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.
• Current optoelectronic devices intended for reading bar codes conventionally comprise a housing containing an electronic scanning sensor, optical means comprising a diaphragm, making it possible to form images on the sensor and defining therewith an optical plane, and light emitting diodes intended to illuminate bar codes and allow the acquisition of images on the sensor.
• These devices finally include processing electronics allowing the control of the sensor and the processing of the signals coming from the latter.
• the diaphragm has a circular opening of small diameter so as to avoid defocusing of the image and / or to increase the depth of field of the device.
• the small diameter of this opening due to the small diameter of this opening, the light intensity reflected by the bar code reaching the sensor is reduced, and in practice, this fact requires the use of light sources having a large light intensity of so as to compensate for the reduction in light intensity.
• Such a solution which can also be associated with that described in patent EP-61000, has optical means having characteristics leading to increasing, along axes parallel to the bar codes, the dimension of the illuminated surface of said bar codes, the image is reflected on the sensor, and thereby increase the sensitivity of the optoelectronic device. It should be noted, moreover, that this increase in the sensitivity of the device resulting from the sole design of the optical means and not the dimensions of the opening of the diaphragm, such a device can be equipped with a conventional diaphragm with circular opening of small dimensions, and therefore optical means of conventional dimensions, low cost and easy to produce.
• the present invention aims to overcome this drawback and the main objective of obtaining a magnification ml in planes (XOZ) parallel to the optical plane greater than the magnification m2 of a plane perpendicular (YOZ) to said optical plane, and this by using optical means of current and easy construction.
• the invention relates to an optoelectronic device for acquiring images, in particular of bar codes, comprising a housing provided with a reading window and containing an electronic scanning sensor, lighting means, and optical means comprising a diaphragm and adapted to ensure the formation of images on the sensor and to obtain, in a plane (XOZ) parallel to the optical plane, a magnification ml greater than the magnification m2 in a plane (YOZ) perpendicular to the optical plane, the sensor and the optical means defining an optical plane with respect to which is centered the reading window, and said sensor, reading window and optical means delimiting a useful optical reading field.
• the optical means comprise: first optical means comprising a first converging lens consisting of a symmetrical lens of revolution around the optical axis, the useful part of which is curved,
• Second optical means comprising a so-called cylindrical lens having a semi-cylindrical diopter, adapted to generate no deviation in the plane (XOZ) parallel to the optical plane and to converge in the plane (YOZ) perpendicular to said optical plane.
• the enlargement ml / m2 is obtained by means of lenses of conventional design, namely
• optical means consisting of a symmetrical lens of revolution and a cylindrical lens leads to perfect results when the optoelectronic device is perfectly aligned with the bar code (product passing in front a fixed optoelectronic device, etc.), the astigmatism introduced by such optical means increases the sensitivity to rotation errors around the optical axis.
• the optical means further comprise a corrective lens associated with the first optical means. It should be noted that the construction of this corrective lens is easy because it is neutral in the XOZ plane where the bar code is used.
• the solution consists, in effect preferentially, in using a symmetrical lens of revolution, mono or multi-element associated with a cylindrical lens of profile of meniscus type of opposite magnification intended to cancel the optical power in the plane (YOZ). This preserves the optical quality commonly achieved for symmetrical optics of revolution necessary in the planes (XOZ). It should also be noted that the whole main lens / corrective lens must be optimized overall, the cylindrical lens introducing an astigmatism on the edges of the fields.
• the corrective lens advantageously consisting of a simple planar / concave cylindrical lens constitutes a correction element which leads to the solution of rotation problems while maintaining the advantage of leading to an increase in the sensitivity of the device.
• the optical means are adapted so that the ml / m2 ratio is such that 3 ⁇ ml ⁇ 5. m2
• This range of ratios constitutes, in fact, a good compromise concerning the performances of the optoelectronic device, which leads to obtaining a significant increase in the sensitivity of the latter compared to current conventional devices, without however penalizing the operation of said device if it is presented in front of the object rotating around the optical plane (XOZ).
