JP2000199988A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of keeping color slurring amount equal to or under a fixed value by controls, such as correction of an exposing position by easily detecting the speed change of a belt body due to wear in the thickness of the belt body or the diameter of a drive roller without necessitating a detection means such as a high-resolution encoder, even if there is a change due to the wear in the thickness of the belt body and the diameter of the drive roller. SOLUTION: A mark 24 is printed at the end of the translucent transfer belt 8 of the image forming device, and a light transmission type detection means 25 for detecting the mark 24 is installed on the belt 8. By circularly turning the belt 8 plural number of times, the passage of the mark 24 is detected by the detection means 25, and the passage interval of the mark 24 is measured by a counter, based on the detected result and compared with an initial value stored previously in a storage means 26. Based on the compared result, the timing of image exposure in plural image forming units juxtaposed along the belt 8 is corrected.

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 capable of forming a full-color image by using an electrophotographic system, and more particularly, to an image forming apparatus such as a copying machine, a printer, and a facsimile.

[0002]

2. Description of the Related Art In recent years, a full-color image forming apparatus has been put to practical use in an image forming apparatus using an electrophotographic process. Conventionally, in order to realize full-color image formation at high speed, it is known to employ a so-called tandem type configuration in which a plurality of image forming units (image forming units) are arranged in a recording material conveyance direction.

In the case of a color image, one of the factors that degrades image quality is a color shift. This occurs when the position of the image of each color is shifted in the sub-scanning direction and the main scanning direction, or is not relatively parallel.

In the above-described tandem-type apparatus configuration, image formation of each color is performed at a plurality of different locations, and therefore, color misregistration occurs as compared with a conventional apparatus having one image forming unit (one photosensitive drum). It's easy to do.

[0005]

When attention is paid to color shifts in the sub-scanning direction, there are static causes and dynamic causes. The static causes are the respective image forming units. The distance between the photosensitive drums, the deviation of the exposure position, the diameter of the drive roller that drives the belt-shaped recording material carrier (for example, a belt such as a transfer belt) that regulates the conveyance speed of the recording material during transfer There are errors mainly at the time of assembling the apparatus and accuracy of components, such as the accuracy of the components. Dynamic causes include fluctuations in the rotation speed of the photosensitive drum and the transfer belt.

The static cause can be corrected and removed at least at the time of product shipment, for example, by electrically adjusting the exposure timing.

On the other hand, it is difficult to remove dynamic causes by correction. The fluctuation of the rotation speed of the photosensitive drum and the fluctuation of the conveying speed of the recording material by the transfer belt must be suppressed as much as possible, and various measures are taken for the accuracy and control method of the driving source such as the driving roller.

For example, in driving the transfer belt, the eccentricity of the drive roller does not contribute to color misregistration by setting the distance between the image forming units to an integral multiple of the drive pitch circle formed by the neutral surface of the transfer belt. I have to.

However, in the case of the belt body, there is a speed variation factor other than the eccentricity of the driving roller. The drive roller is
A rubber layer is provided on the surface in order to transmit the rotational driving force to the transfer belt without slipping.For example, as a result of long-term use, the drive roller surface is worn or the inner and outer peripheral surfaces of the belt are worn. Since the radius of the belt neutral surface from the center of the driving roller changes, the linear velocity of the belt changes.

The above-mentioned abrasion causes a color shift in a very small amount. For example, the diameter of the driving roller of the belt is D (m
m), the belt thickness is T (mm), and the image forming speed is V
(Mm / sec), the diameter of the neutral surface of the belt (diameter of the pitch circle) is D + T (mm), and the distance between each image forming unit is N ×
Since π × (D + T), the distance between each image forming unit is π × (D + T) when the size of the apparatus is minimized.
(Mm).

Assuming that the amount of decrease in the thickness of the belt is ΔT and the amount of decrease in the diameter of the driving roller is ΔD, the amount of change in the image forming speed is (ΔT + ΔD) / (T + D) × V (mm / sec) 1)

Normally, since a full-color image is formed by four image forming units, the distance between the farthest image forming units is 3
× π × (T + D) (mm) and the original image forming speed, it takes 3 × π × (T + D) / V (seconds) to pass (2).

Therefore, the amount of image misregistration caused by belt and roller wear can be calculated by multiplying Expressions (1) and (2) between the most distant image forming units to obtain 3 × π × (ΔT + ΔD).・ (3)

That is, even when the roller diameter is reduced by only 5 μm and the belt thickness is reduced by 5 μm due to wear, the amount of color misregistration reaches about 94 μm according to the equation (3), and two pixels when the resolution is 600 dpi. More than a minute gap occurs.

As a method for preventing the above-described color shift, or for preventing the occurrence of color shift due to other disturbances,
Conventionally, (a) a means for reading an image recorded on a belt body, and controlling an exposure timing and an exposure position based on a reading result; (b) a speed of the belt body from a pattern formed on the belt body; May be detected at any time, and the speed, exposure timing, and exposure position of the belt body during image formation are controlled as needed based on the detection result.

However, the method (a) requires a means for reading the formed image and a mechanism for correcting the exposure position in the image forming apparatus, so that the cost, complexity and size of the apparatus cannot be avoided.

In the method (b), a high-resolution encoder needs to be formed on the belt body, and has a similar difficulty in controlling the transport speed and the exposure position of the belt body during image formation as needed. I was

An object of the present invention is to provide an image forming apparatus which does not cause color misregistration even if the thickness of a belt member or the diameter of a driving roller for driving the belt member changes with time without complicating the apparatus. To provide.

[0019] Other objects of the present invention will become apparent from a reading of the following detailed description.

