Registers – Coded record sensors – Particular sensor structure
Reexamination Certificate
2001-02-20
2004-03-30
Le, Thien M. (Department: 2876)
Registers
Coded record sensors
Particular sensor structure
C235S462160, C235S462410
Reexamination Certificate
active
06712271
ABSTRACT:
BACKGROUND
I. Field of the Invention
The present invention relates to a device and a method for reading coded information. The invention also relates to a device for detecting a luminous signal diffused by a support containing coded information.
II. Related Art and Other Considerations
As known, coded information readers (for example, optical readers) capable of locating and decoding the information contained on a support (for example, an optical code associated to an object) which is into a predetermined reading area have been launched on the market in recent years.
In this description and following claims, the expression “coded information reader” refers to any device capable of acquiring information relating to an object (for example distance, volume, size, or its identification data) through the acquisition and processing of a luminous signal diffused by the same object. The expression “coded information” refers to all identification data contained in an optical code. The expression “optical code” refers to any graphic representation having the function of storing a coded information. A particular example of optical code comprises linear or two-dimensional codes wherein the information is coded through suitable combinations of elements having predetermined shape, such as for example squares, rectangles or hexagons, dark-colored (usually black), separate by light elements (spaces, usually white) such as bar codes, stacked codes, and two-dimensional codes in general, color codes, etc. Moreover, the expression “optical code” comprises, more in general, also other graphic patterns having function of coding the information, including light printed characters (leffers, numbers, etc.) and particular patterns (such as for example stamps, logos, signatures, digital fingerprints, etc.). The expression “optical code” also comprises graphic representations detectable not only in the field of visible light but also in the wavelength range comprised between infrared and ultraviolet.
Only by way of example, and for the purpose of making the following description clearer, explicit reference shall be made to a linear optical code reader (linear reader). Of course, a man skilled in the art shall understand that what said is also applicable to different readers, such as for example two-dimensional optical code readers (matrix or area readers).
Typically, optical code readers comprise an illumination system intended to emit a luminous signal towards the support containing the coded information to be read (optical code) and a reception system intended to pick-up the luminous signal diffused by the illuminated optical code. In particular, said luminous signal is picked up on suitable photo-receiving means (or means for detecting the luminous signal diffused by the illuminated optical code and picked-up through the optical reception system), which in turn generates an electrical signal proportional to the picked-up luminous signal; the electrical signal is intended to be afterwards elaborated and/or processed and decoded, so as to extract the information content.
In a typical embodiment of a conventional linear optical reader, the illumination system comprises an array of LEDs (or more arrays, in matrix or area readers), optionally followed by one or more diaphragms and one or more focalization lenses. Each one of the LEDs of the above mentioned array generates a light beam having a variable luminosity, with a maximum value at the LED optical emission axis, and with decreasing values as the emission angle increases. LEDs are typically aligned so as to be equidistant and parallel to one another and to the reader optical axis. In this way, the light beam exiting from the reader has a luminosity which is variable along the LED alignment direction, with a pattern that is function of the contribution of each LED, of the position of the LED with respect to the reader optical axis, and of the distance of the reader from the illuminated optical code. In fact, it has been noted that, for relatively small distances between reader and code, the profile of the luminous emission beam is not very even along the LED alignment direction and it is possible to distinguish in the profile, at local peaks, the contribution of each LED. As the distance between reader and code increases, besides the decrease of the luminous intensity of the light emission beam, said profile becomes more and more even, and the contribution of each LED becomes less and less clear; said pattern is an intrinsic operation feature of the optical illumination system described above.
The reception system typically comprises one or more lenses and/or diaphragms intended to pick-up, on the photo-receiving means, the light beam diffused by the illuminated code. The system exhibits the feature of transmitting light in a quantitatively different manner depending on whether the light passes through it in the axis, or at the margins of the field of view. In particular, the power per area unit of the luminous beam diffused by the illuminated code and picked-up by the above lenses and/or diaphragms on the photo-receiving means progressively decreases from the center towards the edges of the same beam. This pattern is an intrinsic operation feature of the optical reception system described above.
The photo-receiving means typically comprises an array of photosensitive elements arranged on one (CCD or C-MOS linear sensors) or more parallel lines (CCD or C-MOS matrix sensors). Each photosensitive element is adapted to detect the light portion diffused by a corresponding portion of the illuminated optical code.
From the above, it can be deduced that the illumination and reception systems described above exhibit the similar feature of attenuating the power per area unit of the luminous beam (respectively, of emission and reception) at the margins of their field of view, thus producing a cumulative effect which accentuates the luminous unevenness between the central portion and the margins of the light beam picked-up on the photo-receiving or sensor means. As a consequence, the photosensitive elements at the ends of the sensor (hit by the light coming from the areas at the edges of the optical code) receive less light than those arranged centrally. Since the electrical signal generated by the sensor is proportional to the quantity of light received by the various photosensitive elements, it shall thus have a different pattern in amplitude depending on the distance from the sensor optical axis. This may cause significant problems for the correct operation of the optical reader and, consequently, for the reliability of the reading performed by it. In fact, it would be desirable to obtain, in output from the sensor, an electrical signal with substantially constant amplitude, so as to ensure high precision and reliability standards in the subsequent optical code digitalization and decoding operations.
For the purpose of reducing the undesired effect of attenuation of the power per area unit of the luminous beam hitting on the photosensitive elements of the sensor depending on the distance from the optical axis of the same, various structural solutions have been identified, which have already been used in conventional optical readers. For example, one of said solutions consists in using an illumination system wherein the various emission LEDs are arranged at a non-constant reciprocal distance, and/or with a reciprocal angle. Another solution consists in using a system for controlling the emission LEDs, intended to control the various LEDs in a differentiated way, so as to evenly illuminate the code at the edges as well as at the centre, or illuminate it more at the edges with respect to the centre, so as to compensate the loss of light at the edges caused by the optical reception system.
Thus, in the various structural solutions described above, the drawback mentioned above is at least partly overcome by structurally intervening on (or upstream of) the reader optical illumination system. However, although advantageous for obtaining the expected purposes, such s
Datalogic S.P.A.
Le Thien M.
Nixon & Vanderhye P.C.
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