Patent Description:
Conventionally, an apparatus described in Patent Literature (PTL) <NUM> has been proposed as an apparatus for performing printing on a fabric to be printed by using an inkjet mechanism. The printing apparatus of PTL <NUM> includes a plurality of nozzles housed in a printhead and eject ink of multiple colors, upstream and downstream driving rollers that are rotationally driven, and an endless conveyance belt that is bridged between these two driving rollers, and supports the fabric on its upper surface to convey the fabric. The fabric is conveyed intermittently at the printing pitch of the printhead. Each time the fabric is intermittently conveyed, the printhead is moved along the direction (the width direction of the fabric) perpendicular to the fabric conveyance direction to eject ink from the nozzles, thus performing printing of a pattern on the surface of the fabric. In inkjet printing, inks of cyan (blue), magenta (red), yellow (yellow), black (black), and the like are overprinted with various densities, which makes it possible to express fine and complicated patterns.

In recent years, inkjet printing has also been performed on cylindrical fabrics used for producing socks, tights, swimwear, and the like. For example, a cylindrical fabric C to be printed is placed on a shaft <NUM>, and a printhead <NUM> is moved by a moving means in the direction of an arrow A along the length direction of the shaft <NUM> to eject ink. When printing in the length direction is completed, the printhead <NUM> is returned to the original position, and at the same time, the shaft <NUM> is rotated in the direction of arrow B by rotating means. The rotation angle α is an angle corresponding to the distance R1 in the circumferential direction in which the surface of the fabric can be printed by the printhead <NUM>. At each such intermittent rotation, the printhead <NUM> is moved in the length direction of the shaft <NUM> to print a pattern on the surface of the fabric. PTL <NUM>, PTL <NUM> and PTL <NUM> disclose further printing apparatuses and methods for printing patterns on the surface of cylindrical fabrics by an inkjet mechanism.

In the printing apparatus described in Patent Literature <NUM>, as shown in <FIG>, the surface of the fabric C placed on the shaft <NUM> is curved, and the distance R2 between the middle of the width of the printhead <NUM> and the fabric C is different from the distance R3 between both ends of the printhead <NUM> and the fabric C. For this reason, ink ejected from the printhead <NUM> is not likely to reach the surface of the fabric C evenly. Accordingly, when inkjet printing is intermittently performed by using the printhead <NUM>, print unevenness is likely to occur between the middle and the both ends in the circumferential direction of the printed part.

The present invention was made in view of the above problem, and an object of the present invention is to provide a fabric printing method and a fabric printing apparatus having less print unevenness.

The fabric printing method according to the present invention is for performing color printing on the surface of a cylindrical fabric by using an inkjet mechanism, wherein a shaft is inserted inside the fabric to be printed through an opening at one end to integrally support the fabric, wherein either the shaft or the inkjet mechanism comprising a plurality of printheads aligned in the length direction of the shaft, or both, are moved in the length direction of the shaft at a moving speed while rotating the shaft to thereby perform helical printing on a surface of the fabric to be printed placed on the shaft, wherein either of the shaft or inkjet mechanism, or both move a distance corresponding to a printing pitch of each printhead along the length direction of the shaft while the shaft rotates once, wherein a distance between parts printed by adjacent printheads is larger than the distance corresponding to the printing pitch of each printhead, or the distance corresponding to the printing pitch of each printhead is larger than the distance between the parts printed by the adjacent printheads.

According to the above method, the printheads relatively move along the curved surface in the circumferential direction in a successive manner relative to the fabric. Accordingly, ink from the printheads reaches the surface of the fabric almost evenly even when the fabric has a curved surface, and thus, print unevenness is less likely to occur.

