JP5390795B2 - Image recording device - Google Patents

Description

  The present invention relates to an image recording apparatus having an ink circulation path.

  Conventionally, an ink jet type image recording apparatus is known. In such an ink jet type image recording apparatus, for example, ink droplets are ejected from a plurality of nozzles provided in a recording head to a recording medium such as recording paper or OHP paper conveyed by a recording medium conveyance device, It is known to form high-speed and high-quality images.

  In such an image recording apparatus, as a method of supplying ink to the recording head, the nozzle portion of the recording head is maintained at a negative pressure by using the water head pressure generated by the difference in height between the recording head and the sub ink tank, thereby the nozzle opening. There is a method of forming a meniscus.

  As another method, as shown in Patent Document 1, the ink between the recording head and the sub ink tank is circulated to keep the nozzle portion of the recording head at a negative pressure, thereby causing a meniscus to be formed at the nozzle opening. There is also a method of forming.

  The ink circulation path shown in FIG. 5 of Patent Document 1 includes a differential pressure valve for generating a negative pressure in the nozzles of the inkjet head in the vicinity of the inkjet head, a reservoir tank, a circulation supply line, and a circulation feedback. Ink is circulated by a pump through the line.

That is, negative pressure is generated at the nozzles of the inkjet head simply by adjusting the differential pressure of the pump with the differential pressure valve. This ink circulation method creates a state in which bubbles are not drawn from the nozzles of the inkjet head, thereby increasing the degree of freedom of the arrangement position of the reservoir tank.
JP 2006-88564 A

   However, in the ink circulation method of Patent Document 1, since the differential pressure valve for adjusting the negative pressure of the nozzle is provided in the vicinity of the ink jet head, the pressure fluctuation of the nozzle is large, and the ink droplet ejection speed and liquid from the ink jet head are large. There is a problem that there is a possibility that the drop amount varies and a high image quality cannot be obtained.

  In order to solve the above-described problems, an object of the present invention is to provide an image recording apparatus which is simple and has a small pressure fluctuation of a nozzle of an inkjet head, and which is small and inexpensive.

  In order to solve the above-described problems, an image recording apparatus of the present invention stores an ink jet head that discharges ink from nozzles and ink to be supplied to the ink jet head, and is disposed at a position higher than the ink jet head in the vertical direction. A first tank, a second tank that stores ink that has not been ejected by the inkjet head, and a pump that circulates ink between the first tank, the inkjet head, and the second tank. An ink circulation path is formed, and a pressure adjusting unit for adjusting an internal pressure in the ink circulation path is communicated with the second tank.

  According to the present invention, it is possible to provide a small and inexpensive image recording apparatus with a simple configuration that causes little pressure fluctuation of the nozzles of the inkjet head.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description, in the drawing, the conveyance direction of the recording medium is the X-axis direction or the sub-scanning direction, and the direction orthogonal to the conveyance direction is the Y-axis direction, the main scanning direction, or the width direction of the recording medium. Further, a direction orthogonal to the X-axis and Y-axis directions is taken as a Z-axis direction or a vertical direction.
(First embodiment)
FIG. 1 is a schematic cross-sectional view of an image recording apparatus according to the first embodiment. As shown in FIG. 1, the image recording apparatus 1 includes a paper feeding unit 2, a paper transport unit 3, an image forming unit 4, a maintenance unit 5, an ink bottle unit 6, a first tank unit 7, a heat exchanging unit 8, and a second. The tank portion 9, the pressure adjustment portion 10, the circulation pump portion 11, the waste liquid bottle 12, the paper discharge portion 13, and the control portion 14.

  The image recording apparatus 1 includes an image forming unit 4, a first tank unit 7, a heat exchange unit 8, a second tank unit 9, a pressure adjustment unit 10, a circulation pump unit 11, and a tube (not shown) that connects the respective units. An ink circulation system for circulating the ink is formed.

  The paper feed unit 2 includes a paper feed table 15 and a pickup roller 16. For example, cut sheets as the recording medium 17 are stacked on the sheet feeding table 15. The pickup roller 16 picks up the recording media 17 loaded on the paper feed tray 15 one by one and feeds it to the paper transport unit 3.

  The paper transport unit 3 includes a paper guide 18, a registration roller 19, a driven roller 21, a tension roller 22, a driving roller 23, a transport belt 24, a platen 25, and a suction fan 26. Yes.

