JP2008233187A - Speed change detection apparatus, image forming apparatus and speed change detection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a speed change detection apparatus which is capable of detecting the high-frequency speed change of a photoreceptor, even when a high-resolution detection means is not used and is without useless toner consumption. <P>SOLUTION: A predetermined periodical latent image pattern is formed on a photoreceptor drum 1 as a latent image carrier. When the period of a latent image pattern is closer to the period of a speed change, a moire appears in the period longer than the original speed change period. The moire is detected by using an alternating current conversion type surface potential sensor 6, so that the high-frequency (=short period) speed change can be detected even by a surface potential sensor having a low resolution. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a technique for detecting a periodic speed fluctuation of a latent image carrier in an image forming apparatus.

JP 2005-338835 A JP-A-2005-17768

  In an image forming apparatus such as an electrophotographic copying machine, printer, facsimile machine, or printing machine, as one of abnormal images derived from the drive / conveyance mechanism, a belt-like density unevenness is periodically or randomly in the sub-scanning direction. There is a banding phenomenon that occurs.

  The main generation mechanism of the banding phenomenon is a vibration source in the drive system of the polygon mirror, the developing device, the fixing device, or the drive system of the photosensitive member or transfer body (transfer conveyance belt, intermediate transfer belt, etc.). It is considered that density unevenness is generated in any one of the exposure means, development and transfer processes, or in a combination of the respective processes due to the transmission of vibration from the photoconductor to the transfer body.

  As a countermeasure against this phenomenon, basically, reduction of vibration transmitted to the photosensitive member or the transfer member is most effective. In particular, the vibration transmitted to the photosensitive member becomes a fluctuation in speed and causes banding in all the steps of exposure means, development and transfer, and therefore needs to be reduced most.

  In order to reduce the speed fluctuation of the photoconductor, it is first necessary to measure what kind of speed fluctuation exists. Conventionally, in general, a rotary encoder is attached to the drive shaft of the photoconductor, or the end of the photoconductor is detected. For example, an end of a photoconductor is used as an encoder by detecting markings formed on the portion at regular intervals using an optical sensor or the like. In these methods, it is possible to detect the speed fluctuation of the photoconductor from the low frequency to the high frequency, but the high frequency speed fluctuation requires a high resolution as an encoder, which increases the cost.

  In Patent Document 1, a simpler sensor can be used to measure even high-speed (= short cycle) speed fluctuations (strictly speaking, in Patent Document 1, banding itself is measured instead of speed fluctuation of a photoconductor). Is disclosed.

  Patent Document 2 discloses an image forming apparatus in which a periodic speed fluctuation of a photosensitive drum is detected using a latent image pattern.

However, in the method described in Patent Document 1, a visible image such as a toner image is detected using an optical sensor, so that there is a problem that toner is consumed for each measurement.
In Reference 2, toner is not consumed for detection by using the latent image pattern. However, since a relatively long cycle of speed fluctuation of one drum rotation period is measured, one cycle of speed fluctuation is used. A large number of pattern latent images are drawn in the pattern, and the density transition of the pattern interval is detected. Accordingly, it is practically difficult to detect a speed fluctuation with a short period such as high-frequency banding by this method because the electrostatic latent image measuring means requires high resolution.

  The present invention solves the above-mentioned problems in the prior art, and can provide a speed fluctuation detecting means capable of detecting a high-speed speed fluctuation without using a high-resolution detecting means and without consuming unnecessary toner. Another object of the present invention is to provide an image forming apparatus and a speed fluctuation detection method.

  According to the present invention, in the speed fluctuation detecting device for detecting the periodic speed fluctuation of the latent image carrier, the periodic latent image pattern formed on the latent image carrier is converted into an AC conversion type surface potential sensor. This is solved by detecting a periodic speed fluctuation of the latent image carrier by using it to detect moire in the latent image.

Further, it is preferable that the period of the periodic latent image pattern is set in the vicinity of a known vibration period to be measured.
Moreover, it is preferable that the periodic latent image pattern is a pattern in which the period is changed stepwise for each of a plurality of predetermined periods.

The periodic latent image pattern is preferably a pattern in which lines extending in the main scanning direction of the latent image carrier form a line along the sub scanning direction.
Further, according to the present invention, the above-described problem is solved by an image forming apparatus including the speed fluctuation detection device according to any one of claims 1 to 4.

