Patent Grant
8965223
This application claims priority from Japanese Patent Application No. 2011-280095 filed Dec. 21, 2011, which is hereby incorporated by reference herein in its entirety.
1. Field of the Invention
The present invention relates to an image forming apparatus which includes a developing device including two electrode members, and further includes a detection mechanism for detecting a capacitance between the two electrode members.
2. Description of the Related Art
An image forming apparatus such as an electrophotographic apparatus conventionally includes a developing device which contains toner, which is a developer. Some developing devices are shipped as preinstalled in the main body of an image forming apparatus. Others are packed and shipped by themselves, and a user mounts such developing devices on an image forming apparatus.
As image forming apparatuses have recently been reduced in size, developing devices have also been becoming smaller. Such small-sized image forming apparatuses and small-sized developing devices have become more likely, because of the smallness, to be transported in various orientations under excessive vibrations and stored in various orientations for long periods of time. The toner in even a new developing device is therefore not necessarily evenly distributed in the longitudinal direction of the developing device.
For example, using a developing device in which toner is unevenly distributed to one side in the longitudinal direction can cause image defects such as a white spot (image missing due to an insufficient density). In addition, a drive torque for rotating a developing roller (toner bearing member) and a stirring member of the developing device can become so high that a drive gear may break down. Japanese Patent Application Laid-Open No. 2001-290356 discusses a method for detecting the state of toner in the longitudinal direction of a developing device by arranging three or more electrodes inside the developing device.
According to the detection method discussed in Japanese Patent Application Laid-Open No. 2001-290356, a plurality of electrodes needs to be arranged in the toner container in addition to the toner bearing member. This increases the number of parts and complicates the configuration of the developing device.
The present invention is directed to an image forming apparatus capable of detecting uneven distribution of toner in a developing device with a simple configuration.
According to an aspect of the present invention, an image forming apparatus includes an image bearing member configured to bear an electrostatic latent image, a developing device configured to include first and second electrode members, store a developer, and develop the electrostatic latent image with the developer, a holding unit configured to hold the developing device and change an orientation of the developing device to first and second orientations, and a detection device configured to detect whether the developer in the developing device is unevenly distributed in a longitudinal direction of the developing device based on a capacitance C1 between the first and second electrode members in the first orientation and a capacitance C2 between the first and second electrode members in the second orientation.
Further features and aspects of the present invention will become apparent from the following detailed description of exemplary embodiments with reference to the attached drawings.
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments, features, and aspects of the invention and, together with the description, serve to explain the principles of the invention.
Various exemplary embodiments, features, and aspects of the invention will be described in detail below with reference to the drawings.
The following exemplary embodiments describe the present invention byway of examples. The scope of an exemplary embodiment of the present invention is not limited to the dimensions, materials, shapes, and relative arrangement of the components described below unless otherwise specified.
The image forming apparatus includes a rotating drum type electrophotographic photosensitive member (hereinafter, referred to as a drum) 1 serving as an image bearing member which bears an electrostatic latent image on its surface. The image forming apparatus further includes a charging unit 2, an image exposure unit 3, a developing unit 5, a transfer unit 6, a drum cleaning unit 7, and a fixing unit 8 as process units that act on the drum 1.
The drum 1 is driven to rotate about a drum axis in a clockwise direction indicated by the arrow R1 at a predetermined speed. The charging unit 2 uniformly charges the surface of the drum 1 to a predetermined polarity (in the present exemplary embodiment, negative polarity) and potential. In the present exemplary embodiment, a contact charging roller is used as the charging unit 2.
The image exposure unit 3 forms an electrostatic latent image on the surface of the drum 1 via a mirror 4. In the present exemplary embodiment, a laser scanner unit is used as the image exposure unit 3. The developing unit 5 is a unit that visualizes the electrostatic latent image formed on the drum surface into a developer image (toner image). In the present exemplary embodiment, the developing unit 5 serving as a developing device is a reversal developing device of contact developing type which uses negatively charged nonmagnetic toner as a developer T.
