JP2022114923A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus capable of suppressing adhesion of toner to a non-image area of an image carrier and reducing toner consumption.SOLUTION: An image forming apparatus comprises: an image carrier whose surface is formed with a photosensitive layer; a charging member; a developing device; a charging voltage power source; a driving device; and a control unit. The charging member charges the surface of the image carrier in a contact state or a non-contact state with the surface of the image carrier. The developing device has a developer carrier for carrying a developer including toner, and develops an electrostatic latent image formed on the surface of the image carrier. The charging voltage power source applies a charging voltage composed of only a DC voltage to the charging member. The driving device rotationally drives the image carrier. The control unit controls the charging voltage power source and the driving device, and applies the charging voltage over the whole area in a period when the image carrier is being rotationally driven.SELECTED DRAWING: Figure 4

Description

The present invention relates to electrophotographic image forming apparatuses such as copiers, laser printers, and facsimiles, and more particularly to an image forming apparatus having a charging member that charges the surface of a photosensitive drum in a contact or non-contact state. is.

In an image forming apparatus using an electrophotographic process, a photosensitive drum is provided as an image carrier, and after the photosensitive drum is uniformly charged by a charging device, the photosensitive drum is irradiated with light by an exposure device. to form an electrostatic latent image in which charging is attenuated. Then, the electrostatic latent image is developed into a toner image by a developing device, and a transfer voltage having a polarity opposite to that of the toner is applied to the transfer device to directly transfer the toner image onto a sheet of paper or primarily transfer it onto an intermediate transfer body. After that, secondary transfer is performed on paper, and a series of processes of thermally fixing the toner image on the paper by a fixing device are executed.

In such an image forming apparatus, a phenomenon in which toner adheres to a non-image area (white background portion) of the photosensitive drum (hereinafter referred to as a fogging phenomenon) is a problem. It is the cause of dirt and a decrease in the number of printable sheets due to an increase in toner consumption. In particular, in the case of a two-component development method using a two-component developer containing toner and a magnetic carrier, since the toner on the developing roller is in contact with the photoreceptor drum, an electric field acts to move the toner toward the photoreceptor drum. Even if the toner is not applied, the fogging phenomenon tends to occur easily due to the physical adhesive force.

Conventionally, as described in Japanese Unexamined Patent Application Publication No. 2002-100002, the potential difference between the surface potential of the non-image area of the photosensitive drum and the development voltage applied to the developing roller is maintained at a predetermined value or more, so that the non-image area is removed from the developing roller. A method of suppressing toner migration to the toner has been used. However, if the potential difference is too small, fogging occurs, and if the potential difference is too large, carrier development occurs in which the carrier adheres to the photosensitive drum. .

Therefore, in Patent Document 2, a configuration is used in which the development DC voltage and the development AC voltage are in a steady output state in the image forming area, and the output of only the development AC voltage is changed in the non-image area. The fog phenomenon is suppressed by making the voltage smaller than the steady output or by setting it to zero.

Japanese Unexamined Patent Application Publication No. 2002-278368 JP 2006-163347 A

However, even if the method of Japanese Patent Laid-Open No. 2002-200002 is adopted, it is conceivable that the fogging phenomenon is rather exacerbated by setting the developing AC voltage to be smaller than the steady-state value or to zero in the non-image range.

SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of suppressing adhesion of toner to a non-image area of an image carrier and reducing toner consumption.

In order to achieve the above object, a first configuration of the present invention includes an image carrier, a charging member, a developing device, a charging voltage power source, a developing voltage power source, a driving device, and a control section. It is an image forming apparatus. The image carrier has a photosensitive layer formed on its surface. The charging member charges the surface of the image carrier with or without contact with the surface of the image carrier. The developing device has a developer carrier that carries a developer containing toner, and develops an electrostatic latent image formed on the surface of the image carrier. A charging voltage power supply applies a charging voltage comprising only a DC voltage to the charging member. The driving device rotationally drives the image carrier. The controller controls the charging voltage power supply and the driving device. The controller applies the charging voltage over the entire period during which the image carrier is rotationally driven.

According to the first configuration of the present invention, the charging voltage is continuously applied over the entire period during which the image carrier is rotationally driven. As a result, while the image carrier is rotating, the surface potential of the image carrier rises due to the charging voltage, thereby suppressing the adhesion of toner from the developer carrier to the non-image area of the image carrier. Therefore, it is possible to suppress the occurrence of the fogging phenomenon and reduce the toner consumption.

