JP2012171255A - Ink jet head, and recording device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink jet head reducing variations in discharging speed caused by a pressure distribution in a common passage.SOLUTION: The ink jet head 5 includes a base substrate 21 with a plurality of discrete passages 25, and two common passages 27 formed. Each discrete passage 25 includes a pressurizing chamber 31, and two supply holes 34 communicating with the pressurizing chamber 31 and respectively opened to the two common passages 27. Among the plurality of discrete passages 25, the order from the upstream side, of first supply holes 34A in the first common passage 27A is reverse to the order from the upstream side, of second supply holes 34B in the second common passage 27B.

Description

  The present invention relates to an inkjet head and a recording apparatus.

  An inkjet head having a plurality of pressurizing chambers that communicate with a plurality of discharge holes, a plurality of supply holes that communicate with the plurality of pressurizing chambers, and a common flow path in which the plurality of supply holes open on the inner peripheral surface is known. (For example, Patent Document 1). The space from the common flow path to the plurality of ejection holes is filled with ink. Then, the volume of the plurality of pressurizing chambers changes to apply pressure to the ink, whereby ink is sent from the plurality of pressurizing chambers to the plurality of ejection holes, and a plurality of ink droplets are ejected from the plurality of ejection holes. Is done. Further, the plurality of pressurizing chambers are replenished with ink from a common flow path via a plurality of supply holes.

JP 2008-200902 A

  In the common flow path, a pressure distribution is generated in which the pressure is lowered toward the downstream side due to pressure loss or the like. On the other hand, the plurality of supply holes are arranged along the flow direction of the common flow path, and the plurality of pressurizing chambers receive different pressures from the common flow path. Therefore, the ink droplet ejection speed varies due to the pressure distribution in the common flow path.

  An object of the present invention is to provide an ink jet head and a recording apparatus that can alleviate variations in ejection speed caused by pressure distribution in a common flow path.

  An ink jet head according to an aspect of the present invention includes a base on which a plurality of individual flow paths and n (n ≧ 2) common flow paths are formed. And n supply holes that open to the n common flow paths, respectively, and communicate with the pressurizing chamber, and regarding the predetermined two common flow paths among the n common flow paths, Among a plurality of individual flow paths, the order from the upstream side of the supply hole in one common flow path is reversed from the order from the upstream side of the supply hole in the other common flow path.

  Preferably, n is an even number, and the order from the upstream side of the i-th supply hole that opens to the i-th (1 ≦ i ≦ n) common channel is m (i). The total sum of m (i) from i = 1 to i = n is equal among the plurality of individual flow paths.

  Preferably, in at least one common channel of the two predetermined common channels, an area of a cross section perpendicular to the channel is larger on the upstream side than on the downstream side.

  Preferably, the two predetermined common flow paths are configured by a forward path and a return path of one flow path extending so as to be folded back.

  Preferably, each individual flow path includes a communication part that communicates the two supply holes that respectively open to the two predetermined common flow paths, and a throttle that communicates the communication part and the pressurizing chamber. It has further.

  A recording apparatus according to an aspect of the present invention includes the inkjet head, a control unit that controls the inkjet head, and a conveyance unit that conveys media relative to the inkjet head.

  According to said structure, the dispersion | variation in the discharge speed resulting from the pressure distribution in a common flow path can be eased.

FIG. 2 is a perspective view schematically illustrating a main part of the recording apparatus according to the first embodiment of the invention. FIG. 2 is a schematic cross-sectional view of a part of the head of the recording apparatus in FIG. 1. FIG. 2 is a plan view schematically showing a partial flow path of the head of the recording apparatus of FIG. 1. FIG. 2 is a diagram for explaining an operation of a head of the recording apparatus of FIG. Sectional drawing which shows the discharge element which concerns on the 2nd Embodiment of this invention. FIG. 6A to FIG. 6F schematically show examples of common channel patterns. FIG. 7A and FIG. 7B are diagrams showing the distribution of pressure applied to the individual flow paths. FIG. 8A to FIG. 8C are schematic views showing modified examples of the flow path of the head. The top view which shows typically the other modification of the flow path of a head.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the embodiment to be described, the same or similar configuration as the configuration of the already described embodiment may be denoted by the same reference numeral as the configuration of the already described embodiment. May be omitted.

<First Embodiment>
FIG. 1 is a perspective view schematically showing a main part of a recording apparatus 1 according to the first embodiment of the present invention.

  The recording device 1 and the inkjet head 5 to be described later may be either upward or downward, but hereinafter, for convenience, the orthogonal coordinate system xyz is defined and the z-direction normal direction is defined. The term “upper surface” or “lower surface” may be used with the side (upper side in FIG. 1) as the upper side.

  The recording apparatus 1 includes, for example, a transport unit 3 that transports a medium (for example, paper) 101 in a direction indicated by an arrow y 1, a head 5 that ejects ink droplets toward the transported medium 101, and ink to the head 5. An ink tank 6 to be supplied and a control unit 7 for controlling operations of the transport unit 3 and the head 5 are provided.

  For example, the transport unit 3 transports a plurality of media 101 stacked on a supply stack (not shown) one by one to a discharge stack (not shown). The transport unit 3 may have a known appropriate configuration. In FIG. 1, the conveyance path is a straight path, and a conveyance unit provided with a roller 9 that contacts the medium 101 and a motor 11 that rotates the roller 9 is illustrated.

  The head 5 is disposed in the middle of the conveyance path of the medium 101 and faces the medium 101 from the positive side in the z direction. The head 5 may be a serial head that performs a shuttle motion in a direction (main scanning direction, x direction) orthogonal to the printing screen and the conveyance direction of the medium 101, or a line fixed (substantially) in the orthogonal direction. It may be a head. In the present embodiment, the case where the head 5 is a line head will be described as an example.