The fabric printing apparatus of the present invention is used for performing color printing on the surface of a cylindrical fabric with an inkjet mechanism. The fabric printing apparatus includes a shaft that is inserted inside the fabric to be printed through an opening at one end to integrally support the fabric, the inkjet mechanism having a plurality of printheads aligned in the length direction of the shaft, a rotation mechanism for axially rotating the shaft, a moving mechanism for moving either the shaft or the inkjet mechanism in the length direction of the shaft, or both, and a control unit for controlling the moving speed of the moving mechanism while rotating the shaft with the rotation mechanism to thereby perform helical printing on a surface of the fabric to be printed placed on the shaft; wherein the control unit is adapted to control the operation of the moving mechanism so that either of the shaft or the inkjet mechanism, or both move a distance corresponding to the printing pitch of each printhead along the length direction of the shaft while the shaft rotates once, such that a distance between parts printed by adjacent printheads is larger than the distance corresponding to a printing pitch of each printhead, or the distance corresponding to the printing pitch of each printhead is larger than the distance between the parts printed by the adjacent printheads.

According to the above structure, a pattern is helically printed on the surface of the fabric by each of the printheads. Since the printheads are moved along the surface of the fabric in the circumferential direction, ink from the printheads reaches the surface of the fabric almost evenly without being affected by the fact that the fabric has a curved surface, and print unevenness is less likely to occur.

The present invention provides a fabric printing method and a fabric printing apparatus ensuring less print unevenness.

An embodiment of the present invention is explained below with reference to the drawings.

<FIG> is a front view showing the entire schematic structure of a fabric printing apparatus <NUM> according to one embodiment of the present invention. The fabric printing apparatus <NUM> is for performing color printing on the surface of a cylindrical fabric C by using an inkjet mechanism, and includes a shaft <NUM> that is inserted inside the fabric C to be printed through the opening at one end to integrally support the fabric C; a head unit <NUM> as an inkjet mechanism having a plurality of printheads 31a to 31f; a rotation mechanism <NUM> for axially rotating the shaft <NUM>; a moving mechanism <NUM> for moving the shaft <NUM> in the length direction X (in the left-right direction in <FIG>) of the shaft <NUM>; and a control unit <NUM> for controlling the head unit <NUM>, the rotation mechanism <NUM>, and the moving mechanism <NUM>. The cylindrical fabric C is preferably seamless. The fabric C is used to produce, for example, socks, tights, swimwear, and clothing sleeves, without particular limitation. The material of the fabric C is not limited, and may be made of natural fibers such as cotton and silk, and artificial fibers such as polyester, rayon, and acetate.

As shown in <FIG>, a base frame <NUM> of the fabric printing apparatus <NUM> is provided with two support columns <NUM>, and a bridge beam <NUM> is bridged between the support columns <NUM>. On the bridge beam <NUM>, the moving mechanism <NUM>, the shaft <NUM> moved by the moving mechanism <NUM>, and the rotation mechanism <NUM> are mounted.

The moving mechanism <NUM> includes a linear motor <NUM> and a slide box <NUM> integrally attached to a mover (not shown) of the linear motor <NUM>. The slide box <NUM> can move along the length direction X of the linear motor <NUM> (the left-right direction in <FIG>). The moving mechanism <NUM> is not limited to the linear motor <NUM>, and may be formed of any structure as long as it can move the shaft <NUM> and the rotation mechanism <NUM>. For example, the moving mechanism <NUM> can be formed of a ball screw and a nut member, or an endless belt and a drive motor.

The rotation mechanism <NUM> is mounted above the slide box <NUM>. The rotation mechanism <NUM> rotatably supports the shaft <NUM> to which the fabric C is attached, and includes a shaft holder <NUM> that is mounted above the slide box <NUM> and supports the shaft <NUM>, and a motor <NUM> and a decelerator <NUM> that are connected to the shaft holder <NUM> and rotate the shaft <NUM> at a predetermined rotation speed. The shaft <NUM> is supported by the shaft holder <NUM> so that the length direction of the shaft <NUM> is along the moving direction of the slide box <NUM> (the left-right direction in <FIG>, i.e., the length direction X). The shaft <NUM> can be moved between a standby position P1 and an operation starting position P2 shown in <FIG> by the moving mechanism <NUM>.

