JP2012131171A - Printing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To support a sheet so that a distance between the sheet and a print head is maintained within an acceptable range while reducing the effect of cockling.SOLUTION: A printing apparatus includes a platen having a support part that supports the sheet conveyed in a first direction at a position opposite to the print head. A plurality of first ribs having the first height are provided along a second direction intersecting to the first direction and a plurality of cells sandwiched by adjacent first ribs are arranged in the support part. Two second cells having the second height that is lower than the first height are provided along in the second direction in the respective cells. Regarding some of the plurality of cells, the third rib whose height is equal to or lower than the second one between two of the second ribs in the second direction.

Description

  The present invention relates to a printing apparatus having a platen that supports a conveyed sheet.

  In ink jet printing, deformation (hereinafter referred to as cockling) such as wrinkles or undulations may occur in a sheet on which ink has been absorbed. When the cockling is increased, the distance between the sheet and the print head is not constant, the ink landing position is deviated, and the image quality is deteriorated. Further, when the sheet floats up, the floated part may come into contact with the print head.

  Patent Document 1 discloses a technique for reducing cockling. The platen that supports the sheet is provided with a plurality of ribs along the sheet conveyance direction, and a spur that locally presses the sheet is provided near the ribs. The shape of the sheet is made to follow the plurality of formed ribs, and minute unevenness that does not affect the image quality is generated in the sheet. The elongation of the sheet that has been swollen by absorbing the ink is absorbed by minute irregularities, thereby preventing unintentional large sheet lifting.

JP 2000-158644 A

  In the configuration of Patent Document 1, all the plurality of ribs are formed at equal intervals. Depending on the size of the sheet to be used, there is a possibility that the end of the sheet jumps greatly and the sheet comes into contact with the print head.

  FIG. 12 is a schematic diagram for explaining the situation. It has a configuration in which adjacent ribs 241 and two ribs 242 provided in a region between them are provided. The rib 241 is higher than the rib 242. The sheet S is pressed from above by the spurs 29 and 30 that are rotating bodies, and has a shape that follows the wave shape on the upper surfaces of the plurality of ribs. Here, it is assumed that the end of the sheet S in the sheet width direction is located in this region. When the spur 30 located at the center of the two ribs 242 presses the seat, the pressed portion sinks between the two ribs 242 and the reaction moves the seat end upward. The rib 241 on the right side in the drawing has a spur 29, so that the lifting of the seat is suppressed. On the other hand, there is no possibility that the sheet end on the left side in FIG. If the sheet jumps larger than the height of the ribs 241, the distance from the print head becomes smaller than the original and the quality of the printed image deteriorates. Further, when the jump is increased, the print head and the sheet come into contact with each other, and there is a possibility that unnecessary ink adheres to the sheet and becomes dirty or damages the print head.

  The present invention has been made in view of the above-described problems, and enables sheet support such that the distance between the sheet and the print head is maintained within an allowable range while reducing the influence of cockling. An object of the present invention is to provide a printing apparatus.

  The printing apparatus of the present invention includes a print head that applies ink to a sheet, and a platen that includes a support unit that supports a sheet conveyed in a first direction at a position facing the print head. A plurality of first ribs having a first height are provided along a second direction intersecting the first direction, and a plurality of cells sandwiched between the adjacent first ribs are formed. In each cell, two second ribs having a second height lower than the first height are provided along the second direction, and some of the plurality of cells are A third rib having a height less than or equal to the second height is provided between the two second ribs in the second direction.

  According to the present invention, it is possible to realize a printing apparatus that can support a sheet while reducing the influence of cockling and maintaining the distance between the sheet and the print head within an allowable range.

1 is a perspective view illustrating an overall configuration of a printing apparatus according to a first embodiment. Perspective view showing the detailed structure of the transport unit Partial enlarged view showing the structure of the platen support Partial conceptual diagram showing the structure of the platen support (front view) Cross section of the platen viewed from the side The figure for demonstrating the state of the sheet | seat on a support part The figure for demonstrating the state of the sheet | seat on a support part The figure for demonstrating the state of the sheet | seat on a support part The perspective view which shows the detailed structure of the conveyance part in 2nd Embodiment. The figure for explaining the state of the sheet on the support part (side view) The figure which shows the example of the arrangement | sequence of the cell on the platen corresponding to the sheet | seat of several sizes The figure for demonstrating the subject of a prior art example

  FIG. 1 is a perspective view showing the overall configuration of the printing apparatus according to the first embodiment of the present invention. A supply unit 201 for supplying a cut sheet or a continuous sheet, a conveyance unit 202 for conveying the supplied sheet, and a print unit 203 (carriage unit) for forming an image by applying ink to the sheet are provided. Further, a recovery unit 204 is provided for performing maintenance such as cleaning in order to maintain the performance of the printing unit 203.

