Detecting unit, sheet feeding unit, and image forming apparatus comprising the same

An image forming apparatus includes a main assembly including an image forming portion; a rotatable member capable of feeding a sheet and configured to rotate; and a detecting unit including an interrelating member configured to rotate in interrelation with rotation of the rotatable member, a detecting member configured to detect rotation of the interrelating member, and a holding member configured to integrally hold the interrelating member and the detecting member. The interrelating member, the detecting member and the holding member are integrally assembled into a unit. The detecting unit is detachably mountable to the main assembly.

FIELD OF THE INVENTION AND RELATED ART

Conventionally, for example, when sheet (paper) feeding control is carried out in a laser beam printer or an ink jet printer of an electrophotographic type, a method of detecting rotation of rollers and gears relating to sheet feeding has been known. Specifically, rotation of a feed roller for feeding a sheet such as paper is detected or rotation of a separating roller for separating and feeding the sheet from a feeding cassette is detected.

Of such image forming apparatuses, an image forming apparatus in which the rotations of the rollers relating to the feeding of the sheets and feeding timing is controlled in order to separate and feed the sheets, one by one, stacked in the feeding cassette has been known.

For example, International Publication No. WO2011/007406 discloses a rotation detecting device for detecting rotation of a retard roller opposing a feed(ing) roller provided downstream of a pick-up roller for picking up a sheet. In WO2011/007406, in order to provide the rotation detecting device coaxial with a member-to-be-measured or on a rotation shaft rotating in interrelation with the rotation detecting device, a unit including a member-to-be-measured as one of constituent elements thereof is provided with the rotation detecting device.

FIG. 12shows a feeding unit having a conventional constitution. A feeding unit101includes a retard roller102. On a retard roller driving shaft105of the retard roller102, a rotation detecting device, constituted by an encoder wheel103and a sensor104, is provided.

In the case where the rotation detecting device is disposed is a sheet (paper) feeding mechanism of the image forming apparatus, there is a possibility that improper detection occurs due to contamination with paper powder, scattered toner, or the like, so that maintenance by a service person is needed in some instances. The sheet feeding mechanism is provided inside a casing of the apparatus, and in many cases, a constitution in which the sheet feeding mechanism is assembled into a unit as a feeding unit and is detachably mountable to an apparatus main assembly is employed. Accordingly, in order to clean and exchange the rotation detecting device, many parts (components) are required to be demounted, and therefore, operativity is poor.

On the other hand, in the case where, as the rotation detecting device, a lever for permitting light transmission and light blocking of a sensor and an encoder wheel are provided in a feeding unit and a detecting means, such as a sensor or the like, is provided in another unit (apparatus casing or the like), when the feeding unit is mounted and demounted, there is a problem in operativity. This is because in a constitution in which the detecting means sandwiches the lever or the encoder wheel, when the feeding unit is mounted and demounted, the detecting means is required to be demounted from the other unit in advance in order not to be damaged by interference with the lever or the encoder wheel.

Further, in order to improve the operativity even a little, in the case where both of the sensor and the lever or the encoder wheel are provided at an end portion of the feeding unit with respect to an axial direction, a length of the feeding unit with respect to the axial direction increases, so that there is a problem such that a width of an apparatus main assembly becomes large.

SUMMARY OF THE INVENTION

A principal object of the present invention is to provide an image forming apparatus capable of improving operativity regarding maintenance, such as exchange of a detecting unit, while suppressing upsizing of the unit, and by extension, to suppression of upsizing of the apparatus using the unit.

According to an aspect of the present invention, there is provided an image forming apparatus comprising: a main assembly including an image forming portion; a rotatable member capable of feeding a sheet and configured to rotate; and a detecting unit including an interrelating member configured to rotate in interrelation with rotation of the rotatable member, a detecting member configured to detect rotation of the interrelating member, and a holding member configured to integrally hold the interrelating member and the detecting member, wherein the interrelating member, the detecting member and the holding member are integrally assembled into a unit, wherein the detecting unit is detachably mountable to the main assembly.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be specifically described with reference to the drawings. Dimensions, materials, shapes and relative positions of constituent elements described in the following embodiments should be appropriately be changed depending on structures and various conditions of mechanisms to which the present invention is applied, and therefore, the scope of the present invention is not intended to be limited to the following embodiments unless otherwise specified.

