Carriage and recording apparatus incorporating the same

A first shaft member extends in a first direction. A second shaft member extends in the first direction. A carriage body is disposed between the first shaft member and the second shaft member. A first slider comes in contact with a circumferential part of the first shaft member to allow the carriage body to slide on the first shaft member in the first direction. A second slider comes in contact with a circumferential part of the second shaft member to allow the carriage body to slide on the second shaft member in the first direction.

BACKGROUND OF THE INVENTION

The present invention relates to carriage for mounting a recording head, and a recording apparatus or a liquid ejecting apparatus having a mechanism for adjusting the distance between the recording head and a recording medium opposed thereto.

Among large-size recording apparatus capable of recording on up to a sheet (recording medium) of a relatively large size such as the A4 to A2 size of the JIS (Japanese Industrial Standards) standard are ink jet printers. In such large-size ink jet printers, a sheet is supplied from and ejected to the front side for the following reason: unlike in small-size ink jet printers, it is difficult to supply a sheet from the back side and eject it to the front side because relatively heavy sheets need to be handled.

An ink jet printer is known in which a sheet supply tray and a sheet ejection tray are disposed on the front side. A sheet that is accommodated in the sheet supply tray is taken out by a sheet supplying roller and then fed to a platen of a recording section by transporting the sheet by a sheet feeding roller and a follower roller while holding it therebetween. Recording is performed on the sheet by ejecting ink droplets from a recording head, and the sheet is then ejected to the ejection tray by transporting it by a sheet ejecting roller and a spur roller serving as a follower roller while holding it therebetween (cf., Japanese Patent Publication No. 11-124271A).

Such an ink jet printer is equipped with a gap adjusting mechanism capable of adjusting the gap between the recording head and the sheet so that it is always kept constant even if the medium thickness is varied (cf., Japanese Patent Publication No. 2002-67428A).

In the above ink jet printer, the carriage is attached to a guide shaft extending in the primary scanning direction via thrust bearings that are attached to the carriage on the back side. A front portion of the carriage is mounted on a frame of the printer and the carriage is slid along the guide shaft and the frame by a belt mechanism. However, if the ink jet printer is of a large size, the carriage is also large and heavy and hence the resistance of sliding on the guide shaft and the frame is high, which may result in wear of the guide shaft and the frame or a bend of the guide shaft. Wear or a bend of the guide shaft or the frame lowers the accuracy of reciprocation of the carriage, which may in turn lower the recording accuracy.

In the above ink jet printer, the gap is adjusted by rotating two eccentric shafts that guide the carriage on the front side and the back side as the carriage is moved. However, since the drive force of a motor for rotating the eccentric shafts is transmitted by a gear mechanism, backlash tends to occur to possibly lower the accuracy of the gap adjustment.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a carriage capable of maintaining its highly accurate reciprocative movement and a recording apparatus and a liquid ejecting apparatus incorporating such a carriage.

It is also an object of the invention to provide a mechanism capable of performing a highly accurate gap adjustment and a recording apparatus and a liquid ejecting apparatus incorporating such a gap adjusting mechanism.

In order to achieve the above objects, according to the invention, there is provided a carriage mechanism, comprising:

a first shaft member, extending in a first direction;

a second shaft member, extending in the first direction;

a carriage body, disposed between the first shaft member and the second shaft member;

a first slider, coming in contact with a circumferential part of the first shaft member to allow the carriage body to slide on the first shaft member in the first direction; and

a second slider, coming in contact with a circumferential part of the second shaft member to allow the carriage body to slide on the second shaft member in the first direction.

With this configuration, since the respective sliders are not entirely in contact with the circumferential parts of the respective shaft members, the sliders can be slid smoothly without enhancing the straightness or parallelism of the shaft members.

Preferably, the first slider comprises a first plate member coming in contact with the circumferential part of the first shaft member, and the second slider comprises a second plate member coming in contact with the circumferential part of the second shaft member.

With this configuration, since the carriage body is not directly in contact with the shaft members, frictional wear of the shaft members due to the slide movement of the carriage body can be avoided. In addition, the respective plate members can be made with wear-proof material. Thus, frictional wear of the plate members due to the slide movement of the carriage body can be avoided, so that high accuracy of the reciprocal movement of the carriage can be maintained.

Here, it is preferable that the second slider comprises an urging member which urges the second plate member against the second shaft member.

With this configuration, the first plate member can be pressed against the first shaft member through the carriage body. In a case where the carriage is reciprocated along the first shaft member serving as a main shaft member, high accuracy of the reciprocal movement of the carriage can be maintained.

It is also preferable that: the first plate member has a C-shaped cross section viewed from the first direction, so that both ends of the C-shaped cross section come in contact with the first shaft member while forming a clearance between the first shaft member and a center part of the C-shaped cross section; and the second plate member has a C-shaped cross section viewed from the first direction, so that both ends of the C-shaped cross section come in contact with the second shaft member while forming a clearance between the second shaft member and a center part of the C-shaped cross section.

With this configuration, the respective plate members can be flexed by such an amount corresponding to the clearances, so that the positioning error or the working error can be absorbed. Accordingly, high accuracy of the reciprocal movement of the carriage can be maintained.

It is also preferable that the first slider comprises a first rolling member coming in contact with the first plate member, and the second slider comprises a second rolling member coming in contact with the second plate member.

With this configuration, the frictional resistance between the carriage body and the respective plate members can be considerably reduced in order to suppress frictional wear of the respective plate members. Accordingly, high accuracy of the reciprocal movement of the carriage can be maintained.

Preferably, the carriage mechanism further comprises:

a recording head, carried by the carriage body; and

an endless belt member suspended by the first shaft member and the second shaft member,

wherein the first shaft member is rotatable about an eccentric axis, and the second shaft member is interlockingly rotated by the endless belt member in accordance with the rotation of the first shaft member, thereby varying a distance between the recording head and a recording target.

With this configuration, backlash liable to be occurred in the gear mechanism can be prevented, so that the gap adjustment can be performed with high accuracy.

Here, it is preferable that the endless belt member is tensed. With this configuration, phase shift of synchronous rotation between the both shaft members can be prevented, so that the gap adjustment can be performed with high accuracy.

In order to achieve the above objects, it is preferable that the recording head is a liquid ejection head from which liquid droplets are ejected toward the recording target.

With this configuration, it is possible to provide a liquid ejection head which attains the above advantages.

According to the invention, there is also provided a carriage mechanism, comprising:

a carriage body;

a first shaft member, extending in a first direction;

a slider, coming in contact with a first circumferential part of the first shaft member to allow the carriage body to slide on the first shaft member in the first direction; and

a support member, which supports the first shaft member, the support member being provided on a second circumferential part of the first shaft member at a longitudinal center portion of the first shaft member.

With this configuration, the flexure of the main guide shaft can be suppressed even when the carriage has large size and weight. Accordingly, high accuracy of the reciprocal movement of the carriage can be maintained.

Preferably, the first shaft member is rotatable about an eccentric axis, and the support member comprises:

an adjuster, fitted with the second circumferential part of the first shaft member, and having an outer peripheral face which is configured such that a distance from the eccentric axis is made constant at anywhere in the outer peripheral face; and

a retainer, which presses the outer peripheral face of the adjuster against the first shaft member.

With this configuration, the adjuster and the retainer can be always kept contacting the first shaft member even when the first shaft member is eccentrically rotated to perform adjustment for the carriage.

