JP2019012245A - Image forming apparatus - Google Patents

Abstract

PURPOSE: To solve the problem in which: when determining whether a developing device is usable by detecting the magnetic permeability inside a developing unit, an image forming apparatus may erroneously determine whether the developing unit is normally driven; and thus to provide an image forming apparatus that can more accurately detect drive abnormality of the developing unit.CONSTITUTION: An image forming apparatus comprises: an image carrier that can carry a developer image; developing means that forms the developer image on the image carrier; driving means that drives the image carrier and the developing means; and determination means that determines the driving state of the developing means on the basis of the state of the value of a current flowing between the image carrier and the developing means before the developing means forms the developer image on the image carrier.SELECTED DRAWING: Figure 5

Description

  The present invention relates to an image forming apparatus that forms an image on a sheet using a developer.

  2. Description of the Related Art Conventionally, a device including an electrophotographic image forming apparatus such as a printer, a copying machine, or a facsimile apparatus is provided with a developing device for attaching toner to an electrostatic latent image on a photosensitive member.

  This type of developing device is detachable from the image forming apparatus, and the drive from the drive source provided in the image forming apparatus is transmitted to the stirring paddle and the developing sleeve in the developing device via a transmission mechanism such as a clutch. In many cases, a configuration is used.

  In such a configuration, the drive is not normally transmitted to the developing device due to an abnormality of the clutch or gear tooth skipping of the transmission mechanism, and the stirring paddle and the developing sleeve in the developing device stop operating. There is a fear. As described above, when the drive is not normally transmitted to the developing device, there is a possibility that a problem such as a decrease in print density may occur due to insufficient supply of toner to the image forming unit.

  Therefore, in Patent Document 1, in order to confirm whether the developing device is driven as intended, the developing device is based on the period of the signal waveform output from the detection unit that detects the magnetic permeability in the developing device. A technique for determining whether or not it can be used has been proposed.

JP 2014-240876 A

  However, when determining whether or not the developing device can be used by detecting the magnetic permeability in the developing device, the output level of the detecting means for detecting the magnetic permeability varies according to the amount of toner in the developing device. In some cases, it is erroneously determined whether or not the developing device is normally driven.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of more accurately detecting a drive abnormality of a developing device in view of the above points.

  An image carrier that can carry a developer image, a developing unit that forms a developer image on the image carrier, a driving unit that drives the image carrier and the developing unit, and development on the image carrier Determination means for determining a driving state of the developing means based on a state of a current value between the image carrier and the developing means when forming the agent image.

  According to the present invention, it is possible to detect an abnormal driving of the developing device more accurately.

Schematic sectional view of the image forming apparatus of the present embodiment Block diagram showing the developer control configuration (A) Schematic sectional view showing normal state of developing sleeve (B) Schematic sectional view showing abnormal state of developing sleeve (A) Example of gradation image, (B) Graph showing an example of development bias output current value transition The flowchart which shows the control operation of the control part 200 at the time of the drive state determination of the developing sleeve 241

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. The following embodiments do not limit the present invention according to the claims, and all combinations of features described in the embodiments are not necessarily essential to the solution means of the present invention. .

<First Embodiment>
Hereinafter, an image forming apparatus according to the present embodiment will be described with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view showing the configuration of the image forming apparatus. The image forming apparatus A includes an image forming apparatus main body 100 and an image reading apparatus 110 provided on the upper part of the image forming apparatus main body 100. In the image forming apparatus main body 100, a sheet feeding unit 10, an image forming unit 20, a fixing unit 30, and a sheet discharging unit are sequentially arranged from the lower side (upstream in the sheet conveying direction) to the upper side (downstream in the sheet conveying direction) in FIG. 40 is provided. A sheet refeeding unit 50 is provided on the right side of the image forming unit 20 and the fixing unit 30.

  In the sheet feeding unit 10, the sheets P stacked on the feeding cassette 11 or the manual feed tray 16 are fed to the image forming unit 20.

  The sheet detection sensor S <b> 1 is a sensor that detects that the sheet P is stored in the feeding cassette 11.