  In the registration roller 19, the recording medium 17 fed by the pickup roller 16 is conveyed to the registration roller 19 via the paper guide 18. The registration rollers 19 temporarily stop the conveyance of the recording medium 17, correct the conveyance posture, adjust the conveyance start timing, and convey the recording medium 17 to the conveyance belt 24.

  The conveyor belt 24 is a belt-like endless belt, and is provided with a number of holes (not shown). The conveyor belt 24 is held in a tensioned state by four rollers, for example, a driven roller 21, two tension rollers 22, and a driving roller 23.

Note that a motor (not shown) is connected to the drive roller 23, and the conveyance belt 24 rotates in the clockwise direction in the drawing by driving the motor.
A platen 25 and a suction fan 26 are provided below the conveyor belt 24. The platen 25 is processed so that at least a region facing the image forming unit 4 is a flat surface, and a large number of holes (not shown) are formed. The suction fan 26 sucks air from the many holes of the platen 25 and the many holes of the conveying belt 24.

As a result, the recording medium 17 conveyed from the registration roller 19 is attracted onto the conveyance belt 24 and conveyed downstream at a predetermined conveyance speed.
The image forming unit 4 is provided to face the paper conveying unit 3. The image forming unit 4 includes head units 27, 28, 29, and 31 (hereinafter referred to as a K color head unit 27, a C color head unit 28, an M color head unit 29, and a Y color head unit 31, respectively) and ink distribution. Containers 32, 33, 34, and 35 (hereinafter referred to as K color ink distributor 32, C color ink distributor 33, M color ink distributor 34, and Y color ink distributor 35), and ink collectors 36 and 37, respectively. , 38, 39 (hereinafter referred to as K color ink recovery device 36, C color ink recovery device 37, M color ink recovery device 38, and Y color ink recovery device 39), and a head unit holding member 42, respectively. ing.

  Each head unit (27, 28, 29, 31) is configured to be equal to or larger than the width of the recording medium 17 in a direction orthogonal to the transport direction, and is held by a head unit holding member.

  In the present embodiment, each head unit (27, 28, 29, 31) has six inkjet heads (short heads) arranged in a staggered manner in a direction perpendicular to the transport direction, thereby recording as a whole. It is comprised so that it may become more than the width of a medium.

  FIG. 2 is a diagram showing a configuration of a short head arranged in a staggered manner on the head unit. FIG. 2 is a perspective view of the short head from the top to the bottom, its nozzle surface, and the structure in the vicinity of the nozzle. FIG. 2 shows only one short head 51 of the K-color head unit 27, but the other short heads and the short heads of the other head units have the same configuration.

  As shown in FIG. 2, the short head 51 includes an ink inflow pipe 52 and an ink outflow pipe 53 in the upper part, and a nozzle plate 55 in which a large number of nozzles 54 are formed in the lower part, in order to protect the nozzle plate 55. The mask plate 56 is provided.

  As shown in the lower part of FIG. 2, the interior of the short head 51 is surrounded by a nozzle plate 55 and a piezoelectric element 57, and an ink chamber 58 communicating with the nozzle 54 is formed. The ink 59 accommodated in the ink chamber 58 forms a meniscus 61 at the ink discharge port of the nozzle 54 by a negative pressure applied to the short head 51 via the head unit.

When the short head 51 is energized to the piezoelectric element 57, the internal volume of the ink chamber 58 varies, and the ink droplet 62 is ejected from the nozzle 54.
The K color ink distributor 32 shown in FIG. 1 is a distributor that distributes ink to each of the six short heads 51 constituting the K color head unit 27. That is, the K color ink distributor 32 is connected to the ink inflow pipe 52 of the short head 51. The same applies to the C color ink distributor 33, the M color ink distributor 34, and the Y color ink distributor 35. The K color ink collector 36 is a collector for temporarily collecting the ink that has not been ejected from the six short heads 51 constituting the K color head unit 27 in one place. That is, the K color ink collector 36 is connected to the ink outflow pipe 53 of the short head 51. The same applies to the C color ink recovery unit 37, the M color ink recovery unit 38, and the Y color ink recovery unit 39.

  The maintenance unit 5 in FIG. 1 is provided corresponding to each head unit (27, 28, 29, 31), and at the time of recording execution, as shown in FIG. 1, four head units (27, 28, 29, 31) are provided. ) On the downstream side in the recording medium conveyance direction, and arranged in parallel with each head unit at the retracted position.

  The maintenance unit 5 is provided for cleaning the short head of the head unit. Although not particularly shown, the maintenance unit 5 is composed of well-known members in the image recording apparatus such as a blade member for wiping the nozzle plate 55 of the short head 51 and a cap member for capping the nozzle plate 55.

