JP2000356936A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image forming device capable of decreasing speed fluctuation by the stretching vibration of a belt and perfectly removing the influence of the eccentricity of a belt driving roller by emphasizing a specified frequency component and controlling the traveling speed of the belt based on the filtered speed information. SOLUTION: In a frequency emphasis filter 12, only a component synchronizing with the eccentricity of a driving roller 1 is outputted after it is emphasized to be a specified multiple from a belt speed error signal detected by a belt comparison part 11. After filtering processing, the belt speed error signal becomes a signal in which only the component synchronizing with the eccentricity of the roller 1 is emphasized and is outputted from the filter 12. Namely, by directly detecting the speed from the belt, the fluctuation component of the stretching vibration superposed on the belt speed is precisely detected, which is fed back to compress the fluctuation component. Therefore, the fluctuation of the belt speed caused by the stretching vibration of the belt is decreased.

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 having an image forming function, such as a printer or a copier, and more particularly, to the effects of eccentricity of a driving roller in the rotation of an endless belt used for image formation. The present invention relates to an image forming apparatus capable of forming a high-definition and high-precision image by reducing both expansion and contraction vibration of a belt.

[0002]

2. Description of the Related Art In an image forming apparatus such as an electrophotographic printer or a copying machine, as the definition of an image is improved, an endless belt (hereinafter, referred to as an image forming belt) used for image formation has a higher precision. In addition, it is required to form an image with high precision.

FIG. 10 shows an example of an electrophotographic printer provided with an image forming belt for such image development. A conventional electrophotographic printer 60 shown in FIG.
In FIG. 1, the image forming belt 3 is stretched between the driving roller 1 and the driven roller 2 without an end, and travels as the driving roller 1 rotates.

The drive roller 1 is connected to a drive motor 5 via a gear train 4, and the rotation of the drive motor 5 is controlled based on the rotation speed of the driven roller 2 detected by an encoder 51.

On the periphery of the image forming belt 3, an image writing device (including a laser or the like) 41, a movable reflection mirror 42,
Three toner units 43a to 43d, a cleaner 44,
An erasing head 45 and a charging head 46 are provided. In such a conventionally known example, for example, 43a, 4a
Reference numerals 3b, 43c, and 43d denote cyan, magenta, yellow, and black toner units, respectively, and a color image is formed on the image forming belt 3 by each of the toner units 43. A paper feed tray 65 is provided below the image forming belt 3, and sheets 66 are stored in the paper feed tray 65.

At the time of image formation, the paper 66 stored in the paper feed tray 65 is fed out by the paper feed roller 64,
The paper 66 is supplied between the drive roller 1 and the transfer backup roller 47 through the feed rollers 67 and 68.
The color image formed on the image forming belt 3 is transferred to the supplied paper 70.

As the image forming belt 3 rotates, first, the toner remaining without being transferred by the cleaner 44 is removed from the image forming belt 3. Next, the erasing head 4
5 operates to remove the charge on the image forming belt 3 in order to erase the image data previously written. Further, the charging head 46 operates so as to be in a uniform charging state over the width of the image forming belt 3.

In this way, after being charged uniformly, the laser beam emitted from the image writing device 41
Scanning is performed by the movable reflection mirror 42, and image data is written on the image forming belt 3. Toner unit 43
Supplies the toner of each color onto the image forming belt 3, and the toner is attracted to the image forming belt 3 according to the charged state based on the written image data, thereby forming toner particles. Image is developed.

In such an image forming apparatus, it is necessary to feed the image forming belt at a constant speed in order to form an image with high accuracy. However, the eccentricity of the belt drive roller,
Due to the backlash of the drive transmission gear, the fluctuation of the load torque, etc., the speed unevenness of the forming belt occurs. In particular, the eccentricity of the belt driving roller causes periodic fluctuations in low frequency, which are relatively influential, resulting in pitch errors and color superposition errors, which significantly reduce image quality.

For this reason, there is a need for a technique for reducing the effects of periodic belt speed fluctuations caused by the eccentricity of the drive roller. As such a technique, for example, Japanese Patent Laid-Open No.
No. 91 is known. In this publication, position information is recorded on an image forming belt, and a laser is scanned in a belt running direction by a galvanometer mirror based on the detected position information so as to compensate for a position error of the image forming belt. There has been proposed a method of adjusting an image writing position.

However, the method proposed in the above publication has the following problems. First, it is difficult to realize a galvanomirror with high positioning accuracy at low cost. Second, the optical system becomes complicated and adjustment of the optical system becomes extremely difficult.

That is, in the first problem, in order to form a high-accuracy image by correcting the writing position so that the influence of the speed fluctuation is not affected at all, the pitch width is much higher than the laser scanning pitch width. This is because the beam needs to be scanned in the belt running direction with high accuracy, and a galvanomirror having high positioning accuracy is required to realize such high-precision scanning. A galvanomirror having such high positioning accuracy cannot be realized at low cost.

The second problem that the optical system becomes complicated and the adjustment of the optical system becomes extremely difficult is as follows. That is, the employed optical system needs to scan the beam of the galvanometer mirror in addition to the movable reflection mirror.

Therefore, in order to obtain a desired high precision of image formation, high-precision optical axis adjustment or the like is required from the time of assembling the apparatus. In order to eliminate such disadvantages of the prior art,
For example, a method has been proposed in which the influence of the eccentricity of the driving roller is suppressed by a control system to keep the belt speed constant.

