Suction fan control device

Abstract

To provide a suction fan control device capable of suppressing vibration of a plurality of suction fans.SOLUTION: A suction fan control device includes: a suction part having first to fourth suction fans 85a to 85d for generating a negative pressure for sucking a print medium; and a control part 70 that controls the first to fourth suction fans 85a to 85d. The control part 70 has the rotation speeds of the first to fourth suction fans 85a to 85d at different rotation speeds from each other, and controls the rotation speed so as to suppress the resonance of vibration due to the rotation of the first to fourth suction fans 85a to 85d.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a suction fan control device that controls a plurality of suction fans that generate negative pressure for adsorbing a printing medium.

Background Art

[0002] Conventionally, an inkjet printing apparatus has been proposed that discharges ink onto a printing medium from an inkjet head while conveying the printing medium made of paper, film, or the like.

[0003] As a conveyance device for a printing medium in such an inkjet printing apparatus, a conveyance device using a conveyance belt has been proposed. Specifically, a suction fan is provided facing the back surface of the installation surface of the printing medium of the conveyance belt, and negative pressure is generated in a large number of suction holes formed in the conveyance belt by the rotation of the suction fan, whereby a conveyance device that adsorbs the printing medium to the conveyance belt has been proposed (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Here, a rotating body such as a suction fan used in the above-described conveyance device generates vibration according to the rotation speed when there is a deviation (eccentricity) of the center of gravity with respect to the rotation axis. This is because the force generated by the eccentricity generates one reciprocating vibration during one rotation of the rotating body.

[0006] In a conveying device using a suction fan, when vibration of the suction fan occurs, the vibration may be transmitted to the conveyor belt and affect the landing position of ink on the printing medium conveyed by the conveyor belt. Specifically, when vibration of the suction fan occurs in the conveying direction of the printing medium, the conveyor belt moves closer to the conveying direction, so the conveyance of the printing medium becomes faster than normal, and the ink landing interval becomes coarser. On the other hand, when vibration of the suction fan occurs in the direction opposite to the conveying direction of the printing medium, the conveyor belt moves closer to the direction opposite to the conveying direction, so the conveyance of the printing medium becomes slower than normal, and the ink landing interval becomes denser. In particular, in the case of a suspended belt platen, it is easily affected by the vibration of the suction fan.

[0007] Further, especially when a plurality of the same suction fans are installed and used at the same rotational speed, the vibrations caused by the rotation of the plurality of suction fans resonate, and the influence is more emphasized. FIG. 13A is a diagram showing the occurrence situation of resonance when four suction fans have the same rotational speed. FIG. 13A shows the occurrence situation of resonance when each suction fan vibrates about 70 times in the process of conveying an A3 size printing medium. The graph shown in FIG. 13B represents the vibration cycle of each suction fan, and the graph shown in FIG. 13A shows the composite wave of the vibration cycles of the four suction fans shown in FIG. 13B. Since the vibration cycles of the four suction fans are the same cycle, in the composite wave, they resonate and are emphasized four times. When such resonance of vibration occurs, periodic density unevenness as shown in FIG. 14 occurs, leading to a deterioration in print quality.

[0008] In view of the above circumstances, an object of the present invention is to provide a suction fan control device capable of suppressing the vibration of a plurality of suction fans.

Means for Solving the Problems

[0009] The suction fan control device of the present invention includes a suction unit having a plurality of suction fans that generate a negative pressure for adsorbing a printing medium, and a control unit that controls the suction fans. The control unit controls the rotation speeds of the plurality of suction fans to rotation speeds that are different from each other and that suppress resonance of vibrations caused by the rotation of the plurality of suction fans.

Advantages of the Invention

[0010] According to the suction fan control device of the present invention, since the rotation speeds of the plurality of suction fans are controlled to rotation speeds that are different from each other and that suppress resonance of vibrations caused by the rotation of the plurality of suction fans, vibrations of the plurality of suction fans can be suppressed.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

[0012] Hereinafter, an inkjet printing apparatus using an embodiment of the suction fan control device of the present invention will be described in detail with reference to the drawings. The inkjet printing apparatus of this embodiment is characterized by a method for controlling the suction fans of the conveyance unit of the print medium. First, the configuration of the entire inkjet printing apparatus will be described. FIG. 1 is a schematic configuration diagram of the inkjet printing apparatus 1 of this embodiment. Note that the up, down, left, and right directions indicated by arrows in FIG. 1 are the up, down, left, and right directions in the inkjet printing apparatus 1 of this embodiment. Also, the front side with respect to the paper surface of FIG. 1 is the front direction, and the back side is the back direction.

[0013] As shown in FIG. 1, the inkjet printing apparatus 1 of this embodiment includes a side paper feeding unit 10, an internal paper feeding unit 20, an image forming unit 30, an upper paper discharging unit 40, a reversing unit 50, a side paper discharging unit 60, a control unit 70, an operation panel 71, and a conveyance unit 80.

