JP2002351182A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform excellent image formation by avoiding image blurring due to a shock made when a developing roller abuts against or leave a photoreceptor drum. SOLUTION: The image forming device has an electrostatic charging device which electrostatically charges a photoreceptor drum 1, an exposure device 3 which exposes the electrostatically charged photoreceptor drum 1 according to an image signal to form an electrostatic latent image, and developing cartridges 4Y, 4M, 4C and 4K which develop the electrostatic latent image formed on the photoreceptor drum 1 by using toner, and also has a rotary housing 40 which makes developing rollers 41 that the developing cartridges 4Y, 4M, 4C and 4K have abut against or leave the photoreceptor drum 1 by rotating and moving the developing cartridges 4Y, 4M, 4C and 4K to and away the photoreceptor drum 1 one after another and an intermediate transfer belt 5 which transfers and carries the toner image on the photoreceptor drum 1, and the developing roller 41 of each developing cartridge abuts against the photoreceptor drum before the exposure device 3 exposes the photoreceptor drum.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus such as a copying machine and a laser beam printer.

[0002]

2. Description of the Related Art Conventionally, a multicolor image forming apparatus using an electrophotographic image forming process is roughly classified into two types.
One of them is an image forming cartridge in which a photoreceptor as an image carrier and a developing mechanism are integrated, four of yellow, magenta, cyan, and black, and an image formed by each image forming cartridge is transferred to a transfer material. To form a multicolor image. On the other hand, a single photoreceptor and a cartridge of each color (yellow, magenta, cyan, black) having a developing mechanism independently of the photoreceptor sequentially face the photoreceptor at the time of image formation to form a multicolor image. It is a method to do. In the former case, image formation of each color can be performed in parallel, and the throughput (the number of images that can be formed within a predetermined time) can be improved. In the latter case, the four developing devices can be housed in a housing having a rotating mechanism, and the cartridge size can be reduced.

The image formed by the image forming unit having the above structure is temporarily transferred to an intermediate transfer member such as a belt, and then transferred to a transfer material after a multicolor image is formed. There is a method of sequentially transferring images of each color to a transfer material carried on a material carrier. The former method has a feature that printing can be performed on various transfer materials, and the latter method has a feature that the configuration can be simplified as compared with the former method.

With respect to the above configuration, an optimum configuration can be selected as appropriate for the required specifications, and each configuration and method has advantages and disadvantages.

The unfixed multicolor image formed on the transfer material as described above is output as a final multicolor image by a heated and pressed fixing device.

The methods of developing a latent image formed on a photoreceptor are roughly classified into a one-component developing method and a two-component developing method. As the developer, a non-magnetic developer is mainly used. In the one-component developing system, the developing unit can be easily formed into a cartridge, and maintenance can be simplified and usability can be improved. On the other hand, the two-component developing method has an advantage in that the developer can be replenished as needed, so that the cost of consumables can be reduced.

In the one-component developing system, the system is roughly classified into two types, and a system in which a developing roller serving as a developer carrier is separated from a photosensitive member serving as an image carrier, that is, a so-called non-contact developing system is used. There is a contact development method which is a method.
In the non-contact developing method, a bias in which an AC voltage is superimposed on a DC voltage is applied to the developing roller, and the developer on the developing roller flies between the developing roller and the photoconductor,
The electrostatic latent image formed on the photoconductor is developed. An image developed by this method has an advantage that the gradation is smooth. On the other hand, in the contact developing method, only a DC voltage is applied to the developing roller, and the developer on the developing roller does not fly between the developing roller and the photosensitive member, and an electrostatic latent formed on the photosensitive member. Since the image is directly developed, there is an advantage that the developer does not fly into the image forming apparatus. Further, the power supply is only the DC power supply, and the cost can be reduced because the AC power supply is not required.

[0008]

However, in the multicolor image forming apparatus having the above-described structure, the developing cartridge is rotated and moved to a position facing one photosensitive member sequentially with respect to one photosensitive member. In the conventional multicolor image forming apparatus, since the developing cartridge rotates and moves with respect to the photosensitive member, and the developing roller contacts the photosensitive member at a position opposed thereto, the developing roller contacts or separates from the photosensitive member. The impact may cause the following image defects.

