JP5039286B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that forms an image on recording paper using an electrophotographic system.

  Hereinafter, a conventional image forming apparatus using a non-magnetic one-component developing system as background art will be described with reference to FIG.

  In the image forming apparatus 200, an electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) 20 having a normal drum shape as an image carrier is uniformly charged by a primary charger 21. Next, corresponding to the image information input from the external device, the exposure device 22 irradiates light onto the photosensitive drum 20 to form a latent image. The electrostatic latent image on the photosensitive drum 20 is converted into a visible image, that is, a toner image by a developer T (hereinafter referred to as toner) T having a frictional charging polarity having the same polarity as the voltage applied to the primary charger 21 in the developing device 60. Is done.

  The toner image is transferred to the transfer material Q by the transfer charger 23. The transfer material Q is separated from the photosensitive drum 20, and subsequently conveyed to the fixing device 25 and fixed, and becomes a permanent image. Further, the toner T on the photosensitive drum 20 remaining without being transferred by the transfer charger 23 is removed by the cleaning device 24, and the photosensitive drum 20 is subjected to the next image forming process.

  The toner T is a negatively chargeable nonmagnetic one-component toner that is negatively charged and contains a pigment of any one of yellow, magenta, cyan, and black. In addition, the toner stirring members 64 and 65 made of plates or screws processed into various shapes are provided so as to rotate in the direction of the arrow in the figure, and the toner T in the toner storage portion is used as a developer carrier. It is conveyed to the developing roller 61.

  The developing container partition plate 66 shown in FIG. 17 has an appropriate partition plate height so that a constant amount of toner T is always supplied onto an RS roller 62 as a toner supply roller in the vicinity of the developing roller 61.

  In the non-magnetic one-component development method, it is impossible to supply toner by magnetic force. Therefore, an RS roller 62 made of urethane sponge is in contact with the developing roller 61. The RS roller 62 rotates in the counter direction at the nip portion with the developing roller 61 to supply the toner T onto the developing roller 61, and at the same time, the toner on the developing roller 61 that has not been developed even when passing through the position facing the photosensitive drum. Is stripped off.

  The developing roller 61 is in contact with a regulating blade 63 as a toner amount regulating member, regulates the toner on the developing roller 61 to form a thin toner layer, and is conveyed to the developing area (drum facing position). The amount is prescribed. The amount of toner conveyed to the development area is determined by the contact pressure and contact length of the regulating blade 63 that contacts the developing roller 61.

  The regulating blade 63 is a chip blade that is adhered or welded onto a thin metal plate such as phosphor bronze or stainless steel having a thickness of several hundreds of μm, and is uniformly brought into contact with the developing roller 61 by the elasticity of the thin metal plate. At this time, the contact condition of the regulating blade 63 is determined by the material, thickness, penetration amount, and set angle of the metal thin plate.

Further, the developing roller 61 is opposed to the surface of the photosensitive drum 20 in a developing region with a predetermined interval (specified by arranging a roller (not shown) around the developing roller 11), and a bias is applied. An oscillating electric field is formed. In the above configuration, the toner T that adheres to the surface of the developing roller 61 with a desired charge amount and a desired layer thickness and is conveyed to the developing region is the toner T that adheres to the surface of the developing roller due to the vibration electric field. The electrostatic latent image formed on the surface of the photosensitive drum is visualized by reciprocating between 61 and the photosensitive drum 20.

Further, in the image forming apparatus 200, when the transfer material Q is thick paper or the like (generally, high-quality dedicated paper of 100 g / m ² or more), the transfer material Q passing through the fixing device 25 is slowed down to improve the fixing property. It is common to perform a raising operation. At that time, when the leading edge of the paper starts to enter the fixing device 25, the trailing edge of the paper performs a developing operation. For this reason, the rotational speeds of the photosensitive drum 20 and the developing roller 61 are similarly reduced (this operation is hereinafter referred to as a high image quality mode).

  The series of image forming operations described above is executed under image forming conditions in which various parameters including a bias voltage applied to each part of the apparatus are combined. In order to perform stable image formation with good image quality, it is important to perform image formation under appropriate image formation conditions. In setting the image forming conditions, it is necessary to satisfy various image constraints.

  In addition to obtaining a desired image density, an image defect called so-called “creaking” in which the density at the rear end of the solid image portion generated in this type of image forming apparatus becomes high, or a background on the photosensitive drum 20. The phenomenon called “fogging” that appears on the transfer paper due to the development of the toner on the part must be suppressed. Therefore, it is necessary to set the image forming conditions so as to always satisfy the above-described constraint conditions. For example, a method of providing a falling specified bias to the development bias has been devised for the gathering (Patent Document 1).

In this type of image forming apparatus, it is known that the image density changes mainly due to changes in the apparatus and toner characteristics in the following cases (1), (2), and (3).
(1) When the user uses the high image quality mode (2) When the usage environment of the apparatus changes (3) When the image forming apparatus is used over a long period of time

In order to prevent the image density change in the above case, a method of changing the surface potential of the photosensitive drum 20 in the case of (1) has been proposed (Patent Document 2). In the case of (2), a method of adjusting the development contrast by changing the charging bias has been proposed (Patent Document 3). In the case of (3), a method of changing the amplitude of the vibration bias and the charging bias in accordance with the operation status of the apparatus has been proposed (Patent Document 4).
JP-A-7-134480 JP-A-7-209933 Japanese Patent Laid-Open No. 5-88496 JP 2004-138687 A

  However, in the cases (1), (2), and (3) described above, when a conventional image forming apparatus is used, not only the image density but also the level of occurrence of blurring and fogging changes. This is because, as described above, the characteristics of the image forming apparatus and toner change in each case.

Here, an image defect called “squeezing” will be described below with reference to FIG. FIG. 18 is a schematic diagram for explaining the mechanism of the contact when the photosensitive drum 20 and the developing roller 61 are observed from the longitudinal direction. It is thought that rushing occurs due to the following mechanism.

  The close-up is a phenomenon in which a large amount of toner collects at the image rear end H as shown in FIG. As shown in FIG. 18, when an AC bias is applied between the photosensitive drum 20 and the developing roller 61, a barrel-shaped electric field D is generated. Then, the toner T adhering to the surface of the developing roller 61 reciprocates between the photosensitive drum 20 and the developing roller 61 along the electric force line S formed by the electric field. Move outward from the nearest point of contact. That is, when an AC bias is applied, the flying toner T1 in the development area always has a velocity component that moves outside the development area.

  Next, a case where the photosensitive drum 20 and the developing roller 61 are rotated in the direction of the arrow shown in FIG. 18 and a latent image is formed on the photosensitive drum 20, that is, a case where actual development is in progress will be described.

  In the latent image formed on the photosensitive drum 20 shown in FIG. 18, the position of the potential of −100 V is the visible portion, that is, the region R1 where the toner image is formed, and the position of the potential of −500 V is the background portion potential of the photosensitive drum. The region R2 where no toner image is formed.

