JP4846602B2 - Endless belt thickness variation measuring apparatus, image forming apparatus manufacturing method, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thickness fluctuation measuring device for an endless belt, capable of measuring fluctuation of the endless belt thickness simply and highly accurately. <P>SOLUTION: This measuring device has the endless belt 1 suspended over a rotating roller 2, a driving means 6 of the endless belt 1, a noncontact type distance measuring means 3 for measuring the distance to the endless belt surface while the endless belt 1 is running, a displacement signal detection means 202 for detecting a signal from the distance measuring means 3 as a displacement signal along the running direction of the endless belt 1, a means 203 for performing Fourier transform of the displacement signal in the state where portions of a plurality of continuous rotations of the endless belt 1 are lumped together, and a means 204 for performing inverse Fourier transform to the signal subjected to the Fourier transform in the restricted state to a frequency band which is dominant to thickness fluctuation of the endless belt 1. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a thickness variation measuring apparatus for an endless belt used for an intermediate transfer member of an image forming apparatus such as an electrophotographic copying machine or a printer.

  An endless belt for intermediate transfer is used in the image forming apparatus. Conventionally, the absolute thickness of the endless belt is measured, and an example thereof is shown below.

  The method described in Japanese Patent Application Laid-Open No. 2002-286405 (Patent Document 1) is a method of measuring the belt thickness with a contact type linear gauge, and GS-1613 is described as a contact type linear gauge in the examples. . When the manufacturer's specifications are examined, the indication accuracy of the GS-1613 is as large as 2 μm, which is not suitable for high-accuracy measurement.

For measurement,
(1) Run the belt for a predetermined distance,
(2) Stop the belt at the measurement point,
(3) Lower the linear gauge, bring it into contact with the belt, measure its thickness,
(4) Raise the linear gauge and evacuate The thickness is measured while repeating the series of operations, so the measurement work is complicated.

  Further, the thickness is measured by pressing a contact linear gauge on the shaft against the belt surface while the belt is suspended from a non-rotating shaft. Since the shaft does not rotate, means for smoothly moving the belt on the shaft is necessary, the structure is complicated, and the measurement work is complicated from this point as well.

  The method described in Japanese Patent Laid-Open No. 2003-185402 (Patent Document 2) is a method of measuring the belt thickness with a contact-type measuring device, and it is described that a differential transformer type is preferable as the contact-type measuring device. .

  When a commercially available product of this differential transformer type measuring device is examined, it is 0.5 μm (full stroke 1 mm) at most even with high linearity, and it cannot be said that high-precision detection is possible. In addition, since the belt thickness is measured by a belt guide (a shaft that does not rotate), the belt thickness is measured by means for smoothly moving the belt on the shaft in the same manner as in Patent Document 1. Is complicated, and the measurement work is complicated.

  The method described in Japanese Patent Application Laid-Open No. 2001-228777 (Patent Document 3) uses a non-contact distance sensor to calculate a difference in distance between when the belt is suspended and when it is not, This is a method for obtaining the thickness of the belt.

In this method, first, the distance is measured when the belt is not suspended. After that, the belt is laid, but mechanical displacement and deformation of the belt suspension mechanism always occur before and after the belt suspension, so it is very difficult to accurately reproduce the distance between the distance sensor and the belt measurement base. (Mounting error is difficult even on the order of 0.1 μm as well as on the order of 1 μm). In addition, this Unexamined-Japanese-Patent No. 2001-228777 (patent document 3) has no description about the specific means for calculating | requiring the thickness fluctuation | variation of a belt.
JP 2002-286405 A JP 2003-185402 A JP 2001-228777 A

  One of the technological trends in image forming apparatuses such as electrophotographic copying machines and printers is to improve color image quality. For example, factors that have a large effect on color misregistration in the sub-scanning direction (paper traveling direction in the image forming apparatus) include fluctuations in the rotational speed of the photoreceptor and fluctuations in the thickness of the intermediate transfer belt. Making the thickness of the intermediate transfer belt as uniform as possible is important for improving the color image quality.

  Known materials for the intermediate transfer belt include polyimide, polyamideimide, polycarbonate, and vinylidene fluoride. In recent years, even an endless belt without a seam can be manufactured with a tolerance of about ± 3 μm in thickness variation. In order to measure this thickness variation, the contact type measuring device described in Patent Documents 1 and 2 is insufficient.

  In addition, since the belt thickness measurement position described in Patent Documents 1 and 2 is on a shaft that does not rotate, a means for smoothly moving the belt on the shaft is necessary, the structure is complicated, and the measurement work is complicated. .

  In the case of an endless belt typified by an intermediate transfer belt, in order to evaluate the thickness of the endless belt for the purpose of minimizing color misregistration, the thickness variation along the running direction of the endless belt should It is very practical and important to pay attention to the measurement.

  In the specification of the present invention, “high accuracy” means that the belt thickness variation can be measured with an accuracy of about 0.1 μm or less. As described in Patent Documents 1 and 2, since the conventional contact displacement measuring device has an indication accuracy of about 2 μm or linearity of about 0.5 μm, it is not suitable for high-accuracy measurement. On the other hand, non-contact type laser displacement meters have high accuracy with a repeatability of 0.01 μm to 0.05 μm, which is suitable for the present invention.