(1) The laser beam applied to the photoreceptor is applied to a position shifted from a predetermined irradiation position (scanning position) due to the above-mentioned impact. As a result, white stripes due to blurring of the scanning position are obtained. An image may be generated.

(2) In the step of transferring the developed image formed on the photoreceptor to the intermediate transfer member or the transfer material carrier (at the time of primary transfer), the developing cartridge may be brought into contact with the photoreceptor during this step. If there is a separation, the impact may cause blurring in the primary transfer portion, resulting in an image defect.

SUMMARY OF THE INVENTION An object of the present invention is to avoid image blur due to the impact of the developer carrier on or away from the image carrier, and to enable good image formation.

[0012]

In order to achieve the above object, an image forming apparatus according to the present invention comprises a charging means for charging an image bearing member, and a charging means for charging the charged image bearing member based on an image signal. Exposure means for exposing to form an electrostatic latent image, and a plurality of developing means for developing the electrostatic latent image formed on the image carrier using a developer, the plurality of developing means on the image carrier A developing device rotating mechanism for rotating or moving the developer carrier of the developing device in contact with or separating from the image carrier, and an intermediate transfer member for transferring and carrying a developed image on the image carrier. The timing at which each of the developing units comes into contact with the image carrier is before the timing at which the exposure unit exposes the image carrier.

Further, in the apparatus having the above-mentioned structure, the timing of the bias applied to the charging means is such that an arbitrary fixed point on the image carrier corresponds to the charging means with respect to the time when the developing means contacts the image carrier. It is characterized by being before the time for moving from the contact position to the developing means contact position.

In order to achieve the above object, the image forming apparatus of the present invention comprises: a charging means for charging the image carrier; and an electrostatic device for exposing the charged image carrier based on an image signal. An exposure unit for forming a latent image, and a plurality of developing units for developing the electrostatic latent image formed on the image carrier using a developer, wherein the plurality of developing units are sequentially rotated with respect to the image carrier. A developing device rotating mechanism for moving or moving the developer carrier of the developing device to or away from the image carrier, and an intermediate transfer body for transferring and carrying the developed image on the image carrier;
The timing at which each of the developing units separates from the image carrier is
It is characterized in that it is after a transfer step of transferring a developed image formed on the image carrier to the intermediate transfer body.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described in detail with reference to the drawings. However,
The dimensions, materials, shapes, relative arrangements, and the like of the components described in the following embodiments should be appropriately changed depending on the configuration of the apparatus to which the present invention is applied and various conditions, and in particular, Unless otherwise described, the scope of the present invention is not intended to be limited to them.

First Embodiment An image forming apparatus according to a first embodiment of the present invention will be described in detail with reference to FIGS. FIG. 1 is a schematic cross-sectional view of a multicolor image forming apparatus using an electrophotographic process which is the basis of the present invention. The multicolor image forming apparatus described in the present embodiment exemplifies a laser beam printer using an electrophotographic process.

Hereinafter, the configuration of each part and the operation mode of the multicolor image forming apparatus will be described along the image forming process.

One rotating drum type electrophotographic photosensitive member 1 (hereinafter, referred to as "photosensitive drum") as an image carrier is disposed in the apparatus main body. The surface of the photosensitive drum 1 is
The charging device 2 as a charging unit uniformly performs a charging process to a predetermined potential. Photoreceptor drum 1 uniformly charged
Is irradiated with a laser beam L emitted from an exposing device 3 as an exposing means based on an image signal.
An electrostatic latent image based on the image signal is formed thereon. As the photosensitive drum 1 rotates, the electrostatic latent image is transferred to the photosensitive drum 1
The toner image is visualized as a toner image by an appropriate bias applied to the developing cartridge 4Y when passing through a developing unit 4Y (hereinafter, referred to as a “developing cartridge”) as a developing unit in contact with the developing unit 4Y. The visualized image (toner image) on the photosensitive drum 1 that has been visualized is temporarily transferred to an intermediate transfer belt 5 as an intermediate transfer body that rotates and moves at substantially the same speed as the photosensitive drum 1. At this time, a transfer bias applying roller 54 serving as an electrode is provided on the opposite side of the photosensitive drum 1 via the intermediate transfer belt 5, and the polarity of the intermediate transfer belt 5 is opposite to that of the toner via the transfer bias applying roller 54. The transfer process on the intermediate transfer belt 5 is performed by applying the bias of (1).