The transfer unit 6 transfers the toner image visualized on the drum surface to a recording material P serving as a transfer material. A transfer roller is used as the transfer unit 6. The drum cleaning unit 7 removes transfer residual toner from the surface of the drum 1 after transfer. A cleaning blade is used as the drum cleaning unit 7.
The toner removed from the drum surface is stored in a cleaner container 71. The recording material P with the transferred toner image is guided into the fixing unit 8, and heated and pressed by a fixing nip portion. The toner image is thereby fixed to the recording material P.
Completing an image forming job on one sheet or a continuous plurality of sheets, the controller unit 100 puts the image forming apparatus into a standby state and waits for the input of a next image formation start signal. Specifically, the controller unit 100 stops driving the drum 1, the laser scanner unit 3, and the transfer unit 6.
The developing unit 5 includes the toner container 13, the developing roller 9, and a supply roller 10. The toner container 13 serves as a toner storage chamber for storing the toner T. The developing roller 9 serves as a toner bearing member for developing the electrostatic latent image formed on the drum 1. The supply roller 10 serves as a toner supply member which contacts the developing roller 9 to supply the toner T.
The developing unit 5 further includes a regulation blade 11 and a leak prevention seal 12. The regulation blade 11 serves as a toner layer thickness regulation member for regulating the toner layer on the developing roller 9. The leak prevention seal 12 prevents leakage of the toner from a gap between the developing roller 9 and the toner container 13. The developing unit 5 further includes a storage unit 15 which stores whether the developing unit 5 is a new one. In the present exemplary embodiment, a noncontact nonvolatile memory is used as the storage unit 15.
The toner container 13 is an oblong container whose longitudinal direction is in the axial direction of the drum 1. The toner container 13 has an opening at its lower portion. The opening extends in the longitudinal direction of the toner container 13 and is opposed to the drum 1. The developing roller 9 is located in the opening and arranged in parallel to the longitudinal direction of the toner container 13. The developing roller 9 is rotatably supported by the toner container 13 via bearing members (not illustrated) that are attached to both longitudinal ends of the toner container 13, respectively.
The supply roller 10 is arranged inside the toner container 13 in parallel with the developing roller 9, on the other side of the developing roller 9 from where the developing roller 9 is opposed to the drum 1. The supply roller 10 is rotatably supported by the toner container 13 via bearings (not illustrated) that are attached to both longitudinal ends of the toner container 13, respectively.
In the present exemplary embodiment, the developing roller 9 has a diameter of φ13. The developing roller 9 includes a φ8 conductive core (first electrode member) 9a which is covered with a base layer of silicon rubber and further coated with acrylic urethane rubber. The developing roller 9 has a volume resistance of 104 to 1012 Ω·m.
The supply roller 10 is a φ15 urethane sponge roller, including a φ6 conductive core (second electrode member) 10a covered with a urethane sponge layer 10b made of a foam layer of open-cell foam. The urethane sponge layer 10b has a volume resistance of around 104 to 1012 Ω·m. In other words, the supply roller 10 includes an open-cell foam.
The distance (center distance) between the core 9a of the developing roller 9 and the core 10a of the supply roller 10 is 13 mm. The urethane sponge layer 10b (foam layer) of the supply roller 10 is pressed into the surface of the developing roller 9 by 1.0 mm.
The regulation blade 11 is a flexible member made of phosphor bronze or urethane rubber. The extremity of the regulation blade 11 slides over the developing roller 9 to form the toner applied to the developing roller 9 into a thin coating layer. The regulation blade 11 is arranged on the toner container 13 with its bottom fixed to the upper edge of the opening.
The leak prevention seal 12 is a flexible member whose top end is in contact with the developing roller 9 to cover a gap between a lower portion of the developing roller 9 and the toner container 13, thereby preventing leakage of the toner. The leak prevention seal 12 is arranged on the toner container 13 with its bottom fixed to the lower edge of the opening.