  The head 5 ejects and attaches ink droplets to the medium 101 at a plurality of positions in the x direction. By repeating this operation as the medium 101 is conveyed, a two-dimensional image is formed on the medium 101.

  The ink tank 6 has a function of holding the ink inside the head 5 at a negative pressure within a certain range in addition to the function of supplying ink to the head 5. Leakage or the like of the ink inside the head 5 is suppressed by being held at a negative pressure within a certain range. As a method for holding the ink at a negative pressure, the capillary force of the porous body is used, or the ink tank 6 is separated from the head 5 and connected to the head 5 through a tube. Thus, the ink level in the ink tank 6 may be a known appropriate method such as lowering the level of the ink than the ejection holes 29a. Further, the ink tank 6 may be disposed together with the head 5 or may be disposed at a position different from the head 5.

  The control unit 7 includes, for example, a CPU, a ROM, a RAM, and an external storage device. The controller 7 applies a desired voltage to the motor 11 by outputting a control signal to the motor driver 13 to control the motor 11. Similarly, the control unit 7 outputs a control signal to the head driver 15 to apply a desired voltage to the head 5 to control the head 5.

  FIG. 2 is a schematic cross-sectional view showing a part of the head 5 in an enlarged manner. Note that the lower side of FIG. 2 is the side facing the medium 101.

  The head 5 is, for example, a piezo-type head that applies pressure to ink by mechanical strain of a piezoelectric element. The head 5 has a plurality of ejection elements 19 that eject ink droplets, and FIG. 2 shows one ejection element 19. The plurality of ejection elements 19 are arranged in the xy plane (see FIG. 3), and each ejection element 19 corresponds to one dot on the medium 101.

  In another aspect, the head 5 includes a base 21 that forms a space for storing ink, and an actuator 23 (partly used for the base 21) that applies pressure to the ink stored in the base 21. Have. The plurality of ejection elements 19 includes a base 21 and an actuator 23.

  Inside the base 21, there are a plurality of individual flow paths 25 (one is shown in FIG. 2), and a first common flow path 27A and a second common flow path 27B (hereinafter simply referred to as the single flow paths 25). “Sometimes referred to as“ common flow path 27 ”). The individual flow path 25 is provided for each ejection element 19, and the common flow path 27 is provided in common for the plurality of ejection elements 19.

  Each individual flow path 25 includes a descender (partial flow path) 29 including a discharge hole 29 a facing the medium 101, a pressurization chamber 31 that communicates with the descender 29, and a supply that communicates the pressurization chamber 31 and the common flow path 27. And a path 33.

  The plurality of individual channels 25 and the common channel 27 are filled with ink. When the volumes of the plurality of pressurizing chambers 31 change and pressure is applied to the ink, the ink is sent from the plurality of pressurizing chambers 31 to the plurality of descenders 29, and a plurality of ink droplets are ejected from the plurality of ejection holes 29a. Is discharged. In addition, the plurality of pressurizing chambers 31 are replenished with ink from a common flow path 27 via a plurality of supply paths 33.

  The two common flow paths 27 are, for example, arranged in a stacked manner in the z direction and extend parallel to each other in the x direction. However, the ink flow directions in the two common flow paths 27 are opposite to each other. Specifically, for example, as indicated by the mark MA, in the first common flow path 27A, the ink flows from the back side to the front side of the paper, and as indicated by the mark MB, in the second common flow path 27B. Ink flows from the front side of the paper to the back side of the paper.

  The two common flow passages 27 have the same shape (cross-sectional shape and planar shape) and size (width, height, and length), and the like. It is preferable that the slopes of the decrease are approximately the same. The cross-sectional shape orthogonal to the flow path direction of the common flow path 27 is, for example, a rectangle.

  The pressurizing chamber 31 is, for example, a rhombus (see FIG. 3) having a constant thickness in the z direction and having diagonal directions in the x direction and the y direction when viewed in the z direction. One corner of the rhombus in the y direction communicates with the descender 29, and the other corner communicates with the supply path 33.

  The pressurizing chamber 31 communicates with both the first common channel 27A and the second common channel 27B. Specifically, for example, the pressurizing chamber 31 communicates with both of the two common channels 27 by branching the supply channel 33 on the common channel 27 side and leading to both of the two common channels 27. ing.

  The supply path 33 is, for example, a first supply hole 34A that opens to the first common flow path 27A and a second supply hole 34B that opens to the second common flow path 27B (hereinafter simply referred to as “supply hole 34”. And a communication portion 33a that communicates these, a squeezing 33b that continues to the communication portion 33a, and an opening 33c that continues to the squeezing 33b and opens to the pressurizing chamber 31. . Note that a portion (opening 33 c) closer to the pressurizing chamber 31 than the squeezing 33 b may be regarded as a part of the pressurizing chamber 31.

  Each supply hole 34 opens, for example, in the common channel 27 (in the z direction) from a wall surface that partitions the two common channels 27. For example, the two supply holes 34 are arranged at the same position in the flow direction (x direction) and the width direction (y direction) of the two common flow channels 27 and overlap in the z direction. The communication portion 33 a passes through the wall surface that partitions the two common flow paths 27 in the z direction and communicates the two supply holes 34. The aperture 33b is opened (in the y direction) on the inner peripheral surface of the communication portion 33a.

  The squeezing 33b is a portion of the supply path 33 in which the area of the cross section perpendicular to the ink flow direction is reduced. For example, the common flow path 27, the supply hole 34, the communication portion 33a, the opening portion 33c, and the pressurizing chamber 31 are used. The cross-sectional area perpendicular to the ink flow direction is smaller than that of the ink flow direction. In addition, the flow direction of the communication part 33a here is the direction between the two supply holes 34 (z direction). For example, the aperture 33b is formed to extend in the y direction.

