JP6357844B2 - Paper thickness detection device and image forming apparatus having the paper thickness detection device - Google Patents

Description

  The present invention relates to a paper thickness detection device and an improvement of an image forming apparatus having the paper thickness detection device.

  In recent years, image forming apparatuses have been configured to maintain image quality by grasping characteristics of transfer paper (medium) and setting optimum image forming conditions. One of the characteristics of the transfer paper is thickness.

  This thickness is a fundamental and important property related to bending stiffness and paper quality. Conventionally, many image forming apparatuses having means for changing image forming conditions (mainly transfer conditions) and fixing conditions based on the detected sheet thickness have been proposed.

  For example, as a paper thickness detection device, there is a technology for estimating the thickness of a sheet by detecting the displacement of the driven roller by using the displacement of the driven roller by the thickness of the sheet when the driven roller nipping and conveying the sheet. Are known.

  Conventionally, there have been many paper thickness detection devices in which the displacement of the driven roller is enlarged by a lever and detected by a displacement sensor. In recent years, sensors capable of directly detecting minute displacements have been developed. For example, optical sensors and hall elements using PSD are one of them. Among these, the Hall element is small and inexpensive, and can output an analog signal. Therefore, the Hall element is suitable for continuously detecting the behavior of the driven roller as an observation waveform.

  As a paper thickness detection device using this type of sensor, the outer peripheral surface rotates in a fixed cycle, and a reference roller as a driving roller, which is a reference for thickness measurement, can be displaced by being in contact with the reference roller. An apparatus including a detection roller as a driven roller provided, a conveyance unit that conveys a sheet, and an angle sensor that outputs displacement of the detection roller as displacement data is known (see Patent Document 1).

  By the way, when the paper thickness is detected by the displacement of the driven roller, the influence of the eccentricity of the driven roller becomes a problem when the thickness of the paper is detected. In particular, in the case of thin paper, the thickness of the paper is about the same as the amount of eccentricity of the driven roller. For this reason, in order to accurately detect the paper thickness, it is important to remove the influence of the eccentricity of the driven roller.

  In general, the driven roller and the drive roller are almost never the same diameter, and the diameter of the drive roller is larger than the diameter of the driven roller. As a result, the observed waveform as an analog output output from the sensor appears in a form in which a waveform affected by the eccentricity of only the driven roller and a waveform affected by the eccentricity of only the driving roller are superimposed. Therefore, it is necessary to eliminate the influence caused by the eccentricity of the driving roller and the influence caused by the eccentricity of the driven roller.

  The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a paper thickness detection device that eliminates the influence of the eccentricity of the driven roller and the driving roller as much as possible and has high estimation accuracy for each paper passing job. .

The paper thickness detection device according to the present invention includes a driving roller that is rotationally driven, a driven roller that is driven to rotate in contact with the driving roller, a sensor that detects a displacement of the driven roller, and a rotation period of the driven roller. And an average calculation time difference corresponding to the rotation period of the driving roller is obtained from a paper passing state observation waveform that means a change in the output of the sensor, and a paper out state of the paper passing state observation waveform An arithmetic processing unit that obtains an average output difference that is a difference between an average output of the sensor within the average calculation section width and an average output of the sensor within the average calculation section width in the paper presence state after the average calculation time difference has elapsed, and the average output and a storage unit for previously storing a relationship between the difference and paper thickness Prefecture as data, the arithmetic processing unit, put from said average output difference between the data stored in the storage unit in the sheet passing state It calculates the paper thickness, and a difference the average calculating section width and the average calculation time, and obtaining a power spectrum of the sheet passing state observed waveform.

  According to the present invention, since the removal process of the eccentric component of the roller can be performed in accordance with the rotational fluctuation of the roller pair including the driving roller and the driven roller for each paper passing job, the paper having high estimation accuracy for each paper passing job. A thickness detection value can be obtained.

  In other words, the optimum roller eccentric component removal process can be performed for each paper passing job, so that it is stable over a long period of time without being affected by the deterioration of transport performance over time such as slip and wear between the driving roller and the driven roller. Can maintain a good paper thickness detection performance.

FIG. 1 is an explanatory diagram schematically showing a configuration for measuring the output characteristics of the Hall sensor. FIG. 2 is an output characteristic diagram showing the relationship between the output characteristic of the Hall sensor shown in FIG. 1 and the amount of displacement, and is an explanatory diagram when the Hall sensor is a Hall element. FIG. 3 is an output characteristic diagram showing the relationship between the output characteristics of the Hall sensor shown in FIG. 1 and the displacement, and is an explanatory diagram when the Hall sensor is a Hall IC. FIG. 4 is a block diagram showing an example of a transport apparatus in which the Hall sensor shown in FIG. 1 is incorporated. FIG. 5 is a schematic diagram illustrating a pair of the driving roller and the driven roller illustrated in FIG. 4 and is an explanatory diagram illustrating a sheet conveyance state. FIG. 6 is an explanatory diagram illustrating an example of a steady-state observation waveform in a steady rotation state of one of the transport apparatuses. FIG. 7 is an explanatory diagram showing an example of a steady state observation waveform in the steady rotation state of the other transport device. FIG. 8 is an explanatory diagram showing a power spectrum obtained by Fourier transforming the steady state observation waveform shown in FIG. FIG. 9 is an explanatory diagram showing a power spectrum obtained by Fourier transforming the steady state observation waveform shown in FIG. FIG. 10 is an explanatory diagram showing an example of a sheet passing state observation waveform in a sheet passing state to one of the conveying devices. FIG. 11 is an explanatory diagram illustrating an example of a sheet passing state observation waveform in a sheet passing state to the other transport device. FIG. 12 shows the time of the Hall sensor for each sheet passing job when the average calculation time difference is fixed to twice the period of the driven roller and the average calculation section width is changed with respect to the period of the driven roller. It is a graph explaining the change of an average output difference and the standard deviation with respect to the time average output difference for 10 sheets. FIG. 13 shows the Hall sensor time for each sheet passing job when the average calculation time difference is fixed to twice the period of the driven roller and the average calculation section width is changed with respect to the period of the driven roller. It is a graph explaining the change of an average output difference and the standard deviation with respect to the time average output difference for 10 sheets. FIG. 14 shows the difference between the time average output of the hall sensors for each sheet passing job when the average calculation time difference is fixed to the driving roller period and the average calculation section width is changed with respect to the driven roller period. It is a graph explaining the standard deviation with respect to the change of 10 and the time average output difference for 10 sheets. FIG. 15 shows a time average output difference of the Hall sensor for each sheet passing job when the average calculation time difference is fixed to the period of the driving roller and the average calculation section width is changed with respect to the period of the driven roller. It is a graph explaining the standard deviation with respect to the change of 10 and the time average output difference for 10 sheets. FIG. 16 is an explanatory diagram schematically showing the case where the eccentricity of the drive roller is 0 and the phase difference between the steady state observation waveform in the absence of paper and the steady state observation waveform in the presence of paper is zero. FIG. 17 is an explanatory diagram schematically showing the case where the eccentricity of the drive roller is 0 and the phase difference between the steady state observation waveform in the absence of paper and the steady state observation waveform in the paper presence state is not zero. FIG. 18 is an explanatory view schematically showing a paper passing state observation waveform with the eccentricity of the driven roller being zero. FIG. 19 shows the Hall sensor with respect to the time average output difference for 10 sheets when the average calculation time difference is fixed to the driving roller period and the average calculation section width is changed with respect to the center of the driven roller period. It is explanatory drawing which shows an average. FIG. 20 is an explanatory diagram showing a standard deviation corresponding to the average output difference shown in FIG. FIG. 21 shows the Hall sensor with respect to the time average output difference for 10 sheets when the average calculation time difference is fixed to the driving roller period and the average calculation section width is changed with respect to the center of the driven roller period. It is explanatory drawing which shows an average. FIG. 22 is an explanatory diagram showing a standard deviation corresponding to the average output difference shown in FIG. FIG. 23 shows the average of the Hall sensors with respect to the time average output difference for 10 sheets when the average calculation time difference is fixed to the period of the driven roller and the average calculation time difference is changed with respect to the driving roller period as the center. It is explanatory drawing which shows. FIG. 24 is an explanatory diagram showing a standard deviation corresponding to the average output difference shown in FIG. FIG. 25 shows the average of the Hall sensors with respect to the time average output difference for 10 sheets when the average calculation time difference is fixed to the period of the driven roller and the average calculation time difference is changed with respect to the center of the driving roller period. It is explanatory drawing which shows. FIG. 26 is an explanatory diagram showing a standard deviation corresponding to the average output difference shown in FIG. FIG. 27 is an explanatory diagram showing an example of a power spectrum obtained by Fourier transforming the paper passing state observation waveform. FIG. 28 is an explanatory view schematically showing another configuration of the transport apparatus according to the present invention. FIG. 29 is an explanatory diagram of a cross-correlation function. FIG. 30 is an explanatory diagram of a waveform for obtaining a cross-correlation function, and is an explanatory diagram of an extracted waveform extracted from a steady-state observation waveform for one of the transport apparatuses. FIG. 31 is an explanatory diagram of a waveform for obtaining a cross-correlation function, and is an explanatory diagram of a waveform extracted from a steady-state observation waveform for the other transport device. FIG. 32 is an explanatory diagram of the cross-correlation function obtained from the extracted waveform shown in FIG. FIG. 33 is an explanatory diagram of a cross-correlation function obtained from the extracted waveform shown in FIG. FIG. 34 is an explanatory diagram showing a fluctuation waveform obtained by applying the simple moving average method to the steady state observation waveform shown in FIG. 6 in order to obtain the rotation period of the driving roller for one of the conveying devices. FIG. 35 is an explanatory diagram showing a fluctuation waveform obtained by applying the simple moving average method to the steady-state observation waveform shown in FIG. 7 in order to obtain the rotation period of the driving roller for the other transport device. FIG. 36 is an explanatory diagram of a cross-correlation function obtained from a paper passing state observation waveform for one of the conveying devices. FIG. 37 is an explanatory diagram of a cross-correlation function obtained from the paper passing state observation waveform for the other transport device. FIG. 38 is an explanatory diagram showing a fluctuation waveform obtained by applying a simple moving average to the paper passing state observation waveform shown in FIG. 10 in order to obtain the rotation period of the driving roller for one of the conveying devices. FIG. 39 is an explanatory diagram showing a fluctuation waveform obtained by applying a simple moving average to the paper passing state observation waveform shown in FIG. 11 in order to obtain the rotation period of the driving roller for the other transport device. FIG. 40 shows the number of time average output differences of the Hall sensor when the average calculation section width is fixed to the rotation period of the driven roller and the average calculation time width is fixed to twice the rotation period of the driven roller for one of the conveying devices. It is a characteristic view which shows the regression relationship of an average and paper thickness. FIG. 41 is a characteristic diagram illustrating a regression relationship between the average number of time average output differences of the Hall sensors and the paper thickness when the average calculation section width and the average calculation time width are variable for one transport device. FIG. 42 shows the number of time average output differences of the Hall sensor when the average calculation section width is fixed to the rotation period of the driven roller and the average calculation time width is fixed to twice the rotation period of the driven roller for the other conveyance device. It is a characteristic view which shows the regression relationship of an average and paper thickness. FIG. 43 is a characteristic diagram showing a regression relationship between the average sheet number of the time average output difference of the Hall sensors and the paper thickness when the average calculation section width and the average calculation time width are variable for the other transport device. FIG. 44 is an explanatory diagram of a paper thickness calculation flow according to the present invention. FIG. 45 is an explanatory diagram of a flow for obtaining the average calculation section width and the average calculation time difference by Fourier transforming the paper passing state observation waveform. FIG. 46 is an explanatory diagram of a flow for obtaining an average calculation section width and an average calculation time difference by a cross-correlation method and a moving average method. FIG. 47 is a schematic configuration diagram showing an embodiment of an image forming apparatus equipped with a paper thickness detecting apparatus according to the present invention.

