JPH10123786A - Color electrophotographic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce transfer color slurring by providing a first supporting body which is used in common for plural photoreceptors, and a second supporting body having a coefficient of thermal expansion smaller than that of the first supporting body. SOLUTION: The frame 4 of the photoreceptor 1 is separated from the frame 6 of a scanning exposure device. That is, this device is provided with the frame 4 which rotatably supports the plural photoreceptors 1 and which is used in common for the plural photoreceptors 1, and the frame 6 which supports at least plural constituting parts among members constituting an exposing means, which is in common with the plural constituting parts, and whose coefficient of thermal expansion is smaller than that of the frame 4. In the case, as to the frame 6 whose temperature change, such material whose coefficient of thermal expansion is small as steel is assembled to be used; and as to the frame 4 whose temperature change is small, resin, etc., whose coefficient of thermal expansion is comparatively large can be used. For example, the coefficient of thermal expansion of the frame 6 connecting each canning exposure device each other is nearly half of that of the frame 4 connecting each photoreceptor each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a color printer,
The present invention relates to a color electrophotographic apparatus applied to a color copying machine, a color fax and the like.

[0002]

2. Description of the Related Art Conventionally, there are various types of color electrophotographic apparatuses, and they are roughly classified into two types: a multi-developing type and a multi-transfer type. Multiple development type (for example, see JP-A-1-195)
No. 774) is a form in which a plurality of toner images are sequentially superimposed and developed on one photoconductor, and has a feature that color misregistration is unlikely to occur. There is a large problem when charging, exposing, and developing from above, and it is difficult to obtain stable color formation. On the other hand, the multi-transfer type is further roughly classified into a single photoconductor, a four-cycle system in which image formation and transfer of a plurality of color toner images are sequentially repeated, and a single photoconductor. There are two types, one-cycle type, in which a single-color toner image is formed. In either case, there is a problem that color shift does not occur when superimposed transfer is performed. There is a feature that the goodness can be applied as it is. In particular, the four-cycle system has been widely adopted in products because it has a disadvantage that the recording speed is slow, but it is relatively easy to overcome the problem of color misregistration. The other one-cycle type (for example, JP-A-61-79)
The color electrophotographic apparatus disclosed in Japanese Patent Application Laid-Open No. 658/658 has a great feature that a higher recording speed can be obtained as compared with the four-cycle type, but color shift is apt to occur. Need and have been adopted only in some expensive products.

An example of a conventional one-cycle type multi-transfer type color electrophotographic apparatus will be described with reference to a plan view of FIG. 12 and a side view of FIG. For example, four electrophotographic process units 30 corresponding to cyan, magenta, yellow, and black
Are composed of a photoconductor 1, a scanning exposure device 11, a charging device (not shown), a developing device 12, a transfer device 13, a cleaning device (not shown), and the like. These electrophotographic process units 30 are fixed to the connection frame 9 or the common frame 4, respectively, so that the toner images of each color can be sequentially transferred onto one image recording medium in each transfer unit 30 </ b> A. It is arranged in a line along. The recording medium transport device 20 includes a transfer belt 2,
It is composed of a transport roll 3 for winding and transporting the transport roll, and a drive device for the transport roll 3 (not shown). The shaft of the transport roll 3 is supported so as to be parallel to each photoconductor 1. In the color electrophotographic apparatus shown in FIGS. 12 and 13, the image recording medium 5 is generally made of plain paper, high-quality paper,
An OHP sheet or the like is supplied in the direction of arrow A by the paper feed roll 10, is supported or attracted by the transfer belt 2, advances in the direction of arrow B, passes through the transfer unit 30A of each electrophotographic process unit 30, and is transferred to each transfer unit. By the operation of the transfer device 13 provided corresponding to 30A, the toner images of different colors are superimposed and received on the toner image.

The image recording medium 5 on which the toner images of each color are superimposed advances to a fixing device 14, where the toner images of each color superimposed on the image recording medium 5 are fixed on the image recording medium 5, and the image recording medium 5 is fixed. To form a color image. The image recording medium 5 includes the transfer belt 2 as described above.
Supported by or adsorbed on each electrophotographic process unit 3
The toner images of different colors formed on the photoreceptor 1 are superimposed on the correct position of the image recording medium 5 while passing through the transfer section 30A of the image forming medium 0. However, it is extremely important to obtain a high-quality color image without color shift. However, in an electrophotographic apparatus, it is generally necessary to frequently remove each color unit in order to perform maintenance or inspection or replace a photoconductor, a developing device, a charging device, etc., which are frequently damaged or worn out.
At this time, in the example of the conventional color electrophotographic apparatus shown in FIGS. 12 and 13, the positional relationship between the scanning exposure apparatus and the photoconductor for each color is fixed as the unit 30 so that there is almost no shift. Since the distance and parallelism between a plurality of colors are determined by the attachment to the common frame 9, in order to obtain a high-quality color image without color shift, the distance between the units 30 of a plurality of colors and the parallel alignment are adjusted each time. Need to be done exactly. Further, when replacing only the periphery of the photosensitive member which is severely damaged or worn, it is uneconomical to replace the entire unit including the scanning exposure apparatus with relatively few failures.

