Patent Publication Number: US-8523334-B2

Title: Ink supply system

Description:
RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. §371 from PCT Application No. PCT/US2008/079503, filed in English on Oct. 10, 2008, which claims the benefit of: Great Britain Application Serial No. 0720135.3 filed on Oct. 12, 2007, Great Britain Application Serial No. 0720051.2 filed on Oct. 15, 2007, and U.S. Application Ser. No. 61/081,283, filed on Jul. 16, 2008, the disclosures of all of which are incorporated by reference herein in their entireties. 
    
    
     The present invention relates to ink jet printing and more particularly to an ink supply system for an ink jet printer such as a continuous ink jet printer. 
     BACKGROUND 
     In ink jet printing systems the print is made up of individual droplets of ink generated at a nozzle and propelled towards a substrate. There are two principal systems: drop on demand where ink droplets for printing are generated as and when required; and continuous ink jet printing in which droplets are continuously produced and only selected ones are directed towards the substrate, the others being recirculated to an ink supply. 
     Continuous ink jet printers supply pressurised ink to a print head drop generator where a continuous stream of ink emanating from a nozzle is broken up into individual regular drops by, for example, an oscillating piezoelectric element. The drops are directed past a charge electrode where they are selectively and separately given a predetermined charge before passing through a transverse electric field provided across a pair of deflection plates. Each charged drop is deflected by the field by an amount that is dependent on its charge magnitude before impinging on the substrate whereas the uncharged drops proceed without deflection and are collected at a gutter from where they are recirculated to the ink supply for reuse. The charged drops bypass the gutter and hit the substrate at a position determined by the charge on the drop and the position of the substrate relative to the print head. Typically the substrate is moved relative to the print head in one direction and the drops are deflected in a direction generally perpendicular thereto, although the deflection plates may be oriented at an inclination to the perpendicular to compensate for the speed of the substrate (the movement of the substrate relative to the print head between drops arriving means that a line of drops would otherwise not quite extend perpendicularly to the direction of movement of the substrate). 
     In continuous ink jet printing a character is printed from a matrix comprising a regular array of potential drop positions. Each matrix comprises a plurality of columns (strokes), each being defined by a line comprising a plurality of potential drop positions (e.g. seven) determined by the charge applied to the drops. Thus each usable drop is charged according to its intended position in the stroke. If a particular drop is not to be used then the drop is not charged and it is captured at the gutter for recirculation. This cycle repeats for all strokes in a matrix and then starts again for the next character matrix. 
     Ink is delivered under pressure to the print head by an ink supply system that is generally housed within a sealed compartment of a cabinet that includes a separate compartment for control circuitry and a user interface panel. The system includes a main pump that draws the ink from a reservoir or tank via a filter and delivers it under pressure to the print head. As ink is consumed the reservoir is refilled as necessary from a replaceable ink cartridge that is releasably connected to the reservoir by a supply conduit. The ink is fed from the reservoir via a flexible delivery conduit to the print head. The unused ink drops captured by the gutter are recirculated to the reservoir via a return conduit by a pump. The flow of ink in each of the conduits is generally controlled by solenoid valves and/or other like components. 
     As the ink circulates through the system, there is a tendency for it to thicken as a result of solvent evaporation, particularly in relation to the recirculated ink that has been exposed to air in its passage between the nozzle and the gutter. In order to compensate for this, “make-up” solvent is added to the ink as required from a replaceable ink cartridge so as to maintain the ink viscosity within desired limits. This solvent may also be used for flushing components of the print head, such as the nozzle and the gutter, in a cleaning cycle. It will be appreciated that circulation of the solvent requires further fluid conduits and therefore that the ink supply system as a whole comprises a significant number of conduits connected between different components of the ink supply system. The many connections between the components and the conduits all represent a potential source of leakage and loss of pressure. Given that continuous ink jet printers are typically used on production lines for long uninterrupted periods reliability is an important issue. Moreover, the presence of multiple conduits in the interior of the ink supply section of the cabinet makes access to certain components difficult in the event of servicing or repair. 
     BRIEF SUMMARY OF THE INVENTION 
     A feature of the present invention, amongst others, to provide for an improved or an alternative ink jet printer and/or an alternative or improved ink supply system for an ink jet printer. 
     According to a first aspect of the present invention there is provided an ink supply system for an ink jet printer, the system comprising: an ink circuit comprising a plurality of circuit components and fluid paths for conveying fluid between components; an ink reservoir for containing ink; and a manifold defining the fluid paths and supported over the reservoir, the manifold having a plurality of ports in fluid communication with the fluid paths and the circuit components being adjacent to the manifold and connected thereto at the ports. 