Hereinafter, a paper thickness detection apparatus and an image forming apparatus including the paper thickness detection apparatus according to an embodiment of the present invention will be described with reference to the drawings.
(Description of output characteristics of the Hall sensor used in the embodiment of the present invention)
First, output characteristics of the Hall sensor used in the paper thickness detection apparatus according to the embodiment of the present invention will be described with reference to FIGS.
In this embodiment, the Hall sensor HS (see FIG. 1) includes the Hall element and the Hall IC.

  As shown in FIG. 1, it is assumed that the permanent magnet MG faces the hall sensor HS via a gap δ. Since the Hall sensor HS is sealed in resin or the like, it is assumed that the gap δ includes a thickness corresponding to the resin.

  In FIG. 1, the permanent magnet MG is reciprocated in the direction of the arrow X, and a line segment connecting the N pole and the S pole (line segment connecting the magnetic poles) NS is parallel to the reciprocating direction. . In FIG. 1, the symbol MFL indicates a magnetic field line.

  In this embodiment, a neodymium magnet is used as the permanent magnet MG. The magnetic flux density of this neodymium magnet is 440 mT (440 millitesla). The neodymium magnet has a quadrangular cross-sectional shape, a cross-sectional area of 3 square millimeters, and a line segment NS connecting the north and south poles is 5 millimeters.

  2 and 3 show the output characteristics of the Hall sensor HS when the permanent magnet MG is reciprocated in the direction of the arrow X. FIG. 2 and 3, the vertical axis represents the output voltage (unit: mV) V as the sensor output of the Hall sensor HS when the permanent magnet MG is displaced by X in the arrow X direction with the reference position of “0”. Represents a change in the output voltage V of the Hall sensor HS when the displacement amount is X (denoted by the same symbol as the arrow X for convenience of explanation).

  FIG. 2 is an output characteristic diagram of the output voltage V when measured using HG-106C (Hall element) manufactured by Asahi Kasei Microdevices Corporation. In FIG. 2, Q1 is an output characteristic curve showing a change in the output voltage V when the gap δ = 0.5 mm, and Q2 is an output characteristic curve showing a change in the output voltage V when the gap δ = 1.0 mm. Q3 is an output characteristic curve showing a change in the output voltage V when the gap δ = 1.5 mm.

  According to this HG-106C (Hall element) manufactured by Asahi Kasei Microdevices Co., Ltd., if the displacement is within ± 1mm (preferably within ± 0.5mm), high linearity between output voltage V and displacement X However, high linearity is not obtained between the output voltage V and the displacement amount X with respect to the displacement amount exceeding ± 1 mm.

  FIG. 3 is an output characteristic diagram of the output voltage V when measured using EQ-711L (linear Hall IC incorporating an amplifier circuit) manufactured by Asahi Kasei Microdevices Corporation. In FIG. 3, Q4 is an output characteristic curve showing the change of the output voltage V when the gap δ = 0.5 mm, and Q5 is an output characteristic curve showing the change of the output voltage V when the gap δ = 1.0 mm. . Q6 is an output characteristic curve showing a change in the output voltage V when the gap δ = 1.5 mm, and Q7 is an output characteristic curve showing a change in the output voltage V when the gap δ = 2.0 mm.

  For the gap δ = 0.5 mm to 1.5 mm, the linearity portion of the output characteristic curves Q1 to Q3 shown in FIG. 2 and the linearity portion of the output characteristic curves Q4 to Q6 shown in FIG. Asahi Kasei Electronics Co., Ltd. HG-106C (Hall element) output voltage V = ± 25mV, Asahi Kasei Electronics Co., Ltd. EQ-711L (Linear Hall IC with built-in amplifier) output voltage V = 0V ~ 5V Almost corresponds.

  Asahi Kasei Electronics Co., Ltd. EQ-711L (Linear Hall IC with built-in amplification circuit) is easier to handle than Asahi Kasei Electronics Co., Ltd. HG-106C (Hall element). .

  The range of displacement that can be detected using these Hall sensors HS is 2 mm or less at the expense of linearity, and 1 mm or less when the linearity is severely considered. The thickness of the paper used in the image forming apparatus and the image reading apparatus is about 50 to 300 μm.

Therefore, when detecting the displacement of the conveying roller (driven roller) on the driven side of the conveying device of the image forming apparatus, if the Hall sensor HS is used, a displacement detecting unit having a small and simple configuration without requiring an enlargement mechanism. Can be calibrated. On the other hand, the sensitivity greatly varies depending on the size of the gap δ, and therefore the dependence on the gap δ is large.
2 and 3, the output characteristic curve of the output voltage V has a negative slope because of the relationship between the Hall sensor HS and the directions of the magnetic poles N and S of the permanent magnet MG.

In FIG. 1, the description has been made assuming that one hall sensor HS is used. However, two hall sensors HS are arranged in the direction of the arrow X of the permanent magnet MG, and the output voltages V1 and V2 of the two hall sensors HS are arranged. If the difference between the two is the output voltage V, better linearity can be obtained over a wide range of displacement.
Hereinafter, description will be made using EQ-711L (linear Hall IC with a built-in amplifier circuit) manufactured by Asahi Kasei Electronics Co., Ltd., which has good linearity of the output voltage V and is easy to handle.

(Schematic diagram of the configuration of the transport device)
FIG. 4 is a schematic diagram showing the configuration of the conveying device of the image forming apparatus according to the embodiment of the present invention.
In FIG. 4, reference numerals 1 and 1 denote side plates. Bearing members 3 and 4 are fixed to the side plates 1 and 1. A rotating shaft 5 is rotatably supported by the bearing members 3 and 4. The rotating shaft 5 is provided with a pair of drive rollers 6 and 6 spaced apart in the axial direction. The diameter φ of the drive rollers 6 and 6 is, for example, φ = 35 mm.

