Toner supply device

A toner supply device is disclosed that supplies toner contained in a toner container to a developing device in an image forming device. The toner supply device includes a conveyance pipe for conveying the toner from the toner container to the developing device downward, and at least one supply pipe for supplying the toner from the conveyance pipe to the developing device downward. The conveyance pipe is connected to the toner container for conveying the toner from the toner container to the developing device. The supply pipe has an upper portion connected to the conveyance pipe and a lower end capable of advancing into the developing device. In addition, a conveyance member is rotatably located in the supply pipe for conveying the toner downward. The supply pipe is located such that a center axis of the supply pipe is slanted relative to the horizontal line at a repose angle of the toner or more.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a toner supply device, and more particularly to a toner supply device for supplying toner from a toner container located apart from a developing device to the developing device.

2. Background Information

An image forming device utilizing an electrophotographic system includes a photosensitive drum as an image bearing member and other devices located circumferentially around the drum, such as a charger, an exposure device, a developing device, a transfer device, a cleaning device, and so on. In addition, a fixing device is provided downstream of the photosensitive drum in a direction in which the transfer device extends. In this image forming device, first, a surface of the photosensitive drum is uniformly charged by the charger. Then, the photosensitive drum is exposed by the exposure device in accordance with image data so that an electrostatic latent image is formed on the photosensitive drum. The electrostatic latent image is developed by the developing device. In a case of the full color image forming device, four developing units are provided for storing cyan developer, magenta developer, yellow developer, and black developer. The developing units develop the latent image to a toner image with four colors (cyan, magenta, yellow, and black). After that, the toner image is transferred to a transfer medium by the transfer device and then fixed to the transfer medium by the fixing device, and the transfer medium is finally discharged to a discharge unit. Residual developer remaining on the photosensitive drum is cleaned by the cleaning device.

In the above-mentioned image forming operation, the toner in the toner container is consumed as the development is carried out so that it is necessary to refill the toner. There are two systems to compensate for the toner consumed by the image forming operation.

The first system is to fill a certain amount of the toner in the developing unit and replace the developing units when the toner is completely consumed, as shown in Japanese Unexamined Patent Publication No. 2004-45960. In this system, the developing unit and the toner container are formed into a cartridge, so that it is not necessary to supply the toner to the developing unit. Consequently, it is easy to maintain the developing unit.

The second system is to provide a toner container outside of the developing unit so as to supply the toner to the developing unit from outside, as shown in Japanese Unexamined Patent Publications No. 2001-134045 and No. 10-198149. Recently, as full color image forming devices have been increasingly used by individuals, there have been demands to reduce the size of the image forming device. It is necessary to reduce the size of the developing units in order to reduce the size of the image forming device. In the second system, by providing the toner container outside of the developing unit, the developing unit will be reduced in size.

In the first system wherein the developing unit and the toner container are formed into a cartridge, it is necessary to fill the toner for about 4,000 sheet printing in the developing unit in advance because the toner is not supplied to the developing unit from outside. As a result, it is difficult to reduce the developing unit in size. Although it is possible to set a printing capability of toner to 4,000 sheets or under, the cost per one sheet increases in that case. In addition, when the toner is completely consumed, it is necessary to replace the developing units each time. As a result, it increases the burden on the environment.

On the contrary, in the system wherein the toner container is provided outside of the developing unit and the toner is supplied to the developing unit from outside, it is necessary to prepare a member for supplying the toner from the toner container to the developing unit. For example, a plurality of toner supply paths are provided for supplying the toner to each of the developing units in the device shown in Japanese Unexamined Patent Publication No. 2001-134045, and a plurality of toner supply pipes are provided for supplying the toner to each of the developing units in the device shown in Japanese Unexamined Patent Publication No. 10-198149. The toner is supplied to the developing units through the toner supply paths or the toner supply pipes from the toner container.

However, in the conventional devices, the toner may remain in the toner supply paths or the toner supply pipes. In particular, in the device shown in Japanese Unexamined Patent Publication No. 10-198149, the toner supply pipes advance and retreat relative to the developing units, so that when the toner supply pipe leaves the developing unit, the toner remaining in the toner supply pipes scatter about so as to contaminate inside of the device.