  By forming the squeeze 33b, when the volume of the pressurizing chamber 31 is reduced, the backflow of ink from the pressurizing chamber 31 to the common flow path 27 is suppressed. In the present embodiment, since each throttle 33b is provided in common for the two common flow paths 27, the space utilization efficiency is increased, and the head 5 can be reduced in size.

  The base body 21 is configured, for example, by stacking a plurality of substrates. Specifically, the base body 21 includes a plurality of substrates 35 in which through holes constituting a plurality of individual channels 25 and a common channel 27 are formed, and a diaphragm 37 that closes the upper surface openings of the plurality of pressurizing chambers 31. have.

  The thickness and the number of layers of the plurality of substrates 35 may be appropriately set according to the shapes of the plurality of individual channels 25 and the common channel 27. The plurality of substrates 35 may be formed of an appropriate material, for example, formed of metal, ceramic, or silicon.

  The actuator 23 is composed of, for example, a unimorph type piezoelectric element that is displaced in a bending mode. Specifically, for example, the actuator 23 includes a diaphragm 37, a common electrode 39, a piezoelectric body 41, and a plurality of individual electrodes 43 that are stacked in order from the pressurizing chamber 31 side. The individual electrode 43 is provided for each ejection element 19.

  The diaphragm 37, the common electrode 39, and the piezoelectric body 41 are provided in common to the plurality of pressurizing chambers 31 so as to cover the plurality of pressurizing chambers 31, for example. On the other hand, the individual electrode 43 is provided for each pressurizing chamber 31. More specifically, the individual electrode 43 is generally similar to the pressurizing chamber 31 (generally rhombus in the present embodiment), and is slightly smaller than the width of the pressurizing chamber 31 and the corners of the individual electrode main body. And an extraction electrode (not shown) connected to the unit.

  The diaphragm 37, the common electrode 39, the piezoelectric body 41, and the plurality of individual electrodes 43 may be formed of an appropriate material. For example, the diaphragm 37 is made of ceramic, silicon oxide, or silicon nitride. The common electrode 39 and the plurality of individual electrodes 43 are made of, for example, platinum or palladium. The piezoelectric body 41 is made of ceramic such as PZT (lead zirconate titanate).

  The piezoelectric body 41 has a thickness direction (z direction) as a polarization direction. Accordingly, when a voltage is applied to the common electrode 39 and the individual electrode 43 to cause an electric field to act on the piezoelectric body 41 in the polarization direction, the piezoelectric body 41 contracts in the plane. Due to this contraction, the diaphragm 37 is bent so as to protrude toward the pressurizing chamber 31, and as a result, the volume of the pressurizing chamber 31 changes.

  The driving method of the ejection element 19 may be appropriately selected from known driving methods such as a pulling method and a pushing method. In addition, gradation may be expressed by increasing or decreasing the number of ink droplets for one dot recording or changing the amount of ink droplets. The start timing of driving the plurality of ejection elements 19 (applying pressure to the pressurizing chamber 31) may be the same as each other, or the flow from the ejection hole 29a to the squeezing 33b in the plurality of adjacent pressurizing chambers 31 may be performed. They may be shifted from each other with a time difference shorter than the natural vibration period of the ink in the path.

  FIG. 3 is a plan view schematically showing a part of the flow path of the head 5. In FIG. 3, the descender 29, the pressurizing chamber 31, the aperture 33b, the communication portion 33a, the first supply hole 34A, and the first common flow path 27A are shown.

  The plurality of pressurizing chambers 31 are arranged along the common flow path 27 (in the x direction) to form a pressurizing chamber row F. For example, the pressurizing chamber rows F are arranged in two rows on both sides of the first common channel 27A and the second common channel 27B. The two pressurizing chamber rows F may have the same position in the x direction (the example in FIG. 3) or may be different from each other.

  The combination of the first common channel 27A, the second common channel 27B, and the pressurizing chamber row F may be arranged in an appropriate number in the y direction. In this case, each common flow path 27 may be a branch portion of the flow path formed in a manifold shape.

  In the individual flow path 25 connected to each pressurizing chamber row F, the plurality of discharge holes 29a have a constant pitch in the x direction. The band-shaped region R having a width in the x direction and extending in the y direction includes the same number of discharge holes 29a as the number of pressurizing chamber rows F in the y direction. All the discharge holes 29a included in the belt-like region R have different positions in the x direction and have a constant pitch in the x direction.

  Therefore, in the head 5, a desired resolution is realized in the x direction as a whole of the plurality of ejection elements 19 arranged in the x direction and the y direction. As an example, when the number of pressurizing chamber rows F in the y direction is 16 (the belt-like region R includes 16 discharge holes 29a), and the width of the belt-like region R is 1 / 37.5 inch The head 5 realizes a resolution of 600 dpi (= 16 / (1 / 37.5)).

  In addition, between the individual flow paths 25 including the plurality of pressurizing chambers 31 arranged in the y direction, the descender 29 moves from the pressurizing chamber 31 toward the discharge hole 29a while shifting the position in the x direction and the y direction. The positions of the discharge holes 29a in the x direction are different from each other.

  Corresponding to the plurality of pressurizing chambers 31 being arranged along the common flow path 27, the plurality of supply holes 34 are also arranged along the common flow path 27. The plurality of supply holes 34 corresponding to one pressurizing chamber row F are arranged at a constant pitch, for example. However, the plurality of supply holes 34 may be arranged so that the pitch changes in consideration of the pressure gradient from the upstream side to the downstream side of the common flow path 27.

  FIG. 4 is a diagram for explaining the operation of the head 5. More specifically, FIG. 4 is a schematic diagram in which a portion corresponding to the region IV in FIG. 3 is extracted. In FIG. 4, the first common flow path 27A, the second common flow path 27B, and these are communicated. A part of the three individual flow paths 25 (the pressurizing chamber 31, the first supply hole 34A, and the second supply hole 34B) is schematically shown.

