JP2010194858A - Printing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a printing apparatus which hardly generates streak-like printing fluctuation on a recording medium. <P>SOLUTION: The printing apparatus includes: p pieces of liquid delivering heads which are equipped with a liquid delivering hole group consisting of n pieces of liquid delivering holes and n pieces of pressing parts, and in which the liquid delivering holes are arranged two-dimensionally in one direction at equal intervals d; a conveying means; and a controlling unit for controlling the pressing parts so that a pixel group arranged in one direction in parallel at equal intervals d to a printing medium by liquid droplets delivered from one liquid delivering head is formed, the pixel groups formed by p pieces of the liquid delivering heads are formed in one direction by shifting d/p by d/p to form one line consisting of pixels parallel in one direction. In the printing apparatus, the liquid delivering heads are arranged in a direction orthogonal to one direction, and at least one of differences of the time ΔT<SB>2</SB>-ΔT<SB>m</SB>from an initial delivering signal among the delivering signals for forming one line to the delivering signals after the second delivering signal, is made different. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a printing apparatus that prints an image by ejecting droplets, and more particularly to a printing apparatus that prints an image using a plurality of liquid ejection heads.

  In recent years, printing apparatuses using inkjet recording methods such as inkjet printers and inkjet plotters are not only printers for general consumers, but also, for example, formation of electronic circuits, manufacture of color filters for liquid crystal displays, manufacture of organic EL displays It is also widely used for industrial applications.

  In such an ink jet printing apparatus, a liquid discharge head for discharging liquid is mounted as a print head. This type of print head includes a heater as a pressurizing unit in an ink flow path filled with ink, heats and boiles the ink with the heater, pressurizes the ink with bubbles generated in the ink flow path, A thermal head system that ejects ink as droplets from the ink ejection holes, and a part of the wall of the ink channel filled with ink is bent and displaced by a displacement element, and the ink in the ink channel is mechanically pressurized, and the ink A piezoelectric method for discharging liquid droplets from discharge holes is generally known.

  In addition, in such a liquid discharge head, recording is performed with respect to a serial type in which recording is performed while moving the liquid discharge head in a direction (main scanning direction) orthogonal to the conveyance direction (sub-scanning direction) of the recording medium, and the main scanning direction. There is a line type in which recording is performed on a recording medium conveyed in the sub-scanning direction with a liquid discharge head longer than the medium being fixed. The line type has the advantage that high-speed recording is possible because there is no need to move the liquid discharge head as in the serial type.

  In order to print droplets at a high density in any of the serial type and line type liquid discharge heads, the density of the liquid discharge holes for discharging the droplets formed in the liquid discharge head must be increased. There is a need to.

  Accordingly, the liquid discharge head includes a flow path member having a liquid discharge hole connecting the liquid discharge head from the manifold to each of the plurality of liquid pressurization chambers, and a plurality of displacement elements provided so as to cover the liquid pressurization chambers. There is known a technique of stacking and configuring actuator units (see, for example, Patent Document 1). In the liquid ejection head, the liquid pressurizing chamber connected to each liquid ejection hole is displaced by a displacement element provided so as to cover it, thereby ejecting ink from each liquid ejection hole, and 600 dpi in the main scanning direction. Printing is possible at the resolution.

JP 2003-305852 A

  However, since the liquid discharge head described in Patent Document 1 is a serial type, high-resolution and high-speed printing is possible. However, in order to arrange the liquid discharge holes at a high density, the liquid discharge head is flown into the flow path member. Since the paths are provided close to each other with high density, there is a possibility that the discharge characteristics for each liquid discharge hole may vary due to crosstalk and flow path arrangement.

  For example, when a certain liquid discharge hole is greatly different from the other liquid discharge holes around the liquid discharge hole or the volume of the liquid droplet is greatly different, the liquid discharge hole is discharged from the liquid discharge hole. Pixels formed by droplet landing have a certain tendency, such as the landing position being shifted in a specific direction or the size of the pixel becoming larger or smaller than the pixels formed around it. Due to the difference in printing density caused by these, linear (straight) printing unevenness occurs in the sub-scanning direction.

  When the variation in the ejection characteristics of the liquid ejection holes is large, the density difference in printing in the main scanning direction becomes large, and stripe-like printing unevenness in the sub-scanning direction becomes more noticeable. In particular, when the variation in the ejection characteristics is caused by the structure of the flow path, periodic density unevenness occurs in the main scanning direction, which may appear to be streaks in the sub-scanning direction.

  Accordingly, an object of the present invention is to provide a printing apparatus in which streak-like printing unevenness hardly occurs on a recording medium.

The printing apparatus according to the present invention includes a liquid discharge hole group including n (n is an integer of 4 or more) liquid discharge holes, and n pressures that pressurize the liquid and discharge liquid droplets from the liquid discharge holes. The liquid discharge hole group is arranged so that the liquid discharge holes are equally spaced d in one direction and do not overlap in a direction orthogonal to the one direction, and a direction orthogonal to the one direction P having a liquid discharge hole array of m rows (m is an integer not less than 2 and not exceeding n / 2) in which the liquid discharge holes are arranged in a line in the one direction at equal intervals (d × m). Individual (p is an integer of 2 or more) liquid ejection heads, transport means for transporting a print medium relative to the liquid ejection head in a direction perpendicular to the one direction, and ejection from one liquid ejection head Parallel to the one direction with respect to the print medium, etc. A group of pixels arranged at intervals d is formed, and the group of pixels formed by the p liquid ejection heads is formed so as to be shifted in the one direction by d / p in parallel to the one direction with respect to the print medium. And a control unit that controls the pressure unit to send an ejection signal so as to form one line of pixels, and the control unit is connected to one liquid ejection hole row of the liquid ejection head. An ejection signal is sent to the pressurizing unit at the same timing, and an ejection signal is sent to the pressurizing unit connected to the adjacent liquid ejection hole row at a different timing, and one pixel group is formed. In order to achieve this, among the discharge signals sent to the pressurizing unit connected to the liquid discharge hole row, the difference in time from the first discharge signal sent to the second and subsequent discharge signals is sequentially ΔT ₂ to. when the ΔT _m And wherein the sending the ejection signal by at least one different of ΔT ₂ ~ΔT _m also two of any of said p number of the liquid discharge head.

The printing apparatus according to the present invention includes a liquid discharge hole group including n (n is an integer of 4 or more) liquid discharge holes, and n pressures that pressurize the liquid and discharge liquid droplets from the liquid discharge holes. The liquid discharge hole group is arranged so that the liquid discharge holes are equally spaced d in one direction and do not overlap in a direction orthogonal to the one direction, and a direction orthogonal to the one direction P having a liquid discharge hole array of m rows (m is an integer not less than 2 and not exceeding n / 2) in which the liquid discharge holes are arranged in a line in the one direction at equal intervals (d × m). Individual (p is an integer of 2 or more) liquid ejection heads, transport means for transporting a print medium relative to the liquid ejection head in a direction perpendicular to the one direction, and ejection from one liquid ejection head Parallel to the one direction with respect to the print medium, etc. A group of pixels arranged at intervals d is formed, and the group of pixels formed by the p liquid ejection heads is formed so as to be shifted in the one direction by d / p in parallel to the one direction with respect to the print medium. And a control unit that controls the pressure unit to send an ejection signal so as to form one line of pixels, and the control unit is connected to one liquid ejection hole row of the liquid ejection head. An ejection signal is sent to the pressurizing unit at the same timing, and an ejection signal is sent to the pressurizing unit connected to the adjacent liquid ejection hole row at a different timing, and one pixel group is formed. In order to achieve this, among the discharge signals sent to the pressurizing unit connected to the liquid discharge hole row, the difference in time from the first discharge signal sent to the second and subsequent discharge signals is sequentially ΔT ₂ to. when the ΔT _m By sending a discharge signal by at least one different of ΔT ₂ ~ΔT _m for any two of said p number of liquid discharge heads may occur in the liquid discharge hole, the liquid discharge hole Since the pixel density difference due to the distribution tendency of the discharge characteristics can be made different, the discharge characteristics in the main scanning direction are averaged, and the density unevenness of the pixels continuous in the sub-scanning direction of the print medium is inconspicuous Can be made.

1 is a schematic configuration diagram of a printer which is a printing apparatus according to an embodiment of the present invention. FIG. 2 is a plan view showing a head body that constitutes the liquid ejection head of FIG. 1. FIG. 3 is an enlarged view of a region surrounded by an alternate long and short dash line in FIG. 2. FIG. 3 is an enlarged view of a region surrounded by an alternate long and short dash line in FIG. It is a longitudinal cross-sectional view along the VV line of FIG. FIG. 5 is a schematic diagram illustrating a relationship between a liquid ejection head of a printing apparatus according to an embodiment of the present invention and printed pixels. It is a functional block diagram of an actuator control part. It is a functional block diagram of a timing instruction | indication part. It is a figure which shows the waveform pattern of four types of pulses which an actuator control part produces | generates. It is explanatory drawing which shows the waveform pattern which concerns on the liquid discharge hole which belongs to each liquid discharge hole row | line | column for every four sub manifold flow paths which the actuator control part shown shows.

  FIG. 1 is a schematic configuration diagram of a color inkjet printer 1 (hereinafter referred to as printer 1) which is a printing apparatus according to an embodiment of the present invention. The printer 1 has eight liquid ejection heads 2. These liquid discharge heads 2 are arranged in groups of two along the conveyance direction of the printing paper P, which is a printing medium, and are fixed in the printer 1. The liquid discharge head 2 has an elongated shape in a direction from the front to the back in FIG. The two liquid discharge heads 2 in a set are fixed while being displaced in the direction from the front side to the back side in FIG.