The shaft <NUM> is covered with a cylindrical support pipe <NUM> shown in <FIG>. The shaft <NUM> is inserted into the support pipe <NUM> through the opening 70a of the support pipe <NUM>. The support pipe <NUM> is inserted inside the fabric C through the opening Ca at one end of the fabric C to integrally support the fabric C. The fabric C may be fixed to the outer surface of the support pipe <NUM> with a fixing means such as a belt or an adhesive that can be easily peeled off. If the fabric C is made of an elastic material, setting the diameter of the support pipe <NUM> to such a size that the fabric C can be fixed to the support pipe <NUM> by the shrinkage force of the fabric C when the fabric C is placed on the support pipe will eliminate the need for the means for fixing the fabric C to the support pipe <NUM> mentioned above.

As shown in <FIG> and <FIG>, the shaft <NUM> is an airshaft that can introduce or remove air. The shaft <NUM> includes a cylindrical shaft body <NUM> to which a support pipe <NUM> is attached, a tube <NUM> that is provided inside the shaft body <NUM> and that expands toward the shaft body <NUM> or shrinks inwardly in response to air introduction or removal, and a plurality of (four in this embodiment) leaves <NUM> that are supported on the shaft body <NUM> to be displaceable in the radial direction.

In the shaft body <NUM>, grooves 21a, the number of which is the same as the number of leaves <NUM>, are formed at regular intervals in the circumferential direction along the length direction X of the shaft body <NUM>.

The tube <NUM> is, for example, a rubber elastic tube that can expand or shrink by elastic deformation, and is disposed in the hollow portion of the shaft body <NUM> through the entire length of the shaft body <NUM>.

Each leaf <NUM> includes a lug 23a that is inserted in a groove 21a of the shaft body <NUM> in a movable manner in the radial direction; a working piece 23c that is provided on the lug 23a at an end inside the shaft body <NUM>, and that has an arc-shaped cross section projecting into the shaft body <NUM> in the retained state; and a plate 23b that is provided on the lug 23a at an end outside the shaft body <NUM>, and that has an arc-shaped cross section along the outer surface of the shaft body <NUM>. The leaf <NUM> also includes a return spring (not shown) for urging the leaf <NUM> inward.

As shown in <FIG>, when the tube <NUM> expands, the tube <NUM> pushes the working pieces 23c of the leaves <NUM> outward so that the plates 23b move outward against the urging force of return springs, and are closely attached to the inner wall of the support pipe <NUM>. The support pipe <NUM> is thereby firmly fixed to the shaft <NUM>.

As shown in <FIG>, when the tube <NUM> shrinks, the working pieces 23c of the leaves <NUM> move inward due to the urging force of the return springs, and the close contact between the plates 23b and the inner wall of the support pipe <NUM> is released. Thus, the support pipe <NUM> can be detached from the shaft <NUM>.

As shown in <FIG>, a cylindrical connecting member <NUM> is connected to the proximal end of the shaft body <NUM> of the shaft <NUM>. The connecting member <NUM> is rotatably supported in the shaft holder <NUM> via a bearing (not shown) provided in the shaft holder <NUM>. A mounting member <NUM> connected to the output shaft of a decelerator <NUM> is provided on the proximal end of the connecting member <NUM>. The connecting member <NUM> and the mounting member <NUM> are hollow, and the inside of these members communicates with the tube <NUM>. Air is introduced into the tube <NUM> through the mounting member <NUM> and the connecting member <NUM> by an air supply source such as a compressor (not shown).

The decelerator <NUM> is connected to a motor shaft of a stepping motor <NUM> via a gear for changing the driving force transmission direction, and rotates the shaft <NUM> via the mounting member <NUM> and the connecting member <NUM>.

The head unit <NUM> is disposed above the shaft <NUM>, and a plurality of (six in this embodiment) printheads <NUM> (31a to 31f) for ink are disposed at predetermined intervals in the length direction X of the shaft <NUM>. Each of the printheads 31a to 31f has nozzles (not shown) that discharges ink to the fabric C. Each of the printheads 31a to 31f is filled with ink of colors such as black, cyan, magenta, yellow, light cyan, and light magenta. The number of printheads <NUM> for ink is not limited to six, and any multiple numbers can be chosen as long as color printing can be performed. Additionally, the colors of ink supplied to the printheads <NUM> for ink are not limited to the present embodiment.

Although not shown, each of the printheads 31a to 31f is connected to an ink tank via a deaeration module. After gasses contained in ink introduced from the ink tank are removed in the deaeration module, the ink is supplied to each of the printheads 31a to 31f.

