JP2020075446A - Liquid circulation system, liquid jet recording device and control method of liquid jet head - Google Patents

Abstract

To provide a liquid circulation system, a liquid jet recording device and a control method of a liquid jet head capable of improving printing image quality.SOLUTION: A liquid circulation system includes a liquid jet head having a plurality of nozzles which jet liquid, an accommodation part which accommodates liquid, a circulation mechanism which contains a circulation channel allowing liquid to flow therethrough and circulates liquid flowing through a circulation channel between accommodation part interior and liquid jet head interior and a control part which controls a circulation direction of liquid flowing through the circulation channel in accordance with operation circumstances of the liquid jet head when the liquid jet head is arranged such that a difference of elevation along a gravity direction between the plurality of nozzles is generated.SELECTED DRAWING: Figure 5

Description

  The present disclosure relates to a liquid circulation system, a liquid jet recording apparatus, and a liquid jet head control method.

  A liquid jet recording apparatus including a liquid jet head is used in various fields. In the liquid ejecting head, the volume inside the pressure chamber is changed by applying a pulse signal to the piezoelectric actuator, so that the liquid filled in the pressure chamber is ejected from the nozzle (for example, Patent Document 1). 1). Further, in the liquid ejecting head, a circulation type liquid ejecting head has been developed in which the liquid is circulated and used between the liquid containing portion and the liquid ejecting head.

JP, 2005-205838, A

  In such a liquid jet recording apparatus, it is generally required to improve print image quality. It is desirable to provide a liquid circulation system, a liquid jet recording apparatus, and a liquid jet head control method capable of improving print image quality.

  A liquid circulation system according to an embodiment of the present disclosure includes a liquid ejecting head having a plurality of nozzles for ejecting a liquid, an accommodating section for accommodating the liquid, and a circulation flow path through which the liquid flows, and A circulation mechanism for circulating the liquid flowing through the circulation flow path between the liquid ejection head and the liquid ejection head, when the liquid ejection head is arranged so that a height difference occurs along the gravity direction between the plurality of nozzles, And a control unit for controlling the circulation direction of the liquid flowing through the circulation flow path according to the operating condition of the liquid ejecting head.

  A liquid jet recording apparatus according to an embodiment of the present disclosure includes the liquid circulation system according to the embodiment of the present disclosure.

  A control method for a liquid ejecting head according to an embodiment of the present disclosure is to circulate a liquid flowing in a circulation flow path between a containing portion that contains a liquid and an inside of the liquid ejecting head, and between a plurality of nozzles. Controlling the circulation direction of the liquid flowing through the circulation flow path according to the operating condition of the liquid ejecting head when the liquid ejecting head is arranged so as to have a height difference along the direction of gravity. It is the one. During the filling operation for filling the liquid into the liquid ejecting head from the storage portion, the circulation direction of the liquid is controlled so that the liquid flows in the liquid ejecting head upward in the gravity direction. Further, during the ejection operation for ejecting the liquid from the liquid ejecting head, the circulation direction of the liquid is controlled so that the liquid flows downward in the gravity direction in the liquid ejecting head.

  According to the liquid circulation system, the liquid jet recording apparatus, and the liquid jet head control method according to the embodiment of the present disclosure, it is possible to improve print image quality.

FIG. 3 is a schematic perspective view illustrating an external configuration example of a liquid jet head according to an embodiment of the present disclosure. FIG. 3 is a schematic diagram illustrating a configuration example of a liquid jet recording apparatus including the liquid jet head illustrated in FIG. 1. FIG. 3 is a block diagram showing a configuration example of the liquid jet recording apparatus shown in FIG. 2. FIG. 3 is a schematic diagram illustrating a detailed configuration example of a circulation mechanism and the like illustrated in FIG. 2. It is a schematic diagram showing the example of a control process of the circulation direction of a liquid. FIG. 6 is a diagram showing numerical examples of pressure difference, flow rate, and the like during liquid filling operation and liquid discharging operation.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The description will be given in the following order.
1. Embodiment (an example of a method of controlling a liquid circulation direction according to an operating condition of a liquid ejecting head)
2. Modification

<1. Embodiment>
[Configuration of Printer 3]
FIG. 1 is a schematic perspective view showing an external configuration example of an inkjet head 1 as a liquid jet head according to an embodiment of the present disclosure. FIG. 2 is a schematic diagram showing a configuration example of a printer 3 as a liquid jet recording apparatus according to an embodiment of the present disclosure, which includes the inkjet head 1. FIG. 3 is a block diagram showing a configuration example of the printer 3. In each drawing used for the description of this specification, the scale of each member is appropriately changed in order to make each member recognizable.

  Further, FIG. 2 shows an example in which the inkjet head 1 is arranged so that a height difference along the gravity direction dg occurs between a plurality of nozzle holes Hn described later in the inkjet head 1. More specifically, in FIG. 2, the details will be described later, but the direction in which the plurality of nozzle holes Hn are arranged (the X-axis direction) intersects the horizontal direction dH (in this example, the gravity direction dg (the vertical direction dV)). )) Has become.

  The printer 3 is an inkjet printer that records (prints) images, characters, and the like on a recording medium (for example, recording paper) using ink 9 described below. As shown in FIGS. 1 to 3, the printer 3 includes an inkjet head 1, an ink container 2, a circulation mechanism 5, an information input unit 30, and a printer control unit 31 (print control unit). The method of controlling the liquid ejecting head according to the embodiment of the present disclosure is embodied in the printer 3 of the embodiment, and therefore will be described below together.

  Here, the inkjet head 1 corresponds to a specific example of “a liquid jet head” in the present disclosure, and the printer 3 corresponds to a specific example of a “liquid jet recording apparatus” in the present disclosure. The ink container 2 corresponds to a specific example of “accommodating portion” in the present disclosure, and the ink 9 corresponds to a specific example of “liquid” in the present disclosure. The inkjet head 1, the ink container 2, the circulation mechanism 5, and the printer control unit 31 correspond to a specific example of “a liquid circulation system” in the present disclosure, and the printer control unit 31 is a specific example of a “control unit” in the present disclosure. Corresponds to the example.

  As shown in FIG. 2, the ink container 2 is a container that contains the ink 9 therein.