FIG. 14 shows another example of a conventional color electrophotographic apparatus, in which a scanning exposure apparatus 11 for each color, an electrophotographic unit including the photoreceptor 1, and a recording medium conveying apparatus 20 are individually and commonly used. The case where it is fixedly installed on the frame 4 is shown. In this case, it is possible to replace only the periphery of the photoconductor, which is heavily damaged or worn, while leaving the scanning exposure device 11, but the scanning exposure device 11 and the electrophotographic unit including the photoconductor 1 are separated from each other. Therefore, accurate alignment adjustment of the electrophotographic unit including the photoreceptor 1 after replacement is more difficult than in the examples of FIGS. Therefore, even if it is a structure that can be replaced only around the photoconductor, it is almost impossible for the user to replace it by himself, and even if a service technician performs it, special jigs and skills -There is a problem that a large amount of work time is required.

As still another example of the conventional color electrophotographic apparatus, there is a concept of integrally combining a scanning exposure apparatus for each color and an electrophotographic unit including a photosensitive member (see Japanese Patent Application Laid-Open No. 8-54817). There is no difference from the example shown in FIG. 14 in that it is fixed to a common frame.
In a one-cycle type multi-transfer type color electrophotographic apparatus as shown in FIGS. 12 to 13 and FIG. This is achieved by adjusting the writing timing of No. 11, but color shift may also occur over time during use. One of the major causes is an alignment adjustment error when the unit is replaced, and the other is a dimensional change due to thermal expansion due to a temperature change in the apparatus. The influence of the latter temperature change can be roughly divided into two. First, when the temperature of the entire apparatus changes, for example, from the reference temperature at the time of initial adjustment, the effect of the dimensions of various parts in the apparatus changing from the reference dimensions according to their respective thermal expansion coefficients. And the other is the effect of the temperature distribution in the device, which causes the degree of dimensional change at each location to differ due to the temperature difference. The temperature change over time in the electrophotographic apparatus is roughly estimated to be about 50 ° C. at the maximum, and the temperature difference in the apparatus at a certain point in time is expected to be about 10 ° C. to 30 ° C. Here, the heat that affects color misregistration is generated by the fixing device relatively far from the electrophotographic process unit, but rather by the polygon motor and control board in the scanning exposure device. Is found by the present inventors' measurements. Therefore, in the above-described conventional example in which the scanning exposure apparatus of each color and the electrophotographic unit including the photoconductor are integrally connected, the distance between the photoconductors is small compared to the expansion of the distance between the scanning exposure apparatuses. Since the bent frame irregularly bends and deforms due to the bimetal effect, the initial adjustment state is lost and a color shift occurs.

Here, in the conventional color electrophotographic apparatus shown in FIGS. 12 to 13 and FIG. 14, the magnitude of color shift in the sub-scanning direction caused by thermal expansion due to a temperature change in the apparatus is shown in FIG. This will be described quantitatively with reference to FIGS. 13 and 15. However, for simplicity, irregular deformation due to the bimetal effect is ignored. In FIGS. 12 and 13,
The distance between the adjacent photoconductors and the distance between the adjacent scanning exposure devices are equal to each other by d. At this time, the scanning exposure image 25 on the photoconductor 1 is visualized by the developing device 12 and becomes a developed image 26 as a developed image 26. 1 and is sequentially transferred onto the image recording medium 5 and superimposed as transfer images 41 to 44 of the first to fourth colors. FIG.
2 to 13 show a state in which the writing timing of the image exposure of the scanning exposure device 11 of each color is correctly set with respect to the positional relationship between the scanning exposure device 11 and the photoconductor 1, and here, for convenience, FIG. It is assumed that when transfer images of the first to fourth colors are illustrated at equal intervals as in transfer images 41 to 44 shown in (1), no color shift occurs between the transfer images of the respective colors.

Next, with reference to FIG. 15, a description will be given of a color shift when the position of the scanning exposure apparatus and the position of the photosensitive member change together with the temperature change in the apparatus. Assuming that the temperature rises from the state in which the color shift does not occur as shown in FIGS. 12 and 13, the connecting frame 9 or the common frame 4 supporting and fixing each electrophotographic process unit 30 expands due to thermal expansion, The distance between adjacent photoconductors and the distance between scanning exposure apparatuses change. It is assumed that the interval between the electrophotographic process units in the fourth color extends e ₁ = κtL in the process direction with respect to the distance L from the first color. Here, κ is a coefficient of thermal expansion of the connection frame or the common frame, and t is a uniform amount of temperature change in the apparatus, for example, a time-dependent amount of temperature change from the time when the power is turned on. Also, for convenience,
The scanning exposure position 11 is almost immediately above the photoconductor 1, and
In addition, it is assumed that the exposure light beam 18 is incident substantially in the normal direction. Since the scanning exposure apparatus 11 nor the photosensitive member 1 moves by e ₁ together, no change in the relative position of the scanning exposure image on the photosensitive member, during the time T ₀ to the transfer from the exposure, the It proceeds from the original transfer position of the fourth color in extended position by e _1. The correct transfer position at this time is determined not by the elongation of the transfer device but by the dimensional change of the transport roll 3. Assuming that the original transfer interval is d, an adjacent scanning exposure apparatus supplies T = d / (2πrω) between image signals at the same location.
The image signal of each color is input such that a delay of the time T represented by the following occurs. Here, r is the radius of the transport roll,
ω is the angular velocity of the transport roll, ω does not change with temperature, but r changes with temperature. Assuming that the coefficient of thermal expansion of the transport roll 3 is γ, the correct transfer interval is d ₁ = 2πr
(1 + γt) ωT = d (1 + γt), and the distance from the first color is 3d = D (1 + γt), so e ₂ = γ
It is necessary to transfer the image when it is extended by tD. Therefore, when the thermal expansion coefficient κ of the connecting frame or the common frame is equal to the thermal expansion coefficient γ of the transport roll, κtD = γtD, that is, e ₁ −e ₂ = 0, and the color is changed merely by changing the dimensions of the system similarly. No shift occurs. However, when the coefficient of thermal expansion κ of the frame is different from the coefficient of thermal expansion γ of the transport roll, a color shift occurs, and the magnitude is expressed as e ₁ −e ₂ = (κ−γ) tD (1) .