By discharging ink from each of the printheads 31a to 31f while successively rotating the shaft <NUM>, printing in the circumferential direction relative to the surface of the fabric C is performed at the width L1 of ink discharged from each of the printheads 31a to 31f, as shown in <FIG>. Since the printing in the circumferential direction is performed while moving the shaft <NUM> in the length direction X, helical printing is performed. The distance that the shaft <NUM> moves in the length direction X while rotating once is referred to as the "printing pitch. " The rotational speed and the moving speed of the shaft <NUM> are set in a manner such that the printing pitch corresponds to the ink discharge width L1, specifically, in such a manner that the fabric C moves only the distance L1 at each rotation of the shaft <NUM>. This prevents gaps or overlapping of patterns helically printed by the printheads 31a to 31f from occurring.

The head unit <NUM> is supported by a vertical movement mechanism <NUM> to enable vertical movement. The position of the head unit <NUM> in the vertical direction is adjusted according to the thickness of the fabric C. The vertical movement mechanism <NUM> may have any structure as long as it can move vertically while keeping the head unit <NUM> horizontal. The vertical movement mechanism <NUM> is composed of, for example, a ball screw, a nut member, a drive motor, or the like.

The control unit <NUM> is composed of, for example, a computer having a CPU, memory, and the like, and controls operations of the stepping motor <NUM> of the rotation mechanism <NUM>, the air supply source, the linear motor <NUM> of the moving mechanism <NUM>, the head unit <NUM>, the vertical movement mechanism <NUM>, and the like. In this embodiment, the control unit <NUM> integrally includes a control panel <NUM> shown in <FIG>. The control unit <NUM> controls the stepping motor <NUM> to successively rotate the shaft <NUM>, and controls the operation of the linear motor <NUM> of the moving mechanism <NUM> so that the shaft <NUM> successively moves a distance corresponding to the printing pitch L1 of the printheads 31a to 31f along the length direction X of the shaft <NUM> each time the shaft <NUM> rotates once. The rotational speed of the shaft <NUM> is set to an appropriate speed according to the outer diameter of the support pipe <NUM>, the printing speed of the printheads <NUM>, or the like.

In the fabric printing method of the present embodiment using the fabric printing apparatus <NUM>, the outer surface of the fabric C placed on the shaft <NUM> is helically printed by printheads <NUM> due to the shaft <NUM> being moved in the length direction X while the shaft <NUM> rotates. <FIG> schematically shows a specific example of the fabric printing method.

<FIG> shows the surface of the fabric C when the fabric C moves in the length direction X of the shaft <NUM> relative to the head unit <NUM>. In <FIG>, the cylindrical fabric C is spread flat at the position closest to the head unit <NUM>, that is, at the upper-end position of the circular cross-section of the fabric C. Specifically, the circumferential direction of the fabric C is described as the vertical direction in <FIG>, and the upper end and the lower end of the fabric C in each of <FIG> form the upper-end position of the cylindrical fabric. In <FIG>, for convenience of explanation, the head unit <NUM> includes four printheads 31a to 31d; the printing pitch L1, which is the width (the length along the length direction X of the shaft <NUM>) in which ink is discharged to the fabric C from the printheads 31a to 31d, is described as the length of the printheads 31a to 31d along the length direction X of the shaft <NUM>; and a distance L2 between the parts printed by the adjacent printheads <NUM> (31a to 31d) is described as the distance between the adjacent printheads <NUM> (31a to 31d). In this embodiment, the distance L2 between the parts printed by the adjacent printheads <NUM> (31a to 31d) is set to be larger than the printing pitch L1, but the distance L2 may be set to be the same as the printing pitch L1, or the printing pitch L1 may be set to be larger than the distance L2.

<FIG> shows the position of the fabric C relative to the head unit <NUM> immediately before the start of printing. The position S at which the printing of the fabric C is started is at position Pa, i.e., the left end of the printhead 31a.

