JP2024047842A - Printing device - Google Patents

Abstract

[Problem] To provide a printing device that can reduce degradation of print image quality. [Solution] A printing unit 3 prints by ejecting ink from head units 21A, 21B onto a printing medium 9 being transported. Encoders 4A, 4B each have a roller 32 that comes into contact with the printing medium 9 and rotates in response to the printing medium 9, and output a pulse signal according to the rotation angle of the roller 32. A control unit 8 controls the ink ejection timing of the head units 21A, 21B of the printing unit 3 based on the pulse signals output by the encoders 4A, 4B. [Selected Figure] Figure 2

Description

The present invention relates to a printing device.

A printing device is known that ejects ink from an ink head to print on a print medium while the print medium is transported by a transport belt (see Patent Document 1).

When printing in such a printing device, the conveyor belt is controlled to move at a constant speed. However, the speed at which the conveyor belt moves can change due to factors such as uneven thickness of the conveyor belt and eccentricity of the roller around which the conveyor belt is wound. If the conveyor belt does not move at a constant speed, the ink ejected from the ink head will land misaligned. Misaligned landing results in a decrease in print image quality.

In response to this, a technology is known that acquires in advance information indicating uneven thickness of the transport belt and information indicating the eccentricity of the roller around which the transport belt is wound, and uses this information to control the timing of ink ejection, thereby suppressing degradation of print image quality due to misalignment of ink droplets.

JP 2021-30538 A

However, for example, in a printing device in which the user prepares a transport unit having a transport belt, it is not possible to obtain information indicating uneven thickness of the transport belt and information indicating eccentricity of the rollers in advance, and it may not be possible to prevent deterioration in print image quality using the above-mentioned technology.

In addition, if the thickness of the conveyor belt is excessively uneven or if the conveyor belt is too long, it may be difficult to prevent deterioration in print image quality using the above-mentioned techniques.

The present invention has been made in consideration of the above, and aims to provide a printing device that can reduce degradation in print image quality.

To achieve the above object, the printing device of the present invention is characterized by comprising a printing unit that prints on the printing medium while moving relative to the printing medium, an encoder that has a roller that contacts the printing medium and rotates in response to the printing medium, and outputs a pulse signal according to the rotation angle of the roller while moving relative to the printing medium, and a control unit that controls the printing timing in the printing unit based on the pulse signal output by the encoder.

The printing device of the present invention can reduce degradation of print quality.

1 is a front view showing a schematic configuration of a printing device according to a first embodiment. FIG. 2 is a plan view showing a schematic configuration of the printing apparatus shown in FIG. 1 . 5A and 5B are explanatory diagrams of a print valid signal and an output pulse signal of an encoder. FIG. 13 is a diagram illustrating a state in which the print medium is tilted with respect to the transport direction. 13 is an explanatory diagram of adjustment of an output pulse signal of an encoder based on a detected effective printing range and a reference value. FIG. FIG. 11 is a plan view showing a schematic configuration of a printing device according to a second embodiment.

The following describes an embodiment of the present invention with reference to the drawings. The same or equivalent parts and components are denoted by the same or equivalent reference numerals throughout the drawings.

The embodiments shown below are examples of devices that embody the technical idea of this invention, and the technical idea of this invention does not specify the materials, shapes, structures, arrangements, etc. of each component part to those described below. The technical idea of this invention can be modified in various ways within the scope of the claims.

[First embodiment]
Fig. 1 is a front view showing a schematic configuration of a printing device according to a first embodiment of the present invention. Fig. 2 is a plan view showing a schematic configuration of the printing device shown in Fig. 1. In the following description, the direction perpendicular to the plane of Fig. 1 is defined as the front-rear direction, and the front direction of the plane of the paper is defined as the forward direction. Furthermore, the top, bottom, left, right, and top, bottom, left, and right directions on the plane of the paper in Fig. 1 are defined as the up, down, left, and right directions. The up and down direction is the vertical direction, and the left and right directions and the front and back directions are mutually perpendicular, and are all perpendicular to the up and down direction and parallel to the horizontal direction.

