JP4193853B2 - Developing device and image forming apparatus using the same - Google Patents

Description

  The present invention relates to a developing device used in, for example, a mono-color or full-color copying machine or printer, and an image forming apparatus using the developing device. More specifically, the developing device is designed to widen the allowable range when setting the bias voltage for development and prevent the occurrence of leakage between the developer carrying member and the image carrying member, and the same. The present invention relates to an image forming apparatus.

  In an electrophotographic image forming apparatus, an electrostatic latent image is formed on a fully charged photosensitive drum by exposure of an optical writing unit, and then the amount of developer carried by a developing roller is made constant using a regulating blade. In this state, the developer is made to adhere to the electrostatic latent image on the photosensitive drum to visualize it, and an image is formed on the recording paper. In that case, a developing bias voltage is applied to the photosensitive drum and the developing roller, and the developer adheres on the photosensitive drum under a predetermined electric field formed between the photosensitive drum and the developing roller.

By the way, in the conventional image forming apparatus, as shown in, for example, Patent Document 1, atmospheric pressure is detected using a sensor for detecting atmospheric pressure, and between the photosensitive drum and the developing roller based on the detected atmospheric pressure. The potential difference is controlled so that leakage (current leakage) does not occur. As a result, a high-quality image is formed on the recording paper regardless of fluctuations in atmospheric pressure.
In the image forming apparatus disclosed in Patent Document 2 or Patent Document 3, the development conditions such as the volume resistance value of the developing roller and the developing bias voltage are limited so that no leakage occurs between the photosensitive drum and the developing roller. Alternatively, the peak-to-peak voltage of the alternating electric field, the dark developing potential, the separation distance between the photosensitive drum and the developing roller, and the like are set within a certain range.
JP-A-5-88434 JP-A-5-11582 JP-A-7-199664

However, according to the conventional image forming apparatuses such as these, when the distance between the photosensitive drum and the developing roller varies depending on individual differences between the apparatuses, the occurrence of leakage may not be prevented. Alternatively, even when the distance between the photosensitive drum and the developing roller is different along the longitudinal direction, the occurrence of leakage may not be prevented.
Therefore, it is necessary to set a developing bias voltage and the like in consideration of a difference in distance between the photosensitive drum and the developing roller. For this reason, the allowable range for setting the developing bias voltage and the like has been extremely narrow.

  The present invention has been made in order to solve the above-described problems, and widens the allowable range when setting the bias voltage for development, and reliably generates leakage between the developer carrier and the image carrier. It is an object of the present invention to provide a developing device and an image forming apparatus using the same.

In order to solve the above problems, according to the present invention, an electrostatic latent image is formed by exposing an image carrier having a thin film layer made of an organic photoconductive material on the surface, and then a developer is applied to the electrostatic latent image. A developing device used for an image forming operation for forming an image on a recording sheet, the developer carrying body carrying a developer to be supplied to the image carrier, and the development In a developing device that applies a voltage (hereinafter referred to as “developing bias voltage”) to a developer carrying member and supplies the developer from the developer carrying member to the image carrying member, the developer is a one-component developer. A control means for controlling the voltage applied to the developer carrier, a toner amount detection means for detecting the amount of toner adhering to the image carrier, the developer carrier before the image forming operation, and The leakage when the leakage occurs between the thin film layers And the leakage generated voltage detecting means for detecting a pressure, on the basis of the detection result of the leak generating voltage detecting means, said and a setting unit leaks to set the range of the voltage which does not occur is provided, the leak generating voltage detection The means applies the voltage while sequentially changing the magnitude of the voltage applied to the developer carrying member by the control means, and detects whether or not a leak image occurs by using the toner amount detecting means. , detect the voltage of when the leakage occurs.

