GB2153617A

GB2153617A - Enlarging multicolour printing apparatus

Info

Publication number: GB2153617A
Application number: GB08310582A
Authority: GB
Inventors: Paul Fuller
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-04-19
Filing date: 1983-04-19
Publication date: 1985-08-21
Also published as: GB8310582D0; AU2660784A

Abstract

Apparatus for producing an enlarged colour copy of an original mounted on flat bed scanner (fig. 2) includes a drum 1 on which the medium to be printed, eg. a carpet is mounted, and a spray-head assembly 6 on which colours and one for black are mounted 10 four air brushes 6', three for the primary so as to be focused on a single spot. The spray-head assembly is mounted for movement parallel to the axis of the drum along tie bars 7 by means of a locked bowden cable 24 driven by motor 20. Signals produced by scanning the original are stored in a memory, and are caused to operate the air brushes in synchronism with rotation of the drum by shaft encoder 3. <IMAGE>

Description

SPECIFICATION Enlarged multicolour printing apparatus The present invention concerns enlarged multicolour printing apparatus for producing substantially enlarged copies of multi-colour originals.

Apparatus of this kind is already well known. An early example of multi-colour printing apparatus can be found in the specification of US PAtent No.

1,709,926 and a more recent example is British Patent No.1,166,005. As can be seen from these prior patents the known apparatus basically comprises a drum on which the colour original is mounted. The original is then scanned by a beam of light and the light reflected from the original broken down into the three primary colours to generate electrical signals which are used to control the feed of primary colour pigments onto a suitable print medium also mounted on a drum.

The present invention has for an object to provide apparatus of this basic type which is relatively simple to manufacture and yet robust and reliable in operation.

Accordingly the present invention consists in enlarged multi-colour printing apparatus comprising electro-optical scanning means for scanning an original to be printed in enlarged form, the scanning means including a flat bed on which the original is mounted, a light source for illuminating the original with light of known spectral composition, and an electro-optical scanning head for receiving light transmitted through the original to derive electrical signals which represent the intensities of the three primary colours in the light so received and also a signal representative of black in the original, and memory means for storing the signals so generated, the apparatus further including a printing unit comprising a drum on which the medium to be printed on is mounted, means for rotating the drum relative to a printing head carrying four air brushes, one for each of the three primary colours and one for black, means for scanning said printing head in a direction parallel to the axis of rotation of said drum, said scanning means comprising a locked bowden cable drive driven by an electric motor, means for controlling the operation of the air brushes in response to the stored signals and in response to a shaft encoder resposive to the angular position of said drum.

In order that the present invention may be more readily understood an embodiment there of will now be described by way of example and with reference to the accompanying drawings, in which; Figure 1 is a diagrammatic plan view of enlarged multi-colour printing apparatus, and Figure 2 is a perspective diagrammatic view of a scanning assembly forming part of the apparatus of Figure 1.

Referring now to the drawings the multicolour printing apparatus shown therein includes a printing assembly comprising a print drum 1 formed in three sections A, B and C coaxially mounted on a single shaft S. Each section is four feet in length and five feet in diameter. The drum is intended to receive a print medium, for example a carpet, so that a coloured picture on an original can be transferred onto it. Secured to the shaft S is a fail safe electro-mechanical brake 2 and a shaft encoder 3.

In operation the shaft S is rotated by an electric motor and reduction gearbox unit. This combined unit is shown at 10 and is coupled to the shaft S by a V-belt drive 9 and an electromagnetic clutch 8.

In normal operation the drum 1 is rotated at 25 RPM. Mounted to one side of the drum 1 is a sprayhead assembly 6 which carries four air brushes 6', one for each of the primary colours and one for black. The air brushes are connected to a supply of compressed air shown at 50 whilst reservoirs of appropriately coloured inks are shown at 51. It will be appreciated that to obtain the necessary gradations of colour that the supply of compressed air to each brush will have to be varied so that each supply line 52 to the air brushes includes a variable valve 53 controlled by the process electronics of the apparatus. Furthermore in known fashion each airbrush has a servocontrolled needle which determines the final flow aperture of the brush.

The sprayhead assembly 6 is mounted for sliding movement along two precision ground tie bars 7 which are exactly parallel to shaft S. In operation the sprayhead 6 is moved along the tie bars 7 by a locked bowden cable arrangement which includes a drum 4 driven by a motor 20 through a clutch 21.

