JP2019010751A - Inkjet printing device - Google Patents

Abstract

To provide an inkjet printing device that can reduce deterioration in printing image quality while suppressing a configuration of the device from being complicated.SOLUTION: A control part 6, when a difference is caused between count values C1 and C2 of output pulse number of encoders 33 and 32 in every prescribed pulse count period of time, controls discharge timing for inkjet heads 41K and 41C on the basis of pulse signals from the encoder 32; adjusts discharge timing for inkjet heads 41K and 41C, according to a magnitude relation between the count values C1 and C2, largeness of a difference ΔC between the count values C1 and C2 and positions in a lateral direction of the inkjet heads 41K and 41C; and controls the discharge timing for inkjet heads 41M and 41Y on the basis of pulse signals from the encoder 33 and adjusts the discharge timing for the inkjet heads 41M and 41Y, according to the magnitude relation between the count values C1 and C2, the largeness of the difference ΔC and the positions in the lateral direction of the inkjet heads 41M and 41Y.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an inkjet printing apparatus that prints an image by ejecting ink from an inkjet head.

  2. Related Art Inkjet printing apparatuses that print an image by ejecting ink from an inkjet head onto a web while conveying a long web as a print medium are known.

  In such an ink jet printing apparatus, ink ejection timing in the ink jet head is controlled based on a pulse signal output from an encoder connected to a roller that is driven to rotate by a web being conveyed.

  Here, in an inkjet printing apparatus that has a plurality of inkjet heads that eject inks of different colors and prints an image on a web using these inkjet heads, the plurality of inkjet heads are arranged in parallel in the web conveyance direction. The

  In such an ink jet printing apparatus, the distance between the ink jet head and the encoder used for controlling the ejection timing differs. As the distance between the encoder and the inkjet head increases, the accuracy of the ink landing position decreases due to the expansion and contraction of the web therebetween. For this reason, there is a possibility that the landing position shift of the ink between the plurality of inkjet heads occurs, and the print image quality is deteriorated.

  On the other hand, Patent Document 1 discloses an ink jet printing apparatus in which a part of a plurality of ink jet heads is arranged upstream of an encoder in the web conveyance direction and the remaining ink jet heads are arranged downstream of the encoder. ing.

  According to this ink jet printing apparatus, the distance between the ink jet head farthest from the encoder and the encoder is smaller than that in the configuration in which the encoder is arranged upstream of the most upstream ink jet head or downstream of the most downstream ink jet head. Shortened. As a result, the deterioration of the print image quality due to the deviation of the ink landing position as described above is reduced.

JP 2008-126516 A

  However, even in the technique of Patent Document 1, when a plurality of inkjet heads are arranged on at least one of the upstream side and the downstream side of the encoder, the distance from the encoder differs for each inkjet head. For this reason, the effect of reducing the deterioration of the print image quality due to the deviation of the ink landing position as described above is not sufficient.

  If an encoder corresponding to each ink jet head is provided in the vicinity of each ink jet head, it is possible to reduce a decrease in print image quality due to the deviation of the ink landing position as described above. However, this complicates the device configuration.

  The present invention has been made in view of the above, and an object of the present invention is to provide an ink jet printing apparatus capable of reducing deterioration in print image quality while suppressing the complexity of the apparatus configuration.

  In order to achieve the above object, an ink jet printing apparatus of the present invention has a plurality of ink jet heads arranged in parallel in the web transport direction, and ejects ink from each ink jet head onto the web to be transported to form an image. A printing unit that prints the web, a conveyance roller that is disposed downstream of the printing unit in the conveyance direction and is rotated by a conveyance motor to convey the web, and between the printing unit and the conveyance roller in the conveyance direction A downstream roller that is driven and rotated by a web being conveyed, a downstream encoder that outputs a pulse signal in accordance with a rotation angle of the downstream roller, and an upstream side of the printing unit in the conveying direction. It is arranged between the brake part for applying the braking force, the brake part in the transport direction and the printing part, and is transported. An upstream roller that rotates following the web, an upstream encoder that outputs a pulse signal according to the rotation angle of the upstream roller, and the downstream while controlling the braking force by the brake unit to be constant at a predetermined braking force. Based on the pulse signal output from the encoder, the web transport speed is controlled so as to maintain a predetermined print transport speed, and the control unit controls the printing unit to print an image on the web, The control unit compares the upstream encoder count value, which is the count value of the number of output pulses of the upstream encoder, with the downstream encoder count value, which is the count value of the number of output pulses of the downstream encoder, for each predetermined pulse count period. As a result of the comparison, there is a difference between the upstream encoder count value and the downstream encoder count value. If there is no difference, the ink ejection timing in each inkjet head is controlled based on the pulse signal output by the downstream encoder, and if there is a difference between the upstream encoder count value and the downstream encoder count value, the downstream encoder The ink ejection timing in the ink jet head near the upstream encoder is controlled based on the pulse signal output from the upstream encoder, the magnitude relationship between the upstream encoder count value and the downstream encoder count value, the upstream encoder count value, Ink discharge from the inkjet head closer to the downstream encoder than the upstream encoder is adjusted according to the magnitude of the difference from the downstream encoder count value and the position of each inkjet head. The output timing is controlled based on the pulse signal output from the downstream encoder, the magnitude relationship between the upstream encoder count value and the downstream encoder count value, and the magnitude of the difference between the upstream encoder count value and the downstream encoder count value. And adjusting according to the position of each inkjet head.

  According to the ink jet printing apparatus of the present invention, it is possible to reduce deterioration in print image quality while suppressing the complexity of the apparatus configuration.

1 is a schematic configuration diagram of an inkjet printing apparatus according to a first embodiment. It is a control block diagram of the inkjet printing apparatus shown in FIG. It is explanatory drawing of the adjustment table in 1st Embodiment. It is a flowchart for demonstrating operation | movement of the inkjet printing apparatus in 1st Embodiment. It is explanatory drawing of correction | amendment of the pulse signal which an encoder outputs. It is a flowchart for demonstrating operation | movement of the inkjet printing apparatus in 2nd Embodiment. It is a schematic block diagram of the inkjet printing apparatus which concerns on 3rd Embodiment. FIG. 8 is a control block diagram of the inkjet printing apparatus shown in FIG. 7. It is explanatory drawing of the adjustment table in 3rd Embodiment. It is a flowchart for demonstrating operation | movement of the inkjet printing apparatus in 3rd Embodiment. It is explanatory drawing of the change rate calculation timing of the conveyance speed of a web. It is a schematic block diagram of the inkjet printing apparatus which concerns on 4th Embodiment. It is a control block diagram of the inkjet printing apparatus shown in FIG.

  Embodiments of the present invention will be described below with reference to the drawings. Throughout the drawings, the same or equivalent parts and components are denoted by the same or equivalent reference numerals.

  The following embodiments exemplify devices for embodying the technical idea of the present invention, and the technical idea of the present invention is the material, shape, structure, arrangement, etc. of each component. Is not specified as follows. The technical idea of the present invention can be variously modified within the scope of the claims.

[First Embodiment]
FIG. 1 is a schematic configuration diagram of an inkjet printing apparatus according to a first embodiment of the present invention. FIG. 2 is a control block diagram of the ink jet printing apparatus shown in FIG. In the following description, the top, bottom, left, and right of the paper surface in FIG. Further, the direction orthogonal to the paper surface of FIG. Further, in the following description, upstream and downstream mean upstream and downstream in the conveyance direction of the web to be printed.

  As shown in FIGS. 1 and 2, the inkjet printing apparatus 1 according to the first embodiment includes an unwinding unit 2, a transport unit 3, a printing unit 4, a winding unit 5, and a control unit 6. .

  The unwinding unit 2 holds the web W that is unwound to the transport unit 3. The web W is a long print medium made of film, paper, or the like. The unwinding unit 2 includes a web roll support shaft 11 and guide rollers 12 to 14.

  The web roll support shaft 11 rotatably supports the web roll 16. The web roll 16 is obtained by winding a web W in a roll shape.

  The guide rollers 12 to 14 guide the web W between the web roll support shaft 11 and a brake unit 21 of the transport unit 3 described later.