(A. Inkjet head 1)
The inkjet head 1 ejects (discharges) a droplet of ink 9 onto a recording medium from a plurality of nozzles (nozzle holes Hn) to be described later, as indicated by broken line arrows in FIGS. 1 and 2. And a head for recording images and characters. As shown in FIGS. 1 to 3, the inkjet head 1 includes a nozzle plate 11, an actuator plate 12 (piezoelectric actuator), an ink supply / discharge port 14, an air damper 15, a drive board 16, a flow direction detection unit 17, It has an attitude detector 18 and a head controller 19.

  The nozzle plate 11 is a plate made of a film material such as polyimide or a metal material, and has a plurality of nozzle holes Hn for ejecting the ink 9, as shown in FIGS. The plurality of nozzle holes Hn are formed in a straight line (one row) at predetermined intervals along the X-axis direction and have a circular shape. In the arrangement example shown in FIG. 2, the plurality of nozzle holes Hn are arranged along the gravity direction dg (vertical direction dV). Therefore, in the arrangement example shown in FIG. 2, the ink 9 is ejected from each nozzle hole Hn in the horizontal direction dH (see the broken line arrow in FIG. 2).

  Each nozzle hole Hn (including nozzle holes Hn1 and Hn2 shown in FIG. 2 to be described later) corresponds to a specific example of “nozzle” in the present disclosure.

  The actuator plate 12 is a plate made of a piezoelectric material such as PZT (lead zirconate titanate). The actuator plate 12 is provided with a plurality of channels (not shown). These channels are portions that function as pressure chambers for applying pressure to the ink 9, and are arranged side by side so as to be parallel to each other at a predetermined interval along the X-axis direction. Each channel is defined by a drive wall (not shown) made of a piezoelectric material, and is a groove portion having a concave shape in a sectional view.

  Such channels include an ejection channel for ejecting the ink 9 and a dummy channel (non-ejection channel) that does not eject the ink 9. In other words, the ejection channels are filled with the ink 9, while the dummy channels are not filled with the ink 9. Further, each ejection channel communicates with the nozzle hole Hn in the nozzle plate 11 described above, while each dummy channel does not communicate with the nozzle hole Hn. These ejection channels and dummy channels are arranged alternately along the X-axis direction.

  A drive electrode (not shown) is provided on each of the opposing inner side surfaces of the drive wall. The drive electrode has a common electrode (common electrode) provided on the inner side surface facing the ejection channel and an active electrode (individual electrode) provided on the inner side surface facing the dummy channel. These drive electrodes and a drive circuit on the drive substrate 16 described later are electrically connected via a plurality of lead electrodes (not shown) formed on a flexible substrate (not shown). As a result, a drive voltage Vd (pulse signal Sp) described below is applied from the drive circuit to each drive electrode via the flexible substrate.

  The ink supply / discharge port 14 (see FIG. 1) supplies the ink 9 from the inside of the ink container 2 to the inside of the inkjet head 1 and discharges the ink 9 from the inside of the inkjet head 1 into the inside of the ink container 2. It is the part that The ink supply / discharge port 14 is provided with a pair (two) of inlet / outlet portions Ta and Tb as schematically shown in FIG. Each of the inlet / outlet portions Ta and Tb functions as an inlet portion Tin or an outlet portion Tout of the ink 9, although details will be described later (FIG. 5).

  It should be noted that these inlet / outlet portions Ta and Tb respectively correspond to specific examples of the “inlet portion” or the “outlet portion” in the present disclosure. Further, the above-described inlet portion Tin and outlet portion Tout correspond to specific examples of the “inlet portion” and the “outlet portion” in the present disclosure, respectively.

  The air damper 15 is a portion through which the ink 9 supplied or discharged via the ink supply / discharge port 14 passes, and the ink 9 is supplied toward each nozzle hole Hn via the actuator plate 12 described above. It is supposed to be done. The air damper 15 has a buffer function that makes it difficult to cause a problem such as so-called nozzle omission even when a physical impact is applied to the inkjet head 1 during the printing operation, and the air damper 15 has various forms. There is.

  The drive substrate 16 is a substrate on which a drive circuit (described above) including a head controller 19 described later is formed. Various information (print data or the like) is supplied to the drive circuit from an information input unit 30 described later via a printer control unit 31 described later. Then, a drive voltage Vd (pulse signal Sp), which will be described later, is applied from the drive circuit to each drive electrode of the actuator plate 12 via the above-mentioned flexible substrate.

  The flow direction detection unit 17 constantly detects the flow direction of the ink 9 in the inkjet head 1 (flow direction information If: see solid line and broken line arrow Fc shown in FIG. 4 described later). It is configured using a sensor and the like. The flow direction information If of the ink 9 detected by the flow direction detection unit 17 in this way is supplied to the printer control unit 31 described later as needed, as shown in FIG.

  The posture detection unit 18 constantly detects the posture of the inkjet head 1 (posture information Ip), and is configured by using, for example, an acceleration sensor or a geomagnetic sensor. Specifically, the posture detection unit 18 detects whether the arrangement direction of the plurality of nozzle holes Hn (X-axis direction: see FIGS. 1 and 2) is parallel to the horizontal direction dH. (See FIG. 2). The posture information Ip of the inkjet head 1 detected by the posture detection unit 18 in this manner is supplied to the printer control unit 31 described later as needed, as shown in FIG.

  The head controller 19 is electrically connected to each component of the inkjet head 1 and transmits / receives signals to / from each other, thereby comprehensively controlling each component. Specifically, the head controller 19 controls various operations in the inkjet head 1 (ejecting operation of the ink 9 and the like). More specifically, as shown in FIG. 3, the head control unit 19 acquires various information (print data or the like) from an information input unit 30 described later via a printer control unit 31 described later. Then, the head controller 19 controls the ejection operation of the ink 9 from each nozzle hole Hn by outputting the above-mentioned drive voltage Vd (pulse signal Sp) to the actuator plate 12.

  Such a head control unit 19 includes a CPU (Central Processing Unit) that executes various arithmetic processes, a ROM (Read Only Memory) that stores a control program and the like to be executed by the CPU, a buffer for various data, and an arithmetic operation. It has a RAM (Random Access Memory) used as a work area for processing.

