JPH1195516A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent deformation of a transfer belt of a tandem type image forming device by using a transfer-belt retraction mechanism which retracts the transfer belt at the time of monochromatic-image formation, thereby separating a photoreceptor drum and the transfer belt which are not involved in the image formation. SOLUTION: The transfer belt is retracted when a monochromatic-print mode is set and a power-source switch is turned off. Also, even when a color- print mode is set, the transfer belt is retracted (step S606) during warm-up (Y in step S603), during standby (Y in step S604), and during preheat (Y in step S605).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a color copying machine or a color printer capable of switching between color image formation and monochromatic image formation.

[0002]

2. Description of the Related Art In recent years, in the field of full-color image forming apparatuses, a plurality of image forming units having a photosensitive drum as a core are arranged along a transfer belt, and a toner image of each color formed by each image forming unit is formed. The so-called tandem type, which transfers images while being superimposed on a transfer material such as transfer paper, is becoming mainstream.

[0003] Such a tandem type image forming apparatus includes:
Since a full-color image can be formed in a single pass, there is an advantage that color printing can be speeded up.

[0004]

However, in this tandem-type image forming apparatus, in order to improve the transfer accuracy at the transfer positions of a plurality of photosensitive drums, usually, a fixed distance is set between the photosensitive drum and the transfer belt. The nip width is formed, so the photosensitive drum is pressed against the surface of the transfer belt with a predetermined pressing force.However, if the photosensitive drum is pressed with a plurality of photosensitive drums, an excessive load is applied to the transfer belt. If the transfer belt tension is excessive and the transfer belt partially extends, or if the photosensitive drum is maintained at a predetermined temperature or higher to prevent dew condensation, etc., only that portion is exposed to heat. The transfer belt becomes deformed and has a shape that is partially wavy. In such a state, when a transfer belt is driven to form a color image, the transfer position of each color is slightly changed, and a color shift occurs in a reproduced image.

On the other hand, in a tandem-type image forming apparatus, when forming a full-color image, an image is formed by bringing a transfer belt, which conveys transfer paper, into contact with all photosensitive drums (hereinafter, this mode is referred to as "color mode"). When a black-only image is formed, the transfer belt is tilted downward to retract the transfer belt from the photosensitive drum that is not involved in image formation, and image formation is performed using only the black image forming unit. (Hereinafter, this mode is referred to as "monochromatic print mode.") By stopping the rotation of the photosensitive drum released from the state of contact with the transfer belt, the photosensitive drum is disposed on the photosensitive surface of the photosensitive drum and the periphery thereof. A cleaner member, a toner in a developing unit, and the like that prevent unnecessary wear and consumption are proposed (for example, Japanese Patent Laid-Open No. 6-258914). Publication).

However, even in such an image forming apparatus capable of retreating the transfer belt, if the image forming apparatus is left in the color print mode for a long time, the above-described problem of the deformation of the transfer belt may occur. Still occurs. The present invention has been made in view of the above-described problems, and has a function of preventing wasteful consumption of an image carrier that is not involved in image formation at the time of monochromatic image formation. It is an object of the present invention to provide an image forming apparatus that forms a high-quality reproduced image without causing any occurrence.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a method for forming an image of each color on each of a plurality of image carriers and transferring the formed image to a transfer belt or a transfer material conveyed on the transfer belt. An image forming apparatus capable of forming a multi-color image by transferring to, when forming a color image, contact the transfer belt and all the image carrier,
When forming a monochromatic image, contact and separation means for relatively separating the other second image carrier and the transfer belt while keeping the first image carrier involved in the monochromatic image in contact therewith; A control unit that controls the second image carrier and the transfer belt to be relatively separated by the contact / separation unit when the apparatus is in a standby state.

In the present invention, the standby state is a state in which a color image forming operation is not being performed. The present invention further includes a fixing unit that thermally fixes the image transferred to the transfer material, wherein the standby state is a state in which a temperature of a fixing unit of the fixing unit is lower than a predetermined fixing temperature. .

Further, the present invention is characterized in that the standby state is a state from the occurrence of a trouble in the apparatus to the elimination of the trouble. Further, the present invention is characterized in that a door that can be opened and closed is provided in a housing of the device, and the standby state is a state where the door is opened.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an image forming apparatus according to the present invention will be described below with reference to a tandem-type color digital copying machine (hereinafter simply referred to as "copying machine"). (1) Overall Configuration of Copying Machine FIG. 1 is a diagram showing the overall configuration of the copying machine 1. As shown in FIG. 1, the copying machine 1 includes an image reader section 10 for reading a document image, and a printer section 20 for printing the read image on a recording sheet and reproducing it.

The image reader section 10 is a known one which reads an image of an original placed on an original glass plate (not shown) by moving a scanner, and is obtained by irradiation of an exposure lamp provided in the scanner. The original document image is formed by a condenser lens, and further separated by a spectroscope into light of three different wavelengths of red (R), green (G), and blue (B). Green CCD image sensor, Blue CC
The light enters the D image sensor. An output signal from each CCD image sensor (hereinafter, referred to as “CCD sensor”) is subjected to AD conversion, thereby obtaining R, G, and B image data of the document.

