JP2004184146A - Nip width detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To facilitate nip width detection work, and to efficiently conduct the work. <P>SOLUTION: This nip width detector for detecting a nip width of a rotor in a printer provided with the rotor for supplying ink to a plate provided on a surface plate while contacting with the plate, and a contact pressure control part for controlling contact pressure between the plate and the rotor is provided with an electrostatic capacity measuring means wherein an electrode layer is formed on a plate face of the plate, wherein a dielectric layer is formed in a portion contacting at least with the plate in an outer circumferential face of the rotor, wherein an electrode layer is formed in a portion formed at least with the dielectric layer in an inner circumferential face of the rotor, and wherein a voltage is impressed between the electrode layer formed on the plate and the electrode layer formed in the rotor to measure an electrostatic capacity of the dielectric layer. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides a printing machine including a rotating body that supplies ink to a plate provided on a surface plate while contacting the plate, and a contact pressure control unit that controls a contact pressure between the plate and the rotating body. The present invention relates to a technical field of a nip width detecting device for detecting a nip width of the rotating body in the above.
[0002]
[Prior art]
In conventional flat-bed offset printing presses, when managing the contact pressure between a plate and a roll (for example, a rubber roll), a plate and a rubber blanket, or a roll, the nip width (the contact width between the plate and the roll or the plate). The width of the contact between the rubber blanket and the contact width between the rolls was measured to control the contact pressure.
[Patent Document 1]
As a method for measuring the nip width, for example, as shown in FIG. 7, a nip width is measured using pressure-sensitive paper, or a solid black copy is disclosed as disclosed in Patent Document 1. It is known to measure the nip width from the trace of the nip formed in the nip.
[0003]
[Problems to be solved by the invention]
However, when measuring the nip width using a pressure-sensitive paper or the like as in a conventional flat-bed offset printing press, for example, the pressure-sensitive paper is installed in the gap between the plate and the rubber roll. When other mechanisms and devices are additionally provided, this operation is difficult, and it takes time to measure the nip width.
[0004]
Also, in the measurement of the nip width using pressure-sensitive paper, the work procedure was performed after mechanical adjustment, so if it was necessary to readjust the measurement result and readjust it, it would be necessary to repeat the same work again. It took time. Furthermore, since the nip width varies depending on the type (sensitivity) of the pressure-sensitive paper used, attention must be paid to evaluation, management, and comparison with other devices.
[0005]
Therefore, the present invention has been made in view of the above-described problem, and has as its object to provide a nip width detecting device capable of facilitating nip width detecting work, improving efficiency, and the like.
[0006]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the invention according to claim 1 includes a rotating body that supplies ink to the plate while being in contact with the plate provided on the surface plate, and a contact pressure between the plate and the rotating body. A nip width detection device for detecting a nip width of the rotating body in a printing press having a contact pressure control unit for controlling, wherein an electrode layer is formed on a plate surface of the plate, and at least the outer peripheral surface of the rotating body. A dielectric layer is formed on a portion that contacts the plate, and an electrode layer is formed on at least a portion of the inner peripheral surface of the rotating body where the dielectric layer is formed, and the electrode layer formed on the plate and the rotation Capacitance measuring means for applying a voltage between electrode layers formed on the body to measure the capacitance of the dielectric layer.
[0007]
According to the first aspect of the present invention, it is possible to measure the capacitance of the dielectric layer corresponding to the nip width (the capacitance that is the basis of nip width detection) without using pressure-sensitive paper or the like. In addition, the nip width is not affected by the pressure-sensitive paper or the like, and the nip width detection operation can be facilitated and efficient. In addition, since the nip width can be detected while performing the mechanical adjustment, the time for the mechanical adjustment can be reduced.
[0008]
The invention described in claim 2 is the nip width detection device according to claim 1, further comprising a nip width calculation unit that calculates the nip width based on the measured capacitance. I do.
[0009]
According to the second aspect of the present invention, the nip width can be detected (calculated) without using pressure-sensitive paper or the like, so that the nip width is not affected by the pressure-sensitive paper or the like, and the nip width detection operation can be performed. Ease and efficiency can be achieved. In addition, since the nip width can be detected while performing the mechanical adjustment, the time for the mechanical adjustment can be reduced.
