JP2009234023A - Evaluation method for degree of eccentricity of roller and printer implementing the method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology for easily and accurately evaluate the degree of eccentricity of a print conveying roller that conveys a recording medium in a sub-scanning direction. <P>SOLUTION: In order to evaluate the degree of eccentricity of the print conveying roller that conveys the recording medium in the sub-scanning direction after a dot line is formed on the medium in a main scanning direction, a test print is output in which a dot line is formed at each predetermined pitch over a predetermined range of rotation angle equal to or greater than one rotation of the print conveying roller. From image data of a dot line group obtained by scanning the test print, the lengths of areas defined by the predetermined number of dot lines are successively calculated as segment lengths while shifted for each dot line in the sub-scanning direction. Based on the behavior of a change in the value of a difference between each calculated segment length and a reference length, the degree of eccentricity is evaluated. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention includes a print head that forms a dot line in a main scanning direction with respect to a recording medium, a print conveying roller that conveys the recording medium in a sub-scanning direction, and a drive unit that rotates the print conveying roller at a predetermined pitch. The present invention relates to a method for evaluating the degree of eccentricity of the print conveying roller in a printing apparatus having the above and a printing apparatus for implementing this method.

  As a technique for preventing the deterioration of image quality due to the eccentricity of the recording paper transport roller, the recording paper transport roller for reciprocating the recording paper and the same area on the recording paper when the recording paper moves forward by the recording paper transport roller A recording unit that performs line-by-line print recording in different colors, a detection unit that detects a rotational angle position of the recording conveyance roller, a registration mark recording unit that records registration marks on a recording sheet at regular time intervals, and Based on the reading means for reading the registration mark, calculation means for calculating the moving speed displacement of the recording paper at each rotation angle position of the recording paper conveyance roller from the reading information of the registration mark, and based on the calculated moving speed displacement of the recording paper Data for creating correction data for line-by-line print recording timing by the recording means at each rotation angle position of the recording paper transport roller And forming means, the image recording apparatus is known which is provided and control means for controlling the printing recording by said recording means on the basis of the correction data created by said data creating means (for example, see Patent Document 1). In this image recording apparatus, first, a registration mark is created on the recording paper at the same timing as the time of image recording, and the registration mark is read, and the movement speed displacement of the recording paper at each rotational angle position of the recording paper transport roller is obtained. To create recording timing correction data for recording dots. Based on the correction data, image recording is performed by correcting the recording timing from the time of image recording of the first color. In this image recording apparatus, the eccentricity of the recording paper conveyance roller is obtained by measuring the individual intervals of the registration marks formed at regular time intervals irrespective of the conveyance speed. In order to obtain the above, it is necessary to shorten the interval between the registration marks and increase the measurement accuracy of the interval. However, in order to increase the measurement accuracy of the interval between the registration marks formed at a short interval, it is necessary to make the registration mark position detector have high performance, which is costly.

  In addition, a recording medium transport rotating body that transports the recording medium, an encoder that detects position or speed information of the recording medium transport rotating body, and a driving force that engages with the recording medium transport rotating body and transmits a driving force. A recording medium conveyance system for moving the recording medium by a predetermined amount by a transmission means and a motor engaged with the driving force transmission means is provided. A drive unit that rotates; a transport unit that transports a recording medium by adding an eccentricity detection amount to a predetermined amount of the drive unit; and a process that performs printing for each transport unit of the recording medium, Ink having means for associating the eccentricity correction value of the recording medium conveyance rotating body with the position information of the encoder by comparing the formed image on the recording medium by the printing process for each rotation of the conveyance rotating body. Jet recording apparatus is also known (e.g., see Patent Document 2). In this ink jet recording apparatus, wide print patterns obtained by performing wide printing for each divided drive amount of the recording medium transport rotator are sequentially overlapped while shifting in the main scanning direction, and by eccentricity of the recording medium transport rotator. The degree of overlap of each print pattern that changes is evaluated. Since the overlapping part of the print pattern that changes due to the eccentricity of the recording medium transport rotating body is a small area of the entire print pattern, it is difficult to evaluate the eccentricity from the density change due to the overlap, and in order to do this accurately Cost burden is also increased.

JP-A-8-101618 (paragraph number 0075-0104, FIG. 6) Japanese Patent Laying-Open No. 2006-192807 (paragraph numbers 0036-0042, FIG. 7)

  In view of the above situation, an object of the present invention is to provide a technique that can easily and accurately evaluate the eccentricity of a print transport roller that transports a recording medium in the sub-scanning direction without a cost burden. It is.

