Incremental printing of symbolic information – Electric marking apparatus or processes – Electrostatic
Reexamination Certificate
1998-07-24
2001-04-24
Le, N. (Department: 2861)
Incremental printing of symbolic information
Electric marking apparatus or processes
Electrostatic
C347S138000, C347S257000
Reexamination Certificate
active
06222565
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a scanning device for scanning an image carrier, comprising a linear array of scanning elements, a holder for the array, which extends in the longitudinal direction of the array, and positioning means to maintain the scanning elements at a predetermined position from the image carrier. A scanning device of this kind is known from European Patent 0 401 316, which describes a scanning device for forming an image on a photoconductive image carrier by means of a linear array of co-operating LEDs and lenses. In this device the lens array focuses the light emitted by the array of LEDs into the plane in which the image carrier moves. In order to keep the linear array in the required position with respect to the imaging plane occupied by the image carrier, the arrays of LEDs and lenses in this known scanning device are fixed on a holder made from relatively thick metal and provided with stiffening ribs in order to keep the linear array in a predetermined focusing position throughout with respect to the image carrier.
Since in order to form an uninterrupted image the linear array holder can bear against the image carrier only outside its operative zone, the array is sensitive to sagging or deflection, and particularly in the case of a long linear array in large-format scanning devices in which the linear array is disposed beneath or above the imaging plane. This manifests itself in the form of locally non-sharp imaging.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a scanning device of the type referred to in the preamble, wherein a linear imaging array can be maintained in a predetermined position with respect to the image carrier without the array having to be made in an extremely stiff construction.
To this end, according to the present invention, positioning means are formed by projections on the holder for the array, which projections extend substantially perpendicular to the array and parallel to one another, and an adjustment means which acts on the projections is provided to adjust the distance between the projections. As a result, the imaging array can, with simple means, be so adjusted that optimum focusing can be set at every part of the linear array, thus compensating for any array sag.
In one advantageous embodiment of the scanning device according to the present invention, the adjustment means comprises a pressure element which exerts on two spaced-apart projections, forces directed away from one another and operative in the longitudinal direction of the array. As a result, a linear array with the projections directed upwardly, which array sags in the middle due to its weight, is pressed straight.
Preferably, the pressure element comprises a first compression spring which presses against one side of a projection which is directed towards the other projection in order to press the two projections apart. As a result, a construction is obtained in which the spring force of the compression spring determines the force with which the linear array is pressed straight.
Further, preferably, the first compression spring is provided with first tensioning means which give the first compression spring an adjustable prestressing. As a result a very sensitive control is obtained for straightening the linear array, for example to compensate for other initial deviations in the straightness of the linear array.
In another embodiment of the scanning device according to the present invention, the adjustment means comprises a tension element which exerts on two spaced-apart projections, forces which are directed towards one another and which act in the longitudinal direction of the array. As a result, the sagging of a linear array disposed beneath the image carrier can be readily compensated. Another effect is that in the case of a linear array disposed above the image carrier and initially having an upwardly deflected form, straightening can be obtained in a simple manner.
REFERENCES:
patent: 5036339 (1991-07-01), Hediger
patent: 5543829 (1996-08-01), Fisli
patent: 5808718 (1998-09-01), Aikoh et al.
patent: 5841463 (1998-11-01), Debesis et al.
patent: 0401316B1 (1990-12-01), None
patent: 05075784A (1993-03-01), None
patent: WO9003015A (1990-03-01), None
patent: WO9302402A (1993-02-01), None
Patent Abstracts of Japan, vol. 096, No. 010, Oct. 31, 1996 & JP 08 164631 A (Ricoh Co Ltd.) Jun. 25, 1996.
Patent Abstracts of Japan, vol. 012, No. 080 (E-590), Mar. 12, 1988 & JP 62 219752 A (Panafacom Ltd.) Sep. 28, 1987.
Le N.
Nguyen Lamson D.
Oce--Technologies B.V.
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