GB2033188A - Apparatus for automatically engraving mimeographic stencil papers - Google Patents

Abstract

In effecting two-colour printing from an original having black and coloured regions, by way of a mimeographic printing technique, apparatus for automatically engraving mimeographic stencil papers decomposes the black or other colours of the original independently into two colours and reads them out to engrave two stencil papers. The apparatus comprises two light- receiving elements 3,4 for reading the original via colour filters 1,2 having different spectral characteristics. The outputs of the two light-receiving elements are selectively connected via a switching arrangement 7,8 to a comparator circuit C which selects the colours to be engraved depending upon the outputs of the light-receiving elements 3,4. The single unit automatic engraving apparatus makes it possible to easily prepare the stencil papers for two-colour printing and to reduce the colour deviation when the original is set on the engraving apparatus. <IMAGE>

Description

SPECIFICATION Apparatus for automatically engraving mimeographic stencil papers The present invention relates to apparatus for automatically engraving mimeographic papers, by which an original is decomposed into two colours, which are read out, to engrave two types of stencil papers.

Conventional apparatus for automatically engraving a mimeographic stencil paper has been designed mainly for making a stencil paper for a single-colour mimeographic printing for use with originals which bears characters of black colour only. Recently, however, the popularized coloured printings have been making increased demands for the development of an automatic engraving machine which is capable of producing a variety of colours even in mimeographic printing.

The automatic engraving machi-nes which are now commercially available and which are capable of effecting multi-colour printing have a rotary colour filter plate in front of a light-receiving element which faces the original, so that the rotating filter plate decomposes the coloured original into three colours, i.e.

red, blue, and yellow, thereby to prepare stencil papers for each of these colours. Therefore, the conventional automatic engraving machines are considerably complex in construction, difficult to manipulate, and expensive.

Another method consists of providing two units of automatic engraving machines, attaching filters of dissimilar colours to the light-receiving elements of each of the engraving machines, and separating the displays of the original depending upon the colours to prepare stencil papers by the separate engraving machines. In this case, however, since the originals and stencil papers are wound on the drums of separate engraving machines, it is difficult to bring their positions into agreement, whereby deviation is developed when the original is set to engrave the stencil paper, thus making it difficult to obtain good coloured printings. Further, use of the two units of-automatic engraving machine involves considerable expense as well as clumsy operation for handling the engraving machines.

There has also been proposed a method of using a single unit of automatic engraving machine. In this case, however, filters of different colours must be used for engraving the displays of the original depending upon the colours. In other words, the colour filter attached to the light-receiving element must be replaced for each colour of the displays on the original, thus being a clumsy operation.

In particular, in effecting colour printing, it is greatly desired to develop an engraving machine which is suitable for simple printing of two colours such as black and red, which are often found in the leaves folded into the newspapers.

The present invention provides an improvement in an apparatus for automatically engraving mimeog raphic stencil papers including a drum for being wound with an original and stencil papers, a light-receiving portion for reading the contents disclosed in the original, and a recording portion for engraving the stencil papers. The improvement comprises two light-receiving elements having colour filters with different spectral characteristics, a comparator circuit for determining the output depending upon the magnitude of input voltages produced by said light-receiving elements, and a switching means which selectively connects the two outputs of said light-receiving elements to the two inputs of said comparator circuit, such that the contents of every colour disclosed in the original are engraved with being decomposed into two colours, e.g.

black and any other colour.

Thus the apparatus can separately read out the displayed contents of black colour and the displayed contents of any other colour of the original to engrave the respective stencil papers for each, so that engraving for colour printing can be easily performed and colour misalignment can be reduced or -eliminated.

The comparator circuit preferably comprises two transformers and two diodes to reliably discriminate the colours, so that the stencil papers can be easily engraved for each colour by way of a single engraving machine.

Preferably a light-receiving pprtion is provided with two light-receiving elements, this contributing to the simplification of the construction of the light-receiving portion, increase of the strength, simplification of manufacture, and reduction of the manufacturing cost A time-constant circuit is preferably provided on an input side of the comparator circuit such that the colours can be reliably elected.

The invention will be described further, by way of example with reference to the accompanying drawings, in which Figure-lisa diagram of a circuit forselecting colour signals in an automatic engraving apparatus according to a preferred embodiment of the present invention; Figure 2 is a front view of a light-receiving unit of the apparatus; Figure 3 is a vertical cross-sectional view showing the internal construction of the light-receiving unit; and Figure 4 is a diagram showing a selection circuit according to another embodiment.

Photodiodes 3 and 4 (serving as light-receiving elements) face an original (not shown) wound on a drum (not shown) of the engraving apparatus, to read out the displayed contents of the original. Colour filters 1 and 2 having different spectral characteristics are securedin front of the respective photodiodes 3, 4. The filters-1,2 may be those which are ayailable:in the market.