     With the manifold being disposed over the reservoir and the component being adjacent to the manifold the invention provides for a compact arrangement that is relatively easy to assemble, service and repair. It eliminates many separate conduits or pipes between components. It is to be understood that the ink circuit may comprise further components that are not connected to the ports. 
     The components are preferably supported on the manifold but could be supported by another means, such as for example the reservoir, whilst still being adjacent to the manifold and connected to the ports. They may be connected directly to the ports. 
     The manifold may be supported on the ink reservoir, preferably a wall of the reservoir. The reservoir may have a base wall and at least one side wall upstanding from the base wall, the at least one side wall having a free end distal from the base wall, the manifold being supported the free end. The manifold may have a flange by which it is supported on the wall or walls. Fixings may connect the flange to at least one of the walls. 
     The at least one side wall of the reservoir may define an open mouth, the manifold being at least partially disposed in the mouth. The manifold may close the mouth in the manner of a lid or cover. A seal may be provided between the reservoir and the manifold. 
     The manifold may have a lower surface facing the reservoir and an opposite upper surface. At least one of the plurality of components may be connected to the lower surface and is disposed in the reservoir. At least one of the plurality of components may be an ink filter assembly which may depend into the reservoir. 
     At least one of the plurality of components may be connected to the upper surface. 
     At least one of the plurality of components connected to the upper surface may be a pump for pumping ink around the circuit. 
     At least one of the ports may have a spigot for connection to a component. The spigot may be received in an inlet or outlet aperture of the component. 
     The manifold may comprise first and second members connected together at interfacing first surfaces. The first and second members may be plate-like. The second member may be disposed in the reservoir. 
     At least one replaceable container of ink and/or solvent may be connected to the manifold or the reservoir. 
     The plurality of components may comprise fluid handling devices and/or transducers for sensing characteristics of the ink. 
     A specific embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic representation of an embodiment of a continuous ink jet printer of the present invention. 
         FIG. 2A  is an exploded perspective view from above of part of the ink supply system of  FIG. 1 . 
         FIG. 2B  is a further exploded perspective view of part of the ink supply system of the printer of  FIG. 1 . 
         FIG. 2C  is a perspective view from below of the ink supply system of  FIGS. 1 ,  2 A and  2 B in a partially assembled condition. 
         FIG. 3A  is a plan view of an upper surface of a feed plate of the ink supply system of  FIGS. 2A and 2B . 
         FIG. 3B  is a plan view of a lower surface of the feed plate of  FIG. 3A , with components removed for clarity. 
         FIG. 3C  is a side view of the feed plate in the direction of arrow A of  FIG. 3B . 
         FIG. 4A  is a plan view of a lower surface of a manifold plate of the ink supply system of  FIGS. 2A and 2B . 
         FIG. 4B  is a plan view of an upper surface of the manifold plate of  FIG. 4A  when fitted with components. 
         FIG. 4C  is a side view of the manifold plate in the direction of arrow A of  FIG. 4B , with components removed for clarity, the feed plate being shown in dotted line and an ink level sensor guard being shown in section. 
         FIG. 5A  is a partially sectioned side view of part of the ink supply system of  FIGS. 1 ,  2 A and  2 B. 
         FIG. 5B  is an enlarged view of the encircled part labelled X in  FIG. 5A . 
         FIGS. 6A and 6B  are end views of part of a filter module of the ink supply system. 
         FIGS. 7A to 7D  are respective perspective, side, side sectioned (along line B-B of  FIG. 7D ) and underneath plan views of the guard of  FIG. 4C . 
         FIG. 8  is an exploded side view of the arrangement shown in  FIG. 2A , a mixer tank of the supply system being shown in partial section; 
         FIG. 9  is a plan view of the mixer tank of  FIG. 8 ; and 
         FIG. 10  is a perspective view from underneath of the mixer tank of  FIG. 9 . 
         FIG. 11  is a rear view of an embodiment of a module. 
         FIG. 12  is a side view of a portion of a manifold of the module of  FIG. 11 . 
         FIG. 13  is a perspective view of an embodiment of a connector for an ink jet printer. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to  FIG. 1  of the drawings, ink is delivered under pressure from an ink supply system  10  to a print head  11  and back via flexible tubes which are bundled together with other fluid tubes and electrical wires (not shown) into what is referred to in the art as an “umbilical” conduit  12 . The ink supply system  10  is located in a cabinet  13  which is typically table mounted and the print head  11  is disposed outside of the cabinet. In operation, ink is drawn from a reservoir of ink  14  in a mixer tank  15  by a system pump  16 , the tank  15  being topped up as necessary with ink and make-up solvent from replaceable ink and solvent cartridges  17 ,  18 . Ink is transferred under pressure from the ink cartridge  17  to the mixer tank  15  as required and solvent is drawn from the solvent cartridge  18  by suction pressure as will be described. 
