Method for controlling circulation device, method for manufacturing circulation device, and circulation device

Abstract

To provide a control method for a circulation device, a manufacturing method for the circulation device, and the circulation device that are able to achieve a desired flow rate of ink circulation.SOLUTION: In a control method for a circulation device according to an embodiment, the circulation device having a plurality of liquid ejection heads controls a flow rate of ink circulation of the plurality of liquid ejection heads, based on a liquid ejection head that is shortest in AL among the plurality of liquid ejection heads.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] FIELD Embodiments of the present invention relate to a method for controlling a circulating device, a method for manufacturing a circulating device, and a circulating device. [Background technology]

[0002] Printing devices equipped with ink-circulation inkjet heads have an internal ink circulation path that constantly supplies ink to the inkjet head, ensuring high ejection reliability. In such printing devices equipped with ink-circulation inkjet heads, the ink circulation path is designed based on the resistance value of the inkjet head and is controlled to obtain the desired ink circulation flow rate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 11-34234 Summary of the Invention [Problem to be solved by the invention]

[0004] The problem to be solved by the present invention is to provide a method for controlling a circulation device, a method for manufacturing a circulation device, and a circulation device that can obtain a desired ink circulation flow rate. [Means for solving the problem]

[0005] A method for controlling a circulation device according to an embodiment controls the ink circulation flow rate of a plurality of liquid ejection heads in a circulation device equipped with the plurality of liquid ejection heads based on the liquid ejection head with the shortest AL among the plurality of liquid ejection heads. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is an explanatory diagram showing the configuration of a liquid ejection device according to a first embodiment. [Figure 2]FIG. 2 is a perspective view showing the configuration of an inkjet head of the liquid ejection device. [Figure 3] 3A and 3B are explanatory diagrams showing examples of connections of inkjet heads of the liquid ejection device. [Figure 4] FIG. 4 is an explanatory diagram showing a flow path resistance in the embodiment; [Figure 5] Graph showing the aspect ratio of the pipe cross section and the pipe friction coefficient ratio. [Figure 6] Graph showing the nozzle average AL and flow path resistance per unit viscosity. DETAILED DESCRIPTION OF THE INVENTION

[0007] A liquid ejection head 1 according to a first embodiment and a liquid ejection device 2 using the liquid ejection head 1 will be described below with reference to FIGS. 1 to 3. FIG. 1 is an explanatory diagram showing the configuration of the liquid ejection device 2 according to the first embodiment, and FIG. 2 is a perspective view showing the configuration of the liquid ejection head 1. FIG. 3 is an explanatory diagram showing the configuration of a portion of the liquid ejection device 2, and FIG. 4 is an explanatory diagram showing the flow path resistance of the embodiment. FIG. 5 is a graph showing the aspect ratio of the pipe cross section and the pipe friction coefficient ratio, and FIG. 6 is a graph showing the nozzle average AL and the flow path resistance per unit viscosity. Note that in each figure, the configuration is enlarged, reduced, or omitted as appropriate for ease of explanation.

[0008] A liquid ejection device 2 having a liquid ejection head 1 will be described with reference to Fig. 1. The liquid ejection device 2 includes a housing 2111, a medium supply unit 2112, an image forming unit 2113, a medium ejection unit 2114, a conveying device 2115 which is a support device, and a control unit 2118.

[0009] The liquid ejection device 2 is an inkjet printer that performs an image formation process on paper P by ejecting liquid such as ink while transporting the paper P as a recording medium, which is the object of ejection, along a predetermined transport path 2001 that runs from a medium supply section 2112 through an image forming section 2113 to a medium ejection section 2114.

[0010] The medium supply unit 2112 includes a plurality of paper feed cassettes 21121. The image forming unit 2113 includes a support unit 2120 that supports paper, and a plurality of head units 2130 that are arranged above and facing the support unit 2120. The medium discharge unit 2114 includes a paper discharge tray 21141.

[0011] The support section 2120 includes a conveyor belt 21201 that is looped in a predetermined area where image formation is performed, a support plate 21202 that supports the conveyor belt 21201 from the back side, and a plurality of belt rollers 21203 that are provided on the back side of the conveyor belt 21201.