Preferably, the carriage mechanism further comprises a second shaft member extending in the first direction. The carriage body is disposed between the first shaft member and the second shaft member. The second circumferential part is opposite to a circumferential part of the first shaft member which opposes to the second shaft member.

With this configuration, even if an urging member is provided in the side of the second shaft member to urge the carriage body toward the first shaft member, the reaction force of the urging member can be absorbed by the first shaft member side. Accordingly, high accuracy of the reciprocal movement of the carriage can be maintained.

Preferably, the carriage body carries a recording head which performs recording operation with respect to a recording medium being transported in a second direction perpendicular to the first direction.

In order to achieve the above objects, it is preferable that the recording head is a liquid ejection head from which liquid droplets are ejected toward the recording target.

With this configuration, it is possible to provide a liquid ejection head which attains the above advantages.

DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be hereinafter described in detail with reference to the accompanying drawings.

As shown inFIG. 1, an ink jet printer (recording apparatus)100according to one embodiment of the invention is a large-size, desk-top printer capable of recording on what is called a cut sheet of a relatively large size such as the A4 to A2 size of the JIS standard and an equivalent rolled sheet. The inside of the ink jet printer100is entirely covered with a housing101that generally assumes a rectangular parallelepiped shape that is long in the width direction.

The top face of the housing101is formed with a rectangular window102, which is covered with a transparent or semi-transparent window cover103. The window cover103is attached so as to be pivotable in directions indicated by arrows “a” inFIG. 1about a pivot axis that is located on the rear side. A user can perform maintenance work or the like on the internal mechanisms through the window102by lifting up the window cover103and thereby opening the window102.

Cartridge chambers104in which plural ink cartridges are to be detachably inserted are formed at the front-right and front-left positions of the housing101. Recording inks of several colors are stored in the respective ink cartridges. The cartridge chambers104are covered with transparent or semi-transparent cartridge covers105, respectively. Each cartridge cover105is attached so as to be pivotable in directions indicated by arrows “b” inFIG. 1about a pivot axis that is located at the bottom. The user can perform ink cartridge replacement work or the like by opening a cartridge chamber104by weakly pushing the cartridge cover105and thereby unlocking a locking portion.

A control panel110by which to input an instruction of a printer operation is provided in a portion of the housing101that is located over the front-right cartridge chamber104. The control panel110is provided with: buttons111such as a power button for activating/deactivating the printer, manipulation buttons for manipulations for positioning a leading end of a recording sheet, ink flashing, etc., and processing buttons for image processing etc.; a liquid crystal panel112for displaying various statuses; and other members. The user can manipulate the buttons111while watching the liquid crystal panel112to check displayed information.

A tank chamber106in which a waste liquid tank120is detachably inserted is formed under the front-right cartridge chamber104. The waste liquid tank120stores waste ink that is discarded at the time of cleaning of a recording head162(seeFIG. 5) or replacement of an ink cartridge. The user can perform, for example, work of discarding the waste ink stored in the waste ink tank120by drawing out the waste ink tank120.

A sheet supplying section130for supplying a part of a rolled sheet is disposed at the rear of the housing101so as to project in a top-rear direction. A rolled sheet holder (not shown) in which one rolled sheet can be set is provided inside the sheet supplying section130, and a flap-type rolled sheet cover131that can be opened and closed is attached to the sheet supplying section130on the front side so as to cover the rolled sheet holder. The user can perform, for example, work of attaching or detaching a rolled sheet by lifting up the rolled sheet cover131and thereby opening the sheet supplying section130. The top face of the rolled sheet cover131is formed into a guide face capable of guiding cut sheets for manual feeding.

A sheet supplying/ejecting section140into and from which a tray unit200to be loaded with unrecorded cut sheets and recorded cut sheets or a recorded part of a rolled sheet is to be inserted and removed is formed in the housing101at the front-center, that is, between the two cartridge chambers104. The sheet supplying/ejecting section140is formed so as to also allow manual feeding of thick sheets that cannot be bent while being transported.

The tray unit200is fixed to the sheet supplying/ejecting section140in such a manner that the head-side half of the tray unit200is inserted in the sheet supplying/ejecting section140and the tail-side half is projected therefrom. The tray unit200assumes a cassette-like shape; unrecorded cut sheets are stacked and accommodated inside and recorded and ejected cut sheets or parts of rolled sheet are stacked thereon. A detailed structure of the tray unit200will be described below with reference toFIGS. 2 to 4.

As shown inFIG. 2, the tray unit200has a box-shaped sheet supply tray210and a lid-shaped sheet ejection tray230that covers the sheet supply tray210from above. Capable of expansion and contraction in the sheet supplying/ejecting direction, the tray unit200can be accommodated compactly while not in use and can accommodate cut sheets of various sizes while in use.

To be mounted with cut sheets in a stacked manner, as shown inFIG. 3, a rolled sheet guiding section240is made flush with the top face of a sheet ejection member239ato form a flat plane together with the top face of the sheet ejection member239a. With this measure, cut sheets that are ejected after passing by a sheet ejecting roller155(seeFIG. 5) are stacked smoothly on an ejected sheet receiving face that is formed by the rear and bottom faces of a guide portion145having an L-shaped cross section and the top faces of sheet ejection members239ato239d.

Sponge mats145aare pasted on the bottom face of the guide portion145. The sponge mats145ahave a slip-preventing function of preventing a phenomenon that when a second cut sheet comes in a state that a first cut sheet is already mounted, the head of the second cut sheet pushes the first cut sheet and makes it fall from the ejected sheet receiving face.

On the other hand, to stack cut parts of rolled sheet, as shown inFIG. 4, the user hooks his finger on a first guide plate241of the rolled sheet guiding section240that is in the same plane as the top face of the sheet ejection member239aand turns it rearward. As a result, second guide plates242are pulled by the first guide plate241, whereby their one ends in the longitudinal direction are lifted up and the other ends in the longitudinal direction slide rearward along respective grooves239aathat are formed in the top face of the sheet ejection member239a. The user turns the first guide plate241until the first guide plate241and the second guide plates242form an acute angle.

As a result, the one ends in the longitudinal direction of the second guide plates242come close to the top of the rear face of the guide portion145and the second guide plates242come to assume slide-like shapes. By virtue of this structure, even if a cut part of rolled sheet that is ejected after passing by the sheet ejecting roller155is curled, its tip portion does not go toward the guide portion145but slides on the slide-shaped second guide plates242and is guided onto the top faces of the sheet ejection members239ato239d. In this manner, cut parts of the rolled sheet are smoothly stacked on an ejected sheet receiving face that is formed by the top faces of the second guide plates242and the sheet ejection members239ato239d.

As shown inFIG. 5, the sheet supplying/ejecting section140, a transporting section150and a recording section160that include important features of the invention, and other components are provided in the housing101. The sheet supplying/ejecting section140is equipped with a hopper141for supplying cut sheets, a sheet supplying roller142, a separator143, etc. The hopper141assumes a flat plate shape capable of being mounted with cut sheets, and is disposed in such a manner that one end is close to the sheet supplying roller142and the separator143and the other end is close to the bottom face of the sheet supply tray210of the inserted tray unit200. One end of a compression spring144is attached to the bottom face of the housing101and the other end is attached to the back face of the hopper141at its one end. The hopper141is rotated about the other end as the compression spring144expands or contracts.