  The sheet P stored in the feeding cassette 11 is fed to the separation roller pair 13 as the pickup roller 12 rotates. When the sheet P is double-fed, it is separated into one sheet by a separating roller pair 13 composed of a normal rotation roller and a reverse roller, and is conveyed to a feeding path PS1 indicated by a solid line.

  The sheet P conveyed to the feeding path PS1 is further conveyed by the feeding roller pair 14, and the skew of the sheet P is corrected by following the leading edge of the nip of the registration roller pair 15 that has stopped rotating. The pre-registration sensor S <b> 2 detects the timing at which the leading edge of the sheet P reaches the nip of the registration roller pair 15.

  When the sheet P placed on the manual feed tray 16 is fed, the sheet is separated into one sheet by the feeding roller 17 and the separation pad 18 and pulled into the apparatus. Then, the sheet is conveyed to the feeding roller pair 14 by the supply roller pair 19, and the skew of the sheet P is corrected by the registration roller pair 15. The sheet P whose skew has been corrected is conveyed to the image forming unit 20 by the registration roller pair 15 rotating at a predetermined timing.

  In the image forming unit 20, the surface of the photosensitive drum 21 is uniformly charged by the charging roller 22. Laser light corresponding to the image information is emitted from the laser unit 23. In the portion of the photosensitive drum 21 irradiated with the laser light, the charge charged by the charging roller 22 is removed, and an electrostatic latent image corresponding to the image information is formed. The electrostatic latent image formed here is visualized as a developer image when the developer is attached by the developing device 24.

  The developer image is conveyed to the transfer nip portion N1 by the rotation of the photosensitive drum 21. In synchronization with this timing, the sheet P is conveyed from the registration roller pair 15 to the transfer nip portion N1. While the conveyed sheet P is nipped and conveyed by the transfer roller 25 in contact with the photosensitive drum 21 in the transfer nip portion N1, the developer image formed on the photosensitive drum 21 is transferred by the transfer roller 25.

  The laser light emitted from the laser unit 23 is controlled based on image data of a document read by the image reading device 110 and image data transmitted from the outside.

  Next, the sheet P on which the developer image is formed is conveyed to the fixing unit 30. In the fixing unit 30, a fixing roller 31 composed of an aluminum roller or the like heated to a predetermined fixing temperature by a heat source such as a halogen lamp disposed therein, and the fixing roller 31 in contact with the fixing roller 31 with a predetermined pressure. A fixing nip portion N2 is formed by the pressure roller 32 that presses the pressure. The sheet P on which the developer image is formed is sent to the fixing nip portion N2, and is nipped and conveyed between the fixing roller 31 and the pressure roller 32, and is heated and pressed, whereby the developer image is fixed on the sheet P. Is done. The fixing sensor S3 detects that the leading edge of the sheet P has passed through the fixing nip portion N2.

  Note that the fixing unit 30 forms the fixing nip portion N2 by pressing the heat source such as a ceramic heater through the endless film, instead of the heating roller method in which the fixing roller 31 heats, An on-demand fixing method in which the sheet P is held and conveyed by the fixing nip portion N2 while being heated and pressed may be used.

  Next, the sheet P on which the developer image is fixed is conveyed to the sheet discharge unit 40 and discharged to the discharge tray 42 by the discharge roller pair 41.

  When images are formed on both sides of the sheet P, the discharge roller pair 41 after the leading edge of the sheet P imaged on the first surface passes through the fixing sensor S3 and before the trailing edge of the sheet P passes through the discharge roller pair 41. Is temporarily stopped, and the discharge roller pair 41 is further rotated in the reverse direction to convey the sheet to the sheet re-feeding unit 50.

