CN111421962A

CN111421962A - Printing apparatus and meandering amount detection method

Info

Publication number: CN111421962A
Application number: CN202010000333.XA
Authority: CN
Inventors: 驹田直也
Original assignee: Konica Minolta Inc
Current assignee: Konica Minolta Inc
Priority date: 2019-01-09
Filing date: 2020-01-02
Publication date: 2020-07-17
Also published as: EP3680107A1; JP7185827B2; JP2020111406A

Abstract

The invention provides a printing device and a meandering amount detection method, which can accurately detect and respond to the meandering amount of a conveyer belt with unevenness at the end even if the conveying speed is changed. While counting pulses of a rotary encoder (25) and measuring the movement amount of a conveyor belt (13), the displacement amount of the end position of the conveyor belt (13) in the belt width direction is measured by displacement sensors (23) arranged at a plurality of measurement points separated in the conveying direction. At this time, the amount of displacement of the same portion of the conveyor belt is measured at each measurement point based on the measured amount of movement and the known distance between the measurement points. Then, the meandering amount of the conveyor belt at the other measurement point with respect to the one measurement point is obtained by obtaining a difference between the displacement amounts of the same portion measured at the one measurement point and the other measurement points, and the printing position of the image is shifted in each of the print heads (PU 1-6) so as to cancel the meandering amount.

Description

Printing apparatus and meandering amount detection method

Technical Field

The present invention relates to a printing apparatus and a meandering amount detection method for generating an image on a recording medium conveyed by a conveyor belt.

Background

As an example of a printing apparatus that conveys a recording medium around an endless conveyor belt mounted on a plurality of rollers and forms an image on the conveyed recording medium, there is a color inkjet printer. In a color ink jet printer, a plurality of print head units of different colors are arranged at predetermined intervals in the transport direction of a transport belt, and ink droplets of different colors ejected from the respective print units are superimposed on a recording medium transported by the transport belt to form a color image.

In this printing apparatus, when a transport belt that transports a recording medium meanders in a direction perpendicular to the transport direction of the transport belt (referred to as a belt width direction), the landing positions of the ink droplets of the respective colors on the recording medium are shifted from the original positions, and color shifts occur.

As a method for dealing with this problem, the following control is performed: the end position of the conveyor belt in the width direction is measured by a sensor, and the variation in the measured value is regarded as a meandering amount, and the printing position of the image is shifted to cancel the meandering amount.

However, if the end of the conveyor belt is rough, the amount of fluctuation of the end position measured by the sensor includes the influence of the roughness of the end of the belt, and the amount of meandering cannot be accurately measured and corrected.

For example, in an ink jet textile printing machine that transports cloth, since a large-sized conveyor having a circumferential length of a conveyor belt of up to 20 meters is used, assembly of the conveyor is generally performed at an installation site. In detail, the following operations are performed at the installation site: after the conveyor belt is fitted over the conveyor rollers and adjusted in length, the ends in the longitudinal direction are welded to each other to form a loop, and then the both ends in the width direction of the conveyor belt are cut according to the size of the conveyor rollers. Further, belt guides such as metal plates are brought into contact with both sides of the conveyor belt in the width direction to prevent the conveyor belt from meandering beyond a certain range and separating from the conveyor rollers.

By cutting at the site of the setup, the end of the conveyor belt can become "rough" rather than smooth. Further, the rough and meandering state of the end portion of the conveyor belt gradually changes due to the installation of the belt guide, and therefore, it is also difficult to cope with the side surface.

Patent document 1 listed below discloses an image forming apparatus that measures the amount of meandering of a conveyor belt having rough ends. In this apparatus, belt position detecting means for detecting the position of a belt end in a direction perpendicular to the belt conveying direction is provided at a plurality of different positions in the belt conveying direction, the same position of the belt is detected by the plurality of belt position detecting means for detecting the position of the belt end in the direction perpendicular to the belt conveying direction, and the difference between the detected values is obtained, so that the influence of the unevenness of the end is cancelled. Then, the difference values are sequentially added to calculate the amount of belt fluctuation in the direction perpendicular to the belt conveying direction.

Prior art documents

Patent document

Patent document 1: japanese patent laid-open No. 2007-114240

In the device disclosed in patent document 1, the displacement of the end of the tape is measured at regular sampling intervals from the detection mark. Therefore, when the traveling speed of the belt greatly changes, the phase between data measured by a plurality of belt position detection units arranged and the measurement location with respect to the belt position are shifted, and even if a difference is obtained, the influence of the unevenness at the belt end cannot be accurately removed.

For example, in the inkjet textile printing printer, the transport speed may be greatly changed during printing by a user operation while checking the printing result and the state of the cloth (whether or not the cloth is bent) or checking the states of the unwinder, winder, and dryer. Therefore, the meandering of the belt cannot be accurately measured by the method of patent document 1 in which detection is performed at a constant sampling interval.

Disclosure of Invention

The present invention has been made to solve the above-described problems, and an object thereof is to provide a printing apparatus and a meandering amount detection method capable of accurately detecting and responding to a meandering amount of a conveyance belt having irregularities at an end portion even when a conveyance speed is changed.

The gist of the present invention for achieving the object is as follows.