An image forming apparatus including a rotation detecting device in Embodiment 1 of the present invention will be described usingFIGS. 1 to 4. An example of a structure of the image forming apparatus including the rotation detecting device will be described usingFIGS. 1 to 3, and then the rotation detecting device will be specifically described usingFIG. 4and subsequent figures.

FIG. 1is a sectional view showing the example of the structure of the image forming apparatus including the rotation detecting device in this embodiment. In this embodiment, an image forming apparatus using an electrophotographic image forming process and having a double-side printing function is shown. As shown inFIG. 1, inside the image forming apparatus1, which is an apparatus main assembly, an image forming portion for forming an image on a sheet is provided. The image forming portion includes a photosensitive drum2, a transfer roller3and the like. In this embodiment, the photosensitive drum2is included in a process cartridge4, and the process cartridge4is detachably mounted to the image forming apparatus1so that a user can exchange the photosensitive drum2. Incidentally, the process cartridge4includes, as process means actable on the photosensitive drum2, an unshown charging roller, a developing roller19, an unshown cleaning device and the like.

In the image forming apparatus1, a feeding cassette5is provided. Sheets, on which an image is to be formed, are stacked in a sheet bundle S in the feeding cassette5. By a controller6, rotation of an unshown driving motor is controlled, so that a pick-up roller7is rotated and starts feeding an uppermost sheet of the sheet bundle S stacked on the feeding cassette5. The fed sheet enters a nip between a feed roller13and a retard roller14. A rotational direction of the feed roller13, as a first rotatable member, is to feed the sheet toward the image forming portion. On the other hand, a driving shaft of the retard roller14, as a second rotatable member, is rotated to feed the sheet in the opposite direction.

The driving shaft of the retard roller14always rotates in one direction. A torque limiter28(shown inFIG. 4) is provided on the driving shaft of the retard roller14, and therefore, a rotational direction of the retard roller14varies depending on a condition of the nip. As shown inFIG. 2, in the case where only one sheet exists in the nip between the feed roller13and the retard roller14, the retard roller14is rotated by a frictional force with the sheet. The rotational sense of the driving shaft of the retard roller14is the same as that of the feed roller13so that the feeding force of the driving shaft of the retard roller14is opposite to that of feed roller13, but the rotation of the retard roller14is absorbed by a slip of the torque limiter28. This is also true for the case where the sheet does not exist in the nip between the feed roller13and the retard roller14.

On the other hand, in the case where a plurality of sheets are fed superposedly, a frictional force between the superposed sheets is relatively low. For that reason, as shown inFIG. 3, the retard roller14rotates in a direction in which the sheet is pushed back toward the feeding cassette5, and the superposed sheet is separated, so that only one sheet is fed by the feed roller13opposing the retard roller14. Thereafter, the sheet is fed in the order of a feeding roller pair8, the photosensitive drum2and the transfer roller3. Incidentally, after the sheet is nipped between the feeding between pair8, by disconnecting an unshown electromagnetic clutch, drive of the pick-up roller7, the feed roller13and the retard roller14is eliminated.

A laser scanner9for writing an image emits laser light L, so that an electrostatic latent image is formed on the surface of the photosensitive drum2electrically charged by the charging roller. Then, the electrostatic latent image on the photosensitive drum2is developed with toner supplied by the developing roller19, so that a toner image is formed on the photosensitive drum2. The toner image is transferred onto a first surface of the sheet between the photosensitive drum2and the transfer roller3. Thereafter, the sheet is heat-fixed by a fixing device10and is fed toward a discharge tray12by a discharging roller pair11.

Next, a structure of the rotation detecting device (rotation detecting means) as a feature of this embodiment will be described specifically with reference toFIGS. 4 and 5.