The image data for each color component obtained by the image reader section 10 undergoes various data processing in the control section 30 and further undergoes cyan (C), magenta (M), yellow (Y), and black (K ) Is converted into image data of each reproduction color (hereinafter, each reproduction color of cyan, magenta, yellow, and black is represented by C, M, Y, and K, and the number of a component related to each reproduction color is represented by C , M, Y, K as subscripts).

The image data is stored in an image memory 33 (see FIG. 5) in the control unit 30 for each reproduced color, and after receiving necessary image correction for positional deviation correction, synchronizing with supply of a recording sheet. Then, it is read out for each scanning line and becomes a drive signal of the laser diode. The printer unit 20 forms an image by a well-known electrophotographic method, and includes a recording sheet transport unit 40 on which a transfer belt 41 is stretched.
And M arranged at predetermined intervals from the upstream side in the recording sheet conveyance direction (hereinafter simply referred to as “upstream side”) to the downstream side in the conveyance direction (hereinafter simply referred to as “downstream side”) in opposition to the transfer belt 41. , C, Y, K image processing unit 50M
To 50K, an exposure scanning unit 60M to 60K provided for each image processing unit, a paper feeding unit 70 for feeding a recording sheet upstream of the recording sheet conveying unit 40, and a fixing unit arranged downstream. 80.

The exposure scanning units 60M to 60K receive a driving signal output from the control unit 30 and emit laser light, and deflect the laser light to scan the photosensitive drums 51M to 51K. A polygon mirror for exposing and scanning in the direction is provided. The image processing units 50M to 50K include photosensitive drums 51M to 51K,
Charging chargers 52M to 52K disposed therearound;
Developing devices 53M-53K and transfer chargers 54M-5
It is made of 4K or the like, is unitized for easy maintenance, and is housed in one casing.

The paper supply section 70 is provided with paper supply cassettes 71 to 74 for accommodating recording sheets of different sizes, pickup rollers 75 to 78 for feeding out the recording sheets from the paper supply cassettes, and timing for feeding the recording sheets to the transfer belt 41. It consists of a registration roller 79 and the like. Before the photosensitive drums 51M to 51K receive the exposure, the remaining toner on the surface is removed by a cleaner (not shown), and the photosensitive drums are irradiated with an eraser lamp (not shown) to remove the charge. When exposed to the laser light in such a uniformly charged state, an electrostatic latent image is formed on the surfaces of the photosensitive drums 51M to 51K.

Each electrostatic latent image is developed by a developing unit 53 of each color.
M to 53K, thereby developing the photosensitive drum 5
M, C, Y, and K toner images are formed on the front surfaces of the recording sheets 1M to 51K, and the recording sheet transport unit is formed at each transfer position by the electrostatic action of the transfer chargers 54M to 54K disposed on the back side of the transfer belt 41. The image is sequentially transferred onto the recording sheet conveyed by 40.

At this time, the image forming operation for each color is executed with a timing shifted from the upstream side to the downstream side so that the toner image is transferred in a superimposed manner at the same position on the conveyed recording sheet. You. The recording sheet on which the toner images of each color have been multiplex-transferred is conveyed to the fixing unit 80 by the transfer belt 41. The fixing roller 801 of the fixing unit 80 includes an internal heater, and the control unit 30 controls energization of the internal heater while maintaining the surface temperature of the fixing roller 801 by the temperature detection sensor SE10 to maintain a predetermined fixing temperature. Here, the recording sheet is pressurized with high heat, and the toner particles on the surface are fused and fixed on the sheet surface.
It is discharged on 1.

At a position substantially below the driven roller 43, there is provided a cleaning blade 49 which comes into contact with the surface of the transfer belt 41 and removes toner of a registration mark transferred to the transfer belt 41 at the time of detecting a displacement amount described later. Have been. An operation panel 90 is provided at an easy-to-operate position on the front surface of the image reader unit 10, from which the operator performs key inputs such as an instruction to start copying, setting of the number of copies, and designation of a print mode. . The operation panel 90 is provided with a display unit composed of a liquid crystal display panel or the like, and displays a copy mode and various messages set by an operator.

A front door 21 which can be opened and closed is provided on a front portion of the printer section 20 of the apparatus housing 11.
The front door is opened forward so that when a paper jam (jam) occurs in the paper transport system, the jammed paper can be removed or maintenance such as toner replenishment can be performed. When the front door 21 is opened, it is detected by a door opening detection sensor SE3 including a limit switch and a slide switch, and a detection signal is sent to the control unit 30.

The other SE4 to SE9 are jam sensors including a reflection type photoelectric sensor and a limit switch, and the control unit 30 detects the front edge of the recording sheet passing through each of the jam sensors SE3 to SE9. When the trailing edge is not detected even after the lapse of the predetermined time, or when the leading edge of the recording sheet is detected by the downstream jam sensor after the lapse of the predetermined time after the upstream jam sensor detects the trailing edge of the recording sheet. If not, it is determined that a paper jam has occurred.

A main power switch 22 is provided substantially at the center of the right side of the apparatus housing 11.
FIG. 2 is an enlarged view showing a main part of the recording sheet transport unit 40. As shown in the figure, the recording sheet transport unit 40 includes a transfer belt 41 and a driving roller 4 on which the belt is stretched.
2, a driven roller 43, a tension roller 44, an auxiliary roller 45, and the like.

