EP1453681A1

EP1453681A1 - Valve unit in a liquid jet printer

Info

Publication number: EP1453681A1
Application number: EP02792141A
Authority: EP
Inventors: Urban Albinsson
Original assignee: Texdot AB
Current assignee: Texdot AB
Priority date: 2001-12-13
Filing date: 2002-12-12
Publication date: 2004-09-08
Also published as: WO2003053700A1; SE0104209D0; AU2002358378A1; SE521081C2; SE0104209L

Abstract

In a liquid ink image forming apparatus a liquid ink valve unit including a moveable elongated valve body is made to increase its maximum controllable frequency by creating a free movement of the valve body. This is attained according to the invention by counteracting undesirable pressure changes across the valve body, especially during movement of the valve body. In a preferred embodiment a liquid ink transport is created between a first cavity at a first end section of the valve body and a second cavity at the second end section of the valve body.

Description

VALVE UNIT IN A LIQUID JET PRINTER

TECHNICAL FIELD

The present invention relates to a printhead structure, and especially a printhead structure valve arrangement, for use in an image forming apparatus, such as an 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 resulting image quality or resulting image resolution. 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 printhead structure which can attain a high resolution and/or high printing speed.

Still another object of the invention is to define a method of increasing the controllability of a liquid ink valve unit.

In a liquid ink image forming apparatus a liquid ink valve unit including a movable elongated valve body is made to increase its maximum controllable frequency by creating a free movement of the valve body. This is attained according to the invention by counteracting undesirable pressure changes across the valve body, especially during movement of the valve body. In a preferred embodiment a liquid ink transport is created between a first cavity at a first end section of the valve body and a second cavity at the second end section of the valve body.

The aforementioned objects are achieved according to the invention by 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 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. The liquid deposition part is arranged in conjunction with the valve units. Each of the valve units 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. Further 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 means which counteract undesirable pressure changes between a first cavity at the first end section and a second cavity at the second end section of the movable valve body, this in addition to any pressure equalizing which might occur by liquid ink transport between the guidance means and the part of the body of the movable valve body guided by the guidance means.

Suitably in some embodiments the undesirable pressure change counteracting means comprises a liquid ink transport coupling that couples the first cavity with the second cavity. The transport coupling can pass by a hollowed, such as tapered, upper limit adjustment screw, and/or through one or more through holes in an upper limit adjustment screw. The transport coupling can pass through one or more through holes in the valve body, or pass by the valve body. Then the valve body is suitably hollowed, suitably ground, milled or manufactured such, in at least one place along the body, i.e. on the body surface, 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, or the guidance means can be 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.

In some embodiments the valve unit comprises a seal, which seals the first cavity from the second cavity between the guidance means and the body of the valve body guided by the guidance means. The seal can be integrated with the guidance means, and/or integrated with the moveable valve body.

In some embodiments the undesirable pressure change counteracting means comprises a liquid ink transport coupling that couples the second cavity with a third cavity, the third cavity being separate from the first cavity. The third cavity can suitably be comprised of a closed vessel, of a closed flexible vessel, or of an open vessel. Then in some of these embodiments the valve unit can comprise a seal, which seals the first cavity from the second cavity between the guidance means and the body of the valve body guided by the guidance means. The seal can be integrated with the guidance means, and/or integrated with moveable valve body. Suitably the third cavity can be arranged to at least be partly filled with liquid ink, and/or at least partly be filled with a gas, and/or at least partly be filled with a liquid.

In some embodiments the undesirable pressure change counteracting means comprises a flexible seal in direct association to the second cavity. In some embodiments the undesirable pressure change counteracting means comprises a moveable seal in direct association to the second cavity.

In embodiments with a third cavity, then a pressure pulse can be applied at the third cavity for actively at least assisting moving the valve body to a valve unit closed state and/or a valve unit open state.

It can sometimes be desirable that at least a part of the undesirable pressure counteracting means is shared by at least one other liquid ink valve unit, or shared with the other liquid ink valve units of a printhead structure. Suitably the valve body movement is at least in one direction effected by an electromagnetic coil. The electromagnetic coil can be at least in part around at least a part of the valve body, or be around first part of a magnetic circuit of which 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 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, but not limited to, 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 control 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 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. Each of the valve units 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 counteracting undesirable pressure changes between a first cavity at the first end section and a second cavity at the second end section of the movable valve body, this in addition to any pressure equalizing which might occur by liquid ink transport between the guidance means and the part of the body of the movable valve body guided by the guidance means.