  An arrow y11 indicates the direction of ink flow in the first common flow path 27A, and an arrow y12 indicates the direction of ink flow in the second common flow path 27B. “High” and “Low” indicated by rectangles on both sides in the flow direction of each common flow path 27 indicate relative levels of pressure in each common flow path 27. That is, the pressure increases on the upstream side, and the pressure decreases on the downstream side.

  The numbers (1 to 3) enclosed by rectangles in the vicinity of each first supply hole 34A indicate the order from the upstream side among the three first supply holes 34A. Similarly, numbers (1 to 3) enclosed by rectangles in the vicinity of each second supply hole 34B indicate the order from the upstream side between the three second supply holes 34B. A number (4) surrounded by a rectangle in each pressurizing chamber 31 indicates the total of the order from the upstream side of the first supply hole 34A and the second supply hole 34B communicating with each pressurization chamber 31.

  As described above, the first common flow path 27A and the second common flow path 27B extend in parallel to each other, and the ink flows are in opposite directions. The first supply hole 34A and the second supply hole 34B communicating with each pressurizing chamber 31 are opened at the same position in the extending direction (x direction) of the first common flow path 27A and the second common flow path 27B. Yes.

  Accordingly, between the plurality of pressurizing chambers 31, the corresponding first supply hole 34 </ b> A is located upstream of the plurality of first supply holes 34 </ b> A, and the corresponding second supply hole 34 </ b> B has the plurality of second supply holes 34 </ b> B. It is on the downstream side between the supply holes 34B. Then, as indicated by the numbers enclosed by the rectangles in each pressurizing chamber 31, the sum of the order from the upstream side of the two supply holes 34 is the same between the plurality of pressurizing chambers 31. Yes.

  Here, the influence of the pressure distribution of the common flow path 27 on the ejection speed of the ink droplets from the ejection holes 29a will be described. First, consider a case where each pressurizing chamber 31 communicates with only one common channel 27 and does not communicate with another common channel 27.

  As described above, the common flow path 27 is maintained at a certain range of negative pressure by the ink tank 6. Further, the pressure in the common flow path 27 is lower at the downstream side due to pressure loss (the pressure is higher at the upstream side).

  Therefore, when the volume of the pressurizing chamber 31 is increased and the pressure of the pressurizing chamber 31 is reduced (the negative pressure is further reduced), the pressurizing chamber 31 leading to the upstream side of the common flow path 27 has a common flow. The pressure difference between the passage 27 and the pressurizing chamber 31 is large. As a result, the pressure chamber 31 leading to the upstream side has a larger amount of ink flowing from the common flow path 27 into the pressure chamber 31, and consequently, the pressure increase in the pressure chamber 31 after the ink has flowed is large (the first chamber). Impact of).

  Further, when the volume of the pressurizing chamber 31 is reduced and the pressure of the pressurizing chamber 31 increases (becomes a positive pressure), the more the pressurizing chamber 31 leading to the upstream side of the common channel 27 is, the more the common channel 27 is. And the pressure difference between the pressurizing chamber 31 is small. As a result, in the pressurizing chamber 31 leading to the upstream side, the backflow of ink to the common flow path 27 is less likely to occur, and the ink easily flows to the descender 29 (second effect).

  Therefore, when ejecting ink droplets by reducing the volume of the pressurizing chamber 31, the ejection speed of the ejecting element 19 having the pressurizing chamber 31 leading to the upstream side of the common flow path 27 is higher due to the second effect described above. Get faster. Furthermore, in the pulling type in which the volume of the pressurizing chamber 31 is increased and then the volume of the pressurizing chamber 31 is reduced to eject ink droplets, not only the second effect described above but also the first effect described above. Therefore, the discharge speed of the discharge element 19 having the pressurizing chamber 31 leading to the upstream side is increased.

  On the other hand, in the plurality of pressurizing chambers 31 of the present embodiment, the pressurizing chamber 31 communicating with the upstream side of the first common channel 27A leads to the downstream side of the second common channel 27B. Therefore, the influence of the pressure distribution of the first common flow path 27A and the influence of the pressure distribution of the second common flow path 27B are canceled out, and variations in the discharge speeds of the plurality of discharge elements 19 are alleviated.

  Further, the base body 21 includes a plurality of communication portions 33a that communicate a plurality of first supply holes 34A and a plurality of second supply holes 34B that communicate with the same pressurizing chamber 31, and a plurality of communication portions 33a. A squeeze 33b is formed to communicate the portion 33a and the plurality of pressurizing chambers 31 respectively. In other words, the two common flow paths 27 communicate with each other through the first supply hole 34 </ b> A and the second supply hole 34 </ b> B without the pressurizing chamber 31 at a plurality of positions in the flow direction. Accordingly, the pressure gradient in the common flow path 27 is alleviated, and the variation in the discharge speed is further alleviated. In addition, since the communication between the two common flow paths 27 is made by the two supply holes 34 for allowing the pressurizing chamber 31 to communicate with the two common flow paths 27, the structure can be simplified.

<Second Embodiment>
FIG. 5 is a cross-sectional view corresponding to FIG. 2 showing an ejection element 219 according to the second embodiment.

  In the base 221 of the discharge element 219, the arrangement of the two common flow paths 27 is different from the base 21 of the discharge element 19 of the first embodiment. Further, the base body 221 is different from the base body 21 in the configuration of the supply path 233 that communicates the common flow path 27 and the pressurizing chamber 31 due to the difference in the arrangement of the common flow path 27. The configurations of the actuator 23, descender 29, and pressurizing chamber 31 are the same as those in the first embodiment.