As shown in Figures 1 and 2, the printing device 1 according to the first embodiment includes a transport unit 2, a printing unit 3, encoders 4A and 4B, an encoder holding unit 5, a medium height sensor 6, a print validity sensor 7, and a control unit 8. Note that the alphabetical suffixes in the symbols of the encoders 4A, 4B, etc. may be omitted to refer to them collectively.

The transport unit 2 transports the print medium 9. The print medium 9 has a printable surface 9a on which printing is performed by the printing unit 3. The printable surface 9a is the front side of the print medium 9 that is placed on the transport unit 2 and transported, and is a vertical surface. The print medium 9 is, for example, a cardboard box.

The conveying unit 2 includes belt conveyors 11A and 11B. The belt conveyors 11A and 11B are arranged side by side along the conveying direction (left-right direction) of the print medium 9.

The belt conveyor 11 comprises a conveyor belt 12, a drive roller 13, and a driven roller 14.

The conveyor belt 12 is a circular belt stretched across a drive roller 13 and a driven roller 14. The conveyor belt 12 is driven to circulate in a clockwise direction in FIG. 1, thereby conveying the print medium 9 placed on the conveyor belt 12 in a conveying direction (corresponding to the relative movement direction) from left to right.

The drive roller 13 rotates the conveyor belt 12 in a clockwise direction in FIG. 1. The drive roller 13 is driven by a motor (not shown).

The driven roller 14 supports the conveyor belt 12 together with the drive roller 13. The driven roller 14 is disposed at a distance from the drive roller 13 in the left-right direction. The driven roller 14 rotates in response to the rotation of the conveyor belt 12.

The printing unit 3 prints on the printing surface 9a of the print medium 9 transported by the transport unit 2. The printing unit 3 is disposed in the left-right direction within the range where the belt conveyor 11B transports the print medium 9 downstream in the transport direction of the print medium 9. The printing unit 3 includes head units 21A, 21B and a head holder 22.

Head units 21A and 21B print by ejecting ink onto the print surface 9a of the print medium 9. In this embodiment, head units 21A and 21B each eject two colors of ink. For example, head unit 21A ejects black (K) and cyan (C) ink, and head unit 21B ejects magenta (M) and yellow (Y) ink. Head units 21A and 21B have the same configuration, except for the colors of ink they eject.

The head unit 21 has multiple inkjet heads 26. In this embodiment, the head unit 21 has six inkjet heads 26.

In the head unit 21, the six inkjet heads 26 are arranged in a staggered pattern in the vertical direction. That is, in the head unit 21, two head rows 27A and 27B, each consisting of three inkjet heads 26 arranged at equal pitches in the vertical direction, are arranged with a gap between them in the left-right direction and offset by half a pitch in the vertical direction. Head row 27B is arranged downstream of head row 27A.

The inkjet head 26 ejects ink in a horizontal direction toward the printing surface 9a of the print medium 9. The inkjet head 26 is formed with a plurality of nozzles (not shown) that eject ink, arranged in the vertical direction, and has two nozzle rows arranged in parallel in the left-right direction.

The two nozzle rows of the inkjet head 26 eject ink of different colors. For example, the inkjet head 26 of head unit 21A ejects black ink from the left (upstream) nozzle row of the two nozzle rows, and ejects cyan ink from the right (downstream) nozzle row. The inkjet head 26 of head unit 21B ejects magenta ink from the left nozzle row of the two nozzle rows, and ejects cyan ink from the right nozzle row.

The head holder 22 holds the head units 21A and 21B.

Encoders 4A and 4B output pulse signals used to control the ejection of ink from head units 21A and 21B, respectively. Encoder 4 has an encoder body 31 and a roller 32.

The encoder body 31 has a rotating shaft (not shown) and outputs a pulse signal according to the rotation angle of this shaft.