[0012] The head unit 2130 as a circulation device includes a plurality of liquid ejection heads 1 which are inkjet heads, a supply tank 2132 connected to the plurality of liquid ejection heads 1, and connection flow paths 2134 and 2135 which connect the liquid ejection heads 1 and the supply tank 2132.

[0013] For example, in the head unit 2130, a circulation flow path is formed by the liquid ejection head 1, a supply tank 2132, and connection flow paths 2134 and 2135. In the head unit 2130, a plurality of heads 1 are connected in parallel to a pair of pressure sources 2136 and 2137 via a plurality of connection flow paths 2134 and 2135.

[0014] For example, the head unit 2130 has a difference in the liquid level between the upstream and downstream tanks, and circulates ink by the difference in potential energy.

[0015] The head unit 2130 is also provided with a pressure adjustment device 2133 such as a pump that adjusts the pressure by letting the fluid in and out of the tank. For example, as the pressure adjustment device 2133, a circulation pump that generates a circulating flow is provided in a circulation flow path that is made up of the liquid ejection head 1, the supply tank 2132, and the connection flow paths 2134 and 2135. The liquid ejection head 1 is supplied with ink as a liquid stored in a supply tank 2132. The liquid ejection head 1 is, for example, a circulation type head that circulates ink.

[0016] In this embodiment, the liquid ejection heads 1 are provided with four colors of liquid ejection heads 1 (cyan, magenta, yellow, and black), and four color supply tanks 2132 that respectively store ink of each color. The supply tanks 2132 are connected to the liquid ejection heads 1 by connection flow paths 2135.

[0017] As shown in FIG. 2, the liquid ejection head 1 is an inkjet head, and includes a nozzle plate 21 having a plurality of nozzles 201, an actuator substrate 22, a manifold 23 bonded to the actuator substrate 22, and a drive circuit 24 (drive unit).

[0018] The actuator substrate 22 is disposed opposite the nozzle 201 and includes an actuator 25 as a liquid ejection unit having a plurality of pressure chambers 26 communicating with the nozzle 201 and a drive element unit 27 adjacent to the plurality of pressure chambers 26. The actuator substrate 22 is configured in a predetermined shape that forms a predetermined flow path including the plurality of pressure chambers 26 between it and the nozzle plate 21.

[0019] An electrode connected to the drive circuit 24 is formed on the drive element portion 27 adjacent to the pressure chamber 26 of the actuator 25. The electrode is connected to the control unit 2118 via a driver of the drive circuit 24 (described later) by, for example, a wire connected to the drive circuit 24, and is configured to be drive-controllable by control by a processor.

[0020] The drive circuit 24 includes a driver IC 241 and various wiring boards 242. The drive circuit 24 drives the actuator 25 by applying a drive voltage to the wiring pattern of the actuator 25 via the driver IC 241, thereby increasing or decreasing the volume of the pressure chamber 26 and causing droplets to be ejected from the nozzles 201 arranged opposite to the actuator 25.

[0021] The liquid ejection head 1 comprises a nozzle plate 21, an actuator substrate 22, and a manifold 23, and defines a predetermined flow path having a pressure chamber 26 therein. The flow path of the liquid ejection head 1 is connected to a connection flow path 2135 of the liquid ejection device. For example, the liquid ejection head 1 is a shared-wall type inkjet head.

[0022] The pressure adjusting device 2133 is connected to the control unit 2118 and is driven and controlled by the control unit 2118. The pressure adjusting device 2133 sends liquid through a connection flow path 2134, and circulates the liquid between the liquid ejection head 1 and the circulation device. That is, the control unit 2118 operates the pressure adjusting device 2133 to supply liquid from the supply tank 2132 to the liquid ejection head 1 and to collect liquid from the liquid ejection head 1, thereby performing a circulation operation. The circulation operation is configured so that the timing of circulation and the circulation flow rate can be controlled. Note that a single supply tank 2132 may be provided in common for multiple heads 1.