  When the visible part reaches the developing area, the toner T on the developing roller 61 adheres to the visible part. As described above, the flying toner T1 has a velocity component that moves outside the developing area. Therefore, it moves to the upstream side of the visible part. In addition, an electric field is generated from the region R2 toward the region R1 at the boundary between the region R1 having a potential of −100V and the region R2 having a potential of −500V. As a result, the toner T1 that has moved to the upstream side of the visible portion stops at this boundary. For this reason, the toner amount at the rear end portion is larger than the upstream portion and the central portion of the visible portion. As a result, such rushing H is formed.

  Regarding the image density, in each of the above-mentioned patent documents (1), (2), and (3), each image forming condition is optimized so that a stable image density is always obtained. However, it is not an effective measure against fog. Furthermore, there are cases in which the effect of countermeasures is insufficient with respect to the level of occurrence of squeeze that changes only by the method described in Patent Document 1.

  Therefore, even in the cases (1), (2), and (3) described above, it is possible to always form a high-quality image in which the occurrence of jamming is suppressed while maintaining the image density and fog appropriately. Establishment of technology that can be done is desired.

  The present invention has been made in view of the above-described problems of the prior art, and the object of the present invention is to stabilize a high-quality image with suppressed lashing even when the rotational speed of the image carrier is changed. Another object of the present invention is to provide an image forming apparatus.

  Another object of the present invention is to provide an image forming apparatus that stably forms a high-quality image with suppressed lashing even when the usage environment changes.

  Another object of the present invention is to provide an image forming apparatus capable of stably forming a high-quality image with suppressed lashing even when the image forming apparatus is used for a long period of time.

In order to achieve the above object, the present invention provides:
An image carrier on which an electrostatic latent image is formed;
A developer carrying body that holds a predetermined distance from the image carrier and carries a developer;
A charging member for charging the image carrier;
Latent image forming means for forming an electrostatic latent image on the charged image carrier;
An image forming apparatus in which a developing bias is applied to the developer carrier to make the electrostatic latent image a visible image.
The developing bias is
An oscillating bias voltage having a peak voltage Vmax for biasing the developer in the direction from the developer carrier to the image carrier and a peak voltage Vmin for biasing the developer in the direction from the image carrier to the developer carrier. Yes,
When the charging bias applied to the charging member is Vc, the background potential of the electrostatic latent image formed on the image bearing member is Vd, and the visible portion potential is Vl, the values of Vc and Vmin are constant values. ,
Vmax is changed so that the absolute value of the potential difference of | Vmax−Vl | becomes smaller and the absolute value of the potential difference of | Vmax−Vd | becomes smaller as the rotational speed of the image carrier becomes slower. To do.

An image carrier on which an electrostatic latent image is formed;
A developer carrying body that holds a predetermined distance from the image carrier and carries a developer;
A charging member for charging the image carrier;
Latent image forming means for forming an electrostatic latent image on the charged image carrier;
An image forming apparatus in which a developing bias is applied to the developer carrier to make the electrostatic latent image a visible image.
The developing bias is
An oscillating bias voltage having a peak voltage Vmax for biasing the developer in the direction from the developer carrier to the image carrier and a peak voltage Vmin for biasing the developer in the direction from the image carrier to the developer carrier. Yes,
When the background potential of the electrostatic latent image formed on the image carrier is Vd and the visible potential is Vl,
| To the potential difference absolute value as a constant value, | Vmin-Vd
Vmax is changed so that the absolute value of the potential difference of | Vmax−Vl | becomes smaller and the absolute value of the potential difference of | Vmax−Vd | becomes smaller as the rotational speed of the image carrier becomes slower. To do.

  According to the present invention, it is possible to stably form a high-quality image in which squeezing is suppressed.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings and embodiments. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. . Further, the materials, shapes, etc. of the members once described in the following description are the same as those in the first description unless otherwise described.

(Image forming device)
An image forming apparatus in this embodiment is shown in FIG. In the image forming apparatus 100, the photosensitive drum 1 as an image carrier on which an electrostatic latent image is formed is uniformly charged by a primary charger 2. Next, in response to image information input from an external device, an exposure device 3 as a latent image forming unit irradiates light onto the photosensitive drum 1 to form an electrostatic latent image. The electrostatic latent image on the photosensitive drum 1 is converted into a toner T having a frictional charging polarity that is the same as the voltage applied to the primary charger 2 in the developing device 10 as a developer carrying member that carries the toner T as a developer. Thus, a visible image, that is, a toner image is obtained.

The toner image is transferred to the transfer material Q by the transfer charger 4. The transfer material Q is separated from the photosensitive drum 1 and subsequently transported and fixed to the fixing device 6 to become a permanent image. The toner T as the developer on the photosensitive drum 1 remaining without being transferred by the transfer charger 4 is removed by the cleaning device 5, and the photosensitive drum 1 is subjected to the next image forming process.

  A photosensitive drum speed changing means 7 is disposed in the driving portion of the photosensitive drum 1, and the rotational speed of the photosensitive drum 1 can be arbitrarily changed based on the type of transfer material Q or external information by a control means (not shown). ing.

(Developer)
Next, the developing device 10 will be described in detail. The developing device 10 in this embodiment is one in which the present invention is applied to a developing device of a non-magnetic one-component non-contact developing system. The developing device 10 is a photosensitive drum 1, a developing roller 11 as a developer carrying member, an RS roller 12 as a developer supplying member, a toner amount regulating member 13, and an insulating nonmagnetic one-component developer. A toner T and a plate-like toner stirring member 14 are provided. Further, the photosensitive drum 1 and the developing roller 11 carrying the toner T are opposed to each other with a predetermined interval.

  Hereinafter, each member provided in the developing device 10 will be described.

  As the photosensitive drum 1, a member configured by coating a photosensitive material such as OPC on the surface of a φ24 mm aluminum base tube is used. As the developing roller 11, a member obtained by spray-coating a phenol resin solution in which carbon and graphite are dispersed on the surface of an aluminum base tube having a diameter of 12 mm is used. SD rollers (not shown) are installed at both ends of the developing roller, and the SD gap (the interval between the developing roller 11 and the photosensitive drum 1) is maintained by abutting against the surface of the photosensitive drum. The SD gap of the developing device 10 in this embodiment is 300 μm. As the RS roller 12, a roller having a diameter of 12 mm in which a polyurethane foam is provided on a core metal is used. As the toner amount regulating member 13, a material obtained by laminating polyamide on the surface of a phosphor bronze plate having a thickness of 0.1 mm is used.

  Next, the operation of the developing device 10 will be described.

  The toner T is a negatively chargeable nonmagnetic one-component toner that is negatively charged and contains a pigment of any one of yellow, magenta, cyan, and black. The toner stirring member 14 is provided so as to be able to rotate in the direction of the arrow in the figure, and conveys the toner T in the toner storage portion to the developing roller 11. In the developing container partition plate 15, the height of the partition plate is optimized so that a constant amount of toner T is always supplied onto the RS roller 12 near the developing roller 11.