The roller 32 is attached to the rotation axis of the encoder body 31 so that its rotation axis coincides with the rotation axis of the encoder body 31. This causes the encoder body 31 to output a pulse signal according to the rotation angle of the roller 32. The roller 32 comes into contact with the upper surface 9b of the print medium 9 and rotates in response to the print medium 9 being transported.

The roller 32 of the encoder 4A is disposed upstream of the upstream nozzle row of the head row 27A of the head unit 21A in the transport direction (left-right direction) of the print medium 9. Note that the roller 32 of the encoder 4A may be disposed in the same position as the upstream nozzle row of the head row 27A of the head unit 21A in the transport direction of the print medium 9.

The roller 32 of the encoder 4B is disposed upstream of the upstream nozzle row of the head row 27A of the head unit 21B in the transport direction of the print medium 9. The roller 32 of the encoder 4B may be disposed in the same position as the upstream nozzle row of the head row 27A of the head unit 21B in the transport direction of the print medium 9.

The encoder holding unit 5 holds the encoders 4A and 4B so that their rollers 32 are in contact with the top surface 9b of the print medium 9. The encoder holding unit 5 presses the rollers 32 against the top surface 9b of the print medium 9 using a spring or the like. The encoder holding unit 5 also has a mechanism for adjusting the height positions of the encoders 4A and 4B using a motor or the like. The encoder holding unit 5 corresponds to an adjustment unit.

The media height sensor 6 detects the height of the print medium 9 transported by the transport unit 2. In other words, the media height sensor 6 detects the height position of the upper surface 9b of the print medium 9, which is the surface with which the roller 32 comes into contact. The media height sensor 6 is disposed upstream of the encoder 4A. The media height sensor 6 corresponds to a media detection unit.

The print effective sensor 7 detects the length of the print surface 9a of the print medium 9 transported by the transport unit 2 in the transport direction as the print effective range. The print effective sensor 7 is arranged above the transport unit 2, upstream of the upstream nozzle row of the head row 27A of the head unit 21A. The distance between the print effective sensor 7 and the upstream nozzle row of the head row 27A of the head unit 21A in the transport direction of the print medium 9 is longer than the length in the transport direction of the print medium 9 that is the longest in the transport direction among the print media 9 that can be printed by the printing device 1. The print effective sensor 7 is arranged in the left-right direction in the range where the upstream belt conveyor 11A transports the print medium 9. The print effective sensor 7 is configured so that the height position can be adjusted. The print effective sensor 7 corresponds to the print effective range detection unit.

The control unit 8 controls the operation of each part of the printing device 1. The control unit 8 is configured with a CPU, RAM, ROM, hard disk, etc.

Specifically, the control unit 8 controls the head units 21A and 21B to eject ink onto the print medium 9 transported by the transport unit 2 to print. The control unit 8 controls the ink ejection timing (printing timing) of each inkjet head 26 of the head units 21A and 21B based on the pulse signals output by the encoders 4A and 4B.

Next, we will explain the operation of the printing device 1.

When the first print medium 9 to be printed in a series of printing operations is transported by the transport unit 2 and reaches the media height sensor 6, the media height sensor 6 detects the height of the print medium 9. Based on the detection result of the media height sensor 6, the control unit 8 controls the encoder holding unit 5 to adjust the height position of the encoders 4A and 4B so that the roller 32 contacts the top surface 9b of the print medium 9.

Here, when printing is performed on multiple print media 9 in a series of printing operations in the printing device 1, it is assumed that all of the print media 9 are of the same shape and size.

When the print medium 9 passes under the print effective sensor 7, the print effective sensor 7 detects the length of the printable surface 9a of the print medium 9 in the transport direction as the print effective range, and outputs a print effective signal indicating the print effective range, as shown in the upper part of Figure 3.

