Abstract:
An optoelectronic device detects labels provided with contrasting patterns. A transmitter emits light rays, and a receiver receives the light rays. The receiver includes a receiver output for outputting receiver signals. A reflecting unit periodically guides the light rays within a monitoring range. An evaluation unit for evaluating the receiver signals from the receiver, The transmitter, receiver, and reflecting unit are arranged such that the light rays are guided from said transmitter to said reflecting unit to the label to said reflecting unit to said receiver. The receiver includes at least one light sensitive surface that at least partially encloses the light rays transmitted from said transmitter to said reflecting unit.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority of German Patent Application No. 102 05 294.8 filed Feb. 8, 2002. The disclosure of the foregoing priority application and of each and every U.S. and foreign patent and patent application mentioned herein are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     The invention relates to an optoelectronic device for detecting labels having contrasting patterns. 
     An optoelectronic device is known from German Patent Document DE 198 44 238 A1. The conventional optoelectronic device is used to detect labels, in particular, barcode labels. The optoelectronic device includes a transmitter with a transmitting optic connected downstream of the transmitter, and a receiver with a receiving optic connected in front of the receiver. The light rays emitted by the transmitter and the receiving light rays reflected by the labels are guided over a reflecting unit. The reflecting unit consists of a rotating polygonal mirror wheel with a plurality of mirror surfaces. The reflecting unit periodically guides the light rays emitted by the transmitter over a monitoring range. 
     Reflecting mirrors, across which the light rays from the transmitted and light rays to the receiver are guided, are arranged between the transmitter and the reflecting unit, as well as between the receiver and the reflecting unit. The reflecting mirrors guide the light rays from the transmitter and the light rays to the receiver over the same mirror surface of the polygonal mirror wheel. 
     The conventional optoelectronic device includes a plurality of optical components over which the light rays from the transmitter and to the receiver must be guided. 
     The individual components, in particular the reflecting mirrors, require an exact calibration. This calibration results in an undesirably high assembly expenditure during the manufacture of the optoelectronic device. In addition, the optoelectronic device has an undesirably large structural shape, particularly since the arrangement of the reflecting mirrors and the receiving optic in front of the receiver require a large amount of space. 
     Another optoelectronic device for detecting barcode labels is known from International publication WO 00/16239. With this optoelectronic device, the transmitter and the receiver are arranged at a distance to each other, one above the other. The light rays emitted by the transmitter and the light rays reflected by the labels are guided over a reflecting unit. The reflecting unit is a polygonal mirror wheel with a plurality of mirror surfaces. The light rays emitted by the transmitter and reflected by the barcodes are respectively guided over the same mirror surface of the polygonal mirror wheel. The light rays from the transmitter and the light rays from the barcodes are guided so as to be spatially separated. Thus, the light rays emitted by the transmitter impinge on the upper partial section of the respective mirror surface on the polygonal mirror wheel while the light rays reflected by the barcodes are guided across the lower partial section a particular mirror surface. 
     To achieve a complete spatial separation of the light rays from the transmitter and the light rays from the barcodes, the partial sections of the mirror surface must be clearly offset relative to each other. 
     This conventional optoelectronic device is relatively miniaturized to some degree because the receiver is installed at a distance opposite the reflecting unit, without a receiving optic in front of the receiver. However, as compared to traditional polygonal mirror wheels, the height of the polygonal mirror wheel in the above-described optoelectronic device must be noticeably increased to obtain the desired separation of the light rays. In turn, this requires an undesirable enlargement of the structural shape of the optoelectronic device. A further disadvantage is that the optical axes of the transmitter and the receiver must be aligned precisely, relative to each other and relative to the position of the reflecting unit, to ensure the desired spatial separation of the light rays from the transmitter and the light rays from the barcodes. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to design an optoelectronic device for detecting barcodes having the smallest possible structural shape. 
     The above and other objects are achieved according to an embodiment of an optoelectronic device of the present invention which is set forth herein by way of example only. Exemplary modifications of the invention are additionally described herein. 
     The optoelectronic device of the present invention detects labels with contrasting patterns. According to an exemplary embodiment, transmitter emits transmitting light rays, and a receiver receives receiving light rays. A reflecting unit is used to guide the light rays from the transmitter periodically inside a monitoring range, and an evaluation unit evaluates the signals output from the receiver. The light rays reflected by the labels are guided via the reflecting unit onto the receiver. The receiver has a light-sensitive surface which at least partially encircles the light rays emitted from the transmitter. 