The present invention relates to a printhead structure 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 liquid droplets deposited on an information carrier, said printhead structure including a plurality of valve units and a liquid deposition unit arranged in conjunction with said valve units, each of said valve units including a movable valve body having a piston with a stop made of essentially inflexible material, a cavity surrounding said piston and stop for holding print liquid, a liquid discharge opening, and a flexible valve seat extending around said 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 said channels having 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.

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 control frequency which is achieved by inhibiting or at least minimizing unvoluntary pressure changes between the two ends of the valve body. 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 across a valve arrangement suitably included in a printhead structure to which the invention is suitably applied,

Fig. 2A-D shows liquid ink flow around the opposite end to the stop portion end of the valve body,

Fig. 3 shows a liquid ink valve arrangement with liquid ink pressure change dampening at the top of the piston/valve body, according to a basic embodiment of the invention,

Fig. 4A-B shows dif erent embodiments of the invention applied to a liquid ink valve arrangement with an adjustment screw, Fig. 5 shows a further embodiment according to the invention with a modified valve body,

Fig. 6A-C shows different embodiments of valve bodies according to the invention,

Fig. 7A-C shows different alternative embodiments of liquid ink pressure change dampening according to the invention,

Fig. 8A-C shows different alternative cavity separator embodiments according to the invention,

Fig. 9A-C shows different integrated membrane embodiments according to the invention,

Fig. 10 shows a two piston valve arrangement embodiment according to the invention,

Fig. 11 shows a liquid ink valve arrangement according to the invention with a displaced electromagnetic coil 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 11.

The present invention relates to a printhead structure 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 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 comprise a predetermined number of similarly spaced image pixels. The information carrier 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, comprising a liquid ink deposition part or arranged in conjunction with a liquid deposition unit.

A valve unit in accordance with the present invention is schematically illustrated in figure 1 and is constructed for controlling the feed of a liquid ink, which is fed 101 to a cavity 119 under pressure, to the liquid deposition part or unit 107 and out through a liquid ink outlet 109. The valve unit comprises generally a 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, 115 of the valve body 110 in such a manner that the valve body 110 is bidirectionally movable along its axis, as indicated by the valve open direction arrow 113 and valve close direction arrow 115. 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 119 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 119, said cavity then having one discharge opening 118 for each valve unit. 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 is 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 end stops 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, corresponding to the number of discharge openings, for example eight or sixteen. 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 control of the valve unit. According to the invention this is accomplished by a valve body which is easier to move during closure and opening of the valve unit, thereby enabling a valve unit with a faster response time resulting in a higher attainable liquid ink deposition frequency. 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 has been discovered that the movement of the valve body is at least in part determined by flow of liquid ink to and from a cavity/space at the opposite end to the stop end of the valve body, during opening and closure of the valve. Figure 2A-D, which shows liquid ink flow around the opposite end to the stop portion end of the valve body during different stages of valve operation. The opposite end to the stop portion end of the valve body will be referenced to as the top end of the valve body, no orientational restrictions intended. Figure 2A shows the top end 223 of the valve body 210 in a state when the valve is closed. A large cavity 220 is thus formed between the top end 223 of the valve body 210 and the encasement 221. During a subsequent phase when the valve is opening, as is shown in Figure 2B, the valve body 210 moves 213 to thereby diminish the cavity 222. Whatever the cavity 220 is filled with, usually liquid ink, has to move/flow 224 somewhere else. The flow will have to pass the small clearances 229 between the valve body 210 and any valve body supports 216, in some embodiments walls of the encasement 221 provide the support. The walls of the encasement 221 will be as close to the valve body 210 as possible, in most cases acting also as support for the valve body, due to a desire to have a very small gap to the electromagnetic coil and a small valve arrangement to be able to fit several side by side. As the flow 224 has to pass small clearances 229, which are necessary to support the valve body 210, a resistance to the flow is created, restricting the speed by which the cavity 222 can be emptied and thus creating a counter force/pressure on the valve body 210. This in turn will influence the movement of the valve body 210, it will move 213 against a dampening force. It is thus difficult to attain a high valve speed.