[0020]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
A belt body, a driving roller that supports the belt body and transmits a driving force to the belt body, and a plurality of images that form a plurality of color images on the belt body or the recording material carried on the belt body, respectively. An image forming unit, a measuring unit that measures a time required for the belt body to move a predetermined distance, and the image forming unit supporting the belt body or the belt body based on the time measured by the measuring unit. And control means for controlling the timing of forming images of a plurality of colors on the recording material, respectively.

According to the present invention, there is provided storage means for storing a target time at which the belt body moves by the predetermined distance, and the control means uses the target time stored in the storage means and the measuring means. Based on the difference from the measured time, the timing at which each of the image forming units starts forming images of a plurality of colors on the belt or on the recording material carried on the belt is controlled. Alternatively, the measuring means measures the time during which the belt body moves the predetermined distance a plurality of times, and each of the image forming means measures the time based on an average value of the plurality of times measured by the measuring means. The image forming means controls the timing for starting to form images of a plurality of colors on the belt or on the recording material carried on the belt.

The measuring means includes a sensor for detecting one mark provided on the belt body. After the sensor detects a mark on the belt body, the mark on the belt body is detected next. Measure the time until you do it. Alternatively, the measuring means includes a sensor that detects a plurality of marks provided on the belt body, and the sensor detects a first mark on the belt body, and then detects a second mark on the belt body. Measure the time until the mark is detected. Alternatively, the measuring means includes a sensor for detecting a detection image formed on the belt body by the image forming means, and the sensor detects a detection image on the belt body, The time until the next detection image on the belt body is detected is measured. Alternatively, the measuring means includes a sensor for detecting a plurality of detection images formed on the belt body by the image forming means, and the sensor detects a first detection image on the belt body. Then, the time until the second detection image on the belt body is detected is measured.

The moving speed of the belt is measured by the measuring means while measuring the time required for the belt to move by a predetermined distance. The moving speed of the belt is measured by the image forming means on the belt or the recording material carried on the belt. The speed is switched to a speed lower than the moving speed of the belt body when images of a plurality of colors are formed. A first mode in which a plurality of color images are sequentially formed on the belt or a recording material carried on the belt by the respective image forming means when the moving speed of the belt is a first moving speed; When the moving speed of the belt member is a second moving speed lower than the first moving speed, images of a plurality of colors are sequentially superimposed on the belt member or the recording material carried on the belt member by the image forming means. The second formed
And the moving speed of the belt body is switched to the second moving speed while the measuring unit measures the time required for the belt body to move the predetermined distance.

Further, each of the image forming means has an image carrier for carrying an image, and images of a plurality of colors on each of the image carriers are formed sequentially on a recording material carried on the belt. Each of the image forming means includes an image carrier for carrying an image, a plurality of color images on each of the image carriers are sequentially formed on the belt body, and the plurality of color images on the belt body are a recording material. And are sequentially transferred. The control unit controls the timing of starting forming a plurality of color images on each of the image carriers based on the time measured by the measuring unit. The belt member is a photoreceptor, and each of the image forming units sequentially forms a plurality of color images on the photoreceptor, and the plurality of color images on the photoreceptor are transferred to a recording material. The control unit controls the timing of starting to form images of a plurality of colors on the photoconductor based on the time measured by the measurement unit.

There is provided cleaning means for cleaning the belt member by contacting the belt member. The cleaning means includes a blade. The drive roller includes a rubber on a surface supporting the belt body. And a driving unit for applying a driving force to the driving roller. The driving means includes a pulse motor.

Further, according to the present invention, there is provided a belt member, a driving roller for supporting the belt member and transmitting a driving force to the belt member, and a recording material carried on the belt member or the belt member having a plurality of colors. In an image forming apparatus having a plurality of image forming means for forming images in a superimposed manner, a measuring means for measuring a time required for the belt body to move a predetermined distance, and a time measured by the measuring means, A control unit for controlling a rotation speed of the driving roller.

According to the present invention, there is provided storage means for storing a target time at which the belt body moves by the predetermined distance, and the control means stores the time measured by the measuring means in the storage means. The rotation speed of the drive roller is controlled so as to reach the target time. The measuring means,
The control unit controls the rotation speed of the driving roller based on an average value of the plurality of times measured by the measuring unit. The measuring means measures the time for the belt body to move the predetermined distance a plurality of times, and the control means determines a rotation speed of the drive roller based on an average value of the plurality of times measured by the measuring means. Control.

[0028]

Embodiments of the present invention will be described below in more detail with reference to the drawings.

Embodiment 1 FIG. 1 shows an electrophotographic image forming apparatus to which the present invention is applied, and a tandem type color copy in which four color toners of yellow, magenta, cyan and black are superposed to form a full-color image. Machine.

In FIG. 1, reference numeral 8 denotes a recording material carrier as a belt, that is, a transfer belt, 10Y, 10M,
Reference numerals 10C and 10K denote yellow, magenta, cyan, and yellow, respectively, arranged on the transfer belt 8 along the transport direction.
An image forming unit (image forming unit) as a black image forming unit. Each image forming unit 10Y, 10M,
10C and 10K have photosensitive drums 13Y, 13M, 13C and 13K above the transfer belt 8, respectively.

After the recording paper as the recording material stored in the cassette 1 is fed by the paper feed roller 2, it is conveyed to the registration roller 7 by the conveyance roller 3. The recording paper is sent out toward the transfer belt 8 at an appropriate timing by correcting skew and the like by the registration roller 7. Transfer belt 8
Is made of an insulating resin sheet material, and is driven by a pulse motor 22 via a driving roller 21. 11
Y, 11M, 11C and 11K are transfer chargers for charging the transfer belt from below the transfer belt 8.

