In view of the above, the features of the present embodiment are roughly divided into two configurations: “a configuration to be adopted in a case where an ink not containing any filler (a filler-less ink) is used”, and “a configuration to be adopted in a case where an ink containing a filler formed with hard particles is used”. Here, the former is referred to as the feature 1, and the latter is referred to as the feature 2. First, the feature 1 is described.

Comparative Example 1

Here, before explanation is started regarding the feature 1 (a configuration to be adopted in a case where an ink not containing a filler (a filler-less ink) is used), a configuration to be compared (Comparative Example 1) is described, and the problem thereof is explained.

FIG. 5 illustrates a configuration according to Comparative Example 1. In a case where a filler-less ink is used, a sealing on-off valve formed with a resin such as a fluororesin is used. This is to fill a V-shaped groove with the member by press fitting. An elastic member 1040 is formed with a fluororesin. Therefore, the on-off valve 31 formed with a fluororesin whose shape easily conforms to the nozzle surface of the nozzle plate 15 that discharges liquid (ink) has the problem of liquid leakage over time due to retraction of an end face 1040b that is the end face of the elastic member 1040. A cause of this problem is described below in detail, with reference to FIGS. 12A and 12B.

Feature 1 in the Present Embodiment

Next, the feature 1 in the present embodiment is described with reference to FIG. 6.

Example 1

FIG. 6 is a diagram illustrating Example 1 of the present embodiment. Example 1 is a configuration that is adopted in a case where an ink not containing any filler (a filler-less ink) is used.

The outermost tip portion of a shaft-like core 310 has a flat recess 312 that can accommodate a columnar member in its central portion. A cylindrical elastic member 40 is provided on the tip side of the recess 312. In the elastic member 40, a discharge-side elastic portion 401 (an example of a first elastic portion) that is an elastic portion located on the discharge side, and a core-side elastic portion 402 (an example of a second elastic portion) that is an elastic portion located on the side of the core 310 are coupled as a two-layer structure. The two elastic portions differ from each other in elastic modulus. As for the material of the discharge-side elastic portion 401, a fluororesin polychlorotrifluoroethylene (PCTFE) is used. As for the material of the core-side elastic portion 402, a perfluoro-rubber sheet, FFKM or FFKO that is fluoro-rubber, or the like is used.

Thus, the liquid discharge head includes: a discharge port (14) through which a liquid is discharged in a discharge direction; a valve body (31) to openably close the discharge port (14); and a driver (32) coupled to the valve body to move the valve body (31) in the discharge direction, wherein the valve body (31) includes: an elastic member (40) including: a first elastic portion (401, 401d, 401f, 411, 411s) having a first elastic modulus; and a second elastic portion (402, 412, 402a, 402b) having a second elastic modulus different from the first elastic modulus, the elastic member (40) to contact the discharge port (14) to close the discharge port (14); and a core (310) attached to the elastic member (40) to support the elastic member (40).

The first elastic portion (401, 401d, 401f, 411, 411s) is closer to the discharge port (14) than the second elastic portion in the discharge direction, and the second elastic portion (402, 412, 402a, 402b) is closer to the core (310) than the first elastic portion (401, 401d, 40ff, 411, 411s) in the discharge direction.

The first elastic modulus of the first elastic portion (401, 401d, 401f, 411, 411s) is higher than the second elastic modulus of the second elastic portion (402, 412, 402a, 402b).

The elastic member 40 has a diameter Φ of 0.6 mm, and the inner diameter φ of the hole of the recess 312 is 0.7 mm. There is a dimensional difference between the two diameters. A gap 311 (an example of a predetermined interval) is provided between the elastic member 40 and the core 310. The gap 311 is provided so as not to hinder deformation in the width direction (a direction orthogonal to the axial direction, which is the leftward direction in FIG. 6) when the elastic member 40 is subjected to a compressive force in the axial direction (a vertical direction in FIG. 6). Further, as the gap 311 is provided, it is possible to achieve an effect to facilitate the elastic member 40 to follow the inclined surface in a case where the nozzle plate 15 is inclined.

Here, the discharge-side elastic portion 401 protrudes from the end portion of the core 310 by about 100 μm. The protrusion is such that the core 310 does not come into contact with the nozzle plate 15 during the operation of sealing the hole of the nozzle 14. A recess 401a is formed at the end portion (an end face 401b) at the tip of the discharge-side elastic portion 401. The recess 401a has a function of ensuring a channel width for the time of discharge of a high-viscosity ink, to lower the fluid resistance.

As described above, the discharge-side elastic portion 401 is formed with a fluororesin. This resin characteristically has a higher elastic modulus than the elastic modulus of perfluoro-rubber, but has a low elastic limit (a small amount of strain) at which plastic deformation starts. Therefore, the characteristics are taken advantage of, to deform the shape so as to conform to the fine undulation or inclination of the nozzle plate 15. Thus, stable sealing can be performed with a small amount of crushing. The “small amount of crushing” mentioned here indicates that the piezoelectric element of the on-off valve is further moved forward for safety from the position at which the flow rate becomes zero, to crush and secure the resin portion in the elastic range in FIGS. 24A to 24F, which will be described later.

Here, the spring constant of the discharge-side elastic portion 401 is set to 1 to 2 N/μm, under the condition that “the diameter Φ of the elastic member is 0.5 to 1 mm, and a thickness of the elastic member is 500 μm”. The spring constant of the discharge-side elastic portion 401 is set to 1 to 2 N/μm so that the discharge-side elastic portion 401 can appropriately close the nozzle 14 while the discharge-side elastic portion 401 is pressed against the nozzle plate 15 by the driver (piezoelectric element 32) such that the thickness of the discharge-side elastic portion 401 decreases by 1 to 2 μm.

The spring constant of the core-side elastic portion 402 is set to 0.05 to 1.0 N/μm, under the condition that “the diameter m of the elastic member is 0.5 to 1 mm, and the thickness thereof is 500 μm”. If the spring constant is lower than 0.05 N/μm, the elastic portion is too soft, and its sealing function is lost. If the spring constant is higher than 1.0 N/μm, the elastic portion becomes too hard, and cannot receive an impact force from the side of the nozzle 14.

For such reasons, the value of the spring constant is set to the above value on the core side.

Meanwhile, the relationship between the thicknesses of the discharge-side elastic portion 401 and the core-side elastic portion 402 in the present embodiment is set as follows, with the spring constant being adjusted so as not to exceed the yield point, a 30 to 50% reduction in the target force generation being taken into account. First, with respect to compression in the thickness direction in a case where the diameter φ of a cross-section is 0.5 to 1.0 mm, the discharge-side elastic portion 401 has a thickness of 0.45 mm when the spring constant is 1 N/μm, and the core-side elastic portion 402 has a thickness of 0.05 mm when the spring constant is 0.1 N/μm.