When performing image formation, a driving force and a developing bias are input to the developing unit 5 in the first orientation from a driving unit (not illustrated) and a power supply unit on the main body side of the image forming apparatus. The developing roller 9 is driven to rotate at a predetermined speed in a counterclockwise direction indicated by the arrow R2 in
The supply roller 10 which makes contact with the developing roller 9 to supply the toner to the developing roller 9 is driven to rotate at a predetermined speed in a counterclockwise direction indicated by the arrow R3. The rotational direction of the supply roller 10 at the drum contact portion is reverse (in a counter direction) with respect to the rotational direction R2 of the developing roller 9.
The rotating supply roller 10 applies the toner to the periphery of the rotating developing roller 9. The regulation blade 11 forms the applied toner into a thin coating film. The thin layer of the toner T is conveyed to a development position by the subsequent rotation of the developing roller 9, and applied to the surface of the drum 1.
A developing bias power supply unit applies a predetermined developing bias or direct-current (DC) voltage in the present exemplary embodiment to the developing roller 9. As a result, the thin layer of the toner on the periphery of the phase roller 9 is selectively transferred to the drum surface according to the electrostatic latent image on the drum surface. The electrostatic latent image is thereby developed as a toner image. The toner not consumed for the development of the electrostatic latent image is conveyed back into the toner container 13 by the subsequent rotation of the developing roller 9.
The supply roller 10 removes the toner from the surface of the developing roller 9 and applies the toner again to the surface of the developing roller 9. Such an operation is repeated to develop the electrostatic latent image on the drum surface.
In the prior example, the longitudinally uneven distribution of toner in a toner container is detected by using three or more electrodes in the toner container. On the other hand, according to the present exemplary embodiment, the detection is performed by using two electrodes.
The basic principle of the method for detecting uneven distribution of toner according to the present exemplary embodiment will be described. In the present exemplary embodiment, a conductive core 10a of the supply roller 10 is used as an electrode member arranged next to the developing roller 9. In the following description, a “capacitance” refers to the capacitance between the conductive core 9a of the developing roller 9 and the conductive core 10a of the supply roller 10.
To detect the capacitance, the bias power supply initially applies a toner uneven distribution detecting bias to the conductive core 10a of the supply roller 10. An alternating-current bias having a frequency of 5 kHz and a voltage of Vpp=200 V is used as the toner uneven distribution detecting bias.
The toner uneven distribution detecting bias induces a voltage on the conductive core 9a of the developing roller 9. The voltage is detected by a detector and rectified by a detection circuit, and whereby the capacitance is detected. In the following description, the capacitance is measured by using an inductance-capacitance-resistance (LCR) meter ZM2354 from NF Corporation.
First, a state where the toner T in the toner container 13 is longitudinally evenly distributed will be described. In the first orientation illustrated in
Here, in the first orientation, an area X is filled with a sufficient amount of toner T. The area X refers to an area that lies between the core 9a of the developing roller 9 and the core 10a of the supply roller 10 and has a large impact on the capacitance.
With the configuration of the present exemplary embodiment, the area X lies upstream of a nip portion (contact nip portion) between the developing roller 9 and the supply roller 10 in the rotational direction of the supply roller 10. The toner T has a dielectric constant approximately three times that of air. The greater the amount of toner T lying in the area X, the higher the capacitance. More specifically, when the developing unit 5 where the toner T in the toner container 13 is longitudinally evenly distributed is held in the first orientation, the capacitance C1 has a large value as illustrated in
The mount 400 on which the developing unit 5 is mounted serves as a turning unit for changing the developing unit 5 to the first orientation illustrated in
The orientation illustrated in
As a result, no toner lies in the area X. When the developing unit 5 where the toner T in the toner container 13 is longitudinally evenly distributed is held in the second orientation, the capacitance C2 has a value smaller than C1 as illustrated in
Next, a state where the toner T in the toner container 13 is unevenly distributed to one side in the longitudinal direction of the toner container 13 (i.e., the axial direction of the developing roller 9) will be described.
