JP7215205B2 - Inkjet printer, ejection timing correction method and program for inkjet printer - Google Patents

Description

The present invention relates to an inkjet printer capable of correcting nozzle ejection timing, an ejection timing correction method for an inkjet printer, and a program.

In an inkjet printer that prints on media such as paper, the media is conveyed by a belt, and ink is ejected onto the media by synchronizing with pulse signals output from an encoder attached to the drive shaft that conveys the belt. doing the printing. FIG. 19 shows a simplified configuration of a general inkjet printer.
In the inkjet printer 1A, an endless transport belt 12 for transporting a medium is stretched over transport rollers 10 and 11, and an encoder 13 is attached to the belt drive shaft 10A to detect the rotation of the belt drive shaft 10A. . Color heads 15K (for black), 15C (cyan), 15M (magenta), and 15Y (yellow) are installed on the transport belt 12 at predetermined intervals. A line-shaped ejection head (not shown) is provided for each of the colors 15K, 15C, 15M, and 15Y. done. Encoder pulses output from the encoder 13 are used for ink ejection from the heads 15K, 15C, 15M, and 15Y of each color.

By the way, generally, the drive shaft and the encoder attached to the drive shaft have a fluctuation component called eccentric component synchronized with the rotation cycle due to mounting accuracy, memory accuracy, variation in the radius of the shaft, and the like. As means for suppressing color misregistration due to the eccentricity component, a method is known and used in which the amount of eccentricity is measured in advance, a correction table is created, and the pulse interval of the encoder is corrected according to the value of the correction table. there is

Furthermore, the thickness of the conveyor belt is not uniform, and errors in thickness are ubiquitous. Especially in the case of steel conveyor belts, the error is large due to the presence of joints.
If the thickness of the conveyor belt is not uniform, the radius of rotation at the joint with the drive shaft will vary, so the amount of belt movement per unit angular velocity will also vary, resulting in a discrepancy between the encoder pulse and the actual amount of movement. occurs. Normally, one rotation of the shaft and one rotation of the belt are asynchronous, so in order to make more accurate corrections, it is necessary to measure both the eccentricity component of the shaft and the fluctuation component of the belt thickness separately. Therefore, it is necessary not only to correct the eccentric component of the drive shaft, but also to obtain the profile of the fluctuation component for one rotation of the belt and correct it.
In other words, in order to perform eccentricity correction with high accuracy, two types of correction tables are required: the eccentricity correction table for the drive shaft and the correction table based on the profile of the entire belt. .

For example, Patent Document 1 proposes a technique of measuring the eccentric component of the drive shaft and the thickness variation of the belt with a displacement variation detector, determining the correction amount from the measurement results, and performing the correction.
Further, in Patent Document 2, there is a technique of measuring speed fluctuations with a laser Doppler, dividing the result into an eccentricity component of a drive shaft or a thickness fluctuation component of a belt from the result of Fourier transform, and setting a correction value in a corresponding correction table. Proposed.

JP 2008-44767 A JP 2011-68065 A

However, the method of Patent Document 1 cannot remove the eccentricity component due to the mounting error of the encoder and the error component of the encoder itself. Moreover, there is a problem that the displacement variation detector becomes expensive when trying to improve the accuracy.

The problem to be solved is to efficiently acquire two types of fluctuation components, ie, the eccentricity correction amount and the profile of the entire belt.
The difference between the encoder pulse and the actual amount of movement is mainly caused by the eccentric component of the drive shaft and the variation component of the thickness of the belt. In general, it is difficult to strictly synchronize one rotation of the belt and one rotation of the drive shaft (even if the ratio is set to be an integer ratio, the position will gradually shift due to a minute amount of misalignment). Ultimately, it will be treated as asynchronous.
Therefore, in order to create a correction table for correcting the movement amount deviation, it is necessary to separate the measured deviation amount into the eccentricity component of the shaft and the component due to the thickness variation of the belt and hold them as independent values.
In Patent Document 2, a laser Doppler sensor is used to measure the actual belt velocity, Fourier transform is performed to obtain frequency components, and the frequencies are separated into shaft components and belt components. However, this method has the disadvantage that it cannot be separated well when the ratio of the circumference of the belt and the circumference of the shaft is close to an integral multiple. There is a drawback that it is not possible to respond to changes over time because it is an adjustment of
There is also the idea of measuring in real time the amount of physical displacement that combines variations in the thickness of the belt and variations in the shaft diameter, and performing correction based on this, but in this case, the eccentricity component of the encoder itself, It has the disadvantages of being unable to handle error components and requiring high measurement accuracy.