  In the specification of the present invention, “simple” means that the thickness variation of the endless belt can be grasped by measuring the one end surface of the endless belt in a non-contact state while running the endless belt. A method of measuring the thickness when the endless belt repeatedly travels (or moves) and stops and measures the thickness when the endless belt is stopped, as in the conventional contact displacement measuring apparatus, is complicated and is not simple as described above. Further, if the thickness is measured by contacting the endless belt while traveling, the measuring device may damage the surface of the endless belt.

  An object of the present invention is to eliminate the disadvantages of the prior art and to measure an endless belt thickness variation measuring device capable of measuring a variation in the endless belt thickness with high accuracy and simply, a method for manufacturing an image forming apparatus, and image formation. To provide an apparatus.

In order to achieve the above object, the first means of the present invention includes, for example, an endless belt suspended on a rotating roller such as a driving roller;
Driving means for rotating the endless belt;
Non-contact distance measurement that measures the distance to the surface of the endless belt portion that is disposed on the opposite side of the endless belt and is wound around the endless belt while the endless belt is running. Means,
A displacement signal detecting means for detecting a distance signal from the distance measuring means as a displacement signal along the traveling direction of the endless belt;
A Fourier transform computing means for performing a Fourier transform on the displacement signals output from the displacement signal detecting means collectively for a plurality of continuous rotations of the endless belt;
And a reverse Fourier transform operation means for performing a reverse Fourier transform on the signal subjected to the Fourier transform by the Fourier transform operation means, limited to a frequency band dominant to the thickness variation of the endless belt. is there.

A second means of the present invention is the first means, wherein a plurality of the distance measuring means are installed at predetermined intervals along the width direction of the endless belt,
Each distance signal output from each distance measuring means is input to the displacement signal detecting means.

According to a third means of the present invention, in the first or second means, the distance measuring means is a laser displacement meter,
The direction of the laser light emitted from the laser displacement meter is directed to the center of the rotating roller.

  According to a fourth means of the present invention, in the first means, the measurement interval by the distance measuring means is shorter than the sampling interval by the displacement signal detecting means.

  According to a fifth means of the present invention, in the first to fourth means, the endless belt is an intermediate transfer belt or a photosensitive belt used in an image forming apparatus.

According to a sixth aspect of the present invention, in the method of manufacturing the image forming apparatus, the toner images of two or more colors formed by the photoconductor are transferred while being superimposed on the intermediate transfer belt.
Color misregistration evaluation criteria based on the thickness variation of the intermediate transfer belt has been set,
The thickness fluctuation of the intermediate transfer belt before being incorporated into the image forming apparatus is measured by the thickness fluctuation measuring device according to claim 1,
Comparing the measurement result and the color misregistration evaluation criteria, the pass / fail judgment of the intermediate transfer belt is performed,
An intermediate transfer belt that passes the color misregistration evaluation criteria is incorporated in an image forming apparatus.

The seventh means of the present invention comprises an intermediate transfer belt for transferring toner images of two or more colors formed by a photoreceptor in an overlapping manner,
A rotation speed control means for controlling the rotation speed of the intermediate transfer belt suspended from a rotation roller;
A non-contact type that measures the distance to the surface of the intermediate transfer belt portion that is disposed on the opposite side of the rotation roller with the intermediate transfer belt interposed therebetween and is wound around the rotation roller while the intermediate transfer belt is running. Distance measuring means,
A displacement signal detecting means for detecting a distance signal from the distance measuring means as a displacement signal along the traveling direction of the intermediate transfer belt;
Fourier transform operation means for performing Fourier transform on the displacement signal output from the displacement signal detection means collectively for a plurality of continuous rotations of the intermediate transfer belt;
An inverse Fourier transform computing means for performing the inverse Fourier transform on the signal subjected to the Fourier transform by the Fourier transform computing means, limited to the frequency band dominant to the thickness fluctuation of the endless belt,
The rotational speed of the intermediate transfer belt is controlled by the rotational speed control means based on the thickness fluctuation signal of the intermediate transfer belt output from the inverse Fourier transform calculation means.

According to an eighth means of the present invention, in the seventh means, a plurality of the distance measuring means are installed at predetermined intervals along the width direction of the intermediate transfer belt,
Each distance signal output from each distance measuring means is input to the displacement signal detecting means.

According to a ninth means of the present invention, in the seventh or eighth means, the distance measuring means is a laser displacement meter,
The direction of the laser light emitted from the laser displacement meter is directed to the center of the rotating roller.

  According to a tenth means of the present invention, in the seventh means, the measurement interval by the distance measuring means is shorter than the sampling interval by the displacement signal detecting means.

  The present invention is configured as described above, and provides an endless belt thickness variation measuring apparatus, an image forming apparatus manufacturing method, and an image forming apparatus capable of easily measuring an endless belt thickness variation with high accuracy. be able to.

  In the present invention, the endless belt is suspended on at least one rotating roller. Specifically, for example, an endless belt is suspended on a traveling system including one drive roller and a plurality of driven rollers. One of the rollers is used for measurement. The circumference of the endless belt is desirably sufficiently longer than the circumference of the roller used for measurement, and is preferably about 10 times or more.