As such a technique, for example, a driven low
Technology for detecting the influence of the eccentricity of the driven roller and controlling the drive motor using the detected eccentricity (for example, JP-A-4-234064), or removing the eccentric component of the driven roller itself from the speed detection signal of the driven roller. (Japanese Patent Application Laid-Open No. 9-267946).

For example, Japanese Patent Application Laid-Open No. Hei 9-267946 discloses such a technique as shown in FIG.
The image forming belt 3 is bridged between a driving roller 1 and a driven roller 2, and the driving roller 1 is driven to move the image forming belt 3 in conjunction with the driving roller 1. The drive roller 1 is connected to a drive motor 5 via a gear train 4. The rotation speed of the driven roller 51 is detected by an encoder 51 connected to the driven roller 51, and the detection signal is converted into a speed signal by an FV converter 52. The speed signal is superimposed with information on the fluctuation synchronized with the eccentricity of the driven roller 51 itself. The filter 53 functions to remove the stationary frequency component of the driven roller 51 from the superimposed speed signal. The comparator 54 compares the commanded speed signal 55 with the speed signal filtered by the filter 53 and outputs a control signal to the motor driver 6 based on the comparison result. The motor driver 6 outputs a drive signal to the drive motor 5 based on the control signal given from the comparator 54.

[0017]

However, the above-described conventional image forming apparatus has the following problems.

The first problem is that it is difficult to sufficiently reduce fluctuations in belt speed due to belt stretching vibration. More specifically, as shown in FIG. 12 (b), in addition to the speed fluctuation detected by the driven roller, information on the speed vibration due to the expansion and contraction of the belt is superimposed on the belt speed. Cannot be sufficiently detected by the encoder attached to the driven roller. As a result,
The fluctuation of the belt speed cannot be sufficiently reduced (see f1 to f3 in FIG. 13B).

Even if the speed of the driven roller itself can be controlled at a constant speed, it is extremely difficult to control the belt speed at a constant speed.

The second problem is that it is difficult to completely remove the influence of the eccentricity of the driving roller. For example, when the amount of eccentricity of the drive roller is large and the fluctuation of the belt speed is large, the method of feeding back the difference between the filtered signal and the command speed signal as shown in FIG. As shown in FIG. 13B and FIG. 13B, the influence of eccentricity cannot be completely suppressed. As a result, fluctuations remain in the belt speed.

Further, as a third problem, an expensive encoder with high resolution is attached to the driven roller, so that it becomes expensive. That is, in order to detect the rotation speed of the driven roller whose rotation speed is extremely low as compared with measuring the rotation speed of the drive motor, and to extract only the fluctuation component from the detected speed, high resolution and high cost are required. However, since a large encoder is naturally required, the cost of the entire apparatus becomes high as a result.

[0022]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the problems associated with the prior art as described above, and it is possible to reduce the speed fluctuation due to the expansion and contraction movement of the belt and to provide a belt driving roller. It is an object of the present invention to provide an image forming apparatus capable of completely removing the influence of eccentricity.

[0023]

An image forming apparatus according to claim 1, wherein the image forming apparatus performs an image forming process by causing a belt to run by a driving roller, wherein the image forming apparatus includes the endless belt. Detecting means for detecting the running speed of the belt, filter means for emphasizing a specific frequency component from the running speed information detected by the detecting means, and running speed of the belt based on the speed information filtered by the filter means. And control means for controlling

According to a second aspect of the present invention, in the first aspect, the frequency emphasized by the filter means is a rotational frequency component of the driving roller.

According to a third aspect of the present invention, there is provided the image forming apparatus according to the first or second aspect, wherein the filter means is configured to change a frequency to be emphasized, and to set a frequency of the variable filter. And a unit.

According to a fourth aspect of the present invention, in the image forming apparatus according to the third aspect, the frequency setting means stores a rotation frequency of the driving roller according to a command value of a traveling speed of the endless belt. It is characterized by being.

According to a fifth aspect of the present invention, in the image forming apparatus according to the third aspect, the frequency setting means calculates a rotation frequency of the driving roller according to a rotation speed of a driving motor driving the driving roller. Means.

According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, the image forming apparatus is provided with a command speed means for generating a command speed signal, and A comparison means for comparing speed information with the command speed signal is further provided.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention has been made in order to achieve the above-mentioned object, and an image forming apparatus for performing an image forming process by rotating an image forming belt is provided.
Detecting means (21, 22, 23, 8, 11 in FIG. 1) for detecting the speed error of the image forming belt, and filter means for enhancing the eccentric frequency component of the driving roller in the speed error information detected by the detecting means (17) and control means (13, 25, 1) for controlling the belt speed based on the speed information filtered by the filter means.
4, 15, 7) and the like. Since the rotation driving device having the above-described configuration directly detects and feeds back the belt speed, the control unit can also suppress the speed fluctuation due to the belt expansion and contraction motion and the like.

Further, since the eccentric frequency component of the drive roller is emphasized and fed back, the speed fluctuation of the frequency is strongly compressed, and the influence of the eccentricity of the drive roller can be completely suppressed. Furthermore, since the belt speed can be detected, for example, by reading the pattern printed on the developing belt, the speed of the belt can be reduced at a lower cost and easily compared to an encoder that requires a scale plate with finer slits according to the resolution. Speed can be detected.

