonal mirror wheel  9  is secured in this way on magnet  17 , so that the insides of the side walls extending from the disk segment form-fit the outside contour magnet  17 . Alternatively, polygonal mirror wheel  9  can be designed so that a space remains between the insides of the side walls for the polygonal mirror wheel  9  and the outside contour or shell surface of magnet  17 . The guide segment  25  of the molded part that forms magnet  17  projects through the bore  26  in the circular disk segment, wherein the edges of the bore  26  fit closely against the guide segment  25 .  
         [0038]    Shaft  15  together with magnet  17  and polygonal mirror wheel  9 , forms a single structural unit. Shaft  15  of the single structural unit is inserted into the bearing bore  22  of bearing  21  in order to mount deflection unit  14  on printed circuit board  18 . FIG. 2 shows that once deflection unit  14  is fully installed, the lower end of shaft  15  rests on bottom  23  of tube  20 .  
         [0039]    The lengths of shaft  15  and the bearing  21  are dimensioned so that, when assembled, an air gap remains between the tube  20  and the coil  16  on the printed circuit board  18  and an air gap exists between coil  16  and the underside of the magnet  17 . Thus, the rotation of the rotatably positioned structural unit including shaft  15 , magnet  17  and polygonal mirror wheel  9  is not obstructed.  
         [0040]    To keep the structural volume of deflection unit  14  as small as possible, the molded part that forms the magnet  17  is provided with a central, symmetrical recess  27 . Recess  27  is formed at the lower edge of the molded part that faces coil  16  when assembled. Tube  20  projects into recess  27 . As a result, a flat and space-saving design is obtained for deflection unit  14 , despite the relatively large height of tube  20 , resulting from the structural shape of the bearing  21 .  
         [0041]    The side walls of polygonal mirror wheel  9  project downward over magnet  17  and, in the process, partially cover the coil  16 . As a result, it is possible to obtained sufficiently large mirror surfaces  9   a  for deflecting transmitted light rays  8  and received light rays  10 , even with a relatively, flat structural shape for deflection unit  14 .  
         [0042]    Optoelectronic device  1  and deflection unit  14  may be integrated into one housing. In this case, the printed circuit board  18  with the motor arranged thereon rests on the housing bottom  28 . The housing ceiling  29  extends just barely above the upper edge of the shaft  15 .  
         [0043]    This embodiment of optoelectronic device  1  is particularly advantageous, since the shaft  15  only need be inserted into bearing bore  22 . That is, shaft  15  does not need to be secured on bearing  21 .  
         [0044]    In case of external interference, for example if impact stresses occur, shaft  15  can be moved to some degree upward inside bearing bore  22 . However, this translational movement is limited by housing ceiling  29 , which functions as an end stop. Since housing ceiling  29  extends just above the upper edge of shaft  15 , small deflections of shaft  15  can push it against housing ceiling  29 . As a result of the rebound and the attraction of the magnet toward coil  16 , shaft  15  is returned to its starting position. Consequently, deflection unit  14  continues to rotate without any operational impairment.  
         [0045]    The invention has been described in detail with respect to preferred embodiments, and it will now be apparent from the foregoing to those skilled in the art, that changes and modifications may be made without departing from the invention in its broader aspects, and the invention, therefore, as defined in the appended claims, is intended to cover all such changes and modifications that fall within the true spirit of the invention.