CN114654896A

CN114654896A - Suction fan control device

Info

Publication number: CN114654896A
Application number: CN202111357565.1A
Authority: CN
Inventors: 大河原弥贵
Original assignee: Riso Kagaku Corp
Current assignee: Riso Kagaku Corp
Priority date: 2020-12-23
Filing date: 2021-11-16
Publication date: 2022-06-24
Also published as: JP2022100083A

Abstract

The invention provides a suction fan control device capable of suppressing vibration of a plurality of suction fans. The suction fan control device is provided with: a suction unit having first to fourth suction fans (85a to 85d) that generate negative pressure for adsorbing the printing medium; and a control unit (70) that controls the first to fourth suction fans (85 a-85 d), wherein the control unit (70) controls the rotational speeds of the first to fourth suction fans (85 a-85 d) to be different from each other, and controls the rotational speeds to be rotational speeds that suppress resonance of vibrations caused by the rotation of the first to fourth suction fans (85 a-85 d).

Description

Suction fan control device

Technical Field

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

Background

Conventionally, there has been proposed an inkjet printing apparatus that performs printing by ejecting ink from an inkjet head onto a printing medium while conveying the printing medium made of paper, film, or the like.

As a conveying device for a printing medium in such an inkjet printing device, a conveying device using a conveyor belt has been proposed. Specifically, the following conveying apparatus is proposed: a suction fan is provided to face a surface of the conveyor belt on the back side of the surface on which the printing medium is provided, and the rotation of the suction fan causes negative pressure to be generated in a plurality of suction holes formed in the conveyor belt, thereby causing the printing medium to be adsorbed to the conveyor belt (see, for example, patent document 1).

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2019-127364

Disclosure of Invention

Problems to be solved by the invention

Here, when the suction fan used in the above-described conveyor is started and the rotating body is displaced (eccentric) from the center of gravity of the rotating shaft, vibration occurs according to the number of revolutions. This is because the force generated by the eccentricity generates one vibration back and forth during one rotation of the rotating body.

Further, in a transport apparatus using a suction fan, there are cases where: in the case where vibration of the suction fan is generated, the vibration is transmitted to the conveying belt to affect the position where ink is landed toward the printing medium conveyed by the conveying belt. Specifically, when vibration of the suction fan occurs in the transport direction of the print medium, the transport belt moves in the transport direction, and therefore the print medium is transported faster than before, and the landing interval of the ink becomes loose. On the other hand, when the vibration of the suction fan is generated in the direction opposite to the conveying direction of the printing medium, the conveying belt moves in the direction opposite to the conveying direction, so that the printing medium is conveyed slower than before, and the landing intervals of the ink are dense. Particularly, in the case of a suspended belt platen, it is susceptible to vibration of the suction fan.

In addition, especially when a plurality of identical suction fans are provided and used at the same rotation speed, resonance occurs in vibration caused by the rotation of the plurality of suction fans, and the influence thereof is further strengthened. Fig. 13 a is a diagram showing a state of occurrence of resonance in the case where the four suction fans are set to the same rotation speed. A in fig. 13 indicates a state of occurrence of resonance in a case where each suction fan vibrates about seventy times in the process of conveying the printing medium of a3 size. The graph shown in B in fig. 13 represents the vibration cycle of each suction fan, and the graph shown in a in fig. 13 represents the composite wave of the vibration cycles of the four suction fans shown in B in fig. 13. Since the vibration periods of the four suction fans are the same period, resonance is intensified four times in the composite wave. When such resonance of vibration occurs, periodic density unevenness as shown in fig. 14 occurs, and the print quality is degraded.

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

Means for solving the problems

The suction fan control device of the present invention comprises: a suction section having a plurality of suction fans that generate negative pressure for adsorbing the printing medium; and a control unit that controls the suction fans, wherein the control unit controls the rotation speeds of the plurality of suction fans to be different rotation speeds from each other, and to be a rotation speed that suppresses resonance of vibration caused by rotation of the plurality of suction fans.

Effects of the invention

According to the suction fan control device of the present invention, the rotation speeds of the plurality of suction fans are controlled to be different from each other, and the rotation speeds are controlled to be rotation speeds at which resonance of vibration caused by rotation of the plurality of suction fans is suppressed.

Drawings

Fig. 1 is a diagram showing a schematic configuration of an inkjet printing apparatus using an embodiment of a suction fan control device according to the present invention.

Fig. 2 is a view of the conveying unit as viewed from above.

