Classifications

• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
  • G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
  • G06K7/10—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation
  • G06K7/10544—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation by scanning of the records by radiation in the optical part of the electromagnetic spectrum
  • G06K7/10821—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation by scanning of the records by radiation in the optical part of the electromagnetic spectrum further details of bar or optical code scanning devices
  • G06K7/10831—Arrangement of optical elements, e.g. lenses, mirrors, prisms

Definitions

• the invention relates to an optoelectronic device for acquiring images, in particular of bar codes.
• the arrangement of the light-emitting diodes of these devices is such that the beams of the different diodes overlap only very partially.
• the brightness of the conventionally used diodes is very disparate, the brightness class of these diodes being able, in fact, to vary from 1 to 4. Owing to this disparity, during aging of the diodes, it is therefore observed local attenuations of the light intensity which are not distributed and correlated over the width of the reading field, which can lead to non-recognition of the bar codes resulting from the extraction of binary signals not emerging from the noise threshold of l processing electronics. Secondly, this arrangement of the diodes leads to a reduction in the performance of the device when any one of the said diodes burns out.
• the optoelectronic device described in patent application FR-2 673 738 overcomes one of the drawbacks of the aforementioned devices, namely the drawback relating to parallax errors.
• this device comprises light-emitting diodes disposed substantially in the optical plane, outside the optical reading field, and adapted to generate beams covering a strip of height between one and six millimeters on either side of the optical plane.
• the diodes of which are arranged in the optical plane makes it possible to avoid parallax errors, and therefore allows remote reading of bar codes.
• it has the other aforementioned drawbacks relating to the non-overlapping of the diode beams and to the lighting of areas outside the reading field.
• Other optoelectronic devices as described in international patent application WO-14471 and patent EP-524349 also make it possible to overcome the drawback relating to parallax errors.
• the lighting means are arranged downstream of the optical means and arranged so that the axis of the lighting beam is intersecting with respect to the optical axis,
• - reflection means suitable for letting the image beam pass and for reflecting the lighting beam are arranged so as to intercept said lighting beam, - said reflection means being inclined, relative to the axis optical, at an angle suitable for the lighting beam to be focused on said optical axis,
• the present invention aims to overcome all of the aforementioned drawbacks of current optoelectronic devices and has the main objective of providing an optoelectronic device combining the following advantages: large depth of field, uniform reduction of the light beam over the width of the useful field of reading, clear delimitation of the edges of the lit area, and low consumption of electrical energy.
• the invention relates to an optoelectronic device for acquiring images of objects, in particular of bar codes, comprising a housing provided with a reading window and containing an electronic scanning sensor, lighting means , and optical means allowing the formation of images on the sensor and comprising a lens, the sensor and the optical means defining an optical axis with respect to which the reading window is centered, said sensors, reading window and optical means delimiting a useful reading optical field.
• This optoelectronic device comprises the characteristics recalled above (by WO-14471 and EP-524349) and, in accordance with the invention, the following characteristics: - the lighting means comprise a lighting source suitable for illuminating the useful optical field over the entire depth of field. the angle ⁇ at which the light source, seen from the plan
• object of the light source is such that ⁇ ⁇ Arc tg -
• depth of field C is understood to define, in a conventional manner, the reading range delimited by the maximum and minimum working distances of the device, functions of the performance of the optical means and of the processing electronics),
• the apex of the angle underlying the reading optical field is on the entrance pupil of the objective
• the light source the main axis of which is co-axial with the optical axis, has an emission angle whose virtual image of the apex, seen from the object, substantially coincides with the entrance pupil of the objective.
• the reflection means comprise a reflecting surface provided with a slit centered on the optical axis, and arranged so as to intercept the light beam, said reflecting surface being inclined, with respect to the optical axis, by an angle adapted so that the reflected light beam is focused on said optical axis.
• the reflection means are provided with an opening taken by the optical path. It should however be noted that such lighting means produce a slightly vertically convergent beam.
• the reflection means decompose the lighting beam into two secondary lighting beams which are not coplanar with the optical plane.