  A general motor (stepping motor, DC motor, or the like) is used as a driving source of the driving roller, and the motor is connected to the driving roller. However, a speed change mechanism such as a gear may be interposed therebetween. The drive roller is rotated at a constant angular velocity by the drive source, and the endless belt is caused to travel.

  In this embodiment, the driving roller is a roller used for measurement. If the roller eccentricity amplitude is about 10 μm to 20 μm, the processing accuracy is sufficiently high. However, as described below, in the present invention, in principle, the eccentricity may exist. Can be large.

  A laser displacement meter is installed in a stationary state as a non-contact type displacement measuring device on the opposite side of the roller used for measurement across the endless belt. As this laser displacement meter, one having a repetition accuracy of 0.01 μm to 0.05 μm is suitable.

  While the endless belt is running, a distance to the endless belt surface within the belt winding angle with respect to the roller is measured using a non-contact displacement measuring device (laser displacement meter).

  If the measurement direction of the non-contact displacement measuring device (laser displacement meter) with respect to the belt is the direction along the radial direction of the roller, that is, the direction toward the center of the roller, it is most preferable that the measurement angle error is not corrected. The measurement interval by the non-contact type displacement measuring device (laser displacement meter) may be continuous in time or intermittent. In the case of intermittent measurement, it is desirable that it is shorter than the sampling interval of the signal processing means described later. A distance signal measured by a non-contact displacement measuring device (laser displacement meter) is input to the signal processing means.

  The signal processing means includes a displacement signal detecting means for detecting the distance signal as a displacement signal at a predetermined sampling interval, a free conversion calculating means for performing a free conversion of the displacement signal, and a free converted signal. On the other hand, it has at least an inverse-Fleer transform operation means for performing an inverse-Fourier transform while limiting to a frequency band that is dominant in the thickness variation of the endless belt.

  In this signal processing means, the total working time of the displacement signal is preferably about 10 rotations or more continuously for the endless belt. With 10 rotations, a frequency resolution of 1/10 of the rotation frequency of the endless belt can be obtained, so that the signal / noise ratio (S / N) of each frequency component of the thickness variation can be increased. In order to shorten the measuring time, the working time may be shortened a little.

  In this signal processing means, the sampling interval may be such that the roller 1 rotation frequency fr component (mainly the eccentric component) at the measurement position can be detected smoothly in time. Here, it is assumed that the higher order frequency of the endless belt is taken into consideration up to the fifth order. For example, if the rotation frequency fb of the endless belt is about 10 times the rotation frequency fr of the measuring roller and the sampling frequency is 32 × fr, 32 × fr = 320 × fb, and the 5 × fb component can be sufficiently detected.

  By this signal processing means, the time waveform of the displacement signal for 10 continuous rotations of the endless belt is collectively subjected to free conversion. Information on the real part and the imaginary part of each frequency component is stored. Further, in order to select a frequency band, for example, a frequency spectrum is displayed on the screen of the signal processing means. Among the AC components, the most prominent signal level is the roller 1 rotation frequency fr (mainly eccentric component). Next, one rotation frequency fb of the endless belt and higher order components of the fb. To what extent higher-order components of fb are considered may be determined by actually measuring an endless belt. Here, as described above, 2 × fb, 3 × fb, 4 × fb, and 5 × fb components other than fb are considered as frequency components of the endless belt.

  In order to remove the rotation frequency fr (mainly eccentric component) and noise of the roller by this signal processing means, for example, only the frequency band of 0.5 × fb to 5.5 × fb is taken out (band-limited). Reverse Fourier transform. The time waveform reproduced as a result is constituted by the dominant component of the thickness variation along the traveling direction of the endless belt. Since the real part information and the imaginary part information are stored at the time of the Fourier transform, the reproduction time waveform stores both the gain and the phase within the band limit.

  In this way, the thickness variation profile of the endless belt that is running can be measured with high accuracy.

  Furthermore, when the endless belt is an intermediate transfer belt of an image forming apparatus, the color misregistration amount can be predicted by simply measuring the thickness fluctuation of the intermediate transfer belt before the intermediate transfer belt is incorporated into the image forming apparatus. Also convenient. Next, this will be specifically described.

  When the intermediate transfer belt is suspended at a winding angle on the driving roller, the traveling speed of the intermediate transfer belt at a position where the winding portion is present can be expressed by the following equation.

Vb (t) = [Rr + a × B (t)] × ωr
Vb (t): traveling speed of the intermediate transfer belt
t: time
Rr: radius of the driving roller (the eccentricity is zero)
a: Coefficient (= 0.5) representing the effective running speed of the intermediate transfer belt
B (t): Absolute thickness of the intermediate transfer belt
ωr: Angular speed of driving roller (constant)
In order to simplify the description, the eccentricity of the drive roller is assumed to be zero. The coefficient a was set to 0.5 in the meaning of the centroid of the thickness of the intermediate transfer belt.

Further, when the thickness of the intermediate transfer belt is divided into a DC component and an AC component,
B (t) = Bdc + ΔB (t)
Bdc: DC component of thickness ΔB (t): AC component of thickness, thickness variation profile obtained with thickness variation measuring apparatus of the present invention
Vb (t) = [Rr + a × (Bdc + ΔB (t))] × ωr
= (Rr + a × Bdc) × ωr + a × ΔB (t) × ωr
The first term on the right side of this equation is the DC component, and the second term is the AC component. When the second term on the right side is ΔVb (t): speed fluctuation component,
ΔVb (t) = a × ΔB (t) × ωr
When the driving roller is rotated at a constant angular velocity ωr, the speed variation of the intermediate transfer belt is proportional to the belt thickness variation.