  The ink bottle unit 6 is a main tank that stores the ink 59 in order to supply the ink 59 discharged from each short head, and for each ink color, the K color ink cartridge 43, the C color ink cartridge 44, and the M color ink. A cartridge 45 and a Y ink cartridge 46 are provided.

  The ink in these ink cartridges 43 to 46 is supplied to the second tank unit 9 described later. Then, ink is supplied from the second tank unit 9 to the short heads of the corresponding colors through the heat exchange unit 8, the first tank unit 7, and the ink distributors 32 to 35, respectively.

  The first tank unit 7 includes a first K color tank 47, a first C color tank 48, a first M color tank 49, and a first Y color tank 50 for each ink color. Each of the first tanks 47 to 50 is provided with a filter and a liquid level detector. Further, each of these first tanks 47 to 50 is configured to be open to the atmosphere.

  The heat exchange unit 8 includes heat exchangers 63 to 66 for each ink color. FIG. 3 is a perspective view showing the heat exchanging unit 8 with a part cut away. Arrows K, C, M, and Y shown in FIG. 3 indicate directions in which inks of K color, C color, M color, and Y color flow, respectively. In FIG. 1, the heat exchangers 63 to 66 for the respective colors are illustrated as independent configurations, but actually, as illustrated in FIG. 3, only the ink flow path portion 67 is individual and other than the ink flow path portion 67. The heater part 68, the heat sink part 69, and the cooling fan 71, which are the constituent parts of FIG.

  In FIG. 3, the ink flow path portion 67 as the M color heat exchanger 65 and the upper end portion of the ink flow path portion 67 as the Y color heat exchanger 66 are exposed so that the configuration can be easily understood. The upper end of the ink channel as the K color heat exchanger 63 and the upper end of the ink channel as the C color heat exchanger 64 are shown in the original configuration covered with the lid 72 and hidden.

  In this heat exchanging portion 8, the ink flow path portion 67 is formed in a plate shape for each color, the inside of the plate shape is partitioned by a plurality of walls, and heat is transmitted to the ink flowing inside. It is configured to be easy.

  A heater section 68 and a heat sink section 69 are provided so as to sandwich the ink flow path section 67 from both sides and directly contact each other. The heat sink 69 has a plurality of fins 85 formed on the plate-like base material 70 so as to stand in parallel in the vertical direction.

The cooling fan 71 is attached to the front end side of these fins 85 so that air outside the apparatus is blown to the fins 85 so that the cooling capacity is not uneven.
As described above, the heater section 68 and the heat sink section 85 are arranged on both sides of the ink flow path section 67, so that the heat resistance between the heat sink section 85 and the ink when the ink is cooled, and when the ink is heated. The thermal resistance between the heater section 68 and the ink can be minimized, and heat exchange can be performed efficiently.

That is, when the ink is cooled, the heat of the ink is conducted from the ink flow path portion 67 to the heat sink portion 69 and is exhausted into the air by the cooling fan 71.
On the other hand, when heating the ink, the heater section 68 is energized to raise the temperature. The heat is applied to the ink through the ink flow path portion 67, whereby the ink is heated. In addition, in order to detect the difference between the target temperature of ink and the actual temperature and control the heat exchanging unit 8, a temperature sensor is disposed in each head unit 27 to 31 or an ink flow path in the vicinity thereof. .

  The heat exchanging unit 8 always monitors the temperature of the ink flowing in the head units 27 to 31 with a temperature sensor, and if the ink temperature is out of the preset allowable range, the ink temperature is within the allowable range. Adjust the temperature to fit. Thereby, it is possible to record an image at an optimum ink temperature.

  The second tank unit 9 includes a second K color tank 73, a second C color tank 74, a second M color tank 75, and a second Y color tank 76 for each ink color. In each of these second tanks 73 to 76, a liquid level adjuster described later in detail is provided.

  A K color circulation pump 77, a C color circulation pump 78, an M color circulation pump 79, and a Y color circulation pump 81 of the circulation pump unit 11 are connected to the second tanks 73 to 76, respectively. Yes.

  FIG. 4 is a perspective view showing the configuration of the circulation pump unit 11. The circulation pump unit 11 includes a motor 82 as a pump drive source, and the four circulation pumps 77 to 81 having a drive shaft connected to the motor 82 in series. These four circulation pumps 77 to 81 are all constituted by gear pumps.