During this time, an original reading device (not shown)
Alternatively, the photosensitive drums 13 </ b> Y, 13 </ b> Y may be provided by image information signals transmitted from an output device (not shown) such as a computer.
Electrostatic latent images corresponding to each color are formed on the surfaces of M, 13C, and 13K. The recording paper sent out from the registration roller 7 is electrostatically attracted onto the charged transfer belt 8, and does not peel off or shift from the transfer belt 8 during conveyance, and the image forming units 10 </ b> Y, 10 </ b> M, The paper is conveyed below 10C and 10K.

Each image forming unit 10 (10Y, 10Y
M, 10C, and 10K) are detachable from the apparatus main body as process cartridges, and as shown in FIG. 2, the photosensitive drums 13 (13Y, 13M, 13C, 13C).
Around K), a primary charger 14, a developing device 16, and a cleaner 17 are arranged. The surface of the photosensitive drum 13 is charged by a primary charger 14, exposed by each LED array 15 as exposure means fixed to the image forming unit main body, and the latent image formed by exposure is developed by a developing device 16. Thus, a toner image of each color is formed on the surface of the photosensitive drum 13 by the electrophotographic process.

The toner images of the respective colors formed on the photosensitive drum 13 are transferred to the respective transfer chargers 11 (11Y, 11Y,
1M, 11C, 11K).

The recording paper on which the toner images of the four colors of yellow, magenta, cyan, and black have been transferred in this manner is separated from the transfer belt 8 by the separation charger 12,
The fixing roller pair 18 and 19 are reached. One fixing roller 1
8 is heated by a heater (not shown), and is heated by the fixing roller 18 and the other fixing roller 19.
By pressing, the toner of each color is melted by heat and fixed on the recording paper to complete a full-color image. The recording paper on which the toner image has been fixed is discharged onto a discharge tray 20 protruding outside the apparatus. Unnecessary matters such as toner adhered to the transfer belt 8 are scraped off by the cleaning blade 30 and collected.

As shown in FIG. 3, the transfer belt 8 is formed in a transfer unit 23 together with a driving roller 21 and the like.

In the present embodiment, the diameter of the drive roller 21 is 29.9 mm, the thickness of the transfer belt 8 is 0.1 mm,
The pitch circle diameter of the transfer belt 8 is 30 mm. In order to eliminate the influence of the eccentricity of the drive roller 21 driven by the motor 22, each image forming unit 10 is separated by a distance equal to the circumference of the drive pitch circle of the transfer belt 8, that is, by 30 × π mm, as described above. It is arranged.

The designed image forming speed (= transfer belt conveying speed) is 100 mm / sec, and one circumference of the belt 8 is 1 mm.
000 mm.

According to the present invention, as shown in FIG. 3, the mark 24 is printed on the inner peripheral surface of the transfer belt 8 at one arbitrary position at the end along the conveying direction.
The passage of the mark 24 (the passage of the transfer belt 8 at a fixed position) can be detected by the detecting means 25 provided at 3. In this embodiment, since the transfer belt 8 is translucent,
A light transmission type photo interrupter is installed as the detection means 25, and this is arranged on the lower track of the transfer belt 8 so as to sandwich the end of the transfer belt 8 so as to detect the passage of the mark 24. .

The measurement of the passage interval of the mark 24 will be described. The transfer belt 8 is driven by the drive roller 21 in the non-image forming state, and after the first passage of the mark 24 is detected, the next passage of the mark 24 is performed. Time to be detected,
That is, the mark 24 corresponding to the transfer speed of the transfer belt 8
The time of the passage interval is measured by a counter. This operation is continuously performed while the transfer belt 8 makes 11 rotations.
A total of ten time data at the passage intervals of 4 are obtained. 10 above
The times of the passing intervals are averaged and stored in the storage means 26 as mark passing interval data.

As described above, by measuring the time for the transfer belt 8 to make one rotation as the minimum unit, the drive roller 21
Even if there is eccentricity, the time required for the belt to make one rotation can be accurately known.

In the present invention, first, at the time of adjustment and shipment of the image forming apparatus product at the factory, the time of the passage interval of the mark 24 of the transfer belt 8 in the shipment state is measured, and the data of the passage interval is set as the initial value of the apparatus. It is stored in the storage means 26. In this state, the image forming apparatus is adjusted so that the color shift in the paper feeding direction caused by errors in the diameter of the drive roller 21, the thickness of the transfer belt 8, the position of each image forming unit, and the like is minimized. .

The initial value of the passage interval is designed so that the circumference of the transfer belt 8 is 1000 mm and the belt conveyance speed is 100 mm.
/ S, which should be 10 seconds. However, due to the influence of the circumference of the transfer belt 8, the diameter of the drive roller 21, the thickness of the transfer belt 8, and the like, the actually measured value (the average value of the ten belts) is 1022
5453 μsec (10.225453 sec) was obtained.

Next, after the product is shipped, the number of image formed sheets is N × 50,000 (N is an integer) in a state of being used by the user.
Each time the first image formation is completed, the passage interval of the mark 24 on the transfer belt 8 is measured.

The actual measured value (average value of 10 marks) of the mark passage interval after the formation of the first 50,000 images is 10226.
267 microseconds (10.226267 seconds) were obtained. The passage interval of the mark 24 is extended by 814 μsec as compared with the time of shipment. This is because the effective driving radius of the transfer belt 8 by the drive roller 21 (the radius of the pitch circle) is reduced due to the abrasion of the drive roller 21 and the transfer belt 8, and the transfer speed of the transfer belt 8 is reduced.

Therefore, the four image forming units 10
If an image is formed at the same timing as the initial time at Y to 10K and the toner images of each color are transferred onto the recording paper conveyed by the transfer belt 8, a color shift occurs in the obtained color image. In view of this, the timing of image formation, that is, the timing of image exposure to each of the photosensitive drums 13Y to 13K is corrected based on the delay of the mark passing interval, so that the color shift is eliminated.

