JP2000338740A - Color printer - Google Patents

Abstract

(57) [Problem] To provide a color printer capable of minimizing the occurrence of a color superimposition defect affected by temperature in consideration of an ambient temperature in a housing of the color printer. A transfer roller pair and a motor for driving a photoreceptor belt formed endlessly, a toner image formed on the photoreceptor belt are transferred to an intermediate transfer means, and a plurality of color images are transferred on the intermediate transfer means. In a color printer in which a toner image is superimposed, and the superimposed toner image is further transferred onto a transfer paper to form a color image, an ambient temperature in a housing of the color printer is detected by a temperature sensor 25, and the detected temperature is stored in a RAM 22. The CPU 20 controls the conveyance speed of the photoreceptor belt, that is, the rotation speed of the motor for driving the photoreceptor belt, according to the temperature difference between the previous printing and the current printing so that printing deviation does not occur. .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color printer using a photosensitive belt and an intermediate transfer member.

[0002]

2. Description of the Related Art Various types of color printers are known, one of which forms an image for each color on a photoreceptor belt and transfers the image to an intermediate transfer body for each color. There is a type in which one color image is formed, and the color image formed on the intermediate transfer body is transferred to a transfer medium such as recording paper. Generally, in a color printer using an intermediate transfer member of this type, a toner image of four colors of black, cyan, magenta, and yellow formed on a photoconductor is often superimposed on the intermediate transfer member to form a full-color image. . As this type, for example, a color printer described in JP-A-7-43970 is known. This known technique is configured to determine the speed of the intermediate transfer member driven by the photosensitive belt by driving the intermediate transfer member with a photosensitive belt and controlling the photosensitive belt to a predetermined speed.

As another method, a method is known in which the conveyance speed of the intermediate transfer body of the previous job is used for each print job.

[0004]

In the prior art such as the former, the speed of the intermediate transfer member driven by the photosensitive belt is determined by controlling the speed of the photosensitive belt to a predetermined speed. However, the speed of the intermediate transfer member depends only on the speed of the photoreceptor belt, but no consideration was given to the speed fluctuation factor due to the slip between the intermediate transfer member and the photoreceptor belt and the difference in thermal expansion between the two. . Therefore, the speed of the intermediate transfer member does not follow the photosensitive belt one-to-one, and the speed is likely to change.

In the latter method, no problem occurs when the number of prints of one job is several, but when the number of prints of the previous job becomes several hundred, the ambient temperature in the color printer is reduced. Is high, and even if the rotational speed in the state where the temperature is high is stored and stored, if the printing this time is performed after a certain period of time, the ambient temperature in the color printer is lowered, There will be a difference between the temperatures. When this happens,
If the photoconductor belt was conveyed at the speed of the previous print job, the previous and current conveyance speeds of the intermediate transfer body would shift due to the difference in size due to thermal expansion, and color overlay defects would easily occur, and the image As a result, the quality deteriorated.

SUMMARY OF THE INVENTION The present invention has been made in view of such a situation of the prior art, and an object thereof is to minimize the occurrence of such a color overlay failure in consideration of the ambient temperature in a color printer. A color printer is provided.

[0007]

To achieve the above object, the present invention provides a driving means for driving an endlessly formed photosensitive belt, and an intermediate transfer of an image formed on the photosensitive belt. A color printer that forms a color image on transfer paper by superimposing images of a plurality of colors on an intermediate transfer device by transferring the image to a transfer device, and a temperature detector that detects an ambient temperature in a housing of the color printer; Control means for controlling the belt conveyance speed according to the temperature difference between the previous printing and the current printing so as not to cause a printing deviation is provided.

More specifically, speed detecting means for detecting the moving speed of the intermediate transfer means, storage means for storing the detected moving speed of the intermediate transfer means, and stored moving speed of the intermediate transfer means Calculating means for calculating the conveying speed of the photoreceptor belt from, the control means,
The moving speed of the photoreceptor belt at the time of previous printing is taken as the moving speed of the photoreceptor belt at the time of current printing, and the ambient temperature at the time of previous printing and the atmospheric temperature at the time of current printing are compared. If there is a temperature difference of more than a predetermined value,
The driving unit operates the intermediate transfer unit via the photoreceptor belt, and calculates the speed of the photoreceptor belt by the speed calculation unit from the moving speed of the intermediate transfer unit detected by the speed detection unit. The conveying speed is controlled based on the speed of the photoconductor belt thus performed.