  In this example, four gear pumps are used for each color as described above, and all four gear pumps (circulation pumps 77 to 81) can be operated by one motor 82 by connecting these four gear pumps. . Moreover, it is also possible to drive each pump individually by using a clutch or the like.

The waste liquid tank 12 is a tank for collecting the waste ink collected by the maintenance unit 5 or the like. The waste liquid tank 12 is open to the atmosphere.
The control unit 14 controls the entire image recording apparatus 1.

  In the image recording apparatus 1 configured as described above, the image forming unit 4 transports the recording medium 17 below the K color head unit 27, the C color head unit 28, the M color head unit 29, and the Y color head unit 31. Then, ink is ejected from each short head to form an image on the recording medium 17.

The recording medium 17 on which the image is formed by the image forming unit 4 is discharged to the paper discharge tray 84 by the paper discharge roller 83 of the paper discharge unit 13.
Next, the configuration of the ink circulation system will be described. The ink circulation system includes an image forming unit 4, a first tank unit 7, a heat exchange unit 8, a second tank unit 9, a pressure adjustment unit 10, a circulation pump 11, and a tube connecting each of them. The configurations of the image forming unit 4, the heat exchanging unit 8, and the circulation pump unit 11 are as described above.

  FIG. 5 is a schematic diagram showing an ink circulation system in the image recording apparatus 1. FIG. 5 representatively shows the ink path of K color ink. Since the other colors C, M, and Y have the same configuration, only the ink paths of the K color ink shown in FIG. 5 will be described, and descriptions of the ink paths of the other colors C, M, and Y ink will be omitted. Further, in FIG. 5, the same constituent parts as those shown in FIG. 1 or the same functional parts are denoted by the same reference numerals as those in FIG.

  The K color ink cartridge 43 of the ink bottle unit 6 shown in FIG. 1 is communicated with the second K color tank 73 via the ink path 86 and the ink supply valve 87 as shown in FIG. Ink is supplied to the second K color tank 73 by opening and closing 87.

The ink supplied to the second K color tank 73 is pumped by the K color circulation pump 77 to the first K color tank 47 via the ink path 88 and the heat exchanger 63.
The second K color tank 73 is provided with a liquid level adjuster 89. The liquid level adjuster 89 includes a float member 91 and a lower end protrusion member 92 extending downward from the float member 91. The lower end protruding member 92 is gently fitted into a cylindrical ink flow path 93 erected from the bottom surface of the second K color tank 73.

  The float member 91 of the liquid level adjuster 89 floats in accordance with the vertical movement of the ink liquid level, so that the amount of ink pumped to the first K color tank 47 by the K color circulation pump unit 77 is increased to the second K color tank 47. Self-adjust according to the height of the ink surface inside.

  In this self-adjustment, when the ink level in the second K color tank 73 is lowered to a certain position, the float member 91 is lowered, and as shown in FIG. The ink outlet of the flow path 93 is closed, the ink supplied to the K color circulation pump 77 is shut off, and the ink pumping by the K color circulation pump 77 is stopped.

  In the present embodiment, the liquid level of the second K color tank 73 of the second tank unit 9 is lower than the surface of the nozzle plate 55 of the short head 51 of the head unit 27 by a height B in the direction of gravity. The second K color tank 73 is arranged so as to be.

The pressure adjusting unit 10 shown in FIG. 1 includes a common air chamber 94, a pressure bellows 95, a weight 96, a position adjusting member 97, and a drive source 98, as shown in FIG.
The pressure bellows 95 is formed of an elastic member, an upper end opening communicates with the common air chamber 94, and a weight 96 is attached to the lower end sealing portion. The position adjusting member 97 is provided to adjust the position of the weight 96 at the lower end of the pressure bellows 95, that is, the position of the pressure bellows 95.

  The position adjusting member 97 is driven up and down by a drive source 98. When the image recording apparatus 1 is not in operation, the position adjusting member 97 compresses the pressure bellows 95 to the upper maximum contracted position, and as shown in FIG. Move to the open position to freely release the movement of the lower end.

  The pressure bellows 95 is pulled down by the weight 96 to generate a negative pressure in the pressure bellows 95. That is, a negative pressure is generated in the common air chamber 94. Since the second K-color tank 73 communicates with the common air chamber 94 via the tube 99, the inside of the second K-color tank 73 similarly has a negative pressure.

  The pressure adjusting unit 10 is configured to be able to respond to negative pressure fluctuation due to printing of the short head 51 of the K color head unit 27 and pressure fluctuation due to the K color ink circulation pump 77 by the weight of the weight 96 and the elasticity of the elastic member. ing. The appropriateness of this response can be adjusted by changing the weight of the weight 96 and changing the elasticity of the elastic member during assembly.