During a subsequent phase, as shown in Figure 2C, the valve is fully open. During this open phase, the cavity 225 is or is almost diminished completely. In a final phase the valve unit closes its outlet, this is shown in Figure 2D. During this closing phase the valve body 210 moves 215 to increase the cavity 228 again. By increasing the cavity 228, an under-pressure is created at the top end 223 of the valve body 210 which will create a flow 226 of liquid ink to fill up the cavity 228 and a counter force on the valve body 210 in dependence on the rate of flow. If the flow 226 is not fast enough, and the force trying to close the valve is great enough, a vacuum will be created, which will create an even larger counter force on the valve body 210 thus influencing the movement 215 of the valve body. The position of the valve body 210 is thus difficult to control.

The cavity 220, 225 accordingly changes volume by the cross sectional area of the valve body times the movement 213, 215 made by the valve body 210. This volume of, in most cases, liquid ink has to be transported 224, 226 back and forth along the sides of the valve body 210, during closure and opening of the valve. This in turn creates a counter force to the desired force on the valve body 210 which counter force opposes any positional changes the valve body 210 is controlled to make.

These counter forces cause problems, especially if the printing speed or the resolution is to be increased. It is possible to trim both hardware and driver software to take into account the counter force the valve body experiences during opening and closure due to the counter pressure created by flow restrictions around the valve body, but such an adjustment will usually have to be redone if any factor such as temperature, liquid ink viscosity, or printing speed changes. Additionally, if the printing speed and/or resolution is to be increased then the force required to move the valve body quickly enough becomes unacceptably large.

According to the invention each valve unit is so arranged as to minimize the counter forces on the valve body during its transitions between closed and open valve unit states. This is accomplished according to the invention by diminishing a pressure change on the top end of the valve body during these transitions.

Figure 3 shows a liquid ink valve unit with liquid ink pressure change dampening means according to one basic embodiment of the invention. A liquid ink valve unit typically comprises a liquid ink inlet 301 , a liquid ink outlet 309, and a movable 332 valve body/piston 310 with a stop portion 317 in a liquid ink cavity/reservoir 319. The liquid ink pressure change dampening means 331 is in this embodiment a connection means, such as a tube, connecting a cavity/space 320 at an end of the piston/valve body 310 opposite to stop portion end 317, with the liquid ink cavity 319 to allow an unrestricted flow 330 of liquid ink to and from the cavity/space 320 during valve opening/closing. By allowing a more unrestricted flow 330 to and from the cavity 320 at the top end of the valve body 310, the valve body 310 can move 332 freely without any unnecessary counter force during transitions. The bigger the tube 331 is, i.e. the smaller the flow resistance it has, the smaller the factor coupling the rate of change of movement to pressure difference between the reservoir 319 and the cavity 320 is.

In many liquid ink valve units it is desirable to have an adjustment screw. Figure 4 shows different embodiments of the invention applied to liquid ink valve units with adjustment screws. Figure 4A shows an upper end of a valve unit having an adjustment screw comprising a tapered part 442 and an upper part 441. The tapered part 442 of the adjustment screw allows a fairly unrestricted flow 443 of liquid ink past the adjustment screw from the cavity 420 above the valve body 410, to, for example, the reservoir of the valve unit. Figure 4B shows an embodiment where a adjustment screw 445 is provided with one of more holes 446 to the cavity 420. The hole or holes 446 provide a fairly unrestricted flow 447 of liquid ink to and from the cavity 420 above the valve body 410 with, for example, the reservoir of the valve unit.

Figure 5 shows a further embodiment according to the invention where the liquid ink pressure change dampening means is a modified valve body 510. In this embodiment the valve body 510 is provided with one or more holes/perforations 550 between the cavity 520 and the reservoir 519. The importance with this modification is that a flow 552 can be led past any bottlenecks. This modification also has the benefit of diminishing the cross sectional area of the valve body 510.