  The conveyance unit 3 conveys the web W unwound from the unwinding unit 2 toward the winding unit 5. The transport unit 3 includes a brake unit 21, a pair of transport rollers 22, a transport motor 23, a motor driver 24, five head support rollers 25, encoder rollers 26 and 27, and guide rollers 28 to 31. Encoders 32 and 33 and an encoder counter 34.

  The brake unit 21 applies tension to the web W between the conveyance rollers 22 by applying a braking force to the web W. The brake unit 21 is disposed on the upstream side of the printing unit 4. The brake unit 21 corresponds to a brake part in claims.

  The brake unit 21 includes a pair of brake rollers 36, a brake 37, and a brake driver 38.

  The pair of brake rollers 36 applies tension to the conveyed web W by the braking force of the brake 37 while nipping the web W. The pair of brake rollers 36 is disposed between the guide roller 14 of the unwinding unit 2 and the guide roller 28 of the transport unit 3.

  The brake 37 generates a braking force for applying tension to the web W. The brake 37 is connected to one of the pair of brake rollers 36 and applies a braking force to the brake roller 36. The brake 37 is a powder brake, for example. The brake driver 38 drives the brake 37.

  The pair of transport rollers 22 transport the web W toward the winding unit 5 while nipping the web W. The pair of transport rollers 22 is disposed on the downstream side of the printing unit 4.

  The transport motor 23 drives the transport roller 22 to rotate. The motor driver 24 drives the carry motor 23.

  The head lower support roller 25 supports the web W below the printing unit 4. The five head lower support rollers 25 are arranged at intervals in the left-right direction.

  The encoder rollers 26 and 27 are rollers provided with encoders 32 and 33, respectively. A web W is wound around the encoder rollers 26 and 27. The encoder rollers 26 and 27 are driven and rotated by the web W being conveyed. The encoder roller 26 is disposed between the brake unit 21 and the printing unit 4 in the web W conveyance direction. The encoder roller 27 is disposed between the printing unit 4 and the conveyance roller 22 in the conveyance direction of the web W. The encoder roller 26 corresponds to an upstream roller in the claims. The encoder roller 27 corresponds to a downstream roller in claims.

  The guide rollers 28 and 29 assist the winding of the web W around the encoder roller 26. The guide rollers 28 and 29 are spaced apart from each other in the left-right direction with the encoder roller 26 interposed therebetween, and are disposed below the encoder roller 26. The guide rollers 28 and 29 are disposed on the upstream side (left side) and downstream side (right side) of the encoder roller 26, respectively. Hold from.

  The guide rollers 30 and 31 assist the winding of the web W around the encoder roller 27. The guide rollers 30 and 31 are spaced apart from each other in the left-right direction with the encoder roller 27 interposed therebetween, and are disposed below the encoder roller 27. The guide rollers 30 and 31 are arranged on the upstream side (left side) and downstream side (right side) of the encoder roller 27, respectively. Hold from.

  The encoders 32 and 33 output pulse signals according to the rotation angles of the encoder rollers 26 and 27, respectively. The upstream encoder 32 corresponds to the upstream encoder in the claims. The downstream encoder 33 corresponds to the downstream encoder in the claims.

  The encoder counter 34 counts the number of output pulses of the encoders 32 and 33.

  The printing unit 4 prints an image on the web W conveyed by the conveyance unit 3. The printing unit 4 includes inkjet heads 41K, 41C, 41M, and 41Y. The ink jet heads 41K, 41C, 41M, and 41Y have the same configuration except that the colors of ink to be ejected are different. In addition, the alphabetic suffixes in the reference numerals of the ink jet heads 41K, 41C, 41M, and 41Y may be omitted and collectively described.

  The inkjet head 41 has a plurality of nozzles (not shown) arranged along the main scanning direction (front-rear direction), and ejects ink from the nozzles. The inkjet heads 41K, 41C, 41M, and 41Y eject black (K), cyan (C), magenta (M), and yellow (Y) inks, respectively. The inkjet heads 41K, 41C, 41M, and 41Y are arranged in parallel in the conveyance direction (left-right direction) of the web W in this order from the upstream side.

  The winding unit 5 winds up the web W printed by the printing unit 4. The winding unit 5 includes a winding shaft 46, a winding motor 47, a motor driver 48, and guide rollers 49 and 50.

  The winding shaft 46 winds and holds the web W. The winding motor 47 rotates the winding shaft 46 clockwise in FIG. The web W is wound around the winding shaft 46 by the rotation of the winding shaft 46. The motor driver 48 drives the winding motor 47.

  The guide rollers 49 and 50 guide the web W between the conveyance roller 22 of the conveyance unit 3 and the winding shaft 46.

  The control unit 6 controls the operation of each unit of the inkjet printing apparatus 1. The control unit 6 includes a CPU, RAM, ROM, hard disk, and the like.

  When printing, the control unit 6 drives the ink jet heads 41K, 41C, 41M, and 41Y of the printing unit 4 while driving the conveyance unit 3 and the winding unit 5 to convey the web W, and images the web W. To print.

  Here, the control unit 6 controls the transport unit 3 so that the transport speed of the web W during printing maintains a predetermined print transport speed. Specifically, the control unit 6 controls the brake force by the brake unit 21 to be constant at a predetermined brake force, and the web W conveyance speed is set to the print conveyance speed based on the pulse signal output from the encoder 33. The conveyance motor 23 is controlled so as to be maintained.

  Further, the controller 6 encodes the count value C1 of the number of output pulses of the downstream encoder 33 and the count value C2 of the number of output pulses of the upstream encoder 32 for each predetermined pulse count period Tc during printing. Obtained from the counter 34. Then, the control unit 6 compares the count values C1 and C2, and if there is no difference between the count values C1 and C2 as a result of the comparison, each inkjet head 41 is based on the pulse signal output by the downstream encoder 33. Ink discharge timing is controlled. The count value C1 corresponds to the downstream encoder count value in the claims, and the count value C2 corresponds to the upstream encoder count value in the claims.

  Here, in the control of the transport motor 23 for maintaining the transport speed of the web W at the print transport speed, the transport motor 23 is repeatedly accelerated and decelerated. Thereby, under the head (below the printing unit 4), a situation occurs in which the conveyance speed of the web W varies depending on the position in the conveyance direction.

  Specifically, when the transport motor 23 accelerates, the tension of the web W gradually increases from the transport roller 22 toward the upstream. For this reason, under the head, the situation where the conveyance speed of the web W is faster toward the downstream side occurs. In such a case, C1> C2. On the other hand, when the conveyance motor 23 decelerates, the tension of the web W gradually decreases from the conveyance roller 22 toward the upstream. For this reason, under the head, the situation where the conveyance speed of the web W is slower toward the downstream side occurs. In such a case, C1 <C2. In addition, the difference between the count values C1 and C2 increases as the difference between the conveyance speed of the web W on the upstream side and the conveyance speed of the web W on the downstream side increases.

  If the ejection timing of all the inkjet heads 41 is controlled by the pulse signal of the encoder 33 in a situation where the web W transport speed changes under the head as described above, the landing positions of the inks between the inkjet heads 41 may be shifted. is there.

  Therefore, when there is a difference between the count values C1 and C2, the control unit 6 is an inkjet head 41 that is closer to the upstream encoder 32 than the downstream encoder 33 in the conveyance path of the web W. The ink ejection timing in the inkjet heads 41K and 41C upstream from the central position of the printing unit 4 in the transport direction is controlled based on the pulse signal output from the upstream encoder 32. At this time, the control unit 6 determines whether the ink jet heads 41K, 41C are in accordance with the magnitude relationship between the count values C1, C2, the magnitude of the difference ΔC between the count values C1, C2, and the positions of the ink jet heads 41K, 41C in the horizontal direction. The ink ejection timing at 41C is adjusted.

  When the difference between the count values C1 and C2 occurs, the control unit 6 is the inkjet head 41 that is closer to the downstream encoder 33 than the upstream encoder 32 in the web W conveyance path. The ink ejection timing in the inkjet heads 41M and 41Y on the downstream side from the central position is controlled based on the pulse signal output from the downstream encoder 33. At this time, the control unit 6 determines the ejection timing of ink in the inkjet heads 41M and 41Y according to the magnitude relationship between the count values C1 and C2, the magnitude of the difference ΔC, and the positions of the inkjet heads 41M and 41Y in the left-right direction. Adjust.