SUMMARY OF THE INVENTION It is an object of the present invention to separately measure both the eccentric component of the drive shaft and the fluctuation of the belt stack without requiring a particularly expensive device. .

Among the inkjet printers of the present invention, the first mode determines based on an encoder pulse indicating the rotational position of a belt drive shaft from ejection nozzles of single or multiple colors of ink on a medium conveyed by an endless conveyor belt. An inkjet printer that prints on the medium by ejecting ink at a specified ejection timing,
a belt reference position detection unit that detects that the conveying belt has made one turn;
a drive shaft reference position detection unit that detects that the belt drive shaft has made one rotation;
a controller capable of setting the ejection timing between the encoder pulse signal and the ejection operation;
The control unit has at least a first correction function of correcting the ejection timing by a first correction table based on the signal from the belt reference position detection unit,
Further, the control unit uses the signal from the drive shaft reference position detection unit as a reference position, and uses heads with different ejection timings to determine the physical distance between the ejection nozzles of the head for N rotations of the belt drive shaft. N is an integer, and a plurality of test patterns are generated on the same medium at positions separated by N≧1), and based on the results of reading the test patterns, the variation in distance between the test patterns is obtained. and determining the first correction table by creating profile data for one rotation of the conveying belt.

According to another aspect of the inkjet invention, in the above aspect of the invention, the control unit corrects the ejection timing by using at least a second correction table based on the signal from the drive shaft reference position detection unit. having a second correction function,
Using the signal from the drive shaft reference position detection unit as a reference position, the control unit performs ejection at different ejection timings to form a plurality of ink droplets on the same medium at separated positions for at least one revolution of the belt drive shaft. A test pattern is generated, and based on the reading result of reading the test pattern, variation in distance between the test patterns is obtained, profile data for one rotation of the drive shaft is created, and the second correction table is determined. It is characterized by

In another aspect of the inkjet invention, in the above aspect of the invention, the control unit performs the test for the second correction table in a state in which a first correction function based on the first correction table is enabled. It is characterized by generating patterns.

According to another aspect of the inkjet invention, in the aspect of the invention described above, the control unit adjusts the second ink jet using the first correction table based on the content of the created profile data for one rotation of the drive shaft. It is characterized by obtaining a correction table.

According to another aspect of the inkjet invention, in the above aspect of the invention, the control unit corrects the ejection timing using the first correction table and the second correction table to execute printing of the job. characterized by

According to another aspect of the inkjet invention, in the above aspect of the invention, the control unit first determines either the first correction table or the second correction table.

According to another aspect of the inkjet invention, in the above aspect of the invention, the control unit determines a first correction table based on the signal from the belt reference position detection unit and the signal from the drive shaft reference position detection unit. Based on this, the timing of placing the medium on the conveying belt is controlled.

In another aspect of the inkjet invention, in the above aspect of the invention, the control unit determines the plurality of test patterns for determining the first correction table by ejection from the ejection nozzles of the same head. It is characterized in that the test pattern is generated for two or more rotations based on the signal from the detection unit, and the variation in the distance between the test patterns at relative positions separated by one rotation is obtained.

According to another aspect of the inkjet invention, in the above aspect of the invention, the control unit simultaneously performs profile data creation by creating the test pattern and measurement with a laser Doppler sensor, and the measurement result with the laser Doppler sensor is obtained as follows. It is separated into an eccentric component and a fluctuation component of the belt thickness.