FIG. 3B shows a belt speed error signal when such control is performed. As is apparent from a comparison between FIG. 12B in which the feedback control is performed by the conventional technique and FIG. Synchronous low-frequency fluctuation component is several decibels ~
It can be seen that tens of decibels are suppressed. FIG. 4B shows the result of frequency analysis of the belt speed error signal. Comparing FIG. 4B with FIG. 13B controlled by the conventional technology, the frequency f0 of the periodic belt speed fluctuation (hereinafter referred to as the eccentric frequency) caused by the eccentricity of the driving roller is extremely small. Compressed into
High-frequency fluctuation frequencies f1 to f3 due to belt expansion and contraction motion
It can also be seen that is also sufficiently suppressed.

<First Embodiment> Hereinafter, a first embodiment of the present invention will be described in more detail with reference to the drawings. FIG. 1 is a configuration diagram of a main part showing a first embodiment of an image forming apparatus according to the present invention. As shown in FIG. 1, the image forming apparatus 60 according to the present invention is configured such that the image forming belt 3
The image forming belt 3 is stretched between the driving roller 1, the driven roller 2, and the transfer backup roller 61, and the image forming belt 3 runs as the driving roller 1 rotates. The drive roller 1 is connected to a drive motor 5 via a gear train 4. The rotation of the drive motor 5 is controlled based on the image forming belt speed detected by the belt speed detecting unit 22. Image forming belt 3
Are arranged on the periphery of. Each developing unit 38 has a similar structure,
Data of different colors are developed on the image belt 3 by the developing unit.

In the present embodiment, 38a, 38b, 38
c and 38d are yellow, magenta, cyan,
Although a developing unit composed of four blacks is shown, the number of developing units is not particularly limited in the present invention.

By each of the developing units 38, a color image is formed on the image forming belt 3. A paper feed tray 65 is provided below the image forming belt 3, and sheets 66 are stored in the paper feed tray 65. At the time of image formation, the paper 66 stored in the paper feed tray 65 is fed out by the paper feed roller 64, and the feed rollers 67, 68,
After passing through 69, it is supplied to the transfer roller 62. The color image formed on the image forming belt 3 is transferred to a transfer roller 62.
First, the intermediate transfer is performed, and the intermediate transferred image is further transferred to the sheet 70 supplied to the transfer roller 62.

The developing unit 38 includes an erasing head, a charging head, an image writing device (including a light source such as a laser) 31a to 31d, a movable reflection mirror 32a to 32d,
Developer rollers 33a-33d, squeegee rollers 34a-
34d, toner trays 35a to 35d, and a liquid toner tank (not shown).

When the image forming belt 3 passes through the developing unit 38, first, the erasing head is moved by the image forming belt 3
To erase the previously written image data. Next, the charging head operates so that the image forming belt 3 is uniformly charged over its width. The laser beam emitted from the image writing device 31 is scanned by the movable reflection mirror 32 on the image forming belt in the uniformly charged state as described above, and the image data is transferred onto the image forming belt 3. Write.

In the present invention, any type of the movable reflecting mirror 32 of the scanning system, such as a type for rotating a polygon mirror and a type for reciprocating a plane mirror, can be adopted.

After writing the image data as described above, the developer roller 33 makes the liquid toner supplied from the liquid toner tank contact the image forming belt 3.
As a result, the toner particles in the liquid toner move to an appropriate uncharged area of the image forming belt 3 and are adsorbed to reproduce an image according to the charge distribution in which the image data is written. At this time, the squeegee roller 34 removes liquid toner other than the toner particles adsorbed on the image forming belt 3 from the image forming belt 3.

The surplus liquid toner of the developer roller 33 and the liquid toner removed by the squeegee roller 34 are collected by the toner tray 35, returned to the liquid toner tank, and reused.

As described above, the image formed by the toner particles is developed by the image forming belt 3 that has passed through the developing unit 38. The image forming belt 3 after being developed in this way is in a sufficiently dry state, so that a new image can be formed on the image forming belt 3 by another developing unit 38 and a new development can be performed.

FIG. 2 shows a first embodiment of the image forming apparatus according to the present invention.
FIG. 3 is a diagram illustrating in detail a configuration of a main part of the embodiment. As shown in FIG. 2, the image forming belt 3 is stretched between the driving roller 1 and the driven roller 2, and rotates and follows the rotation of the driving roller 1. In the present invention, the driving roller 1 is
Although connected to the drive motor 5 via the gear train 4, the present invention is not limited in any way as long as the drive from the drive roller can be transmitted. For example, the drive roller 1 can be connected without any gear train 4. It is also possible to configure the drive motor 5 to be directly coupled.

The drive motor 5 is connected via the gear train 4 as described above.
The gear train 4 is composed of two or more gears. Here, 2 of 4a and 4b
Although only one gear is shown, the number of gears constituting the gear train is not particularly limited.

In such an image forming apparatus of the present invention, analog information (analog signal) obtained by detecting the rotation speed of the drive motor 5 by the encoder 7 is converted into digital information (digital signal) by the encoder counter 8. .

On the inner periphery of the image forming belt 3, an identifier for detecting the belt speed is formed by printing or the like as, for example, a pattern 16 as shown in FIG. As shown in FIG. 2, such a pattern (identifier) is measured by a reflection type photo sensor 17 provided on the image forming belt 3, and the speed of the image forming belt 3 is detected. Thereafter, the information detected by the pulse counter 18 is converted into digital information as described above.