Thus, the discharge-side elastic portion (401, 401d, 401f, 411, 411s) has: a diameter of 0.5 to 1 mm and a thickness of 450 to 500 μm; and a spring constant of 1 to 2 N/μm, and the core-side elastic portion (402, 412, 402a, 402b) has: a diameter of 0.5 to 1 mm and a thickness of 50 to 500 μm; and a spring constant of 0.05 to 1 N/μm.

The discharge-side elastic portion (401, 401d, 401f, 411, 411s) may have: a diameter of 0.5 to 1 mm and a thickness of 450 to 500 μm; and a spring constant of 0.05 to 1 N/μm, and the core-side elastic portion (402, 412, 402a, 402b) may have: a diameter of 0.5 to 1 mm and a thickness of 50 to 500 μm; and a spring constant of 1 to 2 N/μm.

In the present embodiment, attention is paid to the mechanical characteristics of the resin member and the rubber member. To suppress excessive plastic deformation of the end face of the on-off valve, a material having lower elasticity and a wider elastic range than the material of the sealing face is included as a backup member. As a result, even when excessive compressive displacement occurs in the end face of the on-off valve (the elastic member), the backup member absorbs most of the displacement. Thus, retraction of the end face of the on-off valve (the elastic member) can be prevented.

In the present embodiment, the inner diameter of the hole of the recess 312 is straight, and there is no undercut or the like. Therefore, there is no need to have a divided structure for assembling the core 310, and thus, an effect of easy assembling can be achieved.

Principles of a Method for Reducing the Gap Between the End Face of the On-off Valve and the Nozzle Plate

FIGS. 7A to 7C are graphs and a view for explaining a method for evaluating the mechanical characteristics of an elastic member. FIGS. 7A and 7B are graphs for explaining that plastic strain remains in the on-off valve (the elastic member) formed with a fluororesin according to the comparative example. FIG. 7C is a view of a dumbbell-shaped test piece. Regarding the mechanical characteristics in the evaluation method in FIGS. 7A to 7C, the results in a plastic tensile test (the plastics standards are compliant with JIS K 7161-1, ISO 527-1) using the dumbbell-shaped test piece illustrated in FIG. 7C are referred to.

First, explanation is made with reference to FIG. 7A. FIG. 7A illustrates the yield point and the elastic limit of the resin member. As illustrated in this drawing, attention is paid particularly to the inclination (Young's modulus) in the elastic range and the elastic limit that is the strain at the limit at which plastic deformation starts. Normally, ink sealing for the nozzle is performed by pressing within the elastic limit (the compressive strain illustrated in FIGS. 24A to 24F described later). However, an excessive strain cl is applied due to thermal deformation of the housing, thermal drift of a piezoelectric stroke, or the like in some cases. This is now described with reference to FIG. 7B. The stress generated at this point of time exceeds the yield point, and reaches a point P1 in FIG. 7B. After that, even when the strain applied by a releasing operation disappears, the strain is released parallel to the elastic inclination, and therefore, a plastic strain ϵ0 remains. This turns into a gap at the rated position in the next use, and ink liquid leakage (leak) occurs.

FIGS. 8A to 8C are graphs for explaining a compound elastic modulus that is observed when two different elastic members are stacked as in the present embodiment. For ease of explanation, the elastic modulus is explained in terms of the spring constant herein. It is known that the spring constant obtained when two different spring constants k1 and k2 are connected in series is normally calculated according to Expression K illustrated in the drawing. Expression K is, K=k1*k2/(k1+k2).

Here, as illustrated in FIG. 8A, the length of one elastic member is represented by L. At the time of series connection, the total length of the spring is 2 L as illustrated in FIG. 8B. In the present embodiment, the thickness of the elastic member (which is the length of the elastic member) is fixed, and L is constant, regardless of the presence or absence of compositing. Further, the spring constant of the combination obtained when springs that have the spring constants k1 and k2, and each have a length of L/2 are coupled to each other, and the total length is fixed is calculated according to Expression Kg illustrated in the drawing (FIG. 8C).

FIG. 9 is a graph illustrating a combined spring constant Kg when the spring constants are replaced with the spring constants k1 and k2 obtained in a case where the thicknesses of the elastic members are halved. This graph takes into account the fact that the length of each spring is halved, and the spring constant is doubled. In this graph, a solid line indicates k1, a dotted line indicates k2, and a dashed line indicates Kg. When the spring constant k1 is set to 1 N/μm, and the spring constant k2 is set to 2 N/μm, the combined spring constant Kg with the fixed total length is 1.33 N/μm according to the expression mentioned above.

Here, a spring constant can be handled synonymously with a Young's modulus in the case of minute deformation in which the change in the cross-sectional area of the load surface is not taken into consideration. Therefore, when the elastic modulus of the discharge-side elastic portion 401 is E1, and the elastic modulus of the core-side elastic portion 402 is E2, E1 has an elastic modulus twice as large, and has a relationship E1=2*E2. Examples 1 to 5 of the feature 1 are described below based on this assumption.

FIG. 10 is a graph for explaining a case where compressive strain is applied in the configuration according to the comparative example (Comparative Example 1). Here, as illustrated in FIG. 10, in the configuration according to Comparative Example 1, a plastic strain εs remains when the compressive strain εl is received. That is, when the compressive strain εl is generated under a load exceeding the elastic limit, the strain does not completely become zero, and the plastic strain εs remains.

FIGS. 11A and 11B are graphs for explaining compressive stress when the elastic member is formed with a plurality of layers. FIGS. 11A and 11B illustrate example cases of Examples 1 to 5. Here, as illustrated in FIG. 11A, the combined Young's modulus is Eg, which is indicated by a dashed line in the graph, and the generated stress is reduced from P1 to P2 by this combined Young's modulus. The strain at that time is distributed to the respective elastic members at a ratio of length a:b=1:2 in the graph, and thus, the plastic strain is reduced. In this manner, the compressive stress when the elastic member is formed with a plurality of layers is reduced. Next, explanation is made with reference to FIG. 11B. FIG. 11B is a graph for explaining the plastic strain when the elastic member is formed with a plurality of layers. In FIG. 11B, P3 is closer to the yield point than P1, and accordingly, the plastic strain is reduced by that amount. P4 represents the elastic range of the core-side elastic portion, and no plastic strain is generated. The plastic strain is reduced from εs to εs' in FIG. 11B. Thus, plastic deformation is prevented, and the gap between the end face of the on-off valve (the elastic member) and the nozzle plate can be reduced.

Although the spring constant k1 is 1 N/μm, and the spring constant k2 is 2 N/μm herein as described above, this is merely an example of the principles of strain reduction. Even if the spring constant changes due to an increase in the number of elastic portions (elastic layers) constituting the elastic member, the fundamental idea does not change from the principles described above.

Difference in the Effect of Preventing Retraction of the End Face of the On-Off Valve

FIGS. 12A-1 to 12A-4 and FIGS. 12B-1 to 12B-4 are cross-sectional views of On-Off Valve illustrating a difference in the effect of preventing retraction of the end face of the elastic member 1040 (on-off valve).