The three waveforms in the top row of FIG. 3 show the waveforms of the print enable signal, the output pulse signal of the encoder 4A, and the eccentricity correction pulse signal, which is the output pulse signal of the encoder 4A corrected based on the eccentricity information of the roller 32 as described below. The two waveforms in the middle row of FIG. 3 show the waveforms of the print enable signal and the eccentricity correction pulse signal of the encoder 4A delayed to control the ejection timing in the nozzle row on the upstream side of the head row 27A of the head unit 21A. The two waveforms in the bottom row of FIG. 3 show the waveforms of the print enable signal and the eccentricity correction pulse signal of the encoder 4A delayed to control the ejection timing in the nozzle row on the downstream side of the head row 27A of the head unit 21A.

When the print medium 9 reaches the encoder 4A, the roller 32 of the encoder 4A comes into contact with the upper surface 9b of the print medium 9 and rotates in response to the print medium 9. This causes the encoder 4A to output a pulse signal according to the rotation angle of the roller 32.

As shown in the upper part of Figure 3, the output pulse signal of the encoder 4A has a variation in pulse period due to the eccentricity of the roller 32.

In response to this, the control unit 8 corrects the output pulse signal of the encoder 4A based on the eccentricity information indicating the eccentricity of the roller 32 of the encoder 4A so as to remove the eccentricity component of the roller 32. As a result, an eccentricity correction pulse signal with a uniform pulse period is generated, as shown in the upper part of Figure 3.

Here, the eccentricity information of the roller 32 indicates the eccentricity component for one revolution of the roller 32. The control unit 8 acquires and stores the eccentricity information of the roller 32 from the encoders 4A and 4B in advance.

As shown in the middle of Fig. 3, the control unit 8 delays the print valid signal shown in the upper part of Fig. 3 according to the distance in the left-right direction between the print valid sensor 7 and the upstream nozzle row of the head row 27A of the head unit 21A. The control unit 8 also delays the eccentricity correction pulse signal of the encoder 4A shown in the upper part of Fig. 3 according to the distance in the left-right direction between the encoder 4A and the upstream nozzle row of the head row 27A of the head unit 21A.

Here, when the conveying speeds of the print medium 9 by the belt conveyors 11A and 11B are different from each other, the control unit 8 modulates the print enable signal according to the ratio of the conveying speeds of the belt conveyors 11A and 11B. For example, when the conveying speed of the belt conveyor 11A is slower than the conveying speed of the belt conveyor 11B, the control unit 8 modulates the print enable signal so that the print effective range becomes smaller according to the ratio of the conveying speeds of the belt conveyors 11A and 11B.

Then, the control unit 8 controls the upstream nozzle row of the head row 27A of the head unit 21A to eject ink based on the print image data within the effective printing range indicated by the effective printing signal in the middle row of Figure 3, at a timing based on the eccentricity correction pulse signal in the middle row of Figure 3.

In addition, as shown in the lower part of FIG. 3, the control unit 8 delays the print enable signal and the eccentricity correction pulse signal shown in the middle part of FIG. 3 according to the distance between the upstream nozzle row and the downstream nozzle row of the head row 27A of the head unit 21A in the left-right direction.

Then, the control unit 8 controls the downstream nozzle row of the head row 27A of the head unit 21A to eject ink based on the print image data within the effective printing range indicated by the effective printing signal in the lower part of Figure 3, at a timing based on the eccentricity correction pulse signal in the lower part of Figure 3.

The control unit 8 also controls the ink ejection timing of the two nozzle rows of the head row 27B of the head unit 21A in the same manner as the two nozzle rows of the head row 27A of the head unit 21A described above. That is, the control unit 8 controls the ink ejection timing of each nozzle row based on a print enable signal delayed according to the left-right position of each of the two nozzle rows of the head row 27B of the head unit 21A and an eccentricity correction pulse signal of the encoder 4A.

When the print medium 9 reaches the encoder 4B, the roller 32 of the encoder 4B comes into contact with the upper surface 9b of the print medium 9 and rotates in response to the print medium 9. This causes the encoder 4B to output a pulse signal according to the rotation angle of the roller 32.