  The printer 1 includes a transport unit that moves the printing paper P, which is a printing medium, relative to the liquid ejection head 2. Specifically, a paper feed unit 114, a transport unit 120, and a paper receiver 116 are sequentially provided along the transport path of the printing paper P. In addition, the printer 1 is provided with a control unit 100 for controlling the operation of each unit of the printer 1 such as the liquid discharge head 2 and the paper feeding unit 114.

  The paper supply unit 114 includes a paper storage case 115 that can store a plurality of printing papers P, and a paper supply roller 145. The paper feed roller 145 can send out the uppermost print paper P among the print papers P stacked and stored in the paper storage case 115 one by one.

  Between the paper feed unit 114 and the transport unit 120, two pairs of feed rollers 118a and 118b and 119a and 119b are arranged along the transport path of the printing paper P. The printing paper P sent out from the paper supply unit 114 is guided by these feed rollers and further sent out to the transport unit 120.

  The transport unit 120 includes an endless transport belt 111 and two belt rollers 106 and 107. The conveyor belt 111 is wound around belt rollers 106 and 107. The conveyor belt 111 is adjusted to such a length that it is stretched with a predetermined tension when it is wound around two belt rollers. Thus, the conveyor belt 111 is stretched without slack along two parallel planes each including a common tangent line of the two belt rollers. Of these two planes, the plane closer to the liquid ejection head 2 is a transport surface 127 that transports the printing paper P.

  As shown in FIG. 1, a conveyance motor 174 is connected to the belt roller 106. The transport motor 174 can rotate the belt roller 106 in the direction of arrow A. The belt roller 107 can rotate in conjunction with the transport belt 111. Therefore, the conveyance belt 111 moves along the direction of arrow A by driving the conveyance motor 174 and rotating the belt roller 106.

  In the vicinity of the belt roller 107, a nip roller 138 and a nip receiving roller 139 are arranged so as to sandwich the conveyance belt 111. The nip roller 138 is urged downward by a spring (not shown). A nip receiving roller 139 below the nip roller 138 receives the nip roller 138 biased downward via the conveying belt 111. The two nip rollers 138 and 139 are rotatably installed and rotate in conjunction with the transport belt 111.

  The printing paper P sent out from the paper supply unit 114 to the transport unit 120 is sandwiched between the nip roller 138 and the transport belt 111. As a result, the printing paper P is pressed against the transport surface 127 of the transport belt 111 and is fixed on the transport surface 127. The printing paper P is transported in the direction in which the liquid ejection head 2 is installed according to the rotation of the transport belt 111. The outer peripheral surface 113 of the conveyor belt 111 may be treated with adhesive silicon rubber. Thereby, the printing paper P can be securely fixed to the transport surface 127.

  The eight liquid ejection heads 2 are arranged close to each other along the conveyance direction by the conveyance belt 111. Each liquid discharge head 2 has a head body 13 at the lower end. A number of liquid ejection holes 8 for ejecting liquid are provided on the lower surface of the head body 13 (see FIG. 4).

  Liquid droplets (ink) of the same color are ejected from the liquid ejection holes 8 provided in the set of liquid ejection heads 2. Since the liquid ejection holes 8 of each liquid ejection head 2 are arranged at equal intervals in one direction (a direction parallel to the printing paper P and perpendicular to the conveyance direction of the printing paper P and the longitudinal direction of the liquid ejection head 2), Printing can be performed without gaps in one direction. Note that the liquid discharge holes 8 are arranged at equal intervals in one direction. More specifically, when the liquid discharge holes 8 are projected perpendicularly to the one direction with respect to a straight line parallel to the one direction, each liquid That is, the discharge holes 8 are arranged at equal intervals. The colors of the liquid ejected from each liquid ejection head 2 in the set are magenta (M), yellow (Y), cyan (C), and black (K), respectively. Each liquid ejection head 2 is disposed with a slight gap between the lower surface of the head body 13 and the transport surface 127 of the transport belt 111.

  The printing paper P transported by the transport belt 111 passes through the gap between the liquid ejection head 2 and the transport belt 111. At that time, droplets are ejected from the head main body 13 constituting the liquid ejection head 2 toward the upper surface of the printing paper P. As a result, a color image based on the image data stored by the control unit 100 is formed on the upper surface of the printing paper P.

  At this time, the images of the respective colors are printed by the pixels on which the liquid droplets ejected from the liquid ejecting head 2 in the set land on the printing paper P. Each color image is formed by arranging pixel lines parallel to one direction in a direction perpendicular to the one direction. Each pixel line is formed by droplets ejected from one liquid ejection head 2. That is, one line is formed by arranging pixels formed by droplets ejected from one liquid ejection head 2 landing on the printing paper P, or by droplets landing as described above. A pixel and a pixel that is blank because a droplet has not landed are formed side by side. The lines arranged at right angles to the one direction are each formed by droplets ejected from one of the two liquid ejection heads 2. In other words, each color image has two liquid ejection heads for each line. It is formed by sharing in 2.

  A separation plate 140 and two pairs of feed rollers 121a and 121b and 122a and 122b are arranged between the transport unit 120 and the paper receiver 116. The printing paper P on which the color image is printed is conveyed to the peeling plate 140 by the conveying belt 111. At this time, the printing paper P is peeled from the transport surface 127 by the right end of the peeling plate 140. Then, the printing paper P is sent out to the paper receiving unit 116 by the feed rollers 121a to 122b. In this way, the printed printing paper P is sequentially sent to the paper receiving unit 116 and stacked on the paper receiving unit 116.

  Note that a paper surface sensor 133 is installed between the liquid ejection head 2 and the nip roller 138 that are the most upstream in the transport direction of the printing paper P. The paper surface sensor 133 includes a light emitting element and a light receiving element, and can detect the leading end position of the printing paper P on the transport path. The detection result by the paper surface sensor 133 is sent to the control unit 100. The control unit 100 can control the liquid ejection head 2, the conveyance motor 174, and the like so that the conveyance of the printing paper P and the printing of the image are synchronized based on the detection result sent from the paper surface sensor 133.

  Next, the head main body 13 constituting the liquid discharge head of the present invention will be described. FIG. 2 is a plan view showing the head main body 13 shown in FIG. FIG. 3 is an enlarged plan view of a region surrounded by a one-dot chain line in FIG. 2 and is a part of the head main body 13. FIG. 4 is an enlarged perspective view of the same position as in FIG. 3, in which some of the flow paths are omitted so that the position of the liquid discharge holes 8 can be easily understood. 3 and 4, in order to make the drawings easy to understand, the liquid pressurizing chamber 10 (liquid pressurizing chamber group 9), the squeezing 12, and the liquid discharge holes which are to be drawn by broken lines below the piezoelectric actuator unit 21. 8 is drawn with a solid line. FIG. 5 is a longitudinal sectional view taken along line VV in FIG.

The head body 13 includes a flat plate-like flow path member 4 and a piezoelectric actuator unit 21 that is an actuator unit on the flow path member 4. The piezoelectric actuator unit 21 has a trapezoidal shape, and is disposed on the upper surface of the flow path member 4 so that a pair of parallel opposing sides of the trapezoid is parallel to the longitudinal direction of the flow path member 4. Further, two piezoelectric actuator units 21 are arranged on the flow path member 4 as a whole in a zigzag manner, two along each of two virtual straight lines parallel to the longitudinal direction of the flow path member 4. Yes. The oblique sides of the piezoelectric actuator units 21 adjacent to each other on the flow path member 4 partially overlap in the short direction of the flow path member 4. Although details will be described later, in the area printed by driving the overlapping piezoelectric actuator unit 21, droplets discharged by the two piezoelectric actuator units 21 are mixed and landed. ,
A manifold 5 that is a part of the liquid flow path is formed inside the flow path member 4. The manifold 5 has an elongated shape extending along the longitudinal direction of the flow path member 4, and an opening 5 b of the manifold 5 is formed on the upper surface of the flow path member 4. A total of ten openings 5 b are formed along each of two straight lines (imaginary lines) parallel to the longitudinal direction of the flow path member 4. The opening 5b is formed at a position that avoids a region where the four piezoelectric actuator units 21 are disposed. The manifold 5 is supplied with liquid from a liquid tank (not shown) through the opening 5b.

  The manifold 5 formed in the flow path member 4 is branched into a plurality of branches (the manifold 5 at the branched portion may be referred to as a sub-manifold 5a). The manifold 5 connected to the opening 5 b extends along the oblique side of the piezoelectric actuator unit 21 and is disposed so as to intersect with the longitudinal direction of the flow path member 4. In a region sandwiched between two piezoelectric actuator units 21, one manifold 5 is shared by adjacent piezoelectric actuator units 21, and the sub-manifold 5 a branches off from both sides of the manifold 5. These sub-manifolds 5 a extend in the longitudinal direction of the head body 13 adjacent to each other in regions facing the respective piezoelectric actuator units 21 inside the flow path member 4.

