JP3225686B2 - Color image forming equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus such as a tandem type color electrophotographic copying machine or a color printer having a plurality of image forming units, and more particularly to a drive system for any one of the plurality of image forming units. The present invention relates to a color image forming apparatus capable of continuing a color image forming operation within a possible range even when a failure occurs.

[0002]

2. Description of the Related Art Conventionally, as a color image forming apparatus such as a tandem type color electrophotographic copying machine or a color printer, for example, there are the following apparatuses. As shown in FIG. 17, the color image forming apparatus includes four color image forming units 100Y, 100Y, 100Y, and 100Y.
00M, 100C, and 100K are arranged in parallel at predetermined intervals, and these image forming units 100Y, 100Y,
A toner image of each color of yellow, magenta, cyan, and black is formed by 100M, 100C, and 100K. The image forming units 100Y, 100M, 10M
The toner image of each color of yellow, magenta, cyan, and black formed by 0C and 100K is conveyed to the conveyor belt 101.
After the image is sequentially transferred onto the transfer paper 102 conveyed by the printer, the toner image transferred onto the transfer paper 102 is fixed to form a color image. The transport belt 101 is
Each image forming unit 100Y, 100M, 100C, 1
It is arranged below 00K so as to form a linear conveyance path over all image forming units.

In the above image forming apparatus,
Each image forming unit 100Y, 100M, 100C, 1
Since the color images are formed by sequentially transferring the toner images of the respective colors formed on the transfer paper 102 conveyed by the conveyance belt 101 to form a color image, the transfer paper is required to obtain a high-quality color image. It is necessary to superimpose the toner images of each color transferred onto the surface 102 with high accuracy.
Therefore, in the above-described image forming apparatus, it is necessary to rotate the photosensitive drums 103Y, 103M, 103C, and 103K of the image forming units 100Y, 100M, 100C, and 100K with high precision.

A technique relating to the drive control device for the photosensitive drum is disclosed in, for example, JP-A-63-7575.
There is one disclosed in Japanese Patent Application Laid-Open No. 9-205. In the image forming apparatus for forming an image on an image carrier that moves endlessly, the drive control device for the image carrier carries the image carrier through a reduction gear train having an integer ratio of teeth as a mechanism for moving the image carrier. A stepping motor to be driven, a memory storing a pulse generation pattern for canceling a rotation change of one rotation of the gear of the last gear of the gear train for one rotation of the last gear, and a detecting means of a home position of the last gear. A pulse is generated based on the pulse generation pattern when the image carrier is moved, and the stepping motor is driven.

However, in the case of the drive control apparatus for an image carrier according to the above proposal, a pulse generation pattern for canceling the rotation fluctuation of the image carrier is previously stored in a memory as a fixed pattern, and is stored in this memory. A pulse is generated based on the fixed pulse generation pattern, and a stepping motor is driven by the pulse, thereby preventing rotation fluctuation of the image carrier. Therefore, if the state of the rotational fluctuation of the reduction gear train for driving the image carrier changes due to environmental change such as temperature change or temporal change due to long-term use, the pulse generation pattern for canceling this rotational fluctuation is stored in the memory. Since the fixed pattern is stored in the memory, it is not possible to cope with an unexpected rotation fluctuation due to an environmental change or the like. As a result, it is not possible to sufficiently suppress the rotation fluctuation of the image carrier caused by environmental change or aging change, and the rotation fluctuation remains on the image carrier, so that a color shift or the like occurs in a formed image. there were.

In order to solve the above problems, the present applicant has already proposed a rotation control method and apparatus in a multiple transfer apparatus disclosed in Japanese Patent Laid-Open No. 43574/1990. The rotation control device according to this proposal is a multi-transfer device in which a plurality of images are multi-transferred onto a common transfer roll, wherein the transfer roll when a drive motor for driving the transfer roll is rotated at a predetermined angular speed in advance. The information on the change in the angular velocity is stored in a storage means, the information on the change in the angular velocity is read from the storage means at the time of transfer, and the angular velocity of the drive motor is changed based on the information.

The rotation control device in the multiple transfer apparatus according to this proposal uses a transfer roll stored in a storage means in advance even if a new rotation fluctuation occurs in the image carrier due to environmental change or aging. When the angular velocity of the drive motor is changed based on this information, the angular velocity can be corrected as a change in the angular velocity, so that it can cope with environmental changes and changes over time. Has become.

However, in the case of the device according to the above proposal,
It has the following problems. That is, in the case of the rotation control method in the multiple transfer device according to the proposal of the present applicant, the information on the change in the angular velocity of the transfer roll is stored in the storage means as it is, and the information on the change in the angular velocity is read out from the storage means. Thus, the angular velocity of the drive motor is directly changed based on the information. Therefore, the change information of the angular velocity of the transfer roll stored in the storage means is
By greatly increasing the number of divisions of the angular velocity to achieve high accuracy of the rotation control of the transfer roll, the amount of change due to the correction gradually increases, and the rotation amount of the transfer roll is changed from the drive motor to the rotation shaft of the transfer roll via a gear. There is a problem that it becomes a vibration source for the system up to the point, and there is a possibility that oscillation occurs or the amplitude of the natural frequency of the system becomes large. In this case, it is necessary to use a high-precision encoder as the encoder for detecting the change information of the angular velocity of the transfer roll in order to increase the precision of the rotation control of the transfer roll, and to increase the cost accordingly. There was also a problem of inviting.

Accordingly, the present applicant has solved the above problem, and even if the speed of the rotating body is controlled with high accuracy, the rotating body does not oscillate or raise the cost. A drive control device has already been proposed (Japanese Patent Application No. 4-80279).

This rotary body drive control device is a rotary body drive control device for controlling the drive of a rotary body used in an image forming apparatus. A rotation detection unit, a second rotation detection unit that is used only when the image forming apparatus is manufactured, and detects the rotation speed of the rotator, and a driving unit that rotationally drives the rotator at a constant speed. And a storage unit for storing the rotation speed information detected by the first rotation detection unit and the second rotation detection unit for each predetermined division section, and by the first rotation detection unit during image formation. The rotation speed of the rotating body is detected, and the rotation speed information of the first rotation detection unit and the second rotation detection unit stored in the storage unit is read out, and the rotation speed detected by the first rotation detection unit is detected. Drive means for averaging the rotation speed information of the first rotation detection means and the second rotation detection means stored in the information and storage means, and for rotationally driving the rotator based on the averaged rotation speed information And control means for controlling the control.

