Image forming apparatus that reduces development gap variation at both end portions of developing roller

An image forming apparatus includes an image forming apparatus body, a first driving mechanism, a first drive unit, an image carrier, a developing device, and a biasing member. The first drive unit includes an input unit to which a rotary drive power is transmitted from the first driving mechanism. The developing device is removably attachable to the image forming apparatus body. The biasing member biases the developing device toward the image carrier side. The developing device includes a developing roller supplying toner onto the image carrier, and a developing unit housing and supporting the developing roller. The first drive unit is located at one end portion in an axial direction of the developing roller. The developing unit swings to come close to the image carrier by the biasing member biasing the developing unit. The developing unit is swingable with respect to the first drive unit.

INCORPORATION BY REFERENCE

This application is based upon, and claims the benefit of priority from, corresponding Japanese Patent Application No. 2014-169787 filed in the Japan Patent Office on Aug. 22, 2014, the entire contents of which are incorporated herein by reference.

BACKGROUND

An image forming apparatus performs to develop a latent image formed on an image carrier, which is constituted of such as a photoreceptor, with a developing device to visualize the latent image as a toner image. The developing device houses a developer including toner in a developing container, includes a developing roller supplying the image carrier with developer, and includes a stir conveying member supplying the developing roller with the developer housed in the developing container with stirring and conveying the developer.

For ensuring a satisfactory image quality, a space between an outer peripheral surface of the developing roller and an outer peripheral surface of a photoreceptor drum (development gap) should be held with high accuracy. In view of this, an image forming apparatus including a developing pulley located at both ends of a rotation shaft of the developing roller and a pressing member located to press the developing roller to the photoreceptor drum is widely employed. In this image forming apparatus, the developing pulley is in contact with the outer peripheral surface of the photoreceptor drum and is rotationally driven with respect to the photoreceptor drum. This ensures the developing roller to rotate with respect to the photoreceptor drum in a state keeping a predetermined development gap.

A typical developing device employs a configuration including a development drive unit to rotatably drive the developing roller in the developing device and transmitting a rotary drive power from the developing device main body side to the development drive unit via a gear. Alternatively, it is also employed that a configuration including a replenishment drive unit to rotatably drive a toner replenishment screw of a toner replenishment container in the developing device and transmitting a rotary drive power from the developing device main body side to the replenishment drive unit via a gear.

An image forming apparatus transmitting a rotary drive power to a developing roller via a gear has been proposed.

SUMMARY

An image forming apparatus according to one aspect of the disclosure includes an image forming apparatus body, a first driving mechanism, a first drive unit, an image carrier, a developing device, and a biasing member. The first driving mechanism is located in the image forming apparatus body. The first drive unit includes an input unit to which a rotary drive power is transmitted from the first driving mechanism. The image carrier carries an electrostatic latent image. The developing device is removably attachable to the image forming apparatus body. The developing device forms a toner image on the surface of the image carrier. The toner image corresponds to the electrostatic latent image. The biasing member biases the developing device toward the image carrier side. The developing device includes a developing roller supplying toner onto the image carrier, and a developing unit housing and supporting the developing roller. The first drive unit is located at one end portion in an axial direction of the developing roller. The developing unit swings to come close to the image carrier by the biasing member biasing the developing unit. The developing unit is swingable with respect to the first drive unit.

DETAILED DESCRIPTION

The following describes embodiments of the disclosure with reference to the drawings.

A description will be given of an image forming apparatus1according to one embodiment of the disclosure with reference toFIG. 1toFIG. 13. As illustrated inFIG. 1, the image forming apparatus1includes an apparatus main body (image forming apparatus body)3with an approximately hexahedron structure. A front side portion of the apparatus main body3facing to a user includes a front cover4and a paper sheet cassette5. The front cover4is mounted so as to be freely open and close facing to the apparatus main body3. When opened, the front cover4functions as a manual paper feed tray. The paper sheet cassette5is removably mounted on the apparatus main body3. On the top of the apparatus main body3, a discharge tray6for paper sheets discharged and an operation unit7including such as a plurality of buttons are located.