  Here, the control unit 6 stores an adjustment table 51 shown in FIG. The adjustment table 51 is used for adjusting the ejection timing of the inkjet head 41 when a difference occurs between the count values C1 and C2 described above. The adjustment table 51 holds a phase adjustment value Δθ for adjusting the ejection timing in each inkjet head 41 according to the magnitude relationship between the count values C1 and C2 and the magnitude of the difference ΔC between the count values C1 and C2. .

  The phase adjustment value Δθ is an adjustment value of the phase of the pulse signal output from the encoders 32 and 33, which is adjusted when adjusting the ejection timing in the inkjet head 41. The phase adjustment value Δθ corresponding to the upstream ink jet heads 41K and 41C is applied to the pulse signal output from the upstream encoder 32. The phase adjustment value Δθ corresponding to the downstream inkjet heads 41M and 41Y is applied to the pulse signal output by the downstream encoder 33.

  In FIG. 3, A1 to A3 are positive values. When the phase adjustment value Δθ is a positive value (A1 to A3), it indicates that the discharge timing is adjusted to be advanced. That the phase adjustment value Δθ is a negative value (−A1 to −A3) indicates that the discharge timing is adjusted to be delayed.

  Here, when C1> C2, between the encoders 32 and 33, the conveyance speed of the web W is faster toward the downstream side. Therefore, as shown in FIG. 3, in the case of C1> C2, when adjusting the discharge timing with reference to the encoder 32 for the inkjet heads 41K and 41C on the downstream side of the upstream encoder 32, Adjustment is performed in a direction to advance the discharge timing. Further, in the case of C1> C2, when adjusting the discharge timing based on the encoder 33 for the inkjet heads 41M and 41Y on the upstream side of the downstream encoder 33, adjust the discharge timing to be delayed. Is done.

  Further, in the case of C1 <C2, between the encoders 32 and 33, the web W conveyance speed becomes slower toward the downstream side. Therefore, as shown in FIG. 3, in the case of C1 <C2, when adjusting the discharge timing based on the encoder 32 with respect to the inkjet heads 41K and 41C on the downstream side of the encoder 32 on the upstream side, Adjustment is performed in the direction of delaying the discharge timing. Further, in the case of C1 <C2, when adjusting the discharge timing with reference to the encoder 33 for the inkjet heads 41M and 41Y located on the upstream side of the downstream encoder 33, adjust the discharge timing to be advanced. Is done.

  The phase adjustment value Δθ corresponding to each inkjet head 41 in the adjustment table 51 is set according to the position of each inkjet head 41 in the web W conveyance direction. Specifically, the phase adjustment value Δθ is set so that the adjustment range of the ejection timing becomes larger as the distance from the upstream encoder 32 is longer with respect to the upstream inkjet heads 41K and 41C. . In addition, the phase adjustment value Δθ is set so that the adjustment range of the ejection timing becomes larger as the distance from the downstream encoder 33 is longer with respect to the downstream inkjet heads 41M and 41Y. That is, in FIG. 3, A1> 0 and A3> A2.

  When there is a difference between the count values C1 and C2, the web W conveyance speed varies depending on the position of each inkjet head 41. Therefore, as described above, the adjustment width is set according to the position of the inkjet head 41. Yes.

  For example, when C1> C2, between the encoders 32 and 33, the conveyance speed of the web W is faster toward the downstream side. That is, in the case of C1> C2, the transport speed of the web W increases as the distance from the upstream encoder 32 to the downstream side increases. Therefore, in this case, the phase adjustment value Δθ for the upstream ink jet heads 41K and 41C is set so that the ink jet head 41C has a larger adjustment width in the direction of earlier ejection timing than the ink jet head 41K. . Further, the phase adjustment value Δθ for the downstream inkjet heads 41M and 41Y is set such that the inkjet head 41M has a larger adjustment width in the direction of delaying the ejection timing than the inkjet head 41Y.

  In addition, the phase adjustment value Δθ is set so that the adjustment range of the ejection timing is larger when the difference ΔC between the count values C1 and C2 is equal to or larger than the predetermined difference threshold Ct than when the difference ΔC is less than the difference threshold Ct. ing. That is, in FIG. 3, A2> 0 and A3> A1. Here, the difference ΔC between the count values C1 and C2 is expressed by the following equation (1).

ΔC = | C1-C2 | (1)
The greater the difference ΔC between the count values C1 and C2, the greater the difference between the web W conveyance speed at the encoder 32 position and the web W conveyance speed at the encoder 33 position. Therefore, as shown in FIG. 3, the phase of the discharge timing adjustment is larger when the difference ΔC between the count values C1 and C2 is greater than or equal to the predetermined difference threshold Ct than when the difference ΔC is less than the difference threshold Ct. An adjustment value Δθ is set.

  The value of the phase adjustment value Δθ and the value of the difference threshold value Ct in FIG. 3 are set in advance based on experiments or the like.

  In the example of FIG. 3, the value of the phase adjustment value Δθ corresponding to the difference ΔC between the count values C1 and C2 is set in two stages according to the difference threshold Ct, but may be three or more stages. .

  Next, the operation of the inkjet printing apparatus 1 will be described.

  FIG. 4 is a flowchart for explaining the operation of the inkjet printing apparatus 1 according to the first embodiment. The process of the flowchart in FIG. 4 starts when a print job is input to the inkjet printing apparatus 1.

  In step S <b> 1 of FIG. 4, the control unit 6 starts conveyance of the web W. Specifically, the control unit 6 starts driving the transport motor 23, the take-up motor 47, and the brake 37. After the start of conveyance, the conveyance speed of the web W is accelerated.

  Next, in step S <b> 2, the control unit 6 determines whether or not the conveyance speed of the web W has reached the printing conveyance speed based on the pulse signal output by the downstream encoder 33. When it is determined that the conveyance speed of the web W has not reached the printing conveyance speed (step S2: NO), the control unit 6 repeats step S2.

  When it is determined that the conveyance speed of the web W has reached the printing conveyance speed (step S2: YES), in step S3, the control unit 6 starts constant-speed conveyance control of the web W at the printing conveyance speed. Specifically, the control unit 6 controls the brake force by the brake unit 21 to be constant at a predetermined brake force, and the web W conveyance speed is set to the print conveyance speed based on the pulse signal output from the encoder 33. The conveyance motor 23 is controlled so as to be maintained.

  Next, in step S4, the control unit 6 determines whether or not it is time to acquire a pulse count value for ejection timing control. Here, the acquisition timing of the first pulse count value is set to a predetermined timing after the start of the constant speed conveyance control of the web W. Subsequent pulse count value acquisition timing is set for each predetermined pulse count period Tc.

  When it is determined that the pulse count value acquisition timing has not come (step S4: NO), the control unit 6 repeats step S4.

  When it is determined that the pulse count value acquisition timing has come (step S4: YES), in step S5, the control unit 6 counts the output pulse count value C1 of the encoder 33 in the pulse count period Tc up to the acquisition timing, and A count value C2 of the number of output pulses of the encoder 32 is acquired from the encoder counter 34.

  Next, in step S6, the control unit 6 determines whether there is a difference between the currently acquired count values C1, C2, that is, whether C1 = C2.

  When it is determined that C1 = C2 (step S6: YES), in step S7, the control unit 6 causes ink to be ejected from each inkjet head 41 by ejection timing control based on the encoder 33 on the downstream side. That is, the control unit 6 controls the ejection timing of ink by all the inkjet heads 41 based on the pulse signal output from the downstream encoder 33.

  Here, when the count values C1 and C2 of this time C1 = C2 are acquired at the acquisition timing of the first pulse count value after the start of conveyance of the web W, the control unit 6 uses each of the encoders 33 based on the encoder 33. Printing based on the print job is started by controlling the ejection timing of the inkjet head 41.

  If this time is not the first pulse count value acquisition timing and there is a difference between the count values C1 and C2 acquired at the previous pulse count value acquisition timing, the timing until the current pulse count value acquisition timing will be described later. The discharge timing control based on the encoders 32 and 33 in step S8 is performed. In this case, if there is no difference between the count values C1 and C2 acquired this time, the ink jet heads 41K and 41C are switched from the discharge timing control based on the upstream encoder 32 to the discharge timing control based on the downstream encoder 33. .