[0014] The side paper feed unit 10 includes a paper feed tray 11 on which a printing medium P such as paper or film is loaded, a primary paper feed roller 12 that feeds the printing medium P loaded on the paper feed tray 11 one by one from above and conveys it toward a registration roller 14 described later, and a registration roller 14 that delivers the printing medium P sent out by the primary paper feed roller 12 to the image forming unit 30 with a predetermined paper interval.

[0015] The internal paper feed unit 20 includes paper feed trays 21a, 21b, 21c, 21d on which the printing medium P is placed, and primary paper feed rollers 22a, 22b, 22c, 22d that feed the printing medium P loaded on the paper feed trays 21a, 21b, 21c, 21d one by one from above and convey it onto the paper feed conveyance path FR.

[0016] The printing medium P sent out from the primary paper feed rollers 22a, 22b, 22c, 22d of the internal paper feed unit 20 is also conveyed toward the registration roller 14, and the printing medium P is further conveyed from the reversing unit 50 toward the registration roller 14.

[0017] In front of the conveyance direction of the registration roller 14, there is a confluence point where the conveyance path of the fed printing medium P and the path through which the paper printed on one side circulates and is conveyed from the reversing unit 50 merge. Based on this confluence point, the path on the paper feed mechanism side is called the paper feed conveyance path FR, and the other paths are called the circulation conveyance path CR.

[0018] The printing medium P fed from the registration roller 14 is conveyed to the conveyance unit 80. The conveyance unit 80 includes a conveyance belt 81, a platen roller 82, a first air chamber 83 and a second air chamber 84, and first to fourth suction fans 85a to 85d. In this embodiment, the first air chamber 83, the second air chamber 84, and the first to fourth suction fans 85a to 85d correspond to the suction unit of the present invention.

[0019] The conveyance belt 81 and the platen roller 82 are suspended and supported directly from the housing of the inkjet printing apparatus 1 or indirectly from members other than the housing provided on the housing.

[0020] The conveying belt 81 is an endless belt, and a large number of suction holes for adsorbing the printing medium P are formed therein. The platen roller 82 is a roller extending in a direction orthogonal to the conveying direction of the printing medium P. In the present embodiment, as shown in FIG. 1, four platen rollers 82 are provided. Specifically, one platen roller 82 is installed in the vicinity of the downstream side of the resist roller 14 and in the vicinity of the upstream side of a first switching mechanism 32 described later, and another set of platen rollers 82 is installed below this set of platen rollers 82.

[0021] As shown in FIG. 1, the conveying belt 81 is stretched over the four platen rollers 82 described above. When the four platen rollers 82 rotate, the conveying belt 81 moves, and the printing medium P adsorbed on the conveying belt 81 is conveyed.

[0022] On the back side of the adsorption surface of the printing medium P on the conveying belt 81, a first air chamber 83 and a second air chamber 84 for generating a negative pressure are provided. The first air chamber 83 and the second air chamber 84 are box-shaped members that form a closed space, communicate with the suction holes of the conveying belt 81, and are each provided with two suction fans.

[0023] FIG. 2 is a view of the conveying unit 80 as seen from above. As shown in FIG. 2, the first air chamber 83 is provided on the upstream side in the conveying direction of the printing medium P, and the second air chamber 84 is provided on the downstream side in the conveying direction of the printing medium P. The first air chamber 83 and the second air chamber 84 are each formed over a range that is half of the installable range of the printing medium P on the conveying belt 81.

[0024] A first suction fan 85a and a second suction fan 85c are provided at the bottom of the first air chamber 83, and a third suction fan 85b and a fourth suction fan 85d are provided at the bottom of the second air chamber 84.

[0025] When the first suction fan 85a and the second suction fan 85c rotate, negative pressure is generated in the suction holes of the conveyor belt 81 distributed in the first air chamber 83 and within the range of the first air chamber 83, causing the printing medium P to be adsorbed onto the conveyor belt 81.

[0026] Also, when the third suction fan 85b and the fourth suction fan 85d rotate, negative pressure is generated in the suction holes of the conveyor belt 81 distributed in the second air chamber 84 and within the range of the second air chamber 84, causing the printing medium P to be adsorbed onto the conveyor belt 81. In this way, with the printing medium P adsorbed onto the conveyor belt 81, as the conveyor belt 81 moves, the printing medium P is conveyed at a predetermined conveyance speed from the upstream side to the downstream side.

[0027] Then, while the printing medium P is being conveyed by the conveyor belt 81 as described above, ink is ejected from the head unit 31 onto the printing medium P, thereby performing a printing process on the printing medium P.

[0028] The image forming unit 30 is provided at a position facing the conveyor belt 81 of the conveyance unit 80 and includes a head unit 31 and a head holder 33.