[0010]
The invention according to claim 3 is the nip width detection device according to claim 1 or 2, wherein the plate is a PS plate, and a photosensitive layer is formed on an electrode layer formed on the plate surface. The capacitance measuring means measures the capacitance of the dielectric layer and the photosensitive layer.
[0011]
According to a fourth aspect of the present invention, in the nip width detecting device according to any one of the first to third aspects, the electrode layer of the plate and the rotating body is separated into a plurality of portions of the plate and the rotating body. A plurality of pairs, and the capacitance measuring means applies a voltage between the plurality of pairs of electrode layers, and measures the capacitance of the dielectric layer in a plurality of portions of the rotating body. Features.
[0012]
According to the fourth aspect of the present invention, the nip widths of a plurality of portions of the rotating body can be detected, so that the nip width can be adjusted uniformly over the entire rotating body.
[0013]
According to a fifth aspect of the present invention, in the nip width detecting device according to any one of the first to fourth aspects, a nip width variation that determines a variation in the nip width based on the measured capacitance. The apparatus further includes a determination unit, wherein the contact pressure control unit adjusts a contact pressure between the plate and the rotating body based on a determination result obtained by the nip width variation determination unit.
[0014]
According to the fifth aspect of the present invention, the printing press can be operated at an appropriate contact pressure at any time.
[0015]
The invention according to claim 6, wherein a nip for detecting a nip width of the rotating body in a printing press provided with two rotating bodies that are pressed against each other in parallel and a contact pressure control unit that controls a contact pressure of the rotating body. A width detecting device, wherein an electrode layer is formed on a surface of one of the rotating bodies, and a dielectric layer is formed on at least a portion of an outer peripheral surface of the other rotating body that contacts the one of the rotating bodies; An electrode layer is formed on at least a portion of the inner peripheral surface of the body where the dielectric layer is formed, and a voltage is applied between the electrode layers formed on the two rotating bodies to reduce the capacitance of the dielectric layer. And a capacitance measuring means for measuring.
[0016]
According to the sixth aspect of the present invention, the capacitance of the dielectric layer corresponding to the nip width (the capacitance on which the nip width is detected) can be measured without using pressure sensitive paper or the like. In addition, the nip width is not affected by the pressure-sensitive paper or the like, and the nip width detection operation can be facilitated and efficient. In addition, since the nip width can be detected while performing the mechanical adjustment, the time for the mechanical adjustment can be reduced.
[0017]
The invention according to claim 7 is the nip width detection device according to claim 6, further comprising a nip width calculating unit that calculates the nip width based on the measured capacitance. I do.
[0018]
According to the seventh aspect of the present invention, the nip width can be detected (calculated) without using pressure-sensitive paper or the like, so that the nip width is not affected by the pressure-sensitive paper or the like, and the nip width detection work can be performed. Ease and efficiency can be achieved. In addition, since the nip width can be detected while performing the mechanical adjustment, the time for the mechanical adjustment can be reduced.
[0019]
According to a ninth aspect of the present invention, in the nip width detecting device according to the sixth or seventh aspect, a plurality of pairs of electrode layers of the rotating body are formed separately in a plurality of portions of the rotating body. The capacitance measuring means applies a voltage between the plurality of pairs of electrode layers and measures the capacitance of the dielectric layer in a plurality of portions of the rotating body.
[0020]
According to the eighth aspect of the present invention, the nip widths of a plurality of portions of the rotating body can be detected, so that the nip width can be uniformly adjusted over the entire rotating body.
[0021]
According to a ninth aspect of the present invention, in the nip width detecting device according to any one of the sixth to eighth aspects, a nip width variation that determines a variation of the nip width based on the measured capacitance. The apparatus further includes a determination unit, wherein the contact pressure control unit adjusts a contact pressure of the rotating body based on a determination result of the nip width variation determination unit.
[0022]
According to the ninth aspect of the present invention, the printing press can be operated with an appropriate contact pressure at any time.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.
[0024]
FIG. 1 is a diagram illustrating a schematic configuration example of a nip width detection device according to an embodiment of the present invention.
[0025]
As shown in FIG. 1, the nip width detecting device 1 is roughly divided into a flatbed offset printing press 11 as a printing press, a capacitance meter 12 as a capacitance measuring unit, and an arithmetic processing unit 13 as a nip width calculating unit. And is comprised.