[0011]

However, the above-mentioned prior art has the following problems. That is, in the case of the drive control apparatus for a rotating body according to the proposal of the present applicant, it is possible to cope with environmental changes, aging, and the like, and to control the speed of the rotating body with high accuracy. Even in such a case, the rotating body does not oscillate or increase the cost.

However, when such a rotary body drive control device is applied to a tandem type color image forming apparatus, each of the image forming units 100Y, 100M, 100
C, 100K photoconductor drums 103Y, 103M, 10
3C and 103K can be driven to rotate with high precision, but the photosensitive drums 103Y, 103M, 103
C, a feedback control system that controls a driving unit based on information on a change in the rotation speed, such as clogging of a slit or disconnection of an optical sensor in an encoder used as a first rotation detection unit that detects a rotation speed of 103K. If a failure occurs in the image forming unit 100,
Y, 100M, 100C, 100K photoconductor drum 10
3Y, 103M, 103C, and 103K cannot be rotationally driven with high accuracy. At this time, the photosensitive drums 103Y, 103M, 103C, and 103K of the normal image forming units 100Y, 100M, 100C, and 100K
Since the rotation state is controlled with high accuracy, even if the rotation fluctuation of the photoconductor drums 103Y, 103M, 103C, and 103K in which the failure has occurred is slight, the rotation fluctuation appears as a remarkable one.

Therefore, in the above-mentioned image forming apparatus,
Each image forming unit 100Y, 100M, 100C, 1
The toner image of each color formed by 00K cannot be accurately superimposed and a predetermined color image cannot be recorded. When the user sees the formed color image, the user notices the failure of the apparatus and calls a service engineer. Therefore, there is a problem that the image forming apparatus cannot be used at all until the repair of the apparatus is completed. Therefore, even if there is another image forming unit that can be driven normally, there is a problem that the image forming operation cannot be continued and the image forming apparatus cannot be used effectively.

Therefore, as a technique which can partially solve such a problem, Japanese Patent Laid-Open No. 4-116571 has already been proposed. The color copying apparatus according to this proposal includes an instruction unit that instructs an operation related to reading and recording of an original image, an input unit that reads the original image according to an instruction from the instruction unit, and inputs an image signal. Detecting means for detecting an internal abnormality, and contents of the internal abnormality detected by the detecting means in a color copying apparatus having a forming means for forming a visible image based on the image signal input by the input means in accordance with the instruction of In accordance with the present invention, a determining means for determining a valid instruction range by the instruction means, and a specifying means for specifying the instruction range determined by the determining means.

However, in the case of the color copying apparatus according to this proposal, when an internal abnormality such as a lack of toner occurs,
This is detected by the detecting means, and the image forming operation is enabled by the forming means other than the image forming means with no toner, and even in the case of this color copying apparatus, When a drive system abnormality occurs, the image forming operation cannot be continued, and there is a problem that the use of the apparatus must be interrupted.

Therefore, the present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to solve the problem even when a drive system failure occurs in any of a plurality of image forming units. It is another object of the present invention to provide an image forming apparatus capable of continuing a color image forming operation within a possible range and enabling the apparatus to operate effectively.

[0017]

According to the present invention, a plurality of image forming units are juxtaposed, and an image formed by each of the image forming units is conveyed to a transfer position of each of the image forming units, and is sequentially transferred. In a color image forming apparatus that forms a color image according to the above, a driving state detecting unit that detects a driving state of each of the image forming units, and an abnormal signal is generated when a detection signal from the driving state detecting unit is abnormal. Determining means for determining whether or not the image forming unit that has been able to form an image by itself and an image forming mode of a color that can be formed by combining other normal image forming units; and determining the image forming mode determined by the determining means. Selecting means for selecting one of the image forming apparatuses; and controlling the driving of each of the image forming units in accordance with the image forming mode selected by the selecting means. It is configured to include a Cormorant control means.

As the driving state detecting means, for example,
A device that measures the interval between output pulses output from a rotary encoder that detects the rotation speed of the photosensitive drum of each image forming unit and detects the driving state is used.

The above-mentioned drive state detecting means is provided when a frequency of a drive pulse supplied to a driver for driving a drive motor for rotatingly driving the photosensitive drum of each image forming unit is greatly deviated from a standard frequency. A device that detects that a failure has occurred in a feedback control system that changes the angular velocity of the drive motor is used.

However, as the driving state detecting means,
Of course, other materials may be used.

As a driving means for driving the image forming unit, for example, a stepping motor is used. In addition, a DC servo motor or a direct drive motor can be used.

[0022]

In the present invention, the driving state of each image forming unit is detected by the driving state detecting means, and when the detection signal from the driving state detecting means is abnormal, the image forming unit which has generated the abnormal signal is activated. The image forming mode of a color that can be formed by combining an image forming unit with another normal image forming unit is determined by the determining unit, and one of the image forming modes determined by the determining unit is determined. When the user makes a selection using the selection unit, the control unit controls the driving of each of the image forming units according to the image creation mode selected by the selection unit. Even if a failure occurs, a color image forming operation can be continued within a possible range.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on the illustrated embodiment.

FIG. 2 shows an embodiment of the color image forming apparatus according to the present invention.

In FIG. 2, 1Y ', 1M', 1C ',
1K ′ indicates an image forming unit that forms a toner image of each color of yellow, magenta, cyan, and black. Each of the above image forming units 1Y ', 1M', 1C ',
1K ′ is a photosensitive drum 1Y, 1Y on which a toner image of each color of yellow, magenta, cyan, and black is formed on its surface.
M, 1C, and 1K, respectively, and these photoconductor drums 1Y, 1M, 1C, and 1K are arranged in parallel at a predetermined interval from each other. Each of the photosensitive drums 1
The surfaces of Y, 1M, 1C, and 1K are primary chargers 2Y, 2Y,
After being uniformly charged by M, 2C and 2K, an exposure optical system 3Y, 3
The images are sequentially exposed by M, 3C, and 3K to form an electrostatic latent image. Each of these photoconductor drums 1Y, 1M, 1
The electrostatic latent images formed on the surfaces of C and 1K are
4M, 4C, and 4K, respectively, are developed with yellow, magenta, cyan, and black toners to form visible toner images. These visible toner images are neutralized by the pre-transfer neutralizers 5Y, 5M, 5C, and 5K. The transfer paper 10 is charged by charging the transfer chargers 6Y, 6M, 6C, and 6K.
It is sequentially transferred to the top.