The ejection timing correcting method for an inkjet printer according to the present invention corrects the ejection timing of a medium conveyed by an endless conveying belt from nozzles for ejecting ink of a single color or a plurality of colors based on an encoder pulse indicating the rotational position of a belt drive shaft. An ejection timing correction method for correcting,
At least, the first correction table based on the signal from the belt reference position can be used to perform the first correction for correcting the ejection timing,
Using the signal from the drive shaft reference position as a reference position, heads with different ejection timings are separated by N rotations of the belt drive shaft (N is an integer, N≧1) due to the physical distance between the ejection nozzles of the heads. A plurality of test patterns are generated on the same medium at the position where the transfer belt is located, and based on the results of reading the test patterns, the variation in the distance between the test patterns is obtained, and the profile data for one rotation of the conveyor belt is obtained. and determining the first correction table.

According to another aspect of the invention, there is provided an ejection timing correcting method for an ink jet printer, in which the ejection timing is corrected according to at least a second correction table based on a signal from the drive shaft reference position. correction can be made,
Using the signal from the drive shaft reference position as a reference position, a plurality of test patterns are generated on the same medium at positions separated by at least one rotation of the drive shaft by ejection with different ejection timings, and the test patterns are read. Based on the read result, the variation in the distance between the test patterns is obtained, profile data for one rotation of the drive shaft is created, and the second correction table is determined.

According to another aspect of the invention of an ejection timing correcting method for an inkjet printer, either the first correction table or the second correction table is determined first in the invention of the above aspect.

The program of the present invention ejects ink from ejection nozzles for single-color or multiple-color ink onto a medium transported by an endless transport belt at ejection timings determined based on encoder pulses indicating the rotational position of the belt drive shaft. A program executed by a control unit of an inkjet printer that prints on the medium by
The program enables at least a second correction for correcting the ejection timing by a second correction table based on the signal from the drive shaft reference position detection section,
Using the drive shaft reference position as a reference position, a plurality of test patterns are generated on the same medium at positions separated by at least one revolution of the drive shaft by ejection with different ejection timings, and the reading result of reading the test patterns. Based on the above, the variation in the distance between the test patterns is obtained, the profile data for one rotation of the drive shaft is created, and the control unit is caused to determine the second correction table.

According to another aspect of the program invention, in the above aspect of the invention, the program further corrects ejection timing by at least a second correction table based on a signal from the drive shaft reference position detection section. Allows correction of 2,
Using the drive shaft reference position as a reference position, a plurality of test patterns are generated on the same medium at positions separated by at least one revolution of the drive shaft by ejection with different ejection timings, and the reading result of reading the test patterns. The variation in the distance between the test patterns is obtained based on the above, profile data for one rotation of the drive shaft is created, and the control unit is caused to determine the second correction table.

As described above, according to the present invention, by measuring the variation in the distance between the impact positions separated by the circumference of the drive shaft, if there is no variation in the thickness of the belt, the distance between the impact positions separated by the circumference is measured. is always the same value because the eccentricity component of the shaft is cancelled. It can be used as a correction value for the fluctuation component of the belt thickness.
In another aspect of the invention, it is possible to measure the amount of variation in the interval between the landing positions for each predetermined number of encoder pulses to measure the variation. The former fluctuation amount and the latter fluctuation amount make it possible to separate and measure the thickness fluctuation component of the belt and the eccentricity component of the shaft.

1 is a diagram showing a schematic configuration of an inkjet printer according to one embodiment of the present invention; FIG. FIG. 11 is a diagram showing a test pattern for the first correction table, which is similarly printed on a medium; Similarly, it is a schematic configuration diagram of the inkjet printer for explaining the operation when performing normal printing. FIG. 10 is a schematic configuration diagram of an inkjet printer for explaining the operation when creating profile data; FIG. 10 is a schematic configuration diagram of an inkjet printer similarly explaining the operation when creating a test chart for the first correction table; It is a figure which shows the test chart for similarly 1st correction tables. FIG. 10 is a schematic configuration diagram of the inkjet printer for explaining the operation when storing the first correction table. Similarly, it is a schematic configuration diagram of an inkjet printer for explaining the operation when creating a test chart for the second correction table. It is a figure which shows the test chart for the same 2nd correction table. FIG. 10 is a schematic configuration diagram of an inkjet printer similarly explaining the operation when storing the second correction table; FIG. 11 is a schematic configuration diagram of an inkjet printer explaining the operation when creating a test chart for the first correction table in another embodiment; It is a figure which shows the test chart for similarly 1st correction tables. Similarly, it is a schematic configuration diagram of an inkjet printer for explaining the operation when creating a test chart for the second correction table. FIG. 10 is a schematic configuration diagram of an inkjet printer similarly explaining the operation when storing the second correction table; It is a figure which shows the test chart for the same 2nd correction table. FIG. 10 is a schematic configuration diagram of the inkjet printer for explaining the operation when storing the first correction table. FIG. 10 is a schematic configuration diagram of an inkjet printer for explaining the operation when performing medium transport timing in still another embodiment; In still another form, it is a diagram showing an example of a test chart. 1 is a diagram showing a schematic configuration of a general inkjet printer; FIG.