     It will be understood from the description that follows that the ink supply system  10  and the print head  11  include a number of flow control valves which are of the same general type: a dual coil solenoid-operated two-way, two port flow control valve. The operation of each of the valves is governed by a control system (not shown in the figures) that also controls operation of the pumps. 
     Ink drawn from the tank  15  is filtered first by a coarse filter  20  upstream of the system pump  16  and then by a relatively fine main ink filter  21  downstream of the pump  16  before it is delivered to an ink feed line  22  to the print head  11 . A fluid damper  23  of conventional configuration and disposed upstream of the main filter  21  removes pressure pulsations caused by the operation of the system pump  16 . 
     At the print head the ink from the feed line  22  is supplied to a drop generator  24  via a first flow control valve  25 . The drop generator  24  comprises a nozzle  26  from which the pressurised ink is discharged and a piezoelectric oscillator  27  which creates pressure perturbations in the ink flow at a predetermined frequency and amplitude so as break up the ink stream into drops  28  of a regular size and spacing. The break up point is downstream of the nozzle  26  and coincides with a charge electrode  29  where a predetermined charge is applied to each drop  28 . This charge determines the degree of deflection of the drop  28  as it passes a pair of deflection plates  30  between which a substantially constant electric field is maintained. Uncharged drops pass substantially undeflected to a gutter  31  from where they are recycled to the ink supply system  10  via return line  32 . Charged drops are projected towards a substrate  33  that moves past the print head  11 . The position at which each drop  28  impinges on the substrate  33  is determined by the amount of deflection of the drop and the speed of movement of the substrate. For example, if the substrate moves in a horizontal direction, the deflection of the drop determines its vertical position in the stroke of the character matrix. 
     In order to ensure effective operation of the drop generator  24  the temperature of the ink entering the print head  11  is maintained at a desired level by a heater  34  before it passes to the first control valve  25 . In instances where the printer is started up from rest it is desirable to allow ink to bleed through the nozzle  26  without being projected toward the gutter  31  or substrate  33 . The passage of the ink into the return line  32 , whether it is the bleed flow or recycled unused ink captured by the gutter  31 , is controlled by a second flow control valve  35 . The returning ink is drawn back to the mixer tank  15  by a jet pump arrangement  36  and a third flow control valve  37  in the ink supply system  10 . 
     As ink flows through the system and comes into contact with air in the tank  15  and at the print head  11 , a portion of its solvent content tends to evaporate. The ink supply system  10  is therefore also designed to supply make-up solvent as required so as to maintain the viscosity of the ink within a predefined range suitable for use. Such solvent, provided from the cartridge  18 , is also used to flush the print head  11  at appropriate times in order to keep it clear of blockages. The flush solvent is drawn through the system  10  by a flush pump valve  40  that is driven by a flow of ink in a branch conduit  41  under the control of a fourth flow control valve  42  as will be described below. The flush solvent is pumped out via a filter  43  through a flush line  44  (represented in dotted line in  FIG. 1 ) that extends from the supply system  10  through the umbilical conduit  12  to the first flow control valve  25  in the print head  11 . After passing through the nozzle  26  and into the gutter  31  the solvent is drawn into the return line  32  via the second control valve  35  and to the third control valve  37 . The returning solvent flows under suction pressure from the jet pump arrangement  36 . 
     The jet pump arrangement  36  comprises a pair of parallel venturi pumps  50 ,  51  that are supplied by pressurised ink from a branch line  53  from the outlet of the main filter  21 . The pumps are of known configuration and make use of the Bernoulli Principle whereby fluid flowing through a restriction in a conduit increases to a high velocity jet at the restriction and creates a low pressure area. If a side port is provided at the restriction this low pressure can be used to draw in and entrain a second fluid in a conduit connected to the side port. In this instance, the pressurised ink flows through a pair of conduits  54 ,  55  and back to the mixer tank  15 , each conduit  54 ,  55  having a side port  56 ,  57  at the venturi restriction. The increase in flow velocity of the ink creates a suction pressure at the side port  56 ,  57  and this serves to draw returning ink and/or solvent through lines  58 ,  59  when the third flow control valve  37  is open. The flow control valve  37  is operated such that the flow of returning ink/solvent to each venturi pump  50 ,  51  can be separately controlled. More specifically, the control system determines whether to allow flow through one or both venturi pumps  50 ,  51  depending on the temperature of the ink determined by a temperature sensor  60  in the branch line  53 . If the ink has a relatively low temperature it will have a relatively high viscosity and therefore greater pumping power is required to draw ink back from the gutter  31  in which case both pumps  50 ,  51  should be operated. In the event that the ink has a relatively high temperature it will have a relatively low viscosity in which case the only one pump  50  is required to generate sufficient suction. Indeed operation of both the pumps should be avoided in the latter circumstance, as there would be a risk of air getting into the supply system, which serves to cause excess evaporation of the solvent, and therefore increased consumption of make-up solvent. 