The temperature detecting means is provided at a position near the downstream side of the nip between the intermediate transfer means and the photoreceptor belt at which an ambient temperature can be detected.

The speed detecting means may be provided with, for example, an encoder on a side face of the intermediate transferring means, and the rotational speed and the moving speed of the intermediate transferring means may be obtained by using the encoder.

In the following embodiments, the drive means is a motor and a drive roller, the intermediate transfer means is an intermediate transfer drum, the control means is a CPU, the speed detection means is an encoder, a decoder and a CPU, and the storage means is a RAM. In addition, the temperature detecting means corresponds to each of the temperature sensors.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic side view showing a mechanical configuration inside a color printer. Color printer 1
Is a photosensitive belt 110 composed of an endless belt
A pair of transport rollers including a drive roller 111 and a driven roller 112 for transporting the photosensitive belt 110 while applying tension thereto, and a photosensitive belt transport mechanism 2 including a motor 24 for driving the drive roller 111; The developing rollers 3a, 4a, 5a, and 6a are placed on developing rollers 3a, 4a, 5a, and 6a that rotate while charging the toner.
Developing unit 3 that contacts the photoreceptor belt 2a to develop
4, 5, 6, a laser light emitting device 7 for forming an electrostatic latent image on the photosensitive belt 2a, a transport roller 9 for transporting a print medium 8 such as paper, and a toner image on the photosensitive belt 110 , A transfer roller 11 for transferring the full-color toner image on the intermediate transfer drum 10 to the print medium 8, and a toner on the print medium 8. It comprises a fixing device 12 for applying heat and pressure to form an image into a permanent image. An encoder 10a for detecting a speed is provided on a side surface of the intermediate transfer drum 10, and the encoder 10a is read by a photodetector 27. Further, a temperature sensor 25 for detecting the ambient temperature in the housing 1a of the color printer 1 is provided near the downstream side of the nip between the intermediate transfer drum 10 and the photosensitive belt 110.
The reason why the temperature sensor 25 is provided at this position is that the temperature sensor 25 is located substantially at the center in the housing and also near the nip which is most important for image formation.

FIG. 2 is a block diagram showing an electrical configuration related to speed control of the color printer 1 according to the present embodiment. In the figure, a temperature sensor 25 and a decoder 2
6 is a CP which controls each part and the whole of the color printer.
U20, and further connected to ROM21 and RAM22. The ROM 21 stores static data, including programs used by the CPU 20,
The RAM 22 functions as a work area for the CPU 20, and stores data used by the CPU 20.
The CPU 20 also has a motor 24 for rotating the drive rollers 111 of the transport rollers 111 and 112 via a gate array 23, black (K), C (cyan), M (magenta), and Y (yellow). Each developing unit 3,
A drive device for moving the 4, 5, 6 forward and backward and transferring the toner of each color to a latent image is connected. A photodetector 27 that optically reads the encoder 10a is connected to the decoder 26, and a read signal is input to the decoder 26. The speed and rotation time detected by the following control are determined by the decoder 26 by the encoder 10.
The read pulse a is decoded, the decoded signal is taken into the CPU 20 and calculated by the CPU 20.

FIG. 3 is a schematic perspective view showing the relationship between the photosensitive belt 110, a pair of conveying rollers (a driving roller 111 and a driven roller 112), and tension rollers 113, 114 and 115.

FIGS. 4 and 5 are flowcharts showing a control procedure for controlling the speed of the photosensitive belt 110 in the embodiment. Hereinafter, the speed control of the photoconductor belt 110 will be described with reference to this flowchart.

