Method and apparatus for reading bar codes

Abstract: A bar code reading arrangement. A laser beam is scanned across a bar code which may be on a remote surface. Two detectors receive light reflected from the bar code, and convert it to an electrical signal. The detectors are laterally spaced on opposite sides of a line defined by the bi-section of the triangular area which is scanned by the laser beam. The electrical signal from the detector receiving only diffusely reflected light is used to identify the content of the bar code. The invention may be practiced in a hand-held unit with trigger means to initiate the bar code reading operation.

Description: This invention relates to bar code readers in accordance with the preamble of claim 1, and more particularly to a bar code reader for reading, using a laser beam, a bar code on a remote surface. Such a bar code reader is already known from document EP-A-0 085 804. The prior art bar code scanner comprises a laser source means for scanning the laser beam across a triangle and first and second detector means to provide an analog signal corresponding to the light amount reflected from a bar code. The prior art bar code reader is not designed to read the bar code symbols from diffusely reflected light only. It is the object of the prior art document to provide a compact light-weight hand-held apparatus for scanning and reading bar code symbols. It has become common practice for sales and inventory control purposes, etc., to print a bar code on the surface of a product which may indicate manufacturer name, product name, price and manufacturing data. The bar code is read, using an optical bar code reader, at appropriate time for obtaining the coded information. Bar code readers are generally either a so called "standing" type or a "handheld" type. The standing type reads a bar code attached to an object when the object and bar code are passed in front of the bar code reader. In contrast, the handheld type must be brought to the object in order to read the bar code. The pen type bar code reader is the most common example of a handheld bar code reader. The pen type has an optical tip which must be physically drawn across the bar code in order to read it. Another variation of the handheld type is the beam scanning bar code reader which has recently been gaining in popularity. The beam scanning reader includes a frame formed in the shape of a pistol. Inside the frame is a laser beam source for generating a laser beam, a laser beam scanning device for causing the laser beam to scan across a bar code to be read, a detecting arrangement including beam receiving elements for receiving laser light reflected from the bar code surface. The detecting arrangement converts the reflected light into an electric signal indicative of the amount of light received. Identifying means interprets the electrical signal so as to "read" the bar code information. A beam scanning system can detect a small spot from a distance, thus it allows the reading of both proximate and remote bar codes. In addition, the beam automatically scans the object so that no touch-and-move operation is required. In contrast, the pen type must have its cylindrical end portion touching the object to read it. The beam scanning bar code reader only requires that the object be held by the hand (for the standing type), or that the bar code be sighted as a target (for the handheld type). The beam reflected from the bar code surface includes two components: a normally reflected beam, and a diffusely reflected beam. The amount of light derived from the normally reflected beam is so intense that changes in the reflected light cannot be differentiated. For this reason, the beam scanning type bar code reader uses the diffusely reflected beam for reading bar codes. However, even in bar code readers which detect the diffusely reflected beam, it often happens that the normally reflected beam also reaches the beam receiving element during the scanning operation. For example, if black characters or symbols appear on a region which is white, the intensity of the normally reflected beam from the black characters or symbols becomes greater than that of the diffusely reflected beam from the white region. As a result, the contrast becomes poor and the bar code cannot be read. Thus, there is a "dead angle" below which a bar code cannot be read. To overcome this problem, one alternative is to provide indirect illumination such as with touch type bar code readers which use charge coupled devices (CCDs). However, another solution must be found for beam scanning bar code readers because direct lighting is required to scan distant bar codes. Another alternative is to restrict the angle at which the bar code reader is used relative to the bar code (such that the normally reflected beam cannot reach the receiving element). However, this makes use of the device more inconvenient. An object of this invention is to provide a method and apparatus for scanning a bar code with a laser beam and identifying the contents of the bar code solely from diffusely reflected light, without restricting the positional and angular relationship of the bar code reader relative to the bar code, i.e. free from the problem of "dead angle". This object is met by the characterizing features of claim 1 and 11. These steps ensure that at least one of the detectors will be receiving only diffuse light, and no "dead angle" will occur. The detecting means is a pair of detectors laterally disposed on opposite sides of a line defined by the bisection of the triangular area over which the laser beam scans, the triangular area having vertices at the point where the laser beam is directed toward the bar code, and on opposite sides of the bar code surface. This ensures that only one of the detectors will receive the normally reflected beam. The other detector will receive only diffusely reflected light. The output signals from the pair of detectors are evaluated by the switching means to determine which detector is receiving only diffusely reflected light. The operation of the switching means ensures that only the signal from the diffuse light receiving detector