  The flow path member 4 has four liquid pressurizing chamber groups 9 in which a plurality of liquid pressurizing chambers 10 are formed in a matrix (that is, two-dimensionally and regularly). The liquid pressurizing chamber 10 is a hollow region having a substantially rhombic planar shape with rounded corners. The liquid pressurizing chamber 10 is formed so as to open on the upper surface of the flow path member 4. These liquid pressurizing chambers 10 are arranged over almost the entire surface of the upper surface of the flow path member 4 facing the piezoelectric actuator unit 21. Accordingly, each liquid pressurizing chamber group 9 formed by these liquid pressurizing chambers 10 occupies a region having almost the same size and shape as the piezoelectric actuator unit 21. Further, the opening of each liquid pressurizing chamber 10 is closed by adhering the piezoelectric actuator unit 21 to the upper surface of the flow path member 4.

  In the present embodiment, as shown in FIG. 3, the manifold 5 branches into four rows of E1-E4 sub-manifolds 5a arranged in parallel with each other in the short direction of the flow path member 4, and each sub-manifold The liquid pressurizing chambers 10 connected to 5a constitute a row of liquid pressurizing chambers 10 arranged in the longitudinal direction of the flow path member 4 at equal intervals, and the four rows are arranged in parallel to each other in the short direction. Yes. Two rows of liquid pressurizing chambers 10 connected to the sub-manifold 5a are arranged on both sides of the sub-manifold 5a.

  As a whole, the liquid pressurizing chambers 10 connected from the manifold 5 constitute rows of the liquid pressurizing chambers 10 arranged in the longitudinal direction of the flow path member 4 at equal intervals, and the rows are 16 rows parallel to each other in the short direction. It is arranged. The number of liquid pressurizing chambers 10 included in each liquid pressurizing chamber row is a pressurizing unit, and gradually decreases from the long side toward the short side corresponding to the outer shape of the displacement element 50 that is an actuator. It is arranged to be. The liquid discharge holes 8 are also arranged in the same manner. As a result, it is possible to form an image with a resolution of 600 dpi in the longitudinal direction as a whole. That is, the individual flow paths 32 are connected to each sub-manifold 5a at intervals corresponding to 150 dpi on average. This is because the individual flow paths 32 connected to each sub-manifold 5a are not necessarily connected at equal intervals when the 600 dpi liquid discharge holes 8 are divided and connected to the four sub-manifolds 5a. That is, the individual flow paths 32 are formed at intervals of an average of 170 μm (25.4 mm / 150 = 169 μm if 150 dpi) in the extending direction of 5a, that is, the main scanning direction.

  Individual electrodes 35 to be described later are formed at positions facing the liquid pressurizing chambers 10 on the upper surface of the piezoelectric actuator unit 21. The individual electrode 35 is slightly smaller than the liquid pressurizing chamber 10, has a shape substantially similar to the liquid pressurizing chamber 10, and fits in a region facing the liquid pressurizing chamber 10 on the upper surface of the piezoelectric actuator unit 21. Is arranged.

  A large number of liquid discharge holes 8 are formed in the liquid discharge surface on the lower surface of the flow path member 4. These liquid discharge holes 8 are arranged at a position avoiding a region facing the sub-manifold 5 a arranged on the lower surface side of the flow path member 4. Further, these liquid discharge holes 8 are arranged in a region facing the piezoelectric actuator unit 21 on the lower surface side of the flow path member 4. These liquid discharge hole groups 7 occupy an area having almost the same size and shape as the piezoelectric actuator unit 21, and the liquid discharge holes 8 are made to drop liquid by displacing the displacement element 50 of the corresponding piezoelectric actuator unit 21. Can be discharged. The liquid discharge holes 8 in each region are arranged at equal intervals along a plurality of straight lines parallel to the longitudinal direction of the flow path member 4.

  Each liquid discharge head 2 has substantially the same flow path structure. Here, “having substantially the same structure” means that the basic structure of the flow path formed in the flow path member 4, that is, a structure in which the manifold 5, the sub-manifold 5 a and the individual flow path 32 are shared, Means that the dimensions of the individual flow passages 32, particularly the dimensions of the respective parts of the squeezing 12 and the liquid pressurizing chamber 10, are matched within the range of variations that occur during manufacturing.

  In the liquid discharge head 2 having substantially the same flow path structure, when driven by the same discharge signal, the discharge characteristics of the liquid droplets discharged from each liquid discharge hole 8, that is, the speed, amount, or main liquid of the liquid droplets The tendency of the generation of minute droplets called satellites that are discharged separately from the droplets is similar. For example, the amount of droplets ejected from the liquid ejection holes 8 connected to a specific sub-manifold 5a may tend to be larger than the amount of droplets ejected from other liquid ejection holes 8. . In such a case, when printing is performed with one liquid ejection head, pixels formed by droplets ejected from the liquid ejection holes 8 are continuously formed in the transport direction of the printing paper P, so that an image is displayed. Streaky density unevenness may be noticeable. Even when printing is performed by arranging a plurality of liquid ejection heads 2 at positions translated in the transport direction, the plurality of liquid ejection heads 2 have a tendency similar to the ejection characteristics of the respective liquid ejection holes 8, and this phenomenon occurs. appear.

Here, printing by the printing apparatus of the present invention will be described in detail with reference to FIG. In FIG. 6, two liquid discharge heads 201 and 202 and lines L ₁ to L ₂ , which are formed on the printing paper P by droplets discharged from the liquid discharge holes 8 provided in them, are arranged in a straight line. the relationship between L ₄ is schematically shown. FIG. 6 is a schematic view of the printer shown in FIG. 1 as viewed from above. The printing paper P is below one of the two liquid discharge heads 201 and 202 that are long in one direction, and the one direction of the liquid discharge heads 201 and 202 Lines L _{1 to} L ₄ of the pixel 210 are formed while being transported in the transport direction that is a direction perpendicular to the line. In FIG. 6, for the sake of explanation, the interval between the pixels 210 is different in the transport direction and the direction orthogonal to the transport direction. However, in actuality, the pixels 210 are formed at the same interval in the transport direction and the direction orthogonal to the transport direction. May be. Further, although omitted in FIG. 6, pixel lines are also formed in front of and behind the lines L _{1 to} L ₄ , and an image is printed on the entire printed pixel 210. This image is a single color image or an image for one color of multicolor printing. In the case of multicolor printing, as described above, another color image is formed by another set of liquid ejection heads, and a multicolor image is printed as a whole.

  The liquid discharge head 201 has liquid discharge holes 8 formed at equal intervals d in one direction. The liquid discharge holes 8 of the liquid discharge head 201 are arranged so as not to overlap in a direction orthogonal to one direction. The liquid ejection holes 8 are provided with 16 rows (m = 16) of liquid ejection hole arrays F1′-1 to F16′-1 arranged in a line in one direction in a direction orthogonal to the one direction. The liquid discharge holes 8 belonging to each of the liquid discharge hole rows F1′-1 to F16′-1 are arranged at equal intervals of 16 × d. The liquid discharge head 201 is formed with a flow path similar to that shown in FIG. In FIG. 6, the liquid discharge holes 8 connected to one sub-manifold 5a are surrounded by a broken line so that the distribution of the liquid discharge holes 8 is easily understood, and the liquid discharge holes 8 are divided into four groups. From the left in FIG. 6, the liquid discharge hole 8 is the leftmost liquid discharge hole 8 of the liquid discharge hole array F1′-1, subsequently the leftmost liquid discharge hole 8 of the liquid discharge hole array F9′-1, and the like. Hole array F5'-1, F11'-1, F2'-1, F10'-1, F6'-1, F14'-1, F3'-1, F9'-1, F7'-1, F15'- 1, the leftmost liquid discharge holes 8 of F4′-1, F12′-1, F8′-1, and F16 are arranged. Next, from the left among the liquid discharge holes 8 belonging to the liquid discharge hole row F1′-1. The second one is arranged, and thereafter repeatedly arranged in the same order.

  The liquid discharge head 202 has substantially the same structure as the liquid discharge head 201. That is, the dimensions of each part of the manifold 5, the sub-manifold 5a, and the individual flow path 32 are the same within the range of variations in manufacturing accuracy. These liquid discharge heads 201 and 202 are arranged in the transport direction and are shifted by 0.5 × d in one direction.

  When p liquid ejection heads are provided, the p liquid ejection heads may be arranged so as to be shifted by p / d. By doing so, each liquid discharge head forms a pixel group arranged at equal intervals d in one direction, and p pixel groups are formed by being shifted by d / p. A pixel is formed, and this is one line to be printed. In other words, if printing with a resolution of one liquid ejection head 600 dpi is possible, printing with a resolution of p × 600 dpi is possible with p liquid ejection heads.

An image is printed on the printing paper P by the pixels 210 formed by droplets ejected from the liquid ejection heads 201 and 202. Each of the lines L _{1 to} L ₄ is formed of pixels 210 formed by droplets ejected from the two liquid ejection heads 201 and 202 under the control of the control unit 100. A pixel group is formed in which pixels 210 formed by droplets ejected from one liquid ejection head 201 are arranged at equal intervals d. The pixels 210 formed by droplets discharged from the other liquid discharge head 202 also form a pixel group arranged at equal intervals d. Then, when these pixel groups land with a shift of 0.5d, the two liquid discharge heads 201 and 202 as a whole form one line in which the pixels 210 are formed at equal intervals d / 2.