Further, even when the thermal expansion coefficient κ of the frame is equal to the thermal expansion coefficient γ of the transport roll, a color shift occurs when there is a temperature distribution inside the apparatus. For example, if Δt represents a temperature difference between the temperature of the frame and the temperature of the transport roll,
The magnitude of the color shift is e ₁ −e ₂ = κ (t + Δt) D−γtD = κΔtD = γΔtD (2)

As shown in FIG. 14, even when the scanning exposure device 11 for each color, the electrophotographic unit including the photoreceptor 1, and the recording medium transport device 2 are individually fixedly mounted on the common frame 4, Since the scanning exposure device 11 and the photoconductor 1 are connected to one frame, the same can be said of the case of FIGS. 12 to 13 described above. As described above, the temperature change of the electrophotographic apparatus over time is roughly estimated to be about 50 ° C. at the maximum, and the temperature difference in the apparatus at a certain time is expected to be about 10 ° C. to 30 ° C. Typical structural materials commonly used in electrophotographic devices include steel, aluminum, glass fiber reinforced products such as AS resin, ABS, polyacetal, and polycarbonate, and their typical thermal expansion coefficients such as non-glass fiber reinforced standard products. 1.1 × 10 ⁻⁵ mm / ° C. and 2.3 × 10 ⁻⁵ mm respectively
^{/℃,3.0×10 -5 mm / ℃, 7.0 ×} 10 -5 mm /
FIG. 16 is a graph showing the amount of dimensional change with respect to the reference dimension for a temperature difference of 50 ° C. with respect to 50 ° C. The dimensional change for a temperature difference of 10 ° C to 30 ° C is 1/5
It can be read by multiplying by 3/5. Important reference dimensions for color misregistration of a one-cycle type multi-transfer type color electrophotographic apparatus as shown in FIGS. 12 and 13 are the distance between the scanning exposure apparatus and the distance between photosensitive members from the first color to the final color. D, which affects the magnitude of color misregistration in the form of the above equations (1) and (2). Here, in general, the magnitude of the color shift for color reproduction that can be tolerated in a color image such as printing is 0.1 mm to 0.15 in consideration of the sensitivity of human eyes.
mm or less. However, when D is in the range of 350 mm to 600 mm as in a conventional color electrophotographic apparatus, as shown in FIG. Even if there is a difference, the allowable limit of color misregistration is 0. mm1-0.1
Since it easily exceeds 5 mm, a control device that detects and corrects a color shift has been required.

For example, in the conventional color electrophotographic apparatus shown in FIGS. 12 to 13, four electrophotographic process units 30 are arranged on a steel frame 9 having a thermal expansion coefficient of 1.1 × 10 ⁻⁵ mm / ° C. at intervals of d. The transport roll 3 is fixedly installed while maintaining a distance, and has a thermal expansion coefficient of 2.3 × 10 ⁻⁵ mm / ° C.
It is assumed that the aluminum core material is covered with thin rubber. At this time, for example, if d is 150 mm, D is 450 mm, and the temperature change from the internal temperature of the apparatus at the time of installation is 30 to 50 ° C., the color shift that occurs in the sub-scanning direction between the first color and the fourth color Is 0.16 mm or more according to equation (1).
0.27 mm. Assuming that the exposure timing of the scanning exposure device at the time of installation is set so that toner images of each color are transferred in an overlapping manner without color shift in the sub-scanning direction, an exposure timing that eliminates color shift after a temperature change. Adjustment is needed again. In order to perform this automatically, a control device that detects and corrects the occurrence of color shift is required.

For example, in the conventional color electrophotographic apparatus shown in FIGS. 12 and 13, four electrophotographic process units 30 are arranged on an aluminum frame 9 having a thermal expansion coefficient of 2.3 × 10 ^-5 mm / ° C. with a distance d = It is assumed that the transfer rolls are fixedly installed at a distance of 150 mm, and the transport rolls are also made of aluminum core material coated with thin rubber. After the color misregistration is adjusted, for example, the temperature of the common frame is increased by continuous operation of the scanning exposure apparatus, and the temperature of the common frame is set to 10 ° C.
If a temperature difference of .times.
There is a problem that a color shift of 10 mm to 0.31 mm occurs.