Figure 6 shows further different embodiments of liquid ink pressure change dampening means as modified valve bodies according to the invention. 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 liquid ink past the valve body. Figure 6A shows a plane view of a first example of a modified valve body 660 according to the invention. The valve body 660 support 616 is in this example unmodified. As discussed earlier, the encasement of the valve body can either be at the inner or outer circumference of the support 616, i.e. the example can either comprise separate supports 616 in addition to the encasement or the supports 616 are integrated with the encasement. The modified valve body 660 comprises one or more groves along the length of the valve body to thereby create one or more passages 667 past any flow restrictions 629. 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 6B which shows another modified valve body 662. This valve body 662 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 668 for flow of liquid ink from the cavity to the reservoir, past any restrictive areas 629. As mentioned previously, by modifying the valve body 660, 662, not only a larger unrestricted path for liquid ink flow is created, but also a smaller area displacing the liquid ink is gained. Figure 6C illustrates an embodiment where the valve body 610 is not modified, but rather the support/encapsulation 665 is modified to create free flow passages 669 as well as support with narrow passages 629. This embodiment can for example be combined with the embodiments of Figure 6A, i.e. a modified valve body with a suitably modified support/encasement.

The release or supply of liquid ink to/from the cavity has so far only been discussed in relation to coupling the cavity with the reservoir in a more unrestricted manner. Figures 7A, 7B, and 7C show three alternative methods according to the invention of allowing liquid ink flow in order to diminish a counter force on the valve body 710 during transitions. Figure 7A shows a method of allowing an open vessel 771 function as a reservoir for the cavity 720. This method is less suitable if the pressure the liquid ink is fed into the valve unit is high. Figure 7B shows an example of using an expandable tank 773 into which liquid ink can be fed into and received from. Figure 7C shows a method of using a closed vessel 775, suitably filled, at least in part, with a compressible medium, such as gas.

The previous embodiments have assumed that the medium that the valve body displaces during transitions is the liquid ink, but according to the invention the displaced medium can be another liquid or a gas. Figures 8A,

8B, and 8C show different embodiments according to the invention of separating the liquid ink from another medium that is used to absorb the displacement of the valve body during transitions. Figure 8A shows a first basic version of a valve unit with a liquid ink inlet 801 feeding liquid ink into a reservoir 819 being separated from a cavity 820 at the other end of the valve body 810. The liquid ink is kept from the cavity 820 by means of one or more seals 880 having a combined function as supports. The cavity 820 can then be filled with any suitable liquid and gas and for example be combined with a vessel/tank according to any one of Figures 7A to 7C. For example, if the cavity 820 is filled with air, then suitably this embodiment is combined with an open vessel according to Figure 7A. Figure 8B shows a version where the seal 882 is attached to the valve body, in contrast to the version according to Figure 8A where the seal 880 is not attached to the valve body 810. Figure 8C shows another embodiment where a movable plate/disc comprises a seal 886 which divides the cavity in two. The primary cavity 820 preferably being filled with the liquid ink, and a secondary cavity 821 which can be filled with a suitable medium of a liquid or gaseous form. As an example, the secondary cavity can be filled with air which is suitably either coupled to an open vessel (Figure 7A) or a closed vessel (Figure 7C). The plate 885 is suitably easily movable and being subjected to a pressure from the secondary cavity 821 which is preferably at least approximately the same as a pressure of the primary cavity 820 during states of rest, i.e. not during transitionary states.

Instead of using a plate 885 with a seal 886, a flexible membrane can be mounted within the encasement as the liquid ink pressure change dampening means as is disclosed in Figures 9A to 9C. Figure 9A shows the valve unit in a closed state with a flexible membrane 987 in a rest position dividing a primary cavity 920 from a secondary cavity. Factors such as how long the valve body 910 is in the different rest states and the tension of the flexible membrane 987, will determine if and how long it will take before the flexible membrane 987 reaches its rest position, and it is assumed in Figure 9A that the flexible membrane 987 has reached its rest position. Figure 9B shows the upper end of a valve unit during a transitional state, the valve body 910 is opening the valve and flexing the flexible membrane 988. Depending on the tension on, and characteristics of, the membrane 988, the pressure difference of the two cavities 920, 921 , and the rate of liquid ink escapement from the primary cavity 920 will determine how quickly it will reach a rest position. In some embodiments the open time is so short in relation to other influencing factors that the flexible membrane does not reach its rest position during valve open states. Figure 9C shows an alternative embodiment of a valve unit with a flexible membrane 989. In this embodiment the valve body 910 relies on an adjustment screw 911 , and the flexible membrane 989 is thus place in the side of the encasement.