The above process is repeated for the other color developing cartridges 4M,
4C and 4K, and the unfixed toner composed of yellow (Y), magenta (M), cyan (C) and black (K) toners is placed on the intermediate transfer belt 5 after the process of all colors is completed. An image is formed.

Incidentally, as shown in FIG. 1, the developing cartridge according to the present embodiment includes the developing cartridges 4Y and 4Y.
In order to bring the M, 4C, and 4K developing rollers 41 into contact with or away from the photosensitive drum 1, each developing cartridge 4
This is a type housed in a rotary housing 40 as a developing means rotating mechanism for rotating Y, 4M, 4C and 4K.

The transfer material P is fed by a feed roller 7 so that the unfixed toner image on the intermediate transfer belt 5 approaches the transfer member 6 as the intermediate transfer belt 5 rotates. Is transferred to a contact portion between the intermediate transfer belt 5 and the transfer member 6. When passing through the contact portion, a predetermined bias is applied to the transfer member 6, and the unfixed toner image on the intermediate transfer belt 5 is transferred to the transfer material P.

The transfer material P to which the unfixed toner image has been transferred is conveyed to the fixing device 8, and is subjected to a heating and pressing action by the fixing device 8 to perform a fixing operation on the transfer material P.
The formation of the desired multicolor image is completed.

The toner remaining on the photosensitive drum 1 after the transfer process to the intermediate transfer belt 5 is cleaned by a cleaning device (cleaning means) 9 for the photosensitive drum 1, and proceeds to the next image forming process. I do.

Further, the toner remaining on the intermediate transfer belt 5 after the step of transferring the toner image onto the transfer material P by the transfer member 6 is applied to the intermediate transfer belt 5 by a biasing means (not shown) at a predetermined timing. The cleaning is performed by the cleaning device 10 in contact therewith, and the process proceeds to the next image forming process.

The multicolor image forming apparatus has a process speed of 94.2 (mm / sec) and can form an image of maximum A4 size (vertical 297 (mm)).

The photoreceptor drum 1 is made of an organic photoreceptor having a diameter of 30 (mm) and having a negative chargeability.

As the charging device 2, a roller type of φ12 (mm) was used. During charging of the surface of the photosensitive drum 1, the charging device 2 converts the DC voltage to -600 (V) as an AC voltage as a peak-to-peak voltage of 1.6 (kVpp) and a frequency of 1.2.
(KHz) is applied.

When the exposure device 3 exposes and irradiates the potential of the photosensitive drum 1 charged with -600 (V) by the exposure device 3, the surface potential of the photosensitive drum 1 becomes -150 (V).
(V) is adjusted to the drum surface light amount.

Developing cartridges 4Y, 4M, 4C, 4K
Uses a non-magnetic one-component developer, and in a developing process, a developing roller 41 as a developer carrier comes into contact with the photosensitive drum 1 with a predetermined penetration amount (about 50 μm), and the developing cartridges 4Y, 4M, 4C , 4K, a DC voltage of -350 (V) is applied. In addition, the developing cartridge 4Y, 4M,
4C and 4K can rotate and move toward the photosensitive drum 1 in the direction of arrow a.

The intermediate transfer belt 5 has a circumference of 440 (m
m), rubber (hydrin) having a thickness of 0.7 (mm) adjusted to a volume resistance value of about 105 (Ω · cm) in the lower layer, and a volume resistance value of 1012 (Ω · cm) as a release layer in the upper layer. A) a belt-like member made of a fluororesin having a thickness of 20 (μm) adjusted before and after the tension roller 51, 5
It is suspended by 2,53.

Further, a transfer bias applying roller 54 is provided at a position facing the photosensitive drum 1 at a position sandwiching the intermediate transfer belt 5. The transfer bias applying roller 54 is used to apply a desired bias to the intermediate transfer belt 5. Therefore, when the toner image on the photosensitive drum 1 is transferred to the intermediate transfer belt 5, +200 (V), +500 (V), +500 (V),
+600 (V) bias is applied to the transfer bias applying roller 5
4 is applied.

The transfer member 6 has a volume resistance of 107 (Ω · c).
m) φ20 (mm) foamed EPDM with resistance adjusted before and after
When the toner image on the intermediate transfer belt 5 is transferred to the transfer material P, the roller
A bias of V is applied.