The apparatus main body3internally includes an image forming unit, a fixing unit, a paper sheet conveyance passage, and similar unit (not shown). The image forming unit transfers a toner image to a supplied paper sheet based on image data retrieved from a host device such as a PC to form an image. The image forming unit includes a photoreceptor drum8, a charging unit, an exposure unit, a developing device2, a transfer roller, a cleaning blade, and similar unit. The photoreceptor drum8carries an electrostatic latent image (described below). The charging unit charges the surface of the photoreceptor drum8. The exposure unit forms the electrostatic latent image corresponding to a document image on the surface of the photoreceptor drum8with such as a laser beam. The developing device2attaches developer to the formed electrostatic latent image to form a toner image (described below). The transfer roller transfers the toner image to a paper sheet. The cleaning blade removes a toner remaining on the surface of the photoreceptor drum. The fixing unit heats and applies pressure to the paper sheet, on which the toner image is transferred, to fix the toner image on the paper sheet.

On the right-side surface of the apparatus main body3, a cover member9is mounted so as to be freely open and close facing to the apparatus main body3. The developing device2described below is replaceable from the right-side surface of the apparatus main body3by opening the cover member9.

Next, a description will be given of a detail structure of a periphery of the developing device2. The image forming apparatus1is a tandem type color printer, and includes the developing devices2and the photoreceptor drums (image carriers)8corresponding to respective colors of magenta, cyan, yellow, and black. Basically, the developing devices2each have a similar configuration and perform similarly. Also, basically, the photoreceptor drums8each have a similar configuration and perform similarly.

As illustrated inFIG. 2, the developing device2is constituted of a developing roller (developer carrier)20, a regulating blade21, a stir conveying member23, a developing container (developing unit)22, and similar unit.

The developing container22constitutes the outside of the developing device2. At the lower portion of the developing container22, the developing container22is divided into a first conveying chamber22cand a second conveying chamber22dby a partition portion22b. The first conveying chamber22cand the second conveying chamber22dhouse a developer containing a magnetic carrier and a toner. The developing container22rotatably holds the stir conveying member23and the developing roller20. Further, the developing container22includes an opening22athat exposes the developing roller20toward the photoreceptor drum8.

The developing roller20faces to the photoreceptor drum8. The developing roller20is located adjacent to the photoreceptor drum8with a predetermined space. The developing roller20supplies the photoreceptor drum8with toner. The stir conveying member23is located approximately downward of the developing roller20. The regulating blade21is fixed and held onto the developing container22at the right obliquely downward of the developing roller20.

The developing roller20includes a rotation shaft20a, a magnetic pole member20b, a development sleeve20c, which is formed of a non-magnetic metallic material in a cylindrical shape, and similar component.

The rotation shaft20ais rotatably supported to the developing container22. This rotation shaft20aholds the development sleeve20cso as to rotate integrally with the rotation shaft20a. Further, the rotation shaft20aholds the magnetic pole member20bmade of a magnet at a position facing to a second spiral23bwith a predetermined distance from the development sleeve20c.

As illustrated inFIG. 2, the stir conveying member23includes two spirals of a first spiral23aand the second spiral23b. The second spiral23bis located in the second conveying chamber22dbelow the developing roller20, while the first spiral23ais located in the first conveying chamber22cadjacently to the left side of the second spiral23b.

The first spiral23aand the second spiral23bstir the developer to charge the toner included in the developer to a predetermined level. This ensures the toner to be held onto carrier. At both end portions of the partition portion22b, which divides the first conveying chamber22cand the second conveying chamber22d, in the long side direction (front and back direction of the paper sheet surface inFIG. 2), communication units are located. When the first spiral23arotates, the charged developer is conveyed from the one communication unit located on the partition portion22bto the second spiral23b, and the developer circulates in the first conveying chamber22cand the second conveying chamber22d. Then, the second spiral23bsupplies the developing roller20with the developer.

The developing container22includes bearing portions22eand22fthat support a swinging shaft10secured to the apparatus main body3(seeFIG. 3andFIG. 4). The developing container22is configured swingably centering the swinging shaft10. The developing container22includes a pressing surface22g(seeFIG. 2andFIG. 5). When the pressing surface22gis pressed by a biasing member11(seeFIG. 2), which is constituted of such as a compression coil spring, the developing container22swings such that the developing roller20comes close to the photoreceptor drum8.