• the slit is sufficiently narrow to introduce a very small parallax error such that the illuminated area corresponding to the depth of field is sufficient.
• the reflecting surface has vertically in its middle portion the shape of an S provided with a substantially vertical wing in which the slot is formed.
• this reflecting surface is preferably articulated on a fixed support by means of an axial hinge system, and adjustment means are arranged above said reflecting surface so as to come to bear on the latter and at allow to adjust its inclination and / or to rotate it.
• adjustment means also advantageously consist in two screws arranged perpendicular to each of the longitudinal ends of the reflecting surface.
• the reflecting surface has an upper stiffening rim.
• the lighting means comprise at least two diodes arranged near one (or some) of (or) other (s) so as to obtain a substantially total overlap of the beams of each diode over the entire depth of field.
• the point source is approached using at least two point sources, arranged so as to obtain a relatively uniform light beam, leading, as previously specified, to a uniform reduction in the illumination during aging of the diodes .
• the device according to the invention makes it possible to overcome the disparities in brightness of the diodes due to the substantially total overlap of the diode beams.
• the device can remain operational because the loss of intensity is reflected, not locally, but substantially uniformly over the entire lighting field.
• the lighting means comprise diodes having a diffusion angle greater than the optical angle, and associated optical means arranged so as to intercept the lighting beam of said diodes, and adapted for converging said lighting beam in the direction of reduction of the emission angles, so as to reduce them to a value combined with that of the optical angle.
• This preferred embodiment makes it possible to obtain an optoelectronic device combining the aforementioned advantages by means of light-emitting diodes of conventional type, therefore of a low cost price.
• Such an optoelectronic device is particularly suitable for allowing the reading of images at distances of the order of 5 to 50 centimeters, and has an increased sensitivity due to the presence of the optical means associated with the focusing diodes. the maximum light energy on the reading optical field.
• the optical means associated with the diodes comprise a convex focusing lens adapted to intercept the lighting beam of all the diodes.
• this focusing lens preferably comprises a convex diopter of toroidal shape.
• toroidal shape it is meant to define a diopter conventionally having a radius of curvature in a first plane parallel to the lighting beam, and a radius of curvature much less along a plane orthogonal to said foreground).
• This toroidal shape of the diopter allows, in addition to focusing the light beam along a plane orthogonal to the bar codes, as mentioned above, to focus this beam in a direction parallel to the bar codes, and therefore to obtain a brush d '' thin lighting focused on the optical axis.
• the focusing lens is a plano-convex lens, and comprises a planar diopter equipped with a recess adapted to accommodate the light-emitting diodes.
• the recess of the planar diopter of this lens is preferably filled with a resin having the same refractive index as said lens.
• This arrangement has the advantage of obtaining a general overall lighting angle, defined by the additional diopter, substantially equivalent to the lighting angles of the diodes.
• the light beams delivered by the diode chips do not undergo any deviation upstream of the convex diopter of the lens.
• FIG. 1 is a perspective view of a device optoelectronics according to the invention
• FIG. 2 is a longitudinal section thereof through an axial plane A
• FIG. 3 is a perspective view, in exploded mode, of the main elements enclosed in the housing of this optoelectronic device
• - Figures 4a and 4b are views respectively in perspective and cross section through a plane B of the reflecting surface of the objective according to the invention
• FIGS. 5 a and 5 b are diagrams representing in orthogonal planes the distances respectively between the object and the light source, and between the object and the diaphragm
• FIG. 6 is a graph showing the lighting profile obtained respectively with 4 diodes and 3 diodes arranged in accordance with the invention.
• the optoelectronic device shown in FIGS. 1 and 2 consists of a bar code reader in the form of a longitudinally bent box, composed of two shells 1, 2 able to be assembled by any means known per se, and a removable rear end piece 3 providing access to a housing 4 for a battery 5.
• this box further comprises a skylight 6 closed by a transparent window 7.
• This box also includes a longitudinal trigger 8 extending through an opening in the lower shell 2, and articulated towards the rear end of said shell.
• an electronic card 9 to which are connected, firstly, a linear CCD sensor 10 and conventional electronic components for processing and decoding allowing the control of said sensor and the processing of signals from this last.
• This electronic card 9 On this electronic card 9, is also connected a switch 11, arranged so as to be actuated by the trigger 8.
• the optical means of this reader are arranged inside a housing 12, closed by a cover 13 secured to said housing by means of screws 14.