The fixing device 8 has a size of φ4 made of silicone rubber.
A pair of 0 (mm) rollers 81 and 82 are heated to 180 ° C. by heaters 83 and 84 arranged inside the rollers.

The dimensions, materials, shapes, relative arrangements, and the like of the components are not limited to those described above, and may be appropriately changed according to the configuration of the apparatus to which the present invention is applied and various conditions. Should be.

Hereinafter, in the image forming apparatus having the above configuration according to the present embodiment, the contact of the developing roller during the image forming operation,
The separation timing will be described in detail.

In the present embodiment, during the image forming operation, the timing of contact of the developing roller 41 with the photosensitive drum 1 is set before the step of exposing the photosensitive drum 1 to light. The timing of separating the developing roller 41 is after the end of the step of exposing the photosensitive drum 1 to light.

That is, when the image forming operation of each color is performed, the operation that affects the operation of the photosensitive drum 1 is the contact and separation operation of the developing roller 41, and the operation that is affected by this operation. It is considered that the irradiation position of the electrostatic latent image formed on the photosensitive drum 1 is shifted. In the present embodiment, it is an object to avoid a deviation in the irradiation position of the laser exposure caused by the contact and separation of the developing roller 41, and to prevent an image defect due to the deviation in the irradiation position.

In the present embodiment, the charging position, the laser irradiation position, the contact position of the developing roller 41, and the contact position of the intermediate transfer belt around the photosensitive drum 1 are defined as having the positional relationship shown in FIG. In this embodiment, the laser irradiation position is set to 0 ° because the laser irradiation position is the reference point. The charging position is -45 with respect to this laser irradiation position.
°, the contact position of the developing roller 41 is + 45 °, and the contact position of the intermediate transfer belt is + 180 °. The photosensitive drum 1 has a process speed of 94.2 (mm / sec). That is, the rotation of the photosensitive drum 1 of φ30 (mm) at the process speed of 94.2 (mm / sec) means that the photosensitive drum 1 rotates once per second.
Accordingly, the time required for an arbitrary fixed point on the photosensitive drum 1 to pass through the charging position, the developing roller 41 contact position, and the intermediate transfer belt contact position with respect to the laser irradiation position is -12.
5 (mmsec), +125 (mmsec), +500
(Mmsec) later.

In the case of the conventional multi-color image forming apparatus, the developing roller 41 sets the photosensitive drum 1 before +125 (mmsec).
Was a necessary condition. However, in the present embodiment, the developing roller 41 is set to 0 (mmsec).
c) Prerequisite contact is a requirement. That is,
Before the exposure process is started on the photosensitive drum 1, the developing roller 41 needs to be already in contact with the photosensitive drum 1.

In actual image formation, there is some time from when the developing roller 41 comes into contact with the photosensitive drum 1 to when the developing roller 41 shifts to a stable rotation operation. It is necessary to consider the abutment timing. However, in the present embodiment, since there is a time allowance of +125 (mmsec) from the exposure position (laser irradiation position) to the developing position (developing roller contact position), a sufficient time for the developing roller 41 to be driven stably is provided. It is. Therefore, it is necessary that the developing roller 41 contacts the photosensitive drum 1 at a minimum of 0 (mmsec).

It is obvious that the timing at which the developing roller 41 is separated from the photosensitive drum 1 is forced to be separated after the exposure step in any situation. Therefore, the separation operation shifts to the separation operation at an arbitrary timing after the end of the developing process of the image forming width of the maximum image size.

At the above timing, the developing roller 41
When the toner contacts the photosensitive drum 1, it is necessary to take measures to prevent the toner on the developing roller 41 from developing on the photosensitive drum 1. That is, the photosensitive drum 1
When the upper surface is not charged, the potential on the photosensitive drum 1 is 0 (V), and the toner on the developing roller 41 to which no bias is applied is developed on the photosensitive drum 1. It will cause so-called ground fog. In order to avoid this phenomenon, it is necessary to charge the potential on the photosensitive drum 1 with which the developing roller 41 contacts to a potential at which neither ground fog nor reverse fog occurs. For this reason, the application timing of the charging bias is set to be −250 (mmsec) at the start of image formation for each color. The application of the developing bias was performed at the same time as the contact of the developing roller 41 with the photosensitive drum 1. Thereafter, at a predetermined image forming timing, a bias under a predetermined image forming condition is applied, and image forming is performed.

