JPH0862969A - Developing device - Google Patents

Abstract

PURPOSE: To reduce the consumption of toner by preventing the futile sticking and scattering of the toner, in a part except the latent image region of an image carrier, in a developing device constituted in such a manner that a second toner carrying means is interposed between the image carrier and a first toner carrying means. CONSTITUTION: The developing device is provided with a first bias supplying means 5 for supplying a bias to the first toner carrying means 3 in such a manner that first and second bias potentials are switched, a second bias supplying means 6 supplying the bias of a third bias potential to the second toner carrying means 2 and stopping the supply and a bias potential switching control means 7 changing over the first and second bias potentials, to electrically transfer the toner T on the first toner carrying means 3 to the second toner carrying means 2 with the timing of the development of a latent image formed on the image carrier 1 and the toner T on the second toner carrying means 2 to the first toner carrying means 3 with the completion timing of the development or nondeveloping timing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device used in an image forming apparatus such as a copying machine, a digital multi-function peripheral, a laser printer, a facsimile and the like.

[0002]

2. Description of the Related Art In FIG. 6, a second toner carrying roller 2 is formed between an image carrier 1 and a first toner carrying roller 2.
It is a principal part block diagram of a step development system. The first toner carrying roller 3 is a roller having a magnetic field generating layer, and the toner is held on its peripheral surface. The doctor blade 4 having elasticity is in contact with this roller. The toner layer thickness of the toner T held on the peripheral surface of the first toner carrying roller 3 is regulated by the doctor blade 4 and frictionally charged with it.

The surface of the second toner carrying roller 2 is an elastic roller having a dielectric layer, and forms a region of a predetermined area and is in contact with the first toner carrying roller 3 and the image carrier 1.
The frictionally charged toner T is transferred and adhered from the first toner carrying roller 3 to the second toner carrying roller 2 by an electric force of the bias voltage Vr applied to the first toner carrying roller 3. Further, by an electric force of the bias voltage Vm applied to the second toner carrying roller 2, the second toner carrying roller 2 transfers and adheres to the latent image portion of the photoconductor on which an image is formed by latent image means (not shown). And visualize it.

[0004]

[Problems to be Solved by the Invention]
The multi-stage developing method includes the image carrier 1 and the second toner carrying roller 2,
Since the second toner carrying roller 2 and the first toner carrying roller 3 are in contact with each other and are connected from the same drive system,
The start and stop of each rotation operation occur at the same time. Therefore, while the image carrier 1 is rotating, the image carrier 1
The second toner conveying roller which is in contact with the roller also rotates while the toner layer is formed on the surface thereof. Further, the first toner carrying roller 3 is adapted to come into contact with the second toner carrying roller 2 and supply the toner while holding the toner on the peripheral surface thereof. Therefore, from the start of the image carrier 1 which is a region other than the latent image of the image carrier 1 to the start of the one page region, from the end of the one page region to the stop of the image carrier 1, and The image carrier 1 receives the toner on the second toner carrying roller 2 between pages, and further from the time when the jam of the recording paper P is removed to the start of a new one-page area. It will be in the form of being. Therefore, among the toners on the second toner carrying roller 2,
Can't hold properly Properly uncharged, low,
The toner having no charging polarity is transferred to the image carrier 1. Therefore, the toner adhered on the image carrier 1 may be collected by the cleaning means or may be scattered, and further, may be transferred to the front and rear end portions of the recording paper P and left as background stain. It was In addition, there has been a problem that toner consumption is increased accordingly.

In the present invention, in a portion other than the latent image area of the image carrier, useless toner adhesion and scattering are prevented, the toner consumption is reduced, and the toner transfer amount can be adjusted. The purpose is to provide a device.