Fig. 3 is a block diagram showing a schematic configuration of a control system of the inkjet printing apparatus shown in fig. 1.

Fig. 4 is a diagram showing a state of occurrence of resonance in the case where the duty ratios of the drive voltages of the first suction fan to the fourth suction fan are controlled by shifting by 10% one by one.

Fig. 5 is a diagram showing an example of the vibration cycles of the first suction fan to the fourth suction fan which form the composite wave shown in fig. 4.

Fig. 6 is a diagram showing a resonance occurrence state in the case where the four rotational frequencies of the first to fourth suction fans are controlled so as to correspond to the four musical intervals forming the dissonance.

Fig. 7 is a diagram showing an example of the vibration cycles of the first suction fan to the fourth suction fan which form the composite wave shown in fig. 6.

Fig. 8 is a diagram of an example in which four first to fourth suction fans are provided with respect to one air chamber.

Fig. 9 is a graph showing changes in uneven intervals corresponding to changes in the rotational speed of the suction fan for each conveyance speed.

Fig. 10 is a diagram showing an example of a table in which the duty ratios of the first suction fan to the fourth suction fan are set in consideration of the vibration of the conveyance motor.

Fig. 11 is a diagram showing an example in which three air chambers are arranged in parallel in a direction orthogonal to the conveyance direction of the printing medium.

Fig. 12 is a flowchart for explaining the flow of the operation of the conveying unit.

Fig. 13 is a diagram showing the occurrence of resonance and the vibration cycle of each suction fan when the four suction fans are set to the same rotational speed.

Fig. 14 is a diagram showing an example of concentration unevenness caused by resonance of vibration due to rotation of a plurality of suction fans.

Description of the reference numerals

1: an inkjet printing device;

10: a side sheet feeding section;

11: a paper feeding table;

12: a primary paper feed roller;

14: aligning rollers;

20: an internal paper feeding section;

21a, 21b, 21c, 21 d: a paper feeding table;

22a, 22b, 22c, 22 d: a primary paper feed roller;

30: an image forming section;

31: a head unit;

32a, 32b, 32c, 32 d: a linear spray head;

32: a first switching mechanism;

33: a head holding section;

40: an upper paper discharge unit;

41: a paper discharge table;

42: a paper discharge roller;

43: a second switching mechanism;

50: a turning part;

51: a turning table;

52: turning over the roller;

53: a conveying roller;

60: a side sheet discharge section;

61: a paper discharge table;

62: a paper discharge roller;

70: a control unit;

71: an operation panel;

80: a conveying unit;

81: a conveyor belt;

82: a platen roller;

83: a first air chamber;

84: a second air chamber;

85 a: a first suction fan;

85 b: a third suction fan;

85 c: a second suction fan;

85 d: a fourth suction fan;

86: an air chamber;

87: a conveying motor;

90: a first air chamber;

91: a second air chamber;

92: a third air chamber;

93 a: a first suction fan;

93 b: a second suction fan;

93 c: a third suction fan;

93 d: a fourth suction fan;

93 e: a fifth suction fan;

93 f: a sixth suction fan;

CR: a circulating conveying path;

FR: a paper feed conveyance path;

p: a print medium.

Detailed Description

Hereinafter, an inkjet printing apparatus using an embodiment of a suction fan control apparatus according to the present invention will be described in detail with reference to the drawings. The inkjet printing apparatus according to the present embodiment is characterized by a method of controlling a suction fan of a printing medium conveyance unit, and first, the overall configuration of the inkjet printing apparatus will be described. Fig. 1 is a schematic configuration diagram of an inkjet printing apparatus 1 according to the present embodiment. Note that the vertical and horizontal directions indicated by arrows in fig. 1 are vertical and horizontal directions in the inkjet printing device 1 according to the present embodiment. The near side is a forward direction with respect to the paper surface of fig. 1, and the far side is a backward direction.

As shown in fig. 1, the inkjet printing device 1 of the present embodiment includes a side sheet feeding unit 10, an internal sheet feeding unit 20, an image forming unit 30, an upper sheet discharging unit 40, a reversing unit 50, a side sheet discharging unit 60, a control unit 70, an operation panel 71, and a conveying unit 80.

The side sheet feeding unit 10 includes: a paper feeding table 11 for feeding paper or stacking printing media P such as films; a primary feed roller 12 that feeds out the printing media P stacked on the feed table 11 one by one from above and conveys the printing media P to a registration roller 14 described later; and a registration roller 14 that conveys the printing medium P fed by the primary paper feed roller 12 to the image forming unit 30 at a predetermined paper interval.