• This housing 12 further comprises four latching tabs such as 15, 16 projecting from its front and rear front walls, arranged to snap into slots such as 17, 18 in the electronic card 9.
• the housing 12 further comprises, on the underside, and juxtaposed to its rear front wall, a housing 19 for the CCD sensor 10, separated from the interior of said housing by a flat wall 20 pierced with a transverse slot 20a.
• the optical means comprise, first of all, a so-called cylindrical lens 21, that is to say having a semi-cylindrical diopter, disposed transversely in a housing 22 of the housing 12 superimposed on the housing 19 of the CCD sensor 10
• This lens 21 has a focal length of 6 mm and is located at a distance from the CCD reader 10 of the order of 2.5 mm.
• Such a lens does not generate deflection of light rays in a plane parallel to the optical plane, and is convergent in a plane perpendicular to the optical plane.
• the optical means further comprise a mirror 23 inclined by 45 ° relative to the lens 21, secured below the wall of the cover 13, itself inclined by 45 °.
• optical means comprise a second lens 24, called acylindrical, having a section in the shape of a warhead.
• This lens 24 is inserted in grooves arranged opposite in the housing 12 and the cover 13. It has a focal length of 20 mm and is arranged at a distance of 29 mm from the CCD sensor 10.
• Such a lens does not cause deflection of light rays in a plane perpendicular to the optical plane, and is convergent in the optical plane.
• the optical means finally comprise a diaphragm 25 provided with a circular entrance pupil with a diameter of 4.5 mm, arranged at a distance of 5 mm from the lens 24, and inserted in grooves arranged opposite in the housing 12 and the cover 13.
• the reader lighting means are, for their part, directly downstream of the housing 12. They firstly comprise four contiguous light-emitting diodes, such as 26, having a diffusion angle of between 120 ° and 130 °. These four diodes 26 are connected to the electronic card 9 and aligned along an axis orthogonal to the optical axis.
• These lighting means further comprise a convex lens 27 for focusing the lighting beam in planes respectively parallel and perpendicular to the optical axis.
• This lens 27 comprises, firstly, a plane diopter provided with a recess 28 of a shape adapted to accommodate the diodes 26.
• this recess 28 is filled with a resin having the same refractive index as the lens 27.
• This lens 27 further comprises two pins, such as 29, projecting from its plane diopter allowing it to be plugged into the electronic card.
• This lens 27 finally comprises a convex diopter of toroidal shape having two respective radii of curvature of 20 mm and 3.25 mm.
• the lighting means comprise, finally, reflection means arranged so as to intercept the lighting beams of the diodes 26, and inclined at an angle of 45 °, adapted so that said lighting beams are focused on the optical axis.
• reflection means consist of a mirror 30 having an upper stiffening edge 30a, and provided with a transverse slot.
• This mirror 30 is, moreover, connected to a support plate 32 by a tongue 33 acting as an axis of articulation between said mirror and support plate.
• This support plate is adapted to be housed in spaces formed between the front wall of the housing 12 and the latching tabs 16, so that the slit 31 of the mirror 30 is centered on the optical axis, position in which said slit is as close as possible to the diaphragm.
• two screws such as 34, each arranged in a tapped bore formed in an arm such as 35 extending projecting from the front wall of the housing 12, are adapted to bear on the mirror 30, so as to allow to adjust the inclination of the latter and / or to rotate it relative to the support plate 32, in order to superimpose the lighting beam with the optical plane.
• the presence of the stiffening edge 30a makes it possible to prevent the mirror 30 from veiling.
• the mirror 30, the diodes 26 and the diaphragm 25 are arranged so that the virtual image of the light source, seen from the object, coincides with the entrance pupil of the diaphragm 25.
• Such lighting means have several advantages: - firstly, the arrangement of the diodes 26 joined together makes it possible to obtain a lighting profile which, as shown in FIG. 5, decreases uniformly if one of the diodes burns out, or if the brightness of the light source decreases over time,
• the optical zone is perfectly delimited, - finally, the depth of the reader field is increased, due to the virtual absence of parallax error.

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• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Engineering & Computer Science (AREA)
• Health & Medical Sciences (AREA)
• General Health & Medical Sciences (AREA)
• Toxicology (AREA)
• Artificial Intelligence (AREA)
• Computer Vision & Pattern Recognition (AREA)
• General Physics & Mathematics (AREA)
• Theoretical Computer Science (AREA)
• Facsimile Scanning Arrangements (AREA)
• Image Input (AREA)

Applications Claiming Priority (3)

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• 1998
  • 1998-04-21 US US09/403,455 patent/US6435411B1/en not_active Expired - Lifetime
  • 1998-04-21 WO PCT/FR1998/000802 patent/WO1998048370A1/fr not_active Application Discontinuation
  • 1998-04-21 EP EP98921577A patent/EP0978084A1/de not_active Withdrawn

Non-Patent Citations (1)

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