Furthermore, in the conventional device, it is difficult to precisely manage the amount of the toner supply when the toner is supplied from the toner container to the developing unit, because the toner in the toner container is supplied to the developing device by free fall.

It is an object of the present invention to restrain the toner from remaining in the toner supply unit and from contaminating the inside of the device when the toner is supplied to the developing unit from the toner container located apart from the developing unit.

It is another object of the present invention to precisely manage the amount of the toner supply to the developing unit with a simple structure.

SUMMARY OF THE INVENTION

A toner supply device according to a first aspect of the present invention supplies toner contained in a toner container to a developing device in an image forming device. The toner supply device comprises a conveyance pipe for conveying the toner from the toner container to the developing device downward, and at least one supply pipe for supplying the toner from the conveyance pipe to the developing device downward. The conveyance pipe is connected to the toner container for conveying the toner from the toner container to the developing device. The supply pipe has an upper portion connected to the conveyance pipe and a lower end capable of advancing into the developing device. In addition, a conveyance member is rotatably located in the supply pipe for conveying the toner downward. The supply pipe is located such that a center axis of the supply pipe is slanted relative to the horizontal line at a repose angle of the toner or more.

In the device, the toner container is located apart from the developing device, and the toner is conveyed to the supply pipe through the conveyance pipe, and then to the developing device downward.

Although the toner is supplied downward to the developing device within the supply pipe, the remainder of the toner within the toner pipe is restrained because the supply pipe is located such that the center axis of the supply pipe is slanted relative to the horizontal line at a repose angle of the toner or more. Consequently, the remaining toner is prevented from contaminating inside of the device when the supply pipes are pulled out from the developing device.

According to a second aspect of the present invention, the toner supply device according to the first aspect further comprises an image bearing member having a surface on which an electrostatic image is formed. The developing device includes a plurality of developing units and a rotary frame. The developing units are located corresponding to different developing colors. The rotary frame maintains the developing units in a circumferential direction in order to place each of the developing units opposite the image bearing member by means of rotation. The supply pipes are located corresponding to the developing units.

As mentioned above, the image forming device comprises a rotary developing device having developing units arranged in the circumferential direction which are placed opposite to the image bearing member by means of rotation. The size of the image forming device as a whole is reduced because the diameter of the rotary frame can be reduced by locating the toner container outside of the developing device.

According to a third aspect of the present invention, in the toner supply device according to the first or second aspects, the supply pipe has a shutter mechanism for prohibiting and allowing toner to be supplied to the developing device.

In the device, the shutter mechanism located at the supply pipe is opened when supplying the toner from the supply pipe to the developing device, while the shutter mechanism is closed when stopping the supply of the toner to the developing device. Accordingly, even if the toner remains in the supply pipe, the toner does not leak from the supply pipe.

According to a fourth aspect of the present invention, in the toner supply device according to the third aspect, the supply pipe includes an inner cylinder having an inner opening in the tip thereof, and an outer cylinder rotatably located around the inner cylinder and having an outer opening in a lateral surface of the tip thereof. The shutter mechanism is formed by means of the inner cylinder and the outer cylinder.

According to a fifth aspect of the present invention, the toner supply device according to the fourth aspect further comprises a driving device and a shutter driving mechanism. The driving device moves the tip of the supply pipe into the developing device and away from the developing device. The shutter driving mechanism aligns at least part of the inner opening of the inner cylinder and the outer opening of the outer cylinder with each other when the tip of the supply pipe advances into the developing device, and misaligns the inner opening with the outer opening when the tip is located outside of the developing device.

In the developing unit, when the toner is supplied, the tip of the supply pipe is moved into the developing device by the driving device and at least part of the inner opening of the inner cylinder and the outer opening of the outer cylinder are aligned. As a result, the toner in the supply pipe is supplied to the developing device. When the supply of the toner is finished, the tip of the supply pipe is retracted from the inside of the developing device. When tip of the supply pipe is moved out of the developing device, the inner opening and the outer opening are misaligned by the shutter driving mechanism so that the toner inside of the supply pipe will not escape, i.e., toner leakage from the supply pipe is prevented.

According to a sixth aspect of the present invention, in the toner supply device according to the fifth aspect, the outer opening of the outer cylinder is larger than the inner opening of the inner cylinder.