In the case of a tandem type image forming apparatus, generally four (for four colors) photoconductors are arranged along the running direction of the intermediate transfer belt. Transfer of toner from the photoreceptor to the intermediate transfer belt is referred to as primary transfer in this specification. When a time interval [ta, tb] in which the intermediate transfer belt passes through the primary transfer position of any two photoconductors in a single primary transfer step is given, the intermediate transfer belt speed fluctuation ΔVb in that interval is given. (T) is integrated over time. This integrated value becomes the color misregistration value. The sign may be positive or negative. As this absolute value increases, the color shift CMR increases. However, the integration interval is time [ta, tb].

CMR: Color misregistration ta, tb: Time when the intermediate transfer belt passes through the primary transfer position of any two photosensitive members in one primary transfer step If the thickness variation profile of the intermediate transfer belt is given as described above, The influence on the color shift can be obtained quantitatively with a simple calculation. By measuring the thickness variation of the intermediate transfer belt before incorporating it into the image forming apparatus using the apparatus of the present invention, it is possible to evaluate and select the intermediate transfer belt as a part based on the evaluation of color misregistration. If only those that pass the standards are incorporated into the image forming apparatus as appropriate parts, the yield can be improved.

  If the image forming apparatus includes at least one non-contact displacement measuring device, it is possible in principle to detect the thickness variation of the intermediate transfer belt (endless belt), and the above-described signal processing function is implemented by hardware. Or (and) it is also possible to incorporate it into an image forming apparatus as software. The detected thickness variation profile of the intermediate transfer belt can be used for image formation control such as drive control of the intermediate transfer belt to improve color misregistration.

  Next, an embodiment of an endless belt thickness varying device when an endless belt is used as an intermediate transfer belt for an image forming apparatus will be described.

  As a material for the intermediate transfer belt, polyimide, polyamideimide, polycarbonate, vinylidene fluoride, or the like is used. The peripheral length of the intermediate transfer belt may be sufficiently longer than the peripheral length of the roller used for measurement.

 FIG. 1 is a simplified diagram showing the function of the present invention. As shown in the figure, the intermediate transfer belt 1 is suspended between a driving roller 2 and two driven rollers 8 and 9. In this embodiment, the roller used for measurement is the drive roller 2. The peripheral length of the intermediate transfer belt 1 is about 10 times or more the peripheral length of the roller (drive roller 2) used for measurement.

 As drive means for running the intermediate transfer belt 1, a motor 6 such as a stepping motor or a DC motor is used and is connected to the drive roller 2 via a connection mechanism 7. A transmission mechanism such as a gear may be interposed. The motor 6 is driven and controlled by a drive circuit (not shown). By this driving means, the driving roller 2 is rotated in the direction of arrow 10 at a constant angular velocity, and the intermediate transfer belt 1 is caused to travel along the direction 11.

 The eccentric amount of the roller (drive roller 2) used for the measurement is 10 μm in one amplitude. As will be described later, in the present invention, since eccentricity may exist in principle, the actual eccentricity may be larger. About 0.2 μm is sufficient as the surface roughness Ra of the roller (drive roller 2) used for measurement.

 On the opposite side of the intermediate transfer belt 1 from the drive roller 2, a laser displacement meter 3a as a non-contact type displacement measuring device is disposed in a stationary state. In FIG. 1, only one laser displacement meter 3 a is provided, but it is efficient for measurement to arrange a plurality of laser displacement meters 3 in the width direction of the intermediate transfer belt 1. An example of arranging a plurality of laser displacement meters 3a will be described with reference to another drawing. The laser displacement meter 3a may have a repetition accuracy of about 0.01 μm to 0.05 μm. As the laser displacement meter 3a, for example, LK-G35 manufactured by Keyence Corporation can be used.

 FIG. 2 is an enlarged view of the vicinity of the measurement point 5a in FIG. Within the range of the winding angle 21 of the intermediate transfer belt 1 with respect to the drive roller 2, the distance to the surface of the intermediate transfer belt 1 is measured from one direction by the laser displacement meter 3a.

 The laser beam 4 a is conceptually represented, and the center of the measurement direction is the direction 22. In the present embodiment, the measurement direction, that is, the emission direction 22 of the laser beam 4a is directed to the radial direction of the drive roller 2, that is, the center of the drive roller 2, whereby the thickness of the transfer belt 1 can be directly measured. The measurement interval by the laser displacement meter 3a may be continuous in time or intermittent. In the case of intermittent, it is desirable that it is shorter than the sampling interval of the signal processing means 201 described later. The distance signal detected by the laser displacement meter 3a is input to the signal processing means 201 shown in FIG.

 The signal processing unit 201 includes a displacement signal detection unit 202 that detects a distance signal from the laser displacement meter 3a as a displacement signal at a predetermined sampling interval, a Fourier transform calculation unit 203 that performs a Fourier transform on the displacement signal, and a Fourier transform thereof. At least an inverse Fourier calculation means 204 that performs inverse Fourier transform on the signal while limiting to a frequency band that is dominant in the thickness variation of the intermediate transfer belt 1 is provided.