[0026]
The flatbed offset printing press 11 includes a rotating body 23 that supplies ink to the plate 22 while being in contact with the plate 22 provided on the surface plate 21, and a contact pressure control that controls a contact pressure between the plate 22 and the rotating body 23. A part 24.
[0027]
For example, a known rubber roll or rubber blanket can be applied to the rotating body 23. FIG. 2 is a diagram illustrating a structure of a rubber roll as an example of the rotating body 23. As shown in FIG. 2, the rubber roll 23 as the rotating body 23 has, for example, an insulating film layer 23b having electrical insulation properties formed on the outer peripheral surface (outer peripheral surface) in the longitudinal direction of a cylindrical iron core 23a. A metal film layer 23c as an electrode layer is formed (laminated) thereon (except for both ends of the iron core 23a), and a rubber layer 23d as a dielectric layer is formed (laminated) thereon. Further, as shown in the drawing, at one end of the iron core 23a, a lead electrode 23e connected to the metal film layer 23c is formed on the insulating film layer 23b. The wiring is extracted from the extraction electrode 23e and connected to one electrode terminal of the capacitance meter 12. Note that the insulating film layer 23b and the metal film layer 23c may have a thickness of about several hundred μm or less as long as their electrical characteristics can be satisfied.
[0028]
Further, the rotating body 23 is rotated by a predetermined amount of rotation by a driving motor (not shown), moves in, for example, the direction A in FIG. 1, and removes ink from an ink container (not shown). The ink is supplied to the plate 22 for filling. The driving mechanism of the rotating body 23 is a known technique and does not directly relate to the present invention, and therefore, detailed description thereof will be omitted.
[0029]
A metal film layer 22 a as an electrode layer is formed on the surface of the plate 22 provided on the surface plate 21, and serves as a counter electrode of the metal film layer 23 c of the rotating body 23. The metal film layer 22a may have a thickness of about several hundreds μm or less as long as its electrical characteristics can be satisfied. Further, a wiring is drawn out from the metal film layer 22 a and connected to the other electrode terminal of the capacitance meter 12. The rubber layer 23d of the rotating body 23 comes into contact with the metal film layer 22a of the plate 22. The contact pressure at this time, that is, the pressure at which the rotating body 23 is pressed in the direction of the plate 22 is controlled by the contact pressure control unit 24. FIG. 3 is a diagram showing a contact width (nip width) at a contact portion between the rotating body 23 (rubber layer 23d) and the plate 22 (metal film layer 22a) at this time. As can be seen from FIG. 3, the nip width fluctuates according to a change in the contact pressure by the contact pressure control unit 24.
[0030]
Further, at a contact portion between the rotating body 23 and the plate 22, a rubber layer 23 d of the rotating body 23 is sandwiched between a pair of electrodes of the metal film layer 23 c of the rotating body 23 and the metal film layer 22 a of the plate 22. The state is a parallel plate capacitor as shown in FIG.
[0031]
The capacitance meter 12 has a function of applying a voltage V between the pair of electrodes through a wiring drawn from the metal film layer 23c and the metal film layer 22a to measure the capacitance C of the rubber layer 23d.
[0032]
The arithmetic processing unit 13 is mainly configured by a CPU, includes a storage unit such as a RAM and a ROM, and has a function of calculating a nip width based on the measured capacitance C.
[0033]
The capacitance C [F: Farato ：] is generally given by the following equation (1).
[0034]
C = Q / V = ε ₀ * ε * S / d (1)
Here, Q is the charge amount [C: Coulomb], ε ₀ is the dielectric constant in vacuum (8.855F * 10 ⁻¹² [F / m]), ε is the relative dielectric constant of the dielectric, and S is The electrode area [m ² ] and d indicate the inter-electrode distance [m], respectively.
[0035]
The electrode area S is given by the following equation (2).
[0036]
S = L * t (2)
Here, L indicates the electrode width, and t indicates the nip width.
[0037]
That is, the nip width t can be obtained by the following equation (3).
[0038]
t = C * d / (ε ₀ * ε * L) (3)
Here, the distance d between the electrodes is the thickness (film thickness) of the rubber layer 23d of the rotating body 23, and the dielectric constant ε _{0 in} vacuum is constant at 8.855F * 10 ⁻¹² [F / m]. The dielectric constant ε is a value specific to the type of rubber (for example, natural rubber, urethane rubber, or the like) of the rubber layer 23d of the rotating body 23, and L is the length of the rubber roll 23 in the longitudinal direction. Therefore, the nip width t can be obtained by measuring the capacitance C.