As shown in Figure 1 , it has so far been assumed that the closure of the valve unit, i.e. movement of the valve body onto the valve seat, was done by valve closure springs. According to the invention a closure piston can be added to a valve unit instead of the closure springs. Such a closure piston can be common for all valve units of a printhead structure. Different modulation of opening times of the individual valve units is then suitably accomplished by opening the different valve units at different times since closure is preferably done at the same time for all in such an embodiment. Figure 10 shows a two piston valve embodiment according to the invention. The valve body 1010 is not necessarily of the same size as the closure piston 1090, especially if there is one closure piston 1090 for several valve units/valve bodies. As can be seen in Figure 10 there is a movable valve body 1010 with a stop portion 1017 for regulating liquid ink through a discharge opening 1018. There is a cavity 1020 which is coupled to the closure piston 1090 allowing a flow 1052. In the shown example, liquid ink couples the valve body with the closure piston, but in other embodiments, a combination with, for example, the embodiments of any one of Figures 8A to 9C, would allow coupling to and action of the closure piston 1090 to be made by another medium, such as another, or the same, liquid or a gas. A primary electromagnetic coil or coils 1012 will move 1013 the valve body 1010 to open the valve unit and also at the same time push 1052 liquid ink towards the closure piston 1090. The closure piston 1090 will preferably comprise rest springs or other means to ensure that it is in a known position when it is needed to close the valve unit or units.

When the valve unit or units are to close, closure piston electromagnetic coil or coils 1092 are activated to thus move 1093 the closure piston 1090 to create a pressure pulse which is coupled 1052 to the valve body 1010 in such a way that the valve body 1010 moves and closes the valve. There is usually no need for any arrangement for holding the valve closed, it usually being sufficient that the liquid ink is at a pressure which is higher than the surrounding pressure.

There are several advantages of not having closure springs on the valve body. The valve unit becomes smaller at the discharge opening 1018 where space is very scarce, and less force is required to open the valve, thus requireing smaller electromagnetic coils and drive electronics. Less force to open the valve is required since the valve body does not have to move against any spring force which is trying to keep the valve closed.

Figure 11 shows a liquid ink valve unit with a displaced electromagnetic coil 1199 according to the invention, i.e the electromagnetic coil does not coil around, i.e. surround, the movable valve body 1110, but around a magnetic core, which forms a first part of a magnetic circuit of which the movable valve body 1110 is a second and separate part. A great advantage of this is that the space consuming electromagnetic coil 1199 is not around the valve body where space is very scarce, particularly if the valve unit is apart of a printhead structure with several valve units. Figure 11 further shows an embodiment of the invention where seals 1182 separate the liquid ink cavity from the cavity 1120 at the end of the valve body opposite to the stop portion 1117 end, thus enabling flow 1152 of a gas or liquid to/from the cavity 1120.

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 as depicted, 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 electro-mechanical 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 whith a valve body with freer movement. This is attained according to the invention by removing the restrictions of transport of whatever, such as liquid ink, is at the opposite end of the valve body to the end which controls the liquid ink outlet. This ensures a rapid movement of the valve body, thus increasing its maximum complete movement frequency.

The invention is not restricted to the above described embodiments, but may be varied within the scope of the following claims.