     The branch line  53  is connected to line  41  that conveys ink to the flush pump valve  40  via the fourth flow control valve  42 . When the control valve  42  is appropriately operated by the control system in order to effect flushing of the print head  11  it allows the flush pump valve  40  to be pressurised by the ink from line  41 . The valve  40  is a rolling diaphragm type in which a resilient “top-hat” diaphragm  61  divides a valve housing  62  into first and second variable volume chambers  63 ,  64 . Ink is supplied under pressure to the first chamber  63  and make up solvent is delivered from the cartridge  18  through a solvent supply line  65  to the second chamber  64  via a pressure transducer  66  and a non-return valve  67 . The higher pressure of the ink entering the first chamber  63  relative to the solvent serves to deflect the diaphragm  61  from its normal position as shown in  FIG. 1 , to a position where the volume of the first chamber  63  has increased at the expense of the volume of the second chamber  64  and solvent is forced out of the second chamber  64  and towards the print head  11  via the flush line  44 . It is to be appreciated that other flush pump designs may be used to achieve the same operation. 
     In use, the atmosphere above the mixer tank  15  soon becomes saturated with solvent and this is drawn into a condenser unit  70  where it is condensed and allowed to drain back into a solvent return line  71  via a fifth control valve  72  of the ink supply system. 
     The ink supply system  10 , represented in circuit form in  FIG. 1 , is physically embodied as a modular unit or core module  200  that is illustrated in  FIGS. 2A to 2C  and  11 . The mixer tank  15  comprises a reservoir with a base wall  75 , upstanding sidewalls  76  and an open top that defines a mouth  77 . The side walls  76  terminate at their upper edge in a peripheral flange  78  around the mouth  77  and provide support for a manifold block  79 , which provides fluid flow conduits between components of the ink supply system, many of which are conveniently supported on the block  79 . 
     The manifold block  79  comprises two vertically stacked, interconnected parts: a tank-side feed plate  80  that supports a number of components over the ink in the tank  15  and an upper manifold plate  81  on which further components are supported. The plates  80 ,  81 , which are shown in detail in  FIGS. 3A to 3C  and  4 A to  4 C, are generally square in outline, with the tank-side feed plate  80  being slightly smaller such that it fits inside the mouth  77  when the peripheral edge  82  of the manifold plate  81  rests on the flange  78  around the tank mouth  77 . A seal  83  is provided between the flange  78  and the edge  82  of the manifold plate  81 . Each of the plates  80 ,  81  has an upper and a lower surface  80   a ,  80   b  and  81   a ,  81   b , and the stacked arrangement is such that the lower surface  81   b  of the manifold plate overlies, and is in interfacing abutment with the upper surface  80   a  of the feed plate  80 . 
     The plates  80 ,  81  are penetrated in a direction substantially perpendicular to the plane of the interfacing surfaces  80   a ,  81   b  by a number of aligned fixing apertures  84  ( FIG. 3A ) for fixing screws (not shown) that are used to connect the plates together. The manifold plate  81  additionally has a plurality of apertures  86  spaced about its periphery for location over upstanding pegs  87  on the flange  78  of the tank  15 , and a plurality of ports  88  (see  FIG. 3A ) for connection to components of the ink supply system  10 . The flow of ink between the ports  88 , and therefore the components of the ink supply system, is provided by a plurality of discrete channels A to K defined in the lower surface  81   b  of the manifold plate  81 . The channels A-K interconnect the ports  88  in a predetermined relationship as can be seen in  FIGS. 3A and 4A . When the interfacing surfaces  80   a ,  81   b  of the plates  80 ,  81  are brought together the channels A-K are covered by the upper surface  80   a  of the feed plate  80  and sealed by a sealing member  89  that is received in a pattern of recesses  90  defined in that surface  80   a . The sealing member  89  is made from a moulded elastomeric material such as synthetic rubber of the kind used in O-ring seals and is compressed in the recesses when the plates  80 ,  81  are fastened together. It is configured such that it comprises a plurality of ring seals, each designed to seal around a particular channel when the plates  80 ,  81  are brought together, the seals being interconnected to form one member for convenience. The sealing member  89  demarcates selected areas  91  of the upper surface  80   a  that generally correspond to the pattern of channels A-K defined on the manifold plate  81 , these areas  91  serving to close the channels A-K whilst the sealing member  89  seals the channels A-K against leakage. Some of the areas  91  bounded by the sealing member  89  contain the ports  88  that allow fluid communication between the channels A-K and the components mounted on the feed plate  80 . A plurality of spigots  92  extend substantially perpendicularly from the ports  88  on the lower surface  80   b  feed plate  80  and provide for easy connection of the components to the ports  88 . 
