JP2008287098A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique to surely prevent carrier from adhering to a photoreceptor in emergency stop, and to suppress a decrease in toner concentration after the emergency stop to actualize rapid startup. <P>SOLUTION: The image forming apparatus includes a control part which controls a power source part so as to apply second bias voltage nearer to potential in a non-image area than first bias voltage when carrying out the emergency stop of developing operation, and controls a toner supply part so as to supply the predetermined amount of toner when performing restoring operation from the emergency stop. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus having a developing portion of a magnetic brush developing system.

In an electrophotographic image forming apparatus, a magnetic brush developing method using a two-component developer is widely used. Also, in recent digital image forming apparatuses, it is common to form an electrostatic latent image in which the non-image area is close to the charged potential of the photoconductor and the image area is close to the ground potential. In order to develop the latent image, development in which the potential of the developing roller (development bias potential) is controlled to be close to the charging potential, so-called reversal development, is frequently used.
In the reverse development, the control of the developing bias voltage at the time of emergency stop has to be more complicated than the development in which the potential of the developing roller is controlled to be close to the ground potential, that is, the so-called forward rotation development. Here, the emergency stop is a process in a case where an image forming operation being executed is stopped as quickly as possible due to occurrence of an event such as a paper jam, for example. The image forming operation includes a developing operation.

  The reason why the control of the developing bias voltage becomes complicated at the time of emergency stop is as follows. As a specific example, a case will be described as an example where the photosensitive member is negatively charged, and thus the developing bias voltage is also negatively charged. At the time of emergency stop, even if the driving of the photosensitive member is stopped, the photosensitive member and the developing roller are not stopped immediately due to the inertia of the driving system, and the surface continues to move for a while. Therefore, development is performed in the developing section until both stop. In this specification, the developing operation at the time of an emergency stop refers to development that is performed after the driving of the photosensitive member is stopped until the both stop. Even if charging is stopped simultaneously with the emergency stop, the non-image area on the surface of the photosensitive member that passes through the developing unit has a charged potential until the surface of the photosensitive member at the portion facing the charger reaches the developing unit. If the application of the developing bias voltage is stopped simultaneously with the emergency stop, and the developing roller becomes the ground potential, the potential of the non-image area becomes negative than the potential of the developing roller (ground potential), and the potential difference is almost equal to the charging voltage. Is equal to When such a large potential difference occurs between the non-image area and the developing roller, the carrier in the developer adheres to the surface of the photoreceptor due to electrostatic force. The adhered carrier damages the surface of the photoreceptor and the cleaning device.

Therefore, at the time of an emergency stop, it is required to devise the charge voltage, the developing bias voltage, and the stop timing so that the carrier does not adhere to the photoconductor. In this regard, there is known a technique in which charging is stopped immediately at the time of emergency stop, and drum driving is stopped after driving the photosensitive drum until the charging stop area reaches the developing area (see, for example, Patent Document 1). This is intended to prevent wasteful adhesion of toner to the surface of the photosensitive member during an emergency stop or subsequent startup. In addition, there is known a control that controls the development bias application stop timing after the stop timing of the developing roller during an emergency stop (see, for example, Patent Document 2). This is intended to prevent the carrier from adhering to the photoreceptor during an emergency stop.
JP-A-10-254310 JP 2000-75663 A

As in the prior art described above, or using a method different from that, a device for suppressing wasteful consumption of toner during an emergency stop and a device for preventing the carrier from adhering to the photoconductor during an emergency stop have been made. Yes. However, if an attempt is made to reliably prevent the carrier from adhering to the photoreceptor during an emergency stop, a certain amount of toner consumption must be allowed. In other words, during an emergency stop, if the potential of the developing roller with respect to the surface potential of the photosensitive member is brought close to the potential of the non-image area to reliably prevent carrier adhesion, the potential of the image area or the potential of the non-charged area and the development The potential difference from the roller potential becomes large, and the area is developed and the toner is consumed.
Usually, the developing unit is provided with a sensor (toner density sensor) for detecting the ratio of toner and carrier in the inside thereof, that is, the toner concentration, and the toner concentration in the developing unit is maintained at a predetermined value. The replenishment amount is controlled. However, control of toner replenishment based on a detection signal from the toner density sensor is suspended until the development unit is stopped and then restarted until the toner and carrier states in the development unit are stabilized. Thereafter, after the toner consumed for the emergency stop is replenished to a predetermined toner density, the subsequent image forming operation is started.