[0006]

To this end, the above-mentioned claim 1
According to the invention, the first bias supply means for switching and supplying the first bias potential or the second bias potential to the first toner transporting means, and the third bias for the second toner transporting means.
Second bias supply means for stopping the supply of the bias potential of the second toner, and the toner on the first toner carrying means for the second toner at the timing of developing the latent image formed on the image carrier.
The first and second biases are configured to electrically transfer the toner to the toner carrying means and to electrically transfer the toner on the second toner carrying means to the first toner carrying means at a development end timing or a non-developing timing. A bias potential switching control means for switching the potential is provided.

The invention according to claim 2 is characterized in that the bias potential supplied from the first bias supply means is made variable.

According to the third aspect of the present invention, the switching timing of the bias potential switching control means for switching the first and second bias potentials is set such that at the start of recording one page, the feeding of the recording paper is started or The time at which the recording paper passes a predetermined position on the paper feed path is T ₀ , the time until the recording paper starts feeding or reaches the transfer position from the predetermined position is t ₁ , and the latent image on the image carrier is The time from the start of formation until the latent image reaches the transfer position is t ₂ , the time until the latent image reaches the developing position is t ₃ , and the second toner carrying means moves from the contact position of the first toner carrying means to the aforesaid position. When the time required for rotation to reach the developing position is t ₄ , T ₁ = T ₀ + t ₁ −
When the time t ₂ + t ₃ −t ₄ is reached, the voltage applied to the first bias supply unit is switched so that the toner on the first toner transfer unit is transferred and attached to the second toner transfer unit. And

According to the fourth aspect of the present invention, the switching timing of the bias potential switching control means for switching the first and second bias potentials is set so that when the recording of one page is completed, the feeding of the recording paper is started or The time at which the recording paper passes a predetermined position on the paper feed path is T ₀ , the time until the recording paper starts feeding or reaches the transfer position from the predetermined position is t ₁ , and the latent image on the image carrier is The time from the start of formation until the latent image reaches the transfer position is t ₂ , the time until the latent image reaches the developing position is t ₃ , and the second toner carrying means moves from the contact position of the first toner carrying means to the aforesaid position. When the required rotation time to reach the developing position is t ₄ , and the required time from the latent image formation start to the latent image formation of one page is t ₅ ,
When the time T ₂ = T ₀ + t ₁ −t ₂ + t ₃ −t ₄ + t ₅ is reached, the first bias supply is performed so that the toner on the second toner carrying means is collected by the first toner carrying means. It is characterized in that the voltage applied to the means is switched.

According to the invention of claim 5, when the time required from the end of latent image formation on the first page to the start of latent image formation on the next page is t ₆ , within t ₆ hours, The voltage applied to the first bias supply unit is switched so that the toner on the second toner transfer unit is collected by the first toner transfer unit.

According to the sixth aspect of the invention, the switching timing of the bias potential switching control means for switching the first and second bias potentials is changed after the jam in the recording paper conveyance system is removed. Simultaneously with the output of the paper feed start signal, the voltage applied to the first bias supply unit is switched so that the toner of the second toner transfer unit is collected by the first toner transfer unit.

According to the seventh aspect of the invention, the predetermined position on the paper feed path is a position for detecting the feeding of the recording paper after the start of feeding.

According to the eighth aspect of the present invention, the predetermined position on the paper feeding path is a position for detecting the feeding of the recording paper after the paper feeding is started.

[0014]

According to the structure of the first aspect, by making the two potentials of the first toner conveying means switchable,
The toner formed on the toner conveying means is supplied to the second toner conveying means or the toner already adhering to the second toner conveying means is collected so that the latent image portion formed on the image carrier is At timings other than the development, the toner on the second toner carrying means is collected so that the toner supply to the second toner carrying means is stopped. Therefore, since the toner that has already adhered to the second toner conveying means can be collected on the first toner conveying means, the second toner conveying means having no toner can contact the image carrier. Therefore, the toner having a low proper charge, the non-charged toner, and the reverse-charged toner do not adhere to the image carrier.