     The upper surface  81   a  of the manifold plate  81  has upstanding side walls  93  spaced inwardly of the peripheral apertures  86 , the area inside the walls  93  being configured to support components of the ink supply system  10 . 
     The arrangement of the channels A-K in the manifold plate  81  is shown clearly in  FIG. 4A , with the sealing recesses  90  and channel closure areas  91  being shown on the feed plate  80  in  FIG. 3A . The relationship of the channels A-K to the flow lines and conduits of the ink system  10  of  FIG. 1  is summarised below. 
     Channel A defines the branch line  53  and connected line  41  for pressurised ink that extend from the outlet of the main filter  21 , which is connected to port A 5  on the feed plate  80 , to the jet pump  36  inlet that is connected to port A 1 . Line  41  is connected to the fourth control valve  42  (which controls activation of the flush pump) via port A 4 . The pressure transducer  61  is in fluid communication with the conduit via port A 3  and a temperature sensor  60  via port A 2 . 
     Channel B interconnects the second venturi jet pump  51  and the third control valve  37  which allows the flow to pump  51  to be switched on and off. Port B 1  in the manifold plate  81  is connected to the valve  37  and port B 2  ( FIG. 3A ) in the feed plate  80  connects to the venturi pump  51 . 
     Channel C defines part of the ink return line  32  from the print head  11  and interconnects the return line (port C 2 ) in the umbilical conduit  12  from the print head  11  to the third control valve  37  (port C 3 ). Port C 1  is not used. 
     Channel D defines the conduit that carries the flow of ink returning from the first chamber  63  of the flush pump  40  (via the fourth control valve  42 ) to the first venturi pump  50  of the jet pump arrangement  36  and/or the recovered solvent from the condenser unit  70 . Port D 1  on the feed plate  80  connects to the first venturi pump  50 , port D 2  on the manifold plate  81  to an outlet of the third control valve  37 , port D 3  to the fourth control valve  42  and port D 4  to the fifth control valve  72  (controlling the flow of recovered solvent from the condenser unit  70 ). 
     Channel E defines the conduit  41  that delivers pressurised ink to the flush pump valve  40  and interconnects an outlet of the fourth control valve  42  (port E 1  in the manifold plate  81 ) to the inlet (port E 2  in the manifold plate  81 ) of the first chamber  63  of the flush pump valve  40 . 
     Channel F defines part of the solvent return line  71  from the condenser unit  70  and interconnects the condenser drain (port F 1  in the manifold plate  81 ) to the fifth control valve  72  (at port F 2  in the manifold plate  81 ). 
     Channel G defines part of the solvent flush line  44  and interconnects that to the flush line tube in the umbilical conduit  12  to the print head  11  (port G 1  on the manifold plate  81 ) and an outlet of the solvent flush filter  43  (port G 2  on the feed plate  80 ). 
     Channel H defines part of the ink feed line  22  and interconnects the outlet of the damper  23  (port H 2  in the feed plate  80 ) and ink feed line tube in the umbilical conduit  12 . 
     Channel I defines the solvent supply line  65  from the solvent cartridge  18  and interconnects the end of a conduit from the cartridge  18  (that end being connected to port  14  in the manifold plate  81 ) to the fifth control valve  72  (port I 1  in the manifold plate  81 ). It also provides fluid communication with the non-return valve  67  (port  12  in the feed plate  81 ) and the pressure transducer  66  (port  13 ). 
     Channel J defines the solvent flow conduit between the non-return valve  67  and the flush pump  40 . Port J 1  in the feed plate  80  provides fluid communication between the inlet to the second chamber  64  of the flush pump  40  and port J 2 , also in the feed plate  80 , with an outlet of the non-return valve  67 . 