  A gear 7 constituting a part of the rotation transmission mechanism is fixed to one end portion of the rotation shaft 5. The gear 7 is connected to a drive motor (not shown) as a drive source (not shown). A rotating shaft 8 faces the rotating shaft 5.

  Both ends of the rotary shaft 8 are rotatably supported by bearing members 9 and 9, respectively. The bearing members 9 and 9 are supported by a support plate 11 via a spring member 10, and the bearing members 9 and 9 can swing in the arrow X direction with respect to the support plate 11.

  The rotating shaft 8 is provided with driven rollers 12 and 12 at intervals in the longitudinal direction. The driven rollers 12 and 12 are brought into contact with the driving rollers 6 and 6 and are driven to rotate by the driving rollers 6 and 6. The driven rollers 12 and 12 have a diameter φ of 20 mm. The linear velocity is 282 mm / s.

  The support plate 11 is fixed to a frame (not shown). In the frame, the side plates 1 and 1 and the driven rollers 12 and 12 are supported so as to be separated from the driving rollers 6 and 6. With this configuration, it is possible to facilitate the paper removal operation when a paper jam occurs.

A permanent magnet MG is fixed to the bearing member 9 on one end side of the rotating shaft 8. A line segment NS (see FIG. 1) connecting the N pole and the S pole of the permanent magnet MG is parallel to the swing direction (the direction of the arrow X).
The hall sensor HS faces the permanent magnet MG via a gap δ (see FIG. 1).

  The permanent magnet MG can be oscillated and displaced in the direction of the arrow X. However, since the movement and rotation of the rotary shaft 8 in the axial direction are constrained by the spring member 10, fluctuations in the gap δ and rotation of the permanent magnet MG are possible. Variations need not be taken into account.

  When two Hall sensors HS are arranged in the swing direction (arrow X direction), the direction of the line segment NS connecting the polarities N and S of the permanent magnet MG is perpendicular to the swing direction of the rotary shaft 8. The permanent magnet MG is arranged so that

(Explanation for generating the acquisition timing signal of the paper passing state observation waveform)
Next, generation of an acquisition timing signal for acquiring a paper passing state observation waveform to be described later will be described.
FIG. 5 shows a drive mechanism on the upstream side in the transport direction and a drive mechanism on the rear side in the transport direction. The support plate 11 shown in FIG. 4 rotates to face the rotating shaft 5 ′ on the front side in the transport direction shown in FIG. A shaft 8 'is provided.

  A drive roller 6 'is provided on the rotary shaft 5' on the upstream side in the transport direction, and a driven roller 12 'is provided on the rotary shaft 8' on the upstream side in the transport direction, as shown in FIG. A driving roller 6 and a driven roller 12 shown in FIG. 4 are provided on the rotation shafts 5 and 8 on the rear side in the transport direction, respectively.

The paper PA is transported in the arrow Y direction from the front side in the transport direction toward the rear side in the transport direction.
As shown in FIG. 5, a photo interrupter 13 is provided in the sheet conveyance area between the rotation shafts 5 ′ and 8 ′ on the upstream side in the conveyance direction and the rotation shafts 5 and 8 on the downstream side in the conveyance direction.

  The photo interrupter 13 is used to detect the edge PAT on the front side of the paper PA. When the edge (tip) PAT of the paper P crosses the photo interrupter 13, the output signal of the photo interrupter 13 changes from high to low. A change from high to low of the output signal of the photo interrupter 13 is used as an acquisition timing signal (trigger signal) of a paper passing state observation waveform to be described later.

That is, the start time 0 of data acquisition of the output voltage V of the hall sensor HS is set.
First, the fluctuation waveform (steady state observation waveform) of the output voltage V observed by the Hall sensor HS when there is no paper PA before the description of the paper passing state observation waveform will be described with reference to FIGS. To do.

(Explanation of fluctuation waveform (steady state observation waveform) of output voltage V observed by Hall sensor HS when paper PA is not present)
Here, the sampling frequency is 1 KHz (1000 per second), and the data acquisition time time of the steady state observation waveforms W1 and W2 is 20 seconds. FIGS. 6 and 7 show steady-state observation waveforms W1 and W2 with the output voltage V sampled for 4 seconds.

  Here, the steady state observation waveforms W1 and W2 (see FIG. 6 and FIG. 7) for the two conveying devices having different degrees of eccentricity of the driving roller 6 and the driven roller 12 will be described. Also, one of the two conveying devices has a relatively small amount of eccentricity of the drive roller 6 compared to the other, and the other of the two conveying devices has a relatively large amount of eccentricity of the driving roller 6 compared to the other. And

  FIG. 6 shows a steady state observation waveform W1 of one transfer device, and FIG. 7 shows a steady state observation waveform W2 of the other transfer device. FIG. 8 shows a power spectrum obtained by Fourier transforming the steady state observation waveform W1, and FIG. 9 shows a power spectrum obtained by Fourier transforming the steady state observation waveform W2.

Since the resolution of the spectral frequency is given by [(frequency range) / (number of sampling points / 2)], (1000/2) / (1000 × 20/2) = 0.05 Hz.
The spectrum frequencies where the powers of the power spectra FW1 and FW2 after Fourier transform are large are f1 = 2.6 Hz and f2 = 4.55 Hz.

When it is assumed that the driving roller 6 and the driven roller 12 are not eccentric, the output voltage V of the hall sensor HS does not fluctuate. If the drive roller 6 and the driven roller 12 are eccentric, the output voltage V fluctuates.
The fluctuation of the output voltage V caused by the eccentricity appears as a superposition of the fluctuation caused by the eccentricity of the driving roller 6 and the fluctuation caused by the eccentricity of the driven roller 12.

  In general, since it is the driving roller 6 that is important in controlling the conveyance speed of the paper PA, the amount of eccentricity of the diameter of the driving roller 6 can be suppressed to be smaller than the amount of eccentricity of the diameter of the driven roller 12 in the process of manufacturing parts. .

  Further, the driving roller 6 and the driven roller 12 are hardly the same diameter, and the diameter of the driving roller 6 is larger than the diameter of the driven roller 12. Further, it is desirable to set the greatest common divisor of both diameters to be “1”.

  The reason is that when one of the driving roller 6 and the driven roller 12 is defective, it is dispersed so as not to repeatedly contact the same position of the other roller.

  When comparing the steady state observation waveform W1 and the steady state observation waveform W2, the steady state observation waveform W2 is more complex than the steady state observation waveform W1. Since the diameter of the driven roller 12 is smaller than the diameter of the driving roller 6, the rotational angular velocity of the driven roller 12 is larger than the rotational angular velocity of the driving roller 6. Therefore, the spectral frequency caused by the eccentricity is The spectral frequency f2 caused by the eccentricity of the driven roller 12 is larger than the spectral frequency f1 caused by the eccentricity of the driven roller 12.

That is, the relative characteristics of each roller appearing in the steady state observation waveforms W1 and W2 are:
Frequency: driving roller 6 <driven roller 12
Amplitude (or power): driving roller 6 <driven roller 12
It is.

  From the steady state observation waveform W1 and the power spectrum FW1, it is understood that the eccentricity of the driven roller 12 is dominant in one of the conveying devices. Further, it is understood from the steady state observation waveform W2 and the power spectrum FW2 that the eccentricity of the driving roller 6 is relatively larger than the eccentricity of the driven roller 12 in the other transport device. The difference between the output values of the steady state observation waveforms W1 and W2 is because there is a difference in the gap δ between the permanent magnet MG and the Hall sensor HS.

(Description of the paper passing state observation waveforms PW1, PW2)
10 and 11 show the paper passing state observation waveforms PW1 and PW2.
The data acquisition conditions of the paper passing state observation waveforms PW1, PW2 are as described below.
The sampling frequency is 1 kHz, the passage timing of the edge PAT of the paper PA with respect to the photo interrupter 13 is “0” seconds, the left side is indicated by “minus −”, and the right side is indicated by “plus +”. That is, the output voltage V of the Hall sensor HS is acquired from about 1 second before to about 1.5 seconds. The period from about 0.9 seconds before to about 1.1 seconds indicates the operation time of the driving roller 6 and the driven roller 12, and the Hall sensor HS has outputs before and after that. 11 shows data acquisition time from −1 second to 1.5 seconds.

  The paper thickness is 97 μm (70 kg paper), and the paper passing size is A4, which is a short feed. In this embodiment, the configuration is such that the edge PAT (see FIG. 5) of the paper PA is indirectly detected by a change in the waveform of the output voltage of the Hall sensor HS after time t = 0s from 0.36s. That is, the edge PAT of the paper PA is detected by the change in the waveform of the output voltage of the Hall sensor HS at tin = 0.36 s.

  Note that the output voltage V of the Hall sensor HS in the state without the paper PA is larger than the output voltage V of the Hall sensor HS in the state with the paper PA in the arrangement direction of the magnetic poles of the Hall sensor HS and the permanent magnet MG. Depending on the relationship. That is, as in FIG. 3, when the displacement of the permanent magnet MS changes (increases) in the positive direction, the output of the Hall sensor HS changes (decreases) in the negative direction.