FIGS. 12A-1 to 12A-4 and FIGS. 12B-1 to 12B-4 each illustrate a behavior in which the elastic member 1040 (on-off valve) formed with a fluororesin conforms to the shape of a minute undulation 15a of an undulating nozzle plate 15. FIGS. 12A-1 to 12A-4 illustrate a configuration according to the present embodiment, and FIGS. 12B-1 to 12-B4 illustrate a configuration according to Comparative Example 1. The sequence in an opening/closing operation is illustrated in FIGS. 12A-1 to FIG. 12A-4, and FIGS. 12B-1 to FIG. 12B-4. First, the configuration according to Comparative Example 1 (the configuration illustrated in FIGS. 12B-1 to 12B-4) is described. Since these configurations are the same except for the opening and closing operation, reference signs are illustrated in FIG. 12A-1 and in FIG. 12B-1, but are not illustrated in the others.

First, FIGS. 12B-1 to 12B-4 illustrate a state in which the undulation 15a is excessively pressed to transfer the undulation to an end face 1040b of the elastic member 1040 (on-off valve), and the end portion of the core 310 is brought close to the nozzle plate 15 at a gap “d” and is then moved away from the core 310. In FIGS. 12B-1 to 12B-2, the end face 1040b comes into contact with the nozzle plate 15. FIG. 12B-3 illustrates a state in which the position of the core 310 is returned to the initial position illustrated in FIG. 12B-1.

As can be seen from FIG. 12B-3, the end face 1040b is deformed. In this case, if the fluororesin is completely plastically deformed, the amount of protrusion of the elastic member 1040 (on-off valve) decreases to the same amount as the gap amount “d” in of FIG. 12B-2, and therefore, the position of the end face 1040b of the elastic member 1040 (on-off valve) retracts. After that, in of FIG. 12B-4, the end portion of the core 310 is brought close to the nozzle plate 15 at the gap “d”, so that the deformed end face 1040b again comes into contact with the nozzle plate 15. However, the amount of protrusion of the elastic member 1040 (on-off valve) decreases to the same amount as the gap amount “d”, and the position of the end face 1040b of the elastic member 1040 (on-off valve) retracts. Therefore, the core 310 cannot sufficiently press the end face 1040b against the nozzle plate 15.

Here, the plasticity of the elastic member 1040 (on-off valve) enables shape transfer (including inclination) of the nozzle plate 15, but the position of the end face of the elastic member 1040 (on-off valve) retracts when plastic deformation advances to an excessive degree. At this point of time, in the opening/closing operation for displacement control such as piezoelectric driving, the sealing function deteriorates over time, leading to a liquid leakage failure. The elastic member 1040 (on-off valve) might then come into contact with the nozzle plate 15 more strongly than a predetermined stroke due to thermal deformation in the liquid discharge head in the actual operating state. At this point of time, if the above-described deformation remains, a gap appears during the sealing operation.

On the other hand, the present embodiment is as illustrated in FIGS. 12A-l to 12A-4. First, in FIGS. 12A-1 to 12A-2, the end face 401b of the elastic member 40 comes into contact with the nozzle plate 15. At this point of time, the end portion of the core 310 is brought close to the nozzle plate 15 at the gap “d”, and the elastic member 40 is compressed and deformed until the amount of protrusion of the elastic member 40 becomes equal to “d” FIG. 12A-3 illustrates a state in which the position of the core 310 is returned to the initial position illustrated in of FIG. 12A-1. As can be seen from FIG. 12A-3, the end face 401b is deformed. However, the core-side elastic portion 402 maintains displacement as an elastic strain. Accordingly, as illustrated in FIG. 12A-3, the amount of protrusion of the on-off valve 31 becomes 1.4 d, which is 1.4 times the previous amount of protrusion. That is, the position of the end face 401b of the elastic member 40 is recovered by 0.4 d.

After that, in FIG. 12A-4, the end portion of the core 310 is again brought close to the nozzle plate 15 at the gap “d”, so that the end face 401b again comes into contact with the nozzle plate 15 in the recovered state. In this case, the amount of protrusion of the elastic member 40 is compressed by 0.4 d from 1.4 d to d (1.0 d), and thus, the end face 401b can be sufficiently pressed against the nozzle plate 15. As can be seen from this fact, the configuration according to the present embodiment has an effect to prevent retraction of the end face of the on-off valve 31, compared with the configuration according to Comparative Example 1. Although a maintenance cycle that is set due to compressive retraction of the fluororesin portion is three months, the cycle is about six months in the configuration according to the present embodiment, and the life can be extended to about twice the life in the configuration according to Comparative Example 1.

Other Examples Related to the Feature 1

Examples related to the feature 1 of the present embodiment include Examples 2 to 5, in addition to Example 1 described above. This example is described below.

Example 2

FIG. 13 is a view illustrating Example 2 of the present embodiment. Example 2 is also adopted in a case where an ink not containing any filler (a filler-less ink) is used.

The configuration according to this example differs from the configuration according to Example 1 in that a flange portion 401c is provided on the outer circumference of the discharge-side elastic portion to eliminate the gap between the core 310 and a discharge-side elastic portion 401f (an example of the first elastic portion). The other components in this example are similar to those in Example 1.

With this arrangement, it is possible to prevent the ink from entering the inside of the recess 312 at the tip of the core 310 (the position at which the core-side elastic portion 402 is located). For example, a material or an elastic body not resistant to ink can be used as the core-side elastic portion 402.

In this example, the inner diameter of the hole of the recess 312 is also straight without any undercut or the like. Accordingly, there is no need to have a divided structure for assembling the core 310.

Example 3

FIG. 14 is a view illustrating Example 3 of the present embodiment. Example 3 is also adopted in a case where an ink not containing any filler (a filler-less ink) is used.

In this example, the flange portion 401c is provided on the outer circumference of the discharge-side elastic portion to eliminate the gap between the core 310 and the discharge-side elastic portion 401f, as in the configuration according to Example 2. Further, the core 310 has a hook-like holding portion 310a that is an undercut. The core-side elastic portion 402 is not a rubber member, but a spring 402a (an example of the second elastic portion) that is a coil spring is used. That is, this example is a configuration in which the core-side elastic portion 402, which is the elastic portion disposed on the core side (the back side) of the recess 312 with respect to the elastic member 40, is a spring. The other components in this example are similar to those in Example 1.

Here, in a case where a rubber member is used for the core-side elastic portion 402, the Young's modulus greatly drops, though the elastic range is normally wide. Therefore, when a plurality of elastic members formed with the rubber member is combined to form a combined structure, there is a problem in that the combined spring constant greatly drops. Therefore, a spring is used as the elastic member, to obtain great deformation and achieve a high Young's modulus. Thus, various sealing forms (variations in the amount of compression and the generated force) can be realized. The combined spring constant described above are as described with reference to FIG. 9.

