JPH0980880A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of a residual image by making residual charges on a developing roller uniform even right after the consecutive development of solid images, and preventing the characteristics of a toner layer formed in a part where toner is consumed from differing from a part where it is not consumed. SOLUTION: A printer is provided with a developing roller 52 facing a photoreceptive belt 2, a supply roller 53 for supplying toner to the developing roller 52, a blade 54 for regulating the thickness of a toner layer on the developing roller 52 in pressure contact with the surface of the developing roller 52, a discharge brush 55 whose conductive part abuts on the surface of the developing roller 52 downstream in a developing area in a circulation path and on the upstream side from the position where it faces the supply roller 53, and a power source 61 for applying a voltage to the conductive part of the discharge brush 55, and it is also provided with a developing device for developing a latent image on the photoreceptive belt 2 with the toner thin layer on the developing roller 52. In this printer, as the voltage which is to be applied to the conductive part of the discharge brush 55, a voltage in which AC voltage overlaps DC voltage is used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine or a printer, which is equipped with a developing device for developing a latent image on an image carrier by a one-component developer carried on a developer carrier. It relates to the device.

[0002]

2. Description of the Related Art Conventionally, a one-component developer (hereinafter simply referred to as "developer") is carried on the surface of a developer carrying member, and the surface is provided along a circulation path including a developing region facing the image carrying member. Of the latent image formed on the image bearing member by the thinned developer on the developer bearing member while transporting the developer carried on the surface by the movement of There is known an image forming apparatus that employs a developing method for developing the image. Further, in this type of image forming apparatus, a developer supply unit for supplying the developer to the developer carrier is provided.

[0003]

By the way, in the image forming apparatus adopting the above-mentioned developing system, when a thin layer of the developer is formed on the developer carrier, the developer adhered to the surface of the developer carrier. The counter charge (counter charge), which has almost the same amount as the charge amount of 1 and the opposite polarity, exists and remains.
The presence and residual of the opposite charges are remarkable especially when the surface resistivity of the developer carrier is 10 ¹² [Ω · cm] or more, and when calculated by the same calculation as the time constant of the capacitor, It is considered to increase as the surface movement of the developer carrier along the circulation path progresses. Therefore, when the image density is high, that is, when the amount of developer consumed is high, mutual charging by the developer supplied to the developer carrier (it can be said that the developer is sequentially replaced from the viewpoint of the developer carrier) is caused. The developer carrier repeats charging, and the residual charge further increases. In particular, the amount of this residual charge is remarkable after continuous solid development, and is considered to take the maximum value at that time.

Further, the residual charge on the surface of the developer carrying member affects the charge amount and the adhesion amount of the developer layer on the developer carrying member. First, the surface of the developer bearing member is along the circulation path for a certain time (for example, the linear velocity of the image bearing member is 6
6 [mm / sec], the linear velocity ratio of the developer carrier to the image carrier is 1.
It is assumed that the linear velocity is set to 5 times and the linear velocity is set to 99 [mm / sec], and the development starts when the thin layer of the developer is saturated by moving for about 4 seconds or more in the case of A4 vertical direction. When the development is started, a portion where the developer is consumed and a portion where the developer is not present appear on the surface of the developer carrier depending on the type of the image. In the portion where the developer is not consumed in the development, both the charge / adhesion characteristics of the developer and the surface potential of the developer carrier are almost saturated, so there is almost no change.
However, only the opposing charges remain on the surface of the developer carrier, which has consumed the developer during the development. New developer is supplied to the portion where only the opposite charges remain by the developer supply means. The newly supplied developer is triboelectrically charged by just one contact, and its adhered state tends to be different from that in the saturated state.
Further, the force for adhering the newly-supplied developer to the surface of the developer carrier by the amount of charge tends to be different from that in the saturated developer, in the portion where only the opposite charges remain. As a result, in the portion of the developer carrying member where the developer is consumed, the surface potential and the amount of the charged / adhered amount of the developer are different from those in which the developer is not consumed. Therefore, in the portion where the developer is consumed, the developing characteristic changes (the developing start voltage changes due to the developing characteristic), and the density that should be originally output on the image becomes higher or lower than the predetermined density. In particular, the deviation of the output image from the predetermined density is remarkable in the low-density image portion immediately after a large amount of the developer such as a solid image is consumed, and is called “afterimage”. For example, depending on whether the solid image is developed by the developer conveyed by the movement of the surface of the developer carrier on the first lap along the circulation path or not, the developer carrier on the second and subsequent laps is developed. The charge amount and the adhesion amount of the developer conveyed by the movement of the surface and the electric potential of the surface are not the same, and the output image densities are different, and an afterimage is likely to occur.