(B. Circulation mechanism 5)
FIG. 4 schematically shows a detailed configuration example of the circulation mechanism 5 shown in FIG. 2 together with the ink container 2 and the inkjet head 1 described above. The solid and dashed arrows Fa1, Fa2, Fb1, Fb2, and Fc shown in FIG. 4 indicate the circulation directions of the ink 9, respectively.

  As shown in FIG. 4, the circulation mechanism 5 includes a circulation flow path 50, a pair of ink auxiliary tanks 51a and 51b, a pair of liquid feed pumps 52a and 52b, a filtration filter 53, and a pair of pressure control devices. 54a and 54b.

(B-1. Circulation channel 50)
The circulation flow path 50 is a flow path that circulates between the inside of the inkjet head 1 and the outside of the inkjet head 1 (inside the ink container 2), and the ink 9 circulates through the circulation flow path 50. There is. The circulation flow path 50 has two flow paths 50a and 50b that are portions that connect the ink container 2 and the inkjet head 1 (see FIG. 4). Although the details will be described later, the flow path 50a is a flow path through which the ink 9 can flow bidirectionally between the ink container 2 and the inkjet head 1 (see solid lines and dashed arrows Fa1 and Fa2 in FIG. 4). ). Similarly, the flow path 50b is a flow path (see solid lines and dashed arrows Fb1 and Fb2 in FIG. 4) through which the ink 9 can flow bidirectionally between the ink container 2 and the inkjet head 1.

  The flow channel 50a is composed of a pair of flow channels 50a1 and 50a2, as shown in FIG. Similarly, the flow channel 50b is also composed of a pair of flow channels 50b1 and 50b2, as shown in FIG.

  The flow path 50a1 is arranged so as to reach the inside of the ink auxiliary tank 51a, which will be described later, from the inside of the ink container 2 via the liquid feed pump 52a and the filtration filter 53, which will be described later. In the flow path 50a1, the ink 9 can flow in both directions between the ink container 2 and the ink auxiliary tank 51a (see solid line and broken line arrow Fa1 in FIG. 4).

  The flow path 50a2 is arranged so as to extend from the ink auxiliary tank 51a to the ink jet head 1. In the flow path 50a2, the ink 9 can flow in both directions between the ink auxiliary tank 51a and the ink jet head 1 (see solid line and broken line arrow Fa2 in FIG. 4). In the inlet / outlet portion Ta (previously described) schematically shown in FIG. 4, the ink 9 flowing through the circulation flow path 50 (flow path 50a2) flows into the inkjet head 1 or is circulated from the inkjet head 1. This is a portion where the ink 9 flows out to the path 50 (flow path 50a2).

  The flow path 50b1 is arranged so as to reach from the inside of the inkjet head 1 to the inside of an ink auxiliary tank 51b described later. In the flow path 50b1, the ink 9 can flow in both directions between the inkjet head 1 and the ink auxiliary tank 51b (see solid line and dashed arrow Fb1 in FIG. 4). In addition, in the inlet / outlet portion Tb (described above) schematically shown in FIG. 4, the ink 9 flows out from the inkjet head 1 to the circulation flow channel 50 (flow channel 50b1), or the circulation flow channel 50 (flow channel 50b1). Ink 9 flowing through the above) flows into the inkjet head 1.

  The flow path 50b2 is arranged so as to reach the inside of the ink container 2 from the inside of the ink auxiliary tank 51b via a liquid feed pump 52b described later. In the flow path 50b2, the ink 9 can flow in both directions between the ink auxiliary tank 51b and the ink container 2 (see solid line and dashed arrow Fb2 in FIG. 4).

(B-2. Ink auxiliary tank 51a, 51b)
The ink auxiliary tank 51a is inserted and installed on the flow path 50a (between the flow paths 50a1 and 50a2). The ink auxiliary tank 51a is a tank that stores the ink 9 in an auxiliary (temporary) manner. The ink auxiliary tank 51b is inserted and installed on the flow path 50b (between the flow paths 50b1 and 50b2). The ink auxiliary tank 51b is also a tank that auxiliary stores the ink 9.

  The liquid feed pump 52a is arranged between the ink container 2 and the filtration filter 53 on the flow path 50a (flow path 50a1). The liquid feed pump 52b is arranged between the ink auxiliary tank 51b and the ink container 2 on the flow path 50b (flow path 50b2).

  The filtration filter 53 is arranged on the flow path 50a (flow path 50a1) between the liquid feed pump 52a and the ink auxiliary tank 51a. The filtration filter 53 is a filter for removing impurities contained in the ink 9.

(B-3. Pressure control device 54a, 54b)
The pressure control device 54a is a device that is connected to the ink auxiliary tank 51a and controls the pressure Pa in the ink auxiliary tank 51a. Specifically, the pressure control device 54a controls the pressure Pa in the ink auxiliary tank 51a to be a positive pressure (positive pressure) by causing air to flow into the ink auxiliary tank 51a. Further, the pressure control device 54a controls the pressure Pa in the ink auxiliary tank 51a to be a negative pressure (negative pressure) by causing air to flow out from the ink auxiliary tank 51a.

  The pressure control device 54b is a device that is connected to the ink auxiliary tank 51b and controls the pressure Pb in the ink auxiliary tank 51b. Specifically, the pressure control device 54b controls the pressure Pb in the ink auxiliary tank 51b to be a positive pressure by causing air to flow into the ink auxiliary tank 51b. Further, the pressure control device 54b controls the pressure Pb in the ink auxiliary tank 51b to be a negative pressure by letting air out from the ink auxiliary tank 51b.

  Here, as will be described later in detail, the ink 9 circulates in the circulation channel in accordance with the pressure difference ΔP (= Pa−Pb) between the pressure Pa in the ink auxiliary tank 51a and the pressure Pb in the ink auxiliary tank 51b. The inside of 50 is circulated at a constant flow rate.

(C. Information input unit 30, printer control unit 31)
As shown in FIG. 3, the information input unit 30 supplies various information (data) to the above-mentioned head control unit 19 in the inkjet head 1 via a printer control unit 31 described below. Is. The information input unit 30 is configured to input various kinds of information as described above and perform various settings and operations. Such an information input unit 30 is configured by using, for example, a touch panel arranged on the housing of the printer 3 or the like. The information input unit 30 may not be provided in the printer 3 itself, but may be, for example, a host computer connected to the printer 3 via a network.