  When this time is not the acquisition timing of the first pulse count value, there is no difference in the count values C1 and C2 acquired at the acquisition timing of the previous pulse count value, and there is no difference in the count values C1 and C2 acquired this time The ejection timing control based on the encoder 33 is continuously performed for all the ink jet heads 41.

  When it is determined in step S6 that C1 = C2 is not satisfied (step S6: NO), in step S8, the control unit 6 controls the discharge timing of the inkjet heads 41K and 41C based on the upstream encoder 32, and the downstream side. Ink is ejected from each inkjet head 41 by controlling the ejection timing of the inkjet heads 41M and 41Y based on the encoder 33.

  That is, the control unit 6 controls the ink ejection timing in the inkjet heads 41K and 41C based on the pulse signal output from the upstream encoder 32. At this time, the control unit 6 refers to the adjustment table 51 on the basis of the magnitude relationship between the count values C1 and C2 and the difference ΔC between the count values C1 and C2, and corresponds to each of the inkjet heads 41K and 41C. The phase adjustment value Δθ is acquired. Then, the control unit 6 adjusts the ejection timing of the inkjet heads 41K and 41C with respect to the ejection timing based on the pulse signal of the encoder 32 based on the phase adjustment value Δθ corresponding to each of the inkjet heads 41K and 41C.

  Further, the control unit 6 controls the ink ejection timing in the inkjet heads 41M and 41Y based on the pulse signal output from the downstream encoder 33. At this time, the control unit 6 refers to the adjustment table 51 based on the magnitude relationship between the count values C1 and C2 and the magnitude of the difference ΔC between the count values C1 and C2, and corresponds to each of the inkjet heads 41M and 41Y. The phase adjustment value Δθ is acquired. Then, the control unit 6 adjusts the ejection timing of the inkjet heads 41M and 41Y with respect to the ejection timing based on the pulse signal of the encoder 33 based on the phase adjustment value Δθ corresponding to each of the inkjet heads 41M and 41Y.

  For example, in the case of C1> C2 and ΔC <Ct, the controller 6 adjusts the ejection timing of the inkjet head 41C to be earlier by A1 ° than the timing based on the upstream encoder 32. Since the phase adjustment value Δθ corresponding to the inkjet head 41K is 0 °, for the inkjet head 41K, the control unit 6 controls the ejection timing while maintaining the timing based on the pulse signal of the encoder 32.

  Further, in this case, the control unit 6 performs adjustment to delay the ejection timing of the inkjet head 41M by A1 ° from the timing based on the downstream encoder 33. Since the phase adjustment value Δθ corresponding to the inkjet head 41Y is 0 °, for the inkjet head 41Y, the control unit 6 controls the ejection timing while maintaining the timing based on the pulse signal of the encoder 33.

  Adjustment to the ejection timing based on the pulse signals output from the encoders 32 and 33 is performed by correcting the pulse signals. For example, when the ejection timing is delayed by the phase adjustment value Δθ, the control unit 6 corrects the rising edge of the pulse signal to be delayed by the phase adjustment value Δθ as shown in FIG. Thereby, the ejection timing of the inkjet head 41 controlled based on the rising timing of the pulse signal is adjusted so as to be delayed by the phase adjustment value Δθ.

  Here, when the count values C1 and C2 that are not C1 = C2 of this time are acquired at the acquisition timing of the first pulse count value, the control unit 6 uses each of the inkjets based on the encoders 32 and 33 as described above. Printing based on the print job is started by controlling the ejection timing of the head 41.

  When this time is not the first pulse count value acquisition timing, there is no difference between the count values C1 and C2 acquired at the previous pulse count value acquisition timing, and there is a difference between the current count values C1 and C2. The inkjet heads 41K and 41C are switched from the discharge timing control based on the downstream encoder 33 to the discharge timing control based on the upstream encoder 32.

  When this time is not the acquisition timing of the first pulse count value, there is a difference in the count values C1 and C2 acquired at the acquisition timing of the previous pulse count value, and there is also a difference in the count values C1 and C2 acquired this time The ejection timing control based on the upstream encoder 32 for the inkjet heads 41K and 41C and the ejection timing control based on the downstream encoder 33 for the inkjet heads 41M and 41Y are continuously performed. However, the adjustment content of the discharge timing based on the adjustment table 51 may change according to the magnitude relationship between the count values C1 and C2 and the change in the difference ΔC between the count values C1 and C2.

  Here, as described above, the ejection timing control of the ink jet heads 41K and 41C may be switched between that based on the downstream encoder 33 and that based on the upstream encoder 32. On the other hand, the pulse signal output from the encoder 32 and the pulse signal output from the encoder 33 may be out of phase with each other. Therefore, when switching between the ejection timing control based on the pulse signal of the encoder 33 and the ejection timing control based on the pulse signal of the encoder 32 with respect to the inkjet heads 41K and 41C, the control unit 6 uses two pulse signals. The discharge timing control after switching is performed while adjusting the amount of phase shift.

  Subsequent to step S7 or step S8 in FIG. 4, in step S9, the control unit 6 determines whether printing based on the print job is completed. If it is determined that printing based on the print job has not ended (step S9: NO), the control unit 6 returns to step S4.

  If it is determined that printing based on the print job has been completed (step S9: YES), in step S10, the control unit 6 ends the conveyance of the web W. Specifically, the control unit 6 stops the transport motor 23, the winding motor 47, and the brake 37. Thereby, a series of operations are completed.

  As described above, in the first embodiment, the controller 6 outputs the count value C1 of the number of output pulses of the downstream encoder 33 and the output of the upstream encoder 32 for each pulse count period Tc during printing. The count value C2 of the number of pulses is acquired. Then, the control unit 6 compares the count values C1 and C2, and if there is no difference between the count values C1 and C2 as a result of the comparison, each inkjet head 41 is based on the pulse signal output by the downstream encoder 33. Ink discharge timing is controlled.

  When there is a difference between the count values C1 and C2, the control unit 6 controls the ink ejection timing in the upstream inkjet heads 41K and 41C based on the pulse signal output from the upstream encoder 32. At this time, the control unit 6 determines the ink ejection timing in the inkjet heads 41K and 41C according to the magnitude relationship between the count values C1 and C2, the magnitude of the difference ΔC, and the position of the inkjet heads 41K and 41C in the left-right direction. Adjust.

  When the difference between the count values C1 and C2 occurs, the control unit 6 controls the ink ejection timing in the downstream inkjet heads 41M and 41Y based on the pulse signal output from the downstream encoder 33. At this time, the control unit 6 determines the ejection timing of ink in the inkjet heads 41M and 41Y according to the magnitude relationship between the count values C1 and C2, the magnitude of the difference ΔC, and the positions of the inkjet heads 41M and 41Y in the left-right direction. Adjust.

  Accordingly, even when the conveyance speed of the web W varies depending on the position in the conveyance direction due to the acceleration / deceleration of the conveyance motor 23 for conveying the web W at a constant speed, it is possible to reduce the landing position deviation of the ink between the inkjet heads 41. . For this reason, it is possible to reduce a decrease in print image quality.

  In addition, the above-described reduction in print image quality can be realized by the two encoders 32 and 33, and it is not necessary to provide an encoder for each inkjet head 41. Therefore, the complexity of the apparatus configuration can be suppressed.

  Therefore, according to the ink jet printing apparatus 1 of the first embodiment, it is possible to reduce deterioration in print image quality while suppressing the complexity of the apparatus configuration.

[Second Embodiment]
Next, a second embodiment in which a part of the first embodiment described above is changed will be described.

  In the first embodiment described above, the controller 6 outputs the downstream encoder 33 while controlling the brake force by the brake unit 21 to be constant at a predetermined brake force in the constant-speed conveyance control of the web W. Based on the pulse signal, the conveyance motor 23 is controlled so that the conveyance speed of the web W maintains the printing conveyance speed.

  On the other hand, in the second embodiment, the control unit 6 performs control so that the rotation speed of the conveyance motor 23 is constant at a predetermined rotation speed in the constant-speed conveyance control of the web W, while the upstream encoder 32 is controlled. Based on the output pulse signal, the brake force by the brake unit 21 is controlled so that the conveyance speed of the web W maintains the printing conveyance speed.

  That is, in the first embodiment, constant speed conveyance control of the web W is performed by acceleration / deceleration of the conveyance motor 23, whereas in the second embodiment, constant speed conveyance control of the web W is performed by adjusting the brake force by the brake unit 21. .

