JP2007078447A - Electric potential measuring apparatus and image formation apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To relatively reduce electric power consumption by improving efficiency in the magnetic field generation of an electromagnetic coil and relatively reduce magnetic noise acting on the vicinity of the electromagnetic coil in an electric potential measuring apparatus to be driven through the use of the electromagnetic coil. <P>SOLUTION: The electric potential measuring apparatus includes a detection electrode 3 at a part opposed to an object to be measured 2, an oscillating member 1 having a magnetic body 9 arranged at another part, and the electromagnetic coil 10 fixed to the magnetic body 9. The periphery of the electromagnetic coil 10 is covered with a shield 12 made of a magnetic material except a part approximately opposed to the magnetic body 9. The relation of arrangement of the magnetic body 9 and the electromagnetic coil 10 can be reversed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a potential measuring device, an image forming apparatus having the potential measuring device, and the like.

Conventionally, in an image forming apparatus such as a copying machine, a printer, or a facsimile, a method of measuring the surface potential of a photosensitive drum and controlling the charge amount of the photosensitive drum is often used to improve the print image quality. It is desirable to measure the surface potential of the photosensitive drum in a non-contact manner, and such a potential measuring device is generally used.

As a measurement principle of such a potential measuring device, the following method is often used. That is, a capacitor is formed with the detection electrode facing a measurement target (object to be measured), and the capacitance of the capacitor is slightly changed by some means. As a result, a current signal having an amplitude proportional to the surface potential of the measurement target is obtained from the detection electrode.

The above principle will be described below using equations. Let S be the area of the detection electrode, and ε be the dielectric constant of the space between the measurement object and the detection electrode. When the distance x between the measurement object and the detection electrode is changed minutely as in Expression (1), the capacitance C (t) of the capacitor formed between the measurement object and the detection electrode is expressed by Expression (2). ). Here, Δx (t) is a periodic function, for example, a function representing a waveform such as a sine wave, a triangular wave, or a pulse. A function obtained by differentiating a periodic function is also a periodic function.
x = x ₀ + Δx (t) [x ₀ >> | Δx (t) |] (1)
C (t) = (ε · S) / (x ₀ + Δx (t)) (2)

Assuming that the surface potential of the object to be measured is V and the change in V is assumed to be sufficiently slow with respect to the change in the distance x (t), the current i (t) obtained from the sensing electrode is defined by the time derivative of the quantity of electricity. ) Is expressed as in equation (3).
i (t) = d (C (t) · V) / dt = V · d (C (t)) / dt
≈− (ε · S) / x ₀ ² · V · d (Δx (t)) / dt (3)
From the expression (3), a periodic current signal having an amplitude proportional to the surface potential V of the measurement object is obtained from the detection electrode by periodically and minutely changing the distance x between the measurement object and the detection electrode. You can see that

As an example of the potential measuring device based on the above principle, there is one shown in FIG. 9 (see Patent Document 1). One end of the diaphragm 1 is fixedly fixed to a spacer 4 disposed on the substrate 8, and the detection electrode 3 is disposed on the surface of the diaphragm 1 that faces the measurement object 2, and the opposite surface (back surface). ) Is provided with a permanent magnet 5. As long as the magnetization direction of the permanent magnet 5 is parallel to the central axis of the electromagnetic coil 6 disposed on the substrate 8, the N-pole direction may be on either the diaphragm 1 side or the electromagnetic coil 6 side (here, The end of the permanent magnet 5 facing the diaphragm 1 is magnetized so as to be an N pole). The inner diameter of the air core portion of the electromagnetic coil 6 is larger than the outer diameter of the permanent magnet 5, and the tip of the permanent magnet 5 can move in the air core portion.