Further, according to the second aspect of the present invention, the potential of the first toner conveying means can be made variable so that the first toner conveying means can be changed.
The toner formed on the toner conveying means can be supplied to the second toner conveying means or the already-adhered toner on the second toner conveying means can be collected, and the magnitude of the electric potential can be adjusted accordingly. The amount of toner supplied to the second toner conveying means can be adjusted, and the development density can be adjusted.

According to the structure of claim 3, 1
When the page recording operation is started, the positions of the recording sheet and the latent image head at the transfer position are previously aligned in advance, so the start point of the latent image and the latent image head of one page come to the developing position. There is no time lag in the timing up to. Therefore, until the head of the latent image of one page reaches the developing position, the second toner carrying means without toner adhesion can be brought into contact with the image carrier. Therefore, the toner having a low proper charge, the non-charged toner, and the reverse-charged toner do not adhere to the image carrier.

According to the structure of claim 4, 1
At the end of the page recording operation, the positions of the recording paper and the latent image head at the transfer position are previously aligned in time,
There is no positional or temporal deviation between the start time of the latent image and the timing from the start of the latent image until the trailing edge of one page reaches the developing position. Therefore, at the timing when the trailing edge of the first page on the image carrier passes the developing position, the toner on the second toner carrier can be collected by the first toner carrier and the toner adheres to the image carrier. It is possible to contact the above-mentioned second toner conveying means which does not have the above. Therefore, the toner having a low proper charge, the non-charged toner, and the reverse-charged toner do not adhere to the image carrier.

Further, according to the fifth aspect of the invention, since the positions of the recording paper and the latent image head at the transfer position are preliminarily aligned between the pages, the latent image start time point and the latent image are determined. There is no positional or temporal shift in the timing from the start until the trailing edge of one page reaches the developing position, and until the beginning of the latent image on the next page reaches the developing position. Therefore, from the timing when the trailing edge of the first page passes the developing position until the start of the latent image of the next page reaches the developing position, the toner on the second toner transporting means is collected by the first toner transporting means, and the toner on the image carrier is collected. The area between the pages can be brought into contact with at least the second toner carrying means without toner adhesion. Therefore, the toner having a low proper charge, the non-charged toner, and the reverse-charged toner do not adhere to the image carrier.

Further, according to the structure of the sixth aspect, when the recording paper is jammed, the toner on the second toner carrying means is transferred to the first toner carrying means at the same time as a new paper feed start signal or a new paper feed detection signal. Therefore, the latent image portion existing on the image carrier at the time of jam,
During the development, the irradiated portion can be contacted with the second toner carrying means without toner adhesion at least at the timing before the start of the latent image of the next page. Therefore, the toner having a low proper charge, the non-charged toner, and the reverse-charged toner do not adhere to the image carrier.

Further, according to the seventh and eighth aspects, since the detection of the recording paper being fed is used as a base point, the timing can be accurately adjusted even if a slippage or the like occurs during the conveyance. .

EXAMPLE An example of the present invention will be described.

FIG. 1 shows the structure of a two-stage developing type developing device according to the first embodiment of the present invention. Reference numeral 1 is an image carrier, and as shown in FIG.
7, a transfer roller 8, a cleaning means 9, and an optical writing means 15 for forming a latent image on the image carrier are arranged. Reference numeral 2 is a second toner carrying roller which is a second toner carrying means, and the peripheral surface thereof is in contact with the image carrying body 1 and
Toner T is transferred and attached to the upper latent image portion. Reference numeral 3 denotes a first toner carrying roller which is a first toner carrying means, and its peripheral surface is in contact with the second toner carrying roller, and the toner T is transferred and adhered onto the second toner carrying roller. A first bias supply unit 5 applies a bias to the first toner carrying roller 3. This first bias supply means 5
Is provided with a first bias potential V ₁ and a second bias potential V ₂ , and bias potential switching control means 5a for switching between them is provided. 6 is a second bias supply means,
A bias is applied to the toner transport roller 2. This is the second bias supply means 6 provided with a bias potential V _3, on the application of the off switch means 6a is performing.