The drive roller 42 is rotatably held at the right end of a swing frame 46 that is held so as to swing up and down about a rotation shaft 431 of the driven roller 43. The drive roller 42 is rotationally driven by a stepping motor (not shown) provided on the swing frame 46. The rotational speed of the drive roller 42 depends on the transfer surface of the transfer belt 41 and the photosensitive drum 51M.
The control unit 30 controls the peripheral speed (system speed) to be the same as the peripheral speed (up to 51K).

The swing frame 46 can be moved up and down by a solenoid 47. When the color print mode is executed, the swing frame 46 is pushed up to the position indicated by the solid line in FIG. (The position of the swing frame 46 at this time is hereinafter referred to as a “non-retreat position”).
That. ). On the other hand, when executing the single-color print mode, the rod 471 of the solenoid 47 is retracted to swing the swing frame 46 downward. At this time, since the auxiliary roller 45 is supported by a body frame (not shown),
As shown by the dashed line in the figure, only the transfer surface of the transfer belt on the upstream side of the auxiliary roller 45 is inclined downward (the position of the swing frame 46 at this time is hereinafter referred to as a “retreat position”), and is used for black image formation. Photoreceptor drums 51M to 51 not involved
Y and the transfer surface of the transfer belt 41 can be separated. Accordingly, even when the photosensitive drums 51M to 51Y are stopped in the single-color print mode, friction does not occur between the photosensitive drums 51M to 51Y, and the photosensitive drums are not affected without adversely affecting image formation. It is possible to prevent unnecessary consumption of the surface and its peripheral members.

The transfer chargers 54Y, 54C, 5
4M is attached to the swing frame 46, and moves downward with the swing operation of the swing frame 46, so that the transfer chargers 54Y, 54C, and 54M prevent the transfer belt 41 from retracting downward. It will not be.
The bearing portion of the tension roller 44 is urged in the direction of the arrow by an urging device (not shown) using an elastic member such as a spring, so that the swing frame 46 is moved to the retreat position and the non-retreat position. , The tension of the transfer belt 41 is kept substantially constant.

SE1 and SE2 are position sensors for detecting that the swing frame 46 is in the non-retreat position and the retreat position, respectively, and are constituted by a reflection type photoelectric sensor, a limit switch, and the like. Above the downstream side of the transfer belt 41, a registration mark detection unit 39 for detecting a registration mark of each color (see FIG. 4) transferred near the edge of the transfer belt 41 is provided.

The registration mark detecting section 39 is provided with an LED
It comprises a reflection-type photoelectric sensor having a light-emitting element such as a light-receiving element and a light-receiving element such as a photodiode, an amplifier for amplifying a detection signal from the photoelectric sensor, an AD converter for converting the amplified detection signal into a digital signal, and the like. Light emitted from the light emitting element of the photoelectric sensor is irradiated onto the transfer belt 41 via the condenser lens, and the light receiving element receives the reflected light and converts it into an electric signal. The detection signal is amplified by an amplifier, converted into a multi-valued digital signal by an AD converter, and output to the CPU 31, whereby a registration mark of each color formed on the transfer belt 41 can be detected. .

The control unit 30 controls the photosensitive drums 51M to 51M of the respective color images based on the registration mark detection results of the respective colors.
The writing position to 51K is corrected for each pixel, and control is performed so that color misregistration does not occur during color image formation. Details will be described later. (2) Configuration of Control Unit 30 Next, the configuration of the control unit 30 will be described with reference to FIG.

As shown in FIG. 1, the control unit 30 includes a CPU
31, image processing unit 32, image memory 33, displacement correction unit 34, laser diode driving unit 35, RAM 36, R
It comprises an OM 37 and an EPROM 38. The image processing unit 32 scans the R, G,
Each of the B electrical signals is converted to generate image data composed of a multi-valued digital signal, and further subjected to corrections such as shading correction and edge enhancement processing, and then to C, M, Y, and K.
Is generated and output to the image memory 33, and the image data is stored for each reproduced color. At this time, the number of pages of the read document and the storage position (address) in the image memory 33 are stored in the management table in the RAM 36 in association with each other.

The displacement correcting section 34 changes the storage position of the image data for each pixel in accordance with an instruction from the CPU 31 to generate a corrected image. Laser diode drive unit 35
Drives each laser diode based on the corrected image data. The RAM 36 temporarily stores, in addition to the management table, various control variables, the number of copies, a print mode, and the like set from the operation panel 90, and also stores a control flag.

The ROM 37 stores a control program for a scanning operation in the image reader unit 10 and an image forming operation in the printer unit 20, a program for correcting image misregistration, a program for controlling the temperature of the fixing unit 80, and the like. The print data of the registration mark is stored. The EPROM 38 stores the displacement amount calculated by the CPU 31 based on a displacement detection operation described later. This EPROM is a non-volatile memory such as a battery-backed SRAM.
And so on.

The CPU 31 includes the sensors SE1 to SE1.
While receiving inputs from various sensors including 0, a necessary program is read from the ROM 37, and data processing in the image processing unit 32, writing / reading of image data in the image memory 33, and detection of a positional shift amount of each color are performed. And controls the content of correction of image data in the displacement correcting unit 34, or executes temperature control of the fixing unit 80, on / off control of a power supply unit (not shown), and other operations of the image reader unit 10 and the printer unit 20. A uniform copying operation is performed by taking control of the timing in a unified manner.