The control unit 8 controls the ink ejection timing in the head unit 21B using the output pulse signal of the encoder 4B in a manner similar to the control of the ink ejection timing in the head unit 21A using the output pulse signal of the encoder 4A described above. That is, the control unit 8 controls the ink ejection timing of each nozzle row based on the print enable signal delayed according to the left-right position of each nozzle row of the head rows 27A and 27B of the head unit 21B and the eccentricity correction pulse signal of the encoder 4B.

However, as shown in FIG. 4, the print medium 9 being transported in the transport section 2 may be tilted relative to the transport direction (left-right direction).

In this case, the length of the printed surface 9a of the print medium 9 in the transport direction is shorter than when the print medium 9 is not tilted. In this state, when ink is ejected from the head unit 21 at a timing based on the output pulse signal (eccentricity correction pulse signal) of the encoder 4 as described above, the print image is reduced in the transport direction (left-right direction).

Therefore, when the effective print range detected by the effective print sensor 7 is smaller than the reference value and the difference is equal to or greater than a predetermined correction judgment threshold (corresponding to a predetermined value) and less than a predetermined error judgment threshold (corresponding to a threshold value) described later, the control unit 8 adjusts the output pulse signals (eccentricity correction pulse signals) of the encoders 4A and 4B to lengthen the pulse period based on the detected effective print range and the reference value.

The above-mentioned reference value is a preset value as the length of the printed surface 9a in the transport direction when there is no inclination of the print medium 9. The correction judgment threshold is a preset value as a threshold for determining whether or not to adjust the output pulse signals (eccentricity correction pulse signals) of the encoders 4A and 4B to suppress reduction of the print image due to inclination of the print medium 9. The error judgment threshold is a preset value as a threshold for determining that an error has occurred, such as excessive inclination of the print medium 9 or transport of a print medium 9 of a different size.

Specifically, when the effective print range detected by the effective print sensor 7 is smaller than the reference value and the difference is equal to or greater than the correction judgment threshold but less than the error judgment threshold, the control unit 8 adjusts the output pulse signal (eccentricity correction pulse signal) of the encoder 4A to lengthen the pulse period according to the ratio of the effective print range to the reference value, as shown in FIG. 5. For example, when the effective print range is k times (k<1) the reference value, the output pulse signal (eccentricity correction pulse signal) of the encoder 4A is adjusted so that the pulse period is 1/k times. The control unit 8 controls the ink ejection timing of the head unit 21A based on the pulse signal (adjusted pulse signal) of the encoder 4A after this adjustment.

The two waveforms in the top row of Figure 5 show the print valid signal when there is no tilt of the print medium 9, and the waveform of the output pulse signal (eccentricity correction pulse signal) of encoder 4A. The two waveforms in the bottom row of Figure 5 show the print valid signal when there is a tilt of the print medium 9 and the difference between the print valid range and the reference value is equal to or greater than the correction judgment threshold and less than the error judgment threshold, and the waveform of the pulse signal (adjustment pulse signal) of encoder 4A after adjustment based on the print valid range and the reference value.

Even if the adjustment pulse signal extends beyond the effective printing range as shown in the lower part of Figure 5, ink is ejected only within the effective printing range. This prevents ink from being ejected outside the printing surface 9a. In this case, the print image may not fit within the printing surface 9a, and part of the print image may not be printed.

While FIG. 5 shows the output pulse signal (eccentricity correction pulse signal) and adjustment pulse signal of encoder 4A, the control unit 8 also performs a similar adjustment on the output pulse signal (eccentricity correction pulse signal) of encoder 4B. Then, based on this adjusted pulse signal (adjustment pulse signal) of encoder 4B, the control unit 8 controls the ink ejection timing in head unit 21B.