[0029] The head unit 31 includes four line heads 32a, 32b, 32c, and 32d. Each of the line heads 32a to 32d includes a plurality of inkjet heads having a plurality of nozzles for ejecting ink.

[0030] Each of the line heads 32a to 32d extends in a direction orthogonal to the conveyance direction of the printing medium P and ejects ink onto the printing medium P conveyed by the conveyance unit 80. As shown in FIG. 1, the four line heads 32a to 32d are arranged at a predetermined interval along the conveyance path of the printing medium P. The four line heads 32a to 32d eject inks of different colors (for example, black, cyan, magenta, and yellow).

[0031] The head holder 33 is a member on which each line head 32a to 32d is installed. The head holder 33 is composed of a box-shaped support member, and a plurality of installation holes are formed on the bottom surface of the head holder 33 into which the respective inkjet heads of each line head 32a to 32d are fitted and installed. The installation holes are through holes, and are formed such that the ink ejection surfaces of the respective inkjet heads are exposed and arranged outside the bottom surface of the head holder 33.

[0032] The printed medium P printed by the image forming unit 30 is conveyed by a conveying roller or the like arranged on the circulation conveying path CR after being carried out from the conveying unit 80. A first switching mechanism 32 is provided on the circulation conveying path CR for switching whether to guide the printed medium P subjected to the printing process to the side paper discharge unit 60 or to the upper circulation conveying path CR. Further, a second switching mechanism 43 is provided on the circulation conveying path CR for switching whether to guide the printed medium P subjected to the printing process and conveyed onto the upper circulation conveying path CR to the upper paper discharge unit 40 or to the circulation conveying path CR on the side of the reversing unit 50.

[0033] The side paper discharge unit 60 has a paper discharge table 61 protruding from the housing of the inkjet printing apparatus 1 and a pair of paper discharge rollers 62 for guiding the printed medium P that has been printed to the paper discharge table 61. Then, the printed medium P guided to the side paper discharge unit 60 by the first switching mechanism 32 is conveyed to the paper discharge table 61 by the paper discharge rollers 62 and placed on the paper discharge table 61 with the printing surface facing up.

[0034] The upper paper discharge unit 40 has a paper discharge table 41 protruding from the housing of the inkjet printing apparatus 1 and a pair of paper discharge rollers 42 for guiding the printed medium P that has been printed to the paper discharge table 41. Then, the printed medium P guided to the upper paper discharge unit 40 by the second switching mechanism 43 is conveyed to the paper discharge table 41 by the paper discharge rollers 42 and placed on the paper discharge table 41 with the printing surface facing down.

[0035] The reversing unit 50 includes a reversing table 51 for reversing the printing medium P, and a reversing roller 52 for conveying the printing medium P from the circulation conveyance path CR to the reversing table 51 or from the reversing table 51 onto the circulation conveyance path CR.

[0036] The printing medium P guided to the reversing unit 50 by the second switching mechanism 43 is conveyed from the circulation conveyance path CR to the reversing table 51 by the reversing roller 52, and after a predetermined time has elapsed, is conveyed again from the reversing table 51 to the circulation conveyance path CR, thereby inverting the front and back sides. Then, the printing medium P with the front and back sides inverted is conveyed toward the image forming unit 30 by a plurality of rollers such as a conveyance roller 53 provided on the circulation conveyance path CR.

[0037] The operation panel 71 is composed of, for example, a touch panel having a liquid crystal display, and receives various setting inputs by the user. In particular, the operation panel 71 of the present embodiment receives setting inputs for the set value of the suction force required for the conveyance belt 81 and the conveyance speed of the conveyance belt 81.

[0038] FIG. 3 is a block diagram showing a schematic configuration of the control system of the inkjet printing apparatus 1 of the present embodiment. The control unit 70 includes a CPU (Central Processing Unit), a semiconductor memory, a hard disk, and the like. The control unit 70 controls the operations of each part of the inkjet printing apparatus 1 by executing a program stored in advance in a storage medium such as a semiconductor memory or a hard disk and operating an electric circuit.

[0039] In particular, the control unit 70 of the present embodiment controls the rotational speed by changing the duty ratio of the drive voltage applied to the drive motors of the first to fourth suction fans 85a to 85d. Specifically, the control unit 70 controls the rotational speeds of the first to fourth suction fans 85a to 85d to be different rotational speeds and rotational speeds that suppress the resonance of the vibration caused by the rotation of the first to fourth suction fans 85a to 85d.

[0040] As a result, the vibrations of the plurality of suction fans as described above can be suppressed. Therefore, the occurrence of density unevenness due to the above vibrations can be suppressed, and the print quality can be improved.

[0041] In the present embodiment, by shifting the duty ratio of the drive voltage applied to the drive motors of the first to fourth suction fans 85a to 85d by 10% each, they are controlled to have different rotational speeds.