In the present embodiment, the correction process from the measurement of the mark passage interval to the exposure timing correction is previously incorporated in the image forming apparatus as a program, and is automatically executed.

FIG. 4 shows the flow of the above correction process. When the measurement mode is selected and the correction process is started, the transfer belt 8 is driven by the driving roller 21 in a non-image forming state.
Is driven, and when the first passage of the mark 24 is detected by the detecting means 25, the passage interval time T until the next passage of the mark 24 is detected is measured by a counter (step S1). This operation is continuously performed while the transfer belt 8 makes 11 rotations, and the operation is performed until a total of ten pieces of time data T of the passage interval of the mark 24 are obtained (S2).

When ten times T of the passage intervals are obtained, they are averaged to obtain T1 as measurement data of the passage intervals (S3). Next, the data T0 (initial value) of the mark passing interval at the time of shipping stored in the storage means 26 is read out (S4) and compared with the measured data T1, and the time increment of the passing interval = T1-T0 (second) is calculated. Calculation is performed (S5).

As described above, the mark passing interval T1 measured after the first 50,000 images have been formed is 10222626.
7 μs, the interval between marks 24 is 8
It extends for 14 μs.

Based on the result, each image forming unit 1
The exposure start timing of 0 is corrected. When the transfer speed of the transfer belt 8 decreases, the leading image forming unit 10Y
In contrast, by sequentially sending the image forming start timings of the downstream image forming units 10M to 10K, the color misregistration amount can be corrected.

In the initial state at the time of shipment, the exposure interval from the first image forming unit 10Y to the second image forming unit 10M is Tym, and the third 10C from the first 10Y.
Exposure interval to Tyc, from the first 10Y to the fourth 10Y
The exposure interval up to M is Tyk.

Since the data of these initial exposure intervals Yym to Tyk are stored in the storage means 26, they are read out in step S6, and new exposure intervals Tym, Tyc, Tyk are calculated in step S7. This is stored and set in the storage means 26 in step 8 as the exposure interval after correction.

The new exposure interval is the diameter D of the driving roller 21, the thickness T of the transfer belt 8, the circumferential length L of the transfer belt 8 (design center value), the interval π × between the image forming units 10. D + T), a new Tym = Tym + 1 × (T1-T0) × π × (D +
T) / L New Tyc = Tyc + 2 × (T1-T0) × π × (D +
T) / L New Tyk = Tyk + 3 × (T1-T0) × π × (D +
T) / L.

That is, according to the passage interval of the mark 24 measured this time, each of the image forming units 10M, 10C and 10K from the first image forming unit 10Y to 77K.
Exposure is started with a delay of μ seconds, 153 μ seconds, and 230 μ seconds.

By the above operation, the transfer speed of the transfer belt 8 is set to (T1−T0) /T0×100=0.0 from the time of shipment.
In the state after image formation of 50,000 sheets, which is reduced by 08% compared to the initial state, it was possible to recover to the initial state in which the amount of color misregistration is almost 0.

Immediately before this correction process is performed, the conveyance speed of the transfer belt 8 is reduced by only 0.008%, so that 3 × π × (D +
T) × 0.008 / 100 = 0.023 mm, that is, a color shift of about 23 μm occurs. Therefore, when this correction is not performed, if the abrasion of the drive roller 21 and the transfer belt 8 proceeds as is, a color shift of about 100 μm occurs when 200,000 sheets of image formation are performed (about 2 pixels at 600 dpi). ).

In the above embodiment, the example in which the correction is performed based on the number of image formations of the apparatus has been described. However, the present invention is not limited to this. For example, the correction is performed for each elapsed time such as every predetermined number of days. It can be carried out. Further, the correction may be made by the operator at any time. In addition to the automatic correction, the correction can be performed by an operator.

Embodiment 2 FIG. 5 is a flowchart showing a correction process according to another embodiment of the present invention. The basic configuration of the image forming apparatus according to the present embodiment is the same as that of the first embodiment, and a description thereof will not be repeated.

In the first embodiment, the passage interval is measured from the detection of the passage of the mark 24 on the transfer belt 8 by the detection means 25,
Based on this, the exposure start timing of each image forming unit 10 is corrected to reduce the amount of color misregistration caused by wear of the drive roller 21 and the transfer belt 8.

In this embodiment, the mark 24 on the transfer belt 8 is
The transfer speed of the transfer belt 8 is further calculated from the passing interval of the transfer belt 8, and based on this, the rotation angular speed of the drive roller 21 is changed, that is, by changing the rotation speed of the drive roller 21, the transfer speed of the transfer belt 8 is changed. The speed was corrected to the initial value, and the amount of color misregistration caused by wear of the drive roller 21 and the transfer belt 8 was reduced.

In this embodiment, as in the first embodiment, the diameter of the drive roller 21 of the transfer unit 23 shown in FIG. 3 is 29.9 mm, the thickness of the transfer belt 8 is 0.1 mm, The pitch circle diameter is 30 mm. Similarly, in order to eliminate the influence of the eccentricity of the drive roller 21, the image forming units 10 are also arranged at a distance of 30 × πmm equal to the circumference of the pitch circle of the transfer belt 8, and the designed image forming speed ( The transfer belt conveyance speed) is 100 mm / sec, and one circumference of the transfer belt 8 is 1000 mm.

Similarly, the detection means 25 installed on the lower track of the transfer belt 8 detects the passage of the mark 24 formed at one end of the inner peripheral surface of the transfer belt 8 along the transport direction. The measurement is performed at the time of the adjustment shipment of the image forming apparatus product at the factory and after every 50,000 sheets of image formation. At each measurement, time data of 10 passage intervals are obtained, and these are averaged and handled as data of the passage intervals at each measurement. The data of the passage interval is stored in the storage means 26 of the apparatus. The measured value (initial value) of the passage interval of the mark 24 at the time of shipment was 10225434 μsec.