[1] A printing apparatus, comprising:

a conveying section for conveying a recording medium by circulating an endless conveyor belt mounted on a plurality of rollers;

a printing section that forms an image on the recording medium conveyed by the conveying section;

a movement amount measuring unit that measures a movement amount of the conveyor belt in a conveying direction;

a plurality of displacement sensors that are disposed at a plurality of measurement points separated in a conveying direction of the conveyor belt and that measure displacement amounts of end portions of the conveyor belt in a belt width direction perpendicular to the conveying direction;

a displacement amount measuring unit that measures the displacement amount of the same portion of the conveyor belt using a displacement sensor of one measuring point and a displacement sensor of another measuring point, based on the movement amount measured by the movement amount measuring unit and a known distance between the measuring points; and

and a meandering amount calculation unit that obtains a meandering amount of the conveyor belt at the other measurement point with respect to the one measurement point by obtaining a difference between the displacement amounts at the same portion measured by the displacement amount measurement unit at the one measurement point and the other measurement point.

In the above invention, the displacement amount of the same portion as the portion at which the displacement amount of the end portion of the conveyor belt is measured by the displacement sensor of one measurement point of the conveyor belt is measured by the displacement sensor of the other measurement point based on the measured movement amount and the known distance between the measurement points, and the meandering amount of the conveyor belt at the other measurement point with respect to the one measurement point is obtained by obtaining a difference between the displacement amounts of the same portion measured at the one measurement point and the other measurement points. Since the same portion is recognized based on the actual moving amount of the conveyor belt, the meandering amount can be obtained from the difference in the displacement amounts obtained by measuring the same portion without being affected by the variation in the conveying speed of the conveyor belt.

[2] The printing apparatus according to [1], wherein the movement amount measuring unit measures the movement amount based on an output pulse of a rotary encoder attached to a shaft of the roller.

In the above invention, the moving amount of the conveyor belt can be accurately obtained in real time.

[3] The printing apparatus according to [1] or [2],

a mark indicating an origin position in one turn of the conveyor belt is marked on the conveyor belt in advance,

the printing device has an origin detecting section for detecting the mark,

the displacement amount measuring section measures the displacement amount at each position in the conveying direction of the conveying belt with reference to the mark,

the meandering amount calculation unit obtains the meandering amount at each position in the conveying direction of the conveyor belt based on the mark.

In the above invention, the absolute position of the conveyor belt can be recognized by detecting the mark of the origin position, and the displacement amount and the meandering amount can be measured. The meandering amount can also be corrected by using the data of the previous turn with reference to the origin position.

[4] The printing apparatus according to any one of [1] to [3], wherein,

the printing section includes a plurality of printing units which are disposed apart from each other in a conveying direction of the conveyor belt and print images with different colors,

the displacement sensor is disposed corresponding to the printing unit.

In the above invention, the displacement sensor is disposed for each printing unit so as to correspond to the printing unit. Suitable for finding the amount of meandering at the position of each printing unit.

[5] The printing apparatus according to any one of [1] to [4], wherein,

the printing apparatus further includes a print control unit that changes a print position of the image printed by the printing unit in the width direction of the conveyor belt so as to cancel out the meandering amount at the position of the printing unit, based on the meandering amount obtained by the meandering amount calculation unit.

In the above invention, the printing position of the image is adjusted so as to cancel out the meandering amount.

[6] The printing apparatus according to [5], wherein the print control section performs the change in accordance with the meandering amount measured in the previous turn.

[7] The printing apparatus according to any one of [1] to [6], wherein the meandering amount calculation unit estimates a meandering amount at a position other than the measurement point by interpolation processing based on meandering amounts at a plurality of measurement points.

In the above invention, even when the displacement sensor cannot be set at the ideal position (for example, the center position in the conveyance direction of each printing unit) due to mechanical restrictions, the meandering amount at the ideal position can be obtained.

[8] The printing apparatus according to any one of [1] to [7], wherein the displacement sensors are provided at both ends of the conveyor belt in a width direction.

In the above invention, the correction can be performed in consideration of the expansion and contraction in the width direction of the conveyor belt.

[9] A meandering amount detection method for detecting a meandering amount of an endless conveyor belt mounted on a plurality of rollers, the meandering amount detection method comprising:

a measuring step of measuring a movement amount of the conveyor belt in a conveying direction and measuring a displacement amount of an end of the conveyor belt in a belt width direction perpendicular to the conveying direction by using displacement sensors arranged at a plurality of measurement points separated in the conveying direction of the conveyor belt; and

a meandering amount calculation step of deriving a meandering amount of the conveyor belt from the displacement amount measured in the measurement step,

in the measuring step, the amount of displacement at the same portion of the conveyor belt is measured using the displacement sensor of one measuring point and the displacement sensors of the other measuring points, based on the measured amount of displacement and the known distance between the measuring points,

in the meandering amount calculation step, the meandering amount of the conveyor belt at the other measurement point with respect to the one measurement point is obtained by obtaining a difference between the displacement amounts at the same portion measured at the one measurement point and the other measurement point.

The invention has the following beneficial effects:

according to the printing apparatus and the meandering amount detection method of the present invention, even if the conveyance speed is changed, the meandering amount of the conveyance belt having the unevenness at the end portion can be accurately detected and dealt with.

Drawings

Fig. 1 is a diagram showing a schematic configuration of a printing apparatus according to an embodiment of the present invention.

Fig. 2 is a plan view of a printing apparatus according to an embodiment of the present invention and a side view of a belt portion.

Fig. 3 is a diagram showing the displacement sensor and its mounting state.

Fig. 4 is a diagram illustrating a nozzle surface of the carriage of the printing unit PU.

Fig. 5 is a block diagram showing an electrical configuration of the printing apparatus.

Fig. 6 is a diagram showing an example of displacement amount data measured at the PU1s position and the PU4s position.