     One advantage of the present invention is that the transmitter and the receiver of the optoelectronic device are positioned opposite the reflecting unit, without reflecting mirrors installed in between. According to an exemplary embodiment, as a result of the large-surface, light-sensitive surface that encloses the path of the light rays transmitted by the transmitter, the light rays from the barcodes are guided by the reflecting unit nearly completely onto the receiver, without the aid of a receiving optic. Thus, the optoelectronic device according to the invention has only a small number of optical components and can be produced cheaply with little assembly expenditure. An extremely small structural shape is achieved as a result of directly coordinating the transmitter and the receiver, without the installation of a receiving optic and without the use of reflecting mirrors. 
     This advantage is further increased in that the light-sensitive surface of the receiver at least partially encloses the light rays emitted by the transmitter, thus resulting in a coaxial guidance of the light rays from the transmitter and the light rays guided to the receiver. 
     The reflecting unit optionally includes a polygonal mirror wheel with a predetermined number of mirror surfaces. The light rays from the transmitter and the light rays from the barcodes are respectively guided over the same mirror surface of the polygonal mirror wheel. 
     As a result of the coaxial guidance of the two types light rays, the transmitting light spot projected onto the respective mirror surface is at least partially surrounded by the receiving light spot projected onto the same mirror surface. This results in an efficient use of the mirror surface of the polygonal mirror wheel because it is illuminated almost totally by the two types of light rays. In turn, the dimensions of the mirror surfaces can be adapted optimally to the cross section of the transmitting light spot and the receiving light spot. As a result, the mirror surfaces and thus the complete polygonal mirror wheel have a smaller structural size. 
     According to an exemplary embodiment, the receiver is arranged on a carrier installed directly downstream of the transmitter. The light-sensitive surface of the receiver and the carrier, however, are each provided with corresponding recesses, and the light rays from the transmitter are guided through the recesses. This type of arrangement for the transmitter and the receiver requires only a small structural volume and the assembly is quick and cost-effective. Moreover, the calibration expenditure is particularly low. 
     For optical separation of the light rays from the transmitter and the light rays to the receiver and to avoid light rays intended for the receiver from entering the transmitter, the recesses in the carrier and the receiver are fitted with a sleeve, the front end of which optionally projects over the receiver front. The light rays from the transmitter are guided inside this sleeve and have a smaller ray diameter than the inside diameter of the sleeve. 
     According to one embodiment, the receiver has a one-piece, coherent, light-sensitive surface. It is advantageous if the light-sensitive surface forms a homogeneous, continuous surface that has a high sensitivity for detecting the impinging light rays. 
     The receiver of another embodiment comprises a number of receiving elements with light-sensitive partial surfaces, which jointly form the light-sensitive surface. Conventional and cost-effective PIN diode elements can be used as receiving elements. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is explained in the following with the aid of the drawings which showing an exemplary embodiment and without restricting the general inventive idea. 
     FIG. 1 illustrates a schematic representation of an exemplary embodiment of the optoelectronic device according to the present invention. 
     FIG. 2 illustrates a detailed representation of a segment of the optoelectronic device shown in FIG.  1 . 
     FIGS. 3-7 illustrate various embodiments of the receiver for the optoelectronic device according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Identical or corresponding parts are given the same reference numerals in the drawings and may not be introduced again. 
     FIG. 1 schematically shows the configuration of an optoelectronic device  1  for detecting labels having defined contrast patterns. The labels can have optional sequences and shapes of adjoining light and dark surfaces, optionally black and white surfaces. In the following description, the labels are barcodes  2 . The barcodes  2  typically include a sequence of black and white bar elements with a defined length and width. The optoelectronic device  1  comprises a transmitter  4  for emitting transmitting light rays  3  and a receiver  6  for receiving the receiving light rays  5 . The transmitter  4 , which is optionally a laser diode, is optionally installed in series upstream from a transmitting optic  7  that focuses the light rays  3 . 
     The light rays  3  emitted by the transmitter  4  and the light rays  5  reflected back by the barcode  2  are each guided over a reflecting unit. The reflecting unit includes of a motor driven polygonal mirror wheel  8  with a plurality of facet-cut mirror surfaces  9 . 
     As a result of a rotational movement of the polygonal mirror wheel  8 , the light rays  3  emitted by the transmitter  4  are periodically guided over a monitoring range  10  located in a scanning plane. The monitoring range  10  extends over a specific angular region that is predetermined by the number of mirror surfaces  9  of the polygonal mirror wheel  8 . 