  Then, when resuming after an emergency stop, a toner replenishment period is inserted before resuming the image forming operation, so that the time required for start-up after the emergency stop becomes longer. In particular, this tendency tends to increase after repeated emergency stops.

  The present invention has been made in consideration of the above-described circumstances, and can reliably prevent carrier adhesion to the photoreceptor during an emergency stop and suppress a decrease in toner concentration after the emergency stop. Thus, a method capable of promptly starting up is provided.

  The present invention has an electrophotographic layer having a substrate and a photosensitive layer formed on the surface thereof, and an electrostatic latent image having a potential level corresponding to each of an image area and a non-image area is formed on the photosensitive layer. A magnetic brush comprising a photosensitive member and a developing roller disposed opposite to the photosensitive layer, and comprising a toner and a carrier charged with opposite polarities on the peripheral surface of the developing roller; A developing unit that attaches toner to the image area by electrostatic force, a power supply unit that applies a bias voltage between the base of the photoreceptor and the peripheral surface of the developing roller, and a toner supply that supplies toner to the developing unit The first bias voltage is applied as the bias voltage during the development operation, and the second bias voltage closer to the potential of the non-image area than the first bias voltage is applied when the development operation is urgently stopped. In Controls the source unit, and, upon return from the emergency stop, to provide an image forming apparatus, characterized in that it comprises a control unit for controlling the toner supply section to supply a predetermined amount of toner.

  In the image forming apparatus of the present invention, the control unit changes the bias voltage at the time of emergency stop from the first bias voltage to the second bias voltage, so that the photosensitive layer is compared with the case where the first bias voltage is held. It is possible to more reliably prevent carrier adhesion to the substrate. Moreover, since a predetermined amount of toner is replenished during the return operation from the emergency stop, it is possible to suppress a decrease in toner concentration after the emergency stop and to quickly start up.

Here, the photoreceptor is not particularly limited in shape and type as long as it can form an electrostatic latent image on the surface, and may be a known one. The shape may be, for example, a drum shape or a belt shape. The type may be, for example, an organic photoreceptor, or a selenium-based or amorphous silicon-based photoreceptor. The toner and carrier may be well known.
For example, if the photosensitive member has a negative charge characteristic, the toner is negatively charged and the carrier is positively charged. Conversely, if the photoreceptor is positively charged, the toner is positively charged and the carrier is negatively charged. This is well known in the electrophotographic art.

Hereinafter, preferred embodiments of the present invention will be described.
The predetermined amount of the toner may be a predetermined amount so as to replenish the toner exiting from the developing unit while applying the second bias voltage.

  The toner replenishing portion is disposed so as to close an opening communicating with the developing portion, and has a toner replenishing roller having a recess on the surface thereof, and the control portion rotates the toner replenishing roller by a predetermined angle. Thus, it may be controlled to replenish a predetermined amount of toner.

  The control unit further includes a drive unit that drives the photoconductor during the developing operation, and a charging unit that is disposed opposite to the surface of the photoconductor and charges the photoconductor layer during the developing operation. When the operation of the driving unit and the charging unit is further controlled to stop the developing operation in an emergency, the driving of the photoconductor is stopped, and the charging operation of the charging unit is stopped, and a predetermined time after the charging operation is stopped. The application of the bias voltage may be stopped. In this way, it is possible to prevent the carrier from adhering to the photoreceptor.

  Further, the predetermined time may be a time determined based on a time until the surface portion of the photoconductor facing the charging portion reaches a position facing the developing roller when the charging operation is stopped.

The charging unit includes a discharging unit and a grid unit, and the power unit applies a voltage to the developing roller and a voltage having a potential difference within a predetermined range with respect to the voltage. It may be configured to be able to.
The various preferable aspects shown here can also be combined.

  Hereinafter, the present invention will be described in more detail with reference to the drawings. In addition, the following description is an illustration in all the points, Comprising: It should not be interpreted as limiting this invention.

Overall Configuration of Image Forming Apparatus Before proceeding to the description of the features of the present invention, the configuration of the image forming apparatus that is the premise thereof will be described.