When a current is supplied from a driving power source (not shown) to the electromagnetic coil 6 so that the surface of the electromagnetic coil 6 facing the diaphragm 1 has an N pole, a magnetic field having an intensity proportional to the magnitude of the current is generated. The permanent magnet 5 receives an attractive force from the electromagnetic coil 6, and the diaphragm 1 is bent downward in FIG. In this state, when a current is supplied from the drive power source to the electromagnetic coil 6 so that the upper direction in FIG. 9 is the south pole, the permanent magnet 5 receives a repulsive force from the electromagnetic coil 6 and the diaphragm 1 is bent upward in FIG. To do. By periodically reversing the direction of the current supplied from the drive power source to the electromagnetic coil 6, the diaphragm 1 periodically oscillates in the vertical direction in FIG. The distance between also varies periodically. As a result, the capacitance between the detection electrode 3 and the measurement object 2 changes periodically, and a current signal proportional to the surface potential of the measurement object 2 is obtained from the detection electrode 3. By converting this current signal using an appropriate signal processing means (not shown), a potential measurement signal of the measurement object 2 is obtained.

Patent Document 1 also describes an embodiment in which the positional relationship between the permanent magnet 5 and the electromagnetic coil 6 is reversed as shown in FIG. 10, and the diaphragm 1 is vibrated by the same method as described above. It is possible to make it. In this embodiment, the strength of the magnetic field in the vicinity of the tip of the permanent magnet 5 is increased by arranging the permanent magnet 5 so as to stand upright in the center of the magnetic circuit member 7 made of a magnetic material. Thereby, the amplitude of the diaphragm 1 is increased, and a larger current signal can be obtained with respect to a constant voltage of the measuring object 2.
JP-A-9-281167

In recent years, the potential measuring apparatus itself has been required to be downsized due to the trend toward downsizing of the image forming apparatus, and the components of the potential measuring apparatus are required to be arranged at higher density. When component parts are arranged with high density in a potential measuring device using an electromagnetic coil as a drive source, the following problems occur. That is, when the electromagnetic coil and the signal processing circuit unit are close to each other, the magnetic noise received by the signal processing circuit unit from the electromagnetic coil increases, and the accuracy of the potential measurement decreases. At this time, if the periphery of the electromagnetic coil is completely covered with a shield made of a magnetic material, it is possible to reduce the magnetic noise that the signal processing circuit section receives from the electromagnetic coil. However, since the magnetic field reaching the permanent magnet arranged on the diaphragm is also reduced at the same time, the amplitude of the diaphragm is reduced, and the magnitude of the current signal obtained from the detection electrode is reduced. As described above, the method of completely covering the periphery of the electromagnetic coil with the shield made of a magnetic material sufficiently reduces the decrease in potential measurement accuracy because the signal size decreases at the same time as the noise size decreases. It is difficult.

In view of the above problems, the potential measuring device of the present invention is a potential measuring device having a vibrating member having a detection electrode and a magnetic body, and an electromagnetic coil, and the periphery of the electromagnetic coil faces the magnetic body. It is covered with a shield made of a magnetic material except for the portion. More specifically, a vibration member having a detection electrode in a portion facing the measurement object and having a magnetic material in the other portion is arranged to be able to vibrate. An electromagnetic coil is fixedly arranged with respect to the magnetic body, and the periphery of the electromagnetic coil is covered with a shield made of a magnetic material except for a portion substantially facing the magnetic body. . In another configuration, the potential measuring device of the present invention is a potential measuring device having a vibrating member having a detection electrode and an electromagnetic coil, and a magnetic body, and the periphery of the electromagnetic coil is connected to the magnetic body. It is characterized by being covered with a shield made of a magnetic material except for the substantially opposing portions. More specifically, a vibration member having a detection electrode in a portion facing the measurement object and having an electromagnetic coil in the other portion is arranged to be able to vibrate. A magnetic body is fixedly arranged with respect to the electromagnetic coil, and the periphery of the electromagnetic coil is covered with a shield made of a magnetic material except for a portion substantially facing the magnetic body. .

In view of the above problems, an image forming apparatus of the present invention includes the above-described potential measuring device, a signal processing device that processes an output signal obtained from the potential measuring device, and an image forming unit. The detection electrode of the potential measuring device is arranged to face the target of potential measurement, and the image forming unit controls image formation based on the signal detection result of the signal processing device.