According to the present invention, the leak occurrence voltage detecting means detects the voltage at which a leak occurs between the developer carrier and the image carrier by increasing or decreasing the voltage applied to the developer carrier during non-development, for example. . Then, the setting means sets a range (for example, an upper limit value) of the developing bias voltage that does not cause a leak based on the detection result.
In this way, the leakage voltage is detected, and the development bias voltage range (preferably the upper limit of the peak-to-peak voltage of the development bias voltage) is set within the range of the detected voltage or less. Even if the distance between the agent carrier and the image carrier is different for each apparatus or along the longitudinal direction, a wide tolerance range for setting the developing bias voltage is secured. Further, the occurrence of leakage between the developer carrier and the image carrier is reliably prevented.

Further, according to the present invention, the leak occurrence voltage detection means uses the toner amount detection means to cause the image carrier to detect a spot in the non-image forming portion or a spot-like density drop in the image forming portion. of including a leakage image detection means to detect the occurrence of the leak images, by detecting using the leakage image detection means whether rie click image occurs, detecting the voltage at which the leakage occurs It is desirable to do.

According to the present invention, it is preferable that the setting means sets a range of the voltage at which the leak does not occur with an upper limit value being a voltage lower than the voltage at which the detected leak occurs. Also, the control unit, the setting set developing bias voltage in the image forming operation (preferably the DC component voltage) within the unit it is desirable to adjust the. In this way, the control unit adjusts the developing bias voltage, whereby an image can be formed with an appropriate density.

The image forming apparatus of the present invention includes any one of the developing devices described above and an image forming unit that forms an image on the image carrier.
In this image forming apparatus, an image is formed on the image carrier by the image forming means and the developing device.

Further, according to the present invention, before SL voltage is superimposed voltage of a DC component and an AC component, the control means, by adjusting the DC component in this state by setting the upper limit value of the AC component It is desirable to control the voltage.

  According to the invention, it is desirable that the setting means sets the voltage range in which the leak does not occur in either the image portion or the non-image portion.

  According to the developing device of the present invention, even if the separation distance between the developer carrier and the image carrier is different or fluctuates from device to device, a wide allowable range for setting the developing bias voltage is secured. In addition, the occurrence of leakage between the developer carrier and the image carrier is reliably prevented. In addition, according to the image forming apparatus of the present invention, since the developing device of the present invention is used, the occurrence of leakage is prevented and a good image is always formed.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will be described below in detail with reference to the drawings. The present embodiment is an electrophotographic image forming apparatus that forms an image using a developer of one-component toner (hereinafter simply referred to as toner G1). FIG. 1 is a schematic view showing a main part of the image forming apparatus according to the embodiment.

  As shown in FIG. 1, a photosensitive drum 12 (image carrier) having a thin film layer made of an organic photoconductive material (OPC) formed on the surface thereof is provided in a substantially central portion in the image forming apparatus 11 in the direction of arrow A. It is provided to be freely rotatable. Around the photosensitive drum 12, a charger 13, a developing device 14, a transfer device 15, and a cleaner 16 are sequentially disposed along the rotation direction of the arrow A, and further, obliquely above the photosensitive drum 12. Is provided with a laser exposure device 17 as an image forming means.

Further, the apparatus 11 is provided with a power supply device 18 for applying a voltage to the charger 13, the developing device 14, the transfer device 15 and the like. In addition to these, a controller 19 (control means) for controlling the power supply device 18 and the like is provided. The controller 19 is also in charge of controlling the charger 13, the developing device 14, the transfer device 15, the cleaner 16, the laser exposure device 17, and the like.
Further, a sensor 20 for detecting the toner density on the photosensitive drum 12 is provided in the vicinity of the photosensitive drum 12. The detection value of the sensor 20 is input to the controller 19. The controller 19 is a microcomputer that is a combination of a well-known CPU, ROM, RAM, and the like, and comprehensively controls various devices in the image forming apparatus 11. In particular, the power supply device 18 can be controlled to change the voltage applied to the developing roller 14a, the photosensitive drum 12, and the like, and to appropriately set the developing bias voltage.