The bias potential switching control means 5a performs switching operation according to a control signal from the control section 7. When electrically transferring the toner T on the peripheral surface of the first toner conveying roller 3 to the peripheral surface of the second toner conveying roller (hereinafter referred to as a normal mode), the first bias potential V ₁ is set,
When the toner on the second toner carrying roller 2 is to be collected by the first toner carrying roller (hereinafter referred to as toner collecting mode), it is switched to the second bias potential V ₂ . The second bias potential V ₂ is the bias potential V ₃ (-4
The bias potential may be higher in the positive direction than (00 V). Wherein the control signal of the switching means 6a the control unit 7 turns on, as a bias potential V ₃ to the second toner conveying roller is applied to the time of the second toner conveying roller driving state, the bias when the stopped state The potential V ₃ is turned off.

FIG. 2 is a block diagram of the essential parts of the first bias supply means of the second embodiment according to the present invention. Reference numeral 8 is a variable potential switching control means for switching the variable bias potential V ₄ .
The variable potential switching control means 8, the case of normal mode, and the variable to the bias potential V ₃ (-400 V) potential lower than (e.g. -800 V), wherein the toner recovery mode, the bias potential V ₃ Bias potential higher than (-400 V) in the positive direction (for example, -200 to 0)
V). Therefore, the amount of toner transferred onto the second toner carrying roller 2 can be adjusted, and the density of the visible image at the time of development can be adjusted.

FIG. 3 is a block diagram of the recording process of the third to tenth embodiments according to the present invention. The reference numerals described in FIG. 6 are omitted. Around the image carrier 1, a charging roller 17 for charging the surface thereof, an optical writing unit 15 for forming a latent image on the charged surface, a developing device 14 for developing the latent image,
A transfer roller 8 for transferring the developed toner image to the recording paper P, and a cleaning means 9 for collecting the residual toner after the transfer on the surface of the image carrier 1 are provided. The recording paper P is provided in the paper feed cassette 16 and is conveyed by the paper feed roller 13. A pair of registration rollers 10 conveys the recording paper P conveyed by the paper feed roller to the transfer roller 8. A fixing roller 11 fixes the toner image on the recording paper P transferred by the transfer roller 8. A pair of paper discharge rollers 12 discharges the recording paper after fixing.

The switching timing of the bias potential switching control means of the third embodiment according to the present invention will be described here. At the start of recording one page, the main motor 18 is started together with the recording mode of the image forming apparatus, and the image carrier 1, the first toner transport roller 3, the second toner transport roller 2, the charging roller 17, The fixing roller 11 rotates in each arrow direction. After a predetermined time such as when the temperature of the fixing roller reaches the fixable temperature, the paper feed roller 13 is started by the paper feed start signal, and the recording paper P is started to be fed. The time when the feeding of the recording paper starts or the time when the recording paper passes a predetermined position on the paper feeding path is T ₀ , the time when the feeding of the recording paper starts or the time when the recording paper reaches the transfer position from the predetermined position is t ₁ , The time from the start of the latent image on the body until the latent image reaches the transfer position is t ₂ , the time until the latent image reaches the developing position is t ₃ ,
The second toner carrying roller 2 is the first toner carrying roller 3
When the time from the position of contact with the developing roller to the developing position is t ₄ , the timing of applying the “normal mode” of the first bias supply means 5 to the first toner carrying roller 3 is T 1. _{1 = T 0 + t 1 -t} 2 + t 3 -t 4
It's time.

The above time may be replaced with a time point.