  FIG. 6 is an explanatory view showing the mechanical structure of an electrophotographic printer which is an aspect of the image forming apparatus of the present invention. In FIG. 6, the image forming apparatus 11 is an image of image data read by an image reading apparatus (not shown) or print data input from an external device (for example, an image processing apparatus such as a personal computer) via a communication line. , And the formed image is transferred onto a printing sheet (printing sheet) and output.

  In the image forming apparatus 11, units for the electrophotographic process are arranged around the photosensitive drum 202, and an image is formed by these operations. The photosensitive drum 202 is formed by forming a photosensitive layer on the peripheral surface of a conductive base material (for example, aluminum). The substrate is electrically grounded. Around the photosensitive drum 202, a charger 203, a developing unit 200, a transfer roller 207, a cleaning unit 208, an optical scanning unit 204, and the like are arranged in this order. The photosensitive drum 202 is driven by a main motor (not shown) and rotates at a constant speed.

  The charger 203 charges the surface of the photosensitive drum 202 uniformly. The charger 203 of this embodiment is of a scorotron type having a corona discharge part and a control grid. The surface of the photosensitive drum 202 is charged to a potential approximately equal to the grid voltage. Note that other methods such as a charging roller may be used for the charger 203. The optical scanning unit 204 scans a light beam on the uniformly charged photosensitive drum 202 to form an electrostatic latent image on the surface thereof. The developing unit 200 accommodates a developer therein, and visualizes the electrostatic latent image written by the optical scanning unit 204 with toner. The developer is composed of toner and a carrier, and the toner is agitated in the developing unit 200 and charged with a positive polarity by friction with the carrier. The developing unit 200 is provided with a toner storage portion 171 that stores toner supplied thereto.

The transfer roller 207 is a roller for transferring an image visualized on the photosensitive drum 202 onto a print sheet and forming a visible image on the sheet. The transfer roller 207 is made of a metallic shaft portion and a conductive elastic material (for example, EPDM, urethane foam, etc.) wound around the peripheral surface thereof. The transfer roller 207 is driven by the process drive motor, and a voltage from a transfer power source described later is applied to the shaft portion. A transfer belt 206 extending on the downstream side in the transport direction is hung on the transfer roller 207. The transfer belt 206 is made of, for example, a resin or rubber having conductivity so that the volume resistivity has a predetermined value (for example, a range of 1 × 10 ⁹ to 1 × 10 ¹³ Ω · cm).

  The cleaning unit 208 removes the developer remaining on the photosensitive drum 202.

  Under the image forming apparatus 11, a sheet supply tray 201 that is built in the main body of the image forming apparatus 11 is disposed. The sheet supply tray 201 is a tray that stores print sheets. The printing sheets stored in the sheet supply tray 201 are separated one by one by the pickup roller 209 and the like, conveyed to the registration roller 210, and synchronized with the image formed on the photosensitive drum 202 by the registration roller 210. Then, the toner is sequentially supplied between the transfer roller 207 and the photosensitive drum 202. A voltage for transfer (transfer voltage) is applied to the transfer roller 207. The toner developed and attached on the photosensitive drum 202 is transferred onto the sheet by a transfer voltage.

  A fixing unit 205 is disposed in the image forming apparatus 11. The fixing unit 205 is a nip portion where the heating roller 211 and the pressure roller 212 are in contact with each other. The toner transferred onto the sheet is melted by heat and fixed to the sheet by pressure.

The sheet that has passed through the fixing unit 205 is further conveyed and discharged to the sheet discharge tray 213.
Although FIG. 6 illustrates a monochrome image forming apparatus, the present invention is not limited to this and can be applied to a full-color image forming apparatus.

