Recording apparatus

A recording apparatus has a pair of bearings 38 having: two surfaces 38a and 38b which support both edge portions of a conveying roller 40; driven rollers 42 which press the conveying roller 40 in the direction where extension lines of the two surfaces 38a and 38b cross; and further, an intermediate bearing 47 which presses the conveying roller 40 in the direction of a point where the extension lines of the two surfaces 38a and 38b cross.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a recording apparatus for recording an image onto a recording sheet which is conveyed through a recording unit and, more particularly, to a conveying roller for conveying the recording sheet and a bearing of the conveying roller.

2. Description of the Related Art

Generally, a recording apparatus having a function of a printer, a copying apparatus, a facsimile, or the like is constructed so as to form an image (including characters, symbols, or the like) onto a recording sheet such as paper, cloth, plastics sheet, OHP sheet, or the like by using recording head on the basis of image information. As a scanning system in the recording apparatus, there are serial and line types. The serial type is a system in which the image is recorded while alternately repeating a main scan for moving the recording head along the recording sheet and a sub-scan for conveying the recording sheet at a predetermined pitch. The line type is a system in which the image is recorded only by the conveyance (sub-scan) of the recording sheet while recording the image of one line in a lump. The recording apparatuses can be classified into an ink jet type, a thermal transfer type, a laser beam type, a thermal sensitive type, a wire dot type, and the like in accordance with the kind of recording head.

In recent years, in recording apparatuses, particularly in ink jet recording apparatuses, image quality of the output image has been improved and the precision necessary regarding the recording operation to realize high image quality is continuing to improve. For example, in ink jet recording apparatus, one means for improving the image quality of the recording image is a means for reducing the ink discharge amount per dot and decreasing the diameter of each dot on the recording sheet, to reduce granularity of the dots of the ink discharged onto the image. When the size of dot decreases, an area where the dots have to overlap enters the state where they do not overlap. In other words, if an arrival position of the dot changes slightly, the non-overlap state appears (or an area where the dots do not have to overlap enters the state where they overlap) and a concentration or hue of this area is deviated. Such a deviation in the concentration or hue becomes a white stripe, a black stripe, or an uneven color, causing a deterioration in image quality. The positional deviation between the dots mentioned here is on the level of tens of μm to a few μm. A means for assuring such a precision is necessary.

One important mechanism regarding the improvement of image quality is the mechanism for conveying the recording sheet by a plurality of conveying rollers. In such a mechanism, in order to improve the image quality, first, it is necessary to improve the eccentricity, cylindricity, and diameter tolerance of the conveying rollers, and the grade of gear. It is also effective to use a construction in which a conveyance amount coincides with an amount of rotation of the number of integer times of the motor or the gear. This makes a stop error of the motor and an eccentricity precision component of the gear cancel one another.

However, in conventional recording apparatus, although consideration has been given to the precision of a theoretical rotation amount (conveying plane movement amount) with respect to the conveying rollers for conveying the recording sheet, a countermeasure against restriction of the positions of the conveying rollers is insufficient. In the conveying roller which is arranged on the downstream side of the recording head (for example, what is called a discharge roller), particularly, a consideration and a countermeasure against such a point are insufficient.FIG. 8is a cross sectional view showing a general conveying roller and its bearing in the conventional recording apparatus, taking an example of a discharge roller. InFIG. 8, there are a discharge roller1001; a bearing1002of the discharge roller; and a driven roller1003. The driven roller1003is pressed to the discharge roller1001by a force Fs by a spring (not shown) in order to produce a conveying force of the recording sheet.

A looseness of the discharge roller1001in the bearing1002causes it the roller to deviate in the downward direction in the diagram because of the pressing force Fs of the driven roller1003. The cross sectional shape of both the discharge roller1001and the bearing1002is circular. Therefore, the apparatus has a construction in which play exists, and the discharge roller1001is easily moved in the directions shown by arrows Y and Y′ on an inner circumference of the bearing1002. Consequently, if an external force due to a disturbance is applied, the discharge roller1001is liable to be moved and the position is difficult to be fixed. Since the position of the discharge roller is difficult to be fixed as mentioned above, it is difficult to maintain the high conveyance precision of the recording sheet and it is difficult to improve the image quality of the recording image.