Fig. 7 is a diagram showing an example of the amount of belt meandering at the PU1s position relative to the PU4s position.

Fig. 8 is a diagram showing the positional relationship between the origin detection sensor and the displacement sensors PU1s and PU4s and the numbers assigned to the respective sections obtained by dividing the circumferential length of the conveyor belt.

Fig. 9 is a diagram showing a measurement process of the amount of meandering in time series.

Fig. 10 is a diagram showing a continuation of fig. 9.

Fig. 11 is a diagram showing a continuation of fig. 10.

Fig. 12 is a flowchart showing a process in which the printing apparatus obtains the meandering amount and performs printing while correcting the meandering amount.

Fig. 13 is a plan view showing a conveying section of the printing apparatus in which displacement sensors are arranged along both left and right end portions of the conveyor belt.

Fig. 14 is an explanatory view showing a state in which the conveyor belt stretches and contracts in the width direction.

Detailed Description

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Fig. 1 is a diagram showing a schematic configuration of a printing apparatus 5 according to an embodiment of the present invention. The printing apparatus 5 is an ink jet printer that ejects ink droplets from a printing unit (print unit) PU and records an image on a recording medium 2 such as a cloth. The printing apparatus 5 includes a transport unit that transports the recording medium 2 by circulating an endless transport belt 13 that is looped around a drive roller 11 and a driven roller 12, and a printing unit PU as a printing unit that ejects ink toward the recording medium 2 transported by the transport belt 13 to print an image, and forms (prints) a desired image on the recording medium 2 by ejecting ink from each printing unit PU toward the transported recording medium 2.

In the printing apparatus 5 shown in fig. 1, six printing units PU1 to PU6 for printing images of different colors are arranged along the conveyor belt 13 from the upstream side to the downstream side in the conveying direction in which the recording medium 2 is conveyed by the conveyor belt 13. As shown in fig. 2, the printing apparatus 5 can mount a maximum of eight printing units PU. The number of the printing units PU may be arbitrary, and is not limited to the above number.

The recording medium 2 is in a rolled or folded state, and is fed from an unwinder, not shown, to the upstream end of the conveyor belt 13. Pressing rollers 14 are provided at the upstream end and the downstream end of the conveyor belt 13, respectively, and the pressing rollers 14 press the recording medium 2 against the belt surface of the conveyor belt 13 (see fig. 1). The recording medium 2 is pressed against the belt surface of the conveying belt 13 by these pressing rollers 14, and is conveyed while moving together with the conveying belt 13. The recording medium 2 is separated from the transport belt 13 at a position passing through the pressing roller 14 on the downstream end side, and is wound on a winding machine, not shown.

The printing unit 5 is a large-sized unit having a circumferential length of about 28m of the conveyor belt 13. The following operations are carried out at the setting site: after the conveying belt 13 is fitted over the driving roller 11 and the driven roller 12 and adjusted in length, ends in the longitudinal direction are welded to each other to form a loop, and then both ends in the width direction of the conveying belt 13 are cut to a desired size. Since the cutting is performed on site in this manner, the end portion of the conveyor belt 13 in the belt width direction is rough and not smooth.

The printing apparatus 5 has belt guides 15, 16 in the vicinity of the upstream end and the downstream end of the conveying belt 13, and the belt guides 15, 16 contact the left and right ends of the conveying belt 13 from the sides to prevent the conveying belt 13 from being detached from the driving roller 11 or the driven roller 12. The tape guides 15, 16 are made of a metal plate or the like. The downstream belt guide 15 is located slightly upstream of the drive roller 11, and abuts both ends of the conveying belt 13 on the outward path side from the driven roller 12 toward the drive roller 11. The upstream belt guide 16 is located slightly downstream of the driven roller 12, and abuts both ends of the conveyor belt 13 on the return side from the drive roller 11 to the driven roller 12.

The shape of the end of the conveyor belt 13 changes due to contact between the downstream-side belt guide 15 and the upstream-side belt guide 16, but does not deform until the end reaches the downstream-side belt guide 15 after passing through the upstream-side belt guide 16.

The conveyor belt 13 is provided with an origin mark G indicating the origin of one belt turn at a position near one end. Here, the origin mark G is a small-diameter hole formed in the conveyor belt 13. The origin mark G is not limited to a hole. An origin detection sensor 21 for detecting the origin mark G is provided slightly downstream of the most downstream printing unit PU.

Further, displacement sensors 23 are provided at a plurality of measurement points separated in the conveying direction of the conveying belt 13, and the displacement sensors 23 measure the amount of displacement of the end of the conveying belt 13 in the belt width direction perpendicular to the conveying direction. The positions and distances of the respective measurement points are known in the printing apparatus 5 by measuring the positions and distances between the measurement points after the setting and inputting the measured positions and distances to the printing apparatus 5.

Here, the displacement sensors 23 are disposed at positions corresponding to the respective printing units PU1 to PU 6. In detail, the displacement sensor 23 is provided at the conveyance direction center position of the corresponding printing unit PU along the end of the conveyance belt 13. Subsequently, the displacement sensors 23 arranged at positions corresponding to the printing units PU1 to PU6 are marked with s at the end of the mark PU of the printing unit to mark the displacement sensors PU1s to PU6 s.

The printing units PU are disposed at equal intervals in the conveyance direction, and the displacement sensors 23(PU1s to PU6s) are disposed at equal intervals in the conveyance direction in accordance with this. Of the measurement points, the measurement point corresponding to the printing unit PU1 is referred to as a reference point.

