Photocopying – Projection printing and copying cameras – Methods
Reexamination Certificate
1999-08-23
2002-03-12
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Methods
C359S196100, C359S197100, C359S204200
Reexamination Certificate
active
06356342
ABSTRACT:
FIELD OF THE ART
The invention relates to a method of exposing light-sensitive materials as stated in the introductory portion of claim
1
, and to an apparatus for performing the method as stated in the introductory portion of claim
13
.
EP 0 589 652 A describes a so-called single raster scanning system (ROS) having a rotating mirror in which a rotating polygonal mirror reflects a “bundle” of laser beams with different wavelengths. The laser beams are very close to each other (10 &mgr;m), but still spatially separated perpendicularly to the axis of rotation of the polygon (fast scan direction), and are split by means of optical filters to optical paths to the associated photo-receptors.
This spatial separation, however, is problemetic in several different connections, since the mechanical structure of the optical system will invariably have an increased complexity, and at worst involves a deterioration of precision and possible exposure resolution.
U.S. Pat. No. 4,962,312 discloses a multi-station printer in which a plurality of light beams with different wavelengths is gathered to a beam by means of a beam splitter and is then conducted to the stations of the printer via a polygon, in dependence on the wavelengths of the light beams.
A serious drawback of this system, however, is that it may be difficult to achieve the necessary coincident optical axes by using beam splitters per se. This has the additional consequence that the system gets more expensive and complex if a reasonable result should be desired.
A further drawback of this structure is that the light beams may be affected critically by temperature gradients, turbulence, etc.
SUMMARY OF THE INVENTION
When at least one additional light source generates in additional light beam with a wavelength &lgr;
x
which is different from &lgr;
1
, said additional light beam with the wavelength &lgr;
x
being conducted via the input end of the optical system to the output end of the optical system so as to be geometrically coincident with the first light beam at the output end of the optical system, said additional light beam being conducted from there to an additional exposure point on the light-sensitive material in dependence on &lgr;
x
or the mutual difference between the wavelengths &Dgr;&lgr;, said light being conducted completely or partly from the input end of the optical system via one or more light guides, preferably optical fibres, to the output end of the optical system, it is possible to optimize the exposure rate, as the necessary mechanical movement between output end and exposure point may be reduced to a minimum. It should moreover be noted that the method may be adapted to the nature and the rate of the mutual movement in a simple manner, thereby allowing the method to be preferred on the same apparatus with a different resolution, as the distance between the first exposure point and the additional exposure point or points may be adjusted e.g. by changing the wavelengths of the light sources. The method is thus extremely flexible and may be adapted for many applications without complicated mechanical or electronic measures.
The invention is thus unique in that light with different wavelengths may be missed in an optimum manner in a light guide, or e.g. an optical fibre, to a geometrically coincident light beam, thereby making the subsequent separation simpler.
The use of an output end in the form of a light guide, e.g. an optical fibre, moreover allows simpler adjustment of the output end relative to the rotating optical element, as, physically, a fibre end is much simpler to handle and to position than a beam splitter per se.
Further, it is also possible to exchange the individual laser sources in the complete application separately, without this requiring a new overall calibration of the optical system.
An additional advantage of using light guides or optical fibre means between laser sources and the output end of the optical system is that it is simpler to position laser sources and optional associated modulators in primary consideration of where the mechanical position is most advantageous for the apparatus concerned. This involves a special advantage for general purpose printers or scanners.
It has also been found that this advantage is particularly pronounced for e.g. multi-station printers as it is frequently desired, for cost-saving reasons, to expose different physically separated exposure points, e.g. one exposure point per colour, with just one rotating optical element, for which reason a geometrical separation of the light beams results in a greater mechanical and optical complexity.
It will likewise be appreciated that, according to the invention, the precision may be maintained even at very high speeds of rotation.
Thus by mixing the various light beams with correspondingly different wavelengths so that these are fed geometrically coincidently from the output end of the optical system, it is possible to carry out a relatively uniform and simple optical control via the rotating reflector to the exposure face.
Thus, by avoiding a spatial separation between the beams at the output end of the optical system it is possible, in a simple manner, to avoid the complicated geometrical relations that exist between the output end and the axially rotating reflector or mirror, thereby avoiding e.g. twisting on the exposure face in a simple manner.
The invention thus allows all light beams to be centered on the rotating reflector, thereby obtaining rotary symmetry for the beams which are subsequently reflected by the exposure face, irrespective of the position of the reflector or the mirror in the path of rotation.
From two to several light sources may be used according to the invention.
The light sources used may be both of the same type or of different types.
The optical system comprises the necessary optical features to conduct light from source to exposure point. If the light sources are not modulated directly, the optical system may also comprise optical modulators.
According to the invention, a reflector is taken to mean e.g. a mirror, a pentaprism, or optical elements having a sufficiently deflecting effect.
Further, it is possible to conduct the light to the exposure points via a compact optical arrangement, as the optical system is hereby well-defined and easy to calibrate.
The use of optical fibres in this connection provides an additional advantage, as the spatial distribution of the complete light beam is improved considerably, since the light from the various light sources is coincident if the light from all light sources is conducted precisely to one optical fibre.
An additional advantage obtained by using optical fibres in this connection is that the precision is improved considerably, considering that the optical reflector performs very fast revolutions with consequent turbulent flows around the rotating optical element of the scanner. The use of optical fibres minimizes the optical temperature-sensitive distance, which is particularly imporatant when using multi-beams whose mutual focusing distance on the exposure face is affected critically by temperature gradients.
Moreover, it is possible to arrange heat-generating components suitably relative to e.g. heat-sensitive components. The light source may thus be positioned freely as desired.
When the light is conducted from the individual light sources to a common optical fibre in the optical system via one or more couplers, a particularly advantageous structure of the optical system may be obtained, as an optical coupler causes relatively low optical losses in the mixing of two or more light waves from two or more optical fibres to one optical fibre.
Thus, in several applications, an optical T-coupler will exhibit very low optical losses in the actual mixing.
The optical coupler is particularly advantageous in connection with e.g. general purpose printers, as optical mixing in a coupler is relatively simple and inexpensive, just as it is possible to exchange laser sources separately and to adjust these to the individual input end, without this
Ballegaard Hans Peter
Buus Niels
Hyldahl Heidi Marianne
Adams Russell
Fuller Rodney
Pitney Hardin Kipp & Szuch LLP
Purup-Eskofot A/S
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