     Channel K defines part of the main ink feed line  22  and extends between the outlet of the system pump  16  (port K 2  on the manifold plate  81 ) and the inlet of the main filter  21  (port K 1  on the feed plate  80 ). 
     Ports L 1  on the manifold plate  81  and L 2  on the feed plate  80  simply allow a direct connection between the outlet of the coarse filter  20  and the inlet of the system pump  16  without any intermediate flow channel. 
     Each of the interfacing surfaces  80   a ,  81   b  of the plates  80 ,  81  has a large cylindrical recess  95   a ,  95   b  which combine when the plates are brought together, so as to form a chamber  95  for housing the flush pump  40 , as best seen in  FIGS. 5A and 5B . Similarly, the non-return valve  67  sits in a small chamber  96  defined between recesses  96   a ,  96   b.    
     Referring back to  FIGS. 2A and 2B , the modular nature of the ink supply system  10  will now be more clearly appreciated. The manifold block  79  configuration allows the various ink supply system components to be plugged simply into fluid communication with the ports  88  (or the spigots extending from the ports) and therefore the fluid flow channels in a modular fashion. 
     Some of the ink supply system components supported on the manifold block  79  will now be described with reference to  FIGS. 2 to 7 . An integrated filter and damper module  100  is connected to the lower surface  80   b  of the feed plate  80  by five spigots  92  as shown in  FIGS. 2B and 2C . Two of the spigots are for mounting purposes only whereas the other spigots  92  extend rearwardly from ports K 1 , G 2  and H 2  in the plate. The module  100 , shown separately in  FIGS. 6A and 6B  comprises a pair of cylindrical housings  103 ,  104  that are integrally formed with a mounting support  105  for the damper  23  (not shown in  FIGS. 6A and 6B  but shown in  FIGS. 2B ,  2 C and  5 A). A first housing  103  contains the main ink filter  21  and the second housing  104  houses the solvent filter  43 . Each of the cylindrical housings  103 ,  104  has a central inlet opening  106  that fits over a respective spigot  92  in a friction fit, the opening for the main ink filter  21  connecting to the spigot at port K 1  and the opening for the solvent filter  43  connecting to the spigot at port J 2 . A suitable sealing ring may be provided between each spigot  92  and inlet opening  106 . The filtered ink egresses from the housing  103  at aperture  102 , passes through the mounting support  105  to an inlet of the damper  23  and exits the damper and support  105  at aperture  23   a  to an integrally formed outlet conduit  107  that extends substantially parallel to the axis of the cylindrical housing  103 ,  104  and connects to the spigot  92  at port H 2 . A further conduit  108  extends from a side opening in the ink filter housing  103  and connects to the spigot  92  at port A 5  from where the ink flows into the branch line  53  defined by channel A. The filtered solvent passes through a side aperture in the housing into a conduit  109  that connects to the spigot  92  at port G 2  from where it flows into the flush line  44  defined by channel G. 
     It will be seen that the inlets  106  and the outlet conduits  107 ,  108 ,  109  are disposed substantially in parallel so that the module  100  can be plugged into the manifold block  79  with relative ease, with the inlets and conduits sliding on to the respective spigots  92 . 
     The filter and damper module  100  also comprises the coarse filter  21  in a further cylindrical housing  110  whose inlet has a take up pipe  111  for connection to a tube (not shown) that extends into the ink  14  at the bottom of the mixer tank  15 . In operation, the system pump  16  (upstream of the coarse filter  21 ) operates to draw ink from the tank  15  through the take up pipe  111  and into the coarse filter  21 . The outlet of the coarse filter  21  directs filtered ink along an integral right-angled outlet conduit  112  that connects to port L 1  in the manifold plate from where ink flows to an inlet pipe  113  ( FIGS. 4C and 5A ) of the system pump  16 , which extends through ports L 2  and L 1  and into the end of the filter outlet conduit  112 . 
     Several components of the ink supply system  10  are mounted on the upper surface  81   a  of the manifold plate  81 , these include in particular the jet pump assembly  36 , system pump  16 , the third to fifth flow control valves  37 ,  42 ,  72 , temperature sensor  60 , pressure transducer  61 , and a circuit board  115  for terminating electrical wiring connecting the valves, pumps and transducers to the control system. Many of these components are hidden from view in  FIG. 4B  by the circuit board  115 . 
     The three flow lines  22 ,  32 ,  44  are partly defined by respective tubes in the umbilical conduit  12  as described above and these connect to the respect ports H 1 , C 2 , G 1  that are conveniently grouped together at a connection block  116  ( FIG. 4B ) defined on the upper surface  81   a  of the manifold plate  81 . The tubes are supported in cut-out notches  117  ( FIG. 2B ) in the side wall  93 . 