Further, at the switching timing of the bias potential switching control means of the fourth embodiment according to the present invention, at the end of recording one page, the "normal mode" at the start of recording one page of the third embodiment. When the time T ₁ = T ₀ + t ₁ −t ₂ + t ₃ −t ₄ is applied, the time t ₅ required for the latent image for one page is added, and the time T ₂ = T ₀ + t ₁ When −t ₂ + t ₃ −t ₄ + t ₅ is reached, the first bias supply means 5 is switched to the “toner recovery mode”.

Further, when there is a continuous page between pages at the switching timing of the bias potential switching control means of the fifth embodiment according to the present invention, at the end of recording one page shown in the fourth embodiment. At T ₂ = T ₀ + t
From the time of _{1 -t 2 + t 3 -t 4} + t 5, is up to the time obtained by adding the time t ₆ to the latent image formation start of the second page, the said first bias supply unit 5 "toner collection mode" It is supposed to be switched to.

The above time may be replaced with a time point.

At the switching timing of the bias potential switching control means of the fourth embodiment according to the present invention, at the end of recording one page, the "normal mode" at the start of recording one page of the third embodiment. When the time T ₁ = T ₀ + t ₁ −t ₂ + t ₃ −t ₄ is applied, the time t ₅ required for the latent image for one page is added, and the time T ₂ = T ₀ + t ₁ When −t ₂ + t ₃ −t ₄ + t ₅ is reached, the first bias supply means 5 is switched to the “toner recovery mode”.

Further, when there is a continuous page between pages at the switching timing of the bias potential switching control means of the fifth embodiment according to the present invention, at the end of recording one page shown in the fourth embodiment. At T ₂ = T ₀ + t
From the time of _{1 -t 2 + t 3 -t 4} + t 5, is up to the time obtained by adding the time t ₆ to the latent image formation start of the second page, the said first bias supply unit 5 "toner collection mode" It is supposed to be switched to.

The above time may be replaced with a time point.

Further, at the switching timing of the bias potential switching control means of the sixth embodiment according to the present invention, after a jam occurs in the recording paper transport system and the jam is removed, a new recording paper feed start signal is output. At the same time, the first bias supply means 5 is switched to the "toner recovery mode". As a result, at the timing before the start of the latent image on the new page, the toner adhesion can be reduced at least for the irradiated portion on the image carrier, the latent image portion, and the developing portion.

At a predetermined position on the paper feed path at the time T _0, the position of the sensor S ₁ for detecting the feeding of the recording paper after the paper feeding is started and the recording paper after the paper feeding is conveyed. in the position of the resist sensor S ₃ for detecting the recording paper which is provided on the discharge side of the registration roller pair 10, when it detects the recording sheet tip is adapted to a latent image is started by the optical writing unit 15.

FIG. 4 shows a time chart of the main part from the start of feeding one page of recording paper to the discharging of it. Optical writing means 1
The start of the latent image by 5 is performed after the start of the feeding of the recording paper or the time T _{0 when the} recording paper passes a predetermined position on the feeding path. The first bias supply means a is in the normal mode in the first bias potential side, and b is in the toner recovery mode in the second mode.
It is on the bias potential side. Both the first and second bias supply means in the figure show the timing of voltage application, but the first toner transfer roller 3 and the second toner transfer roller 2 equipped with the first and second bias supply means are shown. The rotation operation is synchronized with the driving of the main motor 18.

FIG. 5 shows a time chart of the main part from the start of paper feed to the discharge of continuous pages of recording paper. In this case, since the main motor 18 is a continuous page, it does not stop between pages and continues to rotate. Therefore, the first toner carrying roller 3 and the second toner carrying roller 2 also rotate in the same manner, and the charging is continued.

[0037]

As described above, according to the first aspect of the invention, the toner supply to the portion other than the latent image area on the image carrier can be positively stopped and collected. Toner with low electrification, reverse electrification, and proper electrification does not adhere to the image carrier, so that toner consumption can be reduced and toner scattering can be prevented. Further, when the toner image is transferred onto the recording paper, the recording output without the background stain can be obtained.