To print a portion from the liquid ejection head 201 of the line L ₁ a (half), as droplets on line L ₁ is landed, the liquid discharge hole from the liquid discharge hole belonging to the liquid discharge hole row F1'-1 The liquid discharge holes belonging to the row F16′-1 are discharged in this order. That is, the liquid connected to the liquid discharge holes belonging to the liquid discharge hole array F16′-1 from the timing when the discharge signal is sent to the liquid pressurizing chamber 10 connected to the liquid discharge holes belonging to the liquid discharge hole array F1′-1. Assuming that the timing at which the discharge signal is sent to the pressurizing chamber 10 is T _{1 to} T ₁₆ in order, T ₁ is the earliest, followed by T _{2 to} T ₁₆ in this order. The same applies to the liquid discharge hole arrays F1′-1 to F16′-1 of the liquid discharge head 202.

  When such printing is performed using substantially the same liquid discharge head, there is a risk that a distribution tendency with a period of d × m appears in the liquid discharge characteristics of the liquid discharge holes 8 in the sub-scanning direction. As described above, by sending a part of the ejection signal sent to each liquid ejection hole row of the liquid ejection head while shifting the time, the ejection characteristics in the main scanning direction are averaged, so that it is continuous in the conveyance direction orthogonal to one direction. This makes it possible to make the uneven density of the pixels inconspicuous. This is because, when solid printing is performed without taking measures as described later, the discharge characteristics are similar, and droplets discharged from the liquid discharge holes land continuously in one direction. For example, when the discharge amount of the liquid discharge hole is small compared to other liquid discharge holes, pixels that have a small diameter and appear thin to the human eye are continuously formed in one direction. Are continuously formed in a direction perpendicular to one direction, and thin streaky density unevenness is conspicuous in the human eye.

As described above, T _{1 to} T ₁₅ are set in order from the earliest timing of the ejection signals for ejecting droplets that land on one line. Further, the time from T ₁ to T _{2 to} T ₁₆ with the earliest timing to be sent is set to ΔT ₂ to ΔT ₁₆ in order. If at least one of ΔT _{2 to} ΔT ₁₆ is made different in different liquid discharge heads, the different liquid discharge heads remain in the flow paths of the manifold 5, the sub-manifold 5 a and the individual flow path 32, or the dew member 4. By changing the state of residual vibration, the distribution tendency of the liquid ejection characteristics with a period of d × m changes, the density unevenness tendency of pixels in one direction m on the printing paper P is averaged, and the conveyance direction orthogonal to one direction Thus, the density unevenness of the continuous pixels can be made inconspicuous.

This point will be explained further in detail, for example, when the liquid droplet from the liquid ejection hole rows F1'-1 is discharged by the discharge signal sent at time T _1, thereafter, the manifold 5, the sub-manifold 5a and the individual channel Residual vibration remains in each of the 32 flow paths or the dew member 4. Thereafter, the liquid droplets from the liquid ejection hole row F2 '-1 is discharged by the discharge signal sent at time T _2, the liquid droplets discharged at that time was simply sent at time T ₂ It is not discharged by the flow of the liquid caused by the displacement element 50 being displaced by the discharge signal, but is discharged by the flow of the liquid in which the flow and the residual vibration remaining before that are combined. Therefore, if the time ΔT ₂ from T ₁ to T ₂ is different between the liquid discharge head 201 and the liquid discharge head 202, the residual vibration state at the time T ₂ is different, so the liquid discharge head 201 and the liquid discharge head 202 are different. in will be differences in the ejection characteristics of the droplet structures of the head ejected by despite discharge signal T ₂ are the same results. In this case, since the time from _{T 1} in the liquid discharge head 201 and the liquid discharge head 202 from _{T 2} be a [Delta] T ₃ are the same up to _{T 3} to _{T 3} becomes different, the discharge signal of _{T 3} Therefore, the ejection characteristics of the ejected droplets are different.

The above is generalized. When p liquid ejection heads having m rows of liquid ejection holes are used, numbers 1 to p are arbitrarily assigned to the liquid ejection heads, and 1 is 1 / p of one line in the liquid ejection head of number i. since the timing of ejection signal to form a group of pixels are sent is m _times, expressed as T i1 _{through T im,} representing the time from _{T i1} to _T i2 _{through T im} and ΔT _i2 ~ΔT _im. For any two of the p liquid ejection heads, sending at least one of ΔT _{2 to} ΔT _m with different ejection signals means that any two of the p liquid ejection heads, for example, When the number i and the number j are selected and ΔT _i2 to ΔT _im are compared with ΔT _j2 to ΔT _jm , at least one of them is made different. In this way, there are no liquid discharge heads in which ΔT ₂ to ΔT _m all match among the p liquid discharge heads. That is, when viewed from the viewpoint of the timing of sending the ejection signal, there is no liquid ejection head having the same liquid ejection characteristics, and the above-described density unevenness can be made inconspicuous.

  The flow path member 4 included in the head body 13 has a stacked structure in which a plurality of plates are stacked. These plates are a cavity plate 22, a base plate 23, an aperture (squeezing) plate 24, supply plates 25 and 26, manifold plates 27, 28 and 29, a cover plate 30 and a nozzle plate 31 in order from the upper surface of the flow path member 4. is there. A number of holes are formed in these plates. Each plate is aligned and laminated so that these holes communicate with each other to form the individual flow path 32 and the sub-manifold 5a. As shown in FIG. 5, the head main body 13 has a liquid pressurizing chamber 10 on the upper surface of the flow path member 4, the sub-manifold 5a on the inner lower surface side, and the liquid discharge holes 8 on the lower surface. Each portion constituting the path 32 is disposed close to each other at different positions, and the sub manifold 5 a and the liquid discharge hole 8 are connected via the liquid pressurizing chamber 10.

  The holes formed in each plate will be described. These holes include the following. First, the liquid pressurizing chamber 10 formed in the cavity plate 22. Second, there is a communication hole that forms a flow path that connects from one end of the liquid pressurizing chamber 10 to the sub-manifold 5a. This communication hole is formed in each plate from the base plate 23 (specifically, the inlet of the liquid pressurizing chamber 10) to the supply plate 25 (specifically, the outlet of the sub manifold 5a). The communication hole includes the aperture 12 formed in the aperture plate 24 and the individual supply flow path 6 formed in the supply plates 25 and 26.

  Third, there is a communication hole that constitutes a flow channel that communicates from the other end of the liquid pressurizing chamber 10 to the liquid discharge hole 8, and this communication hole is referred to as a descender (partial flow channel) in the following description. . The descender is formed on each plate from the base plate 23 (specifically, the outlet of the liquid pressurizing chamber 10) to the nozzle plate 31 (specifically, the liquid discharge hole 8). Fourthly, there is a communication hole constituting the sub-manifold 5a. The communication holes are formed in the manifold plates 27 to 29.

  Such communication holes are connected to each other to form an individual flow path 32 from the liquid inflow port (the outlet of the submanifold 5a) from the submanifold 5a to the liquid discharge hole 8. The liquid supplied to the sub manifold 5a is discharged from the liquid discharge hole 8 through the following path. First, from the sub-manifold 5a, it passes through the individual supply flow path 6 and reaches one end of the throttle 12. Next, it proceeds horizontally along the extending direction of the aperture 12 and reaches the other end of the aperture 12. From there, it reaches one end of the liquid pressurizing chamber 10 upward. Further, the liquid pressurizing chamber 10 proceeds horizontally along the extending direction of the liquid pressurizing chamber 10 and reaches the other end of the liquid pressurizing chamber 10. While moving little by little in the horizontal direction from there, it proceeds mainly downward and proceeds to the liquid discharge hole 8 opened on the lower surface.

  As shown in FIG. 5, the piezoelectric actuator unit 21 has a laminated structure including two piezoelectric ceramic layers 21a and 21b. Each of these piezoelectric ceramic layers 21a and 21b has a thickness of about 20 μm. The total thickness of the piezoelectric actuator unit 21 is about 40 μm. Each of the piezoelectric ceramic layers 21a and 21b extends so as to straddle the plurality of liquid pressurizing chambers 10 (see FIG. 3). The piezoelectric ceramic layers 21a and 21b are made of a lead zirconate titanate (PZT) ceramic material having ferroelectricity.

  The piezoelectric actuator unit 21 includes a common electrode 34 made of a metal material such as Ag—Pd and an individual electrode 35 made of a metal material such as Au. As described above, the individual electrode 35 is disposed at a position facing the liquid pressurizing chamber 10 on the upper surface of the piezoelectric actuator unit 21. One end of the individual electrode 35 is drawn out of a region facing the liquid pressurizing chamber 10 to form a connection electrode 36. The connection electrode 36 is made of, for example, gold containing glass frit, and has a convex shape with a thickness of about 15 μm. The connection electrode 36 is electrically joined to an electrode provided in an FPC (Flexible Printed Circuit) (not shown). Although details will be described later, an ejection signal is supplied to the individual electrode 35 from the control unit 100 through the FPC.

  The common electrode 34 is formed over almost the entire surface in the area between the piezoelectric ceramic layer 21a and the piezoelectric ceramic layer 21b. That is, the common electrode 34 extends so as to cover all the liquid pressurizing chambers 10 in the region facing the piezoelectric actuator unit 21. The thickness of the common electrode 34 is about 2 μm. The common electrode 34 is grounded in a region not shown, and is held at the ground potential. In the present embodiment, a surface electrode (not shown) different from the individual electrode 35 is formed on the piezoelectric ceramic layer 21b at a position avoiding the electrode group composed of the individual electrodes 35. The surface electrode is electrically connected to the common electrode 34 through a through-hole formed in the piezoelectric ceramic layer 21b, and is connected to another electrode on the FPC in the same manner as many individual electrodes 35. ing.