FIG. 1 is a schematic cross-sectional view showing the overall configuration of an image forming apparatus 100 according to one embodiment of the present invention; FIG. 1 is a partial enlarged view of the periphery of an image forming portion Pa in FIG. FIG. 2 is a block diagram showing an example of a control path of the image forming apparatus 100; Timing chart showing transitions of the driving state of the photosensitive drums 1a to 1d and charging voltage and developing voltage during warm-up in the image forming apparatus 100 according to the first embodiment of the present invention. Timing chart showing transitions of the driving state of the photosensitive drums 1a to 1d and charging voltage and developing voltage during image formation in the image forming apparatus 100 of the first embodiment. Graph comparing changes in toner adhesion amount when the development potential difference (V0-Vdc) is changed with and without applying a developing AC voltage. Timing chart showing transitions of the driving state of the photosensitive drums 1a to 1d and charging voltage and development voltage during warm-up in the image forming apparatus 100 according to the second embodiment of the present invention. Timing chart showing transitions of the driving state of the photosensitive drums 1a to 1d and charging voltage and developing voltage during image formation in the image forming apparatus 100 of the second embodiment. Graph showing changes in toner consumption when the application timings of the charging voltage and developing AC voltage are changed in the example.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram showing the configuration of an image forming apparatus 100 according to an embodiment of the invention, and FIG. 2 is an enlarged view of the vicinity of an image forming portion Pa in FIG. Note that the image forming units Pb to Pd also have basically the same configuration, so description thereof will be omitted. Four image forming units Pa, Pb, Pc, and Pd are arranged in order from the upstream side in the transport direction (the right side in FIG. 1) in the main body of the image forming apparatus 100 (here, a color printer). These image forming units Pa to Pd are provided corresponding to images of four different colors (cyan, magenta, yellow and black). and black images are sequentially formed.

Photoreceptor drums 1a, 1b, 1c and 1d carrying visible images (toner images) of respective colors are provided in these image forming portions Pa to Pd, respectively. Further, an intermediate transfer belt 8 that is entrained around a plurality of rollers including a tension roller 10 and a driving roller 11 and rotates clockwise in FIG. 1 is provided adjacent to each of the image forming portions Pa to Pd. As shown in FIG. 2, around the photosensitive drum 1a, a charging device 2a, a developing device 3a, a cleaning device 5a, and a neutralization lamp 20 are arranged along the drum rotation direction (counterclockwise direction in FIG. 2). A primary transfer roller 6a is arranged with the intermediate transfer belt 8 interposed therebetween.

The photoreceptor drums 1a to 1d are composed of a base tube 19a as a support (conductive base) and a photosensitive layer 19b formed on the surface of the base tube 19a. In this embodiment, a positively-charged single-layer organic photoconductive layer containing a charge generating agent, a charge transporting agent, a binding resin (binder), and a filler is contained in the same layer as the photosensitive layer 19b on the surface of the cylindrical aluminum tube 19a. A photosensitive layer (OPC) is laminated.

The charging devices 2a to 2d have a charging roller 21 that contacts the photosensitive drum 1a and applies a charging voltage (DC voltage) to the surface of the drum, and a charging cleaning roller 23 that cleans the charging roller 21. . In the present invention, in order to reduce the amount of generated ozone and to reduce the cost of the charging voltage power supply 52 (see FIG. 3), a charging voltage consisting of only DC voltage is applied to the charging roller 21 .

The developing devices 3a to 3d are of two-component developing type having two agitating and conveying screws 25 and developing rollers 29, and each of the two-component developing devices contains cyan, magenta, yellow and black toners and magnetic carriers. A predetermined amount of agent is filled. A magnetic brush is formed on the surface of the developing roller 29 using a two-component developer, and the magnetic brush is brought into contact with the surface of the photosensitive drum 1a while a developing voltage having the same polarity (positive) as that of the toner is applied to the developing roller 29. Toner is applied to form a toner image. When the ratio of the toner in the two-component developer filled in each developing device 3a to 3d falls below a specified value due to the formation of the toner image, each developing device 3a to 3d is removed from a toner container (not shown). Toner is supplied to the

When image data is input from a host device such as a personal computer, first, the main motor 40 (see FIG. 3) starts rotating the photosensitive drums 1a to 1d. Further, the rotation of the intermediate transfer belt 8 is started by the belt drive motor 41 (see FIG. 3). Next, the surfaces of the photosensitive drums 1a to 1d are uniformly charged by charging devices 2a to 2d. Then, the exposure device 4 irradiates the photosensitive drums 1a to 1d with light according to the image data to form electrostatic latent images according to the image data. Toner is supplied onto the photosensitive drums 1a to 1d by the developing devices 3a to 3d, and adheres electrostatically to form a toner image corresponding to the electrostatic latent image.