  The RS roller 12 is in contact with the developing roller 11 and rotates in the counter direction at the nip portion so that the toner T is supplied onto the developing roller 11 and at the same time is not developed even when passing through the photosensitive drum facing position. The toner on the developing roller 11 is removed.

  The developing roller 11 is in contact with a regulating blade as a toner amount regulating member 13, regulates the toner on the developing roller 11 to form a thin toner layer, and regulates the amount of toner conveyed to the developing area. The toner is charged.

  In the above configuration, the toner T that adheres to the surface of the developing roller 11 with a desired charge amount and a desired layer thickness and is conveyed to the developing region is developed with the developing roller 11 and the photosensitive drum by a developing bias applied to the developing roller 11. The electrostatic latent image formed on the surface of the photosensitive drum 1 is visualized by performing a reciprocating motion with the photosensitive drum 1.

(Each setting condition in the image forming apparatus)
The photosensitive drum 1 is normally rotated at a speed of 50 mm / sec in the direction of the arrow shown in FIG. 1 and can be changed to speeds of 25 mm / sec and 16 mm / sec by the photosensitive drum speed changing means 7. Further, the development bias switching means 18 as the bias control means switches the development bias according to the photosensitive drum speed.

  The developing roller 11 rotates in the direction of the arrow shown in FIG. 1 and rotates at a rotational speed with a circumferential speed difference of 150% with respect to the photosensitive drum 1. In order to make the toner on the surface of the developing roller a uniform thin layer, the toner amount regulating member 13 is in contact with the developing roller 11 at a linear pressure of 15 g / cm in the counter direction with respect to the rotation direction of the developing roller 11.

(Development bias voltage waveform)
Next, the developing bias voltage waveform applied to the developing roller 11 in this embodiment will be described with reference to FIG.

  In this embodiment, the developing bias voltage is an oscillating bias voltage in which an AC bias is superimposed on a DC bias. Here, as shown in FIG. 2, the flying voltage Vmax1 is set to -1150V, the pullback voltage Vmin1 is set to + 650V, and the time average voltage Vdc is set to -250V. As a result, the peak-to-peak voltage Vpp (potential difference between Vmax and Vmin) is 1800 V, and the duty ratio is 50%.

  Here, the flying voltage Vmax means that the negatively charged toner T on the developing roller 11 flies against the background potential Vd and the minimum visible portion potential Vl of the electrostatic latent image formed on the photosensitive drum 1. This is the voltage that is energized in the direction to be applied. In other words, it is a peak voltage that urges the toner T, which is a developer, in a direction from the developing roller 11, which is a developer carrier, toward the photosensitive drum 1, which is an image carrier.

  The pullback voltage Vmin is a voltage that urges a part and most of the toner that has jumped to the background portion potential Vd and the visible portion minimum potential Vl in a direction to pull back the toner to the developing roller 11. In other words, it is a peak voltage that urges the toner T in the direction from the photosensitive drum 1 toward the developing roller 11.

  The duty ratio indicates the application time of the flying voltage Vmax1 with respect to the sum of the application time (Tmax1) of the flying voltage Vmax1 and the application time (Tmin1) of the pullback voltage Vmin1 (that is, the time Ts of one cycle of the AC waveform). The AC frequency is fixed at 3 kHz.

  Next, the potential on the photosensitive drum will be described. After charging the photosensitive drum surface by applying a charging bias Vc by the primary charger 2, the photosensitive drum 1 is irradiated with light by an exposure device 3 as a latent image forming means to form an electrostatic latent image. Thus, the background portion potential Vd on the photosensitive drum is set to −500 V, and the visible portion minimum potential Vl is set to −100 V.

  Next, a detailed description of this embodiment will be given.

  Table 1 shows setting values for developing bias control in this embodiment. In this embodiment, the value of | Vmax−Vl | is changed by changing the value of the flying voltage Vmax. When the value | Vmax−Vl | is changed, the duty ratio is adjusted, and the time average voltage Vdc is fixed at −250V. Table 1 shows the setting conditions of the developing bias with respect to the photosensitive drum speed in Example 1.

  The close-up is more conspicuous as the latent image potential difference on the photosensitive drum is larger. For example, it is likely to occur in a region where the latent image potential changes suddenly such that there is a solid white image next to the solid image. FIG. 3 shows a part of an image pattern used for examining the effect of the present invention. This is an image in which a solid white image follows a solid image of 30 mm × 20 mm in length × width. This image is taken into a personal computer by an image scanner system, and the image density is converted into numerical data of 0 to 255. FIG. 4 shows the density distribution with respect to the Y axis of the sample image.

  Next, a method for measuring the numerical value of the gathering portion will be described.

In FIG. 4, the density from Yb to Yc is higher than the density from Ya to Yb. That is, the area from Yb to Yc is a gathering area. The shaded portion in the figure is the integrated value of the gathering density, and the density change per millimeter is taken as the gathering value. In the case of the contact data shown in the figure, the value of the contact area Yb-Yc is 4 (mm), and the integrated value (shaded portion in the figure) of the contact density is 160 (dig). Therefore, the threshold value is 160/4 = 40 (dig / m
m).

According to the experiments by the present inventors, when the contact value is 20 (dig / mm) or less, the contact by visual observation becomes inconspicuous. Therefore, a good image is obtained with an intrusion value of 20 or less.

  The effects of the present invention will be described below using comparative examples.

(Comparative Example 1)
As Comparative Example 1, the configuration of the image forming apparatus and the developing device is the same as that of Example 1, but the developing bias having the same condition is used even when the rotational speed of the photosensitive drum is changed. The development bias of Comparative Example 1 is the same as that at the photosensitive drum speed of 50 mm / sec in Example 1, and is a rectangular shape having a peak-to-peak voltage Vpp = 1800 V, an AC frequency of 3 kHz, a time average voltage Vdc = −250 V, and a development duty ratio of 50%. It is formed by waves.

  As a comparative experiment, 50 sheets were printed at a normal photosensitive drum speed of 50 mm / sec, 10 sheets were printed at a photosensitive drum speed of 25 mm / sec, and 50 sheets were printed at a photosensitive drum speed of 50 mm / sec. After that, 120 sheets are printed in one cycle, that is, 10 sheets are printed under the condition that the photosensitive drum speed is 16 mm / sec. That is, every time 50 sheets were printed at a photosensitive drum speed of 50 mm / sec, 50 mm / sec → 25 mm / sec and 50 mm / sec → 16 mm / sec were repeated, and a total of 360 sheets were printed. Then, the solid density of each image was measured using a commercially available reflection type density measuring device, and the threshold value was measured by the method described above. FIG. 5 shows a timing chart at that time and a correspondence diagram of the average solid image density and the gathering value of 10 print images.

  As shown in FIG. 5, in the first comparative example, when the photosensitive drum speed is changed, the solid image density and the close-up value are greatly changed. On the other hand, in the first embodiment, even when the photosensitive drum speed is changed, the solid image density and the gathering value are both substantially constant.

  The reason will be described in detail below.