A printing apparatus comprising: a print head that forms a dot line in a main scanning direction with respect to a recording medium; a print conveying roller that conveys the recording medium in a sub-scanning direction; and a drive unit that rotates the print conveying roller. In order to solve the above problems in a method for evaluating the degree of eccentricity of a print transport roller, in the present invention, a test print in which dot lines are formed at predetermined pitches over a predetermined rotation angle range of one or more rotations of the print transport roller is provided. A step of outputting, a step of scanning the test print to obtain image data of a dot line group, and a length of an area defined by a predetermined number of dot lines from the image data as a segment length, Calculate sequentially while shifting in the sub-scanning direction in units of dot lines. A step, from the change behavior for each segment length calculated with the step of evaluating the polarization concentricity.
A dot here is a minimum print pixel formed by a print head. For example, in the case of an ink jet printing apparatus, one dot is a pixel formed on a recording medium by one unit of ink droplets ejected from an ink nozzle. It is. Therefore, the dot line here means a line segment created by continuously forming such dots in the main scanning direction.

  In this roller eccentricity evaluation method, the process of forming one dot line every time the recording medium is conveyed in the sub-scanning direction by the rotation of the print conveyance roller at a predetermined pitch is a predetermined value of one or more rotations of the print conveyance roller. Over the rotation angle range. As a result, a test print in which a large number of dot lines affected by variations in the recording medium feeding in the sub-scanning direction due to the eccentricity of the print transport roller is output. Next, a process of calculating the length of an area defined by a predetermined number of dot lines, for example, the length between the first and Nth lines, as the segment length from the scanned image data of the test print is sequentially performed. While shifting in the scanning direction, that is, the second and N + 1th lines are performed next, the third and N + 2nd lines are performed next, and the segment lengths sequentially shifted are obtained. Since the segment length corresponds to the circumferential length of the specific rotation angle range of the print transport roller defined by the predetermined pitch, the variation in the segment lengths is within the specific rotation angle range caused by the eccentricity. This corresponds to variations in circumference. Therefore, for example, the eccentricity of the print transport roller can be evaluated from the change behavior related to each segment length. At that time, for example, the segment length itself may be used as the change behavior related to each segment length. However, the reference length is calculated as the segment length corresponding to the ideal circumference without eccentricity. It is preferable to calculate the difference value of the segment length and to evaluate the eccentricity of the print transport roller from the change behavior of the difference value along the sub-scanning direction. it can. In the present invention, instead of measuring the length between the first dot line and the second dot line, the length between the dot lines extending over a plurality of dot lines is used as the segment length, and image processing is used. Therefore, it is advantageous from the viewpoint of measurement error, and it is not necessary to employ an expensive high-performance measurement system.

  Since the conveyance error caused by the eccentricity of the print conveyance roller is repeated every rotation, the eccentricity of the print conveyance roller is evaluated by using a dot line formed during at least one rotation of the print conveyance roller. be able to. However, the transport error caused by the eccentricity of the print transport roller is a cyclic error that occurs in one rotation + error and -error, and the segment length calculation is continuously performed along the sub-scanning direction. In view of the above convenience, in the preferred embodiment of the present invention, the predetermined rotation angle range is one and a half rotations, and the region is defined by the number of dot lines formed during the half rotation. It is considered as an area.

  In order to evaluate the eccentricity of the print transport roller in association with the absolute rotation angle, it is necessary to associate each dot line with the rotation angle position of the print transport roller. For this purpose, in a preferred embodiment of the present invention, a reference rotation angle position is set on the print transport roller, and one of the dot lines formed on the test print is used to detect the reference rotation angle position. It is associated.

  In an ink jet print head in which a print pixel corresponding to one color pixel is formed by a large number of dots, the degree of eccentricity of the print transport roller greatly affects the image quality. Also, the smaller the dot line width used for this eccentricity evaluation, the more measurement errors caused by image processing can be suppressed. For this reason, the eccentricity evaluation according to the present invention is particularly suitable for a printing apparatus using an ink jet print head. In this case, the dot line is preferably formed as a one-dot-width line by one ink nozzle. .