By applying a predetermined transfer electric field between the primary transfer rollers 6a to 6d and the photoreceptor drums 1a to 1d by the primary transfer rollers 6a to 6d, yellow, cyan, magenta and yellow on the photoreceptor drums 1a to 1d are transferred. A black toner image is primarily transferred onto the intermediate transfer belt 8 . Toner and the like remaining on the surfaces of the photosensitive drums 1a to 1d after primary transfer are removed by cleaning devices 5a to 5d.

The transfer paper P onto which the toner image is transferred is accommodated in a paper cassette 16 arranged in the lower part of the image forming apparatus 100 . The transfer paper P is transferred between a secondary transfer roller 9 provided adjacent to the intermediate transfer belt 8 at a predetermined timing via a paper supply roller 12a and a pair of registration rollers 12b, and a nip portion (secondary transfer nip department). The transfer paper P on which the toner image on the intermediate transfer belt 8 is secondarily transferred by the secondary transfer roller 9 is conveyed to the fixing section 7 .

The transfer paper P transported to the fixing section 7 is heated and pressed by the fixing roller pair 13 to fix the toner image on the surface of the transfer paper P, forming a predetermined full-color image. The transfer paper P on which the full-color image has been formed is discharged to the discharge tray 17 by the discharge roller pair 15 as it is (or after being distributed to the reversing conveying path 18 by the branching section 14 and images are formed on both sides).

Next, the control path of the image forming apparatus 100 of the invention will be described. FIG. 3 is a block diagram showing an example of control paths used in the image forming apparatus 100 of the invention. Since various parts of the apparatus are controlled when the image forming apparatus 100 is used, the overall control path of the image forming apparatus 100 is complicated. Therefore, here, the portion of the control path that is necessary for implementing the present invention will be mainly described.

The control unit 90 includes a CPU (Central Processing Unit) 91 as a central processing unit, a read-only memory (ROM) 92, a readable/writable memory (RAM) (Random Access Memory) 93, a temporary A temporary storage unit 94 for temporarily storing image data and the like, a counter 95 for accumulating and counting the number of printed sheets, a control signal for transmitting a control signal to each device in the image forming apparatus 100, and an input signal from the operation unit 60. At least a plurality of (here, two) I/Fs (interfaces) 96 are provided. Also, the control unit 90 can be arranged at any place inside the main body of the image forming apparatus 100 .

The ROM 92 stores a program for controlling the image forming apparatus 100 and data such as numerical values necessary for control that are not changed while the image forming apparatus 100 is in use. The RAM 93 stores necessary data generated during control of the image forming apparatus 100, data temporarily necessary for controlling the image forming apparatus 100, and the like. The ROM 92 (or RAM 93) also stores application timings of charging voltages and developing AC voltages, which will be described later.

Further, the control unit 90 transmits a control signal from the CPU 91 to each part and device in the image forming apparatus 100 through the I/F 96 . Signals and input signals indicating the state of each part and device are transmitted to the CPU 91 through the I/F 96 . Parts and devices controlled by the control unit 90 include, for example, the image forming units Pa to Pd, the exposure device 4, the primary transfer rollers 6a to 6d, the secondary transfer roller 9, the main motor 40, the belt drive motor 41, and the image input. A unit 50, a voltage control circuit 51, an operation unit 60, and the like are included.

The image input unit 50 is a receiving unit that receives image data transmitted from a personal computer or the like to the image forming apparatus 100 . The image signal input from the image input section 50 is converted into a digital signal and sent to the temporary storage section 94 .