Incidentally, as a means for removing unnecessary charges accumulated on the developer carrying member, JP-A-61-42672 is known.
In the publication, the conductive brush bristles of the static elimination brush are brought into contact with the surface of the development sleeve at the downstream side of the development region along the rotation direction of the development sleeve as the developer carrying member, and the static elimination brush is attached to the surface of the development sleeve. It is disclosed that the same amount of voltage as that applied to the conductive substrate is applied so as to make the charge amount on the surface of the developing sleeve uniform. However, even in this configuration, immediately after continuous solid development, the charge removal effect on the portion where the developer is consumed is reduced as compared to the undeveloped portion, and there is a possibility that an afterimage may occur. there were.

The present invention has been made in view of the above problems, and an object thereof is to even out the electric charge remaining on the surface of the developer carrying member even immediately after continuously developing a solid image. The present invention provides an image forming apparatus capable of suppressing the occurrence of an afterimage by performing the above-mentioned processing so that the characteristics of the developer layer formed in the portion where the developer is consumed are not different from those in the portion where the developer is not consumed. .

[0007]

In order to achieve the above object, the invention of claim 1 is carried on the surface by moving the surface along a circulation path including a developing region facing the image carrier. A developer carrying body for carrying the developer, a developer supplying means for supplying the developer to the developer carrying body, and a layer of the developer on the developer carrying body by being in pressure contact with the surface of the developer carrying body. A layer thickness regulating member that regulates the thickness and a conductive portion made of a conductive material are applied to the surface of the developer carrier at a position downstream of the developing region in the circulation path and upstream of a position facing the developer supply unit. The latent image on the image carrier is formed by a thinned developer on the developer carrier, which has a static eliminator in contact and a voltage applying means for applying a voltage to a conductive portion of the static eliminator. In the image forming apparatus equipped with a developing device for developing, As the voltage applied to, it is characterized in that was used by superimposing an AC voltage on a DC voltage.

According to a second aspect of the invention, in the image forming apparatus according to the first aspect, the voltage applying means is provided so that the setting of the peak-to-peak value of the AC voltage and the value of the DC voltage can be changed independently. It is characterized by being configured.

[0009] The invention of claim 3 is based on claim 1 or 2.
In the image forming apparatus, the surface potential detecting means for detecting the surface potential of the developer carrier downstream of the developing area in the circulation path and upstream of the contact position of the charge removing member, and the detection by the surface potential detecting means. Control means for controlling the voltage application means is provided so as to change the setting of the voltage applied to the conductive portion of the charge eliminating member based on the result.

The invention of claim 4 is the same as claim 1 or 2.
Image forming apparatus, a reference latent image forming means for forming a reference latent image on the image carrier, and an image of the reference visible image on the image carrier formed by developing the reference latent image by the developing device. Image density detecting means for detecting the density, and control means for controlling the voltage applying means so as to change the setting of the voltage applied to the conductive portion of the static eliminating member based on the detection result of the image density detecting means. It is characterized by that.

According to the first aspect of the present invention, the developer carried on the surface of the developer carrier is conveyed by moving the surface of the developer carrier along a circulation path including a developing region facing the image carrier. The developer layer carried on this developer carrier is
After controlling the layer thickness with a layer thickness regulating member that presses against the surface,
Used for developing the latent image on the image carrier in the developing area. Then, the surface of the developer carrying member that has passed through the developing area is de-charged by a charge removing member having a conductive portion in contact with the surface, and then the developer is supplied to the developer carrying member by the developer supplying means.

Here, by superimposing an AC voltage on the DC voltage applied to the conductive portion of the static eliminating member by the voltage applying means, immediately after continuously developing a solid image, unlike the case where only the DC voltage is applied. Even in this case, the charge is satisfactorily removed and the charges remaining on the surface of the developer carrier are made uniform. Furthermore, by setting the value of the DC voltage applied to the conductive portion of the charge eliminating member to a predetermined voltage, the characteristics of the developer layer formed in the portion where the developer is consumed are not different from the portions where the developer is not consumed. To do so.

In the invention of claim 2, since the setting of the peak-to-peak value of the AC voltage can be changed independently of the DC voltage, it is necessary to prevent the applied voltage from leaking and to eliminate static electricity according to environmental changes. Even when the setting of the peak-to-peak value of the AC voltage is changed, the value of the DC voltage is maintained as it is or the setting is changed to an optimum value, and the characteristics of the developer layer formed in the portion where the developer is consumed. Is not different from the part that is not consumed.

According to a third aspect of the invention, the surface potential of the developer carrying member is detected by the surface potential detecting means, and the surface of the portion of the developer carrying member where the developer is consumed is detected based on the detection result. By changing the setting of the voltage applied to the conductive portion of the charge removing member according to the magnitude of the potential, the charge remaining on the surface of the developer carrier immediately after continuous development of a solid image is made uniform. At the same time, the characteristics of the developer layer formed in the portion where the developer is consumed are not different from those in the portion where the developer is not consumed.