FIGURE 1 , a valve unit of a printhead structure to which the invention is suitably applied,

101 liquid ink inlet,

105 bottom seal, valve seat, of liquid ink valve,

107 nozzle plate,

109 liquid ink outlet, 110 movable valve body, piston,

111 upper limit adjustment screw,

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, 119 liquid ink cavity,

FIGURE 2, liquid ink flow around the opposite end to the stop portion end of the valve body, which is referenced to as the top end of the valve body, 210 movable valve body, piston,

213 direction of movement of movable valve body/piston during valve opening, 215 direction of movement of movable valve body/piston during valve closure, 216 piston/valve body support(s),

220 cavity above piston filled with liquid ink during valve closed state, 221 encasement of top part of valve body, part of liquid ink reservoir/cavity,

222 cavity above piston emptying liquid ink during valve opening phase, 223 valve body/piston opposite end to the stop portion end, the so called top end,

224 liquid ink flow from cavity above piston during valve opening phase,

225 cavity above piston filled with little or no liquid ink during valve open state,

226 liquid ink flow to cavity above piston during valve closure phase,

228 cavity above piston filling with liquid ink during valve closing phase,

229 liquid ink escape/inlet space to cavity/space,

FIGURE 3, a liquid ink valve unit with liquid ink pressure change dampening at the top of the piston/valve body, according to a basic embodiment of the invention, 301 liquid ink inlet, 309 liquid ink outlet,

310 movable valve body, piston,

317 stop portion of valve body,

319 liquid ink cavity/reservoir,

320 cavity/space at end of piston/valve body opposite to stop portion end,

330 flow of liquid ink, according to the invention, to/from cavity/space during valve opening/closing,

331 liquid ink pressure change dampening means,

332 direction of movement of valve body,

FIGURE 4, different embodiments of the invention applied to a liquid ink valve unit with an adjustment screw, 410 movable valve body, piston,

420 cavity/space at end of piston/valve body opposite to stop portion end, 441 upper part of upper limit adjustment screw, 442 lower tapered end of upper limit adjustment screw,

443 flow of liquid ink, according to the invention, to/from cavity/space during valve opening/closing, around tapered end of upper limit adjustment screw, 445 perforated upper limit adjustment screw, 446 one or more holes through upper limit adjustment screw,

447 flow of liquid ink, according to the invention, to/from cavity/space during valve opening/closing, through hole(s) in upper limit adjustment screw,

FIGURE 5, a further embodiment according to the invention with a modified valve body, 510 movable valve body, piston,

519 liquid ink cavity/reservoir,

520 cavity/space at end of piston/valve body opposite to stop portion end,

550 hole or holes through' movable valve body/piston to/from cavity/space, 552 flow of liquid ink, according to the invention, to/from cavity/space during valve opening/closing, through the movable valve body/piston,

FIGURE 6, different embodiments of valve bodies according to the invention, 610 unmodified movable valve body/piston,

616 unmodified piston/valve body support, 629 constriction between piston and piston support

660 first modified form of movable valve body/piston,

662 second modified form of movable valve body/piston, 665 modified piston/valve body support,

667 free flow space in cut-out(s) of modified piston, for liquid ink to/from cavity space during valve opening/closing,

668 free flow space between difference in circumference shape of piston and piston support, for liquid ink to/from cavity space during valve opening/closing,

669 free flow space in cut-out(s) of modified piston support, for liquid ink to/from cavity space during valve opening/closing,

FIGURE 7, different alternative embodiments of liquid ink pressure change dampening according to the invention, 710 movable valve body, piston,

720 cavity/space at end of piston/valve body opposite to stop portion end, 771 open ended containement,

773 expandable containement, balloon,

775 closed containement,

FIGURE 8, different alternative cavity separator embodiments according to the invention,

801 liquid ink inlet,

810 movable valve body, piston,

819 liquid ink cavity/reservoir,

820 cavity/space at end of piston/valve body opposite to stop portion end,

821 enclosed additional cavity,

832 direction of movement of piston,

880 piston support(s) with seal,

882 piston end with seal, 885 plate, loosely fitted to be movable in the same direction as piston by pressure variations in cavity, 886 seal on/of plate to isolate cavity from additional cavity FIGURE 9, different integrated membrane embodiments according to the invention, 910 movable valve body, piston, 911 upper limit adjustment screw,

920 cavity/space at end of piston/valve body opposite to stop portion end,

921 additional cavity,

987 flexible membrane in relaxed state, 988 flexible membrane in a flexed state when, as illustrated, valve is opening and piston is moving towards membrane, 989 side mounted flexible membrane,

FIGURE 10, a two piston valve embodiment according to the invention, 1010 movable valve body, piston,