The internal paper feed unit 20 includes: paper feeding tables 21a, 21b, 21c, 21d on which the printing medium P is placed; and primary paper feed rollers 22a, 22b, 22c, and 22d that feed out the print media P stacked on the paper feed tables 21a, 21b, 21c, and 21d one by one from above and convey the print media P onto the paper feed conveyance path FR.

The print medium P fed out from the primary feed rollers 22a, 22b, 22c, and 22d of the internal feed unit 20 is also conveyed toward the registration rollers 14, and further, the print medium P is also conveyed from the reversing unit 50 toward the registration rollers 14.

In the front of the registration rollers 14 in the conveyance direction, there is a point of confluence where the conveyance path of the supplied printing medium P and the path along which the paper printed on one side is circulated and conveyed from the reversing unit 50 are merged. With this point of confluence as a reference, the path on the paper feed mechanism side is referred to as a paper feed conveyance path FR, and the other path is referred to as a circulating conveyance path CR.

The printing medium P fed from the registration roller 14 is conveyed to the conveying unit 80. The conveyance unit 80 includes a conveyance belt 81, a platen roller 82, first and

second air chambers

83 and 84, and first to fourth suction fans 85a to 85 d. In the present 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.

The conveyor belt 81 and the platen roller 82 are suspended and supported directly from the housing of the inkjet printing apparatus 1 or indirectly from a member provided outside the housing.

The conveying belt 81 is an endless belt and is formed with a plurality of suction holes for sucking the printing medium P. The platen roller 82 is a roller extending in a direction orthogonal to the conveyance 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 provided near the downstream side of the registration roller 14 and near the upstream side of the first switching mechanism 32 described later, and another platen roller 82 is provided below the one platen roller 82.

As shown in fig. 1, the conveyor belt 81 rotates by being bridged between the four platen rollers 82 and the four platen rollers 82, and the conveyor belt 81 moves to convey the printing medium P adsorbed on the conveyor belt 81.

A first air chamber 83 and a second air chamber 84 that generate negative pressure are provided on the back side of the suction surface of the printing medium P in the conveyance belt 81. The first air chamber 83 and the second air chamber 84 are box-shaped members forming a closed space, communicate with the suction holes of the conveyor belt 81, and are provided with two suction fans, respectively.

Fig. 2 is a view of the conveying unit 80 as viewed from above. As shown in fig. 2, the first air cell 83 is disposed on the upstream side in the conveyance direction of the print medium P, and the second air cell 84 is disposed on the downstream side in the conveyance direction of the print medium P. The first air chamber 83 and the second air chamber 84 are formed over a half of the range of the conveyor belt 81 in which the printing medium P can be set.

Further, 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.

The first suction fan 85a and the second suction fan 85c are rotated to generate a negative pressure in the first air chamber 83 and the suction holes of the conveying belt 81 distributed over the range of the first air chamber 83, whereby the printing medium P is adsorbed to the conveying belt 81.

In addition, the third suction fan 85b and the fourth suction fan 85d rotate to generate a negative pressure in the second air chamber 84 and the suction holes of the conveying belt 81 distributed in the range of the second air chamber 84, whereby the printing medium P is adsorbed to the conveying belt 81. In this way, the transport belt 81 moves with the print medium P attracted to the transport belt 81, and the print medium P is transported at a predetermined transport speed from the upstream side to the downstream side.

Then, the printing process is performed on the printing medium P by ejecting ink from the head unit 31 to the printing medium P while conveying the printing medium P by the conveyor belt 81 as described above.

The image forming unit 30 is provided at a position facing the conveyor belt 81 of the conveyor unit 80, and includes a head unit 31 and a head holding portion 33.

The head unit 31 includes four

line heads

32a, 32b, 32c, and 32 d. Each of the line heads 32a to 32d includes a plurality of inkjet heads having a plurality of nozzles for ejecting ink.

The line heads 32a to 32d extend in a direction orthogonal to the transport direction of the printing medium P, and eject ink onto the printing medium P transported by the transport unit 80. As shown in fig. 1, the four line heads 32a to 32d are arranged at predetermined intervals along the transport 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), respectively.