 The total time taken for the displacement signal is preferably a time corresponding to a time for which the intermediate transfer belt 1 is continuously rotated about 10 times or more. If it is 10 rotations, a frequency resolution of 1/10 of one rotation frequency of the intermediate transfer belt 1 can be obtained, so it is easy to increase the signal / noise ratio. In order to shorten the measurement time, the capture time may be shortened a little.

 The sampling interval may be such that the component (mainly the eccentric component) of one rotation frequency fr of the roller (drive roller 2) used for measurement can be detected smoothly in time. In this embodiment, the sampling frequency is about 50 × fr. Further, it is assumed that the high-order frequency of the intermediate transfer belt 1 is taken into consideration up to the fifth order (the intermediate transfer belt 1 used in the experiment was about this level). Further, the one rotation frequency fr of the roller (drive roller 2) and the one rotation frequency fb of the intermediate transfer belt 1 have a relationship of fr = 20 × fb.

 FIG. 3 is a diagram showing a time waveform corresponding to the variation of the displacement signal measured by the laser displacement meter. The abscissa represents one rotation time of the intermediate transfer belt (time interval t0 to t1), and the ordinate represents only the variation of the displacement signal by subtracting the average distance between the laser displacement meter and the surface of the intermediate transfer belt. .

 A display function as shown in FIG. 3 is provided in the signal processing means 201, but is not shown in FIG. In the signal processing unit 201, the displacement signal detection unit 202 actually captures the time waveform of the displacement signal for 10 continuous rotations of the intermediate transfer belt 1. FIG. 3 shows one of the rotations, and it can be seen that the eccentric amplitude of the eccentricity of the drive roller 2 is about 10 μm, 20 cycles, and an amplitude component of a lower frequency is superimposed.

 In FIG. 4, the displacement signals for 10 continuous rotations of the intermediate transfer belt 1 obtained by the displacement signal detection means 202 are collectively subjected to Fourier transform by the Fourier transform calculation means 203, with the horizontal axis representing frequency and the vertical axis representing displacement amplitude. It is the figure expressed in conversion. Information on the real part and the imaginary part of each frequency component subjected to Fourier transform is stored in a storage unit (not shown).

 In order to select a frequency band that is dominant in the thickness fluctuation of the intermediate transfer belt 1, the vertical axis is converted into a displacement as shown in FIG. 4 and displayed on the screen (not shown) of the signal processing means 201. As can be seen from the amplitude of the vertical axis in FIG. 4, the eccentric piece amplitude of one rotation frequency fr (= 20 × fb) of the driving roller 2 is about 10 μm. Among the other AC components, what is remarkable as the signal level is the high-order components of the one-rotation frequencies fb and fb of the intermediate transfer belt 1. The extent to which higher-order components of fb are considered may be determined by actually measuring the intermediate transfer belt 1, but here, the first to fifth orders of fb are considered.

 FIG. 5 shows that the Fourier transform result is extracted from the frequency band of 0.5 × fb to 5.5 × fb using the inverse Fourier transform operation means 204 (see FIG. 1) (band-limited). It is the figure which represented the result of having performed reverse Fourier transform as a time waveform.

 In FIG. 4, the frequency band to be left is only a place dominant to the thickness variation of the intermediate transfer belt 1, and the frequency band to be removed is one rotation frequency fr component (eccentric component) or noise component of the driving roller 2. is there. The time waveform reproduced with the band limited is constituted by the dominant component of the thickness variation along the traveling direction of the intermediate transfer belt 1. Since the real part information and the imaginary part information are stored at the time of the Fourier transform, the gain and phase within the band limit are stored in the reproduction time waveform. In this way, the thickness variation profile along the traveling direction of the intermediate transfer belt 1 during traveling can be measured with high accuracy.

 The influence of the undulation of the surface of the roller (driving roller 2) used for the measurement can be considered. In FIG. 1, another laser displacement meter 3a is prepared (not shown), and the distance between the surface 5a of the intermediate transfer belt 1 and the surface 2a of the drive roller 2 is measured simultaneously. At these measurement points 5a and 2a, the frequency spectrum of the displacement amplitude is created after the free transformation as in FIG.

 FIG. 6 is a diagram showing a frequency spectrum in terms of displacement amplitude on the surface 2 a of the drive roller 2. As is apparent from this figure, the component of one rotation frequency fr of the driving roller 2 is dominant. Although the amplitude of the one rotation frequency fb of the intermediate transfer belt 1 is also slightly visible, this is not due to the thickness fluctuation of the intermediate transfer belt 1, but the mechanism system is structurally based on the amplitude of the one rotation frequency fb of the intermediate transfer belt 1. This is to vibrate. If the amplitude of one rotation frequency fb of the intermediate transfer belt 1 is small, it can be ignored.

 When it is not negligible compared with the thickness fluctuation of the intermediate transfer belt 1, real part and imaginary part information of one rotation frequency fb of the intermediate transfer belt 1 is stored, for example, 0.5 × fb to 5.5 ×. The inverse Fourier transform is performed by limiting to the frequency band of fb. By subtracting the reproduction time waveform from the thickness fluctuation waveform (see FIG. 5) obtained by measuring the surface of the intermediate transfer belt 1, the thickness fluctuation profile of the intermediate transfer belt 1 can be obtained with higher accuracy.