The rotation of the motor is transmitted to the drive roller 11 via a belt or the like and rotated. A rotary encoder 25 is attached to the shaft of the drive roller 11.

The rotary encoder 25 includes a disk having an outer periphery formed with a plurality of slits at equal angular intervals and concentrically mounted on the drive roller 11, and a detection unit fixedly provided in the vicinity of the outer periphery of the disk and detecting passage of the slits of the rotating disk. The detection unit outputs pulse signals (a-phase signal and B-phase signal) each time the passage of the slit is detected. The rotary encoder 25 outputs, for example, 4096 times a-phase pulse signals during one rotation of the drive roller 11. By counting the pulse signals, the movement amount (conveyance distance) of the conveyor belt 13 can be recognized accurately and in real time. The amount of movement of the conveyor belt 13 may be measured by a device other than the rotary encoder 25, for example, a laser doppler meter.

Fig. 3 shows an example of the displacement sensor 23. Here, as the displacement sensor 23, a transmission type laser displacement sensor is used. The displacement sensor 23 is mounted on a conveyor side frame 27 extending along the end of the conveyor belt 13.

The transmission type laser displacement sensor includes a light projecting section 23a and a light receiving section 23b, in which the light projecting section 23a emits band-shaped laser light of a predetermined width that is made parallel by a lens, and the light receiving section 23b receives the laser light emitted from the light projecting section 23a by a line CCD. The light receiver 23b is disposed opposite to the light emitter 23a with a predetermined distance from the light emitter 23 a. Each displacement sensor (transmission type laser displacement sensor) 23 is provided along the end of the conveying belt 13: the conveyor belt 13 blocks a part of the band-shaped laser beam emitted from the light emitter 23a between the light emitter 23a and the light receiver 23 b. The displacement sensor (transmission type laser displacement sensor) 23 detects the position of the end of the conveyor belt 13 in the width direction by detecting the position of the shadow caused by the conveyor belt 13 blocking the laser beam by the light receiving unit 23 b.

Fig. 4 is a diagram illustrating the front surface (nozzle surface) of the carriage 31 of the printing unit PU.

The carriage 31 is a frame member for holding the plurality of recording heads 32 in an accurate positional relationship, and is formed of a metal plate or the like having high rigidity. The carriage 31 has a plurality of recording heads 32 arranged in a staggered manner in the main scanning direction, and the plurality of recording heads 32 share the printing range of one line in the width direction (main scanning direction) of the conveyor belt 13. Each recording head 32 ejects an ink droplet from the ink ejection port 33 in accordance with an input drive signal. The print unit PU incorporates a carriage 31 on which a plurality of recording heads 32 are mounted, and a head drive circuit 43 described later.

When the displacement sensor 23 is disposed in correspondence with the printing unit PU, the displacement sensor may be in a range that converges in the thickness of the printing unit PU in the conveyance direction, and preferably, may be in the center position of the thickness. As shown in fig. 4, when a plurality of nozzle rows exist in one printing unit PU, the center positions of the plurality of nozzle rows are preferable. In addition, when the interpolation process described later is performed, even if the interpolation process is arranged at a position deviated from the ideal center position, the meandering amount at the ideal center position can be estimated.

Fig. 5 is a block diagram showing an electrical configuration of the printing apparatus 5. The printing device 5 includes a conveyance control unit 41 that controls conveyance by the conveyance unit, a print data generation unit 42, a head drive circuit 43 in the printing unit PU, a meandering correction control board 50, and the like.

The conveyance control section 41 controls the driving of the motor that drives the drive roller 11, thereby controlling the conveyance of the conveyance belt 13. The print data generation unit 42 performs RIP processing or the like on the basis of a print job received from an external device, generates print data corresponding to an image to be printed, and outputs the print data to the head drive circuit 43 in the print unit PU. The head drive circuit 43 generates a drive signal in accordance with the print data input from the print data generation section 42, and outputs the drive signal to the corresponding recording head 32.

The meandering correction control board 50 functions to perform control and calculation for detecting the measurement of the meandering amount of the conveyor belt 13, and to output meandering information indicating the detected meandering amount to the head drive circuit 43 of each print unit PU.

The meandering correction control board 50 includes a CPU (Central Processing Unit) 51, a ROM (Read Only Memory) 52, a RAM (Random Access Memory) 53, a meandering information output Unit 54, an I/O input Unit 55, an encoder input Unit 56, an ADC (Analog-to-digital converter) 57, and the like, which are connected to a bus.

The I/O input unit 55 receives a detection signal from the origin detection sensor 21, and the encoder input unit 56 receives an output signal from the rotary encoder 25. The output of each displacement sensor 23 is input to the ADC 57.

The CPU51 executes programs stored in the ROM 52, and the RAM 53 temporarily stores various data when the CPU51 executes the programs. The CPU51 functions as the movement amount measuring unit 61, the displacement amount measuring unit 62, and the meandering amount calculating unit 63 by executing programs.

The movement amount measuring unit 61 continuously measures the movement amount of the conveyor belt 13 in the conveying direction. Here, by counting the pulse signal output from the rotary encoder 25 with reference to the time point at which the origin detection sensor 21 detects the origin mark G, the moving amount (conveying distance) of the conveyor belt 13 from the time point at which the origin mark G reaches the origin detection sensor 21 is measured in real time. Since the moving amount of each pulse is a fixed value fixed in the apparatus and is known, the moving amount (conveying distance) can be accurately obtained in real time from the count value of the pulse signal output from the rotary encoder 25.

