WO2009098494A2

WO2009098494A2 - Improvements in or relating to continuous inkjet printers

Info

Publication number: WO2009098494A2
Application number: PCT/GB2009/000365
Authority: WO
Inventors: Jonathan Morgan
Original assignee: Domino Printing Sciences Plc
Priority date: 2008-02-08
Filing date: 2009-02-06
Publication date: 2009-08-13
Also published as: GB2484589B; GB0802349D0; GB2470156B; GB201014862D0; WO2009098494A3; GB2484589A; GB2470156A; GB201117546D0

Abstract

The invention describes a continuous inkjet printer having a print head which is detachably mounted to an umbilical. The umbilical and print head are configured to separate out the electrical connections from the fluids connections to ensure fluids cannot inadvertently come into contact with the electrical connections during mounting and de-mounting of the print head.

Description

IMPROVEMENTS IN OR RELA TING TO CONTINUOUS INKJET PRINTERS

Field of the Invention

This invention relates to continuous inkjet (CIJ) printers and, more particularly, to a print head for a CIJ printer and the connection of that print head to the printer processing unit.

Background to the Invention

Continuous inkjet printing involves the formation of electrically charged drops from a jet of ink, and the subsequent deflection of the charged drops by an electric field to produce an image on a print medium. In a typical embodiment of a single jet printer of this type, electrically conducting ink is forced through a nozzle by applying pressure to the ink. A controlled sequence of drops, each with identical drop volumes and with constant separation between adjacent drops, can be formed by modulating the jet to give active and controlled drive to the natural process of jet break up. This is usually achieved by modulating the ink pressure in a sinusoidal way at fixed frequency and amplitude, or by modulating the ink velocity relative to the nozzle. A range of options and techniques to introduce pressure modulation, velocity modulation or a combination of both so that uniform drop sequences are obtained, are known to those skilled in the art.

Charge is induced on individual drops through capacitive coupling. Desired levels of charge are induced on drops by applying a voltage to the electrodes at the time the drop separates from the jet. The desired levels of charge are highly dependent on the size of the droplet, and hence the size of the nozzle and the operating frequency of the printing head. Modulating the voltages at the same frequency as the jet guarantees that the correct level of charge is present on the drops, although care must be taken to time the modulated charge pulses so that they have a fixed relationship with the time that the droplet breaks from the ink stream.

After charging, drops travel through a constant electric field arranged so that it is perpendicular to the jet. Charged drops are deflected by an amount that approximately scales with the charge on the drops. Unused drops are collected by a gutter for ink re-flow and re-use.

The ink jet print head comprises a unit which includes a droplet generator, a charge electrode, a phase detection sensing electrode, a deflection field

(formed by spaced charged and earth plates), and a gutter or catcher to collect non-printing drops. The print head is positioned over or adjacent to a moving line on which items to be marked are transported past the print head. The print head is connected to a printing machine or processor by an umbilical which envelops individual lines for ink supply and recirculation; and electrical lines - both high voltage supply for the creation of the charge and deflection fields, and lower voltage for passing various electrical and electronic signals between the print head and the printing machine. The printing machine includes an ink supply system and electronics for controlling the creation and correct placement of individual ink drops on the substrates to be marked.

The sensitivity of print heads to their installation, operating environment, and ink characteristics means that, traditionally, skilled service technicians have been required to install and set-up print heads. However, there is a growing demand for replaceable print heads which can be installed by plant operators.

UK Patent 2 250 235 describes a continuous inkjet printer having a replaceable print head. However the print head is supplied fixed to the conduit or umbilical. Individual fluid and electronic lines must be plumbed into the printing machine and thus this arrangement requires a significant level of skill. Further, once connected, data characterising the print head must be passed to the printer processor. This is a task not normally left to unskilled personnel.

