FR2673738A1 - Opto-electronic device for capturing linear images, especially bar-codes - Google Patents

Abstract

The invention relates to an opto-electronic device for capturing linear images, comprising a housing furnished with a reading window (16) and enclosing a linear sensor (6) with electronic scanning, lighting means (4, 5), and means (7) for forming images on the linear sensor (6). According to the invention, the lighting means (4, 5) are arranged substantially in the optical plane, outside the useful optical field, and are adapted for producing beams which cover, beyond the reading window (16) and over a distance representing the reading range, a strip of height, on either side of the optical plane, of substantially between one millimetre and six millimetres.

Description

OPTOELECTRONIC IMAGE ACQUISITION DEVICE
LINEAR, IN PARTICULAR FROM BAR CODES.

 The invention relates to an optoelectronic device for acquiring images, in particular of bar codes.

 Current optoelectronic devices intended for reading bar codes conventionally comprise a bent box enclosing a linear sensor with electronic scanning, optical means making it possible to form the images on the sensor and defining with it an optical plane, and light-emitting diodes intended to illuminate bar codes and to allow the acquisition of images on the sensor, and arranged in a plane offset from the optical plane. These devices finally include electronic processing and decoding allowing the control of the linear sensor and the processing of the signals coming from the latter.

Such optoelectronic devices, described in particular in US patents 4,408,120 and EP 101,939 have two main drawbacks which lead to limitations as to their possibility of use. Indeed, and in the first place, these devices are well suited for reading on contact but do not allow reading from a distance. In addition, they do not allow easy targeting of bar codes. This second drawback is however solved thanks to the device described in the patent.
EP 238.067 which is equipped on the one hand with aiming diodes located on each side of the linear sensor, and on the other hand, lighting diodes offset with respect to the optical plane.

On the other hand, like the previous ones, this device is well suited for reading on contact but not for reading from a distance.

 The present invention aims to overcome this drawback and has the main objective of providing an optoelectronic device making it possible to obtain good reading from a distance with a large depth of field.

 Another objective of the invention is to provide an optoelectronic device allowing easy targeting of the images to be acquired.

 Another objective is to provide an optoelectronic device facilitating manual aiming on the fly of the images.

 To this end, the invention relates to an optoelectronic device for acquiring linear images, in particular bar code, comprising a box provided with a reading window and containing a linear sensor with electronic scanning, lighting means, and means for forming images on the linear sensor, the sensor and the means for forming images defining an optical plane in which the reading window is centered, and said sensor, window and focusing means delimiting a useful optical field of reading.

According to the invention, this optoelectronic device is characterized in that the lighting means
are arranged substantially in the optical plane, outside the useful optical field, so that the light beams intersect said useful optical field between the image-forming means and the reading window,
are adapted to generate beams covering, beyond the reading window and over a distance representing the reading range and depending on the characteristics of the imaging means, a height band, on either side of the plane optical, substantially between one millimeter and six millimeters.

 This device comprising lighting means arranged in the optical plane and adapted to generate a narrow lighting beam beyond the reading window, makes it possible to illuminate and therefore to read images over a distance which is limited, not not by the lighting means, but by the constraints of the imaging optics.

 Therefore it allows to obtain a good reading from a distance with a significant depth of field.

In practice, such an optoelectronic device thus allows the reading of images at a distance of up to 30 centimeters, while the reading limit of current devices corresponds to a distance of the order of 2 to 3 centimeters.

 In addition, the lighting means being arranged in the optical plane, they are therefore located in the line of sight, which facilitates the aiming of the images.

 According to another characteristic of the invention, the lighting means are adapted to generate lighting beams covering at right of the reading window a height band, on either side of the optical plane, substantially between a and six millimeters.

 Almost all of the energy supplied by the lighting means thus passes through the reading window, and this results in a notable reduction, on the one hand, of the energy loss which would have resulted from the stopping of the beams through the housing and, on the other hand, stray reflections inside this housing.

 Consequently, such a device can operate with lighting means of power and therefore of consumption lower than those of the lighting means of known devices. Thus, it requires a lower energy source, which is particularly advantageous when this energy source is autonomous and consists of cells, batteries, etc. It should also be noted that the energy required remains less than that known devices, and whether the reading is carried out by contact or remotely.

 In addition, and preferably, the reading window has a height substantially less than the height band covered by the lighting beam at the right of said window. As a result, the lower and upper limits of the lighting beam which, conventionally, are not perfectly homogeneous are eliminated.

 Furthermore, according to a first preferred embodiment, the lighting means consist, on either side of the optical field, of at least one lighting source delivering a lighting beam whose angle at the apex , according to a plane orthogonal to the optical plane, is substantially between 4 and 18 degrees.

 In addition, the lighting means are then preferably constituted on either side of the optical field, of light sources arranged so that, on the reading range and along an axis of the optical plane parallel to the reading window , the lighting intensity is increasing from the center of the useful optical field towards its lateral ends. Such an arrangement makes it possible to compensate for the vignetting effect of the image-forming optics.