<FIG> shows a case where the position S of the fabric C is at position Pb, i.e., the right end of the printhead 31a. <FIG> shows a state in which the position S of the fabric C moves from the state of <FIG> to the position Pb by the distance corresponding to the printing pitch L1 while the fabric C is rotated once. Helical printing is started from the end in the length direction of the fabric C by the printhead 31a. At the beginning of printing by the printhead 31a, since the entire length of the printhead 31a in the length direction X is not above the fabric C, the printhead 31a discharges ink only from a portion positioned over the fabric C to perform printing, and the printed part Aa (Aa-<NUM>) has a triangular shape when the fabric C is spread out.

<FIG> shows a case where the position S of the fabric C is at position Pc, i.e., the left end of the printhead 31b. <FIG> shows a state in which the position S of the fabric C moves from the state of <FIG> to the position Pc by the distance corresponding to the distance L2 between the parts printed by the adjacent printheads <NUM> while the fabric C is rotated. Since the distance L2 is longer than the printing pitch L1, the fabric C is rotated more than one time from the state of <FIG>. The parts Aa (Aa-<NUM>) printed by the printhead 31a are the second and the third helically printed parts continuing to the previously printed part Aa (Aa-<NUM>), and there are no gaps or overlapping between the previously printed part Aa (Aa-<NUM>) and the second helically printed part, or between the second helically printed part and the third helically printed part.

<FIG> shows a case where the position S of the fabric C is at position Pd, i.e., the right end of the printhead 31b. <FIG> shows a state in which the position S of the fabric C moves from the state of <FIG> to the position Pd by the distance corresponding to the printing pitch L1 while the fabric C is rotated once. Helical printing is started from the end in the length direction of the fabric C by the printhead 31b. At the beginning of printing on the fabric C by the printhead 31b, the printed part Ab has a triangular shape when the fabric C is spread out. Additional printing is further performed by the printhead 31a, and the resulting printed part Aa is a helically printed part continuing to the previously printed part Aa.

<FIG> shows a case where the position S of the fabric C is at position Pe, i.e., the right end of the printhead 31c. <FIG> shows a state in which the position S of the fabric C moves from the state of <FIG> to the position Pe by the distance corresponding to the distance L2 between the parts printed by the adjacent printheads <NUM> and the printing pitch L1 while the fabric C is rotated. Helical printing is started from the end in the length direction of the fabric C by the printhead 31c. At the beginning of printing on the fabric C by the printhead 31c, since the entire length of the printhead 31c in the length direction X is not above the fabric C, the printed part Ac has a triangular shape when the fabric C is spread out. Additional printing is further performed by the printheads 31a and 31b, and the resulting printed parts Aa and Ab are helically printed parts respectively continuing to the previously printed parts Aa and Ab.

<FIG> shows a case where the position S of the fabric C is at position Pf, i.e., the right end of the printhead 31d. <FIG> shows a state in which the position S of the fabric C moves from the state of <FIG> to the position Pf by the distance corresponding to the distance L2 between the parts printed by the adjacent printheads <NUM> and the printing pitch L1 while the fabric C is rotated. Helical printing is started from the end in the length direction of the fabric C by the printhead 31d. At the beginning of printing on the fabric C by the printhead 31d, since the entire length of the printhead 31d in the length direction X is not above the fabric C, the printed part Ad has a triangular shape when the fabric C is spread out. Printing by the printheads 31a, 31b, and 31c is continued, and the resulting printed parts Aa, Ab, and Ac are helically printed parts respectively continuing to the previously printed parts Aa, Ab, and Ac.

Thereafter, by continuously moving the shaft <NUM>, the entire fabric C in the length direction X is printed by the printheads 31a to 31d.

Next, the operation of the fabric printing apparatus <NUM> is explained.