  The charger 13 charges the entire surface of the thin film layer on the surface of the photosensitive drum 12 while rotating in the direction of arrow B. The charger 13 is connected to the power supply device 18 as described above, and normally the surface potential on the photosensitive drum 12 is charged to about -600 V to -1000 V by applying a voltage of about -1000 V to -1400 V. To do. In this case, as the charger 13, a conductive roller may be used in addition to the one using a conductive brush, and a conductive wire or a needle electrode may be used.

  Further, the laser exposure device 17 exposes the surface of the photosensitive drum 12 with laser light 17a based on the image information, and forms an electrostatic latent image on the surface of the photosensitive drum 12. Therefore, the laser exposure device 17 is controlled by the controller 19 based on image information input from a facsimile device, an image reading device, and a computer (not shown). In this case, the surface potential of the photosensitive drum 12 after receiving the laser beam 17a is greatly different between the image portion where the electrostatic latent image is formed and the non-image portion where the electrostatic latent image is not formed. For this reason, the negatively chargeable toner G1 is attached only to the image portion where the electrostatic latent image is formed, and is visualized corresponding to the electrostatic latent image. However, as a means for exposing the surface of the photosensitive drum 12, an LED head may be used, or a shutter means such as a liquid crystal panel or PLZT may be used.

  The developing device 14 visualizes the latent image formed on the photosensitive drum 12 using the toner G1. In the developing device 14, a developing roller 14 a (developer carrier) that rotates in the direction of arrow C is disposed at a position adjacent to the photosensitive drum 12. The developing device 14 has a toner hopper 14b for storing the toner G1, and a regulating blade 14c extending toward the developing roller 14a is disposed on the toner hopper 14b. A toner G1 supply / collection roller (hereinafter simply referred to as a supply roller) 14d is disposed so as to be close to the developing roller 14a in the toner hopper 14b. Further, a stirring blade 14e that stirs the toner G1 and supplies the toner G1 to the supply roller 14d is provided on the inner side of the toner hopper 14b.

The supply roller 14d can supply the toner G1 to the developing roller 14a while rotating in the direction of arrow D (the same direction as the arrow C direction) while being in contact with the developing roller 14a. Therefore, the regulating blade 14c made of a spring member is in contact with the developing roller 14a on the downstream side in the rotation direction (arrow C direction) of the developing roller 14a. This is because the thickness of the thin layer of the toner G1 carried on the developing roller 14a is made constant. Specifically, the regulating blade 14c is pressed against the developing roller 14a with a pressure of about 4 gf / mm. As a result, when the toner G1 passes between the regulating blade 14c and the developing roller 14a, a toner layer having a developer adhesion amount of 0.7 mg / cm ² and a developer charge amount of about −20 μC / g is obtained. .
Here, the toner G1 is a non-magnetic one-component toner. In other words, a polyester or styrene-acrylic resin as a main component, and a colorant (carbon or pigment), a charge control agent, WAX, etc. dispersed in the resin, is surfaced by a fluidizing agent such as silica. It has been processed. In the present embodiment, a magenta toner mainly composed of a polyester resin used in a color printer manufactured by our company is used.

In addition, the developing roller 14a faces the photosensitive drum 12 with a distance L1 (for example, about 0.2 mm) in the developing region where the toner G1 is supplied to the photosensitive drum 12. Then, the toner G1 is applied to the photosensitive drum 12 while rotating in the arrow C direction.
In this case, the developing roller 14a has an elastic rubber layer having a volume resistance value of about 10 ⁵ Ω to 10 ⁶ Ω on the core metal member, and a surface resistance of about 10 ⁶ Ω to 10 ⁷ Ω on the surface of the elastic rubber layer. A developing bias voltage is applied to the developing roller 14a.