In the device, when the outer cylinder rotates relative to the inner cylinder, even if there are some errors in the rotational angle, it is possible to supply the toner to the developing device. Furthermore, for example, by closing a gap between the inner cylinder and outer cylinder, the toner will not go into the gap between the inner cylinder and the outer cylinder so that the toner will neither scatter nor contaminate the inside of the device during toner replacement.

According to a seventh aspect of the present invention, in the toner supply device according to the fifth aspect, the shutter driving mechanism rotates the outer cylinder as the supply pipe is moved by means of the driving force of the driving device.

According to an eighth aspect of the present invention, in the toner supply device according to the seventh aspect, the shutter driving mechanism includes a guide portion located on an outer circumference of the outer cylinder and a spiral guide groove around the outer cylinder into which the guide portion is inserted.

In the device, the guide portion provided on the surface of the outer cylinder moves along the spiral guide groove located around the outer cylinder so that the outer cylinder rotates in accordance with the movement of the guide portion.

According to a ninth aspect of the present invention, in the toner supply device according to the second aspect, the developing unit is formed with a toner supply opening, and a shutter is provided at the toner supply opening of the developing unit.

In the device, the shutter is provided at the toner supply opening of the developing unit, so that the shutter is opened to supply the toner to the developing device through the supply pipe, and the shutter is closed to stop supplying the toner. Consequently, the toner will not leak from the toner supply opening to the inside of the device.

According to a tenth aspect of the present invention, an image forming device comprises an image forming unit, a sheet conveyance unit, and a toner supply unit. The image forming unit forms a toner image and transfers the toner image onto a sheet (transfer medium). The sheet conveyance unit conveys the sheet to the image forming unit. The toner supply unit supplies the toner to the image forming unit and includes a toner supply member for supplying the toner to the image forming unit, a toner container for storing the toner, and a toner conveyance unit having a toner conveyance member inside for conveying the toner in the toner container to the toner supply member. The toner conveyance unit has a portion upstream in a toner conveyance direction that is lower than a downstream portion thereof in the toner conveyance direction.

In the image forming device, in the event of toner supply, the toner in the toner container is conveyed to the toner supply member through the toner conveyance unit. The toner inside the toner container is conveyed to the toner supply member through the portion upstream in the toner conveyance direction that is lower than the portion downstream in the toner conveyance direction. In this case, the toner is unlikely to free fall, and is conveyed by means of conveyance force by the toner conveyance member because the downstream side is higher than the upstream side in the toner conveyance direction.

The amount of the toner supply to the toner supply member by the toner conveyance member is precisely managed compared to conventional ones because the free fall of the toner is restrained.

According to an eleventh aspect of the present invention, in the toner supply device according to the tenth aspect, a connected portion between the toner conveyance unit and the toner container is located lower than a connected portion between the toner conveyance unit and the toner supply member.

According to a twelfth aspect of the present invention, in the toner supply device according to the tenth aspect, the amount of the toner conveyed by the toner conveyance unit is less than the amount of toner supplied by the toner supply member.

The toner supply member is less likely to become plugged up with the toner conveyed by the toner conveyance unit, because the amount of the toner supply by the toner supply member to the image forming unit is more than the amount of the toner conveyed by the toner conveyance unit to the toner supply member. Consequently, the amount of the toner supply is precisely managed.

According to a thirteenth aspect of the present invention, in the toner supply device according to the twelfth aspect, the amount of toner supplied from the toner container to the toner conveyance unit is less than the amount of toner conveyed by the toner conveyance unit.

The toner conveyance unit is less likely to become plugged up with the toner supplied from the toner container because the amount of the toner conveyed to the toner supply member by the toner conveyance unit is more than the amount of toner supplied from the toner container to the toner conveyance unit. Consequently, the amount of the toner supply is precisely managed.

According to a fourteenth aspect of the present invention, in the toner supply device according to the tenth aspect, a connected portion between the toner supply member and the toner conveyance unit is positioned in a position higher than a portion upstream side near the connected portion between the toner container and the toner conveyance unit.

In the device, the present invention is realized by a simple structure.

As mentioned above, in the present invention, it is possible to restrain the toner from remaining inside the toner pipe in the developing device when the toner is conveyed from the outside to the upper portion of the supply pipe, and then supplied downward to the developing device through the supply pipe, because the supply pipe is located such that the center axis of the supply pipe is slanted relative to the horizontal line at a repose angle of the toner or more. Consequently, the problem of contamination inside the device by the residual toner in the supply pipe is solved.

