JP2003263005A - Tandem type color image forming apparatus, and method for setting distance between image carriers in image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tandem type color image forming apparatus capable of forming an image whose color drift is little practically. <P>SOLUTION: In the tandem type color image forming apparatus having image carriers (photoreceptor drums) 102Y, 102M, 102C and 102Bk arranged in parallel with a transfer belt 201 in order to transfer toner images carried on their surfaces respectively to the belt 201, and a driving roller 203 for driving the belt 201 in a frictional contact state, there is a relation L=2πär(1+α)+1/2t} when a distance (q) between the drums 102Y, 102M, 102C and 102Bk is defined as L, the radius of the roller 203 is defined as (r), the thickness of the belt 201 is defined as (t) and a slip rate between the roller 203 and the belt 201 is defined as α. The slip rate α is within the range of 0.01 to 0.3%. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus used in an electrophotographic copying machine, a printer or the like, and more specifically, it has a plurality of image carriers and an intermediate transfer belt or a transfer material conveying belt. The present invention relates to a so-called tandem color image device and a method for setting a distance between image carriers of the tandem color image device.

[0002]

2. Description of the Related Art A so-called tandem type color output device using a plurality of photoconductors has the advantages that the number of output sheets per unit time is large and the production efficiency is high, but it is difficult to align the writing position for each color. The tandem type color output device has a type of directly transferring to the final transfer member and a type of transferring to the final transfer member via an intermediate transfer member.

The direct transfer method is a method of directly transferring from the image carrier (photosensitive drum) 102 to the final transfer member 151 as shown in FIG. In the intermediate transfer method, the transfer member is not the final transfer member 151 as shown in FIG.
This is a method of transferring to the final transfer member 151 after transferring to 01b. FIG. 3 shows the Bk image forming unit 101 shown in FIG.
FIG. 2 is a side view showing Bk in an enlarged manner and also showing the Bk image forming unit 101Bk shown in FIG. 1 from the opposite side. In the following description, yellow is Y, magenta is M, cyan is C, and black is Bk, and Y, M, C, and Bk are attached to the components related to the color.

The intermediate transfer system will be described with reference to FIG. 2. The intermediate transfer member 201b advances in the clockwise direction, and image carriers (photosensitive drums) 102Y, 102M,
The toner images of Y, M, C and Bk on 102C and 102Bk are sequentially transferred to the transfer means 105Y, 105M, 105C and 10.
The image is transferred to the intermediate transfer member 201b by 5Bk (hereinafter referred to as primary transfer). After that, the transfer roller pair 30
It is transferred to the final transfer member 151 between 4 and 306 (hereinafter referred to as secondary transfer). The toner image on the final transfer member 151 is heated and fixed by the fixing unit 107, and is discharged to the outside of the apparatus via the paper discharge roller 108. Further, after the secondary transfer, the transfer is not performed 100% on the intermediate transfer belt 201b, and some untransferred toner remains. Therefore, the surface thereof is cleaned by the cleaning blade 110 to restore the belt surface to the initial state.

In the method using the intermediate transfer member (intermediate transfer method), since the material of the transfer member is constant when transferring from the image forming unit, the alignment of each color may be better than that of the direct transfer method. It has the feature that a high quality color image with little deviation can be obtained.

In the direct transfer method, the intermediate transfer member 201b
Instead, the toner images of Y, M, C, and Bk are sequentially transferred to the transfer member 151 on the conveyor belt 201a by the transfer units 105Y, 105M, 105C, and 105Bk sequentially. The subsequent steps are the same as those of the above-mentioned intermediate transfer method.

[0007]

[Problems to be Solved by the Invention] Intermediate transfer belt 201
b or the transfer material transport belt 201a (hereinafter, the intermediate transfer belt 201b and the transfer material transport belt 201a are collectively simply referred to as a belt 201) is used to sequentially pass through each image forming unit to obtain a color image. In the apparatus, maintaining a constant speed of the image carrier 102 and the belt 201 is indispensable for preventing color misregistration of an image, and the degree of color misregistration is largely controlled by the belt speed accuracy. That is, as shown in FIG. 4, the driving roller 203 that frictionally drives the belt 201 is required to have high accuracy without circumferential runout, and the gear trains 204 and 206 that transmit the driving force of the motor 205 to the driving roller 203 are also high. Precision is required.

