Alignment of laser imaging assembly

Details Alignment of laser imaging assembly Alignment of laser imaging assembly

1999-06-16

2001-04-24

Nguyen, Thinh (Department: 2861)

Incremental printing of symbolic information

Light or beam marking apparatus or processes

Scan of light

C347S256000, C228S049100, C228S049500, C385S080000, C385S091000

Reexamination Certificate

active

06222579

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to digital printing apparatus and methods, and more particularly to a system for imaging of recording media such as lithographic printing members.
BACKGROUND OF THE INVENTION
U.S. Ser. No. 09/245,102, filed on Jan. 25, 1999 (the entire disclosure of which is hereby incorporated by reference) describes configurations that permit a single laser crystal to be driven by multiple pumping sources to obtain discrete, collimated outputs without substantial thermal crosstalk.
FIG. 1
illustrates a generalized configuration as disclosed in this earlier-filed application. A recording medium
50
, such as a lithographic plate blank or other graphic-arts construction, is affixed to a support during the imaging process. In the depicted implementation, that support is a cylinder
52
around which recording medium
50
is wrapped, and which rotates as indicated by the arrow. If desired, cylinder
52
may be straightforwardly incorporated into the design of a conventional lithographic press, serving as the plate cylinder of the press. Cylinder
52
is supported in a frame and rotated by a standard electric motor or other conventional means. The angular position of cylinder
52
is monitored by a shaft encoder associated with a detector
55
. The optical components may be mounted in a writing head for movement on a lead screw and guide bar assembly that traverses recording medium
50
as cylinder
52
rotates. Axial movement of the writing head results from rotation of a stepper motor, which turns the lead screw and indexes the writing head after each pass over cylinder
52
.
Imaging radiation, which strikes recording medium
50
so as to effect an imagewise scan, originates with a series of pumping laser diodes
60
, four of which are representatively designated D
1
, D
2
, D
3
, D
4
. The optical components concentrate laser output onto recording medium
50
as small features, resulting in high effective power densities. A controller
65
operates a series of laser drivers collectively indicated at
67
to produce imaging bursts when the outputs of the lasers
60
are directed at appropriate points opposite recording medium
50
.
Controller
65
receives data from two sources. The angular position of cylinder
52
with respect to the laser output is constantly monitored by detector
55
, which provides signals indicative of that position to controller
65
. In addition, an image data source (e.g., a computer)
70
also provides data signals to controller
65
. The image data define points on recording medium
50
where image spots are to be written. Controller
65
, therefore, correlates the instantaneous relative positions of the focused outputs of lasers
60
and recording medium
50
(as reported by detector
55
) with the image data to actuate the appropriate laser drivers at the appropriate times during scan of recording medium
50
. The driver and control circuitry required to implement this scheme is well-known in the scanner and plotter art.
The output of each of the lasers
60
is conducted, by means of an optical fiber
72
1
,
72
2
,
72
3
,
72
4
to an alignment bench
75
that has a series of parallel grooves
77
for receiving the fibers. Bench
75
, which may be fabricated from materials such as metal or silicon, is aligned with a laser crystal to direct the outputs of lasers
60
at appropriate points on the anterior face of laser crystal
80
. To avoid substantial thermal crosstalk, the anterior face of the laser crystal (i.e., the side facing the pumping sources) may be provided with a series of parallel grooves and a pair of spaced-apart metal strips extending across the anterior face of the crystal perpendicular to the grooves. The strips and grooves serve to isolate thermomechanically the regions they define, and are aligned with the pumping sources such that the pumping-source outputs strike the anterior crystal face in the centers of the regions bounded by the strips and the grooves.
It is the emissions of crystal
80
that actually reach the recording medium
50
. A first lenslet array
82
concentrates the outputs of lasers D
1
-D
4
onto crystal
80
, and a second lenslet array
84
concentrates the outputs from crystal
80
onto a focusing lens
85
. The latter lens, in turn, demagnifies the incident beams in order to concentrate them further and draw them closer together on the surface of recording medium
50
. The relationship between the initial pitch or spacing P between beams from crystal
80
and their final spacing on recording medium
50
is given by P
f
=P/D, where P
f
is the final spacing and D is the demagnification ratio of lens
85
. For example, the grooves
77
of bench
75
may be spaced 400 &mgr;m apart, which also determines the pitch P. If the demagnification ratio of lens
85
is 4:1, then the spots will be spaced 100 &mgr;m apart on the surface of recording medium
50
.
Optimal performance requires precise alignment between fibers
72
and crystal
80
. This can be difficult to achieve if, as is typically the case, bench
77
and crystal
80
are separate components mounted during assembly within a common fixture.
DESCRIPTION OF THE INVENTION
Brief Summary of the Invetion
In accordance with the present invention, an optical device—such as the grooved bench described above or other source of imaging radiation—is aligned with respect to a stationary surface using a solder circuit that is itself mounted on the surface. The solder circuit includes a quantity of solder, a resistive element associated with the solder, and terminals for establishing electrical connection to the terminals. An electric current produces heat across the resistive element, which melts the solder. With the solder in the molten state, the device is aligned with respect to the stationary surface, and the alignment is secured by allowing the solder to solidify with the device immobilized.


REFERENCES:
patent: 5196866 (1993-03-01), Ferschl et al.
patent: 5559918 (1996-09-01), Furuyama et al.
patent: 5745624 (1998-04-01), Chan et al.

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