  In the paper passing state observation waveform PW1, the fine vibration is generated at the time of activation-t1 (about 0.9 s) with respect to the time “0” and after the detection time tin (0.36 s) on the leading end side of the edge PAT of the paper PA. Has occurred. In the paper passing state observation waveform PW2, the fine vibration appears at the time t1 (before about 0.9 s).

  Here, at the time of activation-before t1 means the time point before the rotation of the pair of the driving roller 6 ′ and the driven roller 12 ′ and the pair of the driving roller 6 and the driven roller 12 is started, and the paper passing state observation waveform PW1. At the time of starting PW2, the fine vibration before t1 is a waveform fluctuation due to noise of the Hall sensor HS.

  When the paper passing state observation waveforms PW1 and PW2 are started up—the large vibration immediately after t1 is due to the impact when the edge PAT of the paper PA is drawn into the driving roller 6 ′ and the driven roller 12 ′, and the edge PAT of the paper PA The vibration of tin at the time of detection is due to an impact generated when the driven roller 12 rides on the paper PA.

  Further, the minute vibration after the time tout of the paper passing state observation waveforms PW1 and PW2 is caused by the noise of the Hall sensor HS immediately after the edge PAT 'on the rear end side of the paper PA passes through the pair of the driving roller 6 and the driven roller 12. Waveform fluctuation. The reason why the output voltage of the Hall sensor HS is different before time t1 and after time t1 is due to the phase state of the driving roller 6 and the driven roller 12 or the like.

For the detection of the paper thickness x of the paper PA, an output difference ΔV between the output voltage V of the Hall sensor HS when there is no paper and the output voltage V of the Hall sensor HS when there is paper is used. The sign ΔV is also used to mean the average output difference.
For this reason, if the detection time tin of the edge PAT of the paper PA includes a vibration component due to the riding on the edge PAT of the paper PA, the reliability of the measured value of the paper thickness x of the paper PA is lowered. Therefore, it is necessary to avoid data extraction during this period.

  Therefore, the time when margin is added to the detection time “tin” of the edge PAT of the paper PA is set as the data extraction start timing (extraction timing of the output voltage V) of the area (paper presence state) through which the paper PA passes. The reference time ts for data extraction is used. Here, the reference time ts = 0.48 s.

  Reciprocal numbers of the peak frequencies f1 and f2 of the power spectra FW1 and FW2 shown in FIGS. 8 and 9 mean the rotation periods of the driving roller 6 and the driven roller 12. Therefore, the rotation period of the driving roller 6 is 0.39 s, and the rotation period of the driven roller 12 is 0.22 s.

  10 and 11, ts = 0.48s is entered as a starting point, which is a candidate for the data extraction start timing (average calculation time difference T2 described later) of the passage area of the paper PA. Note that the time corresponding to the rotation period of the driven roller 12 is too small at 0.22 s, and the time-averaging section overlaps with the paper tip passage time, so it is set to 0.44 s, which is twice this.

  In the paper passing state observation waveform PW1 obtained by one of the conveying devices, the eccentric component of the driven roller 8 is large. Therefore, it can be confirmed that the paper passing state observation waveform PW1 is in phase with T2 = 0.44s behind. However, it is not clear from the paper passing state observation waveform PW2 obtained by the other transport device. At first glance, it can be considered that data extraction with an average calculation time difference T2 = 0.44 s can obtain a result with less variation.

  Comparing the output difference ΔV of the output voltage V of the hall sensor HS of the paper passing state observation waveform PW1 shown in FIG. 10 with the amplitude ΔPW of the paper passing state observation waveform PW1, it can be seen that they are comparable. .

  Further, when the output difference ΔV of the output voltage V of the hall sensor HS of the paper passing state observation waveform PW2 shown in FIG. 11 is compared with the amplitude ΔPW of the paper passing state observation waveform PW2, they are also comparable. I can see it.

  That is, it can be seen that the eccentric amounts of the driving roller 6 and the driven roller 12 and the paper thickness x of the paper PA are approximately the same. Under such circumstances, in order to accurately extract the information on the paper thickness x, it is necessary to remove the eccentric components of the driving roller 6 and the driven roller 12.

  In order to remove the eccentric amounts of the drive roller 6 and the driven roller 12, the extraction data of N rotations of the driven roller 12 (N is a natural number of 1 or more) is usually averaged. However, the diameters of the driving roller 6 and the driven roller 8 are hardly the same, and the diameter of the driving roller 6 is larger than the diameter of the driven roller 12.

  For this reason, even if the data for N rotations of the driven roller 12 are averaged, the eccentric component of the drive roller 6 remains. If the eccentric amount of the driving roller 6 is further reduced, the eccentric component of the driving roller 6 can be removed. However, since it takes time to process the drive roller 6, the manufacturing cost increases. Therefore, an effective method that can simultaneously suppress the influence of both eccentricities is desired.

(Relationship between average calculation time difference T2 and average calculation interval width T1)
Therefore, the concepts of average calculation time difference T2 and average calculation interval width T1 are introduced.
Here, the average calculation time difference T2 starts extraction of the output voltage V of the Hall sensor HS when there is no paper PA and the output voltage V of the Hall sensor HS when there is paper PA. The time difference from the time.

  The average calculation section width T1 refers to the width of a section in which the output voltage V of the hall sensor HS is extracted (sampled) and time-averaged.

  The average calculation time difference T2 is fixed to 0.44 s, which is twice the rotation cycle of the driven roller 12, and the average calculation section width T1 between the paper presence region and the paper absence region is set to 0.22 s, which is the rotation cycle of the driven roller 12. The output difference ΔV of the output voltage V of the Hall sensor HS when changing from +0.2 s to −0.2 s at the center will be described with reference to FIGS. 12 and 13.

  Here, the output difference ΔV of the hall sensor HS means a difference between the time average output of the hall sensor HS in the paper area and the time average output of the hall sensor HS in the paper area.

  In FIGS. 12 and 13, the output difference ΔV of 10 individual Hall sensors HS is shown. A curve indicated by σ is a standard deviation curve for 10 sheets when the average calculation section width T1 is changed. In FIGS. 12 and 13, the measurement is performed using 70 kg paper as the paper PA.

  In both FIGS. 12 and 13, the output difference ΔV has a very small change based on the difference in the average sending section width T1 for all 10 sheets. On the other hand, the variation of the output difference ΔV shown in FIG. 13 obtained using the other conveying device is larger than the variation of the output difference ΔV shown in FIG. 12 obtained using one conveying device. There is no average calculation interval width T1 that minimizes the standard deviation σ, and the variation remains large.

  14 and 15, the average calculation time difference T2 is fixed to 0.39 s that is the rotation period of the driving roller 6, and the average calculation section width T1 between the area with paper passing and the area without paper passing is determined as the rotation of the driven roller 12. The output difference ΔV of the Hall sensor HS when changing from +0.2 s to −0.2 s centering on the period 0.22 s is shown.

  14 and 15 also show individual output differences ΔV for 10 sheets of paper passing jobs, as in FIGS. 12 and 13. Similarly, a curve indicated by σ is a curve of a standard deviation when the average calculation section width T1 is changed, and FIGS. 14 and 15 are measured using 70 kg paper as the paper PA.

  In FIGS. 14 and 15, the output difference ΔV for 10 sheets of paper passing jobs changes with various inclinations. However, in FIG. 14, when the average calculation section width T1 is 0.222s and in FIG. 15, the average calculation section width T1 is 0.221s, the variation is the smallest.

  That is, the standard deviation σ is minimized in the vicinity of the average calculation section width T1 = 0.22 s. Compared to FIGS. 12 and 13, the standard deviation σ is approximately ½ in one transport device, and approximately ½ in the other transport device. It can be suppressed to 1/3.

  That is, the average calculation section width T1 is set to the rotation cycle of the driven roller 12, the average calculation time difference T2 is set to be the rotation cycle of the driving roller 6, and the Hall sensor HS is set in the paper absence region and the paper presence region. If the data of the output voltage V is extracted and averaged, it is considered that a detected value of the paper thickness x with a small variation can be obtained.

(Reason why the detected value of the paper thickness x with small variation is obtained when the average calculation section width T1 is set to the rotation period of the driven roller 12 and the average calculation time difference T2 is set to the rotation period of the driving roller 6)
16 and 17, the detected value of the paper thickness x with small variation is obtained when the average calculation section width T1 is set to the rotation period of the driven roller 12 and the average calculation time difference T2 is set to the rotation period of the driving roller 6. It is explanatory drawing which drew the fluctuation | variation of the paper passing state observation waveform typically in order to explain the reason for being made.

  FIGS. 16 and 17 are graphs in which the observed waveform MPW schematically illustrated is superimposed on the presence / absence of the paper PA when the eccentric amount of the driving roller 6 is assumed to be “0”. FIG. 16 shows a state where the phase difference φ = 0 between the observation waveform MPW1 schematically shown when there is no paper PA and the observation waveform MPW2 schematically shown when the paper PA exists.