The configuration and action of an inkjet to which the present invention is applied will be described below with reference to the accompanying drawings.
In the inkjet printer 1, as shown in FIG. 1, an endless transport belt 12 for transporting a medium is stretched over transport rollers 10 and 11. As shown in FIG. An encoder 13 is attached to the belt drive shaft 10A to detect the rotation of the belt drive shaft 10A.
Color heads 15K (for black), 15C (cyan), 15M (magenta), and 15Y (yellow) are installed on the transport belt 12 at predetermined intervals. A line-shaped ejection head (not shown) is provided for each of the colors 15K, 15C, 15M, and 15Y. done.

While the encoder 13 is outputting, the Z-phase pulse is sent to the printing data generation unit 20, and the encoder pulse output from the encoder 13 is used for ink ejection in the heads 15K, 15C, 15M, and 15Y of each color.

FIG. 2 shows a test pattern printed on media for the first correction table of the present invention.
A plurality of test patterns 150K linearly formed by the ejection nozzles of the head 15K are printed on the paper P at predetermined intervals in the transport direction. Furthermore, a plurality of test patterns 150M are printed at intervals in the direction perpendicular to the transport direction at the same intervals in the transport direction as the test patterns.
The test pattern 150K and the test pattern 150M are formed such that corresponding lines are separated from each other by a distance L1 . . . Ln corresponding to one rotation of the belt driving shaft.
These test patterns 150K and 150M are read by an image reading device such as an in-line sensor, and variations in the distance Ln (n=1 . . . ) are measured.

In the above description, line ejection (thinning the line interval as necessary) is performed in a direction perpendicular to the medium conveying direction in synchronization with the encoder pulse for one rotation of the Z phase as a reference. Discharge is performed in the same way for different colors. However, it is assumed that ink is ejected at a timing delayed by one rotation or more from the above line ejection due to the difference in physical positions between heads. Ejection may be performed in a plurality of rotations N (integer; N≧1).
Between the above two colors, the distance between the lines corresponding to the Z phase is measured. Since the distance between the corresponding lines is offset by the circumferential length of the drive shaft, the eccentricity component of the drive shaft is canceled out, and if there is no variation in the thickness of the belt, the lines should be equally spaced. That is, if there is a variation in the distance between corresponding lines, it becomes a variation component of the belt thickness.

According to the principle described above, first, the thickness variation data for one week of the belt can be acquired, and the first correction table corresponding to one rotation of the belt can be created.
Also, the ejection distance between lines of the same color is obtained for one rotation of the drive shaft, and a second correction table is created as the eccentric component of the drive shaft. The second correction table may be obtained by applying a correction process using the correction values in the first correction table, and the above correction contents and the first correction table are used to obtain the second correction table. A correction table may be obtained.
In actual printing, the synthesized result of the first correction table and the second correction table is applied.

A detailed operation of the inkjet printer 1 will be described.
First, normal printing will be described with reference to FIG.
The inkjet printer 1 has the following configuration in addition to the configuration described with reference to FIG.
The head drive signal generator 21 generates a drive signal for each head and transmits it to each head. The head drive signal generator 21 receives the output of the print data generator 20 .

