WO2004048112A1

WO2004048112A1 - A valve unit of a liquid jet printer

Info

Publication number: WO2004048112A1
Application number: PCT/SE2003/001526
Authority: WO
Inventors: Urban Albinsson
Original assignee: TEXDOT AB
Current assignee: TEXDOT AB
Priority date: 2002-11-27
Filing date: 2003-10-02
Publication date: 2004-06-10
Anticipated expiration: 2005-05-27
Also published as: EP1565320A1; AU2003265200A1; SE522637C2; SE0203515D0; SE0203515L

Abstract

In a liquid ink image forming apparatus a liquid ink valve unit including a movable elongated valve body is made to increase its maximum operatable frequency by cooling the valve body. This is attained according to the invention by letting at least a part of, preferably the return of, print liquid pumped into the valve unit or units pass by the valve body. This will prevent the valve unit from overheating when operated at high frequencies. In a preferred embodiment the print liquid is temperature regulated before it reaches the valve unit or units.

Description

A VALVE UNIT OF A LIQUID JET PRINTER

TECHNICAL FIELD

The present invention relates to a printhead structure and arrangement therefore, and especially a printhead structure valve unit arrangement, for use in an image forming apparatus, such as a liquid-jet printer, in which a computer generated image information is converted into an image pattern formed of selectively discharged ink droplets deposited on an information carrier.

BACKGROUND

An image forming apparatus, such as for example a liquid-jet printer of a kind which is disclosed in US patent No 4,826,135, generally include one or several printhead structures in which a plurality of valve units are used to feed a print liquid to an outlet aperture through which liquid droplets are selectively ejected toward an information carrier to form an image configuration. The printhead structure is generally movable across the entire width of the information carrier to perform line by line scan printing in consecutive transversal lines. During each print sequence, one or several transversal lines are printed as the printhead structure is caused to move across the information carrier. In order to ensure high print uniformity, the outlet apertures are disposed in a predetermined pattern corresponding to pixel locations in the image configuration to be recorded on the information carrier.

There is always an interest in increasing the speed of forming an image. However, it is usually not possible to increase printing speed by simply increasing the speed of movement of the printhead structure without degrading the quality of a resulting image or the resolution of the resulting image since there is a limit to the frequency with which a valve can operate. Further, in most practical applications, it is not feasable to create a printhead structure across the whole image area to thereby form an image without movement of the printhead structure. This is because the initial cost of such a printhead would be very high, the dimensions of each outlet would have to be very small to attain a desired resolution, and such a printhead would most probably demand frequent maintenance attention due to, among other things, its complexity. There is thus a demand for improvement of liquid jet printers to enable higher image forming speeds and/or improved quality of a formed image in a simple and cost effective manner.

SUMMARY An object of the invention is to provide a printhead structure of a liquid jet printer which overcomes the previously mentioned drawbacks.

Another object of the invention is to define a valve unit of a printhead structure which can attain a high resolution at a high speed printing.

Still another object of the invention is to define a valve unit of a printhead structure which can attain a high operating frequency, especially without causing failure of the valve unit due to over-heating, and especially without causing variations of the print liquid viscosity due to temperature variations of the valve unit due to variations in usage of the valve unit.

A further object of the invention is to define a method of increasing the maximum frequency with which a liquid ink valve unit can be operated.

The aforementioned objects are achieved according to the invention in a liquid ink image forming apparatus having a liquid ink valve unit including a movable elongated valve body. According to the invention the valve unit is made to increase its maximum operatable frequency by cooling the valve body. This is attained according to the invention by letting at least a part of, preferably the return of, print liquid pumped into the valve unit or units pass by the valve body. This will prevent the valve unit from overheating when operated at high frequencies. In a preferred embodiment the print liquid is temperature regulated before it reaches the valve unit or units.

