DE4014047A1 - Stroke position correction device for CRT reproduction system - using correction of X deflection to synchronise Y deflection frequency with stroke release frequency - Google Patents

Abstract

The correction device is used to correct the position of the successive strokes obtained across the surface of the CRT screen (2) during the relative movement of the latter. The intermediate imaging objective (4) to the photosensitive recording material (6) lies on the opposite side of the objective (4) to the screen (2). The correction is effected via the X deflection circuit for the CRT beam, when the stroke release frequency or phase does not confirm to the CRT deflection frequency (14). ADVANTAGE - Improved quality of image projected onto photosensitive medium.

Description

The invention relates to a method and a device for accurate Positioning strokes on a photosensitive material during the Exposure process, which by a cathode ray tube (CRT) on the fluorescent screen at the same place and delivered one after the other, finally large exposure lines (strokes), during a relative movement and are correctable regardless of the speed of movement, namely if it is determined that the mismatch in the stroke trigger frequency or phase with the deflection frequency of the cathode ray Electronics would cause a location error on the photosensitive material.

Cathode ray tubes are used alongside as a recording light source for the reproduction of black and white and also colored original images and other uses for a long time for high quality and fast photo-setting machines are used. Here was it was common at first to write whole letters, characters or figures one after the other to display on the fluorescent screen and by means of an object on the image or record photosensitive material. This material, usually a film, then serves as a print template for various subsequent ones Printing processes.  

With the technical progress of these photo typesetting machines to digital imagesetters it was now possible, in addition to texts in corresponding types and Sizes, line art and graphic elements also include rasterized images produce. With small dots (pixels) that can be created on the film, e.g. B. from approx. 0.01 mm diameter, rasterized images can now be higher Resolution or even the color separations of a colored image or that colored picture yourself.

If you line up point by point on the cathode ray tube, you get one Line (stroke). This is vertical, that is, it lights up in the Y direction Line is light-keyed one after the other in different lengths. Becomes at the same time the cathode ray tube in the X direction to the photosensitive material moved, so can be Line up the lines of the area to be exposed, for example one to be generated between an outer and an inner contour Letter, expose. That means that one is always in the same place on the The cathode ray tube finally produced a large line with continuous motion and clocked light keying an exposed bar on the would produce photosensitive material.

The typographic quality of a typesetting work using a CRT digital imagesetter has also been manufactured essentially depends on using what fineness, i.e. resolution or number of lines per unit of measure Cathode ray tube is operated and how exactly these lines are accurate the required location of the photosensitive material can be placed. More or less, the above-mentioned CRT imagesetters must be able to be a predetermined arbitrary surface to a likewise predetermined Fill in the location on the photosensitive material according to the exposure. Primary the exposed area should be as clear and exact as possible  Contour transition to the unexposed area, where none visible change in position of individual exposure beams (strokes) Contour course, for example of characters, interrupts.

The geometrical position of the writing beam, that is, the place where the It is well known that the beam strikes the photosensitive material in the imaging plane also in photo typesetting machines using very fine ones Glass grid rails, checked by means of obtoelectronic means. In several Known CRT imagesetters become the X-ray tube that can be moved monitored by means of such a grid rail in order to To be able to space exactly next to each other in the direction of the beam. This process is also called stroke pattern process. The one on the Illuminated screen of a cathode ray tube strokes strobed in sequence can be affected by various errors in their positional accuracy will. These include, for example, uneven running of the driven optics and CRT car above the fixed photosensitive Material. It can happen that the stroke trigger frequency does not match the deflection frequency of the CRT electronics and it thus there is a position inaccuracy. Likewise, the continuous Move this optics and CRT carriage in the X direction to one Tilting of the strokes on the photosensitive material.

From DE-OS 36 15 126 a digital imagesetter is known, in which one A cathode ray tube, a deflecting mirror and an imaging object continuously are moved over the photosensitive material and a specific one Expose the width area with appropriate pixels or strokes can. If now the trigger frequency of the strokes does not match the deflection frequency the CRT electronics is synchronized, only the next complete Stroke can be exposed by the CRT electronics. But then the cathode ray tube  already moved a bit further with the imaging lens and so the stroke would be exposed in the wrong position.