Configuration of Developing Unit In this embodiment, details of the developing unit 200 and the toner container 171 will be described. FIG. 7 is a cross-sectional view showing details of the developing unit 200 and the toner container 171 in the image forming apparatus 11 of FIG. As shown in FIG. 7, the developing roller 187 of the developing unit 200 is disposed so as to face the surface of the photosensitive drum 202. The developing roller 187 supplies toner to the surface of the photosensitive drum 202 and attaches the toner to the electrostatic latent image to make a visible image. The developing roller is driven by the process drive motor. The surface of the developing roller is made of a non-magnetic conductive member (for example, aluminum material), and a voltage is applied to the conductive member from a high voltage power source. In the developing unit 200, the toner density sensor 186 detects the toner density so as to constantly supply a predetermined density of toner around the developing roller. A control unit (not shown) obtains the output of the toner density sensor 186 and controls the supply of toner. The toner is supplied from the toner container 171. The toner storage unit 171 includes a toner hopper 178 that stirs toner and a toner bottle mounting unit 172 that mounts a cylindrical toner bottle 174. The toner bottle 174 is attached by the user. Toner bottle 174 contains toner. The toner in the toner bottle 174 is transported to the toner supply port 173 by a toner transport mechanism (not shown). The toner transport mechanism is driven by a toner transport motor (see FIG. 4) described later, and transports toner.

  The toner supplied from the toner supply port 173 is guided into the toner hopper 178. In the toner hopper 178, a stirring roller 175 that is driven by a toner supply motor (not shown) and rotates in the direction of the arrow J1 is provided. The agitation roller 175 agitates the toner to make the fluidity uniform, and conveys the toner to the toner reservoir 179 near the toner supply roller 176. Further, the toner storage unit 171 is provided with a toner transport sensor 177 that detects that the toner in the toner hopper 178 is less than a predetermined amount and generates a signal for supplying toner from the toner bottle. The toner conveyance sensor 177 is a light reflection detection sensor that detects the presence or absence of toner in the toner hopper 178 using the principle of irradiating the detection target with light and determining the state of the target based on how the light is reflected. In accordance with the output of the toner transport sensor 177, a control unit (not shown) controls the operation of the toner transport mechanism. As a result, the toner amount in the toner hopper 178 is kept within a predetermined range.

  The toner supply roller 176 is a roller for supplying a predetermined amount of toner to the developing tank 200. The toner replenishing roller 176 is formed, for example, by winding a porous elastic body such as ester polyurethane foam, so-called sponge, around a solid shaft made of stainless steel. Below the toner supply roller 176, a slit-shaped toner dropping opening 183 that communicates with the developing tank 200 is provided. The toner supply roller 176 is disposed so as to cover the entire surface of the toner dropping opening 183 with the elastic porous member. The toner supply roller 176 is driven by the toner supply motor and rotates in the direction of arrow J2.

  When the toner supply roller 176 rotates, the toner in the toner reservoir 179 enters the hole on the surface of the elastic porous member. When the toner reaches the toner drop opening 183, the surface of the toner supply roller 176 contacts the edge of the toner drop opening 183 and deforms. Due to the deformation, the toner is separated from the hole, and falls into the developing tank 200 from the toner dropping opening 183 by its own weight.

  When the toner supply roller 176 stops, the entire surface of the toner drop opening 183 is covered with the elastic porous member of the toner supply roller 176 in that state. Therefore, when the toner supply roller 176 is stopped, the toner in the toner hopper 178 does not move to the developing unit 200.

  The toner dropped into the developing unit 200 from the toner dropping opening 183 is transported by the transport screw 184 in the developing tank and stirred with the carrier by the stirring screw 185. Further, it is supplied to the surface portion of the developing roller 187 by the action of the stirring screw 185.

  A toner density sensor 186 is provided at the bottom of the developing unit 200. The toner density sensor 186 detects the density of toner supplied to the surface portion of the developing roller 187. Here, the toner concentration refers to the ratio of the weight of the toner to the weight of the developer formed by combining the carrier and the toner. When the electrostatic latent image on the photosensitive drum 202 is developed, toner is consumed. When the control unit (not shown) recognizes that the toner in the developing unit 200 has decreased by a signal from the toner density sensor 186, the control unit rotates the toner supply motor. When the toner supply motor rotates, the stirring roller 175 and the toner supply roller 176 rotate, and the toner is supplied into the developing unit 200. Further, the control unit stops the toner supply motor when the toner density reaches a predetermined value. In this way, the toner density in the developing unit 200 is controlled within a predetermined range.

Control of Development Operation at Emergency Stop Next, a functional configuration relating to development operation control in the image forming apparatus 11 of FIG. 6 will be described. FIG. 2 is a block diagram showing a functional block configuration related to the control of the developing operation. In FIG. 2, the emergency stop event detection unit 12 is a block that detects the occurrence of an event that requires an emergency stop. A specific example is a sheet detection sensor disposed in the sheet conveyance path. A different example is an abnormality detection circuit (not shown) provided for detecting an abnormality of the charger 203. A further different example is an abnormality detection circuit (not shown) that detects the lock of the main motor.