  If the rotation of the print conveying roller for a predetermined pitch is not performed precisely, the accuracy of the eccentricity evaluation is adversely affected. Therefore, it is preferable that the rotation of the print transport roller for a predetermined pitch is performed based on detection of a predetermined number of pulses output from the encoder. However, even if a high-resolution encoder is used, a difference (detection difference) may occur between the target pulse count value and the actual pulse count value on which the dot line is formed. In that case, the reliability of the calculated segment length can be maintained by compensating the error of the segment length based on the difference when calculating the segment length.

  The present invention includes not only the roller eccentricity evaluation method described above, but also a roller eccentricity evaluation program for realizing such a method on a printing apparatus and a printing apparatus employing such a method. . For example, in a printing apparatus having a print head that forms dot lines in a main scanning direction with respect to a recording medium, a print conveying roller that conveys the recording medium in a sub-scanning direction, and a drive unit that rotates the print conveying roller. In order to solve the above-described problem, in the present invention, a test print output management unit that manages the output of a test print in which dot lines are formed at predetermined pitches over a predetermined rotation angle range of one or more rotations of the print transport roller; An image data input unit for inputting image data of a dot line group obtained by scanning the output test print, and a length of an area defined by a predetermined number of dot lines from the image data. The segment length is calculated sequentially while shifting in the sub-scanning direction in dot line units. And segment length calculating unit for, eccentric degree evaluation unit that evaluates the roller polarized concentricity of the print conveyance rollers from a change behavior for each segment length calculated is provided. The printing apparatus configured in this way also has the effects described in the above-described roller eccentricity evaluation method, and can include various additional characteristic configurations described above. For example, a difference value calculation unit that calculates a difference value between each of the calculated segment lengths and a reference length is provided, and the eccentricity evaluation unit calculates a roller deviation of the print transport roller from a change behavior of the difference value in the sub-scanning direction. It is also possible to configure so as to evaluate the coreness.

  Further, in order to automatically adjust the sub-scanning direction conveyance based on the evaluated roller eccentricity, the rotation of the print conveyance roller based on the roller eccentricity evaluation data output from the eccentricity evaluation unit It is preferable that the drive unit is provided with an adjustment unit that adjusts the angular velocity.

Hereinafter, an embodiment of a printing apparatus employing an eccentricity evaluation technique according to the present invention will be described with reference to the drawings.
As shown in FIGS. 1 and 2, this printing apparatus feeds print paper P as a recording medium stored in a roll shape to a printing mechanism 2 by a feed conveyance mechanism 1 to print an image. A discharge conveyance mechanism 4 is provided that sequentially conveys the paper P to the cutting unit C, the back printing unit B, and the decurling unit D and discharges the paper P to a discharge tray 31 attached to the outside of the housing 30. The discharge / conveyance mechanism 4 includes a plurality of nipping / conveying roller pairs 40.

  Since the printing apparatus is configured as an ink jet system, the print mechanism 2 includes an ink jet print head 20 that reciprocates in the main scanning direction. As shown in FIGS. 3 and 4, inside the housing 30, a suction unit 33, an ink storage unit IB, which is disposed at a position facing the print head 20 across the transport path of the print paper P, A control unit 5 is provided. The suction unit 33 incorporates an electric fan (not shown) that sucks air from a large number of openings formed on the upper surface of the case-like unit and sends it out downward.

  The feed conveyance mechanism 1 includes a print conveyance roller 10 on the upstream side of the printing mechanism 2 in the conveyance direction. Two press rollers 11 and 12 are attached to the print transport roller 10, and the print paper P is sandwiched and transported by pressing the print paper P against the print transport roller 10 by the press rollers 11 and 12. The print transport roller 10 creates the transport of the print paper P in the sub-scanning direction during printing, and the rotational displacement amount of the roller peripheral surface becomes the displacement amount of the print paper P in the sub-scanning direction. The print transport roller 10 uses a transport motor M1 formed of a DC servo motor as a drive source. A rotary encoder E is attached to the rotation shaft of the print transport roller 10 and has a resolution capable of generating 32768 pulses by one rotation of the print transport roller 10. The feed conveyance mechanism 1 is further provided with a pull-in conveyance roller pair 13, whereby the cut paper set on the manual feed tray 32 is drawn in and delivered to the print conveyance roller 10, whereby the cut paper is transferred to the print mechanism 2. Can be supplied.