  The common air chamber 94 of the pressure adjusting unit 10 communicates with the second K-color tank 73 on the one hand through the tube 99, and on the other hand through the other tube 101 and the air release valve 102 to the waste liquid tank 103. Communicate. The waste liquid tank 103 is opened to the atmosphere by a cylindrical body 104 erected on the top. That is, the atmosphere release valve 102 is an atmosphere release valve of the second K color tank 73.

A pressure generating unit 105 is formed as a whole by the pressure adjusting unit 10, the second K color tank 73, the K color circulation pump 77, and the motor 82.
In this embodiment, the liquid feeding capacity of the K color circulation pump 77 is designed so that more ink than the amount of ink flowing into the second K color tank 73 can be fed to the first K color tank 47. ing. This is to prevent the overflow of the second K color tank 73.

  That is, the second K color tank 73 is prevented from overflowing by increasing the ink flow rate that can be pumped out by the K color circulation pump 77 rather than the ink flow rate that flows into the second K color tank 73 in the normal use state. To.

The liquid level adjuster 89 provided in the second K color tank 73 is provided to control the amount of ink pumped out by the K color circulation pump 77.
The pressure generation unit 105 opens the atmosphere release valve 102 when the ink is not circulating to open the second K color tank 73 to the atmosphere, and closes the atmosphere release valve 102 when the ink is circulating. The inside of the second K color tank 73 is set to be a negative pressure in a sealed state.

  Thus, during ink circulation, the second K color tank 73 applies a negative pressure to the short head 51 of the K color head unit 27 via the ink discharge path 106, the K color ink collector 36, and the ink outflow pipe 53. Will give.

  Ink pumped up to the first K color tank 47 via the K color ink heat exchanger 63 is adjusted to a temperature suitable for ejection from the short head 51. The first K color tank 47 includes a filter 107 and a liquid level detector 108.

  In the present embodiment, the liquid level of the first K color tank 47 (first tank portion 7) is higher than the surface of the nozzle plate 55 of the K color head unit 27 by a height A so as to be above the gravitational direction. One K color tank 47 is arranged.

  Ink pumped up from the second K color tank 73 via the heat exchanger 63 passes through the filter 107 to become clean ink, and passes through the ink path 109, the K color ink distributor 32, and the ink inflow pipe 52. Into the short head 51.

Here, when the liquid level detector 108 is turned off for a certain time, a signal is sent to the control unit 14, the ink supply valve 87 is opened, and a necessary amount of ink is supplied to the second K color tank 73. Is done.
The first K color tank 47 is provided with an air release valve 113 via the air release path 112.

  In the present embodiment, the air release valve 113 is closed and the first K color tank 47 is in a sealed state during non-ink circulation. At the time of ink circulation, the atmosphere release valve 113 is opened, and the first K color tank 47 is set to be in the atmosphere release state.

As a result, the first K color tank 47 applies positive pressure to the short head 51 of the K color head unit 27 during ink circulation.
Since the atmosphere release path 112 communicates with the waste liquid tank 103, if the ink in the first K color tank 47 becomes excessive, the ink is transferred to the waste liquid tank 103 via the atmosphere release path 112. Collected.

  Here, the K color circulation pump 77 is located in the vicinity of the lowermost portion of the ink circulation path described above. This is because when ink is first introduced into the ink circulation system, the K color ink is fed from the K color ink cartridge 43 to the K color circulation pump 77 through the ink path 86, the ink supply valve 87, and the second K color tank 73. This is because the ink is introduced into the entire ink circulation system by driving the K color circulation pump 77 thereafter.

  By doing so, the capacity required for the K-color circulation pump 77 is minimized. Further, as described in FIG. 4, the K color circulation pump 77 employs a gear pump system, thereby minimizing pulsation applied to the ink circulation system.

  Further, the ink circulation path will be described. The ink pumped from the second K color tank 73 to the first K color tank 47 passes through the ink path 109, the K color ink distributor 32, and the ink inflow pipe 52 to form a short head. 51 communicates. Further, the short head 51 returns to the second K color tank 73 via the ink outflow pipe 53, the K color ink collector 36, and the ink path 106.

  At the time of head maintenance, the air release valves 102 and 113 are closed and the position adjusting member 97 of the pressure adjusting unit 10 is raised to compress the pressure bellows 95 so that the inside of the ink circulation path becomes positive pressure. Ink is pushed out from the nozzle 54 of the head 51 to the maintenance unit 5. The pushed ink is collected in the waste liquid tank 103 via the waste liquid path 114.