Further, when the image forming apparatus is adjusted and shipped at a factory, the image forming apparatus is caused by errors in the diameter of the drive roller 21, the thickness of the transfer belt 8, the position of each image forming unit, and the like in a shipping state. The color shift in the paper feed direction is adjusted to be minimum.

In this embodiment, the driving roller 2 shown in FIG.
A five-phase pulse motor of 2000 pulses / 1 rotation was used as one motor 22, and the drive roller 21 was driven at a 1/4 reduction ratio. Therefore, the image forming speed of the design value 1
In order to obtain 00 mm / sec, the driving frequency must be 8488.
26 Hz, which is set as the initial value of the drive frequency corresponding to the initial value of the transport speed of the transfer belt 8 and stored in the storage means 26.

The correction process according to this embodiment will be described with reference to FIG.

In the same procedure as in the first embodiment, the time T of the passage interval of the mark 24 while the transfer belt 8 makes 11 revolutions is continuously measured, and the time data T of the passage interval of the mark 24 is counted by 10 in total. Are obtained (steps S1 and S2), and the ten passing intervals T are averaged to obtain T1 as the passing interval measurement data.
Is obtained (S3).

The passage interval T1 of the mark measured after the first 50,000 sheets of image formation was 1,226,267 μsec, and the passage interval of the mark 24 was extended by 833 μsec as compared with the time of shipment. Due to the wear of the belt 8,
The effective driving radius of the transfer belt 8 has decreased, and the transport speed of the transfer belt 8 has decreased.

Accordingly, a color shift occurs in the color image formed on the recording paper on the transfer belt 8 as it is. In this embodiment, the angular velocity of the drive roller 21 is corrected and the transport speed of the transfer belt 8 is reduced. Modify to the initial state.

The drive roller 21 is provided with a rubber layer on its surface in order to transmit the rotational drive force to the transfer belt 8 without slippage. Therefore, by correcting the rotation speed (each speed) of the drive roller 21, the rotation speed of the transfer belt 8 can also be properly corrected.

First, the data T0 (initial value) of the mark passing interval at the time of shipping stored in the storage means 26 is read out (S4), and compared with the measurement data T1, the time increase rate of the passing interval = (T1-T0). ) / T0 (%) is calculated (S
5). Next, the current drive frequency F (initial value) is read out (S6), and a value ΔF (Hz) obtained by multiplying this by the time increase rate (T1-T0) / T0 obtained in step S5 is calculated. This is set as a new drive frequency F in addition to F (S7). That is, new F = F + (T1−T0) / T0 × F.

That is, since 8488.26 Hz was set as the value of the drive frequency F at the time of shipment, ΔF =
(T1−T0) /T0×F=0.69 Hz is obtained, and the new drive frequency F increases by 0.69 Hz, and F = 8
488.26 + 0.69 = 8.8488.95 Hz.

In step S8, the new driving frequency F
Is set as the corrected drive frequency and stored in the storage means 26. As a result, the subsequent drive roller 21
By increasing the drive frequency of the pulse motor 22 by 0.69 Hz to increase the rotational speed (angular speed) of the drive roller 21 itself, the transfer belt decreased due to wear of the diameter of the drive roller 21 and the thickness of the transfer belt 8. The transport speed of 8 is corrected to the initial value.

Thereafter, similar to the first embodiment, the image formation
The above process is repeated every time the number of prints reaches an integral multiple of ten thousand sheets, and the occurrence of color misregistration is always maintained at a certain value or less even if the diameter of the drive roller 21 or the thickness of the transfer belt 8 changes due to wear.

In the above, the case where the drive roller 21 is driven by the pulse motor 22 has been described as an example. However, the present invention is not limited to this. For example, the drive roller is driven at a constant speed by PLL control by a DC servo motor. The case can also be applied. That is, if the frequency of the reference pulse compared with the encoder pulse is changed in the above-described process, the control target value of the PLL control can be changed, and the angular velocity of the drive roller can be set arbitrarily.

Embodiment 3 FIG. 6 shows still another embodiment of the image forming apparatus to which the present invention is applied.

The image forming apparatus of this embodiment is of an intermediate transfer type, and is an intermediate transfer belt as a belt member which is wound around a driven roller 302, a transfer roller 303 and a drive roller 304 and is rotated in the direction of arrow A. 301.
On the intermediate transfer belt 301, four-color image forming units 10Y, 10Y each having photosensitive drums 306Y, 306M, 306C, and 306K along the moving direction.
M, 10C, and 10K are arranged side by side to transfer toner images of respective colors formed by the image forming units of respective colors to the intermediate transfer belt 301.
The toner image is superimposed on the recording material, and the toner images of the respective colors are collectively transferred onto a recording material.

The distance between the image forming units 10Y to 10K has the same relationship as that of the first embodiment with respect to the thickness of the intermediate transfer belt 301 and the diameter of the drive roller 304, and the basic operation is the same. Detailed description is omitted. The image forming process is as follows.

The photosensitive drums 306C, 306M, 306M, 306M,
Electrostatic latent images corresponding to the respective colors are formed on the image transfer rollers 06Y and 306K, and toner images of the respective colors developed by the developing devices (not shown) are transferred onto the intermediate transfer belt 301 by transfer chargers 307Y, 307M and 307C. , 307K, and the images are transferred in a superimposed manner.
A full color image is formed thereon.

On the other hand, the recording paper is corrected for skew and the like by the registration roller 309, and is sent out to the transfer portion of the intermediate transfer belt 301 where the transfer roller 303 is located at a predetermined timing in synchronization with the image forming process. The four color toner images on the intermediate transfer belt 301 are collectively transferred onto the recording material by the inner transfer roller 303 and the outer charger 311.