  The control unit 13 controls the operation of the image forming apparatus 11, and a specific example is one in which a microcomputer, a memory element, and an input / output circuit are mounted on a substrate. The main motor drive unit 15 is a drive circuit that drives the above-described main motor, and is controlled by a control signal from the control unit 13. The toner supply motor driving unit 17 is a drive circuit that drives the above-described toner supply motor, and is controlled by a control signal from the control unit 13. The high-voltage power supply 21 includes a charger power supply unit that applies a voltage to the corona discharge unit of the charger 203, a grid bias power supply unit that applies a voltage to the charging control grid, and a development bias power supply that applies a development bias voltage to the developing roller 187. And a transfer power supply unit for applying a voltage to the transfer roller 207. However, the grid bias power supply unit and the development bias power supply unit may generate a voltage from one power supply circuit.

  The image processing unit 31 is a block that processes image data read by the image reading apparatus and print data input from an external device via a communication line. Specifically, it is composed of an image processing unit in which an LSI having an image processing circuit integrated therein, a memory, and a CPU for processing image data are mounted on a substrate. The LD driver 33 controls the light emission of the laser element disposed in the optical scanning unit 204 based on the output signal from the image processing unit 31, and converts the intensity of the light beam that scans the photosensitive drum 202 into image data. It is a circuit that changes in response.

  FIG. 4 is a time chart showing how the controller 13 stops the main motor, turns off the charger, and controls the developing bias voltage after an emergency stop event occurs. As shown in FIG. 4, when the emergency stop event detection unit 12 detects an emergency stop event, the control unit 13 stops driving the main motor. However, due to the inertia of the drive type, it takes a while for the main motor to completely stop. In FIG. 4, this time is indicated as “overrun time”. Further, the control unit 13 changes the developing bias voltage from the voltage value DVbias1 during the developing operation to the voltage value DVbias2 at the time of emergency stop. As a specific example, as shown in FIG. 3 to be described later, DVbias1 is −400V, and DVbias2 is −525V.

  The control unit 13 turns off the charger power supply unit and turns off the grid bias power supply unit after the elapse of the period t1 after stopping the driving of the main motor. Further, after the elapse of the period t2, the developing bias voltage is turned off.

  FIG. 3 shows the relationship between the potential VL corresponding to the darkest part of the image area, the potential V0 of the non-image area (equal to the control grid bias potential Vgrid), and the development bias potential DVbias during normal development operation and emergency stop. It is explanatory drawing which shows. (A) shows a normal developing operation, and (b) shows an emergency stop. In FIG. 3, | V2 | is called a cleaning field and is a potential difference between the potential of the developing roller, that is, the potential of the developing bias potential DVbias and the potential of the non-image area. This potential difference is ensured so that toner does not adhere to the non-image area. In other words, it is a potential difference that gives a force to electrostatically repel non-image areas and toner. However, for a carrier charged to a polarity opposite to that of the toner, it becomes a suction force to the non-image area. As the cleaning field increases, the suction force increases, and the carrier adheres to the photoreceptor by overcoming the magnetic force holding the carrier on the developing roller. Therefore, at the time of emergency stop, the cleaning field is made smaller than that at the time of the normal developing operation to reliably prevent carrier adhesion. During an emergency stop, the moving speed of the photosensitive member and the developing roller is slower than usual, and the relative speed of the two changes. This is to prevent the carrier from adhering even under conditions where the carrier easily adheres to the photoreceptor.