When the difference between the effective print range detected by the effective print sensor 7 and the reference value is equal to or greater than the error determination threshold, the control unit 8 determines that an error has occurred. The control unit 8 controls the head units 21A and 21B so as not to print on the print medium 9 where the effective print range whose difference from the reference value is equal to or greater than the error determination threshold has been detected. The control unit 8 then displays error information on a display unit (not shown) to notify the user that an error has occurred.

As described above, in the printing device 1, the rollers 32 of the encoders 4A and 4B come into contact with the print medium 9 and rotate in response to the print medium 9 being transported. The control unit 8 controls the ink ejection timing of each inkjet head 26 of the head units 21A and 21B based on the pulse signals output by the encoders 4A and 4B in accordance with the rotation angle of each roller 32. As a result, even if there is unevenness in the transport speed of the print medium 9 due to uneven thickness of the transport belt 12, the ink ejection timing can be controlled in accordance with the movement of the print medium 9, thereby reducing ink landing deviation. As a result, deterioration in print image quality can be reduced.

In addition, in the printing device 1, the medium height sensor 6 detects the height position of the top surface 9b of the printing medium 9. Based on the height position of the top surface 9b detected by the medium height sensor 6, the control unit 8 controls the encoder holding unit 5 to adjust the height positions of the encoders 4A and 4B so that the roller 32 contacts the top surface 9b. This makes it possible to accommodate various printing media 9 with different heights.

In addition, in the printing device 1, the control unit 8 corrects the output pulse signals of the encoders 4A and 4B based on the eccentricity information of the rollers 32 of the encoders 4A and 4B. This reduces the ink landing deviation caused by the eccentricity of the rollers 32, thereby further reducing the deterioration of print image quality.

In addition, in the printing device 1, the control unit 8 controls the head units 21A and 21B to eject ink within the effective printing range detected by the effective printing sensor 7. This makes it possible to prevent ink from being ejected outside the printing surface 9a of the printing medium 9 with high precision.

In addition, in the printing device 1, when the effective print range detected by the effective print sensor 7 is smaller than the reference value and the difference is equal to or greater than the correction judgment threshold and less than the error judgment threshold, the control unit 8 adjusts the output pulse signals (eccentricity correction pulse signals) of the encoders 4A and 4B based on the detected effective print range and the reference value to lengthen the pulse period. This makes it possible to reduce the reduction of the printed image on the printing medium 9 that is tilted relative to the transport direction.

In addition, in the printing device 1, the control unit 8 determines that an error has occurred if the difference between the effective print range detected by the effective print sensor 7 and the reference value is equal to or greater than the error determination threshold. This makes it possible to detect errors such as excessive inclination of the print medium 9 or conveyance of a print medium 9 of a different size.

[Second embodiment]
Next, a second embodiment in which the printing device 1 of the first embodiment is partially modified will be described below. Fig. 6 is a plan view showing a schematic configuration of the printing device according to the second embodiment.

As shown in FIG. 6, the printing device 1A according to the second embodiment is configured in such a way that the encoder holding unit 5 is replaced with an encoder holding unit 5A and the medium height sensor 6 is omitted, in comparison with the printing device 1 according to the first embodiment described above.

The encoder holding unit 5A holds the encoders 4A and 4B so that their rollers 32 are in contact with the rear side 9c of the print medium 9. The encoder holding unit 5A presses the rollers 32 against the side 9c of the print medium 9 using a spring or the like. The encoder holding unit 5 also has a mechanism for adjusting the positions of the encoders 4A and 4B in the front-to-rear direction using a motor or the like. The encoder holding unit 5A corresponds to an adjustment unit.

In the printing device 1A, the print effective sensor 7 detects the print effective range and detects the front-to-rear position of the side surface 9c of the print medium 9, which is the surface that the roller 32 contacts. In other words, the print effective sensor 7 corresponds to the print effective range detection unit and the medium detection unit.