1012 primary electromagnet coil(s),

1013 direction of movement of piston/valve body when activating primary electromagnet,

1017 stop portion of valve body, 1018 discharge opening,

1019 liquid ink cavity/reservoir,

1020 cavity/space at end of piston/valve body opposite to stop portion end,

1052 flow of liquid ink to/from cavity, 1090 closure piston, or in some version as an additional valve opening piston, or a combination of both,

1092 closure piston electromagnet coil(s),

1093 direction of movement of closure piston when activating closure piston electromagnet,

FIGURE 11 , a liquid ink valve unit according to the invention with a displaced electromagnetic coil according to the invention, 1110 movable valve body, piston,

1117 stop portion of valve body,

1119 liquid ink cavity/reservoir,

1120 cavity/space at end of piston/valve body opposite to stop portion end,

1152 flow of gas/liquid to/from cavity,

1182 seal in combination with piston support,

1198 magnetic core,

1199 electromagnet coil,

Claims

1. 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 (109, 309) 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 including at least two valve units and the liquid deposition part is arranged in conjunction with the valve units, each of the valve units including a movable elongated valve body (110, 210, 310, 410, 510, 610, 660, 662, 710, 810, 910, 1010,1110) which by a first end section (117, 317, 1017, 1117) of the valve body and its movement (113, 213, 215, 332, 832, 1013) regulates print liquid through a liquid discharge opening (118, 1018) of each corresponding valve unit, each discharge opening being associated with a corresponding liquid ink outlet, the moveable valve body further comprising a second end section (223) 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 (116, 216, 616, 665, 880, 1182) at least during a part of the movement, characterized in that the liquid ink valve unit comprises means (331 , 442, 445, 550, 667, 668, 669, 771 , 773, 775, 886, 988, 989) which counteract (330, 443, 447, 552, 1052, 1152) undesirable pressure changes between a first cavity (119, 319, 519, 819, 1019, 1119) at the first end section and a second cavity (220, 222, 225, 228, 320, 420, 520, 720, 820, 920, 1020, 1120) at the second end section of the movable valve body, this in addition to any pressure equalizing which might occur by liquid ink transport between (229, 629) the guidance means and the part of the body of the movable valve body guided by the guidance means.

2. The liquid ink valve unit according to claim 1 , characterized in that the undesirable pressure change counteracting means comprises a liquid ink transport coupling (331 , 550, 667, 668, 669) that couples the first cavity with the second cavity.

3. The liquid ink valve unit according to claim 2, characterized in that the transport coupling passes by a hollowed upper limit adjustment screw (442, 445).

4. The liquid ink valve unit according to claim 2 or 3, characterized in that the transport coupling passes through one or more through holes (446) in an upper limit adjustment screw (445).

5. The liquid ink valve unit according to any one of claims 2 to 4, characterized in that the transport coupling passes through one or more through holes (550) in the valve body.

6. The liquid ink valve unit according to any one of claims 2 to 5, characterized in that the transport coupling passes by (667, 668, 669) the valve body.

7. The liquid ink valve unit according to claim 6, characterized in that the valve body (660, 662) is hollowed (667, 668) in at least one place along the body of the valve body, in relation to the guidance means (616), the guidance means only providing guidance at other places than at the at least one hollowed place along the body of the valve body.

8. The liquid ink valve unit according to claim 6 or 7, characterized in that the guidance means (665) is hollowed (669) in at least one place along the body of the valve body (610), the guidance means only providing guidance at other places than at the at least one hollowed place.

9. The liquid ink valve unit according to any one of claims 1 to 8, characterized in that the valve unit comprises a seal (880, 882), which seals the first cavity from the second cavity between the guidance means and the body of the valve body guided by the guidance means.

10. The liquid ink valve unit according to claim 9, characterized in that the seal (880) is integrated with the guidance means.

11. The liquid ink valve unit according to claim 9 or 10, characterized in that the seal (882) is integrated with moveable valve body.

12. The liquid ink valve unit according to claim 1 , characterized in that the undesirable pressure change counteracting means comprises a liquid ink transport coupling (1052, 1152) that couples the second cavity with a third cavity (771 , 773, 775), the third cavity being separate from the first cavity.