However, as mechanical factors of the speed fluctuation of the belt 201, the eccentricity of the driving roller 203, the roller 2
Although the eccentricity of the member that drives 01, for example, the gears 204 and 206 is an important factor for speed fluctuation, in addition to this, the thickness of the belt 201 is not uniform, the belt 201 and the drive roller 20
Considering the slip between 3 is important for practically reducing the color shift. It is desirable that the belt 201 has a uniform thickness over the entire circumference, but in manufacturing, uneven thickness (t1, t2) occurs as shown in FIG. The belt speed V is determined by V = 2NπR = 2Nπ (r + 1 / 2t) (N: driving roller rotation number, R = actual driving radius, r = driving roller radius t = belt thickness). Even if it is constant, if the actual driving radius R changes, the belt speed V also changes. That is, the nonuniformity of the belt thickness t causes the belt speed fluctuation.

Further, since the driving roller 203 and the belt 210 are frictionally driven, the driving force is transmitted with a slight slip ratio α. In particular, when the belt 210 has a load such as the cleaning blade 110 as in this apparatus, it is difficult to obtain an image with less color misregistration by ignoring the slip ratio α. Thus, the belt speed V is determined by several factors.

By the way, Japanese Patent Publication No. 6-13373 discloses that in a transfer material conveying belt mechanism of a direct transfer system, "the distance between a plurality of image carriers is the distance the belt is conveyed when the driving roller makes one rotation". If there is a relationship of "multiplying by an integer", a technology is disclosed that enables good alignment without processing or assembling the drive roller with high accuracy.
No mention is made of slip ratio α and belt thickness deviation.

As another conventional technique, a technique for keeping the belt speed V constant is disclosed in JP-A-63-81370, JP-A-63-81372, JP-A-63-81373, and JP-A-63. No. 151970 is disclosed. In these known techniques, a pickup roller for speed detection is brought into contact with the back surface of the conveyor belt, the rotation of the pickup roller that rotates with the belt movement is detected by a shaft encoder, and the detected speed is fed back to a PLL servo control circuit for driving. The speed is controlled so that it is always equal to the predetermined speed.

This method can correct the speed fluctuation due to the above-mentioned mechanical factor. If slippage occurs between the roller of the speed detecting portion and the belt surface, speed fluctuation may be caused. Furthermore, a speed detector must be newly provided, which tends to increase the cost.

In view of the above-mentioned problems of the conventional example, the present invention sets a distance between image carriers of a tandem type color image forming apparatus and a tandem type color image forming apparatus capable of practically forming an image with little color shift. To provide a method.

[0014]

In order to achieve the above object, the first means is to transfer the toner image carried on each surface to a belt-shaped intermediate transfer member. And a plurality of image carriers arranged in parallel, and a drive roller for driving the belt-shaped intermediate transfer member in frictional contact, and color images are sequentially formed on the intermediate transfer member to form a color image. In the tandem color image forming apparatus, the distance between the image carriers is set based on the diameter of the drive roller, the thickness of the belt-shaped intermediate transfer body, and the slip ratio between the belt-shaped intermediate transfer body and the drive roller. It is characterized by having done.

A second means is the same as the first means, wherein the distance between the image carriers is L, the radius of the drive roller is r, the thickness of the belt-shaped intermediate transfer body is t, the drive roller and the When the slip ratio of the belt-shaped intermediate transfer member is α, the distance L between the image carriers is set to be L = 2π {r (1 + α) + 1 / 2t}.

A third means is a plurality of means arranged in parallel with the belt-shaped carrying member for transferring the toner images respectively carried on the respective surfaces to a transfer member carried by the belt-like carrying member. An image carrier, and a drive roller for driving the belt-shaped conveying member by frictional contact,
In a tandem-type color image forming apparatus for forming a color image by sequentially superposing each color image on a transfer member, the distance between the image carriers is determined by the diameter of the driving roller, the thickness of the belt-shaped conveying member, and the belt-shaped member. It is characterized in that it is set based on the slip ratio between the conveying member and the driving roller.