  FIG. 17 shows that the phase difference between the observed waveform MPW1 schematically shown when there is no paper PA and the observed waveform MPW2 shown schematically when the paper PA exists is φ = φ0 (φ0 is not “0”). ).

  In FIG. 16, since there is no phase difference φ between the observed waveform MPW1 and the observed waveform MPW2, when the average calculation section width T1 is made to coincide with the rotation period of the driven roller 12, the driven roller 12 is within the average calculation section width T1. The average output difference ΔV between the two waveforms corresponds to the paper thickness x of the paper PA. This corresponds to the detection results shown in FIGS.

  The average output difference ΔV referred to here is when the output voltage V1 of the Hall sensor HS and the paper PA are not present when the paper PA is divided into N (N is an integer of 2 or more) within the average calculation section width T1. The difference of the time average with the output voltage V2 of the Hall sensor HS.

  Even if the average calculation section width T1 does not coincide with the rotation period of the driven roller 12, there is no phase difference between the two waveforms, so the output voltage V of the Hall sensor HS only varies by the paper thickness x. The average output difference ΔV corresponds to the paper thickness x.

  Here, a case where the eccentricity of the drive roller 6 having a small eccentric amount and a long cycle is added will be considered. In this case, the fluctuation of the interval between the states of the observed waveform MPW1 and the observed waveform MPW2 mainly increases, and the variation of the average output difference ΔV increases. As a result, there is a large variation with respect to the average calculated section width T1, and the state shows a stable change. That is, the standard deviation σ is substantially constant, and this corresponds to the measurement result when the average calculation time difference T2 shown in FIGS. 12 and 13 is 0.44 s.

  As shown in FIG. 17, even when there is a phase difference φ between when the paper PA is present and when the paper PA is not present, if the average calculation section width T1 is made to coincide with the rotation period of the driven roller 12, The influence of the eccentricity of the driven roller 12 can be eliminated, and the average output difference ΔV between the two observed waveforms MPW1 and MPW2 within the average calculation section width T1 similarly corresponds to the paper thickness x.

  This is because when the average calculation section width T1 coincides with the rotation period of the driven roller 12, the average output difference ΔV is N as the sum of the individual output value differences (V1−V2) subdivided and sampled. This is because the average output difference obtained by dividing is the same.

  On the other hand, when the average calculation section width T1 does not coincide with the rotation period of the driven roller 12, the average output difference ΔV is the sum of the differences (V1−V2) of the individual output voltages V subdivided and sampled. It is not the same as the average output difference ΔV obtained by dividing by N, and increases or decreases according to the shift amount of the phase φ.

When the eccentricity of the driving roller 6 is added to this, the phase difference changes depending on the combination of the rotational state (phase) of the driving roller 6 and the driven roller 12. As a result, there is a difference except when the average calculation section width T1 coincides with the rotation period of the driven roller 12, and the standard deviation σ corresponding to the square of the difference is the average calculation section width T1 corresponding to the period of the driven roller 12. It becomes the minimum in the state where it corresponds. This corresponds to the measurement results shown in FIGS. 14 and 15 when the average calculation time difference T2 is 0.39 s.
Therefore, a condition for removing both the influence of the eccentricity of the driving roller 6 and the eccentricity of the driven roller 12 will be considered.

(Conditions for removing the influence based on the eccentricity of the driving roller 6 and the influence based on the eccentricity of the driven roller 12 to obtain the measured value of the paper thickness x)
FIG. 18 schematically shows an observed waveform MPW ′ when measurement is performed assuming that the eccentricity of the driven roller 12 is “0”.

  The average calculated section width T1 when there is no paper PA is KT ', the average calculated section width T1 when the paper PA is present is KT ", and the average calculated section width T1 is the rotation of the driven roller 12. It is assumed that it matches the period.

  It is assumed that N pieces of data are sampled at locations KT ′ and KT ″ of the average calculation section width T1. Further, the detection time of the edge PAT on the leading edge side of the paper PA by the hall sensor HS is tin, The passing time when the edge PAT ′ on the end side passes through the pair of the driving roller 6 and the driven roller 12 is defined as tout, and the reference time ts for starting the data extraction in the area with paper is 0.48s as described above. It is.

  Since the eccentricity of the driven roller 12 is assumed to be “0”, the observed waveform MPW ′ is a superposition of the paper thickness x and the eccentricity of the driving roller 6. In this case, the data sampled within the average calculation section width T1 when there is no paper PA and the data sampled within the average calculation section width T1 when there is the paper PA are less than one rotation of the drive roller 6. Data for one rotation of the driven roller 12.

  Therefore, the average output of the Hall sensor HS of N data sampled in the average calculation section width T1 when there is no sheet PA and the N samples sampled in the average calculation section width T1 when there is the sheet PA. The average output of the data hall sensor HS varies under the influence of the eccentricity of the drive roller 6.

However, assuming that the phase of the observed waveform observed when there is no paper PA with respect to the driving roller 6 and the phase of the observed waveform observed when the paper PA is present, both have the same variation pattern. Therefore, the average output difference ΔV corresponding to the data of the paper thickness x can be maintained in a state where the error is kept small.
Even when the phase of the observed waveform observed when there is no paper PA with respect to the driving roller 6 and the phase of the observed waveform observed when the paper PA exists do not match, the average calculation time difference T2 is constant. The average calculation section width T1 of the two reflects the value including the phase difference of the drive roller 6, and the average output of the two does not change the difference ΔV, but contains a relatively large error. It becomes.

Therefore, if the average calculation section width T1 can be adjusted to the rotation period of the driven roller 12 and the average calculation time difference T2 can be adjusted to the rotation period of the driving roller 6, a stable detection value of the paper thickness can be obtained.
The results of investigations on various paper thicknesses based on this concept will be described below.

(Measurement results when the paper thickness x of the paper PA is changed)
For various paper thicknesses, the average calculation time difference T2 is fixed at T2 = 0.39 s, which is the rotation cycle of the driving roller 6, and the average calculation section width T1 is 0.22 s, which is the rotation cycle of the driven roller 12. FIG. 19 to FIG. 22 show the measurement results of investigating how the number average ΔV ′ of the time average output difference of the Hall sensor HS and the standard deviation σ change when changed.
Note that, for any measurement result of the paper thickness x, the number of sheets passed is 10.

  FIG. 19 shows the number average ΔV ′ of the time average output difference of the Hall sensor HS with respect to various paper thicknesses x for one conveyance device, and FIG. 20 shows the standard of the number average ΔV ′ of the time average output difference shown in FIG. 21 shows a change curve of the deviation σ, FIG. 21 shows the number average ΔV ′ of the time average output difference of the Hall sensor HS with respect to various paper thicknesses x for the other transport device, and FIG. 22 shows the time average output shown in FIG. A change curve of the standard deviation σ of the difference number average ΔV ′ is shown.

  In either one of the conveying apparatuses and the other conveying apparatus, the number average ΔV ′ of the time average output difference is stable even when the paper thickness x is changed. However, the standard deviation σ is not all the minimum at the average calculation interval width T1 = 0.22s, and there is variation, and the measurement result of the other transfer device is more than the measurement result of the one transfer device. Variation is large.

  Therefore, when various paper thicknesses x are passed through one conveying device and the other conveying device, the average calculation section width T1 is fixed to T1 = 0.22 s, and the average calculation time difference T2 is changed. The number average ΔV ′ of the time average output difference and the standard deviation σ are examined for changes. The number of sheets to be passed is 10.

  FIG. 23 shows the time average output difference of the paper thickness x when the average calculation section width T1 is fixed to 0.22 s and the average calculation time difference T2 is changed with respect to various paper thicknesses x. It is a measurement result of the number average ΔV ′. FIG. 24 shows the change of the standard deviation σ calculated using the measurement results shown in FIG. 23 with respect to the average calculation time difference T2.

  FIG. 25 shows the time average output difference of the paper thickness x when the average calculation section width T1 is fixed to 0.22 s and the average calculation time difference T2 is changed with respect to various paper thicknesses x for the other transport device. It is a measurement result of the number average ΔV ′. FIG. 26 shows a change of the standard deviation σ calculated using the measurement result shown in FIG. 25 with respect to the average calculation time difference T2.

  As shown in FIG. 23 and FIG. 25, the number average ΔV ′ of the time average output difference is stable in one of the transport apparatuses and the other transport apparatus. However, the standard deviation σ is not all the minimum for each paper thickness x at the average calculation time difference T2 = 0.39 s, and the average calculation time difference T2 that is the minimum varies. In particular, the measurement results of the other transport device vary greatly.

  When the change of the standard deviation σ shown in FIG. 20 is compared with the change of the standard deviation σ shown in FIG. 24, the change in the standard deviation σ with respect to the change in the average calculation section width T1 is the average calculation time difference for one transport device. It is larger than the change of the standard deviation σ with respect to the change of T2.