     Signals output from the receiver  6  are amplified in an amplifier (not shown) and evaluated in an evaluation unit  21 . 
     The light rays  5  reflected from the barcodes  2 , experience an amplitude modulation that corresponds to the sequence of black and white bar elements in the barcode  2 . The signals output from receiver  6  have a corresponding amplitude modulation. The analogue, amplitude-modulated signals are evaluated in the evaluation unit  21  with the aid of a threshold value unit. As a result, binary signal sequences are generated which are used to detect the barcode  2  through a comparison with stored contrast patterns for the barcodes  2 . 
     The light rays  3  emitted by the transmitter  4  are guided onto the reflecting unit, and the light rays  5  that are reflected by the labels back to the receiver  6 , via the reflecting unit, take a coaxial path. 
     The coaxial guidance is achieved in that the light-sensitive surface  11  of receiver  6 , which is installed downstream from the transmitter  4  and the transmitting optic  7 , at least partially surrounds the light rays  3 . 
     The transmitter  4  and the receiver  6  are positioned at a distance to the polygonal mirror wheel  8  such that the light rays  3  and the light rays  5  are guided across the same mirror surface  9  of the polygonal mirror wheel  8 . The mirror surfaces  9  of the polygonal mirror wheel  8  are oriented perpendicular to the axes of the light rays  3  and the light rays  5  in one exemplary embodiment. The receiving light point projected onto the mirror surface  9  at least partially encloses the transmitting light point of the light rays  3  projected onto the same mirror surface  9 . The mirror surfaces  9  are adapted to the geometric dimensions of the light rays  3  and the light rays  5 , such that the light rays  3 ,  5  illuminate the mirror surface  9  as completely as possible. 
     FIG. 2 shows a detailed view of the optical components of the optoelectronic device  1  according to FIG.  1 . 
     A laser diode functioning as the transmitter  4  is secured in a holder (not shown in FIG.  2 ). A lens holder  12  is downstream of the transmitter  4  and holds a lens functioning as transmitting optic  7 . The lens holder  12  includes a plastic molded part or the like and is provided with a diaphragm  13  on the front. The diaphragm  13  limits the beam diameter of the light rays  3  that are focused with the transmitting optic  7 . The transmitter  4 , the lens holder  12  and the transmitting optic  7  together form a transmitter module. 
     A receiver module can be installed directly behind the transmitter module. The receiver module comprises a carrier  14  and the receiver  6  which is fit onto the carrier  14 . 
     The carrier  14  is provided with connectors  15  in the form of pins, which project from one edge of the carrier  14 . The pins are used to attach and solder the carrier  14  to a board (not shown) on which the evaluation unit is integrated. 
     The carrier  14  and the receiver  6  respectively and contain a single recess  16  in an exemplary embodiment. For the exemplary embodiment shown in FIG. 2, the recesses  16  are formed as congruent, coaxial bores. 
     A light-impermeable sleeve  17  is inserted into the bores  16  and forms a component of the receiver module. The sleeve  17  comprises a light-impermeable plastic molded part. In one exemplary embodiment, the sleeve  17  has a hollow-cylindrical shape with a ring-shaped shoulder  18  on the back end projecting from the outer shell surface. The sleeve  17  extends through the bores in the carrier  14  and the receiver  6  and projects with its front edge slightly over the front of the receiver  6  with the light-sensitive surface  11 . 
     The sleeve  17  is inserted from the back of the carrier  14  into the bores of the carrier  14  and the receiver  6  until the shoulder  18  fits against the back wall of the carrier  14  to stabilize the position of sleeve  17 . 
     The longitudinal axis of sleeve  17  extends coaxial to the optical axes of the transmitter  4  and the transmitting optic  7 . The beam diameter of the light rays  3  are smaller than the inside diameter of the sleeve  17  such that the light rays  3  pass through the sleeve  17 . 
     The sleeve  17  functions to optically decouple the light rays  3  and the light rays  5 . 
     The light-sensitive surface  11  of the receiver  6  is positioned opposite the reflecting unit without a receiving optic installed in between. The light-sensitive surface  11  of the receiver  6 , as well as the mirror surfaces  9  of the polygonal mirror wheel  8 , are oriented in a vertical plane that extends perpendicular to the axes of the light rays  3  and the light rays  5 . 