The above is a description of a case where a plurality of scanning exposure apparatuses and a plurality of photosensitive members are connected by a common frame. On the other hand, Japanese Patent Application Laid-Open No. 1-169466 discloses an example in which a frame for connecting scanning exposure apparatuses and a frame for connecting photoconductors are separately provided.
And JP-A-8-62920. However, in the former, only a uniform temperature change is considered in the entire apparatus, and a change in speed of the recording medium transporting apparatus is not considered. Therefore, as described above, a scanning exposure apparatus is used in an actual color electrophotographic apparatus. If the temperature rise is larger than the temperature rise of the photoconductor, there is a problem that not only the color shift is not corrected, but also the color shift is increased rather than the case where all are connected by a common frame. In the latter case, although the speed change of the recording medium transport device is taken into consideration, it is possible to cope only with a uniform temperature change in the entire device, and the correction effect is obtained when there is a temperature difference between both frames. There is a problem that can not be.

[0014]

SUMMARY OF THE INVENTION In view of the above problems, the present invention overcomes the problem of color misregistration in a one-cycle multi-transfer type color electrophotographic apparatus, and provides a high-quality color image. An object is to provide a color electrophotographic apparatus.

[0015]

According to the first aspect of the present invention, an electrostatic latent image is formed by being exposed to light while rotating. A plurality of photoconductors having a cylindrical outer shape,
Forming each electrostatic latent image by scanning exposure light modulated by each image information on each of the plurality of photoconductors, each corresponding to each of the plurality of photoconductors, and an exposure unit having a plurality of components. Each electrostatic latent image formed on each of the plurality of photoconductors is developed with a toner of each color to obtain each toner image, and a process of sequentially transferring each toner image is performed. In a color electrophotographic apparatus for forming a color image fixed on a medium, a plurality of photoconductors are rotatably supported, a first support common to the plurality of photoconductors, and a member constituting an exposure unit. And a second support that supports at least the plurality of components and has a coefficient of thermal expansion smaller than the coefficient of thermal expansion of the first support common to the plurality of components. Characterized by

Here, in the first color electrophotographic apparatus of the present invention, the second support has a coefficient of thermal expansion that is almost half of the coefficient of thermal expansion of the first support. It is preferred that In the first color electrophotographic apparatus of the present invention, the plurality of photoconductors may be arranged in the order of transfer of the toner images formed on each of the plurality of photoconductors. The distance along the transfer path between the two transfer units where the toner images formed on the two photosensitive members are transferred is less than 150 mm. , Preferably supported by the first support, or, instead of being less than 150 mm,
The plurality of photoconductors are two of the two photoconductors that are the most distant along the transfer order of each toner image formed on each of the plurality of photoconductors. It is supported by the first support so that a distance along a transfer path between transfer portions to which respective toner images formed on the respective photoconductors are transferred is less than 100 mm. Is more preferable.

In this case, the plurality of photoconductors are two adjacent photoconductors in the order of transfer of the toner images formed on the plurality of photoconductors among the plurality of photoconductors. Between the transfer portions where the toner images formed on the two photoconductors are transferred, respectively.
It is preferable to be supported by the first support so that the distance along the transfer path is less than 33 mm.

Further, in the first color electrophotographic apparatus according to the present invention, the plurality of structures of the first support are arranged at a central portion in the arrangement direction of the plurality of photoconductors and the second support is formed. It is preferable that the central portions of the portions in the arrangement direction are fixedly connected to each other. A second color electrophotographic apparatus among the color electrophotographic apparatuses of the present invention that achieves the above object has a plurality of cylindrical external forms, each of which has an electrostatic latent image formed by being exposed to light while rotating. Through a process of forming each electrostatic latent image on each of the plurality of photoconductors, developing each electrostatic latent image with a toner of each color to obtain each toner image, and sequentially transferring each toner image. Finally, in a color electrophotographic apparatus for forming a color image fixed on an image recording medium, the plurality of photoconductors,
Of the plurality of photoconductors, two of the two photoconductors farthest along the transfer order of the toner images formed on each of the plurality of photoconductors were formed on each of the two photoconductors. It is characterized in that it is arranged so that the distance along the transfer path between transfer portions where the toner images are transferred is less than 150 mm.

Alternatively, in the second color electrophotographic apparatus, the plurality of photoconductors may be formed on each of the plurality of photoconductors instead of the requirement of less than 150 mm. Along the transfer path between the two photoconductors that are furthest apart in the order of transfer of the toner images, and between the transfer units where the toner images formed on the two photoconductors are transferred. Distance is 100mm
It is preferable to be provided so that it is less than.

In this case, the plurality of photoconductors are two of the plurality of photoconductors which are adjacent to each other in the transfer order of the toner images formed on the plurality of photoconductors. Between the transfer portions where the toner images formed on the two photoconductors are transferred, respectively.
More preferably, they are arranged so that the distance along the transfer path is less than 33 mm.

Here, in the second color electrophotographic apparatus of the present invention, it is preferable to provide a first support which rotatably supports the plurality of photosensitive members and which is common to the plurality of photosensitive members. Further, in the second color electrophotographic apparatus of the present invention, each of the plurality of photosensitive members is formed by scanning each of the plurality of photosensitive members with exposure light modulated by image information. Exposure means provided with a plurality of components corresponding to each of the bodies, and a second component common to the plurality of components, which supports at least the plurality of components among components constituting the exposure device. It is also a preferred embodiment to include a support.