  The supply unit 201 supplies sheets of a size set by the user corresponding to sheets of a plurality of sizes (meaning sheet width). The conveyance unit 202 includes a conveyance roller 21, a discharge roller 23, and a motor 26 for rotationally driving them, and step-conveys the sheet in the sub-scanning direction (first direction). The printing unit 203 includes a carriage that reciprocates in the main scanning direction (second direction) that intersects (orthogonally in the present embodiment) with the sub-scanning direction, and a print head 200 that is mounted on the lower portion of the carriage (not shown in FIG. 1). It is composed of The print head 200 has an ink jet head in which a plurality of nozzles are arranged, and an element for applying energy for ejecting ink, such as a heating element, a piezoelectric element, an electrostatic element, and a MEME element, is provided for each nozzle. A sheet printed by the printing unit 203 is nipped between a discharge roller 23 and a spur 25 (roller) that rotate in conjunction with the conveyance roller 21 and is discharged to a discharge tray 28.

  The printing apparatus according to the present embodiment employs a so-called serial printing method. An image is printed on the entire sheet by alternately repeating a printing operation for ejecting ink from the print head in synchronization with the reciprocating movement of the carriage (main scanning) and a sheet feeding operation for step-feeding (sub-scanning) the sheet at a predetermined pitch. Will be formed. The present invention is not limited to the serial printing method, and may be a line printing method.

  The recovery unit 204 is for maintaining and recovering a normal state by eliminating nozzle clogging and the like of the print head. The recovery unit 204 includes a pump that generates pressure for sucking or discharging ink from the discharge port, a cap for covering the discharge port to prevent drying, and a wiper for wiping and cleaning the discharge port surface.

  FIG. 2 is a perspective view showing a detailed structure of the transport unit 202. The platen 24 has a support portion that supports the sheet S conveyed in the first direction at a stable height position, and the support portion is provided at a position facing the print head 200. The conveyance roller 21 is located upstream of the support portion of the platen 24 and the print head 200 in the first direction (the direction in which the sheet is conveyed during printing). The rotation center (rotation shaft) of the pinch roller 22 is arranged offset from the rotation center (rotation shaft) of the conveyance roller 21 on the downstream side in the conveyance direction, and is urged by the conveyance roller 21 to be driven to rotate. Due to this offset, the sheet S nipped between the pair of rollers composed of the conveying roller 21 and the pinch roller 22 is pressed against the support portion of the platen 24 in a printed state. A code wheel 31 for reading rotation by an encoder sensor is attached to the transport roller 21 coaxially with the rotation, and rotates together with the transport roller 21.

  The discharge roller 23 is located downstream of the print head 200 in the first direction. The spur 25, which is a rotating body, is energized by the discharge roller 23 and rotated. The discharge roller 23 includes a roller portion 23 a and a shaft portion 23 b having a smaller diameter than the roller portion 23, and the shaft portion 23 b does not contact the sheet S. A gear 33 is attached to the discharge roller 23 coaxially. The discharge roller 27 assists the discharge roller 23. The spur 29 is urged by the discharge roller 27 and rotated. As with the discharge roller 23, the discharge roller 27 includes a roller portion 27a and a rotating shaft 27b. The spur 30 is provided between the adjacent spurs 29. The spur 30 is provided as an urging member that locally pushes the surface of the conveyed sheet S in a direction away from the print head 200. The spur 25, the spur 29, and the spur 30 are all urged by a spring that is an elastic body. Instead of the spur that is a rotating body, a fixed protrusion that locally contacts the sheet without rotating to the same position may be provided as the urging member.

  The conveying roller 21, the discharging roller 23, and the discharging roller 27 are rotated so that the driving force of the motor 26 is transmitted through the gear train of the gear 32, the gear 33, the gear 34, and the gear 35 and the sheet S is conveyed at substantially the same speed. To do.