13. The liquid ink valve unit according to claim 12, characterized in that the third cavity is comprised of a closed vessel (775).

14. The liquid ink valve unit according to claim 12, characterized in that the third cavity is comprised of a closed flexible vessel (773).

15. The liquid ink valve unit according to claim 12, characterized in that the third cavity is comprised of an open vessel (771).

16. The liquid ink valve unit according to any one of claims 12 to 15, characterized in that the valve unit comprises a seal (880, 882), which seals the first cavity from the second cavity between the guidance means and the body of the valve body guided by the guidance means.

17. The liquid ink valve unit according to claim 16, characterized in that the seal (880) is integrated with the guidance means.

18. The liquid ink valve unit according to claim 16 or 17, characterized in that the seal (882) is integrated with moveable valve body.

19. The liquid ink valve unit according to any one of claims 12 to 18, characterized in that the third cavity is arranged to at least partly be filled with liquid ink.

20. The liquid ink valve unit according to any one of claims 16 to 19, characterized in that the third cavity is arranged to at least partly be filled with a gas.

21. The liquid ink valve unit according to any one of claims 16 to 18, characterized in that the third cavity is arranged to at least partly be filled with a liquid.

22. The liquid ink valve unit according to claim 1 , characterized in that the undesirable pressure change counteracting means comprises a flexible seal (987, 988, 989) in direct association to the second cavity.

23. The liquid ink valve unit according to claim 1 , characterized in that the undesirable pressure change counteracting means comprises a moveable seal (885) in direct association to the second cavity.

24. The liquid ink valve unit according to claim 12, characterized in that a pressure pulse (1090, 1052, 1152) is applied at the third cavity for actively at least assisting moving the valve body to a valve unit closed state.

25. The liquid ink valve unit according to claim 12 or 24, characterized in that an underpressure pulse (1052, 1152) is applied at the third cavity for actively at least assisting moving the valve body to a valve unit open state.

26. The liquid ink valve unit according to any one of claims 1 to 25, characterized in that at least a part of the undesirable pressure counteracting means is shared by at least one other liquid ink valve unit.

27. The liquid ink valve unit according to any one of claims 1 to 25, characterized in that at least a part of the undesirable pressure counteracting means is shared with the other liquid ink valve units of a printhead structure.

28. The liquid ink valve unit according to any one of claims 1 to 27, characterized in that the valve body movement (113, 332) is at least in one direction effected by an electromagnetic coil (112, 1012, 1199).

29. The liquid ink valve unit according to claim 28, characterized in that the electromagnetic coil (112, 1012) is at least in part around at least a part of the valve body.

30. The liquid ink valve unit according to claim 28, characterized in that the electromagnetic coil (1199) is around first part of a magnetic circuit of which circuit the valve body forms a separate second part.

31. The liquid ink valve unit according to any one of claims 28 to 30, characterized in that the electromagnetic coil when actuated moves (113, 1013) the valve body so that the liquid ink valve unit opens.

32. A method of increasing the maximum control 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 (109, 309) 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 including at least two valve units and the liquid deposition part is arranged in conjunction with the valve units, each of the valve units including a movable elongated valve body (110, 210, 310, 410, 510, 610, 660, 662, 710, 810, 910, 1010,1110) which by a first end section (117, 317, 1017, 1117) of the valve body and its movement (113, 213, 215, 332, 832, 1013) regulates print liquid through a liquid discharge opening (118, 1018) of each corresponding valve unit, each discharge opening being associated with a corresponding liquid ink outlet, the moveable valve body further comprising a second end section (223) 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 (116, 216, 616, 665, 880, 1182) at least during a part of the movement, characterized in that the method comprises the step of counteracting (330, 443, 447, 552, 1052, 1152) undesirable pressure changes between a first cavity (119, 319, 519, 819, 1019, 1119) at the first end section and a second cavity (220, 222, 225, 228, 320, 420, 520, 720, 820, 920, 1020, 1120) at the second end section of the movable valve body, this in addition to any pressure equalizing which might occur by liquid ink transport between (229, 629) the guidance means and the part of the body of the movable valve body guided by the guidance means.