Suppose that the developing unit 5 is held in the first orientation illustrated in
Next, the developing unit 5 is held in the second orientation illustrated in
When the developing unit 5 where the toner T in the toner container 13 is unevenly distributed is held in the second orientation, the capacitance C2′ has a value similar to that of C1′ as illustrated in
As described above, when the toner T in the toner container 13 is longitudinally evenly distributed, the difference ΔC between the capacitance in the first orientation and the capacitance in the second orientation has a larger value. When the toner in the toner container 13 is unevenly distributed to one side in the longitudinal direction, the difference ΔC′ between the capacitance in the first orientation and the capacitance in the second orientation becomes smaller than ΔC. This shows that a difference ΔC between the capacitance in the first orientation and the capacitance in the second orientation can be calculated to detect the state of uneven distribution of the toner T in the toner container 13.
Next, a method for determining the state of uneven distribution of the toner T in the toner container 13 based on a difference ΔC will be described based on the result of an experiment made by the present inventors (
Initially, the difference ΔC of the developing unit 5 was measured. Then, an operation for breaking up the toner T in the toner container 13 to resolve the uneven distribution of the toner T (toner break-up sequence) was performed. In the present exemplary embodiment, the toner break-up sequence was performed by quickly swinging the mount 400 between the first orientation and the second orientation several times. The measurement of the difference ΔC and the toner break-up sequence were alternately repeated.
Before the toner break-up sequence (after zeroth) is performed, the difference ΔC of the developing unit 5 was measured to have a small value as illustrated in
As the toner break-up sequence was repeated, the difference ΔC increased gradually. After the fourth toner break-up sequence, the developing unit 5 caused no white-spot image defect. ΔCp will be defined as a threshold for determining the absence of uneven toner distribution. If the difference ΔC exceeds ΔCp, it is determined to be no uneven toner distribution. If the difference ΔC falls below ΔCp, it is determined to be uneven toner distribution.
Next, an operation when the developing unit 5 is mounted on the image forming apparatus will be described with reference to
In step S1, the user mounts the developing unit 5 on the mount 400. In step S2, with the developing unit 5 mounted on the mount 400, the controller unit 100 accesses the memory 15 of the developing unit 5 and determines whether the developing unit 5 is a new one. If the developing unit 5 is not a new one (NO in step S2), then in step S3, the controller unit 100 enters a standby state. If the developing unit 5 is a new one (YES in step S2), then in step S4, the controller unit 100 controls the driving unit 402 to swing the developing unit 5 about the shaft 401 so that the developing unit 5 is held in the first orientation illustrated in
In step S5, an uneven distribution detection device 100a (uneven distribution detection unit) applies the toner uneven distribution detecting bias to the conductive core 10a of the supply roller 10 and detects the capacitance C1. In step S6, the controller unit 100 drives the driving unit 402 to perform a swing control so that the developing unit 5 is held in the second orientation illustrated in
In step S7, the uneven distribution detection device 100a detects the capacitance C2 like the first orientation. In step S8, the controller unit 100 calculates a difference between the detected capacitances C1 and C2, i.e., ΔC=|C1−C2|.
In step S9, the controller unit 100 compares the difference ΔC with the threshold ΔCp. If ΔC is greater than ΔCp (NO in step S9), then in step S3, the controller unit 100 enters a standby state, determining that the toner T in the toner container 13 is longitudinally evenly distributed. If ΔC is smaller than or equal to ΔCp (YES in step S9), the controller unit 100 determines that the toner T in the toner container 13 is unevenly distributed to one side in the longitudinal direction.
If the toner is determined to be unevenly distributed (YES in step S9), then in step S10, the controller unit 100 determines the number of times the toner break-up sequence has been performed. If the number of times is less than or equal to a predetermined number (YES in step S10), then in step S11, the controller unit 100 performs the toner break-up sequence. In step S12, after the completion of the sequence, the controller unit 100 stores the total number of times the sequence has been performed. In step S4, the controller unit 100 makes the developing unit 5 held in the first orientation again, and performs the capacitance detection routine described above.
If such an operation is repeated and the toner T is still determined to be unevenly distributed when the number of times of the toner break-up sequence exceeds the predetermined number (NO in step S10), then in step S13, the controller unit 100 notifies a display unit 100b of the “uneven toner distribution” to instruct the user to dismount and shake the developing unit 5.