  In the second embodiment, when there is no difference between the count values C1 and C2 for each pulse count period Tc, the control unit 6 determines the ink in each inkjet head 41 based on the pulse signal output from the upstream encoder 32. The discharge timing is controlled.

  Also in the second embodiment, the control unit 6 stores the adjustment table 51 of FIG. 3 as in the first embodiment. And when the difference arises in count value C1, C2, the control part 6 refers to the adjustment table 51, and performs the discharge timing control similar to 1st Embodiment.

  Here, in the control of the brake unit 21 in the constant speed conveyance control of the web W, the increase and decrease of the brake force are repeatedly performed. As a result, as in the first embodiment, a situation occurs in which the conveyance speed of the web W varies depending on the position in the conveyance direction under the head.

  Specifically, when the brake force of the brake unit 21 is reduced, the tension of the web W gradually decreases from the brake roller 36 toward the downstream side. For this reason, under the head, the situation where the conveyance speed of the web W is faster toward the downstream side occurs. In such a case, C1> C2. On the other hand, when the braking force of the brake unit 21 increases, the tension of the web W gradually increases from the brake roller 36 toward the downstream. For this reason, under the head, the situation where the conveyance speed of the web W is slower toward the downstream side occurs. In such a case, C1 <C2.

  That is, in the second embodiment, when the braking force of the brake unit 21 is reduced, C1> C2 as in the case where the transport motor 23 in the first embodiment is accelerated. In the second embodiment, when the braking force of the brake unit 21 increases, C1 <C2 as in the case where the transport motor 23 in the first embodiment decelerates.

  Next, the operation of the inkjet printing apparatus 1 in the second embodiment will be described with reference to the flowchart of FIG.

  The processes in steps S11 and S12 in FIG. 6 are the same as the processes in steps S1 and S2 in FIG. 4 described above.

  In step S13, the control unit 6 starts constant-speed conveyance control of the web W at the printing conveyance speed. Specifically, the control unit 6 controls the rotation speed of the conveyance motor 23 to be constant at a predetermined rotation speed, while the conveyance speed of the web W determines the print conveyance speed based on the pulse signal output from the encoder 32. The brake force by the brake unit 21 is controlled so as to be maintained.

  The process of steps S14 to S16 is the same as the process of steps S4 to S6 of FIG. 4 described above.

  When it is determined in step S16 that C1 = C2 (step S16: YES), in step S17, the control unit 6 causes ink to be ejected from each inkjet head 41 by ejection timing control based on the upstream encoder 32. . That is, the control unit 6 controls the ink ejection timings of all the inkjet heads 41 based on the pulse signal output from the upstream encoder 32.

  The processes in steps S18 to S20 are the same as the processes in steps S8 to S10 in FIG. 4 described above. When the conveyance of the web W is finished in step S20, a series of operations is finished.

  As described above, also in the second embodiment, when there is a difference between the count values C1 and C2, the control unit 6 is similar to the first embodiment in the upstream inkjet head based on the upstream encoder 32. 41K and 41C ejection timing control and downstream inkjet head 41M and 41Y ejection timing control based on the downstream encoder 33 are performed.

  As a result, even if a situation occurs in which the conveyance speed of the web W varies depending on the position in the conveyance direction due to a change in the brake force of the brake unit 21 for conveying the web W at a constant speed, the landing position deviation of the ink between the inkjet heads 41 is shifted. Can be reduced. For this reason, it is possible to reduce a decrease in print image quality.

  Also in the second embodiment, as in the first embodiment, the above-described reduction in print image quality can be realized by the two encoders 32 and 33, and it is not necessary to provide an encoder for each inkjet head 41. Complexity can be suppressed.

  Therefore, also in the second embodiment, it is possible to reduce deterioration in print image quality while suppressing the complexity of the apparatus configuration.

[Third Embodiment]
FIG. 7 is a schematic configuration diagram of an ink jet printing apparatus according to the third embodiment. FIG. 8 is a control block diagram of the inkjet printing apparatus shown in FIG.

  As shown in FIGS. 7 and 8, the inkjet printing apparatus 1 </ b> A according to the third embodiment has a configuration in which the conveyance unit 3 of the inkjet printing apparatus 1 according to the first embodiment described above is replaced with a conveyance unit 3 </ b> A.

  3 A of conveyance parts are the structures which abbreviate | omitted the encoder roller 26, the guide roller 28, and the encoder 32 with respect to the conveyance part 3 of 1st Embodiment mentioned above. Here, in the transport unit 3A, the guide roller 29 guides the web W between the brake roller 36 and the uppermost head lower support roller 25. The encoder roller 27 of the transport unit 3A corresponds to a driven roller in claims.

  In the third embodiment, the controller 6 controls the encoder 33 while controlling the braking force by the brake unit 21 to be constant at a predetermined braking force in the constant speed conveyance control of the web W, as in the first embodiment. Is controlled so that the conveyance speed of the web W maintains the printing conveyance speed.

  Further, the control unit 6 controls the ejection timing of the ink in each inkjet head 41 based on the pulse signal output from the encoder 33 to print an image on the web W being conveyed.

  Here, as described above, in the control of the transport motor 23 for maintaining the transport speed of the web W at the print transport speed, the transport motor 23 is repeatedly accelerated and decelerated. Thereby, the situation where the conveyance speed of the web W changes with the position in a conveyance direction under a head generate | occur | produces.

  Specifically, when the transport motor 23 accelerates, the tension of the web W gradually increases from the transport roller 22 toward the upstream. For this reason, under the head, the situation where the conveyance speed of the web W is faster toward the downstream side occurs. On the other hand, when the conveyance motor 23 decelerates, the tension of the web W gradually decreases from the conveyance roller 22 toward the upstream. For this reason, under the head, the situation where the conveyance speed of the web W is slower toward the downstream side occurs. Further, the greater the acceleration and deceleration of the transport motor 23, the greater the difference between the transport speed of the web W on the upstream side and the transport speed of the web W on the downstream side under the head.

  If the ejection timing of each inkjet head 41 is controlled based on the pulse signal of the encoder 33 in the situation where the web W conveyance speed changes under the head as described above, there is a possibility that the landing position deviation of the ink between the inkjet heads 41 may occur. is there.

  Therefore, the control unit 6 calculates the change rate (acceleration, deceleration) α of the web W conveyance speed at the position of the encoder roller 27 at a predetermined change rate calculation cycle Th based on the pulse signal output from the encoder 33. . Then, the control unit 6 adjusts the ink ejection timing in each inkjet head 41 according to the calculated change rate α and the position of each inkjet head 41.

  In the third embodiment, the control unit 6 stores an adjustment table 52 shown in FIG. The adjustment table 52 is used for adjusting the discharge timing described above. The adjustment table 52 holds a phase adjustment value Δθ for adjusting the ejection timing in each inkjet head 41 according to the change rate α of the conveyance speed of the web W.

  In FIG. 9, B1 to B7 are positive values. When the phase adjustment value Δθ is a positive value (B1 to B7), it indicates that the discharge timing is adjusted to be advanced. The phase adjustment value Δθ being a negative value (−B1 to −B7) indicates that the discharge timing is adjusted to be delayed. In FIG. 9, the change rate threshold values αt1 and αt2 are positive values.

  Here, when the conveyance motor 23 is accelerating, that is, when the rate of change α is a positive value, the conveyance speed of the web W is faster toward the downstream side under the head as described above. For this reason, as shown in FIG. 9, when the rate of change α is a positive value, that is, when αt1 ≦ α <αt2 and when α ≧ αt2, adjustment is performed in the direction of delaying the discharge timing.

  Further, when the transport motor 23 is decelerating, that is, when the change rate α is a negative value, the transport speed of the web W is slower toward the downstream side under the head as described above. For this reason, as shown in FIG. 9, when the rate of change α is a negative value, that is, when −αt2 <α ≦ −αt1 and α ≦ −αt2, the adjustment is performed in the direction of increasing the discharge timing. Is called.

  The phase adjustment value Δθ corresponding to each inkjet head 41 in the adjustment table 52 is set according to the position of each inkjet head 41 in the web W conveyance direction. Specifically, the value of the phase adjustment value Δθ is set such that the adjustment range of the ejection timing is larger as the inkjet head 41 is farther away from the encoder 33, in other words, as the upstream inkjet head 41 is. . That is, in FIG. 9, B3> B2> B1> 0 and B7> B6> B5> B4.