As illustrated inFIG. 4, at both ends of the rotation shaft20aof the developing roller20, developing pulleys20dare located. The developing pulley20dhas a radius formed in a size where a size of the development gap is added to the radius of the development sleeve20c. In view of this, when the developing pulleys20dare in contact with the outer peripheral surface of the photoreceptor drum8and rotationally driven by the photoreceptor drum8, the developing roller20rotates with respect to the photoreceptor drum8in a state keeping a predetermined development gap.

As illustrated inFIG. 3, at one end portion and the other end portion of the developing container22in the longer side direction (axial direction of the developing roller20), a replenishment drive unit (first drive unit)30and a development drive unit (second drive unit)40are respectively located.

The development drive unit40transmits rotary drive power to the developing roller20and the stir conveying member23. As illustrated inFIG. 6andFIG. 7, the development drive unit40includes an input gear41, a developing roller gear42, transmission gears43and44, and a cover member45, which covers the side portion of these gears.

The input gear41is configured to receive the rotary drive power from a development driving mechanism (second driving mechanism) via a coupling joint46. The development driving mechanism includes a motor, a gear train, and similar component, which are located in the apparatus main body3(not shown). The input gear41is configured to transmit the rotary drive power to the developing roller gear42and the transmission gears43and44.

The developing roller gear42is secured to an end portion of the rotation shaft20aof the developing roller20. The developing roller gear42is configured to transmit the rotary drive power to the development sleeve20cof the developing roller20to rotate the development sleeve20c. The transmission gear43is secured to a transmission shaft47engaging with the second spiral23b, while the transmission gear44is secured to a transmission shaft48engaging with the first spiral23a. This ensures the development sleeve20c, the first spiral23a, and the second spiral23bto rotate when the input gear41rotates.

The development drive unit40is secured to the developing container22. This ensures the development drive unit40to swing centering the swinging shaft10when the developing container22swings centering the swinging shaft10.

As illustrated inFIG. 3, the replenishment drive unit30transmits the rotary drive power to a toner replenishment screw12aof a toner replenishment container12, which houses a toner to replenish to the developing device2. As illustrated inFIG. 8andFIG. 9, the replenishment drive unit30includes an input gear (input unit)31, a transmission member32, and a cover member33, which rotatably supports the input gear31and the transmission member32.

The input gear31is configured to receive the rotary drive power from a replenishment driving mechanism (first driving mechanism)51via a gear51a(seeFIG. 10). The replenishment driving mechanism (first driving mechanism)51includes a motor (not shown), a gear train, and similar component, which are located in the apparatus main body3. The input gear31is configured to transmit the rotary drive power to a gear portion32aof the transmission member32.

The transmission member32includes the gear portion32aand an engaging portion32b. The gear portion32ameshes with the input gear31. The engaging portion32bengages with the toner replenishment screw12a(seeFIG. 3) located in the toner replenishment container12. The transmission member32transmits the rotary drive power from the input gear31to the toner replenishment screw12ato rotate the toner replenishment screw12a. The rotation of the toner replenishment screw12acauses the toner in the toner replenishment container12to be replenished by a predetermined amount from an opening22h(seeFIG. 4) located upstream side of the first conveying chamber22cin the developing container22.

At the lower portion of the cover member33, an insertion hole33ato which the bearing portion22fof the developing container22(seeFIG. 4) is inserted is formed. The replenishment drive unit30is configured swingably with respect to the developing container22. On the other hand, the replenishment drive unit30is secured to the apparatus main body3by positioning of the insertion hole33aand the rotation shaft of the input gear31. This ensures the developing container22to swing with respect to the replenishment drive unit30centering the swinging shaft10. A center shaft for swinging (swinging shaft10) of the developing container22with respect to the replenishment drive unit30is located coaxially with a center shaft for swinging (swinging shaft10) of the developing container22with respect to the apparatus main body3.