A fourth means is the same as the third means, wherein the distance between the image carriers is L, the radius of the drive roller is r, the thickness of the belt-shaped conveying member is t, the drive roller and the belt. The distance L between the image carriers is set to be L = 2π {r (1 + α) + 1 / 2t}, where α is the slip ratio of the sheet conveying member.

A fifth means is characterized in that, in the second or fourth means, the slip ratio α is in the range of 0.01% to 0.3%.

A sixth means is for transferring the toner image carried on each surface to a belt-shaped intermediate transfer member or a transfer member which is conveyed by a belt-shaped conveying member. Setting of the distance between the image carriers of a tandem type color image forming apparatus having a plurality of image carriers arranged in parallel to each other and a driving roller for driving the belt-shaped intermediate transfer member in frictional contact In the method, the distance between the image bearing members is L, the radius of the drive roller is r, the thickness of the belt-shaped intermediate transfer member or the transport member is t, and the drive roller and the belt-shaped intermediate transfer member or the transport member are When the slip ratio is α, the distance L between the image carriers is set so that L = 2π {r (1 + α) + 1 / 2t}.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a tandem color image forming apparatus according to the present invention, and FIG. 2 is a second tandem color image forming apparatus according to the present invention.
Of the embodiment of FIG. 3, FIG. 3 is an enlarged view of the Bk image forming unit of FIGS. 1 and 2, and FIG.
5 is an enlarged view of the belt drive roller portion of FIG. 5, FIG. 5 is an explanatory view showing the radius of the drive roller and the thickness of the belt of FIGS. 1 and 2, and FIG. 6 is an explanatory view showing the fluctuation cycle of the drive roller. 7 is an explanatory diagram showing a change in thickness in the belt circumferential direction, and FIG. 8 is an explanatory diagram showing a slip ratio according to a load.

FIG. 1 is a diagram showing the overall structure of a direct transfer type, and FIG. 2 is a diagram showing the overall structure of an intermediate transfer type. Here, description will be given with reference to FIG.
As shown in FIG. 2, four image forming units 101Y, 101M and 101 for forming four color images respectively.
C, 101Bk and the intermediate transfer belt 201b, a paper feed tray for accommodating the transfer member (transfer paper) 151, a paper feed roller 152 for picking up the transfer member 151 from the paper feed tray and feeding it, and a conveyance path 155. A pair of conveying rollers 153 for conveying the picked-up transfer member 151,
A registration roller 154 for sending out the transfer member 151 in time with the front end of the image formed on the intermediate transfer belt 201b, and an overlap transfer toner image formed on the intermediate transfer belt 201b on the transfer member (transfer paper) 151. The transfer member (transfer paper) 1 includes secondary transfer rollers 304 and 305 for secondary transfer, a fixing roller 107 for fixing the secondary-transferred toner image, and a plurality of conveying rollers.
51 is sent out at a predetermined timing and is conveyed at a constant speed.

Image forming units 101Y, 101M, 1
Reference numerals 01C and 101K are for forming an image by an electrostatic copying method, and as shown in detail in FIG. 3, image carriers (photosensitive drums) 102Y, 102M and 1 are continuously arranged in parallel.
The main components are 02C and 102Bk. Then, the photosensitive drums 102Y, 102M, 102C, 10
Around the 2Bk, the photosensitive drums 102Y, 102M,
Charging means 103Y, 103M, 103C, 103Bk for uniformly charging the surfaces of 102C, 102Bk, and optical writing means for forming a required electrostatic latent image on the photoconductor drums 102Y, 102M, 102C, 102Bk according to image information. 110Y, 110M, 110C, 110Bk, and developing devices 104Y, 104M, 10 for developing electrostatic latent images
4C, 104Bk, and a cleaning unit 106 for cleaning the toner remaining on the image carriers (photosensitive drums) 102Y, 102M, 102C, 102Bk after development.
Y, 106M, 106C and 106Bk are arranged. That is, the color image forming apparatus is a tandem type in which the image forming units are continuously arranged in parallel, and the printing speed is increased and the apparatus is made compact.