In addition, the present invention, the amount of the toner supply from the toner container to the image forming unit is precisely managed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1shows a color printer1as a color image forming device according to one embodiment of the present invention.FIG. 1is a view showing a frame format of locations of each of the components, and thus the details of each of portions are omitted.

Overall Structure

The color printer1is connected to a computer, for example, and is capable of printing a color image on a sheet in accordance with image data sent from the computer. In this color printer1, the right side ofFIG. 1is the side from which an operator operates the color printer1. In the below description, the right side inFIG. 1is referred to as the “front side” and the left side inFIG. 1is referred to as the “rear side”.

The color printer1includes a photosensitive drum2, a rotary developing device3, a laser unit4, a toner container5, a toner supply device6, an intermediate transfer belt7, a secondary transfer roller8, and a fixing device9. In this device, the photosensitive drum2, the rotary developing device3, the laser unit4, the intermediate transfer belt7, and the secondary transfer roller8constitute an image forming unit.

Photosensitive Drum

The photosensitive drum2has a surface on which an electrostatic latent image is formed, and is rotatably mounted substantially in the center of the device. The rotational axis of the photosensitive drum2is located such that the axis extends in a lateral direction seen from the front side of the device, i.e., perpendicular to the plane ofFIG. 1. On an upper portion of the photosensitive drum2, a charge roller10for uniformly charging a surface of the photosensitive drum2is mounted. On a lateral side of the photosensitive drum2, a drum cleaning device11is mounted for cleaning residual toner and other matter on the surface of the photosensitive drum2.

Rotary Developing Device

The rotary developing device3is a device for developing an electrostatic latent image formed on the photosensitive drum2with each color toner. The rotary developing device3is located adjacent to the photosensitive drum2and has a center substantially corresponding to the center of the photosensitive drum2in a vertical direction. The rotary developing device3includes a rotary frame15and four developing units16corresponding to four color toners and supported by the rotary frame15. The rotary frame15is a cylindrical member rotatable around an axis in parallel with the rotational axis of the photosensitive drum2and is driven by a driving mechanism including a motor and gears (not illustrated). In addition, the rotary frame15is formed with four compartments divided into quarters by partitions extending from the center of the rotational axis radially outward. Each of the compartments accommodates each of the developing units16corresponding to four colors toners such as yellow, cyan, magenta, and black.

Each of the developing units16has a common structure and includes a developing roller capable of being located so as to be opposed to the photosensitive drum2, and an agitation roller for agitating the toner. One of the four developing units16is shown inFIG. 2. In the present invention, a toner container (later described) is separately located apart from the developing units16so that toner containment space of the developing units themselves in the present embodiment is smaller. In other words, the developing units16are downsized compared to a developing unit including a toner container inside. On an outer surface of a case17of the developing unit16, a toner supply portion18is provided as shown inFIG. 2so as to supply the toner from the toner container5into the developing unit16. The toner supply portion18having an elastic member with a slit18ais located at an opening of the case17.

Laser Unit

The laser unit4is a device to scan and expose the photosensitive drum2in accordance with image data sent from the external computer, and is located above the photosensitive drum2and on the rear side of the rotational axis of the rotary developing device3. More accurately, the front end of the laser unit4, the end from which a laser light is emitted, is located immediately above the rotational axis of the rotary developing device3, and the rear end is located below an upper end of the rotary developing device3, with the whole of the laser unit4slanting downward toward the rear end. The inner construction of the laser unit4is common with that of conventional laser units, and includes a laser light source, a polygon mirror, a motor for driving the polygon mirror, and so on. In addition, on the front side of a laser light path from the laser unit4, a reflective mirror20is provided so that the laser light emitted from the laser unit4is reflected by the reflective mirror20, then passes on the front side of and above the rotary developing device3, and is finally applied to the surface of the photosensitive drum2as shown in dotted lines inFIG. 1.

Toner Container

The toner container5is a member for storing toner to be supplied to each of the developing units16of the rotary developing device3, and is located above the photosensitive drum2and on a side opposite to the laser unit4(on a front side in the device). The toner container5includes, as shown inFIG. 5, four containers5a,5b,5c, and5darranged in a lateral direction, i.e., in a direction perpendicular to the plane ofFIG. 1, for storing color toners such as yellow, cyan, magenta, and black. The toner container5can be pulled out toward the front side of the device.