  The cutting unit C includes a disk-shaped cutter 34 that cuts the print paper P, and an operating mechanism 35 that reciprocates the disk-shaped cutter in the main scanning direction. The back print unit B includes a print head 3 that prints information on the back side of the print paper P. In order to correct the curl of the print paper P, the decurling unit D is configured to convey the print paper P while curving it in a direction opposite to the winding direction of the roll-shaped print paper P, and a guide plate 42. And. A plurality of ink cartridges (not shown) are set in the ink reservoir IB, and ink sent from the ink reservoir IB is supplied from an intermediate tank (not shown) to the print head 20 via a flexible tube. .

  The print head 20 includes a carriage 21 and an ink discharge unit 23 that is connected to the carriage 21 and discharges ink onto the print paper P to print information, and has a carriage cover 22 that covers the carriage 21. Yes. The ink discharge unit 23 has a first nozzle unit 23a and a second nozzle unit 23b disposed at two positions on the lower surface thereof that are separated in the sub-scanning direction. Each nozzle unit 23a and 23b is formed with a large number of ink nozzles 24 for ejecting ink.

  In the print mechanism 2, a pair of guide rods 26 having a circular cross-sectional shape are arranged in a parallel posture in the main scanning direction. The carriage 21 is supported so as to be slidable with respect to the pair of guide rods 26. One side surface of the carriage 21 in the sub-scanning direction is provided with a pair of slide guides 25 in which circular holes are formed so as to be fitted on one guide rod 26, and the other guide rod 26 is provided on the other side surface. The slide block 25 is provided with a recess that is engaged with the slide block 25. Further, a belt driving mechanism 27 including a driving pulley 27a, a driven pulley 27b, and a timing belt type driving belt 27c wound around the driving pulley 27a is disposed along the main scanning direction on the side portion of the carriage 21. The drive belt 27c and the carriage 21 are connected, and a rotational driving force is transmitted to the drive pulley 27a from the drive motor M2.

  In order to construct the linear encoder system 28 that acquires the position of the print head 20 in the main scanning direction, a belt-like linear strip 28a is fixed to the housing 30 at a position near the print head 20 in a posture parallel to the main scanning direction. A sensor unit 28b for optically acquiring scale information of the linear strip 28a is supported by the carriage 21 of the print head 20. The linear encoder system 28 is configured to specify the position of the print head 20 in the main scanning direction by counting the scale information of the linear strip 28a when the print head 20 moves.

  The control unit 5 acquires information such as images and characters to be printed and converts them into print data. The control unit 5 controls the transport motor M2 while checking the pulses from the encoder E based on the print data, thereby realizing the sub-scan transport of the print paper P by the feed transport mechanism 1 and the signal from the linear encoder system 28. By controlling the drive motor M2 based on the above, the reciprocation of the print head 20 in the main scanning direction is realized. In synchronism with these movements, the control unit 5 controls the ink discharge mechanism built in the ink discharge unit 23 based on the print data, thereby controlling the ink nozzles 24 of the first nozzle unit 23a and the first nozzle unit 23b. Ink is ejected to form an image of dot groups on the print paper P. More specifically, the print head 20 is moved in one of the main scanning directions, and printing is performed while ejecting ink through the ink nozzles 24 of the ink ejection unit 23. As a result, when the print head 20 reaches the moving end, the print paper P is transported by a predetermined pitch in the sub-scanning direction by the feed transport mechanism 1. After this conveyance, the print head 20 is moved to the other side of the main scanning direction (in the reverse direction), and an image is formed on the print paper P while ejecting ink through the ink nozzles 24 of the ink ejection unit 23 again.

The control unit 5 of the printing apparatus also has a function of evaluating the eccentricity of the print transport roller 10. FIG. 5 is a functional block diagram illustrating functions related to the roller eccentricity evaluation in the control unit 5. This functional block diagram includes an image data input unit 51, a memory 52 for developing input image data, an image processing unit 53 for processing input image data, and print data for generating print data from the processed image data The generation unit 54, the print head control unit 55 that controls the ink ejection mechanism of the print head 20 and the drive motor M2 that moves the print head 20 in the main scanning direction based on the print data, and the print conveyance roller that performs the sub-scan conveyance of the print paper P Some of them are also used for normal image printing such as a conveyance motor control unit 56 that controls ten conveyance motors M1 based on a pulse signal from an encoder E. A process for outputting a test print TP in which a number of dot lines extending in the main scanning direction are formed as shown in FIG. 6 as an apparatus mainly used for evaluating the degree of eccentricity of the roller. A test print output management unit 57 and an eccentricity evaluation means 58 for managing the above are included.

