Registers – Coded record sensors – Particular sensor structure
Reissue Patent
1997-08-29
2001-01-16
Phan, Trong (Department: 2818)
Registers
Coded record sensors
Particular sensor structure
C235S441000, C235S462010, C235S462490
Reissue Patent
active
RE037017
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a bar code reader which uses a laser beam.
DISCUSSION OF THE RELATED ART
The use of a laser beam generated by a solid-state diode or by a NeHe gas tube to read bar codes is known.
In order to read the bar code, the laser beam is first focused by means of an appropriate optical system and then deflected by means of a polygonal rotor fitted with mirrors, which is rotated rapidly so as to perform a periodic scanning of the region in which the bar code is located.
In applications of this type, the image of the laser source in the focusing point must remain within very precise limits which are in practice set by the thickness of the bars of the code. The reading of the code would in fact be erroneous if the wavefront of the beam had such a diameter as to cover more than two bars.
Moreover, if the source of the laser beam is a solid-state diode, the emitted light beam has a spherical divergent wavefront.
In order to keep the diameter of the light beam within the limits which allow to decode the bar code, the use of an optical system arranged in front of the laser source, which focuses the light beam at a preset distance from the concentration lens, is known. By way of example,
FIG. 1
schematically illustrates the method of operation of such a known focusing system.
In
FIG. 1
, the reference numeral
1
indicates the laser source and the numeral
2
indicates the lens which concentrates the light beam in a point P which has a distance d from the lens. Once the point P has been passed, the light beam diverges again, so that its diameter remains within the limits required for practical use only in a rather narrow region
2
s around the focusing point P.
Outside the region
2
s thus defined, the diameter of the laser beam is greater than the thickness of the bars of the code, and accordingly the light signal received by the reader does not allow a correct reconstruction of the alternation of the light and dark bars of the code.
The narrowness of the focusing region furthermore reduces the scanning area of the laser beam, and ultimately the read area is reduced, such read area being shown by
FIGS. 2 and 3
, which illustrate two read areas A
1
and A
2
which have an equal width at a different distance from the laser source, depending on the location of the focusing point of the laser beam.
In order to expand the read area, for example to read an area equal in width to the sum of the widths of A
1
and A
2
, solutions have already been proposed which entail movable focusing systems driven by an external sensor. These systems allow to vary the focusing point and thus adapt the optical system to the point in which the passage of the bar code occurs, so that the reading capability is thus increased in practice.
However, such systems are disadvantages for the following reasons: a) the need arises for an external sensor which detects the position of the bar code and activates the variation of the focusing point;
b) a slowness in reacting to the activation of the sensor occurs, since the focusing point is changed by means of a mechanical movement, the execution whereof requires a long time;
c) the possibility of error presents itself, due to an incorrect match between the placement of the bar code and the dimensions of the object on which it is applied; and,
d) low reliability becomes inherent.
SUMMARY OF THE INVENTION
The technical aim of the present invention is therefore to provide a bar code reader which can operate on a significantly larger read area and does not have the disadvantages described above in conventional readers.
This aim is achieved by a laser-beam bar code reader, according to the present invention, as defined in the appended claims.
REFERENCES:
patent: Re. 36251 (1999-07-01), Marchi
patent: 4315245 (1982-02-01), Nakahara et al.
patent: 4508422 (1985-04-01), Karlsson
patent: 4704519 (1987-11-01), Kulikaukas
patent: 5042619 (1991-08-01), Kohno
patent: 5552590 (1996-09-01), Obata et al.
patent: 3311352 (1984-03-01), None
patent: 360250 (1990-03-01), None
Mazzone Claudio
Stanzani Giuseppe
Datalogic S.p.A.
Phan Trong
Sughrue Mion Zinn Macpeak & Seas, PLLC
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