[0039]
That is, the arithmetic processing unit 13 stores the value of each parameter in the expression (3) in the storage unit, receives the value of the capacitance C measured by the capacitance meter 12, and executes the operation of the expression (3). By doing so, the nip width t is calculated. The nip width t calculated in this way is stored and managed in the storage unit, and is output and displayed from the arithmetic processing unit 13 on, for example, a display (not shown). Thereby, for example, the operator can perform mechanical adjustment through the contact pressure control unit 24 or the like, and adjust the contact pressure to an appropriate value.
[0040]
As described above, according to the above embodiment, the nip width t can be detected without using pressure-sensitive paper or the like, so that the nip width t is not affected by the pressure-sensitive paper or the like, and the nip width t can be detected. Work can be facilitated and efficiency can be improved. Further, since the nip width t can be detected while performing the mechanical adjustment, the time for the mechanical adjustment can be reduced.
[0041]
In the above embodiment, the metal film layer 22a as an electrode layer is formed on the surface of the plate 22. However, even if a PS (Pre-sensitized) for offset printing is used as the plate 22, The same effect as described above can be obtained. This PS plate has a photosensitive layer formed on an aluminum plate surface, and this aluminum plate is used as an electrode layer. That is, in the contact portion between the rotating body 23 and the PS plate, the dielectric 1 (the rubber layer 23d of the rotating body 23) and the dielectric 1 are located between the pair of electrodes of the metal film layer 23c of the rotating body 23 and the aluminum plate of the PS plate. By sandwiching the dielectric 2 (PS layer photosensitive layer), a parallel plate capacitor as shown in FIG. 5 is obtained.
[0042]
In this case, the capacitance C [F: Farato ゛] is given by the following equation (4).
[0043]
C = {(ε ₀ * ε ₁ * S / d ₁ ) ⁻¹ + (ε ₀ * ε ₂ * S / d ₂ ) ⁻¹ } ⁻¹ (4)
Here, epsilon ₁ is the dielectric constant of the rubber layer 23d, epsilon ₂ is the dielectric constant of the photosensitive layer, d ₁ is the rubber layer 23d thickness (film thickness), d ₂ is the thickness of the photosensitive layer (thickness ) Are shown. Since these values are known, the nip width t can be calculated from the equation (2) by measuring the capacitance C, as in the above embodiment.
[0044]
Further, when the conductive rubber is used for the rubber layer 23d, the metal film layer 23c and the rubber layer 23d become the electrode layers. Therefore, a pair of electrodes of the rubber layer 23d of the rotating body 23 and the PS plate aluminum plate are used. In the meantime, it can be considered that the parallel plate capacitor sandwiches the photosensitive layer of the PS plate as a dielectric, and the nip width t can be calculated in the same manner as described above.
[0045]
In the above embodiment, the pair of electrode layers formed on the plate 22 and the rotating body 23 have been described. However, as a modified example, a plurality of pairs of electrode layers are separated into a plurality of portions of the plate 22 and the rotating body 23 ( (Division). In this case, the wiring is drawn out from each of the plurality of pairs of electrode layers and connected to the electrode terminal of the capacitance meter 12, and the capacitance meter 12 applies a voltage between the plurality of pairs of electrode layers, and the dielectric substance in the plurality of portions of the rotating body 23. layer (e.g., rubber layer 23d of the rotary member 23) to measure the capacitance _C 1 -C _n, respectively. For example, at the center in the longitudinal direction of the rotating body 23, the electrode layer is separated (divided) into two, and a voltage is applied between two pairs of left and right electrode layers, and the capacitance C of the dielectric layer in the left and right portions of the rotating body 23 is changed. ₁ and _{C 2} to be measured. In addition, for example, the electrode layer is separated (divided) into three at the left, center, and right in the longitudinal direction of the rotating body 23, and a voltage is applied between each of three pairs of left, center, and right electrode layers, and the rotating body 23 is rotated. left, center, respectively measuring the capacitance C ₁ -C ₃ of the dielectric layers in the right part. Then, the arithmetic processing unit 13 calculates the nip widths t _{1 to} t _n at the respective portions of the rotating body 23 based on the capacitances C _{1 to} C _n calculated in this manner. According to such a configuration, mechanical adjustment is performed so that the nip widths t _{1 to} t _n in the respective portions of the rotating body 23 are equal, and the nip width can be made uniform in the longitudinal direction of the rotating body 23.