[0022]

Embodiments of the present invention will be described below. 1 and 2 are a plan view and a side view, respectively, showing a first embodiment of the color electrophotographic apparatus of the present invention. As described above, according to the measurement by the present inventor, the heat that affects the color shift is mainly the heat generated by the polygon motor and the control board in the scanning exposure apparatus. Therefore, FIG.
In the structure of the conventional color electrophotographic apparatus shown in FIGS. 13 and 14, it is inevitable that a color shift occurs due to a temperature change. Therefore, in the first color electrophotographic apparatus of the present invention, the photoconductor 1 And the frame 6 of the scanning exposure apparatus are separately divided. The reason will be described with reference to FIG.

In FIG. 3, the frame of the scanning exposure apparatus and the frame of the photoreceptor are separated from each other, and their respective thermal expansion coefficients are α and β. The coefficient is set to γ, and the temperature change from the installation temperature of each of the scanning exposure apparatus frame 6, the photoconductor frame 4, and the transport roll 3 (see FIG. 2) is represented by t ₁ ,
Let t ₂ and t ₃ . At this time, assuming that the exposure or transfer distance between the first color, which is the reference dimension before the temperature change, and the final color, for example, the fourth color, is D, the change in the distance D due to the temperature change is e ₁ = αt for the scanning exposure apparatus. ₁ D, the photoreceptor e ₂ = βt ₂ D, is e ₃ = γt ₃ D for transfer position. In FIG. 3, when the influence of the change of the distance D on the color matching of the first color and the fourth color is individually viewed, the shift of the exposure position causes the transfer position to be advanced by e ₁ = αt ₁ D, and the shift of the photoconductor is determined by the exposure position. Is delayed by e ₂ and the time T from the exposure is
Transfer position after the ₀ also because delayed by e _2, a total of 2e
₂ = 2βt ₂ D is delayed. Further, a change in the transfer conveyance speed, that is, a change in the transfer position appears as an effect of advancing by e ₃ = γt ₃ D, so that the magnitude of the color misregistration is the sum of these, and e ₁ −2e ₂ + e ₃ = (αt _1). −2βt ₂ + γt ₃ ) D (3) Here, since the temperature change of the scanning exposure apparatus is large, it can be simplified to t ₁ > t ₂ = t _3. Therefore, the color shift is represented by (αt ₁ − (2β−γ) t ₂ ) D (4) . Further, the photoconductor frame 4 and the transport roll 3
When the same material or a material having the same coefficient of thermal expansion is selected as the material of the color shift, the color shift becomes (αt ₁ −βt ₂ ) D (5). The present invention is intended to reduce the color misregistration represented by the formulas (3), (4), (5), etc., and also reduce the color misregistration occurring at the time of maintenance and inspection or replacement of parts.

In the color electrophotographic apparatus of the present invention as shown in FIGS. 1 and 2, the materials of the scanning exposure apparatus frame 6, the photoreceptor frame 4, and the transport roll 3 are, for example, steel which is most commonly used as a structural member. ,aluminum,
The value of Expression (5) in the case where the material of the photoreceptor frame 4 is the same as the material of the transport roll 3 is selected from the glass fiber reinforced resins, and the value of the expression (5) can be calculated for some of the reference dimensions D. Here, 0 ° C ≦ t ₁ ≦ 50 based on the actual temperature change measurement result inside the color electrophotographic apparatus.
In the temperature range of 0 ° C., 0 ° C. ≦ t ₁ −t ₂ ≦ 30 ° C., eight kinds of temperature change patterns as shown in Table 1 and FIG. 4 are assumed.

[0025]

[Table 1]

The magnitude of the color misregistration is calculated for these combinations, and a graph for D = 300 mm is shown in FIG. The actual size of the color shift is almost the same as the calculated value except for the one due to irregular deformation in three dimensions. Can be approached. 300
For various values of D other than mm, a graph as shown in FIG. 5 is drawn, and the maximum value of the color shift in each temperature change pattern is obtained, for example, as shown in Table 2.

[0027]

[Table 2]

In Table 2, the magnitude of the color shift is 0.15 m.
Numerical values below m are generally acceptable levels. Further, in FIG. PS corresponds to combination 3 in Table 2,
P in P-S indicates that the material of the scanning exposure apparatus frame 6 is a reinforced resin, and S in P-S indicates
And that the material of the transport roll 3 is steel. Here, A represents aluminum.

In Table 2, in particular, D = 200 mm and D =
From the result of 300 mm, the color shift is small in the combinations 1, 4, 7, 8 using the material having a small coefficient of thermal expansion as the scanning exposure apparatus frame 6 having a large temperature change.
In this case, the photoconductor frame 4 having a small temperature change has
A resin or the like having a relatively large coefficient of thermal expansion may be used. Of course, the color misregistration is the smallest in the case of the combination 1 in which steel having a low coefficient of thermal expansion is used for every frame. However, the weight of the steel and the difficulty of the processing are difficult due to the difficulty of unit replacement and high cost. In particular, it is preferable to use light and inexpensive resin or aluminum for the frame of the replacement unit. In order to select the material of the frame 4 in this manner, the frame of the photoreceptor and the frame 6 of the scanning exposure device must be separated from each other. And the photoreceptor were combined into one unit, or the scanning exposure apparatus and the photoreceptor of each color were all connected and fixed to a common frame, and eventually the combination 5 shown in FIG. The color misregistration does not always become small as inferior to the combination 8 with. Conversely, it is also shown that the combination having a large color misregistration is a case where a material having a larger thermal expansion coefficient than that of the photoconductor frame 4 is used for the scanning exposure apparatus frame 6 like the combinations 3, 6, and 2.