As the developing bias voltage, a voltage in which a DC component is superimposed on a rectangular wave alternating electric field as shown in FIG. 2 is used. Specific voltages include, for example, a voltage difference of 1.7 kV (peak-to-peak voltage), a DC component voltage of −500 V (peak-to-peak voltage center voltage), a frequency of 3 kHz, and a duty ratio of 40% (alternating electric field). The ratio of the time T ₂ during which the developing electric field is actually applied to the time T ₁ of one period of the waveform is used. However, the above numerical values are not always used. As will be described in detail later, the voltage at which leakage occurs between the developing roller 14a and the photosensitive drum 12 is detected, and the controller 19 sets the range of the developing bias voltage at which leakage does not occur based on the detected voltage. is there. Note that ΔV _dev shown in FIG. 2 indicates the potential difference in the image portion, and ΔV _back indicates the potential difference in the non-image portion.
When such a developing bias voltage is applied to the developing roller 14a, the toner G1 on the developing roller 14a moves back and forth between the developing roller 14a and the photosensitive drum 12 in the developing region. It adheres to the drum 12.

  A paper feed cassette 21 that stores the recording paper P is installed below the image forming apparatus 11. A pair of transport rollers 22 for transporting the recording paper P is disposed downstream of the paper feed cassette 21 in the paper transport direction. Further, a paper path 23 toward the photosensitive drum 12 is formed on the downstream side of the conveying roller 22. The recording paper P transported in the paper path 23 is guided to a transfer area sandwiched between the photosensitive drum 12 and the transfer device 15 by a pair of transport rollers 22.

Thereafter, in order to transfer the image of the toner G1 on the photosensitive drum 12 onto the recording paper P in the transfer area, the transfer unit 15 records the recording sent in synchronization with the movement of the image of the toner G1 on the photosensitive drum 1. From the back side of the paper P, a positive transfer electric field opposite to the charging polarity of the toner G1 is applied. Specifically, the transfer unit 15 is made of a conductive roller and is connected to the power supply device 18 and is usually applied with a voltage of about 2 kV.
As a result, the image of the toner G1 on the photosensitive drum 12 is transferred to the recording paper P, and an image is formed on the recording paper P. However, the transfer device 15 may use a corona discharge by a conductive wire or a needle electrode. Further, since the recording paper P is charged, in order to improve the separation from the photosensitive drum 12 and to prevent the peeling discharge, a discharging means such as a discharging needle or a charger to which the discharging charge is applied is provided. May be.

  A paper transport member 25 that guides the recording paper P separated from the photosensitive drum 12 to the fixing device 24 is provided on the downstream side of the transfer region. Further, on the downstream side, a fixing device 24 is provided, and the fixing device 24 heats and presses the recording paper P to fix the image of the toner G1 transferred in the transfer region. The recording paper P sent to the fixing device 24 is discharged onto the paper discharge stack 26 after fixing.

  The cleaner 16 removes the toner G1 remaining on the photosensitive drum 12 after the transfer, and has a cleaning blade 16a for removing the toner G1. The cleaning blade 16a is made of a rubber member having elasticity, and scrapes off the toner G1 on the photosensitive drum 12 while contacting the photosensitive drum 12 rotating in the direction A in the drawing. The toner G1 that has fallen therefrom is accommodated in the cleaner 16. However, in addition to using a cleaning blade, for example, a conductive brush or a magnetic brush may be used. Then, the photosensitive drum 12 from which the toner G1 has been removed is charged again by the charger 13.

  In addition, you may provide an electric charge removal means between the cleaner 16 and the charger 13 as needed. The charge removing means may be one that uses an eraser lamp or the like, or a charger that consists of a wire or a needle electrode. Alternatively, the static electricity may be removed by applying an alternating electric field to a conductive film provided in contact with or close to the photosensitive drum 12.