With the above configuration of the present invention, the magnetic field generation efficiency of the electromagnetic coil with respect to the magnetic material can be improved, power consumption can be relatively reduced, and magnetic noise applied to the vicinity of the electromagnetic coil can be relatively reduced. In addition, when the signal processing circuit unit is provided close to the electromagnetic coil, the magnetic noise received by the signal processing circuit unit can be reduced, so that the effects of both reducing power consumption and improving potential measurement accuracy can be achieved simultaneously. Can be obtained.

Hereinafter, an embodiment of the present invention will be described while explaining the principle of operation and effect of the present invention.

FIG. 1 shows a potential measuring device according to an embodiment of the present invention. In this embodiment, the flat diaphragm 1 which is a vibration member is fixed to a spacer 4 arranged at one end on a substrate 8 and is detected on the surface of the diaphragm 1 facing the measurement object 2. The electrode 3 is disposed, and the movable magnetic body 9 is disposed on the opposite surface. On the other hand, the electromagnetic coil 10 is immovably disposed on the substrate 8 with respect to the movable magnetic body 9, and a core 11 made of a magnetic material is inserted into the air core portion of the electromagnetic coil 10. The surface around the electromagnetic coil 10 is covered with a shield 12 with an opening made of a magnetic material having an opening in a portion substantially opposed to the movable magnetic body 9. Here, the phrase “substantially oppose” indicates that the movable magnetic body 9 and the opening portion of the shield 12 are substantially opposed to each other. That is, the movable magnetic body 9 and the opening portion of the shield 12 do not need to be arranged strictly in parallel, and their center positions may be shifted. Here, the electromagnetic coil 10 has a donut shape, and accordingly, the shield 12 has a cylindrical shape, and its opening and the movable magnetic body 9 have a circular shape (see FIG. 7).

Of course, the form of the potential measuring device of the present invention is not limited to the above form, and various forms are possible. For example, the arrangement relationship between the electromagnetic coil and the magnetic body may be reversed (see the example in FIG. 2), and the vibration mode of the vibrating member is not only cantilever type, but also vibrates in the rotational direction around the central axis ( (See the example in FIG. 3). In addition, the location of the movable magnetic body in the vibration member, the shape of the electromagnetic coil, the shape of the shield, the shape and number of the openings, the shape of the magnetic body, the shape of the core, etc. What is necessary is just to determine suitably according to a case. Furthermore, in addition to the shield with an opening that has an opening that does not exist in the part that is almost opposite to the magnetic material, the shield closes the opening with a conductor such as aluminum, which is a material that transmits a magnetic field, and does not require dust. It is also possible to use a shield that can completely prevent from entering the shield. The core made of the magnetic material of the air core part of the electromagnetic coil can be omitted. Further, it is possible to adopt a configuration in which the diaphragm itself is made of a conductive material such as metal or silicon, and the surface to be measured also serves as the detection electrode unit.

In short, the arrangement relationship between the electromagnetic coil and the magnetic body only needs to be established so that the vibration of the vibration member can be performed without any problem. And the magnetic field generation efficiency with respect to the magnetic body of the electromagnetic coil is ensured, and the circumference of the electromagnetic coil is made of a magnetic material except for the portion substantially facing the magnetic body so that the magnetic field does not leak much in unnecessary places. It only needs to be covered with a shield.

The operation of the above embodiment is performed as follows. By periodically supplying and interrupting current from a drive power source (not shown) to the electromagnetic coil 10, the diaphragm 1 periodically vibrates in the vertical direction of FIG. The distance between the electrode 3 and the measuring object 2 also changes with the same period. As a result, a current signal proportional to the surface potential of the measurement object 2 is obtained from the detection electrode 3 based on the principle described above. By applying signal processing such as detection and rectification to the current signal using the signal processing circuit unit 13, a potential measurement signal of the measurement object 2 is obtained.

In the potential measuring device having such a configuration, the magnetic field generation efficiency for the magnetic material of the electromagnetic coil can be ensured, and the power consumption can be relatively reduced. This will be described in detail.

