Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
1999-04-02
2001-09-04
Le, N. (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S243000, C347S245000
Reexamination Certificate
active
06285390
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a rotatable mirror assembly, for example for use in an image exposing device such as an internal drum image setter.
DESCRIPTION OF THE PRIOR ART
In the field of image reproduction, it is common to cause a radiation beam such as a laser beam which has been modulated with image information to scan across a record medium at high speed. This scanning action is achieved by directing the beam onto an angled mirror which is rotated. In order to increase the rate at which a record medium is exposed, it is conventional to rotate the mirror at very high speed, a typical example is 30000 revolutions per minute. At these high rates of rotation, the materials from which the mirror is made can distort with the result that the beam impinging on the record medium suffers from astigmatism and poor spot quality. In general, a focusing lens which focuses the beam onto the record medium, has to be positioned at different locations along the beam to achieve optimum focus in the scanning direction and orthogonal to the scanning direction. The distance between these focusing positions is a measurement of the astigmatism and it is desirable to minimise that distance.
One method of dealing with this problem involved providing a special profile to the mirror so that when the mirror is rotated, it takes up a substantially planar configuration. This suffers from disadvantages, including the fact that the profile can only give the correct compensation at one speed of rotation.
SUMMARY OF THE INVENTION
In accordance with the present invention, a rotatable mirror assembly comprises a rotatably mounted support; and a mirror mounted to the support, for rotation therewith, at a position laterally offset from the axis of rotation of the support, the mirror being spaced from the remainder of the support to allow the mirror to distort when it is rotated.
Instead of attempting to modify the mirror itself, we have devised a new approach in which the mirror is allowed to distort in such a way that relatively little astigmatism is produced. This is achieved by mounting the mirror to the support at a position laterally offset from the axis of rotation of the support. This leaves the front part of the mirror free to distort in such a way that it compensates for the distortion of the top part of the mirror.
Typically, the mirror presents a substantially planar reflective surface when stationary. However, in some cases, a different mirror form may be desired at high speed so the reflective surface will be formed accordingly.
In one preferred arrangement, the support includes a spigot which is fixed in a slot in the mirror so as to mount the mirror to the support. Typically, the spigot will be glued with a suitable adhesive in the slot but other forms of connection such as splines and the like could be used. In a modification of this arrangement, the mirror could include a spigot which is fixed in a slot in the support.
In an alternative arrangement, the support and the mirror are formed integrally with a slot being cut into the front part of the mirror. This can provide a simpler construction in some cases and the assembly will be quieter to operate.
To achieve exactly the compensation required for a particular design, the size and location of the spigot may be varied, or the shape and extent of the cut.
As in conventional mirror assemblies, one or more balance weights may be provided in the support and/or the mirror to ensure smooth rotation.
Typically, the mirror defines a reflective surface which extends at a non-orthogonal angle to the axis of rotation of the support. This is advantageous since a beam to be deflected can be directed towards the mirror along the axis of rotation.
The mirror may define a reflective surface having an elliptical shape in plan but other shapes are also possible.
As mentioned previously, the invention is particularly applicable for use in an image exposing device which further includes a radiation beam source for generating a radiation beam which impinges on the mirror; a record medium support onto which the beam is incident following reflection by the mirror; and a modulator for modulating the beam with image information. An example is a conventional internal drum imagesetter.
REFERENCES:
patent: 4105296 (1978-08-01), Tomlin
patent: 4571036 (1986-02-01), Gebelein
patent: 5148313 (1992-09-01), Schwemin
patent: 5642150 (1997-06-01), Takahshi
patent: 5739939 (1998-04-01), Merritt
patent: 195 15 887 A1 (1996-10-01), None
patent: 0 596 301 A1 (1994-05-01), None
patent: 0 814 358 A2 (1997-12-01), None
Patent Abstracts of Japan, vol. 095, No. 004, May 31, 1995 (JP 07 013094 A).
Fujifilm Electronic Imaging Ltd.
Le N.
Nguyen Lamson
Sughrue Mion Zinn Macpeak & Seas, PLLC
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