Incidentally, the state of the thin layer of the toner G1 on the developing roller 14a varies depending on the influence of the environment, durability, and the like, but the image forming apparatus 11 adheres to the electrostatic latent image on the photosensitive drum 12 in response to this variation. A clear image can be formed on the recording paper P by setting the amount of the toner G1 to be appropriate.
Specifically, the developer adhesion amount varies in the range of 0.6 to 0.8 mg / cm ² depending on the environment and durability, and the developer charge amount is in the range of about −15 to −25 μC / g. fluctuate. When the state of the toner layer on the developing roller 14a varies as described above, the amount of toner G1 attached to the electrostatic latent image on the photosensitive drum 12 varies. That is, when the adhesion amount of the toner G1 on the developing roller 14a decreases or the charge amount of the toner G1 increases, the amount of toner G1 attached to the electrostatic latent image on the photosensitive drum 12 decreases. . On the other hand, when the adhesion amount of the toner G1 on the developing roller 14a increases or the charge amount of the toner G1 decreases, the amount of the toner G1 adhered to the electrostatic latent image on the photosensitive drum 12 Will be more.

However, in the image forming apparatus 11 of this embodiment, the sensor 20 detects the amount of the toner G1 adhering to the photosensitive drum 12, and outputs the detected value to the controller 19. The controller 19 that has input the detection value controls the DC component voltage (the center voltage of the peak-to-peak voltage). That is, when the detected value is small (if the amount of toner G1 adhering to the photosensitive drum 12 is small as it is), the controller 19 performs control so that the DC component voltage becomes large. On the other hand, when the detected value is large (if the amount of toner G1 adhering to the photosensitive drum 12 is large as it is), the DC component voltage is controlled to be small.
For this reason, even if the state of the thin layer of the toner G1 on the developing roller 14a changes depending on the environment and durability, the controller 19 controls the DC component voltage of the developing bias voltage to form an electrostatic latent image on the photosensitive drum 12. A clear image can be formed on the recording paper P by setting the amount of the adhered toner G1 to an appropriate amount.

  Incidentally, the distance L1 between the photosensitive drum 12 and the developing roller 14a is different for each apparatus, or the separation distance L1 between the photosensitive drum 12 and the developing roller 14a is different along the longitudinal direction. There are things to do. For this reason, the amount of the toner G1 attached to the electrostatic latent image on the photosensitive drum 12 may be affected by this. However, the image forming apparatus 11 can cope with this variation as follows.

  FIG. 3 shows development characteristics when the distance L1 between the photosensitive drum 12 and the developing roller 14a varies. Here, FIG. 3 shows a developing bias voltage and a developing amount (substitute with image density) when the distance L1 between the photosensitive drum 12 and the developing roller 14a varies between 0.15 and 0.35 mm. It is a graph which shows the relationship. The horizontal axis of the graph represents the DC component voltage of the developing bias voltage, and the vertical axis of the graph represents the image density. From this, it can be seen that the image density increases as the DC component voltage increases.

  Here, FIG. 3A shows a case where the peak-to-peak voltage of the developing bias voltage is set to 1.7 kV, and FIG. 3B shows that the peak-to-peak voltage is set to 2.5 kV. This is the case. According to the graphs of FIGS. 3A and 3B, it can be seen that when the distance L1 between the photosensitive drum 12 and the developing roller 14a is 0.20 mm or less, the developing characteristics are substantially constant. In contrast, when the distance L1 is 0.20 mm or more, it can be seen that the image density decreases as the distance L1 increases. Furthermore, it can be seen that when the DC component voltage is 500 V or higher, the image density is higher in FIG. 3B than in FIG. 3A.

FIG. 4 is a graph showing the relationship between the adhesion amount of the toner G1 on the recording paper P and the image density. The horizontal axis of the graph represents the amount of toner G1 attached, and the vertical axis of the graph represents the image density. As shown by the curve K1 in this graph, it can be seen that the image density increases as the adhesion amount of the toner G1 increases. According to this graph, when the adhesion amount of the toner G1 on the recording paper P is 0.7 mg / cm ² , the image density is 0.9.