During the printing operation of the printing device 1A, the control unit 8 controls the encoder holding unit 5A to adjust the positions of the encoders 4A and 4B in the front-to-rear direction based on the position of the side 9c of the print medium 9 in the front-to-rear direction detected by the print validity sensor 7 so that the roller 32 contacts the side 9c.

Other than this, the operation of the printing device 1A is the same as that of the printing device 1 of the first embodiment described above.

As described above, in the printing device 1A, the print validity sensor 7 detects the front-to-rear position of the side 9c of the print medium 9. Based on the front-to-rear position of the side 9c of the print medium 9 detected by the print validity sensor 7, the control unit 8 controls the encoder holding unit 5A to adjust the front-to-rear position of the encoders 4A and 4B so that the roller 32 contacts the side 9c. This makes it possible to accommodate various print media 9 with different widths (lengths in the front-to-rear direction).

In addition, in the printing device 1A, the roller 32 comes into contact with the side surface 9c of the printing medium 9. Therefore, when the printing medium 9 is a cardboard box, the roller 32 passes over the step at the butt joint of the flaps on the top surface 9b, which can prevent the output pulse signals of the encoders 4A and 4B from being disrupted.

[Other embodiments]
As described above, the present invention has been described by the first and second embodiments, but the descriptions and drawings forming part of this disclosure should not be understood as limiting the present invention. Various alternative embodiments, examples and operating techniques will become apparent to those skilled in the art from this disclosure.

In the first and second embodiments described above, a configuration is described in which two encoders 4A and 4B are provided corresponding to the head units 21A and 21B, respectively. However, it is also possible to omit the encoder 4B and control the ink ejection timing of each inkjet head 26 of the head units 21A and 21B based on the output pulse signal of the encoder 4A.

In the first and second embodiments described above, the output pulse signals of the encoders 4A and 4B are corrected based on the eccentricity information of the roller 32, but this correction may be omitted. For example, this correction may be omitted in cases where the ink landing deviation caused by the eccentricity of the roller 32 can be tolerated.

In the first and second embodiments described above, the reference value for the effective print range is a preset value. However, the average value of the effective print range of a predetermined number of print media 9 most recently transported may be used as the reference value for the effective print range.

In the first and second embodiments described above, when the effective print range detected by the effective print sensor 7 is smaller than the reference value and the difference is equal to or greater than the correction determination threshold and less than the error determination threshold, the pulse period of the output pulse signal (eccentricity correction pulse signal) of the encoders 4A and 4B is adjusted to be longer.

On the other hand, due to individual variations in the printing medium 9, an effective printing range may be detected that is larger than the reference value and whose difference from the reference value is equal to or greater than the correction judgment threshold and less than the error judgment threshold. In this case, the output pulse signals (eccentricity correction pulse signals) of the encoders 4A and 4B may be adjusted to lengthen the pulse period based on the detected effective printing range and the reference value so that the print image is enlarged according to the length of the print surface 9a in the transport direction. For example, when the effective printing range is m times the reference value (m>1), the output pulse signals (eccentricity correction pulse signals) of the encoders 4A and 4B may be adjusted so that the pulse period is m times. This makes it possible to form a print image according to the length of the print surface 9a in the transport direction.

In the first and second embodiments described above, the process of determining that an error has occurred when the difference between the effective print range detected by the effective print sensor 7 and the reference value is equal to or greater than the error determination threshold may be omitted. In this case, when the difference between the effective print range detected by the effective print sensor 7 and the reference value is equal to or greater than the correction determination threshold, the control unit 8 adjusts the output pulse signals (eccentricity correction pulse signals) of the encoders 4A and 4B based on the detected effective print range and the reference value.

In the first and second embodiments described above, the inkjet printing devices 1 and 1A are described, but the present invention can also be applied to other types of printing devices, such as electrophotographic printing devices.

In the first and second embodiments described above, the line-type inkjet printing device 1, 1A was described. However, the present invention is not limited to this, and can be applied to a printing device in which the printing unit and the encoder move relative to the printing medium, and the printing timing in the printing unit is controlled based on the output pulse signal of the encoder to print on the printing medium.