Also, the first correction table 41 and the second correction table 42 are stored in the memory 40 in a readable manner. The encoder correction logic 30 is connected to the memory 40, and the encoder correction logic 30 notifies the memory 40 of the address to obtain the correction value 1 in the first correction table or the correction value 1 in the second correction table. Store or retrieve correction value 2. Further, the encoder correction logic 30 is supplied with the output of the drive shaft reference position detection section 14A provided in the transport roller 10, and the information of the A phase and Z phase in the encoder 13 is obtained. Further, the output of the belt reference position detector 14B arranged near the conveying belt 12 is output to the encoder correction logic 30. FIG. A reference numeral 10B denotes a drive motor for rotating the transport roller 10 .

The encoder correction logic 30 is connected to the ejection clock generation logic 22 , and the corrected A-phase is output from the encoder correction logic 30 to the ejection clock generation logic 22 . The ejection clock generation logic 22 receives the detection result of the medium passage sensor 14C that detects the passage of the medium, generates an ejection clock, and sends the ejection clock to the head drive signal generation section 21 .
The head drive signal generator 21 generates a head drive signal based on the print data and the ejection clock, and ink is ejected from each of the heads 15K, 15C, 15M, and 15Y.

In normal printing, correction data 1 for correcting the belt thickness component is read from the first correction table 41 based on the signal from the belt reference position detection unit 14B that detects one rotation of the belt. Based on the phase, the correction data 2 for correcting the eccentric component of the drive shaft is read out from the second correction table 42, and based on the correction data obtained by synthesizing the correction data 1 and the correction data 2, the A-phase signal is input from the encoder. print after correcting the interval between
Note that the encoder correction logic 30 and the ejection clock generation logic 22 in the above configuration function as part of the configuration of the control section of the present invention.

Next, a procedure for creating profile data will be described with reference to FIG.
To implement this embodiment, an inline sensor 16 that reads an image formed on a medium in synchronization with an ejection clock, and an image analysis that analyzes the image from the inline sensor 16 and calculates a correction value+correction value calculation. A logic 25 and a medium transport timing control unit 26 for controlling the transport timing of the medium based on the signal from the belt reference position detector 14B and the Z phase are additionally mounted in order to print the test chart efficiently. and
At this time, the signal from the belt reference position detection unit 14B is input to the correction value calculation logic 25, and the calculated correction value and the positional relationship on the conveyor belt 12 are associated with each other.
Also, the ejection clock generation logic 22 is supplied with a Z-phase signal and has a function of waiting for both medium transport and Z-phase to start printing.

Next, procedures for obtaining the first correction table 41 and the second correction table 42 will be described. The following procedure can be accomplished by a control program running on the controller.

[Step 1]
As shown in FIG. 5, the correction process is disabled and a test chart for detecting the thickness of the belt is printed.
As shown in FIG. 6, the test chart 1 is basically parallel lines corresponding to one rotation of the drive shaft (in this example, magenta and black patterns), and the physical ejection timing is separated by one rotation of the drive shaft. Moreover, it is assumed that each color waits for both detection of the medium and the Z phase before printing is started.
Further, the medium transport timing control unit 26 controls the transport timing of the medium, and adjusts the transport timing so that the test chart fits on the medium even if printing is performed after waiting for the Z phase.
The ejected data is read by the in-line sensor 16, and the image analysis + correction value calculation logic 25 measures the amount of variation in the interval between the corresponding lines for each color, thereby calculating the correction value due to the thickness of the belt.

[Step 2]
As shown in FIG. 7, the medium conveyance timing control section 26 determines which part of the conveyance belt 12 the correction value calculated from the output of the belt reference position detection section 14B corresponds to, and cooperates with the medium conveyance timing control section 26. Then, correction data covering one rotation of the conveying belt is obtained.
After the acquisition of one rotation of the conveying belt is completed, the correction values are set in the first correction table 41 in the memory 40 .

[Step 3]
As shown in FIG. 8, the correction logic validates only the correction value 1 to perform correction processing, and prints a test chart 2 for measuring the eccentricity component as shown in FIG. (In this example, a monochrome test pattern 150K with only K is printed.)
At this time as well, the ejection clock generation logic 22 waits for both medium detection and Z-phase signals before printing the test chart. In addition, the medium transport timing control unit controls the timing of transporting the medium, and adjusts the transport timing so that the test chart can fit on the medium even if printing is performed after waiting for the Z phase.
The ejected data is read by the in-line sensor 16, and the image analysis+correction value calculation logic 25 measures the variation between individual lines and calculates the correction value of the eccentricity component.