Before the start of operation of the fabric printing apparatus <NUM>, the shaft <NUM> waits at the standby position P1 shown in <FIG>. When an operator inputs an instruction to start operation of the fabric printing apparatus <NUM> via the control panel <NUM>, the control unit <NUM> moves the shaft <NUM> to the operation starting position P2. The operator attaches the support pipe <NUM> covered with the fabric C to the shaft <NUM> positioned at the operation starting position P2. More specifically, when the operator places the support pipe <NUM> over the shaft <NUM>, and inputs an instruction to start printing via the control panel <NUM>, the control unit <NUM> controls the air supply source to supply air into the tube <NUM> of the airshaft <NUM>. This moves the leaves <NUM> of the airshaft <NUM> outward in the radial direction, and the plates 23b of the leaves <NUM> are closely attached to the inner wall of the support pipe <NUM>. Then, the control unit <NUM> operates the moving mechanism <NUM> and the rotation mechanism <NUM> to move the shaft <NUM> from the operation starting position P2 to the standby position P1 along the length direction X while rotating the shaft <NUM>, and at the same time, the control unit <NUM> operates the head unit <NUM> to perform printing as shown in <FIG>. The control unit <NUM> stores, in advance, information on the length and the rotational speed of the shaft <NUM>, the patterns of parts to be printed by the printheads 31a to 31f, etc. Based on this information, the control unit <NUM> controls the moving mechanism <NUM>, the rotation mechanism <NUM>, and the head unit <NUM>.

When printing on the fabric C is completed, the control unit <NUM> returns the shaft <NUM> to the operation starting position P2, and controls the air supply source to remove air from the tube <NUM> of the airshaft <NUM>. This moves the leaves <NUM> of the airshaft <NUM> inward in the radial direction to release the close contact between the leaves <NUM> and the inner wall of the support pipe <NUM>, allowing the support pipe <NUM> to be detached from the shaft.

When the operator removes the support pipe <NUM> and inputs an instruction to end printing via the control panel <NUM>, the control unit <NUM> returns the shaft <NUM> to the standby position P1 and ends the operation. If printing is successively performed on another fabric C, after the operator removes the support pipe <NUM>, the operator inserts the support pipe <NUM>, which has been covered with a fabric C to be printed next, into the shaft <NUM>, and inputs an instruction to start printing.

According to the above format, patterns are helically printed on the surface of the fabric C by the printheads 31a to 31f. Since the printheads 31a to 31f relatively move in a successive manner in the circumferential direction relative to the fabric C, print unevenness is less likely to occur.

Further, since the airshaft is used as the shaft <NUM> that supports the support pipe <NUM> covered with the fabric C, a support pipe <NUM> having a slightly different inner diameter can also be fixed to the shaft <NUM>.

One embodiment of the present invention is explained above; however, the present invention is not limited to this embodiment, and may be carried out with various modifications within a scope in which the gist of the present invention is maintained.

For example, the moving mechanism <NUM> moves the shaft <NUM> in the length direction X of the shaft <NUM> in this embodiment; however, it is also possible to provide the moving mechanism <NUM> in the head unit <NUM>, and move the head unit <NUM> relative to the shaft <NUM>.

Claim 1:
A fabric printing method for performing color printing on a surface of a cylindrical fabric by using an inkjet mechanism (<NUM>),
wherein a shaft (<NUM>) is inserted inside the fabric (C) to be printed through an opening at one end to integrally support the fabric (C),
wherein either the shaft (<NUM>) or the inkjet mechanism (<NUM>) comprising a plurality of printheads (31a, 31b, 31c, 31d, 31e, 31f) aligned in the length direction (X) of the shaft (<NUM>), or both, are moved in the length direction (X) of the shaft (<NUM>) at a moving speed while rotating the shaft (<NUM>) to thereby perform helical printing on a surface of the fabric (C) to be printed placed on the shaft (<NUM>), wherein either of the shaft (<NUM>) or inkjet mechanism (<NUM>), or both move a distance (L1) corresponding to a printing pitch of each printhead (31a, 31b, 31c, 31d, 31e, 31f) along the length direction (X) of the shaft (<NUM>) while the shaft (<NUM>) rotates once,
wherein a distance (L2) between parts printed by adjacent printheads (31a, 31b, 31c, 31d, 31e, 31f) is larger than the distance (L1) corresponding to the printing pitch of each printhead (31a, 31b, 31c, 31d, 31e, 31f), or the distance (L1) corresponding to the printing pitch of each printhead (31a, 31b, 31c, 31d, 31e, 31f) is larger than the distance (L2) between the parts printed by the adjacent printheads (31a, 31b, 31c, 31d, 31e, 31f).