  As shown in FIG. 5, the common electrode 34 and the individual electrode 35 are disposed so as to sandwich only the uppermost piezoelectric ceramic layer 21b. A region sandwiched between the individual electrode 35 and the common electrode 34 in the piezoelectric ceramic layer 21b is referred to as an active portion, and the piezoelectric ceramic in that portion is polarized. In the piezoelectric actuator unit 21 of the present embodiment, only the uppermost piezoelectric ceramic layer 21b includes an active portion, and the piezoelectric ceramic 21a does not include an active portion and functions as a diaphragm. The piezoelectric actuator unit 21 has a so-called unimorph type configuration.

  As will be described later, when a predetermined ejection signal is selectively supplied to the individual electrode 35, pressure is applied to the liquid in the liquid pressurizing chamber 10 corresponding to the individual electrode 35. As a result, droplets are ejected from the corresponding liquid ejection holes 8 through the individual channels 32. That is, the portion of the piezoelectric actuator unit 21 that faces each liquid pressurizing chamber 10 corresponds to an individual displacement element 50 (actuator) corresponding to each liquid pressurizing chamber 10 and the liquid discharge hole 8. That is, in the laminate composed of two piezoelectric ceramic layers, the displacement element 50 having a unit structure as shown in FIG. 5 is provided immediately above the liquid pressurizing chamber 10 for each liquid pressurizing chamber 10. Are formed by a diaphragm 21a, a common electrode 34, a piezoelectric ceramic layer 21b, and individual electrodes 35, and the piezoelectric actuator unit 21 includes a plurality of displacement elements 50. In the present embodiment, the amount of liquid discharged from the liquid discharge hole 8 by one discharge operation is about 5 to 7 pL (picoliter).

  A large number of individual electrodes 35 are individually electrically connected to the actuator control means via contacts and wirings on the FPC so that potentials can be individually controlled.

In the piezoelectric actuator unit 21 in the present embodiment, when an electric field is applied to the piezoelectric ceramic layer 21b with the individual electrode 35 different in potential from the common electrode 34, the portion to which this electric field is applied becomes the piezoelectric effect. Acts as an active part that is distorted by At this time, the piezoelectric ceramic layer 21b expands or contracts in the thickness direction, that is, the stacking direction, and tends to contract or extend in the direction orthogonal to the stacking direction, that is, the surface direction, due to the piezoelectric lateral effect. On the other hand, since the remaining piezoelectric ceramic layer 21a is an inactive layer that does not have a region sandwiched between the individual electrode 35 and the common electrode 34, it does not spontaneously deform. That is, the piezoelectric actuator unit 21 uses the upper piezoelectric ceramic layer 21b (that is, the side away from the liquid pressurizing chamber 10) as a layer including the active portion and the lower side (that is, close to the liquid pressurizing chamber 10). In this configuration, the individual electrodes 35 are connected to the common electrode 34 by the actuator control means so that the electric field and the polarization are in the same direction. When the potential is positive or negative, the portion (active portion) sandwiched between the electrodes of the piezoelectric ceramic layer 21b contracts in the plane direction. On the other hand, since the piezoelectric ceramic layer 21a which is an inactive layer is not affected by an electric field, the piezoelectric ceramic layer 21a does not spontaneously shrink and tries to restrict deformation of the active portion. As a result, there is a difference in the strain in the polarization direction between the piezoelectric ceramic layer 21b and the piezoelectric ceramic layer 21a, and the piezoelectric ceramic layer 21b is deformed so as to protrude toward the liquid pressurizing chamber 10 (unimorph deformation). .

  In the actual driving procedure in this embodiment, the individual electrode 35 is set to a potential higher than the common electrode 34 (hereinafter referred to as a high potential) in advance, and the individual electrode 35 is temporarily set to the same potential as the common electrode 34 every time there is a discharge request. (Hereinafter referred to as a low potential), and then set to a high potential again at a predetermined timing. As a result, the piezoelectric ceramic layers 21a and 21b return to the original shape at the timing when the individual electrode 35 becomes low potential, and the volume of the liquid pressurizing chamber 10 is compared with the initial state (the state where the potentials of both electrodes are different). To increase. At this time, a negative pressure is applied to the liquid pressurizing chamber 10 and the liquid is sucked into the liquid pressurizing chamber 10 from the manifold 5 side. Thereafter, at the timing when the individual electrode 35 is set to a high potential again, the piezoelectric ceramic layers 21a and 21b are deformed so as to protrude toward the liquid pressurizing chamber 10, and the volume of the liquid pressurizing chamber 10 is reduced so that the inside of the liquid pressurizing chamber 10 Becomes a positive pressure, the pressure on the liquid rises, and droplets are ejected. That is, an ejection signal including a pulse based on a high potential is supplied to the individual electrode 35 in order to eject a droplet. The ideal pulse width is AL (Acoustic Length), which is the length of time during which the pressure wave propagates from the manifold 5 to the liquid discharge hole 8 in the liquid pressurizing chamber 10. According to this, when the inside of the liquid pressurizing chamber 10 is reversed from the negative pressure state to the positive pressure state, both pressures are combined, and the liquid droplet can be ejected with a stronger pressure.

  In gradation printing, gradation expression is performed by the number of droplets ejected continuously from the liquid ejection holes 8, that is, the droplet amount (volume) adjusted by the number of droplet ejections. For this reason, the number of droplet discharges corresponding to the specified gradation expression is continuously performed from the liquid discharge hole 8 corresponding to the specified dot region. In general, when liquid ejection is performed continuously, it is preferable that the interval between pulses supplied to eject liquid droplets is AL. As a result, the period of the residual pressure wave of the pressure generated when discharging the previously discharged liquid droplet coincides with the pressure wave of the pressure generated when discharging the liquid droplet discharged later, and these are superimposed. Thus, the pressure for discharging the droplet can be amplified.

  Next, the discharge signal control of the present invention will be described in detail. Each of the liquid pressurizing chambers 10 belonging to the liquid pressurizing chamber group 9 communicates with the liquid discharge hole 8 at one end of the long diagonal line, and is connected to one of the sub-manifolds E1 to E4 via the throttle 12 at the other end. It is communicated. The liquid pressurizing chambers 10 are adjacently arranged in a matrix in a staggered arrangement pattern in two directions of the arrangement direction A and the arrangement direction B. The shorter diagonal line of the liquid pressurizing chamber 10 is parallel to the arrangement direction A described above. The arrangement direction B is an oblique side direction of the liquid pressurizing chamber 10 having an obtuse angle θ with the arrangement direction A. Both acute angle portions of the liquid pressurizing chamber 10 are located between two adjacent liquid pressurizing chambers.

  As shown in FIG. 3, the liquid pressurizing chambers 10 are arranged along the arrangement direction A so as to be separated by a distance corresponding to 37.5 dpi. Further, 16 liquid pressurizing chambers 10 are arranged in the arrangement direction B. That is, in one piezoelectric actuator unit 21, liquid pressurization chamber rows 11 extending in the arrangement direction A are formed in 16 rows in the arrangement direction B, and printing can be performed with a resolution of 600 dpi as a whole.

  These 16 liquid pressurizing chamber rows 11 are adjacent to each other through a predetermined gap, and a liquid pressurizing chamber group 9 is configured. The liquid pressurizing chamber row 11 has the first liquid pressurizing chamber row 11a and the second liquid pressurizing according to the relative positions with respect to the sub-manifolds E1 to E4 when viewed from the direction orthogonal to the paper surface of FIG. It is divided into a pressure chamber row 11b, a third liquid pressurizing chamber row 11c, and a fourth liquid pressurizing chamber row 11d. These first to fourth liquid pressurizing chamber rows 11a to 11d are periodically arranged in the order of 11c → 11d → 11a → 11b → 11c → 11d → ... → 11b from the upper side to the lower side of the piezoelectric actuator unit 21. Four are arranged.

  In the liquid pressurizing chamber 10a constituting the first liquid pressurizing chamber row 11a and the liquid pressurizing chamber 10b constituting the second liquid pressurizing chamber row 11b, the direction C taken in the direction orthogonal to the arrangement direction A The liquid discharge holes 8 are unevenly distributed on the lower side and face the vicinity of the lower end of the corresponding liquid pressurizing chambers 10 respectively. On the other hand, in the liquid pressurization chamber 10c constituting the third liquid pressurization chamber row 11c and the liquid pressurization chamber 10d constituting the fourth liquid pressurization chamber row 11d, the liquid discharge hole 8 is located on the upper side in the direction C. And are opposed to the vicinity of the upper end portion of the corresponding liquid pressurizing chamber 10, respectively. That is, the liquid discharge holes 8 associated with the liquid pressurization chambers 10a belonging to the first liquid pressurization chamber row 11a form the liquid discharge hole rows 15a shown in FIG. 4 and belong to the second liquid pressurization chamber row 11b. The liquid discharge holes 8 related to the liquid pressurizing chamber 10b form a liquid discharge hole row 15b shown in FIG. And the liquid discharge hole 8 which concerns on the liquid pressurization chamber 10c which belongs to the 3rd liquid pressurization chamber row | line | column 11c forms the liquid discharge hole row | line | column 15c shown in FIG. 4, and belongs to the 4th liquid pressurization chamber row | line | column 11d. The liquid discharge holes 8 associated with the liquid pressurizing chamber 10d form a liquid discharge hole row 15d shown in FIG.

