GB2099655A - Light beam scan type marking- off device - Google Patents

Abstract

For marking cutting lines and instructions onto the surface of a steel plate (18), a marking device comprises means (8) for generating a laser beam (11) and (7) for modulating the beam with data to be marked from a controller (4) fed by a computer (2); part of the modulated beam (11') is reflected from a mirror (10) to a detector (9) which feeds back to the controller for synchronising purposes, and the remainder of the beam is directed onto the surface of the plate (18). The plate may be moved on a carriage (16) at constant speed perpendicular to the one-dimensional direction of scan of the beam provided by a mirror drum (15) to form a two-dimensional raster image on a layer of photoconductive toner powder deposited from a unit (12) prior to the scanning. Means are provided for removing unexposed powder (13) and for fixing the powder image (14, 15). The cutting line data may be generated by scanning an original or may be computer generated. A second laser beam of different color may be combined with the marking beam for reflection by the mirror (10) to the photodetector (9) which is a linear detector having an array of slits; this ensures correct positioning of the beam on the plate, by an electronic control system. <IMAGE>

Description

SPECIFICATION Light beam scan type marking-off device This invention relates to an improvement in an electronic photographic marking-off device which is used in the course of building a ship, and more particularly to a device for marking cutting lines and writing on steel plates with a light beam such as a laser beam.

In the process of building a ship, steel plates are cut into desired shapes, and the resulting plates are then welded together to prepare component blocks forming various parts of the hull.

In this process, one of the following three methods are generally employed: (1) the steel plates are manually cut, after being manually marked; (2) the steel plates are manually cut, after being marked with an automatic marking-off device; or (3) the steel plates are cut directly by an automatic cutter.

Examples of the automatic marking-off device are NC (numerical control) marking-off devices and electronic photographic marking-off devices. An example of the automatic cutter is an NC cutter.

It is absolutely necessary to mark notes, working instructions, etc. on a steel plate which is to be cut. Accordingly, no matter which one of the above-described three methods is employed, marking must be carried out manually or automatically; that is, it cannot be omitted.

Accordingly, sometimes a method which lies between the second and third methods described above is employed. In this method, the steel plate is marked off with an electronic photographic marking-off device, and is then cut with the NC cutter.

In this case, the electronic photographic marking-off device is effective only in marking notes and work instructions.

The employment of such an intermediate method is due to the following reasons: (1) The accuracy of the marking of the electronic photographic marking-off device is lower than the accuracy of the NC device (marking or cutting).

(2) With the NC marking-off device, the marking is carried out with single strokes; and therefore a large amount of time is required to deal with one piece of steel plate. On the other hand, with the electronic photographic markingoff device, the marking is carried out twodimensionally, and therefore substantial amounts of data can be marked in a short time.

In the case of the electronic photographic marking-off device, an original diagram on a scale of 1:10 (1/10 scale), which is prepared by inking a transparent film is enlarged and projected in an exposure operation, so that a steel plate is marked off electro-photographically. Therefore, this device is disadvantageous in that the formation of an original diagram requires substantial time and is costly. Furthermore, the fact that the marking accuracy of the electronic photographic markingoff device is lower than the accuracy of the NC device is attributable primarily to the fact that the original diagram is enlarged ten times in the projection operation.

Therefore, recently an automatic drawing machine has been employed for the preparation of original diagrams, and data to be marked have been previously numerically controlled. Thus, there has been a strong demand for a device wherein marking is performed directly with the electronic photographic marking-off device by utilizing the drawing data. In satisfying this demand, the cost can be reduced and the accuracy increased while the advantages of the electronic photographic marking-off device are fully realized, which provides advantages to the user.

The device according to the invention comprises: light beam generating means; means for modulating said light beam; light beam deflecting means; light beam scan position detecting means; and means for causing the surface of a material to be marked-off to be scanned by a light beam from said light beam generating means in a manner so as to form a raster thereon.

The device will be described in detail with reference to the accompanying drawings, wherein: Fig. 1 is an explanatory diagram, partly as a block diagram, showing the arrangement of a light beam scan type marking-off device according to the invention; and Fig. 2 is an explanatory diagram, partly as a block diagram, for describing the control of the optical system in the invention.