The sheet supplying roller142, which has a D-shaped cross section frictionally transports cut sheets from the hopper141by rotating intermittently. The separator143, which has a rough top face, frictionally separates lower cut sheets from the uppermost one when plural cut sheets are supplied by the sheet supplying roller142. A relationship between the cut sheets mounted on the hopper141and the sheet supplying roller142will now be described with reference toFIGS. 6A and 6B.

FIG. 6Ashows a case that a maximum number of cut sheets P are mounted on the hopper141. Settings are made so that in this case when the hopper141is elevated the uppermost cut sheet P1does not touch the cut portion of the sheet supplying roller142but touches an arc start point142aor a point on the circumference that is slightly distant from the arc start point142a.

FIG. 6Bshows a case that a minimum number (one) of cut sheet P1is mounted on the hopper141. The settings are made so that in this case when the hopper141is elevated the cut sheet P1touches a point142bof the sheet supplying roller142that is a little distant from the arc start point142a. The contact point142bis such a point that the circumferential length between the contact point142band an arc end point142cis the same as the interval “a” between the leading end PS of the sheet P1and a contact point151a of a sub roller151and its follower roller152a.

With the above settings, if the number of cut sheets P mounted on the hopper141is smaller than or equal to the maximum number, the uppermost cut sheet P1is not released from the sheet supplying roller142until the leading end PS of the cut sheet P1reaches the contact point151aof the sub roller151and its follower roller152a. Therefore, the cut sheet P1can be delivered reliably to the sub roller151and erroneous sheet delivery can be avoided.

The transporting section150is equipped with the sub roller151and its follower rollers152a,152b, and152cfor transporting a sheet, a sheet feeding roller153and its follower roller154, a sheet ejecting roller155and its follower roller unit156that constitute an ejecting section, sensors157aand157bfor detecting a sheet, and other components. To eject, to the sheet ejection tray230, a cut sheet that is supplied from the sheet supply tray210, the sub roller151transports the cut sheet along a U-shaped path (the transport direction is reversed) while holding it together with the follower rollers152a,152b, and152c. To eject, to the sheet ejection tray230, a part of rolled sheet that is supplied from the sheet supplying section130, the sub roller151transports it while holding it together with the follower roller152c.

The sheet feeding roller153sends out, to a platen163, a cut sheet that has been transported with reversal in direction or a supplied part of rolled sheet while holding it together with the follower roller154. The sheet ejecting roller155ejects, onto the sheet ejection tray230, a recording sheet that has passed by the platen163while supporting it solely or together with the follower roller unit156. The sensor157adetects a transport length of a supplied cut sheet at the time of skew correction. The sensor157bdetects a transport length of a cut sheet that has been transported with reversal in direction or a supplied part of rolled sheet at the time of leading end positioning.

The follower roller unit156is equipped with sets of a spur roller11and a smooth roller12that are brought in contact with or separated from the recording face of a recording sheet being transported on the sheet ejecting roller155and a switching shaft14for switching the rollers11and12between a contact state and a separated state. Having saw-toothed projections on the circumferential face, the spur roller11serves to transport a recording sheet reliably by cutting into its recording face while holding it together with the sheet ejecting roller155.

Having a smooth circumferential face, the smooth roller12serves to transport a recording sheet reliably by pressing on its recording face while holding it together with the sheet ejecting roller155. The spur roller11, the smooth roller12, and a releaser13where neither the spur roller11nor the smooth roller12is provided are disposed around the switching shaft14at prescribed intervals in the circumferential direction, and plural sets of the rollers11and12and the releaser13are arranged in the axial direction at prescribed intervals.

The above-configured follower roller unit156can arbitrarily switch between the spur rollers11and the smooth rollers12, between the spur rollers11and the releasers13, and between the smooth rollers12and the releasers13by rotating the switching shaft14. The switching between the spur rollers11and the releasers13or between the smooth rollers12and the releasers13is equivalent to bringing the spur rollers11or smooth rollers12into contact with or separating those from the recording face of a recording sheet. Therefore, this switching makes it possible to adapt to many kinds of recording sheets having respective attributes. Although the follower roller unit156is equipped with, in each set, the three kinds of single members, that is, the spur roller11, the smooth roller12, and the releaser13, the invention is not limited to such a case. One or more kinds of members may be combined arbitrarily, the number of members of each kind being two or more.

The recording section160is equipped with a carriage161, a recording head162, the platen163, a support rib unit164, etc. As shown inFIG. 13, the carriage161is connected to a carriage belt165. As the carriage belt165is driven by a carriage motor166, the carriage161is moved together with the carriage belt165and is thereby reciprocated above a recording sheet perpendicularly to the sheet transport direction being guided by a main guide shaft61and an auxiliary guide shaft62. The carriage161is mounted with the recording head162capable of ejecting ink droplets toward an underlying recording sheet.

For example, the recording head162is equipped with plural black ink recording heads for ejecting two kinds of black ink and plural color ink recording heads for ejecting ink droplets of six colors of yellow, dark yellow, cyan, light cyan, magenta, and light magenta, respectively. The recording head162is provided with pressure generating chambers and nozzle orifices that communicate with the respective pressure generating chambers. Ink is stored in each of the pressure generating chambers and pressurized at a prescribed pressure, whereby ink droplets having a controlled size are ejected toward the recording sheet on the platen163. A guide face163aas the top face of the platen163supports and guides, by itself or together with the support rib unit164, a recording sheet being transported from the sheet feeding roller153and the follower roller154to the sheet ejecting roller155and the follower roller unit156.

To enable recording on many kinds of recording sheets having respective attributes (i.e., different thicknesses), a platen gap adjusting mechanism170for adjusting the gap between the nozzle formation face of the recording head162that is mounted on the carriage161and the recording face of a recording sheet being transported on the guide face163aof the platen163is provided (seeFIG. 18). The main guide shaft61and the auxiliary guide shaft62are rotatable about respective eccentric rotation axes. The platen gap adjusting mechanism170adjusts the gap so that it is always kept constant by rotating the main guide shaft61and the auxiliary guide shaft62synchronously.

As shown inFIG. 22, the support rib unit164is equipped with support ribs (projections)21that protrude or retract from slits163bthat are formed in the guide face163aof the platen163and a switching shaft22for switching the support ribs21between protrusion and retraction. Each support rib21is a generally triangular plate member, and one rounded apex portion protrudes from the guide face163aand supports a recording sheet. The two ends of the switching shaft22are pivotally supported by side faces163cof the platen163. Plural support ribs21are fixed to the switching shaft22so as to be arranged in the axial direction at prescribed intervals.

The above-configured support rib unit164makes it possible to arbitrarily switch between the one apex portion and the flat portion of each support rib21in the slit163bthat is formed in the guide face163aof the platen163by rotating the switching shaft22. That is, the support rib21can be protruded by positioning the one apex portion of the support rib21with respect to the slit163bthat is formed in the guide face163aof the platen163, and the support rib21can be retracted by positioning the flat portion of the support rib21with respect to the slit163b. Therefore, the above switching makes it possible to adapt to many kinds of recording sheets having respective attributes (described later in detail).

As shown inFIG. 7, a follower roller driving device50for controlling the operation of bringing the follower rollers152a,152b, and152cinto contact with or separating those from the sub roller151and the operation of bringing the follower roller154into contact with or separating it from the sheet feeding roller153may be provided. This makes it possible to lower the power consumption of the ink jet printer100and to thereby reduce its size.