When the change in the standard deviation σ shown in FIG. 22 is compared with the change in the standard deviation σ shown in FIG. 26, the change in the standard deviation σ with respect to the change in the average calculation time difference T2 is the average calculation section width for the other transport device. It is larger than the change of the standard deviation σ with respect to the change of T1.
This corresponds to the magnitude of the eccentricity of the driving roller 6 and the eccentricity of the driven roller 8 shown in FIGS.

From FIG. 20, FIG. 22, FIG. 24, and FIG. 26, it can be considered that the rotation period of the driving roller 6 and the rotation period of the driven roller 12 fluctuate for each sheet passing job. This is considered to be caused by a reaction between the driving roller 6 and the driven roller 12 due to slip or impact. As a result, it appears as if the optimum value (average calculation section width T1) at which the standard deviation σ is minimized differs for each paper thickness.
For example, if the rotation cycle varies for each sheet passing job due to slippage of the driven roller 12 or the like, the positions of the curves representing the average output difference ΔV in FIG.
If the number of sheets passed is sufficiently large, it is considered that the average calculation section width T1 at which the variation is minimized does not change. Looks like you are doing. That is, the average calculation section width T1 deviates from the theoretical rotation period of the driven roller 12 to be originally set, and individual optimum values of the average calculation section width T1 cannot be statistically determined. It is necessary to obtain the optimum average calculation section width T1 for each time.

  Therefore, if the average calculation section width T1 and the average calculation time difference T2 are set incorrectly, there is a possibility that the variation in the detected value of the paper thickness x becomes larger than before. Here, calculation results for data acquired by passing 10 sheets are described.

  However, in reality, highly accurate paper thickness information is required for each paper passing job, and it is meaningless to obtain highly accurate paper thickness information for the paper thickness measurement result after passing 10 sheets. . Therefore, it is necessary to obtain an optimum data sampling condition for each paper passing job and to calculate a detected value of the paper thickness x with high accuracy.

  In any case, it is necessary to obtain the rotation cycles of the driving roller 6 and the driven roller 12. First, a method for obtaining the rotation cycles of these rollers will be described.

(Method of obtaining the rotation period of the driving roller 6 and the driven roller 12 by Fourier transforming the paper passing state observation waveform PW)
FIG. 27 shows sampling data of the section width of −0.7 s to 1.0 s when the driving roller 6 and the driven roller 12 are rotated from the sampling data of the paper passing state observation waveforms PW1 and PW2 shown in FIGS. The power spectrum obtained by Fourier transforming the data is shown. The reason why there is a difference between the power spectrum waveforms shown in FIGS. 8 and 9 and the power spectrum waveform shown in FIG. 27 is that the frequency resolution differs depending on the number of sampling data.

  In the power spectrum waveform shown in FIG. 27, the frequency resolution is (1000/2) / (1000 × 1.7 / 2) = 0.588 Hz. Since the frequency resolution increases as the number of sampling data increases, it depends on the paper passing size.

  Therefore, if the rotation time of the driving roller 6 and the rotation time of the driven roller 12 are controlled to be a certain level or more, it is possible to avoid a decrease in frequency resolution when a small-size paper PA is passed. In addition, the measurement was performed about one conveyance apparatus and the other conveyance apparatus.

  In FIG. 27, the peak frequencies of the power spectrum for the other transport device are 2.35 Hz and 4.70 Hz. Therefore, the rotation period of the driving roller 6 is 1 / 2.35 s, and the rotation period of the driven roller 12 is 1. /4.70s.

(Method of detecting the rotation period of the driving roller 6 using a photo sensor)
FIG. 28 is an explanatory diagram of a method for detecting the rotation period of the drive roller 6 using a photosensor.
A filler FIR is attached to one end of the rotating shaft 5 so that the photo interrupter FOT faces the rotation region of the filler FIR.

The filler FIR is made of a strip-shaped member (rectangular thin piece). By detecting a change in light due to transmission / reflection when the filler FIR crosses the photo interrupter FOT with the photo interrupter FOT, the rotation period of the drive roller 6 (the rotation period of the rotation shaft 5) can be detected.
In addition, it can also be set as the structure which detects the rotation period of the driven roller 12 using a photosensor by applying the same structure to the driven roller 12. FIG.

  In the case of a mechanism that does not cause a delay in the driving force transmission process, such as driving the rotary shaft 5 directly by a drive motor (not shown), an encoder (not shown) incorporated in the drive motor (not shown) itself. The driving roller can also be obtained by counting (coefficient) the number of encoder pulses per unit time and the number of driving pulses output from the control unit (not shown) per unit time. 6 rotation cycles can be detected.

(Method of detecting the rotation period of the driven roller 12 using the cross-correlation function of the paper passing state observation waveform PW)
For convenience of explanation, first, a case where the rotation period of the driven roller 12 is obtained using the steady state observation waveforms W1 and W2 will be described.
FIG. 29 is an explanatory diagram showing an example of a method for detecting the rotation period of the driven roller 12 using the cross-correlation function of the steady state observation waveforms W1 and W2.

  The cross-correlation function is a calculation method generally used for obtaining a delay time between two waveforms. For the two signals x (t) and y (t), the cross-correlation function rxy (τ) is defined by equation (1) shown in FIG. Here, τ is a delay time, and when the cross-correlation function rxy (τ) is obtained while changing the delay time τ, rxy (τ) becomes maximum at the delay time τ0 where the degree of coincidence of the two waveforms is high.

When the expression (1) is applied to the sampled data, the expression (2) is rewritten, and the actual calculation is performed using the expression (2).
By utilizing the property that the cross-correlation function rxy (τ) is maximized when the degree of coincidence between the two waveforms is high, the rotation period of the driven roller 12 can be obtained.

  That is, a waveform for approximately one rotation of the driven roller 12 is extracted using the steady state observation waveforms W1 and W2 as basic waveforms, and this is used as an extracted waveform. When the cross-correlation function between the extracted waveform, the steady state observation waveforms W1 and W2, and the extracted waveform is calculated, the degree of coincidence of the waveform increases for each rotation period of the driven roller 12. Thereby, the fluctuation waveform which means the rotation period of the driven roller 12 is obtained. The period of the fluctuation waveform at this time is the rotation period of the driven roller 12.

(Specific example for obtaining cross-correlation function)
30 shows an extracted waveform extracted from the steady state observation waveform shown in FIG. 6 (a waveform observed when there is no paper PA), and FIG. 31 shows an extracted waveform extracted from the steady state observation waveform shown in FIG. Show.

  In order to show the stability of the rotation period of the driven roller 12 with respect to the extraction width, two levels of the extraction width corresponding to the period of the driven roller 12 (0.22 s) and the period corresponding to the period of the driving roller 6 (0.39 s) are used. did.

  In addition, if the steady state observation waveforms W1 and W2 have an offset, a correct result cannot be obtained. Therefore, an offset adjustment for subtracting the average of the extracted waveform sections was performed in advance on the extracted waveform and the basic waveform. The extracted waveforms shown in FIGS. 30 and 31 show waveforms after offset adjustment. The section average of the extracted waveform is, for example, a value obtained by dividing the total sum of the output voltages V of the Hall sensor HS sampled within 0.22 s by the number of samples when the extraction width is 0.22 s.

  FIG. 32 shows a fluctuation waveform showing the result of calculating the cross-correlation function rxy (τ) using the extracted waveform shown in FIG. 30 and the steady state observation waveform W1 shown in FIG. 6, and FIG. 33 shows the extracted waveform shown in FIG. 8 shows a fluctuation waveform indicating the result of calculating the cross-correlation function rxy (τ) using the steady-state observation waveform W2 shown in FIG.

  If the time lag is about 0.4 seconds, it becomes a transient region. Therefore, if excluded, the rotation periods 0.222 s and 0.224 s of the driven roller 12 with respect to each of the steady state observation waveforms are determined for the steady state observation waveforms W1 and W2. Each is obtained. Since the same result is obtained when the extraction width is 0.39 s, the extraction width may be rough and the calculation result of the rotation period is stable. That is, it can be seen that the rotational period of the driven roller 12 having a large eccentric component is represented.

(Method for obtaining the rotation period of the driving roller 5 by a simple moving average)
6 and FIG. 7, the N data (N is a positive integer) existing in the section width corresponding to the rotation period of the driven roller 12 are shifted one by one, and the total of the N data is expressed as N. The periodic component of the driven roller 12 and the harmonics of the driven roller 12 are removed by the simple moving average of dividing by.

Further, other high-frequency components are also suppressed, and as a result, a rotation cycle component of the drive roller 6 that is longer than the rotation cycle of the driven roller 12 is extracted.
34 and 35 show the rotation cycle of the driving roller 6 obtained by simple moving average of the steady state observation waveforms W1 and W2 shown in FIGS. 6 and 7, and the rotation cycle of the driving roller 6 is 0.392 s and 0, respectively. .376s.

