Data processing: measuring – calibrating – or testing – Calibration or correction system – Position measurement
Reexamination Certificate
2003-01-31
2004-12-28
Barlow, John (Department: 2863)
Data processing: measuring, calibrating, or testing
Calibration or correction system
Position measurement
C101S483000
Reexamination Certificate
active
06836740
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a method of determining the relative position of a first imaging or imagesetting device with respect to a second imaging or imagesetting device by setting images on an imaging medium assigned thereto. The invention further relates to a method of correcting the position of a point of projection of a first imaging device with respect to a point of projection of a second imaging device by changing the relative position of the point of projection of the first imaging device with respect to the point of projection of the second imaging device from an actual position to a nominal or reference position, in particular, in a printing form exposer or in a printing unit of a printing press.
In order to set an image on a two-dimensional surface of an imaging medium with the aid of one or more imaging devices, the surface is scanned, in two linearly independent coordinate directions for covering the area thereby, by providing a relative movement between the surface and the imaging device or devices, which is produced by a suitable actuator mechanism. The scanning is typically performed in a so-called fast scanning direction and a so-called slow scanning direction, so that all the points to be imaged on the surface are swept over by the imaging devices, more precisely by a number of imaging beams. In this regard, an imaging beam may be a light beam, in particular a laser light beam, whether in the infrared, visible or ultraviolet spectral ranges, a heat pulse, a gas jet or a droplet of a chemical substance or the like. An imaging device, also referred to as an imaging or imagesetting module, may have one or more imaging beams. In this regard, imaging media include printing forms, printing plates, so-called printing form precursors, films or the like. For setting images on imaging media in the graphics industry, whether at the pre-printing stage in printing form exposers or in the printing stage in printing units (on-press imaging or direct imaging printing units), laser light sources, in particular, are especially widespread in imaging devices. Frequently, laser light sources are diode lasers or solid body lasers, such as lasers with reinforcing media of Ti:sapphire or Nd:YLF, preferably pumped by a diode laser. Several laser light sources may be located on one or more assembled diode laser bars in one imaging device.
An imaging device may include one imaging channel or a group of imaging channels. Several imaging devices may be integrated into a block. For the purpose of imaging or inscribing, the imaging channels are switched on and off (timed releasing). Depending upon the imaging method that is selected, while at least one imaging channel is switched on, a relative movement may or may not take place between the point of projection and the imaging medium. By the use of an imaging medium whereon an image has been set or written, an image can be transferred to a printing material. Typical printing materials are paper, pasteboard or cardboard, organic polymer films or the like, whether they are in sheet or web form.
If a number of imaging devices are used, whether in a printing form exposer or exposing device, or in a printing unit, it is very important that the relative positions of the imaging devices with respect to one another and, assuming that a plurality of imaging beams emanate from one imaging device, that the imaging beams from the imaging device are aligned with one another. If appropriately accurate imaging optics is used on the imaging medium, it is consequently then possible for the relative position of the imaging beams on the imaging medium to be set up or calibrated with great precision relative to one another. As a result, without restricting the general number of imaging beams in an imaging device, merely for simplifying the drawings and description, it is assumed that each imaging device has one imaging beam, respectively. Furthermore, without restricting the general number of the imaging devices, likewise for simplifying the drawings, the description hereinbelow is directed to a first and a second imaging device, with the knowledge that more than two imaging devices may be involved.
The procedure for setting up or calibrating the relative position of a first imaging device with respect to a second imaging device (of a first with respect to a second imaging channel or of a first group of imaging channels with respect to a second group of imaging channels) can be required firstly in the assembly of the imaging devices and secondly in the event of maintenance of the apparatus or the press with which the imaging devices are associated, be it in a workshop or at the customer. According to a widespread procedure, therefore, a considerable amount of effort is associated in particular with the installation of printing presses with on-press imaging printing units. For each printing unit, test imaging of a printing form (imaging medium) is carried out, part of the printing form with an image set on it is cut out and the part is examined by a reader, so that correction values for the relative position can be determined. The correction values are used for making changes in the relative position, for example, this information is made available to the control system, and the imaging devices are adjusted with respect to one another. The aforedescribed method for determining the relative position is iterated until the desired or required precision has been reached. The relative position deviation can be determined both for the fast scanning direction and for the slow scanning direction, and the relative position can consequently be adjusted. However, the high outlay for material and of time is a disadvantage when this method is used.
For example, the published Non-prosecuted German Patent Application DE 44 37 284 A1, corresponding to U.S. Pat. No. 5,832,415, discloses that a calibration of a control system for the deflection of a laser beam can be performed as follows. A light-sensitive medium is irradiated by the laser beam in order to produce a test image and, therefrom, digitized image sections which are recorded by a CNC-controlled camera are then generated. A calculation of correction data for the control system for the diffraction or deflection of the laser beam is performed based upon a comparison between the actual positions of the laser beam, which are measured by recording the image sections, and predefined intended positions. The disadvantage when this method is employed is likewise the outlay for material and is in addition the requirement for using a precise CNC control system for the camera, which is also consequently quite expensive.
German Published, Non-prosecuted Patent Application DE 197 32 668 A1 discloses a calibration device for a beam scanning device, which has a surface with defined markings. With a detector device, the light reflected from the surface or transmitted light from the beam scanning the surface is registered. When the beam strikes a marking, only a low intensity is reflected and transmitted, respectively. From the registered variation in intensity of the radiation in reflection or transmission, the actual position of the laser beam is determined and, in a control system, is compared with the nominal or desired position anticipated for this location. From this comparison, a correction value can be determined and made available to the control system, for example stored as a tabular entry in a memory. A disadvantage of this calibration device is that a surface with precise markings must be made available. However, such a surface is sensitive and furthermore is little suited to be moved to various locations or to be accommodated in different machines, frequently with changes in shape, which may possibly lead to distortions of the coordinate system.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method for determining the relative position of first and second imaging devices, a method of correcting a position of a point of projection of the de
Kähler Thomas
Zintzen Bernhard
Barlow John
Greenberg Laurence A.
Heidelberger Druckmaschinen AG
Locher Ralph E.
Stemer Werner H.
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