is switched through to the identification means. In this manner the dead angle can be eliminated by switching between the dual detectors, one of which must be receiving only diffusely reflected light. Preferred embodiment(s) of the invention will be described in detail with reference to the drawings wherein like reference numerals denote like or corresponding parts throughout. FIGURE 1 is a perspective view showing the internal configuration of a bar code reader; and FIGURE 2 is a schematic view showing the reflection paths of a laser beam. Fig. 1 is a perspective view showing a beam scanned bar code reader A of the handheld type. Bar code reader A includes hand-held package 10 which contains its other components. A laser beam source 1 generates a laser beam. A laser beam scanner 2 causes the laser beam to scan along a bar code 7. A pair of detectors 3, which may be photodiodes or the like, receive a beam reflected from a bar code surface 8 and convert the received beam into an electric signal proportional to the amount of laser light received. A signal processing circuit 4 processes the electrical signal from detectors 3. Processing circuitry includes control means 41, switching means 42 and identifying means 43. Package 10 is formed in the shape of a pistol. The muzzle of the pistol is provided with an aperture 20 for passing the laser beam and its reflected beam. A signal cord 40 extends from the frame 10 for supplying an output signal from the processing circuit 4 to an external unit. A trigger 6 initiates the bar code reading operation. The laser beam source 1 includes a laser beam generating element 11 which can be a semiconductor laser element or a laser diode, and a lens 12 for converging the output beam of laser beam generating element 11. Scanner 2 includes a rotating polygonal mirror 21 for causing the output beam from the laser beam source 1 to horizontally scan over a triangular area F defined by a predetermined angle α, and having vertices at the point where the laser beam is directed toward the bar code by the polygonal mirror, and on opposite sides of the bar code surface. Scanner 2 also includes a motor 22 for rotating the polygon mirror 21. The beam which is reflected by the polygonal mirror 21 is irradiated onto the bar code surface 8. Detectors 3 are set to a beam receiving level optimal for the intensity of the diffusely reflected beam coming from the bar code surface 8. Detectors 3 are vertically disposed so as to interpose therebetween a line G formed by the bisection of the triangular area F which is scanned by the laser beam. A pair of cylindrical lenses 5 guide the reflected beam from the bar code surface 8 into the detectors 3. A beam receiving element 30 detects the scanning operation by directly receiving the reflected beam from the polygon mirror 21. Control means 41 controls the driving of the beam source 11 and the motor 22. The switching means 42 determines which of the output signals from the detectors 3 is to be input to the identifying means 43. This switching operation is based on a scanning division signal from the beam receiving element 30 which detects the scanning operation. The identifying means 43 shapes the signal outputted by the detector and obtains data corresponding to the subject bar code by binary-coding the bar code. The contents of the bar code are identified based on this binary coded signal. When trigger 6 is operated, a laser beam is generated by the laser beam source 1, and, at the same time, mirror 21 is rotated by motor 22. The laser beam is reflected by a surface of the rotating polygonal mirror 22, and is caused to scan across a predetermined angle α which corresponds to the rotation of the reflecting surface. The scanning laser beam travels to the bar code surface 8 through the aperture 20. The beam reflected from the bar code surface 8 is received by the pair of detecting means through the lenses 5. As shown in FIG. 2, the pair of detectors 3 are disposed so as to interpose therebetween the line G formed by the bisection of the triangular area F scanned by the laser beam. The normally reflected beam L1 is reflected to only one of the detectors 3, depending on the angular and positional relationship between the bar code reader A and the bar code surface 8. The other detector 3 receives only the diffusely reflected beam L2. It is always possible for at least one of the detecting means 3 to receive the proper amount of the reflected beam in a scanning operation, regardless of the positional and angular relationship of the bar code reader to the bar code. Referring back to FIG. 1, the output signal from the detector which is receiving only diffusely reflected light is switched through to the identifying means 43 by the switching means 42, whereby the bar code 7 can be identified based on the proper amount of reflected light. The normally reflected beam is received by only one of the two detectors 3, whereby it is ensured that the other detector receives no normally reflected light. As the laser beam scans across the bar code, the switching means 42 operates to switch an output signal from one detector 3 through to the identifying means. The switching means 42 will only switch through a signal from a detector 3 which is receiving diffusely reflected light. Therefore the bar code can be identified from diffusely reflected light without imposing any positional or angular relationship restrictions on the bar code reader with respect to the bar code. A further embodiment of the present invention includes a bar code reader of the standing type. In this embodiment, the components of the scanning bar code reader are contained in a stationary package. An object containing a bar code must be held in front of the bar code reader for the scanning operation to occur. According to the bar code reader of this invention, in which a pair of detectors are disposed so as to interpose therebetween a line formed by the bisection of the triangular area scanned by the laser beam, the bar code can be identified from diffusely reflected light without imposing any positional or angular relationship restrictions on the bar code reader with respect to the bar code.