SUMMARY OF THE INVENTION

It is an object of the invention to stabilize the position of a conveying roller in use. Another object of the invention is to provide a recording apparatus in which when a recording sheet is conveyed only by a conveying roller or when a rear edge of the recording sheet comes out from another conveying roller arranged on an upstream side of a recording head, movement of the conveying roller is suppressed, and the recording sheet can be conveyed with high precision.

DESCRIPTION OF THE EMBODIMENTS

An embodiment of the invention will be specifically explained hereinbelow with reference to the drawings. In all of the drawings, the same or corresponding portions are designated by the same reference numerals.FIG. 1is a perspective view of the embodiment of a recording apparatus to which the invention is applied.FIG. 2is a perspective view of an internal construction of the embodiment of the recording apparatus to which the invention is applied.FIG. 3is a vertical sectional view of the recording apparatus ofFIG. 2.FIGS. 1,2and3show an example of a case where the recording apparatus is an ink jet recording apparatus. InFIGS. 1,2and3, the recording apparatus has a sheet-feeding unit2, a sheet sending unit3, a sheet discharging unit4, a recording unit5, a recovery processing unit6, and a U-turn conveying unit8. The recording unit5is constructed in such a manner that while a recording medium is scanned, an image is recorded by a reciprocatively moveable recording head7mounted on a carriage50. A sheet feeding tray and a sheet discharging tray which can be opened and closed as will be explained hereinafter are provided for an exterior-mounting portion of the apparatus.

First, the sheet feeding unit2will be explained. The sheet feeding unit2is constructed by attaching a pressing plate21on which a recording sheet is stacked, a feed roller28for feeding the recording sheet, a separating roller241for separating the recording sheet, and the like onto a base20. A sheet feeding tray26to hold a rear edge side of each of the recording sheets stacked on the pressing plate21is attached to the exterior-mounting portion in the rear portion of the apparatus. The feed roller28is an arc-shaped roller in a shape obtained by cutting away a part of a circle. The separating roller241is provided at a position closer to a reference surface to restrict a side edge position of the recording sheet. The feed roller28is driven by a motor69which is used in common with the recovery processing unit6. Speed control of the feed roller28is made by PWM value control for controlling an electric power on the basis of a detection value of a rotational speed.

A movable side guide23to restrict the stacking position of the recording sheets is slidably attached to the pressing plate21. The pressing plate21can swing around an axial core, as a rotational center, provided for the base20and is urged to the feed roller28by a pressing plate spring212. A separating sheet213to prevent an overlap feeding of the recording sheets is provided at a position of the pressing plate21which faces the feed roller. The separating sheet is made of a material of a large coefficient of friction. The pressing plate21is come into contact with and is away from the feed roller28at predetermined timing by a pressing plate cam (not shown).

A separating roller holder24having the separating roller241to separate the recording sheets one by one is attached to the base20. The separating roller holder can rotate around a rotary axis provided for the base20as a rotational center and is urged to the feed roller28by a separating roller spring (not shown). The separating roller241is axially supported through a clutch spring (torque limiter). When a load torque of a predetermined value or more acts, the separating roller241is rotated. The separating roller can be moved into contact with and away from the feed roller. The positions of the pressing plate21, separating roller241, and the like are detected by an ASF (Automatic Sheet Feeder) sensor29.

The sheet sending unit3will now be described. An upstream conveying roller36for conveying the recording sheet and a PE (paper edge) sensor32are provided for the sheet sending unit3. The upstream conveying roller36is a roller in which the surface of a metal axis has been coated with micro particles of ceramics. The upstream conveying roller36is axially supported in metal axis portions at both ends by bearings38provided for a chassis11. A plurality of pinch rollers37have been come into contact with the upstream conveying roller36so as to be driven-rotated. Each pinch roller37is a rotor which is driven-rotated in association with the upstream conveying roller36. The pinch rollers37are held by a pinch roller holder30. When the pinch rollers37are urged to the upstream conveying roller36by a pinch roller spring31, a conveying force is produced.

A pulley361is provided for an axis of the upstream conveying roller36. The upstream conveying roller36is driven by transferring a rotational force of a conveying motor to the pulley361by a timing belt. A code wheel362to detect a conveyance amount is provided for an axis of the upstream conveying roller36. A marking of this code wheel is read by an encoder sensor363attached to an adjacent portion, so that the conveyance amount is detected. The recording sheet can be accurately conveyed by the upstream conveying roller36through the recording unit5, which will be explained hereinafter. The image is recorded onto the whole recording sheet by alternately repeating the image recording which is executed by the recording head7and the conveyance of the recording sheet.