FIG. 6 is a flowchart for explaining the ink circulation operation in the image recording apparatus 1. In the description of this process as well, a description will be given by taking the K ink circulation as an example.
When receiving a print signal from an external host device (not shown) (step S0), the control unit 14 shown in FIG. 1 first drives the circulation pump (step S1). In this process, the K-color circulation pump 77 is driven.

  Next, the control unit 14 opens the atmosphere release valve 113 (step S2), and simultaneously closes the atmosphere release valve 102 (step S3). In this process, the inside of the first K color tank 47 is opened to the atmosphere, and the inside of the second K color tank 73 is sealed.

  Then, the control part 14 produces | generates a negative pressure with the pressure bellows 95 (step S4). In this process, the position adjusting member 97 that has compressed the pressure bellows 95 of the pressure adjusting unit 10 in the non-printing state is lowered to freely release the weight 96. As a result, the pressure bellows 95 is pulled down by the weight of the weight 96, and negative pressure is applied to the short head 51 as described above.

  Subsequently, the control unit 14 sets the ink circulation to a fixed state (step S5). In this process, ink is pumped up from the second K color tank 73 to the first K color tank 47 via the heat exchanger 63 by the K color circulation pump 77, and from the first K color tank 47 to the ink path 109. Ink is supplied to the short head 51 through the ink distributor 32 and the ink inflow pipe 52.

From the short head 51, the ink is returned to the second K color tank 73 via the ink outflow pipe 53, the K color ink collector 36, and the ink path 106.
In this state, the control unit 14 starts printing (step S6). In this process, the recording medium 17 is unloaded from the paper feed tray 15 and conveyed to the downstream direction by the conveying belt 24, and ink is ejected from the short head 51 of the K-color head unit 27 to the recording medium 17. Control.

When printing is completed (step S7), first, the control unit 14 stops the circulation pump (step S8). As a result, the driving of the K color circulation pump 77 is stopped.
Subsequently, the control unit 14 closes the atmosphere release valve 113 (step S9). As a result, the first K-color tank 47 is sealed from the atmosphere.

Next, the control unit 14 opens the atmosphere release valve 102 (step S10). As a result, the second K color tank 73 is opened to the atmosphere.
Furthermore, the control part 14 performs initialization of a pressure bellows position (step S11). In this process, the position adjusting member 97 rises to the top, compresses the pressure bellows 95 to the upper maximum contracted position, and maintains that state.

Thereafter, the control unit 14 shifts to a standby state (step S12).
As described above, the height from the surface of the nozzle plate 55 of the short head 51 of the K-color head unit 27 to the liquid surface of the second K-color tank 73 is lowered by the height B by the height B. However, the position of the height B is such that a predetermined nozzle pressure is applied to the short head 51 during non-ink circulation.

  That is, since the atmosphere release valve 113 is closed and the atmosphere release valve 102 is opened during non-ink circulation, the pressure applied to the short head 51 is reduced between the surface of the nozzle plate 55 of the short head 51 and the second K. It is determined by the water head difference from the ink in the color tank 73.

Therefore, the height B is set so as to be a nozzle pressure at which ink does not drip from the short head 51.
Here, the nozzle pressure of the short head 51 during ink circulation will be described in detail. In the following description, the short head 51 refers to the short heads 51 of all the color head units 27 to 31 in which the short heads 51 are arranged in a staggered manner.

  In addition, for the circulation pump and other configurations, the term “K color” is taken from the head of the configuration name, but the number given for convenience of explanation is the number of the K color configuration described above. ing. This is to make it easy to refer to the description of FIGS. 1 to 6 which has been described by taking the configuration of the K color as a representative.

  First, in order to obtain a high-quality image on the recording medium 17 by ejecting ink onto the recording medium 17 by the short head 51, it is necessary to stably generate an appropriate nozzle pressure in the ink chamber 58.

  Factors that cause the nozzle pressure to fluctuate mainly include pulsation caused by the circulation pump 77, back pressure when the ink 59 is ejected from the short head 51, and pressure fluctuation caused by the pressure generator 105. In this embodiment, the fluctuation of the nozzle pressure is absorbed by the expansion and contraction of the pressure bellows 95.

  For example, when the pressure in the ink path becomes positive by the circulation pump 77, the pressure bellows 95 expands, and when the pressure in the ink path becomes negative, the pressure bellows 95 contracts to stabilize the nozzle pressure. Is generated.