We refer now to Fig. 1, which is a diagram outlining the arrangement of a marking-off device according to the invention. In Fig. 1, reference numeral 1 designates an image sensor for reading image data from a paper or film; and 2, a computer.

When data a such as cutting line data, note data and work data, or data b obtained by reading an image B with the image sensor, are inputted to the computer 2, marking data are converted into raster data. In this case, marking raster data for one operation may be obtained by directly combining the input data a and the input data b from the image sensor.

The marking raster data thus obtained is temporarily applied to a memory medium 3 such as a magnetic tape or magnetic drum, or applied directly to an electronic photographic marking-off device control unit 4.

Further in Fig. 1, reference numeral 18 designates a steel plate which is to be marked.

The steel plate is conveyed in the direction of the arrow by a carriage 16 which runs on rails 19.

As the carriage 16 is run, a charged photoconductive powder (e.g. "Photoner" (trade name) manufactured by the Fugi Photographic Film Co., Ltd.) is uniformly scattered on the surface of the steel plate 18, so that the photo-conductive powder sticks to the steel plate by electrostatic force. The photo-conductive powder is scattered on the steel plate while the latter is in a dark room or place. Reference number 12 designates a unit for charging and scattering the photo-conductive powder.

The photo-conductive powder on the steel plate 18 is exposed to a laser beam 1 1'.

Reference numeral 11 also designates the laser beam.

In Fig. 1, reference numeral 8 designates a laser source. The laser beam 11 from the source 8 is modulated by an optical modulator 7, and is then one-dimensionally scanned by a scanner 5 such as a rotary mirror assembly having a number of mirrors (hereinafter referred to as rotary multimirror assembly, when applicable) or a galvano-m7rror, to provide the laser beam 11 t.

The scanner 5 is driven by a drive source 6.

A part of the laser beam thus scanned is applied to a photo-detector 9 by reflection from a mirror 10. The photo-detector 9 detects the position of the scanned laser beam.

The modulation of the optical modulator 7 is controlled by a signal from the photo-detector 9, so that the powder is exposed to the laser beam according to the marking raster data.

The carriage 16 is provided with a drive source 17 such as a DC motor or pulse motor. The steel plate 18 is moved at a constant speed by controlling the output of the drive source 1 7.

Therefore, in combination with the (onedimensional) laser beam scan, the steel plate 18 is exposed to the laser beam two-dimensionally, as a result of which an electrostatic image is formed in the layer of photo-conductive powder on the steel plate.

The above-described optical scanning according to the marking raster data is controlled by the control unit 4.

The photo-conductive powder layer, in which the electrostatic latent image has been formed, is passed below a developing unit 13. During this operation, the part of the photo-conductive ponder which has lost its electrostatic sticking force due to exposure to the laser beam, is removed and recovered from the steel plate, so that the latent image is developed.

The developed image is formed by the remainder of the photo-conductive powder. This powder is fixed onto the steel plate by spraying a fixing agent 20. In Fig. 1, reference numeral 14 designates a fixing unit and 15, a fixing agent spraying unit.

The photo-conductive powder used above, as well as the powder charging and scattering unit and the development of the latent image are known per sue in the photographic arts, and thus a detailed description thereof is not believed necessary.

Fig. 2 shows one example of the laser optical system in the invention.

In Fig. 2, reference numeral 21 designates a laser source, such as argon laser, which produces a blue or green laser beam 35. Reference numeral 23 designates a first optical system for converging the laser beam 35.

Reference numeral 22 designates a reading laser source, such as a helium neon laser, which produces a red laser beam 36.

Reference numeral 24 designates a second optical system for converging the laser beam 36.

The recording laser beam 35 which has passed through the converging optical system 23 is modulated with a video signal (described hereafter) by an optical modulator 25, and is then passed through a dichroic mirror 26.

On the other hand, the reading laser beam 36, which has passed through the converging optical system 24, is reflected by a mirror 27 and the dichroic mirror 26 and is then combined with the recording laser beam 36 which has passed through the dichroic mirror 26. Thus, the two beams thus combined follow the same optical path 37.

The dichroic mirror operates to pass blue or green laser light and to reflect red laser light.

The laser beams 37 thus combined are deflected by being reflected by a rotary multimirror assembly 28 (5 in Fig. 1) which rotates about its shaft 28' at a constant speed in the direction of the arrow.