The sheet P conveyed to the sheet re-feeding unit 50 is conveyed on a re-feed path PS2 indicated by a broken line by re-feed roller pairs 51 and 52, the sheet P is reversed, and the re-feed roller pair 53 registers. It is conveyed to the roller pair 15. Then, after the skew is corrected by the registration roller pair 15, the developer image is formed on the second surface of the sheet P by being conveyed to the transfer nip portion N1. Thereafter, the developer image is fixed to the sheet P by being conveyed through the fixing nip portion N2 in the same manner as when the image is formed on the first side, and the sheet P on which the image is formed on both sides is discharged by the discharge roller pair 41 to the discharge tray. 42 is discharged.

FIG. 2 is a block diagram showing a control configuration of the developing device 24 in the present embodiment.
In the present embodiment, the main motor 211 of the main drive unit 210 is driven by signals transmitted from the system controller 201 and the engine controller 202 of the control unit 200. The main motor 211 is controlled by the control unit 200 so as to have a constant target speed while performing speed control with a DC motor or the like. The driving by the main motor 211 is transmitted to the photosensitive drum 21 and the registration roller pair 15 via a transmission mechanism (not shown) and the like, and is transmitted to the developing device 24 via the developing clutch 212.

  In this embodiment, connection and disconnection of the drive connection of the developing sleeve 241 and the stirring member 242 in the developing device 24 can be selected from the main motor 211 by the developing clutch 212. With the developing clutch 212, the developing sleeve 241 and the stirring member 242 can be driven and stopped at a predetermined timing with respect to the photosensitive drum 21 and the registration roller pair 15. At this time, the engine controller 202 can control the developing clutch 212 and the high-pressure controller 203 based on the detection result of the magnetic permeability sensor 243 that detects the state of the toner in the developing device 24.

  The high pressure control unit 203 in the control unit 200 outputs a high pressure developing bias to the developing sleeve 241 based on a signal from the engine controller 202. In general, a constant voltage is applied to the developing sleeve 241 and a voltage difference is generated between the high-voltage developing bias output here and the photosensitive drum 21 to develop the latent image on the photosensitive drum 21. Constant voltage control is often used. The high voltage control unit 203 can input the output current value of the high voltage developing bias output to the developing sleeve 241 by the current detecting unit 204 to the engine controller 202 as a current monitor signal.

  In the present embodiment, an image forming job is received from the user via the operation unit 205. The operation unit 205 includes a display monitor (not shown) and the like, and can notify an error to the user.

In such a configuration, conventionally, when some abnormality has occurred in the main motor 211, the control unit 200 stops driving by detecting that the target speed of the main motor 211 is not maintained. Abnormal measures may be taken.
However, when the developing clutch 212 or the developing sleeve 241 itself downstream of the main motor 211 is abnormal and the developing sleeve 241 cannot be rotationally driven, it cannot be detected. This is because the main motor 211 itself can continue to be driven without detecting an abnormality, and an abnormality such as the developing sleeve 241 cannot be detected. For this reason, the processing is continued even when the developing sleeve 241 is not rotated, and an abnormal image such as a blank sheet in which no image is formed on the sheet may be output.

In view of this, the present embodiment includes a configuration for detecting an abnormal rotation of the developing sleeve 241 based on the output current value of the high-voltage developing bias described above. Below, the detailed structure is demonstrated.

3A and 3B are schematic cross-sectional views of the photosensitive drum 21 and the developing sleeve 241. FIG. 3A is a cross-sectional view when the developing sleeve 241 is normally driven, and FIG. 3B is an abnormality in driving of the developing sleeve 241. FIG.
At this time, if the distance between the photosensitive drum 21 and the developing sleeve 241 is d, the dielectric constant is ε, and the area between the photosensitive drum 21 and the developing sleeve 241 is S, the distance between the photosensitive drum 21 and the developing sleeve 241 is The capacitance C formed by is expressed by the following equation (1).

[Formula 1] C = ε (S / d) (1)
As described above, the capacitance C is proportional to the adjacent area between two different conductors, and the relationship inversely proportional to the distance between adjacent conductors is known. Therefore, the capacitance C decreases as the distance d between the photosensitive drum 21 and the developing sleeve 241 increases.

  The impedance Z of the developing sleeve 241 is expressed by the following formula (2).