The aforementioned objects are also achieved according to the invention by a liquid ink valve unit of a printhead structure of a liquid ink image forming apparatus in which image information is converted into an image pattern on an information carrier. The image pattern is formed by selectively discharging print liquid through liquid ink outlets of a liquid deposition part of the printhead structure with coordinated movement of the printhead structure in a first direction across the information carrier. Thereby creating a scanline from each outlet. The liquid deposition part is arranged in conjunction with the valve unit. The valve unit includes a movable elongated valve body which by a first end section of the valve body and its movement regulates print liquid through a liquid discharge opening. The discharge opening is associated with a corresponding liquid ink outlet. The moveable valve body further comprises a second end section located along the valve body at an opposite end to the first end section. At least a part of a body of the moveable valve body is guided by guidance means at least during a part of the movement. According to the invention the liquid ink valve unit comprises one or more cooling passages through which, at least along a part of the valve body, print liquid is passed to thereby cool the valve unit.

Suitably in some embodiments the print liquid is passed through the one or more cooling passages towards the second end section. The liquid ink valve unit can suitably be pressure fed with print liquid passing through the liquid ink valve unit from a forward feed to a return feed of a circulating print liquid system. Then the print liquid can suitably be passed through to at least a part of the return feed after having passed the one or more cooling passages. Advantageously at least a part of the forward feed is shared with other liquid ink valve units of a printhead structure. In some embodiments at least a part of the liquid ink of the return feed passes by a hollowed upper limit adjustment screw or passes through one or more through holes in an upper limit adjustment screw.

Suitably the one or more cooling passages passes through one or more through holes in the valve body, or passes by the valve body. The valve body can be hollowed in at least one place along the body of the valve body, in relation to the guidance means, the guidance means will then only provide guidance at other places than at the at least one hollowed place along the body of the valve body. The guidance means can be hollowed in at least one place along the body of the valve body, the guidance means will then only provide guidance at other places than at the at least one hollowed place.

Preferably the valve body movement is at least in one direction effected by an electromagnetic coil. Then the electromagnetic coil is either at least in part around at least a part of the valve body, or around a first part of a magnetic circuit of which magnetic circuit the valve body forms a separate second part. The electromagnetic coil when actuated moves the valve body so that the liquid ink valve unit opens, and/or so that the liquid ink valve unit closes.

The aforementioned objects are also achieved according to the invention by a printhead structure of a liquid ink image forming apparatus. According to the invention the printhead structure comprises at least two liquid ink valve units according to any one of the previously described valve units.

The aforementioned objects are also achieved according to the invention by a liquid ink image forming apparatus. The liquid ink image forming apparatus in converts image information is into an image pattern on an information carrier. The image pattern is formed by selectively discharging print liquid through liquid ink outlets of a liquid deposition part of a printhead structure with coordinated movement of the printhead structure in a first direction across the information carrier. Thereby creating a scanline from each outlet. The liquid deposition part is arranged in conjunction with a valve unit. The valve unit includes a movable elongated valve body which by a first end section of the valve body and its movement regulates print liquid through a liquid discharge opening. The discharge opening is associated with a corresponding liquid ink outlet. According to the invention the apparatus comprises at least one printhead structure previously described that comprises valve units according to any one of the previosuly described valve units. Suitably the apparatus further comprises a print liquid temperature regulating unit, which regulates the print liquid temperature before it enters a valve unit or printhead structure.

The aforementioned objects are also achieved according to the invention by a liquid ink image forming apparatus in which image information is converted into an image pattern on an information carrier. The image pattern is formed by selectively discharging print liquid through liquid ink outlets of a liquid deposition part of a printhead structure of a print unit with coordinated movement of the print unit in a first direction across the information carrier. The information carrier and the print unit are coordinatedly moved in relation to each other in a second direction, which second direction is perpendicular to the first direction. According to the invention the print unit comprises at least one printhead structure comprising at least one liquid ink valve unit according to any above described embodiment.