Photoreceptor drums 102Y, 102M, 102
Immediately below C, 102Bk, the photosensitive drums 102Y, 102M, 102C, 1 with respect to the intermediate transfer belt 201b.
Primary transfer units 105Y, 105M, 105C, and 105Bk that primarily transfer the visualized toner image are arranged on 02Bk. The intermediate transfer belt 201b is an endless belt having a medium resistivity. Reference numeral 211 is a belt position detection mark, and 310 is a sensor for detecting the belt position detection mark. The belt position detection mark 211 detected by this sensor 310 detects the rotational position of the intermediate transfer belt 201b.

Further, based on the recorded information, in the optical writing means 110Y, 110M, 110C, 110Bk,
Laser light corresponding to each reproduced color is modulated and emitted. On the other hand, the photosensitive drums 102Y, 102M, 102
C, 102Bk are rotating at a constant speed in the direction of the arrow in FIG. 2, and charging means 103Y, 103M, 103C,
After the surface is uniformly charged by 103Bk, it is exposed and scanned by the optical writing means 110Y, 110M, 110C and 110Bk. By this exposure, the photosensitive drum 102
The electrostatic latent images formed on the Y, 102M, 102C, and 102Bk corresponding to the respective reproduced colors are the developing devices 104Y, 104M, 104C, and 104Bk that contain the toners of the respective reproduced colors.
To develop the toner images of the respective colors. These toner images are transferred to the photosensitive drums 102Y and 10Y.
2M, 102C, 102Bk and intermediate transfer belt 201b
At each of the facing parts of the primary transfer means 105Y, 105
M, 105C, 105Bk, intermediate transfer belt 20
1b is sequentially transferred and transferred.

The intermediate transfer belt 201b is stretched by a belt drive roller 203, a pair of secondary transfer rollers 304 and 306, and a driven roller 202, and is driven by a motor 205 shown in FIG. Rotates and the intermediate transfer belt 201b runs.

After that, the transfer toner image formed by being superposed on the intermediate transfer belt 201b is transferred to the secondary transfer roller pair 3
It is conveyed to the part opposite to 04 and 305. Then, the toner image on the intermediate transfer belt 201b is transferred to the transfer member 151 fed from the paper feed tray by the secondary transfer roller pair 304, 30.
6 is secondarily transferred. Then, the transfer member 151 to which the toner image is transferred is conveyed to the fixing roller 107,
The toner image of each color is melted by being heated here to obtain a full-color image. On the other hand, the intermediate transfer belt 201b after the transfer
Is cleaned by the cleaning blade 101 to prepare for the next image formation.

Although the intermediate transfer belt type has been described above, in the case of the direct transfer type conveyor belt type shown in FIG. 1, instead of transferring to the intermediate transfer belt 201b, the resist roller 154 transfers the transfer member 151. The image of Y, M, C, and Bk is sent directly to the transfer member 151 so as to be superimposed and transferred. Then, the transferred transfer member 151 is fixed by the fixing roller 107 and then ejected from the ejection roller 108. Other parts that are not particularly described are the same as those in the case of the intermediate transfer system of FIG.

Here, the belt 201b is the driving roller 20.
It is friction driven by 3. As shown in FIG. 5, this substantial drive roller radius (radius r of the drive roller 203 is
+ 1/2 of the belt thickness t) has a circumferential length equal to the distance L between the image carriers. That is, when the substantial driving radius is R, the relationship is 2πR = L. When the drive roller 203 has eccentricity due to processing and assembly, eccentricity of the drive transmission gears 204 and 206, the speed V of the belt 201b is one rotation of the drive roller as shown in A (transfer belt speed state without slip) in FIG. With a period T1. That is, Japanese Patent Fairness 6
As described in Japanese Patent Publication No. -13373, the period T1 of the waveform coincides with the time required to move from one image carrier to the next.

However, since the drive is transmitted with a constant slip ratio α between the belt 201b and the drive roller 203, the belt speed V decreases as shown by B (slip transfer belt speed state) in FIG. The belt movement distance by one rotation of the drive roller 203 does not necessarily match the distance L between the image carriers. That is, the cycle T of one rotation of the drive roller does not match the cycle T1 of moving from one image carrier to the next image carrier, and the belt 201b needs to move from the image carrier to the next image carrier. As shown in FIG. 5, the drive roller 203 needs a rotation angle of 360 ° + θ.