European Patent 1 497 134 describes a form of CIJ print head which can be readily detached from, and attached to, the umbilical but in this arrangement, both electrical and fluids connections are arranged on the same faces. This means that an unskilled plant operator could mis-align the inks and electrical connections during assembly. Whilst the geometry does not allow a connection to be made, there is a significant possibility that some ink could find its way into contact with the electrical connections. Given the volatile and corrosive nature of some of the inks used, this is undesirable at least, and in extreme circumstances could be dangerous.

UK 2 250 235, referred to above, also discloses a method of characterising a particular print head for subsequent matching to a printing machine processor. At manufacture each print head is test-operated with ink controlled to have a chosen calibration viscosity within the operating range of the ink droplet generator. The operating parameters of the print head are varied to determine the values which provide the best print quality and these values are recorded to provide for each print head an individual calibration code. As described in the patent, the code may be a 14-digit number and this number is entered into the printer operating processor each time a new print head is mounted. This calibration number may be entered manually, in which event an opportunity for error arises, or may be recorded and transferred electronically.

It is an object of this invention to provide apparatus and/or methods which go at least some way to addressing the problems described above; or which will at least provide a novel and useful alternative.

Summary of the Invention

Accordingly, in one aspect, the invention provides a continuous inkjet printer having a print head; a print processor; and an umbilical connecting said print head to said print processor, said umbilical enveloping a plurality of fluids conductors and a plurality of electrical conductors, said umbilical and said print head being configured in a complimentary manner such that a plurality of electrical connections between said umbilical and said print head can be established in a first single action and a plurality of fluids connections between said umbilical and said print head can be established in a second single action, said printer being characterised in that said first action differs from said second action.

Preferably said umbilical and said print head are configured so that said second action cannot be effected until completion of said first action. Still further, said umbilical and said print head are preferably configured so that said first action cannot be reversed until after reversal of said second action.

Preferably said print head is brought into contact with said umbilical along a connection axis, said first action being effected along said connection axis and said second action being effected in a direction substantially perpendicular to said connection axis.

Preferably the electrical connections between said umbilical and said print head are included in a socket provided in said umbilical and a complimentary spigot provided on said print head, said printer further including a seal configured to engage with, and seal between, said socket and said spigot on completion of said first action.

In a second aspect the invention provides a detachable print head for incorporation in a continuous inkjet printer as set forth above.

In a third aspect the invention provides a method of configuring a continuous inkjet printer having a print head and a printer operating processor, said method being characterised in that it includes programming said printer operating processor to derive a nozzle size and printing head geometry from said print head upon connection of said print head to said printer operating processor and to set printer operating parameters accordingly.

Preferably said method involves the use of binary logic.

Many variations in the way the present invention can be performed will present themselves to those skilled in the art. The description which follows is intended as an illustration only of one means of performing the invention and the lack of description of variants or equivalents should not be regarded as limiting. Wherever possible, a description of a specific element should be deemed to include any and all equivalents thereof whether in existence now or in the future.

Brief Description of the Drawings

The various aspects of the invention will now be described with reference to the accompanying drawings in which:

Figure 1 : Shows an exploded isometric view of a CIJ umbilical and print head connection embodying the invention; Figure 2: shows an end view of the umbilical part of the connection shown in Figure 1 ;

Figure 3 : shows an end view of the print head part of the connection shown in Figure 1 ; and

Figure 4: shows a schematic illustrating possible alternative connections which allow the printer to automatically configure to the print head.

Detailed Description of Working Embodiment

The invention provides a method of, and apparatus for, connecting the print head of a continuous inkjet (CIJ) printer, to the printer operating unit, by means of an umbilical.

Referring to Figure 1, a print head 5 is joined to umbilical 6 by a connection provided in part on the print head and in part on the umbilical. The connection, which will be described in greater detail below, allows the print head unit to be readily detached from the umbilical, and replaced. As will be apparent from the description which follows, the exercise of detaching and replacing can be undertaken safely and reliably by non-skilled persons and thus provides a significant advantage over prior art arrangements.