On the other hand, a command speed signal 9 for designating a desired belt speed, digital information of the belt speed converted by the pulse counter 18 and digital information of the motor angular speed converted by the encoder counter 8 are input to the control device 10. Is output to the motor driver 6 as a voltage command. In the control device 10, the command speed signal 9, the digital information of the belt speed, and the digital information of the motor angular speed are subjected to predetermined control processing, and are used as drive commands, such as a voltage command for the drive motor 5, as described above. Is output to The command speed signal is
For example, as shown in FIG. 8, the command is a command for instructing the belt speed to be Va. Such a command may be generated from, for example, a CPU that controls the entire image forming apparatus, or may be generated from a command having a processing operation function provided independently of the CPU that controls the entire image forming apparatus. And the above C
It may be generated from a program that receives a command from the PU and executes the command. Such a command may be provided in a digital format or may be provided in an analog format. This command may be externally input from the Internet or the like.

In this embodiment, the belt speed is detected by
Although a unit composed of a combination of the printed pattern 16 and the reflective photosensor 17 is used, the present invention is not limited to this, and it is also possible to detect with another configuration.

For example, a magnetic tape on which magnetic information has been written is attached along the inner periphery of the belt, and this is used as an identifier. From this identifier, the belt speed can be detected by a magnetic detection sensor (for example, a Hall element). . By using such a Hall element or the like, it is possible to detect the belt speed from a point magnetically separated. In the present invention, as the identifier, a barcode-shaped pattern, a magnetic tape, or the like is used as described above, and the identifier is used by arranging materials having different physical properties at substantially equal intervals. Such an identifier can be obtained by using materials having different physical properties, but basically, a material capable of detecting a difference in physical properties as an accurate speed may be used as the identifier, and optical properties such as brightness, saturation, and color may be used. Combinations of patterns composed of different combinations, magnetic reversals, and magnetic tapes composed of two types having different magnetic intensities can be used as identifiers. In addition, in order to detect the speed of the belt, besides the method of non-contact detection using the identifier as described above, for example, a wheel having a built-in small and lightweight encoder is slightly contacted with the belt to detect the speed. It is also possible to adopt a method of doing so. Note that the contacting member is not limited to a wheel, and a member having an encoder function may be appropriately used.

In the present embodiment, the pattern 16 and the reflection type photosensor 17 can be arranged near the outer periphery (near the outer edge) of the image forming belt 3. In order to eliminate a detection speed error due to toner contamination or the like, or to reduce a problem that the speed cannot be detected, and not to newly provide a space for disposing a sensor, the arrangement of the identifier is determined by using the outer periphery. It is preferable to set the inner circumference, which is a portion other than the above.

Further, as described above, the control device 10 controls the command speed signal 9 for designating a desired belt speed, the digital information of the belt speed converted by the pulse counter 18 and the motor angular speed converted by the encoder counter 8. The digital information is processed and output to the motor driver 6 as a voltage command for the drive motor 5.

As shown in FIG. 2, such a control device 10 is configured on a digital circuit as follows. In the control device 10, the belt comparison unit 11 compares the command speed signal 9 with the belt speed converted by the pulse counter 18, and outputs a belt speed error signal to the frequency emphasizing filter 12. The frequency emphasis filter 12 emphasizes (extracts and amplifies) only the eccentric frequency component of the driving roller 1 in the belt speed error signal, and outputs the signal to the belt controller 13. The belt control unit 13 performs a calculation process of the belt control based on the belt speed error signal after the filtering process,
As the command angular velocity signal of the drive motor 5, the motor comparison unit 1
4 is output. The motor comparing section 14 compares the commanded angular velocity signal of the driving motor 5 with the driving motor angular velocity converted by the encoder counter 8 and outputs a motor angular velocity error signal to the motor control section 15. The motor control unit 15 performs motor control arithmetic processing based on the motor angular velocity error signal, and outputs the result to the motor driver 6 as a motor drive signal such as a voltage command signal for the drive motor 5.

Although the control device 10 is constituted by a digital circuit as described above and the drive motor 5 is controlled by a digital control system as described above, the drive unit 10 may be constituted by a similar analog circuit. It is possible. in this case,
Pulse counter 1 in control device 10 used in the present invention
8, the encoder counter 8 can be replaced by an FV converter, and the frequency emphasis filter 12 can be replaced by a digital filter by an analog filter.

The operation of the image forming apparatus according to the first embodiment of the present invention will be described in detail below.

The drive motor 5 starts rotating with the drive voltage given from the motor driver 6. This rotation is transmitted to the drive roller 1 via the gear train 4 and the drive roller 1
, The image forming belt 3 rotates. Drive motor 5
For the rotation of, a pulse signal corresponding to the rotation speed is output by the encoder 7 and the output pulse signal is detected by the encoder counter 8 (step S1). For example, in this detection, the rotation speed is detected by counting the number of pulses per unit time. In this way, the number of pulses per unit time is converted into, for example, a motor angular velocity signal. The rotational speed is detected by the reflection type photo sensor 17 (step S3), and the rotational speed is converted into a digital signal by A / D conversion by a pulse counter (step S4), and this digital signal is input to the belt comparator. . The belt comparator compares the digital signal from the pulse counter with the signal input from the command speed signal (step S6).

