JP2006105940A - Potential measuring apparatus, and image forming apparatus using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce an effect onto a signal generated in a detection electrode affected by a noise resulting from a magnetic field, in a potential measuring instrument for modulating a coupling capacitance between a measuring object and the detection electrode by mechanical motion by a driving mechanism using magnetic force. <P>SOLUTION: This potential measuring apparatus has the detection electrodes 105, 106 for measuring a potential of the measuring object 201 based on a change of induced electric energy, capacitance modulating means 230, 204 for modulating the coupling capacitance between the measuring object 201 and the detection electrodes 105, 106 by the mechanical motion using the magnetic force, and a preventing/restraining means 202 for preventing or restraining the magnetic field resulting from the magnetic force from reaching to the detection electrodes 105, 106. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a non-contact type potential measuring device that measures the potential of a measurement object by the amount of electricity induced by a detection electrode, and an image forming apparatus having the potential measuring device applicable to a copying machine, a printer, and the like.

2. Description of the Related Art Conventionally, for example, in an image forming apparatus that has a photosensitive drum and forms an image by an electrophotographic method, in order to obtain a stable image quality at all times, the potential of the photosensitive drum is appropriately set (typically, typically). , Uniformly). For this reason, the charged potential of the photosensitive drum is measured using a potential measuring device (potential sensor), and feedback control is performed so as to keep the potential of the photosensitive drum uniform by using the result.

As a conventional potential sensor, there is a non-contact type potential sensor, and a system called a mechanical AC electric field induction type is often used here. In this method, the potential of the surface to be measured is a function of the magnitude of the current i taken from the sensing electrode built in the potential sensor,
i = dQ / dt = d / dt [CV] (1)
It is given by the formula. Here, Q is the amount of charge appearing on the detection electrode, C is the coupling capacitance between the detection electrode and the measurement object, and V is the surface potential of the measurement object. Also, this capacity C is
C = AS / x (2)
It is given by the formula. Here, A is a proportional constant related to the dielectric constant of the substance, S is the detection electrode area, and x is the distance between the detection electrode and the measurement object.

Using these relationships, the potential V of the surface of the measurement target is measured, but in order to accurately measure the charge amount Q appearing on the detection electrode, the size of the capacitance C between the detection electrode and the measurement target is set. It has been found so far that it should be modulated periodically. That is, the amount of charge Q appearing on the detection electrode is a very small value and is easily affected by the noise existing around it. For this reason, in order to accurately measure minute Q, the magnitude of the coupling capacitance C between the sensing electrode and the measurement target is periodically modulated by an appropriate means, and the same frequency component is detected from the measured signal. In many cases, synchronous detection is used to obtain a necessary signal.

As a method of modulating the capacitance C, a method of periodically changing the position of the detection electrode is known. In a typical example of this method, a sensing electrode is arranged at the tip of a plate-like vibrator, and the position of the sensing electrode and the measurement object is periodically changed by vibrating the plate with an electromagnet, thereby modulating the capacitance C. (See Patent Document 1).
US Pat. No. 5,212,451

In the potential sensor as described above, an electromagnet is often used as a drive mechanism for vibrating the detection electrode. However, noise due to an alternating magnetic field generated by an electromagnet may affect the detection electrode, and it may be difficult to measure with high accuracy. Therefore, as shown in Patent Document 1, the electromagnet is provided as far as possible from the detection electrode.

On the other hand, in recent years, as the diameter of the photosensitive drum is reduced and the density around the drum is increased, the potential sensor is also required to be reduced in size and thickness. However, in order to reduce the size of the potential sensor described above, it is necessary to bring the positions of the electromagnet and the detection electrode as close as possible, and it is difficult to achieve both measurement accuracy and size reduction.

In view of the above problems, the potential measuring device of the present invention includes a sensing electrode for measuring a potential of a measuring object by an induced change in electric quantity, and a coupling capacitance between the measuring object and the sensing electrode by mechanical movement using magnetic force. And a capacitance modulation means for modulating the magnetic field, and a prevention / suppression means for preventing or suppressing the magnetic field caused by the magnetic force from reaching the detection electrode.

