Inkjet recording apparatus

A carriage with a recording head mounted therein is movably supported by a first guide member extending in a direction intersecting with a recording medium transport direction “a”. The first guide member elastically deforms accompanying movements of the carriage and is arranged deviated from a gravity center of the carriage in the transport direction “a”. An area of a second guide member that is in contact with the carriage curves in a direction containing a component of a direction parallel to the recording medium transport direction “a” in order to guide rotation of the carriage owing to the carriage's own weight when the carriage moves along the first guide member.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an inkjet recording apparatus.

2. Description of the Related Art

In an inkjet recording apparatus, a recording head has a certain distance to a recording medium, and an image is recorded onto the recording medium as a result of an ink discharged from the recording head flying through a space between the recording head and the recording medium and reaching the recording medium. Accordingly, when there is variation in the ink flight time and/or discharge vector, the ink landing positions on the recording medium become different from one another, causing image deterioration. The recording head is mounted in a carriage, which reciprocates in a direction intersecting with a transport direction of the recording medium, and thus, in order to provide favorable image recording, it is important to maintain the parallelism of reciprocation of the carriage and the flatness of the recording medium itself.

In order to maintain the parallelism of reciprocation of the carriage, that is, for a guide member for making the carriage run in parallel to a recording surface of the recording medium, a carriage shaft and a guide shaft are used. A carriage shaft movably supporting the carriage is a linear member. Since opposite ends of the carriage shaft are secured to the chassis, the carriage shaft slightly elastically deforms owing to its own weight and the weight of the carriage when the carriage moves along the carriage shaft. Accordingly, the distance between the recording head and the recording surface of the recording medium varies according to the position of the carriage when the carriage moves. As a result, variation occurs in the ink flight time, causing image deterioration.

In order to deal with the image deterioration resulting from variation in ink flight time, Japanese Patent Application Laid-Open No. 2007-136728 discloses a method in which ink discharge timing is changed according to the elastic deformation of a carriage shaft, and the moving direction and position of a carriage, thereby making an ink land at a target position.

However, the aforementioned method of changing the ink discharge timing is a method used for correcting deviation of an ink landing position from a target position on a recording medium in the carriage movement direction. Accordingly, in the aforementioned method, no consideration is given for the case where deviation of an ink landing position from a target position occurs in the recording medium transport direction, which intersects with the carriage movement direction.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an inkjet recording apparatus enabling reduction of deviation of an ink landing position from a target position occurring in a recording medium transport direction owing to elastic deformation of a carriage shaft.

In order to attain the above-mentioned object, there is provided an apparatus comprising a carriage configured to hold a recording head that discharges an ink so as to face a recording medium transported in a first direction, and to reciprocate along a second direction intersecting with the first direction; a first guide member with opposite ends thereof secured, wherein the reciprocation of the carriage is guided along the first guide member while the carriage is supported by the first guide member, and the carriage is supported in such a manner that the carriage can rotate with reference to the first guide member, and wherein, viewed from the second direction, the first guide member is arranged at a position deviating from a position of a gravity center of the carriage supporting the recording head in the first direction, and the first guide member deforms in a direction containing a gravity direction and the first direction, upon receipt of a load from the carriage supported by the first guide member; and a second guide member configured to guide the carriage while being in contact with a part of the carriage when the carriage reciprocates, wherein when the second guide member comes into contact with the part of the carriage, the rotation of the carriage with reference to the first guide member is restricted, and an area of the second guide member that is in contact with the part of the carriage has a shape curved in a direction containing the first direction.

DESCRIPTION OF THE EMBODIMENTS

FIG. 1is a schematic cross-sectional view of an inkjet recording apparatus according to the present embodiment, which illustrates a cross section along a recording medium transport direction.

An inkjet recording apparatus10includes a recording head1, a carriage2with the recording head1mounted therein, and a carriage shaft3(first guide member) and a guide shaft4(second guide member), each extending in a direction intersecting with a transport direction of “a” recording medium7. The inkjet recording apparatus10also includes a platen5arranged at a position facing the recording head1, the platen5supporting the recording medium7, and a pair of transport rollers6aand6b, which is a transport mechanism that transports the recording medium7while making the recording medium7be in contact with the platen5to form a recording surface. By means of the transport mechanism, the recording medium7is transported in a first direction.