Suitably the liquid ink image forming apparatus comprises a control unit, which control unit controls the valve units of a printhead structure. The liquid ink image forming apparatus can suitably be arranged to print with up to either four or six different liquid ink colors. The print unit can suitably either comprise one or two printhead structures for each different liquid ink color.

The aforementioned objects are also achieved according to the invention by a method of increasing the maximum operating frequency of a liquid ink valve unit of a printhead structure of a liquid ink image forming apparatus in which image information is converted into an image pattern on an information carrier. The image pattern is formed by selectively discharging print liquid through liquid ink outlets of a liquid deposition part of the printhead structure with coordinated movement of the printhead structure in a first direction across the information carrier, thereby creating a scanline from each outlet. The printhead structure can suitably include at least two valve units and the liquid deposition part is arranged in conjunction with the valve units. A valve unit includes a movable elongated valve body which by a first end section of the valve body and its movement regulates print liquid through a liquid discharge opening of each corresponding valve unit. Each discharge opening is associated with a corresponding liquid ink outlet. The moveable valve body further comprises a second end section located along the valve body at an opposite end to the first end section. And at least a part of a body of the moveable valve body is guided by guidance means at least during a part of the movement. According to the invention the method comprises the step of passing print liquid at least along a part of the valve body thereby cooling the valve unit with the print liquid.

Advantageously print liquid is passed at least along a part of the valve body towards the second end section. After print liquid is passed at least along a part of the valve body, it is suitably passed out of the valve unit to thereby avoid print liquid with an elevated temperature being discharged through a liquid ink outlet. Preferably print liquid is temperature regulated before it is entered into a valve unit to ensure that there are no variations of the print liquid viscosity which so as to ensure a uniform print liquid deposition.

The present invention relates to a valve unit in a printhead structure for use in an image forming apparatus such as a liquid-jet printer in which computer- generated image information is converted into an image pattern formed of selectively discharged liquid droplets deposited on an information carrier. The printhead structure will preferably include a plurality of valve units and a liquid deposition unit arranged in conjunction with the valve units. Each of the valve units include a movable valve body having a piston with a stop made of essentially inflexible material, a cavity surrounding said piston, a stop for holding print liquid, and a liquid discharge opening. The printhead structure further includes a liquid deposition part or unit which includes a plurality of channels, each of which extends from a corresponding liquid discharge opening to an outlet aperture arranged in a predetermined position with respect to said information carrier. All of the channels have at least substantially a same length and at least substantially a same cross-section so as to ensure a uniform liquid deposition regardless of variations of the liquid viscosity or other factors. In some embodiments the channels are only the connection between discharge opening and outlet aperture.

By providing a valve unit of a printhead structure according to the invention a plurality of advantages over prior art printhead structures are obtained. Primary purposes of the invention are to provide a printhead structure which is able to print with a higher resolution and/or with a higher speed by enabling an increased valve unit operating frequency, i.e. opening and closing of the valve unit. At lower operating frequencies or very short intervalls of higher operating frequencies, the generated heat of a valve unit can dissipate to the environment. But sustained higher operating frequencies will result in a heat build-up since a valve unit on its own is not capable of dissipating all of the generated heat. The sustained higher operating frequency of the valve units is achieved according to the invention by cooling the valve unit, and especially by using the print liquid as coolant. The valve units and printhead structure are suitable arranged for a circulating pressurized print liquid system. Then suitably at least a part of the print liquid that is exiting the valve unit/printhead structure is used to cool the valve unit. This has the advantage that any rise in temperature of the print liquid due to cooling the valve unit, leaves the valve unit. A temperature rise of 6° has been measured. This results in that the print liquid that is used for printing is unaffected by the cooling of the valve unit. The print liquid is suitably temperature regulated before it enters a valve unit/printhead structure. Temperature variations of the print liquid causes viscosity variations, which are undesirable. Other advantages of this invention will become apparent from the detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in more detail for explanatory, and in no sense limiting, purposes, with reference to the following figures, in which

Fig. 1 shows a schematic section view of a valve arrangement to which the invention is suitably applied,

Fig. 2 shows a liquid ink valve arrangement according to the invention,

Fig. 3A-C shows different embodiments of valve bodies according to the invention,

Fig. 4 shows a different alternative embodiment of a valve body according to the invention,

Fig. 5A-B shows different alternative embodiments of valve units with adjustment screws according to the invention.