  The two common flow paths 27 extend in the x direction side by side in the y direction. Each supply hole 34 opens, for example, on the upper surface of the corresponding common flow path 27, and is preferably located on the upper surface of the two common flow paths 27 adjacent to each other. The communication portion 233a of the individual flow channel 225 communicates the two supply holes 34 in the y direction on the upper side. The squeezing 33b opens on the upper surface of the communication part 233a, and communicates the communication part 233a with the pressurizing chamber 31.

  Although not particularly illustrated, a plurality of individual flow paths 225 such as the pressurizing chamber 31 and the supply holes 34 are arranged along the common flow path 27 (in the x direction) as in the first embodiment. Further, as in the first embodiment, the ink flow directions of the two common flow paths 27 are opposite to each other. Accordingly, also in the second embodiment, the corresponding first supply holes 34A between the plurality of pressurization chambers 31 are located on the upstream side between the plurality of first supply holes 34A. The supply hole 34B is on the downstream side between the plurality of second supply holes 34B.

  In FIG. 5, only the individual flow path 225 located on one side of the common flow path 27 is illustrated. However, as in FIG. 2, the individual flow paths 225 are provided on both sides of the common flow path 27. May be formed. In this case, the individual channel 225 on one side of the common channel 27 and the individual channel 225 on the other side of the common channel 27 are the positions of the supply hole 34 and the communication portion 233a in the x direction. Are formed so as to be shifted from each other.

  Also in the second embodiment, as in the first embodiment, in the plurality of pressurizing chambers 31, the pressurizing chamber 31 leading to the upstream side of the first common channel 27 </ b> A is downstream of the second common channel 27 </ b> B. By being connected to the side, the influence of the pressure distribution of the first common flow path 27A and the influence of the pressure distribution of the second common flow path 27B are offset, and the effect of reducing the variation in the discharge speed is achieved. Further, the effect of alleviating the pressure gradient due to the communication of the two common flow paths 27 through the supply holes 34 is achieved.

  Note that the first embodiment is more advantageous than the second embodiment in reducing the size of the head in the y direction and integrating the ejection holes 29a in the y direction. The second embodiment is advantageous in reducing the size (thinning) of the head (substrate) in the z direction as compared to the first embodiment. When the substrate 21 is thinned, the descender 29 is shortened, and the ejection cycle of the ink droplets can be shortened, which is advantageous in increasing the printing speed.

<Common channel pattern example>
Regarding a plurality of (two) common flow paths 27 extending in parallel with each other and having ink flow directions opposite to each other, there are various kinds of specific configurations such as arrangement of inlets and the like through which ink flows into the common flow path 27. Can be considered. Below, the number pattern is illustrated.

  FIG. 6A to FIG. 6F are diagrams schematically showing the common flow path 27. 6 (a) and 6 (b) show the common flow path 27 of the comparative example, and FIGS. 6 (c) to 6 (f) show the common flow path 27 of the example according to the embodiment. .

  These figures may be taken as plan views or side views. In these drawings, a common flow path 27 and an inlet 45 through which ink flows into the common flow path 27 are shown. In addition, the direction of ink flow in the common flow path 27 is indicated by an arrow, and the relative height of pressure is indicated by “high” and “low” surrounded by a rectangle, as in FIG. .

  6 (a) and 6 (b), one supply hole 34 is shown by one circle overlapping with one common flow path 27, and in FIGS. 6 (c) to 6 (f), 2 is provided. A pair of first supply holes 34A and second supply holes 34B are indicated by a single circle overlapping the two common flow paths 27. A plurality of supply holes 34 are arranged along the common flow path 27. In these drawings, only one supply hole 34 or a set of the first supply hole 34A and the second supply hole 34B is shown.

  The inflow port 45 may be opened to the surface of the head 5 and supplied with ink from the ink tank 6, or when the common flow path 27 is a branch portion of a manifold-shaped flow path. It may be a branch point of a manifold-like flow path.

  In the comparative example of FIG. 6A, the inflow ports 45 are located at both ends of the common flow path 27, and the ink flows from the both end sides of the common flow path 27 to the center side. That is, the pressure in the common flow path 27 is relatively high on both sides of the common flow path 27. Further, each pressurizing chamber 31 communicates with only one common flow path 27 through one supply hole 34. Accordingly, the discharge speed is affected by the pressure distribution in the common flow path 27, and the discharge speed including the pressurizing chamber 31 leading to both ends of the common flow path 27 is higher.

  In the comparative example of FIG. 6B, the inlet 45 is located at one end of the common flow path 27, and the ink flows from one end side to the other end side of the common flow path 27. That is, the pressure in the common flow path 27 is relatively high on one end side of the common flow path 27. Further, each pressurizing chamber 31 communicates with only one common flow path 27 through one supply hole 34. Therefore, the discharge speed is affected by the pressure distribution in the common flow path 27, and the discharge speed increases as the discharge element includes the pressurizing chamber 31 leading to one end side of the common flow path 27.

  In the example of the embodiment of FIG. 6C, the inlet 45 is located at the center of the first common flow path 27A, and the ink flows from the center side of the first common flow path 27A to both ends. That is, the pressure of the first common channel 27A is relatively high on the center side of the first common channel 27A. On the other hand, in the second common flow path 27B, as in the common flow path 27 of FIG. 6A, the inlets 45 are located at both ends, and the pressure of the second common flow path 27B is the second common flow path. It is relatively high on both end sides of 27B.

  Accordingly, in the first common flow path 27A and the second common flow path 27B, the ink flow directions are opposite to each other, and as a result, the level of pressure is opposite to each other with respect to the flow path direction. Each pressurizing chamber 31 communicates with the two common flow paths 27 via the two supply holes 34, and the influence of the pressure distribution of the common flow path 27 is alleviated as described above. In the example of FIG. 6C, the first common flow path 27A and the second common flow path 27B are formed on the left side and the right side of the paper, respectively, with the central inlet 45 as a boundary (the whole) 2 sets of the first common flow path 27A and the second common flow path 27B are formed).