In the present invention, the rotation speed (belt running speed) is determined by an encoder which requires high processing accuracy in order to increase the slit density for moving the pattern 16 with the rotation of the image forming belt 3. When identifiers are alternately provided in black and white at the peripheral end of the belt as shown in FIG. 9, for example, the distance from the peripheral end (or the inner edge) to a certain distance and the subsequent part are repeated as the black and white part. Period and half period or 1 / n period (n is a natural number)
The rotation speed can be measured more accurately by continuously or discontinuously displacing the rotation speed. Further, in addition to providing the identifiers at different intervals as described above, by providing two or more continuous / non-continuous black and white alternate identifiers having a 1 / n cycle, variations in rotational speed can be reduced. It is possible to collect information for accurately grasping the information and to increase the density of the information. In this way, it is possible to dramatically improve the control performance for image formation. Note that such an identifier is not limited to a black and white periodic one, and the above-described magnetic material or the like can be used as the identifier.

FIG. 3A shows an example of the belt speed error signal detected by the belt comparing section 11 before the control according to the first embodiment is performed. FIG. 4A shows the result of frequency analysis of the belt speed error signal. In FIG. 4A, the horizontal axis is frequency, and the vertical axis is intensity (dB). As can be seen from FIG. 3 (a), the error signal of the belt running performed without any special feedback function includes a low-frequency fluctuation component synchronized with the eccentricity of the drive roller 1 (the axis of the horizontal 0 axis). A component that fluctuates symmetrically and alternately.A high-frequency vibration component (such as frequencies f1 to f3 in FIG. 4A) accompanying the belt expansion and contraction is superimposed on the frequency f0 in FIG. You can see that.

From the frequency-analyzed spectrum shown in FIG. 4A, a frequency component synchronized with the eccentric frequency f0 of the driving roller 1 can be seen on the low frequency side. Further, three frequency components f1, f2, f corresponding to the stretching vibration mode of the belt itself.
3 appears on the high frequency side. By simply feeding back the belt speed error signal to control the drive motor 5, a certain reduction effect can be obtained for each of the fluctuation components (see, for example, FIG. 12B). However, according to this method, a component synchronized with the eccentricity of the driving roller 1 having a particularly large amplitude cannot be sufficiently compressed, and such a component remains as a speed fluctuation.

Therefore, the frequency emphasis filter 12 emphasizes (amplifies) only a component synchronized with the eccentricity of the driving roller 1 to a specific multiple from the belt speed error signal detected by the belt comparing unit 11 and outputs the same. In other words, the frequency characteristic of the filter is such that the gain G (G> 1) at the eccentric frequency f0 of the drive roller 1 is a peak, and the gains in the low and high frequencies apart from that frequency are 1. Such a frequency emphasis filter 12 can be realized as firmware on a digital circuit, and can also be realized as, for example, a secondary digital filter. In addition, a steeper peak can be realized by using a third-order or higher digital filter. After being filtered as described above, the belt speed error signal becomes a signal in which only the component synchronized with the eccentricity of the drive roller 1 is enhanced, and is output from the frequency enhancement filter 12 (step S7).

The belt controller 13 receives the filtered belt speed error signal, calculates the drive speed of the drive motor 5 necessary for setting the belt speed error signal to 0, and calculates the result. It is output to the motor comparison unit 14 as a motor command angular velocity signal (step S8). This arithmetic processing can be realized by, for example, a first-order integrator (linear integrator). In addition to this arithmetic processing, it is also possible to adopt a method of inserting a filter for suppressing high-frequency belt stretching vibration.

The motor comparator 14 compares the motor angular velocity signal converted by the encoder counter 8 with the motor command angular velocity signal calculated by the belt controller, and outputs it as a motor angular velocity error signal (step S9). .
The motor control unit 15 receives the motor angular velocity error signal, calculates the drive voltage of the drive motor 5 necessary to make the motor angular velocity error signal substantially zero, and uses the result as a voltage command signal as a motor driver signal. 6 (step S10). The motor driver 6 receives the voltage command signal, generates a voltage for driving the drive motor 5, and outputs the generated voltage to the drive motor 5 (step S11). Here, the drive motor 5 is described as a voltage drive type, but may be a current drive type. In this case, the same drive operation can be performed by replacing the drive voltage with the drive current.

FIG. 3B shows a belt speed error signal when control is performed according to the present embodiment as described above. Comparison with FIG. 12B, in which the feedback of the belt speed controlled by using the conventional technique, is not performed, the low-frequency fluctuation component synchronized with the eccentricity of the driving roller 1 is almost eliminated, and the belt is expanded and contracted. It can clearly be seen that the high frequency vibrations associated with the movement are also reduced. Also,
FIG. 4 shows an example of frequency analysis of the belt speed error signal.
(B). The scales of these vertical and horizontal axes are the same as those in the corresponding figures.

From the comparison with FIG. 4A in which the feedback of the belt speed is not performed, the eccentric frequency f0 of the driving roller 1 is obtained.
Is strongly compressed (in the present invention, the dB intensity of f0 is a negative value), and three fluctuation components f1, f2 and f3 corresponding to the stretching vibration mode of the belt itself are several minutes. It can be seen that one or one digit or more has been reduced.

As is clear from the comparison between FIG. 3B and FIG. 12B, the eccentric frequency of the driving roller 1 achieves a compression with a large fluctuation compared to the prior art. . Further, as is clear from the comparison between FIG. 4B and FIG. 13B, it can be seen that the suppression of the belt stretching vibration, which was impossible in the past, has been achieved to a sufficiently satisfactory degree.