DETAILED DESCRIPTION

In order to clarify the method and device according to the invention, some examples of its use will now be described in connection with Figures 1 to 5.

The present invention relates to valve units in a printhead structure and arrangement therefore for use in an image forming apparatus, such as a liquid ink printer, in which a computer generated image information is converted into an image pattern formed of selectively discharged print liquid, such as for example ink, deposited on an information carrier, such as for example a sheet of textile material. The image pattern is formed of transversal image lines each of which comprises a predetermined number of similarly spaced image pixels. The information carrier, such as a sheet of textile material, is caused to move stepwise in a first, longitudinal direction relative to the printhead, such that each step corresponds to a whole number of image pixels. During each print sequence, the printhead is caused to move across the width of the information carrier in a second, transversal direction in order to achieve line by line scan printing. Generally, an image forming apparatus of the kind described in the invention is used to record large-size color images on textile material, each color image being composed of four different color pigments such as, conventionally, cyan, yellow, magenta and black. In a preferred embodiment of an image forming apparatus according to the invention, each color image is composed of six different color pigments, such as light cyan, cyan, yellow, light magenta, magenta, and black. Generally one or several printheads of the kind described in the present invention are utilized for each color pigment, the total number of printheads included in the apparatus being consequently a whole multiple of the number of pigments used.

A printhead structure in accordance with the present invention includes generally a plurality of valve units according to the invention that are fed with liquid ink under pressure and comprises a liquid ink deposition part or is arranged in conjunction with a liquid deposition unit.

Figure 1 shows a schematic section view of a valve arrangement to which the invention is suitably applied. The valve arrangement is constructed for controlling the feed of a liquid ink, which is fed 101 by a forward feed 125 to a cavity under pressure, to the liquid deposition part or unit 107 and out through a liquid ink outlet 109. The print liquid pressurizing ssystem is preferably aof a circulating type which comprises a return feed 126 in which print liquid 102 is returned to a pump 121 or other means of pressurizing and circulating the print liquid. The valve unit comprises generally an movable valve body 110 having an elongated shape, a substantially cylindrical cavity surrounding the movable valve body and an electromagnetic element 112, used for controlling the movement 113 of the valve body 110 in such a manner that the valve body 110 is bidirectionally movable along its axis and supports 116, as indicated by the valve open direction arrow 113. The electromagnetic element 112 has a fixed portion which forms part of the valve unit, and a movable portion which forms part of the valve body 110. The cavity has a front part which forms a liquid container for holding a print liquid. A liquid discharge opening 118 is arranged on the front surface of the liquid container. The liquid discharge opening 118 suitably has a circular shape.

The valve body 110 includes a piston part which is provided with a stop 117 made of essentially inflexible material, which stop 117 is caused to move away from or toward the liquid discharge opening 118 so as to permit or restrict a liquid discharge through the opening. When caused to move toward the opening, the stop is brought in contact with a valve seat 105 to inhibit liquid flowing through the discharge opening 118 and out through the liquid ink outlet 109. A part of the piston is surrounded by one or more springs 114 which exert a force 115 such that the stop 117 is forced towards the valve seat. The stop 117 is caused to move away from the valve seat and discharge opening 118 by means of activating the electromagnet element 112 which then causes a force 113 on the valve body 110 overwinning the spring force 115. By balancing the force 113 of the electromagnetic element 112 and the force 115 of the spring 114 then complete control of the stop 117 in relation to the discharge opening 118 is attained. Thereby full control of an amount of liquid to be fed through the discharge opening 118 is attained.