The temperature control of the fixing roller 801 of the fixing section 80 by the CPU 31 is performed by controlling the temperature to the fixing temperature (warm-up) and maintaining the temperature at the fixing temperature.
If the key input has not been performed for a predetermined period of time in the state where the fixing temperature has been reached, control (preheating) for lowering and maintaining the temperature lower than the fixing temperature of the fixing roller 801 to save power is included. FIG. 4 is a diagram illustrating an example of a registration mark formed on the transfer belt 41 at the time of the above-described position shift amount detection operation.

The registration marks 48M to 48K of each color are
Each has the same V-shape, and includes a first linear portion orthogonal to the transport direction A and a second linear portion making an angle of 45 ° with the first linear portion. These image data for registration mark printing are stored in the ROM 37 in advance, and in a state in which color transfer does not occur in the transferred images on the photosensitive drums 51M to 51K, the image data in the direction (main scanning direction) orthogonal to the transport direction A is used. They are formed on the transfer belt 41 at the same position and at a distance D from each other in a direction (sub-scanning direction) parallel to the transport direction A.

The registration marks 48M to 48 formed on the transfer belt 41 by the photosensitive drums 51M to 51K.
Each linear portion of K is detected by the registration mark detection unit 39 on the detection line of the dashed line in the figure as the transfer belt 41 moves, and the detection signal is sent to the CPU 31. FIG. 5 is a diagram showing a waveform of a detection signal after AD conversion.

The detection signals 481 to 488 are waveforms obtained when the linear portions of the registration marks 48M to 48K are sequentially detected from the downstream side in FIG. Since the photoelectric sensor in the registration mark detection unit 39 has a constant sensing width, the waveform of the detection signal has a peak, and therefore, it is difficult to determine the exact position of each linear portion.

Then, the CPU 31 determines the center position (or peak position) of the detected value as a reference position from the detected signal value by a method of calculating the center of gravity or the like, and determines that position as the first linear portion of each registration mark on the detection line. (Ky to Mm in the lower part of the waveform of the detection signal indicate the reference position of each linear portion. In the same figure, for example, “Ky” is used. Is
The first linear portion of the black registration mark, and “Kn” indicates the second linear portion of the black registration mark. The same applies to other colors. ).

The CPU 31 has a clock generation circuit therein, and the first linear portion, the second linear portion,
The number of clocks at the time of detecting each reference position of the linear portion is RA
M36, and the difference between these values is calculated to determine the second straight line portion from the first straight line portion detection in each of the registration marks 48M to 48K.
Times Tk to Tm required to detect a linear portion, and times T required from detection of the first linear portion of the registration mark 48K to detection of the first linear portions of the other registration marks 48Y to 48M.
ky, Tkc, and Tkm are obtained.

Here, assuming that the traveling speed of the transfer belt 41 during image formation is V, the distance between the first linear portion of the registration mark 48K and the registration mark 48Y is V · Tk.
Similarly, the distance between the first linear portion of the registration mark 48K and each of the first linear portions of the registration marks 48C and 48M is V · Tkc and V · Tkm, respectively. As described above, when there is no color shift, each of the registration marks 48M
Since the interval between .about.48K should be D, the amount of misalignment of each first linear portion of each of the registration marks 48Y, 48C, 48M with respect to the registration mark 48K (that is, the position in the sub-scanning direction) Displacement) is D
Assuming that 1ky, D1kc, and D1km, they can be obtained by the following equations, respectively.

D1ky = DV · Tky D1kc = 2D−V · Tkc D1km = 3D−V · Tkm On the other hand, each of the registration marks 48M-
The distance between the first linear portion and the second linear portion at 48K (hereinafter, referred to as
It is simply called “line spacing”. ) Is Dk, Dy, D
Assuming that c and Dm, these values are obtained by the following equations using the times Tk to Tm required from the detection of the first linear portion to the detection of the second linear portion in each of the registration marks 48M to 48K. .

Dk = V · Tk Dy = V · Ty Dc = V · Tc Dm = V · Tm Therefore, the line spacing Dk of black and the line spacing D of other colors
The differences from y, Dc, and Dm are represented by D2ky, D2k, respectively.
Assuming that c and D2km, the following equations are obtained.

D2ky = Dk-Dy D2kc = Dk-Dc D2km = Dk-Dm As described above, the first linear portion of each of the registration marks 48M to 48K is orthogonal to the transport direction (sub-scanning direction),
Since the straight line portion forms an angle of 45 ° with the first straight line portion, the difference between the line interval of the black registration mark on the detection line and the line interval of the other colors is the black image in the main scanning direction. This is equivalent to the amount of displacement between the writing position and the image writing position for another color.

As described above, the amount of displacement (D1ky, D1k) of the image writing position of another color in the sub-scanning direction with reference to the black image writing position.
c, D1 km) and the amount of displacement (D2ky, D2kc, D2km) in the main scanning direction are calculated by the CPU 31. The CPU 31 sends each of the calculated displacement amounts to the displacement correction unit 34.

The misregistration correction unit 34 includes an address change unit for each reproduced color and a corrected image memory unit. The address change unit changes the address of the image data read from the image memory 33 and stores the address in the corrected image memory based on the calculated positional shift amount, generates a corrected image, and thereby corrects the image writing position. Like that.