The photosensitive drums 1Y, 1M, 1C, 1K
The transfer paper 10 that receives the transfer of the toner image sequentially from the transfer drum 10 is supplied from a paper feed cassette (not shown), and is conveyed while being electrostatically held on the transfer body conveyance belt 12. The sheet is sequentially conveyed to a transfer position located below 1C and 1K. Then, each photosensitive drum 1Y,
The transfer paper 10 onto which the toner images of each color are sequentially transferred from 1M, 1C, and 1K is separated from the transfer body transport belt 12 and transported to the fixing unit 13 by the fixing unit 13. And the color image is fixed.

On the other hand, the surfaces of the photosensitive drums 1Y, 1M, 1C, and 1K on which the transfer of the toner images has been completed are subjected to the charge of the post-transfer chargers 7Y, 7M, 7C, and 7K, and are discharged and cleaned. After the residual toner and the like are removed by the devices 8Y, 8M, 8C, and 8K, the erase lamps 9Y,
The charge is removed by 9M, 9C, and 9K to prepare for the next image formation.

FIG. 3 shows a mechanism for rotating and driving the photosensitive drum.

In the figure, reference numerals 1Y, 1M, 1C and 1K denote the respective photosensitive drums. Each of the photosensitive drums 1Y, 1M, 1C and 1K has a drive motor 15 comprising a stepping motor and A first gear 16 fixed to the drive shaft of the drive motor 15, a second gear 17 meshing with the first gear 16, a third gear 18 fixed to the same shaft as the second gear 17, The third gear 18 is rotatably driven by a photoreceptor gear 19 fixed to the rotating shafts of the photoreceptor drums 1Y, 1M, 1C and 1K meshing with each other. In addition, the photosensitive drums 1Y, 1M, 1
A flywheel 30 as an inertial body is attached to each of the rotation shafts C and 1K.

The photosensitive drums 1Y, 1M, 1M
A rotary encoder 21 and a calibration rotary encoder 22 are attached to the rotation shafts of C and 1K. The rotary encoder 21 and the calibration rotary encoder 22 are mounted on the photosensitive drums 1Y, 1M,
This is for detecting the angular velocity of rotation of 1C and 1K. The rotary encoder 21 and the calibration rotary encoder 22 are connected to a control unit 20, and a drive motor 15 is connected to the control unit 20. A relatively low-precision rotary encoder is used as the rotary encoder 21, for example, one that outputs 180 or 360 pulses per rotation. On the other hand, the calibration rotary encoder 2
As 2, a high-precision one that outputs, for example, 10,000 thousands of pulses per rotation is used.
The calibration rotary encoder 22 is attached to the rotating shafts of the photosensitive drums 1Y, 1M, 1C, and 1K only when adjusting the color image forming apparatus before shipment at a factory, for example. When it is removed from the device.

FIG. 4 is a block diagram showing a circuit configuration of the control unit.

In the figure, reference numeral 23 denotes a photosensitive drum 1Y, 1
M, 1C, and 1K control the CPU, 24 is a PROM that stores programs executed by the CPU 23 and predetermined data, and 25 is the rotary encoder 2
RA that stores the time interval of each divided section, which is data read from the calibration rotary encoder 22 and the like.
M and 21 are photosensitive drums 1Y and 1 at the time of image recording.
A rotary encoder for detecting the rotation speeds of M, 1C and 1K, 22 is a calibration rotary encoder for calibrating the rotary encoder 21 at the time of adjustment before shipment of the apparatus, and 26 is a pulse output from the calibration rotary encoder 22. A pulse counter 27 for dividing the pulse signal output from the pulse oscillator 28 and outputting a drive pulse of a predetermined command frequency, and 29 based on the drive pulse output from the interval counter 27 A drive motor driver for rotating the drive motor 15.

Before the drive control of this embodiment, the rotation driving mechanism of the photosensitive drum includes a drive motor 15 for rotating and driving the photosensitive drums 1Y, 1M, 1C and 1K.
Even if the command frequency to the photosensitive drum 1 is kept constant,
Y, 1M, 1C, 1K eccentricity of the rotating shaft and the drive gear 1
As shown in FIG. 5, the rotation of the photoconductor drums 1Y, 1M, 1C, and 1K is caused by the position error (rotational angular velocity variation in the photoconductor shaft portion) due to the meshing error of 6, 17, 18, and 19 and the like. Which represents the deviation from the ideal position).

The relationship between the fluctuation of the rotational angular velocity and the position error when the photosensitive drum rotates is generally expressed by the following equation (1). The integration of the position error X (t) is performed from 0 to t.

(Equation 1) ω (t) = ω ₀ + Δω ₁ · cos ω ₁ t + ... + Δω _i · cos ω _i t +... X (t) = ∫ω (t) dt = ω ₀ · t + (Δω ₁ / ω _{1 ) · sinω 1 t + ... ...} + (Δω i / ω i) · sinω i t + ... where, omega _0; average angular velocity [Delta] [omega _i of the photosensitive body shaft portion; angular amplitude in the vibration frequency f _i (0~pe
ak) f _i ; vibration frequency X (t); rotation angle

The results of fast Fourier transform (FFT) analysis of the angular velocity of the photosensitive drum are as shown in FIG.

As described above, before the drive control of the photosensitive drum is performed, the frequency f _i and the system resonance frequency f _{n are controlled.}
In addition, a high amplitude level peak appears near a high frequency caused by the driving gear, and color shift or color unevenness occurs in a color image sequentially transferred on the transfer paper 10 due to the rotation fluctuation of the angular velocity of the photosensitive drum. Appears.

The rotation fluctuation of the angular velocity of the photosensitive drum is
Low-frequency fluctuations or the eccentricity component is generated by a rotation of the photosensitive drum as one period, variation of the intermediate frequency corresponding to the resonant frequency f _n of the system, or the like variations in the high-frequency component due to the drive gear.

In this embodiment, the photosensitive drums 1Y, 1M, 1C,
A rotary encoder 22 for calibration is attached to the rotation shaft of 1K in addition to the rotary encoder 21, and the following correction table creation operation is performed. here,
The operation of creating a correction table for the photosensitive drum 1Y will be described, but the same operation is performed for the other photosensitive drums 1M, 1C, and 1K.