As mentioned before, several valve units are usually mounted within the same liquid cavity, said cavity then having one discharge opening 118 for each valve unit and a common forward feed 125 and return feed 126 of the print liquid. Such an arrangement of at least one and suitably several valve units within a common liquid ink cavity is commonly referred to as a printhead structure. A printhead structure commonly traverses an image receiving surface such as a two meter wide textile material. An image receiving surface rs moved stepvise underneath the printhead structure in a direction which is perpendicular to the transverse movement of the printhead structure. The printhead structure is usually moved by means of some transversal printhead structure movement arrangement across the image receiving surface. The movement arrangement will sweep the liquid ink outlets across the image receiving surface between a first end stop and a second end stop. The endstops define the printable width. The printhead structure with its liquid ink outlets will print along scan lines, which are spaced apart a same distance as the liquid ink outlets are spaced apart, during each travel across the image receiving surface between the end stops. Depending on the type of printer, it can either only print during one transversal direction or during both transversal directions. Some printers will only print with a resulting pitch equal to the scan line interdistance, i.e. between each print run, the image receiving surface moves, such as for example, the equivalent of eight scan lines. In other printers the printhead structure prints lines in between already printed scan lines to thereby attain a pitch in the longitudinal direction which is smaller than the scan line interdistance. For the purpose of this description, scan lines and scan line interdistance is what and where a printer and thus a printhead structure prints during travel of the printhead structure in one direction.

According to the invention an improved printing speed and/or a higher resolution/quality is attained by improving the possible maximum operating frequency of the valve unit. According to the invention this is accomplished by cooling a valve body of a valve unit, thereby not limiting an upper operating frequency due to generated heat during valve operation. To attain a higher resolution/quality and/or a higher printing speed a higher liquid ink deposition frequency is necessary since for a given liquid ink deposition frequency a higher resolution results in a slower printing speed and a higher printing speed will result in a lower attainable resolution/quality. According to the invention it is preferable to use the print liquid that is circulated through the valve units to cool the valve body, suitably by creating cooling passages around the valve body. The print liquid used for cooling is preferably fed out of the valve unit directly thereafter, suitably to the return feed, to avoid using print liquid with an elevated, and unpredictable, temperature in the printing process.

Figure 2 shows a liquid ink valve arrangement according to the invention. As before, the valve unit comprises a valve body 210, which also in this example is movable by a electromagnet 212 and supported by supports 216. Print liquid is fed 201 into the valve unit by means of a pressurizer/pump 221 , and printed 209 onto an information carrier. According to the invention each valve unit is so arranged as to maintain a reasonable operating temperature even though the operating frequency increases. This is accomplished according to the invention by cooling the valve unit. Preferably the valve unit comprises cooling passages through which passages print liquid flows 204. In a preferred embodiment, the cooling passages lead the cooling flow 204 to the return feed 227 so that print liquid that has cooled the valve unit flows 203 back to the pump without being used for printing. Depending on the cooling needs and the rate of flow of both inlet 201 and cooling flow 204, a direct return feed 226 might be needed to accomodate the additional flow 202 of print liquid. The liquid ink valve arrangement also suitably includes a temperature regulator 223 on the forward feed 201 to thereby ensure an even printing temperature of the print liquid used for printing 209.

Figure 3 shows different embodiments of modified valve bodies according to the invention to create cooling passages, seen at section A-A of Figure 2. All of these valve bodies and encasements which are modified according to the invention provide the advantage of lowering the valve body cross sectional area within an available encasement cross sectional area. This will increase the available cross sectional area for flow of print liquid, such as liquid ink, past the valve body cooling it in the process. Figure 3A shows a plane view of a first example of a modified valve body 360 according to the invention. The valve body 360 support 316 is in this example unmodified. The encasement of the valve body can either be at the inner or outer circumference of the support 316, i.e. the example can either comprise separate supports 316 in addition to the encasement or the supports 316 are integrated with the encasement. The modified valve body 360 comprises one or more groves along the length of the valve body to thereby create one or more cooling passages 367 past any flow restrictions 329. The one or more grooves can be provided along the whole length of the valve body, but are at least provided past any bottlenecks, such as unmodified supports.