In the fourth aspect of the invention, the reference latent image is formed on the image carrier by the reference image forming means after the image consuming a large amount of the developer and the image consuming a small amount of the developer.
Then, the image density of the reference visible image on the image carrier formed by developing the reference latent image by the developing device is detected by the image density detecting means, and based on the detection result, the image density of each reference visible image is By changing the setting of the voltage applied to the conductive portion of the charge eliminating member so as to be substantially the same, it is possible to suppress the occurrence of afterimages immediately after continuous development of solid images.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment in which the present invention is applied to a full-color printer (hereinafter referred to as "printer") 1 as an image forming apparatus equipped with a rotary developing device having a plurality of developing units will be described below. First, the schematic configuration of the printer will be described with reference to FIG. A belt-shaped photoconductor (hereinafter referred to as “photoconductor belt”) 2 as an image carrier is uniformly charged by a charging roller 3 as a charging unit, and then based on image information by a laser optical device 4 as an exposing unit. Scanning exposure is performed to form an electrostatic latent image on the surface. Here, the image information to be exposed is monochromatic image information obtained by decomposing a desired full-color image into yellow, magenta, cyan, and black color information. The electrostatic latent image formed on the photoconductor belt 2 is developed by a rotary developing device 5 to be described later with a predetermined developer such as yellow toner, magenta toner, cyan toner and black toner, and the electrostatic latent image is formed on the photoconductor belt 2. A toner image of each color is formed on the.

Photoreceptor belt 2 rotating in the direction of arrow A in the figure
The toner images of the respective colors formed above are sequentially superimposed and transferred for each single color of yellow, magenta, cyan and black onto the intermediate transfer belt 6 which rotates in the direction B in the figure in synchronization with the photoconductor belt 2. The yellow, magenta, cyan, and black images superposed on the intermediate transfer belt 6 are transferred onto a transfer paper 10 as a transfer material which is conveyed from a paper feed table 7 through a paper feed roller 8 and a registration roller 9 to a transfer section. , Are collectively transferred by the transfer roller 11. After the transfer is completed, the transfer paper is fixed on the fixing device 1.
It is fixed by 2 and a full color image is completed.

The toner on the photoconductor belt 2 that has not been transferred to the intermediate transfer belt 6 is removed from the photoconductor belt 2 by the photoconductor cleaner 13. In addition, the transfer paper 10
The toner on the intermediate transfer belt 6 that has not been transferred onto the
The intermediate transfer belt cleaner 14 removes the intermediate transfer belt 6 from the intermediate transfer belt 6.

Next, the rotary developing device 5 will be described with reference to FIGS. As shown in FIG. 2, a rotary developing device (also referred to as a revolver developing device or a rotary developing device; hereinafter simply referred to as “developing device”) 5 is arranged near the photosensitive belt 2 as described above. In this developing device 5, a casing 5 forming a rotating body
0 is rotatably provided around the rotation axis, and the casing 5
0 is rotated in the direction of arrow C by a drive mechanism (not shown). The casing 50 has a shape that divides the developing device into four parts, and developing units 51Y, M, C, and K are formed in each of the four divided regions.

FIG. 3 is a front view showing one developing unit 51 of the developing device together with the photosensitive belt 2.
The four developing units 51K, 51C, 51M, 5
Since 1Y has the same configuration, description of each is omitted. In the developing position of FIG. 3, the developing unit 51
In the opening 51a formed in the upper part of K, a cylindrical developing roller 52 as a developer carrying member facing the photoconductor belt 2 is provided at the same speed as the photoconductor belt 2 or at a predetermined peripheral speed ratio. Is in the same direction as the photosensitive belt moving direction (arrow D in the figure)
Direction). The material of the developing roller 52 is preferably one that is charged with the opposite polarity to the toner 58 as a developer, and examples thereof include silicone rubber, butadiene rubber, EPDM, and silicone resin. In this example, since the toner 58 is negatively charged, the developing roller 52 is basically positively charged. A developing bias voltage (negative DC voltage in this example) is applied to the core of the developing roller 52 from the developing power source 59, and the core of the developing roller 52 and the photosensitive belt 2 are exposed during development. A predetermined developing potential is formed between the body and the body.

As the toner 58, a toner obtained by mixing a polyester base with a charge control agent and adding silica (SiO2) as an external additive was used. Examples of the charge control agent include salicylic acid derivative Zn salt and ammonium salt.

Below the developing roller 52, a supply roller 53 as a developer supplying means made of an elastic material such as foamed polyurethane slides on the developing roller 52 and at the sliding portion, the developing roller 52. On the other hand, it is provided so as to rotate in the same direction (direction of arrow E in the figure) with a predetermined peripheral speed ratio. A replenishing bias voltage (negative DC voltage in this example) is applied to the core metal portion of the supply roller 53 from the toner replenishing power source 60, and the core metal portion of the developing roller 52 and the core metal portion of the supply roller 53 are connected to each other. A predetermined supply potential is formed in the meantime.