First, the correction table for the photosensitive drum 1Y is
In order to form the photosensitive drum 1Y, the photosensitive drum 1Y rotates at a constant angular velocity.
Driven. That is, the photosensitive drum 1Y is rotated.
As shown in FIG. 4, the drive motor 15 to be driven
Output pulse S of the oscillator 28 _OSCIs an interval count
The driving pulse S having a predetermined frequency_DPWhen
Supplied. This drive pulse S_DPIs P
The standard frequency f is stored in the ROM 24._SPre-stored as
You. The CPU 23 reads the standard frequency f from the PROM 24._Sof
Read the data and use it as the preset data S_PSAs
The data is loaded into the interval counter 27. interval
The counter 27 outputs the pulse output from the pulse oscillator 28.
The pulse count value is preset
Data S_PSDrive pulse S every time_DPIs output. So
The photosensitive drum 1Y is provided with a drive motor driver 2
9, a predetermined frequency f supplied to the drive motor 15 via_S
Drive pulse S_DPIs driven to rotate.

Then, with the rotation of the photosensitive drum 1Y, the rotary encoder 21 and the calibration rotary encoder 22 attached to the rotating shaft of the photosensitive drum 1Y output the signals shown in FIGS. d) As shown in (e), the output pulses S1 _RE and S2 _RE and the zero-phase pulse S
1 ₀ is output to the CPU 23. At this time, the output pulse S2 _RE of the rotary encoder 22 for calibration is output to the CPU 23 via the pulse counter 26. The output pulses S1 _RE and S2 _RE are output from the rotary encoder 2
1 and a signal output each time the calibration rotary encoder 22 rotates by a predetermined angle. Further, the zero phase pulse S1 ₀ is for the rotary encoder 21 is output at the reference position upon rotation, both encoders 2
The reference positions 1 and 22 are set to the same position.
Incidentally, the pulse counter 26, as shown in FIG. 7 (c), divides the output pulse S2 _RE output from the rotary encoder 22 for calibration, C as an interrupt signal S _INT
The data is output to the PU 23.

When the correction table is created, the rotation fluctuation of the photosensitive drum 1Y is changed by the rotary encoder 2
1 and the rotary encoder 22 for calibration. Pulses S1 _RE and S2 output from the rotary encoder 21 and the calibration rotary encoder 22
_RE is output at almost constant intervals unless the rotation of the photosensitive drum 1Y is changed, and the number of pulses output in a predetermined divided section is always constant. However, if the rotation of the photosensitive drum 1Y fluctuates, the output intervals of the pulses S1 _RE and S2 _RE output from the rotary encoder 21 and the calibration rotary encoder 22 change.
As shown in (1), the time interval output in a predetermined divided section differs depending on each divided section.

Therefore, the CPU 23 is provided with a calibration rotary
-Output pulse S2 of encoder 22 _REThe pulse counter
Interrupt signal S divided by 26_INTIs entered each time
The interval driven by the output of the pulse oscillator 28
The count value of the counter 27b is read and shown in FIG.
As described above. That is, the CPU 23
Is the zero-phase pulse S1 from the rotary encoder 21.₀
Is input, the first interrupt signal S_INTInterrupted by
When there is, count of interval counter 27b
Interval T corresponding to the first section by reading the value
₁And stored in the RAM 25. Then, the next section
Corresponding interrupt signal S_INTIs also read when
Of the interval counter 27b previously read.
Calculate the difference between the interval and the interval T_TwoBut
It is measured and stored in the RAM 25. This work is for calibration
This is repeated for one cycle of the rotary encoder 22.

[0044] At this time, the zero-phase pulse S1 ₀ of the rotary encoder 21 is supplied to the CPU 23, as a reference the zero phase pulse S1 ₀ initial value of the address is C
The interval T _(N) of each divided section is set by the PU 23 and thereafter, by adding an address by a fixed value and specifying the address for each section, that is, each time the interrupt signal S _INT is input, the RAM 25. Is stored in

Each time the output pulse S 1 _RE of the rotary encoder 21 is input, the CPU 23 sets an interval counter 27 driven by the output of the pulse oscillator 28.
b, and reads out the count value in the RAM as shown in FIG.
25. That is, the CPU 23 controls the rotary encoder 2 similarly to the calibration rotary encoder 22.
After the zero-phase pulse S1 ₀ is input from 1 and the next output pulse S1 _RE is input, the interval counter 2
The count value of 7b is read and stored in the RAM 25 as an interval T _L1 corresponding to the first section. Then, when the output pulse S1 _RE corresponding to the next section is input, the pulse is read in the same manner, the difference from the count value of the previously read interval counter 27b is calculated, and the interval T _{L2 of the} section is measured. Is stored in This operation is also repeated for one cycle of the rotary encoder 21.

At this time, the calibration rotary encoder 22
There number of interrupt signals S _INT output during one rotation is set equal to the number of output pulses S1 _RE to be printed between the rotary encoder 21 rotates once. That is,
The divided sections for counting the time intervals of the pulses S2 _RE and S1 _RE output from the calibration rotary encoder 22 and the rotary encoder 21 are both set to the same number.

The interval counter 27b
Is driven by the output S _OSC of a constant frequency from the pulse oscillator 28, the count value of the interval counter 27b indicates the elapsed time.

Next, the CPU 23 calculates the difference C _(N) = _{TL (N)} between the interval T of the divided section of the rotary encoder 22 for calibration stored in the RAM 25 and the interval _TL of the divided section of the rotary encoder 21. −T _(N) is calculated for each divided section, and the calculation result C _(N) is stored in the RAM 25 for each divided section, as shown in FIG.

Thus, the operation of creating the correction table is completed. The work of creating this correction table is, as described above,
This is performed when adjusting the color image forming apparatus in the factory.

When the user uses the color image forming apparatus, the CPU 23 controls the rotary encoder 21 during the image forming operation based on the following correction equation.
Is corrected, and the photosensitive drum is rotationally driven.

[0051] (number 2) f _n = f _{s [1 + α {FILS / T ID} -1} + β {T ID / (FILD-ΣDIFF) -1} ]

The correction equation is not limited to the equation (2), and a correction equation as shown in the following equation (3) may be used.