In this example, the flange portion 401c is provided on the outer circumference of the discharge-side elastic portion 401f to eliminate the gap between the core 310 and the discharge-side elastic portion 401. However, there is a possibility that a very small amount of ink will enter the recess 312. In that case, the spring 402a might be corroded by the ink. Therefore, it is preferable to use a corrosion-resistant metal such as a titanium alloy or Hastelloy® as the material of the spring 402a. Resin may also be used as the material of the spring 402a. In that case, a fluororesin may be used.

In this example, it may be difficult to join the discharge-side elastic portion 401f and the spring 402a with high accuracy. Therefore, as illustrated in FIG. 14, a hook-like holding portion 310a (an example of a holding member) that is an undercut is formed on the side of the core 310. As a result, a preliminary pressure (preload) is applied, and a division line 310c is formed so that the joining is performed at the location. Examples of the method of this coupling include bonding and fastening with a screw.

In this example, a coil spring is used as the spring 402a as described above.

In this manner, the elastic energy per unit volume at the time of deformation is greater than the energy of any other spring component, and the energy absorption efficiency is high. Thus, there is an effect that the space necessary for attaching a spring can be made relatively small. Since the Young's modulus of a material is not used as it is as illustrated in FIG. 13, spring constants of various hardness can be achieved with the shapes of springs.

Example 4

In this example, another type of spring can be used. FIG. 15 is a view illustrating Example 4 of the present embodiment. Example 4 is also adopted in a case where an ink not containing any filler (a filler-less ink) is used. In the configuration according to Example 3 in FIG. 14, the core-side elastic portion 402 is the coil spring 402a. This example differs from the configuration according to Example 3 in that a spring 402b (an example of the second elastic portion) that is a disc spring is used instead of a coil spring. The other components in this example are similar to those in Example 3.

In this example, a disc spring is used as the spring 402b as described above. In this manner, various spring characteristics can be obtained by combining disc springs, and this example can be developed to forms for various kinds of use, such as a configuration that can change the spring height as a whole, for example.

In this example, resin can also be used as the material of the spring 402b. In that case, a disc spring can easily form a harder spring than a coil spring as in this example.

Example 5

FIG. 16 is a view illustrating Example 5 of the present embodiment. Example 5 is also adopted in a case where an ink not containing any filler (a filler-less ink) is used.

This example differs from Example 1 in that the core 310 has a hook-like holding portion 310a that is an undercut. Further, in the core 310, a triangular (jagged) holding portion 310b (an example of the holding member) is formed in the vicinity of the center portion in the axial direction of the recess 312 at which the elastic member 40 is located. Along with this, a discharge-side elastic portion 401d (an example of the first elastic portion) has a holding portion 401g formed with triangular irregularities or jagged surface. The other components in this example are similar to those in Example 1.

The core (310) has a jagged surface on an inner surface of the recess to hold the elastic member (40) in the recess (312). The triangular (jagged) holding portion 401g acts with a weak resistance when the elastic member 40 is pushed into the recess 312 (the back side of the core 310), and conversely, acts as a strong resistance against external force when the elastic member 40 is pulled out toward the discharge side (the side of the nozzle 14).

As for the method for assembling the configuration according to this example, the discharge-side elastic portion 401d is pressed-fitted from the opening at the tip, while the core-side elastic portion 402 is disposed beforehand in the recess 312. By this press fitting, the elastic member 40 expands in the radial direction, and fills the holding portion 401g. Accordingly, with the configuration of an integrated core, for example, it is possible to form an assembly in which a preload is applied to the discharge-side elastic portion 401d and the core-side elastic portion 402. As the assembling can be performed by simple press fitting, the configuration of this example excels in assembling properties.

Other Features in the Present Embodiment

Next, the feature 2 according to the present embodiment (a configuration to be adopted in a case where an ink containing a filler formed with hard particles is used) is described. Before that description, configurations to be compared (Comparative Examples 1 and 2) are described, and the problems thereof are explained.

Comparative Example 1

Referring back to FIG. 5, a problem in a case where a filler-containing ink is used in the configuration according to Comparative Example 1 is described. In the configuration according to Comparative Example 1, the elastic member 1040 is formed with a fluororesin as described above. A filler is interposed at the tip of the fluororesin elastic member 1040. FIGS. 17A to 17D are views illustrating a state in which the fluororesin on-off valve in the configuration according to Comparative Example 1 is subjected to indentation by the filler, and the ink is coming out (leaking). The sequence is from FIG. 17A to FIG. 17D. Since the configurations in FIGS. 17A to 17D are basically the same, reference signs are illustrated in FIG. 17A, but are not illustrated in the others.

From FIG. 17A to FIG. 17B, the tip of the elastic member 1040 comes into contact with the nozzle plate 15. As can be seen from FIG. 17C, a large number of minute recesses 1040d are formed at the tip of the elastic member 1040 by the indentation by the filler. Therefore, in FIG. 17D, the tip of the elastic member 1040 again comes into contact with the nozzle plate 15, but the aggregate of the minute recesses 1040d forms a gap between the tip and the nozzle plate 15, which causes liquid leakage. The configuration according to Comparative Example 1 has been explained not only in this case but also in the description of the feature 1, and therefore, liquid leakage also occurs due to retraction of the end face of the on-off valve (the elastic member).

Comparative Example 2

Next, Comparative Example 2, which is another comparative example, is described. FIG. 18 illustrates a configuration according to Comparative Example 2. As illustrated in FIG. 18, Comparative Example 2 is a configuration in which a rubber film is formed on the surface layer of a metallic core 1310 by compression molding, and is used as an on-off valve 1031. In a case where a filler-containing ink is used, an on-off valve formed with a rubber such as perfluoro-rubber is used in this manner. The rubber on-off valve 1031 is less likely to be damaged by a filler.

FIGS. 19A to 19E are views for explaining a problem in the configuration according to Comparative Example 2. The sequence herein is from FIG. 19A to FIG. 19D. Since the configurations in FIGS. 19A to 19D are basically the same, reference signs are illustrated in FIG. 19A, but are not illustrated in the others. In the configuration in FIG. 19A to FIG. 19E, the metallic core 1310 is molded and covered with the fluorine-based elastic member 1041. From FIG. 19A to FIG. 19B, the tip of the elastic member 1041 comes into contact with the nozzle plate 15. As can be seen from FIG. 19C, no indentation due to the filler is formed at the tip of the elastic member 1041. That is, this drawing illustrates a situation in which indentation formation by the filler is prevented. In FIG. 19D, the tip of the elastic member 1041 again comes into contact with the nozzle plate 15. However, minute recesses like those in the configuration according to Comparative Example 1 are not formed at the tip, and thus, any gap is not formed. Accordingly, liquid leakage is less likely to occur than in the configuration according to Comparative Example 1. However, such a configuration has the problem described below.

It is difficult to strictly ensure parallelism between the end face of the tip of the on-off valve (the elastic member) and the plane of the nozzle plate 15 in the assembling process. Therefore, as illustrated in FIG. 19E, the nozzle plate 15 is normally inclined with respect to the end face of the tip of the elastic member 1041.