First, when the power of the color printer 1 is turned on (step S1), a predetermined color, for example, black, of black (K), cyan (C), magenta (M), and yellow (Y) is developed. The photoconductor belt 110 is rotated at a preset speed while only the device 3 is in contact with the photoconductor belt 110. As the photoreceptor belt 110 rotates, the intermediate transfer drum 10 also rotates, and the rotation state of the encoder 10 is read by the photodetector 27 in a state where slippage has disappeared and normal rotation has been assumed. The read information is input to the decoder 26, and the information decoded from the decoder 26 is input to the CPU 20. CPU2
At 0, the information from the decoder 26 is converted into a rotation time,
It is stored in a rotation time information storage area provided in the RAM 22. The CPU 20 also calculates the speed of the photosensitive belt 110 from the rotation time of the intermediate transfer drum 10 and the rotation time when it is considered that the stored target rotation time has been reached.
It is stored in the speed information storage area provided in M22 (step S2).

Next, the same operation as described above is performed for the other three developing units, namely, the cyan developing unit 4, the magenta developing unit 5, and the yellow developing unit 6. Each of the three developing units is set for each color in the same manner as in the case of black developing. The speed of the photoreceptor belt 110 is stored in a predetermined area of the RAM 22 (steps S3, S4, S4).
5). Note that what is performed for each color is the developing rollers 3a, 3
This is because the contact positions and contact pressures of b, 3c, and 3d with the photoreceptor belt 110 are different from each other. On the other hand, the temperature information of the ambient temperature in the color printer is detected by the temperature sensor 25 and stored in the temperature information storage area provided in the RAM 22 (step S6). A series of operations from step S2 to step S6 is collectively called an initial operation (step S7).

According to such a procedure, the speed of the photosensitive belt 110 in each of the developing devices 3 to 6 at the time of startup can be obtained as data. From this data, the relationship between the transport speed of the photoconductor belt 110 at the time of rising and the drive roller 111 of the belt transport mechanism is obtained. By setting the speed of the motor 24 that drives the drive roller 111 based on this speed relationship, the speed of the intermediate transfer drum 10 can be set to a desired speed.

Next, a control method at the time of printing will be described.

When the power is turned on, the above-described initial work (step S7) is performed. The first print job counted from power-on is called job 1, the second print job is called job 2, and the N-th print job is called job N. In printing the first sheet of the job 1, information on the rotation time obtained in the initial work (step S7) is obtained (step S8), and the speed of the motor 14 for driving the drive roller 111 is determined based on the obtained rotation time information. Then, the intermediate transfer drum 10 is set to a desired rotation time (step S9). Also, at the time of printing the first sheet, the speed of the photosensitive belt 110 is calculated from the actual rotation time of the intermediate transfer drum 10 rotated based on the rotation time of the intermediate transfer drum 10 set in step S9, and the speed of the RAM 22 is calculated. The actual rotation time of the intermediate transfer drum 10 is stored in the information time storage area of the RAM 22 (step S1).
0). The temperature information in the color printer 1 is detected by the temperature sensor 25 and stored in the temperature information storage area of the RAM 22 (step S11).

In the printing of the second sheet, the step S1 of the first sheet
0 based on the rotation time information obtained in
Of the intermediate transfer drum 10 is set to a desired rotation time (step S1).
2). At the time of printing the second sheet, the speed of the photosensitive belt 110 is calculated from the actual rotation time of the intermediate transfer drum 10 rotated based on the rotation time of the intermediate transfer drum 10 set in step S12, and the speed of the RAM 22 is calculated. Store in the information storage area. Further, the actual rotation time of the intermediate transfer drum 10 is stored in the rotation time storage area of the RAM 22 (step S13).

In the printing of the third sheet, the step S1 of the second sheet
3. The driving roller 11 based on the rotation time information obtained in
Of the intermediate transfer drum 10 is set to a desired rotation time (step S1).
4). At the time of printing the third sheet, the speed of the photosensitive belt 110 is calculated from the actual rotation time of the intermediate transfer drum 10 rotated based on the rotation time of the intermediate transfer drum 10 set in step S14, and the speed of the RAM 22 is calculated. In addition to the storage in the information storage area, the actual rotation time of the intermediate transfer drum 10 is stored in the rotation time storage area of the RAM 22 (step S15).