• the ratio of the ml / m2 magnifications of the first and second optical means is such that ml / m2 is greater than 1,
• the first optical means are arranged near the diaphragm between said diaphragm and the second optical means.
• the lens of revolution is advantageously of the aspherical type and has the shape of a warhead, so as to avoid geometric aberrations.
• the linear sensor and the diaphragm are arranged so as to be focused on orthogonal axes, a mirror inclined at an angle of 45 ° relative to said axes being positioned so as to reflect the images on said sensor.
• This arrangement has the advantage of leading to a reduction in the size of the optical means and therefore to an optimization of the size of the housing.
• FIG. 1 is a perspective view of an optoelectronic device 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 contained in the casing of this optoelectronic device,
• FIG. 4 is a perspective view of a lens constituting the first optical means of this device
• FIG. 5 is a longitudinal section through a plane C of this lens
• FIGS. 6a and 6b are block diagrams representing the trajectory of the image beams according to the two orthogonal planes (YOZ) and (XOZ)
• 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.
• the housing At its front end face, the housing further comprises a skylight 6 closed by a transparent window 7.
• This housing 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.
• a switch 11 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 box 12 closed by a cover 13 secured to said box at screw means 14.
• This housing 12 further comprises four latching tabs such as 15, 16 projecting from its front and rear front walls, arranged so as to snap into notches such as 17, 18 provided 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, in turn, firstly, a lens 21, called cylindrical, that is to say having a semi-cylindrical diopter, arranged 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 cause deflection of light rays in a plane parallel to the optical plane, and is convergent in a plane perpendicular to the optical plane.
• the otic means further comprise a mirror 23 inclined by 45 ° relative to the lens 21, secured on the underside of a wall of the cover 13, itself inclined by 45 °.
• the optical means also comprise a symmetrical lens of revolution 40, the useful part 40a of which can be semi-cylindrical or domed, inserted in grooves arranged opposite in the housing 12 and the cover 13.
• optical means further comprise a correction lens 50 consisting of a surface having a radius of curvature of 7.5 mm.
• optical means comprise, finally, a diaphragm 25 provided with a circular entrance pupil with a diameter of 4.5 mm disposed at a distance of 58 mm from the lens 24, and inserted in grooves made opposite in the housing 12 and the cover 13.
• a diaphragm 25 provided with a circular entrance pupil with a diameter of 4.5 mm disposed at a distance of 58 mm from the lens 24, and inserted in grooves made opposite in the housing 12 and the cover 13.
• FIGS. 6a, 6b and 7 such optical means make it possible to "enlarge”, along the axis Y perpendicular to the optical plane, the dimension of the illuminated surface of the bar codes including the image is reflected on the sensor, and therefore, increase the sensitivity of the player.
• the lighting means of the reader are in turn disposed directly downstream of the housing 12. They firstly comprise four contiguous light-emitting diodes, such as 26, having a diffusion angle of 125 °. 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, first of all, 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 also comprises two pins such as 29, projecting from its plane diopter, enabling it to be plugged into the electronic card 9.
• This lens 27 finally comprises a convex diopter of toroidal shape having respective radii of curvature of 20 mm and 3.25 mm.
• the lighting means finally comprise 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 provided with a transverse slot 31 allowing the image beam to pass and having, at the top, a stiffening edge 30a.
• the 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 32 is adapted to be housed in spaces formed between the front wall of the housing 12 and the latching tabs 16, so that the slot 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 disposed in a threaded bore formed in an arm such as 35 extending projecting from the front wall of the housing 12, are adapted to come 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.

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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)
• Lenses (AREA)

Applications Claiming Priority (3)

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• 1998
  • 1998-04-21 US US09/403,483 patent/US6375076B1/en not_active Expired - Lifetime
  • 1998-04-21 WO PCT/FR1998/000803 patent/WO1998047377A1/fr not_active Application Discontinuation
  • 1998-04-21 EP EP98921578A patent/EP0978085A1/de not_active Withdrawn

Non-Patent Citations (1)

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