The head holding portion 33 is a member on which the line heads 32a to 32d are provided. The head holder 33 is formed of a box-shaped support member, and a plurality of mounting holes into which the inkjet heads of the line heads 32a to 32d are fitted are formed in the bottom surface of the head holder 33. The installation hole is a through hole, and is formed so that the ink ejection surface of each inkjet head is exposed to the outside of the bottom surface of the head holding portion 33.

The print medium P printed by the image forming unit 30 is conveyed by a conveying roller or the like disposed on the circulating conveying path CR after being discharged from the conveying unit 80. The circulating transport path CR is provided with a first switching mechanism 32, and the first switching mechanism 32 switches between guiding the print medium P subjected to the printing process to the side sheet discharge portion 60 and guiding the print medium P to the upper circulating transport path CR. Further, a second switching mechanism 43 is provided on the circulating transport path CR, and the second switching mechanism 43 switches between guiding the printing medium P, which has been subjected to the printing process and is transported to the upper circulating transport path CR, to the upper sheet discharge unit 40 and guiding the printing medium P to the circulating transport path CR on the reversing unit 50 side.

The side sheet discharge unit 60 includes: 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 printing medium P to the paper discharge table 61. The printed printing medium P guided to the side paper discharge portion 60 by the first switching mechanism 32 is conveyed to the paper discharge table 61 by the paper discharge rollers 62, and is placed on the paper discharge table 61 with the printing surface facing upward.

The upper paper ejection portion 40 includes: 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 printing medium P to the paper discharge table 41. The printed printing 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 is placed on the paper discharge table 41 with the printing surface facing downward.

The turning unit 50 includes: a reversing table 51 that reverses the printing medium P; and a reversing roller 52 that conveys the printing medium P from the circulating conveyance path CR to the reversing table 51, or conveys the printing medium P from the reversing table 51 onto the circulating conveyance path CR.

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, and is reversed. The print medium P having been reversed is then conveyed toward the image forming unit 30 by a plurality of rollers such as a conveying roller 53 provided on the circulating conveying path CR.

The operation panel 71 is configured by, for example, a touch panel having a liquid crystal display, and receives various setting inputs made by a user. In particular, the operation panel 71 of the present embodiment receives a set value of the suction force required for the conveyor belt 81 and a set input of the conveying speed of the conveyor belt 81.

Fig. 3 is a block diagram showing a schematic configuration of a control system of the inkjet printing apparatus 1 according to 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 the respective units of the inkjet printing apparatus 1 by operating the electric circuit while executing a program stored in advance in a storage medium such as a semiconductor memory or a hard disk.

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

This can suppress the vibration of the plurality of suction fans as described above. Therefore, the occurrence of density unevenness due to the vibration can be suppressed, and the print quality can be improved.

In the present embodiment, the duty ratios of the drive voltages applied to the drive motors of the first to fourth suction fans 85a to 85d are shifted by 10% one by one, and the drive voltages are controlled to different rotation speeds.

Specifically, for example, the control unit 70 sets the duty ratios of the driving voltages applied to the driving motors of the first to fourth suction fans 85a to 85d to the values shown in table 1 below.

TABLE 1

	Duty cycle
		First suction fan	70％
Second suction fan	80％
		Third suction fan	50％
Fourth suction fan	60％

Fig. 4 is a diagram showing a state of occurrence of resonance in the case where 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. Graphs shown in a of fig. 5 to D of fig. 5 represent vibration cycles of the first to fourth suction fans 85a to 85D, and a graph shown in fig. 4 represents a composite wave of the vibration cycles of the first to fourth suction fans 85a to 85D. As shown in fig. 4, when compared with the resonance occurrence state in the case where the four suction fans shown in a in fig. 13 are set to the same rotation speed, it is found that the amplitude of the composite wave is locally reduced and the resonance can be suppressed. This can suppress density unevenness caused by resonance of vibrations of the first to fourth suction fans 85a to 85 d. Further, it is experimentally found that the amplitude of the composite wave shown in a in fig. 4 and 13 affects the printed image from the vicinity of 75% or more of the amount (three quarters) of the three suction fans.

In the present embodiment, as shown in table 1 above, the duty ratio (rotational speed) of the first suction fan 85a and the second suction fan 85c provided in the first air chamber 83 is set to be larger (higher) than the duty ratio (rotational speed) of the third suction fan 85b and the fourth suction fan 85d provided in the second air chamber 84.