As such, the present invention naturally includes various embodiments not described here. Therefore, the technical scope of the present invention is determined only by the invention-specific matters related to the scope of the claims that are appropriate from the above explanation.

[Additional Notes]
This application discloses the following inventions.

(Appendix 1)
a printing unit that prints on the printing medium while moving relatively to the printing medium;
an encoder having a roller that comes into contact with the print medium and rotates in accordance with the print medium, the encoder moving relatively to the print medium and outputting a pulse signal in accordance with the rotation angle of the roller;
a control unit that controls print timing in the printing unit based on the pulse signal output by the encoder.

(Appendix 2)
a medium detection unit that detects the position of the surface of the print medium that the roller contacts;
An adjustment unit that adjusts a position of the encoder is further provided,
The printing device described in Appendix 1, characterized in that the control unit adjusts the position of the encoder to the adjustment unit so that the roller contacts the surface based on the position of the surface detected by the medium detection unit.

(Appendix 3)
3. The printing device according to claim 1, wherein the control unit corrects the pulse signal output by the encoder based on eccentricity information of the roller.

(Appendix 4)
a printable area detection unit that detects the length of the print surface of the print medium in the direction of relative movement between the print medium and the printing unit as the printable area;
3. The printing device according to claim 1, wherein the control unit controls the printing unit so as to perform printing within the effective print range detected by the effective print range detection unit.

(Appendix 5)
The printing device described in Appendix 4, characterized in that when the difference between the effective print range detected by the effective print range detection unit and a reference value is equal to or greater than a predetermined value, the control unit adjusts the pulse signal output by the encoder based on the detected effective print range and the reference value.

(Appendix 6)
The printing device described in Appendix 4, characterized in that the control unit determines that an error has occurred when the difference between the effective print range detected by the effective print range detection unit and a reference value is equal to or greater than a threshold value.

REFERENCE SIGNS LIST 1, 1A Printing device 2 Transport section 3 Printing section 4, 4A, 4B Encoder 5, 5A Encoder holder 6 Media height sensor 7 Effective print sensor 8 Control section 9 Printing medium 9a Printed surface 9b Top surface 9c Side surface 11, 11A, 11B Belt conveyor 21, 21A, 21B Head unit 26 Inkjet head 27A, 27B Head row 31 Encoder body 32 Roller

Claims (6)

a printing unit that prints on the printing medium while moving relatively to the printing medium;
an encoder having a roller that comes into contact with the print medium and rotates in accordance with the print medium, the encoder moving relatively to the print medium and outputting a pulse signal in accordance with the rotation angle of the roller;
a control unit that controls print timing in the printing unit based on the pulse signal output by the encoder. a medium detection unit that detects the position of the surface of the print medium that the roller contacts;
An adjustment unit that adjusts a position of the encoder is further provided,
The printing device according to claim 1 , wherein the control unit controls the adjustment unit to adjust the position of the encoder so that the roller contacts the surface, based on the position of the surface detected by the medium detection unit. The printing device according to claim 1 or 2, characterized in that the control unit corrects the pulse signal output by the encoder based on the eccentricity information of the roller. a printable area detection unit that detects the length of the print surface of the print medium in the direction of relative movement between the print medium and the printing unit as the printable area;
3. The printing apparatus according to claim 1, wherein the control unit controls the printing unit so as to perform printing within the effective print range detected by the effective print range detection unit. The printing device according to claim 4, characterized in that the control unit adjusts the pulse signal output by the encoder based on the detected effective print range and the reference value when the difference between the effective print range detected by the effective print range detection unit and the reference value is equal to or greater than a predetermined value. The printing device according to claim 4, characterized in that the control unit determines that an error has occurred when the difference between the effective print range detected by the effective print range detection unit and a reference value is equal to or greater than a threshold value.