More specifically, when a corrected image is formed for a yellow image, the sub-scanning main direction and the main scanning direction of the black registration mark image and the yellow registration mark image obtained by the above-described position shift amount calculation are considered. The direction displacement amounts in the directions are D1ky and D2ky, respectively.
Therefore, the address may be changed so that these positional deviation amounts become substantially “0” when the image is reproduced on the recording sheet.

That is, if the distance between each pixel in the reproduced image is h (for example, if the image is reproduced at a density of 400 dpi, h is about 64 μm), then [D1ky / h in the sub-scanning direction. ] In the main scanning direction [D2ky /
h] (where [N] indicates, for example, the maximum integer value not exceeding N. In addition, it may be an integer value obtained by rounding off the decimal part of N.) That is, the determined address may be determined and stored in the corrected image memory. Whether the address is changed in the positive or negative direction is determined according to the positive / negative position shift amount.

By executing the above-described corrected image based on the amount of misalignment between black and cyan and between black and magenta, a full-color image without color misregistration can be reproduced with reference to the black image. Become. (3) Control Operation by Control Unit 30 Next, the control operation by the control unit 30 will be described with reference to the flowcharts of FIGS.

FIG. 6 is a flowchart showing a main routine of the control operation of the entire copying machine. Power switch 22
Is turned on, first, the registers in the CPU 31 and the contents stored in the RAM 36 are set to the initial state (step S
1), an internal timer of the CPU 31 is started (step S2).

Thereafter, it is determined whether or not the off edge of the power switch 22 (the edge portion where the signal falls from H to L) is detected (step S). If the off edge is detected, the current position of the swing frame 46 is detected. To the position sensors SE1, SE
2 and if it is in the non-retreat position, the swing frame 4
6, the transfer belt 41 is retracted, and the power supply unit is turned off (steps S8, S9, S1).
0). Thus, when the power is turned off, the transfer belt 41 is always kept in the retracted state.

If it is determined in step S3 that the off edge of the power switch has not been detected, the image of the original is read by the image reader unit 10 (step S4), and the transfer belt 41 is moved in accordance with the set print mode. Evacuation
The image forming process is executed by executing the non-evacuating operation (step S5). Then, in other cases, the transfer belt is retracted (step S6), and processing other than the above, for example, input processing using the operation panel 90, temperature control of the fixing unit 80, and the like are performed (step S7).

Thereafter, after the internal timer has expired, the flow returns to step S2, and the loop processing of steps S3 to S7 is repeated (step S11). FIG. 7 is a flowchart showing a subroutine of the image forming process in step S5. First, it is determined whether or not the print flag is set to "1". This print flag is a flag that is set in the RAM 36 when the start key of the setting operation panel 90 is pressed.

If the print flag is not "1", the process returns to the main routine, and if "1", it is determined whether or not the color print mode is currently set (step S502). This determination can be made, for example, by designating a print mode by key input from the operation panel 90 before the operator presses the start key, and setting a flag corresponding to the designated print mode in the RAM 36. It can be easily executed by confirming the setting state of the flag by the CPU 31. The setting operation of the flag for determining the print mode and the print flag is executed in the other processing in step S7.

If it is determined in step S502 that the color print mode has been set, it is next determined whether or not the transfer belt 41 is at the non-retreat position (step S503). This determination is based on the position sensor SE.
1, executed based on the detection signal of SE2 (FIG. 2). If the transfer belt 41 is at the retracted position (Step S5)
03 (“N”), the solenoid 47 is driven to move the transfer belt 41 to the non-retreat position (step S504),
When it comes to the non-retreat position, the position shift correction flag is set to "1".

Then, it is determined whether or not the transfer belt 41 is rotating (step S507). If the transfer belt 41 has not yet rotated, its rotation drive is started (step S508), and the transfer belt 41 is rotated during normal image formation. After a lapse of a predetermined time from the speed (system speed) at which the control is performed to the stable control (step 509), it is determined whether or not the displacement correction flag is “1”. Performs the above-described position shift amount detection operation in the next steps S10 to S12.

That is, the registration mark print data of each color is read out from the ROM 37, a registration mark image as shown in FIG. 4 is written and formed on the transfer belt 41 (step S 511). The marks 48M to 48K are detected to obtain the detection waveform of FIG. 5 (step S512). From this, the amount of displacement in the main scanning direction and the sub-scanning direction of the image of another color based on the black image is obtained, and the EPROM 38
Then, the data of each positional deviation amount in the previous positional deviation amount detection operation, which has already been stored, is updated and stored (step S513).

After the end of the displacement detection operation, the displacement correction flag is reset to "0" (step S5).
14). Then, the storage positions of the Y, C, and M image data are changed based on the position shift correction amount in the EPROM 38 to create a corrected image (step S515), and recorded based on the image data of each corrected image. A color image is formed on the sheet (step S516).

If the position shift correction flag is not "1" in step S510, it is determined that the position shift correction amount detecting operation is not necessary yet, and step S510 is executed.
The process proceeds to 515, where a corrected image is generated based on the positional shift correction amount stored in the EPROM 38, and a color image is formed based on the corrected image (step S516). When the color image formation is executed, it is determined whether or not the image formation is the final copy (step S517). This decision
For example, in a case where the originals are placed one by one on the original glass plate of the image reader unit 10 and N multi-copy is designated, the number of image formation is counted by the internal counter of the CPU 31 and the counted number becomes N. When it is seen, it is judged as the last copy. Also, the image reader unit 10
If an automatic document feeder (ADF) is installed in the printer and a plurality of originals are placed on the ADF and continuous copying is performed one by one, the number of originals is counted at the time of reading the original and the number of image formation is reduced. When the count value is reached, it is determined that the copy is final. Further, the determination can be made by referring to the management table in the RAM 36.