  FIG. 1 is a flowchart showing a development control procedure executed by the control unit 13 at the time of emergency stop and at the time of start-up after the emergency stop. A processing procedure will be described with reference to FIG. When an event that should be urgently stopped occurs, the control unit 13 stops the light emission of the laser elements in the main motor and the optical scanning unit 204 (step S11). This corresponds to time t0 in FIG. The main motor continues to move for about 1 second after stopping due to inertia of the drive system. Furthermore, the control unit 13 switches the developing bias voltage from DVbias1 which is a predetermined voltage value during the developing operation to DVbias2 which is a predetermined voltage value at the time of emergency stop. (Step S13). Thereafter, the control unit waits until time t1 is reached (step S15), and turns off the application of the voltage of the charging control grid (step S17). Thereafter, the control unit 13 waits for further elapse of time t2 (step S19), and then turns off the application of the developing bias voltage (step S21). Then, it waits for an emergency stop cancellation event (step S23). Specifically, the emergency stop cancellation event is, for example, as follows. Assume that an emergency stop occurs due to a paper jam. Assume that after the stoppage, the paper in the machine is removed by the user and a cabinet (not shown) is closed. The control unit 13 obtains an output of a sensor (not shown) that detects the open / close state of the cabinet, recognizes that the cabinet is closed, and uses a signal from a sheet detection sensor (not shown) arranged in the sheet conveyance path as a trigger. Confirm. When none of the sensors detects the presence of the sheet, the control unit 13 determines that the return condition is satisfied. This is an emergency stop cancellation event.

  After the occurrence of the emergency stop cancellation event, the control unit 13 turns on the main motor as a startup process (step S25). Further, the voltage value DVbias1 is applied as the developing bias voltage (step S27). Further, the charging grid voltage is turned on (step S29). In this way, the state of the photoconductor is initialized in a process. Further, during initialization of the photoreceptor, the control unit 13 replenishes the developing unit with a predetermined amount of toner by 200. That is, the toner supply roller 176 is rotated (step S31), and after a predetermined amount of toner is supplied (step S33), the rotation of the toner supply roller 176 is stopped (step S35). Here, the toner supply amount is substantially proportional to the rotation angle of the toner supply roller 176. The toner replenishing roller 176 is driven by a toner replenishing motor and rotates at substantially the same speed. As a result, the toner replenishment amount is substantially proportional to the rotation time of the toner replenishment motor. Therefore, the toner motor may be rotated for a predetermined time in order to supply a predetermined amount of toner. The amount of toner to be replenished per unit time may be determined in advance through experiments.

  The amount of toner consumed in one emergency stop may be obtained in advance by experiments. FIG. 5 is a graph of an experimental example for obtaining the toner consumption during an emergency stop. The horizontal axis of the graph represents the number of emergency stops, and the vertical axis represents the total weight of the developing unit 200 and the toner concentration in the developing unit 200. Since the difference between the initial mass of the developing unit 200 and the mass after repeating 300 emergency stops is 105 g, the toner consumption in one emergency stop is calculated as 0.35 g.

The power supply for developing bias, the power supply for biasing the grid section, and the power supply section for developing the grid bias and the power supply section for developing bias can be individually controlled and controlled by the control section, but generate voltage from one voltage source. You may comprise. The latter case will be described. FIG. 8 is an explanatory diagram showing a configuration in the case where the grid bias power supply unit and the development bias power supply unit are composed of one voltage source.

In FIG. 8, a power supply unit Vbias is a voltage source that supplies a grid bias voltage and a development bias voltage. Zener voltages V _Z1 , V _Z2 , and V _Z3 of the Zener diodes ZD ₁ , ZD ₂ , and ZD ₃ are 50V, 150V, and 75V, respectively. The zener diodes ZD ₁ and ZD ₂ are for regulating the potential difference between the grid bias and the developing bias during normal operation in the range of 50 to 150V. The switch SW is turned on and off by the control unit. At the time of emergency stop, the control unit turns on the switch to make ZD ₃ conductive. In this case, the potential difference between the grid bias and the developing bias is regulated to a range of 50 to 75V. That is, the Zener diode ZD ₃ is for regulating the upper limit of the potential difference between the grid bias and the developing bias at the time of emergency stop to 75V.

When the potential difference of the grid and the developing bias is increased beyond 50 V, the transistor Q ₁ is turned on, whereby the transistor Q ₂ is turned off. On the other hand, when the potential difference grid and the developing bias is 50V or less, the transistor Q ₁ is turned off. This transistor Q ₂ is turned on to raise the grid bias voltage. As a result, a potential difference of 50 V or more is secured as the potential difference between the grid bias and the developing bias. The resistors R ₁ and R ₃ are for preventing the transistors Q ₁ and Q _{2 from} being turned on due to malfunction.