  3 is a partially enlarged view (perspective view) showing the structure of the support portion of the platen, FIG. 4 is a partially enlarged view (front view) showing the structure of the support portion of the platen, and FIG. 5 is a sectional view of the platen as viewed from the side. It is. In order to support the sheet S conveyed during printing, the support portion is provided with a plurality of ribs extending along the first direction and having convex cross-sectional shapes having different heights along the second direction. There are three types of ribs: a first rib 241, a second rib 242, and a third rib 243. The first rib 241, the second rib 242, and the third rib 243 are all provided upstream of the roller portion 27 a of the discharge roller 27 in the first direction (sheet conveyance direction). The conveyed sheet is supported by the first rib 241, the second rib 242 and the third rib 243.

  The first rib 241 has the highest first height, and a plurality of first ribs 241 are provided along the second direction. A plurality of regions (hereinafter referred to as cells) sandwiched between adjacent first ribs 241 are formed along the second direction. In each of the plurality of cells, two second ribs 242 having a second height lower than the first height are provided along the second direction. Further, in some of the plurality of cells, a third rib 243 having a height equal to or lower than the second height is provided between the two second ribs 242 in the second direction. In the present embodiment, the third rib 243 has the same height as the second rib 242, but may have a slightly lower height.

  The first rib 241 includes an upper surface portion 241a and an inclined portion 241b, the second rib 242 includes an upper surface portion 242a and an inclined portion 242b, and the third rib 243 includes an upper surface portion 243a and an inclined portion 243b. The upper surface portions 241a, 242a, and 243a are parallel to the nozzle forming surface 2001 of the print head 200. In the first direction, the length of the third rib 243 is shorter than the length of the second rib 242, and the length of the second rib 242 is shorter than the length of the first rib 241.

  A roller portion 27a and a spur 29 are provided downstream of the first rib 241 in the first direction as rollers that locally nip the surface of the conveyed sheet. Further, in the cell provided with the third rib 243, a spur 30 as a biasing member that pushes the surface of the conveyed sheet locally in the direction away from the print head downstream of the third rib 243 in the first direction. Is provided. Furthermore, a similar spur 30 is provided at a position corresponding to a position between the two second ribs 242 (intermediate position) even in a cell in which the third rib 243 is not provided. As shown in FIG. 4, the spur 30 is configured such that the lowermost point of the spur is bitten in the direction of the platen rather than the upper surface portions of the second rib 242 and the third rib 243 in a state where there is no sheet S. Has been.

  Further, as shown in FIG. 4, the region A between the adjacent first ribs 241 of the cell provided with the third rib 243 and the adjacent first rib 241 of the cell not provided with the third rib 243 are provided. Comparing the region B between them, the region A is wider than the region B. That is, the cell in which the third rib 243 is provided is wider in the second direction than the cell in which the third rib 243 is not provided. In addition, the cell in which the third rib 243 is provided has a wider interval between the two second ribs 242 than the cell in which the third rib 243 is not provided.

  Thus, the interval between the plurality of first ribs 241 and the interval between the second ribs 242 in the cell are not uniform. The reason for this will be described. The printing apparatus according to the present embodiment can handle sheets having a plurality of sizes (sheet width in the second direction). In this case, if the interval between the first ribs 241 and the interval between the second ribs 242 that are optimal for a certain size sheet are set, there is a possibility that trouble may occur when conveying other size sheets. For example, when a sheet of another size is set, there is a possibility that the first rib 241 or the second rib 242 is positioned very close to the sheet end in the sheet width direction. As a result, the nip of the sheet by the discharge roller 23 and the spur 25 becomes unstable, and there is a possibility that the end of the sheet warps or a conveyance jam occurs. In order to avoid such a situation, for each of a plurality of size sheets assumed to be used, ribs are arranged as a cell array in which cells having third ribs are formed at positions where the end portions of the sheets pass. The interval is no longer uniform.

  In the present embodiment, so-called center reference that corresponds to five sizes of A3, B4, A4, B5, and A5 and supplies sheets with different sizes aligned with the center of the sheet width center line in the second direction as a reference. Assume that a sheet is supplied. By arranging the cells at non-uniform intervals as shown in FIG. 11, the sheet end portion can be positioned in the cell having the third rib with respect to all the sheet sizes. In the figure, the dimension in the width direction of the cell (A) provided with the third rib 243 is 25 mm, and the dimension in the width direction of the cell (B) not provided with the third rib 243 is 23.5 mm.