Here, it is assumed that the desired image density is 0.9. According to FIG. 3A, when the distance L1 is about 0.35 mm, the image density cannot be 0.9 even if the DC component voltage is −700 V or more. However, according to FIG. 3B, when the distance L1 is about 0.35 mm, the image density can be 0.9 when the DC component voltage exceeds −550V.
Therefore, when the desired image density is 0.9 and the separation distance L1 between the photosensitive drum 12 and the developing roller 14a is about 0.35 mm, the peak-to-peak voltage is 1. It can be seen that the DC component voltage should be made larger than -550V while changing from 7 kV to 2.5 kV.

However, if the peak-to-peak voltage of the developing bias voltage is set too high, a local leak may occur between the photosensitive drum 12 and the developing roller 14a. In that case, the toner G1 adheres to the non-image forming portion on the surface of the photosensitive drum 12 in the form of spots, or the toner G1 attached to the image forming portion on the surface of the photosensitive drum 12 returns to the developing roller 14a again. There is a possibility that a leaked image such as a spot-like decrease in density occurs.
Here, the relationship between the peak-to-peak voltage of the developing bias voltage and the leaked image generated between the photosensitive drum 12 and the developing roller 14a is shown in FIG. FIG. 5 shows the relationship between the distance L1 and the peak-to-peak voltage when the surface potential of the photosensitive drum 12 is set to -600V and the DC component voltage of the developing bias voltage is set to -500V. The horizontal axis of the graph is the distance L1, and the vertical axis of the graph is the peak-to-peak voltage.

Whether a leaked image is generated is determined almost uniquely by the electric field strength between the photosensitive drum 12 and the developing roller 14a. A leak image is generated in a region where the peak-to-peak voltage is higher than the curve K2 shown in FIG. On the other hand, a leak image does not occur in a region where the peak-to-peak voltage is lower than the curve K2. Specifically, when the distance L1 is about 0.3 mm, no leak image is generated if the peak-to-peak voltage is 3 kV or less.
For example, when the distance L1 is about 0.25 mm, the peak-to-peak voltage of the developing bias voltage needs to be set higher (for example, 2.5 kV) so that an appropriate image density can be obtained. However, when the peak-to-peak voltage is fixed at 2.5 kV, for example, if the distance L1 becomes narrow (for example, about 0.15 mm) due to individual differences in product manufacture and fluctuations during use, etc., leakage occurs. An image is likely to occur. On the contrary, when the peak-to-peak voltage of the developing bias voltage is set low (for example, 1.0 kV) so that a leak image does not occur when the distance L1 is about 0.15 mm, the distance L1 is When it becomes wide (for example, about 0.25 mm), an appropriate image density cannot be obtained.

Therefore, prior to the image forming operation, the controller 19 uses the sensor 20 to detect a voltage at which a leak image is generated between the developing roller 14 a and the photosensitive drum 12. Specifically, when the surface potential of the photosensitive drum 12 is set to −600 V and the DC component voltage of the developing bias voltage is set to −500 V, the peak-to-peak voltage is set to every 500 V between 1 kV and 3 kV. Apply while changing to.
At that time, in consideration of the change in the distance L1 due to the shake of the developing roller 14a, etc., a constant peak-to-peak voltage is applied to the developing roller 14a while the developing roller 14a makes one rotation or more for each voltage. The controller 19 uses the sensor 20 to detect whether or not a leak image is generated during that time.

When the occurrence of a leak image is detected, the magnitude of the voltage at which the leak image is generated is detected in more detail. That is, the controller 19 subdivides the voltage difference between the peak-to-peak voltage at which the leaked image is generated and the peak-to-peak voltage immediately before the leaked image is generated, for example, every 100V. A peak-to-peak voltage is sequentially applied to the developing roller 14a to detect at which voltage the leaked image is generated.
Thus, when the controller 19 detects the occurrence of a leak image, the peak-to-peak voltage at this time is stored in a RAM (storage device) in the controller 19. Further, a potential difference at which a leaked image is generated is calculated from the surface potential of the photosensitive drum 12 and the DC component voltage of the developing bias voltage, and the potential difference is stored in the RAM.