The recording paper on which the four color toner images have been transferred is
The fixing roller pair 316 is conveyed by the conveying belt 312.
Reach The fixing roller 316 includes a heater (not shown)
, And the toner of each color is melted by heating and pressurizing, and is fixed on the recording paper to complete a full-color image. The recording paper on which the toner image has been fixed is discharged outside the apparatus.

Also in this embodiment, since the full-color image is formed by sequentially superimposing the toner images created by the plurality of image forming units on the intermediate transfer belt 301, the thickness of the intermediate transfer belt 301 and the diameter of the driving roller 304 are reduced. If it changes due to wear, the speed of the intermediate transfer belt 301 fluctuates, and a color shift occurs in a full-color image formed on the intermediate transfer belt 301.

Therefore, according to the present embodiment, at a predetermined time, a mark provided on the intermediate transfer belt 301 is detected, and the passage interval of the mark is measured. Is performed, the color shift can be eliminated to a certain value or less.

Embodiment 4 In this embodiment, as shown in FIG. 7, a driven roller 402, a transfer roller 403 and a drive roller 40 are used as image carriers.
The image forming unit 400 </ b> Y of four colors of yellow, magenta, cyan, and black is configured to include the photosensitive belt 401 along the moving direction of the photosensitive belt 401. , 4
00M, 400C, and 400K are provided side by side. Each of the image forming units 400Y to 400K includes a primary charger 406, an image exposure device 407, a developing device 408, and the like.

An image information signal sent from an original reading device (not shown) or an output device (not shown) such as a computer causes the image forming units 400Y to 400K on the photosensitive belt 401 to correspond to the respective colors. An electrostatic latent image is formed, and each latent image is sequentially developed by each developing unit 408 to form a color image in which toner images of each color are superimposed on the photosensitive belt 401.

The recording paper is corrected by a registration roller 410 for skew and the like, and sent out via a guide 411 to the transfer portion of the photosensitive belt 401 where the transfer roller 403 is located at a predetermined timing in synchronization with the image forming process. It is.
The four color toner images on the photosensitive belt 401 are collectively transferred onto recording paper by the inner transfer roller 403 and the outer charger 412.

The recording paper after the transfer is conveyed by the conveyance belt 413 and reaches the fixing roller pair 417. The fixing roller 417 is heated by a heater (not shown), and the toner of each color is melted by heating and pressurizing and is fixed on the recording paper to complete a full-color image. The recording paper on which the toner image has been fixed is discharged outside the apparatus.

Also in this embodiment, a plurality of image forming units 4
00Y to 400K, the toner image of each color is
01 to form a full-color image on the photosensitive belt 401,
When the thickness of the roller 1 and the diameter of the driving roller 404 change due to abrasion and the speed of the photosensitive belt 401 fluctuates, a color shift occurs in a full-color image formed on the photosensitive belt 401.

Therefore, similarly to the first to third embodiments, at a predetermined time, a mark provided on the photosensitive belt 401 is detected, a passage interval of the mark is measured, and a similar correction process is executed. Thus, the color shift can be reduced to a certain value or less.

In the above embodiment, an example has been described in which the transport speed of the belt when measuring one cycle of the belt is equal to the image forming speed. However, the transport of the belt when measuring one cycle is described. The speed and the image forming speed may be different.

For example, by making the conveying speed of the belt body smaller than the image forming speed when measuring one cycle of the belt body, the relative detection accuracy of the measured time is improved. That is, it is preferable to detect the time required for the belt body to make one revolution at a predetermined resolution, so that the error caused when the running speed of the belt body is slower is reduced.

Further, there is an apparatus having a plurality of image forming speeds according to the type of recording material on which an image is formed. this is,
As is well known, a press sheet having a relatively thin recording material (normal mode), a relatively thick sheet (thick paper mode), an OHP
And transparent resin sheets (OHP mode)
The appropriate fixing conditions of the toner to the recording material are different depending on the difference in heat capacity, and the fixing speed is reduced in the order described above. 1/3 for thick paper
And a fixing rate of 1/4 for a transparent resin sheet is preferred). In this case, the image formation is performed such that the speed at which the image is formed (the conveying speed of the belt member, the rotation speed of the photosensitive drum, etc.) is substantially equal to the fixing speed.

In such an apparatus having a plurality of image forming speeds (fixing speeds), when measuring one cycle of the belt body, the belt body is moved at a speed other than the speed in the normal mode.
That is, it is preferable to convey at a speed in the thick paper mode or the OHP mode. Of course, among the above three modes,
It goes without saying that the OHP mode is optimal. With such a configuration, it is not necessary to set the conveying speed of the belt body for measuring one cycle of the belt body, and the amount of information stored in the ROM as the storage means can be reduced.

In the above embodiment, the time taken for the belt to make one revolution is measured. However, the present invention is not limited to this. Two marks are provided on the belt and detected by the passage detecting means. By comparing with the above, the above-described correction control of the exposure timing and the rotation speed of the driving roller may be performed. With such a configuration, it is possible to reduce the time required for the detection sequence for detecting the time during which the belt body moves. Naturally, the passage detecting means (sensor) and the mark are arranged only at one end (front side) of the belt body. However, for example, both sides of the front side and the back side (both ends in the direction substantially orthogonal to the belt conveyance direction) ), The marks are displaced from each other in phase (displaced from each other), and the time from when the front mark is detected by the passage detection means to when the back mark is detected by the passage detection means is It may be measured.

In the above embodiment, one cycle of the belt body was measured using a belt body provided with a mark in advance. However, the present invention is not limited to this. It is good also as a structure which detects by a detection means. For example, in a configuration in which two detection toner images are formed on the belt body and the passage time of the belt body is measured by one sensor, the two detection toner images are formed on the belt body at predetermined time intervals. The time from when the sensor starts detecting the toner image for one detection until the end of the detection of the toner image for the other detection is stored in the storage means as a target time, and in performing the correction control, The measured passing time of the belt body is compared with the target time.