(When the rotation period of the driven roller 12 and the driving roller 6 is obtained by applying the cross-correlation method and the simple moving average method to the paper passing state observation waveforms PW1 and PW2 in the conveyance state of the paper PA)
FIG. 36 shows a fluctuation waveform obtained by extracting the waveform from the paper passing state observation waveform PW1 shown in FIG. 10 and calculating the cross-correlation number rxy (τ), and the rotation period of the driven roller 12 is 0. .218s.

  FIG. 37 shows a fluctuation waveform obtained by extracting the waveform from the paper passing state observation waveform PW2 shown in FIG. 11 and calculating the cross-correlation number rxy (τ), and the rotation period of the driven roller 12 is 0. .226s.

  FIG. 38 shows the fluctuation waveform obtained by shifting the N data existing in the section width corresponding to the rotation period of the driven roller 12 one by one and obtaining the simple moving average of the fluctuation waveform shown in FIG. Thereby, a rotation period of 0.380 s of the driving roller 6 is obtained.

FIG. 39 shows the fluctuation waveform obtained by shifting the N data existing in the section width corresponding to the rotation period of the driven roller 12 one by one and obtaining the simple moving average of the fluctuation waveform shown in FIG. Thereby, the rotation period 0.374 s of the driving roller 6 is obtained.
Next, the correlation between the paper thickness x and the average output difference ΔV of the hall sensor HS will be described.

(Explanation of the correlation of the number average ΔV ′ of the time average output difference of the Hall sensor HS with respect to each paper thickness x)
In FIG. 40, using one conveying apparatus, the average calculation section width T1 is T1 = 0.22 s which is the rotation cycle of the driven roller 12, and the average calculation time difference T2 is T2 which is twice the rotation cycle of the driven roller 12. FIG. 8 is an explanatory diagram showing a relationship between the sheet thickness x and the sheet number average ΔV ′ of the time average output difference of the Hall sensor HS for seven types of papers fixed at 0.44 s and having different paper thicknesses x.

Here, the relationship between the paper thickness x and the number average ΔV ′ of the time average output difference of the Hall sensor HS is represented by a regression equation y for the data for each sheet thickness of 10 sheets. In FIG. 40, R ² represents a contribution rate (or determination coefficient).

  In FIG. 41, the average output difference ΔV and the paper thickness x of the Hall sensor HS for seven types of papers having different paper thickness x using one transport device and varying the average calculation section width T1 and the average calculation time difference T2. It is explanatory drawing which shows these relationships.

  Similarly, the regression equation y shows the relationship between the paper thickness x and the average sheet number ΔV ′ of the time average output difference of the Hall sensor HS for the data of 10 sheets. In addition, what was calculated | required by the number of cross correlations shown in FIG. 36 was shown to average calculation area width T1, and what was calculated | required by the moving average shown in FIG. 38 was shown to average calculation time difference T2.

  When comparing FIGS. 40 and 41, the variation in the thin paper is smaller when the average calculation section width T1 and the average calculation time difference T2 are variable. Note that the regression equation y and the coefficient of determination are the calculation results for the average value of each paper thickness x, and there is no significant difference between the regression equation y shown in FIG. 40 and the regression equation y shown in FIG.

  FIG. 42 shows a hole for seven types of paper having different paper thicknesses x using the other transport device, fixing the average calculation section width T1 to T1 = 0.22 s and the average calculation time difference T2 to T2 = 0.44 s. It is explanatory drawing which shows the relationship between the sheet number average (DELTA) V 'of the time average output difference of sensor HS, and paper thickness x. Similarly, the regression equation y shows the relationship between the paper thickness x and the average sheet number ΔV ′ of the time average output difference of the Hall sensor HS for the data of 10 sheets.

  FIG. 43 shows the average output difference ΔV and the paper thickness x of the Hall sensor HS for seven types of paper having different paper thickness x using the other transport device and changing the average calculation section width T1 and the average calculation time difference T2. It is explanatory drawing which shows these relationships.

  Similarly, the regression equation y shows the relationship between the paper thickness x and the average sheet number ΔV of the time average output difference of the Hall sensor HS for the data of 10 sheets. In addition, what was calculated | required by the number of cross correlations shown in FIG. 37 in the average calculation area width T1, and what was calculated | required by the moving average shown in FIG. 39 were shown in the average calculation time difference T2.

42 and 43 are compared, the variation in the average calculation section width T1 and the average calculation time difference T2 is smaller as a whole.
That is, when the average calculation section width T1 is obtained from the rotation cycle of the driven roller 12 and the average calculation time difference T2 is obtained from the rotation cycle of the driving roller 6 for each paper passing job, the paper thickness with high accuracy for the job is obtained. A detection value of x can be obtained, and conditions of the transfer portion and the fixing portion can be set based on the detection value.
In general, a commercially available image forming apparatus includes a plurality of paper feeding units. Considering that various types of paper are passed, it is meaningless to obtain the thickness after passing 10 sheets. Yes, it is important to obtain highly accurate paper thickness information for each paper passing job. Accordingly, the average calculation section width T1 and the average calculation time difference T2 are obtained for each paper passing job, and the optimum paper thickness calculation condition is set.

The regression equation y and the coefficient of determination are the calculation results for the average value of 10 sheets of each paper thickness x, and there is no significant difference between the regression equation y shown in FIG. 42 and the regression equation y shown in FIG.
The determination coefficient of the regression equation y shown in FIGS. 42 and 43 is based on the difference in the gap δ between the hall sensor HS and the magnet MG, and the input / output characteristics with respect to the hall sensor HS of one transport device and the regression equation y are determined. It is different from the coefficient.

(Paper thickness calculation flow)
Next, the paper thickness calculation flow will be described with reference to FIGS.
First, the paper passing state observation waveform PW1 or PW2 shown in FIGS. 10 and 11 is acquired as data (see S.1 in FIG. 44). Next, an average calculation section width T1 and an average calculation time difference T2 are calculated (S.2).
The average calculation section width T1 and the average calculation time difference T2 are calculated by the processing flow shown in FIG.

(When calculating the power spectrum of the frequency of the observed waveform to determine the rotation period of the driving roller 6 and the driven roller 12)
As shown in FIG. 45, data of the paper passing state observation waveform PW1 or PW2 is extracted from the section in which the driving roller 6 and the driven roller 12 are being rotationally driven (S.21). Next, a power spectrum is calculated by performing Fourier transform on the extracted data shown in FIG. 27 (S.22).

  Next, the rotation speed (frequency) in the job at the time of passing the sheet is obtained from the peak in the vicinity of the frequency corresponding to the rotation speed of the driving roller 6 and the driven roller 12 (S.23). Then, a rotation cycle which is the reciprocal number is obtained from the obtained rotation number, and an average calculation section width T1 and an average calculation time difference T2 are calculated from the rotation cycle (S.24).

(When calculating the rotation period of the driving roller 6 and the driven roller 12 using the cross-correlation function of the paper passing state observation waveform PW1 or PW2 and the simple moving average)
As shown in FIG. 46, a waveform corresponding to approximately one rotation of the driven roller 12 is extracted from the paper passing state observation waveform PW1 or PW2 (S.21 ′). Next, offset adjustment of the extracted waveform is performed. As shown in FIGS. 30 and 31, an offset amount at which the average value of the extracted waveforms is “0” is obtained (S.22 ′).

  Next, the basic waveform offset adjustment is performed by subtracting the offset amount from the basic waveform using the paper passing state observation waveform PW1 or PW2 as a basic waveform (S.23 '). As a result, by calculating the cross-correlation function rxy (τ) in a later-described step, fluctuations in the rotation cycle of the driven roller 12 are manifested.

  A cross-correlation function rxy (τ) is calculated based on the equation (2) shown in FIG. 29 from the fundamental waveform and the extracted waveform after the offset adjustment (S.24 '). Thereby, for example, fluctuation waveforms shown in FIGS. 36 and 37 are obtained.

From the cross-correlation function rxy (τ) meaning the fluctuation waveform, the rotation period of the driven roller 12 of this job, that is, the average calculation section width T1 is obtained from the peak interval or the like (see S.25 ′). Then, in S.26 ′, a simple moving average is performed on the basic waveform (with or without offset adjustment) using the average calculation section width T1 obtained in step S.25 ′ as the section width, thereby moving average. (See also FIGS. 38 and 39).
From the moving average obtained in S.26 ′, the rotational period T2 of the driving roller 6 is calculated from the moving average using the peak interval or the like (S.27 ′).

Next, “paper presence section setting” is set (S.3). This paper presence section setting is a step of setting the data extraction start time ts of the paper presence area.
The setting of the start time ts is performed as described below.

As shown in FIG. 18, the relationship between the reference time ts for extracting the data in the paper area and the detection time tin for the edge PAT of the paper PA is that the two extraction sections need to be in each area.
ts-T2 + T1 '<tin
It is.