According to the invention of claim 2, in addition to the effect of claim 1, the toner supply amount at the time of development can be adjusted, and the density of the visible image can be adjusted.

According to the third aspect of the invention, at the start of recording one page, the toner supply is stopped and the toner is collected from the start of sheet feeding until the latent image start portion on the image carrier reaches the developing position. Therefore, the toner consumption can be surely reduced and the toner scattering can be prevented. Further, the background dirt in that range can be prevented. Therefore, at the time of transfer, it is possible to obtain a print output that is free of background stains on the portion of the recording paper.

According to the fourth aspect of the invention, at the end of recording one page, after the latent image for one page on the image carrier passes the developing position and until the second toner conveying means stops driving, Since the toner supply is stopped and the toner is collected, the toner consumption can be surely reduced and the toner scattering can be prevented. Further, the background dirt in that range can be prevented. Therefore, at the time of transfer, it is possible to obtain a print output that is free of background stains on the portion of the recording paper.

According to the invention of claim 5, the toner supply is stopped and the toner is collected between the continuous one-page latent image area and the next one-page latent image area. Toner consumption can be reliably reduced and toner scattering can be prevented. Further, the background dirt in that range can be prevented. Therefore, at the time of transfer, it is possible to obtain a print output that is free of background stains on the portion of the recording paper.

According to the sixth aspect of the present invention, since the toner supply is stopped and the toner is collected from the jam removal to the start portion of the latent image on the new first page, the irradiation at the time of the jam is performed. Parts, latent images,
It is possible to reduce the adhesion of the toner to the developing part and the like and prevent the toner from being scattered, the consumption of the toner can be reduced accordingly, and the background can be prevented from being soiled.

According to the seventh and eighth aspects of the invention, since the passage of the recording paper conveyance is detected by the sensor, even if the paper feed delay occurs due to the slip of the paper feed roller or the like, the paper is not transferred at the transfer position. No deviation occurs.

[Brief description of drawings]

FIG. 1 is a configuration diagram of essential parts of a developing device of the present invention.

FIG. 2 is a configuration diagram of essential parts of a first bias supply means of the present invention.

FIG. 3 shows a block diagram of a recording process of the present invention.

FIG. 4 shows a time chart on page 1 of the present invention.

FIG. 5 shows a time chart in a continuous page of the present invention.

FIG. 6 shows a main configuration of a conventional developing device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Image carrier 2 ... 2nd toner conveyance roller 3 ... 1st toner conveyance roller 4 ... Doctor blade 5 ... 1st bias supply means 5a ... Bias electric potential switching control means 6 ... 2nd bias supply means 6a ... Switch means 7 ... Control unit 8 ... Transfer roller 9 ... Cleaning means 10 ... Registration roller pair 11 ... Fixing roller 12 ... Paper ejection roller pair 13 ... Paper feeding roller 14 ... Developing device 15 ... Optical writing means 16 ... Paper feeding cassette 17 ... Charging roller 18 ... Main motor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Iwamatsu Matsumae 1-3-6 Nakamagome, Ota-ku, Tokyo Stock company Ricoh Co., Ltd. (72) Yoshiro Tanaka 1-3-3 Nakamagome, Ota-ku, Tokyo Stocks Inside Ricoh Company (72) Inventor Hiroshi Hosokawa 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Company Ricoh (72) Inventor Manjiro Uno 1-3-6 Nakamagome, Tokyo Stockholder Ricoh Company (72) Inventor Hiroshi Saito 1-3-6 Nakamagome, Ota-ku, Tokyo, within Ricoh Company (72) Inventor Eiji Takenaka 1-3-6 Nakamagome, Ota-ku, Tokyo In-house, Ricoh (72) Invention Toshihiro Sugiyama 1-3-6 Nakamagome, Ota-ku, Tokyo Stock company in Ricoh (72) Inventor Tetsuo Yamanaka 1-3-6 Nakamagome, Ota-ku, Tokyo Stock company In Ricoh (72) Inventor Satoru Komatsubara 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd.