     An ink level sensor device  120  shown in  FIGS. 2B ,  2 C, and  4 C is provided on the manifold block  79  in order to detect the level of ink in the mixer tank at any given time. It comprises four electrically conductive pins  121 ,  122 ,  123 ,  124  that depend from the lower surface  81   b  of the manifold plate  81 . They extend through a slot  125  in the feed plate  80  and into the tank  15  where they are designed to dip into the ink  14 . The first and second pins  121 ,  122  are of the same length; a third  123  of intermediate length and the fourth  124  has the shortest length. The pins are connected to one or more electrical sensors (e.g. current or a capacitance sensors) and an associated electrical circuit  115  mounted on the upper surface  81   a  of the manifold plate  81 . The sensor  120  is designed to sense the presence of the electrically conductive ink when it completes an electrical circuit between the first pin  121  and one or more of the other pins  122 ,  123 ,  124 . For example, when the level of ink in the tank is relatively high the ends of all of the pins  121 - 124  will be immersed in the ink and the sensor(s) detects that all the circuits are complete. On the other hand when the level of ink is relatively low only the longer first and second pins  121 ,  122  are immersed in ink and therefore a circuit is completed only between those two. A signal indicative of the measured level of ink is sent to the control system, which can then take a decision on whether more ink should be delivered into the tank  15 . It is to be appreciated that other forms of ink level sensing devices may be used to the same effect. 
     In operation, ink and solvent returning into the tank from the return line  32  may cause turbulence, particularly at the surface of the ink  14 , such that foam of bubbles is formed on the surface of the ink owing to surfactants present in the ink. It is known that a deflector plate may be used at the outlet of the return line to reduce the turbulence caused by the returning ink/solvent but this does not always eliminate foam entirely. The presence of the foam can mask the real level of ink in the tank and lead to erroneous readings by the level sensor  120 . In order to counteract interference with the correct operation of the level sensor  120 , a guard  130  is connected to the lower surface  80   b  of the feed plate  80  and depends downwards into the tank  15  such that it shields the pins  120 - 124  from any surface foam generated by incoming ink or solvent. This is illustrated in  FIG. 4C . The guard  130 , shown in detail in  FIGS. 7A-D , comprises a continuous thin wall made from, for example, a porous polypropylene material that has an upper end  130   a  with an integral laterally extending flange  131  for connecting to the feed plate  80  and a lower end  132  that, in use, is proximate to the base wall  75  of the tank  15 . The wall tapers inwardly between its upper and lower end  130   a ,  130   b  and surrounds the pins  120 - 124  such that the ink within its confines is maintained substantially free of foam and a correct level reading can therefore be determined. It will be appreciated that the guard  130  may be used with any form of level sensor that depends upon immersion within the ink in the tank and that the wall may be manufactured from any suitable material, porous or otherwise. 
     The mixer tank  15  is shown in more detail in  FIGS. 8 to 10 . The base wall  75  of the tank  15  has a generally planar upper surface that is interrupted by a recess that defines a small, shallow well  151  in one corner  152 . The well  151  is substantially square in the embodiment shown but it will be readily appreciated that any suitable shape may be adopted. The rest of the base wall  75  is inclined downwardly from the opposite corner  153  to the well  151  such that, in use, any residual ink remaining in the bottom of an otherwise empty tank will collect in the well  151  at the bottom of the incline. The inclination will be evident from an inspection of  FIGS. 8 and 10 . In the embodiment shown the base wall is inclined downwardly in two orthogonal directions as represented by arrows A and B in  FIGS. 9 and 10 . The base wall  75  is supported on its underside by a plurality of tapering ribs  154 ,  155  that provide strength and rigidity. A first set of three spaced parallel ribs  154  extend in a first direction and a second set of three spaced parallel ribs  155  extend in a second direction which is perpendicular to the first direction. 
     It will be appreciated that as an alternative to the base wall itself being inclined it may be sufficient for just the upper surface to be inclined relative to a lower surface of the wall. 
     When the manifold block  79  is mounted on the tank  15  the tube  150  that depends from the take up pipe  111  of the filter and module  100  is positioned such that its end extends into the well  151 . Alternatively the take up pipe  111  may extend directly into the well  151  without the need for a separate tube  150 . Thus, in circumstances when volume of ink in the tank  15  approaches empty, the system pump  16  is able to draw on the residue ink that has collected in the well  151 . This ensures that very little of the available ink in the tank  15  is wasted and that the supply of ink is not interrupted until the last possible moment. 