A swing angle (swing range) of the developing container22with respect to the replenishment drive unit30is regulated. Specifically, as illustrated inFIG. 11, the developing container22includes a regulating piece22i, while the cover member33has a regulating hole (regulating portion)33bto which the regulating piece22iis inserted. In view of this, when the developing container22swings with respect to the replenishment drive unit30, the developing container22can swing within a movable range of the regulating piece22iwith respect to the regulating hole33b.

Next, a description will be given of a case where the developing device2and the photoreceptor drum8are mounted on the apparatus main body3. Firstly, as illustrated inFIG. 12, the developing container22, at one end portion and the other end portion of which the replenishment drive unit30and the development drive unit40are respectively mounted, is mounted to the apparatus main body3in a state where the photoreceptor drum8is removed. At this time, as illustrated inFIG. 13, pressing the pressing surface22gof the developing container22by the biasing member11causes the developing container22and the development drive unit40to swing in the right rotation direction so as to come close to the photoreceptor drum8. The swing angles of the developing container22and the development drive unit40are regulated by the regulating piece22iof the developing container22and the regulating hole33bof the cover member33.

Then, mounting the photoreceptor drum8from the top surface side of the apparatus main body3causes the photoreceptor drum8to press the developing pulley20dof the developing roller20. Accordingly, the developing container22and the development drive unit40reverse a little (swing in the left rotation direction).

In this embodiment, as described above, the developing container22is swingable with respect to the replenishment drive unit30. This reduces the swing of the developing container22due to the rotary drive power, which is transmitted from the replenishment driving mechanism51to the replenishment drive unit30, when the rotary drive power is transmitted from the replenishment driving mechanism51, which is secured to the apparatus main body3, to the replenishment drive unit30. This reduces the variation of development gaps between the developing roller20and the photoreceptor drum8at both end portions of the developing roller20, thus ensuring satisfactory image quality.

As described above, when the rotary drive power is transmitted to the replenishment drive unit30from the replenishment driving mechanism51via the gear51a, the power causes the replenishment drive unit30to swing with respect to the developing container22with engaging of the gear51aand the input gear31. However, as described above, securing the replenishment drive unit30to the apparatus main body3can cause the apparatus main body3to absorb the power acting on the replenishment drive unit30to swing.

As described above, when the rotary drive power is transmitted to the development drive unit40from the development driving mechanism secured to the apparatus main body3via the coupling joint46, the development drive unit40may be secured to the developing container22because the transmitted rotary drive power is less likely to act on the developing container22to swing.

As described above, the center shaft for swinging (swinging shaft10) of the developing container22with respect to the replenishment drive unit30is coaxial with the center shaft for swinging (swinging shaft10) of the developing container22with respect to the apparatus main body3. This achieves space saving compared with the case where the center shaft for swinging of the developing container22with respect to the replenishment drive unit30is not coaxial with the center shaft for swinging of the developing container22with respect to the apparatus main body3.

As described above, the developing container22includes the regulating piece22i, while the replenishment drive unit30includes the regulating hole33b. The regulating hole33bregulates the swing range of the developing container22with respect to the replenishment drive unit30by the regulating piece22iin contact with the regulating hole33b. This ensures regulating the swing range of the developing container22with respect to the replenishment drive unit30easily.

For example, the above-described embodiment shows an exemplary case where the center shaft for swinging of the developing container22with respect to the replenishment drive unit30is located coaxially with the center shaft for swinging of the developing container22with respect to the apparatus main body3. However, the disclosure should not be construed in a limiting sense. The center shaft for swinging of the developing container22with respect to the replenishment drive unit30may be located not coaxially with the center shaft for swinging of the developing container22with respect to the apparatus main body3.

While in the above-described embodiment the developing container22is configured swingably with respect to the replenishment drive unit30and the development drive unit40is secured to the developing container22, the disclosure should not be construed in a limiting sense. For example, the developing container22may be configured swingably with respect to the development drive unit40. In this case, using such as a flexible joint ensures transmitting the rotary drive power from the development drive unit40to the developing container22easily. A drive unit other than the replenishment drive unit30may be located such that the developing container22is configured to be swingable with respect to the drive unit.