The voltage control circuit 51 is connected to a charging voltage power source 52, a developing voltage power source 53, and a transfer voltage power source 54, and operates these power sources according to output signals from the control section 90. According to a control signal from the control circuit 51, the charging voltage power supply 52 applies charging voltage to the charging rollers 21 in the charging devices 2a to 2d. A development voltage power supply 53 applies a development voltage obtained by superimposing a development AC voltage on a development DC voltage to the development rollers 29 in the development devices 3a to 3d. A transfer voltage power supply 54 applies predetermined primary transfer voltage and secondary transfer voltage to the primary transfer rollers 6a to 6d and the secondary transfer roller 9, respectively.

The operation unit 60 is provided with a liquid crystal display unit 61 and LEDs 62 indicating various states. Various settings of the forming apparatus 100 are set to the default state. The liquid crystal display unit 61 indicates the state of the image forming apparatus 100, and displays the image forming state and the number of print copies. Various settings of the image forming apparatus 100 are performed from the printer driver of the personal computer.

(First embodiment)
4 and 5 show the driving states of the photosensitive drums 1a to 1d, the charging voltage applied to the charging roller 21, and the developing voltage applied to the developing roller 29 in the image forming apparatus 100 according to the first embodiment of the present invention. 4 is a timing chart showing changes in voltage; FIG. 4 shows a timing chart during power-on and during warm-up from sleep mode (power saving mode) to a printable state, and FIG. 5 shows a timing chart during image formation. The application control of the charging voltage and the developing voltage in the image forming apparatus 100 of the first embodiment will be described with reference to FIGS. 4 and 5 while referring to FIGS. 1 to 3 as necessary.

First, the warm-up control performed when the image forming apparatus 100 is powered on or returned from sleep mode (power saving mode) will be described. As shown in FIG. 4, when the power of the image forming apparatus 100 is turned on or when an instruction to return from the sleep mode (power saving mode) is received (t1 in FIG. 4), the control unit 90 controls the main motor 40. A signal is transmitted, and rotation of the photosensitive drums 1a to 1d is started. In addition, a control signal is transmitted from the control unit 90 to the charging voltage power source 52 via the voltage control circuit 51, and in synchronization with the start timing of rotation driving of the photosensitive drums 1a to 1d, the charging rollers 21 of the charging devices 2a to 2d are charged. Application of the charging voltage is started.

At this time, the charging voltage applied to the charging roller 21 is stepped through a plurality of intermediate voltages until the surface potentials of the photosensitive drums 1a to 1d are charged to the reference potential during image formation, as will be described later. is the same as the first stage intermediate voltage (V1 in FIG. 5) when the voltage is increased to .

After that, when the warm-up ends (t2 in FIG. 4), the rotational driving of the photosensitive drums 1a to 1d is stopped, and at the same time, the application of the charging voltage to the charging roller 21 is also stopped. During warm-up, the development DC voltage and the development AC voltage are kept off.

Next, control during image formation will be described. As shown in FIG. 5, when a print command is input (t1 in FIG. 5), a control signal is sent from the control section 90 to the main motor 40, and rotation of the photosensitive drums 1a to 1d is started. In addition, a control signal is transmitted from the control unit 90 to the charging voltage power supply 52 via the voltage control circuit 51, and the charging rollers 21 of the charging devices 2a to 2d are supplied to the charging rollers 21 of the charging devices 2a to 2d in synchronization with the start timing of the rotational driving of the photosensitive drums 1a to 1d. An intermediate voltage V1 is applied as a charging voltage.

As a result, the surfaces of the photosensitive drums 1a to 1d are charged to an intermediate potential Vh1 (100 V) lower than the reference potential Vh (eg, 500 V) during printing. The intermediate potential Vh1 is a potential difference between the potential (approximately 0 V) of the developing roller 29 in a state where no development DC voltage is applied and the intermediate potential Vh1 of a predetermined value (carrier in the magnetic brush carried on the surface of the developing roller 29). is set so as not to exceed the lower limit of the potential difference adhering to the photosensitive drums 1a to 1d.

When a predetermined time has passed since the rotation of the photosensitive drums 1a to 1d was started (t2 in FIG. 5), an intermediate voltage V2 (>Vc1) is applied to the charging roller 21 to flatten the surfaces of the photosensitive drums 1a to 1d. It is charged to an intermediate potential Vh2 (150 V) higher than the intermediate potential Vh1. At the same time, voltage control circuit 51 applies predetermined intermediate development DC voltage Vdc1 (100 V) and development AC voltage Vac from development voltage power supply 53 to development roller 29 . Intermediate development voltage Vdc1 is lower than intermediate potential Vh2, and the potential difference from intermediate potential Vh2 does not exceed a predetermined value. There is no risk of sticking to

After that, an intermediate voltage V3 (>V2) is applied to the charging roller 21 to charge the surfaces of the photosensitive drums 1a to 1d to an intermediate potential Vh3 (250 V). At the same time, the voltage control circuit 51 applies a predetermined intermediate development DC voltage Vdc2 (200 V) from the development voltage power supply 53 to the development roller 29 . Intermediate development DC voltage Vdc2 is lower than intermediate potential Vh3, and the potential difference from intermediate potential Vh3 does not exceed a predetermined value. There is no risk of sticking to 1d.