  Here, it is examined whether all the cells can be made the same size. The width of the sheet in the second direction is A3 = 297 mm, B4 = 257 mm, A4 = 210 mm, B5 = 182 mm, and A5 = 148 mm. Here, in order to suppress the influence of cockling, it is desirable that the interval between the adjacent first ribs 241 is about 20 to 30 mm, and further, the spur 30 is disposed substantially at the center of the first rib 241. The distance between one rib 241 and the nearest spur 30 is about 10 to 15 mm. Further, considering the skew and the component tolerance during sheet supply and conveyance, the distance between the sheet end, the first rib 241 and the spur 30 needs to be at least 2 to 3 mm. That is, it is necessary to arrange the sheet end portions in a limited area of 5 to 10 mm. When the sheet is supplied on the basis of the center, the distance between the corresponding end portions of the respective sizes is 14 mm, 17 mm, 23.5 mm, and 20 mm, and cannot be arranged in the limited region described above. Therefore, it can be seen that it is difficult to allocate the cells at equal intervals so as to satisfy all these dimensions.

  Next, the state of the sheet on the platen support will be described in more detail. The sheet S is supplied from the supply unit 201 as a sheet having an arbitrary size among the sizes expected to be used. As shown in FIG. 5, the pinch roller 22 is arranged slightly offset downstream from the conveying roller 21, so that the sheet S conveyed while being nipped by the conveying roller 21 and the pinch roller 22 is placed on the platen 24. Pressed against the support.

  The sheet S is nipped and conveyed by the conveying roller 21 and the pinch roller 22 and the discharging roller 27 and the spur 29 on the platen. At this time, the spur 30 pushes the surface of the sheet S locally in a direction away from the print head 200 (direction approaching the platen 24). FIG. 6A shows the state at that time as viewed from the front. By the pressing action of the spur 30, the sheet S becomes a undulating state of minute irregularities with the position of the spur 30 as a valley that bulges downward and the position of the first rib 241 as the top of a mountain that bulges upward. A solid line (a) shows the actual shape of the sheet S. In the area A, since the third rib 243 is provided at substantially the center of the second rib 242, the amount by which the seat S is pushed down by the spur 30 is restricted so as not to become too large. A broken line (b) shows the shape of the sheet S when the third rib 243 is not provided in the region A. From this comparison, it can be seen that in the region A, the change in the distance between the print head 200 and the sheet S falls within a certain range due to the presence of the third rib 243. This range is set so as not to affect the quality of the printed image.

  On the other hand, the third rib 243 is not provided in the region B. The dimensions are set so that the distance between the first ribs 241 and the distance between the second ribs 242 in the area B are narrower than the distance between the first ribs 241 and the distance between the second ribs 242 in the area A, respectively. The amount by which the sheet S is pushed down by the spur 30 is regulated by the interval between the first ribs 241 and the interval between the second ribs 242. The amount to be pushed down is mainly determined by the distance between the two second ribs 242 and the urging force of the spur 30. Even in the region B, the change in the distance between the print head 200 and the sheet S falls within a range that does not affect the image quality.

  By the way, when high duty (high density) image printing is performed on the sheet S, a large amount of ink droplets are ejected onto the sheet S from the print head 200. If the material of the sheet S has water absorption like paper, the sheet S swells due to moisture absorption. The more moisture that is absorbed, the greater the swelling. At this time, the sheet S tends to extend in a direction in which the amplitude of the wavy state increases. This is cockling.

  In the vicinity of the platen 24, the surface of the sheet S is pressed by a spur 25, a spur 29, and a spur 30. The back surface of the sheet S is supported by a first rib 241, a second rib 242, and a third rib 243 formed on the support portion of the platen 24. In addition, by the pinch roller 22 whose axis is offset with respect to the conveying roller 21, a force urging the sheet S on the downstream side to the support portion of the platen 24 acts. By correcting the shape of the sheet by these combined actions, the influence of cockling is suppressed.

  FIG. 6B is a diagram illustrating a sheet state in high duty printing. A solid line (a) is a state of the sheet S before ink is applied or when a small amount of ink is applied, and a broken line (c) is a state of the sheet S when a large amount of ink is applied. Even if the sheet is greatly swollen by a large amount of ink, in the region A, the sheet is in the region restricted by the spur 29, the spur 30, the first rib 241, the second rib 242, and the third rib 243 as indicated by a broken line (c). The elongation of S is absorbed. Similarly, in the region B, the elongation of the sheet S is absorbed in the region regulated by the spur 29, the spur 30, the first rib 241 and the second rib 242. As a result, it is possible to suppress the sheet S from floating in the direction of the print head in both the area A and the area B.