This makes it possible to increase the negative pressure generated in the first air chamber 83 on the upstream side relative to the negative pressure generated in the second air chamber 84 on the downstream side. That is, the suction force of the conveyor belt 81 in the range corresponding to the upstream side first air chamber 83 can be made stronger than the suction force of the conveyor belt 81 in the range corresponding to the downstream side second air chamber 84.

Here, since the conveying belt 81 has high rigidity at the side of the printing medium P entering, the printing medium P warped with respect to the suction surface of the conveying belt 81 needs to be flatly sucked, and thus a stronger suction force is required.

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

On the other hand, since the sucked printing medium P is held only on the delivery side of the printing medium P on the conveying belt 81, a strong suction force is not required.

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 second air chamber 84 on the downstream side can be made lower than the negative pressure generated in the first air chamber 83 on the upstream side. That is, the suction force of the conveyor belt 81 in the range corresponding to the second air chamber 84 on the downstream side can be made weaker than the suction force of the conveyor belt 81 in the range corresponding to the first air chamber 83 on the upstream side.

Accordingly, the power consumption of the third suction fan 85b and the fourth suction fan 85d can be reduced on the delivery side of the conveyor belt 81, and the load on the conveyor motor 87 that drives the platen roller 82 can also be reduced, thereby further reducing the power consumption.

In addition, the duty ratios of the driving voltages of the first to fourth suction fans 85a to 85d are not limited to the values shown in table 1 above, and resonance can be further suppressed by setting the duty ratios shown in table 2 below. Each duty ratio of the driving voltage shown in table 2 below is a combination of duty ratios corresponding to the ratio of the rotational frequencies of the first to fourth suction fans 85a to 85d capable of further suppressing resonance. Specifically, the four rotational 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 of four frequencies corresponding to four musical intervals forming an incongruity.

It is found that when the frequencies of the dissonant sound are synthesized, resonance is suppressed, and the amplitude of the synthesized wave becomes small. Therefore, by setting the four rotational frequencies of the first to fourth suction fans 85a to 85d in the relationship of four frequencies corresponding to the four musical intervals forming dissonance as described above, the frequencies of the vibrations caused by the rotation of the first to fourth suction fans 85a to 85d can be set in the relationship of four frequencies of dissonance. That is, resonance of vibration caused by rotation of the first to fourth suction fans 85a to 85d can be suppressed. Further, any combination may be used as long as the relationship of the rotational frequencies (duty ratios) of the first to fourth suction fans 85a to 85d is a relationship in which resonance of vibration caused by the rotation of the first to fourth suction fans 85a to 85d is suppressed.

TABLE 2

	Duty cycle
		First suction fan	72％
Second suction fan	100％
		First-suction fan	50％
Fourth suction fan	36％

Fig. 6 is a diagram showing a resonance occurrence state in the case where the duty ratios of the drive voltages applied to the drive motors of the first to fourth suction fans 85a to 85d are controlled as shown in table 2 above. Graphs shown in a of fig. 7 to D of fig. 7 represent vibration cycles of the first to fourth suction fans 85a to 85D, and a graph shown in fig. 6 represents a synthesized waveform of the vibration cycles of the first to fourth suction fans 85a to 85D. As shown in fig. 6, when compared with the resonance occurrence state (see fig. 4) in the case where the duty ratio shown in table 1 is set, it is found that the portion where the amplitude of the composite wave exceeds 75% is further reduced, and resonance can be further suppressed. This can further suppress concentration unevenness.

In addition, when the duty ratios of the first to fourth suction fans 85a to 85d are set as shown in table 2 above, it is preferable that the duty ratios of the first and

second suction fans

85a and 85c provided in the first air chamber 83 are set to 100% and 72%, and the duty ratios of the third and

fourth suction fans

85b and 85d provided in the second air chamber 84 are set to 50% and 36%. This makes it possible to increase the negative pressure generated in the first air chamber 83 on the upstream side relative to the negative pressure generated in the second air chamber 84 on the downstream side.

In the case where the duty ratios of the first to fourth suction fans 85a to 85d are set as described above, and the suction amount of the downstream second air chamber 84 cannot be secured, 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 ratio of table 2, and the suction amount of the downstream second air chamber 84 can be secured.

In addition, in the inkjet printing apparatus 1 of the above embodiment, two air chambers of the first air chamber 83 and the second air chamber 84 are provided, but the present invention is not limited thereto, and 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 one air chamber, the negative pressure generated by the rotation of the first to fourth suction fans 85a to 85d is uniformly generated on the installation surface of the printing medium P on the conveyor belt 81, and the suction force is also uniform.