When the operation of job 1 is completed, the operation shifts to the operation of job 2. In the printing of the first sheet of this job 2, first, it is acquired by the temperature sensor 25 (step S1).
6) The temperature inside the color printer 1 is compared with the temperature stored at the time of printing the first sheet of the job 1 (step S6) (step S17). If the temperature difference is within a certain value, the speed of the motor 24 for driving the drive roller 111 is set based on the information on the rotation time obtained in step S10 of the first sheet of job 1, and the intermediate transfer drum 10 Is set to a desired rotation time (step S18). Job 2
When printing the first sheet, the speed of the photosensitive belt 110 is calculated from the actual rotation time of the intermediate transfer drum 10 rotated based on the rotation time of the intermediate transfer drum 10 set in step S18, and the speed information in the RAM 22 is calculated. The rotation time is stored in the storage area, and the actual rotation time of the intermediate transfer drum 10 is stored in the rotation time information storage area (step S19).

In the printing of the second sheet of the job 2, the speed of the motor 24 for driving the drive roller 111 is set based on the information on the rotation time obtained in step S13 of the second sheet of the job 1, and the intermediate transfer drum 10 Is set to a desired rotation time (step S20). At the time of printing the second sheet, the speed of the photosensitive belt 110 is calculated from the actual rotation time of the intermediate transfer drum 10 rotated based on the rotation time of the intermediate transfer drum 10 set in step S20, and the speed of the RAM 22 is calculated. The information is stored in the information storage area and the actual intermediate transfer drum 10
Is stored in the rotation time information storage area of the RAM 22 (step S21).

In the printing of the third sheet of the job 2, the speed of the motor 24 for driving the driving roller 111 is set based on the information on the rotation time obtained in step S15 of the third sheet of the job 1, and the intermediate transfer drum 10 Is set to a desired rotation time (step S22). At the time of printing the third sheet, the speed of the photosensitive belt 110 is calculated from the actual rotation time of the intermediate transfer drum 10 rotated based on the rotation time of the intermediate transfer drum 10 set in step S22, and the speed of the RAM 22 is calculated. The information is stored in the information storage area and the actual intermediate transfer drum 10
Is stored in the rotation time information storage area of the RAM 22 (step S23).

In the printing of the fourth sheet of the job 2, since there is no information of the fourth sheet of the job 1, the driving roller 1 based on the information of the rotation time obtained in step S21 of the third sheet of the job 2
The speed of the motor 24 that drives the motor 11 is set, and the intermediate transfer drum 10 is set to a desired rotation time (step S2).
4). At the time of printing the fourth sheet, the speed of the photosensitive belt 110 is calculated from the actual rotation time of the intermediate transfer drum 10 rotated based on the rotation time of the intermediate transfer drum 10 set in step S24, and the speed of the RAM 22 is calculated. In the information storage area, the actual rotation time of the intermediate transfer drum 10 is
It is stored in the rotation time information storage area of the AM 22 (Step S25). Hereinafter, the jobs up to the job N-2 are executed in the same manner.

FIG. 5 is a flowchart showing processing after job N-1. Basically, this job N-1 is the same as the procedure of the above-mentioned job 1, and steps S9, S10,
11, 12, 13, 14, and 15 are each performed in step S3.
1, 32, 33, 34, 35, 36, and 37, and a description thereof will be omitted.

When the processing of the job N-1 is completed and the processing of the job N is to be performed, the ambient temperature in the color printer 1 in the job N is detected and stored in the temperature sensor 25 (step S38). The temperature is compared with the ambient temperature acquired in step S33 of job (N-1) (step S33).
39) If the temperature difference is within a certain value, the first sheet of the job (N-1) is printed in step S32 for the first sheet of the job N
The speed of the motor 24 for driving the drive roller 111 is set on the basis of the rotation time information obtained in step (1), and the intermediate transfer drum 10 is set to a desired rotation time (step S).
40). Then, based on the actual rotation time of the intermediate transfer drum 10 rotated based on the rotation time of the intermediate transfer drum 10 set at the time of printing the first sheet of the job N, the photosensitive belt 1
10 is calculated and stored in the speed information storage area of the RAM 22, and the actual rotation time of the intermediate transfer drum 10 is stored in the RAM.
22 (step S4).
1). On the other hand, the temperature information in the color printer acquired from the temperature sensor 25 is stored in the temperature information storage area of the RAM 22 (step S38), and as described above, step S3
9 is also used in the determination processing.