[0042] Specifically, the control unit 70 sets, for example, the duty ratio of the drive voltage applied to the drive motors of the first to fourth suction fans 85a to 85d to the magnitudes shown in Table 1 below.

Table 1

[0043] FIG. 4 is a diagram showing the occurrence status of resonance when the duty ratio of the drive voltage applied to the drive motors of the first to fourth suction fans 85a to 85d is controlled as shown in Table 1 above. The graphs shown in FIGS. 5A to 5D represent the vibration periods of the first to fourth suction fans 85a to 85d, and the graph shown in FIG. 4 shows the composite wave of the vibration periods of the first to fourth suction fans 85a to 85d. As shown in FIG. 4, when compared with the occurrence status of resonance when the four suction fans shown in FIG. 13A have the same rotational speed, it can be seen that the amplitude of the composite wave is partially smaller, indicating that resonance can be suppressed. As a result, the density unevenness generated by the resonance of the vibrations of the first to fourth suction fans 85a to 85d can be suppressed. It has been experimentally found that the amplitude of the composite wave shown in FIGS. 4 and 13A affects the printed image when it is 75% or more of three suction fans (three-quarters).

[0044] Further, in the present embodiment, as shown in Table 1 above, the duty ratios (rotation speeds) of the first suction fan 85a and the second suction fan 85c provided in the first air chamber 83 are set to be larger (higher) than the duty ratios (rotation speeds) of the third suction fan 85b and the fourth suction fan 85d provided in the second air chamber 84.

[0045] Thereby, the negative pressure generated in the upstream first air chamber 83 can be made higher than the negative pressure generated in the downstream second air chamber 84. That is, the suction force of the conveyor belt 81 in the range corresponding to the upstream first air chamber 83 can be made stronger than the suction force of the conveyor belt 81 in the range corresponding to the downstream second air chamber 84.

[0046] Here, regarding the entry side of the printing medium P on the conveyor belt 81, since the stiffness is strong and it is necessary to flatten and adsorb the printing medium P that is warped with respect to the adsorption surface of the conveyor belt 81, a stronger suction force is required.

[0047] Therefore, as in the present embodiment, by making the suction force of the conveyor belt 81 in the range corresponding to the upstream first air chamber 83 stronger than the suction force of the conveyor belt 81 in the range corresponding to the downstream second air chamber 84, the printing medium P can be sufficiently adsorbed on the entry side of the conveyor belt 81, and flatness can be ensured.

[0048] On the other hand, regarding the exit side of the printing medium P on the conveyor belt 81, since it only needs to hold the printing medium P that has been adsorbed once, a strong suction force is not required.

[0049] Therefore, by controlling the rotation speeds of the first to fourth suction fans 85a to 85d as described above, the negative pressure generated in the downstream second air chamber 84 can be made lower than the negative pressure generated in the upstream first air chamber 83. That is, the suction force of the conveyor belt 81 in the range corresponding to the downstream second air chamber 84 can be made weaker than the suction force of the conveyor belt 81 in the range corresponding to the upstream first air chamber 83.

[0050] As a result, on the unloading side of the conveyor belt 81, the power consumption of the third suction fan 85b and the fourth suction fan 85d can be reduced, and the load on the conveyor motor 87 that drives the platen roller 82 can also be reduced. Therefore, further power consumption can be reduced.

[0051] Also, the duty ratios of the drive voltages of the first to fourth suction fans 85a to 85d are not limited to the values shown in Table 1 above, but by setting the duty ratios as shown in Table 2 below, resonance can be further suppressed. Each duty ratio of the drive voltages shown in Table 2 below is a combination of duty ratios corresponding to the rotation frequency ratios of the first to fourth suction fans 85a to 85d that can further suppress resonance. Specifically, the four rotation frequencies of the first to fourth suction fans 85a to 85d determined by the four duty ratios are set so as to have a relationship with the four frequencies corresponding to the four musical intervals that form dissonant sounds.

[0052] When the frequencies of dissonant sounds are synthesized, it has been found that resonance is suppressed and the amplitude of the synthesized wave becomes small. Therefore, by setting the four rotation frequencies of the first to fourth suction fans 85a to 85d as described above to have a relationship with the four frequencies corresponding to the four musical intervals that form dissonant sounds, the frequencies of the vibrations caused by the rotation of the first to fourth suction fans 85a to 85d can be made to have a relationship with the four frequencies of dissonant sounds. That is, the resonance of the vibrations caused by the rotation of the first to fourth suction fans 85a to 85d can be suppressed. Note that the relationship of the rotation frequencies (duty ratios) of the first to fourth suction fans 85a to 85d may be any combination as long as the resonance of the vibrations caused by the rotation of the first to fourth suction fans 85a to 85d is suppressed.