Further, it is preferable that vibration generation means is provided, and the vibration generation means generate vibration having a phase opposite to the periodic speed fluctuation of the latent image carrier detected by the speed fluctuation detection device.
Further, according to the present invention, in the speed fluctuation detecting method for detecting the periodic speed fluctuation of the latent image carrier, the periodic latent image pattern formed on the latent image carrier is converted into an AC conversion type surface potential sensor. This is solved by detecting the periodic speed fluctuation of the latent image carrier by detecting the moiré in the latent image using.

  According to the speed fluctuation detecting device of claim 1 and the speed fluctuation detecting method of claim 7, the high frequency (= short cycle) speed fluctuation in the latent image carrier is detected by using an AC conversion type surface potential sensor with a low area resolution. It can be detected with high accuracy and low cost. Further, toner or the like is not consumed for detection.

With the configuration of the second aspect, by setting the pattern used for detection in the vicinity of a known vibration (speed fluctuation) cycle, it is possible to effectively detect the resonance of the housing, the vibration of the gear, and the like.
According to the configuration of the third aspect, effective detection can be performed even when there are a plurality of speed fluctuation periods.

The configuration of claim 4 is also effective for detecting an unknown speed fluctuation period.
According to the image forming apparatus of the fifth aspect, it is possible to check the performance at the time of development / manufacturing by detecting the periodic speed fluctuation of the latent image carrier. It is also effective in identifying the cause when banding occurs during actual use.

  According to the configuration of the sixth aspect, it is possible to reduce the periodic speed fluctuation of the latent image carrier, reduce the banding generated in each step of exposure, development and transfer, and obtain a high quality image.

  In recent years, in the case of a mainstream digital electrophotographic apparatus, a halftone image is composed of spaced dots and lines. In the exposure process, it is considered that the period or width of the dots or lines of the latent image fluctuates due to the periodic speed fluctuation of the photoreceptor, and this is visible as banding after development.

  When a periodic pattern is formed with dots or lines, if the period is close to the period of speed fluctuation, an apparent density fluctuation called moire occurs in a period longer than the original speed fluctuation period. This is the same for both toner images and latent images. Therefore, if the moire generated on the latent image is read by the surface potential sensor, the period is 1 mm or less even with the resolution of the surface potential sensor (about 2 to 5 mm used in the current commercially available image forming apparatus). It becomes possible to detect a certain speed fluctuation.

  In most cases, the vibration that becomes the source of the speed fluctuation has a known period such as the resonance frequency of the casing and the pitch of the gear. Therefore, it is effective to set the period of the periodic pattern in the vicinity of such a known vibration (speed fluctuation) period.

When there are a plurality of known speed fluctuation periods, it is effective to prepare a plurality of periodic patterns corresponding to the respective speed fluctuation periods and sequentially form each latent image pattern.
As a specific example of the periodic pattern, a pattern in which line latent images extending in the main scanning direction form columns at equal intervals along the sub scanning direction is effective.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a configuration diagram showing the vicinity of an image forming unit in an example of an image forming apparatus provided with a speed fluctuation detecting device according to the present invention. In the present embodiment, the present invention will be described using a tandem drum configuration / intermediate transfer type multicolor / color image forming apparatus in which a plurality of image carriers (photoconductors) are arranged side by side along an intermediate transfer belt. Needless to say, the present invention can be applied to other configurations such as a direct transfer system as an image forming apparatus and a belt-shaped photoconductor as an image carrier.

  In FIG. 1, four image forming units 10 (Y, C, M, Bk) are arranged in parallel along the upper running side of an intermediate transfer belt 11 as an intermediate transfer member. The intermediate transfer belt 11 wound around the support rollers 12 and 13 is driven to run counterclockwise in the figure. The right support roller 13 is a transfer counter roller, and a secondary transfer roller 14 is pressed against the support roller 13 with the belt 11 interposed therebetween.

  Each image forming unit 10 has the same configuration except for the color of toner to be handled, and includes a photosensitive drum 1 as an image carrier as shown in detail in FIG. A charging unit 2, a developing device 3, a cleaning unit 4 and the like are arranged around the photosensitive drum 1, and a transfer roller as a primary transfer unit is disposed inside the intermediate transfer belt 11 so as to face each photosensitive drum 1. 5 is provided. In the rotational direction of the photosensitive drum 1 that is driven to rotate in the clockwise direction in the figure, a surface potential sensor 6 is disposed on the downstream side of the writing position where the scanning light L is irradiated and on the upstream side of the developing device 3. The surface potential sensor 6 will be described in detail later.