The object of the present invention was therefore a method and a To create circuit with which it is possible to achieve the above Disadvantages of a cathode ray tube in a reproduction device thereby improve that location errors or inclinations of strokes before Exposure can be recognized and corrected.

According to the invention, this object is achieved by a method and device solved according to the features of the claims.

The method and the circuit result in advantages, for example consist of the stroke trigger frequency and the CRT deflection frequency no longer have to match, that is, it can be different Speeds during the acceleration phases and restless drives of movable tubes and imaging lenses be exposed.

Another advantage of the invention is that the misalignment of strokes, characterized by the continuous movement between light source and recording material is balanced.

Another advantage is that the purely electronic processing of the Location signals practically inertia compared to a mechanical solution is. This can cause uneven running of the drive, which is no longer corrected can be compensated.

Another advantage of this method is the fact that the lateral  Correction shift of the stroke over a range of at least two stroke widths, the phosphor of the tube is much less stressed and so that the service life of the cathode ray tube is increased.

The invention will now be described using an exemplary embodiment and explained in more detail with reference to the corresponding drawings.

The drawings show

Fig. 1 is a perspective view of a Digitalbelichters with a cathode ray tube,

Fig. 2, the corresponding correction circuit,

Fig. 3 shows the waveform for the circuit shown in Fig. 2.

Fig. 1 shows a digital imagesetter with a cathode ray tube 1 , on the fluorescent screen 2, a stroke 3 lights up with an arbitrarily shown length. This stroke 3 is directed via a lens 4 and deflecting mirror 5 onto a photosensitive material 6 in order to fill in the space between an inner and outer contour of a character "A", for example, as shown. The cathode ray tube 1 , objective 4 and deflecting mirror 5 are continuously moved in the direction of the arrow X. Fixed in place like the photosensitive material 6, there is a glass grid scale 7 , the grid lines 8 of which are located next to one another and are scanned by a sensor 9 and a receiver 10 and fed via line 11 to control electronics 12 in order to generate a position and speed signal or to specify the stroke triggering frequency . In the computer and control electronics 12 , the length of the strokes through the Y deflection 14 and the lateral position through the X deflection 15 are also fed via line 16 to the cathode ray tube 1 .

Usually, the cathode ray tube 1 , objective 4 and deflecting mirror 5 sit on a carriage which is continuously moved by a drive unit, not shown, and which is moved back and forth over the photosensitive material 6 in the X direction in accordance with the width of the typesetting work to be exposed.

During the initial acceleration and also during the braking process moving light source and the imaging lens as well as due to unrest in the drive area it can happen that there is no match between the stroke trigger frequency and the deflection frequency of the CRT electronics exists, so that a location error of a stroke to be imaged occurs can, as will be explained in more detail below.

The circuit of FIG. 2 consists of two identical augebauten resettable integrators 21 and 22. The integrators each consist of an operational amplifier 27 , resistor 23 , capacitor 25 and switch S 1 for resetting. The outputs of the integrators 21 and 22 can optionally be switched to the output 30 via the two switches S 2 and S 4 . If S 2 and S 4 are still open, output 30 is pulled to ground via resistor 29 .

The circuit works as follows:

A speed signal proportional to the X movement is applied to the integrators 21 and 22 via the line 11 . If the switch S 1 is now opened at a specific point in time, the speed signal 11 is integrated by the integrator 21 from this point in time. The output signal of the integrator 21 is proportional to the distance that the CRT unit has traveled after opening the switch S 1 .