  In this embodiment, the drive unit that rotates the print transport roller 10 at a predetermined pitch includes a transport motor M 1, an encoder E, and a transport motor control unit 56.

  The test print management unit 57 stores test print data for the test print TP shown in FIG. 6. The test print management unit 57 supplies the test print data to the print data generation unit 54 as necessary, and outputs the test print TP. . This test print TP is enlarged and displayed in FIG. In this embodiment, the print conveyance roller 10 is intermittently rotated with a rotation angle range in which 128 pulses are output from the encoder E as a predetermined pitch, and the sub-scan conveyance is performed. The main scanning movement of the print head 20 is performed at every predetermined pitch, and one ink nozzle 24 is driven to form a dot line having a width of one dot. In this test print TP, this dot line is formed over the rotation angle range of one and a half rotations of the print conveying roller 10. Since this encoder E has a resolution that generates 32768 pulses per rotation, 256 dot lines are formed by one rotation of the print conveyance roller 10 and 385 dot lines are formed by one and a half rotations of the print conveyance roller 10. Will be. In order to make it easy to understand, in FIG. 7, the first one is given the number 1 and the last one is given the number 385 in that order.

  The output test print TP is converted into a digital image by using an image reading device such as a flatbed scanner 60 and developed as test print image data in the memory 52 through the image data input unit 51.

  The eccentricity evaluation means 58 includes a segment length calculation unit 58a, a difference value calculation unit 58b, and an eccentricity evaluation unit 58c. The segment length calculation unit 58a calculates, from the test print image data developed in the memory 52, the length of the area defined by a predetermined number of dot lines as the segment length. The segment length is sequentially calculated while shifting the defined area in the sub-scanning direction in dot line units. In this embodiment, the length of the area defined by 128 dot lines, which corresponds to the length of a half circumference of the print transport roller 10, is set as a predetermined number of lines. The segment length sequentially calculated in this manner is indicated by S [i] (i is a natural number) in FIG. That is, the segment length S [1] is the length from the No. 1 dot line to the No. 129 dot line, and similarly the segment length S [257] is No. 257 from the No. 257 dot line. Length up to .385 dot line.

  Each dot line is created every time the encoder E generates 128 pulses, but may have an error of 128 ± α depending on the detection delay of the pulse count. Since the error α is grasped by the conveyance motor control unit 56, information on the error α is sent from the conveyance motor control unit 56 to the eccentricity evaluation means 58 in a form corresponding to each dot line. Therefore, the segment length calculation unit 58a corrects the value of the segment length S [i] using the information on the error α. In other words, if the number of pulses included in the segment defining the segment length is less than the original number of pulses, increase the segment length value to compensate for that, and conversely define the segment length. If the number of pulses included in a certain area is larger than the original number of pulses, the segment length value is reduced so as to compensate for that. As a result, the segment length S [i] varies depending only on the eccentricity of the print transport roller 10.

The difference value calculation unit 58b performs sub-scanning by each segment length S [i] calculated by the segment length calculation unit 58a and the print conveyance roller 10 without eccentricity while the encoder E generates 128 pulses. The difference value is calculated using the transport distance as the reference length. That is, if the reference length is S0, each difference value ΔS [i] is
ΔS [i] = S [i] −S0
It becomes.

  The eccentricity evaluation unit 58c evaluates the roller eccentricity of the print transport roller 10 from the change behavior of the difference value calculated by the difference value calculation unit 58b. For example, i of segment length S [i], which is a numerical value corresponding to the pulse count value of encoder E indicating the amount of movement in the sub-scanning direction, is assigned to the horizontal axis, and segment length S [i] is assigned to the vertical axis. Then, a waveform having periodicity as shown in FIG. 8 is obtained. This waveform indicates the degree of eccentricity of the print transport roller 10. When a marker that defines the reference rotation angle position is set on the print transport roller 10 and the first dot line is formed in response to the detection signal from the marker detector MD that detects this marker, The rotation angle position showing the maximum eccentricity can be obtained from FIG. In addition, the degree of eccentricity at each rotational angle position can also be grasped. Accordingly, the eccentricity evaluation unit 58c creates eccentricity evaluation data including such information, and sends it to the adjustment unit 56a built in the conveyance motor control unit 56, whereby the adjustment unit 56a is connected to the print conveyance roller 10. The conveyance motor M1 can be controlled to compensate for the roller eccentricity. As a result, accurate sub-scanning conveyance is realized regardless of the roller eccentricity of the print conveyance roller 10.