The valve body can assume many different shapes according to the invention, as can be seen in Figure 3B which shows another modified valve body 362. This valve body 362 is only supported in two smaller areas, suitably at least three points/areas spread out in the circumference are used, thereby providing a large area 368 for flow of print liquid from the cavity to the return feed, past any restrictive areas 329. As mentioned previously, by modifying the valve body 360, 362, not only a larger unrestricted path for liquid ink flow is created, but also a smaller area displacing the liquid ink when moving the valve body is gained.

Figure 3C illustrates an embodiment where the valve body 310 is not modified, but rather the support/encapsulation 365 is modified to create free flow cooling passages 369 as well as support with narrow passages 329. This embodiment can be combined with the embodiments of Figures 3A and 3B, i.e. a modified valve body with a suitably modified support/encasement.

Figure 4 shows a different alternative embodiment of a valve body according to the invention where the print liquid, such as liquid ink, flows thorugh cooling passages 450 within the valve body 410. In this embodiment the valve body 410 is provided with one or more holes/perforations 450 between the forward feed 401 and the return feed 403, 427. The importance with this modification is that a flow 405 can be led past any bottlenecks, such as the valve body supports 416. This modification also has the benefit of diminishing the cross sectional area of the valve body 410. By keeping the cooling flow 405 directly to the return feed 427, the print liquid 409 used for printing is kept at a desired pressure by a pump 421 , and at a desirable temperature by means of the print liquid temperatur regulator 423. The printed print liquid 409 is not affected by any temperature variations due to cooling the valve unit, since these variations will only appear in the return feed 403.

In many liquid ink valve units it is desirable to have an adjustment screw. Figure 5 shows different embodiments of the invention applied to liquid ink valve units with adjustment screws. Figure 5A shows an upper end of a valve unit having an adjustment screw comprising a tapered part 542 and an upper part 541. The tapered part 542 of the adjustment screw allows a fairly unrestricted flow 543 of print liquid, such as liquid ink, past the adjustment screw from the cavity past the valve body to the return feed. Figure 5B shows an embodiment where a adjustment screw 545 is provided with one of more holes 546. The hole or holes 546 provide a fairly unrestricted flow 547 of print liquid to the return feed after having cooled the valve unit and valve body 510.

The control functions and monitoring of a liquid ink printer according to the invention can be handled by a control unit. The described control unit is merely one example of an embodiment. All the different parts of a control unit can be separated into physically distinct features, or be integrated to a higher or lower degree. A user, commonly a user computer or scanner, is connected to an I/O interface of the control unit. The I/O interface in turn is connected to the other parts of the control unit by means of a data/control bus. The data/control bus allows communication between the different parts of the control unit. A control unit will further suitably comprise some kind of processing means, in this example a CPU, which will receive its intructions from a program memory and use a scratchpad memory for calculations and storage of data. Control and monitoring of various mechanical and electromechanical components of the printer is usually done by means of an I/O interface with inputs from the printer itself or buttons, and outputs to motors and/or lamps. The liquid ink printer receiving image data to be printed either directly or after appropriate processing is suitably stored in one or more bitmaps, where each bitmap will control a plurality of liquid ink valves, as previously described. A typical liquid ink printer according to the invention will comprise six different colors, but may, depending on the specific embodiment comprise more or less colors.

The basic principle of the invention is to provide a valve unit which is kept at a reasonable operating temperature even though its operating frequency increases. This is attained according to the invention by cooling the valve body, preferably by means of the print liquid used. The invention is not restricted to the above described embodiments, but may be varied within the scope of the following claims.