[0046]
Further, in the above embodiment, the arithmetic processing unit 13 functions as a nip width variation determining unit that determines the variation of the nip width t based on the capacitance C measured by the capacitance meter 12, and the contact pressure control unit 24 The contact pressure between the plate 22 and the rotating body 23 may be automatically adjusted based on the determination result. For example, the capacitance C corresponding to the optimum nip width t obtained by the above configuration is stored in the arithmetic processing unit 13 and compared with the capacitance C measured when the flatbed offset printing press 11 is operating. Then, when a predetermined difference occurs, it is determined that the nip width t is fluctuating, and a contact pressure adjustment command (for example, pressurization amount information) is output (feedback) to the contact pressure control unit 24. (Dotted line in FIG. 1). The contact pressure control unit 24 adjusts to an appropriate contact pressure according to the command. According to such a configuration, the flatbed offset printing press 11 can be operated with an appropriate contact pressure at any time.
[0047]
In the above embodiment, the contact width (nip width) at the contact portion between the rotating body 23 and the plate 22 at this time is configured to be detected. However, as a modification, the contact width between the rotating body and the rotating body is detected. You may comprise so that width (nip width) may be detected. FIG. 6 is a diagram showing an example of a schematic configuration of a nip width detection device according to this modification.
[0048]
The nip width detecting device 2 shown in FIG. 6 includes a rotating body 51 instead of the platen 21 in the nip width detecting device 1 shown in FIG. The rotator 51 and the rotator 23 are pressed against each other in parallel, and a metal film layer 51a as an electrode layer is formed on the surface of the rotator 51. The metal film layer 51a faces the metal film layer 23c of the rotator 23. It is an electrode. That is, as in the above-described embodiment, at the contact portion between the rotating body 51 and the rotating body 23, the rotating body 23 is disposed between the pair of electrodes of the metal film layer 51a of the rotating body 51 and the metal film layer 23c of the rotating body 23. By sandwiching the rubber layer 23d, a state of a parallel plate capacitor is obtained.
[0049]
The wiring is drawn out from the metal film layer 51a and connected to the other electrode terminal of the capacitance meter 12, so that the capacitance meter 12 is connected to the metal film layer 23c and the wiring drawn out from the metal film layer 51a. A voltage V is applied between the electrodes, and the capacitance C of the rubber layer 23d is measured, and the measured data is output to the arithmetic processing unit 13. As described in the above embodiment, the arithmetic processing unit 13 calculates the nip width t by receiving the measurement data (the value of the capacity C) and executing the calculation of the equation (3). Note that a known rubber roll or rubber blanket can be applied to the rotating body 51 as in the case of the rotating body 23. The metal film layer 51a may have a thickness of about several hundred μm or less as long as its electrical characteristics can be satisfied.
[0050]
According to such a configuration, the contact width (nip width) between the rotating bodies can be detected without using pressure-sensitive paper or the like, and the work of detecting the nip width t is facilitated and the efficiency is improved. be able to.
[0051]
Note that, in the modified example in which the contact width (nip width) between the rotating bodies is detected, as described above, a plurality of pairs of electrode layers are separated into a plurality of portions of the rotating body 51 and the rotating body 23 ( (Division). In addition, the arithmetic processing unit 13 functions as a nip width variation determination unit that determines a variation in the nip width t based on the capacitance C measured by the capacitance meter 12, and the contact pressure control unit 24 outputs Based on this, the contact pressure between the rotating body 51 and the rotating body 23 may be automatically adjusted.
[0052]
【The invention's effect】
As described above, according to the present invention, it is possible to measure the capacitance of the dielectric layer corresponding to the nip width (the capacitance that is the basis of nip width detection) without using pressure-sensitive paper or the like. Therefore, the nip width is not affected by the pressure-sensitive paper or the like, and the nip width detection operation can be facilitated and efficient. In addition, since the nip width can be detected while performing the mechanical adjustment, the time for the mechanical adjustment can be reduced.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a schematic configuration example of a nip width detection device according to an embodiment of the present invention.
FIG. 2 is a diagram showing a structure of a rubber roll as an example of a rotating body 23.