[0053] (number 3) f _n = f _{s [1 + α {FILS / T ID} -1} ] × _{[1 + β {T ID / (} FILD-ΣDIFF) -1} ]

Here, f _n ; interval frequency after correction f _s ; standard frequency FILS previously stored in PROM 24; interval value T _(N) of rotary encoder 22 for calibration stored in RAM 25 as a correction table; Interval value after averaging from section (N) to the previous section of m, ie, FILS = 1 / m (T _{(N-m + 1)} + T _{(N-m + 2)} + T
_{(N-m + 3)} +... + T _(N-1) + T _(N) ) FILD; ideal value ΣT _ID one section ahead of correction operation stored in advance in PROM 24 and interval of rotary encoder 22 read in real time value oT 'calculated value of the difference between _{(N) (ΣT ID -ΣT'} (N)) , the value after averaging over only interval earlier m from the interval (N), i.e. FILD = 1 / M ｛(ΣT _ID −ΣT ' _{(N-m + 1)} ) + (Σ
T _ID -ΣT ' _{(N-m + 2)} ) + (ΣT _ID -ΣT' _{(N -m + 3)} )
+ ... + (ΣT _ID -ΣT ' _(N-1) ) + (ΣT _ID -ΣT'
_(N) ) Σ ΣDIFF; interval values _{TL (N)} and T _(N) of the rotary encoder 21 and the rotary encoder 22 for calibration are set to the section from the section (N) to m before the same as FILS. After averaging over these values, a value obtained by integrating the difference data (FILS-FILS) of these values from the zero-phase pulse, that is, ΣDIFF = Σ (FILS-FILS) 0 to N = Σ ｛1 / m ( _{TL (N-m + 1)} + _{TL (N-m + 2)} + _{TL (N-m + 3)} +
... + _{TL (N-1)} + _{TL (N)} )-1 / m (T _{(N-m + 1)} + _{TL
(N-m + 2)} + T _{(N-m + 3)} + ... + T _(N-1) + T _(N) )｝ (Σ
The 0~N up) T _ID; ideal calculated value of one section previously stored in PROM24, i.e., the interval value of the first section in an ideal state without completely rotational fluctuation in the rotation shaft of the photosensitive drum α; PROM24 Is a constant of the feed-forward section stored in advance in the PROM 24, and is a constant of the feedback section stored in the PROM 24 in advance. Each of the above equations employs averaging. However, depending on the system, weighting may be used to change the coefficient of each section.

By the experimental data and the logic analysis using only the feedforward control, when α = 1, there is no response delay, so that the value known in advance can be corrected by that amount, so that the correction effect is the best. Therefore, when α = 1 is substituted into the equation (1) (α is selected to be close to 1 depending on the system), the following equation 4 is obtained.

[0056] (number 4) f _n = f _{s [1 + α {FILS / T ID} -1} + β {T ID / (FILD-ΣDIFF) -1} ] _{= f s × (FILS / T} ID) + f s × β _{{T ID / (FILD-ΣDIFF} ) -1} = f s × (FILS / T ID) + β × {f s · T ID / (FILD-ΣDIFF) -f s}

In this embodiment, Equation 4 is used as a correction equation.

In the image forming apparatus according to this embodiment, the drive control of the photosensitive drum is performed as follows. That is, in order to form a color image in the color image forming apparatus, as shown in FIG. 2, the photosensitive drums 1Y, 1M, 1C, and 1K are rotationally driven, and these photosensitive drums 1Y, 1M, 1C, A toner image of each color of yellow, magenta, cyan, and black is formed on the surface of 1K. At this time, the photosensitive drums 1Y, 1M, 1C, 1
The rotation state of K is controlled as follows.

When starting the formation of a color image, CP
U23, as shown in FIG. 4, drives the drive motor 15 in the normal frequency f _s, the photoreceptor drums 1Y, 1M, 1
C and 1K are rotated. And the rotor encoder 2
After detecting the zero phase pulse S1 ₀ of 1, the correction and the interval value T table stored _(N), based on the output from the rotary encoder 22 measured interval value T _(N) in each section , And calculates the correction frequency f _n for the next section (N + 1), and outputs it to the drive motor 15.

The correction of the driving frequency based on the equation (4) is as follows.
It is always performed, but may be performed at a predetermined time as needed.

Then, the CPU 23 outputs the corrected data of the driving frequency f _n to the interval counter 27, and the interval counter 27
Counts the pulses output from the count value of the pulse to output a driving pulse S _DP every time reaches the value corresponding to the driving frequency f _n of the corrected. As a result, the photosensitive drum 1Y is driven to rotate by a drive pulse S _DP drive frequency f _n of the corrected to be supplied to the drive motor 15 via the drive motor driver 29.

If there is no fluctuation in the rotation of the photosensitive drum 1Y, FILS, FILD and Σ
Each value of DIFF is, the FILS and FILD is T _ID,
Since ΣDIFF becomes 0, the expression 4, next to f _n = f _s, of course, the drive frequency f _n of the corrected is equal to the standard frequency f _s.

Next, when the interval value of the correction table for the K-th section to be corrected is long, that is, when the angular velocity of the photosensitive drum 1Y when the drive motor 15 is rotated at a constant angular velocity is the K-th section , The interval values T _(K) and T ′ _{(K) of the section} are T
Since larger than _ID, the correction frequency f _n increases as follows. Note that the value of T ' _(K) is strictly unknown because it is read in real time. That is, in the four correction equations, FILS, FILD, and ΣDIF
Each value of F is as follows.

FILS is 1 / m (T_{(N-m + 1)}+ T
_{(N-m + 2)}+ T_{(N-m + 3)}+ ... + T_(N-1)T_(N-1)+
T_(N)), So T_IDIt becomes a value larger than. Ma
FILD is 1 / m１ ／ (｛T_ID-'T'_{(N-m + 1)})
+ (ΣT_ID-'T'_{(N-m + 2)}) + (ΣT _ID-'T'
_{(N-m + 3)}) + ... + (ΣT_ID-'T'_(N-1)) + (ΣT_ID
-'T'_(N))｝, So T_ID, But T_IDThan
Is also a small value. Furthermore, $ DIFF is $ 1 / m
(T_{L (N-m + 1)}+ T_{L (N-m + 2)}+ T_{L (N-m + 3)}+ ... + T_{L (N-1)}
+ T_{L ( N)}) -1 / m (T_{(N-m + 1)}+ T_{(N-m + 2)}+ T
_{(N-m + 3)}+ ... + T_(N-1)+ T_(N))｝
The interval values of the rotary encoders 21 and 22 are equal
If it is 0, the calibration rotary encoder 22
If the global value is larger,
If the interval value of coder 21 is larger,
And its value is a small value close to zero.