 According to a second preferred embodiment, the lighting means consist, on either side of the optical field, of at least one lighting source and, for each of these lighting sources, of a system optics adapted to focus the lighting beam on a strip of height substantially between one and six millimeters on either side of the optical plane.

 In addition, each optical system then preferably comprises a collimating lens adapted to converge the light beam towards a convergence zone located beyond the reading range.

 These lenses make it possible to obtain an increasing concentration of energy as one moves away from the reading window, and thus to compensate for the dispersion of energy proportional to this distance.

 In addition, in order to compensate for the vignetting effect of the optics, each optical system advantageously comprises a homogenization lens adapted so that, over the reading range and along an axis of the optical plane parallel to the reading window, the he lighting intensity is increasing from the center of the useful optical field towards its lateral ends.

 Furthermore, preferably, the collimation lens has an astygmatic and / or prismatic shape so as to also play the role of homogenization lens.

 According to another characteristic of the invention, the lighting means are arranged in the optical plane on either side of the focusing means, substantially at the same distance from the reading window as said focusing means. This arrangement makes it possible to obtain an illumination which best covers and does not exceed the useful optical field of reading.

 Furthermore, the lighting means can conventionally consist of lighting sources emitting in the visible spectrum.

According to another embodiment, they can also be constituted
- light sources emitting in the visible spectrum and arranged so as to allow targeting of the images,
- And light sources emitting in the non-visible spectrum and arranged so as to allow the acquisition of images.

The choice of the type of lighting means to be used must be adapted to the type of support on which the information to be read is located. Indeed, there is for each support a lighting spectrum allowing to obtain an optimal contrast. This spectrum is not necessarily in the visible, so we can opt according to the support
- either for a visible spectrum source ensuring the aiming and lighting allowing the acquisition of images,
- either for a visible spectrum source ensuring the sighting and a non-visible spectrum source, such as infrared LEDs, providing the lighting allowing the acquisition of images.

Other characteristics, objects and advantages of the invention will emerge from the detailed description which follows with reference to the appended drawings which show by way of non-limiting example a preferred embodiment. On these drawings which form an integral part of the present description
FIG. 1 is a perspective view, in exploded mode, of an optoelectronic device according to the invention,
FIG. 2 is a block diagram, seen in plan, of a device according to the invention,
- Figure 3 is a block diagram, seen in elevation.

FIG. 4 is a schematic perspective view representing the light beams emitted by a device according to the invention,
The optoelectronic device represented in FIG. 1 constitutes a bar code reader whose particularity is to allow a good reading to be obtained from a distance with a significant depth of field.

 This barcode reader is in the form of an elongated rectilinear box, composed of two half-shells 1, 2, able to be assembled by means of screws (not shown). These two half-shells 1, 2 are further shaped so that the housing has an open end face.

Inside this box is housed a chassis 3 on which are mounted lighting means 4, 5, a linear sensor 6 with electronic scanning, of the type
CCD, and an optical system 7 for forming images on said CCD sensor, comprising an elongated diaphragm, in the rectangular example.

 This chassis 3 comprises a rear section 8, extending away from the open end face of the housing, and having a cross section in the shape of an inverted U, each wing 8a of which is extended by an orthogonal return 9, arranged to rest on the internal face of the half-shell 2 vis-à-vis.

 This chassis 3 is provided, first of all, with means 10 for holding the CCD sensor 6 adapted to secure the latter against the end of the rear section 8. I1 also comprises means for holding the optics 7 arranged so that the latter is located at a distance from the CCD sensor 6 so as to delimit a dark room with the latter.

 The lighting means 4, 5 are in turn arranged on the returns 9, that is to say on the outside of the rear section 8 of the chassis 3, so as not to directly illuminate the C.C.D 6 sensor.

These lighting means consist, arranged on each of the returns 9, of a light-emitting diode 4 or
Led, and an astygmatic lens 5.

Furthermore, the housing also contains, and in a conventional manner, an electronic card 11 arranged to be clipped onto the chassis 3, and connected to the sensor
CCD 6 and Leds 4 by an electrical cable and circuit 12. This card 11 is also connected to a cord 13 for connection to a data reception terminal.

 The housing contains, finally, a transverse plate 14 arranged to be clipped onto the front end of the chassis 3 which for this purpose comprises two latching lugs 15, in a position where said plate is substantially set back from the face d open end of this housing. This transverse plate 14 has a longitudinal window 16, called a reading window.

 Finally, the reader has a spout 17 adapted to cover the open end face of the housing and provided with a light 18 arranged opposite and conjugate with the reading window 16 of this housing.

 The various elements making up the bar code reader according to the invention having been described above, their own characteristics and their arrangement relative to one another are explained below with reference to FIGS. 2 to 4. It should however be noted that in FIG. 4, each lens 5 is shown broken down into two lenses 5a, 5b in order to illustrate the two functions of the lighting optics.

 First, the Leds 4, the astygmatic lenses 5, the C.C.D sensor 6, the optics 7 and the reading window 16 are arranged so as to extend rigorously in the same plane constituting the optical plane (O).