However, in performing the above-described correction control, it is more preferable that a mark is provided on the belt body in advance than when a toner image is formed on the belt body. This is because the toner image for detection formed on the belt member is not formed well, and the toner image may be scattered, and the detection accuracy by the detection unit is reduced.

[0097]

As described above, according to the present invention,
A mark or the like is formed at an arbitrary fixed position on the belt body, the passage of the fixed position of the belt body is detected by detecting the mark or the like by an optical detection unit, and a passage interval of the fixed position is measured. Compare the passage interval of the belt body with the initial value,
Based on the comparison result, the image forming start timing and the like in a plurality of image forming units arranged side by side in the movement direction of the belt body are controlled to be corrected, so that the thickness of the belt body and the change in the diameter of the drive roller due to wear are reduced. Even if it does, the amount of color misregistration can be maintained below a certain value, and the control cost can be reduced because no detection means such as a high-resolution encoder is required.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of an image forming apparatus of the present invention.

FIG. 2 is a cross-sectional view illustrating each image forming unit of the image forming apparatus of FIG.

FIG. 3 is a perspective view illustrating a transfer unit of the image forming apparatus of FIG. 1;

FIG. 4 is a flowchart showing a correction process performed in the embodiment of FIG. 1;

FIG. 5 is a flowchart showing a correction process performed in another embodiment of the present invention.

FIG. 6 is a sectional view showing still another embodiment of the image forming apparatus of the present invention.

FIG. 7 is a sectional view showing still another embodiment of the image forming apparatus of the present invention.

[Explanation of symbols]

 Reference Signs List 8 transfer belt 10, 10Y to 10K image forming unit 13, 13Y to 13K photosensitive drum 21, 304, 404 drive roller 22 motor 23 transfer unit 24 mark 25 passage detection means 26 storage means 301 intermediate transfer belt 401 photosensitive belt

Claims (39)