As shown inFIG. 8, the follower roller driving device50is equipped with pivot members51and52, a cam shaft53, and gear units54and55. The follower roller152cis rotatably attached to one end of the pivot member51and the other end of the pivot member51is to contact the cam shaft53. And the follower roller152cswings about a central shaft51a.The follower roller154is rotatably attached to one end of the pivot member52and the other end of the pivot member52is to contact the cam shaft53. And the follower roller154pivots about a central shaft52a.

The cam shaft53is separately provided with a cam53a(seeFIG. 9) that acts on the pivot member51and a cam53b(seeFIG. 11) that acts on the pivot member52. An intermittent gear53cto mesh with the gear unit54and an intermittent gear53dto mesh with the gear unit55are fit in the cam shaft53at one end. The gear unit54is provided with a planetary gear54afor intermittently transmitting drive force of a motor (not shown) to the intermittent gear53cof the cam shaft53. The gear unit55is provided with a lever55bthat is rotatable and can be operated manually and that is formed with a gear55ato mesh with the intermittent gear53dof the cam shaft53. How the above-configured follower roller driving device50operates will be described below with reference to the drawings.

FIGS. 9 and 10show a case that only the follower roller152cis caused to operate.FIG. 9shows a state that the follower roller152cis in contact with the sub roller151and the follower roller154is in contact with the sheet feeding roller153. In this state, the planetary gear54ais separated from the intermittent gear53cand the cam53ais separated from the other end of the pivot member51. The lever55bis located at a contact position, and the cam53bis separated from the other end of the pivot member52(not shown inFIG. 9).

FIG. 10shows a state that the planetary gear54ahas been driven by the motor (not shown) and is thereby meshed with the intermittent gear53c. As a result, the cam53apushes the other end of the pivot member51and hence the follower roller152cwhich is pivotally supported by the pivot member51at the one end is separated from the sub roller151.

When a recording sheet is supplied, to reliably deliver it from the sub roller151to the sheet feeding roller153, it is necessary that as shown inFIG. 9the follower roller152cbe in contact with the sub roller151and the follower roller154be in contact with the sheet feeding roller153. On the other hand, when recording is performed on a recording sheet, it is necessary that as shown inFIG. 10the follower roller152cbe separated from the sub roller151and the follower roller154be in contact with the sheet feeding roller153, because contact of the follower roller152cto the sub roller151would adversely affect the sheet feed accuracy.

FIGS. 11 and 12show a case that the follower rollers152cand154are caused to operate simultaneously.FIG. 11shows a state that the follower roller152cis in contact with the sub roller151and the follower roller154is in contact with the sheet feeding roller153. In this state, the planetary gear54ais separated from the intermittent gear53cand the cam53ais separated from the other end of the pivot member51(not shown inFIG. 11). The lever55bis located at the contact position, and the cam53bis separated from the other end of the pivot member52.

FIG. 12shows a state that the lever55bis moved manually from the contact position to a release position, whereby the gear55ais meshed with the intermittent gear53dand rotates the latter. As a result, the cam53a(not shown inFIG. 12) pushes the other end of the pivot member51and hence the follower roller152cwhich is pivotally supported by the pivot member51at the one end is separated from the sub roller151. Further, since the cam53bpushes the other end of the pivot member52and hence the follower roller152cwhich is pivotally supported by the pivot member52at the one end is separated from the sheet feeding roller153.

When a recording sheet is supplied, to reliably deliver it from the sub roller151to the sheet feeding roller153, it is necessary that as shown inFIG. 11the follower roller152cbe in contact with the sub roller151and the follower roller154be in contact with the sheet feeding roller153. On the other hand, when a sheet is fed manually, it is necessary that as shown inFIG. 12the follower rollers152cand154be separated from the sub roller151and the sheet feeding roller153, respectively, because the sheet would interfere with the follower rollers152cand154if the follower rollers152cand154were in contact with the sub roller151and the sheet feeding roller153, respectively.

As shown inFIGS. 13 to 15, the main guide shaft61is disposed behind the carriage161so as to extend in the primary scanning direction and the auxiliary guide shaft62is disposed in front of the carriage161so as to extend approximately parallel with the main guide shaft61. The main guide shaft61and the auxiliary guide shaft62assume circular rod shapes, and both ends of each of the main guide shaft61and the auxiliary guide shaft62are supported by and fixed to side frames (not shown).

The main guide shaft61is provided with main guide plates63that assume elongated rectangular shapes and extend from one end to the other end of the main guide shaft61, and the auxiliary guide shaft62is provided with auxiliary guide plates64that assume elongated rectangular shapes and extend from one end to the other end of the auxiliary guide shaft62. More specifically, two main guide plates63are arranged side by side in the circumferential direction so as to cover an approximately half of a circumferential face of the main guide shaft61a side of which faces the carriage161, and two auxiliary guide plates64are arranged side by side in the circumferential direction so as to cover an approximately half of a circumferential face of the auxiliary guide shaft62a side of which faces the carriage161. That is, the two main guide plates63and the two auxiliary guide plates64are arranged so as to cover top portions and bottom portions of the approximately half of the circumferential faces of the main guide shaft61and the auxiliary guide shaft62opposing to each other.

Both longer-side end portions of each main guide plate63and those of each auxiliary guide plate64are slightly bent toward the main guide shaft61or the auxiliary guide shaft62so as to form a generally C-shaped cross section. With this sectional shape, when the main guide plates63and the auxiliary guide plates64are attached to the circumferential faces of the main guide shaft61and the auxiliary guide shaft62, both longer-side end portions of each main guide plate63and those of each auxiliary guide plate64contact the circumferential face of the main guide61or the auxiliary guide62and central portions of the main guide plates63and the auxiliary guide plates64are slightly separated from the circumferential faces of the main guide shaft61and the auxiliary guide shaft62to provide play therebetween. Both ends of each main guide plate63and those of each auxiliary guide plate64are also supported by the above-mentioned side frames, and providing play in these support portions enables sheet metal alignment.

The carriage161is provided with slide members70having the same structure on the back side at the two end positions in the primary scanning direction, as well as with slide members80having the same structure on the front side at the two end positions in the primary scanning direction. In each slide member70, two radial bearings71are attached to a fixed seat72that is screwed to the carriage161and are arranged and oriented so as to form approximately a right angle in the vertical plane containing those. That is, the two radial bearings71are pivotally supported by the fixed seat72so as to be brought into contact with the two respective main guide plates63attached to the main guide shaft61and to be able to slide in the longitudinal direction of the main guide plates63.

In each slide member80, two radial bearings81are attached to a movable seat82that is movably attached to the carriage161and are arranged and oriented so as to form approximately a right angle in the vertical plane containing those. That is, the two radial bearings81are pivotally supported by the movable seat72so as to be brought into contact with the two respective auxiliary guide plates64attached to the auxiliary guide shaft62and to be able to slide in the longitudinal direction of the auxiliary guide plates64. One end portion of each of shafts83is fixed to the fixed seat72and the other end portion penetrates through the movable seat82with a spring84interposed in between. The movable seats82are thus movable along the respective shafts83. Play that occurs when each movable seat82is moved can be eliminated by adjusting the length of the support portion of the shaft83that is close to the movable seat82.