In Fig. 3, the time sequences of the electrical signals are illustrated by an example. The falling edge 60 of the stroke trigger signal signals to the electronics that a stroke is to be exposed onto the photosensitive material 6 at this moment. The switch S 1 opens and integrates the speed signal assumed to be constant. At the output of the integrator 21 , a linearly increasing voltage appears proportional to the moving path of the CRT unit. To expose the requested stroke, the next full stroke of the Y deflection must be waited for. This is represented by the falling sawtooth flank 61 of the Y deflection. As soon as this edge begins, the signal of the integrator 21 is switched through to the output 30 via the switch S 2 and, via the X deflection 15 from FIG. 1, shifts the stroke 3 on the CRT 2 just enough that the incorrect position of the stroke 3 ' On the photosensitive material 6 , which would have resulted from the further processing of the CRT unit, is compensated. After this stroke has been exposed, the integrator 21 is reset to zero volts by closing S 1 . The second stroke request 62 is processed in the same way as the first, only by the integrator 22, the switches S 3 and S 4 . The saw tooth flank 63 of the Y deflection is used to expose this stroke. The next stroke request 64 is processed again by the integrator 21 , etc.

In the diagram for the output of the correction circuit 30 it can be seen that the correction signal continues to rise linearly after the respective closing of the switches S 2 or S 4 . This increase in the correction voltage causes a slight inclination of the stroke 3 on the CRT 2 via the X deflection 15 from FIG. 1, as a result of which the stroke 3 ' on the photosensitive material 6 is avoided. This inclination would otherwise result from the vertical position of the stroke 3 due to the continuous X movement of the CRT unit.

The method and the circuit according to the invention are extremely effective when there is a knowledge that the strokes lying closely and exactly next to one another on the light-sensitive material 6 could deviate from their predetermined position. If, for example, the location signal via line 11 from the grid scale 8 provides for a spacing of each stroke of 0.0075 mm, and because of the continuous movement of the tube 1, there is a knowledge that the Y deflection, which for example runs continuously at a frequency of 35 kHz, would bring the next stroke to the wrong position on the photosensitive material 6 , a correction is made in such a way that only the next stroke with its predetermined length from the X deflection 15 in the X direction of the tube is corrected by the amount that is meanwhile the optical carriage is to be moved further, as the time difference between the point in time at which the stroke should actually have been palpated and the point in time at which the next stroke appears above the Y deflection frequency. this is also clear from FIG. 3 with a corresponding description.

It can also be seen that speed fluctuations during the sliding movement of the tube with the optics, which is a misalignment of the Strokes on the light-sensitive material could, e.g. B. by improper guidance of the optics guide Fluctuations in drive electronics or other continuous ones Movement negatively influencing means, now no effects on the exact positioning of the strokes or pixels to be exposed.  

It should also be mentioned that the same procedure also applies to Cathode ray tube imagesetters with fiber optics apply where that to be exposed Material pulled in front of the tube over the curvature of the front becomes. Here, however, X and Y deflections are then exchanged be.

Claims (4)

1. A method for the exact positioning of strokes in a cathode ray tube used for reproduction with an imaging lens between the fluorescent screen and the recording material, the finite exposure lines (strokes) being emitted on the fluorescent screen of the tube at the same location and in succession during the relative movement of the tube and the lens Recording material can be corrected, characterized in that when the non-conformity of the continuous Y deflection frequency ( 14 ) with the location signal of the stroke trigger frequency ( 8, 9, 10 ) is detected, only the next stroke ( 3 ) is palpated, the desired exact position on the recording material ( 6 ) by a spatial correction of the X deflection ( 15 ) for this stroke on the fluorescent screen ( 2 ). 2. The method according to claim 1, characterized in that the stroke ( 3 ) to be exposed in dependence on the stroke trigger frequency ( 8, 9, 10 ) by means of the X deflection ( 15 ) assumes a position inclined to the direction of movement deviating from the Y direction . 3. Device for correcting the position of a stroke that is palpated for exposure on the fluorescent screen of a cathode ray tube, characterized in that the speed signals ( 60, 62, 64 ) emitted by the stroke triggering ( 8, 9, 10 ) are optionally fed to a resettable integrator ( 21, 22 ) are compared with the agreement of a signal of the Y deflection ( 61, 63 ), and that if the X deflection ( 15 ) does not match, a correction signal ( 30 ) can be applied. 4. Device for position correction according to claim 3, characterized in that two integrators ( 21, 22 ) are connected in parallel.