Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
2001-12-17
2003-09-09
Pham, Hai (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S255000
Reexamination Certificate
active
06618070
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
A multi-beam scanning apparatus can be used with a recording device that has an internal cylindrical bearing face for receiving a recording medium. The multi-beam scanning go apparatus, in particular, can be used with an internal-drum exposure device. The multi-beam scanning apparatus includes a scanner unit for scanning the recording medium with at least one exposure beam. The scanner unit includes one acousto-optical deflector or modulator and one deflection element that is axially displaceable and rotatable relative to a cylinder axis of the bearing face. The deflection element is for deflecting the exposure beam emerging from the acousto-optical deflector or modulator. In the reproduction industry, internal-drum laser exposure devices serve to expose a photosensitive recording medium, spread over the inside of a cylindrical drum, line by line, using an intensity-modulated laser beam.
In U.S. Pat. No. 6,052,216, an internal-drum exposure device of the type defined at the outset has already been disclosed in which a single exposure beam, originating in a stationary laser light source, after passing through two likewise stationary acousto-optical modulators is deflected onto a deflection element in the form of an axially displaceable rotating mirror. From the mirror, the exposure beam is reflected onto a photosensitive medium on an inner drum surface of the exposure device. Since the optical axis of the exposure beam in such an arrangement must be located on the axis of rotation of the rotating mirror, if line-by-line exposure of the photosensitive medium to light is to be made possible, the exposure beam emerging from the acousto-optical modulators is an undiffracted zero-order beam of light.
That is, an exposure beam that is nonaxial relative to the pivot axis would, after reflection from the mirror, not move in the circumferential direction over the bearing face and thus would not permit line-by-line scanning of the medium perpendicular to the axis.
From U.S. Pat. No. 4,444,470, in an optical multi-beam modulation and deflection device, it is also already known, to increase the recording speed, using an acousto-optical deflector disposed in a stationary fashion between a laser light source and a rotating mirror. A number of exposure beams located side by side in the same plane are generated and are then reflected, using a rotating mirror, onto a photosensitive recording medium on the outer circumference of a drum. Since not all of the exposure beams can be located on the same axis, a polygonal mirror must be used to reflect the exposure beams; its rotating axis forms an angle with the optical axis of the undiffracted laser beam so that the plane of the deflected exposure beams is perpendicular to the axis of the drum. However, such an arrangement requires a relatively large amount of space, and it can be employed only in external-drum exposure devices, but not in internal-drum exposure devices where the drum axis coincides with the pivot axis of the rotating deflection element.
From Published German Application DE 41 20 103 A1, it is in fact already known per se, in a housing that rotates about the drum axis and that is axially displaceable relative to the inner drum in an internal-drum exposure device, to provide a deflection element and additionally to provide a light source that rotates together with the deflection element about the drum axis. The light source can be formed by a multi-channel laser diode line, from which the exposure beams emerge spaced apart from the drum axis and strike the deflection element. Since the spacings of the individual laser diodes in commercially available laser diode lines are relatively great, however, the laser diode line and the deflection element must be positioned at an angle relative to one another, by rotating one of the two relative to the other about a pivot axis, in order to achieve linear conjugation, that is, a partial overlap of the pixels created on the recording medium. If the exposure beams from all of the laser diodes of the laser diode line are to strike the recording medium, despite the positioning of the diodes in a plane perpendicular to the pivot axis, the individual laser diodes must be triggered with a time lag in accordance with the axial motion of the deflection element relative to the recording medium, which involves additional effort and expense for calculating the time lag and calibrating the exposure device.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a multi-beam scanning apparatus which overcomes the above-mentioned disadvantages of the prior art apparatus of this general type.
In particular, it is an object of the invention to provide a multi-beam scanning apparatus of the type defined at the outset, to enable line-by-line scanning of the recording medium with one or more exposure beams originating in an arbitrary laser light source, which do not strike the deflection element along the cylinder axis of the bearing face and whose spacings are variable.
With the foregoing and other objects in view there is provided, in accordance with the invention, a multi-beam scanning apparatus for use with a recording medium located on an at least partially cylindrical inner bearing face of a recording device, in which the bearing face has a cylinder axis. The scanning apparatus includes a scanner unit for scanning the recording medium with at least one exposure beam. The scanner unit includes an acousto-optical element that is either an acousto-optical deflector or an acousto-optical modulator. The scanner unit includes a deflection element that is axially displaceable and rotatable relative to the cylinder axis of the bearing face. The acousto-optical element is mounted to rotate together with the deflection element about the cylinder axis.
In accordance with an added feature of the invention, the acousto-optical element is simultaneously actuated with voltage signals at different frequencies on a plurality of channels to split a laser beam, which is delivered from outside the acousto-optical element into the acousto-optical element, into a series of exposure beams.
In accordance with an additional feature of the invention, the frequencies of the voltage signals are each modulated differently to independently vary intensities of the exposure beams.
In accordance with another feature of the invention, a high-frequency driver is provided for triggering the acousto-optical element with the voltage signals.
In accordance with a further feature of the invention, the driver receives a video input signal, and the driver modulates the carrier frequency of each one of the voltage signals in accordance with the received video input signal.
In accordance with a further added feature of the invention, devices are provided for transmitting the voltage signals from the driver to the acousto-optical element. The devices either capacitively transmit the voltage signals or inductively transmit the voltage signals. The driver is not rotating.
In accordance with a further additional feature of the invention, there is provided, a non-rotating laser light source feeding a laser beam along the cylinder axis into the acousto-optical element.
In accordance with yet an added feature of the invention, a laser light source generates a laser beam having a beam path, and a device is disposed in the beam path upstream of the acousto-optical element. The acousto-optical element has an optical entry face, and the device deflects the laser beam to the optical entry face at a defined angle.
In accordance with yet an additional feature of the invention, the device includes an optical wedge.
In accordance with yet another feature of the invention, the device rotates together with the acousto-optical element.
In accordance with yet a further feature of the invention, the device includes an optical wedge that has a light entry face oriented toward the laser light source. The optical wedge has a light exit face oriented toward the acousto-optical element. Downstream of
Fischer Jörg-Achim
Jacobsen Thomas
Greenberg Laurence A.
Heidelberger Druckmaschinen AG
Mayback Gregory L.
Pham Hai
Stemer Werner H.
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