Claims: A bar code reader (A) comprising: laser beam source means (1) for generating a beam of laser light (F); laser beam scanning means (21) for causing the laser beam to scan across a bar code (7) said laser beam scanning means being configured so as to cause the laser beam to scan across an area defined by a triangle having vertices at the point where the laser beam is directed toward the bar code (7), and on opposite sides of the bar code surface (8); detecting means (3) including two light detectors for receiving laser light (L1,L2) reflected from the bar code (7), and generating an electrical signal indicative thereof and identification means (43) for identifying, from the electrical signal, the content of a bar code; characterized in that said first detector (3) is adapted to convert said light into a first electrical signal corresponding to the amount of laser light received and said second detector (3) is adapted to convert said light into a second electrical signal corresponding to the amount of laser light received; and the first detector (3) and the second detector (3) are vertically spaced such that, at any point in time, at least one of said detectors is not receiving laser light normally reflected from a bar code; and by switching means (42) for receiving the first electrical signal and the second electrical signal, and for selectively outputting one of said signals to the identification means (43), said switching means (47) selecting one of said electrical signals outputted from one of said detectors receiving only laser light diffusely reflected from a bar code, and not selecting one of said electrical signals outputted from one of said detectors (3) receiving normally reflected laser light from a bar code (7). The bar code reader of claim 1, wherein the first detector is vertically disposed on one side of a line formed by the bisection of said triangle running from the bar code reader and the second detector is laterally disposed on the other side of said line. The bar code reader of claim 2, wherein said detectors (3) are equidistant from said line. The bar code reader of claim 1, further including switching means (42) for selectively inputting the first electrical signal, or the second electrical signal to said identification means. The bar code reader of claim 4, wherein said switching means (42) selects one of said electrical signals when the amplitude of said signal falls between a lower threshold and an upper threshold, and the switching means (42) does not select one of said electrical signals when the amplitude of said signal falls outside of said upper and lower thresholds. The bar code reader of claim 5, wherein the switching means (42) selects one of said electrical signals outputted from one of said detectors (3) receiving only laser light diffusely reflected from a bar code, and does not select one of said electrical signals outputted from one of said detectors receiving both diffusely reflected laser light and normally reflected laser light from a bar code (7). The bar code reader of claim 1, wherein the laser beam scanning means (21) further includes a rotating polygonal mirror. The bar code reader of claim 1, wherein the detecting means further includes a first lens (5) for guiding reflected laser light to the first detector (3), and a second lens (5) for guiding reflected laser light to the second detector (3). The bar code reader of claim 1, further including a hand held package (10) for containing the laser beam source means (1), laser beam scanning means (21) detecting means (3), switching means (42) and identification means (43). The bar code reader of claim 9, wherein the hand held package further includes trigger means for initiating a bar code reading operation. A method of reading bar codes comprising the steps of: generating a beam of laser light (F); causing the laser beam to scan across a bar code (7), the area scanned by said laser beam defined by a triangle; receiving laser light reflected from the bar code (7) using detecting means (3) comprising a first detector (3) for receiving laser light reflected from the bar code (7), and a second detector (3) for receiving laser light reflected from the bar code, and converting said light received from said detection in an electrical signal, characterized in that the first detector (3) and the second detector (3) being vertically spaced such that at any point in time, at least one of said detectors is not receiving laser light normally reflected from a bar code; and by converting said light received from said first detector (3) into a first electrical signal corresponding to the amount of laser light received thereby, and converting said light received from said second detector (3) into a second electrical signal corresponding to the amount of laser light received thereby; and inputting the first electrical signal and the second electrical signal to a switching means (42) for selecting one of said electrical signals outputted from one of said detectors (3) receiving only laser light diffusely reflected from a bar code (7), and not selecting one of said electrical signals outputted from one of said detectors (3) receiving normally reflected laser light from a bar code, outputting the selected signal to an identification means (43) for identifying the content of a bar code therefrom.

Inventors: NAKAZAWA ATSUSHI, NAKAZAWA, ATSUSHI, NAKAZAWA, ATSUSHI, C/O OSAKA WORKS
Applicants: SUMITOMO ELECTRIC INDUSTRIES, SUMITOMO ELECTRIC INDUSTRIES, LTD.
Application year: 1990
Main classification: G06K7
IPC codes: G06K7