In the case of the configuration having one air chamber as shown in fig. 8, the control unit 70 preferably controls the average of the rotation speeds of the first to fourth suction fans 85a to 85d to be close to the same rotation speed so as to obtain the same suction force as that generated when all the rotation speeds of the first to fourth suction fans 85a to 85d are set to the same rotation speed.

Thus, 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.

In the inkjet printing device 1 according to the above-described embodiment, the duty ratios (rotational speeds) are controlled in consideration of the resonance of the vibrations of the first to fourth suction fans 85a to 85d, but the duty ratios (rotational speeds) of the first to fourth suction fans 85a to 85d may be set in consideration of the vibrations caused by the rotation of the conveyance motor 87 that drives the platen roller 82. That is, the duty ratios (rotational speeds) of the first to fourth suction fans 85a to 85d may be set so as to suppress resonance of vibration of the conveyance motor 87 and vibration caused by rotation of the first to fourth suction fans 85a to 85 d. This can suppress density unevenness caused by resonance of vibration of the conveyance motor 87 and vibration of the first to fourth suction fans 85a to 85d, and can further improve print quality. Hereinafter, resonance between vibration of the suction fan and vibration of the conveyance motor of the platen roller will be described.

Fig. 9 is a graph showing changes in uneven intervals corresponding to changes in the rotational speed of the suction fan, and the graph shows the conveyance speed of the conveyance motor for each platen roller (hereinafter, simply referred to as conveyance speed). The horizontal axis of the graph shown in fig. 9 represents the rotation speed of the suction fan, and the vertical axis represents the variation of the uneven intervals. Further, as for the rotation speed of the suction fan, it is expressed by frequency (Hz). The graph a shown in FIG. 9 shows a case where the conveying speed is 700mm/s, the graph b shows a case where the conveying speed is 600mm/s, and the graph c shows a case where the conveying speed is 500 mm/s.

As shown in fig. 9, as the rotation speed of the suction fan is higher, the uneven intervals caused by the vibration due to the rotation are narrower. Further, the faster the conveying speed, the wider the uneven intervals caused by the vibration of the suction fan.

On the other hand, it is known that the uneven intervals caused by the vibration of the conveyance motor of the platen roller are determined by a mechanism such as the vibration generation cycle of the conveyance motor itself and the ratio of gears connected to the conveyance motor and the platen roller, and are fixed regardless of the speed change of the conveyance motor. Also, the interval of the vibration of the conveying motor is set to 6mm here.

In this case, the case where the vibration caused by the rotation of the suction fan and the vibration caused by the conveyance motor resonate refers to, for example, the case where the conveyance speed is 700mm/s, and the case where the duty ratio of the suction fan is 70%. That is, when the conveyance speed is 700mm/s, if the first to fourth suction fans 85a to 85d have a suction fan with a duty ratio of 70%, the vibration of the suction fan and the vibration of the conveyance motor 87 resonate, that is, the intervals between the unevenness of the suction fan and the intervals between the unevenness of the conveyance motor overlap each other, and the density unevenness increases. Similarly, when the transport speed is 600mm/s, if a suction fan with a duty ratio of 40% is present, the vibration of the suction fan and the vibration of the transport motor 87 resonate, and the density unevenness increases. When the conveyance speed is 500mm/s, if a suction fan with a duty ratio of 20% is present, the vibration of the suction fan and the vibration of the conveyance motor 87 resonate with each other, and the density unevenness increases.

That is, the relationship between the transport speed and the duty ratio of the suction fan to be avoided at the transport speed is shown in table 3 below.

TABLE 3

Therefore, if there is a duty ratio with respect to 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 can be corrected and set. Hereinafter, the duty ratio of the suction fan is corrected in detail.

Fig. 10 shows an example of a table in which the duty ratios are set so that the rotational frequencies of the first to fourth suction fans 85a to 85d have the relationship of the dissonant frequencies 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 the average value thereof approaches the set value of the table.

The set values in the table shown in fig. 10 are values appropriately set according to the suction force required by the conveying belt 81, and are set according to the type of the printing medium P, for example. The setting values are set and input on the operation panel 71 by the user, for example. The average value of the table shown in fig. 10 represents an actual average value when the duty ratios of the first to fourth suction fans 85a to 85d are calculated as described above.