If it is determined in step S517 that the image is not the final copy, the process returns to the main routine, and after a cycle of the routine, an image is formed on the next recording sheet in step S516, and the final copy is performed in step S517. Is completed, the print flag is reset to "0", and the rotational drive of the transfer belt 41 is stopped (steps S518, S519), and the process returns, thereby ending the execution of the color print mode.

If it is determined in step S502 that the mode is not the color print mode, the process proceeds to step S520 to execute the single color print mode, and it is determined whether the transfer belt 41 is at the retracted position. If the transfer belt 41 is not at the retreat position, the solenoid 47 is driven to move the transfer belt 41 to the retreat position (step S521).
It is determined whether or not is rotating (step S522,
If it is not rotating (S523), the rotation driving of the transfer belt 41 is started (Step S524), and the monochrome image formation is started (Step S525). Here, the step of waiting for a predetermined time from the start of the rotation of the transfer belt (step S509) as in the case of executing the color print mode is not particularly provided. In the monochrome print mode, the image is formed only on the black photosensitive drum 51K at the most downstream black position. In order to execute the formation, the transfer belt 41 reaches the system speed between the time when the recording sheet is supplied to the transfer belt 41 at the start of image formation and the time when the leading end of the recording sheet reaches the transfer position of the photosensitive drum 51K. This is because it is considered to be possible.

After the image formation on the recording sheet is completed, it is determined whether or not this is the last copy (step S517). If it is determined that the copy is not the last copy, the process returns to the main routine. After this cycle, the image formation on the next recording sheet is executed in step S525, and when it is determined that the final copy is completed, the print flag is reset to “0” and the rotation of the transfer belt 41 is driven. Is stopped (step S51).
8, S519), and returns to the main routine.

As described above, in the image forming process in step S5, the transfer belt 41 is moved to the retracted position or the non-retracted position according to the print mode set by the operator, and each image is formed. As a result, the transfer belt 41 must be
However, since the photosensitive drums are separated from the photosensitive drums 51Y, 51C and 51M, the rotation of these photosensitive drums can be stopped to extend the life.

When the transfer belt 41 is moved from the retracted position to the non-retracted position to form a color image, the amount of displacement of the image writing position of each color is always detected and the correction amount is updated. Therefore, a color image without color shift can be formed without being affected by the evacuation / non-evacuation operation. Next, the subroutine of the transfer belt retracting process in step 6 in FIG. 6 will be described. This transfer belt retreating process is a process for retreating other than the case where the transfer belt 41 is retracted in accordance with the print mode change in the image forming process in step S5 or the detection of the off-edge of the power switch 22 in step S3. It is executed based on the flowchart of FIG.

First, in step S601, it is determined whether the current mode is the color print mode. If the mode is not the color print mode, that is, if the mode is the single color print mode, the transfer belt 41 is always kept in the retracted state in the above-described image forming process (see steps S502 and S520 to S522 in FIG. 7), so the retracting operation is performed again. And it just returns.

If the color print mode has been set, the flow advances to step S602 to determine whether or not a color image printing operation is in progress. Here, “during printing operation” means a state in which, when a series of copy jobs, for example, a plurality of originals are copied one by one, formation of color images is continuously performed. I have. If it is determined in step S602 that a print operation is being performed,
Since the transfer belt 41 cannot be separated, the process returns. However, if it is determined in step S602 that the printing operation is not being performed, first, it is determined whether or not warm-up is currently being performed (step S6).
03). This warm-up is performed by turning the power switch 22 ON.
N or from the preheat state, the fixing unit 80
Means a period from when the fixing roller 801 is heated to reach a predetermined fixing temperature, and whether or not warm-up is being performed is determined based on a detection signal of the temperature detection sensor SE10 or a control signal from the CPU 31. be able to. If it is not during the warm-up, it is determined whether the apparatus is in a standby state (step S604). Here, "during standby" means a state where the warm-up is completed and copying can be started at any time by pressing the start key by the operator. If it is not during standby, it is next determined whether or not preheating is being performed (step S60).
5). This preheating means a mode in which the temperature of the fixing roller 801 is maintained at a temperature lower than the fixing temperature to save power when there is no key input from the operator even if the standby state continues for a certain period of time.

If the above is not during warm-up, standby, or pre-heating (step S603,
In the case of "N" in both S604 and S605)
If it is, the process returns as it is, but if any of them is "Y", the transfer belt 41 is moved to the retreat position (step S606). Thereby, the state in which the transfer belt 41 is at the non-retreat position can be reduced as much as possible without hindering the formation of a color image, and the transfer belt 41 is pressed by all four photosensitive drums 51M to 51K for useless time. It is possible to prevent the transfer belt 41 from being deformed. (4) Modifications It is needless to say that the present invention is not limited to the above embodiment, and the following modifications can be considered.