Thereafter, similarly, an intermediate voltage V4 (>V3) is applied to the charging roller 21 to charge the surfaces of the photosensitive drums 1a to 1d to an intermediate potential Vh4 (350 V). At the same time, the voltage control circuit 51 applies a predetermined intermediate development DC voltage Vdc3 (300 V) from the development voltage power supply 53 to the development roller 29 . Intermediate development DC voltage Vdc3 is lower than intermediate potential Vh4, and the potential difference from intermediate potential Vh4 does not exceed a predetermined value. There is no risk of sticking to 1d. Thereafter, a reference voltage Vs (>V4) is applied to the charging roller 21 to charge the surfaces of the photosensitive drums 1a to 1d to the reference potential Vh (500V). Further, a reference developing DC voltage Vdc (350 V) during printing is applied to the developing roller 29 to execute the printing operation.

On the other hand, when the printing operation is finished, the charging voltage applied from the charging voltage power supply 52 to the charging roller 21 is lowered stepwise from the reference voltage Vs to the intermediate voltages V4 to V1 in order, and the photosensitive drums 1a to 1d are charged. The surface potential is lowered stepwise from the reference potential Vh to intermediate potentials Vh4 to Vh1. Further, the voltage control circuit 51 switches the development voltage applied from the development voltage power source 53 to the development roller 29 of each of the development devices 3a to 3d in steps from the reference development DC voltage Vdc to Vdc2 to Vdc1.

When the charging voltage is switched to the intermediate voltage V1 (t3 in FIG. 5), the voltage control circuit 51 stops the application of the intermediate developing DC voltage Vdc1 from the developing voltage power supply 53 to the developing roller 29 (0 V). When the printing operation ends (t4 in FIG. 5), the rotational driving of the photosensitive drums 1a to 1d is stopped, and the application of the intermediate voltage V1 to the charging roller 21 is also stopped at the same time.

In this embodiment, the charging voltage is continuously applied over the entire period during which the photosensitive drums 1a to 1d are rotationally driven during warm-up and image formation. As a result, while the photosensitive drums 1a to 1d are rotating, the surface potential of the photosensitive drums 1a to 1d rises, thereby suppressing the adhesion of toner from the developing roller 29 to the non-image areas of the photosensitive drums 1a to 1d. . Therefore, it is possible to suppress the occurrence of the fogging phenomenon and reduce the toner consumption.

Conventionally, in consideration of damage to the photosensitive drums 1a to 1d due to the application of the charging voltage when the photosensitive drums 1a to 1d are stopped, the charging voltage is applied after a certain period of time from the start of rotational driving of the photosensitive drums 1a to 1d. was applied. However, as shown in FIGS. 4 and 5, the intermediate voltage V1 applied to start rotating the photosensitive drums 1a to 1d is used to charge the surface potential of the photosensitive drums 1a to 1d to the reference potential Vh during image formation. Since the voltage is lower than the reference voltage Vs, the photosensitive drums 1a to 1d are hardly damaged.

Therefore, in FIGS. 4 and 5, the period during which the photosensitive drums 1a to 1d are rotating coincides with the period during which the charging voltage is applied, but the rotation of the photosensitive drums 1a to 1d is started. It is also possible to extend the application period of the charging voltage before or after the rotation of the photosensitive drums 1a to 1d is stopped.

Further, in this embodiment, as shown in FIG. 5, the charging voltage is increased stepwise through a plurality of intermediate voltages V1 to V4 until the surface potential of the photosensitive drums 1a to 1d is charged to the reference potential Vh. In accordance with this, the development DC voltage is also increased stepwise via a plurality of intermediate development DC voltages Vdc1 to Vdc3. As a result, the surface potential of the photosensitive drums 1a to 1d becomes too large with respect to the development DC voltage, and the adhesion of carriers to the surfaces of the photosensitive drums 1a to 1d and the surface potential of the photosensitive drums 1a to 1d On the other hand, it is possible to suppress both adhesion of toner to the non-exposed area (white background portion) due to excessive development DC voltage.