The recording unit5will now be described. The recording head7to record the image onto the recording sheet on the basis of the image information is provided for the recording unit constructed on the downstream side in the conveying direction of the upstream conveying roller36. The recording head7is mounted on the carriage50which can be moved back and forth in the width direction of the recording sheet. The recording head of the embodiment is an ink jet recording head.FIG. 4is a perspective view of the recording head7mounted on the carriage50inFIG. 2. InFIG. 4, the recording head7has an ink discharging unit having a plurality of discharge ports for discharging ink droplets on the basis of the image information. A discharge surface formed with a plurality of discharge port trains comprising an array of discharge ports is formed in the ink discharging unit. An ink tank70of each color is exchangeably attached to the ink discharging unit. The ink discharging unit can be for example one having an electro-thermal converting system in which heat energy is applied to the ink in the ink discharge port by a heater and the ink is film-boiled by the heat. That is, the ink droplet is discharged from the discharge port of the recording head7by a pressure change that is caused by a growth or contraction of a bubble formed by the film boiling. By selectively discharging the ink droplet from each discharge port on the basis of the image information, the image can be recorded onto the recording sheet.

The carriage50is guided and supported along a guide shaft52and a guide rail53so that it can be reciprocatively moved in the width direction of the recording sheet. The guide shaft52is attached to the chassis11. The guide rail53is formed integratedly with the chassis. The carriage50is driven by a carriage motor54through a timing belt541suspended between a motor pulley and an idle pulley542. A codes strip561is provided in parallel with the guide shaft52. Markings have been formed on the codes strip561at a pitch of, for example, 150 to 300 lpi. By reading the markings by an encoder sensor mounted onto the carriage50, the position and speed of the carriage50can be detected. A flexible board57to transmit a head signal to the recording head7is provided for the carriage50. In the recording unit5, the recording sheet is conveyed through the image forming position by the upstream conveying roller36and the pinch rollers37. By moving the carriage50to the recording sheet, the image of one line is recorded by the recording head7on the basis of the image information. The image is recorded onto the whole recording sheet by alternately repeating the conveying operation and the recording of the image of one line.

The sheet discharging unit4will now be explained. The sheet discharging unit4has two downstream conveying rollers40and41. Those downstream conveying rollers are coupled with the upstream conveying roller36through a gear train or the like and driven synchronously with the upstream conveying roller36. A driven roller42is urged to each downstream conveying roller so that the roller can be driven-rotated. In the embodiments, the downstream conveying rollers40and41are attached to a platen34. The driving force of the upstream conveying roller36is transferred to the first downstream conveying roller40and the driving force of the first downstream conveying roller40is transferred to the second downstream conveying roller41through an idle gear. Each of the driven rollers42which are driven-rotated in association with the downstream conveying rollers40and41has a structure in which a thin plate made of SUS or the like and having a plurality of convex shapes around the circumference is molded integratedly with a resin portion. Each driven roller42is rotatably supported to a driven roller holder43by a shaft formed by a coil spring. The driven rollers42are pressed to the downstream conveying rollers40and41by the coil springs. The recorded sheet is sandwiched by nip portions between the downstream conveying rollers40and41and the driven rollers42, conveyed, and ejected to the outside from the apparatus main body.

The recovery processing unit6will now be described. The ink jet recording apparatus is provided with the recovery processing unit6for preventing a clog of the discharge port of the recording head and maintaining and recovering ink discharge performance. The recovery processing unit6has a suction pump60, a cap61, and a wiper62. The cap61is adhered to the discharge surface of the recording head7and covers the discharge port, thereby reducing drying of the ink in the recording head. The suction pump60operates in the state where the discharge port is hermetically sealed by the cap61, thereby sucking the ink from the discharge port and refreshing the ink in the discharge port. The wiper62sweeps and cleans the discharge surface of the recording head. As a suction pump60, besides a pump of a piston cylinder type, what is called a tube pump or the like which allows a negative pressure generated in a tube to act on the discharge port or the like is used.