FIG. 3 is a timing chart summarizing the above timings. The timing for applying the charging bias is charging 1. The timing of the developing roller 41 is the first development in which the contact of the developing roller 41 with the photosensitive drum 1 and the timing of the application of the developing bias are performed simultaneously. Since it is desirable that the charging 1 shown in FIG. 3 is applied before the developing roller 41 is brought into contact, it is desirable that the charging 1 is before -250 (mmsec). But,
In the present embodiment, the simultaneous timing of -250 (mmse
c).

In the above-described multi-color image forming apparatus, when an image is formed at the above-mentioned timing, it is possible to obtain a good image without causing image blurring due to a contact (and separation) shock of the developing roller 41. It has become possible.

[Second Embodiment] An image forming apparatus according to a second embodiment of the present invention relates to the timing at which the developing roller 41 contacts and separates from the photosensitive drum 1.
More specifically, in the present embodiment, the operation of contacting and separating the developing roller 41 from the photosensitive drum 1 is performed at a timing when the transfer process from the photosensitive drum 1 to the intermediate transfer belt 5 is not performed. It is a feature.

An object of the present embodiment is to perform a transfer process from the photosensitive drum 1 to the intermediate transfer belt 5 (hereinafter, referred to as a transfer process).
This step is called a “primary transfer step”. ), Developing roller 41
The object of the present invention is to avoid a phenomenon in which a shock caused when the photosensitive drum 1 comes into contact with or separates from the photosensitive drum 1 causes the photosensitive drum 1 to vibrate and cause transfer blurring in the primary transfer section. Thereby, stable primary transfer is realized and a good image is formed.

In the present embodiment, there is a predetermined timing for each of the timing at which the developing roller 41 contacts and the timing at which the developing roller 41 separates.

At the time of contact of the developing roller 41, the contact timing of the first color does not matter in particular, but it is required that the second color and the subsequent colors come into contact after the primary transfer process of the previous color is completed. Further, the separation of the developing roller 41 is required to be separated after the primary transfer process of the own color is completed.

As described above, the developing roller 41 of the photosensitive drum
It is only necessary to consider the timing at the time of separation when determining the contact and separation with respect to. That is, in the case of the timing of separation after the end of the transfer process of the own color, the contact is necessarily made after the end of the primary transfer process of the previous color.

As in the first embodiment, the timing in the case of the positional relationship shown in FIG. 2 will be described. When viewed from an exposure position (laser irradiation position) serving as a timing reference, the contact time of the developing roller 41 is +125 (mmsec).
c) After that, the time to the primary transfer position is +500 (mmsec)
c). Therefore, the separation timing of the developing roller 41 is after +500 (mmsec). Since the intermediate transfer belt 5 is 440 (mm) and the maximum image size is A4 size (297 (mm)), the non-image area, that is, the time given for replacing the developing device is about 1518 (mmsec). After the process is completed, +375 (mmsec), which is required until the separation, is a time that does not cause any problem in switching the developing device.

FIG. 4 is a timing chart summarizing the above timings as a chart. In the present embodiment, since the timing relates to the timing at the end of image formation,
The timing immediately after the completion of the image formation on the A4 size transfer material based on the exposure position is shown. Specifically, since the A4 size is 297 (mm), the exposure end time is 3200 (mm) in consideration of the mask area of the image.
sec). Therefore, from this time, the developing roller 41
(3700 (mmsec)) and the end timing of primary transfer (3700 (mmsec)).

Here, the timing for separating the developing roller 41 from the photosensitive drum 1 and the timing for terminating the primary transfer are shown at the same time, but it is more preferable that the separating operation of the developing roller 41 is performed after the end of the primary transfer.

Since this timing is the same for each color, only the timing of the first color is described.

In the case of this embodiment, the relationship with the charging potential is not so important, but since the developing roller 41 must be kept in contact with the photosensitive drum 1 even after the end of the original developing process, the charging Similarly, the application time of the bias and the developing bias is also delayed by +375 (mmsec).