Further, a blade as a layer thickness regulating member made of a thin metal plate such as stainless steel or an elastic body such as urethane rubber is provided in the vicinity of the opening 51a on the downstream side of the supply roller 53 in the moving direction of the developing roller 52. 54 is provided so that the vicinity of one end thereof is in contact with the developing roller 52. It is considered that the material of the blade 54 is preferably metal, resin, or the like that promotes toner charging and is less likely to wear with time.

Further, in the developing unit 51, a destaticizing brush 55 as a destaticizing member, which will be described in detail later, and a developing for conveying and circulating toner between the developing unit 51 and a hopper (not shown) as a developer accommodating portion. Toner transfer screws 56 and 57 are provided as agent transfer means.

In each developing unit 51 having the above structure,
The toner 58 supplied by the supply roller 54 adheres to the developing roller 52 by frictional charging. The toner 58 supplied to the developing roller 52 is recharged by the blade 54 and leveled into a uniform thin layer. This developing roller 2
The upper thinned toner layer is conveyed to the developing area of the opening 51 a as the developing roller 2 rotates, and is used for developing the electrostatic latent image formed on the photosensitive belt 2.
At this time, the toner carried on the surface of the developing roller 52 is partially consumed by the above-mentioned development, but is adhered to the portion of the surface of the developing roller 52 that has passed through the developing area where the toner has been consumed. The opposite charge, which has almost the same charge amount as that of the toner, remains. In order to reduce the influence of the opposite charges remaining on the surface of the developing roller 52 on the image quality, the conductive portion of the static eliminating brush 55 as a static eliminating member is brought into contact with the surface of the developing roller 52, and the developing roller 52 after the development is completed.
The residual charge on the surface is made to be the same as the portion where the toner was not consumed in the development. (Hereinafter, margin)

Next, the material and shape of the static elimination brush 55 will be described. The brush material forming the conductive portion of the static elimination brush 55 is basically a synthetic fiber material such as acrylic, nylon, rayon, etc., in which a conductive material such as carbon black is uniformly dispersed to obtain an electric resistance (volume specific resistance). Is lowered, and the fiber is spun based on it. Particularly, in order to improve the efficiency of homogenization, the volume resistivity and the flock density of the brush material are important. The adjustable range of the volume resistivity of the brush material is about 10 to 10 ¹⁰ [Ω · cm] depending on the amount of dispersed carbon. Further, the above brush material has a density of 50,000-
The hair is planted within the range of 100,000 [F / inch (2.54 cm) ² ]. Here, the efficiency is improved as the density of the brush material is increased, but problems such as hair loss and fluffing are more likely to occur, so the above upper limit is set.

Next, the voltage applied to the conductive portion of the static elimination brush 55 and the effect of the voltage application will be described. As described above, the opposing charge remaining in the portion where the toner is consumed by the development on the first rotation of the developing roller 52 is
It affects the supply of toner from the supply roller 53 to the developing roller 52, the formation of a thin toner layer, and the development at the time of rotation after the first round. First, due to the charging of the toner on the surface of the developing roller 52, the potential of the portion charged with the opposite polarity to the toner (the portion where the opposite charge remains) changes toward the positive electrode by the amount of the opposite charge, and the supply roller 53. The effective replenishment potential between the core metal and the core metal is increased by the amount of the opposite charge. As a result, it is considered that a larger amount of toner is triboelectrically charged and is carried on the surface of the developing roller 52 at the same time as the toner is not consumed. Further, it is estimated that the charging at this time further increases the charging amount on the surface of the developing roller 52. Next, the toner layer supplied to and carried by the developing roller 52 is further pressed with a strong force against the developing roller 52 by contact with the blade 54, and the excess toner is also scraped off and charged at the same time. . Next, at the time of development, the charge on the surface of the developing roller 52 influences the direction in which development is hindered, that is, the effective developing bias is deepened. By passing through the above three steps, the developing characteristic at the time of the subsequent development of the portion where the toner is consumed in the first developing of the developing roller is determined, and the developing characteristic is It will be different from the part that was not consumed.

Further, in order to eliminate the opposite charges remaining on the developing roller 52, an electricity removing brush 55 to which an electricity removing bias voltage is applied by an electricity removing power source 61 as a voltage applying means is applied to the surface of the developing roller 52 as in the present printer. Although a configuration in which they are brought into contact with each other is conceivable, as a result of research conducted by the present inventors, a single voltage (DC voltage) is used as the static elimination bias voltage as in the conventional example.
It was found that the above opposite charges cannot be satisfactorily removed only by applying.