The foregoing number of times may be determined as appropriate depending on the configuration including the ease of break-up of the toner T and the driving speed of the mount 400. In the present exemplary embodiment, the predetermined number of times was set to five based on the result of the foregoing experiment.
As described above, in the present exemplary embodiment, the developing unit 5 is changed to the first orientation in which the toner T lies in the area between the cores 9a and 10a and the second orientation in which at least part of the toner T lying in the area between the cores 9a and 10a in the first orientation moves out of the area. Whether the toner T in the toner container 13 is unevenly distributed is detected based on a comparison between the capacitance C1 between the cores 9a and 10a in the first orientation and the capacitance C2 between the cores 9a and 10b in the second orientation. The uneven distribution of the toner T in the toner container 13 can thus be detected with a simple configuration.
In the present exemplary embodiment, the uneven distribution of the toner T is detected based on a difference between the capacitances C1 and C2. However, the uneven distribution of the toner T may be detected based on a ratio between the capacitances C1 and C2. For example, the toner T may be determined to be unevenly distributed and the toner break-up sequence may be performed if the ratio C2/C1 exceeds a threshold. The uneven distribution detection apparatus 100a can thus detect whether the toner T in the toner container 13 is unevenly distributed based on a comparison between the capacitances C1 and C2.
While the present exemplary embodiment performs the toner break-up sequence, a warning prompting the user to shake the developing unit 5 may be issued instead of the sequence. While the present exemplary embodiment employs a contact developing method, a noncontact developing method (jumping developing method) is also applicable.
The image forming apparatus according to the second exemplary embodiment includes a plurality of developing units 5 serving as developing units. More specifically, the image forming apparatus includes first to fourth four developing units 5. A rotary 14 serving as a holding unit holds the plurality of developing units 5. The rotary 14 is rotatably supported and can rotate and move a desired developing unit 5 (for example, the developing unit 5a) to a development position A where the developing unit 5 is opposed to and makes contact with the photosensitive drum 1.
The image forming apparatus according to the second exemplary embodiment further includes a transfer belt 61 serving as an intermediate transfer member. The transfer belt 61 is rotatably stretched around a plurality of rollers. The photosensitive drum 1 and the transfer belt 61 are pressed against and make contact with each other in a primary transfer position B, where a primary transfer roller 62 is arranged to sandwich the transfer belt 61 between the photosensitive drum 1 and the primary transfer roller 62.
A toner image formed in the development position A is transferred to the transfer belt 61 in the primary transfer position B. A recording material P and the transfer belt 61 are pressed against and make contact with each other in a secondary transfer position C, where a secondary transfer counter roller 63 and a secondary transfer roller 64 are arranged. The transfer belt 61 is stretched around the secondary transfer counter roller 63. The secondary transfer roller 64 is configured to be able to come into contact with and draw away from the transfer belt 61.
A cleaning device 65 is arranged downstream of the secondary transfer position C in the moving direction of the transfer belt 61. The cleaning device 65 is arranged in contact with the transfer belt 61 so that a blade of the cleaning device 65 can scrape toner off the transfer belt 61.
Next, an operation for forming a four-color full color image will be described. The photosensitive drum 1 is driven to rotate in the direction of the arrow R4 at a predetermined speed. The charging unit 2 uniformly charges the drum surface to a predetermined potential.
The image exposure unit 3 and a reflection mirror 4 form an electrostatic latent image on the drum surface corresponding to an image signals of each color. A developing unit 5 develops the formed electrostatic latent image in the development position A to form a toner image.
The developing unit 5 to be located in the development position A is determined according to the color-specific image signals. The rotary 14 is rotated in the direction of the arrow R6 in advance to locate a developing unit 5 of a desired color in the development position A.
Toner images are develop in fixed color order. In the present exemplary embodiment, toner images are formed in the order of yellow, magenta cyan, and black. The toner image formed on the drum 1 is transferred to the transfer belt 61 in the primary transfer position B. The transfer belt 61 is driven in the direction arrow R5. Formed toner images are successively superposed on previously transferred ones to form a full color toner image on the intermediate transfer belt 61.