  FIG. 6 shows the transition of the threshold value when the photosensitive drum speed is decreased. FIG. 7 shows the transition of the solid image density when the photosensitive drum speed is decreased. In the case of Comparative Example 1 in which the developing bias is constant, the broken line indicates the value of | Vmax−Vl | in a state where | Vmin−Vd | is fixed in accordance with the decrease in the rotation speed of the photosensitive drum in the configuration of the first embodiment. In this case, the absolute value of the potential difference is reduced.

  In each embodiment, the state in which | Vmin−Vd | is fixed is described, but the normal background portion potential Vd takes a constant value corresponding to the set value of the charging bias Vc. Therefore, by controlling the values of the charging bias Vc and the pullback voltage Vmin to be constant values, substantially the same effect can be obtained, and density change, a close-up image, and fog can be reduced.

  As shown in FIG. 6, in the case of Comparative Example 1 in which the developing bias is constant, the contact worsens as the photosensitive drum speed decreases and exceeds the contact value 20. Further, as shown in FIG. 7, the image density increases as the photosensitive drum speed decreases. On the other hand, in the configuration of the first embodiment, even if the photosensitive drum speed is changed, the bringing-in value can be suppressed to 20 or less, and the image density can be kept constant.

  The reason why the configuration of the first embodiment can reduce the close-up image and the density change is as follows.

  First, the close-up image will be described. As described above, the close-up image is generated by the reciprocating motion of the toner between the photosensitive drum and the developing roller. Accordingly, the larger the number of reciprocating movements of the toner, the more likely the contact is worsened. This is why the close-up image deteriorates as the photosensitive drum speed decreases.

  On the other hand, the rushing tends to be worsened when the barrel electric field between the developing roller and the photosensitive drum is strong. For example, when the number of reciprocating movements of the toner is the same and the barrel electric field is strong (that is, when the development Vpp is large), the toner receives a stronger force in the direction outside the development area and the speed in that direction. By increasing the component, the close-up image appears more strongly.

  In Example 1, compared to Comparative Example 1, with the | Vmin−Vd | fixed, by reducing | Vmax−Vl | Can be made. This is the reason why there is a difference in the close-up image between the comparative example 1 and the example 1. On the other hand, although it is considered that the number of reciprocating movements of the toner is somewhat increased by this control, the effect of weakening the electric field is more effective.

  Next, the image density will be described. The image density increases as the amount of toner contributing to development increases. When the rotational speed of the photosensitive drum is reduced in Comparative Example 1, a developing bias is applied for a sufficient time to the toner adhering to the developing roller by electrostatic reflection force. Therefore, the toner that has not been separated from the developing roller so far and has not contributed to the development can be separated from the developing roller and contribute to the development. As a result, the image density increases when the rotational speed of the photosensitive drum is decreased.

  On the other hand, in the first embodiment, control is performed to reduce the absolute value of the potential difference of | Vmax−Vl | according to the change in the rotational speed of the photosensitive drum, particularly in a state where | Vmin−Vd | is fixed. Accordingly, the image density can be kept constant by selectively weakening the electric field for the toner on the developing roller to fly and making the amount of toner contributing to development constant.

  It should be noted that, even when control is performed to reduce the peak-to-peak voltage Vpp of the vibration bias in accordance with the photosensitive drum speed, there is a certain effect with respect to the close-up image as in the case of the control in the present invention. . This is considered to be the same reason that the above-described effect of the present invention was obtained.

  However, this method is undesirable mainly from the viewpoint of fogging. The reason is as follows. For example, when the speed of the photosensitive drum is changed from 50 mm / sec to 25 mm / sec, if the developing bias is kept constant at the setting of 50 mm / sec, the image density becomes deeper as shown in Comparative Example 1, and the close-up Will get worse. As described above, this is a state of excessive development with a large amount of toner contributing to development. At that time, so-called background fogging, which increases the amount of toner developed to the background portion potential Vd on the photosensitive drum, is deteriorated.

  FIG. 8 shows the change in fog on the paper with respect to the photosensitive drum speed when the developing bias is constant (Comparative Example 1), when Vpp control is performed, and in the first embodiment. In the Vpp control method, Vpp is decreased by the same value as | Vmax−Vl | is decreased in the first embodiment. Here, the fog was measured using a REFECTMETER MODEL TC-6DS manufactured by Tokyo Denshoku Co., Ltd. and calculated from the following equation.

Fog (reflectance) (%) = reflectance of standard paper (%) − reflectance of sample non-image area (%)
As shown in FIG. 8, with the decrease in the photosensitive drum speed, the fog is remarkably deteriorated in the constant bias control of Comparative Example 1. Furthermore, the fog suppression effect is not sufficient even by Vpp control. On the other hand, in this embodiment, the fog is stable at a low value regardless of the decrease in the speed of the photosensitive drum.

  Regarding fog, the effect obtained by the Vpp control is different from that obtained in the first embodiment for the following reason. Table 2 shows a correspondence table showing the difference in bias control between the case of Vpp control and the case of Example 1. Here, as an example, the case where the photosensitive drum rotation speed is changed from 50 mm / sec to 25 mm / sec is shown. In both Vpp control and Example 1, the peak-to-peak voltage is controlled to be reduced by 100V. The time average voltage Vdc is constant in both cases, and Vdc = −250V.

  As shown in Table 2, in the case of the Vpp control, a voltage | Vmax−Vd | that is energized so that the toner T flies from the developing roller to the background portion B1 that is the background portion potential Vd on the photosensitive drum. The voltage | Vmin−Vd | energized so as to fly from the background B1 on the photosensitive drum onto the sleeve becomes smaller than that in Example 1, and becomes smaller than that in Example 1. As a result, the force for the toner T to fly to the background B1 is increased, the amount of toner adhering to the background B1 on the photosensitive drum is increased, and the background fog is deteriorated.

There is a control method in which the time average voltage Vdc is adjusted while the duty ratio is maintained at 50%, and the flying voltage Vmax and the pullback voltage Vmin are the same as those in the first embodiment. In this case, however, the time average voltage Vdc must be −200V. The image density is significantly reduced. On the other hand, in the present embodiment, while | Vmin−Vd | is fixed, | Vmax−Vl | is decreased, and the duty ratio is adjusted to keep Vdc constant, and the image density is appropriately adjusted while suppressing fogging. It becomes possible to keep.

  In the present embodiment, the above effect was obtained by controlling the value of the flying voltage Vmax. However, by changing the light irradiation amount of the exposure apparatus by the control means and changing the value of the visible portion minimum potential Vl. However, it is possible to obtain the effect of suppressing the deterioration of the brought-in image due to the decrease in the photosensitive drum speed and the change in the image density.

  The reason why the above effect is obtained is different from the case of controlling the value of the flying voltage Vmax. For example, when the speed of the photosensitive drum is changed from 50 mm / sec to 25 mm / sec, if | Vmax−Vl | is reduced by controlling the visible portion minimum potential Vl = −100 V → Vl = −150 V, | Vd−Vl | The latent image contrast becomes smaller. This reduces the edge effect electric field from Vd to Vl. As a result, the damming effect of the toner by the edge electric field is eased, so that the close-up can be improved. At the same time, the development contrast of | Vdc−Vl | becomes small, so that an increase in image density can be suppressed.