  The nozzle pressure of the short head 51 is a second pressure from the surface of the nozzle plate 55 of the short head 51 and the positive pressure due to the water head difference A between the ink liquid level of the first tank 47 and the surface of the nozzle plate 55 of the short head 51. The negative pressure due to the water head difference B to the ink liquid level in the tank 73, the negative pressure of the pressure bellows 95, the negative pressure created by the circulation pump 77 and the liquid level adjuster 89, and the ink returning to the second tank 73 It is generated by the pressure (the value converted to the water head difference is C) that is the sum of the positive pressures.

  In this embodiment, the water head difference H required to form an appropriate nozzle pressure in the ink chamber 58 is −190 mm to −310 mm. In order to generate this hydraulic head difference, the hydraulic head differences A and B and the negative pressure C are set.

  In other words, as shown in the equation “H = A + B + C”, if the sum of the water head differences A, B, and C is the water head difference H required to form an appropriate nozzle pressure, high-quality discharge is achieved. Accuracy can be obtained.

  In this example, the water head difference A is 210 mm to 220 mm, the water head difference B is −110 mm to −120 mm, the negative pressure C is −300 mm to −400 mm (the negative pressure C is a value converted into a water head difference, The negative pressure C can be changed by changing the weight).

Therefore, the installation positions of the second tank 73, the first tank 47, and the short head 51 can be freely set as long as the water head difference A, the water head difference B, and the negative pressure C satisfy the above expressions.
In this embodiment, by connecting the pressure adjusting unit 10 to the second tank 73, the second tank 73 becomes a buffer, and the nozzle pressure can be stabilized.

The pressure bellows 95 of the pressure adjusting unit 10 uses an elastic body that can linearly follow pressure fluctuations. In this embodiment, the rubber hardness of the elastic body is 30 to 50 °.
As described above, a stable pressure can be supplied to the ink chamber 58 as a nozzle pressure by generating a positive pressure and a negative pressure due to a water head difference, and the negative pressure by the pressure bellows 95 is constituted by an elastic member. The pressure fluctuation can be minimized.

  Further, since the gear pump system is adopted for the circulation pump 77, the pulsation is kept low. Furthermore, by using not only the water head difference but also a negative pressure source such as the pressure adjusting unit 10, the degree of freedom of the positions of the second tank 73, the first tank 47, and the short head 51 is increased. And an ink circulation path that can be reduced in size can be provided.

  In the present embodiment, the first tank 47 is disposed above the short head 51 and the second tank 73 is disposed below the short head 51, but the pressure adjusting unit 10 of the present invention is provided. In such an image recording apparatus 1, the second tank 73 may be disposed above the short head 51.

At this time, the negative pressure generated by the pressure adjusting unit 10 may be increased so that the pressure applied to the nozzles during ink circulation becomes a predetermined nozzle pressure.
Further, when the second tank 73 is disposed above the short head 51, the air release valve 102 and the air release valve 113 are both closed during the non-ink circulation, the inside of the circulation system is sealed, and a predetermined nozzle is provided. If the pressure of the pressure adjusting unit 10 is adjusted so that the pressure is applied, ink does not drip from the nozzles of the short head 51.

Although the circulation pump 77 is a gear pump, it may be a normal diaphragm / piston pump as long as the pressure bellows 95 can absorb pulsation.
In addition, this invention is not limited to the said embodiment, In the implementation stage, it can change variously in the range which does not change the summary.