The secondary transfer roller 64 and the cleaning device 65 are separated from the transfer belt 61 until the formation of a full color toner image is formed, and put into contact with the transfer belt 61 after the formation.
A recording material P is conveyed in synchronization with the timing at which the formed full color toner image reaches the secondary transfer position C. The secondary transfer roller 64 and the secondary transfer counter roller 63 sandwich the recording material P and the transfer belt 61 together to transfer the full color toner image to the recording material P.
The recording material P with the transferred full color toner image is conveyed to the fixing unit 8. The fixing unit 8 applies heat and pressure to the full color toner image on the recording material P, and whereby the full color toner image is fixed to the recording material P as a final image.
Next, a method for detecting uneven distribution of toner according to the present exemplary embodiment will be described with reference to
The following description deals with the method for detecting the uneven distribution of the toner in the developing unit 5a. The method can be similarly performed on the not-mentioned developing units (5b, 5c, and 5d). The uneven distribution of the toner in the developing unit 5a is detected by an uneven toner distribution detection device 100a. When the developing unit 5a is mounted on the image forming apparatus, the controller unit 100 accesses the memory 15 of the developing unit 5a and determines whether the developing unit 5a is a new one.
If the developing unit 5a is determined to be a new one, the developing unit 5a is held in the position D of
The uneven toner distribution detection device 100a performs capacitance detection on the developing unit 5a in the first orientation to detect a capacitance C1y. The rotary 14 is then driven to rotate and hold the developing unit 5a in the position E in the second orientation. The uneven toner distribution detection device 100 similarly changes a switch to make contact with only the developing unit 5a in the position E.
The uneven toner distribution detection device 100a performs capacitance detection on the developing unit 5a in the second orientation to detect a capacitance C2y. The controller unit 100 calculates a difference between the detected C1y and C2y, and compares the difference with a threshold ΔCp to determine whether the toner in the toner container is longitudinally unevenly distributed.
If the toner is determined to be unevenly distributed, the controller unit 100 performs a toner break-up sequence. For the toner break-up sequence, for example, an operation for rotating the rotary by 90° and stopping the rotary 14 is performed for a single rotation of the rotary 14. The toner break-up sequence is not limited to such an operation. The rotary 14 may be rotated back and forth. The rotary 14 may be rotated by 30° and stopped. Any operation may be performed as long as the toner in the toner container spreads out in the longitudinal direction.
After the completion of the toner break-up sequence, the uneven toner distribution detection device 100a detects the uneven distribution of the toner again. The toner break-up sequence and the detection of the uneven distribution of the toner are then alternately repeated. If the toner is not determined to be evenly distributed even after the toner break-up sequence is performed several time, a warning like “the toner is unevenly distributed” may be displayed on the display unit 100b of the operation unit to prompt the user to dismount and shake the developing unit 5a.
In the present exemplary embodiment, the uneven distribution of the toner is detected based on a difference between the capacitances C1y and C2y. However, the uneven distribution of the toner may be detected based on a ratio between the capacitances C1y and C2y. For example, the toner may be determined to be “unevenly distributed” and the toner break-up sequence may be performed if the ratio C2y/C1y exceeds a threshold.
The uneven toner distribution detection device 100a can thus detect whether the toner in the toner container is unevenly distributed based on a comparison between the capacitances C1y and C2y.
While the present exemplary embodiment employs a contact developing method, a noncontact developing method (jumping developing method) is also applicable.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all modifications, equivalent structures, and functions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-280095 | Dec 2011 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5987269 | Allen et al. | Nov 1999 | A |
| 6463223 | Karakama et al. | Oct 2002 | B1 |
| 20110069978 | Yamamoto | Mar 2011 | A1 |
| Number | Date | Country |
|---|---|---|
| 11-174775 | Jul 1999 | JP |
| 2001-290356 | Oct 2001 | JP |
| 2010-026497 | Feb 2010 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20130163999 A1 | Jun 2013 | US |