Claims (8)

[Claims] 1. A first toner conveying means for adhering and conveying a one-component high-resistance toner charged by friction or charge injection, and a first toner conveying means, which is in contact with the first toner conveying means. A developing device comprising: a second toner carrying unit that electrically transfers and attaches the toner; and an image carrier that develops the charged toner transferred from the second toner carrying unit into a visible image. First bias supply means for switching and supplying the first bias potential or the second bias potential to the first toner transport means, and second bias supply means for suspending supply of the third bias potential to the second toner transport means. At the timing of developing the latent image formed on the image carrier, the toner on the first toner transporting means is electrically transferred to the second toner transporting means, and there is a development end timing. Or bias potential switching control means for switching the first and second bias potentials so as to electrically transfer the toner on the second toner carrying means to the first toner carrying means at a non-developing timing. Developing device. 2. The developing device according to claim 1, wherein the bias potential supplied from the first bias supply means is variable. 3. The switching timing of the bias potential switching control means for switching the first and second bias potentials is such that at the start of recording one page, the feeding of the recording paper is started or the recording paper is on the paper feeding path. The time when the recording sheet passes the predetermined position is T ₀ , the time when the recording paper starts feeding or reaches the transfer position from the predetermined position is t ₁ , and the latent image is transferred from the start of latent image formation on the image carrier. The time required to reach the position is t ₂ , the time required for the latent image to reach the developing position is t ₃ , and the rotation time required for the second toner carrying means to reach the developing position from the contact position of the first toner carrying means. Is set to t _4, and when the time of T ₁ = T ₀ + t ₁ −t ₂ + t ₃ −t ₄ is reached,
2. The voltage applied to the first bias supply unit is switched so that the toner on the first toner transfer unit is transferred and attached to the second toner transfer unit.
The developing device described. 4. The switching timing of the bias potential switching control means for switching the first and second bias potentials is such that, when recording of one page is completed, the feeding of the recording sheet or the recording sheet is on the sheet feeding path. The time when the recording sheet passes the predetermined position is T ₀ , the time when the recording paper starts feeding or reaches the transfer position from the predetermined position is t ₁ , and the latent image is transferred from the start of latent image formation on the image carrier. The time required to reach the position is t ₂ , the time required for the latent image to reach the developing position is t ₃ , and the rotation time required for the second toner carrying means to reach the developing position from the contact position of the first toner carrying means. Is t ₄ , and the time required from the start of latent image formation to the end of latent image formation for one page is t ₅ , T ₂ = T ₀ + t ₁ −t ₂ + t ₃ −t ₄ + t ₅
When the time is reached, the toner on the second toner transporting means is collected to the first toner transporting means by the first toner transporting means.
The developing device according to claim 1, wherein the applied voltage of the bias supply means is switched. When the time required from 5. 1 page of latent image formation ends up latent image formation start of the next page was t _6, in the this t ₆ hours, the toner on the second conveying means Is collected by the first toner conveying means,
The developing device according to claim 4, wherein the applied voltage of the first bias supply means is switched. 6. The switching timing of the bias potential switching control means for switching the first and second bias potentials is set to output a new recording paper feed start signal after removing a jam in the recording paper transport system. 2. The developing device according to claim 1, wherein at the same time, the applied voltage of the first bias supply unit is switched so that the toner of the second toner transfer unit is collected by the first toner transfer unit. 7. The predetermined position on the paper feed path is a position for detecting paper feed of recording paper after the paper feed is started. The developing device according to the item. 8. The predetermined position on the paper feed path is a registration sensor position for detecting a recording sheet provided on a discharge side of a registration roller that conveys the recording sheet after the feeding is started. Item 4. The developing device according to any one of Items 3, 4, 5, and 6.