The U-turn conveying unit8will now be described. A U-turn conveying path for enabling duplex printing is provided for the U-turn conveying unit8. A sheet-feeding cassette81in which the recording sheets have been enclosed is attached to a position near the front side of a lower portion of the apparatus main body. A pressing plate for allowing the stacked recording sheets to be put into contact with a feed roller821is provided in the sheet feeding cassette81. The top one of the recording sheets is separated and conveyed to the U-turn conveying path by the cooperation of the feed roller821, a separating roller831, and the separated sheet. The recording sheet is conveyed toward the recording unit5by first and second intermediate rollers86and87provided at two positions on the U-turn conveying path and by pinch rollers861and871urged to the intermediate rollers86and87.

A change-over flapper883is arranged at a meeting point of the conveying path of the sheet feeding unit2and the conveying path of the U-turn conveying unit8. The recording sheet conveyed from the U-turn conveying unit8is turned upside down and, thereafter, fed to a portion between the upstream conveying roller36and the pinch roller37through the change-over flapper883. The subsequent operation is substantially the same as that of the recording sheet which is fed from the sheet feeding unit2. That is, the recording sheet is conveyed by the sheet sending unit3, the image is recorded onto the recording sheet by the recording unit5, and the sheet is ejected to the outside from the sheet discharging unit4.

FIG. 4is a perspective view showing a construction around the downstream conveying rollers in the first embodiment of the recording apparatus to which the invention is applied.FIG. 5is a cross sectional view showing the downstream conveying roller inFIG. 4and a bearing thereof.FIG. 6is a partial perspective view showing details of the bearing portion of the downstream conveying roller inFIG. 4and showing the pressing direction and the position restricting direction. The construction and operation for stabilizing the position of the conveying roller in the embodiment will now be described with reference toFIGS. 4,5and6. The case where the conveying roller to stabilize the position is the downstream conveying roller40will now be explained as an example. That is, by stabilizing the position of the downstream conveying roller40, the occurrence of an error of the conveyance amount of the recording sheet that is caused by the movement of the downstream conveying roller40is prevented. The movement of the downstream conveying roller40is liable to occur, for example, when the rear edge of the recording sheet is taken away from the upstream conveying roller36or when the recording sheet is conveyed only by the downstream conveying rollers40and41.

As shown inFIG. 4, both edges of the downstream conveying roller40are supported by the bearings38. An intermediate bearing47having a bore surface which comes into contact with the peripheral surface of the downstream conveying roller40is provided between (inside) the two bearings38. One end portion of the downstream conveying roller40is supported by the chassis11and a bushing49and the other end portion is supported by a bearing of the platen34fitted and attached to the chassis11. It is also possible to use a construction in which both of the edges of the downstream conveying roller40are supported by the chassis11or the platen34. In the embodiment, a bore portion of the intermediate bearing47which axially supports the discharge roller40has a circular shape and an outer diameter of the downstream conveying roller40and the bore (inner diameter) of the intermediate bearing47are set so that the downstream conveying roller40and the intermediate bearing47are fitted in the state where play of between 10 and 90 μm is permitted.

The position of the intermediate bearing47can be selected to any desired position so long as it lies within a region that is between the two bearings38and outside of the maximum width of the recording sheet which can be conveyed. A portion which has been press-molded into a U-character cross sectional shape is provided on the front surface of the chassis11. In order to assure the strength of the chassis11, a front chassis12as another part made of sheet metal is provided for the front surface in parallel with the downstream conveying roller40. The intermediate bearing47is downwardly urged by an intermediate bearing spring48as shown by arrow A inFIG. 6. In one end portion of the intermediate bearing spring48, the spring48is hooked and retained to a hook-shaped portion of the intermediate bearing47. In the other end portion, the spring48is hooked and retained to a hook-shaped portion of the front chassis12. Thus, the downstream conveying roller40is put into pressure contact with an upper portion of the circular bearing surface of the intermediate bearing47and the necessary looseness occurs in the lower portion.

FIG. 5shows a structure of the bearings38in both end portions of the downstream conveying roller40. As shown inFIG. 3, the driven rollers42are pressed to the downstream conveying rollers40and41by springs44, respectively. The driven rollers42are attached to the driven roller holder43through the springs44. InFIG. 5, a pressing force of the driven rollers42and a pressing force of the intermediate bearing47by the intermediate bearing spring48act on the downstream conveying roller40.

The two driven rollers42are attached to a driven roller attaching portion at one position of the holder43. A force of the springs44which press the two driven rollers42is set to, for example, 30 to 60 gf. Thus, a total of the pressing forces of a plurality of driven rollers42which are pressed by the downstream conveying roller40is equal to, for example, 300 to 600 gf. On the other hand, a pressing force which acts on the downstream conveying roller40from the intermediate bearing47by the intermediate bearing spring48is set to, for example, 200 to 400 gf.