  For the reasons described above, when the rotational speed of the photosensitive drum is reduced as in the first embodiment of the present invention, the absolute value of the potential difference of | Vmax−Vl | is reduced while | Vmin−Vd | is kept constant. By performing the control, the image density and the background fog which fluctuate in accordance with the decrease in the rotational speed of the photosensitive drum can be suppressed, and the rushed image can be reduced.

  In the first embodiment, values of | Vmin−Vd | = 1150 V, | Vmax−Vl | = 1050 V, 950 V, and 900 V are used. However, the optimum values are obtained depending on various conditions such as the SD gap, the photosensitive drum, and the developing roller diameter. The value changes. Therefore, the effects of the present invention can be obtained by using arbitrary values according to various conditions of each image forming apparatus for the fixed value of | Vmin−Vd | and the amount of change of | Vmax−Vl |. It is also possible to set the developing bias with higher accuracy by detecting the background portion potential Vd and the visible portion minimum potential Vl by a potential sensor (not shown) and performing feedforward control or feedback control. In this embodiment, the constant value of Vdc = −250 V is used so that the effects of the present invention can be easily understood. However, the present invention is not limited to this, and any value can be used as long as the solid black density on the image is sufficiently obtained. good.

  The present embodiment relates to an invention for performing the above-described development bias control when the use environment of the image forming apparatus changes.

The image forming apparatus in this embodiment will be described. Except for the points described below, they are basically the same as those in the first embodiment, and a description thereof will be omitted to avoid duplication. The image forming apparatus according to the second exemplary embodiment includes a sensor that detects ambient environment information, and has a function of obtaining absolute humidity (g / m ³ ) in the environment by detecting temperature and humidity. (Not shown).

  Next, the developing bias in this embodiment will be described.

  The developing bias in this embodiment is based on the relationship shown in FIG. 2 described in the first embodiment. The AC frequency is fixed at 3 kHz.

  Next, the potential on the photosensitive drum in this embodiment will be described.

In this embodiment, a charging bias Vc is applied by the primary charger 2 shown in FIG. 1 to charge the surface of the photosensitive drum. In general, when the charging bias Vc is constant regardless of the change in absolute humidity, the background portion potential Vd on the photosensitive drum changes according to the absolute humidity in the air.

Table 3 shows the variation of Vd with respect to the absolute humidity and the variation of the visible portion minimum potential Vl when Vc is constant. For example, the absolute humidity 5.8 (g / m ³ ) listed in Table 3 refers to an environment having a temperature of 22 ° C. and a humidity of 35%.

  In this embodiment, the effect of the present invention is verified when the charging bias Vc is constant. An operation of adjusting Vmin in accordance with Vd changing in each environment is performed, and control is performed so as to keep the value of | Vmin−Vd | constant as will be described later.

  Next, a detailed description of this embodiment will be given.

  Table 4 shows the relationship between the absolute humidity of each environment and the setting conditions for developing bias control in this embodiment. In the present embodiment, control is performed so as to decrease the | Vmax−Vl | value while the | Vmin−Vd | value is fixed to a constant value as the absolute humidity increases. Here, the value of | Vmax−Vl | value is changed by changing the Vmax value. In addition, the duty is adjusted in each environment so that Vdc is constant at −250V.

The effects of the present invention will be described below using comparative examples.
(Comparative Example 2)
As a comparative example 2, the configuration of the image forming apparatus is the same as that of the second embodiment. However, an apparatus that controls the developing bias to the same condition even when the absolute humidity changes due to the environmental detection is used. The developing bias in Comparative Example 2 is equivalent to that in Example 2 with an absolute humidity of 1.4 g / m ³ , the vibration bias amplitude Vpp = 1800 V, the AC frequency 3 kHz, the developing duty is adjusted, and the time average voltage Vdc = −250 V. It is said.

  As a comparative experiment, printing was performed ten sheets at a time in the three types of usage environments listed in Table 4 using the same image forming apparatus in each environment. The solid density of each image was measured using a commercially available reflection type densitometer, and the average value was taken. As for close-up, each image was measured by the method shown in Example 1, and the average value was taken.

  FIG. 9 shows a plot of absolute humidity on the horizontal axis and threshold value on the vertical axis based on the results obtained from the above experiment. FIG. 10 shows a plot of absolute humidity on the horizontal axis and solid density on the vertical axis. The broken line shows the control of Comparative Example 2 with a constant developing bias, and the solid line shows the control of this embodiment shown in Table 4. As shown in FIG. 9, in Comparative Example 2, when the absolute humidity is changed, the rushing deteriorates and exceeds the lashing value 20.

  Also, as shown in FIG. 10, the image density increases as the absolute humidity increases. On the other hand, in the configuration of the second embodiment, the threshold value can be suppressed to 20 or less and the image density can be kept constant even if the absolute humidity changes.

  The reason why the configuration of the second embodiment can reduce the close-up image and the density change is as follows. First, the gathering image will be described.

  As the absolute humidity increases, the toner charge amount distribution on the developing roller changes as shown in FIG. As the absolute humidity increases, the charge amount distribution shifts to the + side (the direction in which the absolute value of the charge amount decreases), and the distribution becomes broader. The reason why this phenomenon occurs can be easily imagined considering that triboelectric charge is likely to occur in a dry environment such as winter.

  Such a change in the charging characteristics of the toner is the reason why the contact is worsened in the configuration of Comparative Example 2 in which the developing bias is constant. As described in the first embodiment, the close-up image is generated by the reciprocating motion of the toner between the photosensitive drum and the developing roller. Accordingly, the larger the number of reciprocating movements of the toner, the more likely the contact is worsened.

  When the toner charge amount distribution shifts to the + side as shown in FIG. 11 due to the use environment of the apparatus, the Coulomb force that the toner receives due to the developing bias decreases. As a result, the number of reciprocating motions until the toner reaches the photosensitive drum from the developing roller is increased, and the contact is worsened.

  On the other hand, the rushing tends to be worsened when the barrel electric field between the developing roller and the photosensitive drum is strong. For example, when the number of reciprocating movements of the toner is the same and the barrel electric field is strong (that is, when the development Vpp is large), the toner receives a stronger force in the direction outside the development area and moves in that direction. As the velocity component increases, the close-up image appears more strongly.

  In Example 2, the barrel-shaped electric field is weakened by decreasing | Vmax−Vl | in a state in which | Vmin−Vd | is fixed as compared with Comparative Example 2, and the close-up image is compared with Comparative Example 2. It can be improved. This is the reason why there is a difference in the close-up image between the comparative example 2 and the example 2. On the other hand, it is considered that the number of reciprocating movements of the toner is slightly increased by this control, but the effect of weakening the electric field is more effective for the close-up image.