  The printer control unit 31 performs various kinds of control (control of printing operation, etc.) on the printer 3 as a whole, and controls various members of the printer 3.

  Here, in the present embodiment, the printer control unit 31 controls the circulation direction (supply direction) of the ink 9 flowing through the circulation flow path 50 according to the operation status of the inkjet head 1, which will be described in detail later. (See solid line and broken line arrows Fa1, Fa2, Fb1, Fb2, Fc in FIG. 4). At this time, the printer control unit 31 controls the values of the pressures Pa and Pb applied to the above-mentioned inlet / outlet portions Ta and Tb (portions that function as the inlet portion Tin or the outlet portion Tout) of the inkjet head 1, respectively. The circulation direction of the ink 9 is controlled (see FIG. 4).

  Further, the printer control unit 31 controls the circulation direction of the ink 9 while confirming the flow direction information If of the ink 9 supplied from the above-described flow direction detection unit 17. Furthermore, the printer control unit 31 controls the circulation direction of the ink 9 using the posture information Ip of the inkjet head 1 supplied from the posture detection unit 18 described above.

  The details of the control process of the circulation direction of the ink 9 by the printer control unit 31 will be described later (FIGS. 5 and 6).

[Motion and action / effect]
(A. Basic operation of the printer 3)
In the printer 3, a recording operation (printing operation) of an image, a character, or the like on a recording medium is performed by using the following ejecting operation of the ink 9 by the inkjet head 1. Specifically, in the inkjet head 1 of the present embodiment, the ejection operation of the ink 9 using the shear (share) mode is performed as follows.

  First, the head controller 19 applies the drive voltage Vd (pulse signal Sp) to the drive electrodes (common electrode and active electrode) in the actuator plate 12 (see FIG. 3). Specifically, the head controller 19 applies the drive voltage Vd to the drive electrodes arranged on the pair of drive walls that define the ejection channels. As a result, each of the pair of drive walls is deformed so as to project toward the dummy channel adjacent to the ejection channel.

  At this time, the drive wall is bent and deformed into a V shape around the middle position of the drive wall in the depth direction. Then, due to such bending deformation of the drive wall, the ejection channel is deformed as if it were swollen. In this way, the volume of the discharge channel increases due to the bending deformation due to the piezoelectric thickness sliding effect on the pair of drive walls. Then, as the volume of the ejection channel increases, the ink 9 is guided into the ejection channel.

  Then, the ink 9 thus guided into the ejection channel becomes a pressure wave and propagates inside the ejection channel. Then, at the timing when this pressure wave reaches the nozzle hole Hn of the nozzle plate 11 (or the timing near that), the drive voltage Vd applied to the drive electrode becomes 0 (zero) V. As a result, the drive wall is restored from the above-described bending deformation state, and as a result, the volume of the discharge channel, which has once increased, returns to the original volume.

  In this way, in the process of returning the volume of the ejection channel to the original value, the pressure inside the ejection channel increases and the ink 9 in the ejection channel is pressurized. As a result, the droplet-shaped ink 9 is ejected to the outside (toward the recording medium) through the nozzle hole Hn (see FIGS. 1, 2, and 4). In this way, the ejection operation (ejection operation) of the ink 9 in the inkjet head 1 is performed, and as a result, the recording operation of the image, the character or the like on the recording medium is performed.

  Particularly, in the inkjet head 1 (circulation type inkjet head) of the present embodiment, the ink 9 circulates in the circulation flow path 50 between the inkjet head 1 and the ink container 2 (see FIG. 4). ..

  Here, in the non-circulation type inkjet head (comparative example), for example, when an ink having a high drying property is used, due to the drying of the ink in the vicinity of the nozzle hole, the ink locally becomes highly viscous or solidifies. As a result, ink ejection failure may occur. On the other hand, in the ink jet head 1 of the present embodiment, which is of the circulation type, since the fresh ink 9 is constantly supplied in the vicinity of the nozzle hole Hn, the above-mentioned defect of ink ejection failure is avoided. It will be.

(B. Control operation by printer controller 31)
Next, the control operation by the printer control unit 31 described above (control processing of the circulation direction of the ink 9 described above) will be described in detail.

  First, in the inkjet head, in recent years, particularly in the industrial field, in particular, there is an increasing demand for printing on various materials such as resin and metal and increasing the printing speed. Therefore, an inkjet head has been commercialized that can eject droplets using a wide variety of inks under conditions such as high frequency and high temperature. Further, since high definition of image quality (improvement of image quality) is also required, for example, by increasing the gradation of the droplet size and performing the ejection operation, small droplets to large droplets are covered. Inkjet heads have also been developed. In this way, inkjet heads are required to have both high definition and high productivity, which means that not only OA (Office Automation) applications such as photographs and documents, but also industrial applications such as cardboard and wood. Is also true.

  By the way, in particular, when printing with an inkjet head (inkjet printing) is applied to the display of a package such as a cardboard, a method of ejecting the ink in the horizontal direction toward the surface to be printed is used (the example of FIG. 2 described above). See). Generally, in inkjet printing, the nozzle surface (arrangement surface of a plurality of nozzle holes) is arranged along the horizontal direction. However, when printing on the side surface of the object as described above, the nozzle surface other than the horizontal direction is printed. The nozzle surface is arranged along the direction (vertical direction or diagonal direction). In addition, the method of arranging the nozzle surfaces along a direction other than the horizontal direction in this way is also used when mass-producing in a line such as a factory.

  The advantage of this method (discharging method) is that even if the product cannot be packaged after being printed or the orientation of the package cannot be changed, it can be handled.

  However, when the nozzle surfaces are arranged along a direction other than the horizontal direction, a height difference occurs along the gravity direction between the plurality of nozzle holes (see FIG. 2), so that the nozzle holes and the liquid surface of the ink are separated from each other. Since a height difference occurs between them, it becomes difficult to obtain the original performance of the inkjet head.

(B-1. Correspondence between Head Difference h and Droplet Volume V during Discharging Operation)
First, in the ejection operation of ejecting the ink 9 from the inkjet head 1, if the control processing of the circulation direction of the ink 9 described later is not performed, the print density varies among the plurality of nozzle holes Hn as described below, and the printing is performed. The image quality may deteriorate.