  An optical writing device 15 is provided above the four image forming units 10. When a laser exposure device is used as the optical writing device 15, the surface of the photosensitive drum 1 of each color image forming unit is irradiated with light-modulated laser light via a polygon mirror, a mirror group, or the like.

  A registration roller 16 is disposed below the secondary transfer portion where the support roller 13 and the secondary transfer roller 14 face each other (upstream side in the paper conveyance direction). A fixing device 17 is disposed above the secondary transfer portion. The fixing device is not limited to the heat roll system shown in the drawing, and a belt fixing device can also be used. Moreover, not only a heater heating system but an induction heating system can also be adopted.

An image forming operation in the image forming apparatus of this example configured as described above will be briefly described.
The photosensitive drum 1 of the image forming unit 10 is rotated in the clockwise direction in the drawing by a driving unit (not shown), and the surface of the photosensitive drum 1 is uniformly charged to a predetermined polarity by the charging unit 2. The charged photosensitive member surface is irradiated with scanning light from the optical writing device 15, thereby forming an electrostatic latent image on the photosensitive drum 1 surface. The potential of the formed latent image is confirmed by the surface potential sensor 6, and toner is applied from the developing device 3 to be visualized as a toner image. The image information exposed on each photosensitive drum 1 of each color image forming unit is monochromatic image information obtained by separating a desired full-color image into color information of yellow, magenta, cyan, and black.

  Further, the intermediate transfer belt 11 is driven to run counterclockwise in the figure, and the respective color toner images are sequentially transferred from the photosensitive drum 1 to the intermediate transfer belt 11 by the action of the primary transfer roller 5 in each image forming unit 10. In this way, the intermediate transfer belt 11 carries a full-color toner image on the surface thereof.

  Note that any one of the image forming units 10 can be used to form a single-color image or a two-color or three-color image. In the case of monochrome printing, image formation is performed using the black unit 10Bk among the four image forming units.

  Residual toner adhering to the surface of the photosensitive drum after the toner image is transferred is removed from the surface of the photosensitive drum by the cleaning unit 4, and then the surface is subjected to the action of a static eliminator (not shown) to obtain the surface potential. Is initialized to prepare for the next image formation.

  On the other hand, a sheet is fed from a sheet feeding tray (not shown), and is sent toward the secondary transfer position by the registration roller pair 16 in synchronization with the toner image carried on the intermediate transfer belt 11. In this example, a transfer voltage having a polarity opposite to the toner charging polarity of the toner image on the surface of the intermediate transfer belt is applied to the secondary transfer roller 14, whereby the toner image on the surface of the intermediate transfer belt is collectively transferred onto the sheet. . When the sheet on which the toner image has been transferred passes through the fixing device 17, the toner image is fused and fixed to the sheet by heat and pressure. The fixed paper is discharged to a paper discharge tray (not shown).

  The surface potential sensor 6 measures the surface potential of the photoconductor after exposure, and is used for correcting the charge amount in the charging means and correcting the exposure amount in the exposure means (writing device). For the correction, a rectangular solid pattern of about 1 to 2 cm square is usually used.

In the present invention, this surface potential sensor is also used for detecting the photosensitive member speed fluctuation. The latent image pattern used in this case has, for example, a form in which line latent images 20 extending along the main scanning direction form a line along the sub scanning direction as shown in FIG. This is a kind of so-called horizontal line pattern. Here, if the repetition cycle of the line is W _P and the speed fluctuation cycle of the photosensitive drum is W _V , the cycle is several times to several tens of times longer than the original speed fluctuation cycle when W _V ≈W _P. Moire occurs. However, when the _W V = _{W P,} the moire is not generated.

The reason will be briefly explained.
The occurrence of moire in the exposure means can be explained as follows in terms of geometry.

First, let us consider basic banding that does not involve moire.
In exposure by raster scanning with a laser beam, when the speed of the sub-scanning direction that varies for example 10%, whereas the line width W _L of one dot unit also does not vary 1% repetition period W _P lines Since it is simply proportional to the speed in the sub-scanning direction, it varies by 10%. Therefore, if there is a speed variation in the sub-scanning direction, the gap between the lines will increase or decrease. Here, both the period and the width are considered as the length in the sub-scanning direction. And, for example, and it outputs the halftone image in the horizontal line pattern of one-dot lines, so only the gap without the line width W _L variation varies, of course, the concentration varies when seeing from a long distance. That is, banding occurs.