  In the example of the embodiment of FIG. 6D, the inlet 45 is located on one end side of each common channel 27 as in the example of FIG. It is high on one end side. However, in the two common flow paths 27, the inflow ports 45 are opened at the ends opposite to each other, so that the pressure levels are reversed with respect to the flow path direction. Each pressurizing chamber 31 communicates with the two common flow paths 27 via the two supply holes 34, and the influence of the pressure distribution of the common flow path 27 is alleviated as described above.

  6C has a larger number of inlets 45 than the example of FIG. 6D, the difference between the maximum value and the minimum value in the pressure distribution of the common flow path 27 is shown. It is easy to suppress the dispersion | variation in discharge speed by making small and by extension. On the other hand, in the example of FIG. 6D, the inlet 45 may be formed at the end of the common channel 27 as compared to the example of FIG. Since it is not necessary to form an inlet), the design is easy.

  In the example of the embodiment of FIG. 6 (e), the position of the inflow port 45 is the same as that of FIG. 6 (c). However, in each common flow path 27, the area of the cross section orthogonal to the flow path is larger on the upstream side than on the downstream side. More specifically, for example, the cross-sectional area of the common channel 27 continuously decreases from the upstream side to the downstream side. The rate of change may be set as appropriate, and is constant, for example.

  Since the flow rate is large in the vicinity of the inlet 45, the pressure gradient becomes steeper as it is closer to the inlet 45. Therefore, by increasing the cross-sectional area of the common flow path 27 in the vicinity of the inlet 45, the pressure gradient can be made closer to a straight line. As a result, it is possible to smooth the pressure distribution and further suppress variations in the discharge speed.

  In the example of the embodiment in FIG. 6F, one end of the pair of first common flow path 27A and second common flow path 27B is connected to each other in the flow path direction. In other words, one common flow path 28 extends so as to be folded back, and the first common flow path 27A and the second common flow path 27B are configured by the forward path and the return path. The inflow port 45 opens at one end of the common flow path 28. Thus, the first common flow path 27A and the second common flow path 27B have the ink flow directions opposite to each other, and the pressure levels are opposite to each other with respect to the flow path direction. Each pressurizing chamber 31 communicates with the two common flow paths 27 via the two supply holes 34, and the influence of the pressure distribution of the common flow path 27 is alleviated as described above.

  In the example of FIG. 6F, since the ink can be supplied to the two common flow paths 27 with one inflow port 45, the size can be reduced as compared with the other examples. However, when the pressurizing chambers 31 are distributed over a wide range, a plurality of common flow paths 28 may be arranged as shown in FIG. 6F so that the common flow paths 28 do not become too long. preferable.

<Example>
(Calculation of pressure distribution)
Specific dimensions and the like are set for the heads of the comparative example and the embodiment, and the distribution of pressure applied from the common flow path 27 to the individual flow path 25 (225) (strictly speaking, in the comparative example, the supply hole 34 is set. And the pressure in the communication portion 33a (233a) in the examples were calculated. Specifically, it is as follows.

(Calculation case)
Calculations were performed for the following four cases.
Comparative example:
Comparative Example 1: Assuming the common flow path 27 of FIG. 6 (a) Comparative Example 2: Assuming the common flow path 27 of FIG. 6 (b) Example Example 1: Assuming the common flow path 27 of FIG. 6 (c) Example 2: Assuming the common flow path 27 of FIG.

(Calculation condition)
The calculation conditions are as follows.
In the embodiment, the same configuration as that in FIG. 3 is assumed. That is, the plurality of first supply holes 34A are arranged in two rows along the first common flow path 27A in the first common flow path 27A, and the plurality of second supply holes 34B are 2 in the second common flow path 27B. A configuration is assumed in which the rows are arranged along the second common flow path 27B. The number of supply holes 34 in each row is 80 (the first supply hole 34A has two rows of 80, a total of 160, and the second supply hole 34B has two rows of 80, a total of 160). .

  In the comparative example, a configuration in which the plurality of second supply holes 34B and the second common flow path 27B are omitted from the embodiment is assumed. That is, it is assumed that the supply holes 34 are arranged in two rows for one common flow path 27 and the number of supply holes 34 in each row is 80 (total of 160 in two rows).

Other calculation conditions are as follows.
Fluid resistance of common flow path: 2.20 × 10 ¹¹ (Ns / m ⁵ )
Ink drop volume: 10.0 (pl)
Drive frequency: 30.0 (kHz)

(Calculation result)
FIGS. 7A and 7B are diagrams illustrating calculation results when ink of the above-described ink droplet amount is ejected from all the ejection holes 29a for each driving cycle (reciprocal of the above-described driving frequency). is there. In these drawings, the horizontal axis indicates the position of the common flow path 27 in the flow direction (x direction) by the number of supply holes 34, and the vertical axis indicates the pressure applied from the common flow path 27 to the individual flow path 25. The pressure difference with respect to the pressure (pressure in the inflow port 45) when it is assumed that there is no pressure loss in the common flow path 27 is shown.

  In FIG. 7A, a line L1 indicates the calculation result of Comparative Example 1, and a line L3 indicates the calculation result of Example 1. From this calculation result, in Comparative Example 1, the distribution is such that higher pressure is applied to the individual flow paths 25 leading to both ends of the common flow path 27. In Example 1, such distribution is flattened. It has been confirmed.

  In FIG. 7B, a line L5 indicates the calculation result of Comparative Example 2, and a line L7 indicates the calculation result of Example 2. From this calculation result, in Comparative Example 2, the distribution is such that a higher pressure is applied to the individual flow path 25 leading to one end side of the common flow path 27. In Example 2, such distribution is flattened. It has been confirmed.