FIG. 5 shows a frequency characteristic (disturbance compression characteristic) from a disturbance applied to the image forming belt 3 to a belt speed in order to clarify the effect of the frequency emphasis filter 12. FIG. 5A shows a case where the frequency emphasis filter 12 is inserted, and FIG. 5B shows a case where it is not inserted. 5A and 5B, the frequency emphasizing filter 12 selectively compresses (removes) only the eccentric frequency component f0 of the driving roller 1 and removes the influence on the belt speed. You can see that there is. This compression ratio is
Since it is determined by the gain G of the frequency emphasizing filter 12 at the eccentric frequency f0, by appropriately setting the gain G, it is possible to easily eliminate the influence of the eccentricity of the driving roller 1 on the belt speed to a level that does not cause a practical problem. Can be. FIG. 6 shows frequency characteristics (target value response characteristics) from the command speed signal 9 to the belt speed. FIG. 6A shows a case where the frequency emphasis filter 12 is inserted, and FIG. 6B shows a case where it is not inserted. 6 (a) and 6 (b), the frequency emphasis filter 12
Has little effect on the target value response characteristics.

That is, the frequency emphasis filter 12 can perform only disturbance compression without changing the target value response characteristics. In the first embodiment as described above, the frequency emphasized by the frequency emphasizing filter is fixed so as to correspond to a single belt speed.

However, in order to cope with a plurality of operation modes, it is possible to change the frequency emphasis filter according to the command speed. Here, the plurality of operation modes refer to a normal print mode, a high-speed print mode, an initialization mode in which a warm-up operation is performed when power is input, a collection mode for detecting and correcting a mechanical deviation, and the like. .

<Second Embodiment> Next, a second embodiment of the present invention will be described.
An embodiment will be described. FIG. 7 shows the second embodiment of the present invention.
FIG. 1 is a main part configuration diagram illustrating main parts of an image forming apparatus used in the embodiment. In the second embodiment, as shown in FIG. 7, the frequency emphasized by the frequency emphasizing filter can be changed according to the command speed signal. This makes it possible to support a plurality of operation modes. Further, in the second embodiment of the present invention, a variable frequency emphasis filter 21 is employed instead of the frequency emphasis filter 12. Further, an eccentric frequency memory 20 is provided to change the emphasis frequency of the filter according to the command speed.

In the second embodiment, the command speed signal 9 given to the control device 10 can be used for comparison with the belt speed signal in the belt comparing section 11 and is input to the eccentric frequency memory 20. You. Eccentric frequency memory 20
In the table, the relationship between the belt command speed and the eccentric frequency of the driving roller is tabulated as shown in FIG. 8, for example.
In response to the input of such a command speed signal, a corresponding eccentric frequency is selected and output to the variable frequency emphasis filter 21.

The variable frequency emphasis filter 21 can change the frequency to be emphasized by an external input. Based on the eccentric frequency input from the eccentric frequency memory 20, the emphasis at the peak center of the variable frequency emphasis filter 21 is obtained. The frequency f0 is changed (Step S26). After the emphasis frequency is changed in this way, the variable frequency emphasis filter 21 is detected by the belt comparison unit 11. The second
In the third embodiment, other operations are the same as those in the first embodiment. That is, as shown in FIG.
The drive motor 5 starts rotating with the drive voltage given from the motor driver 6. This rotation is transmitted to the drive roller 1 via the gear train 4, and the image forming belt 3 rotates in conjunction with the drive roller 1. For the rotation of the drive motor 5, a pulse signal corresponding to the rotation speed is output by the encoder 7, and the output pulse signal is
(Step S21). Further, similarly to the first embodiment, the rotational speed is detected (step S23),
This is converted into a digital signal by A / D conversion by a pulse counter (step S24), and the digital signal from the pulse counter is compared with a signal input from the command speed signal (step S25).

After being filtered as described above, the belt speed error signal is output to the variable frequency emphasis filter 2 based on the eccentric frequency input from the eccentric frequency memory 20.
The emphasis frequency f0 which is the peak center of 1 is changed, and only this component becomes a emphasized signal, which is output from the frequency emphasis filter 12 (step S26).

The belt controller 13 receives the filtered belt speed error signal, calculates the drive speed of the drive motor 5 necessary for setting the belt speed error signal to 0, and calculates the result. It is output to the motor comparison unit 14 as a motor command angular velocity signal (step S27).

The motor comparator 14 compares the motor angular velocity signal converted by the encoder counter 8 with the motor command angular velocity signal calculated by the belt controller and outputs it as a motor angular velocity error signal (step S2).
8). The motor control unit 15 receives the motor angular velocity error signal, calculates the drive voltage of the drive motor 5 necessary to make the motor angular velocity error signal substantially zero, and uses the result as a voltage command signal as a motor driver signal. 6 (step S29). The motor driver 6 receives the voltage command signal, generates a voltage for driving the drive motor 5, and outputs the generated voltage to the drive motor 5 (step S30).

<Third Embodiment> Next, a third embodiment of the present invention will be described.
An embodiment will be described. FIG. 9 is a main part configuration diagram illustrating in detail a main part of an apparatus used in the third embodiment of the present invention. The image forming apparatus according to the second embodiment is characterized in that a signal from a command speed signal section is changed in frequency by a frequency emphasizing filter via an eccentric frequency memory. On the other hand, in the third embodiment, what kind of operation is performed by inputting the signal from the encoder counter to the variable frequency emphasizing filter via the eccentric frequency calculating section and changing the frequency emphasized by the frequency emphasizing filter. In this case, the influence of the eccentricity of the driving roller can be removed. Therefore, in the third embodiment of the present invention, the use of the variable frequency emphasis filter 21 is the same as that of the second embodiment, but an eccentric frequency calculation unit 22 is used instead of the eccentric frequency memory 20. .