  That is, as described above, when the nozzle surface of the inkjet head 1 is arranged along a direction other than the horizontal direction dH, the head difference h of the ink 9 influences the droplet amount V ejected from each nozzle hole Hn. It will be. Specifically, as the head difference h increases, the back pressure generated in the meniscus of the nozzle hole Hn increases, so that the ejection amount of the ink 9 decreases.

  Here, in normal inkjet printing (when the ink 9 is ejected from each nozzle hole Hn toward the vertical direction dV (gravitational direction dg)), the value of the head difference h does not change in each nozzle hole Hn (a constant value). Therefore, the droplet amount V is uniform in all the nozzle holes Hn. On the other hand, unlike the arrangement example shown in FIG. 2, the arrangement direction of the plurality of nozzle holes Hn is not the horizontal direction dH, but the height difference along the gravity direction dg is generated between the plurality of nozzle holes Hn. When the inkjet head 1 is arranged, it is as follows. That is, in the arrangement example of FIG. 2, since the ink 9 is ejected from each nozzle hole Hn in the horizontal direction dH, a difference in the head difference h of the ink 9 occurs between the nozzle holes Hn.

  Specifically, in the example shown in FIG. 2, the nozzle head Hn1 on the upper side (uppermost end) along the gravity direction dg has a water head difference h1, and the lower side (lowermost end) along the gravity direction dg. In the nozzle hole Hn2 of), the head difference h2 (<head difference h1).

  In this case, the ink 9 is supplied from the inside of the ink container 2 in the nozzle hole Hn1 having a relatively large water head difference h (water head difference h1) as compared with the nozzle hole Hn2 having a relatively small water head difference h (water head difference h2). Since it becomes difficult, the droplet amount V of the ejected ink 9 becomes small. That is, the droplet amount V1 in the nozzle hole Hn1 (water head difference h1) is smaller than the droplet amount V2 in the nozzle hole Hn2 (water head difference h2) (droplet amount V1 <droplet amount V2). Therefore, the nozzle hole Hn1 (water head difference h1) having a relatively large water head difference h has a smaller print density than the nozzle hole Hn2 having a relatively small water head difference h (water head difference h2). The print density varies between the nozzle holes Hn. The amount of change in the droplet amount V between the head differences h1 and h2 (difference between the droplet amounts V1 and V2) is, for example, about 4%.

  In this way, when the inkjet head 1 is arranged so that there is a height difference along the gravity direction dg between the plurality of nozzle holes Hn as in the arrangement example shown in FIG. .. That is, due to the pressure gradient due to the influence of gravity (the difference in the value of the water head difference h of the ink 9 between the nozzle holes Hn) as described above, the print density varies among the plurality of nozzle holes Hn. There is a risk that

  The difference between the water head differences h1 and h2 described above corresponds to the effective print length of the inkjet head 1 (see FIG. 2). For this reason, it can be said that the above-mentioned problem becomes particularly remarkable in the case of a so-called long type ink jet head having a large number of nozzle holes Hn (nozzle number). By the way, the difference (effective print length) between the head differences h1 and h2 is about 72 mm, for example.

(B-2. Regarding retention of bubbles in ink during filling operation)
On the other hand, during the filling operation for filling the ink 9 from the ink container 2 into the inkjet head 1, if the control processing of the circulation direction of the ink 9 described later is not performed, the following accumulation of bubbles in the ink 9 may occur. As a result, defective ejection of the ink 9 may occur.

  Specifically, as described above, when the nozzle surface of the inkjet head 1 is arranged along a direction other than the horizontal direction dH, the above-described influence of gravity (the value of the water head difference h of the ink 9 between the nozzle holes Hn is calculated. Difference) makes it easier for air bubbles to stay in the ink 9 in the inkjet head 1. When air bubbles stay in the ink 9 in the inkjet head 1, ejection failure of the ink 9 may occur due to the stay of such air bubbles, and the print image quality may deteriorate. ..

  In this way, when the nozzle surface of the inkjet head 1 is arranged along the direction other than the horizontal direction dH, the control process of the circulation direction of the ink 9 described in detail below is not performed, and the ink 9 is filled and ejected. At any time during the operation, the print quality may be deteriorated.

(B-3. Control processing of circulation direction of ink 9)
Therefore, in the inkjet head 1 of the present embodiment, the control of the circulation direction of the ink 9 by the printer control unit 31 is performed as described below to suppress the above-described deterioration of print image quality.

  Here, FIG. 5 schematically shows an example of control processing of the circulation direction of the ink 9. Specifically, FIG. 5A shows an example of control processing of the circulation direction of the ink 9 during the filling operation of the ink 9 described above. Further, FIG. 5B shows an example of control processing of the circulation direction of the ink 9 at the time of the ejection operation of the ink 9 described above. 5A and 5B, the height difference along the gravity direction dg is generated between the plurality of nozzle holes Hn in the same manner as in the example of FIG. It is assumed that the inkjet head 1 is arranged. That is, it is assumed that the arrangement direction (X-axis direction) of the plurality of nozzle holes Hn is the direction intersecting the horizontal direction dH (gravitational direction dg (vertical direction dV)).

  FIG. 6 shows the pressures Pa and Pb, the pressure difference ΔP (= Pa−Pb), and the pressure difference during the filling operation (FIG. 6A) and the discharging operation (FIG. 6B). Each numerical example of the absolute value | ΔP | of ΔP and the flow rate F of the ink 9 flowing through the circulation flow path 50 is shown.

  As described above, the printer control unit 31 controls the circulation direction of the ink 9 flowing through the circulation flow path 50 in accordance with the operation status of the inkjet head 1 (during the filling operation or the ejection operation) (in FIG. 4). See solid and dashed arrows Fa1, Fa2, Fb1, Fb2, Fc). At this time, the printer control unit 31 controls the values of the pressures Pa and Pb applied to the inlet / outlet portions Ta and Tb (inlet portion Tin and outlet portion Tout) of the inkjet head 1 described above, thereby circulating the ink 9. Control the direction (see FIG. 4).

(During filling operation)
First, during the filling operation shown in FIGS. 5A and 6A, the printer control unit 31 causes the ink 9 to flow upward in the inkjet head 1 in the gravity direction dg. Control circulation direction.