The displacement amount measuring unit 62 functions as follows: the displacement amount of the end of the conveyor belt 13 in the belt width direction perpendicular to the conveying direction is measured by the displacement sensor 23 of one measurement point, and the displacement amount of the conveyor belt 13 at the same position as the position at which the displacement amount is measured by the displacement sensor 23 of one measurement point is measured by the displacement sensors 23 of the other measurement points on the basis of the known distance between the movement amount measured by the movement amount measuring section 61 and the measurement point, and the measurement data is recorded.

For example, the displacement amount measuring unit 62 measures the displacement amount at the output timing of the pulse signal by each displacement sensor 23 for each pulse signal output from the rotary encoder 25, and records the displacement amount measured by each displacement sensor 23 in the RAM 53 in association with the movement amount (conveying distance) of the conveying belt at that time measured by the movement amount measuring unit 61.

The distance between the measurement points is set to be an integral multiple of the conveyance distance in the measurement cycle of the displacement amount (in this example, the conveyance distance per one pulse of the rotary encoder 25). Thereby, the same portion in the conveying direction of the conveyor belt 13 is measured by the displacement sensor 23 at each measurement point.

The measurement cycle of the displacement amount may be any cycle as long as the integral multiple of the conveyance distance in the measurement cycle is a value that can be the distance between the measurement points. For example, the measurement period may be set to a conveyance distance corresponding to a pixel pitch in the conveyance direction.

The snake movement amount calculation unit 63 performs the following calculation: the snake movement amount of the conveyor belt 13 at the other measurement point with respect to the one measurement point is obtained by obtaining the difference between the displacement amounts of the same portion measured and recorded at the one measurement point and the other measurement point by the displacement amount measuring unit 62.

Fig. 6 shows an example of measurement data recorded by the displacement amount measuring unit 62. The upper graph a in the figure is a graph of measurement data obtained by recording the displacement amount measured by the displacement sensor 23(PU1s) disposed at the position corresponding to the printing unit PU1 in association with the movement amount (conveyance distance) of the conveyance belt 13 from the detection of the origin mark G by the origin detection sensor 21. The vertical axis represents the displacement amount, and the horizontal axis represents the movement amount (conveyance distance) after the origin mark G is detected. The graph B on the lower side in the figure is a graph corresponding to measurement data obtained by recording the displacement amount measured by the displacement sensor 23(PU4s) disposed at the position corresponding to the printing unit PU4 in association with the movement amount (conveyance distance) of the conveyance belt 13 from the detection of the origin mark G by the origin detection sensor 21.

For example, assuming that the reference point is the position of PU4s and the measurement point is the position of PU1s located 3.14m upstream of the reference point, the amount of meandering of the conveyor belt 13 at the position of PU1s (the position of printing unit PU 1) relative to the position of PU4s (the position of printing unit PU 4) is determined by shifting the measurement data measured by PU4s by 3.14m (shifting the entire graph B by 3.14m to the left) and subtracting the measurement data of PU1s from the shifted measurement data of PU4 s.

In addition, by removing the DC component from the output signal of the displacement sensor 23, the displacement amount component of the end portion of the conveyor belt 13 can be extracted regardless of the absolute position of the displacement sensor 23. Therefore, it is not necessary to accurately set the relative mounting positions of the plurality of displacement sensors 23 on a straight line.

Fig. 7 shows a graph C taking the difference of graph B and graph a shifted to the left by 3.14 meters. Graph C shows the relationship between the movement amount (conveyance distance) of the conveyance belt 13 from the time point at which the origin mark G is detected by the origin detection sensor 21 and the meandering amount of the conveyance belt 13 at the position of the displacement sensor PU1s with respect to the position of the displacement sensor PU4 s.

The meandering correction control board 50 outputs data obtained by applying low-pass filtering to the data of the difference value to remove sharp noise (noise due to fluff at the end of the conveyor belt 13, vertical movement of the conveyor belt 13, vibration, or the like) to the head drive circuit 43 of the corresponding printing unit PU as meandering information. Here, by applying the low-pass filter, the meandering amount is rounded to about the pixel pitch in the main scanning direction. The reason why the pixel pitch is about the same is that the correction of the print position by the print control section 43a, which will be described later, cannot be made finer than the pixel pitch in the main scanning direction.

The print control unit 43a (see fig. 5) of the head drive circuit 43 of each print unit PU changes the print position of the image in the width direction (main scanning direction) of the conveyor belt 13 so as to cancel out the meandering amount (meandering amount with respect to the reference point) at the position of the print unit PU based on the meandering information input from the meandering correction control board 45. For example, when the reference point is the position of the printing unit PU4 and the amount of meandering at the position of the printing unit PU1 relative to the reference point at the predetermined position of the transport belt is a distance of three pixels toward the left end portion side of the transport belt 13, the image of the line printed when the predetermined position of the transport belt reaches the position of the printing unit PU1 is shifted by three pixels toward the left end portion side of the transport belt 13 and printed.

The meandering of the conveyor belt 13 repeats substantially the same change at a cycle of one turn of the conveyor belt 13. The amount of meandering gradually changes due to the fluctuation of the air temperature and the contact of the end of the conveyor belt 13 with the downstream-side belt guide 15 or the upstream-side belt guide 16, but the change occurs slowly and hardly changes from the previous turn.

On the other hand, the displacement amount of the end of the conveyor belt 13 is measured by the displacement sensor 23 provided at the position of the printing unit PU, and the meandering amount is calculated, thereby making it difficult to control the printing position shift in real time.