In such a case, it is necessary to maintain a sufficient rubber thickness t for the end face so that a height change D1 caused in the nozzle plate 15 by the inclination can also be absorbed, and sealing can be performed. In that case, however, the elastic member 1041 is a rubber member, and therefore, the elastic member 1041 is not easily deformed plastically, and excels in elastic recovery. Because of this, the elastic member 1041 does not easily conform to the inclined surface of the nozzle plate 15. Therefore, there is a problem in that a long stroke is necessary to open and close the on-off valve. This problem will be described later in detail, with reference to FIGS. 21A-I to 21B-2.

Feature 2 in the Present Embodiment

The present embodiment copes with the above problem as described below. The feature 2 in the present embodiment is now described with reference to the drawings.

Example 6

FIGS. 20A and 20B are views illustrating Example 6 of the present embodiment. Example 6 is a configuration to be adopted in a case where an ink containing a filler formed with hard particles (hereinafter referred to as a filler-containing ink) is used. This example is also the same as the examples regarding the feature 1 in being designed to reduce liquid leakage. However, the type of ink to be used is different, and therefore, the cause of liquid leakage differs from the cause of ink leakage in the examples described above. Accordingly, the configuration also differs from the configurations of the foregoing examples. This is described in detail below.

A fluororesin is known to have excellent elastoplastic properties. Accordingly, the shape of a pressure member is easily transferred. In a case where a filler-containing ink is used, a rubber member having a high yield stress needs to be disposed on the size of the nozzle 14. In view of this, this example takes advantage of the characteristics.

First, this example differs from Examples 1 to 5 described above in the elastic member 40 that has a rubber member and a resin member that are disposed opposite to each other on the discharge side and the core side, and are combined.

That is, as illustrated in FIG. 20A, this configuration includes: a discharge-side elastic portion 411 (an example of the first elastic portion) that is formed with a rubber member and is disposed on the contact face side of the nozzle plate 15; and a core-side elastic portion 412 (an example of the second elastic portion) that is formed with a resin member and is disposed in the recess 312 on the side of the core 310. The core 310 has a hook-like holding portion 310f (an example of the holding member), and the holding portion 310f is disposed at the portion (the deepest portion) closest to the core 310 in the recess 312 of the core 310.

FIG. 20B is a view illustrating a case where, at the time of assembling, the core-side elastic portion 412 is plastically deformed beforehand so as to conform to the inclination of the surface of the nozzle plate 15 with a large amount of crushing (when being moved further forward in the positive direction from the point of zero on the H axis illustrated in FIGS. 24A to 24F described later), and the gap is then again adjusted. The combined spring constant described with reference to FIG. 9 can be applied not only to the feature 1 but also to the feature 2, which is the present feature. A combination of two elastic members is harder than an elastic member formed with a rubber member. Accordingly, the elastic member 40 is plastically deformed, and this plastic deformation is taken advantage of herein. Returning back to FIGS. 20A and 20B, the description is continued. Since the tip of the discharge-side elastic portion 411 is deformed so as to be substantially parallel to the inclined nozzle plate 15, the opening and closing driving of the on-off valve can be performed with the minimum stroke, without the inclination thereof being taken into account.

Difference in Opening/Closing Amount Between the Configuration According to This Example and the Configuration According to Comparative Example 2

The configuration described above is adopted in this example, and the reason for that is now described with reference to FIGS. 21A-1 to 21B-2. FIGS. 21A-1 to 21B-2 are views illustrating a difference in the opening/closing amount between the configuration according to this example and the configuration according to Comparative Example 2. FIG. 21A-1 is a view for explaining a distance relationship between the elastic member and the nozzle plate in this example (Example 6). FIG. 21A-2 is a view for explaining a case where the on-off valve (the elastic member) is driven to open and close in a state where the nozzle plate is inclined in this example. On the other hand, FIG. 21B-1 is a view for explaining the distance relationship between the elastic member and the nozzle plate in the comparative example (Comparative Example 2). FIG. 21B-2 is a view for explaining a case where the on-off valve (the elastic member) is driven to open and close in a state where the nozzle plate is inclined in the comparative example.

In FIG. 21A-1, J represents the distance between the contact face of the nozzle plate 15 with the elastic member 40 in the configuration according to this example and a parallel line extending through a point G1 at the left end portion of the tip of the elastic member 40. This parallel line also extends through a point G2 at the right end portion of the tip of the elastic member 40. Accordingly, the distance between the point G2 and the contact face of the nozzle plate 15 with the elastic member 40 is equal to J. In FIG. 21A-2, J1 represents the distance between a point G3 on the contact face of the nozzle plate 15 with the elastic member 40 in the configuration according to this example and the point G1. The distance J1 is also the distance between the point G2 and a point G4 on the contact face of the nozzle plate 15 with the elastic member 40.

On the other hand, in FIG. 21B-1, R represents the distance between the contact face of the nozzle plate 15 with the elastic member 1041 and a parallel line extending through a point Q1 at the left end portion of the tip of the elastic member 1041 in the configuration according to Comparative Example 2. D represents the distance between the contact face of the nozzle plate 15 with the elastic member 1041 and a parallel line extending through a point Q2 at the right end portion of the tip of the elastic member 1041 in the configuration according to Comparative Example 2.

The magnitude relationship herein is expressed as D>R. In FIG. 21B-2, R1 represents the distance between a point Q3 on the contact face of the nozzle plate 15 with the elastic member 1041 and the point Q1 at the left end portion of the tip of the elastic member 1041 in the configuration according to Comparative Example 2. Further, D1 represents the distance between a point Q4 on the contact face of the nozzle plate 15 with the elastic member 1041 and the point Q2 at the right end portion of the tip of the on-off valve 31 in the configuration according to Comparative Example 2. The magnitude relationship herein is expressed as D1>R1. Each of the lines G1-G3, G2-G4, Q1-Q3, and Q2-Q4 is parallel to the opening/closing direction (the driving direction) of the on-off valve (the elastic member).

First, the configuration according to Comparative Example 2 (which is referred to simply as the comparative example herein) is described. In the comparative example illustrated in FIG. 21B-1, the elastic member 1041 that is a rubber member is covered with the core 1310. In the configuration according to the comparative example, the thickness t of the rubber of the elastic member may be made greater. In a case where the nozzle plate 15 is inclined in the configuration according to the comparative example, the distance to the face of the nozzle plate 15 to be in contact with the tip of the elastic member 1041 differs between the left end portion and the right end portion of the tip of the elastic member 1041, as indicated by R and D. In this case, when the on-off valve is driven, moving the on-off valve by the distance R1 as illustrated in FIG. 21B-2 is not sufficient, and it is necessary to move the on-off valve by the distance D1, which is longer than the distance R1. In such a case, the device is larger in size, and furthermore, it is necessary to drive the on-off valve by a long opening/closing distance (which is a longer stroke).