Toner Supply Device

The toner supply device6is a device to supply each of toners contained in the toner container5to corresponding developing units16, and is located above the photosensitive drum2and in a space between the laser unit4and the toner container5. The toner supply device6includes, as shown inFIG. 3, four toner supply pipes25that are vertically movable, four conveyance pipes26for connecting portions storing each color toner in the toner container5with corresponding toner supply pipes25, and a drive mechanism27for moving the toner supply pipes25up and down.

Each toner supply pipe25extends vertically and is inclined such that an upper end is on the front side in the device and a lower end is on the rear side in the device. The center axis of the toner supply pipe25is designed to have a repose angle of toner (θ) or more relative to the horizontal line. In this embodiment, a repose angle of the black toner is 50 degrees and a repose angle of the color toner is 40 degrees so that the center axis of the toner supply pipe25is set to makes an angle of 70 degrees (θ) relative to the horizontal line. The toner supply pipe25has a tapered tip, which can advance into the inside of the developing unit16through the slit18aof the toner supply portion18when the toner supply pipe25moves downward. Inside of the toner supply pipe25, a spiral member30for conveying the toner is rotatably installed.

The conveyance pipe26is a member for conveying the toner supplied from the toner container5to the toner supply pipe25and is so flexible that the pipe26can follow vertical movements of the toner supply pipe25. As shown inFIG. 3, the conveyance pipe26has a first connection portion26afor connecting the conveyance pipe26and the toner container5, a second connection portion26bfor connecting the conveyance pipe26and the toner supply pipe25, and a toner conveyance portion26clocated between the first connection portion26aand the second connection portion26bfor conveying the toner. As shown inFIG. 3, the second connection portion26bis positioned higher than the first connection portion26aeven when the toner supply pipe25is positioned in the lowest position. The toner conveyance portion26cis a part for conveying the toner from the first connection portion26ato the second connection portion26band is inclined upward from the first connection portion26ato the second connection portion26b. Inside of the conveyance pipe26, a coil spring31is provided for conveying the toner to the toner supply pipe25within the conveyance pipe26when the coil spring31is rotated by a drive mechanism (not illustrated).

The drive mechanism27includes racks32provided on the outer circumference of the toner supply pipes25extending in the axial direction of the pipes25, and pinion gears33engaged with the racks32. The pinion gear33is rotatably supported by a frame of the device and is driven by a motor33aand a worm, a worm wheel, and a train of reduction gears, as shown inFIG. 4. The drive mechanism27makes it possible for the four toner supply pipes25to move between a retracted position upward shown in solid lines inFIG. 1and a supply position downward shown in double-dashed lines inFIG. 1, wherein the tip is inserted into the developing unit16. As mentioned above, the laser light of the laser unit4passes above and on the front side of the rotary developing device3. Namely, the laser light path and moving paths of the toner supply pipes25are crossed with each other so that although the laser light path is not blocked by the toner supply pipes25when the toner supply pipes25is positioned in the retracted position, the laser light path is blocked by the toner supply pipe25when the toner supply pipe25is positioned in the supply position.

The toner supply pipe25has a shutter mechanism which opens only when the toner supply pipe25is positioned in the supply position. More specifically, as shown inFIGS. 3to6, the toner supply pipe25has an overlapped structure of an inner cylinder251and an outer cylinder252, and tips of the cylinders251and252are formed with openings251aand252ahaving a circumferential length. The opening252aof the outer cylinder252has an opening angle larger than the opening251aof the inner cylinder251. In addition, as shown inFIG. 4, the outer cylinder252is formed with a protruding portion252bengaged with a rotary cam28having a spiral guide portion28alocated around the outer cylinder252. The rotary cam28is shown in an exploded view for better understanding inFIG. 4. When the toner supply pipe25is in the retracted position upward, the opening251aof the inner cylinder251and the opening252aof the outer cylinder252do not overlap with each other (shutter closed, shown inFIG. 6(a)) so that the toner does not leak outside. On the contrary, when the toner supply pipe25moves downward, the outer cylinder252rotates by means of the engagement between the protruding portion252band the spiral guide portion28aof the rotary cam28, the tip of the toner supply pipe25is inserted into the developing unit16. Then, when the toner supply pipe25reaches the supply position, the opening251aof the inner cylinder251and the opening252aof the outer cylinder252overlap with each other (shutter opened, inFIGS. 6(b) and (c)) so that the inside toner is supplied to the inside of the developing unit16from the openings251aand252a.