  In addition to the embodiments described above, there can be various modifications of the present invention. These modifications should not be construed as not belonging to the scope of the present invention. The present invention should include the meaning equivalent to the scope of the claims and all modifications within the scope.

It is a flowchart which shows the procedure of the development control which the control part 13 performs at the time of emergency stop and the starting after an emergency stop. It is a block diagram which shows the structure of the functional block regarding control of developing operation. FIG. 6 is an explanatory diagram showing a relationship among a potential VL corresponding to the darkest part of an image area, a potential V0 of a non-image area, and a development bias potential DVbias during a normal development operation and during an emergency stop. 6 is a time chart showing how the control unit stops the main motor, turns off the charger, and controls the developing bias voltage after an emergency stop event occurs. It is a graph of the experiment example which calculates | requires the toner consumption at the time of an emergency stop. 1 is an explanatory diagram showing a mechanical structure of an electrophotographic printer which is an aspect of an image forming apparatus according to the present invention. FIG. FIG. 7 is a cross-sectional view illustrating details of a developing unit 200 and a toner storage unit 171 in the image forming apparatus 11 of FIG. 6. In this embodiment, it is explanatory drawing which shows the structure of the power supply part for grid bias, and the power supply part for developing bias.

Explanation of symbols

11 Image forming apparatus 171 Toner storage unit 172 Toner bottle mounting unit 173 Toner supply port 174 Toner bottle 175 Stirrer roller 176 Toner supply roller 177 Toner transport sensor 178 Toner hopper 179 Toner reservoir 183 Toner drop opening 184 Transport screw 185 Stir screw 186 Toner Density sensor 187 Developing roller 200 Developing unit 201 Sheet supply tray 202 Photosensitive drum 203 Charger 204 Optical scanning unit 205 Fixing unit 206 Transfer belt 207 Transfer roller 208 Cleaning unit 209 Pickup roller 210 Registration roller 211 Heating roller 212 Pressure roller 213 Sheet Discharge tray

Claims (6)

An electrophotographic photosensitive member having a substrate and a photosensitive layer formed on the surface thereof, and an electrostatic latent image having high and low potentials corresponding to an image region and a non-image region, respectively, is formed on the photosensitive layer;
A magnetic brush comprising a developing roller disposed opposite to the photosensitive layer and composed of toner and a carrier charged with opposite polarities is formed on the peripheral surface of the developing roller, and is transferred to the image area of the electrostatic latent image. A developing unit that attaches toner by electrostatic force;
A power supply unit for applying a bias voltage between the photosensitive body and the peripheral surface of the developing roller;
A toner supply unit for supplying toner to the developing unit;
A power supply unit applies a first bias voltage as the bias voltage during the developing operation, and applies a second bias voltage closer to the potential of the non-image area than the first bias voltage when the developing operation is urgently stopped. And a control unit that controls the toner supply unit so as to replenish a predetermined amount of toner during a return operation from an emergency stop.   The image forming apparatus according to claim 1, wherein the predetermined amount of toner is a predetermined amount so as to replenish the toner exiting from the developing unit while applying the second bias voltage. The toner replenishing portion is disposed so as to close an opening communicating with the developing portion, and has a toner replenishing roller having a concave portion on the surface thereof.
The image forming apparatus according to claim 1, wherein the control unit performs control so as to supply a predetermined amount of toner by rotating a toner supply roller by a predetermined angle. A drive unit for driving the photosensitive member during the developing operation;
A charging unit disposed opposite to the surface of the photoreceptor and charging the photoreceptor layer during the developing operation;
The control unit further controls operations of the driving unit and the charging unit,
4. When the development operation is urgently stopped, the driving of the photosensitive member is stopped, the charging operation of the charging unit is stopped, and the application of the bias voltage is stopped a predetermined time after the charging operation is stopped. The image forming apparatus according to any one of the above.   5. The image according to claim 4, wherein the predetermined time is a time determined based on a time until the surface portion of the photoreceptor facing the charging portion reaches a position facing the developing roller when the charging operation is stopped. Forming equipment. The charging unit has a discharge unit and a grid unit,
The image forming apparatus according to claim 4, wherein the power supply unit is configured to apply a voltage to the developing roller and to apply a voltage having a potential difference within a predetermined range to the voltage to the grid unit. apparatus.

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