Further, in view of the above problems, the potential measurement method of the present invention modulates the coupling capacitance between the detection electrode and the object to be measured by mechanical movement using magnetic force, and changes the amount of electricity induced in the detection electrode by this modulation. When measuring the potential of the measurement object, there is provided a prevention / suppression means for preventing or suppressing the magnetic field caused by the magnetic force from reaching the detection electrode.

In view of the above problems, an image forming apparatus of the present invention includes the above-described potential measuring device and an image forming unit, and the surface of the detection electrode of the potential measuring device faces the surface of the image forming unit that is a potential measurement target. And the image forming means controls image formation using the signal detection result of the potential measuring device. The image forming unit may have a copying function, a printing function, a facsimile function, or the like.

In the present invention, in a potential measuring device that employs capacitance modulation means for modulating the coupling capacitance between the measurement target and the sensing electrode by mechanical movement by a driving mechanism using magnetic force, the magnetic field caused by such magnetic force is the cause. Since it is possible to reduce the influence of noise on the signal generated at the detection electrode due to the presence of the preventing / suppressing means, the performance of the potential measuring device can be improved.

Embodiments of the present invention will be described below. In one embodiment, the capacity modulation means is composed of an electromagnet and a permanent magnet, and the prevention / suppression means is composed of a magnetic shield member made of a magnetic material. A vibration member having a detection electrode on one surface and a permanent magnet on the other surface is provided, a magnetic shield member is formed between the permanent magnet and the vibration member, and the vibration member is formed from the outside of the vibration member by an electromagnet. By oscillating due to the interaction between the applied magnetic field and the magnetic field of the permanent magnet provided on the vibrating member, the electrical signal generated at the sensing electrode for measuring the potential of the measurement target is modulated, and this electrical signal is Arithmetic processing is performed.

The vibration member can take the form of a rocking body that is pivotally supported around a torsion spring or a cantilever-like vibration member. The arrangement relationship between the permanent magnet and the electromagnet can be reversed. Further, the capacity modulation means can be constituted by two electromagnets provided on the fixed side and the movable side.

Hereinafter, more specific embodiments of the present invention will be described in detail with reference to the drawings.
Example 1
First, a first embodiment of the present invention will be described with reference to FIG. 1, FIG. 2, and FIG. FIG. 1 shows a configuration of a potential measuring apparatus according to the present embodiment. An opening 101 is formed at the center of the support substrate 100, and a flat plate-like oscillator 104 is supported by two torsion springs 102 and 103 in the center hollow portion of the opening 101. The oscillating body 104 has a line-symmetric structure with respect to a center line AA ′ connecting the long-axis center lines of the torsion springs 102 and 103. On one surface of the oscillating body 104, two flat detection electrodes 105 and 106 are arranged symmetrically with respect to the center line AA ′. The electrodes 105 and 106 are connected to a signal processing circuit 109 installed outside the support substrate 100 by electrode wirings 107 and 108 formed on the torsion spring 103.

FIG. 2, which is a B-B ′ sectional view of FIG. 1, shows a state in which the potential sensor shown in FIG. 1 is arranged with respect to the measurement target surface 201. The measurement target surface 201 is, for example, a photosensitive drum, and rotates around an axis extending in the left-right direction in the drawing or an axis extending in the direction perpendicular to the paper surface. When the surface 201 to be measured facing the oscillating body 104 is substantially planar, the oscillating body 104 is disposed so as to be substantially parallel to the neutral position.

A magnetic shield layer 202 made of a magnetic material such as a soft magnetic material is formed on the surface of the oscillating body 104 opposite to the measurement target surface 201, and a permanent magnet 203 is installed on the surface of the magnetic shield layer 202. ing. Here, the magnet 203 is magnetized in a direction perpendicular to the rotation center axis of the oscillator 104 as shown in FIG.