The laser beams thus deflected are applied to a dichroic mirror 30 (10 in Fig. 1) after passing through a third converging optical system 29.

Similarly to the dichroic mirror 26, the dichroic mirror 30 transmits the recording laser beam 35 and reflects the reading laser beam 36. The reading laser beam 36 reflected by the dichroic mirror 30 is focused on a reading photo-detector 31 (corresponding to 9 in Fig. 1).

The recording laser beam 35, which has passed through the dichroic mirror 30 is focused on the steel plate 34 (18 in Fig. 1) which is to be marked. The recording laser beam, which has been focused on the steel plate 34, scans the steel plate along a straight line 38, in the direction of the arrow, as the rotary multi-mirror assembly 28 rotates.

As the steel plate is moved on its carriage (16, Fig. 1) at a constant speed by a drive source, the laser beam 35 scans the steel plate twodimensionally.

The reading photo-detector 31 has an array of slits 48 which are arranged at equal intervals, for instance. The reading laser beam, which has passed through the slit array 48, is introduced to a photo-detector 33, for instance, through a bundle of optical fibers 32.

As the rotary multi-mirror assembly 28 rotates, the reading laser beam 36 scans the array of slits 48 on the reading photo-detector 31. Therefore, a digital optical signal is applied to the photodetector 33.

Therefore, if the photo-detector 31 is so designed and positioned that the position of the beam on the scanning line 38 on the steel plate 34 corresponds exactly to the position of the beam on the array of slits 48, then the position of the beam on the scanning line 38 can be detected.

Now, the control of the optical system shown in Fig. 2 will be described.

In Fig. 2, reference numeral 39 designates a counter circuit for counting the output of the photo-detector 33. The counter circuit 39 is reset, for instance, whenever the reading laser beam 36 scans the reading photo-detector 31. Thus, the position of the beam on the scanning line 38 may be detected.

The output thus counted is applied to a clock signal generator 41 so that a reference clock signal is generated by the latter. Reference numeral 40 designates marking image data in the form of a raster, which is applied to a video signal generator 42.

In the video signal generator 42, the reference clock signal from the clock signal generator 41 and the raster data are combined, to provide a video signal.

The video signal thus provided is amplified by an optical modulation drive circuit 43, so that the optical modulator 25 is driven by the amplified signal.

Thus, scanning with the recording laser beam 35 is carried out along the scanning line 38 according to the marking image data with high accuracy.

After being frequency-divided by a frequency division circuit 44, the reference clock signal outputted by the clock signal generator 41 is applied to a drive unit 45 for a steel plate conve#ying means (for instance a carriage) and is then amplified to operate a drive source 46 for the steel'plate conveying means.

Reference numeral 47 designates a detector for detecting the speed of the steel plate conveyor, i.e., the speed of the steel plate.

Depending on the speed detected, the detector 47 applies a signal to the drive unit 45, to control the speed of the conveyor.

Thus, the steel plate is conveyed in synchronization with the laser scanning, so that a two-dimensional raster scan is effected on the steel plate 34.

In the case of Fig. 2, the two-dimensional laser scanning is carried out by moving the steel plate; however, it may also be carried out according to a method in which the optical system is moved with the steel plate maintained stationary, or by a method as disclosed in Japanese Patent Application Laid Open No. 19025/1981 for instance, in which both the steel plate and the optical system are maintained stationary.

A conventional acousto-optical modulator or electro-optical modulator may be employed as the optical modulator 25 of Fig. 2.

The reading photo-detector 31 is a so-called linear encoder. The reading photo-detector 31 operates to detect the laser beam which has passed through the array of slits 48, as was described above. However, a reading photodetector which optically detects a reflected laser beam, or uses photo-electric conversion elements instead of the array of slits, may be employed.

Furthermore, instead of the bundle of optical fibers 32, a converging optical system may be used.

In the device shown in Fig. 2, a rotary multimirror assembly is employed; however, a galvanomirror may also be used, depending upon the scanning speed.

When the relation between the spectral sensitivity of the photo-sensitive material and the recording laser wave-length is taken into consideration, a recording laser having a wavelength in the range of the spectral sensitivity of the photo-sensitive material is generally selected. However, as spectral sensitization can provide a photo-sensitive material having a spectral sensitivity in agreement with the recording laser wavelength, a variety of combinations of photo-sensitive material spectral sensitivities and recording laser wavelengths are possible. Thus, it should be understood that Fig. 2 shows only one example of the laser source.