The recording head1includes a plurality of nozzle rows, each including a plurality of nozzles for discharging ink, as described later. The nozzle rows are arranged in parallel in a direction orthogonal to a nozzle row direction. The recording head1is mounted in the carriage2in such a manner that the recording head1can move in the direction in which the nozzle rows are arranged in parallel. The carriage2is guided for reciprocation movements in a second direction intersecting with, in the present embodiment, substantially orthogonal to, the transport direction “a” of the recording medium7(i.e., a direction orthogonal to a plane of a paper on which theFIG. 1is drawn, by the carriage shaft3. The guide shaft4is provided as a guide for keeping a posture of the carriage2when the carriage2moves.

The carriage shaft3is a shaft-like member having a circular cross-sectional shape and extending in the direction intersecting with the transport direction “a” of the recording medium7. The carriage shaft3movably supports the carriage2along the shaft direction of the carriage shaft3while supporting the carriage2in such a manner that the carriage2can rotate with reference to the carriage shaft3. Opposite ends of the carriage shaft3are secured to a chassis8b(which may be a frame that can be regarded as being equivalent to a chassis) of the apparatus. When the carriage2moves along the shaft direction, as described later, the carriage shaft3elastically deforms mainly owing to a load from the carriage2. Meanwhile, the guide shaft4serves to guide the carriage2, which moves along the carriage shaft3, while being in contact with the carriage2via a rotator2aattached at an upper portion of the carriage2. The guide shaft4is secured to the chassis8avia a plurality of securing members9, and accordingly, has a sufficiently-high bending stiffness and causes only a small amount of elastic deformation that can be ignored. When the carriage2moves along the shaft direction of the carriage shaft3, the guide shaft4has almost no deformation compared to deformation of the carriage shaft3. In the present embodiment, the guide shaft4is a shaft member having a circular cross-sectional shape as is the carriage shaft3.

Next, the principle of the carriage shaft3elastically deforming upon receipt of a load from the carriage2when the carriage2moves along the carriage shaft3in the inkjet recording apparatus10according to the present embodiment will be described with reference toFIG. 2.

As isFIG. 1,FIG. 2is a cross-section diagram schematically illustrating the inkjet recording apparatus according to the present embodiment.FIG. 2illustrates only a part related to the carriage2in order to describe loads exerted on the carriage2, in which loads exerted on the carriage2and the carriage shaft3are indicated with several arrows.

Forces exerted on the carriage2in a gravity direction (third direction) include a gravity force exerted downward (see arrow G in the Figure) and an upward force from the carriage shaft3(see arrow Z in the Figure). In the present embodiment, as can be seen fromFIGS. 1 and 2, the carriage shaft3is arranged away from a vertical line (see the dotted line inFIG. 2) passing through a gravity center of the carriage2, upstream in the recording medium transport direction “a”. Accordingly, the carriage2is urged to rotate counterclockwise in the Figure with reference to the carriage shaft3by its own weight (see arrow G in the Figure); however, because of the carriage2being in contact with the guide shaft4, such rotation is restricted. Here, the guide shaft4is positioned above a horizontal line passing through a shaft center of the carriage shaft3in the gravity direction. Accordingly, a force including a component of a direction (the first direction) opposite to the recording medium transporting direction “a”, which restricts such rotation, is exerted on the carriage2by the guide shaft4(see arrow X in the Figure). Meanwhile, a load in a direction opposite to the direction of such force is exerted on the carriage2by the carriage shaft3(see arrow Y in the Figure).

A load that is a force (see arrow F in the Figure) counteracting loads exerted on the carriage2(arrows Z and Y in the Figure) is exerted on the carriage shaft3, resulting in the carriage shaft3elastically deforming in the direction of arrow F. Arrow F contains a gravity direction component and a horizontal direction component. As described above, since the opposite ends of the carriage shaft3are secured to the chassis, the amount of elastic deformation of the carriage shaft3increases as the carriage2moves closer to a center portion of the carriage shaft3and reaches a maximum when the carriage2is positioned at the center of the carriage shaft3. Meanwhile, the guide shaft4receives a force counteracting the load indicated by arrow X from the carriage2; however, as described above, the guide shaft4is secured to the chassis8via the plurality of securing members9, and thus, has a sufficiently-high bending stiffness, and causes only a small amount of elastic deformation that can be ignored.