In the printing of the second sheet of the job N, the job (N
-1) The motor 24 that drives the drive roller 111 based on the rotation time information obtained in step S35 of the second sheet
Is set, and the intermediate transfer drum 10 is set to a desired rotation time (step S43). The job (N-
The speed of the photosensitive belt 110 is calculated from the actual rotation time of the intermediate transfer drum 10 rotated based on the rotation time of the intermediate transfer drum 10 set at the time of printing the second sheet of 1), and the speed information of the RAM 22 is stored. The rotation time of the intermediate transfer drum 10 is stored in the rotation time information storage area of the RAM 22 (step S43).

In the printing of the third sheet of the job N, the job (N
-1) The motor 24 that drives the drive roller 111 based on the rotation time information obtained in step S37 of the third sheet
Is set, and the intermediate transfer drum 10 is set to a desired rotation time (step S44). The job (N-
1) The actual intermediate transfer drum 1 rotated based on the rotation time of the intermediate transfer drum 10 set at the time of printing the third sheet
The speed of the photoreceptor belt 110 is calculated from the rotation time of 0 and stored in the speed information storage area of the RAM 22, and the actual rotation time of the intermediate transfer drum 10 is stored in the rotation time information storage area of the RAM 22 (step S45).

In the printing of the fourth sheet of the job N, the job (N
Since there is no information of the fourth sheet of -1), the speed of the motor 24 for driving the drive roller 111 is set based on the information of the rotation time obtained in step S45 of the third sheet of the job N,
The intermediate transfer drum 10 is set to a desired rotation time (step S46). Further, the speed of the photosensitive belt 110 is calculated from the actual rotation time of the intermediate transfer drum 10 rotated based on the rotation time of the intermediate transfer drum 10 set at the time of printing the fourth sheet, and the calculated speed is stored in the speed information storage area of the RAM 22. The stored rotation time of the intermediate transfer drum 10 is stored in the RAM 22.
(Step S4)
7).

On the other hand, if it is determined in step S39 that the temperature difference between the atmosphere temperature stored in job (N-1) (step S33) and the atmosphere temperature stored in job N (step S38) does not fall within a predetermined value, Step S7 again
(Step S4)
8) The rotation time information is obtained and stored in the RAM 22 (step S49). Then, the speed of the motor 24 that drives the drive roller 111 is set based on the rotation time information stored in step S49, and the intermediate transfer drum 10 is set to a desired rotation time (step S50). Then, at the time of printing the first sheet of the job N, the photosensitive belt 110 is calculated based on the actual rotation time of the intermediate transfer drum 10 rotated based on the rotation time of the intermediate transfer drum 10 set in step S50.
And stores the actual rotation time of the intermediate transfer drum 10 in the RAM 22.
(Step S5)
1).

In the printing of the second sheet of the job N, the speed of the motor 24 for driving the drive roller 111 is set based on the rotation time information (step S51) obtained on the first sheet of the job N, and the intermediate transfer is performed. The drum 10 is set to a desired rotation time (step S52). When printing the second sheet of job N, the intermediate transfer drum 10 set in step S52 is used.
The speed of the photoreceptor belt 110 is calculated from the actual rotation time of the intermediate transfer drum 10 rotated based on the rotation time of the intermediate transfer drum 10 and stored in the speed information storage area of the RAM 22, and the actual rotation time of the intermediate transfer drum 10 is stored in the RAM 22. (Step S53).

Similarly, in printing the third and fourth sheets of the job N, the rotation time of the intermediate transfer drum 10 is set (steps S54 and S56), and the rotation time information is stored (steps S55 and S57).

In the flowchart of FIG. 4, the case where the determination in step S17 is NO is not particularly described. However, if the temperature difference is larger than the predetermined value in step S17, the same processing from step S48 is performed. Then, the process is repeated from the initial process.

By doing so, the job (N-
If there is no predetermined temperature difference between the ambient temperature in the housing 1a of the color printer 1 between the job 1) and the job N, the job (N-1)
By using the rotation time information, the printing time can be reduced. On the other hand, if there is a temperature difference, the initial process (step S7) is repeated from the initial procedure, and the transport speed of the photosensitive belt 110 for each color and the housing 1
The temperature information in a is stored, and the printing process is executed based on the rotation time information stored from the beginning of the next job. By performing such processing, the intermediate transfer drum 1 due to the temperature difference
0 or color misregistration due to temperature expansion of the photoreceptor belt 110 and poor color overlay can be prevented, and high quality printing can be performed.