In Table 2, good results were obtained with different material combinations in the case of steel and aluminum of combination 4, steel and reinforced resin of combination 7, and aluminum and reinforced resin of combination 8. In these, the thermal expansion coefficient α of the scanning exposure device frames 6 connecting the respective scanning exposure devices is almost half of the thermal expansion coefficient β of the photoconductor frames 4 connecting the respective photoconductors. This Table 1 and shown in FIG. 4, the temperature distribution pattern selected from the actual measurement results, t ₁ the larger the temperature rise during the distribution pattern of color shift (e) ~ (h) and t ₂
Changes approximately around t ₁ = 2t ₂ , the expression (5)
This is because in order to reduce the magnitude (αt ₁ −βt ₂ ) D of the color misregistration shown by the above, it is preferable that α = (１ ／) β.

Next, a second embodiment of the present invention will be described. Regarding the dimensional change due to the thermal expansion due to the temperature change in the apparatus, which is one of the constant color shifts in the sub-scanning direction, in order to keep the color shift to an allowable level, as in the first embodiment described above, the frame member is required. The color shift due to the temperature change in the apparatus can be reduced by 0.1 mm to 0.1
Although it can be made 5 mm or less, it is desirable that color misregistration can be similarly suppressed preferably without restriction on material selection.
Therefore, here, the distance D between the transfer portions on the photosensitive member from the first color to the final color is less than 150 mm, preferably 100 mm.
mm, the color shift due to the influence of temperature is reduced to 0.1.
mm to 0.15 mm or less. 12 and 13
Table 2 shows an example of a conventional color electrophotographic apparatus in which the scanning exposure apparatus and the photosensitive member are connected to a common frame as shown in FIG.
Corresponds to combinations 1, 5, and 9, but even in such a case, as can be read from Table 2, the reference dimension D is 1
If it is less than 50 mm, the color shift can be sufficiently suppressed to an allowable level. Further, in order to suppress the effect of temperature change on color misregistration in almost all combinations including the resin-based material as the material of the frame and the side plate, it is necessary to select a smaller reference dimension D. From the results shown in Table 1, D is 100mm
It is desirable to be less than.

FIGS. 6 and 7 show a plan view and a side view of the second embodiment, that is, a color electrophotographic apparatus in which the transfer medium traveling distance D between the transfer portions of the respective photosensitive members is small. To assemble such a small color electrophotographic device,
For example, when D is 90 mm and FIGS. 6 and 7 are examples of four-color superposition, in the case of three-color superposition, that is, d is 45 m
In the case of m, the electrophotographic process unit can be configured by setting the diameter of the photosensitive drum 1 to 22 mm and the diameter of the developing roll 12 to 12 mm. At this time, it can be seen from Table 2 that the scanning exposure apparatus frame 6 and the photoreceptor frame 4 can be made of any material of steel, aluminum, and glass fiber reinforced resin. For example, if D is 9
In the case of 0 mm and four-color superposition as shown in FIGS. 6 and 7, that is, when d is 30 mm, for example, the electrophotographic process unit is configured with a photosensitive drum diameter of 15 mm and a developing roll diameter of 10 mm. Also, the scanning exposure apparatus frame 6 and the photoreceptor frame 4 can be made of any material.

Next, a third embodiment of the present invention will be described. In the above-described second embodiment, the color misregistration is kept below the allowable level by reducing the reference size that is subjected to the dimensional change due to the temperature change, but a color misregistration of a certain size still remains. In order to further reduce this, the first
In combination with the embodiment, the scanning exposure apparatus and the photoconductor may be integrally connected with each other by a frame member having an appropriate coefficient of thermal expansion. Conventional photoconductor distance D is about 3
In a color electrophotographic apparatus having a size of 50 mm to 600 mm, if the scanning exposure apparatus and the photoconductor are connected as an integral unit, each unit becomes too large, and it is not easy to replace the entire heavy unit. At the time of component replacement, it was necessary to replace individual scanning exposure devices and photoconductors. However, as in the second embodiment shown in FIGS. 6 and 7, the scanning exposure is performed in a color electrophotographic apparatus in which the distance D between the photoconductors from the first color to the final color is less than 150 mm, preferably in a color electrophotographic apparatus having a distance of less than 100 mm. The unitary connection between the apparatus and the photoreceptor makes it easy to attach and detach the unit when exchanging the scanning exposure device or the photoreceptor, and furthermore, between the scanning exposure device and the photoreceptor. There is an advantage that the parallelism and the positional relationship are not broken.