In addition, since the extraction section of the paper area needs to be within the passage time of the paper PA,
tin <ts <tout-T1 ”
It is.
The reference time ts is set so that these conditions are satisfied and a predetermined margin is obtained for the detection time tin and the time tout (see FIG. 18).

Next, the average output voltage V of the Hall sensor HS with respect to the average calculation section width T1 ″ in the basic waveform is calculated (S.4).
Next, the paper-free section width shown in FIG. 18 is set by setting the data extraction start time tx and the average calculated section width T1 ′ based on the reference time ts−T2 (S.5). Next, the average output voltage V of the Hall sensor HS is calculated with respect to the extraction interval width T1 ′ of the paperless area in the fundamental waveform (S.6).

Next, an average output difference ΔV is obtained by obtaining a difference between the average output voltage V in the section with paper and the average output voltage V in the section without paper (S.7).
Next, in S.8, the average output difference ΔV is converted into a paper thickness x based on the obtained regression equation (see also FIGS. 41 and 43).

This paper thickness detection apparatus is mounted on, for example, the image forming apparatus shown in FIG.
The printer unit 100 of the image forming apparatus has an intermediate transfer unit in the center of the drawing, and an intermediate transfer belt that is an endless belt is disposed in the intermediate transfer unit. The intermediate transfer belt is stretched around the first to third support rollers, and is driven to rotate clockwise.

  The intermediate transfer belt has a photosensitive drum 40, a charger unit, a developing unit, and a cleaning unit for each color of black (K), yellow (Y), magenta (M), and cyan (C) along the moving direction. An image forming device is arranged.

  A writing unit that irradiates each photosensitive drum 40 with laser light for image formation is disposed above the image forming apparatus. A secondary transfer unit is disposed below the intermediate transfer belt. Next to the secondary transfer unit, a fixing unit 25 for fixing the transfer image on the paper is disposed, and the recording paper on which the toner image is transferred is sent to the fixing unit 25.

  Next, document reading will be described. Here, when there is a document on the document feeder 30 of the ADF (automatic document feeder) 400, the document is conveyed onto the contact glass 32 by operating a start button of an operation unit (not shown).

  When there is no document on the document table 30, the scanner of the image reading unit 300 is driven to read the manually placed document on the contact glass 32, and the first carriage 33 and the second carriage 34 are driven for reading scanning. .

  At that time, when the contact glass 32 is irradiated with light from the light source on the first carriage 33, the reflected light from the document surface by this light is reflected by the first mirror on the first carriage 33 and directed to the second carriage 34. Then, the light is reflected by a mirror on the second carriage 34 and forms an image on a CCD (Charge Coupled Device) 36 as a reading sensor through an imaging lens 35.

  When the start switch is operated, the intermediate transfer belt is driven to rotate. At the same time, preparation for image formation of each unit of the image forming apparatus is started, and an image forming sequence for each color image is started. That is, an exposure laser modulated based on the recording data of each color is projected onto the photosensitive drum 40 for each color, and each color toner image is superimposed on the intermediate transfer belt as one image by each color image forming process. Transcribed.

  The sheet PA is fed to the secondary transfer unit at a timing so that the leading edge of the sheet PA enters the secondary transfer unit at the same time as the leading edge of the toner image enters the secondary transfer unit. As a result, the toner image on the intermediate transfer belt is transferred to the recording paper, and the recording paper on which the toner image has been transferred is sent to the fixing unit 25 where the toner image is fixed.

  The above-described recording paper is fed as follows. That is, by selecting and rotating one of the paper feed rollers of the paper feed table 200, the paper (sheet) PA is fed out from one of the paper feed trays 44 provided in multiple stages in the paper feed unit 43, and is separated by the separation roller. Only one sheet is separated and placed in the conveyance path 46.

  The paper PA that has entered the transport path 46 is transported by the transport roller 47 and is guided to the transport path 48 in the printer unit 100, abuts against the registration roller in the transport path 48, and then temporarily stops at the above-described timing. Sent to the unit. Paper feeding can also be performed by inserting a recording paper on the manual feed tray 51.

  The paper PA discharged after receiving the fixing process in the fixing unit 25 is discharged onto the paper discharge tray 57. The transport apparatus (see FIG. 4 or FIG. 28) according to the embodiment of the present invention is provided in the transport path 48, for example.

  The output of the hall sensor HS is input to the arithmetic processing unit CPU, and the CPU calculates the average output voltage V of the paper sensor area and the paper absence area of the hall sensor HS according to the flowchart shown in FIG. Ask.

A storage unit MEMO is connected to the arithmetic processing unit CPU. In the memory unit MEMO, a regression equation y obtained in advance by experiments is stored as a table.
The arithmetic processing unit CPU calculates the paper thickness x from the regression equation y stored in the storage unit MEMO and the average output difference ΔV.
Since the correlation coefficient R of the regression equation is almost close to 1, the detection accuracy of the obtained paper thickness x is high.

  In this embodiment, if the power spectrum of the paper passing state observation waveform during the paper passing operation is calculated by Fourier transform, the peak frequency of the driven roller 12 and the peak frequency of the driving roller 6 can be detected, so that the processing procedure is simple and simple. .

If the rotation time of the driven roller 12 is controlled to ensure a certain level or more, it is possible to avoid a decrease in frequency resolution when a small-size paper PA is passed.
In addition, a dedicated rotation detection sensor is not required.

  If the cross-correlation function is calculated based on the paper passing state observation waveform of the driven roller 12 and the extracted waveform, the periodicity of the driven roller 12 clearly appears and the average calculation section width with high accuracy can be calculated. In addition, a dedicated rotation detection sensor is not required.

  If the rotation period of the driven roller 12 included in the job is specified by the cross-correlation function and the corresponding section width is calculated by a simple moving average, the frequency higher than the rotation frequency of the driven roller 12 can be effectively removed and suppressed. As a result, the remaining periodic components of the drive roller 6 can be extracted effectively, and the average calculation time difference T2 can be set.

If the rotation cycle of the driving roller 6 is directly detected by the sensor, highly accurate rotation cycle data can be easily acquired.
If the rotation period of the driving roller 6 is detected using the existing motor control information, it is not necessary to prepare a new sensor or data processing algorithm, and the paper thickness detection device can be manufactured at low cost.

  In the embodiments described above, the paper thickness is detected by obtaining the average calculation section width and average calculation time difference for one rotation of the driving roller 6 and the driven roller 12, but the present invention is not limited to this. Alternatively, the paper thickness may be detected by obtaining an average calculated section width of two rotations or more.

6 ... Driving roller,
12 ... driven roller
HS ... Hall sensor (sensor)
T1… Average calculation interval width,
T2 ... Average calculation time difference,
PW: Paper feed state observation waveform,
ΔV: Average output difference,
CPU ... arithmetic processing unit,
MEMO… memory part x… paper thickness

JP-A-5-294512

Claims (4)

A driving roller that is driven to rotate;
A driven roller that is rotated in contact with the driving roller;
A sensor for detecting the displacement of the driven roller;
An average calculation section width corresponding to the rotation period of the driven roller and an average calculation time difference corresponding to the rotation period of the driving roller are obtained from a paper passing state observation waveform which means a change in the output of the sensor, and the paper passing state Arithmetic processing for obtaining an average output difference that is a difference between the average output of the sensor within the average calculation interval width in the absence of paper of the observed waveform and the average output of the sensor within the average calculation interval width in the paper presence state after the lapse of the average calculation time Equipment,
And a storage unit for previously storing a relationship between the average output difference and paper thickness Prefecture as data,
The arithmetic processing unit calculates a paper thickness in a paper passing state from the average output difference and the data stored in the storage unit ,
The paper thickness detection apparatus, wherein the average calculation section width and the average calculation time difference are obtained from a power spectrum of the paper passing state observation waveform . A driving roller that is driven to rotate;
A driven roller that is rotated in contact with the driving roller;
A sensor for detecting the displacement of the driven roller;
An average calculation section width corresponding to the rotation period of the driven roller and an average calculation time difference corresponding to the rotation period of the driving roller are obtained from a paper passing state observation waveform which means a change in the output of the sensor, and the paper passing state Arithmetic processing for obtaining an average output difference that is a difference between the average output of the sensor within the average calculation interval width in the absence of paper of the observed waveform and the average output of the sensor within the average calculation interval width in the paper presence state after the lapse of the average calculation time Equipment,
And a storage unit for previously storing a relationship between the average output difference and paper thickness Prefecture as data,
The arithmetic processing unit calculates a paper thickness in a paper passing state from the average output difference and the data stored in the storage unit ,
The paper thickness detecting apparatus, wherein the average calculation section width is obtained by calculating a cross-correlation function between the paper passing state observation waveform and an extracted waveform extracted from the paper passing state observation waveform . The paper thickness detection apparatus according to claim 2 , wherein the average calculation time difference is obtained using a period of a fluctuation waveform obtained by applying a simple moving average to the paper passing state observation waveform. An image forming apparatus comprising the paper thickness detecting device according to any one of claims 1 to 3 .