  The elongation of the sheet grows as time passes after ink is applied, that is, as the sheet is conveyed downstream. As described above with reference to FIG. 3, the upper surface portion 243 a of the third rib 243 is configured to be shorter in the first direction than the upper surface portion 241 a of the first rib 241 and the upper surface portion 242 a of the second rib 242. For this reason, even if the elongation of the sheet becomes large, the local portion of the sheet S that has come off the third rib 243 downstream of the ink application region can be released in the direction away from the print head 200.

  FIG. 7 is a diagram illustrating a state of the sheet S when an end portion in the width direction of the sheet S is positioned in a cell in which the third rib 243 is provided. FIG. 7A is a view for explaining the role of the third rib 243. In this example, the sheet S is supported by the second rib 242 and the third rib 243, and the sheet end is in a position where it does not contact the outer first rib 241. That is, the end of the sheet S is not nipped by the discharge roller 27 and the spur 29. The solid line (a) shows the state of the sheet S in the configuration in which the third rib 243 is provided, and the broken line (b) shows the state of the sheet S when the third rib 243 is not present. When there is no third rib 243, the sheet S is pushed down below the height of the second rib 242 by the spur 30. Then, as indicated by a broken line (c), the sheet S is supported by the two second ribs 242 and has a concave curved shape, and the end portion of the sheet S jumps upward. When the end portion is lifted higher than the first rib 241, the print head 200 may come into contact with the end portion. This is the same phenomenon as described above with reference to FIG.

  On the other hand, in the configuration of the present embodiment in which the third rib 243 is provided at substantially the center of the second rib 242, the amount by which the sheet S is pushed down by the spur 30 is restricted to an allowable range. Therefore, as indicated by the solid line (a), the vicinity of the end of the sheet is along the support portion defined by the two second ribs 242 and the third rib 243, and the sheet is relative to the nozzle forming surface 2001 of the print head 200. It becomes almost horizontal.

  FIG. 7B is a diagram illustrating a sheet state in high duty printing. A solid line (a) is a state of the sheet S before ink is applied or when a small amount of ink is applied, and a broken line (c) is a state of the sheet S when a large amount of ink is applied. Even if the sheet is greatly swollen by a large amount of ink, the elongation of the sheet S is absorbed in the cell as indicated by a broken line (c). Since the sheet S is not nipped outside the spur 30 and is in an open state, the extension of the sheet is absorbed by the end portion of the sheet S being displaced outward. Inside the spur 30, the sheet S is bent between the first rib 241 and the second rib 242 so that the elongation of the sheet is absorbed. As a result, the end of the sheet S is prevented from floating in the direction of the print head.

  Thus, since the cell which has the 3rd rib 243 is formed in the position where the edge part of the sheet | seat of the size assumed to use passes, the big lift of a sheet | seat edge part is suppressed. As a result, the quality of the high print image is high, and a part of the sheet is prevented from coming into contact with the print head. If the cells in FIG. 7 are the outermost cells, that is, the cells corresponding to the end of the maximum size sheet that is assumed to be used, the outer spur 29 and the first rib 241 do not touch the sheet, so May be omitted.

  FIG. 8 shows a modification of the platen support. The difference from the above-described embodiment is that the height of the second rib 242A provided in the cell (region A) having the third rib 243 is the second height provided in the cell (region B) not having the third rib. It is lower than the height of the rib 242B. The two second ribs 242 and the third ribs 243 in the region A have the same height. In the high duty printing, the sheet S has a shape as indicated by a broken line (c). In the broken line (c), the lowest portion of the sheet between the second rib 242A and the third rib 243 in the region A and the lowest portion of the sheet between the two second ribs 242B in the region B , The heights of the sheets are almost equal. That is, the height variation of the sheet S due to the occurrence of cockling is almost equal between the region A and the region B.

  As described above, according to the first embodiment, the sheet is supported so as to maintain the distance between the sheet and the print head within an allowable range while reducing the influence of cockling. This realizes a printing apparatus that can obtain high image quality over the entire sheet.

<Second Embodiment>
A printing apparatus according to a second embodiment of the present invention will be described. In this embodiment, borderless printing can be performed. Borderless printing is a mode in which an image is formed without margins at the edge of the sheet S. In consideration of cutting error of the sheet S, conveyance error, skewing, and the like, ink is applied to an area slightly larger than the sheet S.