Table 2

[0053] FIG. 6 is a diagram showing the occurrence status of resonance when the duty ratio of the drive voltage applied to the drive motors of the first to fourth suction fans 85a to 85d is controlled as shown in Table 2 above. The graphs shown in FIGS. 7A to 7D represent the vibration periods of the first to fourth suction fans 85a to 85d, and the graph shown in FIG. 6 shows the composite waveform of the vibration periods of the first to fourth suction fans 85a to 85d. As shown in FIG. 6, when compared with the occurrence status of resonance (see FIG. 4) in the case of the duty ratio shown in Table 1 above, the portion where the amplitude of the composite wave exceeds 75% is further reduced, and it can be seen that resonance can be further suppressed. Thereby, the density unevenness can be further suppressed.

[0054] When setting the duty ratios of the first to fourth suction fans 85a to 85d as in Table 2 above, it is preferable to set the duty ratios of the first suction fan 85a and the second suction fan 85c provided in the first air chamber 83 to 100% and 72%, respectively, and set the duty ratios of the third suction fan 85b and the fourth suction fan 85d provided in the second air chamber 84 to 50% and 36%, respectively. Thereby, the negative pressure generated in the upstream first air chamber 83 can be made higher than the negative pressure generated in the downstream second air chamber 84.

[0055] When the duty ratios of the first to fourth suction fans 85a to 85d are set as described above, if the suction amount of the downstream second air chamber 84 cannot be ensured, for example, the duty ratios of the first to fourth suction fans 85a to 85d may be set at intervals of ±5% or more from the duty ratios in Table 2 above so as to ensure the suction amount of the downstream second air chamber 84.

[0056] In addition, in the inkjet printing apparatus 1 of the above embodiment, two air chambers, i.e., the first air chamber 83 and the second air chamber 84, are provided. However, the present invention is not limited to this, and only one air chamber may be provided. FIG. 8 is a diagram showing an example in which four first to fourth suction fans 85a to 85d are provided for one air chamber 86. In the case of the example shown in FIG. 8, since there is only one air chamber, the negative pressure generated by the rotation of the first to fourth suction fans 85a to 85d is evenly generated on the installation surface of the printing medium P of the conveyor belt 81, and the suction force is also evenly distributed.

[0057] When the configuration has only one air chamber as shown in FIG. 8, the control unit 70 preferably controls the rotation speeds of the first to fourth suction fans 85a to 85d so that the average value of the rotation speeds of the first to fourth suction fans 85a to 85d approaches the same rotation speed, so as to obtain the same suction force as that generated when the rotation speeds of the first to fourth suction fans 85a to 85d are all the same rotation speed.

[0058] Thereby, a desired suction force can be obtained, and the duty ratios of the first to fourth suction fans 85a to 85d can be calculated by simple arithmetic processing.

[0059] In addition, in the inkjet printing apparatus 1 of the above embodiment, the duty ratio (rotation speed) is controlled in consideration of the resonance of the vibrations of the first to fourth suction fans 85a to 85d. However, the duty ratio (rotation speed) of the first to fourth suction fans 85a to 85d may also be set in consideration of the vibration caused by the rotation of the conveyance motor 87 that drives the platen roller 82. That is, the duty ratio (rotation speed) of the first to fourth suction fans 85a to 85d may be set so as to suppress the resonance between the vibration of the conveyance motor 87 and the vibration caused by the rotation of the first to fourth suction fans 85a to 85d. Thereby, the density unevenness due to the resonance between the vibration of the conveyance motor 87 and the vibration of the first to fourth suction fans 85a to 85d can be suppressed, and the print quality can be further improved. Hereinafter, the resonance between the vibration of the suction fan and the vibration of the conveyance motor of the platen roller will be described.

[0060] FIG. 9 shows a graph indicating the change in the unevenness interval in response to the change in the rotational speed of the suction fan, and shows the above graph for each conveyance speed (hereinafter simply referred to as the conveyance speed) of the conveyance motor of the platen roller. The horizontal axis of the graph shown in FIG. 9 is the rotational speed of the suction fan, and the vertical axis indicates the change in the unevenness interval described above. Note that the rotational speed of the suction fan is represented by frequency (Hz). Graph a shown in FIG. 9 is for the case of a conveyance speed of 700 mm / s, graph b is for the case of a conveyance speed of 600 mm / s, and graph c is for the case of a conveyance speed of 500 mm / s.

[0061] As shown in FIG. 9, the faster the rotational speed of the suction fan, the narrower the interval of the unevenness generated by the vibration due to the rotation. Also, the faster the conveyance speed, the wider the interval of the unevenness due to the vibration of the suction fan.

[0062] On the other hand, the interval of the unevenness due to the vibration of the conveyance motor of the platen roller is determined by the vibration generation cycle of the conveyance motor itself and mechanisms such as the ratio of the gears connected to the conveyance motor and the platen roller, and is known to be constant regardless of the speed change of the conveyance motor. Here, the interval of the vibration of the conveyance motor is set to 6 mm.