Accordingly, the number of correction equations before expanding the equation (4)
4 ′, (FILS / T _ID) Is close to 1
However, the value is larger than 1 and T_ID/ (FILD-ΣD
The value of (IFF) is close to but greater than 1.

The value of β in the correction equation (2) is set as appropriate.

As a result, the value of f _n in equation (4) is f
_s become a value greater than, the correction frequency f _n increases. Thereby, the photosensitive drum 1 driven by the drive motor 15
The angular speed of the rotation of Y is controlled to be constant, and the peripheral speed of the photosensitive drum 1Y is constant.

In addition, the expansion and contraction of the shape and dimensions due to a change with time, a temperature change, and the like affect the runout of the tooth groove of the gear or the meshing error of the entire pitch, thereby changing the eccentric component. If the angular velocity of the K-th section is increased due to such a change over time or a change in temperature, that is, if the interval value of the correction table of the K-th section to be corrected is short, the interval value T of the section is used. _{Since L (K)} and T _(K) are smaller than T _ID , the correction frequency f _n
Is reduced as follows. That is, in the four correction equations, the values of FILS, FILD, and $ DIFF are as follows.

FILS is 1 / m (T _{(N-m + 1)} + T
_{(N-m + 2)} + T _{(N-m + 3)} + ... + T _(N-1) + T _(N-1) + T
_(N) ), the value is smaller than T _ID . Also,
FILD is 1 / m ｛(ΣT _ID −ΣT ′ _{(N-m + 1)} ) +
(ΣT _ID -ΣT ' _{(N-m + 2)} ) + (ΣT _ID -ΣT'
_{(N-m + 3)} ) + ... + (ΣT _ID −ΣT ' _(N-1) ) + (ΣT _ID
Because it is -ΣT _'(N))}, is close to T _ID value larger than T _ID. Furthermore, $ DIFF is $ 1 / m
( _{TL (N-m + 1)} + _{TL (N-m + 2)} + _{TL (N-m + 3)} + ... + _{TL (N-1)}
+ _{TL ( N)} )-1 / m (T _{(N-m + 1)} + T _{(N-m + 2)} + T
_{(N-m + 3)} +... + T _(N-1) + T _(N) )｝, so that if the interval values of the rotary encoders 21 and 22 are equal, the interval value of the calibration rotary encoder 22 is Is larger when the interval value of the rotary encoder 21 is larger, and the value is a smaller value close to 0.

Accordingly, the number of correction equations before expanding the equation (4)
4 ′, (FILS / T _ID) Is close to 1
However, the value is smaller than 1 and T_ID/ (FILD-ΣD
The value of (IFF) is close to 1, but smaller than 1.

As a result, the value of f _n in equation (4) is f
_s becomes a smaller value than the correction frequency f _n is low. Thereby, the photosensitive drum 1 driven by the drive motor 15
The angular speed of the rotation of Y is controlled to be constant, and the peripheral speed of the photosensitive drum 1Y is constant.

As described above, according to the present embodiment, not only can the change in the angular velocity of the photosensitive drum unique to each image forming apparatus be corrected, but also the dynamic angular velocity caused by aging, temperature change, etc. Changes can also be corrected.

Further, the rotary encoders 21 and 22
Are used for correction after averaging by the CPU 23.
Even if the number of divisions of the angular velocity of the photosensitive drum angular velocity change information stored in the RAM 25 is greatly increased, the interval values output from the rotary encoders 21 and 22 are averaged, and the amount of change due to correction becomes large. Thus, it becomes a vibration source for the system from the drive motor 15 to the rotating shaft of the photosensitive drum via the gear, and it is possible to prevent the possibility of oscillation or an increase in the amplitude of the natural frequency of the system.

The rotary encoder 22 for calibration is used only at the time of adjustment at the factory, and is removed from the color image forming apparatus at the time of shipment from the factory, so that the cost of the color image forming apparatus can be increased without increasing the cost. Accuracy can be controlled.

As a result, the four photosensitive drums 1Y, 1Y
The speed of each of the transfer units M, 1C, and 1K becomes constant, and the displacement between the transfer units can be reduced. For example, the position error Δx after the correction becomes very small as shown in FIG.

The position error is measured by a measuring device based on the output of the rotary encoder 21 by the method described below.

That is, the output of the rotary encoder 21 is F / V converted, A / D converted, and the digital value is stored at an appropriate sampling period. Then, the digital values stored in the memory are averaged, and a difference between each digital value and the average value is obtained. Since this difference is a speed difference, the position error is obtained by time integration of the difference.

Further, in this embodiment, since the flywheels 30 as the inertial bodies are respectively mounted on the rotating shafts of the photosensitive drums 1Y, 1M, 1C and 1K, the height is increased by the gear teeth. It is possible to prevent the frequency component from fluctuating, and to prevent color unevenness from occurring in the image.

That is, the fluctuation of these high frequency components can be suppressed by optimally selecting the flywheel 30 as the inertial body.

It has been found that when the size of the flywheel 30 (moment of inertia J _L ) is within the following range, the high-frequency component can be reduced and the correction control works effectively. J _L ≦ 0.5Kg ・ cm ・ s ²

FIG. 13 shows the photosensitive drums 1Y, 1M, 1C, 1
FIG. 14 shows a case where the flywheel 30 of J _L = 0.25 Kg · cm · s ² is attached to the rotation axis of K, and FIG. 14 shows the flywheel 30 attached to the rotation axis of the photosensitive drums 1Y, 1M, 1C, and 1K. No case is shown. As is apparent from these figures, the photosensitive drums 1Y, 1M, 1C, 1
By attaching the flywheel 30 to the K rotation shaft, high-frequency components near 100 Hz can be reduced.

By combining the above methods, the position error and the FFT analysis result due to the fluctuation of the rotational angular velocity at the shaft of the photosensitive drum are as shown in FIGS. 11 and 12.
It can be seen that the rotation fluctuation can be kept very small.

In the above embodiment, only feedback control is possible. In this case, an adjustment step such as mounting of a high-precision encoder for creating a fixed pattern is not required, and a memory for the fixed pattern is also required. Since it becomes unnecessary, the cost is reduced.