One advantage of the device of the invention resides in that, as the exposure can be achieved without using an original optical diagram, the loss of time consumed in forming the optical original diagram may be eliminated. Since this makes it unnecessary to use expendables such as films for original diagrams and inks for inking the films, the device is more economical by this degree.

A second advantage of the device of the invention resides in that, since a raster scan is carried out in-the invention, the system according to the invention is higher in exposure accuracy than the conventional system. Furthermore, data conversion can be readily achieved by processing the raster data with a computer. This is effective as a correcting means especially in the case where the steel plate has warps.

A third advantage of the invention resides in that a completely automatic marking operation can be carried out. In the conventional electronic photographic marking-off device, an original diagram must be loaded manually. However, according to the invention, this troublesome operation is unnecessary; that is, the marking-off operation can be completely automatically carried out.

Also in the invention, as the amount of exposure is controlled so as to be constant, the S/N ratio of the resultant electrostatic latent image is stable, and the image quality is therefore improved.

In the conventional electronic photographic marking-off device, an original diagram obtained by inking a transparent film is projected in the exposure operation. Therefore, if the inking density is variable, the resultant electrostatic latent image is variable in potential, and accordingly the image quality is unsatisfactory.

Furthermore, in the conventional electronic photographic marking-off device, the original diagram is enlarged and projected by a lens system, and therefore the resultant image is not uniform in illuminance.

On the other hand, in the invention, as a light beam such as a laser beam is used for the constant speed scanning operation, the illuminance is uniform over the image, and accordingly the resultant electrostatic latent image is high in S/N ratio. Thus, a steel plate can be marked off with uniformity.

Claims (13)

Claims

1. A marking-off device, comprising: light beam generating means; means for modulating said light beam; light beam deflecting means; light beam scan position detecting means; and means for causing the surface of a material to be marked-off to be scanned by a light beam from said light beam generating means in a manner so as to form a raster thereon.

2. A device as claimed in Claim 1, wherein said light beam deflecting means comprises: a rotary multi-mirror assembly for performing a onedimensional scan, said light beam scan position detecting means comprising a reading light beam generating source and a linear encoder.

3. A device as claimed in Claim 2, further comprising control means operating in response to an output of said light beam scan position detecting means, and means for conveying said material to be marked-off, the speed of said conveying means being controllable by said control means.

4. A device as claimed in Claim 3, wherein an output of said linear encoder is applied to counter means connected to a clock signal generating means, a drive unit for said conveying means being operable in response to an output of said signal generating means.

5. A device as claimed in Claim 4, wherein an output of said signal generating means is combined in a video signal generator with image data in the form of a raster, to produce a video signal to be applied to said modulator.

6. A device as claimed in Claim 3, 4 or 5, wherein said conveying means is arranged to transport said material to be marked-off in a direction perpendicular to said one-dimensional scanning direction, whereby the surface of said material is two-dimensionally scanned by said light beam in a manner so as to form a raster thereon.

7. A device as claimed in any of Claims 2 to 6, wherein said light beam generating means comprises a first laser beam source and said reading light beam generating source comprises a second laser beam source.

8. A device as claimed in Claim 7, which includes means whereby in use of the device said first laser beam is modulated with a video signal, and is passed through a first dichroic mirror.

9. A device as claimed in Claim 8, which is arranged so that in use said second laser beam is reflected by said dichroic mirror and combined with said first laser beam, prior to inpinging upon said rotary multi-mirror assembly.

10. A device as claimed in Claim 9, further including a second dichroic mirror passing said first beam to said material to be marked off, and reflecting said second beam to said linear encoder.

11. A device as claimed in any preceding claim, further comprising means for forming a layer of charged photo-conductive powder on the surface of said material to be marked-off, which layer is in use selectively exposed to light from said light beam generating means to form an image thereon, and means for removing said powder so exposed.

12. A marking-off device, substantially as hereinbefore described with reference to Figure 1 or Figures 1 and 2 of the accompanying drawings.

13. A method of marking the surface of a sheet of material, when carried out by means of a device as claimed in any preceding claim.