  FIG. 9 is a partially enlarged view showing the structure of the support portion of the platen, and FIG. 10 is a sectional view seen from the side. The platen has a support portion divided into an upstream support portion 241 and a downstream support portion 242 with a groove 240 for receiving ink ejected from the print head interposed therebetween. An ink absorber 100 is provided in the groove 240, and the ink absorber 100 receives ink ejected to the outside of the sheet S during borderless printing.

  The upstream support portion 241 is provided with a first rib 241-1, second ribs 242-1A, 242-1B, and a third rib 243-1 in the same arrangement as in the above-described embodiment. The relationship between the heights of these ribs is the same as in the above-described embodiment. The downstream support portion 242 is also provided with the first rib 241-2, the second ribs 242-2A, 242-2B, and the third rib 243-2 at the same arrangement and interval as the upstream support portion 241. Yes.

  As shown in FIG. 10, the upstream support 241 and the groove 240 are mainly opposed to the nozzle forming surface 2001 of the print head 200. Therefore, the distance between the print head 200 and the sheet S is mainly determined by the first rib 241-1, the second ribs 242-1A, 242-1B, the third rib 243-1, and the downstream side of the upstream support 241. This is the first rib 241-2 of the side support 242. The influence of the second ribs 242-2A, 242-2B and the third ribs 243-2 of the downstream support 242 is small.

  The cockling of the sheet S grows as it is transported downstream after transporting ink. Therefore, the extension of the sheet S on the downstream side support 242 is larger than that on the upstream side support 241. In the downstream support 242, the height of the second ribs 242-2A and the third ribs 243-2 in the region A is slightly lower than the second ribs 242-2B in the region B, thereby swelling the sheet S. The space to absorb is widened so that larger elongation can be absorbed. In this manner, the seat cockling is configured to grow with time.

  According to the second embodiment, the sheet is supported so that the distance between the sheet and the print head is maintained within an allowable range while reducing the influence of cockling. Therefore, a printing apparatus that can obtain high image quality over the entire sheet and can perform borderless printing is realized.

24 platen 29 spur 30 spur 200 print head 241 first rib 242 second rib 243 third rib

Claims (11)

A print head for applying ink to the sheet;
A platen having a support portion for supporting a sheet conveyed in the first direction at a position facing the print head;
The support portion includes
A plurality of first ribs having a first height are provided along a second direction intersecting the first direction, and a plurality of cells sandwiched between the adjacent first ribs are formed.
In each of the plurality of cells, two second ribs having a second height lower than the first height are provided along the second direction,
In some of the plurality of cells, a third rib having a height equal to or lower than the second height is provided between the two second ribs in the second direction. A printing device.   2. The urging member that pushes the surface of the conveyed sheet locally in a direction away from the print head is provided downstream of the third rib in the first direction. Printing device.   The urging member that pushes the surface of the conveyed sheet locally in the direction away from the print head is further provided downstream of the first rib in the first direction. The printing apparatus as described.   The printing apparatus according to claim 2, wherein the urging member is a rotating body that rotates following contact with the sheet.   5. The printing apparatus according to claim 1, wherein a cell having the third rib is formed at a position through which an end of a sheet of a size that is assumed to be used passes. .   6. The cell according to claim 1, wherein the cell provided with the third rib is wider in the second direction than a cell not provided with the third rib. 7. The printing apparatus as described.   The printing apparatus according to claim 6, wherein a cell provided with the third rib has a wider interval between the two second ribs than a cell not provided with the third rib.   The height of the second rib provided in the cell having the third rib is lower than the height of the second rib provided in the cell not having the third rib. 8. The printing apparatus according to any one of 7 above.   The length of the third rib is shorter than the length of the second rib in the first direction, and the length of the second rib is shorter than the length of the first rib. The printing apparatus according to any one of 1 to 8.   In the platen, the support portion is divided into an upstream support portion and a downstream support portion with a groove portion for receiving ink ejected from the print head, and the second rib provided on the upstream support portion. The height of each of the third ribs is higher than the height of each of the second ribs and the third ribs provided in the downstream support portion. The printing apparatus according to item 1.   In the second direction, there is provided a roller pair composed of a conveyance roller and a pinch roller closer to the print head than the conveyance roller for nipping and conveying the sheet upstream of the support portion of the platen. 11. The printing apparatus according to claim 1, wherein a rotation center of the pinch roller is offset from a rotation center of the conveyance roller at a downstream side.

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