Therefore, in the printer according to the present embodiment, in order to satisfactorily remove and equalize the opposite charges, a voltage obtained by superimposing an AC voltage on the DC voltage Vbr (DC) as a discharging bias voltage is a conductive portion of the discharging brush 55. The static elimination power source 61 is configured so that it can be applied to. Specifically, FIG.
As shown in (b), the DC power supply unit 61a and the AC power supply unit 61b are connected in series between the conductive portion of the static elimination brush 55 and the ground to form the static elimination power source 61. Further, the peak-to-peak value Vpp of the AC voltage is set independently of each other so that the developing characteristics of the portion where the toner is consumed and the portion where the toner is not consumed during the first development of the developing roller are the same. The setting of the value Vbr (DC) of the DC voltage is changed so that the surface potential of the developing roller 52 can be maintained at a predetermined potential. Specifically, the control signal generator (PWM Generator) 62 connected to a main control unit (not shown) outputs a control signal PWM1 for the DC voltage and a control signal PWM2 for the AC voltage respectively to the DC power supply unit 61a and the AC. It is configured so that the peak-to-peak value Vpp of the AC voltage and the value Vbr (DC) of the DC voltage can be changed independently by outputting to the power supply unit 61b. And these values Vp
p and Vbr (DC) are set to be changed based on setting data input by an operator operating a predetermined changeover switch of an operation unit (not shown) and output values of various sensors (for example, a thermo-hygrometer). Can be controlled.

Since the peak-to-peak value Vpp of the AC voltage of the static elimination bias voltage affects the effect of removing the opposite charges on the surface of the developing roller 52, it depends on the difference in environment such as high humidity, normal humidity and low humidity. 500 ≦ Vpp ≦ 1000
It is possible to switch within the range of [V] so that the opposite charges can be satisfactorily removed even when the environment changes. Regarding the frequency f of the AC voltage, when the image was actually evaluated by superimposing AC voltages of various frequencies within the range of 1000 ≦ f ≦ 2500 [Hz], the output image was different due to the difference in frequency f. There seems to be a slight difference, but it is judged to be almost nonexistent considering the error.

FIG. 4 shows the peak-to-peak value Vpp of the AC voltage of the static elimination bias voltage applied to the static elimination brush 55 and 1
The data indicating the relationship with the charge removal amount [μC / m ² ] which is the difference between the amount of charge on the rotated developing roller 52 before and after passing through the charge removal brush is indicated by the symbol “□”. Here, the frequency f of the AC voltage is f = 2 [kHz], and the replenishment bias voltage Δ
Vsp = -300 [V], DC voltage value Vbr (DC) =-40
It is 0 [V]. Further, the data of the symbols "○" and "△" in the figure are the data when the static elimination brush 55 is not provided and when the direct current voltage Vbr (DC) =-200 [V] is applied to the static elimination brush 55, respectively. is there. According to the characteristic diagram of FIG. 4, the static elimination amount [μC / m ² ] increases as the peak-to-peak value Vpp of the AC voltage increases under the condition that the DC voltage value Vbr (DC) is constant. I understand.

Further, as a result of the research conducted by the present inventors, with respect to the value Vbr (DC) of the DC voltage of the static elimination bias voltage, the increase amount becomes minimum with respect to the initial value of the surface potential of the developing roller 52, and at the same time, It has been found that it is desired that the characteristics of the toner supplied from the supply roller 53 to the developing roller 52, in particular, the value that does not change the adhesion amount on the developing roller. In the printer according to the present embodiment, the opposite charges are removed, and at the same time, the surface potential of the developing roller 52 is maintained at a certain constant potential, so that the developing characteristics such as the amount of toner supplied to the developing roller 52 are maintained on the developing roller 52. The portion where toner is consumed is not different from the portion where toner is not consumed.

In FIG. 5, the peak-to-peak value Vpp of the AC voltage of the static elimination bias voltage is set to 500 [V], and the DC voltage value ΔVbr (DC) is changed from -200 [V] to -50 [V]. Developing roller 5 after passing through the static elimination brush 55
2 shows the surface potential Esp of No. 2. Here, the data of symbols “◯”, “□” and “Δ” in the figure are data after 1 rotation and 8 rotations after saturation (after continuous solid consumption, corresponding to the entire surface). From the characteristic diagram of FIG. 5, ΔVbr
It can be seen that the surface potential Esp increases as the value of (DC) increases.

Further, FIGS. 6A, 6B and 6C show
Replenishment bias voltage ΔVsp applied to the supply roller 53
Between the surface potential Esp and the surface potential Esp (ΔVsp-Esp) and the characteristics of the thin toner layer formed on the developing roller 52 (toner adhesion amount m / a, toner charge amount q / m, q / a). Is shown. Symbols "○", "□" and "△" in the figure
The data of is the same as in Fig. 5, at the time of saturation, after one rotation,
The data is after 8 rotations (corresponding to the entire surface after continuous solid consumption), and the numerical value in each data in the figure is the value of DC voltage ΔVbr
(DC) is shown. From the characteristic diagram of FIG. 6, when saturated,
Even if the toner consumption condition is different from that after one rotation and after eight rotations (after continuous solid consumption), by controlling the Esp, it is possible to obtain particularly required adhesion characteristics.