In the above-described multicolor image forming apparatus, when an image is formed at the above timing, a good image can be obtained without causing image blurring of the primary transfer portion due to the contact and separation shock of the developing roller 41. It became possible.

[Other Embodiments] In the above embodiment,
Although four developing cartridges are used for forming a multicolor image, the number of used cartridges is not limited, and may be appropriately set as needed.

In the above-described embodiment, the exposing device (laser scanner unit) 3 is used as the exposing means. However, the present invention is not limited to this. For example, an LED array or the like may be used.

In the above-described embodiment, a printer is exemplified as an image forming apparatus. However, the present invention is not limited to this. For example, another image forming apparatus such as a copying machine or a facsimile apparatus, An image forming apparatus may be used, in which a transfer conveyance belt is used as a body and toner images of each color are sequentially superimposed and transferred on a transfer material such as a recording sheet carried on the transfer conveyance belt. Similar effects can be obtained by applying the invention.

[0059]

As described above, according to the present invention,
By setting the timing at which the developer carrier of each developing unit contacts the image carrier before the exposure timing of the exposure device at the image carrier, the developer carrier contacts or separates from the image carrier. Image blur due to the impact of the image can be avoided, and a good image can be formed.

Further, according to the present invention, the timing at which the developer carrier of each developing means separates from the image carrier is set after the end of the transfer step from the image carrier to the intermediate transfer body. Image blur due to the impact of contact or separation with the image carrier can be avoided, and good image formation can be achieved.

[0061]

[Brief description of the drawings]

FIG. 1 is a schematic sectional view illustrating a multicolor image forming apparatus according to a first embodiment.

FIG. 2 is a diagram showing a positional relationship of each unit related to image formation.

FIG. 3 is a timing chart showing the first embodiment.

FIG. 4 is a timing chart illustrating a second embodiment.

[Explanation of symbols]

 L: Laser light P: Transfer material 1: Photoconductor drum 2: Charging device 3: Exposure device 4Y, 4M, 4C, 4K: Developing cartridge 5: Intermediate transfer belt 6: Transfer member 7: Feed roller 8: Fixing device 9 , 10 Cleaning device 40 Rotary housing 41 Developing roller 51, 52, 53 Tension roller 54 Transfer bias applying roller 81, 82 Roller 83, 84 Heater

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03G 15/04 G03G 15/16 103 15/043 15/04 120 15/16 103 21/00 372 21/14 F term (for reference) 2H027 DA04 DA06 DA07 DA32 EA01 EA02 EA03 EA04 EA20 EB04 ED03 ED06 ED08 ED24 EE01 EE05 EF01 2H030 AA01 AD02 AD17 BB01 BB12 BB16 BB24 BB33 BB42 BB01 GA41 BB46 BB56 BB46 BB46 HA02 HA28 HA29 HB12 JA01 JB06 JC03 PA10

Claims (3)

[Claims] A charging unit configured to charge the image carrier; an exposure unit configured to expose the charged image carrier based on an image signal to form an electrostatic latent image; A plurality of developing means for developing the electrostatic latent image by using a developer, and the plurality of developing means are sequentially rotated with respect to the image carrier to thereby move the developer carrier of the developing means to the image carrier; A developing means rotating mechanism for contacting or separating the developing means, and an intermediate transfer body for transferring and carrying the developed image on the image carrier. The timing at which the developing means contacts the image carrier is determined by the exposure means. An image forming apparatus, which is located before a timing of exposing an image carrier. 2. The timing of the bias applied to the charging means is such that an arbitrary fixed point on the image carrier is moved from the contact position of the charging means to the developing means with respect to the time when the developing means contacts the image carrier. The image forming apparatus according to claim 1, wherein the time is before a time for moving to the contact position. A charging means for charging the image carrier; an exposure means for exposing the charged image carrier based on an image signal to form an electrostatic latent image; A plurality of developing means for developing the electrostatic latent image by using a developer, and the plurality of developing means are sequentially rotated with respect to the image carrier to thereby move the developer carrier of the developing means to the image carrier; A developing means rotating mechanism for abutting or separating the developing means, and an intermediate transfer body for transferring and carrying the developed image on the image carrier, and the timing at which each developing means separates from the image carrier is
An image forming apparatus, which is provided after a transfer step of transferring a developed image formed on the image carrier to the intermediate transfer body.