  Further, the phase adjustment value Δθ is set so that the adjustment range of the ejection timing is larger when the absolute value | α | of the change rate α is equal to or larger than the change rate threshold value αt2 than when the absolute value | α | is less than the change rate threshold value αt2. Is set. That is, in FIG. 9, B7> B3, B6> B2, B5> B1, B4> 0. The greater the absolute value | α | of the rate of change α, the greater the acceleration and deceleration of the web W, and thus the phase adjustment value Δθ is set in this way.

  The values of the phase adjustment value Δθ and the change rate threshold values αt1 and αt2 in FIG. 9 are set in advance based on experiments or the like.

  In the example of FIG. 9, the phase adjustment value Δθ corresponding to the change rate α is divided into two stages by the change rate threshold value αt2 for each of the cases where the change rate α is a positive value and a negative value. Although set separately, it may be three or more stages.

  Next, the operation of the inkjet printing apparatus 1A will be described.

  FIG. 10 is a flowchart for explaining the operation of the inkjet printing apparatus 1A. The process of the flowchart of FIG. 10 starts when a print job is input to the inkjet printing apparatus 1A.

  The processes in steps S21 to S23 in FIG. 10 are the same as the processes in steps S1 to S3 in FIG. 4 described above.

  After starting the constant speed conveyance control of the web W at the printing conveyance speed, in step S24, the control unit 6 starts executing the print job. Specifically, the control unit 6 drives each inkjet head 41 based on the print job to print an image on the web W. Here, the control unit 6 controls the ejection timing of the ink in each inkjet head 41 based on the pulse signal output from the encoder 33.

  Next, in step S <b> 25, the control unit 6 determines whether or not the web W conveyance speed change rate calculation timing has come. Here, the change rate calculation timing is set at a predetermined change rate calculation cycle Th as shown in FIG. 11 after the start of the constant speed conveyance control of the web W. When it is determined that the change rate calculation timing has not come (step S25: NO), the control unit 6 repeats step S25.

  When it is determined that the change rate calculation timing has come (step S25: YES), in step S26, the control unit 6 at the position of the encoder roller 27 between the previous change rate calculation timing and the current change rate calculation timing. A change rate α of the conveyance speed of the web W is calculated. The change rate α is calculated by the following equation (2).

α = (Vn−Vp) / Th (2)
Here, Vn is the conveyance speed of the web W at the position of the encoder roller 27 at the current change rate calculation timing. Vp is the conveyance speed of the web W at the position of the encoder roller 27 at the previous change rate calculation timing. The conveyance speeds Vn and Vp are calculated based on the pulse signal of the encoder 33.

  Next, in step S27, the control unit 6 determines whether or not the absolute value | α | of the change rate α calculated in step S26 is greater than or equal to the change rate threshold value αt1.

  When it is determined that the absolute value | α | of the change rate α is greater than or equal to the change rate threshold value αt1 (step S27: YES), the control unit 6 adjusts the ejection timing of each inkjet head 41 in step S28.

  Specifically, the control unit 6 refers to the adjustment table 52 based on the change rate α, and acquires the phase adjustment value Δθ corresponding to each inkjet head 41. Then, the control unit 6 adjusts the ejection timing of each inkjet head 41 with respect to the ejection timing based on the pulse signal of the encoder 33 based on the phase adjustment value Δθ corresponding to each inkjet head 41. The adjustment of the discharge timing is performed until the change rate α is calculated at the next change rate calculation timing.

  For example, in the case of αt1 ≦ α <αt2, the control unit 6 performs adjustment to delay the ejection timing of the inkjet heads 41K, 41C, and 41M by B3, B2, and B1, respectively, from the ejection timing based on the pulse signal of the encoder 33. Do. Since the phase adjustment value Δθ corresponding to the inkjet head 41Y is 0 °, for the inkjet head 41Y, the control unit 6 controls the ejection timing while maintaining the timing based on the pulse signal of the encoder 33.

  After step S28, the controller 6 proceeds to step S29. If it is determined in step S27 that the absolute value | α | of the change rate α is less than the change rate threshold value αt1 (step S27: NO), the control unit 6 skips step S28 and proceeds to step S29. .

  In step S29, the control unit 6 determines whether printing based on the print job is finished. If it is determined that printing based on the print job has not ended (step S29: NO), the control unit 6 returns to step S25.

  If it is determined that printing based on the print job has ended (step S29: YES), the control unit 6 ends the conveyance of the web W in step S30. Thereby, a series of operations are completed.

  As described above, in the third embodiment, the control unit 6 determines the ink in each inkjet head 41 according to the change rate α of the conveyance speed of the web W at the position of the encoder roller 27 and the position of each inkjet head 41. Is adjusted with respect to the discharge timing based on the pulse signal of the encoder 33.

  Accordingly, even when the conveyance speed of the web W varies depending on the position in the conveyance direction due to the acceleration / deceleration of the conveyance motor 23 for conveying the web W at a constant speed, it is possible to reduce the landing position deviation of the ink between the inkjet heads 41. . For this reason, it is possible to reduce a decrease in print image quality.

  Further, the above-described reduction in print image quality can be realized by one encoder 33, and it is not necessary to provide a plurality of encoders, so that the complexity of the apparatus configuration can be suppressed.

  Therefore, the inkjet printing apparatus 1A of the third embodiment can also reduce the deterioration of the print image quality while suppressing the complexity of the apparatus configuration.

[Fourth Embodiment]
FIG. 12 is a schematic configuration diagram of an inkjet printing apparatus according to the fourth embodiment. FIG. 13 is a control block diagram of the ink jet printing apparatus shown in FIG.

  As shown in FIGS. 12 and 13, the inkjet printing apparatus 1 </ b> B according to the fourth embodiment has a configuration in which the conveyance unit 3 of the inkjet printing apparatus 1 according to the first embodiment described above is replaced with a conveyance unit 3 </ b> B.

  The conveyance unit 3B has a configuration in which the encoder roller 27, the guide roller 31, and the encoder 33 are omitted from the conveyance unit 3 of the first embodiment described above. Here, in the conveyance unit 3 </ b> B, the guide roller 30 guides the web W between the most downstream head lower support roller 25 and the conveyance roller 22. The encoder roller 26 of the transport unit 3B corresponds to a driven roller in the claims.

  In the fourth embodiment, in the constant speed conveyance control of the web W, the controller 6 controls the encoder 32 while controlling the rotation speed of the conveyance motor 23 to be constant at a predetermined rotation speed, as in the second embodiment. Is controlled by the brake unit 21 so that the conveyance speed of the web W maintains the printing conveyance speed.

  Further, the control unit 6 controls the ink ejection timing in each inkjet head 41 based on the pulse signal output from the encoder 32 to print an image on the web W being conveyed.

  Here, as described above, in the control of the brake unit 21 in the constant speed conveyance control of the web W, the increase and decrease of the braking force are repeatedly performed. Thereby, the situation where the conveyance speed of the web W changes with the position in a conveyance direction under a head generate | occur | produces.

  Specifically, when the brake force of the brake unit 21 is reduced, the tension of the web W gradually decreases from the brake roller 36 toward the downstream side. For this reason, similarly to the case where the conveyance motor 23 is accelerated in the third embodiment, a situation occurs in which the conveyance speed of the web W is faster toward the downstream side under the head. On the other hand, when the braking force of the brake unit 21 increases, the tension of the web W gradually increases from the brake roller 36 toward the downstream. For this reason, the situation where the conveyance speed of the web W is slower toward the downstream side occurs under the head as in the case where the conveyance motor 23 is decelerated in the third embodiment.

  Therefore, the control unit 6 calculates the change rate (acceleration, deceleration) α of the web W conveyance speed at the position of the encoder roller 26 at a predetermined change rate calculation cycle Th based on the pulse signal output from the encoder 32. . Then, the control unit 6 adjusts the ink ejection timing in each inkjet head 41 according to the calculated change rate α and the position of each inkjet head 41.

  Here, also in the fourth embodiment, the control unit 6 stores the adjustment table 52 of FIG. 9 as in the third embodiment, and the adjustment table 52 is used to adjust the ejection timing of the ink in each inkjet head 41. Is used.