In this example, on the other hand, the core side is formed with a member that is easily plastically deformed. With this arrangement, the member is plastically deformed, and the tip of the elastic member 40 is inclined. In this case, as illustrated in FIG. 21A-1, when the nozzle plate 15 is inclined, the distances to the face of the nozzle plate 15 to be in contact with the tip of the elastic member 40 from the left end portion and the right end portion of the tip of the on-off valve 31 are both equal to J. Therefore, as illustrated in FIG. 21A-2, when the on-off valve is driven, the on-off valve is moved by the distance J1. This eliminates the need to drive the on-off valve over a long distance. For this reason, the above arrangement is adopted.

Here, the spring constants of the respective elastic portions in the configuration according to the feature 2 are reversed between the discharge side and the core side compared with the feature 1, but the same numerical values are basically set. Specifically, the spring constant of the discharge-side elastic portion 411 is set to 0.05 to 1.0 N/μm under the condition that “the diameter Φ of the elastic member is 0.5 to 1 mm, and the thickness thereof is 500 μm”. On the other hand, the spring constant of the core-side elastic portion 412 is set to 1 to 2 N/μm under the condition that “the diameter (D of the elastic member is 0.5 to 1 mm, and the thickness thereof is 500 μm”.

Regarding the thicknesses of the elastic portions in this example, the thickness of the core-side elastic portion 412 is greater than the thickness of the discharge-side elastic portion 411 in the magnitude relationship in terms of thickness. The configuration according to this example needs to have a function of enclosing the filler contained in the ink in the rubber layer on the surface of the discharge-side elastic portion 411 and contact-sealing the flat portion of the nozzle plate 15. Specifically, a size that is about five to ten times the filler diameter is necessary. The particle size also varies depending on the purpose of use. For example, the mean particle size is about 2 μm for vehicle coating, and the mean particle diameter is about 20 μm for battery electrodes. Therefore, with the mean particle size of the filler taken into account, the thickness of the discharge-side elastic portion 411 is set to about 100 to 300 μm, to maintain a certain degree of strength. The thickness of the core-side elastic portion 412 is about 500 to 1000 μm.

In this example, the configuration is simple, and the number of parts is small. This is advantageous for weight reduction. It is also possible to prevent liquid leakage, and provide a sealing on-off valve that can respond to a high frequency with a short stroke. Thus, heat generation, residual vibration, and the like can be reduced.

FIGS. 22A-1 to 22A-4 and FIGS. 22B-1 to 22B-4 are views illustrating a difference in the opening/closing drive operation of the on-off valve. FIGS. 22A-1 to 22A-4 illustrate the configuration according to this example, and FIGS. 22B-1 to 22B-4 illustrate the configuration according to Comparative Example 2. The sequence in the opening/closing operation is illustrated in FIGS. 22A-1 to 22A-4, and in FIGS. 22B-1 to 22B-4. Since these configurations are the same except for the opening/closing operation, reference signs are illustrated in FIG. 22A-1 and in FIG. 22B-1, but are not illustrated in other figures. In both FIGS. 22A-1 and 22B-1, D2 represents the distance between the right end portion of the elastic member and the nozzle plate. First, the configuration according to Comparative Example 2 (the configuration illustrated in FIGS. 22B-1 to 22B-4) is described.

From in FIG. 22B-1 to 22B-2, the left end portion of the elastic member 1041, which is a rubber member, comes into contact with the nozzle plate 15. As can be seen from FIG. 22B-3, the right end portion of the elastic member 1041 has a gap from the nozzle plate 15. To bring the right end portion into contact with the nozzle plate 15, it is necessary to adjust the amount of opening and closing of the on-off valve to the right end portion.

Therefore, it is necessary to make the distance D2 longer. After that, as illustrated in of FIG. 22B-4, when the elastic member 1041 and the nozzle plate 15 are separated from each other, the elastic member 1041 no longer conforms to the inclination of the nozzle plate 15. Therefore, the distances from the left end portion and the right end portion of the elastic member 1041 to the nozzle plate 15 are different. In the configuration according to Comparative Example 2, it is necessary to make the rubber thickness t greater.

However, the rubber member cannot conform to (cannot follow) the shape of the nozzle plate 15 inclined by the on-off valve formed with a metal cored bar compatible with the filler. Therefore, the gap amounts at both end portions of the tip of the elastic member 1041 are different, and it is necessary to open and close the on-off valve in accordance with the larger gap amount. Because of this, it is necessary to drive the on-off valve with a larger opening/closing amount.

On the other hand, this example is as illustrated in FIGS. 22A-1 to 22A-4. From of FIG. 22A-1 to 22A-2, the left end portion of the discharge-side elastic portion 411 comes into contact with the nozzle plate 15. As the core-side elastic portion 412 (a fluororesin in this case) on the core side (back side) of the recess 312 is provided, the discharge-side elastic portion 411 conforms to (can follow) the shape of the inclined nozzle plate 15.

Accordingly, as illustrated in of FIG. 22A-3, the right end portion of the discharge-side elastic portion 411 also comes into contact with the nozzle plate 15. After that, as can be seen from FIG. 22A-4, when the discharge-side elastic portion 411 and the nozzle plate 15 are separated from each other, the tip of the discharge-side elastic portion 411 is inclined with respect to the nozzle plate 15. That is, the gap amounts between the nozzle plate 15 and both end portions of the discharge-side elastic portion 411 become substantially the same.

Therefore, the distance D2 related to opening and closing the on-off valve is not necessarily as long as the corresponding distance in the configuration according to Comparative Example 2. In such a manner, the discharge-side elastic portion 411 (a fluoro-rubber sheet) can be made as thin as possible, and the surface of the on-off valve can be maintained with a gap parallel to the nozzle plate 15 even when the on-off valve is opened and closed.

Other Examples Related to the Feature 2

Examples related to the feature 2 of the present embodiment include Example 7, in addition to Example 6 described above.

This example is described below.

Example 7

FIG. 23 is a view illustrating Example 7 of the present embodiment. Example 7 is also a configuration to be adopted in a case where a filler-containing ink is used, like Example 6. This example differs from the configuration according to Example 6 primarily in that a holding plate 310g is provided on the core 310. The other components in this example are similar to those in Example 6.

First, in the elastic member 40 of this example, a discharge-side elastic portion 411s (an example of the first elastic portion) formed with a rubber member is disposed on the contact face side with the nozzle plate 15, and the core-side elastic portion 412 formed with a resin member is disposed in the recess 312 on the side of the core 310. Here, the discharge-side elastic portion 411s is the hatched portion in FIG. 23, and is formed in a sheet-like shape.

In this example, the elastic member 40 includes a plurality of elastic bodies. However, in a case where a chemically stable fluororesin or fluoro-rubber is used for each elastic body of the plurality of elastic bodies, it might be difficult to bond or join elastic bodies at an elastic body interface. Therefore, the holding plate 310g is provided on the core 310. The holding plate 310g is used to secure the elastic member 40 to the core 310, and accordingly, assembling can be performed while a compression preload is applied. Thus, breakage can be prevented even in a case where the adhesive force at the elastic body interface is weak. For the material of the holding plate 310g, a material such as metal or resin can be used. As for the method for securing the holding plate 310g to the core 310, it is possible to use a method suitable for the material of the holding plate 310g, such as adhesion, fastening with a screw, caulking, pressure bonding, or heat welding. For example, in a case where the material of the holding plate 310g is a heat-shrinkable fluororesin, the holding plate 310g is disposed so as to cover the periphery of the core 310, and is then heated. In this manner, the holding plate 310g is pressure-bonded to the core 310 by thermal contraction of the holding plate 310g. As a result, the holding plate 310g is secured to the core 310, without use of an adhesive or a screw.