FIG. 4is a perspective view showing a structure from the pick-up roller7, the feed roller13and the retard roller14to the rotation detecting device. In the case where a feeding operation is carried out, an electromagnetic clutch39is connected, so that a driving force transmitted from an unshown driving source is transmitted to the feed roller13through a feed roller driving shaft20via a gear train, and thus the feed roller13is driven. The driving force is transmitted from the feed roller13to the pick-up roller7through a gear train21. The driving force is branched by the gear train and is transmitted to the retard roller14through the torque limiter28from a retard roller driving gear22which is on a first shaft, and thus the retard roller14is driven. The retard roller driving gear22always rotates at a certain speed, but in the case where a torque exceeds a set torque of the torque limiter28, the retard roller driving shaft23and the retard roller14fluctuate in rotational speed.

A first sensor gear24has a function of rotating a second sensor gear25and an encoder wheel26. The second sensor gear25(second gear) engages with the first sensor gear24rotating integrally with rotation of the retard roller14and rotates. The encoder wheel26is bonded to the second sensor gear25and integrally rotates with the second sensor gear25.

The first sensor gear24is provided on the retard roller driving shaft23, and therefore rotation transmitted to the second sensor gear25is rotation of the retard roller14. The encoder wheel26is an interrelating member rotating in interrelation with the rotation of the retard roller14via the first sensor gear24and the second sensor gear25. The first sensor gear24is a first gear rotating integrally with the rotation shaft23of the retard roller14. In this embodiment, a constitution in which the first sensor gear24and the second sensor gear25are interposed between the retard roller14and the encoder wheel26is described, but the present invention is not limited to this constitution. For example, a constitution such that the first sensor gear24and the second sensor gear25do not exist and the encoder wheel26is directly fitted around the retard roller driving shaft23and thus the retard roller14and the encoder wheel26rotate in a 1:1 relationship may also be employed.

A constitution of a rotary encoder as the rotation detecting device in this embodiment is, for example, comprised of the encoder wheel prepared by printing slits in a thin disk of a transparent resin material with regular intervals and optical sensor27as a detecting member provided so as to sandwich a flat surface of the encoder wheel26. The sensor27optically detects transmission and blocking of light by rotation of the encoder wheel26. The sensor27detects the rotation of the encoder wheel26. The sensor27outputs a signal to a controller6at timing of a transparent portion (light transmission) and a printed portion (light blocking), and the controller6calculates a rotational speed of a member-to-be-measured (the retard roller14in this embodiment). Incidentally, there is also an encoder wheel26of a type in which an opaque member is provided with a slit (opening).

As described above, in this embodiment, the constitution in which the first sensor gear24and the second sensor gear25are interposed between the retard roller14and the encoder wheel26is employed in this embodiment. In such a constitution, by changing a gear ratio between the first sensor gear24and the second sensor gear25, the rotational speed of the encoder wheel26can be increased or reduced relative to the retard roller14. As one of advantages of the above-described constitution, it is possible to obtain a rotation detecting means which is broad in width of the slit (opening) and which is advantageous for deposition of a foreign matter without lowering detection accuracy by increasing the rotational speed while broadening the width of the slit provided in the encoder wheel26. Further, as another advantage, a rotation center of the encoder wheel26can be disposed so as to be offset relative to the retard roller driving shaft23correspondingly to a gap between the shafts of the first sensor gear24and the second sensor gear25, and therefore, an arrangement of the rotation detecting means can be designed with a latitude to some extent.

By the constitution as described above, the rotational speed of the retard roller14is detected. By a numerical value of a fluctuation in detected rotational speed of the retard roller14, the controller6discriminates that a leading end of a subsequent sheet reached a nip between the feed roller13and the retard roller14, and controls timing when an electromagnetic clutch39eliminates drive of the feed roller13, the pick-up roller7and the retard roller14.

FIG. 5shows a structure of the rotation detecting device. As described above, the second sensor gear25, to which the encoder wheel26is bonded, is mounted in a resin-made holder member29, to which the sensor27is fixed, as shown by an arrow A. That is, the encoder wheel26is provided integrally with the second sensor gear25and is mounted into the sensor27by being slid in a direction parallel to a flat surface of the encoder wheel26. Thus the flat surface of the encoder wheel26is disposed by being sandwiched by the sensor27. This state is shown inFIG. 6.