With the above-configured carriage161, the slide members70and80do not directly contact the main guide shaft61and the auxiliary guide shaft62, respectively, which prevents wear of the main guide shaft61and the auxiliary guide shaft62. Therefore, the reciprocation of the carriage161in the primary scanning direction can be kept highly accurate. Wear of the main guide plates63and the auxiliary guide plates64can also be reduced by making those of a material that is less prone to wear such as stainless steel, which also contributes to keeping the reciprocation of the carriage161in the primary scanning direction highly accurate.

Since the radial bearings81of the slide members80press on the auxiliary guide plates64attached to the auxiliary guide shaft62because of the restoration forces of the springs84, the reaction forces cause the radial bearings71of the slide members70to press on the main guide plates63, whereby the main guide plates63are bent by an amount corresponding the play and are pressed against the main guide shaft61. Therefore, the carriage161always slides along the main guide shaft61and its reciprocation in the primary scanning direction is kept highly accurate. The use of the radial bearings71and81instead of conventional thrust bearings contributes to cost reduction.

Since as described above both ends of the main guide shaft61are supported by and fixed to the side frames, the main guide shaft61may be bent by the loads from the springs84that act on the main guide shaft61in its radial direction. In view of this, a support member65for sustaining the above loads is disposed behind the center of the main guide shaft61. However, the main guide shaft61is made rotatable about an eccentric rotation axis so that the gap between the nozzle formation face of the recording head162mounted on the carriage161and the recording face of a recording sheet being transported on the guide face163aof the platen163is always kept constant even if the recording sheet thickness is varied. Therefore, if a simple support member were disposed behind the center of the main guide shaft61, a gap might occur between the support member and the main guide shaft61depending on the rotation position of the main guide shaft61. To prevent occurrence of such a gap, the support member65has the following structure.

As shown inFIG. 16, the support member65is provided with a press member65aand an adjustment member65b. The press member65ais screwed to a frame107that is disposed behind the main guide shaft61. The adjustment member65bis partially buried in the rear side of the main guide shaft61at the center. The press member65aand the adjustment member65bcontact each other and thereby sustain the loads from the springs84that act on the main guide shaft61in its radial direction.

Whereas the contact face of the press member65ais flat, the contact face of the adjustment member65bhas a curved face whose distance from the eccentric rotation axis R of the main guide shaft61is always kept constant, that is, does not vary depending on the rotation position. With this measure, no gap is formed between the support member65and the main guide shaft61even if the above-mentioned gap adjustment is performed by rotating the main guide shaft61about the eccentric rotation axis. Therefore, the support member65can always sustain the loads (indicated by an arrow inFIG. 17) from the springs84that act on the main guide shaft61in its radial direction. The main guide shaft61is prevented from being bent by the loads and hence the recording accuracy can be kept high.

As shown inFIG. 18 to 21B, the platen gap adjusting mechanism170is equipped with eccentric bushings171a,171b,172a, and172bthat support the main guide shaft61and the auxiliary guide shaft62in an eccentric manner, a belt173for synchronously rotating the eccentric bushings171aand172athat are located on one side, and tension pulleys174that act on the belt173from both sides to give tension to it. The platen gap adjusting mechanism170is also equipped with a motor175, a gear unit176for coupling the motor175to the eccentric bushings171aand172a, and first fixing members177and a second fixing member178that fix the main guide shaft61and the auxiliary guide shaft62.

As shown inFIG. 18 to 21B, the two ends of the main guide shaft61and the two ends of the auxiliary guide shaft62are fixed to the eccentric bushings171a,171b,172a, and172b, respectively, and the eccentric bushings171a,171b,172a, and172bare attached rotatably to the two side frames (not shown). This enables eccentric rotation of the main guide shaft61and the auxiliary guide shaft62. As shown inFIGS. 18 to 20, the belt173is stretched between the eccentric bushings171aand172a, which prevents backlash that would otherwise occur in the case where gears are used. The tension pulleys174are screwed to the side frame (not shown), which prevents a phase deviation between the main guide shaft61and the auxiliary guide shaft62when they rotate.

As shown inFIGS. 18 to 20, the gear unit176is provided with a bushing gear176athat is fitted with one end of the eccentric bushing171a,a first intermediate gear176bthat is in mesh with the motor175, a planetary gear176cthat is in mesh with the first intermediate gear176b, a second intermediate gear176dthat meshes with the planetary gear176cintermittently, a third intermediate gear176ethat is in mesh with the second intermediate gear176d, and a fourth intermediate gear176fthat is in mesh with the third intermediate gear176e. The planetary gear176chas a function of switching between the gap adjustment driving and the switching driving for the switching shafts14and22plus the release driving for the follower rollers152a,152b, and152cin accordance with the normal/reverse rotation of the motor175.

As shown inFIG. 18 to 21B, the first fixing members177are fixed to the respective eccentric bushings171a,171b,172a, and172b. The first fixing members177are screwed to the two side frames (not shown) after the horizontality of the plane defined by the first guide shaft61and the second guide shaft62is adjusted. As shown inFIGS. 18,19B,21A and21B, the second fixing member178is attached to the eccentric bushing171bthat is located on the other side. The second fixing member178is screwed to a flange171bathat is integral with the eccentric bushing171bafter a gap adjustment is performed by eccentric rotation of the main guide shaft61and the second guide shaft62.

During a gap adjustment, the carriage161is moved in the vertical direction, which may cause deviation of the main guide plates63and the auxiliary guide plates64that are provided between the main guide shaft61and the second guide shaft62. However, since the main guide plates63and the auxiliary guide plates64are attached to the side frames with some play, simplified sheet metal alignment can be performed. Complete sheet metal alignment can then be performed by leveling the main guide plates63and the auxiliary guide plates64by reciprocating the carriage161in the primary scanning direction.

With the above-configured platen gap adjusting mechanism170, the carriage161can be moved in the vertical direction by automatically rotating the main guide shaft61and the auxiliary guide shaft62in phase in an eccentric manner. Therefore, a highly accurate gap adjustment can be performed so that the gap between the nozzle formation face of the recording head162mounted on the carriage161and the recording face of a recording sheet being transported on the guide face163aof the platen163is always kept constant even if the recording sheet thickness is varied.

During a gap adjustment, a recognition sensor of the carriage161is moved in the vertical direction in synchronism with a vertical movement of the carriage161. A linear encoder scale that is part of a position sensor for the carriage161needs to be kept out of contact with a linear encoder that is attached to the carriage161. Therefore, a mechanism is provided that makes it possible to adjust the position of the linear encoder scale by using levers that are attached to the two respective sides of the linear encoder scale.

FIGS. 22 and 23show a detailed structure of the follower roller unit156.FIG. 23is different fromFIG. 22in that a lever40is removed. The two ends of the switching shaft14are rotatably supported by respective frames15so as to be movable in elliptical holes15athat are formed in the respective frames15. Plural sets of a spur roller11, a smooth roller12, and a releaser13(seeFIG. 5) where neither the spur roller11nor the smooth roller12is provided are arranged in the axial direction at prescribed intervals. In each set, the spur roller11, the smooth roller12, and the releaser13are disposed around the switching shaft14at prescribed intervals in the circumferential direction.