[Step 4]
The correction values measured in procedure 3 are set as correction values in the second correction table 42 of the memory 40 as shown in FIG.
This completes the setting of the values in the two correction tables 41 and 42, after which normal printing operations can be performed.

As explained above, the variation in the distance between the impact positions separated by the circumference of the shaft is measured (if there is no variation in the thickness of the belt, the distance between the impact positions separated by the circumference is This value is used as the correction value for the fluctuation component of the belt thickness, and the correction data for one rotation of the belt is obtained first. By measuring the amount of variation in the gap and measuring the correction value for the eccentricity component of the shaft therefrom, it is possible to measure the thickness variation component of the belt and the eccentricity component of the shaft separately.

Specifically, with the Z phase of the drive shaft as the starting position, a straight line perpendicular to the medium conveying direction is drawn for one circumference of the drive shaft (encoder) in synchronization with the encoder signal attached to the drive shaft. Do the same drawing with a different color. At this time, it is essential that the physical distance between the two color heads be equal to or more than the circumferential length of the drive shaft. The physical distance between corresponding straight lines for each color varies (because the turning radius changes) due to variations in belt thickness. Applying this principle, the profile data of the thickness variation of the belt is created by measuring the variation of the intervals of the corresponding straight lines for one rotation of the belt. Next, after correction based on the belt profile information, the Z phase of the drive shaft is set as the start position again, and a straight line perpendicular to the medium conveying direction is set to the drive shaft (encoder) in synchronization with the encoder signal attached to the drive shaft. 1) Draw around. The eccentricity for one rotation of the encoder can be measured by measuring the variation in the interval of each straight line with respect to this drawing result. As a result, the belt thickness variation component and the drive shaft eccentricity component can be measured separately, and highly accurate correction can be performed based on the combined result.

Next, procedures of other embodiments will be described.
[Step 1]
As shown in FIG. 11, a test chart 3 is printed by disabling the correction process and extracting only the eccentricity component of the drive shaft.
As shown in FIG. 12, the test chart 3 is basically parallel lines corresponding to one revolution of the drive shaft (cyan and black test patterns 150C and 150K in this example), and its physical ejection timing corresponds to one revolution of the drive shaft. It is assumed that they are separated and that each color waits for both media detection and the Z phase before printing begins.

In test chart 3, by comparing the measured values of g1, g2, g3, g4, . .
Also, by comparing the measurement results of d1, d2, d3, d4, . By subtracting this value from the correction value obtained by synthesizing both factors of the eccentricity of the shaft and the thickness of the belt, it is possible to calculate the correction value consisting of only the eccentricity component of the shaft.

Further, the medium transport timing control unit 26 controls the transport timing of the medium, and adjusts the transport timing so that the test chart fits on the medium even if printing is performed after waiting for the Z phase.
The ejected data is read by the in-line sensor 16, and the image analysis + correction value calculation logic 25 measures the amount of variation in the interval between the corresponding lines for each color, thereby calculating the correction value due to the thickness of the belt.
At the same time, by measuring the variation in the interval of each line in the same color (black in this case), a correction value (combining factors of both shaft eccentricity and belt thickness) is calculated. From there, a second correction value consisting of only the eccentricity component of the shaft is calculated, excluding the calculation result of the correction value due to the thickness of the belt.

[Step 2]
A second correction value composed only of the eccentricity component of the shaft calculated in procedure 1 is set in the second correction table 42 as shown in FIG.

Procedure 3]
As shown in FIG. 14, in the correction logic, correction processing is performed with only correction value 2 enabled, and test chart 4 for measuring the amount of variation caused by the thickness of conveying belt 12 is printed. (In this example, a 150K monochrome test pattern with only K is printed.)
At this time as well, the ejection clock generation logic 22 prints the test chart based on the detection of the medium and the amount of delay from the belt reference position detection signal. Assume that the test chart includes reference marks based on the amount of delay with respect to the belt reference position, as shown in FIG.
Further, the medium transport timing control unit 26 controls the timing of transporting the medium, and prints the test chart so that the test chart efficiently covers the entire belt.
The ejected data is read by an in-line sensor, image analysis + correction value calculation logic measures variations between individual lines, and calculation of correction values based on variations in belt thickness is performed.