Here, this example has advantages as described below. For example, in the configuration according to Example 6, it is necessary to mold or machine a component having a shape in which a V-shaped cut is formed in the end face of the tip of the discharge-side elastic portion 411 on the side of the nozzle 14. Therefore, to form the elastic member 40, adhesion or the like is eventually performed between the discharge-side elastic portion 411 and the core-side elastic portion 412. Meanwhile, it is normally difficult to bond a fluorine-based rubber member and a resin member, and some special bonding means might be used depending on the types of the members.

In this example (Example 7), on the other hand, the discharge-side elastic portion 411s can be manufactured from a general-purpose sheet material. Further, the discharge-side elastic portion 411s is formed in a sheet-like shape and is held and secured by the holding plate 310g. Therefore, adhesion or the like between the discharge-side elastic portion 411s and the core-side elastic portion 412 is unnecessary. When the elastic layer of the core-side elastic portion 412 deteriorates, the elastic layer is simply replaced with a new one, so that the core-side elastic portion 412 can be prepared for use.

Relationship Between the Position (Displacement) of the On-Off Valve and the Ink Discharge Amount

FIGS. 24A to 24F are a graph and views illustrating the relationship between the position (displacement) of the on-off valve and the ink discharge amount. First, the operator of the driver (the piezoelectric element) of the on-off valve moves the driver of the on-off valve (brings the driver into contact with the nozzle plate) gradually from a state in which the on-off valve (the elastic member) discharges ink in a non-contact manner, and searches for the displacement position at which the ink flow rate reaches the zero point. With the initial sealing position being the zero point on the H axis, the driver of the on-off valve is further moved forward within the elastic range of the on-off valve (the elastic member). As for a temperature change, the driver of the on-off valve is moved to a position at which ink leakage does not occur even when a piezoelectric stroke varies, and is secured to the head housing with a setscrew. To positively activate the shape conformation as in this example, the driver of the on-off valve is moved forward from the zero point on the H axis to a point beyond the elastic limit, and the flow-rate zero point is newly searched for after the fluororesin portion is plastically deformed once. In this manner, the function of this example can be efficiently achieved.

The working method is now described more specifically. In FIG. 24E, (a) to (d) indicate the respective discharge amounts in cases where the elastic member 40 is disposed at the respective positions illustrated in FIGS. 24A to 24D. Further, as illustrated in FIG. 24F, the displacement H of the tip of the elastic member 40 is positive in the direction of arrow in FIG. 24E, and is negative in the direction opposite to the arrow. That is, the direction in which the distance between the elastic member 40 and the nozzle plate 15 decreases is the positive direction, and the direction in which the distance between the elastic member 40 and the nozzle plate 15 increases is the negative direction. Here, in the state illustrated in FIG. 24A, the tip portion of the elastic member 40 is at the position farthest from the nozzle 14. At this point of time, the ink discharge amount is maximized. As illustrated in FIG. 24B, the ink discharge amount decreases as the tip portion of the elastic member 40 approaches the nozzle 14. Further, when the tip portion of the elastic member 40 approaches the nozzle 14, and the elastic member 40 comes into contact with the nozzle plate 15 as illustrated in FIG. 24C, the ink discharge amount becomes almost zero. In this state, however, the nozzle 14 is not completely sealed. To completely seal the nozzle 14, it is necessary to press the tip portion of the elastic member 40 against the nozzle plate 15, and compress the elastic member 40, as illustrated in FIG. 24D. However, when the elastic member 40 retreats into the recess 312 as described above after the tip portion of the elastic member 40 is pressed against the nozzle plate 15, a sufficient amount of compression of the elastic member 40 is not ensured, and therefore, the nozzle 14 is not sealed. In view of this, it is necessary to shift the reference position (the initial position) of the on-off valve in the forward direction by the distance by which the elastic member 40 is to retreat, so as to ensure a sufficient amount of compression of the elastic member 40.

On the other hand, when the reference position of the on-off valve is shifted in the forward direction, a change is caused in the position of the on-off valve in a state where the nozzle 14 is open, because the amount of expansion and contraction of the piezoelectric element is constant (about 20 to 30 μm, for example). In a state where the nozzle 14 is open, to obtain a predetermined ink discharge amount, it is necessary to ensure a sufficiently wide gap (5 μm or wider, for example) between the elastic member 40 and the nozzle 14. Therefore, in the position adjustment for the on-off valve, it is necessary to perform control to ensure a sufficiently wide gap between the elastic member 40 and the nozzle 14 for a time of opening the nozzle 14, and ensure a sufficient amount of compression of the elastic member 40 for a time of closing the nozzle 14. It is difficult to achieve both a correct position of the on-off valve for a time of opening the nozzle 14 and a correct position of the on-off valve for a time of closing the nozzle 14, and great amounts of effort and time are used for the adjustment work. Therefore, the above examples of the present embodiment aim to eliminate the problems due to degradation of the elastic function of the elastic member and changes in the position of the end portion of the elastic body, to facilitate the position adjustment work for the on-off valve.

Evaluation of the End Face of an On-Off Valve

FIGS. 25A and 25B are a view and a graph illustrating functional evaluation prior to shipment. The device illustrated in FIG. 25A is an evaluation machine that checks whether retraction of the end face of an elastic member is observed, as the functional evaluation prior to shipment. Specifically, a needle-like on-off valve is pushed into (forward) and pulled back (backward) from a force sensor by 1 μm at a time, the needle displacement to load during that process is measured, and the relationship is plotted on a chart for evaluation. When retraction of the end face of the elastic member occurs, different paths are followed in the outward path (forward) and the return path (backward) of compression, and the difference in the horizontal axis position at the zero load point is the plastic strain amount. Further, as caulking is performed, the hysteresis that is the difference between the outward path and the return path increases, and the elastic modulus (a primary coefficient) decreases. The elastic modulus of a resin is about 1 N/μm. The waveform in FIG. 25B is similar to the waveform by a nanoindentation evaluation method (ISO 14577), and it has been confirmed that plastic deformation similar to deformation caused by insertion of an indenter has occurred. Here, the curve in the graph in FIG. 25B has an irregular shape as if to draw an ellipse. The reason for this is that the elastic characteristics of a rubber member have temporal responsiveness, and the generated force is not fixed to one force when compressive displacement is caused.

Configuration of an Embodiment of a Liquid Discharge Apparatus

Next, the configuration of an embodiment of a liquid discharge apparatus is described with reference to the drawings.