(Dispersion of discharge speed)
The pressure applied from the common flow path 27 to the individual flow path 25 was converted into the discharge speed of the ink droplets from the discharge holes 29a. Then, the difference between the maximum discharge speed and the minimum discharge speed was calculated for each calculation case.

The calculation conditions are as follows.
Squeezing fluid resistance: 3.01 × 10 ¹³ (Ns / m ⁵ )
Fluid resistance of descender (including discharge hole): 2.43 × 10 ¹⁴ (Ns / m ⁵ )
Discharge speed when assuming that there is no pressure loss in the common flow path (discharge speed of the discharge element including the pressurizing chamber leading to the vicinity of the inlet 45): 8 (m / s)
The ink droplet amount and the drive frequency are the same as the calculation conditions for the pressure applied from the common channel 27 to the individual channel 25.

The calculation results are shown below.
Comparative Example 1: 0.126 (m / s)
Example 1: 0.029 (m / s)
Comparative Example 2: 0.509 (m / s)
Example 2: 0.126 (m / s)

  As described above, it has been confirmed that the variation in the discharge speed is reduced by reducing the influence of the pressure distribution of the common flow path 27 on the pressure difference between the plurality of pressurizing chambers 31.

  The present invention is not limited to the above embodiment, and may be implemented in various aspects.

  The plurality of embodiments and the like described above may be combined as appropriate. For example, the first embodiment and the second embodiment may be combined so that each pressurizing chamber communicates with four common flow paths. The shape in which the cross-sectional area of the common flow path 27 shown in FIG. 6E increases on the upstream side is not only the example of FIG. 6C, but also the example of FIG. 6D or the example of FIG. Or may be applied to the four common flow paths as described above. FIG. 8C shows a schematic diagram similar to FIG. 4 when the number of common flow paths 27 is four.

  The method for applying pressure to the pressurizing chamber may be an appropriate method. That is, the ink jet head is not limited to a piezo head, and may be a thermal head that applies pressure to ink by heating the ink to generate bubbles. In addition, the piezo-type inkjet head is not limited to the flexure mode head, and may be, for example, a longitudinal mode head that contracts the piezoelectric body in the vibration direction of the diaphragm, or a shear mode that uses shear deformation of the piezoelectric body. It may be a head. The flexure mode head is not limited to a unimorph type head, and may be a bimorph type head having two piezoelectric bodies facing each other.

  The number of common channels that each pressurizing chamber communicates (in the case of FIG. 6 (f), it may be regarded as the number of specific portions of one common channel. Hereinafter, the same applies unless otherwise specified. .) Is not limited to two or four as described above, and may be three or five or more.

  In the embodiment, as shown in FIG. 4, each pressurizing chamber 31 communicates with the two common flow paths 27 via the two supply holes, and the total of the order from the upstream side of the two supply holes 34 is plural. The pressure chambers were identical to each other. And the influence of the pressure distribution of the two common flow paths 27 was suitably canceled (it does not need to be completely canceled) in each pressurizing chamber. When such a state is expanded (generalized) when each pressurizing chamber leads to a plurality (not limited to 2) of common flow paths, the supply hole that opens to the i-th common flow path is defined as the i-th supply hole. (1 ≦ i ≦ n, where n is an even number of 2 or more), and when the order from the upstream side among the plurality of i-th supply holes of the i-th supply hole corresponding to each pressurizing chamber is m (i) In addition, the sum (m (1) + m (2) +... + M (n)) of m (i) from i = 1 to i = n is equal among the plurality of pressurizing chambers (FIG. 8 (c)).

  Note that the order from the upstream side of the supply holes at this time may be between a plurality of pressurizing chambers that communicate with the same combination of common flow paths (as will be described later, between some of the pressurizing chambers. .). For example, in FIG. 8A, which is a schematic diagram similar to FIG. 4, for the common flow path 27C at the center of the paper, three supply holes 34 that lead to the three pressurizing chambers on the top of the paper, and the bottom of the paper Two supply holes 34 (5 supply holes 34 in total) communicating with the two pressurizing chambers are opened. However, when calculating m (1) + m (2) +... + M (n), the order of the supply holes 34 in the common flow path 27C is not determined between the five supply holes, It is determined separately between the three supply holes 34 that communicate with the upper three pressurizing chambers or between the two supply holes 34 that communicate with the two pressurization chambers on the lower side of the drawing.

  Further, the order from the upstream side of the supply holes is determined between a predetermined number of pressurizing chambers in which it is determined whether m (1) + m (2) +... + M (n) are equal to each other. For example, FIG. 3 shows a number of pressurizing chambers 31 included in two rows of pressurizing chambers F leading to a combination of two identical common flow paths 27. In FIG. The pressurization chamber 31 was extracted and the order of the supply holes 34 was determined, indicating that m (1) + m (2) + m (3) are equal to each other. Thus, the order of the supply holes is determined between some of the pressurizing chambers (which may or may not be continuous in the flow direction of the common flow path), and m (1) + m (2 ) +... + M (n) may be determined as to whether or not the relationship is established.

  In the two pressurization chamber rows F in FIG. 3, the pressurization chambers 31 adjacent in the y direction have the same position (position in the x direction) from the upstream side of the supply hole 34. Predetermined numbers for determining whether or not the relationship that m (1) + m (2) +... + M (n) are equal to each other is established between the pressurizing chambers having the same order from the upstream side of the supply holes. If it is included in the pressurization chamber (determination target), the determination may be difficult. Therefore, it is preferable that one of the two pressurization chambers having the same supply hole order is excluded from the determination target. Similarly, when there are three or more pressurizing chambers in which the order of the supply holes is the same, it is preferable to exclude one pressurizing chamber from the determination target. However, for example, four pressurizing chambers are extracted such that the order of the supply holes from the upstream side in one common channel is No. 1, No. 2, No. 2 (No. 2 is No. 2), No. 4 In this case, for the sake of convenience, the order may be determined such as No. 1, 2.5, 2.5, and 4, and the determination may be performed.