  In the first and fourth liquid pressurizing chamber rows 11a and 11d, when viewed from the direction orthogonal to the paper surface of FIG. It overlaps with E4. On the other hand, in the second and third liquid pressurizing chamber rows 11b and 11c, almost the entire areas of the liquid pressurizing chambers 10b and 10c do not overlap with the sub-manifolds E1 to E4. For this reason, the liquid pressurizing chambers 10 belonging to any of the liquid pressurizing chamber rows 11 can have the widths of the submanifolds E1 to E4 while preventing the liquid discharge holes 8 communicating therewith from overlapping the submanifolds E1 to E4. It is possible to smoothly supply droplets to each liquid pressurizing chamber 10 as wide as possible.

  FIG. 4 shows a strip-shaped region R having a width (678.0 μm) corresponding to 37.5 dpi in the longitudinal direction of the flow path member 4 and extending in the short direction (direction C) of the flow path member 4. Has been. In the belt-like region R, one liquid ejection hole 8 exists for each of the liquid ejection hole arrays 15a to 15d, and a total of 16 liquid ejection holes 8 are included. The positions of the 16 liquid discharge holes 8 projected from the same direction on a virtual straight line extending in the arrangement direction A are separated by an interval corresponding to 600 dpi, which is the resolution at the time of printing, and are equally spaced. .

  As shown in FIG. 4, a plurality of liquid discharge holes 8 are arranged along the extending direction (arrangement direction A) of the sub-manifolds E1 to E4, and 16 liquid discharge hole arrays 15 parallel to each other are arranged. Forming. The liquid discharge hole rows 15 correspond to the liquid pressurizing chamber rows 11a to 11d, respectively, and are divided into liquid discharge hole rows 15a to 15d. The liquid discharge hole row 15c is located between the liquid discharge hole row 15a and the liquid discharge hole row 15b. This is because the acute angle portion between the liquid pressurization chambers 10 belonging to the second and third liquid pressurization chamber rows 11b and 11c overlaps in the direction C, and the liquid pressurization is performed on the acute angle portion side. This is because the liquid discharge holes 8 related to the chamber 10 are unevenly distributed.

As a result, the liquid discharge holes 8 related to the liquid pressurization chambers 10 belonging to the third liquid pressurization chamber row 11c are arranged between the liquid discharge holes 8 related to the first and second liquid pressurization chamber rows 11a and 11b. ing. That is, as shown in FIG. 3, each liquid pressurization chamber row | line | column 11a-11d is represented as F1-F16 in order from the bottom to the top in the figure. Further, when F1 ′ to F16 ′ are written in the liquid discharge hole rows 15a to 15d corresponding to the liquid pressurizing chamber rows 11a to 11d, as shown in FIG. 4, F4 ′ corresponding to the liquid discharge hole rows 15b and 15c. , F 5 ′, F 8 ′, F 9 ′, F 12 ′, and F 13 ′ are different from the alignment of the liquid pressurizing chamber row 11, and are changed in the direction C. The liquid discharge holes 8 are separated by a distance corresponding to 37.5 dpi along the longitudinal direction (arrangement direction A) of the flow path member 4. As described above, each of the liquid discharge hole rows 15a to 15d is arranged at a position not facing the four sub-manifolds E1 to E4. The sixteen liquid discharge holes 8 belonging to one strip region R are arranged in the arrangement direction A. When the sixteen liquid discharge holes 8 are expressed as (1) to (16) in order from the left of the projected position on the straight line extending to, the sixteen liquid discharge holes 8 are From (1), (9), (13), (15), (5), (7), (11), (16), (3), (8), (12), (14), They are arranged in the order of (4), (6), (10), (2). In the liquid discharge head 2 configured as described above, when the piezoelectric actuator unit 21 is appropriately driven in accordance with the conveyance of the printing paper, it is possible to draw characters, figures, and the like having a resolution of 600 dpi in the arrangement direction A.

  First, the control of the ejection signal of the liquid ejection head 201 alone will be described. FIG. 7 shows a functional block diagram of the actuator control unit 153. As shown in FIG. 7, the actuator control unit 153 includes a waveform output unit 154, four delay units 155, a timing instruction unit 156, and a waveform amplification unit 157. The waveform output unit 154, the delay unit 155, and the timing instruction unit 156 are configured by digital circuits, and the waveform amplification unit 157 is configured by an analog circuit.

The waveform output unit 154 generates and outputs an ejection signal for ejecting a desired volume of ink from the liquid ejection holes 8 based on the execution contents of printing input from the communication unit 151. As for the discharge signal sent to form one line, the waveform output unit 154 outputs the discharge signal sent to F1 earliest, followed by the discharge signals sent sequentially from F2 to F16. If the timings at which the discharge signals sent to F1 to F16 are output are Tg ₁ to Tg ₁₆ , respectively, the time difference ΔTg ₂ from Tg ₂ to Tg ₁ is connected to F2 from the liquid discharge hole 8 connected to F1. This corresponds to the time required for the recording paper P to move from the liquid discharge hole 8. Similarly, ΔTg _{3 to} ΔTg ₁₆ correspond to the time required for the recording paper P to move from the liquid discharge hole 8 connected to F1 to the liquid discharge hole 8 connected to F3 to F16. Further, ΔTg _{2 to} ΔTg ₁₆ are common to the plurality of liquid ejection heads 201 and 202 used.

  Each of the four delay units 155 corresponds to one of the liquid discharge hole arrays 15a to 15d for each of the sub-manifold channels E1 to E4, and delays the discharge signal output from the waveform output unit 154 for a predetermined time. The delayed ejection signal is further output. Further, based on the instruction from the timing instruction unit 156, the delay unit 155 selects any one of four delay times: no delay, delay time td, delay time td × 2, and delay time td × 3 (see FIG. 10). Can be set. The delay of the ejection signal becomes the delay of the ejection timing of the ink from the liquid ejection hole 8. That is, the delay unit 155 sets four types of ink ejection timings from the liquid ejection holes 8 in units of liquid ejection hole arrays in the four liquid ejection hole arrays 15a to 15d for each of the sub-manifold channels E1 to E4. Can do.

  The timing instruction unit 156 sets the above-described delay time (droplet discharge timing) for each delay unit 155 so as to be different from each other. The waveform amplifier 157 amplifies and outputs the ejection signal output from the delay unit 155. The ejection waveform output from the waveform amplification unit 157 is supplied to the corresponding individual electrode 35 of the piezoelectric actuator unit 21.

  The timing instruction unit 156 will be described in detail with reference to FIG. FIG. 8 is a functional block diagram of the timing instruction unit 156. As illustrated in FIG. 9, the timing instruction unit 156 includes a table storage unit 161 and a selector 162. The table storage unit 161 stores different delay times of ejection signals supplied to the individual electrodes 35 corresponding to the liquid ejection hole arrays 15a to 15d. Tables 1 and 2 show examples of delay times stored in the table storage unit 161. In Tables 1 and 2, no delay is represented as “0”, delay time td as “1”, delay time td × 2 as “2”, and delay time td × 3 as “3” ( (See FIG. 9). Table 1 shows the liquid discharge hole rows 15a to 15d arranged for each of the sub-manifolds E1 to E4, and Table 2 shows Table 1 arranged in order of the projection point numbers. In Tables 1 and 2, the row numbers of the liquid discharge hole rows 15a to 15d are represented by F1 ′ to F16 ′ in the same manner as described above.

  In the present embodiment, the delay time td is 3.2 μs, which is the minimum value of the period during which no structural crosstalk occurs between the adjacent liquid pressurizing chambers 10, but is not limited thereto. When the plurality of liquid pressurizing chambers 10 are arranged at high density, structural crosstalk cannot be ignored. Therefore, if the delay time td is set to a period in which no structural crosstalk occurs, the influence of the structural crosstalk can be reduced even if the plurality of liquid pressurizing chambers 10 are arranged at high density. The td value is appropriately determined depending on the positional relationship (arrangement density) of the liquid pressurizing chambers 10 and the surrounding rigidity.

  Tables 1 and 2 show delay amounts to be set when using the two liquid discharge heads 201 and 202. The delay times of the discharge signals of the liquid discharge hole arrays 15a to 15d related to the sub-manifolds E1 to E4 are set to be different from each other. Further, as shown in Table 2, at the projection points of the liquid discharge holes 8 belonging to the respective liquid discharge hole rows 15a to 15d, the delay times of the discharge signals of the adjacent liquid discharge holes 8 are also set different from each other. . In the timing instruction unit 156, a delay time is set for each of the four delay units 155 based on the delay time of each of the liquid discharge hole arrays 15a to 15d. Note that the delay time in the present embodiment is four types corresponding to the number of liquid pressurization chamber rows for each of the sub-manifolds E1 to E4, but may be two or more types. The selector 162 selects a delay time for each of the liquid ejection hole arrays 15 a to 15 d stored in the table storage unit 161 and sets a delay time for the delay unit 155.