  Next, the operation of the inkjet printing apparatus 1B will be described.

  The operation of the inkjet printing apparatus 1B is performed according to the procedure shown in the flowchart of FIG. 10 in the same manner as the operation of the inkjet printing apparatus 1A of the third embodiment described above.

  However, in the inkjet printing apparatus 1B, in the constant speed conveyance control started in step S23, the control unit 6 controls the pulse output by the encoder 32 while controlling the rotation speed of the conveyance motor 23 to be constant at a predetermined rotation speed. Based on the signal, the brake force by the brake unit 21 is controlled so that the conveyance speed of the web W maintains the printing conveyance speed.

  Further, in the inkjet printing apparatus 1B, during the execution of the print job started in step S24, the control unit 6 controls the ink ejection timing in each inkjet head 41 based on the pulse signal output from the encoder 32.

  In the inkjet printing apparatus 1B, the change rate α calculated in step S26 is the change rate of the web W conveyance speed at the position of the encoder roller 26. That is, the control unit 6 calculates the rate of change α according to the equation (2) using the transport speeds Vn and Vp calculated based on the pulse signal of the encoder 32.

  In the inkjet printing apparatus 1B, the control unit 6 adjusts the ejection timing of each inkjet head 41 in step S28 with respect to the ejection timing based on the pulse signal of the encoder 32.

  As described above, in the fourth embodiment, the control unit 6 determines the ink in each inkjet head 41 according to the change rate α of the conveyance speed of the web W at the position of the encoder roller 26 and the position of each inkjet head 41. The discharge timing is adjusted with respect to the discharge timing based on the pulse signal of the encoder 32.

  As a result, even if a situation occurs in which the conveyance speed of the web W varies depending on the position in the conveyance direction due to a change in the brake force of the brake unit 21 for conveying the web W at a constant speed, the landing position deviation of the ink between the inkjet heads 41 is shifted. Can be reduced. For this reason, it is possible to reduce a decrease in print image quality.

  Further, the above-described reduction in print image quality can be realized by one encoder 32, and since it is not necessary to provide a plurality of encoders, complication of the apparatus configuration can be suppressed.

  Therefore, the inkjet printing apparatus 1B according to the fourth embodiment can also reduce the deterioration in print image quality while suppressing the complexity of the apparatus configuration.

[Other Embodiments]
As described above, the present invention has been described according to the first to fourth embodiments. However, it should not be understood that the description and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

  In the first to fourth embodiments described above, the configuration in which the printing unit 4 includes the four inkjet heads 41 has been described. However, the number of inkjet heads 41 is not limited to four, and may be plural.

  As described above, the present invention naturally includes various embodiments not described herein. Therefore, the technical scope of the present invention is defined only by the invention specifying matters according to the scope of claims reasonable from the above description.

[Appendix]
The present application discloses the following inventions.

(Appendix 1)
A plurality of inkjet heads arranged in parallel in the web conveyance direction, and a printing unit that prints an image by ejecting ink from each inkjet head onto the web to be conveyed;
A transport roller that is disposed downstream of the printing unit in the transport direction and is rotationally driven by a transport motor to transport the web;
A downstream roller disposed between the printing unit and the transport roller in the transport direction and driven to rotate by the web being transported;
A downstream encoder that outputs a pulse signal according to the rotation angle of the downstream roller;
A brake unit disposed on the upstream side of the printing unit in the transport direction, and applies a braking force to the web;
An upstream roller that is disposed between the brake unit and the printing unit in the transport direction and is driven to rotate by a web being transported;
An upstream encoder that outputs a pulse signal according to the rotation angle of the upstream roller;
Control the conveyance motor so that the web conveyance speed maintains a predetermined printing conveyance speed based on the pulse signal output from the downstream encoder while controlling the braking force by the brake unit to be constant at a predetermined braking force. And a control unit that controls the printing unit to print an image on the web,
The controller is
For each predetermined pulse count period, the upstream encoder count value, which is the count value of the number of output pulses of the upstream encoder, is compared with the downstream encoder count value, which is the count value of the number of output pulses of the downstream encoder. As a result, when there is no difference between the upstream encoder count value and the downstream encoder count value, based on the pulse signal output from the downstream encoder, the ink ejection timing in each inkjet head is controlled,
When a difference occurs between the upstream encoder count value and the downstream encoder count value,
Ink jet timing closer to the upstream encoder than the downstream encoder is controlled based on a pulse signal output from the upstream encoder, and the upstream encoder count value and the downstream encoder count value are related in magnitude. Adjust according to the magnitude of the difference between the encoder count value and the downstream encoder count value, and the position of each inkjet head,
Controlling the ejection timing of ink in the inkjet head closer to the downstream encoder than the upstream encoder based on the pulse signal output by the downstream encoder, and the magnitude relationship between the upstream encoder count value and the downstream encoder count value, An ink jet printing apparatus that adjusts according to the magnitude of the difference between an upstream encoder count value and the downstream encoder count value and the position of each ink jet head.

(Appendix 2)
A plurality of inkjet heads arranged in parallel in the web conveyance direction, and a printing unit that prints an image by ejecting ink from each inkjet head onto the web to be conveyed;
A transport roller that is disposed downstream of the printing unit in the transport direction and is rotationally driven by a transport motor to transport the web;
A downstream roller disposed between the printing unit and the transport roller in the transport direction and driven to rotate by the web being transported;
A downstream encoder that outputs a pulse signal according to the rotation angle of the downstream roller;
A brake unit disposed on the upstream side of the printing unit in the transport direction, and applies a braking force to the web;
An upstream roller that is disposed between the brake unit and the printing unit in the transport direction and is driven to rotate by a web being transported;
An upstream encoder that outputs a pulse signal according to the rotation angle of the upstream roller;
While controlling the rotation speed of the conveyance motor to be constant at a predetermined rotation speed, based on the pulse signal output from the upstream encoder, the brake unit brakes the web conveyance speed to maintain the predetermined print conveyance speed. And a control unit that controls the printing unit and controls the printing unit to print an image on the web,
The controller is
For each predetermined pulse count period, the upstream encoder count value, which is the count value of the number of output pulses of the upstream encoder, is compared with the downstream encoder count value, which is the count value of the number of output pulses of the downstream encoder. As a result, when there is no difference between the upstream encoder count value and the downstream encoder count value, based on the pulse signal output by the upstream encoder, the ink ejection timing in each inkjet head is controlled,
When a difference occurs between the upstream encoder count value and the downstream encoder count value,
Ink jet timing closer to the upstream encoder than the downstream encoder is controlled based on a pulse signal output from the upstream encoder, and the upstream encoder count value and the downstream encoder count value are related in magnitude. Adjust according to the magnitude of the difference between the encoder count value and the downstream encoder count value, and the position of each inkjet head,
Controlling the ejection timing of ink in the inkjet head closer to the downstream encoder than the upstream encoder based on the pulse signal output by the downstream encoder, and the magnitude relationship between the upstream encoder count value and the downstream encoder count value, An ink jet printing apparatus that adjusts according to the magnitude of the difference between an upstream encoder count value and the downstream encoder count value and the position of each ink jet head.

(Appendix 3)
A plurality of inkjet heads arranged in parallel in the web conveyance direction, and a printing unit that prints an image by ejecting ink from each inkjet head onto the web to be conveyed;
A transport roller that is disposed downstream of the printing unit in the transport direction and is rotationally driven by a transport motor to transport the web;
A driven roller that is disposed between the printing unit and the transport roller in the transport direction and is driven to rotate by a web being transported;
An encoder that outputs a pulse signal according to the rotation angle of the driven roller;
A brake unit disposed on the upstream side of the printing unit in the transport direction, and applies a braking force to the web;
While controlling the brake force by the brake unit to be constant at a predetermined brake force, the transport motor is controlled based on the pulse signal output from the encoder so that the web transport speed maintains a predetermined print transport speed. And a control unit that controls the ejection timing of the ink in each inkjet head based on the pulse signal output from the encoder and prints an image on the web,
The control unit calculates a change rate of the web conveyance speed at the position of the driven roller at a predetermined change rate calculation period based on a pulse signal output from the encoder, and the calculated change rate, and each inkjet head An ink jet printing apparatus, wherein the ink ejection timing in each ink jet head is adjusted according to the position of the ink jet head.

