Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
2001-09-04
2003-12-09
Pham, Hai (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S256000
Reexamination Certificate
active
06661446
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is directed to a device for determining the positional deviation of n points, n being a natural number, from their n disjunct reference positions, using an electromagnetic radiation source, imaging optics, and a photosensitive detector, the positional information being converted into information on intensity.
To image flat or curved printing forms, whether it be in a printing-form imaging unit, in a print unit, or in a printing press, arrays of light sources, typically lasers, are used. With the array, which is usually oriented perpendicularly to the straight lines defined by the optical axis of the imaging optics, one produces a number n of individual light beams, whose image points from light sources, such as laser diodes, formed through an optical lens system, are distributed over a surface of a plurality of millimeters times micrometers, situated for the most part on a plane or even straight lines, on the printing form. A point or image point is understood in this context to be both a mathematical point, as well as a multi-dimensional, limited surface. The image points of an individual beam usually have a diameter of several micrometers, and they are spaced apart by several 100 micrometers. Often, the printing form does not abut so as to be flat against the base, be it a flat or curved surface, because the base is soiled by powder dust, other dust particles, or the like. Rather, local bulges having a diameter of several millimeters can form. The imaging optics of the array, both those which are identical for all n beams, as well as the individual ones, are generally configured such that the reference positions of the image points, in other words, their desired position at a reference distance to the optical lens system, are substantially located in one plane. However, because of the bulges, it necessarily follows that image points of individuals beams lie in a plane other than the plane which is defined by the reference position and which is perpendicular to the straight line defined by the optical axis of the imaging optics. To achieve a desired imaging result at these locations in the image field as well, depending on the method employed, one must either change the optical power for the affected light sources in the array, or, however, particularly when the image points in the reference position are a question of the beam waist of the light source, one must shift the focus of the imaging optics, either by varying the object distance, the image distance, or by shifting the main planes of the imaging optics. In both cases, one must determine the position of the current image point with respect to its reference position, since this quantity is needed as an input value to calculate the required change in power or the required variation in the imaging optics. Typically, the result of a ranging or distance measurement of this kind is used to generate a control signal. A control signal can be produced, for example, by further processing a signal from a photosensitive detector, thus from a measurement of light intensity. Optical distance-measuring devices are used, in particular, in autofocusing devices.
U.S. Pat. No. 4,546,460 describes an autofocusing device for an optical system having a laser as a light source, a light-reflecting surface, and a photodetector having at least two photosensitive regions. The laser beam is converged through an objective lens and projected onto the light-reflecting layer. The laser light reflected off of the layer is projected through the objective lens and other optical components onto the surface of the photodetector. In response to displacement of the objective lens along the optical axis, the laser beam is deflected, and the pattern projected onto the surface of the photodetector moves in a specific direction. When the objective lens lies at a distance shorter than a predetermined distance from the light-reflecting layer, the pattern is formed on the first photosensitive region. When the objective lens is located at a distance greater than the second predetermined distance, the pattern is likewise formed on the first photosensitive region. When the objective lens is located at a distance greater than the first predetermined distance and shorter than the second predetermined distance from the light-reflecting layer, the pattern is formed on the second photosensitive region of the photodetector. From the determination of the position of the pattern, one can deduce the distance of the light-reflecting layer to the optical system. Moreover, the focus of the imaging optics can be shifted by shifting the objective lens.
A system of this kind has the drawback of only allowing the position of one single point to be determined with respect to a reference position, and one single focus to be shifted.
U.S. Pat. No. 5,302,997 describes, for example, an arrangement of photometric and range finding elements in an array for use in automatic focus control and automatic exposure measurement for an associated optical system. The arrangement has a two-dimensional, photosensitive element in the center and, on either side thereof, a linearly disposed number of photosensitive elements in an image field. A lens system is provided for projecting an image onto the arrangement. In this context, the photosensitive elements disposed in a linear array receive light from a fractional portion of the image field and are used to measure the intensity of the light received, while the two-dimensional photosensitive element is composed of a number of individual regions and is used to generate a signal for automatic focus adjustment.
Here again, the disadvantage of this arrangement is that only the position of one single point is employed in focus control. Although an array of photosensitive elements is provided for measuring intensity, the corresponding signals are only employed in automatic exposure measurement.
The described devices are not suited for determining the deviation of the position of n image points from their reference positions for the n light sources of an array, in particular from lasers, since the n image points cannot be spatially resolved, and only one signal is produced for the entire image field. Successively measuring n deviations or distances implies an n-fold measuring time. This is not acceptable for the desired purpose of the application, particularly with respect to a device for forming an image on printing forms.
SUMMARY OF THE INVENTION
An object of the present invention is, therefore, to provide a device for determining the deviation of the position of n points from their n disjunct reference positions, which will render possible high-speed measurements of the n deviations or distances.
The present invention provides a device for determining the positional deviation of n points (P), n being a natural number, from their n disjunct reference positions, using a source of electromagnetic radiation (
1
), imaging optics (
2
,
4
,
9
), and a photosensitive detector (
10
), with the positional information being converted into information on intensity. Substantially simultaneous or concurrent in time n signals are produced by the detector (
10
), each of the n signals being uniquely assigned to one of the n points (P).
The present invention also provides a method for determining the positional deviation of n points (P) from their n reference positions, n being a natural number, comprising the following steps: illumination of each individual one of the n points (P) using electromagnetic radiation; conversion of the positional information on points (P) into path information on the light radiation; conversion of the positional information into intensity information; and discriminating detection of the reflected light from at least two of the n points (
8
); wherein the method steps are carried out simultaneously or concurrently in time for all n points (
8
).
In the device according to the present invention for determining the deviation of the position of n points from their disjunct reference positions us
Beier Bernard
Vosseler Bernd
Davidson Davidson & Kappel LLC
Heidelberger Druckmaschinen AG
Pham Hai
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