By the way, as described above, the photosensitive drum 1
Even when the rotations of Y, 1M, 1C, and 1K are controlled with high precision, clogging of the slits and disconnection of the optical sensor may occur in the rotary encoder 21 that detects the rotation speed of each of the photosensitive drums 1Y, 1M, 1C, and 1K. If the failure occurs or a failure occurs in the feedback control system that changes the angular speed of the drive motor based on the rotation speed information, the failed photosensitive drums 1Y, 1M, 1C, and 1K are driven to rotate with high accuracy. Can not be done. Therefore, in the image forming apparatus, it is impossible to accurately record the toner images of the respective colors formed by the respective photosensitive drums 1Y, 1M, 1C, and 1K and record a predetermined color image.

Therefore, in this embodiment, the driving state detecting means for detecting the driving state of each image forming unit, and when the detection signal from the driving state detecting means is abnormal, the image forming apparatus which generates the abnormal signal Determining means for determining whether the unit can form an image independently and determining an image forming mode of a color that can be formed by combining other normal image forming units; and one of image forming modes determined by the determining means. And a control unit for controlling the driving of each of the image forming units in accordance with the image forming mode selected by the selecting unit.

FIG. 1 is a block diagram showing a control system for controlling the operation of the color image forming apparatus when a failure occurs in the drive system of the color image forming apparatus according to this embodiment.

In FIG. 1, reference numerals 40 and 41 denote driving state detecting means for detecting the driving state of each image forming unit. As shown in FIG. 4, the drive state detecting means 40 determines the interval between the output pulses S1 _RE output from the rotary encoder 21 based on the count value of the interval counter 27b.
When the interval of the output pulse S1 _RE output from the controller is out of the predetermined range, it is detected as an abnormality of the rotary encoder or the optical sensor 21. The other driving state detection means 41, as shown in FIG. 4, if the frequency of the drive pulse S _DP supplied to the driver 29 for driving the drive motor 15 is greatly deviated from the standard frequency f _s, the drive It detects that a failure has occurred in the feedback control system that changes the angular velocity of the motor 15. These drive state detecting means 40 and 41 are configured so that, for example, the CPU 23 shown in FIG. Further, each image forming unit 1Y ', 1M', 1
When the intervals of the output pulses S1 _RE output from the rotary encoders 21 of C ′ and 1K ′ are compared with each other and are out of a predetermined range, it is detected that the rotary encoder or the optical sensor 21 is abnormal. Further, the drive pulse S supplied to the driver 29 for driving each drive motor 15 of each image forming unit 1Y ', 1M', 1C ', 1K'.
_The failure of the feedback control system in which the frequency of the _DP changes the angular velocity of the drive motor 15 may be detected.

Reference numeral 42 denotes each image forming unit 1Y ', 1
M ′, 1C ′, and 1K ′ are determination units to which signals from the drive state detection units 40 and 41 are input.
Reference numeral 2 denotes each image forming unit 1Y ', 1M', 1C ', 1
Which image forming unit 1 is based on the driving state detection signals output from the driving state detecting means 40 and 41 of K ′.
This is to determine whether a failure has occurred in Y ', 1M', 1C ', and 1K'. Reference numeral 43 denotes a selection unit that selects an image forming mode in which an image forming operation is to be performed based on a determination signal from the determination unit 42. 44, each of the image forming units 1Y ', 1M',
The control means 1C 'and 1K' are controlled by the CPU 23 shown in FIG. 4, for example.

In the above configuration, in the color image forming apparatus according to this embodiment, the rotary encoder 21 for reading the change information of the rotation state of each of the photosensitive drums 1Y, 1M, 1C, and 1K is provided as follows. Even if clogging or disconnection of the optical sensor occurs, or if a failure occurs in the feedback control system that changes the angular speed of the drive motor based on the change information of the rotation state, the color image forming operation is continued in a possible image forming mode. You can do it.

That is, as shown in FIG. 15, the above-described color image forming apparatus first has the image forming units 1Y ′,
The driving of M ', 1C', and 1K 'is started (step 1). Next, in the color image forming apparatus, as shown in FIG. 1, the driving state of each image forming unit 1Y ', 1M', 1C ', 1K' is detected by the driving state detecting means 40, 41 (Step 2). . If the image forming units 1Y ', 1M', 1C ', and 1K' are normally driven, a normal image forming operation is performed (step 3).

On the other hand, the image forming units 1Y ', 1Y'
When an abnormality is detected in the driving states of M ′, 1C ′, and 1K ′, the detection signals of the driving state detection units 40 and 41 determine whether the image forming unit in which the abnormality is detected can form an image. It is determined (step 4). In this case, for example, a driver that drives the drive motor 15 even when an abnormality is detected by the drive state detection unit 40 that detects an abnormality of the rotary encoder 21 based on an interval of the output pulse S1 _RE output from the rotary encoder 21. If the frequency of the drive pulse S _DP supplied to the power supply 29 does not significantly deviate from the standard frequency f _s , it is determined that an image can be formed.

Thereafter, when it is determined by the determining means 42 shown in FIG. 1 that image formation is possible (step 5),
The image forming possible mode is selected by the selecting means 43 (step 6). Here, for example, when an abnormality occurs in the black image forming unit 1K ', the other yellow, magenta, and cyan image forming units 1Y', 1M 'can be used without using the black image forming unit 1K'. ,
By using 1C ′, a normal color image can be formed, so that three colors of yellow, magenta, and cyan can be used.
A full-color image forming mode by color is selected. Further, if an abnormality occurs in the yellow image forming unit 1Y ′, full-color image formation becomes impossible, and therefore, other color image forming modes except the color image formation of the color in which the yellow color is superimposed are set. Is selected.

In this case, as shown in FIG. 16, the image forming available mode selected by the selection means 43 is blinking, although the display unit 50 of the operation panel has a failure in the "yellow mode". The color can be copied "message appears. Also, in FIG.
Reference numeral 1 denotes a keyboard on which a number of keys 52 for designating an image-formable color are arranged. In addition to this display, a message urging the repair of the failed image forming unit is also displayed on the operation panel as usual.

When the user designates a color on which images can be formed on the operation panel, the image forming unit in which the abnormality has occurred does not perform the feedback control and the oscillator 28
Is opened only by the drive pulse _SDP via the interval counter 27 (step 7), and the image of the color formed by the image forming unit in which the abnormality has occurred is formed independently. .
This means that even if the image forming unit
This is because if it is possible to form an image by itself, it is possible to form an image with no hindrance to image quality. The other normal image forming units execute the color image forming mode of a color that can be formed by combining them (step 8), and form a color image (step 9).