(Second embodiment)
Next, a second embodiment of the invention will be described. FIG. 6 is a graph comparing changes in the toner adhesion amount when the development potential difference (V0-Vdc) is changed with and without application of the AC voltage for development. As shown in FIG. 6, when the developing AC voltage is applied (squared data series in FIG. 6), the development potential difference is greater than when the developing AC voltage is not applied (square data series in FIG. 6). It can be seen that the toner adhesion amount is 0.01 to 0.02 mg/cm ² less regardless of the thickness.

This is because when the AC voltage for development is applied, an electric field (reverse electric field) is generated for collecting toner from the photosensitive drums 1a to 1d toward the developing roller 29, and the toner that has once adhered to the surfaces of the photosensitive drums 1a to 1d is collected. It is considered that the toner is collected on the developing roller 29 side by the electric field. Therefore, by applying the developing AC voltage in addition to the charging voltage while the photosensitive drums 1a to 1d are rotationally driven, the fogging phenomenon in the non-image portion can be suppressed more effectively and the toner consumption can be reduced. can be further reduced.

7 and 8 show the driving states of the photosensitive drums 1a to 1d, the charging voltage applied to the charging roller 21, and the developing voltage applied to the developing roller 29 in the image forming apparatus 100 according to the second embodiment of the present invention. 4 is a timing chart showing changes in voltage; FIG. 7 shows a timing chart during power-on and during warm-up from sleep mode (power saving mode) to a printable state, and FIG. 8 shows a timing chart during image formation. The application control of the charging voltage and the developing voltage in the image forming apparatus 100 of the second embodiment will be described with reference to FIGS. 7 and 8 while referring to FIGS. 1 to 3 as necessary.

First, the control during warm-up will be described. As shown in FIG. 7, when the image forming apparatus 100 is powered on (t1 in FIG. 7), a control signal is sent from the control unit 90 to the main motor 40, and the photosensitive drums 1a to 1d start rotating. be done. Further, a control signal is transmitted from the control section 90 to the charging voltage power supply 52 via the voltage control circuit 51, and application of the charging voltage to the charging rollers 21 of the charging devices 2a to 2d is started. The charging voltage applied to the charging roller 21 at this time is the same as the first stage intermediate voltage (V1 in FIG. 5) applied during image formation.

In addition, a control signal is transmitted from the control unit 90 to the developing voltage power supply 53 via the voltage control circuit 51, and in synchronism with the start timing of the rotational driving of the photosensitive drums 1a to 1d, the developing rollers 29 of the developing devices 3a to 3d are supplied with a control signal. Application of the developing AC voltage is started. The developing AC voltage applied to the developing roller 29 at this time is the same as the developing AC voltage (Vac in FIG. 5) applied during image formation.

After that, when the warm-up ends (t2 in FIG. 7), the rotational driving of the photosensitive drums 1a to 1d is stopped, and at the same time, the application of the charging voltage to the charging roller 21 and the application of the developing AC voltage to the developing roller 29 are also stopped. be stopped. During warm-up, the development DC voltage is kept off.

Next, control during image formation will be described. As shown in FIG. 8, when a print command is input (t1 in FIG. 8), a control signal is sent from the control section 90 to the main motor 40, and rotation of the photosensitive drums 1a to 1d is started. In addition, a control signal is transmitted from the control unit 90 to the charging voltage power supply 52 via the voltage control circuit 51, and the charging rollers 21 of the charging devices 2a to 2d are supplied to the charging rollers 21 of the charging devices 2a to 2d in synchronization with the start timing of the rotational driving of the photosensitive drums 1a to 1d. Application of the intermediate voltage V1 is started. Further, a control signal is transmitted from the control unit 90 to the developing voltage power source 53 through the voltage control circuit 51, and the developing rollers 29 of the developing devices 3a to 3d are supplied to the developing rollers 29 of the developing devices 3a to 3d in synchronization with the start timing of the rotational driving of the photosensitive drums 1a to 1d. Application of the developing AC voltage Vac is started.