 Next, the thickness variation measuring apparatus will be described, particularly focusing on the structure and operation of the mechanism system. FIG. 7 is a diagram illustrating an implementation example of the thickness variation measuring apparatus of the intermediate transfer belt 1. This measuring apparatus includes a housing unit 141, a plurality of laser displacement meters 3 a, 3 b, 3 c installed in the housing unit 141, an intermediate transfer belt unit 3 1 fixed to the housing unit 141, and a signal processing unit 201. And is mainly composed.

 The signal processing unit 201 has the same configuration and function as the signal processing unit 201 shown in FIG. 1, but is configured to be able to signal-process the outputs from the three laser displacement meters 3a, 3b, and 3c. The three (plural) laser displacement meters 3a, 3b, 3c are installed at a predetermined interval in the width direction of the intermediate transfer belt 1, that is, in the direction orthogonal to the traveling direction of the intermediate transfer belt 1. Thereby, the thickness variation over almost the entire width region of the intermediate transfer belt 1 can be measured.

 FIG. 8 is an exploded perspective view showing only the mechanism part of FIG. The intermediate transfer belt unit 31 is incorporated in the housing unit 141 by fixing members 171a, 171b, 171c, and 171d made of screws or the like. The housing unit 141 is configured in a box shape with a front plate 142, a rear plate 143, a right side plate 144, and a right side plate 145. The connecting means for each plate is not shown. In order to fix the intermediate transfer belt unit 31 to the housing unit 141, grooves 147a and 147b are provided on the upper portion of the front plate 142, and grooves 147c and 147d are provided on the upper portion of the rear plate 143, respectively.

 FIG. 9 is an exploded perspective view of the intermediate transfer belt unit 3 1. The intermediate transfer belt unit 31 mainly includes a belt roller 41, a front plate 61, a rear plate 81, and fixing members 101a, 101b, 101c, and 101d.

 The belt roller 41 has attachment portions 2d, 2e, 8d, 8e, 9d, and 9e to the bearing portions at both ends of the driving roller 2 and the driven rollers 8 and 9, respectively.

 The front plate 61 includes a plate portion 62, bearing portions 63a, 63b, and 63c, a spring 64 for pressing the stationary side of the bearing portion 63b, and protrusions 65a and 65b for fixing the housing unit 141. The bearing parts 63a, 63b, and 63c are inner ring rotating and outer ring fixing. The spring 64 has a conceptual structure that applies tension to the intermediate transfer belt 1, but actually has a structure (not shown) in which the spring force can be adjusted. When the intermediate transfer belt 1 is attached / detached, a mechanism (not shown) is used that reduces the belt tension and switches the intermediate transfer belt 1 to apply a predetermined tension during measurement.

 The rear plate 81 has a plate portion 82, bearing portions 83a, 83b, 83c, a spring 64 for pressing the stationary side of the bearing portion 83b, and protrusions 65a, 65b for fixing the housing unit 141. The bearing portions 83a, 83b, and 83c are inner ring rotating and outer ring fixed. The motor 6 may be connected to the bearing portion 83c of the rear plate 81 via the coupling 7a, and a speed change mechanism (not shown) may be built in the motor 6.

 FIG. 10 is a schematic configuration diagram of a tandem type image forming apparatus according to Embodiment 2 of the present invention. First, the main configuration and main operation of the image forming apparatus 401 will be described.

 Although not shown, the optical unit 411 contains optical components such as a light source composed of a semiconductor laser, a rotating polyhedral mirror, and a lens group. The four photoconductors 421a, 421b, 421c, and 421d correspond to yellow, magenta, cyan, and black.

 A charging potential is applied to each of the photosensitive members 421a, 421b, 421c, and 421d by a charger (not shown). The photosensitive units 421a, 421b, 421c, and 421d are exposed from the optical unit 411 with laser beams 412a, 412b, 412c, and 412d, and image potentials are applied to form an electrostatic latent image to be recorded.

 The electrostatic latent image is developed by developing units 431a, 431b, 431c, and 431d that incorporate toners corresponding to yellow, magenta, cyan, and black to form toner images. This toner image is transferred to the intermediate transfer belt 441 by the primary transfer units 451a, 451b, 451c, and 451d.

 In the intermediate transfer belt unit 440, the intermediate transfer belt 441 is suspended between a drive roller 442 and two driven rollers 448 and 449, and the drive roller 442 is connected to a drive motor 444 via a connection mechanism 443. The drive motor 444 is driven by a motor drive circuit 446, the drive roller 442 rotates at a constant angular velocity, and the intermediate transfer belt 441 travels along the arrow direction 445. The intermediate transfer belt 441 is given a predetermined tension by a tension adjusting mechanism (not shown). If necessary, a meandering correction mechanism (not shown) of the intermediate transfer belt 441 may be added.

 The toner image primarily transferred to the intermediate transfer belt 441 reaches the secondary transfer position 462 by the secondary transfer roller 461. On the other hand, a sheet (not shown) picked up from the sheet cassette 471 moves on the transport path 472 and is secondarily transferred in accordance with the secondary transfer timing of the transfer toner. The sheet on which the toner image is transferred in this manner is fixed 482 by the fixing roller 481 and is discharged from the image forming apparatus 401. The scanner 491 is used only when the copy function is used.