Although the effects of the AC voltage and the DC voltage of the static elimination bias voltage have been separately described above, the peak-to-peak value Vpp of the AC voltage that can be independently set as described below.
And the value of the DC voltage ΔVbr (DC) are combined, the effect is different. In FIG. 7, the same developing roller 52 is used, 750 V or 500 V is selected as the peak-to-peak value Vpp, and the DC voltage value ΔVbr (DC) is -20.
It shows the afterimage ratio by image evaluation when changing from 0V to 0V. From the characteristic diagram of FIG. 7, it can be seen that the optimum value of ΔVbr (DC) that minimizes the afterimage ratio depends on the peak-to-peak value Vpp. Vpp =
At 750V, the optimum ΔVbr (DC) = 0V, and Vpp = 5
At 00 [V], the optimum value is ΔVbr (DC) = − 150V.
The reason why the optimum ΔVbr (DC) varies depending on the peak-to-peak value Vpp is considered as follows. As described above, the peak-to-peak value Vpp of the AC voltage mainly has a static elimination effect, and in this example, the positively charged opposite charges on the surface of the developing roller 52 are reduced by the charge injection. On the other hand, the DC voltage value ΔVbr (DC) gives an absolute surface potential at the time of forming the toner thin layer and after passing through the static elimination brush 55 without affecting the static elimination effect by Vpp. That is, the effective replenishment potential is determined by the opposite charge reduced by the AC voltage and the absolute surface potential given by the DC voltage. Therefore, the higher Vpp is, the higher the static elimination effect is, but on the contrary, the appropriate replenishment potential in the toner supply unit is reduced. Such a deviation from the appropriate value of the replenishment potential is caused by the DC voltage ΔVbr
It can be compensated by the setting value of (DC).

On the contrary, the peak-to-peak value V
When pp is lowered, static elimination becomes insufficient and the replenishment potential becomes higher than the proper value. Therefore, in order to make this replenishment potential an appropriate value, the value of the DC voltage ΔVbr (DC) becomes low. You can also change the direction. This makes it possible to set Vpp low in order to prevent the leak when the ambient voltage changes and the relative humidity becomes high and the applied voltage easily leaks.

FIG. 8 shows the time variation of the surface potential Esp of the developing roller 52 after the actual continuous solid development.
In the characteristic diagram of FIG. 8, in the case where the charge eliminating brush 55 is not used (data of “□”), the surface potential is considerably increased after the developing roller 52 makes one rotation. Further, in the case where only the DC is applied to the static elimination brush 55 (data of “Δ”), the change amount of the surface potential is small after the developing roller 52 makes one rotation, and there is no problem even for an image, but it is increased by about 100 V in the continuous solid development are doing. Compared to them, in the case where AC + DC is applied to the static elimination brush 55 as in the embodiment of the present invention (data of “◯”), the change amount of the surface potential Esp is about 60 [V after the developing roller 52 makes one rotation. ], And a high-quality image with almost no problems on the image was obtained.

In the printer having the above structure, the surface potential of the developing roller 52 is detected by the surface potential detecting means, and the peak-to-peak value Vpp and / or DC of the AC voltage of the discharging bias voltage is detected based on the detection result. It may be configured to change the setting of the voltage value ΔVbr (DC).
In FIG. 9A, a probe 63 of a surface electrometer serving as the surface potential detecting means is provided in a non-contact state downstream of the developing position and at a position facing the developing roller 52 so that the surface potential of the developing roller 52 can be detected. There is. Since an alternating electric field is applied during actual development, various waveforms are detected, so the development bias voltage, replenishment bias voltage, and
The application of the static elimination bias voltage is stopped and the surface potential is measured. By this measurement, the surface potential of the developing roller 52 at the portion where the toner is consumed due to the solid phenomenon, that is, the charge amount can be observed. Further, the probe 63 of the surface electrometer is perpendicular to the traveling direction of the surface of the developing roller 52, that is, the traveling direction of the surface of the photosensitive belt 2 and parallel to the surface of the developing roller 52, as shown in FIG. 9B. So that it can be moved to the
Can be moved along. Then, the surface potentials of the rear portion where the continuous solid development is performed and the rear portion where the toner is not consumed are detected. Since a change in the surface potential of the developing roller 52 after a predetermined time can be observed, the setting of the peak-to-peak voltage Vpp of the static elimination bias voltage applied to the conductive portion of the static elimination brush 55 is changed in the direction of minimizing the change amount. After that, the setting of the DC voltage value ΔVbr (DC) is changed. These settings are changed based on the data table shown in Table 1 below. For example, the initial setting is Vpp (priority 1) = 500V, ΔVbr (DC)
(Priority 2) =-150V is used to form an image, and if the detected value of the surface potential at that time is 50 to 100V in the upper stage, Vpp = 600V of priority 1 is selected, and priority is given after detection and evaluation in the next sequence. Feedback control is performed to set ΔVbr (DC) to the optimum condition by changing the item 2 to make the detected value of the surface potential as close as possible to “0”. The value indicated by "*" in Table 1 is an initial setting value. (Hereinafter, margin)