It should be noted here that if the speed reduction due to slip is to be corrected by increasing the rotation speed of the drive roller 203, the transfer belt when the rotation speed of the drive roller is increased is shown in FIG. 6C. As shown in (velocity state), the cycle of one rotation of the drive roller is T2 = T1−δT, and T1 = T2. In order to prevent color misregistration, the one rotation cycle of the drive roller needs to match the cycle T1. The cycle can be matched with the cycle T1 by making the radius r of the drive roller multiplied by the slip ratio. That is, if the radius is r (1 + α), they can be matched.

Up to this point, the distance between the adjacent image carriers has been discussed, but the farthest distance between the image carriers has a greater effect, and the drive roller 203 needs a rotation angle of 360 ° + 3θ, and thus the phase is greatly increased. It will result in deviation. If the diameter of the driving roller 203 is 1/2, 360 ° + 6θ
Therefore, the phase shift becomes larger and larger.

Next, it will be described that the thickness deviation (nonuniformity) of the belt 201b affects the color misregistration. Belt thickness t
Is non-uniform between t1 and t2, the speed of the belt 201b is not constant and causes a speed fluctuation. It occurs because the effective drive radius changes as R1 = r + 1 / 2t1 R2 = r + 1 / 2t2. If the fluctuation cycle of the thickness t is equal to the distance cycle of each image carrier, color misregistration does not occur as described above, but the fluctuation cycle t of the belt thickness is the maximum thickness t2 per belt circumference as shown in FIG. , There is usually a minimum thickness t1.

Since the substantial driving radius of the driving roller 203 is represented by R = r + 1 / 2t (r: radius of the driving roller 203, t: belt thickness), if the radius r is large, it depends on the thickness variation of the belt 201b. The speed fluctuation of the belt 201b has a small effect,
When the driving roller radius r is small, the fluctuation of the belt thickness t greatly affects the speed fluctuation of the belt 201b. Therefore,
It is desirable that the radius r of the drive roller 203 be as large as possible.

On the other hand, the radius r is "a plurality of image carriers 1
The distance between the two is made to be an integral multiple of the distance that the belt 201b is conveyed when the drive roller 203 makes one rotation. ”And the radius r holds the relationship of L = 2π (r + 1 / 2t). . That is, the maximum radius is limited to the radius that makes the distance between the belts that move for one rotation of the drive roller equal to the distance between the image carriers.

In FIG. 7, when the belt thickness t is expanded in the circumferential direction, the plotted points are the measured values of the thickness t of that portion, and the solid line is the polynomial approximation curve. The change is ± δt with respect to the target belt thickness t. According to the inventor's example, 1 is set for the thickness t = 100 μm of the driving roller and the transfer belt 201b which maintain the relationship of L = 4π (r + 1 / 2t) and the driving roller L = 2π (r + 1 / 2t).
As a result of an experiment using a transfer belt having a thickness deviation of about 0 μm, the deviation from the ideal position due to the nonuniformity of the belt thickness t could be reduced by half.

Next, the slip ratio between the drive roller 203 and the belt 201b will be described. Originally, the drive roller 20
It is desirable that no slip occurs between No. 3 and the belt 201b. If the slip ratio is large, belt running becomes unstable, and normal constant speed running is difficult. Therefore, the drive roller 2
33 It is important to increase the friction coefficient of the surface, increase the belt winding angle, and increase the belt tension to reduce slip. When there is no load on the belt 201b, there is almost no slip between the drive roller 203 and the belt 201b. However, as described above, the toner remaining on the surface of the belt is cleaned by pressing the blade made of urethane rubber against the surface of the belt for cleaning, which causes a load on the running of the belt.

FIG. 8 shows that the slip ratio α changes depending on the load condition. In this, an encoder is provided coaxially with the drive shaft, and the pulse count number of the encoder when the belt 201b makes one revolution is measured. That is, the number of rotations of the driving roller 203 required for one round of the belt is obtained, and the slip ratio α is calculated. If the load is too large, on the contrary, the cleaning effect is reduced, slip is increased, and normal belt running becomes difficult. 0.01-0.
The normal running state of the belt is that the load is the slip rate α within the range of 5%.

[0038]

As described above, according to the present invention, based on the diameter of the driving roller, the thickness of the belt as the intermediate transfer member or the conveying member of the transfer member, and the slip ratio between the belt and the driving roller. Since the distance between the image bearing members is set, it is possible to form an image with little color shift practically.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a tandem type color image forming apparatus according to the present invention.