  Specifically, the printer control unit 31 causes the pressure Pa applied to the entrance / exit portion Ta, which functions as the entrance portion Tin, to be a positive pressure (> 0) and is applied to the entrance / exit portion Tb that functions as the exit portion Tout. The pressure Pb is controlled to be a negative pressure (<0) (see FIGS. 5A and 6A). In this way, the pressure difference ΔP (= Pa−Pb) between the pressures Pa and Pb becomes a positive value (> 0) (see FIG. 6A), so that the direction of gravity dg in the inkjet head 1 is increased. The ink 9 will flow upward (see solid arrow Fc in FIG. 5A).

(During discharge operation)
Further, during the ejection operation shown in FIGS. 5B and 6B, the printer control unit 31 controls the ink 9 so that the ink 9 flows downward in the gravity direction dg in the inkjet head 1. Control circulation direction.

  Specifically, the printer control unit 31 causes the pressure Pb applied to the inlet / outlet portion Tb functioning as the inlet portion Tin to be a positive pressure (> 0) and is applied to the inlet / outlet portion Ta functioning as the outlet portion Tout. The pressure Pa is controlled so as to be a negative pressure (<0) (see FIGS. 5B and 6B). In this way, the pressure difference ΔP (= Pa−Pb) between the pressures Pa and Pb becomes a negative value (<0) (see FIG. 6 (B)), so that the gravity direction dg in the inkjet head 1. The ink 9 will flow downward (see the dashed arrow Fc in FIG. 5B).

  In this way, the printer control unit 31 inverts the positive and negative values of the pressures Pa and Pb (and the pressure difference ΔP) between the filling operation and the discharging operation, thereby performing the filling operation and the discharging operation. Thus, the circulation direction of the ink 9 is reversed. During the filling operation, for example, after the ink 9 is filled in the inkjet head 1, the circulation of the ink 9 between the ink container 2 and the inkjet head 1 may be stopped. Good.

  Here, comparing each numerical example at the time of charging operation and at the time of discharging operation shown in FIG. 6 (A) and FIG. 6 (B) respectively, it is as follows. That is, first, the flow rate F of the ink 9 flowing through the circulation flow path 50 is substantially the same between the filling operation and the ejection operation. On the other hand, as for the absolute value | ΔP | of the pressure difference ΔP described above, compared with the time of the filling operation (the ink 9 flows upward in the gravity direction dg), the time of the ejection operation (downward in the gravity direction dg). Ink 9) is smaller. In other words, the pressure gradient due to the effect of gravity described above is alleviated during the discharging operation as compared with during the filling operation. Therefore, it can be said that, during the ejection operation, the above-mentioned variation in print density among the plurality of nozzle holes Hn due to such a pressure gradient can be suppressed.

(C. Action / effect)
In this way, in the inkjet head 1, when the inkjet head 1 is arranged so that there is a height difference along the gravity direction dg among the plurality of nozzle holes Hn, depending on the operating condition of the inkjet head 1, The circulation direction of the ink 9 flowing through the circulation flow path 50 is controlled.

  As a result, in the present embodiment, for example, the inkjet head 1 is arranged such that the arrangement direction of the plurality of nozzle holes Hn is not the horizontal direction dH but a height difference along the gravity direction dg is generated between the plurality of nozzle holes Hn. Even if it is (see FIG. 2 and FIG. 5), it is as follows. That is, the deterioration of the ejection characteristics of the inkjet head 1 due to the influence of gravity (the difference in the value of the water head difference h of the ink 9 between the nozzle holes Hn) as described above is suppressed. As a result, with the inkjet head 1 of the present embodiment, it is possible to improve the print image quality.

  In addition, as shown in FIGS. 2 and 5, particularly when a plurality of nozzle holes Hn are arranged along the gravity direction dg, the following is performed. That is, if the control of the circulation direction of the ink 9 is not performed, the deterioration of the ejection characteristics of the inkjet head 1 due to the influence of the gravity becomes the largest. Therefore, by controlling the circulation direction of the ink 9 as described above, the effect of suppressing the deterioration of the ejection characteristics of the inkjet head 1 is maximized, and as a result, the effect of improving the print image quality can be maximized.

  Furthermore, during the filling operation of the ink 9 into the inkjet head 1, the circulation direction of the ink 9 is controlled so that the ink 9 flows upward in the inkjet head 1 in the gravity direction dg. (See FIG. 5 (A)), as follows. That is, for example, as described above, even when the inkjet head 1 is arranged so that the height difference is generated between the nozzle holes Hn, the influence of gravity (the head difference h of the ink 9 between the nozzle holes Hn is h. The occurrence of defective ejection of the ink 9 due to the retention of air bubbles in the ink 9 in the inkjet head 1 due to the difference (value of) is suppressed. Specifically, by controlling the ink 9 to flow upward in the inkjet head 1 in the direction of gravity dg, the bubbles in the ink 9 described above are easily removed from the inkjet head 1. The occurrence of ejection failure of No. 9 is suppressed. Therefore, it is possible to improve the print image quality by utilizing the circulation direction control of the ink 9 at the time of the filling operation described above.

  In addition, when the ink 9 is ejected from the inkjet head 1, the circulation direction of the ink 9 is controlled so that the ink 9 flows downward in the inkjet head 1 in the gravity direction dg. (See FIG. 5 (B)), as follows. That is, for example, as described above, even in the case where the inkjet head 1 is arranged so that the height difference is generated between the nozzle holes Hn, the plurality of nozzle holes caused by the pressure gradient due to the influence of the gravity described above. Variations in print density between Hn can be suppressed. Specifically, first, a nozzle hole Hn (for example, the nozzle hole in FIG. 2) located on the upper side in the gravity direction dg (the water head difference h1 of the ink 9 from the liquid surface of the ink container 2 is relatively large). Hn1) is as follows. That is, compared with the nozzle hole Hn2 (for example, the nozzle head Hn2 in FIG. 2) located on the lower side in the gravity direction dg (the water head difference h2 of the ink 9 is relatively small), it is caused by the above-mentioned pressure gradient. Since the ink 9 is less likely to be supplied, the amount V of ejected droplets also becomes smaller, resulting in a decrease in print density. Therefore, by controlling the ink 9 to flow downward in the gravity direction dg in the inkjet head 1, between the upper nozzle hole Hn and the lower nozzle hole Hn along the gravity direction dg. As a result of the decrease in the pressure gradient of, the variation in print density is suppressed. Therefore, it is possible to improve the print image quality by utilizing the circulation direction control of the ink 9 at the time of the ejection operation described above.