  In the description of the above-described embodiment, the ink jet method is used as the print head. However, the present invention is not limited to the ink jet method, and the dots as the minimum print pixels formed by the print head are in the main scanning direction. The present invention can be applied to a technique using all types of print heads in which a line segment created by being continuously formed can be called a dot line.

A perspective view schematically showing the configuration of an ink jet printing apparatus Side view schematically showing the configuration of an ink jet printing apparatus The perspective view explaining the operation mechanism of the print head Side view explaining the configuration of the print head Functional block diagram showing functions related to roller eccentricity evaluation in control unit Plan view showing test print for evaluating roller eccentricity Explanatory drawing explaining the relationship between the dot line formed on the test print and the roller eccentricity evaluation Graph showing an example of roller eccentricity evaluation results

Explanation of symbols

E Encoder P Print paper (recording medium)
TP test print M1 conveyance motor MD marker detector 10 print conveyance roller 20 print head 51 image data input unit 56 conveyance motor control unit 56a adjustment unit 57 print output management unit 58 eccentricity evaluation means 58a segment length calculation unit 58b difference value Calculation unit 58c Eccentricity evaluation unit

Claims (9)

A printing apparatus comprising: a print head that forms a dot line in a main scanning direction with respect to a recording medium; a print conveying roller that conveys the recording medium in a sub-scanning direction; and a drive unit that rotates the print conveying roller. In the roller eccentricity evaluation method of the print transport roller,
Outputting a test print in which dot lines are formed at predetermined pitches over a predetermined rotation angle range of one or more rotations of the print transport roller;
Scanning the test print to obtain image data of a dot line group;
From the image data, sequentially calculating the length of the region defined by a predetermined number of dot lines as a segment length while shifting in the sub-scanning direction in units of the dot lines;
Evaluating the eccentricity from the calculated change behavior for each segment length;
A roller eccentricity evaluation method comprising:   The roller eccentricity evaluation method according to claim 1, wherein the change behavior is a change behavior in a sub-scanning direction of a difference value between the calculated segment length and a reference length.   The roller eccentricity evaluation method according to claim 1 or 2, wherein the predetermined rotation angle range is one and a half rotations, and the region is a region defined by the number of dot lines formed during the half rotation.   4. The reference rotation angle position is set on the print transport roller, and one of the dot lines formed on the test print is associated with detection of the reference rotation angle position. 5. The roller eccentricity evaluation method as described.   5. The roller eccentricity evaluation method according to claim 1, wherein the print head is an ink jet print head, and the dot line is a one-dot width line formed by one ink nozzle. 6. 6. The rotation of the print transport roller for the predetermined pitch is performed based on detection of a predetermined number of pulses output from an encoder, and a detection error at that time is compensated when the segment length is calculated. The roller eccentricity evaluation method as described in any one of Claims. In a printing apparatus having a print head that forms a dot line in a main scanning direction with respect to a recording medium, a print conveying roller that conveys the recording medium in a sub-scanning direction, and a drive unit that rotates the print conveying roller.
A test print output management unit for managing output of a test print in which dot lines are formed at predetermined pitches over a predetermined rotation angle range of one or more rotations of the print transport roller;
An image data input unit for inputting image data of a dot line group obtained by scanning the output test print;
From the image data, a segment length calculation unit that sequentially calculates the length of a region defined by a predetermined number of dot lines as a segment length while shifting in the sub-scanning direction in units of the dot lines;
An eccentricity evaluation unit that evaluates the roller eccentricity of the print conveying roller from the calculated change behavior regarding each segment length;
A printing apparatus comprising:   A difference value calculation unit that calculates a difference value between each of the calculated segment lengths and a reference length; and the eccentricity evaluation unit detects a roller of a print transport roller based on a change behavior of the difference value in the sub-scanning direction. The printing apparatus according to claim 7, wherein the degree of eccentricity is evaluated.   9. The printing apparatus according to claim 7, wherein the drive unit includes an adjustment unit that adjusts a rotational angular velocity of the print transport roller based on roller eccentricity evaluation data output from the eccentricity evaluation unit. .

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