In FIG. 2, an electromagnet 204 is installed below the rocking body 104, that is, below the surface opposite to the measurement target surface 201. An alternating magnetic field is generated by passing an alternating current through the electromagnet 204, and the rocking body 104 is swung around the long axes of the torsion springs 102 and 103 by the interaction between the alternating magnetic field and the magnet 203 installed on the rocking body 104. Can move. Due to this swing, the distance between the detection electrodes 105 and 106 installed on the surface of the swing body 104 and the measurement target surface 201 changes in an opposite phase, and the coupling capacitance between the detection electrodes 105 and 106 and the measurement target surface 201 is periodically changed. Therefore, the potential of the measurement object can be measured from the equation (1). In this case, the electrical signals from the detection electrodes 105 and 106 are subjected to differential processing. Of course, based on the electrical signal from one of the detection electrodes, the potential of the object to be measured can also be measured from Equation (1).

Next, the effect of the magnetic shield layer 202 of this embodiment will be described with reference to FIG. (1) of FIG. 3 is a schematic diagram in the case of a potential sensor not provided with a magnetic shield layer. Here, for simplicity, the magnet 203 is not shown. In this case, the lines of magnetic force 301 generated from the coils of the electromagnet 204 are distributed so as to penetrate the oscillator 104 and the detection electrodes 105 and 106 while interacting with the lines of magnetic force from the magnet 203. At this time, the magnetic field 301 generated from the coil of the electromagnet 204 is an alternating magnetic field for oscillating the oscillating body 104, and when the oscillating body 104 oscillates in the magnetic field 301, the detection electrodes 105 and 106 also have the magnetic field 301. Exercise inside. Therefore, an induced current is generated in the detection electrodes 105 and 106, which is a noise and an electric signal generated in the detection electrode due to a periodically changing coupling capacitance between the measurement target surface 201 having a potential. Become.

On the other hand, in (2) of FIG. 3 showing the case of this embodiment, a magnetic shield layer 202 is provided on the surface of the oscillator 104 on the electromagnet 204 side (again, for simplicity, the magnetic shield layer 202 is provided). The upper magnet 203 is not shown). Since the magnetic shield layer 202 typically formed of a soft magnetic material has an effect of guiding the magnetic lines of force to the inside, in FIG. 3B, the magnetic lines of force 302 are the magnets 203 provided on the magnetic shield layer 202. Although it interacts with the magnetic field lines from the magnetic field, it passes through the inside of the magnetic shield layer 203 and is guided to the left and right in the figure to escape. As a result, as compared with the case of (1) in FIG. 3, the number of magnetic lines penetrating the detection electrodes 105 and 106 can be reduced, and the amount of induced current that becomes noise is reduced with respect to the detection signal of the detection electrode. Be made.

Therefore, a high-performance potential sensor can be realized. Furthermore, the distance between the electromagnet and the detection electrode can be made smaller than before, the degree of freedom of arrangement of components in the sensor is increased, and the potential sensor can be miniaturized. In this way, it is possible to reduce the size, increase the sensitivity, and increase the reliability of the potential sensor that uses the electromagnet as the driving device.

(Example 2)
Next, a second embodiment will be described with reference to FIGS. In this embodiment, as shown in FIG. 4, a cantilever-like vibrating member 402 supported by a supporting member 401 is provided on a substrate 400, and a detection electrode 403 is provided on the upper surface of the vibrating member 402. In addition, a magnetic shield layer 405 and a permanent magnet 406 are provided in a lower portion thereof, that is, a surface on the coiled electromagnet 404 side. A coiled electromagnet 404 is provided below the magnetic shield layer 405 and the permanent magnet 406.

Also in the present embodiment, the alternating magnetic field generated by the coiled electromagnet 404 interacts with the magnet 406 attached to the vibrating member 402, and the vibrating member 402 is vibrated up and down in a cantilever manner. In this way, the distance between the measurement object 407 and the detection electrode 403 is modulated. Here, the magnet 406 is magnetized in the vertical direction of FIG. 4, and the same magnetic pole appears on the lower surface thereof. The number of detection electrodes 403 may be one or a plurality, but even in the case of a plurality of detection electrodes 403, the coupling capacitance with the measurement object 407 periodically changes in phase. Measurements will be made in the same way as for the two sensing electrodes.

Also in this embodiment, the magnetic shield layer 405 acts to guide the magnetic lines of force 408 generated from the electromagnet 404 to the left and right in FIG. 4, so that the amount of the magnetic lines 408 penetrating the detection electrode 403 can be reduced. . Therefore, noise generated in the detection electrode 403 by the magnetic force lines 408 can be reduced.