In the third embodiment, the motor angular velocity signal detected by the encoder counter 8 is used for comparison with the motor command angular velocity signal by the motor comparing section 14 and is input to the eccentric frequency calculating section 22. . The eccentric frequency calculator 22 calculates the eccentric frequency of the drive roller from the motor angular velocity signal according to a specific calculation formula (step S5).
3), whereby the output is output to the variable frequency emphasis filter 21. The variable frequency emphasis filter 21 can change the frequency to be emphasized by an external input. Based on the eccentric frequency input from the eccentric frequency calculation unit 22, the emphasis frequency f0 which is the peak center of the variable frequency emphasis filter 21 is used. Is changed (step S57).

After the emphasis frequency has been changed in this way, the variable frequency emphasis filter 21
The belt speed error signal detected in step 1 is filtered and output to the belt control unit 13.

FIG. 8 is a block diagram for explaining the operation of the eccentric frequency memory. The eccentric frequency memory 20 stores a plurality of belt command speeds and the eccentric frequencies of the drive rollers when the belt operates at the speeds in association with each other. When the command speed signal 9 is input to the eccentric frequency memory 20, a matching command speed is selected from the stored command speeds. Next, an eccentric frequency corresponding to the selected command speed is selected, and this is newly output to the variable frequency emphasis filter 21. The variable frequency emphasis filter 21 changes the filter parameter so that the center of the frequency to be emphasized becomes a new eccentric frequency.

The broken line in FIG. 8 shows the signal flow before changing the command speed, and the solid line shows the signal flow after changing the command speed. When the command speed changes from Va to Vc, the eccentric frequency selected accordingly also switches from fa to fc, and this eccentric frequency fc is output to the variable frequency emphasis filter 21.

In the third embodiment, the emphasis frequency of the variable frequency emphasis filter 21 matches the eccentric frequency of the drive roller 1 even when the command speed is switched, and the eccentricity of the drive roller 1 gives the belt speed. The effect can be effectively eliminated.

An equation for calculating the eccentric frequency of the driving roller from the motor angular velocity signal in the eccentric frequency calculating section 22 will be described. Assuming that the motor angular velocity signal is wm and the gear ratio between the motor 5 and the driving roller 1 by the gear train 4 is Gr,
The angular velocity ω0 of the drive roller is ω0 = G · wm. Therefore, the eccentric frequency f0 is f0 = (Gr · wm) / (2
π). More simply, the coefficient Gr / (2
π) is stored in the memory as gain B = Gr / (2π), and f0 = B · wm can be obtained.

Further, in the third embodiment, a method of calculating the eccentric frequency using the belt speed signal detected by the pulse counter 18 instead of the motor angular speed signal can be adopted. In this case, the radius of the driving roller 1 is R
Then, the belt speed Vb is Vb = R · ω0. Therefore, the eccentric frequency f0 is f0 = Vb / (2π · R)
Required by More simply, the coefficient 1 / (2π ·
R) is stored in the memory as the gain C = 1 / (2π · R), and f0 = C · Vb.

However, in the case of using the above method, since the fluctuation synchronized with the eccentric frequency of the driving roller and the high frequency vibration accompanying the expansion and contraction of the belt are superimposed on the belt speed signal, the variable frequency is changed by these fluctuations. It is necessary to extract only the DC component so that the emphasis frequency of the emphasis filter does not change. For this purpose, a low-pass filter may be appropriately inserted before the eccentric frequency calculator 22. The low-pass filter can be realized in the control device 10 as a digital averaging filter having a sufficiently long sampling period.

In the present embodiment, the emphasis frequency of the variable frequency emphasis filter 21 always coincides with the eccentric frequency of the driving roller 1 irrespective of the belt speed, and the eccentricity of the driving roller 1 becomes equal to the belt speed. The effect can be effectively removed. However, when the belt speed changes abruptly as in the case of acceleration / deceleration, the emphasis frequency of the variable eccentricity frequency filter 21 is switched within a short time, which is not a control advantage. In order to avoid such a sudden change in the emphasis frequency, the updating of the eccentric frequency may be stopped during acceleration / deceleration. The operation of the third embodiment is almost the same as the operation shown in the first embodiment, and this operation is shown in the flowchart of FIG. That is, as shown in FIG. 16, the drive motor 5 starts rotating by the drive voltage given from the motor driver 6. This rotation is transmitted to the drive roller 1 via the gear train 4, and the image forming belt 3 rotates in conjunction with the drive roller 1. For the rotation of the drive motor 5, a pulse signal corresponding to the rotation speed is output by the encoder 7, and the output pulse signal is
(Step S51). Further, similarly to the first embodiment, the rotational speed is detected (step S54),
This is converted into a digital signal by A / D conversion by a pulse counter (step S55), and the digital signal from the pulse counter is compared with a signal input from the command speed signal (step S56).

After being filtered as described above, the belt speed error signal is output to the variable frequency emphasis filter 2 based on the eccentric frequency input from the eccentric frequency memory 20.
The emphasis frequency f0, which is the peak center of 1, is changed, and only this component becomes a signal that is emphasized, and is output from the frequency emphasis filter 12 (step S57).