  Next, the image density will be described.

  The image density increases as the amount of toner contributing to development increases. When the use environment of the apparatus fluctuates and the absolute humidity increases, the toner charge amount distribution changes as described above. As a result, the electrostatic reflection force between the toner and the developing roller is reduced, so that the toner is easily separated from the developing roller. As a result, the amount of toner contributing to development increases and the image density increases. Therefore, in this embodiment, the electric field for the toner on the developing roller to fly is controlled by reducing the absolute value of the potential difference of | Vmax−Vl | in a state where | Vmin−Vd | is fixed according to the use environment of the apparatus. By selectively weakening the toner amount contributing to development, the image density can be kept constant.

  On the other hand, by performing control to reduce the peak-to-peak voltage Vpp of the vibration bias in accordance with the increase in absolute humidity, as in the case of the control in the present invention, there is a certain effect with respect to the close-up image. is there. This is considered to be the same reason that the above-described effect of the present invention was obtained.

  However, this method is not desirable from the viewpoint of fogging as described in the first embodiment. The reason is as follows.

For example, if the use environment is changed to the absolute humidity of ^{1.4g / m 3 → 18g / m} 3, when the developing bias kept constant remains at 1.4 g / ^{m 3,} the image as shown in Comparative Example 2 Concentrations become deeper and creaking gets worse. As described above, this is an overdeveloped state in which the amount of toner that contributes to development has increased. At the same time, the so-called background fogging phenomenon, in which the amount of toner developed to the background portion potential Vd on the photosensitive drum increases, becomes worse.

FIG. 12 shows the change in fog on the paper with respect to each absolute humidity (g / m ³ ) when the developing bias is constant, when Vpp control is performed, and in this embodiment. In the Vpp control method, Vpp is changed, and Vpp is reduced by the same value as | Vmax−V1 | is reduced in the second embodiment.

  As shown in FIG. 12, with the change in absolute humidity, the fog is remarkably deteriorated in the constant bias control of Comparative Example 2. Furthermore, the fog suppression effect is not sufficient even by Vpp control. On the other hand, in this embodiment, the fog is stable at a low value even when the absolute humidity changes.

  Regarding the fog, the reason why the effect obtained by the Vpp control is different from the effect obtained in the second embodiment has been described in the first embodiment, and therefore will be omitted here.

  In the present embodiment, the above-mentioned effect is obtained by controlling the Vmax value. However, as described in the first embodiment, the Vl value is also changed, so that the adversity image deteriorates due to the decrease in the photosensitive drum speed. The effect of suppressing changes in image density can be obtained. The reason for this is the same as that of the first embodiment, and is omitted here.

  For the reasons described above, when the operating environment of the apparatus changes as in the second embodiment of the present invention, | Vmin−Vd | remains constant as | Vmax−Vl as the absolute humidity increases. By controlling the absolute value of the | potential difference to be small, fluctuations in the image density and ground fog can be suppressed, and the rushed image can be reduced.

  In the second embodiment, values of | Vmin−Vd | = 1100 V, | Vmax−Vl | = 1110, 1000 V, and 890 V are used. However, the optimum values are obtained depending on various conditions such as the SD gap, the photosensitive drum, and the developing roller diameter. The value changes. Therefore, the effects of the present invention can be obtained by using arbitrary values according to various conditions of each image forming apparatus for the fixed value of | Vmin−Vd | and the amount of change of | Vmax−Vl |. In this embodiment, the constant value of Vdc = −250 V is used so that the effects of the present invention can be easily understood. However, the present invention is not limited to this, and any value can be used as long as the solid black density on the image is sufficiently obtained. good.

  In this embodiment, Vmin is controlled so as to correct the potential on the photosensitive drum, which fluctuates depending on absolute humidity, and | Vmin−Vd | is kept constant. On the other hand, the result of environmental detection is fed back. A method of adjusting the charging bias Vc and keeping Vd constant regardless of the use environment is also conceivable. In this case, by setting Vmin to a constant value, | Vmin−Vd | can be set to a constant value regardless of the environment. Further, even when the charging biases Vc and Vmin are set to constant values regardless of the use environment of the apparatus, the effect of the present invention can be obtained by performing the control to change | Vmax−Vl | according to the use environment. Obviously you can.

  This embodiment relates to an invention for performing the above-described development bias control in accordance with usage information of an image forming apparatus.

  The image forming apparatus in this embodiment will be described. Except for the points described below, they are basically the same as those in the first embodiment, and a description thereof will be omitted to avoid duplication. The image forming apparatus according to the third embodiment stores information such as the number of printed sheets, the remaining amount of toner, the number of rotations of the developing sleeve, and the control value of the developing bias voltage in a separately provided storage medium (not shown). Is controlled by the control unit of the image forming apparatus main body so that the developing bias can be freely controlled.

  Next, the developing bias in this embodiment will be described.

  The developing bias in this embodiment is based on the relationship shown in FIG. 2 described in the first embodiment. The AC frequency is fixed at 3 kHz.

  Next, the potential of the photosensitive drum surface in this embodiment will be described. The primary charger 2 applies a charging bias Vc to charge the surface of the photosensitive drum. Accordingly, the background portion potential Vd = −500V and the visible portion minimum potential Vl = −100V are set. In this embodiment, Vc and Vmin are constant regardless of the number of durable sheets, and the potential on the photosensitive drum is constant depending on the number of durable sheets. In this embodiment, since the non-contact development method is used, the surface layer of the photosensitive drum is less worn due to durability, and the fluctuations of Vd and Vl are small.

  Next, a detailed description of this embodiment will be given.

  Table 5 shows the setting conditions for developing bias control performed according to the usage information of the storage medium. In this embodiment, the number of printed sheets is used as usage information, and control is performed so as to decrease the | Vmax−Vl | value while fixing the | Vmin−Vd | value to a constant value according to the durable number. Here, the method of changing the value of | Vmax−Vl | value by changing the Vmax value was used. Further, the duty is adjusted for each durable sheet so that Vdc is constant at −250V.

  The effects of the present invention will be described below using comparative examples.

(Comparative Example 3)
As Comparative Example 3, the configuration of the image forming apparatus is the same as that of Example 3, but the developing bias having the same conditions was used even when the number of durable sheets was changed. The development bias of Comparative Example 3 is equivalent to that in the initial state of Example 3, and the vibration bias amplitude Vpp = 1800V, the AC frequency 3 kHz, the development duty is adjusted, and the time average voltage Vdc = −250V.

As a comparative experiment, 10 sheets were printed for each durable number listed in Table 5 using the same image forming apparatus in each environment. The solid density of each image was measured using a commercially available reflection type densitometer, and the average value was taken. As for close-up, each image was measured by the method shown in Example 1, and the average value was taken.

  FIG. 13 shows a plot of the durable number on the horizontal axis and the threshold value plotted on the vertical axis based on the results obtained by the above experiment. FIG. 14 shows a plot in which the number of durable sheets is plotted on the horizontal axis and the solid density is plotted on the vertical axis. The broken line represents the control of Comparative Example 3 with a constant developing bias, and the solid line represents the control of this embodiment shown in Table 5. As shown in FIG. 13, in Comparative Example 3, as the number of durable sheets increases, the crease deteriorates and exceeds the crease value 20.