  Further, in FIG. 8A, it is understood that the total (4) of the order in the pressurizing chamber 31 on the upper side of the paper is not equal to the total (3) of the order in the pressurizing chamber 31 on the lower side of the paper. , M (1) + m (2) +... + M (n) are equal to each other between a plurality of pressurizing chambers leading to a combination of the same common flow paths (as described above, a part of the pressurization) It may be established between the rooms.

  Regarding two predetermined common channels, the order from the upstream side of the supply holes in one common channel and the order from the upstream side of the supply holes in the other common channel are reversed between the plurality of individual channels. Or the relationship that m (1) + m (2) +... + M (n) are equal to each other is the same for all the pressure chambers of the head or the same common flow. It is not necessary to establish all the pressurizing chambers that lead to the combination of paths. For example, a pressurizing chamber that leads to only one common flow path may be included on the upstream side or the downstream side of the head or the range shown in FIG. In consideration of the specific common flow path arrangement or the specific pressure gradient of the common flow path, the above mentioned only for some pressure chambers so that a suitable head can be obtained from various viewpoints as a whole. The relationship may be established.

  It is preferable that the number of common flow paths through which each pressurizing chamber communicates is an even number from the viewpoint of preferably offsetting the influence of the pressure distribution. However, as shown in FIG. 8B, which is a schematic diagram similar to FIG. 4, the number of common flow paths 27 through which each pressurizing chamber 31 communicates may be an odd number.

  The shape of the individual flow path including the pressurizing chamber and the like and the shape of the common flow path are not limited to those exemplified in the embodiment. For example, the descender, the pressurizing chamber, and the supply path may be partially or entirely integrated, and the boundary position may not necessarily be clear. For example, in the thermal head, the nozzle and the pressurizing chamber may be integrated.

  Further, for example, the common flow path may extend in a transport direction or a direction that obliquely intersects the transport direction, or may extend while being curved. The plurality of common flow paths may have different cross-sectional areas, cross-sectional shapes, lengths, and the like. In the embodiment, two pressure chamber rows are arranged on both sides of one set of common flow paths, but one pressure chamber row may be arranged for one set of common flow paths, or three or more The pressurizing chamber row may be arranged. The supply holes are not limited to the upper and lower surfaces of the common flow path, and may be opened on the side surfaces.

  The shape of the supply path (33, 233) for communicating the pressurizing chamber and the plurality of common flow paths is not limited to the shape branched on the common flow path side with respect to the squeezing.

  For example, as shown in FIG. 9, which is a schematic diagram similar to FIG. 3, two (a plurality) of orifices 33 b are provided for one pressurizing chamber 31, and two supply holes 34 are provided in the two orifices 33 b. They may be connected individually. In other words, the supply path may be branched closer to the pressurizing chamber 31 than the throttle 33b. In this case, since the area of the inner peripheral surface with respect to the cross-sectional area of the squeezing 33b is increased, the vibration flow of the ink is easily attenuated. As in the embodiment, in the case of the single restriction 33b, the two supply holes 34 are communicated by the communication portion 33a without passing through the restriction 33b. The effect of relieving the pressure gradient in the common flow path 27 is high.

  Although not particularly illustrated, the supply path is not branched, but two (a plurality of) supply paths are provided for one pressurization chamber 31 so that one pressurization chamber 31 has two common flow paths. You may lead to the road. In other words, the two openings 33 c may open to the pressurizing chamber 31. Further, as shown in FIG. 9, the two supply holes 34 may not have the same position in the flow path direction of the common flow path.

  The common channel having the upstream cross-sectional area larger than the downstream cross-sectional area may be only a part of the plurality of common channels, such as only one of the two common channels. In addition, when one common flow path (28) extends so as to be folded back and a plurality of common flow paths (27) are configured by the forward path and the return path, the number of common flow paths (27) (forward path and return path) Is not limited to two and may be three or more.

  DESCRIPTION OF SYMBOLS 5 ... Inkjet head, 21 ... Base | substrate, 27A ... 1st common flow path, 27B ... 2nd common flow path, 29 ... Descender, 29a ... Discharge hole, 31 ... Pressurization chamber, 34A ... 1st supply hole, 34B ... 1st 2 supply holes.

Claims (6)

Having a base on which a plurality of individual flow paths and n (n ≧ 2) common flow paths are formed;
Each individual channel is
A pressure chamber;
N supply holes communicating with the pressurizing chamber and opening to the n common flow paths,
Including
Regarding the predetermined two common flow channels among the n common flow channels, between the plurality of individual flow channels, the order from the upstream side of the supply hole in one common flow channel, and the other The inkjet head in which the order from the upstream side of the supply hole in the common channel is reversed. n is an even number, and when the order from the upstream side of the i-th supply hole that opens to the i-th (1 ≦ i ≦ n) common flow path is m (i), the plurality The inkjet head according to claim 1, wherein the sum of m (i) from i = 1 to i = n is equal between the individual flow paths. 3. The inkjet according to claim 1, wherein in at least one of the predetermined two common channels, an area of a cross section perpendicular to the channel is larger on the upstream side than on the downstream side. 4. head. The inkjet head according to any one of claims 1 to 3, wherein the two predetermined common flow paths are configured by a forward path and a return path of a single flow path extending so as to be folded back. Each individual channel is
A communicating portion that communicates the two supply holes that respectively open to the predetermined two common flow paths;
A squeezing that connects the communication part and the pressurizing chamber;
The inkjet head according to claim 1, further comprising: The inkjet head according to any one of claims 1 to 5,
A control unit for controlling the inkjet head;
A recording unit having a conveyance unit configured to convey the medium relative to the inkjet head.

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