  Further, the circulation direction of the ink 9 is controlled by controlling the values of the pressures Pa and Pb applied to the inlet / outlet portions Ta and Tb (the inlet portion Tin and the outlet portion Tout) of the inkjet head 1. It looks like this: That is, the circulation direction of the ink 9 can be easily controlled by utilizing such control of the values of the pressures Pa and Pb. Therefore, it is possible to easily improve the print image quality.

  Further, the above-described control of the circulation direction of the ink 9 is performed according to the attitude (attitude information Ip) of the inkjet head 1 detected by the attitude detection unit 18, and thus the following is performed. That is, the deterioration of the ejection characteristics of the inkjet head 1 due to the influence of the gravity described above can be more effectively suppressed, and as a result, the print image quality can be further improved.

  In addition, while confirming the flowing direction (flow direction information If) of the ink 9 in the inkjet head 1 detected by the flow direction detecting unit 17, the above-described control of the circulation direction of the ink 9 is performed. It looks like this: That is, the deterioration of the ejection characteristics of the inkjet head 1 due to the influence of the gravity described above can be more reliably suppressed, and as a result, the print image quality can be further improved.

<2. Modification>
Although the present disclosure has been described above with reference to the embodiment, the present disclosure is not limited to this embodiment, and various modifications can be made.

  For example, in the above-described embodiment, the configuration example (shape, arrangement, number, etc.) of each member in the printer 3 and the inkjet head 1 is specifically described, but the present invention is not limited to that described in the above-described embodiment. Other shapes, arrangements, numbers, etc. may be used. Further, the values, ranges, magnitude relationships, etc. of various parameters described in the above embodiments are not limited to those described in the above embodiments, and other values, ranges, magnitude relationships, etc. may be used.

  Specifically, for example, in the above-described embodiment, the one-row type inkjet head 1 (a type in which a plurality of nozzle holes Hn are arranged along one row) has been described as an example. Is not limited. That is, for example, an inkjet head of a type having two or more rows may be used. Also, the shape of the nozzle hole Hn is not limited to the circular shape described in the above embodiment, and may be, for example, a polygonal shape such as a triangular shape, an elliptical shape, or a star shape.

  Further, in the above embodiment, the case where the circulation mechanism 5 includes the ink auxiliary tanks 51a and 51b has been described, but the present invention is not limited to this example, and the ink auxiliary tanks 51a and 51b are provided. You may not be allowed to. In other words, while the ink 9 is circulated using the liquid feed pumps 52a and 52b, the liquid feed operation of the liquid feed pumps 52a and 52b (instead of utilizing the pressure difference ΔP as described in the above embodiment) is performed. It may be used to control the circulation direction of the ink 9 flowing through the circulation flow path 50.

  Further, as the structure of the inkjet head 1, each type can be applied. That is, for example, it may be a so-called side shoot type inkjet head 1 that ejects the ink 9 from the central portion in the extending direction of each ejection channel in the actuator plate 12. Alternatively, for example, it may be a so-called edge shoot type inkjet head 1 that ejects the ink 9 along the extending direction of each ejection channel.

  In addition, the method of the printer 3 is not limited to the method described in the above embodiment and the like, and various methods such as a MEMS (Micro Electro Mechanical Systems) method can be applied.

  Further, in the above-described embodiment, an example of control processing of the circulation direction (supply direction) of the ink 9 by the printer control unit 31 has been specifically described, but the present invention is not limited to the example described in the above-described embodiment. You may make it control using another method. Specifically, for example, the circulation direction of the ink 9 is controlled without using the flow direction information If detected by the flow direction detection unit 17 or the posture information Ip detected by the posture detection unit 18. Good. It should be noted that the flow direction detecting unit 17 and the posture detecting unit 18 are not provided inside the inkjet head 1 as described in the above embodiments, but are provided outside the inkjet head 1 in the printer 3, for example. You may do it. Further, the operation status of the inkjet head 1 when controlling the circulation direction of the ink 9 is not limited to the status of the filling operation and the discharging operation of the ink 9 described in the above embodiment, and other operation status. May be included or replaced with other operating conditions to control the circulation direction.

  In addition, the series of processes described in the above embodiments may be performed by hardware (circuit) or software (program). When the software is used, the software is composed of a program group for causing a computer to execute each function. Each program may be installed in the computer in advance and used, or may be installed in the computer from a network or a recording medium and used.

  Further, in the above-described embodiment, the printer 3 (inkjet printer) has been described as a specific example of the “liquid jet recording apparatus” in the present disclosure, but the present invention is not limited to this example, and an apparatus other than the inkjet printer. Also, the present disclosure can be applied. In other words, the “liquid ejecting head” (inkjet head 1) of the present disclosure may be applied to a device other than the inkjet printer. Specifically, for example, the “liquid ejecting head” of the present disclosure may be applied to a device such as a facsimile or an on-demand printing machine.

  Furthermore, the various examples described so far may be applied in an arbitrary combination.

  It should be noted that the effects described in this specification are merely examples and are not limited, and may have other effects.