The switching shaft14of the follower roller unit156and the switching shaft22of the support rib unit164are rotated interlocking with each other by a gear unit30. The gear unit30is equipped with a roller gear31that is fitted with one end of the switching shaft14, a rib gear32that is fitted with one end of the switching shaft22, a first intermediate gear33and a second intermediate gear34that are in mesh with each other and with the roller gear31and the rib gear32, respectively, and a planetary gear35that meshes with the second intermediate gear34intermittently. The planetary gear35has a function of switching between the driving for the switching shafts14and22and the release driving for the follower rollers152a,152b, and152cin accordance with the normal/reverse rotation of the motor (not shown).

The switching shaft14of the follower roller unit156and the switching shaft22of the support rib unit164are rotated interlocking with each other by a gear unit30. The gear unit30is equipped with a roller gear31that is fitted with one end of the switching shaft14, a rib gear32that is fitted with one end of the switching shaft22, a first intermediate gear33and a second intermediate gear34that are in mesh with each other and with the roller gear31and the rib gear32, respectively, and a planetary gear35that meshes with the second intermediate gear34intermittently. The planetary gear35has a function of switching between the driving for the switching shafts14and22and the release driving for the follower rollers152a, and152cin accordance with the normal/reverse rotation of the motor (not shown).

The gear unit30is also equipped with an arm37that supports the respective shafts of the first intermediate gear33and the second intermediate gear34and is connected to the frame15via a spring36, a positioning cam38(seeFIG. 23) that is fitted with the one end of the switching shaft14, a positioning lever40that is connected to the arm37via a spring39and is locked with the cam38, and a limit switch41that is turned on or off in accordance with the position of the arm37. As shown inFIGS. 24A to 24C, a phase detection cam42that is fitted with the other end of the switching shaft14and a limit switch43that is turned on or off in accordance with the rotation position of the phase detection cam42are also provided.

The spring36urges the arm37downward, whereby the switching shaft14is ordinarily placed at the bottom stationary positions in the holes15a.The circumferential face of the positioning cam38is formed with three positioning notches38athat correspond to switching positions for the switching shaft14, that is, switching positions for the spur rollers11, the smooth rollers12, and the releasers13. The positioning lever40is provided with, at one end, a projection40athat is to engage with the positioning notches38aof the positioning cam38. The positioning lever40is slidably attached to the side face of the arm37so that the projection40acan slide along the circumferential face of the positioning cam38.

The spring39urges the positioning lever40in the sliding direction, whereby the projection40aof the positioning lever40is always pressed against the circumferential face of the positioning cam38. The circumferential face of the phase detection cam42is formed with three phase detection cuts42athat correspond to switching positions for the switching shaft14, that is, switching positions for the spur rollers11, the smooth rollers12, and the releasers13.

With the above gear unit30, the drive force of the motor175is transmitted to the rib gear32via the planetary gear35and the second intermediate gear34as well as to the roller gear31via the planetary gear35, the second intermediate gear34, and the first intermediate gear33. Therefore, the switching shafts22and14are rotated interlocking with each other, whereby the switching between the protrusion and retraction of the support ribs21and the switching between the spur rollers11, the smooth rollers12, and the releasers13can be performed simultaneously. Alternatively, instead of the gear unit, the switching shaft14of the follower roller unit156and the switching shaft22of the support rib unit164can be rotated interlocking with each other by using a pulley/belt mechanism.

When switching is performed between the spur rollers11, the smooth rollers12, and the releasers13, the positioning cam38and the phase detection cam42rotate together with the switching shaft14, the projection40aof the positioning lever40is disengaged from one positioning notch38aof the positioning cam38and slides along its circumferential face, and the lever of the limit switch43is disengaged from one phase detection cut42aof the phase detection cam42and slides along its circumferential face. The fact that the switching operation is being performed can be detected reliably on the basis of a signal from the limit switch43. If an abnormality that the switching shaft14goes up from the bottom stationary positions in the holes15aoccurs due to a certain external cause, the arm37is separated from the limit switch41. Therefore, the occurrence of the abnormality can be detected reliably on the basis of a signal from the limit switch41.

The switching between the spur rollers11, the smooth rollers12, and the releasers13is completed when the projection40aof the positioning lever40is brought into engagement with another positioning notch38aof the positioning cam38and the lever of the limit switch43is brought into engagement with another phase detection cut42aof the phase detection cam42. Since as described above the projection40aof the positioning lever40is engaged with the positioning notches38aof the positioning cam38, the spur rollers11, the smooth rollers12, and the releasers13can be set reliably to the prescribed phases. Further, the completion of the above switching operation can be detected reliably on the basis of a signal from the limit switch43.

FIG. 25Ashows a state that the follower roller unit156is switched to the releasers13and the spur rollers11and the smooth rollers12are separated from the sheet ejecting roller155and that in the support rib unit164the support ribs21are retracted from the guide face163aof the platen163.FIG. 25Bshows a state that the follower roller unit156is switched to the spur rollers11or the smooth rollers12and the spur rollers11or the smooth rollers12are in contact with the sheet ejecting roller155and that in the support rib unit164the support ribs21are retracted from the guide face163aof the platen163.

FIG. 25Cshows a state that the follower roller unit156is switched to the spur rollers11or the smooth rollers12and the spur rollers11or the smooth rollers12are in contact with the sheet ejecting roller155and that in the support rib unit164the support ribs21are protruded from the guide face163aof the platen163. This kind of switching makes it possible to realize a sheet ejection form that is most suitable for the attribute of a recording sheet.

FIG. 26is a table showing switching states of the follower roller unit156and the support rib unit164that correspond to respective attributes of recording sheets. As shown in the row of condition1, where the recording sheet type is a cut sheet and the recording sheet state is “normal,” an optimum sheet ejection form can be realized by making switching to the spur rollers11and switching the support ribs21to a protruded state. This is because normal cut sheets are less prone to jag traces but tend to rise.

As shown in the row of condition2, where the recording sheet type is a cut sheet and the recording sheet state is “delicate,” an optimum sheet ejection form can be realized by making switching to the smooth rollers12and switching the support ribs21to a protruded state. This is because smooth rollers having smooth circumferential faces are less prone to scratch delicate cut sheets.

As shown in the row of condition3, where the recording sheet type is a rolled sheet and the recording sheet state is “normal,” an optimum sheet ejection form can be realized by making switching to the releasers13and switching the support ribs21to a retracted state. This is because normal rolled sheet needs to be cut with a cutter and hence interference might occur if the spur rollers11or the smooth rollers12exist on the path, and normal rolled sheet is curled and hence might rub against the support ribs21if they exist in the path.

As shown in the row of condition4, where the recording sheet type is a rolled sheet and the recording sheet state is “thin,” an optimum sheet ejection form can be realized by making switching from the releasers13to the spur rollers11only during paper ejection and always keeping the support ribs21in a retracted state. This is because static electricity tends to occur in thin rolled sheet and hence it may stick to the platen163or the like to become hard to eject, and thin rolled sheet is curled and hence might rub against the support ribs21if they existed in the path.

As shown in the row of condition5, where the recording sheet type is a rolled sheet and the recording sheet state is “hygroscopic,” an optimum sheet ejection form can be realized by keeping, from recording to paper ejection, a state that switching is made to the spur rollers11from the releasers13and switching the support ribs21to a retracted state. This is because highly hygroscopic roller paper tends to rise because of what is called cockling, and highly hygroscopic roller paper is curled and hence might rub against the support ribs21if they exist in the path.