[Expression 2] Z = R / (1 + jωRC) (2)
That is, the distance d between the photosensitive drum 21 and the developing sleeve 241 and the impedance Z are in a proportional relationship.

  Here, the difference between when the developing sleeve 241 is driven normally and when it is abnormal will be described. When the drive of the developing sleeve 241 is normal, as shown in FIG. 3A, even after the toner image is transferred to the photosensitive drum 21, the developing sleeve 241 continues to rotate and the developing sleeve 24 In order to carry the toner T, the toner T is carried in a region facing the photosensitive drum 21 on the developing sleeve 241. Therefore, the electrostatic capacitance C1 formed between the developing sleeve 241 and the photosensitive drum 21 when the driving is normal is expressed by the following Expression 3.

[Formula 3] C1 = ε (S / d1) (3)
As described above, when the developing sleeve 241 is driven normally, the distance d1 between the photosensitive drum 21 and the developing sleeve 241 is reduced by the amount of the toner T carried on the developing sleeve 241.

  On the other hand, when the driving of the developing sleeve 241 is abnormal, as shown in FIG. 3B, the developing sleeve 241 cannot rotate, and the area facing the photosensitive drum 21 after the toner is transferred to the photosensitive drum 21. There is no toner. Accordingly, the capacitance C2 formed between the developing sleeve 241 and the photosensitive drum 21 when the driving is abnormal is expressed by the following Expression 4.

[Expression 4] C2 = ε (S / d2) (4)
As described above, when the driving of the developing sleeve 241 is abnormal, the distance d2 between the photosensitive drum 21 and the developing sleeve 241 is the thickness of the toner T carried on the developing sleeve 241 with respect to d1 when the driving is normal. Increased by d3. Therefore, the electrostatic capacity C2 when the driving of the developing sleeve 241 is abnormal is reduced as compared with the electrostatic capacity C1 when the driving is normal.

  Further, the impedance Z1 of the developing sleeve 241 when the driving is normal is expressed by the following formula 5, and the impedance Z2 of the developing sleeve 241 when the driving is abnormal is expressed by the following formula 6.

[Formula 5] Z1 = R / (1 + jωRC1) (5)
[Expression 6] Z2 = R / (1 + jωRC2) (6)
In this case, the relationship of Z1 <Z2 is satisfied by the relationship of C1> C2 as described above. Therefore, the impedance of the developing sleeve 241 increases when the driving is abnormal as compared to when the driving is normal. Further, when the output current of the high-voltage developing bias is I, the output voltage is V, and the impedance of the developing sleeve 241 is Z, the relationship of the following Expression 7 is generally established.

[Expression 7] V = IZ (7)
In the present embodiment, the constant voltage control is performed to develop the latent image on the photosensitive drum 21, so that the output voltage V is constant. Accordingly, the output current value I flowing through the developing sleeve 241 varies with the variation of the impedance Z. Therefore, from the relationship of Z1 <Z2 as described above, the relationship between the output current value I1 of the developing bias when the driving is normal and the output current value I2 of the developing bias when the driving is abnormal satisfies the relationship of I1> I2. That is, the value of the output current flowing through the developing sleeve 241 decreases when the driving is abnormal as compared to when the driving is normal. Therefore, by detecting the output current value flowing through the developing sleeve 241, it can be determined whether the driving of the developing sleeve 241 is normal or abnormal.

Next, the relationship between the toner image formed on the photosensitive drum 21 and the output current value flowing through the developing sleeve 241 will be described.
4A and 4B are diagrams for explaining the transition of the output current value of the developing bias when a gradation image is formed. FIG. 4A shows an example of the gradation image, and FIG. 4B shows the developing bias. It is a graph which shows an example of transition of an output current value.

  FIG. 4A shows a gradation image in which the left end is solid white with a toner concentration of 0% and the right end is solid black with a toner concentration of 100%. When such a gradation image is formed, as shown in FIG. 4B, the output current value of the developing bias tends to decrease as the toner density increases.