[0039]

[Table 1]

FIG. 10 is a flow chart showing an example of the static elimination bias voltage control based on the output value of the surface electrometer. In FIG. 10, first, the timing until the surface of the developing roller 52 that contributed to the development is opposed to the probe 43 of the surface electrometer after the development is measured, and Vpp = 500V, ΔVbr
Development is performed by setting (DC) =-150V (step 1,
2). Then, the surface potential (V0) of the developing roller 52 immediately after the start of development and the surface potential (V8) of the developing roller 52 immediately after the toner consumption of A4 solid development are detected, and Vdif = V8−
Set to V0 (steps 3 and 4). Based on this Vdif value, Vpp when 100 ≦ Vdif <150 [V]
= 700 [V], change the setting and perform further development.
When Vdif <100 [V], the setting is changed to Vpp = 600 [V] and further development is performed (steps 5 to 8). When 0 ≦ Vdif <50 [V], the value of the DC voltage Δ
Development is performed while changing Vbr (DC) to −200, −100, −50, 0 [V], and ΔV at which the above Vdif becomes minimum.
br (DC) is obtained by feedback control, and the application condition of the static elimination bias voltage is determined (steps 9 to 12).

In the printer having the above structure, the density of the reference image formed on the photosensitive belt 2 is detected by the image density detecting means, and the peak-to-peak value of the AC voltage of the static elimination bias voltage is detected based on the detection result. The setting of Vpp and / or the value ΔVbr (DC) of the DC voltage may be changed. In FIG. 11A, a photo sensor 65 including a light emitting portion and a light receiving portion as the image density detecting means.
Are arranged in a non-contact state downstream of the developing position and at a position facing each other so that the image density of the reference image on the photosensitive belt 2 can be detected. Further, the photo sensor 65 is shown in FIG.
As shown in the case of the surface of the developing roller of (b), along the two rods 64 so as to be movable in the direction perpendicular to the traveling direction of the photosensitive belt 2 and parallel to the surface of the photosensitive belt 2. It can be moved by a driving device (not shown). Then, at a timing other than the normal image formation, as shown in FIG. 9B, after the solid image 66, the toner adhesion amount is about 0.2 to 0.6 [mg / cm ² ], which is a relatively low density. Halftone image 6 as a uniform reference image
7 is formed on the photoconductor belt 2, and the image density of the halftone image after the solid image is detected, and compared with the image density of the halftone image in the portion where the toner is not consumed due to the consumption by the solid image. Check whether there is a difference in the image density of. That is, the light reflectance of the halftone image on the photosensitive belt 2 at the rear portion where the solid image is continuously solid-developed and at the rear portion where the toner is not consumed is detected, and both of them are detected. When it is determined that there is a difference in image density, the AC of the neutralization bias voltage applied to the conductive portion of the neutralization brush 55 depends on whether the halftone image after toner consumption is darker or lighter. Peak-to-peak value of voltage Vpp
After changing the setting of, the setting of the DC voltage ΔVbr (DC) is changed. These settings are changed based on the data table shown in Table 2 below, and the detected value of the difference in image density, that is, the difference in adhesion amount is fed back to the voltage condition applied to the static elimination brush 55. Although the relationship between the light reflectance and the toner adhesion amount is shown in FIG. 11B, it is almost linear in the adhesion amount region used in this embodiment. (Hereinafter, margin)

[0042]

[Table 2]

[0043]

According to the first aspect of the present invention, by superimposing an AC voltage on the DC voltage applied to the conductive portion of the static eliminator by the voltage applying means, a continuous voltage is provided unlike the case where only the DC voltage is applied. Immediately after the solid image is developed, good charge removal is performed to uniformize the electric charge remaining on the surface of the developer carrying member. Furthermore, by setting the value of the DC voltage applied to the conductive portion of the charge eliminating member to a predetermined voltage, the characteristics of the developer layer formed in the portion where the developer is consumed are not different from the portions where the developer is not consumed. To do so. Therefore, there is an effect that it is possible to prevent the occurrence of an afterimage even immediately after the continuous development of solid images.

According to the second aspect of the present invention, since the setting of the peak-to-peak value of the AC voltage can be changed independently of the DC voltage, it is possible to prevent leakage of the applied voltage and perform static elimination according to environmental changes. Even when the setting of the peak-to-peak value of the AC voltage is changed, the value of the DC voltage is maintained as it is or the setting is changed to an optimum value, and the developer layer formed in the portion where the developer is consumed is formed. Since it is possible to prevent the characteristics from being different from those in the unconsumed portion, it is possible to prevent the occurrence of an afterimage.