(Appendix 4)
A plurality of inkjet heads arranged in parallel in the web conveyance direction, and a printing unit that prints an image by ejecting ink from each inkjet head onto the web to be conveyed;
A transport roller that is disposed downstream of the printing unit in the transport direction and is rotationally driven by a transport motor to transport the web;
A brake unit disposed on the upstream side of the printing unit in the transport direction, and applies a braking force to the web;
A driven roller that is arranged between the brake unit and the printing unit in the transport direction and is driven to rotate by a web being transported;
An encoder that outputs a pulse signal according to the rotation angle of the driven roller;
While controlling the rotation speed of the conveyance motor to be constant at a predetermined rotation speed, based on the pulse signal output from the encoder, the braking force by the brake unit is maintained so that the web conveyance speed maintains the predetermined print conveyance speed. And a control unit that controls the ejection timing of ink in each of the inkjet heads to print an image on a web based on the pulse signal output from the encoder,
The controller is
Based on the pulse signal output by the encoder, the change rate of the web conveyance speed at the position of the driven roller is calculated at a predetermined change rate calculation cycle, and the change rate is calculated according to the calculated change rate and the position of each inkjet head. An ink jet printing apparatus that adjusts ink discharge timing in each ink jet head.

DESCRIPTION OF SYMBOLS 1,1A, 1B Inkjet printing apparatus 2 Unwinding part 3,3A, 3B Conveying part 4 Printing part 5 Winding part 6 Control part 21 Brake unit 22 Conveying roller 23 Conveying motor 26, 27 Encoder roller 32, 33 Encoder 36 Brake roller 37 Brake 41, 41K, 41C, 41M, 41Y Inkjet head 51, 52 Adjustment table

Claims (4)

A plurality of inkjet heads arranged in parallel in the web conveyance direction, and a printing unit that prints an image by ejecting ink from each inkjet head onto the web to be conveyed;
A transport roller that is disposed downstream of the printing unit in the transport direction and is rotationally driven by a transport motor to transport the web;
A downstream roller disposed between the printing unit and the transport roller in the transport direction and driven to rotate by the web being transported;
A downstream encoder that outputs a pulse signal according to the rotation angle of the downstream roller;
A brake unit disposed on the upstream side of the printing unit in the transport direction, and applies a braking force to the web;
An upstream roller that is disposed between the brake unit and the printing unit in the transport direction and is driven to rotate by a web being transported;
An upstream encoder that outputs a pulse signal according to the rotation angle of the upstream roller;
Control the conveyance motor so that the web conveyance speed maintains a predetermined printing conveyance speed based on the pulse signal output from the downstream encoder while controlling the braking force by the brake unit to be constant at a predetermined braking force. And a control unit that controls the printing unit to print an image on the web,
The controller is
For each predetermined pulse count period, the upstream encoder count value, which is the count value of the number of output pulses of the upstream encoder, is compared with the downstream encoder count value, which is the count value of the number of output pulses of the downstream encoder. As a result, when there is no difference between the upstream encoder count value and the downstream encoder count value, based on the pulse signal output from the downstream encoder, the ink ejection timing in each inkjet head is controlled,
When a difference occurs between the upstream encoder count value and the downstream encoder count value,
Ink jet timing closer to the upstream encoder than the downstream encoder is controlled based on a pulse signal output from the upstream encoder, and the upstream encoder count value and the downstream encoder count value are related in magnitude. Adjust according to the magnitude of the difference between the encoder count value and the downstream encoder count value, and the position of each inkjet head,
Controlling the ejection timing of ink in the inkjet head closer to the downstream encoder than the upstream encoder based on the pulse signal output by the downstream encoder, and the magnitude relationship between the upstream encoder count value and the downstream encoder count value, An ink jet printing apparatus that adjusts according to the magnitude of the difference between an upstream encoder count value and the downstream encoder count value and the position of each ink jet head. A plurality of inkjet heads arranged in parallel in the web conveyance direction, and a printing unit that prints an image by ejecting ink from each inkjet head onto the web to be conveyed;
A transport roller that is disposed downstream of the printing unit in the transport direction and is rotationally driven by a transport motor to transport the web;
A downstream roller disposed between the printing unit and the transport roller in the transport direction and driven to rotate by the web being transported;
A downstream encoder that outputs a pulse signal according to the rotation angle of the downstream roller;
A brake unit disposed on the upstream side of the printing unit in the transport direction, and applies a braking force to the web;
An upstream roller that is disposed between the brake unit and the printing unit in the transport direction and is driven to rotate by a web being transported;
An upstream encoder that outputs a pulse signal according to the rotation angle of the upstream roller;
While controlling the rotation speed of the conveyance motor to be constant at a predetermined rotation speed, based on the pulse signal output from the upstream encoder, the brake unit brakes the web conveyance speed to maintain the predetermined print conveyance speed. And a control unit that controls the printing unit and controls the printing unit to print an image on the web,
The controller is
For each predetermined pulse count period, the upstream encoder count value, which is the count value of the number of output pulses of the upstream encoder, is compared with the downstream encoder count value, which is the count value of the number of output pulses of the downstream encoder. As a result, when there is no difference between the upstream encoder count value and the downstream encoder count value, based on the pulse signal output by the upstream encoder, the ink ejection timing in each inkjet head is controlled,
When a difference occurs between the upstream encoder count value and the downstream encoder count value,
Ink jet timing closer to the upstream encoder than the downstream encoder is controlled based on a pulse signal output from the upstream encoder, and the upstream encoder count value and the downstream encoder count value are related in magnitude. Adjust according to the magnitude of the difference between the encoder count value and the downstream encoder count value, and the position of each inkjet head,
Controlling the ejection timing of ink in the inkjet head closer to the downstream encoder than the upstream encoder based on the pulse signal output by the downstream encoder, and the magnitude relationship between the upstream encoder count value and the downstream encoder count value, An ink jet printing apparatus that adjusts according to the magnitude of the difference between an upstream encoder count value and the downstream encoder count value and the position of each ink jet head. A plurality of inkjet heads arranged in parallel in the web conveyance direction, and a printing unit that prints an image by ejecting ink from each inkjet head onto the web to be conveyed;
A transport roller that is disposed downstream of the printing unit in the transport direction and is rotationally driven by a transport motor to transport the web;
A driven roller that is disposed between the printing unit and the transport roller in the transport direction and is driven to rotate by a web being transported;
An encoder that outputs a pulse signal according to the rotation angle of the driven roller;
A brake unit disposed on the upstream side of the printing unit in the transport direction, and applies a braking force to the web;
While controlling the brake force by the brake unit to be constant at a predetermined brake force, the transport motor is controlled based on the pulse signal output from the encoder so that the web transport speed maintains a predetermined print transport speed. And a control unit that controls the ejection timing of the ink in each inkjet head based on the pulse signal output from the encoder and prints an image on the web,
The control unit calculates a change rate of the web conveyance speed at the position of the driven roller at a predetermined change rate calculation period based on a pulse signal output from the encoder, and the calculated change rate, and each inkjet head An ink jet printing apparatus, wherein the ink ejection timing in each ink jet head is adjusted according to the position of the ink jet head. A plurality of inkjet heads arranged in parallel in the web conveyance direction, and a printing unit that prints an image by ejecting ink from each inkjet head onto the web to be conveyed;
A transport roller that is disposed downstream of the printing unit in the transport direction and is rotationally driven by a transport motor to transport the web;
A brake unit disposed on the upstream side of the printing unit in the transport direction, and applies a braking force to the web;
A driven roller that is arranged between the brake unit and the printing unit in the transport direction and is driven to rotate by a web being transported;
An encoder that outputs a pulse signal according to the rotation angle of the driven roller;
While controlling the rotation speed of the conveyance motor to be constant at a predetermined rotation speed, based on the pulse signal output from the encoder, the braking force by the brake unit is maintained so that the web conveyance speed maintains the predetermined print conveyance speed. And a control unit that controls the ejection timing of ink in each of the inkjet heads to print an image on a web based on the pulse signal output from the encoder,
The controller is
Based on the pulse signal output by the encoder, the change rate of the web conveyance speed at the position of the driven roller is calculated at a predetermined change rate calculation cycle, and the change rate is calculated according to the calculated change rate and the position of each inkjet head. An ink jet printing apparatus that adjusts ink discharge timing in each ink jet head.