For example, when the set value is 20%, the four duty ratios calculated so as to have a relationship of frequencies of dissonance are 24%, 33%, 17%, and 12%, and the average value thereof is about 22%. In this case, when the four duty ratios are compared with the duty ratio to be avoided shown in table 3 above, the difference between the duty ratios 24% and 17% of the four duty ratios and the duty ratio to be avoided 20% corresponding to the conveyance speed 500mm/s in table 3 above is less than 5%.

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

When the difference between the duty ratio of the first to fourth suction fans 85a to 85d and the duty ratio to be avoided is less than 5%, the duty ratio may be changed by a method larger than or smaller than the duty ratio shown in fig. 10, but it is preferable 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%, the average value is larger than the set value, and therefore, it is preferable that the duty ratio be changed to be smaller than the duty ratio shown in fig. 10 as a method of changing the duty ratio. This enables the duty ratio to be changed so that the average value approaches the set value.

When the set value is 20% and the conveyance speed is set to 700mm/s or 600mm/s, the control unit 70 sets the duty ratios of the first to fourth suction fans 85a to 85d to the four duty ratios of the table shown in fig. 10.

For example, when the set value is 30%, the four duty ratios calculated so as to have a relationship of frequencies of dissonance are 36%, 50%, 25%, and 18%, and the average value thereof is about 32%. In this case, when the four duty ratios are compared with the duty ratio to be avoided shown in table 3 above, the difference between the duty ratio of 18% of the four duty ratios and the duty ratio of 20% to be avoided corresponding to the conveyance speed of table 3 above is less than 5%. The difference between the duty ratio of 36% and the duty ratio of 40% to be avoided, which corresponds to the conveyance speed of 600mm/s in table 3 above, is less than 5%.

Therefore, when the set value is set to 30% and the conveyance speed is set to 500mm/s, the control unit 70 changes the duty ratio of the fourth suction fan 85d to 18% to 15% so that the difference from the duty ratio to be avoided of 20% is 5% or more. When the set value is set to 30% and the transport speed is set to 600mm/s, the control unit 70 changes the duty ratio of the first suction fan 85a to 36% to 35% so that the difference from the duty ratio to be avoided, which is 40%, is 5% or more. When the set value is set to 30% and the transport speed is set to 700mm/s, the control unit 70 sets the duty ratios of the first to fourth suction fans 85a to 85d to the four duty ratios of the table shown in fig. 10.

For example, when the set value is 40%, the four duty ratios calculated so as to have a relationship of frequencies of dissonance are 48%, 67%, 33%, and 24%, and the average value thereof is about 43%. In this case, when the four duty ratios are compared with the duty ratio to be avoided shown in table 3 above, the difference between the duty ratio 24% of the four duty ratios and the duty ratio to be avoided 20% corresponding to the conveyance speed 500mm/s in table 3 above is less than 5%. The difference between the duty ratio 67% and the duty ratio 70% to be avoided, which corresponds to the conveyance speed 700mm/s in table 3 above, is less than 3%.

Therefore, when the set value is set to 40% and the transport speed is set to 500mm/s, the control unit 70 changes the duty ratio 24% of the fourth suction fan 85d to 15% so that the difference from the duty ratio 20% to be avoided is 5% or more. When the set value is set to 40% and the conveyance speed is set to 700mm/s, the duty ratio of the second suction fan 85c is changed from 67% to 65%, and the difference from the duty ratio to be avoided, which is 70%, is set to 5% or more. When the set value is set to 40% and the transport speed is set to 600mm/s, the control unit 70 sets the duty ratios of the first to fourth suction fans 85a to 85d to the four duty ratios of the table shown in fig. 10.

In addition, by the same idea, when the set values are 50%, 60%, 70%, and 80%, the control unit 70 sets the duty ratios of the first to fourth suction fans 85a to 85d by changing the duty ratios as shown in the column of the method of changing the table shown in fig. 10, and otherwise sets the four duty ratios of the table shown in fig. 10. When the set value is 80%, the average value is 78% and is smaller than the set value. Therefore, when the duty ratio of the third suction fan 85b is changed to 67%, the control unit 70 changes the duty ratio to 75% so that the average value approaches the set value, instead of 65%.

When the duty ratios of the first to fourth suction fans 85a to 85d are set based on the table shown in fig. 10, the number of air chambers may be two or one as described above.

Further, 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, but the present invention is not limited to this, and for example, as shown in fig. 11, three air chambers of the first air chamber 90, the second air chamber 91, and the third air chamber 92 may be provided in parallel in a direction orthogonal to the conveyance direction of the printing medium P.