When the light L reflected by the original is incident uppn thk photodiodes 3 and 4, the output characteristics at the signal levels in the respective outputs 01,02 of the photodiodes 3,4forwhite (background) and for each of the colours black, red, and blue become approximately as tabulated in Table 1, owing to the colourfilters 1 and 2.

TABLE 1 Black White Red Blue Output 01 0 1 0.9 - I 0.7-0.8 Output 02 0 1 0.2-0.3 0.2-0.3 DC amplifiers 5 and 6, each containing an inverter, are connected to the respective outputs of the photodiodes 3 and 4, whereby the signals at the outputs 01 and 02 are reversed at the outputs P1,P2 and become as shown in Table 2.

TABLE 2 Black White Red Blue Output P1 1 0 0-0.1 0.2-0.3 Output P2 1 0 0.7-0.8 0.7-0.8 The signal levels for each of the colours shown in Table 2 have the following meanings. Namely, when the photodiode 3 reads black on the original, the output P1 produces a signal of a level close to "1" (high voltage} and when it reads white, red, or blue, the output P1 produces a signal of a level close toi "O" (low voltage}.

Similarly, when the photodiode 4 reads black, red, or blue on the original, the output P2 produces a signal of a level closeto "1" (high voltage) and when it reads white,theoutput P2 producesasignal of a levelcioseto "O" (lowvoltage).

Reference numerals 7 and 8 denote switches that will be manually operated and that are interlocked. A contact 7b of the switch 7 is connected to the output Pa of the DC amplifier 5, while contacts 7c and 7d are connected to the output P2 of the DC amplifier 6. Contacts 8b and 8d of the switch 8 are free terminals, and a contact 8c is connected to the output P1 of the DC amplifier 5.

An AC power supply 9 is connected to the primary side of a transformer 10. The secondary side of the transformer 10 is connected to the primary side of another transformer 11 via diodes 12 and 13. The secondary side of the transformer 11 is connected to a power amplifier 75 which produces output signals such that a discharge needle (not shown) will perform the engraving of a stencil paper depending upon the colours.

A comparator circuit C consisting of transformers rio, 1 T, and diodes Z,13 substantially selects the displays on the original to be engraved depending upon the magnitude of voltages at points Q1 and Q2.

These voltages are selectively obtained from the signals at the outputs Pt,P2 via a moving contact piece 7a of the switch 7 connected to the neutral point of a secondary winding of the transformer 10 and via a moving contact piece 8a of the switch 8 connected to a neutral point Q2 of a primary winding of the transformer 11.

The operation of the above-mentioned circuit is described below.

Let is be supposed that the original has a description in black and one other colour (on a white background). First, the switches 7,8 are set to the contacts 76,86. In this case, the display contents in black only of the original are read out and are engraved. The principle is described below.

When the lighfreceiving photodiodes 3,4 scanning the original face the black displays, voltages of the level close to "1" are produced at the output P1,P2 as will be obvious from Table 2. Here, the signal from the output P1 is applied to he point Ql only on the secondary side of the transformer 10 via the switch 7. Hence, the point Q1 acquires a high voltage as compared with the point Q2r whereby engraving signals are produced via the diodes 12,13, the transformer 11, and the power amplifier 15. Accordingly, the displays of black colour are engraved on a first stencil paper.

In this case, when the photodiodes 3 and 4 face displays of a colour other than black, the output PX acquires the level close to "0" and the output P2 acquiresthe level close to "1" as will be obvious from Table 2. In this case, however, the output P1 of the level "0" only is produced at the point Q1 on the secondary side of the transformer 10. Therefore, the engraving output is not produced by the power amplifier 15, and a display of a colour other than black is not engraved. When the photodiodes 3,4 face white areas (blank portions of the original), the engraving signals are not produced.

Subsequently, the switches 7,8 are set to the contacts 7c,8c. In this case, the displayed contents in a contour other than black are read out and engraved on a second stencil paper.

When the photodiodes 3,4 scanning the original face displays of a colour other than black, the output P1 acquires the level close to "0" and the output P2 acquires the level close to "1" according to Table 2. The voltage of the output P2 only is applied to the point Q1 on the secondary side of the transformer 70 via the switch 7, whereby the engraving signals are produced via the diodes 12,13, the transformer 11, and the power amplifier 15, so that the coloured displays are engraved.