Intermediate Transfer Belt

The intermediate transfer belt7is a member on which the toner images in each color formed on the photosensitive drum2are sequentially transferred and is located below the photosensitive drum2and the toner container5. The intermediate transfer belt7is looped over a driving roller35and a follower roller36located in the opposite directions. A portion of the transfer belt7facing the photosensitive drum2is constructed so as to be brought into contact with the photosensitive drum2by a pair of primary transfer rollers37aand37b.

The arrangement of the above-mentioned components will be described in more detail. The driving roller35is located immediately below contact portions of the photosensitive drum2and the rotary developing device3, and the center is positioned below the lowest end of the rotary developing device3. The driving roller35is driven by a driving unit including a motor and a gear (not illustrated). The follower roller36is located adjacent to a bottom of the toner container5and on the front side in the device, and its position in a vertical direction is substantially the same with a position of the photosensitive drum2. The follower roller36is urged by a spring38in the direction opposite to the driving roller35so that the intermediate transfer belt7is tensioned. In addition, the primary transfer rollers37aand37bare located adjacent to each other below the photosensitive drum2so that a certain range of the transfer belt7is in contact with the photosensitive drum2.

A belt cleaning device40for cleaning the transfer belt7is located on the rear side of the driving roller35and below the rotary developing device3. The belt cleaning device40includes a fur brush41located in a position facing the driving roller35and in sliding contact with the surface of the transfer belt7, a cleaning roller42located above the fur brush41so as to be in contact with the fur brush41, a blade43having a tip located so as to be in contact with a surface of the cleaning roller42, and a recovery spiral44located below the blade43side by side.

In this cleaning device40, matter attached to the intermediate transfer belt7is scraped off by the fur brush41, and then are recovered to the cleaning roller42. This matter is scraped off by the blade43from the surface of the cleaning roller42and then recovered to a recovery unit (not illustrated) by the recovery spiral44.

Secondary Transfer Roller

The secondary transfer roller8is a member to transfer the image transferred on the intermediate transfer belt7onto the conveyed sheet and is located below the driving roller35and facing the driving roller35. Bias voltage is applied to the secondary transfer roller8by an energizing means (not illustrated) so as to transfer the image to the sheet.

Fixing Device

The fixing device9is a device to fix the toner image transferred onto the sheet by fusion and is located below the rotary developing device3and on the rear side in the device. The fixing device9includes a heating roller9ahaving a built-in heater and a pressure roller9bpressing against the heating roller9afor pinching the sheet therebetween so as to convey the sheet.

Discharge Unit

In the printer1, on a surface of an upper portion of the device, i.e., above the laser unit4, the toner supply device6and the toner container5, the discharge unit50is provided onto which the image-formed sheet is discharged. The discharge unit50consists of a curved portion gradually increasing the height from the lowest portion on the laser unit4side (on the rear side in the device) to the other side on the toner container5side (on the front side in the device), and a flat portion continuous with the curved portion located above the toner container5.

Sheet Feeding Unit

At the bottom of the device, the sheet feeding unit51for storing and dispatching sheets is provided. The sheet feeding unit51includes a sheet feeding cassette52having a stack plate on which the sheets are stacked, a forward feeding roller53and a multiple feeding prevention mechanism54for sending individual sheets of paper into the conveyance path. The sheet feeding cassette52can be pulled out toward the front side of the device.

Conveyance Mechanism

The conveyance mechanism for conveying sheets is located between the sheet feeding unit51and the discharge unit50. The conveyance mechanism includes a first conveyance path55from the sheet feeding unit51to the secondary transfer roller8, a second conveyance path56from the secondary transfer roller8to the fixing device9, and a third conveyance path57from the fixing device9to the discharge unit50. At an exit of the fixing device9, a branching claw58is provided, and a return conveyance path59is provided between the branching claw58and a middle of the first conveyance path55for returning the sheet to the first conveyance path55.