As described above, the carriage shaft3curves in a direction including a component of a downward direction in the gravity direction. Accordingly, when the carriage2moves, the space between the recording head1and the recording medium changes. In order to exclude the effect of such change, the present embodiment provides such a configuration that a fixed space is kept between the area of a carriage shaft supporting the carriage and the area of a platen that faces the area when the carriage moves along the carriage shaft. More specifically, the platen has a curved supporting surface (non-planar surface) according to deformation of the carriage shaft3in the gravity direction so as to suppress change of the space between the platen and the nozzle rows of the recording head1when the carriage moves along the first guide member. Consequently, the carriage2can move along the carriage shaft3in a state in which the space between the carriage2and the recording medium supported by the platen is kept substantially constant.

Next, with reference toFIGS. 3A and 3B, the principle of image deterioration being caused as a result of such deviation of an ink landing position from a target position that occurs in the transport direction “a” of the recording medium7due to elastic deformation of the carriage shaft3will be described.

FIGS. 3A and 3Bare schematic diagrams each illustrating the carriage2and the carriage shaft3with the opposite ends thereof secured to the chassis8bon a plane parallel to the recording medium7in the inkjet recording apparatus10illustrated inFIG. 1.FIGS. 3A and 3Billustrate a state in which nozzles D1and D2provide discharge at a predetermined position b in a direction intersecting with the recording medium transport direction “a”, that is, substantially a direction of carriage movement, respectively. While in the recording head1, a plurality of nozzle rows, each including a plurality of nozzles for discharging ink, are arranged in parallel in a direction orthogonal to the nozzle row direction, the nozzles D1and D2are nozzles belonging to different nozzle rows but equal to each other in position in the nozzle row direction. The dotted lines inFIG. 3Bindicate the carriage2and the carriage shaft3inFIG. 3A. Arrow “a” in the Figures indicates the recording medium transport direction.

As described above, the amount of elastic deformation of the carriage shaft3changes according to the position of the carriage2. In other words, the amount of elastic deformation of the carriage shaft3increases so as to move the carriage2upstream in the transport direction “a”, as a result of the carriage2moving by the space between the nozzles D1and D2in the shaft direction. Consequently, the nozzle D2in the carriage2illustrated inFIG. 3Bdeviates upstream in the recording medium transport direction “a” from the nozzle D1in the carriage illustrated inFIG. 3Aby a distance W at the predetermined position “b”. Accordingly, where inks discharged from the nozzles fly perpendicularly to the recording medium (which is parallel to a plane of a paper on which the Figure is drawn), the nozzle position deviation causes deviation of an ink landing position on the recording medium, and consequently causes image deterioration.

In the present embodiment, in order to reduce ink landing position deviation resulting from such nozzle position deviation, the angle of the carriage2relative to the recording medium7when the carriage2moves changes according to the position of the carriage2. In other words, in the present embodiment, the guide shaft4that guides rotation of the carriage2when the carriage2moves is formed so as to have a large curve in a direction containing a component of an upstream direction in the transport direction. The principle of ink landing position deviation being reduced by the guide shaft4formed as described above will be described with reference toFIGS. 4A and 4B, and the states of the guide shaft4are illustrated inFIGS. 5A and 5B.

FIGS. 4A and 4Bare schematic cross-sectional diagrams of the inkjet recording apparatus according to the present embodiment as isFIG. 1, which each illustrate a cross section along the recording medium transport direction.FIG. 4Aindicates a state in which a frontmost nozzle (for example, the nozzle D1inFIGS. 3A and 3B) provides discharge at a predetermined position. The arrow connecting the recording head1and the recording medium7indicates a trajectory of an ink discharged from the frontmost nozzle landing on the recording medium7. Meanwhile,FIG. 4Bindicates a state in which a following nozzle (for example, the nozzle D2inFIG. 3A and 3B) whose position in the nozzle row direction is equal to that of the frontmost nozzle provides discharge at the predetermined position. The dotted lines illustrated inFIG. 4Bindicate the recording head1, the carriage shaft3and the guide shaft4illustrated inFIG. 4A.FIGS. 5A and 5Bare diagrams each schematically illustrating the carriage2, the carriage shaft3and the guide shaft4in the inkjet recording apparatus10according to the present embodiment on a plane parallel to the recording medium7.FIG. 5Ais a diagram corresponding to the inkjet recording apparatus10illustrated inFIG. 4B, andFIG. 5Bis a diagram illustrating the inkjet recording apparatus10when the carriage2is located at the center of the carriage shaft3.