Further, the present disclosure can also take the following configurations.
(1)
A liquid ejecting head having a plurality of nozzles for ejecting a liquid;
A container for containing the liquid,
A circulation mechanism that includes a circulation flow path through which the liquid flows, and a circulation mechanism that circulates the liquid that flows through the circulation flow path between the accommodation portion and the liquid ejection head.
When the liquid ejecting head is arranged so that a height difference along the direction of gravity is generated between the plurality of nozzles, the circulation of the liquid flowing through the circulation flow path is performed according to the operating condition of the liquid ejecting head. A liquid circulation system with a control unit that controls the direction.
(2)
The control unit is
During the ejection operation for ejecting the liquid from the liquid ejecting head,
The liquid circulation system according to (1), wherein the circulation direction of the liquid is controlled so that the liquid flows downward in the direction of gravity in the liquid ejecting head.
(3)
The control unit is
At the time of the filling operation for filling the liquid into the liquid ejecting head from the storage portion,
The liquid circulation system according to (1) or (2) above, wherein the circulation direction of the liquid is controlled so that the liquid flows upward in the direction of gravity in the liquid ejecting head.
(4)
The liquid jet head,
An inlet part through which the liquid flowing through the circulation flow path flows into the liquid ejecting head;
And an outlet portion through which the liquid flowing through the circulation flow path flows out of the liquid ejecting head.
The liquid circulation according to any one of (1) to (3), wherein the control unit controls the circulation direction of the liquid by controlling the value of the pressure applied to each of the inlet and the outlet. system.
(5)
Further comprising a posture detection unit that detects the posture of the liquid jet head,
The liquid circulation system according to any one of (1) to (4), wherein the control unit controls the circulation direction of the liquid according to the posture of the liquid jet head detected by the posture detection unit.
(6)
Further comprising a flow direction detection unit for detecting a flow direction of the liquid in the liquid ejecting head,
The liquid circulation system according to claim 1, wherein the control unit controls the circulation direction of the liquid while confirming the flow direction of the liquid detected by the flow direction detection unit.
(7)
The liquid circulation system according to any one of (1) to (6), wherein the plurality of nozzles are arranged along the gravity direction.
(8)
A liquid jet recording apparatus comprising the liquid circulation system according to any one of claims 1 to 7.
(9)
A method for controlling a liquid ejecting head having a plurality of nozzles for ejecting a liquid, comprising:
Circulating the liquid flowing in the circulation flow path between the inside of the liquid jet head and the inside of the containing portion for containing the liquid;
When the liquid ejecting head is arranged so that a height difference occurs along the direction of gravity between the plurality of nozzles, the circulation of the liquid flowing through the circulation flow path according to the operating condition of the liquid ejecting head. Controlling the direction,
At the time of a filling operation for filling the liquid into the liquid ejecting head from the storage portion, the circulation direction of the liquid is changed in the liquid ejecting head so that the liquid flows upward in the gravity direction. Control and
During the ejection operation for ejecting the liquid from the liquid ejecting head, the liquid ejecting head controls the circulation direction of the liquid so that the liquid flows downward in the gravity direction in the liquid ejecting head. Control method.

  DESCRIPTION OF SYMBOLS 1 ... Inkjet head, 11 ... Nozzle plate, 12 ... Actuator plate (piezoelectric actuator), 14 ... Ink supply / exhaust port, 15 ... Air damper, 16 ... Drive board, 17 ... Flow direction detection part, 18 ... Attitude detection part, 19 ... Head control unit, 2 ... Ink container, 3 ... Printer, 30 ... Information input unit, 31 ... Printer control unit (printing control unit), 5 ... Circulation mechanism, 50 ... Circulation flow path, 50a (50a1, 50a2), 50b (50b1, 50b2) ... Flow path, 51a, 51b ... Ink auxiliary tank, 52a, 52b ... Liquid feed pump, 53 ... Filtration filter, 54a, 54b ... Pressure control device, 9 ... Ink, Hn, Hn1, Hn2 ... Nozzle Hole, h, h1, h2 ... Head difference, V, V1, V2 ... Drop volume, dH ... Horizontal direction, dV ... Vertical direction, dg ... Gravity direction, Sp ... Pulse signal, Vd ... Driving voltage, If ... Flow direction Information, Ip ... Attitude information, Ta, Tb ... Inlet / outlet part, Tin ... Inlet part, Tout ... Outlet part, Pa, Pb ... Pressure, .DELTA.P ... Pressure difference, F ... Flow rate.

Claims (9)

A liquid ejecting head having a plurality of nozzles for ejecting a liquid;
A container for containing the liquid,
A circulation mechanism that includes a circulation flow path through which the liquid flows, and a circulation mechanism that circulates the liquid that flows through the circulation flow path between the accommodation portion and the liquid ejection head.
When the liquid ejecting head is arranged so that a height difference along the direction of gravity is generated between the plurality of nozzles, the circulation of the liquid flowing through the circulation flow path is performed according to the operating condition of the liquid ejecting head. A liquid circulation system with a control unit that controls the direction. The control unit is
During the ejection operation for ejecting the liquid from the liquid ejecting head,
The liquid circulation system according to claim 1, wherein a circulation direction of the liquid is controlled in the liquid ejecting head so that the liquid flows downward in the gravity direction. The control unit is
At the time of the filling operation for filling the liquid into the liquid ejecting head from the storage portion,
The liquid circulation system according to claim 1, wherein a circulation direction of the liquid is controlled so that the liquid flows upward in the direction of gravity in the liquid ejecting head. The liquid jet head,
An inlet part through which the liquid flowing through the circulation flow path flows into the liquid ejecting head;
And an outlet portion through which the liquid flowing through the circulation flow path flows out of the liquid ejecting head.
The liquid according to any one of claims 1 to 3, wherein the control unit controls a circulation direction of the liquid by controlling values of pressures applied to the inlet portion and the outlet portion, respectively. Circulation system. Further comprising a posture detection unit that detects the posture of the liquid jet head,
The liquid circulation system according to claim 1, wherein the control unit controls the circulation direction of the liquid according to the posture of the liquid ejecting head detected by the posture detection unit. Further comprising a flow direction detection unit for detecting a flow direction of the liquid in the liquid ejecting head,
The liquid circulation system according to any one of claims 1 to 5, wherein the control unit controls the circulation direction of the liquid while confirming the flowing direction of the liquid detected by the flow direction detection unit. .. The liquid circulation system according to claim 1, wherein the plurality of nozzles are arranged along the gravity direction. A liquid jet recording apparatus comprising the liquid circulation system according to any one of claims 1 to 7. A method for controlling a liquid ejecting head having a plurality of nozzles for ejecting a liquid, comprising:
Circulating the liquid flowing in the circulation flow path between the inside of the liquid jet head and the inside of the containing portion for containing the liquid;
When the liquid ejecting head is arranged so that a height difference along the direction of gravity is generated between the plurality of nozzles, the circulation of the liquid flowing through the circulation flow path is performed according to the operating condition of the liquid ejecting head. Controlling the direction,
At the time of a filling operation for filling the liquid into the liquid ejecting head from the storage portion, the circulation direction of the liquid is changed in the liquid ejecting head so that the liquid flows upward in the gravity direction. Control and
During the ejection operation of ejecting the liquid from the liquid ejecting head, the liquid ejecting head controls the circulation direction of the liquid so that the liquid flows downward in the direction of gravity in the liquid ejecting head. Control method.

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