The belt controller 13 receives the filtered belt speed error signal, calculates the drive speed of the drive motor 5 necessary for setting the belt speed error signal to 0, and calculates the result. The signal is output to the motor comparing section 14 as a motor command angular velocity signal (step S58).
The motor comparing section 14 compares the motor angular velocity signal converted by the encoder counter 8 with the motor command angular velocity signal calculated by the belt control section and outputs it as a motor angular velocity error signal (step S59). The motor control unit 15 receives the motor angular velocity error signal, calculates the drive voltage of the drive motor 5 necessary to make the motor angular velocity error signal substantially zero, and uses the result as a voltage command signal as a motor driver signal. 6 (Step S6)
0). The motor driver 6 receives this voltage command signal, generates a voltage for driving the drive motor 5, and outputs it to the drive motor 5 (step S61). If it is difficult to directly provide an identifier for detecting the belt speed (belt transfer speed) on the belt due to a change in the material of the belt, a speed observer such as a state estimator is provided in the control device 10. By incorporating a speed observer outside the control device or by using a signal obtained by detecting or estimating the belt speed from an encoder signal for detecting the belt speed as described above, control can be performed in the same manner as described above. . Note that such an encoder signal may be an encoder pulse as described above. In addition, such encoders or devices with built-in encoders
For example, it can be attached to a driving roller.

The preferred embodiment of the image forming apparatus according to the present invention has been described above. However, the image forming apparatus according to the present invention is not limited to the configuration of the above-described embodiment. Various modifications and alterations as appropriate without departing from the spirit of the present invention from the configuration of the embodiment are also included in the scope of the present invention.

[0085]

First, by detecting the speed directly from the belt, the fluctuation component of the stretching vibration superimposed on the belt speed can be clearly detected, and the fluctuation component can be compressed by feeding back the fluctuation component. Therefore, the fluctuation of the belt speed due to the stretching vibration of the belt can be reduced.

Second, by incorporating a frequency emphasis filter into the control system, only the eccentric frequency component of the drive roller can be selectively and arbitrarily compressed to an arbitrary amount. It can be removed to a degree that does not cause a problem in practical use.

Thirdly, the belt speed can be detected by an inexpensive pattern printed on the belt, and the resolution can be easily increased because only the print pattern needs to be fine. Does not require a simple encoder.

[Brief description of the drawings]

FIG. 1 is a main part configuration diagram for explaining main parts according to a first embodiment of the present invention.

FIG. 2 is an overall configuration diagram illustrating a configuration of a first exemplary embodiment of the present invention.

FIG. 3 is a belt speed error waveform illustrating an effect of the first exemplary embodiment of the present invention.

FIG. 4 is a diagram showing a frequency analysis result of a belt speed error waveform when the first embodiment of the present invention is used.

FIG. 5 is a disturbance compression characteristic illustrating an effect of the first exemplary embodiment of the present invention.

FIG. 6 is a target value response characteristic for explaining the effect of the first embodiment of the present invention.

FIG. 7 is a main part configuration diagram illustrating a main part of a second embodiment of the present invention.

FIG. 8 is a configuration diagram illustrating an operation of an eccentric frequency memory according to a second embodiment of the present invention.

FIG. 9 is a main part configuration diagram illustrating a main part of a third embodiment of the present invention.

FIG. 10 is an overall configuration diagram illustrating a configuration of a conventional image forming apparatus.

FIG. 11 is a main part configuration diagram illustrating main parts of a conventional image forming apparatus.

FIG. 12 is a belt speed error waveform illustrating an effect of the conventional image forming apparatus.

FIG. 13 is a frequency analysis result of a belt speed error waveform for explaining the effect of the conventional image forming apparatus.

FIG. 14 is a flowchart illustrating an operation of the image forming apparatus according to the first exemplary embodiment of the present invention.

FIG. 15 is a flowchart illustrating an operation of the image forming apparatus according to the second exemplary embodiment of the present invention.

FIG. 16 is a flowchart illustrating an operation of the image forming apparatus according to the third exemplary embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 drive roller 2 driven roller 3 image forming belt 4 gear train 5 drive motor 6 motor drive 7 encoder 8 encoder counter 9 command speed signal 10 control device 11 belt comparison unit 12 frequency emphasis filter 13 belt control unit 14 motor comparison unit 15 motor control Unit 16 pattern 17 reflection type photo sensor 18 pulse counter 20 eccentric frequency memory 21 variable frequency emphasis filter 22 eccentric frequency calculation unit

Claims (6)

[Claims] 1. An image forming apparatus for performing an image forming process by causing a belt to run by a driving roller, wherein the image forming apparatus detects a traveling speed of the belt, and detects the traveling speed of the belt. Filter means for emphasizing a specific frequency component based on the traveling speed information; and control means for controlling the traveling speed of the endless belt based on the speed information filtered by the filter means. Image forming apparatus. 2. The image forming apparatus according to claim 1, wherein the specific frequency component emphasized by the filter unit is substantially the same as a rotation frequency component of the driving roller. 3. The apparatus according to claim 1, wherein said filter means comprises: a variable filter section capable of variably adjusting a frequency component to be emphasized; and a frequency setting section for setting a frequency of said variable filter section. Or 2
An image forming apparatus according to claim 1. 4. The image forming apparatus according to claim 3, wherein the frequency setting unit includes a storage unit that stores a rotation frequency of the driving roller according to a command value of a traveling speed of the belt. 5. The image according to claim 3, wherein the frequency setting unit includes a calculation unit that calculates a rotation frequency of the drive roller according to a rotation speed of a drive motor that drives the drive roller. Forming equipment. 6. The image forming apparatus according to claim 1, further comprising command speed means for generating a command speed signal, and further comprising comparing means for comparing said traveling speed information with said command speed signal. The image forming apparatus according to any one of claims 1 to 5.