       FIG. 11  shows an assembled core module  200 . The module  200  is part of the ink supply system  10 . As previously described, the core module  200  preferably contains such components as the filter module  100 , the ink reservoir/mixer tank  15 , system pump  16 , solvent filter  43 , and so forth. Disposed on the surface of the module  200  is a connection manifold  202 . As also shown in  FIG. 12 , connection manifold  202  includes a plurality of connection ports  204 , which are in fluid communication with manifold block  79  (as shown in  FIG. 2A ). Connection manifold  202  is adapted to be connected with the ink jet printer  8  to provide ink, solvent, and so forth to the printer  8 . Ports  204  may be located on a single surface  206  of the module  200 . 
       FIG. 13  shows a connector  220  of printer  8  that is configured for connection to manifold  200  to provide fluid communication between the module  200  and the printer  8 . Connector  220  includes barbs  222 ,  224 ,  226  configured for connection to feed lines (not shown) of the ink jet printer  8 . Additionally, openings  232 ,  234  of connector  220  are configured for connection to connection ports  204  of manifold  202 . Although a particular configuration of ports, barbs, and openings is shown in the figures, other suitable configurations are possible. The configuration of connection ports  204  and connector  220  is preferably such that connector  220  is easily connected to the connection ports  204  of manifold  202  in an easy, one-step connection. 
     The core module  200  may be connected to an ink jet printer  8  (as schematically shown in  FIG. 1 ) as follows. The printer connector  220  is connected to the manifold  202  to provide fluid communication of ink between the module components and the ink jet printer  8 . An electrical connection (not shown) between the module  200  and the ink jet printer  8  may also be provided. The electrical connection may be any suitable connection, but preferably includes electrical wires with a socket connection. The ink jet printer  8  may include a receiving bay (not shown) disposed in cabinet  13 . The core module  200  may be disposed in the receiving bay of the cabinet  13  while the printer is in use. 
     In particular, in one embodiment, the core module  200  is capable of being operably connected to the ink jet printer  8 , to provide ink filtration and a fluid reservoir for the ink jet printer  8 , in no more than three steps. The three steps include disposing the module  200  adjacent to the printer  8  (such as within the printer cabinet  13 ); providing an electrical connection between the module  200  and the printer  8 ; and connecting the connector  220  to the manifold  202 . The electrical connection may include a plurality of wires with a socket connection between the printer  8  and the core module  200 , thus providing all electrical connections within a single connection. 
     The fluid communication into and out of the module  200  between the ink circuit and the ink jet printer  8  may be solely provided through the plurality of connection ports  204 . In particular, the connection between manifold  202  and connector  220  provides all the fluid communication between module  200  and ink jet printer  8 , without the need for additional connections. This arrangement greatly simplifies the process of installing and replacing the module  200 . 
     The configuration of the manifold block and in particular the channels defined at the interface between the manifold plate and the feed plate obviates the need for many pipes, tubes, hoses or the like that interconnect the components of the ink supply system. The arrangement is thus much simpler to assemble thus reducing the time associated with building the system and the likelihood of errors occurring. In general, the area inside the cabinet is much tidier such that it is easier to access individual components. The manifold block also eliminates connectors associated with such pipes, which are potential sources of leaks. The reliability of the system is therefore improved thus reducing servicing requirements. 
     The general structure of the manifold block provides for a compact arrangement. 
     It will be appreciated that numerous modifications to the above described design may be made without departing from the scope of the invention as defined in the appended claims. For example, the particular arrangement of the components in the ink circuit may vary. Moreover, the particular manner in which the components connect to the ports of the manifold block may vary but since they are adjacent to the manifold they can connect to the ports in such a way that eliminates the need for pipes and hoses extending between them. 
     The described and illustrated embodiments are to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiments have been shown and described and that all changes and modifications that come within the scope of the inventions as defined in the claims are desired to be protected. It should be understood that while the use of words such as “preferable”, “preferably”, “preferred” or “more preferred” in the description suggest that a feature so described may be desirable, it may nevertheless not be necessary and embodiments lacking such a feature may be contemplated as within the scope of the invention as defined in the appended claims. In relation to the claims, it is intended that when words such as “a,” “an,” “at least one,” or “at least one portion” are used to preface a feature there is no intention to limit the claim to only one such feature unless specifically stated to the contrary in the claim. When the language “at least a portion” and/or “a portion” is used the item can include a portion and/or the entire item unless specifically stated to the contrary.