When a predetermined period of time has elapsed since the rotation of the photosensitive drums 1a to 1d was started (t2 in FIG. 8), the charging voltage is increased stepwise from the intermediate voltage V1 to the reference voltage Vs via the intermediate voltages V2 to V4. . Further, when the charging voltage is switched to the intermediate voltage V2, the application of the developing DC voltage to the developing roller 29 is started, and is gradually increased to the reference developing DC voltage Vdc through the intermediate developing DC voltages Vdc1 to Vdc3. Execute the print operation.

On the other hand, when the printing operation is finished, the charging voltage applied from the charging voltage power source 52 to the charging roller 21 is lowered stepwise from the reference voltage Vs to the intermediate voltages V4 to V1 in order. In addition, the development DC voltage applied to the development roller 29 from the development voltage power supply 53 is lowered stepwise from the reference development DC voltage Vdc in the order of Vdc3 to Vdc1.

When the charging voltage is switched to the intermediate voltage V1 (t3 in FIG. 8), the voltage control circuit 51 stops the application of the intermediate developing voltage Vdc1 from the developing voltage power supply 53 to the developing roller 29 (0 V). When the printing operation ends (t4 in FIG. 8), the rotational driving of the photosensitive drums 1a to 1d is stopped, and at the same time, the intermediate voltage V1 is applied to the charging roller 21 and the developing AC voltage Vac is applied to the developing roller 29. be stopped.

According to this embodiment, the charging voltage and the developing AC voltage are continuously applied over the entire period during which the photosensitive drums 1a to 1d are rotationally driven during warm-up and image formation. As a result, while the photosensitive drums 1a to 1d are rotating, the effect of suppressing the adhesion of toner to non-image areas due to the increase in the surface potential of the photosensitive drums 1a to 1d and the effect of toner collection due to the toner collection electric field are combined. As a result, the adhesion of toner to the non-image areas of the photosensitive drums 1a to 1d is effectively suppressed. Therefore, the fogging phenomenon can be further suppressed and the toner consumption can be further reduced as compared with the first embodiment.

In FIGS. 7 and 8, the period during which the photosensitive drums 1a to 1d are rotating coincides with the period during which the charging voltage and the developing AC voltage are applied. It is also possible to extend the application period of the charging voltage and the developing AC voltage until before the start of the development or after the rotation of the photosensitive drums 1a to 1d is stopped.

In addition, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the present invention. For example, in each of the above-described embodiments, the charging voltage is raised in five stages from the intermediate voltages V1 to V4 to the reference voltage Vs at the start of the printing operation, and at the end of the printing operation from the reference voltage Vs through the intermediate voltages V4 to V1 to approximately 0V. However, the control is not limited to five steps, and the charging voltage may be raised and lowered in two or more steps. Similarly, the development DC voltage is not limited to four-stage rise and fall through the intermediate development DC voltages Vdc1 to Vdc3, but may be controlled in two or more stages.

Further, in each of the above-described embodiments, the developing devices 3a to 3d of the two-component developing method using the two-component developer containing the toner and the magnetic carrier are used. The same fog suppressing effect and toner consumption reducing effect can be expected even in a contact one-component developing system developing device in which the toner is brought into contact with 1d to 1d.

In each of the above embodiments, the charging roller 21 is configured to charge the surfaces of the photosensitive drums 1a to 1d while being in contact with the surfaces of the photosensitive drums 1a to 1d. Substantially the same effect can be achieved with substantially the same action in an embodiment arranged close to the surface of the body drums 1a-1d and configured for non-contact charging.

The present invention is not limited to the tandem type color printer as shown in FIG. 1, but can of course be applied to various image forming apparatuses such as monochrome printers, digital multi-function machines, and color copiers. EXAMPLES Hereinafter, the effects of the present invention will be described more specifically with reference to examples.

Investigation was made on fluctuations in the amount of toner consumed when the application timing of the charging voltage and developing AC voltage during image formation was changed. In the test method, as shown in FIG. 5, when a charging voltage is applied throughout the rotation period of the photosensitive drums 1a to 1d (present invention 1), as shown in FIG. When the charging voltage and the developing AC voltage are applied over the entire rotation period of (Invention 2), and when the charging voltage and the developing AC voltage are applied after a predetermined time has elapsed from the start of rotation of the photosensitive drums 1a to 1d ( For Comparative Example), 1,000 sheets of A4 landscape size paper with a print rate of 5% were intermittently printed (single print) as a test image at room temperature (25°C). Consumption was compared.