  Also, as shown in FIG. 14, the image density increases as the number of durable sheets increases. On the other hand, in the configuration of the third embodiment, even when the number of durable sheets increases, the threshold value can be suppressed to 20 or less, and the image density can also be kept constant.

  The reason why the above results were obtained in Comparative Example 3 and Example 3 will be described below. Generally, as the number of durable sheets increases, the toner charge amount distribution on the developing roller changes as shown in FIG. The reason why this phenomenon occurs is that the toner that has not been used (printed) in the development process described in the first embodiment repeatedly rubs with the toner amount regulating member 13 and the RS roller 12 in FIG. This is because the charge amount gradually decreases due to embedding of the agent in the toner or peeling. Such a change in the charging characteristics of the toner is the reason why the gathering deteriorated in the configuration of Comparative Example 3 in which the developing bias was constant. Further, since the electrostatic charge amount between the toner and the developing roller is reduced due to the decrease in the charge amount of the toner, the toner amount contributing to the development is increased and the image density is increased.

  On the other hand, by adjusting the developing bias by decreasing | Vmax−Vl | in a state where | Vmin−Vd | is fixed in accordance with the increase in the number of durable sheets in the third embodiment, Reduced. The reason for this is substantially the same as that of the second embodiment, so that the second embodiment will be referred to and omitted.

  On the other hand, even if control is performed to reduce the peak-to-peak voltage Vpp of the vibration bias in accordance with the increase in absolute humidity, as in the case of the control in the present invention, a certain effect is obtained with respect to the close-up image. is there. This is considered to be the same reason that the effect of the present invention was obtained.

  However, this method is not desirable from the viewpoint of fogging as described in the first and second embodiments. The reason is as follows.

  For example, when the number of endurance sheets increases from 0 to 2000, if the developing bias is kept constant in the initial state, the image density becomes high as shown in Comparative Example 3, and the creaking becomes worse. As described above, this is an overdeveloped state in which the amount of toner that contributes to development has increased. At the same time, the phenomenon of so-called background fogging, in which the amount of toner developed to the background portion potential Vd on the photosensitive drum increases, is worsened.

FIG. 16 shows the change in fog on the paper with respect to the number of durable sheets when the developing bias is fixed, when Vpp control is performed, and in this embodiment. In the Vpp control method, Vpp is reduced by the same value as | Vmax−Vl | is reduced in the third embodiment. Here, the fog was measured using a REFECTMETER MODEL TC-6DS manufactured by Tokyo Denshoku Co., Ltd. and calculated from the following equation.
Fog (reflectance) (%) = reflectance of standard paper (%)-reflectance of sample non-image area (%)
As shown in FIG. 16, the fog is remarkably deteriorated in the constant bias control of Comparative Example 3 as the number of durable sheets increases. Furthermore, the fog suppression effect is not sufficient even by Vpp control. On the other hand, in the present embodiment, the fog is stable at a low value as the number of durable sheets increases.

  As for the fog, the difference between the effects obtained by the Vpp control and the present embodiment has been described in the first embodiment, and will be omitted here.

  In the present embodiment, the above-mentioned effect is obtained by controlling the Vmax value. However, as described in the first and second embodiments, the squeezed image due to the decrease in the photosensitive drum speed can also be obtained by changing the Vl value. The point that the effect of suppressing the deterioration of the image density and the change in the image density can be obtained is the same as that described in the first embodiment, and is omitted here.

  For the reasons described above, the absolute value of the potential difference of | Vmax−Vl | is reduced with | Vmin−Vd | kept constant as the number of durable sheets of the image forming apparatus increases as in the third embodiment of the present invention. By performing such control, it is possible to suppress image density and background fogging that vary depending on the number of endurance sheets, and to reduce rush images.

  In the third embodiment, values of | Vmin−Vd | = 1100 V, | Vmax−Vl | = 1050, 1000 V, and 950 V are used. However, the optimum values are obtained depending on various conditions such as the SD gap, the photosensitive drum, and the developing roller diameter. The value changes. Therefore, the effects of the present invention can be obtained by using arbitrary values according to various conditions of each image forming apparatus for the fixed value of | Vmin−Vd | and the amount of change of | Vmax−Vl |. In this embodiment, the constant value of Vdc = −250 V is used so that the effects of the present invention can be easily understood. However, the present invention is not limited to this, and any value can be used as long as the solid black density on the image is sufficiently obtained. good.

  In this embodiment, Vc and Vmin are constant depending on the number of durable sheets. However, if the variation in the potential on the photosensitive drum due to the durability is large, Vmin is adjusted in accordance with the variation in Vd as in the second embodiment. It is apparent that the effects of the present invention can be obtained even if the control is performed so that | Vmin−Vd | is constant regardless of the number of durable sheets.

  As described above, according to the present invention described with reference to the embodiments, the following effects can be obtained.

  (1) Even when the rotation speed of the image carrier is changed, density change, a close-up image, and fogging can be reduced. (2) Even when the environment in which the image forming apparatus is used varies, it is possible to reduce the density change, the close-up image, and the fog. (3) It is possible to reduce density change, a close-up image, and fog with a low-cost configuration without providing a new detection mechanism. (4) It is possible to reduce the density change, the close-up image, and the fog that change according to the usage information of the image forming apparatus.

1 is a schematic cross-sectional view of an image forming apparatus according to Embodiment 1 of the present invention. FIG. 4 is a diagram illustrating a development bias waveform in an initial state in the image forming apparatus according to the first exemplary embodiment of the present invention. It is a figure which shows the sample image used in order to explain a close-up. It is a graph which shows density distribution with respect to the Y-axis of the sample image shown in FIG. FIG. 6 is a diagram illustrating a correspondence relationship between a timing chart, a density change, and a pull-in value in a comparative experiment between the image forming apparatuses according to Example 1 and Comparative Example 1. 6 is a graph showing the relationship between the photosensitive drum speed and the contact value according to Example 1 and Comparative Example 1 of the present invention. 6 is a graph showing the relationship between the photosensitive drum speed and the solid image density according to Example 1 and Comparative Example 1 of the present invention. 6 is a graph showing the relationship between the photosensitive drum speed and fog on paper according to Example 1 and Comparative Example 1 of the present invention. It is a gram which shows the relationship between the absolute humidity which concerns on Example 2 and the comparative example 2 of this invention, and a threshold value. It is a graph which shows the relationship between the absolute humidity which concerns on Example 2 and Comparative Example 2 of this invention, and a solid image density. 6 is a graph illustrating a toner charge amount distribution for each use environment of the image forming apparatus according to the second embodiment of the present invention. It is a graph which shows the relationship between the absolute humidity which concerns on Example 2 of this invention, and fog on paper. It is a graph which shows the relationship between the durable number which concerns on Example 3 of this invention, and a threshold value. It is a graph which shows the relationship between the durable number of sheets and solid image density which concern on Example 3 of this invention. 7 is a graph showing the relationship between the number of durable sheets and the toner charge amount distribution according to Example 3 of the present invention. It is a graph which shows the relationship between the durable number which concerns on Example 3 of this invention, and fog on paper. It is a schematic sectional drawing of the conventional image forming apparatus. It is a schematic diagram for demonstrating the mechanism of gathering.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Primary charger 3 Exposure apparatus 7 Photosensitive drum speed change means 10 Developing apparatus 11 Developing roller 18 Developing bias switching means 100 Image forming apparatus Q Transfer material T Toner Vc Charging bias Vd Background part potential Vdc Time average voltage Vl Visible part Minimum potential Vmax Flight voltage Vmin Pullback voltage Vpp Peak-to-peak voltage