Next, a fourth embodiment of the present invention will be described. In order to reduce the color misregistration as described above, the respective photoconductors and the respective scanning exposure apparatuses are integrally connected by frame members having an appropriate coefficient of thermal expansion, respectively.
A photoreceptor unit and a scanning exposure device unit are formed. In order to further exert the effects described above, both of these units are, for example, shown in FIGS.
9 or 10 to 11 may be combined. In FIGS. 8 to 9 or FIGS. 10 to 11, the alignment direction of the photoconductor and the scanning exposure device is adjusted by the positioning pin 35 or the positioning pin 37 between the frame member 4 of the photoconductor unit and the frame member 6 of the scanning exposure device unit. Are connected and fixed at two locations near the center of The fastening pin 35 or the fastening pin 37 may be fixed so that the photoconductor unit and the scanning exposure apparatus unit do not shift in the direction in which the photoconductor and the scanning exposure apparatus are aligned. Assisted. The main purpose of the fastening screw 36 or the fastening screw 38 is to fix the photoconductor unit and the scanning exposure apparatus unit in the other direction, and the fixing screw 36 or the fixing screw 38 is not easily fixed in the direction in which the photoconductor and the scanning exposure apparatus are arranged. It is desirable to have a mechanism. In this way, the reference dimension can be substantially D / 2 instead of D, but the magnitude of the resulting color shift will not be halved. This is because, as described above, the color misregistration has two directions of advance and delay, and the magnitude of the color misregistration occurring on both sides from the center is 、, but each occurs in a different direction. When the two are combined, the size becomes the same as the color shift with respect to the reference dimension D. The reason for fixing near the center is to reduce the amount of thermal expansion by half, suppress warpage and distortion of the frame caused by the bimetal effect, prevent three-dimensional irregular deformation, and suppress extra color shift That's why. By doing so, the color shift according to the calculated value of the color shift shown in Table 2 is realized. In each of the embodiments of the present invention described above, an example in which the electrophotographic process unit is provided for four colors has been described. However, the present invention is not limited to four colors, and an image is formed using two or more colors. Can be applied in case. In each of the above-described embodiments of the present invention, an example in which an image recording medium such as plain paper, high-quality paper, or an OHP sheet is conveyed while being supported or attracted to a transfer belt has been described. The present invention is not limited to this example, and the present invention can also be applied to a method of transferring from a photoconductor to an intermediate transfer medium and transferring from the intermediate transfer medium to an image recording medium. Further, in each of the embodiments of the present invention described above, an example in which the endless belt member is used as the recording medium conveying device is shown, but the present invention is not limited to this, and has other forms such as a sheet member, a drum member, and a gripper member. The present invention can be applied to such cases. Further, in each of the above-described embodiments of the present invention, an example in which a plurality of photoconductors are arranged on a straight line has been described. However, the present invention relates to a case where a plurality of photoconductors are arranged on an arc or another curve. Can also be adopted. In this case, a value measured along each curve is used as the recording medium travel distance D.

A one-cycle type scanning exposure apparatus for a color electrophotographic apparatus is disclosed in, for example, Japanese Patent Application Laid-Open No. 62-2691.
No. 68, there is a system in which some optical systems such as a polygon mirror are commonly used for each color. In such a scanning exposure apparatus, among the scanning exposure apparatuses, a scanning exposure beam for each color is used. The components that determine the distance between them and that correspond to each color only need to be supported by the common frame. That is, one scanning exposure apparatus including a common optical system may be supported by one frame, or an optical system unique to each color, excluding the common optical system, is not necessarily the entire scanning exposure apparatus. A supporting frame may be employed.

[0036]

As described above, according to the first color electrophotographic apparatus of the present invention, a plurality of photoconductors are rotatably supported, and a first support common to the plurality of photoconductors is provided. ,
Among the members constituting the exposing means, at least a plurality of components corresponding to the plurality of photoconductors are supported, and a thermal expansion smaller than a thermal expansion coefficient of a first support common to the plurality of components. Since the second support having the ratio is provided, the difference in the dimensional change due to the temperature change between the two supports is reduced, and the transfer color shift of each color can be reduced. As a result, it is possible to provide an inexpensive and high-speed color electrophotographic apparatus, which eliminates the need for a control device for detecting and correcting color misregistration while utilizing the characteristics of a one-cycle type color electrophotographic apparatus having a high recording speed. it can. Further, since the photoconductors of each color are connected by a common support, it is easy to perform color matching adjustment after maintenance and inspection or replacement of parts. In addition, the scanning exposure apparatus having a relatively long life can be left in the main body, and only the units around the photoreceptor that are frequently damaged or worn can be economically replaced.

Further, according to the second color electrophotographic apparatus of the present invention, since the interval between the photoconductors is kept smaller than the predetermined interval, the color shift can be reduced to an allowable level or less. Further, a control device for detecting and correcting color misregistration is not required, and an inexpensive and small-sized color electrophotographic apparatus can be provided.

[Brief description of the drawings]

FIG. 1 is a plan view of an embodiment of the present invention.

FIG. 2 is a side view of an embodiment of the present invention.

FIG. 3 is a schematic diagram illustrating how color misregistration occurs and the size according to the embodiment of the present invention.

FIG. 4 is a graph showing the magnitude of occurrence of color misregistration in the embodiment of the present invention.

FIG. 5 is a diagram illustrating the magnitude of color misregistration with respect to temperature distribution, which results in different combinations of thermal expansion coefficients.

FIG. 6 is a plan view of the embodiment of the present invention.

FIG. 7 is a side view of an embodiment of the present invention.

FIG. 8 is a plan view of the embodiment of the present invention.

FIG. 9 is a side view of an embodiment of the present invention.

FIG. 10 is a plan view of the embodiment of the present invention.

FIG. 11 is a side view of an embodiment of the present invention.

FIG. 12 is a plan view of a conventional example.

FIG. 13 is a side view of a conventional example.

FIG. 14 is a side view of another conventional example.