The test conditions were as follows: a testing machine (ECOSYS P5026cdw, manufactured by Kyocera Document Solutions Co., Ltd.) as shown in FIG. driven. The developing devices 3a to 3d are two-component developing systems, and the linear speed ratio (S/D) of the developing roller 29 to the photosensitive drums 1a to 1d is set to 1.8. Table 1 shows the charging voltage, development DC voltage, and development AC voltage application conditions, and FIG. 9 shows the results of comparison of toner consumption.

※本発明１、比較例では中間電位Ｖ１のとき０Ｖ

*In the present invention 1 and the comparative example, 0 V at intermediate potential V1

As shown in FIG. 9, in Invention 1 in which the charging voltage was applied over the entire rotation period of the photosensitive drums 1a to 1d, the toner consumption per printed sheet was 16.3 mg. In Invention 2, in which the charging voltage and the developing AC voltage were applied over the entire rotation period of the photosensitive drums 1a to 1d, the toner consumption per printed sheet was 15.5 mg.

On the other hand, in the comparative example in which the charging voltage and developing AC voltage were applied after a predetermined time had elapsed from the start of rotation of the photosensitive drums 1a to 1d, the toner consumption per printed sheet was 17.2 mg. As described above, in the present inventions 1 and 2, the toner consumption per printed sheet is smaller than in the comparative example, and the charging voltage and developing AC voltage are applied over the entire rotation period of the photosensitive drums 1a to 1d. , it was confirmed that the amount of toner consumed during printing was reduced.

In addition, it was confirmed from the comparison between Invention 1 and Invention 2 that the toner consumption can be further reduced when both the charging voltage and the developing AC voltage are applied over the entire rotation period of the photosensitive drums 1a to 1d. was done.

INDUSTRIAL APPLICABILITY The present invention can be applied to an image forming apparatus having a charging member that charges the surface of a photosensitive drum in a contact or non-contact state. By using the present invention, it is possible to provide an image forming apparatus capable of suppressing adhesion of toner or carrier to the surface of an image carrier regardless of the usage environment.

Pa to Pd image forming unit 1a to 1d photosensitive drum (image carrier)
2a to 2d charging device 3a to 3d developing device 19a base tube 19b photosensitive layer 21 charging roller (charging member)
29 development roller (developer carrier)
40 main motor (driving device)
51 voltage control circuit 52 charging voltage power supply 53 developing voltage power supply 90 control unit 100 image forming apparatus

Claims (7)

an image carrier having a photosensitive layer formed on its surface;
a charging member that charges the surface of the image carrier with or without contact with the surface of the image carrier;
a developing device having a developer carrier that carries a developer containing toner and developing an electrostatic latent image formed on the surface of the image carrier;
a charging voltage power supply that applies a charging voltage consisting of only a DC voltage to the charging member;
a driving device that rotationally drives the image carrier;
a control unit that controls the charging voltage power source and the driving device;
In an image forming apparatus comprising
The image forming apparatus, wherein the control section applies the charging voltage throughout a period in which the image carrier is rotationally driven. 2. The image forming apparatus according to claim 1, wherein a period during which said image carrier is rotationally driven by said driving device coincides with a period during which said charging voltage is applied. The control unit applies the charging voltage at a voltage lower than that during image formation when rotating the image carrier when the power of the image forming apparatus is turned on or when returning from a power saving mode. 3. The image forming apparatus according to claim 1 or 2. The control unit applies the charging voltage stepwise through a plurality of intermediate voltages until the surface potential of the image carrier is charged to a reference potential during image formation,
4. The intermediate voltage of the first stage during the image formation is applied when the image carrier is rotationally driven when the power of the image forming apparatus is turned on or when returning from the power saving mode. The image forming apparatus according to . a development voltage power supply for applying a development DC voltage and a development AC voltage to the developer carrier;
5. The image forming apparatus according to claim 1, wherein the control section applies the developing AC voltage throughout a period in which the image carrier is rotationally driven. The developing device is a two-component developing system using a two-component developer containing the toner and a magnetic carrier, or a contact one-component developing system in which a one-component developer containing only the toner is brought into contact with the image carrier. 6. The image forming apparatus according to any one of claims 1 to 5, characterized by: 7. The image forming apparatus according to claim 1, wherein the image carrier has an organic photosensitive layer as the photosensitive layer.

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