As shown in the row of condition6, where the recording sheet type is a rolled sheet and rolled sheet is to be cut shortly, an optimum sheet ejection form can be realized by making switching from the releasers13to the spur rollers11only during paper ejection and always keeping the support ribs21in a retracted state. This is because a short-cut part of rolled sheet may play on the platen163and become hard to eject, and a shortly cut part of the rolled sheet is curled and hence might rub against the support ribs21if they exist in the path.

As shown in the row of condition7, where the recording sheet type is a hand-fed sheet and the recording sheet state is “thick,” an optimum sheet ejection form can be realized by making switching to the releasers13and switching the support ribs21to a retracted state. This is because thick hand-fed sheets might interfere with the spur rollers11, the smooth rollers12, or the support ribs21if they exist in the path. The switching of the follower roller unit156and the support rib unit164can be performed automatically by storing the above kind of data in a controller of the ink jet printer100in the form of a table.

In the above-described embodiment, the switching shaft14of the follower roller unit156and the switching shaft22of the support rib unit164are rotated interlocking with each other by the gear unit30. However, the invention is not limited to such a case. Separate gear units or the like may be provided so that the switching shaft14of the follower roller unit156and the switching shaft22of the support rib unit164are rotated independently of each other. Further, adaptation to many kinds of recording sheets having respective attributes is possible even if only the follower roller unit156is provided, that is, the support rib unit164is not provided.

As shown inFIGS. 27 and 28, the follower roller driving device50is equipped with the intermittent gear53cand the planetary gear54afor operating the follower roller152cand an intermittent gear53C and a planetary gear54A for operating the follower rollers152aand152b. The platen gap adjusting mechanism170is equipped with the belt173, the tension pulleys174, and the gear unit176. The follower roller unit156and the support rib unit164are coupled to the gear unit30. The follower roller driving device50, the platen gap adjusting mechanism170, the follower roller unit156, and the support rib unit164are driven and switched by the single motor175.

More specifically, as shown inFIG. 28, if the motor175is rotated counterclockwise, the planetary gear176cis moved to such a position as to be able to drive the follower roller driving device50, the follower roller unit156, and the support rib unit164. In this state, if the motor175rotated clockwise, the planetary gear35is moved to such a position as to be able to drive the follower roller unit156and the support rib unit164. If the motor175is rotated counterclockwise, the driving by the planetary gear35is suspended. On the other hand, when the motor175is rotated clockwise, the planetary gear54A is moved to such a position as to separate the follower rollers152aand152bfrom the sub roller151and the planetary gear54ais moved to such a position as to separate the follower roller152cfrom the sub roller151. When the motor175is rotated counterclockwise, the planetary gear54A is moved to such a position as to bring the follower rollers152aand152binto contact with the sub roller151and the planetary gear54ais moved to such a position as to bring the follower roller152cinto contact with the sub roller151.

On the other hand, if first the motor175is rotated clockwise, the planetary gear176cis moved to such a position as to be able to drive the platen gap adjusting mechanism170. In this state, if the motor175is rotated clockwise, the platen gap (i.e., the distance between the head face and the platen163) is increased. If the motor175is rotated counterclockwise, the platen gap is decreased.

As shown inFIG. 30A, if first a motor93is rotated counterclockwise, a planetary gear91is moved to such a position as to be able to drive an automatic sheet supplying mechanism including the hopper141and the sheet supplying roller142. In this state, if the motor93is rotated counterclockwise, the automatic sheet supplying mechanism operates in the normal rotation direction. If motor93is rotated clockwise, the automatic sheet supplying mechanism operates in the reverse rotation direction. On the other hand, if first the motor93is rotated clockwise, the planetary gear91is moved to such a position as to be able to drive a cleaning mechanism90. In this state, if the motor93is rotated counterclockwise, a wiper is driven. If motor93is rotated clockwise, a pump95is driven.FIG. 30Bis a perspective of the mechanisms shown inFIG. 28.

The switching between the drive subject switching operation and the drive force transmitting operation that relate to the motors175and93is made by a lever92operated by the carriage161as shown inFIG. 29. For the driven subject switching, the lever92is moved to an unlock position (indicated by arrow UL). For the drive force transmission, the lever92is moved to a lock position (indicated by arrow L).

As shown inFIG. 31, the sensor157bis attached to the pivot member52that supports the follower roller154that is associated with the sheet feeding roller155. A hole163cis formed in the platen163at a position right under the sensor157b. A vertical wall163d, a wall163ethat forms an angle of about 135° with the wall163d, and a wall163fthat forms an angle of about 90° with the wall163dare formed inside the hole163c.

The sensor157b, which is generally a photoreflector, may operate erroneously due to incidence of external light (sunlight) or reflection of light generated by itself. However, light generated by the sensor157bitself does not return to the sensor157bbecause it passes through the hole163c, is reflected by the face of the wall163eto change the path by about 90°, and is again reflected by the face of the wall163fto change the path by about 90° (indicated by a dashed line inFIG. 31): an erroneous operation can thus be prevented. External light (sunlight) does not shine on the sensor157bbecause it is interrupted by the back face of the wall163e: an erroneous operation can thus be prevented.

An operation that is performed when the ink jet printer100having the above configuration performs recording on a normal cut sheet will be described with reference toFIGS. 32A and 32BandFIGS. 33A and 33B. First, the control section automatically switches the follower roller unit156and the support rib unit164for normal cut sheets. More specifically, switching is made to the spur rollers11in the follower roller unit156and the support ribs21of the support rib unit164are retracted. The cut sheets P that are stacked and accommodated in the sheet supply tray210of the tray unit200that is inserted in the sheet supplying/ejecting section140are pressed against the sheet supplying roller142because the hopper141is elevated by the restorative force of the compression spring144in synchronism with the rotation of the sheet supplying roller142(the synchronization is achieved mechanically). Only the uppermost cut sheet P is separated by the separator143and supplied to the transporting section150.

When the thus-supplied cut sheet P reaches a contact point151aof the sub roller151and its follower roller152a(seeFIG. 32A), skew correction of the cut sheet P is performed. The method of skew correction depends on the thickness of a recording sheet. In the case of a cut sheet that is as thin as or thinner than an ordinary sheet, first, the leading end portion of the cut sheet P is slightly inserted between the sub roller151and its follower roller152a. The rollers151and152aare thereafter rotated in the reverse direction to bend the cut sheet P and thereby align the leading end of the cut sheet P to correct the skew.

On the other hand, in the case of a thick cut sheet that is thicker than an ordinary sheet, the leading end of the cut sheet P is knocked against the contact point151aof the sub roller151and its follower roller152aand the sheet supplying roller142is caused to slip, whereby the leading end of the cut sheet P is aligned to correct the skew. The insertion length or the knock-in length is detected by the sensor157aand the skew correction is controlled on the basis of the detected length.

The reason why the skew correction depends on the recording sheet thickness is that a thin cut sheet is brittle and hence the sheet supplying roller142may send out the cut sheet without slipping on it, and that a thick cut sheet is a lamination of thin cut sheets and hence a thin cut sheet may peel off when the rollers151and152aare rotated in the reverse direction.

After completion of the skew correction, the cut sheet P is reversed (i.e., the traveling direction is changed to the direction opposite to the sheet supply direction) as it travels along the U-shaped path while being held between the sub roller151which is driven by a sheet fed motor (not shown) and its follower rollers152a,152b, and152c. When the leading end of the cut sheet P reaches a detection position DP of the sensor157b(seeFIG. 32B), the leading end positioning (i.e., determination of a recording start position) of the cut sheet P is performed.