More specifically, as described above, the waveform output unit 154 outputs ejection signals sent to F1 ′ to F16 ′ to form one line at timings Tg ₁ to Tg ₁₆ , respectively. If the timing of the discharge signal sent to F1'~F16' and _T 1 _{through T 16} as described _above, Tg 1 _{C. to Tg 16} and _T 1 _{through T 16} is the time delay shown in Table 1 and 2 Only different. In the liquid ejection head 201, the difference in time of ejection signals sent to F1' a discharge signal sent to F3' is .DELTA.Tg ₃ before being delayed, after being delayed, T ₁ is T ₃ is not delayed Is delayed by td × 1, ΔT ₃ becomes ΔTg ₃ + td × 1. In the liquid ejection head 202, the time difference between the ejection signal sent to F3 ′ and the ejection signal sent to F1 ′ is ΔTg ₃ before being delayed, T ₁ is delayed by td × 2, and T ₃ is not delayed. Therefore, ΔT ₃ is ΔTg ₃ −td × 2. Since ΔTg ₃ is common to the liquid ejection heads 201 and 202, ΔT ₂ is different between the liquid ejection head 201 and the liquid ejection head 202. In the different liquid discharge heads, the residual vibration state remaining in each flow path of the manifold 5, the sub-manifold 5a, and the individual flow path 32 changes, so that the distribution tendency with the cycle of d × m of the liquid discharge characteristics changes, It is possible to suppress the density unevenness of the pixels from occurring continuously in the transport direction on the printing paper P, thereby making it difficult to generate a streak density distribution parallel to the transport inspection direction.

  FIG. 9 shows the waveform patterns of the discharge signals to which the four types of delays output from the actuator control unit 153 are applied. The vertical axis indicates the potential, and the horizontal axis indicates time, and is a waveform pattern of the discharge signal corresponding to the liquid discharge hole rows 15a to 15d related to the sub-manifold E1. Delay 0 indicates a waveform pattern without delay, Delay 1 indicates a waveform pattern with delay time td, Delay 2 indicates a waveform pattern with delay time td × 2, and Delay 3 indicates a waveform pattern with delay time td × 3. ing. Among these, the waveform pattern indicated by delay 0 is applied to the liquid ejection hole row 15b (F1 ′), and the waveform pattern indicated by delay 1 is applied to the liquid ejection hole row 15a (F2 ′). Further, the waveform pattern indicated by delay 2 is added to the liquid ejection hole row 15d (F3 ′), and the waveform pattern indicated by delay 3 is added to the liquid ejection hole row 15c (F4 ′). In the present embodiment, a pulse based on a high potential is supplied to the individual electrode 35 in order to eject a droplet. The waveform pattern shown in FIG. 9 includes an ejection pulse and a cancel pulse. The ejection pulse is for ejecting a droplet from the liquid ejection hole 8, and one droplet can be ejected with one pulse. The waveform pattern shown in FIG. 10 includes three ejection pulses. With the waveform pattern of delay 0 as a reference, the waveform pattern of delay 1 has a start time delayed by time td, the waveform pattern of delay 2 has a start time delayed by time td × 2, and the waveform pattern of delay 3 The start time is delayed by time td × 3.

  The cancel pulse is for removing residual pressure remaining in the individual flow path 32 after droplet discharge. The cancel pulse causes a new pressure to be generated in the individual flow path 32 at the timing of the cycle reversed with respect to the cycle of the residual pressure. As a result, the residual pressure is almost offset by the pressure generated by the cancel pulse. This makes it easier for the liquid ejected by the last ejection pulse to be collected into a single droplet, generating minute droplets called satellites that land around the original landing position of the droplet without being collected in the droplet. It becomes difficult. In addition, it becomes difficult to be affected by the residual stress at the time of discharge from the surrounding liquid pressurizing chamber 10 or the next discharge from the same liquid pressurizing chamber 10.

  When such a waveform pattern is added, there is a possibility that the speed of the liquid droplet ejected by the delayed ejection signal varies slightly compared to the speed of the liquid droplet ejected by the ejection signal not delayed. At this time, the printing position accuracy can be increased by changing the discharge speed by changing the voltage between the delayed discharge signal and the non-delayed discharge signal.

  Since the speed of the liquid droplets ejected by the delayed ejection signal tends to be slow due to the influence of crosstalk, it is preferable to increase the voltage of the delayed ejection signal.

  In the present embodiment, since the liquid pressurization chamber 10 and the manifold 5 are disposed as described above, the time td may be generated when the liquid pressurization chamber 10 is adjacent as described above. The shortest time (3.2 μs) that is not affected by a certain structural crosstalk is set. Therefore, as shown in FIG. 9, the period Tm from the first ejection pulse with delay 0 to the cancel pulse with delay 3 is also shortened. When the time required for the printing paper P to be transported by a distance corresponding to the printing resolution in the transport direction is defined as a printing cycle, it is only the time when there is no influence due to residual pressure that cannot be canceled out by the cancel pulse after droplet discharge. Even if it waits, one printing cycle can be shortened by the amount corresponding to the shortened period Tm. That is, it contributes to high-speed printing. The unit distance in the present embodiment is about 40 μm because the resolution in the transport direction of the printing paper P is 600 dpi.

  Here, the four types of discharge signals for each of the sub-manifolds E1 to E4 will be described. FIG. 10 is an explanatory diagram showing a waveform pattern related to the liquid ejection holes 8 belonging to the liquid ejection hole arrays 15a to 15d for each of the four sub-manifolds. As shown in FIG. 10, the projecting point numbers of the liquid discharge holes 8 are (1), (9), (13), and the individual electrodes 35 respectively corresponding to the liquid discharge hole rows 15a to 15d related to the sub-manifold E1. The waveform patterns of delay 0, delay 1, delay 2 and delay 3 are supplied in order to (5). Similarly, the individual electrode 35 corresponding to each of the liquid discharge hole rows 15a to 15d related to the sub-manifold E2 has the projection point number of the liquid discharge hole 8 of (15), (7), (11), (3). In addition, waveform patterns of delay 0, delay 1, delay 2, and delay 3 are supplied in this order. The individual electrode 35 corresponding to each of the liquid discharge hole rows 15a to 15d related to the sub manifold E3 has the projection point numbers of the liquid discharge holes 8 in order of (16), (8), (12), and (4). Waveform patterns of delay 1, delay 0, delay 3 and delay 2 are supplied. Similarly, the individual electrode 35 corresponding to each of the liquid discharge hole rows 15a to 15d related to the sub-manifold E4 has the projection point number of the liquid discharge hole 8 of (14), (6), (10), (2). In this order, waveform patterns of delay 1, delay 0, delay 3, and delay 2 are supplied. In this way, discharge signals are supplied at different discharge timings between adjacent liquid pressurizing chamber rows or adjacent projection points of the liquid discharge holes 8. In this way, ejection signals of four types of delay patterns are supplied to the individual electrodes 35 associated with the liquid ejection hole arrays 15a to 15d, and the piezoelectric actuator unit 21 is driven. From the corresponding liquid discharge hole 8, an amount of liquid droplets corresponding to the waveform pattern is discharged at a timing corresponding to the type of delay. Then, dots of a desired gradation are formed on the printing paper P. In the present embodiment, the waveform patterns of delay 0 to delay 3 as shown in FIG. 9 are repeated every printing cycle.

According to the modification, the selector 162 in the present embodiment sets a delay time for the delay unit 155 so as to supply ejection signals having the same delay waveform pattern to the individual electrodes 35 associated with the same liquid ejection hole arrays 15a to 15d. Although it is set, the delay time is set for the delay unit 155 so that the discharge signals having different waveform patterns with different delays are supplied to the individual electrodes 35 associated with the same liquid discharge hole arrays 15a to 15d. It may be. That is, the waveform pattern of the delay of the ejection signal supplied to the individual electrode 35 in the first printing cycle may be different from the waveform pattern of the delay of the ejection signal supplied to the individual electrode 35 in the next printing cycle. .
Even in this case, since the delay time td has a minimum value so as to shorten the period Tm, the influence of crosstalk is less likely to occur in the next printing cycle while keeping one printing cycle short.

According to the liquid discharge head 2 in the present embodiment as described above, the discharge signals are supplied to the corresponding individual electrodes 35 at different discharge timings between the adjacent liquid pressurizing chamber rows 11a to 11d. It is possible to reduce the influence of dynamic crosstalk. That is, the temporal difference in ejection timing is set to a time that is not influenced by structural crosstalk even if it is short. Therefore, no structural crosstalk is received from the adjacent liquid pressurizing chambers 10 regardless of the adjacent combination between the liquid pressurizing chamber rows 11.
Furthermore, even when the density is increased, the influence of structural crosstalk can be kept low. In addition, the presence of a plurality of ejection timings within one printing cycle also means that the power consumption timing is divided according to the number of ejection timings. As a result, it is possible to avoid a momentary increase in the power consumption peak, and to make the power supply device small and simple.

  Further, four types of delays 0 to 3 are applied to the corresponding individual electrode 35 between the four liquid pressurization chamber rows 11a to 11d formed by the plurality of liquid pressurization chambers 10 communicating with the same sub-manifolds E1 to E4. Since an ejection signal having a waveform pattern is supplied, the influence of fluidic crosstalk can be reduced. Here, fluid crosstalk means that in the manifold 5, the pressure waves propagated from the liquid pressurizing chambers resonate with each other to generate a standing wave, and the standing wave communicates with the sub-manifold. This affects the droplet discharge in the liquid pressurizing chamber. Due to the influence of such fluidic crosstalk, variations occur in the droplet ejection characteristics. In order to reduce the influence of such fluidic crosstalk, in the present embodiment, a plurality of liquid pressurizing chambers 10 communicating with the same sub-manifolds E1 to E4 are arranged between the liquid pressurizing chamber rows 11a to 11d. Discharge signals are supplied to the corresponding individual electrodes 35 at four different discharge timings.