  This is because the output current value of the developing bias of the developing sleeve 241 depends on the distance between the photosensitive drum 21 and the developing sleeve 241. As described above, the distance between the photosensitive drum 21 and the developing sleeve 241 varies depending on the amount of toner carried on the developing sleeve 241. When forming the gradation image shown in FIG. 4A, the developing sleeve 241 is transferred from the developing sleeve 241 to the photosensitive drum 21 when the right solid image is formed as compared with the case where the left solid image is formed. A large amount of toner moves. Accordingly, when a solid black image is formed, the toner amount on the developing sleeve 241 is reduced as compared with the case where a solid white image is formed. Therefore, the distance between the photosensitive drum 21 and the developing sleeve 241 is increased, and the output current value is increased. Decrease. That is, the distance between the developing sleeve 241 and the photosensitive drum 21 varies depending on the toner image to be formed, and the output current value of the developing bias varies.

  As described above, when the driving state of the developing sleeve 241 is determined using the output current value flowing through the developing sleeve 241, the output current value varies depending on the image to be formed. Therefore, in this embodiment, the gradation image shown in FIG. 4A is formed, and the change in the output current value of the developing bias with respect to each toner density is stored in a memory (not shown). Then, based on the output current value for each toner density, a threshold value for determining the driving state of the developing sleeve 241 for each toner density of the formed image is calculated. Accordingly, it is possible to determine the driving state of the developing sleeve 241 by comparing the output current value at the time of actual image formation with the threshold value of the output current value of the toner density corresponding to the image to be formed. . At this time, when the difference between the threshold value of the output current value stored in the memory (storage means) and the output current value at the time of actual image formation is large, it is determined that the driving state of the developing sleeve 241 is abnormal. Here, the determination is made based on a difference greater than or equal to a predetermined value because the output current value may differ depending on the formed image even if the toner density is the same.

In addition, the output current value flowing through the developing sleeve 241 varies depending on the apparatus depending on the distance between the photosensitive drum 21 and the developing sleeve 241 and the tolerance of the material. However, as described above, by storing the output current value when an image corresponding to each toner density is formed and setting it as a threshold value based on each density, a threshold value suitable for each apparatus can be set.

Next, a control configuration for determining the driving state of the developing sleeve 241 in this embodiment will be described with reference to FIG.
FIG. 5 is a flowchart illustrating the control operation of the control unit 200 when determining the driving state of the developing sleeve 241 in the present embodiment.

  When receiving an instruction to start an image forming operation by the user via the operation unit 205, the control unit 200 determines the toner density of the image from the received print job (S501). Based on the toner density determined in S501, a threshold value of the output current value for each toner density stored in a memory (not shown) is calculated (S502).

  Thereafter, the engine controller 202 of the control unit 200 drives the main motor 211 and the development clutch 212 to operate the development sleeve 241 and the stirring member 242, and applies a development bias to the development sleeve 241 via the high-pressure control unit 203. Thus, an image forming operation for creating an image is started (S503). At this time, the drive by the main motor 211 is also transmitted to the photosensitive drum 21 and the registration roller pair 15 via a transmission mechanism (not shown).

  Accompanying the start of the image forming operation, the current detection unit 204 starts acquiring the output current value of the developing bias (S504). Furthermore, it is determined whether or not the difference between the threshold value of the output current value calculated in S502 and the output current value at the time of image formation acquired in S504 is greater than or equal to a predetermined value (S505). If the difference at this time is not equal to or larger than the predetermined value (No in S505), it is determined that the driving of the developing sleeve 241 is normal, and the process proceeds to S506. In S506, it is determined whether or not the accepted print job has been completed. If the print job has not been completed (No in S506), the process returns to S501 to continue the print job. If the received print job has ended (S506: Yes), the flowchart of FIG. 5 ends.

  If the difference between the threshold value of the output current value calculated in S502 and the output current value at the time of image formation acquired in S504 is greater than or equal to a predetermined value in the determination in S505 (YES in S505), the developing sleeve 241 is abnormally driven. The job is interrupted (S507). Then, it is determined whether or not the subsequent sheet remains in the apparatus (S508). If the subsequent sheet does not remain in the apparatus (No in S508), the process proceeds to S510. If the subsequent sheet remains in the apparatus (Yes in S508), the sheet is discharged from the sheet discharge unit 40 to the outside of the apparatus without forming an image on the sheet (S509).