FIG. 5 is an upper perspective view of the potential sensor described in the second embodiment. A potential sensor having such a shape has conventionally existed, but a piezoelectric element is often used as a driving method for vibrating the detection electrode unit. However, in general, the piezoelectric element is expensive. On the other hand, although the coiled electromagnet is very inexpensive, the coil cannot be installed near the detection electrode 403 due to the influence of noise caused by the generated magnetic field, and the cantilevered vibrating member 402 can be efficiently used. It was difficult to vibrate. In this embodiment, these problems are solved.

FIG. 6 is a conceptual diagram of a conventional potential sensor using such a coil-type magnet 604. On the substrate 600, a balanced beam-like vibrating member 602 supported by the member 601 is provided. A detection electrode 603 is provided on the upper surface of the one end, and a coiled electromagnet 604 is provided on the substrate 600 at a position opposite to the detection electrode 603 with the support member 601 interposed therebetween. A magnet 605 is provided on the lower surface of the other end portion of the beam-like vibrating member 602 above 604.

Here, the alternating magnetic field generated by the coiled electromagnet 604 interacts with the magnet 605 mounted on the vibrating member 602, and the vibrating member 602 vibrates up and down in a balance manner around the vibration center portion 606. The distance between the measurement object 607 and the detection electrode 603 is modulated.

In the example based on this prior art, the arrangement of the electromagnet 604 is set as far as possible from the detection electrode 603 so that the alternating magnetic field generated from the electromagnet 604 does not affect the detection electrode 603. Therefore, as clearly seen in comparison with the second embodiment of the present invention shown in FIG. 4 based on the example of FIG. 6 based on the prior art, by using the technique of the present invention, the coil is reduced while reducing the influence of noise. It becomes possible to dispose the electromagnet directly under the detection electrode. Thus, the potential measuring device according to the present invention can be miniaturized while maintaining the performance.

By the way, the present invention vibrates a shutter structure (which constitutes a capacity modulation means) having an opening in parallel with a driving means using magnetic force in parallel directly above the detection electrode, and thereby an effective exposure area of the detection electrode with respect to the measurement object. The present invention can also be applied to a potential measuring device that measures the potential of a measurement object by periodically changing the voltage. Also in this case, a magnetic shield member can be provided at an appropriate position between the driving means using magnetic force and the detection electrode, so that the magnetic field reaching the detection electrode from the driving means using magnetic force can be prevented or suppressed. As described above, the present invention provides a sensing electrode for measuring the potential of a measurement object by an induced change in the amount of electricity, and for modulating a coupling capacitance between the measurement object and the detection electrode by a mechanical motion using magnetic force. It can be applied to any type of potential measuring device equipped with a capacity modulation means, and has an adverse effect on the detection electrode by providing a prevention / suppression means for preventing or suppressing the magnetic field caused by the magnetic force from reaching the detection electrode. Is prevented or suppressed.

(Example 3)
FIG. 7 illustrates an image forming apparatus according to the third exemplary embodiment. FIG. 7 is a schematic view around the photosensitive drum of the electrophotographic developing apparatus using the potential measuring apparatus according to the present invention. Around the photosensitive drum 2108, a charger 2102, a potential measuring device 2101, an exposure unit 2105, and a toner supply unit 2106 are installed. A latent image is obtained by charging the surface of the drum 2108 with the charger 2102 and exposing the surface of the photosensitive drum 2108 with the exposure device 2105. Toner is attached to the latent image by a toner supplier 2106 to obtain a toner image. The toner image is transferred to a transfer material 2109 sandwiched between the transfer material feed roller 2107 and the photosensitive drum 2108, and the toner on the transfer material is fixed. Image formation is achieved through these steps.