 Next, an example in which the thickness variation of the intermediate transfer belt 441 is measured and applied to speed control for keeping the traveling speed constant will be described with reference to FIG.

 The controller 601 includes a laser displacement meter 603, a signal processing unit 604, and a correction amount calculation unit 605. Although not shown, the signal processing means 604 includes at least a displacement detection means, a Fourier transform calculation means, and a band-limited inverse Fourier transform calculation means.

 The laser displacement meter 603 measures a change in distance to the surface of the intermediate transfer belt 441 on the driving roller 442 with a laser beam 602. The signal processing unit 604 performs the same signal processing as the signal processing unit 201 and calculates the thickness variation profile of the intermediate transfer belt 441.

 Based on this profile, the correction amount calculation means 605 gives a correction profile to the drive circuit 446 of the intermediate transfer belt 441 so that the intermediate transfer belt 441 travels at a constant speed. This correction profile may be updated in real time or from time to time. The thickness variation profile of the intermediate transfer belt 441 can be used for drive control of the intermediate transfer belt 441 to improve color misregistration.

 Next, embodiments of other signal processing means will be described. There is a method of processing a displacement signal from the laser displacement meter through a low-pass filter (LPF). When the rotation frequency of the endless belt is fb and the rotation frequency of the measuring roller is fr, fr = 20 × fb. Further, the roller eccentric half amplitude is set to 10 μm, and after passing through the LPF, the roller can be compressed to 0.1 μm or less (1/100 or less). In order to realize this, an 8th order Butterworth LPF is suitable.

 FIG. 11 is a modification of the contents of the signal processing means shown in FIG. This signal processing means 301 includes at least a displacement signal detection means 302 for detecting a distance signal from the laser displacement meters 3a, 3b, 3c, an 8th order Butterworth LPF 303, and a phase correction means 304 as shown in the figure. It is connected.

 FIG. 12 is a diagram showing gain characteristics and phase characteristics of the 8th-order Butterworth LPF 303. As shown in FIG. 12A, when the breakpoint frequency (−3 dB frequency) is 10 × fb, the gain slope at a frequency greater than 10 × fb is −48 dB / Oct. It is assumed that the frequency band to be considered for the endless belt thickness variation needs to be considered from fb, 2 × fb, 3 × fb, 4 × fb, 5 × fb, that is, the first to fifth orders of fb.

 From the gain characteristic of FIG. 12A, the gain of fb to 5 × fb does not change. Furthermore, the eccentric frequency component 20 × fb of the roller is also −48 dB (1/100 or less), and there is no problem with respect to the gain.

 On the other hand, because of the phase characteristic of FIG. 12B, a phase shift of about −30 degrees to −160 degrees occurs with respect to fb to 5 × fb. Therefore, the waveform passing through the LPF is an actual endless belt thickness fluctuation. The waveform is different from that of, and cannot be used as it is. Although it is a complicated work, since the phase characteristics of this LPF are known in advance, different amounts of phase correction are performed for the frequency components fb, 2 × fb, 3 × fb, 4 × fb, and 5 × fb, respectively. It can be solved by doing.

The effects of the above embodiment are as follows.
(1) A thickness variation profile can be obtained with high accuracy of about 0.1 μm along the traveling direction of the endless belt.
(2) There are conveniences such as measuring the distance to the endless belt surface only from one side, not depending on the eccentricity of the measuring roller, and being able to run while running the endless belt.
(3) The measurement surface of the endless belt is not damaged.
(4) When an endless belt is used as an intermediate transfer belt of an image forming apparatus, the amount of color misregistration in the running direction due to the thickness variation of the intermediate transfer belt can be predicted with high accuracy before the intermediate transfer belt is incorporated into the image forming apparatus. Based on the result, the intermediate transfer belt can be selected as a part, and the yield can be improved.
(5) If the thickness variation measuring function is incorporated in the image forming apparatus, the color shift in the running direction due to the thickness variation can be improved.

 The present invention is not limited to the above-described embodiments. For example, in an image forming apparatus, the present invention can be applied to a photosensitive belt in addition to an intermediate transfer belt. As an influence on the image formation due to the variation in the thickness of the photosensitive belt, the variation in the running speed is caused by the variation in the thickness along the circumferential direction of the photosensitive belt, which causes the above-described variation in the thickness of the intermediate transfer belt. In the same manner as described above, image misalignment and color misregistration occur. As an image forming apparatus using a photoreceptor belt, for example, a photoreceptor belt, four developing units for each color installed along the photoreceptor belt, and one installed on the photoreceptor belt. There is an image forming apparatus including an intermediate transfer drum. Further, the present invention can be applied to an endless belt in other fields other than the image forming apparatus.