Claims (7)

An image carrier on which an electrostatic latent image is formed;
A developer carrying body that holds a predetermined distance from the image carrier and carries a developer;
A charging member for charging the image carrier;
Latent image forming means for forming an electrostatic latent image on the charged image carrier;
An image forming apparatus in which a developing bias is applied to the developer carrier to make the electrostatic latent image a visible image.
The developing bias is
An oscillating bias voltage having a peak voltage Vmax for biasing the developer in the direction from the developer carrier to the image carrier and a peak voltage Vmin for biasing the developer in the direction from the image carrier to the developer carrier. Yes,
When the charging bias applied to the charging member is Vc, the background potential of the electrostatic latent image formed on the image bearing member is Vd, and the visible portion potential is Vl, the values of Vc and Vmin are constant values. ,
Vmax is changed so that the absolute value of the potential difference of | Vmax−Vl | becomes smaller and the absolute value of the potential difference of | Vmax−Vd | becomes smaller as the rotational speed of the image carrier becomes slower. Image forming apparatus. An image carrier on which an electrostatic latent image is formed;
A developer carrying body that holds a predetermined distance from the image carrier and carries a developer;
A charging member for charging the image carrier;
Latent image forming means for forming an electrostatic latent image on the charged image carrier;
An image forming apparatus in which a developing bias is applied to the developer carrier to make the electrostatic latent image a visible image.
The development bias is
An oscillating bias voltage having a peak voltage Vmax for biasing the developer in the direction from the developer carrier to the image carrier and a peak voltage Vmin for biasing the developer in the direction from the image carrier to the developer carrier. Yes,
When the background potential of the electrostatic latent image formed on the image carrier is Vd and the visible potential is Vl,
| To the potential difference absolute value as a constant value, | Vmin-Vd
Vmax is changed so that the absolute value of the potential difference of | Vmax−Vl | becomes smaller and the absolute value of the potential difference of | Vmax−Vd | becomes smaller as the rotational speed of the image carrier becomes slower. Image forming apparatus. An image carrier on which an electrostatic latent image is formed;
A developer carrying body that holds a predetermined distance from the image carrier and carries a developer;
A charging member for charging the image carrier;
Latent image forming means for forming an electrostatic latent image on the charged image carrier;
An image forming apparatus in which a developing bias is applied to the developer carrier to make the electrostatic latent image a visible image.
The developing bias is
An oscillating bias voltage having a peak voltage Vmax for biasing the developer in the direction from the developer carrier to the image carrier and a peak voltage Vmin for biasing the developer in the direction from the image carrier to the developer carrier. Yes,
When the charging bias applied to the charging member is Vc, the background potential of the electrostatic latent image formed on the image bearing member is Vd, and the visible portion potential is Vl, the values of Vc and Vmin are constant values. ,
Vmax is changed so that the absolute value of | Vmax−Vl | becomes smaller and the absolute value of | Vmax−Vd | becomes smaller as the absolute humidity of the environment in which the image forming apparatus is used increases. An image forming apparatus. An image carrier on which an electrostatic latent image is formed;
A developer carrying body that holds a predetermined distance from the image carrier and carries a developer;
A charging member for charging the image carrier;
Latent image forming means for forming an electrostatic latent image on the charged image carrier;
An image forming apparatus in which a developing bias is applied to the developer carrier to make the electrostatic latent image a visible image.
The developing bias is
An oscillating bias voltage having a peak voltage Vmax for biasing the developer in the direction from the developer carrier to the image carrier and a peak voltage Vmin for biasing the developer in the direction from the image carrier to the developer carrier. Yes,
When the background potential of the electrostatic latent image formed on the image carrier is Vd and the visible potential is Vl, the absolute value of the potential difference of | Vmin−Vd |
Vmax is changed so that the absolute value of | Vmax−Vl | becomes smaller and the absolute value of | Vmax−Vd | becomes smaller as the absolute humidity of the environment in which the image forming apparatus is used increases. An image forming apparatus. An image carrier on which an electrostatic latent image is formed;
A developer carrying body that holds a predetermined distance from the image carrier and carries a developer;
A charging member for charging the image carrier;
Latent image forming means for forming an electrostatic latent image on the charged image carrier;
An image forming apparatus in which a developing bias is applied to the developer carrier to make the electrostatic latent image a visible image.
The developing bias is
An oscillating bias voltage having a peak voltage Vmax for biasing the developer in the direction from the developer carrier to the image carrier and a peak voltage Vmin for biasing the developer in the direction from the image carrier to the developer carrier. Yes,
When the charging bias applied to the charging member is Vc and the visible part potential of the electrostatic latent image formed on the image carrier is Vl, the values of Vc and Vmin are constant values,
As the amount of use of the image forming apparatus based on the usage information of the image forming apparatus increases, the potential difference absolute value of | Vmax−Vl | becomes smaller and the potential difference absolute value of | Vmax−Vd | becomes smaller. An image forming apparatus characterized by changing the angle. An image carrier on which an electrostatic latent image is formed;
A developer carrying body that holds a predetermined distance from the image carrier and carries a developer;
A charging member for charging the image carrier;
Latent image forming means for forming an electrostatic latent image on the charged image carrier;
An image forming apparatus in which a developing bias is applied to the developer carrier to make the electrostatic latent image a visible image.
The developing bias is
An oscillating bias voltage having a peak voltage Vmax for biasing the developer in the direction from the developer carrier to the image carrier and a peak voltage Vmin for biasing the developer in the direction from the image carrier to the developer carrier. Yes,
When the background portion potential of the electrostatic latent image formed on the image carrier is Vd and the visible portion potential is V1, the absolute value of the potential difference of | Vmin−Vd | Vmax is set so that the absolute value of the potential difference of | Vmax−Vl | becomes smaller and the absolute value of the potential difference of | Vmax−Vd | becomes smaller as the usage amount of the image forming apparatus based on the usage information of the forming apparatus increases. An image forming apparatus characterized by being changed.   7. The image formation according to claim 5, wherein the usage information includes at least one information among the number of printed sheets, the number of rotations of the image carrier, the number of rotations of the developer carrier, and the remaining amount of the developer. apparatus.

Images