When the photodiodes 3,4 face to the black displays on the original, the outputs P"P2 acquire the level close to "1" according to Table 2, whereby the output P1 is applied to the point Q2 on the primary side of the transformer 11 as a terminal voltage of a resistor 14 via the switch 8, and the output P2 is applied to the point Q1 on the secondary side of the transformer 10 via the switch 7. Therefore, voltages at the points Q1,Q2 become equal; no potential difference is produced, and the engraving signals are not pred. d. Namely, when the coloured displays are engraved, the black displays are not engraved. Further, when the Bphotodiodes 3,4 face white areas, the engraving signals are not produced.

If the switches 7,8 are set to the contacts 7d, 8d, engraving is effected like an ordinary single-colour engraving in which the displayed contents of whatever colour on the original are all engraved on a single stencil paper.

When the photodiodes 3,4 are faced to the displays of the original, the output P2 acquires a voltage of the level close to "1" irrespective of the colour of the display and is applied to the point Q1 on the secondary side of the transformer 10 via the contact 7d of the switch 7. The signal output P1 is always cut off by the switch 8, and is not applied to the point Q2 on the primary side of the transformer 11. Consequently, the displays of the original are engraved on the same stencil paper irrespective of their colour.

As mentioned above, by attaching the colour filters 1,2 having different spectral characteristics to the two photodiodes 3,4, it is possible to completely separate black displays and displays of a colour other than black of the original, thereby to separately engrave them on the stencil papers using a single unit of automatic engraving apparatus. By manipulating the switches 7,8, the engraving can be very simply performed from the same original wound on the drum.

The light-receiving unit equipped with the colour filters 1,2, and the photodiodes 3,4 (light-receiving elements) is shown in Figures 2 and 3, wherein Figure 2 is a front view and Figure 3 is a vertical cross-sectional view.

A cylindrical case 20 made of a synthetic resin is formed as a unitary structure, and in it are arrayed two sets of filters and photodiodes in parallel with each other between a light incident port 21 and a port 22 at the opposite end of the case 20. The filters 1,2 and photodiodes 3,4 may simply be fitted into the case 20 to assemble the light-receiving unit. The output terminals 3a,4a of the photodiodes 3,4 are connected to lead wires 23, 24 which extend through the port 22. The case is sealed with a solidifying agent 25, such as an adhesive, in order to protect the output terminals 3a, 4a from damage.

When the light-receiving unit is viewed from the front, the relation in positions of the photodiodes 3,4 is orientated in the upper and lower directions on a vertical line as shown in Figure 2; the photodiodes are separated by a distance W of about 6 mm. By employing the two-input system for the light-receiving unit, the displays can be separately engraved as explained in the foregoing. Besides, the light-receiving unit can be formed very compactly.

Figure 4 shows a colour selection circuit according to another embodiment of the present invention, in which the same parts as those of the circuit of Figure 1 are denoted by the same reference numerals.

According to this circuit, a time-constant circuit consisting of a diode 40 and a capacitor 41 is inserted in a line connecting the output P1 and the contact 8c of the switch 8 of Figure 1. With this circuit, it is possible to completely prevent the engraving of black displays when the displays of a colour other than black are being engraved. With the circuit shown in Figure 1, when the photodiode 3 faces a colour other than black and the photodiode 4 faces black, the output P1 acquired the level "0", and the output P2 instantaneously acquires the level "1", such that the black displays are slightly engraved. According to the circuit shown in Figure 4, on the other hand, the output P1 is maintained at the level close to "1 " for a predetermined period of time, utilizing the charging-discharging function of the capacitor 41, thereby to prevent the black displays from being engraved. Thus, it is made possible to engrave the black displays and the displays of a colour other than black in a completely separate manner from the same original wound on the drum. Consequently, it is possible to prepare the stencil papers for effecting vivid two-colour printing.

Claims (6)

1. Apparatus for automatically engraving mimeographic stencil papers, including a drum for being wound with an original and stencil papers, a light-receiverfor reading the original, and a recorder for engraving the stencil papers, the light-receiver comprising two light-receiving elements having colour filters with different spectral characteristics, a comparator whose output depends upon the magnitude of input signals applied to two inputs of the comparator, and a switching means which selectively connects the outputs of the two light-receiving elements to the two inputs of the comparator, such that the original is decomposed into two colours engraved separately by the recorder.

2. Apparatus as claimed in claim 1, wherein the comparator includes two transformers and two diodes.

3. Apparatus as claimed in claim 1 or 2, wherein the two light-receiving elements are arranged in parallel with each other in a single light-receiving unit.

4. Apparatus as claimed in any of claims 1 to 3, wherein a time-constant circuit is provided on an input side of the comparator.

5. Apparatus as claimed in any of claims 1 to 4, in which the original is decomposed into black and another colour.

6. Apparatus for automatically engraving mimeographic stencil papers, substantially as described with reference to, and as shown in, Figures 1 to 3 or Figure 4 of the accompanying drawings.