Therefore, in the present embodiment, the meandering correction control board 50 outputs the meandering information obtained by the measurement of the previous turn to the print control section 43a of the head drive circuit 43, and the print control section 43a corrects the print position based on the meandering information of the previous turn. By using the meandering information of the previous cycle in this way, it is possible to calculate the meandering amount and control the printing position shift with a sufficient time margin.

Further, by using the meandering information of the previous turn, the reference point can be set at an arbitrary position such as the center position in the conveying direction as the position corresponding to the printing unit PU 4. For example, even when the conveyor belt 13 is deflected to one direction monotonously from the upstream to the downstream, the correction of the printing position can be divided into ± two directions by setting the center position in the conveying direction as the reference point as the position of the printing unit PU4, and therefore, the correction of the meandering amount can be performed by a smaller correction amount regardless of which end portion side the conveyor belt is meandering as compared with the case where the reference point is set at the position of the printing unit PU which is the most upstream or the most downstream.

Next, the process of calculating the amount of meandering will be described more specifically.

Here, a case where the meandering amount of the conveyor belt 13 at the position of the displacement sensor PU1s with respect to the position of the displacement sensor PU4s is obtained is taken as an example. Assume that the displacement sensor PU1s is located at the position of the printing unit PU1, and the displacement sensor PU4s is located at the position of the printing unit PU 4.

In this example, the circumferential length of the conveyor belt 13 is divided into 14 sections, and the displacement sensors 23(PU1s, PU4s) and the origin detection sensor 21 are arranged in the positional relationship shown in fig. 8. In the figure, starting point positions of respective sections divided into 14 sections starting from the position of the origin mark G are denoted by numbers 0 to 13 on the conveyor belt 13. Fig. 9 to 11 show the measurement state in time series.

First, the measurement is started with the time when the origin detection sensor 21 detects the origin mark G as a reference for starting the measurement by each displacement sensor 23(PU1s, PU4s) (Q1 in fig. 9). Fig. 9 to 11 are graphs each showing a belt end position (displacement amount) measured by the displacement sensor 23(PU1s), a belt end position (displacement amount) measured by the displacement sensor 23(PU4s), and a belt meandering amount at the PU1s position with respect to the PU4s position. The vertical axis indicates the belt end position (displacement amount) or meandering amount, the horizontal axis indicates the position on the conveyor belt with the position of the origin mark G set to 0, and the numerical value on the horizontal axis corresponds to the number given when the circumferential length is divided into 14.

Since the positional relationship between the origin detection sensor 21 and each of the displacement sensors 23(PU1s, PU4s) is known, it is possible to grasp which position on the conveyor belt 13 PU1s, PU4s is measuring at the time when the origin detection sensor 21 detects the origin mark G. For example, at the start of the measurement, PU1s is located at position number 5, and PU4s is located at position number 3.

Fig. 9 (Q2) shows the measurement state at the time when 1 interval is conveyed from the start of measurement. The displacement sensor PU1s measures the belt end position (amount of displacement) from number 5 to number 6 of the conveyor belt 13, and the displacement sensor PU4s measures the belt end position (amount of displacement) from number 3 to number 4. Fig. 9 (Q3) shows the measurement state at the time when 2 intervals are conveyed from the start of measurement. The displacement sensor PU1s measures the belt end position (amount of displacement) from number 5 to number 7 from the start of measurement, and the displacement sensor PU4s measures the belt end position (amount of displacement) from number 3 to number 5.

Then, since the measurement data of PU1s and PU4s are complete for the same portion (portion No. 5 and thereafter) on the tape, the calculation for obtaining the snake row amount by obtaining the difference between the same portions is started. Fig. 10 (Q4) shows the measurement status and the amount of hunting of the calculation result at the time when 3 intervals are transmitted from the start of measurement. Since the measurement data of the same portion are already complete in the range from number 5 to number 6, the snake amount is calculated by obtaining the difference between the measurement data of PU1s and the measurement data of PU4 s.

Fig. 10 (Q5) shows the measurement status and the amount of hunting of the calculation result at the time when 13 intervals are transmitted from the start of measurement.

Fig. 10 (Q6) shows the measurement status and the amount of meandering of the calculation result at the time when 14 intervals are conveyed from the start of measurement (when one rotation is made). When the origin detection sensor 21 again detects the origin mark G and recognizes that the conveyor belt 13 makes one turn, the meandering correction control board 50 starts to feed back (output) meandering information to the head drive circuit 43. That is, since there is meandering amount data at the PU1s position relative to the PU4s position from the position of number 5, the timing at which the position of number 5 reaches the position of the printing unit PU1 (or slightly advanced in consideration of the processing time in the head driving circuit 43) starts outputting meandering information to the head driving circuit 43 of the printing unit PU 1.

The head drive circuit 43 of the print unit PU1 performs printing by shifting the image in the main scanning direction so as to cancel the meandering amount, based on the meandering information received from the meandering correction control board 50.

Then, as shown in (Q7) and (Q8) of fig. 11, the process is repeated while the tape end position (displacement amount) and the meandering amount are updated by the latest data rewriting.