FIG. 15 is a schematic diagram showing how color misregistration occurs and its size in a conventional example.

FIG. 16 is a graph showing the magnitude of color shift due to each material.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photoconductor 2 transfer belt 3 transport roll 4 photoconductor frame 5 image recording medium 10 paper feed roll 11 scanning exposure device 12 developing device 13 transfer device 14 fixing device 20 recording medium transport device 25 scanning exposure image 26 developed images 41, 42, 43, 44 Transfer image

Claims (11)

[Claims] 1. A plurality of photosensitive members having a cylindrical outer shape on which an electrostatic latent image is formed by receiving an exposure while rotating, and exposure light modulated on each of the plurality of photosensitive members by respective image information. Forming an electrostatic latent image by scanning a plurality of photoconductors, each of which corresponds to each of the plurality of photoconductors, and an exposure unit having a plurality of components. Each electrostatic latent image is developed with a toner of each color to obtain a toner image, and a color image is formed through a process of sequentially transferring the toner images to finally form a color image fixed on an image recording medium. In the photographic apparatus, a first support member rotatably supporting the plurality of photoconductors, a first support member common to the plurality of photoconductor members, and supporting at least the plurality of constituent parts of members constituting the exposure unit Do this Common color electrophotographic apparatus is characterized in that a second support having a first coefficient of thermal expansion smaller thermal expansion coefficient than in the support into a plurality of components. 2. The color electronic device according to claim 1, wherein said second support has a coefficient of thermal expansion that is approximately に of a coefficient of thermal expansion of said first support. Photo equipment. 3. The method according to claim 1, wherein the plurality of photoconductors are two of the plurality of photoconductors that are furthest apart in the order of transfer of toner images formed on each of the plurality of photoconductors. ,
It is supported by the first support so that a distance along a transfer path between transfer portions to which respective toner images formed on the two photoconductors are transferred is less than 150 mm. The color electrophotographic apparatus according to claim 1, wherein 4. The method according to claim 1, wherein the plurality of photoconductors are two of the two photoconductors that are furthest apart in the order of transfer of toner images formed on each of the plurality of photoconductors. ,
The two photoconductors are supported by the first support so that the distance along the transfer path between the transfer portions to which the toner images formed on the respective photoconductors are transferred is less than 100 mm. The color electrophotographic apparatus according to claim 1, wherein 5. The method according to claim 1, wherein the plurality of photoconductors are two photoconductors that are adjacent to each other in the order of transfer of the toner images formed on each of the plurality of photoconductors. The first support is supported by the first support so that a distance along a transfer path between transfer portions to which respective toner images formed on the two photoconductors are transferred is less than 33 mm. 5. The color electrophotographic apparatus according to claim 4, wherein: 6. A central portion of the first support in the arrangement direction of the plurality of photoconductors and a central portion of the second support in the arrangement direction of the plurality of components are fixedly connected to each other. The color electrophotographic apparatus according to claim 1, wherein 7. A plurality of photosensitive members having a cylindrical outer shape on which an electrostatic latent image is formed by receiving an exposure while rotating, and forming each electrostatic latent image on each of the plurality of photosensitive members. Each electrostatic latent image is developed with a toner of each color to obtain each toner image, and through a process of sequentially transferring each toner image,
Finally, in a color electrophotographic apparatus for forming a color image fixed on an image recording medium, the plurality of photoconductors, out of the plurality of photoconductors, each formed on each of the plurality of photoconductors In the transfer path between the two photoconductors farthest along the transfer order of the toner images, between the respective transfer portions where the toner images formed on the two photoconductors are transferred, respectively. 150mm along the distance
A color electrophotographic apparatus, wherein the color electrophotographic apparatus is provided so as to be less than. 8. An image forming apparatus comprising: a plurality of photosensitive members having a cylindrical outer shape on which an electrostatic latent image is formed by receiving an exposure while rotating; and forming each electrostatic latent image on each of the plurality of photosensitive members. Each electrostatic latent image is developed with a toner of each color to obtain each toner image, and through a process of sequentially transferring each toner image,
Finally, in a color electrophotographic apparatus for forming a color image fixed on an image recording medium, the plurality of photoconductors, out of the plurality of photoconductors, each formed on each of the plurality of photoconductors In the transfer path between the two photoconductors farthest along the transfer order of the toner images, between the respective transfer portions where the toner images formed on the two photoconductors are transferred, respectively. Along 100mm
A color electrophotographic apparatus, wherein the color electrophotographic apparatus is provided so as to be less than. 9. The method according to claim 9, wherein the plurality of photoconductors are two photoconductors farthest along the transfer order of toner images formed on each of the plurality of photoconductors. ,
The distance between the transfer portions to which the respective toner images formed on the two photoconductors are transferred is less than 33 mm along the transfer path. The color electrophotographic apparatus according to claim 8, wherein 10. The color electrophotographic apparatus according to claim 7, further comprising a first support which rotatably supports said plurality of photoconductors and is common to said plurality of photoconductors. 11. A plurality of constituent parts each forming a respective electrostatic latent image by scanning each of said plurality of photoconductors with exposure light modulated by respective image information, each of which corresponds to each of said plurality of photoconductors An exposure unit having: a second member common to the plurality of components that supports at least the plurality of components among members constituting the exposure device.
9. A support according to claim 7, wherein
The color electrophotographic apparatus according to the above.