Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Patent
1997-10-31
1999-06-01
Le, N.
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
347242, 359210, G03F 724
Patent
active
059092360
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a laser exposure apparatus for exposing exposure material in form of light-sensitive offset printing plates, said apparatus comprising a relatively heavy base member of for instance granite and an optical scanning unit employing a movable mirror deflecting a laser beam, and where the base member comprises a semi-cylindrical or planar exposure surface, on which the exposure material can be placed, and where a bridge is arranged above said base member, said bridge being displaceable along said base member in one direction thereof by means of an advancing device, and where the mirror is mounted on said bridge.
BACKGROUND ART
A laser exposure apparatus is known which comprises a semi-cylindrical base member, and where a bridge in form of a carriage extends transverse to the base member, said carriage at one side being supported and advanced by an advancing device and at the opposite side resting on a guide. Such a mounting of the bridge is not quite satisfying due to a lack of accuracy. In order to obtain an improved accuracy it is also known to place a screw drive in the longitudinal centre plane of the base member and parallel to said base member, but such an arrangement is not preferred because it is thereby difficult to obtain the necessary room for mounting the exposure material on the base member.
BRIEF DESCRIPTION OF THE INVENTION
The object of the invention is to provide a laser exposure apparatus of the above type, which allows an improved accuracy during the exposure of the exposure material, and which furthermore allows an easy access for the mounting of said material on the base member.
The laser exposure apparatus according to the invention is characterised in that the advancing device is placed along one side of the base member, and that the bridge is mounted in a substantially balanced manner relative to the advancing device by means of a counterweight provided on a projecting portion of the bridge, the centre of gravity of said counterweight being placed opposite the optical scanning unit relative to the advancing and in the vicinity of said device, and that the bridge rests on supporting surfaces on the base member. The resulting exposure is much more accurate than hitherto known, and as the advancing device is positioned at one side of the base member the access to the semi-cylindrical surface of the base member is easy when the exposure material is to be mounted thereon.
According to the invention the bridge may preferably rest on longitudinal supporting surfaces on the base member.
According to the invention, the bridge may rest on the longitudinal supporting surfaces of the base member by means of non-contact bearings, such as air-cushion bearings or magnetic bearings, whereby the stability and consequently the position accuracy of the bridge are increased.
According to the invention, at least one of the supporting surfaces may be inclined relative to the longitudinal centre plane of the base member, whereby the stability of the bridge is further increased.
Moreover according to the invention, the counterweight may be integrally formed with the bridge with the result that a particularly simple manufacture of the bridge is obtained.
According to the invention, non-contact bearings may be provided between the counterweight and the base member at an inclined supporting surface and/or a substantially vertical supporting surface, respectively, on said base member, while a third non-contact bearing may be provided at the end of the bridge farthest away from the counterweight, said third non-contact bearing co-operating with a substantially horizontal supporting surface on the base member. As a result, a further possibility is obtained of an accurate speed control/positioning of the bridge.
Moreover according to the invention, it is particularly advantageous to place the common centre of gravity of the bridge and of the equipment and the counterweight mounted thereon substantially vertically above or below or within the advancing device.
Finally, ac
REFERENCES:
patent: 3632207 (1972-01-01), Wachter
patent: 4099800 (1978-07-01), Bell et al.
patent: 4455641 (1984-06-01), Sliski
patent: 5592324 (1997-01-01), Inagaki et al.
Krause Danmark A/S
Le N.
Pham Hai C.
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