[Step 4]
As shown in FIG. 16, the correction values measured in step 3 are set as correction values in the first correction table.
This completes the setting of the values of the two correction tables, and the normal printing operation can be performed thereafter.

Another embodiment will now be described with reference to FIG.
The medium transport timing control section 26 controls the rotation of the transport roller 50A and the impingement roller 50B.
The medium transported by rotating the transport roller 50A is transported to the position of the impingement roller 50B (normally not rotating) and stops at the position of the impingement roller 50B.
Based on the signal from the belt reference position detector 14B and the Z-phase signal from the encoder 13, the medium transport timing control unit 26 rotates the impingement roller 50B to rotate the medium. Control to push out onto the conveyor belt is performed.

Next, still another embodiment will be described.
FIG. 18 shows an example of the test chart 5 used in this embodiment. The test chart 5 is a pattern corresponding to the number of encoder pulses for two rounds, and is a pattern in which the printing position in the second round is shifted by a distance K so that the determination between the first round and the second round is easy.
In this test chart as well, the medium transport timing control unit 26 controls the transport timing based on the Z phase so that the print result fits on the medium.
By measuring the distance between the horizontal lines in the print result of the test chart and having a positional relationship one round apart, it is possible to calculate the correction value due to the variation in the thickness component of the conveying belt.

In addition, in a device that measures the amount of belt movement with a laser Doppler sensor and can measure the amount of variation in the amount of belt movement with respect to the pulse interval of an encoder attached to the drive shaft, the measured amount of variation is the deviation of the drive shaft. It is a value obtained by synthesizing the core component and the variation component of the belt thickness. By performing the measurement with the laser Doppler sensor and the test pattern printing of this embodiment at the same time, the measurement result with the laser Doppler sensor can be accurately separated into the eccentricity component and the fluctuation component of the belt thickness.

As described above, the present invention has been described based on the above embodiments, but the scope of the present invention is not limited to the contents of the description of the above embodiments. Appropriate changes are possible.

1 inkjet printer 10 transport roller 11 transport roller 10A belt drive shaft 12 transport belt 13 encoder 14A drive shaft reference position detector 14B belt reference position detector 14C medium passage sensor 16 in-line sensor 20 print data generator 21 head drive signal generator 22 Ejection Clock Generation Logic 25 Correction Value Calculation Logic 26 Medium Conveyance Timing Control Unit 30 Encoder Correction Logic 40 Memory 41 First Correction Table 42 Second Correction Table 50A Conveyance Roller 50B Impact Roller

Claims (14)