In the form shown the print head unit 5 comprises a droplet generator 8, charge electrode 9, deflection plates 10 and gutter 1 l.The overall arrangement of the print head does not form part of the invention though the form of droplet generator described in our pending International Patent Application WO 2006/030018 is ideal for use in the application of the invention. Similarly the precise form of umbilical 6 may is not critical though it is convenient to use a form of umbilical as described in our published British Patent Application No. GB 2 435 447.

As known in the art, and described in GB 2 435 447, the umbilical 6 envelops a number of electrical and fluids conductors or lines. As shown in Figure 2, the electrical conductors of the umbilical are arranged together in a set which terminates at end face 15. End face 15 includes one half 16 of a 30-pin connector and also includes a socket 17 for a high voltage connector. Also mounted on the end face 15, on the opposite side of the connector half 16 to the high voltage socket 17, is a further socket 18 to receive an alignment pin projecting from the mating face of print head 5.

It will be noted from Figure 1 that the electrical connections on end face 15 are surrounded by a collar 20, the collar 20 and the face 15 defining a somewhat larger socket which is configured to receive a spigot 21 extending from the rear of the print head unit 5. A seal, preferably in the form of an O- ring 22, is provided about the spigot 21 so that, when the print head unit 5 is fully engaged with the umbilical 6, the O-ring 22 seals against the inner surface of collar 20 and thus seals the electrical connections against contact with any environmental contaminants and fluids, particularly ink and make-up fluid.

The rear edge of the print head 5, and more particularly of the spigot 21, includes a face 25 configured to engage with the face 15 on the umbilical, the face 25 having connections which compliment the connections on face 15 of the umbilical. It will be noted that the faces 15 and 25 are substantially perpendicular to a connection axis 26 along which the print head is brought into engagement with the umbilical. Referring now to Figure 3, the face 25 includes half 27 of 30-ping connector which compliments and connects to connector half 16 on face 15. The face 25 also includes high voltage pin 28 and alignment pin 29.

An important feature of the invention is the separation of electrical and fluids connections. Whilst the fluids lines and the electrical lines are both contained within umbilical 6, the fluids lines do not exit through end face 15 but, instead, exit through end face 30 of the collar 20. Thus, when the print head 5 is engaged with the umbilical 6, any fluids seeping from the fluids connection cannot come into contact with the electrical connections.

In the form shown, ink, make-up and flush lines 31, 32 and 33 from the umbilical extend outwardly beyond the collar 20 and are terminated at a manifold 35. The manifold includes spigots configured to engaged in sockets 36 provided on the upper side of the droplet generator 8.

Also projecting from end face 30 of collar 20 are a gutter pipe 38 and a positive air pressure pipe 39, the latter serving to provide positive air pressure around the print head 5 when holster 40 is positioned over the print head. This helps avoid contamination of the print head in dusty environments. In addition, the pressure pipe 39 can pass dry air about the print head in humid environments. The gutter pipe 38 can be a simple push-fit with the gutter 7 as this connection is maintained under vacuum when the printer is operating.

It will be understood that, to assemble the print head 5 on to the umbilical 6, the spigot 21 , a first action is undertaken to effect connection of the electrical conductors. The first action is, essentially, displacement of the print head relative to the umbilical along connection axis 26. At completion of the first action the electrical connections are fully engaged and a seal is established, by O-ring 22, between the collar and the spigot. Completion of the first action allows the fluid conductors to be connected in a second action, namely displacement of manifold 35 into engagement with the droplet generator 8 in a direction substantially perpendicular to the connection axis 26.

The print head has been designed so that, when it is attached to the printing processor, the processor can determine the type of head present, and set the printer operating parameters automatically. This is in contrast to prior art arrangements, such as GB 2 250 235 which require data characterising each particular print head to be transferred to the printing processor.

The print head uses binary logic to determine print head geometry and nozzle size. In this context print head geometry means a long print head or a short print head. As is well known in the aft, for a given nozzle pressure, smaller drops (emanating from smaller nozzles) travel a lesser distance. Thus print heads fitted with smaller nozzles are positioned, and/or are fitted with shorter deflector plates, to ensure that acceptable print quality is achieved.