If the horizontal line pattern is formed by two dots line or a thick line will vary even line width W _L by the sub-scanning direction of the velocity fluctuation. When the ratio of the variation amount with respect to the original length and variable rate, rate of change in the line width W _L As increasing the number of dots constituting the width of the line increases, approaching the rate of change in the repetition cycle WP of the line. From the above, when the sub-scanning direction speed fluctuation with the same amplitude is given, the density fluctuation of the horizontal line pattern composed of one dot line is most remarkable, and the density increases as the line width increases to 2 dots / 4 dots. The fluctuation becomes smaller.

Next, consider moire.
Moire is a kind of so-called “beat”, and when two different spatial frequency image patterns are given, it is a phenomenon that is visible as a density fluctuation of the spatial frequency corresponding to the difference between the two. thing always likely to be moire is also observed to choose the repetition period W _P of line appropriately in the pattern, but, so far, not been able to observe the moire only in the case of the above-described W _{V =} W _P. This is only the case, I think Averaging speed varies during the repetition period W _P of the line that it to become substantially zero. In this case, not the repetition period W _P of line fluctuations, since the line width WL is less than the speed fluctuation period WV at Sonoippo, speed be averaged in a period of the line width WL varies, the line width W _L Also fluctuate. For this reason, as in the case of banding in the horizontal dot pattern of one dot line described above, significant density fluctuations can occur.

When the speed fluctuation period W _V are known, the repetition period W _P lines, near the speed fluctuation period W _V, within 20% ± As a guideline, yet the period of the moire becomes detectable range surface potential sensor It is desirable to set as follows. On the other hand, the line width W _L, compared with the speed fluctuation period W _V sufficiently short, it is desirable as a guideline is 1/2 or less.

If a known velocity fluctuation period W _V there are a plurality, it has a latent image pattern having a repetition period W _P of the line corresponding to each of the speed fluctuation period W _V is required. For example, as shown in FIG. 4, it is effective to arrange them stepwise along the sub-scanning direction. In FIG. 4, latent image patterns 21, 22, and 23 corresponding to three types of speed fluctuation periods (W _V ) are assumed, but of course, there may be any number of speed fluctuation periods.

Additionally, in order to explore the unknown velocity fluctuation period W _V, stepwise enumeration of the latent image pattern as shown in FIG. 4 is valid. In this case, to comprehensively change the repetition period W _P of the line.

In the above manner, by detecting the moire, firstly it can be identified velocity fluctuation period W _V. The amplitude of the speed fluctuation can also be specified by the conversion formula based on the above-mentioned concept, but the relationship between the actual moire and the amplitude of the speed fluctuation is, for example, the overlap amount of the scanning line or the difference in the development process characteristics, etc. Therefore, it is more accurate and desirable to use it after comparing with other speed fluctuation measurement methods and obtaining a characteristic curve.

  The obtained speed fluctuation period and amplitude may be used for performance confirmation during development / manufacturing, and may also be used to identify the cause when banding occurs during user use. In addition, if the periodic speed fluctuation is highly reproducible, it is possible to control to reduce the speed fluctuation by generating an anti-phase vibration (with a vibration generator mounted on the image forming apparatus). Banding that occurs in each process of exposure, development, and transfer can be reduced due to fluctuations in the speed of the photoreceptor.

  Since the image forming apparatus is originally equipped with a surface potential sensor for the purpose of measuring the charging potential and latent image potential of the electrophotographic photosensitive member, this sensor is also used as a sensor for detecting the periodic speed fluctuation of the photosensitive member. It is possible to detect periodic speed fluctuations of the photoconductor with low cost and high accuracy without adding a new sensor or consuming toner by a toner mark or the like. Become.