  Thereafter, the job data interrupted in S507 is stored in a memory (not shown) or the like, and job data backup processing is performed (S510). This is a process for enabling the interrupted job to be resumed when an abnormality that has occurred in driving of the developing sleeve 241 is improved by component replacement by a service person.

Then, the control unit 200 notifies the user of an error by displaying on the display monitor of the operation unit 205 that an abnormality has occurred in the developing sleeve 241 and indicating that the printing operation is impossible (S511).

<Other embodiments>
In the embodiment described above, the threshold value of the output current value for each toner density is acquired in advance. However, the present invention is not limited to this. For example, a configuration may be adopted in which a threshold value of an output current value for each toner concentration is acquired once when an apparatus is assembled or installed, and the threshold value is read from a memory at the time of a print job. Alternatively, the threshold may be acquired by forming an image that can acquire the threshold of the output current value corresponding to each toner density, such as a gradation image, at the beginning of the print job.

  In the above-described embodiment, the output current value (threshold value) for each toner density is acquired by forming a gradation image. However, the output current value for each toner density can be acquired even for other images. Any image can be used.

  In the above-described embodiment, the threshold value for each toner density is compared with the actual output current value. However, the average of the threshold value in the predetermined section and the average of the actual output current value for each image to be formed are calculated. The structure to compare may be sufficient. Further, it may be determined that an abnormality has occurred in driving of the developing sleeve 241 when the difference between the threshold value and the actual output current value is equal to or greater than a predetermined interval.

In the above-described embodiment, the threshold value of the output current value for each toner concentration is acquired. However, without acquiring the threshold value for each toner concentration, a change in potential difference between the photosensitive drum 21 and the developing sleeve 241 or a change in current value is obtained. Based on the above, it may be determined that an abnormality has occurred in the driving of the developing sleeve 241.

A ... Image forming apparatus 20 ... Image forming section 21 ... Photosensitive drum (image carrier)
24 ... Developer (developing means)
200 ... Control unit 202 ... Engine controller (determination means, acquisition means)
203 ... High voltage control unit 204 ... Current detection unit 211 ... Main motor (drive means)
212 ... Development clutch 241 ... Development sleeve

Claims (6)

An image carrier capable of carrying a developer image;
Developing means for forming a developer image on the image carrier;
Driving means for driving the image carrier and the developing means;
Determination means for determining a driving state of the developing unit based on a state of a current value between the image carrier and the developing unit when a developer image is formed on the image carrier. An image forming apparatus. The determination means is a predetermined value determined based on a current value flowing through the developing means when a developer image is formed on the image carrier and a developer concentration of the developer image formed on the image carrier. The image forming apparatus according to claim 1, wherein an abnormality in driving of the developing unit is determined based on a difference from a current value. The image forming apparatus further includes an acquisition unit configured to acquire a current value flowing through the developing unit when a developer image for acquiring a predetermined current value based on the developer concentration is formed on the image carrier. The image forming apparatus according to claim 2. When the difference between the current value flowing through the developing unit and the predetermined current value based on the developer concentration acquired by the acquiring unit is greater than or equal to a predetermined value, the determination unit has an abnormality in driving the developing unit. The image forming apparatus according to claim 3, wherein the image forming apparatus is determined to have occurred. The acquisition unit acquires a predetermined current value based on the developer concentration by forming a gradation image having a plurality of developer concentrations on the image carrier by the developing unit. The image forming apparatus according to claim 3 or 4. A storage unit that stores in advance a predetermined current value based on the developer concentration acquired by the acquisition unit;
The determination unit is based on a difference between a current value flowing through the developing unit when a developer image is formed on the image carrier and a predetermined current value based on the developer concentration stored in the storage unit. The image forming apparatus according to claim 3, wherein an abnormality in driving of the developing unit is determined.

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