FIG. 3 is a diagram showing a contact width (nip width) at a contact portion between a rotating body 23 and a plate 22;
FIG. 4 shows a state of a parallel plate capacitor formed by sandwiching a rubber layer 23d of a rotating body 23 between a pair of electrodes of a metal film layer 23c of a rotating body 23 and a metal film layer 22a of a plate 22. FIG.
FIG. 5 is a diagram showing a state of a parallel plate capacitor formed by sandwiching two layers of dielectric material between a pair of electrodes of a metal film layer 23c of a rotating body 23 and an aluminum plate.
FIG. 6 is a diagram illustrating a schematic configuration example of a nip width detection device according to another embodiment of the present invention.
FIG. 7 is a view showing a state in which a nip width is measured using pressure-sensitive paper in a conventional flatbed offset printing press.
[Explanation of symbols]
1, 2 Nip width detecting device 11 Flatbed offset printing machine 12 Capacitance meter 13 Arithmetic processing unit 21 Surface plate 22 Plate 22a, 51a Metal film layer 23, 51 Rotating body 23a Iron core 23b Insulating film layer 23c Metal film layer 23d Rubber layer 24 Contact pressure control section

Claims (9)

The rotating body in a printing press, comprising: a rotating body that supplies ink to the plate provided in contact with the plate provided on the surface plate; and a contact pressure control unit that controls a contact pressure between the plate and the rotating body. A nip width detecting device for detecting a nip width of
An electrode layer is formed on the plate surface of the plate,
A dielectric layer is formed on at least a portion of the outer peripheral surface of the rotating body that contacts the plate, and an electrode layer is formed on at least a portion of the inner peripheral surface of the rotating body where the dielectric layer is formed,
A nip for applying a voltage between an electrode layer formed on the plate and an electrode layer formed on the rotating body to measure a capacitance of the dielectric layer. Width detector. The nip width detection device according to claim 1,
The nip width detection device further comprising a nip width calculation unit that calculates the nip width based on the measured capacitance. The nip width detection device according to claim 1, wherein
The plate is a PS plate, wherein a photosensitive layer is formed on an electrode layer formed on the plate surface,
The nip width detecting device, wherein the capacitance measuring means measures capacitances of the dielectric layer and the photosensitive layer. The nip width detection device according to any one of claims 1 to 3,
An electrode layer in the plate and the rotating body is formed in a plurality of pairs separately in a plurality of portions of the plate and the rotating body,
A nip width detecting device, wherein the capacitance measuring means applies a voltage between the plurality of pairs of electrode layers and measures the capacitance of a dielectric layer in a plurality of portions of the rotating body. The nip width detection device according to any one of claims 1 to 4,
The apparatus further includes a nip width variation determination unit configured to determine a variation in the nip width based on the measured capacitance.
The nip width detection device, wherein the contact pressure control unit adjusts a contact pressure between the plate and the rotating body based on a result of the determination by the nip width variation determination unit. A nip width detection device that detects a nip width of the rotating body in a printing press including two rotating bodies that are pressed in parallel and a contact pressure control unit that controls a contact pressure of the rotating body,
An electrode layer is formed on the surface of one of the rotating bodies,
A dielectric layer is formed on at least a portion of the outer peripheral surface of the other rotating body that contacts the one rotating body, and an electrode layer is formed on at least a portion of the inner peripheral surface of the rotating body where the dielectric layer is formed. And
A nip width detection device comprising: a capacitance measuring unit that measures a capacitance of the dielectric layer by applying a voltage between electrode layers formed on the two rotating bodies. The nip width detection device according to claim 6,
The nip width detection device further comprising a nip width calculation unit that calculates the nip width based on the measured capacitance. The nip width detecting device according to claim 6 or 7,
The electrode layer in the rotating body is formed in a plurality of pairs separately in a plurality of portions of the rotating body,
A nip width detecting device, wherein the capacitance measuring means applies a voltage between the plurality of pairs of electrode layers and measures the capacitance of a dielectric layer in a plurality of portions of the rotating body. The nip width detection device according to any one of claims 6 to 8,
The apparatus further includes a nip width variation determination unit configured to determine a variation in the nip width based on the measured capacitance.
The nip width detecting device, wherein the contact pressure control unit adjusts a contact pressure of the rotating body based on a result of the determination by the nip width variation determining unit.

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