When the carriage2moves from the state illustrated inFIG. 4Ato the state illustrated inFIG. 4B, a part of the carriage shaft3that supports the carriage2deforms upstream in the transport direction “a” of the recording medium7in such a manner that the part comes close to the recording medium7as described with reference toFIG. 2(seeFIG. 4B). The guide shaft4has a large curve so that the amount of displacement of the point of contact between the guide shaft4and the carriage2is larger than the amount of deformation of the carriage shaft3in such state (seeFIGS. 5A and 5B). Accordingly, as illustrated inFIG. 4B, the carriage2rotates clockwise in the Figure with reference to the carriage shaft3, entering a state in which the carriage2is inclined upstream in the transport direction “a” of the recording medium7. Consequently, an ink discharged from the following nozzle at the predetermined position also flies not perpendicularly to the recording medium7, but with an inclination, resulting in the ink landing on the recording medium7at a position downstream in the transport direction “a” of the nozzle position in the recording head1. In other words, the curve of the guide shaft4reduces deviation of a position on the recording medium at which an ink discharged from a nozzle lands, which is caused by the effect of elastic deformation of the carriage shaft3. As illustrated inFIG. 3B, even if there is a deviation in position between the two nozzles, positions on which inks discharged from those different positions land come close to each other along the recording medium transport direction, enabling reduction of image deterioration. The shape of the guide shaft4can be determined so that the displacements in the transport direction of the nozzle positions due to elastic deformation of the carriage shaft3and the displacements of the ink landing positions due to change of the inclination of the carriage2relative to the recording medium7cancel each other out. As illustrated inFIG. 5B, in the present embodiment, a largest amount L1of displacement in the transport direction “a” of the guide shaft4is larger than a largest amount L2of elastic deformation of the carriage shaft3when the carriage2is located at the center of the carriage shaft3.

As described above, deviation of a position on the recording medium at which an ink discharged from a nozzle lands, which is caused by the effect of elastic deformation of the carriage shaft3when the carriage2moves along the carriage shaft3, is reduced. Furthermore, relative deviation of positions on the recording medium at which inks discharged from a plurality of nozzles that are equal to each other in position in the nozzle row direction land can be reduced (ideally, the ink landing positions are made to correspond to each other). Consequently, image deterioration resulting from deviation of ink landing positions from target positions, which is caused by elastic deformation of the carriage shaft in the recording medium transport direction, can be reduced.

Although in the present embodiment, the guide shaft4is a shaft member having a curved arc shape, any member that can change the inclination of the carriage shaft according to the position of the carriage may be employed, and thus, any member whose area in contact with the carriage is curved in a direction containing a component of the upstream direction in the transport direction may be employed. For example, a plate member having a contact surface in a semicircular or crescentic arc shape can be used instead of the guide shaft4.

It should be noted that the effects provided by the present invention do not depend on the recording medium transport direction. In other words, although in the present specification, as illustrated inFIG. 1, description has been given in terms of the case where the carriage shaft is arranged away from the vertical line, which includes the gravity center of the carriage, upstream in the recording medium transport direction, as an example, the present invention is not limited to this example. In other words, the carriage shaft may be arranged out of the vertical line downstream in the recording medium transport direction, and in such case, the guide shaft may be formed so as to curve downstream in the transport direction. In other words, for example, in the configuration illustrated inFIG. 1, the recording medium transport direction may be either leftward or rightward in the Figure.

This application claims the benefit of Japanese Patent Application No. 2010-015334, filed Jan. 27, 2010, which is hereby incorporated by reference herein in its entirety.