According to the third aspect of the present invention, by changing the setting of the voltage applied to the conductive portion of the charge eliminating member based on the detection result of the surface potential of the developer carrier, solid images can be continuously formed. Since the charge remaining on the surface of the developer carrier immediately after development can be made uniform, and the characteristics of the developer layer formed in the portion where the developer has been consumed can be the same as the unconsumed portion, There is an effect that it is possible to precisely control the prevention of the occurrence of the afterimage immediately after the continuous development of solid images.

According to the invention of claim 4, based on the detection result of the image density of the reference visible image formed on the image carrier,
By changing the setting of the voltage applied to the conductive portion of the charge eliminating member so as to suppress the occurrence of an afterimage, it is possible to accurately control the prevention of the afterimage immediately after the continuous development of solid images.

[Brief description of drawings]

FIG. 1 is a front view showing a schematic configuration of a printer according to an embodiment of the invention.

FIG. 2 is a front view showing a schematic configuration of a developing device used in the printer.

FIG. 3A is a front view showing a schematic configuration of one developing unit of the developing device. FIG. 6B is an explanatory diagram of a charge eliminating power source of the developing unit and a control unit thereof.

FIG. 4 is a graph showing the relationship between the peak-to-peak value Vpp of the static elimination bias voltage and the static elimination amount.

FIG. 5 is a graph showing the relationship between the DC voltage ΔVbr (DC) of the discharging bias voltage and the surface potential Esp of the developing roller after passing the discharging brush.

6A, 6B, and 6C show the difference (ΔVsp−) between the replenishment bias voltage ΔVsp and the surface potential Esp of the developing roller.
9 is a graph showing the relationship between Esp) and the characteristics of the thin toner layer formed on the developing roller.

FIG. 7 is a graph showing the relationship between the DC voltage ΔVbr (DC) of the static elimination bias voltage and the afterimage rate.

FIG. 8 is a graph showing the change over time of the surface potential Esp of the developing roller.

FIG. 9A is a front view showing a schematic configuration of a developing unit of a developing device according to a modification. FIG. 7B is an explanatory diagram of a drive mechanism of the surface electrometer used in the developing unit.

FIG. 10 is a flowchart showing an example of control of a static elimination bias voltage in the developing device.

FIG. 11A is a front view showing a schematic configuration of a developing unit of a developing device according to another modification. (B) is a graph showing the relationship between the toner adhesion amount and the light reflectance in the image on the photoconductor belt.

[Explanation of symbols]

 2 photoconductor belt 5 developing device 51 developing unit 52 developing roller 53 supply roller 54 blade 55 static elimination brush 58 toner 61 static elimination power source 61a direct current power source 61b alternating current power source 62 control signal generator 63 surface potential meter 65 photo sensor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Yuichi Ueno 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (72) Ucuke Fujishiro 1-3-6 Nakamagome, Ota-ku, Tokyo In Ricoh Co., Ltd. (72) Mayumi Miyao, Inc. 1-3-6 Nakamagome, Ota-ku, Tokyo In Ricoh Co., Ltd.

Claims (4)

[Claims] 1. A developer carrier carrying a developer carried on the surface by moving the surface along a circulation path including a developing region facing the image carrier, and a developer on the developer carrier. A developer supply unit for supplying the developer, a layer thickness regulating member for pressing the surface of the developer carrier to regulate the layer thickness of the developer on the developer carrier, and a downstream of the developing region in the circulation path. And a charge removing member in which a conductive portion made of a conductive material is brought into contact with the surface of the developer carrying member upstream of a position facing the developer supplying means, and a voltage for applying a voltage to the conductive portion of the charge removing member. An image forming apparatus having a developing device for developing a latent image on the image bearing member with a thinned developer on the developer bearing member, wherein: The voltage to be applied is a DC voltage with an AC voltage superimposed. An image forming apparatus characterized by being used. 2. The image forming apparatus according to claim 1, wherein the voltage applying unit is configured so that the settings of the peak-to-peak value of the AC voltage and the value of the DC voltage can be independently changed. Image forming apparatus. 3. The image forming apparatus according to claim 1, wherein a surface potential for detecting a surface potential of the developer carrying member is downstream of the developing region in the circulation path and upstream of a contact position of the charge removing member. And a control unit for controlling the voltage applying unit so as to change the setting of the voltage applied to the conductive portion of the static eliminating member based on the detection result of the surface potential detecting unit. Image forming apparatus. 4. The image forming apparatus according to claim 1, wherein the reference latent image forming means forms a reference latent image on the image carrier, and the reference latent image is developed by the developing device. Image density detecting means for detecting the image density of the reference image on the image carrier, and the voltage for changing the setting of the voltage applied to the conductive portion of the static eliminating member based on the detection result of the image density detecting means. An image forming apparatus comprising: a control unit that controls an application unit.