1 is a schematic cross-sectional view of an image recording apparatus according to a first embodiment. It is a figure which shows the structure of the short head arrange | positioned at the head unit of the image recording device in 1st Embodiment in zigzag form. FIG. 3 is a perspective view showing a partially cutaway configuration of a heat exchange unit of the image recording apparatus according to the first embodiment. It is a perspective view which shows the structure of the circulation pump part of the image recording device in 1st Embodiment. FIG. 3 is a schematic diagram illustrating an ink circulation system of the image recording apparatus according to the first embodiment. 3 is a flowchart illustrating an ink circulation operation of the image recording apparatus according to the first embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image recording device 2 Paper feed part 3 Paper conveyance part 4 Image formation part 5 Maintenance unit 6 Ink bottle unit 7 1st tank part 8 Heat exchange part 9 2nd tank part 10 Pressure adjustment part 11 Circulation pump part 12 Waste liquid bottle DESCRIPTION OF SYMBOLS 13 Paper discharge part 14 Control part 15 Paper feed stand 16 Pickup roller 17 Recording medium 18 Paper guide 19 Registration roller 21 Driven roller 22 Tension roller 23 Drive roller 24 Conveyor belt 25 Platen 26 Suction fan 27 K color head unit 28 C color Head unit 29 M color head unit 31 Y color head unit 32 K color ink distributor 33 C color ink distributor 34 M color ink distributor 35 Y color ink distributor 36 K color ink collector 37 C color ink collector 38 M Color ink collector 39 Y color ink collector 42 Unit holding member 43 K color ink cartridge 44 C color ink cartridge 45 M color ink cartridge 46 Y color ink cartridge 47 First K color tank 48 First C color tank 49 First M color tank 50 First Y color Tank 51 Short head 52 Ink inflow pipe 53 Ink outflow pipe 54 Nozzle 55 Nozzle plate 56 Mask plate 57 Piezoelectric element 58 Ink chamber 59 Ink 61 Meniscus 62 Ink droplet 63 K color ink heat exchanger 64 C color ink heat exchanger 65 M color ink heat exchanger 66 Y color ink heat exchanger 67 Ink flow path portion 68 Heater portion 69 Heat sink portion 70 Plate-like base material 71 Cooling fan 72 Lid 73 Second K color tank 74 Second C color tank 75 Second M color tank 76 Second Y color tank 77 K Color circulation pump 78 C color circulation pump 79 M color circulation pump 81 Y color circulation pump 82 Motor 83 Paper discharge roller 84 Paper discharge stand 85 Fin 86 Ink path 87 Ink supply path 88 Ink path 89 Liquid level adjuster 91 Float member 92 Lower end protrusion member 93 Cylindrical ink flow path 94 Common air chamber 95 Pressure bellows 96 Weight 97 Position adjustment member 98 Drive source 99, 101 Tube 102 Atmospheric release valve 103 Waste liquid tank 104 Tubular body 105 Pressure generating unit 106 Ink path 107 Filter 108 Liquid level detector 109 Ink path
112 Atmospheric release route 113 Atmospheric release valve

Claims (7)

An inkjet head that ejects ink from nozzles;
A first tank for storing the ink to be supplied to the inkjet head and disposed at a position higher than the inkjet head in a vertical direction;
A second tank for storing the ink that has not been ejected by the inkjet head;
Forming an ink circulation path with a pump for circulating the ink between the first tank, the inkjet head and the second tank;
A pressure adjusting unit for adjusting the internal pressure in the ink circulation path communicates with the second tank.
The pressure adjusting unit is configured by an elastic member that absorbs an internal pressure variation in the ink circulation path, and a weight is attached to the elastic member, and the weight of the weight and the elasticity of the elastic member during the ink circulation. Absorbing internal pressure fluctuations in the ink circulation path by force,
An image recording apparatus. When circulating the ink in the ink circulation path, the first tank is opened to the atmosphere, and the second tank is sealed.
The pressure adjusting unit generates a negative pressure, sets the internal pressure in the second tank to a negative pressure state,
The image recording apparatus according to claim 1, wherein the second tank is disposed at a position lower than the inkjet head in the vertical direction. The water head difference between the inkjet head and the first tank is a water head difference A,
The water head difference between the inkjet head and the second tank is a water head difference B,
A value obtained by converting the internal pressure in the second tank into a water head difference is a water head difference C,
When the water head difference required to form an appropriate nozzle pressure for the nozzle of the inkjet head is a water head difference H,
H = A + B + C become so, the pressure adjustment unit, an image recording apparatus according to claim 1 or 2, characterized in that to adjust the internal pressure of the second tank. The internal pressure in the second tank is a sum of a negative pressure by the pressure adjusting unit, a negative pressure by the pump, and a positive pressure by the ink returning from the inkjet head to the second tank. The image recording apparatus according to claim 3 . The pressure adjusting unit is provided with a common air chamber, and a said resilient member,
The elastic member has an upper end communicating with a common air chamber , the weight is attached to a lower end sealing portion, and the common air chamber communicates with the second tank ;
The image recording apparatus according to claim 4 . The pressure adjusting unit includes a position adjusting member and a drive source,
The position adjusting member adjusts the position of the weight at the lower end of the elastic member;
The image recording apparatus according to claim 5 . The position adjustment member is driven up and down by a drive source,
When the image recording apparatus is not in operation, the elastic member is moved to an initial position where the elastic member is compressed to an upper maximum contracted position and an open position where the movement of the lower end of the elastic member is freely released;
The image recording apparatus according to claim 6 .