The holder member29, to which the sensor27is fixed, includes an arm portion29aas a gear holding portion for holding the second sensor gear25. During the mounting of the second sensor gear25into the holder member29, the arm portion29ais flexed, and after the mounting, the arm portion29ais caught by the second sensor gear25, so that the second sensor gear25is prevented from being disconnected from the holder member29. Then, the holder member29, to which the sensor27is fixed and in which the second sensor gear25is mounted, is fixed to a cover member30as shown by an arrow B inFIG. 5. The sensor27, the encoder wheel26and the second sensor gear25can be integrally mounted in the cover member30by using the holder member29, and therefore, operativity is good. Finally, the holder member29and the cover member30are fixed with a screw shown by an arrow C.

The cover member30has a function as a holding member (holder) for holding the rotation detecting device and, simultaneously, also has a function as a cover for preventing or alleviating entrance of dust and dirt, causing erroneous detection, into a detecting portion. Further, the sensor27is an optical sensor, and in order to prevent erroneous detection due to stray light coming from an outside, the cover member30may preferably be molded from a black resin material. Further, in the cover member30, a wiring guide40for holding a wiring lead connected with the sensor27is formed by molding.

As described above, the encoder wheel26, the second sensor gear25and the sensor27are integrally assembled with the cover member30into a unit as encoder unit31which is shown inFIG. 7.FIG. 7is a perspective view of the encoder unit31as seen from an inside of the cover member30. The encoder unit31is a detecting unit for integrally holding the encoder wheel26and the sensor27by the cover member30.

An end surface of a center hole25cof the second sensor gear25has a tapered portion25a. For that reason, when the encoder unit31is mounted to the apparatus main assembly of the image forming apparatus1, a shaft32(second shaft) (FIG. 10) projecting from the apparatus main assembly side easily enters the center hole25cof the second sensor gear25. The shaft32which is a rotation shaft of the second sensor gear25is provided as a part of the apparatus main assembly or the feeding unit mounted in the apparatus main assembly. This is because when the shaft32is provided as a part of a member which is the same member as a member for holding an object (member-to-be-measured, rotatable member) for which rotation is to be generated, an axis interval between the gears can be ensured with high accuracy.

Here, the function of the holder member29will be described. InFIG. 8, (a) and (b) are sectional views for illustrating a portion holding the second sensor gear25and are the sectional views in which the portion cut along an axial portion of the second sensor gear25is seen from below of the structure in the state shown inFIG. 6. In a state before the encoder unit31is mounted to the apparatus main assembly, as shown in (a) ofFIG. 8, the holder member29holds a rotation center portion25bof the second sensor gear25so as not to be disconnected (demounted). On the other hand, in a state in which the encoder unit31is mounted to the apparatus main assembly, as shown in (b) ofFIG. 8, the rotation center hole25cof the second sensor gear25is held by the shaft32(FIG. 10) extending from the feeding unit, so that a rotation center is fixed. As a result, in the state of (b) ofFIG. 8, the rotation center portion25bof the second sensor gear25is held by the holder member29with a gap with respect to a radial direction. For this reason, the rotation center portion25bof the second sensor gear25does not interfere with the holder member29and does not constitute a load during the rotation, so that it is possible to obtain an accurate detection result.

By employing the constitution described above, even in the case where the encoder unit31is positioned and fixed to the apparatus main assembly, only the second sensor gear5is positioned with respect to the shaft32of the feeding unit as a rotation center thereof. Accordingly, a positional relationship between the shaft32and the encoder unit31relative to the apparatus main assembly is not influenced even when is minutely deviated.

Next, a mounting method of the encoder unit31will be described. In this embodiment, a constitution as shown inFIG. 9is employed. A feeding unit33(conveying unit) is prepared by integrally assembling a sheet feeding mechanism including the pick-up roller7, the feed roller13and the retard roller14into a unit. This feeding unit33as the conveying unit is detachably mountable to an apparatus main assembly frame34with respect to an arrow X direction. On the other hand, the encoder unit31is detachably mountable to the apparatus main assembly frame34with respect to an arrow Y direction. A mounting and demounting direction of the encoder unit31relative to the apparatus main assembly frame34is a roller axis direction (axial direction of the shaft32) of the feeding unit33and is the arrow Y direction perpendicular to the arrow X direction which is a mounting and demounting direction of the feeding unit33relative to the apparatus main assembly frame34. By mounting the encoder unit31along this direction, the shaft32can constitute the rotation center of the second sensor gear25and the encoder wheel26. The order of the mounting is such that first, the feeding unit33is mounted to the apparatus main assembly frame34and then the encoder unit31is mounted to the apparatus main assembly frame34. In the case of demounting these units, the order is the reverse of the mounting order.