In fig. 11 (Q7), in the calculation for obtaining the meandering amount by obtaining the difference between the belt end positions of numbers 3 to 5, the measurement data of the displacement sensor PU4s is the data of the second turn, whereas the measurement data of the displacement sensor PU1s is the data of the previous turn. Since the tape end does not contact the tape guides 15 and 16 from the upstream tape guide 16 to the downstream tape guide 15, it is considered that the shape of the tape end does not change if the data is of the same turn, but the shape of the tape end may change due to contact with the upstream tape guide 16 or the like if the data is of different turns. Therefore, the difference measurement value is preferably obtained in the same cycle.

Therefore, for example, it is sufficient to hold data of two rounds, update the latest data in sequence, and obtain the difference between the measurement data of the same round to obtain the hunting amount. Before printing, the conveyor belt 13 may be moved two or more times, the meandering amount may be determined from the measured values of the same rotation at all belt positions, and then actual printing may be started.

Fig. 12 is a flowchart showing a process of correcting the meandering amount and performing printing by the printing apparatus 5. For simplicity of explanation, the case where the meandering amount of the conveyor belt 13 at the position of PU1s with respect to the position of PU4s is obtained to correct the image data is shown in the same manner as in fig. 9 to 11. Assume that the displacement sensor PU1s is located at the position of the printing unit PU1, and the displacement sensor PU4s is located at the position of the printing unit PU 4. In addition, the same processing is actually performed for all of the print units PU1 to PU6 (except for PU4 when PU4 is the reference point).

It is assumed that the counter that counts the number of times of origin detection is reset to 0 in the initial state. First, the conveyor belt 13 is driven to start conveyance (step S101). If the conveyance (printing) is not completed (step S102; no), it is checked whether or not the origin detection sensor 21 detects the origin mark G (step S103). When the conveyance (printing) is finished (step S102; YES), the process is finished.

When the origin mark G is detected (step S103; yes), the positions on the belt (positions in the conveying direction with respect to the origin mark G) measured by the displacement sensors PU1S and PU4S are reset based on the known positional relationship between the origin detection sensor 21 and the displacement sensors PU1S and PU4 (step S104), the number of times of origin detection is increased by 1 (step S105), and the process proceeds to step S107.

When the origin detection sensor 21 does not detect the origin mark G (step S103; no), the position on the belt (position in the conveyance direction with respect to the origin mark G) measured by the displacement sensors PU1S and PU4S is updated by adding the conveyance distance from the detection of the origin mark G by the origin detection sensor 21 (distance obtained by counting the output pulses of the rotary encoder 25 from the time of the detection of the origin mark G) (step S106), and the process proceeds to step S107.

In step S107, the tape end position (displacement amount) detected by the displacement sensor PU1S is stored in association with the tape position of the displacement sensor PU1S, and the tape end position (displacement amount) detected by the displacement sensor PU4S is stored in association with the tape position of the displacement sensor PU 4S.

Then, it is checked whether the number of origin detections is less than a predetermined value (e.g., 2 or 3), and if so (step S108; NO), the process returns to step S102 to continue the processing.

When the number of origin detections is equal to or greater than the predetermined value (step S108; YES), the difference between the measured values (belt end positions (displacement amounts)) of PU1S and PU4S of the previous turn corresponding to the current belt position of the displacement sensor PU1S is obtained, and the belt meandering amount at the PU1S position with respect to the PU4S position is calculated (step S109). Then, the meandering amount obtained by applying the low-pass filter to the belt meandering amount (step S110) is output and fed back to the head drive circuit 43 of the print unit PU1 (step S111).

When printing is being executed (step S112; yes), the head drive circuit 43 displaces the image data in the main scanning direction (tape width direction) so as to cancel out the meandering amount (step S113), ejects ink from each recording head 32 based on the displaced image data, prints an image on the recording medium 2 (step S114), returns to step S102, and continues the processing.

If printing is not executed (step S112; NO), the process returns to step S102 without executing step S113 and step S114, and the process continues.

As described above, by actually measuring the movement amount (conveying distance) of the conveyor belt 13 in real time based on the output pulse of the rotary encoder 25, it is possible to recognize at which position in the conveying direction of the conveyor belt 13 the displacement sensor 23 at each measurement point is measuring the belt end position (displacement amount), and therefore, even if the conveying speed of the conveyor belt 13 varies, it is possible to obtain the difference between the measurement values at the same position on the conveyor belt 13 measured at each measurement point without being affected by the variation, and it is possible to obtain an accurate meandering amount and correct the meandering amount by canceling the meandering amount.

< interpolation processing >

The amount of meandering at a position other than the measurement point where the displacement sensor 23 is arranged is estimated by interpolation processing based on the amount of meandering at a plurality of measurement points. For example, when the displacement sensor 23 cannot be provided at the center position (ideal position) in the conveyance direction of each print unit PU due to mechanical restrictions, the displacement sensor 23 is provided at a position different from the ideal position (preferably, in the vicinity of the ideal position within a possible range), and the meandering amount at the ideal position is obtained by interpolation processing based on the meandering amounts measured by the plurality of displacement sensors 23. In the case where the displacement sensors 23 are arranged at positions deviated from the ideal positions, it is preferable that the displacement sensors 23 be equally deviated from the respective ideal positions. This makes it possible to perform the same interpolation processing, and the interpolation processing as a whole becomes easy.

For example, assuming that the distance from the reference point to the first measurement point is L1, the distance from the reference point to the second measurement point is L2, the distance from the reference point to the predetermined print unit PU (ideal position) is L3 (L1 < L3 < L2), the meandering amount at the first measurement point related to the same portion of the conveyor belt 13 is D1, and the meandering amount at the second measurement point is D2., the meandering amount Dx at the ideal position with respect to the reference point at the portion on the belt can be obtained by the following calculation.