Next, the AC conversion type surface potential sensor used in the present invention will be described.
FIG. 5 is a schematic diagram illustrating a configuration example of an AC conversion type surface potential sensor. In FIG. 5, reference numeral 31 denotes an object to be measured such as a photoreceptor having a charged surface. Reference numeral 32 denotes a chopper composed of a tuning fork type vibrator that oscillates electric force lines incident on the detection electrode 33 from the object to be measured 31 in the X direction for chopping. Reference numeral 34 denotes a preamplifier that impedance-converts and amplifies a minute alternating current signal induced in the detection electrode 33 and outputs a detection output to the terminal A. Reference numeral 35 denotes a shield case provided with a window 36 that transmits electric lines of force radiated from the object 31 to be measured, and is drawn in the shape of a plate for simplification, but houses the chopper 32, the detection electrode 33, and the like. Box-shaped or can-shaped. Reference numeral 37 denotes a piezoelectric element that vibrates by a driving power source (not shown) and vibrates the chopper 32 in the X direction. A temperature sensor 38 is attached to the chopper 32 and measures the temperature of the chopper. The temperature sensor 38 does not have to be attached in contact with the chopper 32 as shown, and may be disposed in a non-contact state in proximity to the chopper 32.

  When measuring the object to be measured 31 with this surface potential sensor, the surface potential sensor is attached at a position where the distance from the object to be measured 31 to the window 36 of the shield case is a distance of several millimeters. When the object to be measured 31 is charged, an electric field is transmitted to the detection electrode 33 via the window 36 and the chopper 32 of the shield case. At this time, the shield case 35 and the chopper 32 are kept at the ground potential. The chopper 32 vibrates so as to open and close the electric field path at a predetermined frequency by driving the piezoelectric element 37 (X direction in the figure). By this opening and closing, the output terminal A via the preamplifier 34 from the detection electrode 33 is shown in FIG. An alternating waveform like this is output.

Here, the amplitude A ₀ of the AC waveform in FIG. 6 is 1) the surface potential Ve of the object to be measured 31, 2) the distance from the surface of the object to be measured 31 to the detection electrode 33, that is, the detection distance d, and 3) the chopper 32. Depends on three fluctuation parameters of the vibration amplitude S. Therefore, in order to measure the surface potential Ve of the DUT 31, the detection distance d and the vibration amplitude S need to be known. For this reason, generally, the calibration is performed after the detection distance d and the vibration amplitude S are kept constant, and then the surface potential Ve at the same d and S is used for measurement.

Conversely, when the vibration amplitude S is constant, if the surface potential Ve of the object to be measured 31 is known, the detection distance d can be obtained from the detection output (amplitude A ₀ ).
At this time, the surface potential Ve of the DUT 31 is measured in advance by some other method. For example, the surface potential Ve can be known without any problem as long as the object to be measured 31 is at least on the surface and can be connected to a voltmeter. Even if the surface of the object 31 is in a float state, it will be described later. If the measurement is performed with an AC conversion type surface potential sensor to which the above feedback control is added, the surface potential Ve can be known almost independently of the detection distance d.

Although the vibration amplitude S may vary depending on the temperature change of the chopper 32, the chopper 32 is made of a low expansion coefficient material, or the temperature S is detected by the temperature sensor 38 and the amplitude S is predicted. or modify the actuator output amplitude S drives the chopper 32 to be constant, a ₀ is possible various corrections, such as the calculation of the detection distance d from dividing a ₀ is proportional to S by S It is.

  7 and 8 show a configuration example of an AC conversion type surface potential sensor to which feedback control is added. As apparent from the comparison with FIG. 5, the AC conversion type surface potential sensor to which this feedback control is added differs from the surface potential sensor shown in FIG. 5 in that the shield case 35, the chopper 32, and the preamplifier 34 are separated from the ground potential. The difference is that the floating state is connected to the terminal B and the terminal B is connected to the signal line B in FIG. 8 and fed back.

That is, the detection output A ₀ is extracted from the signal waveform at the terminal A by the synchronous detection circuit 40 in FIG. 8 and fed back to the terminal B in FIG. Since A ₀ extracted by the synchronous detection circuit 40 is proportional to the difference between the potential Ve of the DUT 31 and the potential of the terminal B, the potential of the feedback B gradually approaches Ve. Then, the potential of the terminal C when sufficiently asymptotically becomes the measured value of the true surface potential Ve of the device under test 31. At this time, A ₀ is almost 0, so even if the vibration amplitude S and the distance d are changed, they are hardly affected. Therefore, by using the AC conversion type surface potential sensor to which this feedback control is added, it is possible to measure the true surface potential regardless of the vibration amplitude S and the distance d.

  In addition, in the AC conversion type surface potential sensor to which this kind of feedback control is added, the whole is put in a floating state and feedback is applied from a high voltage amplifying unit using an insulating transformer, but this point is omitted here. ing.