In this configuration, the charged state of the drum 2108 is measured by the small and high-performance potential measuring device 2101 of the present invention, the signal is processed by the signal processing device 2103, and the high voltage generator 2104 is fed back, for example. By controlling 2102, stable drum charging is realized, and stable image formation is realized. At this time, the potential distribution on the photosensitive drum can be measured by monitoring the output of the potential measuring device 2101 in synchronization with the rotation of the photosensitive drum 2108, and the light to be exposed on the photosensitive drum 2108 based on the measured potential distribution. By controlling the amount of light or controlling the charger 2102, image unevenness can be reduced.

Further, even if the potential measuring device of the present invention is applied to a system composed of a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.), one device (for example, a copying machine, a facsimile device). You may apply to the apparatus which consists of.

It is a figure which shows the 1st Example of this invention. It is sectional drawing which shows the positional relationship of the electric potential measuring apparatus of 1st Example of this invention, and a measuring object, and the arrangement | positioning relationship between a detection electrode, a magnetic shield layer, and a magnet. It is a figure which shows distribution of a magnetic force line, and demonstrates the effect which introduced the magnetic shielding layer in the 1st Example of this invention. It is sectional drawing which shows the structure of the electrical potential measuring apparatus of the 2nd Example of this invention, and the positional relationship between it and a measuring object. It is a general | schematic top view of the electric potential measuring apparatus of the 2nd Example of this invention. It is sectional drawing which showed the electric potential measuring apparatus using the prior art for comparing with a 2nd Example. It is a typical block diagram of an example of the image forming apparatus incorporating the electric potential measuring apparatus of this invention.

Explanation of symbols

104, 402 ... Vibration member (oscillator, cantilever-like vibration member)
105, 106, 403 ... detection electrodes 201, 407, 2108 ... potential measurement object (photosensitive drum)
202, 405 ... Prevention / suppression means (magnetic shield layer)
203, 204, 404, 406 ... Capacity modulation means (magnet, coiled electromagnet)
301, 302, 408 ... Magnetic field lines 2101 ... Potential measuring device

Claims (8)

A sensing electrode for measuring the potential of the object to be measured by an induced change in the amount of electricity; a capacity modulating means for modulating the coupling capacity between the object to be measured and the sensing electrode by a mechanical movement using magnetic force; An electric potential measuring device having a prevention / suppression means for preventing or suppressing the magnetic field caused by the magnetic field from reaching the detection electrode. A vibration member having the detection electrode on one surface and a magnetic force generation part constituting the capacity modulation means on the other surface is provided, and a magnetic shield layer constituting the prevention / suppression means is provided between the magnetic force generation part and the vibration member. The vibration member formed between them vibrates due to the interaction between the magnetic field applied from the outside of the vibration member by another magnetic force generation unit constituting the capacity modulation means and the magnetic field from the magnetic force generation unit provided in the vibration member. The electric potential measuring device according to claim 1, wherein the electric signal generated by the detection electrode is modulated and the electric signal is processed by a circuit. An electric signal generated when the vibration member is pivotally supported around a torsion spring and the spatial position of at least one detection electrode installed on the surface of the vibration member is changed by the capacitance modulation means. The potential measurement device according to claim 2, wherein the potential is detected. The vibration member is a cantilever-like vibration member, and detects an electric signal generated when the spatial position of at least one detection electrode installed on the surface of the vibration member is changed by the capacitance modulation means. Item 3. The potential measuring device according to Item 2. 5. The potential measuring device according to claim 2, wherein at least one of the magnetic force generation unit and the other magnetic force generation unit provided in the vibration member is an electromagnet. The potential measuring apparatus according to claim 1, wherein the prevention / suppression means is a magnetic shield member made of a magnetic material provided at a position between the capacitance modulation means and the detection electrode. Due to the magnetic force, the coupling capacitance between the sensing electrode and the object to be measured is modulated by a mechanical motion using magnetic force, and the potential of the object to be measured is measured by the change in the amount of electricity induced in the sensing electrode due to this modulation. A potential measurement method comprising a prevention / suppression means for preventing or suppressing a magnetic field from reaching a detection electrode. An electric potential measuring apparatus according to claim 1 and an image forming means, wherein the surface of the detection electrode of the electric potential measuring apparatus is arranged to face the surface of the image forming means that is the object of electric potential measurement. An image forming apparatus, wherein the forming unit controls image formation using a signal detection result of the potential measuring device.

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