FIGURE 1 , shows a schematic section view of a valve arrangement to which the invention is suitably applied,

101 print liquid, such as liquid ink, inlet flow,

102 return feed flow, to pressurizer/pump, 105 bottom seal, valve seat, of liquid ink valve,

107 nozzle plate,

109 print liquid outlet,

110 movable valve body, piston, 112 electromagnet coil(s), 113 direction of movement of valve body when activating electromagnet,

114 valve closure springs,

115 direction of spring force,

116 piston/valve body support(s), 117 stop portion of valve body,

118 discharge opening,

121 pressurizer/pump of circulating print liquid system,

125 forward feed, into valve unit from pump,

126 return feed, out of valve unit into pump.

FIGURE 2, shows a liquid ink valve arrangement according to the invention,

201 print liquid, such as liquid ink, inlet flow,

202 return feed flow, to pressurizer/pump,

203 return feed flow, to pressurizer/pump from cooling passages, 204 flow in cooling passages,

209 print liquid outlet,

210 movable valve body, piston, 212 electromagnet coil(s),

216 piston/valve body support(s), 221 pressurizer/pump of circulating print liquid system,

223 temperatur regulator for print liquid before it enters valve unit,

226 possible return feed, out of valve unit into pump, 227 return feed, out of valve unit into pump from cooling passages.

FIGURE 3, shows different embodiments of valve bodies according to the invention at sectio A-A of figure 2, 310 unmodified movable valve body/piston,

316 unmodified piston/valve body support,

329 constriction between piston and piston support,

360 first modified form of movable valve body/piston,

362 second modified form of movable valve body/piston, 365 modified piston/valve body support,

367 free flow space in cut-out(s) of modified piston, for print liquid from cavity space to return feed,

368 free flow space between difference in circumference shape of piston and piston support, for print liquid from cavity space to return feed,

369 free flow space in cut-out(s) of modified piston support, for print liquid from cavity space to return feed.

FIGURE 4, shows a further embodiment according to the invention with a modified valve body,

401 print liquid, such as liquid ink, inlet flow,

403 return feed flow, to pressurizer/pump from cooling passages,

405 flow of print liquid, according to the invention, through the movable valve body/piston to return feed, 409 print liquid outlet,

410 movable valve body, piston,

416 piston/valve body support(s),

421 pressurizer/pump of circulating print liquid system,

423 temperatur regulator for print liquid before it enters valve unit, 427 return feed, out of valve unit into pump from cooling passages,

450 hole or holes through movable valve body/piston to return feed from cavity. FIGURE 5, shows different embodiments of the invention applied to liquid ink valve units with adjustment screws, 510 movable valve body, piston, 541 upper part of upper limit adjustment screw,

542 lower tapered end of upper limit adjustment screw,

543 flow of liquid ink, according to the invention, to return feed from cavity, around tapered end of upper limit adjustment screw,

545 perforated upper limit adjustment screw, 546 one or more holes through upper limit adjustment screw,

547 flow of liquid ink, according to the invention, to return feed from cavity, through hole(s) in upper limit adjustment screw.

Claims

1. A liquid ink valve unit of a printhead structure of a liquid ink image forming apparatus in which image information is converted into an image pattern on an information carrier, the image pattern being formed by selectively discharging print liquid through liquid ink outlets of a liquid deposition part of the printhead structure with coordinated movement of the printhead structure in a first direction across the information carrier, thereby creating a scanline from each outlet, the liquid deposition part is arranged in conjunction with the valve unit, the valve unit includes a movable elongated valve body which by a first end section of the valve body and its movement regulates print liquid through a liquid discharge opening, the discharge opening is associated with a corresponding liquid ink outlet, the moveable valve body further comprises a second end section located along the valve body at an opposite end to the first end section, and where at least a part of a body of the moveable valve body is guided by guidance means at least during a part of the movement, characterized in that the liquid ink valve unit comprises one or more cooling passages through which, at least along a part of the valve body, print liquid is passed to thereby cool the valve unit.