[Claims] 1. A belt body, a driving roller supporting the belt body and transmitting a driving force to the belt body, and superimposing images of a plurality of colors on the belt body or a recording material carried on the belt body, respectively. A plurality of image forming means, a measuring means for measuring a time required for the belt body to move a predetermined distance, and the belt member or the belt means by each of the image forming means based on the time measured by the measuring means. An image forming apparatus comprising: a control unit that controls timing for forming a plurality of color images on a recording material carried on a belt member. 2. A storage means for storing a target time at which the belt body moves by the predetermined distance, wherein the control means comprises:
Based on the difference between the target time stored in the storage means and the time measured by the measurement means, a plurality of color images are formed on the belt member or the recording material carried on the belt member by the image forming means. The image forming apparatus according to claim 1, wherein the control unit controls the timing of starting each of the image forming processes. 3. The measuring means measures a time taken for the belt body to move the predetermined distance a plurality of times, and each of the image forming means measures an average value of the plurality of times measured by the measuring means. 2. The image forming apparatus according to claim 1, wherein timings at which each of the image forming means starts forming a plurality of color images on the belt or a recording material carried on the belt is controlled. 4. The measuring means includes a sensor for detecting one mark provided on the belt body. After the sensor detects a mark on the belt body, the mark on the belt body is changed to a next mark. The image forming apparatus according to claim 1, wherein a time until the detection is performed is measured. 5. The measuring means includes a sensor for detecting a plurality of marks provided on the belt body, and after the sensor detects a first mark on the belt body, the measuring means detects the first mark on the belt body. The image forming apparatus according to claim 1, wherein a time until the second mark is detected is measured. 6. The measuring means includes a sensor for detecting a detection image formed on the belt body by the image forming means, and the sensor detects a detection image on the belt body. 2. The image forming apparatus according to claim 1, wherein a time until the next detection image on the belt body is detected is measured. 7. The measuring means includes a sensor for detecting a plurality of detection images formed on the belt body by the image forming means, wherein the sensor is configured to detect a first detection image on the belt body. The image forming apparatus according to claim 1, wherein a time period from when the image is detected to when a second detection image on the belt body is detected is measured. 8. The moving speed of the belt body is measured by the measuring means while the time required for the belt body to move by a predetermined distance is measured by the recording means carried by the image forming means on the belt body or the belt body. The image forming apparatus according to any one of claims 1 to 7, wherein the speed is switched to a speed lower than a moving speed of the belt when a plurality of color images are formed on the material. 9. When the moving speed of the belt is a first moving speed, a plurality of color images are sequentially formed on the belt or a recording material carried on the belt by the respective image forming means. In the first mode, when the moving speed of the belt member is a second moving speed lower than the first moving speed, a plurality of colors are applied to the belt member or the recording material carried on the belt member by the image forming means. And a second mode in which the images are sequentially superimposed, and while the measuring unit measures the time for the belt body to move the predetermined distance, the movement speed of the belt body is the second movement. The image forming apparatus according to claim 1, wherein the speed is switched to a speed. 10. An image forming apparatus according to claim 1, wherein each of said image forming means includes an image carrier for carrying an image, and images of a plurality of colors on each of said image carriers are sequentially formed on a recording material carried on said belt. Item 10. The image forming apparatus according to any one of Items 1 to 9. 11. Each of the image forming means includes an image carrier for carrying an image, and images of a plurality of colors on each of the image carriers are sequentially formed on the belt body, and a plurality of colors on the belt body are formed. The image forming apparatus according to any one of claims 1 to 9, wherein the image is sequentially transferred onto a recording material. 12. The image forming apparatus according to claim 10, wherein the control unit controls a timing of starting forming a plurality of color images on each of the image carriers based on the time measured by the measuring unit. . 13. The belt member is a photosensitive member, and each of the image forming means sequentially forms a plurality of color images on the photosensitive member, and transfers the plurality of color images on the photosensitive member to a recording material. The image forming apparatus according to claim 1, wherein: 14. The controller according to claim 13, wherein the controller controls timing for starting to form a plurality of color images on the photoconductor based on the time measured by the measuring unit.
Image forming apparatus. 15. A cleaning device for cleaning the belt member by contacting the belt member.
15. The image forming apparatus according to any one of items 14 to 14. 16. The image forming apparatus according to claim 15, wherein said cleaning means includes a blade. 17. The image forming apparatus according to claim 1, wherein the driving roller has a rubber on a surface supporting the belt body. 18. The image forming apparatus according to claim 1, further comprising a driving unit that applies a driving force to the driving roller. 19. The image forming apparatus according to claim 18, wherein said driving means includes a pulse motor. 20. A belt body, supporting the belt body,
An image forming apparatus comprising: a driving roller that transmits a driving force to the belt body; and a plurality of image forming units configured to form a plurality of color images on the belt body or a recording material carried on the belt body, respectively. An image forming apparatus comprising: a measuring unit configured to measure a time required for the belt body to move a predetermined distance; and a control unit configured to control a rotation speed of the driving roller based on the time measured by the measuring unit. apparatus. 21. A storage unit for storing a target time at which the belt body moves by the predetermined distance, wherein the control unit stores the target time stored in the storage unit by a time measured by the measurement unit. 21. The image forming apparatus according to claim 20, wherein the rotation speed of the driving roller is controlled so as to satisfy the following. 22. The measuring unit measures the time for the belt body to move the predetermined distance a plurality of times, and the control unit determines the time based on an average value of the plurality of times measured by the measuring unit. 22. The image forming apparatus according to claim 20, wherein the rotation speed of the driving roller is controlled. 23. The measuring means measures the time for the belt body to move the predetermined distance a plurality of times, and the control means based on an average value of the plurality of times measured by the measuring means, 22. The image forming apparatus according to claim 20, wherein the image forming apparatus controls a rotation speed of the driving roller. 24. The measuring means includes a sensor for detecting one mark provided on the belt body. After the sensor detects a mark on the belt body, the mark on the belt body is changed to a next mark. The image forming apparatus according to any one of claims 20 to 23, wherein a time until detection is performed is measured. 25. The measuring means includes a sensor for detecting a plurality of marks provided on the belt body, and after the sensor detects a first mark on the belt body,
24. The image forming apparatus according to claim 20, wherein a time until a second mark on the belt body is detected is measured. 26. The measuring means comprises a sensor for detecting a detection image formed on the belt body by the image forming means, and the sensor detects a detection image on the belt body. The image forming apparatus according to any one of claims 20 to 23, wherein a time until a next detection image on the belt body is detected is measured. 27. The measuring means includes a sensor for detecting a plurality of detection images formed on the belt body by the image forming means, wherein the sensor is a first sensor on the belt body.
21. A time period from when the detection image is detected to when the second detection image on the belt body is detected.
24. The image forming apparatus according to any one of Items 23 to 23. 28. While the measuring unit measures the time required for the belt body to move a predetermined distance, the moving speed of the belt body is recorded by the image forming unit on the belt body or the recording carried on the belt body. The image forming apparatus according to any one of claims 20 to 27, wherein the speed is switched to a speed lower than a moving speed of the belt when a plurality of color images are formed on a material. 29. When the moving speed of the belt member is the first moving speed, a plurality of color images are sequentially formed on the belt member or a recording material carried on the belt member by the respective image forming means. In the first mode, when the moving speed of the belt member is a second moving speed lower than the first moving speed, a plurality of colors are applied to the belt member or the recording material carried on the belt member by the image forming means. And a second mode in which the images are sequentially superimposed on each other, and while the measuring unit measures the time required for the belt body to move the predetermined distance, the moving speed of the belt body is the second movement. The image forming apparatus according to any one of claims 20 to 27, wherein the speed is switched to a speed. 30. A driving unit for applying a driving force to the driving roller, wherein the control unit controls a driving force applied to the driving roller by the driving unit based on a time measured by the measuring unit. The image forming apparatus according to any one of claims 20 to 29. 31. The image forming apparatus according to claim 30, wherein the driving unit includes a pulse motor. 32. Each of the image forming means includes an image carrier for carrying an image, and images of a plurality of colors on each of the image carriers are formed sequentially on a recording material carried on the belt. Item 32. The image forming apparatus according to any one of Items 20 to 31. 33. Each of the image forming means has an image carrier for carrying an image, and a plurality of color images on each of the image carriers are sequentially formed on the belt body, and a plurality of color images on the belt body are formed. The image forming apparatus according to any one of claims 20 to 31, wherein the images are sequentially superimposed on the recording material and transferred. 34. The image forming apparatus according to claim 32, wherein the control unit controls a timing of starting forming a plurality of color images on each of the image carriers based on the time measured by the measuring unit. . 35. The belt member is a photosensitive member, and each of the image forming means sequentially forms a plurality of color images on the photosensitive member, and transfers the plurality of color images on the photosensitive member to a recording material. The image forming apparatus according to any one of claims 20 to 31, wherein the image forming apparatus comprises: 36. The controller according to claim 35, wherein the controller controls timing of starting to form images of a plurality of colors on the photoconductor based on the time measured by the measuring unit.
Image forming apparatus. 37. A cleaning device for cleaning the belt member by contacting the belt member.
The image forming apparatus according to any one of Items 0 to 36. 38. The image forming apparatus according to claim 37, wherein said cleaning means includes a blade. 39. The image forming apparatus according to claim 20, wherein the driving roller includes a rubber on a surface supporting the belt member.