Although each nozzle size performs optimally with a specific drive frequency and attendant geometry, for practical purposes a range of frequencies and nozzle sizes can be accommodated, particularly when using a non-resonant droplet generator of the type shown in our published International Patent Application No. WO 2006/030018, the droplet generator including a nozzle manufactured in accordance with our published International Patent Application No. WO 2005/069943. A droplet generator so configured performs to an acceptable level with a wide range of inks over a wide range of frequencies. The only physical difference between print heads is the nozzle size. By way of example, a limited number of print head variants can be established as follows:

Nozzle Size Head Geometry Available Frequencies

75μm Long 64kHz 60μm Long 64kHz or 84kHz

50μm Short 84kHz or 12OkHz

40μm Short 12OkHz

Referring now to Figure 4, at assembly the physical print head electronics and drop generator electronics are connected so that intelligence within the printer can deduce geometry (Long or Short) and nozzle size. Once a connection is made between the print head and the print processor, the print processor is programmed to determine the active connections and to set the necessary operating parameters.

As can be seen in the drawings, the intelligence within the printer, in this case in the form of a field programmable gate array (FGPA) is connected to the print head and to the droplet generator by single wires. Pull-up resistors A determine the presence or absence of a link, a low voltage indicating the presence of the link whilst a high voltage indicates the absence of a link.

Within the print head and the drop generator there are two possible states B and C indicating long/short and nozzle size respectively. These can be effected by hard wiring or by configuring the electronics of the print head and drop generator so that the alternative states can be recognized by the FGPA.

Where there is a choice of operating frequencies, the printer is preferably programmed to adopt the lower frequency but will, on the user interface, allow a user to over-ride the default setting or otherwise to select the desired frequency (high or low).

With the nozzle size and head geometries being known, when these are combined with the simple variant of operating frequency, the necessary operating parameters for the printer including start and operating pressures, start/stop sequences and the like, can be readily determined, automatically, by the printer accessing a look-up table. It will be appreciated that this considerably simplifies the printer electronics as well as minimising the opportunity for operator error.

It will thus be appreciated that the invention, at least in the case of the embodiment thereof described herein, has the advantage that alternative print heads can be mounted safely on to the umbilical without fluids coming into contact with electrical connections, and the printer can automatically determine suitable operating parameters without the need for variable data to be transferred from the print head.

Claims

1. A continuous inkjet printer having a print head; a print processor; and an umbilical connecting said print head to said print processor, said umbilical enveloping a plurality of fluids conductors and a plurality of electrical conductors, said umbilical and said print head being configured in a complimentary manner such that a plurality of electrical connections between said umbilical and said print head can be established in a first single action and a plurality of fluids connections between said umbilical and said print head can be established in a second single action, said printer being characterised in that said first action differs from said second action.

2. A printer as claimed in claim 1 wherein said umbilical and said print head are configured so that said second action cannot be effected until completion of said first action.

3. A printer as claimed in claim 1 or claim 2 wherein said umbilical and said print head are configured so that said first action cannot be reversed until after reversal of said second action.

4. A printer as claimed in any one of claims 1 to 3 wherein said print head is brought into contact with said umbilical along a connection axis, said first action being effected along said connection axis and said second action being effected in a direction substantially perpendicular to said connection axis.

5. A printer as claimed in any one of claims 1 to 4 wherein the electrical connections between said umbilical and said print head are included in a socket provided in said umbilical and a complimentary spigot provided on said print head, said printer further including a seal configured to engage with, and seal between, said socket and said spigot on completion of said first action.

6. A detachable print head for incorporation in a continuous inkjet printer as claimed in any one of claims 1 to 5.

7. A method of configuring a continuous inkjet printer having a print head and a printer operating processor, said method being characterised in that it includes programming said printer operating processor to derive a nozzle size and printing head geometry from said print head upon connection of said print head to said printer operating processor.

8. A method as claimed in claim 7 involving the use of binary logic.