[0063] In this case, the case where the vibration due to the rotation of the suction fan and the vibration due to the conveyance motor resonate is, for example, when the conveyance speed is 700 mm / s and the duty ratio of the suction fan is 70%. That is, when the conveyance speed is 700 mm / s, if there is a suction fan with a duty ratio of 70% among the first to fourth suction fans 85a to 85d described above, the vibration of the suction fan and the vibration of the conveyance motor 87 resonate, that is, the interval of the unevenness of the suction fan and the interval of the unevenness of the conveyance motor overlap, and the density unevenness becomes large. Similarly, when the conveyance speed is 600 mm / s, if there is a suction fan with a duty ratio of 40%, the vibration of the suction fan and the vibration of the conveyance motor 87 resonate, and the density unevenness becomes large. Also, when the conveyance speed is 500 mm / s, if there is a suction fan with a duty ratio of 20%, the vibration of the suction fan and the vibration of the conveyance motor 87 resonate, and the density unevenness becomes large.

[0064] That is, the relationship between the conveyance speed and the duty ratio of the suction fan to be avoided in the case of that conveyance speed is as shown in Table 3 below. [Table 3]

[0065] Therefore, when there is a duty ratio for the conveyance speed shown in Table 3 above among the duty ratios of the first to fourth suction fans 85a to 85d, the duty ratio may be corrected and set. Hereinafter, the correction of the duty ratio of the suction fan will be described in detail.

[0066] FIG. 10 shows an example of a table in which the duty ratio is set such that the rotational frequencies of the first to fourth suction fans 85a to 85d have a relationship with the frequency of the dissonance as described above. The duty ratios of the first to fourth suction fans 85a to 85d in the table shown in FIG. 10 are values calculated such that their average value is close to the set value in the above table.

[0067] The set value in the table shown in FIG. 10 is a value appropriately set according to the suction force required for the conveyor belt 81, and is set, for example, according to the type of the printing medium P. The above set value is set and input by the user on the operation panel 71, for example. The average value in the table shown in FIG. 10 indicates the actual average value when the duty ratios of the first to fourth suction fans 85a to 85d are calculated as described above.

[0068] For example, when the set value is 20%, the four duty ratios calculated to have a relationship with the frequency of the dissonance are 24%, 33%, 17%, and 12%, and their average value is about 22%. In this case, when comparing the four duty ratios with the duty ratio to be avoided shown in Table 3 above, the differences between the duty ratios 24% and 17% among the four duty ratios and the duty ratio 20% to be avoided corresponding to the conveyance speed of 500 mm / s in Table 3 above are less than 5%.

[0069] Therefore, when the set value is 20% and the conveying speed is set to 500 mm / s, the control unit 70 changes the duty ratio of the first suction fan 85a from 24% to 15% and the duty ratio of the third suction fan 85b from 17% to 15%, so that the difference from the duty ratio of 20% to be avoided is 5% or more.

[0070] When the difference between the duty ratios of the first to fourth suction fans 85a to 85d and the duty ratio to be avoided is less than 5%, as methods for changing the duty ratio, there are a method of increasing it and a method of decreasing it compared to the duty ratio shown in FIG. 10. However, it is desirable to determine which value to change based on the relationship between the set value and the average value. That is, when the set value is 20% and the average value is 22%, since the average value is larger than the set value, as a method for changing the duty ratio, it is desirable to change it to be smaller than the duty ratio shown in FIG. 10. Thereby, the duty ratio can be changed so that the average value approaches the set value.

[0071] In addition, when the set value is 20% and the conveying speed is set to 700 mm / s or 600 mm / s, the control unit 70 sets the duty ratios of the first to fourth suction fans 85a to 85d to the four duty ratios in the table shown in FIG. 10.

[0072] Also, for example, when the set value is 30%, the four duty ratios calculated so as to be related to the frequency of the dissonance are 36%, 50%, 25%, and 18%, and the average value thereof is about 32%. In this case, when comparing the four duty ratios with the duty ratio to be avoided shown in Table 3 above, among the four duty ratios, the duty ratio of 18% has a difference of less than 5% from the duty ratio of 20% to be avoided corresponding to the conveying speed of 500 mm / s in Table 3 above. Also, the duty ratio of 36% has a difference of less than 5% from the duty ratio of 40% to be avoided corresponding to the conveying speed of 600 mm / s in Table 3 above.

[0073] Therefore, when the set value is 30% and the conveying speed is set to 500 mm / s, the control unit 70 changes the duty ratio of the fourth suction fan 85d from 18% to 15% to make the difference from the duty ratio of 20% to be avoided 5% or more. Also, when the set value is 30% and the conveying speed is set to 600 mm / s, the control unit 70 changes the duty ratio of the first suction fan 85a from 36% to 35% to make the difference from the duty ratio of 40% to be avoided 5% or more. In addition, when the set value is 30% and the conveying speed is set to 700 mm / s, the control unit 70 sets the duty ratios of the first to fourth suction fans 85a to 85d to the four duty ratios in the table shown in FIG. 10.