A feature of this embodiment is that parts around the encoder are not mounted to the feeding unit33, but are assembled into a unit detachably mountable to the apparatus main assembly. In the neighborhood of the sheet feeding and conveying portion, paper powder generate and are deposited on a detecting portion of the encoder and cause an erroneous operation in some instances. Further, there is also a possibility that a contamination of scattered toner causes a similar inconvenience. As regards this problem, in this embodiment, the cover member for the detecting portion of the encoder has a function of alleviating the deposition of the contaminant. On the other hand, it is difficult to completely prevent the contamination with minute powder dust or dirt or the like, and it would be still considered that there is a need to clean or exchange the parts around the encoder. An advantage of the constitution in this embodiment is such that from a mounted state shown inFIG. 10, the encoder unit31can be singly demounted from and mounted to the apparatus main assembly frame34along the arrow direction without demounting the feeding unit33. Further, as regards also a device structure, latitude in layout is enhanced, and therefore leads to downsizing of the apparatus.

Next, an image forming apparatus including a rotation detecting device according to Embodiment 2 will be described. Incidentally, a constitution and an image forming operation of the image forming apparatus in this embodiment are the same as those described in Embodiment 1. As regards the constitution and an effect which are the same as those in Embodiment 1, constituent elements are represented by the same reference numerals or symbols and will be omitted appropriately from description.

In this embodiment, as shown inFIG. 11, a driving portion such as gears for operating the image forming apparatus is concentrated and constituted as a driving unit35detachably mountable to the apparatus main assembly. The driving unit35is constituted by a motor36, a gear train37, an encoder unit31, a driving unit frame38and the like. Here, the encoder unit31is fixed to the driving unit frame38so as to be detachably mountable to the driving unit frame38. The encoder unit31is integrally assembled with the driving unit35so as to be detachably mountable to the apparatus main assembly frame34.

A feature of this embodiment is such that the encoder unit31and the driving unit35are integrally assembled into a unit detachably mountable to the apparatus main assembly.

By employing the above-described constitution, for example, in the case where the encoder unit31and the driving unit35are mounted to a perpendicular surface as shown inFIG. 11, the encoder unit31is mounted to the driving unit35in advance, an assembling property during assembling of these units can be simplified. Further, it becomes also possible to improve positional accuracy of the encoder unit31relative to the driving unit35. On the other hand, it is also possible to mount only the encoder unit31while putting the driving unit35in the mounted state to the apparatus main assembly, and therefore, whether the driving unit35is mounted and demounted or the encoder unit31is mounted and demounted is selectable depending on a situation, so that operativity is improved.

Other Embodiments

In the above-described embodiments, the rotation detecting device for use with the image forming apparatus was described as an example, but the present invention is not limited thereto. A similar effect can be obtained even when the present invention is applied to a rotation detecting device for use with a sheet feeding device (apparatus) including a rotatable member such as roller for feeding the sheet. As the sheet feeding device, not only a sheet feeding device for feeding a sheet, to be subjected to recording, such as recording paper, but also a sheet feeding device for feeding a sheet, to be read, such as an original may be used. Even when the rotation detecting device is applied to these sheet feeding devices, a similar effect can be achieved.

Further, in the above-described embodiments, as the image forming apparatus, the printer was described as an example, but the present invention is not limited thereto. For example, the image forming apparatus may also be other image forming apparatuses, such as a copying machine, a facsimile machine and a multi-function machine having a combination of functions of these machines. The present invention is applied to the rotation detecting device for use with these image forming apparatuses, whereby it is possible to obtain a similar effect.

According to the present invention, it is possible to improve operativity of exchange of the encoder wheel and the detecting means while suppressing upsizing of the image forming apparatus and to realize downsizing of the image forming apparatus.

This application claims the benefit of Japanese Patent Application No. 2016-093590 filed on May 9, 2016, which is hereby incorporated by reference herein in its entirety.