(4-1) In the retreating process of the transfer belt in step S6 in the above embodiment (FIG. 8), the retreating operation of the transfer belt 41 is performed during any of warm-up, standby, and preheating. Let me run
Although the contact time between all the photosensitive drums 51M to 51Y and the transfer belt 41 is reduced, the purpose is further enhanced, and the transfer belt 41 is always moved to the retreat position except during printing of a color image. You may do so.

That is, as shown in the flowchart of FIG. 9, in step S621, it is determined whether or not the current mode is set to the color print mode. If the color print mode has been set, the flow advances to step S622 to determine whether a color image printing operation is in progress. Here, if it is determined that the printing operation is being performed, the transfer belt 41 cannot be separated, so the process returns as it is. If it is determined that the printing operation is not being performed, the transfer belt 41 is moved to the retreat position. (Step S62)
3).

(4-2) On the other hand, if the transfer belt 41 is always retracted when the color image printing operation is not being executed as described above, the transfer belt 41 is always used when the color image printing operation is executed. 41 must be moved to the non-retracted position, and image formation must be started after the rotation speed reaches the system speed, which results in slow copy execution of the first page.

Therefore, when it is desired to give priority to the copy processing speed even in the color print mode, the save processing may be executed only when the following abnormal situation occurs. FIG. 10 is a flowchart showing a subroutine of the transfer belt retracting process in this case.

First, it is determined whether or not a jam has occurred based on the detection signals from the jam detection sensors SE4 to SE9 (step S631). If a jam has occurred ("Y" in step S631), the jam is detected. If it is determined that the front door 21 is open based on the detection signal of the door opening detection sensor SE3 (“N” in step S631 and “Y” in step S632) even if it has not occurred,
It is determined whether the transfer belt 41 is currently at the non-retreat position (step S633). If the transfer belt 41 is at the non-retreat position, the transfer belt 41 is moved to the retreat position (step S634). Then, the power of the display unit and the drive system of the operation panel 90 is turned off, and the process returns to the main routine.

Thus, when a jam occurs,
The transfer belt is always retracted and the rotation of the transfer belt is stopped, and the load on the transfer belt 41 by the photosensitive drums 51M to 51Y is removed to prevent the transfer belt 41 from deforming. Since it is lowered downward, there is an advantage that the jam paper removing operation (jam processing) can be easily performed without damaging the photosensitive surface of the photosensitive drum.

When the front door 21 is normally opened, the printing operation is interrupted, and in many cases the toner is replaced or other maintenance is performed in addition to the above-described jam processing. In this case, the transfer belt 41 is retracted. Transfer belt 41
Is stopped, the deformation of the transfer belt 41 during this period can be prevented, and the maintenance work can be facilitated.

In step S631, not only the presence or absence of a jam but also other troubles, for example,
It is also possible to determine whether or not paper shortage (paper empty) or running out of toner has occurred, and to retreat the transfer belt even when these troubles occur. At this time, the paper shortage is detected by, for example, the jam detection sensors SE6 to SE6.
9 can be determined by detecting that the next recording sheet is no longer fed to the paper feed port of the currently selected paper feed cassette. In addition, when the toner runs out, a test pattern is periodically formed on the photosensitive drum surface. The developing device is formed by irradiating it with detection light and detecting the amount of toner adhesion from the amount of reflection, or when a two-component developing device using ferrite as a carrier is used, The determination can be made by detecting the ratio of the ferrite component in the stirred developer with a magnetic sensor or the like.

(4-3) In the above embodiment, the displacement correction amount is calculated based on the detection result of the registration mark detection unit 39, and the displacement correction unit 3 is calculated based on the correction amount.
The misregistration correction of each color is executed by forming a corrected image in step 4. However, the same applies when the timing of starting image writing in the main scanning direction and the sub-scanning direction is controlled based on the misregistration correction amount. Position shift correction can be achieved.

(4-4) In the above embodiment, in the monochromatic print mode, the photosensitive drum which is not involved in the image formation and the transfer belt 41 are brought into contact with and separated from each other, so that the swing frame 46 which supports the drive roller 42 (see FIG. 2) is driven to swing up and down by the solenoid 47. However, the means of this swing drive is not limited to the solenoid, but may be other actuators or cam mechanisms. Further, without providing a swing frame, the transfer belt 41 is stretched so that the photosensitive belt not involved in image formation and the transfer belt 41 are separated from each other, and the transfer belt is transferred by the transfer roller at the transfer position of the separated photosensitive drum. 41
May be pushed up. Further, instead of moving the transfer belt 41, the photosensitive drum may be moved upward to separate the transfer belt and the photosensitive drum.

(4-5) The setting of the print mode is not limited to the operation performed by the operator through the operation panel 90 as described above. For example, based on the image data read by the image reader unit 10, A document discriminating unit for discriminating whether a document is a color document or a monochrome document may be provided so that the print mode can be automatically set based on the discrimination result. As a method of the original discrimination, saturation data is obtained from R, G, and B image data of each pixel read by the image reader unit 10, and pixels having a predetermined saturation are counted. When a predetermined ratio (for example, 0.1%) is reached with respect to the number of pixels on the entire page of the document, the document may be determined to be a color document.