 The C.C.D sensor 6, the optics 7 and the reading window 16 further delimit, in this optical plane (0), a useful optical reading field defining the field of vision of the bar code reader.

 The optic 7 is also arranged so that the major axis of its diaphragm extends orthogonally relative to the optical plane (0).

 The two light-emitting diodes 4 are, for their part, arranged on either side of the optics 7 substantially at the same distance from the reading window 16 as the latter. These two diodes 4 and the associated lenses 5 are, moreover, arranged so as to be situated outside the useful optical field for reading.

Furthermore, the lenses 5, by their astygmatic shape, fulfill two functions represented in a dissociated manner in FIG. 4 and consisting
for the lens 5a, to make the beams coming from the diodes 4 diverge according to the optical plane (0) so that the latter cover the total length of the reading window 16,
for the lens 5b, to be made to converge in a plane orthogonal to the optical plane (0), the beams, so that the latter, on the one hand, cover at the right of the reading window 16 a strip of height substantially greater than the width of this window and, on the other hand, converge towards a convergence zone situated beyond the reading range.

 The barcode reader described above has the essential advantage of enabling both contact reading and remote reading.

 Furthermore, the rectilinear shape of the box facilitates manual aiming on the fly of bar codes, because during this aiming the box extends in the natural extension of the user's arm.

Claims (14)

 1 / - Op toelectronic device for acquiring linear images, in particular of bar codes, comprising a housing (1, 2) provided with a reading window (16) and containing a linear sensor (6) with electronic scanning , lighting means (4, 5), and means (7) for forming images on the linear sensor (6), the sensor (6) and the means (7) for forming images defining an optical plane (O) in which the reading window (16) is centered, and said sensor, window and image-forming means delimiting a useful optical reading field, said optoelectronic device being characterized in that the lighting means (4 , 5) ::  are arranged substantially in the optical plane (Q), outside the useful optical field, so that the light beams intersect said useful optical field between the image-forming means (7) and the reading window ( 16),  are adapted to generate beams covering, beyond the reading window (16) and over a distance representing the reading range and depending on the characteristics of the image forming means (7), a height band, on the other hand and on the other side of the optical plane (O), substantially between one millimeter and six millimeters.  2 / - Optoelectronic device according to claim 1, characterized in that the lighting means (4, 5) are adapted to generate lighting beams covering the right of the reading window (16) a strip of height, of on either side of the optical plane (O), substantially between one and six millimeters.  3 / -An optoelectronic device according to claim 2, characterized in that the reading window (16) has a height substantially less than the height band covered by the lighting beam at the right of said window.  4 / - Optoelectronic device according to one of claims 2 or 3, characterized in that the lighting means consist, on either side of the optical field, of at least one lighting source delivering a beam of lighting whose apex angle, in a plane orthogonal to the optical plane (O), is substantially between 4 and 18 degrees.  5 / - Optoelectronic device according to claim 4, characterized in that the lighting means consist, on either side of the optical plane (O), of light sources arranged so that, on the reading range and along an axis of the optical plane parallel to the reading window (16), the lighting intensity is increasing from the center of the useful optical field towards its lateral ends.  6 / - Optoelectronic device according to one of claims 2 or 3, characterized in that the lighting means consist, on either side of the optical field (O), of at least one lighting source ( 4) and, for each of these lighting sources, an optical system (5) adapted to focus the lighting beam on a strip of height substantially between one and six millimeters on either side of the optical plane .  7 / - Optoelectronic device according to claim 6, characterized in that each optical system (5) comprises a collimating lens (5a) adapted to converge the light beam towards a convergence zone located beyond the range of reading.  8 / - Optoelectronic device according to one of claims 6 or 7, characterized in that each optical system (5) comprises a homogenization lens (5b) adapted so that, on the reading range and along an axis of the optical plane parallel to the reading window (16), the lighting intensity is increasing from the center of the useful optical field towards its lateral ends.  9 / - Optoelectronic device according to claims 7 and 8 taken together, characterized in that the collimating lens (5a) has an astygmatic and / or prismatic shape so as to also play the role of homogenizing lens (5b).  10 / - Optoelectronic device according to one of the preceding claims, characterized in that the lighting means (4, 5) are arranged in the optical plane on either side of the image forming means (7) substantially at the same distance from the reading window (16) as said image forming means.  11 / -An optoelectronic device according to one of the preceding claims, characterized in that the image forming means (7) comprise an elongated diaphragm having a major axis orthogonal to the optical plane (O).  12 / -An optoelectronic device according to one of the preceding claims, characterized in that the boot (1, 2) is provided with an open front face, partially closed by means of a spout (17).  13 / -An optoelectronic device according to one of the preceding claims in which the lighting means (4, 5) consist of lighting sources (4) emitting in the visible spectrum.  14 / -An optoelectronic device according to one of claims 1 to 12, characterized in that the lighting means (4, 5) comprise  - light sources emitting in the visible spectrum and arranged so as to allow targeting of the images,  - lighting sources emitting in the non-visible spectrum and arranged so as to allow the acquisition of images.