It is explanatory drawing which simplified and represented the function of this invention. FIG. 2 is an enlarged view around a measurement point in FIG. 1. It is a figure showing the time waveform for the variation of the displacement signal measured with the laser displacement meter. It is the figure which carried out Fourier transform of the displacement signal. It is a figure showing the time waveform which restricted the frequency band and carried out inverse Fourier transform. FIG. 5 is a diagram obtained by performing Fourier transform on a displacement signal on the surface of a driving roller. FIG. 3 is a diagram illustrating a thickness variation measuring apparatus for an intermediate transfer belt. FIG. 4 is an exploded perspective view showing a state in which an intermediate transfer belt unit is assembled in a housing unit. 2 is an exploded perspective view of an intermediate transfer belt unit. FIG. 1 is a schematic configuration diagram of an image forming apparatus incorporating a thickness variation measuring device. It is a figure showing the thickness variation measuring device of the intermediate transfer belt concerning other examples. It is a figure which shows the Geni characteristic and phase characteristic of the 8th-order Butterworth type LPF which the thickness variation measuring apparatus of the intermediate transfer belt uses.

Explanation of symbols

  1: intermediate transfer belt, 2: drive roller, 3a-3c: laser displacement meter, 4a: laser beam, 5a: measurement point, 6: motor, 7: coupling mechanism, 8: driven roller, 9: driven roller, 21: Wrapping angle, 22: Laser beam emission direction, 31: Intermediate transfer belt unit, 201: Signal processing means, 202: Displacement signal detection means, 203: Fourier transform calculation means, 204: Inverse Fourier transform calculation means, 440: Intermediate Transfer belt unit, 441: intermediate transfer belt, 442: drive roller, 444: drive motor, 446: motor drive circuit, 448: driven roller, 449: driven roller.

Claims (10)

An endless belt suspended on a rotating roller;
Driving means for rotating the endless belt;
Non-contact distance measurement that measures the distance to the surface of the endless belt portion that is disposed on the opposite side of the endless belt and is wound around the endless belt while the endless belt is running. Means,
A displacement signal detecting means for detecting a distance signal from the distance measuring means as a displacement signal along the traveling direction of the endless belt;
A Fourier transform computing means for performing a Fourier transform on the displacement signals output from the displacement signal detecting means collectively for a plurality of continuous rotations of the endless belt;
And an inverse Fourier transform operation means for performing inverse Fourier transform on the signal subjected to Fourier transform by the Fourier transform operation means to limit the frequency band dominant to the thickness variation of the endless belt. Thickness variation measuring device. In the endless belt thickness variation measuring device according to claim 1,
A plurality of the distance measuring means are installed at predetermined intervals along the width direction of the endless belt,
Each distance signal output from each distance measuring means is input to the displacement signal detecting means. In the endless belt thickness variation measuring device according to claim 1 or 2,
The distance measuring means is a laser displacement meter,
An endless belt thickness variation measuring apparatus, wherein the laser beam emitted from the laser displacement meter is directed toward the center of the rotating roller. In the endless belt thickness variation measuring device according to claim 1,
An endless belt thickness variation measuring apparatus, wherein a measurement interval by the distance measuring means is shorter than a sampling interval by the displacement signal detecting means. 5. The endless belt thickness variation measuring apparatus according to claim 1, wherein the endless belt is an intermediate transfer belt or a photosensitive belt used in an image forming apparatus. Variation measuring device. In a method for manufacturing an image forming apparatus for transferring a toner image of two or more colors formed by a photoreceptor on an intermediate transfer belt,
Color misregistration evaluation criteria based on the thickness variation of the intermediate transfer belt has been set,
The thickness fluctuation of the intermediate transfer belt before being incorporated into the image forming apparatus is measured by the thickness fluctuation measuring device according to claim 1,
Comparing the measurement result and the color misregistration evaluation criteria, the pass / fail judgment of the intermediate transfer belt is performed,
An image forming apparatus manufacturing method, wherein an intermediate transfer belt that passes the color misregistration evaluation criteria is incorporated into an image forming apparatus. An intermediate transfer belt for transferring two or more color toner images formed by a photoconductor in an overlapping manner;
A rotation speed control means for controlling the rotation speed of the intermediate transfer belt suspended from a rotation roller;
A non-contact type that measures the distance to the surface of the intermediate transfer belt portion that is disposed on the opposite side of the rotation roller with the intermediate transfer belt interposed therebetween and is wound around the rotation roller while the intermediate transfer belt is running. Distance measuring means,
A displacement signal detecting means for detecting a distance signal from the distance measuring means as a displacement signal along the traveling direction of the intermediate transfer belt;
Fourier transform operation means for performing Fourier transform on the displacement signal output from the displacement signal detection means collectively for a plurality of continuous rotations of the intermediate transfer belt;
An inverse Fourier transform computing means for performing the inverse Fourier transform on the signal subjected to the Fourier transform by the Fourier transform computing means, limited to the frequency band dominant to the thickness fluctuation of the endless belt,
An image forming apparatus characterized in that the rotational speed of the intermediate transfer belt is controlled by the rotational speed control means based on a thickness fluctuation signal of the intermediate transfer belt output from the inverse Fourier transform computing means. The image forming apparatus according to claim 7.
A plurality of the distance measuring means are installed at a predetermined interval along the width direction of the intermediate transfer belt,
Each distance signal output from each distance measuring means is input to the displacement signal detecting means. The image forming apparatus according to claim 7 or 8,
The distance measuring means is a laser displacement meter,
An image forming apparatus, wherein the laser beam emitted from the laser displacement meter is directed toward the center of the rotating roller. The image forming apparatus according to claim 7.
An image forming apparatus, wherein a measurement interval by the distance measuring unit is shorter than a sampling interval by the displacement signal detecting unit.

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