The first conveyance path55includes a curved path55afor reversing the conveyance direction as well as conveying the sheet sent out from the sheet feeding cassette52upward, and a straight path55bextending from the curved path55ato the secondary transfer roller8. These conveyance paths are composed of guide plates and pairs of rollers for guiding the sheets as well as conveying them, and include sensors installed at places for sensing the sheet. In addition, a pair of registration rollers60is provided in the straight path55bfor controlling conveyance timing of the sheet.

The second conveyance path56extends in a rectilinear direction, and is composed of guide plates and pairs of rollers for guiding the sheets as well as conveying them, and includes sensors installed at places for sensing the sheet.

The third conveyance path57includes a vertical conveyance path formed downstream of the branching claw58in the conveyance direction. Namely, the sheet is conveyed upward in the vertical direction after passing the branching claw58and is discharged to the discharge unit50. The third conveyance path57is also composed of guide plates and pairs of rollers for guiding the sheets as well as conveying them.

The return conveyance path59is a conveyance path which branches off downward from the third conveyance path57at a place where the branching claw58is mounted and extends below the fixing device9, the second conveyance path56, the secondary transfer roller8and the pair of the registration rollers60, and then extends upward so as to join upstream of the pair of the registration rollers60in the first conveyance path55in the conveyance direction. Namely, the return conveyance path59is a conveyance path located vertically between the sheet feeding cassette52and straight path55bof the first conveyance path55as well as the second conveyance path56. The path59returns the sheet passed through the fixing device9upstream of the pair of the registration rollers60, which is located upstream of the secondary transfer roller8. The return conveyance path59is also composed of guide plates and pairs of rollers for guiding the sheets as well as conveying them, and includes sensors installed at places for sensing the sheets.

Sheet Feeding Tray

Below the toner container5and above the sheet feeding cassette52, the sheet feeding tray65is provided so as to form a lateral wall on the front side of the device. The sheet feeding tray65has a lower end pivotably supported in the vicinity of the curved path55aof the first conveyance path55such that the sheet feeding tray65can take an open position and a closed position. The upper end of the sheet feeding tray65can be reclined toward the front side of the device around a rotation center65ain the lower end. Accordingly, when the sheet feeding tray65is opened, it is possible to put the sheet on the sheet feeding tray65and supply the curved path55aof the first conveyance path55with the sheets.

Image Forming Operation

Next, the image forming operation will be explained in a simplified manner. First, when the power is applied to the color printer1, a variety of parameters are initialized and initialization is executed such as setting a temperature of the fixing device. Then, when the image data from the computer connected to this printer is inputted and an instruction to start printing is given, the image forming operation is carried out as follows. It should be noted that during the image forming operation, the toner supply pipe25is moved to the retracted position upward so that the laser path is not blocked by the toner supply pipe25.

First, the charge roller10charges the photosensitive drum2. After that, the photosensitive drum2is scanned and exposed by the laser unit4in accordance with the image data so that the electrostatic latent image is formed on the photosensitive drum2. Next, the rotary developing device3is rotated and the developing unit16whose color is designated is opposed to the photosensitive drum2. In this state, the electrostatic latent image on the photosensitive drum2is developed with the designated toner color. The developed image is transferred to the intermediate transfer belt7. The above-mentioned operation is sequentially carried out color by color so that the full color image is formed on the intermediate transfer belt7. It should be noted that residual toner on the photosensitive drum2is cleaned by the drum cleaning device11and is discarded into a discarded toner container (not illustrated).

In the sheet feeding unit51, a sheet is taken out from the sheet feeding cassette52by the forward feeding roller53and multiple feeding prevention mechanism54, and is conveyed to the pair of the registration rollers60through the first conveyance path55. Then, the sheet is conveyed from the pair of the registration rollers60to the intermediate transfer belt7with timing of image forming thereon and guided to the secondary transfer roller8. The secondary transfer roller8is in contact with the intermediate transfer belt7and the full color image formed on the intermediate transfer belt7is transferred to the sheet by transfer bias applied to the secondary transfer roller8. The sheet is guided to the fixing device9through the second conveyance path56, and the image is fixed to the sheet by heat and pressure in the fixing device9. In the case of one-side printing, the sheet is guided to the third conveyance path57by means of the branching claw58, and then is discharged to the discharge unit50.