FIGS. 26A and 26B are schematic configuration diagrams of an entire liquid discharge apparatus 100 (an example of a liquid discharge apparatus). FIG. 26A is a side view of the liquid discharge apparatus, and FIG. 26B is a plan view of the liquid discharge apparatus. The liquid discharge apparatus 100 is disposed facing a liquid application target 500, which is an example of the object. The liquid discharge apparatus 100 includes an X-axis rail 101, a Y-axis rail 102, and a Z-axis rail 103. The Y-axis rail 102 intersects the X-axis rail 101, and the Z-axis rail 103 intersects the X-axis rail 101 and the Y-axis rail 102. In particular, in the present embodiment, the X-axis rail 101, the Y-axis rail 102, and the Z-axis rail 103 extend in directions orthogonal to one another.

The Y-axis rail 102 holds the X-axis rail 101 so that the X-axis rail 101 is movable in the Y-axis direction. The X-axis rail 101 holds the Z-axis rail 103 so that the Z-axis rail 103 is movable in the X-axis direction. The Z-axis rail 103 holds a carriage 1 (an example of a support unit) so that the carriage 1 is movable in the Z-axis direction.

The liquid discharge apparatus 100 includes a first Z-direction driver 92 and an X-direction driver 72. The first Z-direction driver 92 moves the carriage 1 in the Z-axis direction along the Z-axis rail 103. The X-direction driver 72 moves the Z-axis rail 103 in the X-axis direction along the X-axis rail 101. The liquid discharge apparatus 100 also includes a Y-direction driver 82 that moves the X-axis rail 101 in the Y-axis direction along the Y-axis rail 102. The liquid discharge apparatus 100 further includes a second Z-direction driver 93 that moves a head holder 70 in the Z-axis direction with respect to the carriage 1.

The liquid discharge head described above is fitted to the head holder 70 so that the nozzles 14 (see FIG. 2) of the liquid discharge head 10 face the liquid application target 500 The liquid discharge apparatus 100 designed as described above discharges ink, which is an example of a liquid, from the liquid discharge head fitted to the head holder 70 toward the liquid application target 500 while moving the carriage 1 in the X-axis. Y-axis, and Z-axis directions, and performs drawing on the liquid application target 500.

Next, the configuration of an inkjet printer 201 that is another embodiment of a liquid discharge apparatus is described with reference to the drawings.

As illustrated in FIG. 27, the inkjet printer 201 according to the present embodiment includes a print head 202, an X-Y table 203, a camera 204, a controller 209, and a driver 211.

The print head 202 is an inkjet liquid discharge head that discharges ink (liquid) toward the coating target surface of a coating target M. The term “ink” used herein also includes “paint”. The print head 202 includes a plurality of valve-type nozzles, and ink is discharged from each valve-type nozzle in a direction perpendicular to the discharge face of the print head 202. That is, the ink discharge face of the print head 202 is parallel to the X-Y plane formed by movement of the X-Y table 203, and the ink dots discharged from each valve-type nozzle are discharged in a direction perpendicular to the X-Y plane. Further, the discharging directions of the ink to be discharged from the respective valve-type nozzles are parallel to one another. Each valve-type nozzle is joined to an ink tank for a predetermined color. Further, as the ink tanks are pressurized by a pressurizing device, if the distance between each valve-type nozzle and the print target surface of the coating target M is about 20 cm, the ink dots can be discharged from each valve-type nozzle onto the print target surface without any problem.

The X-Y table 203 has mechanisms that move the print head 202 and the camera 204 in the X direction and the Y direction, which are orthogonal to each other. Specifically, the X-Y table 203 has an X-axis moving mechanism 205 that moves a slider holding the print head 202 and the camera 204 described later in the X direction, and a Y-axis moving mechanism 206 that moves the X-axis moving mechanism 205 in the Y direction while holding the X-axis moving mechanism with two arms. The Y-axis moving mechanism 206 has a shaft 207, and a robot arm 208 holds and drives the shaft 207, so that the print head 202 can be placed at a predetermined position where printing is to be performed on the coating target M. For example, in a case where the coating target M is an automobile, the robot arm 208 can place the print head 202 on an upper portion of the automobile as illustrated in FIG. 28, or at a side position of the automobile as illustrated in FIG. 29. The operation of the robot arm 208 is controlled on the basis of a program stored beforehand in the controller 209.

The camera 204 is an imaging unit such as a digital camera that images the print target surface of the coating target M. The camera 204 performs imaging of a predetermined region on the print target surface of the coating target M at constant short intervals while being moved in the X direction and the Y direction by the X-axis moving mechanism 205 and the Y-axis moving mechanism 206. The specifications such as the lens and the resolution of the camera 204 are selected appropriately so that a plurality of subdivided images of the predetermined region on the print target surface can be obtained. The imaging of the plurality of subdivided images of the print target surface by the camera 204 is continuously and automatically conducted by the controller 209 described later.

The controller 209 operates the X-Y table 203 on the basis of image editing software S for editing images taken by the camera 204 and a preset control program, to control a print operation (an ink discharge operation) of the print head 202. The controller 209 is formed with a microcomputer, and includes: a storage device that records and stores various programs, data of taken images, data of images to be printed, and the like; a central processing unit that performs various processes according to the programs; input devices such as a keyboard and a mouse; and, if necessary, a DVD player. The controller 209 further includes a monitor 210. The monitor 210 displays information to be input to the controller 209, a result of processing performed by the controller 209, and the like.

The controller 209 uses image processing software to perform image processing on a plurality of pieces of subdivided image data taken by the camera 204, and generates a combined print surface that is a flat surface on which a print target surface that is not the flat surface of the coating target M is projected. The controller 209 also superimposes, on the combined print surface, a drawing target image to be printed so as to be continuous with the image already printed on the print target surface, and performs editing so that the drawing target image becomes continuous with the edge portions of the printed image. Thus, a drawing target edited image is generated. For example, as for a print image 252b that is a drawing target image illustrated in FIG. 30C, the print image 252b is edited to match the combined print surface so that a non-print region 253 is not formed between the print image 252b and an adjacent print image 252a. Thus, a drawing target edited image is generated. Ink is then discharged from the print head 202 onto the print target surface on the basis of the generated drawing target edited image. Thus, a new image is printed without any gap formed between the new image and an already printed image. The operation of taking the plurality of subdivided images with the camera 204, and the operation of printing by discharge of ink from each nozzle of the print head 202 are conducted by the driver 211 under the operation control of the controller 209.

FIG. 30A illustrates the discharging direction of ink that is discharged from each inkjet nozzle mounted on a nozzle head 250 in a case where a two-dimensional quadrangle is formed by an inkjet nozzle on the spherical surface of a liquid application target 251 that is a spherical object. In FIG. 30B, the ink to be discharged from each inkjet nozzle mounted on the nozzle head 250 is discharged in a direction perpendicular to the nozzle head 250. Therefore, the print image 252a printed on the surface of the liquid application target 251 has a quadrangular shape in which the periphery is distorted, as illustrated in FIG.