[0074] Also, for example, when the set value is 40%, the four duty ratios calculated to be in the relationship of the frequency of dissonance are 48%, 67%, 33%, and 24%, and the average value thereof is about 43%. In this case, when comparing the four duty ratios with the duty ratios to be avoided shown in Table 3 above, among the four duty ratios, the difference between the duty ratio of 24% and the duty ratio of 20% to be avoided corresponding to the conveying speed of 500 mm / s in Table 3 above is less than 5%. Also, the difference between the duty ratio of 67% and the duty ratio of 70% to be avoided corresponding to the conveying speed of 700 mm / s in Table 3 above is less than 3%.

[0075] Therefore, when the set value is 40% and the conveying speed is set to 500 mm / s, the control unit 70 changes the duty ratio of the fourth suction fan 85d from 24% to 15% to make the difference from the duty ratio of 20% to be avoided 5% or more. When the set value is 40% and the conveying speed is set to 700 mm / s, the control unit 70 changes the duty ratio of the second suction fan 85c from 67% to 65% to make the difference from the duty ratio of 70% to be avoided 5% or more. In addition, when the set value is 40% and the conveying speed is set to 600 mm / s, the control unit 70 sets the duty ratios of the first to fourth suction fans 85a to 85d to the four duty ratios in the table shown in FIG. 10.

[0076] In addition, when the set values are 50%, 60%, 70%, and 80%, in the same way of thinking, the control unit 70 changes and sets the duty ratios of the first to fourth suction fans 85a to 85d as shown in the column of the table change method shown in FIG. 10. In other cases, it is set to the four duty ratios of the table shown in FIG. 10. When the set value is 80%, the average value is 78%, which is smaller than the set value. Therefore, when the control unit 70 changes the duty ratio of the third suction fan 85b from 67% to 75% instead of 65%, the average value approaches the set value.

[0077] Also, when setting the duty ratios of the first to fourth suction fans 85a to 85d according to the table shown in FIG. 10, the number of air chambers may be two or one as described above.

[0078] In the inkjet printing apparatus 1 of the above embodiment, the first air chamber 83 is provided on the upstream side in the conveyance direction of the printing medium P, and the second air chamber 84 is provided on the downstream side in the conveyance direction. However, the present invention is not limited to this. For example, as shown in FIG. 11, three air chambers, i.e., a first air chamber 90, a second air chamber 91, and a third air chamber 92, may be arranged side by side in a direction orthogonal to the conveyance direction of the printing medium P.

[0079] In this case, a first suction fan 93a and a second suction fan 93b may be provided in the first air chamber 90, a third suction fan 93c and a fourth suction fan 93d may be provided in the second air chamber 91, and a fifth suction fan 93e and a sixth suction fan 93f may be provided in the third air chamber 92. Then, the duty ratios may be set so that the rotation frequencies of the first to sixth suction fans 93a to 93f are in the relationship of the frequencies of the dissonant sounds.

[0080] Also, as shown in FIG. 11, when providing three air chambers, i.e., a first air chamber 90, a second air chamber 91, and a third air chamber 92, it is preferable to set the duty ratios of the first to sixth suction fans 93a to 93f such that the suction forces of the first air chamber 90 and the third air chamber 92 on both sides are higher than the suction force of the central second air chamber 91. Thereby, it is possible to suppress the warping of both end portions extending in the conveyance direction of the print medium P, prevent jamming of the print medium P due to the warping, and suppress a decrease in print quality.

[0081] Further, in the inkjet printing apparatus 1 of the above embodiment, when setting the rotation speeds of a plurality of suction fans, it is preferable to actually check the intensity of the influence on the printed matter with the suction fans individually stopped in advance, check the intensity of vibration for each suction fan, and set the rotation speed of the suction fan with large vibration to a value lower than the average value of the rotation speeds of all the suction fans. Thereby, it is possible to efficiently suppress the vibration caused by the rotation of the suction fans.

[0082] Next, the operation flow of the conveyance unit 80 of the inkjet printing apparatus 1 of the above embodiment will be described with reference to the flowchart shown in FIG. 12.

[0083] First, before the start of the paper feeding operation of the print medium P, the conveyance speed of the conveyance unit 80 is set (S10). Then, the conveyance motor 87 is driven by the control unit 70, and the platen roller 82 rotates at a rotation speed corresponding to the conveyance speed set in S10, and the conveyance belt 81 moves (S12).

[0084] Next, the control unit 70 sets the duty ratios of the drive voltages of the first to fourth suction fans 85a to 85d to the above-described duty ratios (S14).