More specifically, the transport length is detected by the sensor157buntil the leading end of the cut sheet P reaches a recording start position HP (seeFIG. 33A) after passing the detection position DP and passing between the sheet feeding roller153and its follower roller154. The leading end positioning is controlled on the basis of the detected transport length. Conventionally, the leading end positioning is performed by using the sensor157athat is located upstream of the sub roller151. In contrast, in this embodiment, since the leading end positioning is performed by using the sensor157bthat is located downstream of the sub roller151, a transport length to be detected is short and, in particular, the accuracy of the leading end positioning can be increased by eliminating a leading end positioning error due to a difference in recording sheet thickness.

The cut sheet P that has been subjected to the leading end positioning is transported to the recording section160while being held between the sheet feeding roller153which is driven by the sheet feed motor (not shown) and its follower roller154. The continuation of the holding of the cut sheet P between the sub roller151and its follower rollers152a,152b, and152cis a factor of lowering the transport accuracy, and hence the follower rollers152a,152b, and152care released from the sub roller151(seeFIG. 33B).

The cut sheet P thus transported is absorbed on the platen163by a suction pump (not shown) and is thereby rendered flat, and recording is performed by the recording head162mounted on the carriage161which is reciprocated for scanning by the carriage motor166and the timing belt165(not shown). The control section of the ink jet printer100performs a high-precision ink dot control, halftone processing, etc. by supplying inks of, for example, a total of seven colors of yellow, light yellow, magenta, light magenta, cyan, light cyan, and black from ink cartridges of the respective colors to the recording head162and controlling the discharge timing of the inks of the respective colors and the driving of the carriage161and the sheet feeding roller153. The recorded cut sheet P is ejected to the sheet supplying/ejecting section140by transporting it while holding it between the spur rollers11and the sheet ejecting roller155which is driven by the sheet feed motor (not shown). The cut sheet P is placed (stacked) on the sheet ejection tray230of the tray unit200.

As described above, in the ink jet printer100according to this embodiment, the carriage161bridges the approximately parallel arranged main guide shaft61and auxiliary guide shaft62in such a manner that sliding contact is made only in part of the circumference of each of the shafts61and62, whereby the carriage161can slide in the axial direction of the shafts61and62. Since the sliding contact between the slide members70and80of the carriage161and the main guide shaft61and the auxiliary guide shaft62is not made in the entire circumference of each of the shafts61and62, the carriage151can be caused to slide smoothly without the need for increasing the accuracy in terms of, for example, the straightness and parallelism of the main guide shaft61and the auxiliary guide shaft62.

The carriage161bridges the approximately parallel arranged main guide shaft61and auxiliary guide shaft62via the main guide plates63and the auxiliary guide plates, respectively, whereby the carriage161can slide in the axial direction of the shafts61and62. Since the slide members70and80of the carriage161are not in direct contact with the main guide shaft61and the auxiliary guide shaft62, respectively, sliding of the carriage161does not cause wear of the main guide shaft61and the auxiliary guide shaft62. Further, the main guide plates63and the auxiliary guide plates64can be made of a material that is less prone to wear. Employment of this measure can reduce the wear of the main guide plates63and the auxiliary guide plates64, which contributes to keeping the reciprocation of the carriage161highly accurate.

Equipped with the springs84for urging the auxiliary guide plates64toward the auxiliary guide shaft62, the slide members80on the side of the auxiliary guide shaft61can press the main guide plates63against the main guide shaft61via the slide members70of the carriage161on the side of the main guide shaft61. Therefore, the carriage161can be reciprocated with the main guide shaft61as a reference and hence the reciprocation of the carriage161can be kept highly accurate.

Since the main guide plates63and the auxiliary guide plates64are attached to the main guide shaft61and the auxiliary guide shaft62with prescribed play, the main guide plates63and the auxiliary guide plates64can bend by an amount corresponding to the play, which makes it possible to absorb attachment errors, working errors, etc. of the main guide plates63and the auxiliary guide plates64and to thereby keep the reciprocation of the carriage161highly accurate.

Since the slide members70and80are equipped with the radial bearings71and81that are in contact with the main guide shaft63and the auxiliary guide shaft64, respectively, the resistance of friction on the main guide plates63and the auxiliary guide plates64can be reduced to a large extent. Therefore, the wear of the main guide plates63and the auxiliary guide plates64can further be reduced and hence the reciprocation of the carriage161can be kept highly accurate.

The gap adjusting mechanism170for adjusting the gap between the recording head162mounted on the carriage161and the platen163opposed to the recording head162is provided, and the gap is adjusted by synchronously rotating the eccentric main guide shaft61and auxiliary guide shaft62by the belt mechanism173and174. Therefore, after the horizontality of the plane defined by the main guide shaft61and the auxiliary guide shaft62and the parallelism of this plane and the guide face163aof the platen163have been adjusted, a highly accurate gap adjustment can be performed by rotating the main guide shaft61and the auxiliary guide shaft62automatically and synchronously by the belt mechanism173and174while backlash is prevented which tends to occur with a gear mechanism.

Since tension is given to the belt173of the belt mechanism173and174by pushing it from both sides, phase deviation can be prevented while the main guide shaft61and the auxiliary guide shaft62are rotated synchronously, which enables a highly accurate gap adjustment.

The carriage161bridges the approximately parallel arranged main guide shaft61and auxiliary guide shaft62so as to be slidable in the axial direction of the shafts61and62, and is equipped with the support member65that supports the main guide shaft61approximately at the center. Therefore, even if the carriage161is large, the bend of the main guide shaft61can be reduced and hence the reciprocation of the carriage161can be kept highly accurate.

The main guide shaft61is rotatable about the eccentric rotation axis R. And the support member65is equipped with the adjustment member65bthat is partially buried in the main guide shaft61and has a face whose distance from the rotation axis R is constant in the rotation range and the press member65afor pressing on this face of the adjustment member65b. Therefore, even if the main guide shaft61is rotated eccentrically for a gap adjustment, the adjustment member65band the press member65acan always be kept in contact with each other and hence the support member65can always support the main guide shaft61approximately at the center.

The support member65supports the main guide shaft61approximately at the center by pressing on it toward the auxiliary guide shaft62. Therefore, even if the springs84for urging the auxiliary guide shaft62are attached to the carriage161and the carriage161is reciprocated with the main guide shaft61as a reference, the main guide shaft61can sustain the reaction forces of the springs84and hence the reciprocation of the carriage161can be kept highly accurate.

The invention can broadly be applied to recording apparatus having a carriage such as a facsimile machine and a copier. The application field of the invention is not limited to a recording apparatus. That is, the invention can be applied to a liquid ejection apparatus in which liquid droplets suitable for an intended use instead of ink droplets are ejected from a liquid ejection head toward a target medium to have those liquid droplets stuck to the subject medium, such as an apparatus having a colorant ejection head to be used for manufacture of color filters of a liquid crystal display device or the like, an electrode material (conductive paste) ejection head to be used for formation of electrodes of an organic EL display, a field-emission display (FED), or the like, a bioorganic material ejection head to be used for manufacture of a biochip, a sample ejection head as precision pipettes, or a like liquid ejection head.