     The largest possible surface is selected for the light-sensitive surface  11  of receiver  6  in order to increase the detection sensitivity, and the surface is optionally adapted to the dimensions of the mirror surfaces  9 . For the embodiment shown in FIG. 2, the light-sensitive surface  11  completely encloses the bore in the receiver  6 , and the area of the bore is considerably smaller than the light sensitive surface  11 . As a result, a high detection sensitivity of the receiver  6  is obtained. As shown in FIG. 2, the light rays  5  that extend coaxial to the light rays  3  nearly completely illuminate the light-sensitive surface  11 . 
     FIGS. 3-7 show different designs for the receiver  6  of the optoelectronic device  1 . 
     FIG. 3 shows the receiver  6  positioned on a square carrier  14  with two connectors  15  projecting from the side for securing the carrier  14  to a board. The receiver  6  is adapted to the size of the carrier  14  so that the receiver&#39;s light-sensitive surface  11  extends over the complete surface of the carrier  14 . The homogeneous, light-sensitive surface  11  has a one-piece design and a square outside contour. As in the carrier  14 , the receiver  6  is provided with a circular, central bore that forms the recess  16  through which the light rays  3  emitted from the transmitter are guided. Since the light-sensitive surface  11  extends continuously over the complete carrier surface, a large portion of the light rays  5  is guided from the reflecting unit onto the receiver  6 , thus resulting in a high detection sensitivity of the receiver  6 . The receiver  6  primarily includes a large-surface PIN diode element. 
     FIG. 4 shows a modification of the embodiment shown in FIG.  3 . The receiver  6  again has a one-piece, homogeneous, light-sensitive surface  11  that extends over the complete area of the square carrier  14 . In contrast to the exemplary embodiment of FIG. 3, the recesses  16  in the carrier  14  and the receiver  6  do not take the form of circular bores. Rather, the recesses  16  in FIG. 4 extend from the center of the carrier  14  and/or the receiver  6  to the edges. Thus, the light-sensitive surface  11  no longer completely encloses the light rays  3  guided through recesses  16 , but instead, the light-sensitive surface only partly encloses the light rays  3  emitted by the transmitter. 
     FIGS. 5-7 show designs for a receiver  6  which comprises multiple parts. The receiver  6  includes a plurality of separate receiving elements  19  that optionally have identical designs and are formed by traditional PIN diode elements. The individual receiving elements  19  have light-sensitive partial surfaces  20  that complement each other and form a single joint light-sensitive surface  11 . For this, the sum of all output signals from the individual receiving elements  19  is determined in the evaluation unit and used to generate the receiving signal for the receiver  6 . The detection sensitivity necessary for receiving the light rays  5  is obtained by connecting the individual receiving elements  19  of the receiver  6 . 
     FIGS. 5-7 show that the carrier  14  respectively has an essentially square cross section formed by a circuit board. Respectively three parallel-extending pins project from the upper edges of the carrier  14  to form the connectors  15  for connecting the carrier to the board. 
     FIG. 5 shows a receiver  6  provided with four identically designed receiving elements  19  that have square, light-sensitive partial surfaces  20 . The centrally positioned circular bore of carrier  14  forms the recess  16  through which the light rays  3  are guided. The receiving elements  19  are arranged in a U shape around the bore so that the light-sensitive partial surfaces  20  in part enclose the light rays  3  which pass through the bore. 
     FIG. 6 shows a first modification of the exemplary embodiment shown in FIG.  5 . As in FIG. 5, the carrier  14  has a central circular bore through which the transmitting light rays  3  pass. In contrast to the embodiment shown in FIG. 5, the receiver  6  in this case is provided with six identical receiving elements  19 . 
     The receiving elements  19  adjoin the edge of the bore and are arranged essentially rotation-symmetrical to the bore such that the light-sensitive partial surfaces  20  form a ring-shaped arrangement and completely enclose the light rays  3  that are guided through the bore. 
     FIG. 7 shows a second modification of the exemplary embodiment according to FIG.  5 . The square carrier  14  is provided with a recess  16  that extends from the center of carrier  14  to its lower edge. The light rays  3  pass through the recess  16  in the central region of the carrier  14 . The receiver  6  is provided with four receiving elements  19  with identical design and square, light-sensitive partial surfaces  20 . The receiving elements  19  adjoin the edge of the recess  16 , thereby forming a U-shaped arrangement. 
     The embodiments of FIGS. 5-7 show that the number of receiving elements  19  and their arrangement on the carrier  14  are selected such that their light-sensitive partial surfaces  20  cover the highest possible share of the carrier  14  surface to obtain a correspondingly high detection sensitivity for the receiver  6 . 
     The invention has been described in detail with respect to exemplary 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.