[0085] Subsequently, the control unit 70 applies the drive voltage with the duty ratio set in S14 to the drive motors of the first to fourth suction fans 85a to 85d, and starts driving the first to fourth suction fans 85a to 85d (S16). Then, the control unit 70 starts the paper feeding operation of the print medium P (S18).

[0086] Regarding the suction fan control device of the present invention, the following additional remarks are further disclosed. (Additional remarks)

[0087] In the suction fan control device of the present invention, a conveying unit for adsorbing and conveying a printing medium can be provided, and the suction unit can generate a negative pressure for causing the conveying unit to adsorb the printing medium.

[0088] In the suction fan control device of the present invention, the suction unit can have air chambers for generating negative pressure by the rotation of the suction fan on the upstream side and the downstream side in the conveying direction of the printing medium, respectively, and the control unit can make the rotational speed of the suction fan for generating negative pressure in the upstream air chamber higher than the rotational speed of the suction fan for generating negative pressure in the downstream air chamber.

[0089] Also, in the suction fan control device of the present invention, the suction unit can have one air chamber for generating negative pressure by the rotation of a plurality of suction fans, and the control unit can control the average value of the rotational speeds of the plurality of suction fans to approach the above-mentioned same rotational speed so that the same suction force as the suction force generated when the rotational speeds of all the plurality of suction fans are set to the same rotational speed can be obtained.

[0090] Also, in the suction fan control device of the present invention, the control unit can set the rotational speeds of a plurality of suction fans based on the conveying speed of the printing medium.

[0091] Also, in the suction fan control device of the present invention, the control unit can set the rotational frequencies of a plurality of suction fans to frequencies corresponding to a plurality of musical intervals that form dissonance.

Explanation of reference numerals

[0092] 1 Inkjet printing device 10 Side paper feeding unit 11 Paper feeding table 12 Primary paper feeding roller 14 Registration roller 20 Internal paper feeding unit Paper feed trays 21a, 21b, 21c, 21d Primary paper feed rollers 22a, 22b, 22c, 22d Image forming unit 30 Head unit 31 Line heads 32a, 32b, 32c, 32d First switching mechanism 32 Head holder 33 Upper paper discharge unit 40 Paper discharge tray 41 Paper discharge roller 42 Second switching mechanism 43 Duplex unit 50 Duplex table 51 Duplex roller 52 Conveyor roller 53 Side paper discharge unit 60 Paper discharge tray 61 Paper discharge roller 62 Control unit 70 Operation panel 71 Conveyor unit 80 Conveyor belt 81 Platen roller 82 First air chamber 83 Second air chamber 84 First suction fan 85a Third suction fan 85b Second suction fan 85c Fourth suction fan 85d Air chamber 86 Conveyor motor 87 First air chamber 90 Second air chamber 91 Third air chamber 92 First suction fan 93a Second suction fan 93b Third suction fan 93c Fourth suction fan 93d Fifth suction fan 93e Sixth suction fan 93f CR Circulation conveyor path FR Paper feed conveyor path P Print medium

Claims

1. A suction unit having a plurality of suction fans that generate a negative pressure for sucking a printing medium; A control unit that controls the suction fans, The control unit uses a table of duty ratios of drive voltages of the plurality of suction fans set in advance, and as the duty ratios of the drive voltages of the plurality of suction fans, different duty ratios from each other and that suppress resonance of vibrations caused by rotation of the plurality of suction fans are determined, Using a table that associates a preset conveyance speed of the printing medium with the duty ratio of the drive voltage to be avoided, the duty ratio of the drive voltage to be avoided corresponding to the conveyance speed of the printing medium during actual printing is determined, When there is a duty ratio within a preset range of the difference between the duty ratio that suppresses the resonance and the duty ratio of the drive data to be avoided corresponding to the conveyance speed of the printing medium among the duty ratios that suppress the resonance, the duty ratio that suppresses the resonance is changed so that the difference between the duty ratio that suppresses the resonance and the duty ratio of the drive voltage to be avoided is outside the range. A suction fan control device.

2. A conveyance unit that sucks and conveys the printing medium is provided, The suction unit generates a negative pressure for sucking the printing medium to the conveyance unit. The suction fan control device according to claim 1.

3. The suction unit has air chambers that generate a negative pressure by rotation of the suction fans on the upstream side and the downstream side in the conveyance direction of the printing medium, respectively, The control unit makes the rotational speed of the suction fan that generates a negative pressure in the upstream air chamber higher than the rotational speed of the suction fan that generates a negative pressure in the downstream air chamber. The suction fan control device according to claim 1.

4. The suction unit has one air chamber that generates a negative pressure by rotation of the plurality of suction fans, The suction fan control device according to claim 1, wherein the control unit controls such that the average value of the rotation speeds of the plurality of suction fans approaches the same rotation speed so as to obtain the same suction force as the suction force generated when the rotation speeds of all the plurality of suction fans are set to the same rotation speed.

Images