  Further, considering the fluctuation of the surface potential on the photosensitive drum 12 and the fluctuation of the voltage of the power supply device 18 from the peak-to-peak voltage stored in the RAM, a voltage about 200 V lower than that voltage is peaked. • Set as the upper limit of to-peak voltage. Specifically, when the peak-to-peak voltage at the time of occurrence of the leak image is 1.7 kV, 1.5 kV, which is about 200 V lower than 1.7 kV, is set as the upper limit value of the peak-to-peak voltage.

In the state where the upper limit value of the peak-to-peak voltage is set as described above, the potential difference ΔV _back of the non-image portion and the potential difference ΔV _{dev of the} image portion shown in FIG. The controller 19 adjusts the DC component voltage of the developing bias voltage. Then, an image pattern for image density detection is developed on the photosensitive drum 12, and the development amount is detected using the sensor 20.
Then, the controller 19 sets the DC component voltage of the developing bias voltage within a range in which a leak image does not occur in order to obtain a developing amount of the toner G1 that achieves an appropriate image density based on the value detected by the sensor 20. adjust. Thereafter, the above-described image forming operation is performed on the recording paper P.

If an appropriate image density cannot be obtained with the adjusted peak-to-peak voltage, the following control is performed. That is, the controller 19 adjusts the peak-to-peak voltage to a larger value (upper limit value within the set range) within a range that does not exceed the peak-to-peak voltage at the time of occurrence of the leak image, thereby developing bias. Adjust the magnitude of the DC component voltage of the voltage. With this adjustment, the image density detection pattern is developed on the photosensitive drum 12. Then, the adjustment of the DC component voltage of the developing bias voltage that obtains a developing amount with an appropriate image density is repeated.
If an appropriate image density cannot be obtained within a range where no leaked image is generated, the controller 19 sets a developing condition for obtaining an image density close to the most appropriate image density. A forming operation is performed. In this case, the image density is slightly different from the desired density, but no image noise such as a leaked image is generated, so that the quality of the image formed on the recording paper P is maintained.

When the DC component voltage of the developing bias voltage described above is set to be low, the potential difference ΔV _{back in} the non-image portion becomes large, and a leak image tends to occur in the non-image portion. For this reason, it is desirable that the surface potential of the photosensitive drum 12 be variable so that the potential difference ΔV _back of the non-image portion is equal to or less than the potential difference of the leaked image. In the above-described embodiment, the controller 19 controls both the peak-to-peak voltage and the DC component voltage of the developing bias voltage, but it is not always necessary to adopt this mode. Either the to-peak voltage or the DC component voltage of the developing bias voltage may be controlled.
Furthermore, the controller 19 may control by combining both the peak-to-peak voltage and the duty ratio as necessary.

  As described above in detail, according to the present embodiment, the developing roller 14a for supplying the toner G1 to the photosensitive drum 12 is provided, and when the toner G1 is supplied onto the photosensitive drum 12, the power supply In the developing device 14 that applies a developing bias voltage to the developing roller 14 a by the device 18, the controller 19 increases or decreases the voltage applied to the developing roller 14 a during non-development, and a leaked image is generated between the developing roller 14 a and the photosensitive drum 12. The generated voltage is detected using the sensor 20, and based on the detected voltage, the upper limit value of the range of the peak-to-peak voltage range of the developing bias voltage is set where no leak image occurs. As a result, even if the distance L1 varies from device to device or depending on the longitudinal direction, the allowable range for adjusting the developing bias voltage is widened, and leakage between the developing roller 14a and the photosensitive drum 12 occurs. It is surely prevented.

Note that the present invention is not limited to the above-described embodiment, and various improvements and modifications can be made without departing from the scope of the invention. For example, it goes without saying that this image forming apparatus may be applied to a full-color copying machine, a facsimile machine or the like. Further, any image forming type image forming apparatus may be used.
Further, since the amount of the toner G1 in the developing device 14 can be indirectly detected by using the detection result of the sensor 20 that detects the amount of the toner G1 carried on the photosensitive drum 12, the sensor 20 develops. It may also serve as an agent detection means.