2. The liquid ink valve unit according to claim 1 , characterized in that the print liquid is passed through the one or more cooling passages towards the second end section.

3. The liquid ink valve unit according to claim 1 or 2, characterized in that the liquid ink valve unit is pressure fed with print liquid passing through the liquid ink valve unit from a forward feed to a return feed of a circulating print liquid system.

4. The liquid ink valve unit according to claim 3, characterized in that the print liquid is passed through to at least a part of the return feed after having passed the one or more cooling passages.

5. The liquid ink valve unit according to claim 3 or 4, characterized in that at least a part of the forward feed is shared with other liquid ink valve units of a printhead structure.

6. The liquid ink valve unit according to any one of claims 3 to 5, characterized in that at least a part of the liquid ink of the return feed passes by a hollowed upper limit adjustment screw or passes through one or more through holes in an upper limit adjustment screw.

7. The liquid ink valve unit according to any one of claims 1 to 6, characterized in that the one or more cooling passages passes through one or more through holes in the valve body.

8. The liquid ink valve unit according to any one of claims 1 to 7, characterized in that the one or more cooling passages passes by the valve body.

9. The liquid ink valve unit according to claim 8, characterized in that the valve body is hollowed in at least one place along the body of the valve body, in relation to the guidance means, the guidance means only providing guidance at other places than at the at least one hollowed place along the body of the valve body.

10. The liquid ink valve unit according to claim 8 or 9, characterized in that the guidance means is hollowed in at least one place along the body of the valve body, the guidance means only providing guidance at other places than at the at least one hollowed place.

11. The liquid ink valve unit according to any one of claims 1 to 10, characterized in that the valve body movement is at least in one direction effected by an electromagnetic coil.

12. The liquid ink valve unit according to claim 11 , characterized in that the electromagnetic coil is either at least in part around at least a part of the valve body, or around a first part of a magnetic circuit of which magnetic circuit the valve body forms a separate second part.

13. A printhead structure of a liquid ink image forming apparatus, characterized in that the printhead structure comprises at least two liquid ink valve units according to any one of claims 1 to 12.

14. A liquid ink image forming apparatus, characterized in that the apparatus comprises at least one printhead structure according to claim 13.

15. The liquid ink image forming apparatus according to claim 14, characterized in that the apparatus comprises a print liquid temperature control unit, which regulates the print liquid temperature before it enters a valve unit.

16. A method of increasing the maximum operating frequency of a liquid ink valve unit of a printhead structure of a liquid ink image forming apparatus in which an image information is converted into an image pattern on an information carrier, the image pattern being formed by selectively discharging print liquid through liquid ink outlets of a liquid deposition part of the printhead structure with coordinated movement of the printhead structure in a first direction across the information carrier, thereby creating a scanline from each outlet, the liquid deposition part is arranged in conjunction with the valve unit, the valve unit includes a movable elongated valve body which by a first end section of the valve body and its movement regulates print liquid through a liquid discharge opening of each corresponding valve unit, each discharge opening being associated with a corresponding liquid ink outlet, the moveable valve body further comprises a second end section located along the valve body at an opposite end to the first end section, and where at least a part of a body of the moveable valve body is guided by guidance means at least during a part of the movement, characterized in that the method comprises the step of passing print liquid at least along a part of the valve body thereby cooling the valve unit with the print liquid.

17. The method according to claim 16, characterized in that print liquid is passed at least along a part of the valve body towards the second end section.

18. The method according to claim 16 or 17, characterized in that after print liquid is passed at least along a part of the valve body, it is passed out of the valve unit to thereby avoid print liquid with an elevated temperature being discharged through a liquid ink outlet.

19. The method according to any one of claims 16 to 18, characterized in that print liquid is temperature regulated before it is entered into a valve unit.