Dx＝D1+(D2-D1)×(L3-L1)/(L2-L1)

The above operation is interpolation based on interpolation, but when interpolation based on extrapolation is performed, the meandering amount at a position downstream of the measurement point can be estimated, and therefore, the printing position can be corrected based on the estimated meandering amount of the current loop without using the meandering amount of the previous loop, and for example, when L1 < L2 < L3, it can be obtained by Dx ═ D2+ (D2-D1) × (L3-L1)/(L2-L1).

< measuring displacement amount at both right and left ends >)

In the above description, the displacement sensor 23 measures the displacement amount of one end of the conveyor belt 13 to obtain the meandering amount, but as shown in fig. 13, the displacement sensor 23 may be disposed along both ends of the conveyor belt 13.

When the circumferential length of the conveyor belt 13 is long, there is not only meandering but also the belt expands and contracts in the width direction as shown in fig. 14, and therefore the ink application position in the width direction (main scanning direction) of the belt may be shifted from the target position. If the displacement sensors 23 are arranged at both left and right ends of the conveyor belt 13, it is possible to detect and correct a change in the expansion and contraction of the conveyor belt 13 in the width direction.

For example, in the case where the meandering amount at the PU1 position relative to the PU4 position is +0.05mm at the right end and +0.03mm at the left end, the average +0.04 is regarded as the meandering amount and corrected.

While the embodiments of the present invention have been described above with reference to the drawings, the specific configurations are not limited to those shown in the embodiments, and modifications and additions that do not depart from the spirit and scope of the invention are also included in the present invention.

Although an inkjet printer is exemplified as the printing device 5 in the embodiment, an L ED printer or the like may be used as long as the recording medium 2 is conveyed by the conveyor belt 13.

Description of the symbols

2: recording medium

5: printing device

11: driving roller

12: driven roller

13: conveying belt

14: press roller

15: downstream side tape guide

16: upstream side tape guide

21: origin detection sensor

23. PU1 s-PU 6 s: displacement sensor

23 a: light projecting part

23 b: light receiving part

25: rotary encoder

27: conveyor side frame

31: sliding rack

32: recording head

33: ink jet nozzle

41: conveyance control unit

42: print data generating section

43: head drive circuit

43 a: print control unit

50: snake correction control substrate

51：CPU

52：ROM

53：RAM

54: snake information output unit

55: I/O input unit

56: encoder input unit

57：ADC

61: moving amount measuring unit

62: displacement measuring unit

63: snake amount calculation unit

G: origin mark

PU (polyurethane): a printing unit.

Claims

1. A printing apparatus, comprising:

and a meandering amount calculation unit that obtains a meandering amount of the conveyor belt at the other measurement point with respect to the one measurement point by obtaining a difference between the displacement amounts of the displacement amount measurement unit at the same portion measured at the one measurement point and the other measurement point.

2. Printing device according to claim 1,

the movement amount measuring section measures the movement amount from an output pulse of a rotary encoder attached to a shaft of the roller.

3. Printing device according to claim 1 or 2,

the printing apparatus has an origin detecting section for detecting the mark,

4. A printing device according to any one of claims 1 to 3,

the printing section has a plurality of printing units which are arranged apart from each other in a conveying direction of the conveying belt and print images with different colors,

the displacement sensor is disposed corresponding to the printing unit.

5. Printing device according to one of claims 1 to 4,

6. Printing device according to claim 5,

the print control section performs the change in accordance with the meandering amount measured in the previous turn.

7. Printing device according to one of claims 1 to 6,

the meandering amount calculation unit estimates a meandering amount at a position other than the measurement point by interpolation processing based on the meandering amounts at the plurality of measurement points.

8. Printing device according to one of claims 1 to 7,

the displacement sensors are provided at both ends of the conveyor belt in the width direction.

9. A meandering amount detection method for detecting a meandering amount of an endless conveyor belt mounted on a plurality of rollers, characterized by comprising:

10. The meandering amount detection method according to claim 9,

in the measuring step, the amount of movement is measured from an output pulse of a rotary encoder mounted on a shaft of the roller.

11. The meandering amount detection method according to claim 9 or 10,

marking a mark indicating an origin position in one turn of the conveyor belt on the conveyor belt,

the snake movement amount detection method has an origin detection step of detecting the marker,

in the displacement amount measuring step, the displacement amount at each position in the conveying direction of the conveying belt is measured with the mark as a reference,

in the snake movement amount calculating step, snake movement amounts at respective positions in the conveying direction of the conveyor are obtained based on the marks.

12. The meandering amount detection method according to any one of claims 9 to 11,

the meandering amount detection method includes a printing step of forming an image on a recording medium conveyed by the conveyor belt by a printing section,

the displacement sensor is disposed corresponding to the printing unit.

13. The method of detecting a meandering amount according to any one of claims 9 to 12,

the meandering amount detection method further includes a print control step of changing a print position of an image printed by the printing unit in the width direction of the conveyor belt so as to cancel out the meandering amount at the position of the printing unit, based on the meandering amount obtained in the meandering amount calculation step.

14. The method of detecting a meandering amount according to claim 10,

in the print control step, the change is performed based on the meandering amount measured in the previous cycle.

15. The method of detecting a meandering amount according to any one of claims 9 to 14,

in the hunting amount calculating step, the hunting amount at a position other than the measurement point is estimated by interpolation processing based on the hunting amounts at the plurality of measurement points.

16. The method of detecting a meandering amount according to any one of claims 9 to 15,