On the other hand, when it is judged by the judging means 42 shown in FIG. 1 that image formation is impossible (step 10), the driving of the image forming unit in which the abnormality has occurred is stopped by the selecting means 43 (step 11). Then, the color of the abnormal unit is displayed on the operation panel (step 12). Here, for example, when an abnormality occurs in the black image forming unit 1K ′ and it is determined that black image formation is impossible,
The black image forming unit 1K 'is stopped. But,
Since a full-color image can be formed without using the black image forming unit 1K ', a full-color image forming mode using three colors of yellow, magenta, and cyan is selected in this case (step 13). Further, if an abnormality occurs in the yellow image forming unit 1Y ′, full-color image formation becomes impossible, and therefore, other color image forming modes except the color image formation of the color in which the yellow color is superimposed are set. Is selected (Step 1
4). Then, an image forming operation of a single color or a plurality of colors is performed (step 15), and the operation ends.

As described above, in the above-described color image forming apparatus, the driving state detecting means 40 and 41 detect the driving state of each of the image forming units 1Y ', 1M', 1C 'and 1K'. When the detection signals from 40 and 41 are abnormal, it is determined whether the image forming units 1Y ', 1M', 1C ', and 1K' which have generated the abnormal signals can form an image by themselves and other normal image forming. Unit 1
The image forming mode of a color that can be formed by combining Y ′, 1M ′, 1C ′, and 1K ′ is determined by the determining unit 42,
When the user selects one of the image forming modes determined by the determining unit 42 by the selecting unit 43, the image forming units 1Y 'and 1M are selected in accordance with the image forming mode selected by the selecting unit 43. ',
The drive control of 1C 'and 1K' is performed by the control means 44.

Therefore, a plurality of image forming units 1
Even if a drive system failure occurs in any of Y ', 1M', 1C ', and 1K', the image forming operation can be continued in a possible image forming mode. Even before the process is completed, the color image can be formed by effectively using the color image forming apparatus.

[0098]

The present invention has the above-described structure and operation. Even if a drive system failure occurs in any one of a plurality of image forming units, a color image forming operation is continued within a possible range. And an image forming apparatus capable of effectively enabling the apparatus. Further, in the case of the present invention, in a color image forming apparatus including a plurality of image forming units, a driving state detecting unit that detects a driving state of each of the image forming units, and a detection signal from the driving state detecting unit. A determination unit that determines whether the image forming unit that has generated the abnormal signal is capable of forming an image alone and determines an image forming mode of a color that can be formed by combining other normal image forming units when the abnormality signal is generated; If you have one,
Even if a drive state abnormality occurs in one of the image forming units, if the image forming unit that has generated the abnormal signal can form an image by itself, the image forming unit that has generated the abnormal signal is operated alone to perform image formation. It is also possible to form Therefore, in the case of the present invention, even if an abnormality occurs in the driving state of any of the image forming units, the image forming operation should be continued as much as possible in a state where the abnormality of the driving state does not appear in the image. The apparatus can be used effectively until the color image forming apparatus is repaired or the like. Further, the invention
In the case of, the image creation mode selected by the selection means
When controlling the drive of each of the image forming units according to
Then, the image forming unit that failed
If the mode to be performed is selected,
Equipped with control means for opening control of the image forming unit
The image forming unit where an error has occurred
If the mode for performing image formation alone is selected,
Open control of the image forming unit in which the abnormality has occurred
Image formation while maintaining a certain level of accuracy
And the open-controlled image format
Since the image forming unit performs image formation independently,
The color image forming device can be repaired
In the meantime, the device can be used effectively.
Wear.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a control unit of an embodiment of a color image forming apparatus according to the present invention.

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

FIG. 3 is a configuration diagram illustrating a drive system of the image forming unit.

FIG. 4 is a block diagram illustrating a drive control system of the image forming unit.

FIG. 5 is a graph showing a rotation fluctuation of the photosensitive drum.

FIG. 6 is a graph showing rotation fluctuations of the photosensitive drum.

FIGS. 7A to 7E are waveform diagrams each showing a control signal.

FIG. 8 is an explanatory diagram showing a table of a memory.

FIG. 9 is an explanatory diagram showing a table of a memory;

FIG. 10 is an explanatory diagram showing a table of a memory;

FIG. 11 is a graph showing rotation fluctuation of the photosensitive drum.

FIG. 12 is a graph showing a rotation fluctuation of the photosensitive drum.

FIG. 13 is a graph showing rotation fluctuation of the photosensitive drum.

FIG. 14 is a graph showing rotation fluctuation of the photosensitive drum.

FIG. 15 is a flowchart showing the operation of one embodiment of the color image forming apparatus according to the present invention.

FIG. 16 is an explanatory diagram showing a display panel.

FIG. 17 is a configuration diagram showing a conventional color image forming apparatus.

[Explanation of symbols]

1Y ', 1M', 1C ', 1K' image forming units,
40, 41 drive state detecting means, 42 determining means, 43
Selection means, 44 control means.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Minoru Kasama 2274 Hongo, Fujina Rocks, Ebina City, Kanagawa Prefecture (72) Inventor Toshio Anzai 2274 Hongo, Hongo, Ebina City, Kanagawa Prefecture Inside Fuji Xerox Corporation (56) References JP-A-61-79659 (JP, A) JP-A-5-80628 (JP, A) JP-A-4-116571 (JP, A) JP-A-4-131866 (JP, A) (58) Survey Field (Int.Cl. ⁷ , DB name) G03G 15/00 303 G03G 21/00 370-540 B41J 2/525 G03G 15/01-15/01 117

Claims (1)

(57) [Claims] 1. A color image forming a color image by arranging a plurality of image forming units side by side, transferring a transfer medium to transfer positions of the image forming units to transfer positions of the image forming units, and sequentially transferring the images. In the forming apparatus, a driving state detecting unit that detects a driving state of each of the image forming units, and when a detection signal from the driving state detecting unit is abnormal, the image forming unit that generates the abnormal signal alone forms an image. Whether it can be formed and if it can be formed alone
Determining means for determining an image forming mode in which a single image can be formed and an image forming mode of a color which can be formed by combining other normal image forming units; and one of the image forming modes determined by the determining means. Selecting means for selecting one, and controlling the driving of each of the image forming units according to the image creation mode selected by the selecting means;
When performing driving control of the respective image forming units according to the selected image forming mode by the selection means, the field of performing image formation in the image forming units alone abnormality occurs
A color image forming apparatus comprising: a control unit configured to open and control the image forming unit in which the abnormality has occurred when the image forming mode is selected.