Further, as a method for generating a leak image, in addition to making the peak-to-peak voltage variable, either the charging potential on the photosensitive drum 12 or the DC component voltage of the developing bias voltage may be controlled. Furthermore, both the charging potential on the photosensitive drum 12 and the DC component voltage of the developing bias voltage may be controlled.
In addition, as a means for detecting the occurrence of a leak image, the sensor 20 has been used in the above embodiment. However, the power supply device 18 for generating the developing bias voltage is provided with a detecting means for detecting the developing current. The detection unit may detect the leak current that flows when the leak image is generated to detect the occurrence of the leak image.

1 is a schematic diagram illustrating a main part of an image forming apparatus according to an embodiment. It is a figure which shows the bias voltage for development applied to a developing roller. FIG. 3A is a graph showing the relationship between the developing bias voltage and the image density when the separation distance between the photosensitive drum and the developing roller varies, and FIG. 3A shows a peak-to-peak voltage of 1. FIG. 3B shows the case where the voltage is set to 2.5 kV. 6 is a graph showing the relationship between the amount of developer deposited on a photosensitive drum and the image density. It is a figure which shows the graph of the relationship between the separation distance between a photoconductive drum and a developing roller, and a peak-to-peak voltage.

Explanation of symbols

G1 toner L1 separation distance P recording paper 11 image forming apparatus main body 12 photoconductor drum 13 charger 14 developing device 14a developing roller 14b toner hopper 14c regulating blade 14d supply roller 14e stirring blade 17 laser exposure device 18 power supply device 19 controller 20 sensor

Claims (7)

An electrostatic latent image is formed by exposing an image carrier having a thin film layer made of an organic photoconductive material on the surface, and then a developer is attached to the electrostatic latent image to make it visible, and the image is recorded on recording paper. A developing device for use in an image forming operation to be formed, comprising a developer carrier for carrying a developer to be supplied to the image carrier, and applying a voltage to the developer carrier to apply the developer carrier In a developing device for supplying a developer to the image carrier from
The developer is a one-component developer,
Control means for controlling the voltage applied to the developer carrier;
Toner amount detecting means for detecting the amount of toner adhering to the image carrier;
Leak generation voltage detection means for detecting the voltage when a leak occurs between the developer carrier and the thin film layer prior to the image forming operation;
On the basis of the detection result of the leak generating voltage detecting means, and setting means are provided to set the range of the voltage which the leakage does not occur,
The leak generation voltage detection unit applies the voltage while sequentially changing the magnitude of the voltage applied to the developer carrying member by the control unit, and uses the toner amount detection unit to determine whether or not a leak image is generated. The developing device is characterized in that the voltage when the leak occurs is detected by detecting the voltage . The leak generation voltage detection means detects the occurrence of a leak image on the image carrier by using the toner amount detection means based on a spot-like density decrease in a non-image forming portion or a spot-like density in an image forming portion. includes a leakage image detection hand stage,
By rie click image detected using the leakage image detection means whether occurring, the developing device according to claim 1, wherein the detecting the voltage when the leakage occurs. 3. The development according to claim 1, wherein the setting unit sets a range of the voltage at which the leakage does not occur with a voltage lower than the detected voltage at which the leakage occurs as an upper limit. apparatus. In the developing device according to any one of claims 1 to 3,
It said control means, a developing device comprising a benzalkonium adjust the voltage at the time of image forming operation within a range set by the setting unit. An image forming apparatus comprising: the developing device according to claim 1; and an image forming unit that forms an image on the image carrier. The developing device according to claim 1 ,
Before SL voltage is superimposed voltage of a DC component and an AC component,
The developing device according to claim 1, wherein the control means controls the voltage by setting an upper limit value of the AC component and adjusting the DC component in that state. In the developing device according to any one of claims 1 to 4,
The developing device, wherein the setting means sets the voltage range in which the leakage does not occur in both the image portion and the non-image portion.

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