[0023] For example, a circulation pump, which is an example of the pressure adjusting device 2133, returns ink accumulated on the downstream side to the upstream side as it circulates. That is, when a circulation operation is performed in which ink circulates due to a pressure difference between the upstream and downstream sides, the ink on the upstream side decreases and the ink on the downstream side increases, so by driving the circulation pump, ink is returned from the pressure source 2137 to the pressure source 2136.

[0024] The connection flow path 2134 is a supply flow path connected to the ink supply pipe of the liquid ejection head 1. The connection flow path 2135 is a recovery flow path connected to the ink discharge pipe of the liquid ejection head 1. For example, if the liquid ejection head 1 is a circulation type, the supply flow path and the recovery flow path are connected to a common tank. The connection flow paths 2134 and 2135 are connected to the head 1 and the tank 2132, respectively, and are configured by tube members that connect the head 1 and the tank 2132, for example.

[0025] Here, the connection flow paths 2134, 2135 connected to the multiple heads 1 are set by an AL (Acoustic Length), which is half the natural vibration period of the pressure chambers of the liquid ejection head 1, and are set based on, for example, an average AL of the nozzles, which differs for each head 1. In other words, the connection flow paths 2134, 2135 of each head 1 are configured to have a flow path resistance corresponding to the average AL of the nozzles of each head 1. The liquid ejection head 1 is equipped with multiple nozzles 201, and the AL corresponding to each nozzle 201 is different. The average AL of the nozzles is the average AL of all the nozzles 201 of one liquid ejection head 1.

[0026] In this embodiment, the circulation flow rate setting value set for the ink circulation device in the liquid ejection device 2 is determined according to the individual variation (AL) of the liquid ejection head 1 installed. That is, in the method for manufacturing the circulation device according to this embodiment, the flow path resistance of the ink circulation device in the device 2 is adjusted according to the individual variation (AL) of the liquid ejection head 1. In this embodiment, the connection flow paths 2134, 2135 are configured so that the flow path resistance can be set according to the individual characteristics of the liquid ejection head 1. For example, the connection flow paths 2134, 2135 are formed of tubular members such as tubes, and the flow path resistance can be changed by adjusting the length and diameter of the tubes. For example, if differences in the circulation flow rate occur due to differences in the AL based on information on the AL of each head 1, the user sets the conditions of the connection flow paths 2134, 2135 so that the difference in the circulation flow rate between multiple heads 1 is minimized or the circulation flow rate is equalized. As a specific example, the tubes constituting the connection flow paths 2134, 2135 are configured so that the length and diameter of the flow path can be changed. For example, a tube member corresponding to AL may be selected and connected from multiple types of tube members configured with different flow path diameters and flow path lengths, or the flow path resistance may be configured to be variable by adjusting the length.

[0027] In this embodiment, the multiple heads 1 arranged in parallel are configured so that the flow path resistance of the connection flow paths 2134, 2135 connecting heads 1 with short ALs is lower than the flow path resistance of the connection flow paths 2134, 2135 connecting heads 1 with long ALs. In other words, for the multiple heads 1 connected in parallel, the tube members constituting the connection flow paths 2134, 2135 connecting heads 1 with short ALs are configured to have shorter flow path lengths or larger flow path diameters than the tube members of the connection flow paths 2134, 2135 connecting heads 1 with long ALs. In this embodiment, as an example, ink with a viscosity of approximately 10 mPa s is used.

[0028] The transport device 2115 transports the paper P along a transport path 2001 that runs from a paper feed cassette 21121 in the medium supply unit 2112, through the image forming unit 2113, to a paper discharge tray 21141 in the medium discharge unit 2114. The transport device 2115 includes a plurality of guide plate pairs 21211-21218 and a plurality of transport rollers 21221-21228 that are arranged along the transport path 2001. The transport device 2115 supports the paper P so that it can move relative to the liquid ejection head 1.

[0029] The control unit 2118 is, for example, a control board, and includes a processor, a ROM (Read Only Memory), a RAM (Random Access Memory), an I / O port that is an input / output port, and an image memory.