FIG. 2 is a configuration diagram showing a second embodiment of a tandem type color image forming apparatus according to the present invention.

FIG. 3 is an enlarged configuration diagram showing the Bk image forming unit shown in FIGS. 1 and 2;

FIG. 4 is an enlarged configuration diagram showing a belt driving roller portion of FIGS. 1 and 2.

5 is an explanatory diagram showing a radius of a drive roller and a thickness of a belt in FIGS. 1 and 2. FIG.

FIG. 6 is an explanatory diagram showing a fluctuation cycle of a drive roller.

FIG. 7 is an explanatory diagram showing a change in thickness in the belt circumferential direction.

FIG. 8 is an explanatory diagram showing a slip ratio according to a load.

[Explanation of symbols]

101Y, 101M, 101C, 101Bk Image forming units 102Y, 102M, 102C, 102Bk Image carrier (photosensitive drum) 201b Intermediate transfer belt 203 Drive roller

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2H030 AA01 AB02 AD05 BB02 BB42                       BB44                 2H200 FA04 FA19 GA12 GA23 GA34                       GA44 GA47 GB12 GB22 HA02                       HA28 HB07 HB12 HB22 JA02                       JB07 JB10 JB16 JB32 JB42                       JB47 JC04 JC07 JC12 JC17                       LA15 LA30 LA40 LB13 MC05

Claims (6)

[Claims] 1. A plurality of image carriers arranged in parallel with the belt-shaped intermediate transfer member for transferring a toner image carried on each surface to the belt-shaped intermediate transfer member, and the belt-shaped intermediate transfer member. A tandem-type color image forming apparatus having a driving roller for driving the intermediate transfer member in frictional contact to form a color image by sequentially superimposing images of respective colors on the intermediate transfer member. A tandem type color image forming apparatus, which is set based on a diameter of a driving roller, a thickness of the belt-shaped intermediate transfer member, and a slip ratio between the belt-shaped intermediate transfer member and the driving roller. 2. The distance between the image carriers is L, the radius of the drive roller is r, the thickness of the belt-shaped intermediate transfer member is t,
The distance L between the image carriers is set to L = 2π {r (1 + α) + 1 / 2t}, where α is the slip ratio between the drive roller and the belt-shaped intermediate transfer member. Claim 1 characterized by the above-mentioned.
The tandem color image forming apparatus described. 3. A plurality of image carriers arranged in parallel with the belt-shaped conveying member for transferring the toner images respectively carried on the respective surfaces to a transfer member conveyed by the belt-shaped conveying member. A tandem type color image forming apparatus having a driving roller for driving the belt-shaped conveying member in frictional contact to form color images by sequentially superimposing color images on a transfer member, and a distance between the image carriers. Is set on the basis of the diameter of the drive roller, the thickness of the belt-shaped transport member, and the slip ratio between the belt-shaped transport member and the drive roller. 4. A distance between the image carriers is L, a radius of the drive roller is r, a thickness of the belt-shaped transport member is t, and a slip ratio between the drive roller and the belt-shaped transport member is α.
The distance L between the image carriers is set to be L = 2π {r (1 + α) + 1 / 2t}.
The tandem color image forming apparatus described. 5. The slip ratio α is 0.01% to 0.3%.
The tandem-type color image forming apparatus according to claim 2 or 4, wherein 6. A belt-shaped intermediate transfer member or a transfer member arranged in parallel to transfer a toner image carried on each surface to a transfer member conveyed by a belt-shaped intermediate transfer member or a belt-shaped transfer member. In a method of setting a distance between the image carriers of a tandem type color image forming apparatus having a plurality of image carriers arranged in a uniform manner, and a drive roller for driving the belt-shaped intermediate transfer member in frictional contact, The distance between the image bearing members is L, the radius of the driving roller is r, the thickness of the belt-shaped intermediate transfer member or the conveying member is t, and the slip ratio of the driving roller and the belt-shaped intermediate transfer member or the conveying member is α. Then, the distance L between the image carriers is set so that L = 2π {r (1 + α) + 1 / 2t}. Image of tandem type color image forming apparatus Setting the distance between the lifting member.