In the case of double-side printing, after fixation in the fixing device9, the sheet is conveyed by the branching claw58toward the third conveyance path57temporarily, and then is conveyed in a reverse direction toward a side of the return conveyance path59after the trail end of the sheet passes the branching claw58, and is finally returned to the first conveyance path55through the return conveyance path59. The sheet is temporarily stopped by the pair of the registration rollers60. The sheet is sent with precise timing toward the secondary transfer roller8after the rear side image is formed on the intermediate transfer belt7in the same operation mentioned before. After that, the same operation is carried out, and the sheet is guided toward the third conveyance path57by means of the branching claw58and is discharged to the discharge unit50.

Toner Supply Operation

When the toner is supplied to the developing units16, the rotary developing device3is rotated such that the developing unit16to which the toner will be supplied is positioned in the supply position as shown inFIG. 1. The rotary developing device3is locked so as not to rotate in this state. Next, the toner supply pipe25is moved downward to the supply position. More specifically, the motor33adrives the pinion gear33with the gears so that the toner supply pipe25to which the rack32is fixed is moved downward. Meanwhile, the toner is conveyed to the second connection portion26bfrom the first connection portion26athrough the toner conveyance portion26cby rotation of the coil spring31in the conveyance pipe26. It should be noted that the toner is unlikely to free fall, and is conveyed by the conveyance force of the coil spring31because the toner conveyance portion26cis inclined upward from the first connection portion26ato the second connection portion26b. Accordingly, the amount of the toner supply to the developing unit16is managed precisely. The tip of the toner supply pipe25advances through the slit18aas a toner supply opening and into the developing unit16after the toner is supplied to the toner supply pipe25by the conveyance pipe26. During the downward movement of the toner supply pipe25, the outer cylinder252rotates relative to the inner cylinder251. Upon the entry of the tip of the toner supply pipe25into the developing unit16, the opening252aof the outer cylinder252and the opening251aof the inner cylinder251correspond to each other. In other words, the shutter mechanism is opened so that the toner inside of the toner supply pipe25is supplied into the developing unit16. In this case, the toner does not remain in the pipe25because the center axis of the toner supply pipe25maintains the repose angle of the toner or more relative to the horizontal line.

The amount of the toner supply from the toner container5to the conveyance pipe26is less than the toner conveyance capacity of the toner conveyance pipe26, i.e., the largest amount of the toner conveyance by the toner conveyance pipe26to the toner supply pipe25, and the toner conveyance capacity of the conveyance pipe26to the toner supply pipe25is less than the toner supply capacity of the toner supply pipe25to the developing unit16. Accordingly, the conveyance pipe26and the toner supply pipe25are unlikely to be plugged up by the toner, so that the management accuracy of the toner supply amount is unlikely to deteriorate.

It should be noted that although the toner supply pipe25blocks the laser light path from the laser unit4to the photosensitive drum2when toner supply pipe25is positioned in the supply position, it is not a cause for concern because the toner supplying operation by the toner supply pipe25and the image forming operation are not carried out simultaneously.

Upon the end of the toner supply, the coil spring31in the conveyance pipe26stops rotating. On the contrary, the spiral member30located in the toner supply pipe25continues to rotate until the toner is completely consumed in the toner supply pipe25. After that, the motor33ais rotated in a reverse direction so as to rotate the pinion gear33in the reverse direction so that the toner supply pipe25to which the rack32is fixed is moved upward. At this time, the outer cylinder252rotates in the reverse direction so that the opening251aof the inner cylinder251and the opening252aof the outer cylinder252are misaligned so as to close the opening, i.e., the shutter is closed. In the toner supply portion18of the developing unit16, when the toner supply pipe25is pulled out from the slit18a, the slit18ais also closed by its elastic force. Accordingly, the toner does not scatter in the device from the toner supply pipe25and the developing unit16.

Any terms of degree used herein, such as “substantially”, “about” and “approximately”, mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed. These terms should be construed as including a deviation of at least ±5% of the modified term if this deviation would not negate the meaning of the word it modifies.

This application claims priority to Japanese Patent Application Nos. 2004-315773, 2005-023821, and 2005-186911. The entire disclosure of Japanese Patent Application Nos. 2004-315773, 2005-023821, and 2005-186911 is hereby incorporated herein by reference.