In this case, the first suction fan 93a and the second suction fan 93b may be provided in the first air chamber 90, the third suction fan 93c and the fourth suction fan 93d may be provided in the second air chamber 91, and the fifth suction fan 93e and the sixth suction fan 93f may be provided in the third air chamber 92. The duty ratio may be set so that the rotational frequencies of the first to sixth suction fans 93a to 93f are in a relationship of frequencies that are not harmonious.

In addition, as shown in fig. 11, when three air chambers of the first air chamber 90, the second air chamber 91, and the third air chamber 92 are provided, the duty ratios of the first to sixth suction fans 93a to 93f are preferably set so 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 second air chamber 91 in the center. This can suppress the warpage of the end portions on both sides extending in the transport direction of the print medium P, prevent the jam of the print medium P due to the warpage, and suppress the degradation of the print quality.

In the inkjet printing apparatus 1 according to the above-described embodiment, when the rotation speeds of the plurality of suction fans are set, it is preferable to actually check the intensity of the influence on the printed matter in a state where the suction fans are individually stopped in advance, check the intensity of the vibration of each suction fan, and set the rotation speed of the suction fan having a large vibration to a value lower than the average value of the rotation speeds of all the suction fans. This can effectively suppress vibration caused by rotation of the suction fan.

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

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

Next, the control unit 70 sets the duty ratio of the drive voltage for the first to fourth suction fans 85a to 85d to the above-described duty ratio (S14).

Next, the control unit 70 applies the driving voltage of the duty ratio set in S14 to the driving 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 portion 70 starts the paper feeding operation of the printing medium P (S18).

The following remarks are also disclosed with respect to the suction fan control device of the present invention. (supplementary note).

The suction fan control device of the present invention may include a transport unit configured to suck and transport the printing medium, and the suction unit may generate a negative pressure for sucking the printing medium to the transport unit.

In the suction fan control device according to the present invention, the suction unit may include air chambers that generate negative pressure by rotation of the suction fan on the upstream side and the downstream side in the conveyance direction of the print medium, respectively, and the control unit may increase the rotation speed of the suction fan that generates negative pressure in the air chamber on the upstream side to be higher than the rotation speed of the suction fan that generates negative pressure in the air chamber on the downstream side.

In the suction fan control device according to the present invention, the suction unit may have one air chamber in which negative pressure is generated by rotation of the plurality of suction fans, and the control unit may control an average of the rotation speeds of the plurality of suction fans to be close to the same rotation speed so that the same suction force as that generated when the rotation speeds of the plurality of suction fans are all set to the same rotation speed can be obtained.

In the suction fan control device according to the present invention, the control unit may set the rotation speeds of the plurality of suction fans based on the conveyance speed of the print medium.

In the suction fan control device according to the present invention, the control unit may set the rotation frequencies of the plurality of suction fans to frequencies corresponding to a plurality of musical intervals forming an incongruity.

Claims

1. A suction fan control device is characterized in that,

the suction fan control device is provided with:

a suction section having a plurality of suction fans that generate negative pressure for adsorbing the printing medium; and

a control part which controls the suction fan,

the control unit controls the rotation speeds of the plurality of suction fans to be different from each other and to be rotation speeds that suppress resonance of vibration caused by rotation of the plurality of suction fans.

2. The suction fan control device according to claim 1,

the suction fan control device is provided with a conveying part for adsorbing and conveying the printing medium,

the suction unit generates negative pressure for causing the printing medium to be attracted to the transport unit.

3. The suction fan control device according to claim 1 or 2,

the suction part has air chambers generating negative pressure by rotation of the suction fan at upstream and downstream sides of the printing medium in a conveying direction,

the control unit sets the rotation speed of the suction fan that generates negative pressure in the upstream side air chamber to be higher than the rotation speed of the suction fan that generates negative pressure in the downstream side air chamber.

4. The suction fan control device according to claim 1 or 2,

the suction part has one air chamber generating a negative pressure by the rotation of the plurality of suction fans,

the control unit controls the average of the rotation speeds of the plurality of suction fans to be close to the same rotation speed in order to obtain the same suction force as that generated when the rotation speeds of all the plurality of suction fans are set to the same rotation speed.

5. The suction fan control device according to any one of claims 1 to 4,

the control unit sets the rotation speeds of the plurality of suction fans based on the conveyance speed of the printing medium.