  In the present embodiment, as described above, the minimum time difference of the ejection timing is set to a time td that does not affect the structural crosstalk between adjacent liquid pressurizing chamber rows. If the timing difference is equal to or greater than this time td, it is not affected by fluidic crosstalk. This time td is determined in accordance with the liquid pressurizing chamber 10, the manifold 5, and the positional relationship and communication form between them, and even if there is a structural difference, at least these times td. What is necessary is just to set according to the arrangement | positioning state and communication state of. That is, the time td when it is difficult to be affected by any crosstalk may be used.

  Further, when the liquid discharge holes 8 belonging to the 16 liquid discharge hole rows 15a to 15d are projected on the virtual straight line from the same direction, the liquid pressurizing chambers 10 related to the adjacent projection points (1) to (16) are projected. Discharge signals are supplied to the corresponding individual electrodes 35 at different discharge timings. Even if fluid crosstalk and structural crosstalk cannot be completely suppressed when ejection signals having different ejection timings are supplied between adjacent liquid pressurization chamber rows, the influence of this residual crosstalk is affected. It will be distributed among the dots on the print medium. For this reason, the difference in dot size due to the crosstalk is less noticeable. For example, even if printing is performed by changing the discharge timing between the adjacent liquid pressurizing chamber rows 11 and between the liquid pressurizing chamber rows 11 communicating with the same manifold, it is formed at the same discharge timing depending on the arrangement state of the liquid discharge holes. The dots may form continuous horizontal lines. As long as the influence of crosstalk is sufficiently removed by changing the ejection timing as described above, if there is an influence of the residual crosstalk, the liquid pressurization chamber row associated with the target dot, for example, Even if 11 and the manifolds are different from each other, the influence of the remaining may appear due to being formed at a specific timing. That is, even a single horizontal line has an effect as a variation in the thickness of the line. Further, the uneven density is eliminated in the printing result on the printing medium. That is, since dots of the same size are formed without being adjacent to each other, the difference in dot size is less noticeable. Therefore, the difference in dot size on the printing medium due to crosstalk is less noticeable, and the printing quality on the printing medium is improved.

  In addition, 16 liquid pressurizing chamber rows 11a to 11d formed by the plurality of liquid pressurizing chambers 10 extend in parallel to the extending direction of the sub-manifolds E1 to E4, and the plurality of liquid pressurizing chambers 10 and 16 are arranged. The mutual positional relationship between the liquid pressurizing chamber rows 11a to 11d and the plurality of sub-manifolds E1 to E4 is a regular relationship. Therefore, the influence of fluid crosstalk and structural crosstalk becomes regular. That is, the liquid pressurizing chambers 10 belonging to the same liquid pressurizing chamber row 11 are affected to the same extent by the crosstalk, so that the discharge signals are applied to the individual electrodes 35 corresponding to the liquid pressurizing chamber rows 11 at different discharge timings. As a result, the influence of each crosstalk is reduced evenly for each liquid pressurizing chamber row 11. Therefore, it is easy to suppress variations in droplet discharge characteristics due to the influence of each crosstalk between the liquid pressurizing chamber rows 11, and the droplet discharge accuracy is improved.

  Then, in order to suppress variations in the ejection characteristics remaining even under such control, printing is performed using a plurality of liquid ejection heads 201 and 202. As shown in Tables 1 and 2, the liquid ejection head 201 and the liquid ejection head 202 change the delay amount of the ejection signal that pressurizes the liquid pressurizing chamber 10 connected to the corresponding liquid ejection hole array. In the liquid discharge head 201 and the liquid discharge head 202, the liquid in the liquid discharge hole 8 is changed because the residual vibration remaining in the flow paths of the manifold 5, the sub-manifold 5a and the individual flow path 32 or the flow path member 4 changes. The tendency of discharge characteristics changes. As a result, even when droplets that land adjacently in one direction are ejected from the same position in the liquid ejection hole groups of the two liquid ejection heads 201 and 202, the timing at which the ejection signal is sent Or different residual vibrations due to different timings of the previously sent ejection signals, resulting in different ejection characteristics, making it difficult to form similar pixels in one direction. It is possible to make the density unevenness of pixels continuous in the transport direction orthogonal to the inconspicuous.

The liquid discharge hole row for changing the delay amount may be one of the 16 rows, but if at least one of the four liquid discharge hole rows connected to each sub-manifold 5a is changed, each sub-manifold 5a Since the remaining residual vibrations change directly, the change in liquid ejection characteristics is relatively large, and the effect of suppressing density unevenness is great. That is, at least one of T ₂ -T ₁ , T ₃ -T ₂ and T ₄ -T ₃ , at least one of T ₅ -T ₄ , T ₆ -T ₅ and T ₅ -T ₄ , At least one of the _{T 12 -T 11, T 11 -T} 10 and _T 10 -T _9, at least one of the _{T 16 -T 15, T 15 -T} 14 and _T 13 _{-T 12,} a total of Preferably, at least four are different. Further, it is preferable that T _n1 −T _n2 (n1 is an odd number, n2 = n1-1) or T _n1 −T _n2 (n1 is an even number, n2 = n1-1) is varied at every timing.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made as long as they are described in the claims.

  The liquid discharge head 2 as described above is manufactured as follows, for example.

  A tape composed of a piezoelectric ceramic powder and an organic composition is formed by a general tape forming method such as a roll coater method or a slit coater method, and a plurality of green sheets that become piezoelectric ceramic layers 21a and 21b after firing are produced. . An electrode paste to be the common electrode 34 is formed on a part of the green sheet by a printing method or the like. Further, if necessary, a via hole is formed in a part of the green sheet, and a via conductor is inserted into the via hole.

  Next, each green sheet is laminated to produce a laminate, and pressure adhesion is performed. The laminated body after pressure contact is fired in a high-concentration oxygen atmosphere, and then the individual electrodes 25 are printed on the fired body surface using an organic gold paste, fired, and then the connection electrode 36 is printed using an Ag paste. And the piezoelectric actuator unit 21 is produced by baking.

  Next, the flow path member 4 is produced by laminating plates 22 to 31 obtained by a rolling method or the like. Holes to be the manifold 5, the individual supply flow path 6, the liquid pressurizing chamber 10, the descender, and the like are processed in the plates 22 to 31 into a predetermined shape by etching.

  These plates 22 to 31 are preferably formed of at least one metal selected from the group consisting of Fe—Cr, Fe—Ni, and WC—TiC, particularly when ink is used as a liquid. Since it is desired to be made of a material having excellent corrosion resistance against ink, Fe-Cr is more preferable.

  The piezoelectric actuator 21 and the flow path member 4 can be laminated and bonded via an adhesive layer, for example. A well-known adhesive layer can be used as the adhesive layer. However, in order not to affect the piezoelectric actuator 21 and the flow path member 4, an epoxy resin, a phenol resin, or a polyphenylene ether having a thermosetting temperature of 100 to 150 ° C. It is preferable to use at least one thermosetting resin adhesive selected from the group of resins. By heating to the thermosetting temperature using such an adhesive layer, the piezoelectric actuator 21 and the flow path member 4 can be heat-bonded.

  Thereafter, in order to electrically connect the piezoelectric actuator 21 and the control circuit 100 as necessary, an electrode such as FPC is joined to the connection electrode 36 to obtain the liquid discharge head 2.

DESCRIPTION OF SYMBOLS 1 ... Printer 2 ... Liquid discharge head 4 ... Flow path member 5 ... Manifold 5a ... Sub manifold 5b ... Opening 6 ... Individual supply flow path 8 ... Liquid discharge hole DESCRIPTION OF SYMBOLS 9 ... Liquid pressurization chamber group 10 ... Liquid pressurization chamber 11a, b, c, d ... Liquid pressurization chamber row | line | column 12 ... Squeeze 15a, b, c, d ... Liquid discharge hole Row 21 ... Piezoelectric actuator unit 21a ... Piezoelectric ceramic layer (vibrating plate)
21b ... Piezoelectric ceramic layer 22-31 ... Plate 32 ... Individual flow path 34 ... Common electrode 35 ... Individual electrode 36 ... Connection electrode 50 ... Displacement element

Claims (1)

a liquid ejection hole group including n (n is an integer of 4 or more) liquid ejection holes, and n pressure units that pressurize the liquid and eject liquid droplets from the liquid ejection holes, respectively. The ejection hole group is arranged so that the liquid ejection holes are equally spaced d in one direction and do not overlap in a direction orthogonal to the one direction, and m rows (m is 2 in a direction orthogonal to the one direction). In the above, p (n is an integer not exceeding n / 2), and the liquid ejection holes are arranged in one line in the one direction at equal intervals (d × m) (p is 2 or more). (Integer) liquid discharge head, transport means for transporting the print medium relative to the liquid discharge head in a direction orthogonal to the one direction, and the liquid droplets discharged from one liquid discharge head A group of pixels arranged at equal intervals d in parallel to the one direction with respect to the medium Forming one pixel line parallel to the one direction with respect to the print medium by forming the pixel group formed by the p liquid ejection heads by shifting the pixel group by d / p in the one direction. And a control unit that controls the pressure unit by sending a discharge signal, and the control unit is the same as the pressure unit connected to one liquid discharge hole row of the liquid discharge head. In order to send an ejection signal at a timing, send an ejection signal to the pressure unit connected to the adjacent liquid ejection hole row at a different timing, and form the pixel group, the liquid ejection hole row When the difference in time from the first discharge signal sent to the second and subsequent discharge signals to ΔT ₂ to ΔT _m in order among the discharge signals sent to the pressure unit connected to Liquid discharge Printing apparatus characterized by sending a discharge signal by at least one different of ΔT ₂ ~ΔT _m for any two of the head.

Images