A helically wound cable 22 on drum 4 rotates a shaft 23 which in turn advances or withdraws a further cable 24 connected to the sprayhead 6. If desired one bowden cable assembly of the kind just described can be used to advance the sprayhead 6 along the tie bars 7 and a second, similar assembly to move the sprayhead in the return direction.

As can be seen in Figure 1 the four air brushes 6' are focussed on a single spot on the printing medium so that there is ne need to introduce an artificial delay into the control signals for the air brushes to compensate for them being staggered.

The control signals for the operation of the printing assembly are provided by a control console 11 on which is mounted a flat bed scanner 12. The console 11 is totally separate from the printing assembly and houses all the process electronics for the entire apparatus.

The console 11 incorporates a light box 30 over which the scanner 12 is, in operation of the apparatus, mounted. The scanner 12 is shown in greater detail in Figure 2 and comprises a translucent base 31 on which any original to be scanned is laid. The scanner 12 also includes a light-sensing head 32 which receives light from the light box 30 transmitted through the original. The light so received is split by dichroic filters into the three primary colours R, G and B which are detected in appropriate photosensors to generate three colour control signals. This arrangement is generally indicated at 33 which also provides a black signal.

The scanning head 32 is mounted on a cross member 34 which can be moved along tie bars 35 by a bowden cable arrangement similar to, but smaller than the arrangement used to drive the sprayhead 6. This enables the sensing head 32 to be scanned in the X direction over the original and the drive motor for the bowden cable drive is associated with a shaft encoder 36 so that the output signals from the sensing head can be digitised for storage in a memory 37 for subsequent use in controlling the air brushes and the movement of drum 1 and the sprayhead 6.

For movement in the Y direction the sensing head 32 is mounted on a nut so that it can be advanced along the cross member 34 by a lead screw driven by an electric motor 38. The sensing head 32 is moved incrementally by this means in the Y direction after each complete scan in the X direction.

The shaft encoder 2, which gives the angular position of the drum 1, is used to ensure correct synchronisation of the control signals to the air brushes 6'.

Claims

1. Enlarged multi-colour printing apparatus comprising opto-electrical scanning means for scanning an original to be printed in enlarged form, the scanning means including a flat bed on which the original is mounted, a light source for illuminating the original with light of known spectral composition, and an opto-electrical scanning head for receiving light modified by the original to derive electrical signals which represent the intensities of the three primary colours in the light so received and also a signal representative of black in the original, and memory means for storing the signals so generated, the apparatus further including a printing unit comprising a drum on which the medium to be printed on is mounted, means for rotating the drum relative to a printing or spraying head carrying four air brushes, one for each of the three primary colours and one for black, means for scanning said spraying head in a direction parallel to the axis of rotation of said drum, said scanning means comprising a locked bowden cable drive driven by an electric motor, and means for controlling the operation of the air brushes in response to the stored signals and in response to a shaft encoder responsive to the angular position of the drum.

2. Apparatus as claimed in claim 1, wherein the air brushes are focussed on a single spot of the printing medium in operation of the apparatus, and have associated therewith a source of compressed air, control valves being provided so that the supply of compressed air to each air brush can be varied in accordance with the intensity of the pigment to be printed.

3. Apparatus as claimed in either claim 1 or claim 2, wherein the sensing head of the scanning means is mounted on a cross member which can be scanned in one direction over an original by a bowden cable arrangement driven by an electric motor, the motor being associated with a shaft encoder thereby to digitise the output signals form the sensing head so that they can be stored in said memory means.

4. Apparatus as claimed in claim 3, wherein the sensing head is movable along said cross member by means of a iead screw and nut.

5. Apparatus as claimed in any one of the preceding claims wherein the drum is driven in operation by an electric motor driving a reduction gearbox the output of which is coupled to the shaft of the drum by a V-belt drive.

6. Apparatus as claimed in any one of claims 3 to 5, wherein said memory means are operative to store at least two lines of an original as scanned by said sensing head, and wherein said drum has a shaft encoder associated therewith whereby data stored in said memory means can be read from said memory means under the control of pulses generated by the drum encoder.

7. Apparatus as claimed in claim 6, wherein said scanning means are arranged to operate at a faster rate than said printing unit whereby said memory means always contains data for read out to the printing unit.

8. Apparatus as claimed in claim 7 wherein said scanning unit always scans an original in one direction only and wherein said drum is continually rotated in operation.

9. Apparatus as claimed in claim 8, wherein in operation of the apparatus the spraying head is continually advanced relative to the drum whereby the air brushes describe a heiix with respect to the drum surface.