[0030] The processor is a processing circuit such as a CPU (Central Processing Unit) that is a controller. The processor controls, via an I / O port, the head unit 2130, drive motor, operation unit, various sensors, and the like that are provided in the liquid ejection device 2. The processor transmits the print data stored in the image memory to the drive circuit 24 in the order of drawing.

[0031] The control unit 2118 also determines an adjusted drop waveform based on the adjustment data, for example, selecting an adjusted drop waveform to be applied from among adjusted drop waveforms that can be set in multiple stages.

[0032] The ROM stores various programs, etc. The RAM temporarily stores various variable data, image data, etc. The I / O port is an interface unit that inputs and outputs data from the outside. Print data from an externally connected device is sent to the control unit 2118 through the I / O port and saved in the image memory.

[0033] The print data is data converted from image data including information on the color and density of each area and input to the head to eject liquid. The liquid ejection head 1 selects a drive waveform based on the print data and applies the drive waveform to the actuator 25.

[0034] A method for controlling the liquid ejection head 1 used in the liquid ejection device 2 according to this embodiment will be described below.

[0035] The control unit 2118 sets the drive waveform to be applied to each drive element based on the print data. For example, the control unit 2118 may select a drive pattern for each element from a plurality of patterns that are set and stored in advance. For example, the control unit 2118 drives each of the plurality of drive elements corresponding to each nozzle of the liquid ejection unit using a waveform pattern based on the print data.

[0036] Furthermore, the control unit 2118 constantly supplies ink to the head as a circulation operation. For example, the control unit 2118 controls the circulation flow rate as a circulation operation. Specifically, the control unit 2118 controls the circulation flow path by adjusting the pressure in the circulation flow path. At this time, the control unit 2118 controls the circulation flow rate of ink based on the head with the shortest AL among the multiple heads 1, thereby ensuring a minimum circulation flow rate of ink flowing through each head. Furthermore, the control unit 2118 controls the circulation operation so that the circulation flow rate of ink flowing through each head is constant.

[0037] The relationship between the circulation flow rate of the head 1, the flow path resistance, and AL will be described below with reference to Figures 3 to 6. Figure 3 is an explanatory diagram showing an example of connection of multiple heads 1 of a liquid ejection device 2. Figure 4 is an explanatory diagram showing the flow path resistance of an embodiment. Figure 5 is a graph showing the aspect ratio of the pipe cross section and the pipe friction coefficient ratio, and Figure 6 is a graph showing the nozzle average AL and the flow path resistance per unit viscosity.

[0038] As described above, in the liquid ejection device 2, the multiple liquid ejection heads 1 are connected to a common pressure adjustment device 2133. That is, common pressure sources 2136, 2137 are provided on the upstream and downstream sides of the liquid ejection head 1 in the circulation flow path, respectively. Note that the upstream and downstream pressure sources 2136, 2137 are not limited to, for example, circulation pumps, and may be configured by other pressure devices provided in the circulation flow path, or may be configured by utilizing potential energy generated by the arrangement of tanks, flow paths, etc.

[0039] For example, as shown in Figure 3, in the case of a parallel connection in which multiple heads 1 are connected to common pressure sources 2136 and 2137, if the pressure of the upstream pressure source 2136 in the ink circulation path is Pup, the pressure of the downstream pressure source 2137 is Pdown, the flow path resistance of the head is RN_h (N = 1, 2, 3, 4, 5, 6), the resistance of the tube from the upstream pressure source 2136 to each head 1 is RN_Utube (N = 1, 2, 3, 4, 5, 6), and the resistance of the tube from each head to the downstream pressure source 2137 is RN_Dtube (N = 1, 2, 3, 4, 5, 6), the pressure and resistance of the ink flowing through the path are as shown in Figure 4 using an equivalent circuit.