In this case, since the print mode can be automatically determined for each document, an automatic document feeder (ADF) is installed in the image reader unit 10, and even if a color document and a black and white document are mixed on this, In accordance with the type of each document, a continuous copying operation can be performed by automatically performing the operation of moving the transfer belt 41 toward and away from the transfer belt 41. (4-6) In the above-described embodiment, the case where the image is directly transferred from the photosensitive drum to the recording sheet has been described. The present invention can also be applied to a device that transfers an image to a recording sheet to form an image.

Conversely, a recording sheet is fed during the misregistration detection operation, a registration mark is formed on the recording sheet, and the misregistration amount is detected by a registration mark detection unit. Is also good. In this case, an extra recording sheet is used to detect the amount of displacement, but since the transfer registration mark image becomes clearer, the detection accuracy is improved and the transfer belt is deformed. Also, the position shift amount can be detected more accurately without being affected by the deformation.

(4-7) In the above embodiment, a full-color tandem-type copying machine has been described.
The present invention is not limited to a copying machine, and is applicable to general tandem-type color image forming apparatuses including a laser printer.

[0079]

As described above, according to the present invention, there is provided an image forming apparatus capable of forming a multicolor image by a plurality of image carriers. Contact the transfer belt and all the image carriers, and when executing a monochromatic image, while the first image carrier involved in the monochromatic image is kept in contact, the other second image carrier and the Since the transfer belt is relatively separated from the transfer belt, and the second image carrier and the transfer belt are relatively separated from each other by the contacting and separating means when the apparatus is in a standby state. At the time of monochromatic image formation, the operation of the second image carrier, which is not involved in image formation, can be stopped to extend its life, and the above-described second method can be performed when the apparatus is in a standby state by using the contact / separation mechanism. Separating the transfer belt from the image carrier 2 Since thereby, suppress the heavy load time to the transfer belt, it is possible to prevent the deformation on the transfer belt occurs as much as possible. This allows
The life of the transfer belt can be extended, and the occurrence of color misregistration during color image formation can be reduced, so that a high-quality reproduced image can be formed.

The standby state may be a state in which a color image forming operation is not performed, or a state in which the temperature of the fixing unit of the fixing unit is lower than a predetermined fixing temperature. Further, a state from the occurrence of a trouble in the apparatus to the elimination of the trouble or a state in which a door provided in a housing of the apparatus is open may be used. In any case, the transfer belt is retracted in a state where the formation of the color image is not hindered, the time during which a large load is applied to the transfer belt can be reduced as much as possible, and the deformation can be prevented.

In particular, when a trouble occurs or the door is opened, the transfer belt is automatically retracted, so that the effect of removing the trouble and performing the maintenance can be easily obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing an entire configuration of a tandem-type full-color copying machine according to an embodiment of the present invention.

FIG. 2 is a perspective view illustrating a configuration of a recording sheet transport unit in the copying machine.

FIG. 3 is a block diagram of a control unit installed in the copying machine.

FIG. 4 is a diagram illustrating an example of a registration mark formed on a transfer belt.

FIG. 5 is a diagram illustrating a waveform of a detection signal obtained by a registration mark detection unit.

FIG. 6 is a flowchart showing a main routine executed by the control unit.

FIG. 7 is a flowchart showing a subroutine of an image forming process in the flowchart of FIG. 6;

FIG. 8 is a flowchart showing a subroutine of a transfer belt retracting process in the flowchart of FIG. 6;

FIG. 9 is a flowchart illustrating a modified example of the subroutine of the transfer belt retracting process.

FIG. 10 is a flowchart showing another modified example of the transfer belt retreating subroutine.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 image reader unit 20 printer unit 30 control unit 31 CPU 32 image processing unit 33 image memory 34 misalignment correction unit 35 laser diode drive unit 36 RAM 37 ROM 38 EPROM 39 registration mark detection unit 41 transfer belt 46 swing frame 47 solenoid 48M ~ 48K Registration mark 51M ~ 51K Photoconductor drum

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Takeshi Minami 2-3-13 Azuchicho, Chuo-ku, Osaka-shi, Osaka Inside Osaka International Building Minolta Co., Ltd. (72) Takeshi Satake Azuchi-cho, Chuo-ku, Osaka-shi, Osaka 2-3-13 Osaka International Building Minolta Co., Ltd.

Claims (5)

[Claims] An image forming apparatus capable of forming a multi-color image by forming an image of each color on each of a plurality of image carriers and transferring the image to a transfer belt or a transfer material conveyed on the transfer belt. An apparatus, wherein a transfer belt is brought into contact with all the image carriers when forming a color image, and a first image carrier involved in the single-color image is contacted when forming a single-color image. Contacting and separating means for relatively separating the other second image bearing member and the transfer belt from the second image bearing member while the apparatus is in a standby state; And a control unit for controlling the transfer belt and the transfer belt to be relatively separated from each other. 2. The standby state according to claim 1, wherein the color image forming operation is not being performed.
The image forming apparatus as described in the above. 3. The fixing device according to claim 1, further comprising a fixing unit configured to thermally fix the image transferred to the transfer material, wherein the standby state is a state in which a temperature of a fixing unit of the fixing unit is lower than a predetermined fixing temperature. Item 2. The image forming apparatus according to Item 1. 4. The image forming apparatus according to claim 1, wherein the standby state is a state after a trouble occurs in the apparatus until the trouble is cleared. 5. The image forming apparatus according to claim 1, wherein the housing of the apparatus includes a door that can be opened and closed, and the standby state is a state where the door is open.