In order to assure the conveying force that is obtained by the downstream conveying roller40, it is preferable to increase the force of the spring44. However, if the force of the spring44is set to be too large, the projection front edge of the driven roller42can cause scratching. Therefore, it is suitable that the pressing force of the driven rollers42to the downstream conveying roller40is set to 300 to 600 gf in total in order to convey the recording sheet without scratching. However, if only the pressing force by the driven rollers42is used, it is insufficient to restrict the position of the downstream conveying roller40. In the embodiment, therefore, in order to supplement the pressing force which is obtained by the driven rollers42, a construction in which the pressing force of the intermediate bearing47mentioned above is made to act on the discharge roller40is used.

Each of the pair of bearings38for rotatably supporting the end portions of the downstream conveying roller40has two surfaces38aand38bfor supporting the downstream conveying roller40in contact with two points or areas (40a,40b) on the circumference of the downstream conveying roller40. The direction of a bisector40cof a line segment connecting the two contact points40aand40bcoincides with the direction in which the driven rollers42are pressed to the downstream conveying roller40by the springs44.

That is, the two planes38aand38bfor supporting the downstream conveying roller40are formed on the bore surface of the bearing38. In the embodiment, the planes38aand38bare formed symmetrically with respect to a vertical line passing through the center of the bearing38. Perpendicular lines at the center positions of the two planes38aand38bpass through the center of the bearing38, as shown inFIG. 5.

The two planes38aand38bare arranged with an angle therebetween of 45 to 135°. The bisector40cof the line segment connecting the two points with which the downstream conveying roller40are come into contact coincides with the pressing direction of the driven rollers42.

With such a construction, so long as the downstream conveying roller40does not float up from the bearing38, the position of the downstream conveying roller40does not deviate in the conveying direction (directions shown by arrows Y and Y′ inFIG. 5). The intermediate bearing47presses the downstream conveying roller40by the intermediate bearing spring48in the direction of the point where extension lines of the two planes38aand38bof the bearings38cross.

The intermediate bearing47is fitted at its outer circumference to the platen34and its position is restricted in the conveying direction of the downstream conveying roller40. In the embodiment, the intermediate bearing47is urged to the downstream conveying roller40by a helical extension spring. In place of the helical extension spring, other biasing means such as for example a helical torsion spring, a plate spring, or the like may be used.

According to the embodiment described above, the position of the downstream conveying roller40in the conveying direction can be stabilized. Thus, it is possible to prevent the movement of the downstream conveying roller40in the conveying direction at the time when the rear edge of the recording sheet is taken away from the upstream conveying roller36or when the recording sheet is conveyed only by the downstream conveying rollers40and41. With such a construction, a good, stable image can be recorded by preventing the occurrence of the error of the conveyance amount of the recording sheet that is caused by the movement of the downstream conveying roller relative to the bearing. Particularly, in the case of the ink jet recording apparatus, by improving the arrival precision of the fine ink droplet, the deviation in the concentration or hue which is caused by the deviation in the dot position is prevented, so that the image quality of the recording image can be improved.

In the embodiment, although the structure of the downstream conveying roller40has been explained as an example, the invention can be also similarly embodied in the upstream conveying roller36and a similar functional effect is obtained.

FIG. 7is a cross sectional view showing a construction around downstream conveying rollers in the second embodiment of the invention. InFIG. 7, the bore surface of the intermediate bearing47comes into contact with two points40dand40eon the circumference of the downstream conveying roller40. The contact points40dand40eare selected to be the middle points of planes47aand47bof the intermediate bearing47which is come into contact with the circumferential surface of the downstream conveying roller40. The direction of a bisector40fof a line segment connecting the two contact points40dand40ecoincides with the bisector of the line segment connecting the two points40aand40bof the downstream conveying roller40which come into contact with the bearings38.

According to the second embodiment, a functional effect in which the movement in the conveying direction due to the recording sheet can be also prevented in the intermediate portion of the downstream conveying roller40is obtained. Thus, the movement of the downstream conveying roller can be prevented and the image quality of the recording image can be improved.

This application claims the priority of Japanese Patent Application No. 2006-042228, filed Feb. 20, 2006, which is hereby incorporated by reference herein in its entirety.