[0040] Here, if the flow path resistance of each head 1 is the same, by setting the upstream tube and the downstream tube to the same flow path resistance value, the flow path resistance of the path from the upstream pressure source 2136 through the head to the downstream pressure source 2137 will be the same value for all paths. RN = RN_Utube + RN_h + RN_Dtube(N = 1,2,3,4,5,6) R1 = R2 = R3 = R4 = R5 = R6 Furthermore, if the flow path resistances of the flow paths connected to the individual heads 1 are the same, the flow path resistance of the ink path of each head 1 will be the same as the flow path resistance of the parallel connected heads, and R = R / 6. Therefore, the flow rate of ink flowing through each head 1 is It is expressed as Q = (Pup - Pdown) / (R / 6).

[0041] Therefore, the flow rate of ink flowing through the plurality of heads is equal, and the same ink circulation flow rate can be achieved in all heads.

[0042] Here, in the case of a shear-mode sidewall type piezoelectric actuator, ink actually flows through the actuator. However, while the head manufacturing process allows for high precision in the actuator's width (nozzle direction) dimensions, precision in the actuator's depth direction tends to be poor. This variation in depth affects the period of the pressure wave inside the actuator (T = 2 * AL, hereafter referred to as AL), resulting in variation in AL for each head. For example, assuming there is no variation in the actuator's width or length, if there is variation in the actuator's depth direction, the AL will be larger if the depth is deep and shorter if the depth is shallow.

[0043] On the other hand, the flow resistance of ink flowing through the actuator inside the inkjet head changes depending on the cross-sectional area (cross-sectional area of ​​the flow path). Specifically, the flow resistance of a pipe with cross-sectional area A (m2), wetted edge length S (m), and pipe length L (m) is expressed by the following formula: where k is the ratio of the pipe friction coefficient between a non-circular pipe and a circular pipe.

[0044]

number

[0045] If the dimension of the actuator in the depth direction differs, k, S, and A in the above relational expression will change. In particular, since the cross-sectional area is proportional to the cube, the deeper the actuator, the smaller the flow path resistance.

[0046] Therefore, as shown in FIG. 6, which shows the relationship between flow path resistance per unit volume and AL, it can be said that variations in the depth direction of the head actuator affect AL and flow path resistance.

[0047] In the equivalent circuit, if we consider the case where the flow path resistance of each head is different, that is, if heads with different AL are used, the resistance of the ink path flowing through each head will be RN = RN_Utube + RN_h + RN_Dtube(N = 1,2,3,4,5,6) It is expressed as:

[0048] In this case, if the dimensions of the upstream and downstream tubes are all the same, in other words, if the flow path resistance of the tubes that make up the connecting flow paths 2134, 2135 is the same, the difference in flow path resistance for each ink path will be the difference in flow path resistance for each head. In other words, the difference in flow path resistance for each head will cause a difference in the ink circulation flow rate for each head.

[0049] Therefore, for example, the flow rate of ink will be small in areas of the head where the flow path resistance is large, and on the other hand, the flow path of ink will be large in areas where the flow path resistance is small, resulting in differences in flow rate for each head 1.

[0050] Here, differences in the flow rate of ink flowing through the heads 1 directly affect ejection reliability, and therefore, if the absolute flow rate is small, ejection reliability will be degraded. Therefore, if an absolute flow rate of 30 mL / min or more is to be achieved for each head, it is necessary to ensure that the flow rate through the head with the highest flow path resistance is 30 mL / min. In this embodiment, the required minimum flow rate can be ensured by using the head with the highest flow path resistance as the reference. Therefore, the liquid ejection device 2 according to this embodiment can ensure the required circulation flow rate by controlling the circulating flow rate of ink using the head with the shortest AL among multiple heads as the reference.

[0051] On the other hand, since the flow path resistance of each head can be estimated from the AL of the head, by varying the length and diameter of the tube connected to the head and setting it so that the total flow path resistance of the tube from the upstream pressure source 2136 to the downstream pressure source 2137 and the head path is the same, it is possible to make the circulating flow rate of ink flowing through each head the same or reduce the difference in flow rate between heads.