In this flowchart, in the initial state, information for each color of black, cyan, magenta, and yellow is acquired, and printing processing is performed for the first and second sheets of job 1, for example. In the case of full color, the photosensitive belt 110 and the intermediate transfer drum 10 make four rotations when forming one image. As described above, the toner is overlapped during the four rotations, and the outer diameter of the printing surface of the intermediate transfer drum 10 is also microscopically different. Therefore, in the initial processing, an initial value is held for each color, and control is performed based on the initial value.

[0039]

As described above, according to the present invention, the temperature detecting means for detecting the ambient temperature in the housing of the color printer, and the conveying speed of the photosensitive belt are set to the temperature at the time of the previous printing and the current printing. A control means is provided to control the printing error according to the difference, so that even if the temperature of the color printer or the installation location rises during printing, color overlay failure due to temperature expansion is minimized and high quality Can be printed.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a mechanical configuration of a color printer according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating an electrical configuration of a portion related to speed control of the color printer according to the embodiment.

FIG. 3 is a schematic diagram illustrating a photosensitive belt transport mechanism of the color printer according to the embodiment.

FIG. 4 is a flowchart illustrating an example of a control procedure at the time of power-on for speed control of the photosensitive belt of the color printer according to the embodiment.

FIG. 5 is a flowchart illustrating an example of a control procedure after power-on of the speed control of the photosensitive belt of the color printer according to the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Color printer 1a Housing 2 Photoreceptor belt conveyance mechanism 3, 4, 5, 6 Developing machine 3a, 4a, 5a, 6a Developing roller 10 Intermediate transfer drum 10a Encoder 11 Transfer roller 12 Fixing machine 20 CPU 21 ROM 22 RAM 24 Motor Reference Signs List 25 temperature sensor 26 decoder 27 photodetector 110 photoreceptor belt 111 drive roller 112 driven roller

Continued on the front page (72) Inventor Kazuo Kikuchi 1-1-1, Higashitaga-cho, Hitachi City, Ibaraki Prefecture Inside the Taga Headquarters, Electrification Equipment Division, Hitachi, Ltd. No. 1-1 Hitachi Electric Co., Ltd.Electrical Equipment Division Taga Headquarters (72) Inventor Tetsushi Takekoshi 1-1-1 Higashitagacho, Hitachi City, Ibaraki Pref. Hitachi Electric Co., Ltd.Electric Equipment Division Taga Headquarters (72) Inventor Nobuaki Fukasawa 1-1-1, Higashitaga-cho, Hitachi City, Ibaraki Prefecture Inside the Taga Headquarters, Electrification Equipment Division, Hitachi, Ltd. In-house (72) Inventor Masaru Nakano 502 Kandate-cho, Tsuchiura-shi, Ibaraki Pref. BB23 BB42 BB53 BB71

Claims (3)

[Claims] 1. A driving unit for driving a photosensitive belt formed endlessly, a toner image formed on the photosensitive belt is transferred to an intermediate transfer unit, and a plurality of color toner images are transferred on the intermediate transfer unit. A color detector for superposing the toner image on the transfer paper to form a color image by superimposing the toner image on the transfer paper. And control means for controlling printing so as not to cause printing deviation in accordance with the temperature difference between the previous printing and the current printing. 2. A speed detecting means for detecting a moving speed of the intermediate transfer means, a storage means for storing the detected moving speed of the intermediate transfer means, and a photosensitive device based on the stored moving speed of the intermediate transfer means. Calculating means for calculating a conveyance speed of the body belt, wherein the control means sets a movement speed of the photosensitive belt at the time of previous printing as a movement speed of the photosensitive belt at the time of current printing, and The ambient temperature at the time of the previous printing is compared with the ambient temperature at the time of the current printing. Is operated, the speed of the photosensitive belt is calculated by the speed calculating means from the moving speed of the intermediate transfer means detected by the speed detecting means, and based on the calculated speed of the photosensitive belt. Color printer of claim 1, wherein the controller controls the conveying speed. 3. A color printer according to claim 1, wherein said temperature detecting means is provided at a position capable of detecting an ambient temperature near a downstream side of a nip between said intermediate transfer means and said photosensitive belt. .