  FIG. 9 shows a configuration example of an AC conversion type surface potential sensor capable of switching the presence or absence of feedback control. In this configuration example, a switch 37 for connecting the shield case 35 and the chopper 32 to the terminal B or the ground potential is provided. The other configuration is the same as the configuration example of FIG.

  The AC conversion type surface potential sensor as described above has an unprecedented feature in that it does not affect the potential measurement value even if the temperature or the distance of the object to be measured changes. It is used in a wide range of industrial fields including copying machines. On the other hand, it has the disadvantage that the area resolution is low (about 3 to 5 mm for a feedback surface potential sensor), so it has not been possible to detect fine density fluctuations (or potential fluctuations) like banding measurement. It was.

  In contrast, in the present invention, as described above, a high-resolution detection means is provided by detecting the moire of the latent image by the AC conversion type surface potential sensor using the latent image pattern as described in FIGS. Without being used, it is possible to detect a speed fluctuation at a high frequency of the photoconductor, and to provide a speed fluctuation detecting unit that does not consume useless toner and an image forming apparatus including the speed fluctuation detecting means. It was.

  As mentioned above, although this invention was demonstrated by the example of illustration, this invention is not limited to this. The configuration of the AC conversion type surface potential sensor is not limited to the illustrated example, and an appropriate one can be used. In addition, the latent image pattern used for detection is also an example, and the size and shape of the latent image, the number of repetitions, the period, and the like can be appropriately set according to the measurement target.

  The configuration of the image forming apparatus is also an example, and a direct transfer method is also possible. The latent image carrier is not limited to a drum shape but may be a belt shape. Of course, the image forming apparatus may be a printer, a copier, a facsimile machine, or a multifunction machine having a plurality of functions.

1 is a configuration diagram illustrating the vicinity of an image forming unit in an example of an image forming apparatus including a speed variation detection device according to the present invention. It is an enlarged view which shows the image forming unit in detail. FIG. 6 is a schematic diagram illustrating an example of a latent image pattern used for detecting a photoreceptor speed variation. It is a schematic diagram showing an example of a latent image pattern in which a plurality of line latent images extending in the main scanning direction are arranged in the sub scanning direction. It is a schematic diagram which shows the structural example of an AC conversion type surface potential sensor. It is a wave form diagram which shows the output waveform in the electric potential sensor. It is a schematic diagram which shows the structural example of the alternating current type | mold surface potential sensor which added feedback control. It is a circuit diagram which shows a feedback circuit. It is a schematic diagram which shows the structural example of the alternating current type | mold surface potential sensor which can switch the presence or absence of feedback control.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 3 Developing device 6 Surface potential sensor 10 Image forming unit 11 Intermediate transfer belt 15 Optical writing device 20 Line latent image 21, 22, 23 Latent image pattern 31 Object to be measured 32 Chopper 33 Detection electrode 34 Preamplifier 35 Shield case 36 Window 38 Temperature sensor 37 Switch

Claims (7)

In the speed fluctuation detecting device for detecting the periodic speed fluctuation of the latent image carrier,
The periodic latent image pattern formed on the latent image carrier is detected by detecting a moiré in the latent image using an AC conversion type surface potential sensor, thereby detecting a periodic speed fluctuation of the latent image carrier. A speed fluctuation detecting device. 2. The speed fluctuation detection device according to claim 1, wherein the period of the periodic latent image pattern is set in the vicinity of a known vibration period to be measured. The speed fluctuation detecting device according to claim 1, wherein the periodic latent image pattern is a pattern in which a cycle is changed stepwise for each predetermined plurality of cycles. The speed variation detection according to claim 3, wherein the periodic latent image pattern is a pattern in which lines extending in the main scanning direction of the latent image carrier form a line along the sub scanning direction. apparatus. An image forming apparatus comprising the speed fluctuation detecting device according to claim 1. 6. The vibration generating unit according to claim 5, further comprising a vibration generating unit, wherein the vibration generating unit generates a vibration having a phase opposite to a periodic speed variation of the latent image carrier detected by the speed variation detecting device. Image forming apparatus. In the speed fluctuation detecting method for detecting the periodic speed fluctuation of the latent image carrier,
The periodic latent image pattern formed on the latent image carrier is detected by detecting a moiré in the latent image using an AC conversion type surface potential sensor, thereby detecting a periodic speed fluctuation of the latent image carrier. Speed fluctuation detection method.

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