[0052] According to this embodiment, in the case of a parallel connection in which multiple heads 1 are connected to a common pressure source 2136, 2137, the circulation flow rate can be controlled based on the head 1 with the highest AL, thereby simplifying control while ensuring the necessary circulation flow rate. Furthermore, according to the above-described embodiment, the flow path resistance of the connecting flow paths 2134, 2135 connecting the pressure sources 2136, 2137 to the heads is adjusted according to the AL of the head 1. By setting the flow path resistance so that the flow rates to each head 1 are equal, the difference in flow rate between the multiple heads connected to the common pressure source 2136, 2137 can be reduced. Therefore, the variation in ejection performance can be reduced. For example, when the AL is short, the flow path resistance of the head is high, so the resistance of the tubes connected to the heads can be reduced. On the other hand, when the AL is long, the flow path resistance of the head is low, so the resistance of the tubes connected to the heads can be increased, thereby reducing the difference in flow path between the heads.

[0053] Although one embodiment of the present invention has been described in detail above, the present invention is not limited to the above embodiment, and modifications and improvements can be made as appropriate.

[0054] For example, the specific conditions of the waveforms are not limited to those in the above embodiments and can be changed as appropriate. For example, the driving method may be any of pull-pulse, push-pulse, push-pull, and the like.

[0055] For example, the configuration of the liquid ejection head 1 is not limited to the above example, and may be used for other types of heads. Furthermore, although the liquid ejection device 2 has been exemplified as an inkjet printer that forms a two-dimensional image using ink on an image forming medium, it is not limited to this and may be, for example, a 3D printer, industrial manufacturing machinery, or medical machinery, and may be, for example, a device that forms a three-dimensional object by ejecting a material or a binder for solidifying the material from an inkjet head.

[0056] In addition, in the above embodiment, an example was shown in which the control operation was performed by the control unit 2118, but the present invention is not limited to this. For example, the liquid ejection head 1 may be provided with a drive circuit that drives the actuator, and the liquid ejection head 1 itself may be a drive device, or may be equipped with a drive device.

[0057] According to at least one of the embodiments described above, it is possible to drive a plurality of heads 1 using a common pressure source, and it is possible to reduce variations in ejection performance.

[0058] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0059] 1...liquid ejection head, 2...liquid ejection device, 21...nozzle plate, 22...actuator substrate, 23...manifold, 24...drive circuit, 25...actuator, 26...pressure chamber, 27...drive element section, 201...nozzle, 242...wiring board, 2001...transport path, 2111...casing, 2112...medium supply section, 2113...image forming section, 2114...medium discharge section, 2115...transport device, 2118...control section, 2120...support section, 2130... Head unit, 2132...supply tank, 2133...pressure regulating device, 2134...connecting flow path, 2135...connecting flow path, 2136...upstream pressure source, 2137...downstream pressure source, 21121...paper feed cassette, 21141...paper output tray, 21201...conveyor belt, 21202...support plate, 21203...belt roller, 21211 to 21218...guide plate pair, 21221 to 21228...conveyor roller, 241...driver IC.

Claims

1. In a circulation device having a plurality of liquid ejection heads, A method for controlling a circulation device, the method controlling the ink circulation flow rate of a plurality of liquid ejection heads based on the liquid ejection head having the shortest AL among the plurality of liquid ejection heads.

2. In a circulation device including a plurality of liquid ejection heads, based on the AL of the plurality of liquid ejection heads, A method for manufacturing a circulation device, comprising adjusting a flow path resistance of a flow path connected to the liquid ejection head.

3. A plurality of inkjet heads; a control unit that controls the ink circulation flow rate of the plurality of liquid ejection heads based on the liquid ejection head with the shortest AL among the plurality of inkjet heads.

4. A plurality of liquid ejection heads; a plurality of connection flow paths connected to the plurality of liquid ejection heads; Equipped with A circulation device in which the flow path resistance of a connection flow path connected to a liquid ejection head having a short AL among the plurality of liquid ejection heads is configured to be smaller than the flow path resistance of a connection flow path connected to a liquid ejection head having a long AL.

5. 5. The circulation device according to claim 4, wherein the connection flow path connected to the liquid ejection head having a short AL among the plurality of liquid ejection heads has a larger flow path cross-sectional area or a shorter flow path length than the connection flow path connected to the liquid ejection head having a long AL.

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