By ejecting ink onto a medium conveyed by an endless conveying belt, ink is ejected onto the medium from ejection nozzles of a single color or multiple colors at ejection timings determined based on encoder pulses obtained by measuring the rotation of a belt drive shaft. An inkjet printer for printing,
a belt reference position detection unit that detects that the conveying belt has made one turn;
a drive shaft reference position detection unit that detects that the belt drive shaft has made one rotation;
a controller capable of setting the ejection timing between the encoder pulse signal and the ejection operation;
The control unit has at least a first correction function of correcting the ejection timing by a first correction table based on the signal from the belt reference position detection unit,
Further, the control unit uses the signal from the drive shaft reference position detection unit as a reference position, and uses heads with different ejection timings to determine the physical distance between the ejection nozzles of the head for N rotations of the belt drive shaft. N is an integer, and a plurality of test patterns are generated on the same medium at positions separated by N≧1), and based on the results of reading the test patterns, the variation in distance between the test patterns is obtained. 1. An ink jet printer, wherein the first correction table is determined by creating profile data for one rotation of the conveying belt. The control unit has at least a second correction function of correcting the ejection timing by a second correction table based on the signal from the drive shaft reference position detection unit,
Using the signal from the drive shaft reference position detection unit as a reference position, the control unit performs ejection at different ejection timings to form a plurality of ink droplets on the same medium at separated positions for at least one revolution of the belt drive shaft. A test pattern is generated, and based on the reading result of reading the test pattern, variation in distance between the test patterns is obtained, profile data for one rotation of the drive shaft is created, and the second correction table is determined. 2. The ink jet printer according to claim 1 , wherein: 3. The inkjet according to claim 2, wherein the control unit generates the test pattern for the second correction table while enabling the first correction function based on the first correction table. printer. 3. The inkjet according to claim 2, wherein the control unit obtains the second correction table using the first correction table based on the profile data for one rotation of the drive shaft. printer. 5. The method according to any one of claims 2 to 4, wherein the control unit corrects the ejection timing by using the first correction table and the second correction table to execute printing of the job. Inkjet printer as described. 6. The inkjet printer according to any one of claims 2 to 5 , wherein the control section first determines one of the first correction table and the second correction table. In order to determine the first correction table, the control section controls the timing of placing the medium on the conveying belt based on the signal from the belt reference position detection section and the signal from the drive shaft reference position detection section. The inkjet printer according to any one of claims 1 to 6 , characterized in that. The control unit creates a plurality of test patterns for determining the first correction table for two revolutions or more by ejection from the ejection nozzles of the same head based on the signal from the drive shaft reference position detection unit. 8. The inkjet printer according to any one of claims 1 to 7 , wherein a change in distance between test patterns at rotationally separated relative positions is obtained. The control unit simultaneously performs profile data creation by creating the test pattern and measurement by the laser Doppler sensor, and separates the measurement result of the laser Doppler sensor into an eccentricity component and a variation component of the belt thickness. The inkjet printer according to any one of claims 1-8 . An ejection timing correction method for correcting the ejection timing of a medium conveyed by an endless conveying belt based on encoder pulses obtained by measuring the rotation of a belt drive shaft from ejection nozzles of single or multiple colors of ink, comprising:
At least, the first correction table based on the signal from the belt reference position can be used to perform the first correction for correcting the ejection timing,
Using the signal from the drive shaft reference position as a reference position, heads with different ejection timings are separated by N rotations of the belt drive shaft (N is an integer, N≧1) due to the physical distance between the ejection nozzles of the heads. A plurality of test patterns are generated on the same medium at the position where the transfer belt is located, and based on the results of reading the test patterns, the variation in the distance between the test patterns is obtained, and the profile data for one rotation of the conveyor belt is obtained. A method for correcting the ejection timing of an ink jet printer, comprising the steps of creating and determining the first correction table. A second correction for correcting the ejection timing can be performed using at least a second correction table based on the signal from the drive shaft reference position,
Using the signal from the drive shaft reference position as a reference position, a plurality of test patterns are generated on the same medium at positions separated by at least one rotation of the drive shaft by ejection with different ejection timings, and the test patterns are read. 11. The inkjet printer according to claim 10 , wherein variation in distance between said test patterns is obtained based on the reading result, profile data for one round of the drive shaft is created, and said second correction table is determined. Ejection timing correction method. 12. The ejection timing correcting method for an ink jet printer according to claim 11 , wherein either said first correction table or said second correction table is determined first. By ejecting ink onto a medium conveyed by an endless conveying belt, ink is ejected onto the medium from ejection nozzles of a single color or multiple colors at ejection timings determined based on encoder pulses obtained by measuring the rotation of a belt drive shaft. A program executed by a control unit of an inkjet printer for printing,
The program enables at least a second correction for correcting the ejection timing by a second correction table based on the signal from the drive shaft reference position detection section,
Using the drive shaft reference position as a reference position, a plurality of test patterns are generated on the same medium at positions separated by at least one revolution of the drive shaft by ejection with different ejection timings, and the reading result of reading the test patterns. A program to be executed by the control unit to determine the variation in the distance between the test patterns, create profile data for one rotation of the drive shaft, and determine the second correction table. The program further
enabling a second correction for correcting ejection timing using at least a second correction table based on the signal from the drive shaft reference position detection unit;
Using the drive shaft reference position as a reference position, a plurality of test patterns are generated on the same medium at positions separated by at least one revolution of the drive shaft by ejection with different ejection timings, and the reading result of reading the test patterns. variation in the distance between the test patterns, profile data for one rotation of the drive shaft is created, and the control unit is caused to determine the second correction table. 13. The program according to 13.

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