The action of the shield such as the shield with opening 12 in the present invention is to improve the magnetic field generation efficiency of the electromagnetic coil. Further, when the signal processing circuit unit is arranged in the vicinity of the electromagnetic coil, the effect of reducing the magnetic field strength in the signal processing circuit unit is exhibited. In order to verify these effects, (a) in the case of only the electromagnetic coil 10 in which the core 11 made of a magnetic material is inserted into the air core, (b) in the case where the shield 12 with an opening is further mounted in the configuration of (a) The two types of cases are compared. 8A and 8B show the spatial distribution of the magnetic field strength of the electromagnetic coil 10 with respect to a constant drive current. These are obtained using numerical analysis. The numbers in the decimal point in the figure showing the results are numerical values representing the magnetic field strength of the electromagnetic coil 10, and the scale of the magnetic field strength is common in FIGS. 8 (a) and 8 (b). In this analysis, it is assumed that Ni—Zn-based ferrite is used as the material of the movable magnetic body 9, the core 11, and the shield with opening 12. Since the effective relative magnetic permeability of the Ni—Zn ferrite with respect to an AC magnetic field of 10 kHz is about 300, the relative magnetic permeability of the member made of a magnetic material is set to 300.

8A and 8B, the magnetic field strength in the vicinity of the movable magnetic body 9 in (b) is more than twice that in (a). It is increasing. From this, it can be seen that the effect of improving the magnetic field generation efficiency of the electromagnetic coil 10 by two times or more can be obtained by mounting the shield 12 with the opening. 8A and 8B, the magnetic field strength in the signal processing circuit unit 13 in FIG. 8B is the same as that in FIG. 8A. Compared to that, it has decreased to less than half. From this, it can be seen that the effect of reducing the magnetic noise received by the signal processing circuit unit 13 to about half by mounting the shield with opening 12 is obtained.

From the above, it can be seen that the effect of improving the magnetic field generation efficiency of the electromagnetic coil can be obtained by mounting a shield such as the shield 12 with an opening. Further, it can be seen that the effect of reducing the magnetic noise received by the signal processing circuit unit can be obtained even when the signal processing circuit unit is arranged in the vicinity of the electromagnetic coil. The above results obtained by numerical analysis can be explained from the theory of leakage flux in the magnetic circuit. Such an effect is not limited to the embodiment as described above, and includes the characteristic matter of the present invention (that is, the periphery of the electromagnetic coil is covered with a shield made of a magnetic material except for a portion substantially facing the magnetic body). It is clear from these theories that this is achieved with construction.

More specific embodiments of the present invention will be described below.
Example 1
As a first embodiment of the present invention, an example of a potential measuring device that vibrates a cantilever diaphragm having a magnetic material by an electromagnetic coil on which an opening shield is mounted will be described.

FIG. 1 shows the potential measuring apparatus of this example. One end of the vibration plate 1 is fixed to a spacer 4 disposed on the substrate 8, the detection electrode 3 is disposed on the surface of the vibration plate 1 facing the measurement object 2, and the movable magnetism is disposed on the opposite surface. A body 9 is arranged. The electromagnetic coil 10 is disposed on the substrate 8, and a core 11 made of a magnetic material is inserted into the air core portion of the electromagnetic coil 10. The surface around the electromagnetic coil 10 is covered with an opening shield 12 having an opening on the surface facing the movable magnetic body 9. The shape of the plate-shaped movable magnetic body 9 corresponds to the shape of the opening of the shield with opening 12 (for example, both are circular, square, etc.).

An example of a method for mounting the shield 12 with the opening on the electromagnetic coil 10 will be described below. As shown in FIG. 7 (a), the shield 12 with an opening is manufactured by dividing it into two parts: a shield lower portion 12a with an opening covering the lower and side surfaces of the electromagnetic coil 10 and an shield upper portion 12b with an opening covering the upper peripheral portion. To do. Then, after the electromagnetic coil 10 having the core 11 inserted in the air core portion is inserted into the shield lower portion 12a with an opening, it is adhered to the shield lower portion 12a with an opening with a magnetic paste or the like so as to cover the shield upper portion 12b with an opening. Or weld. The magnetic material of the shield and the core may be the same or different. It is also possible to integrally form the rod-shaped core 11 on the lower surface of the shield lower portion 12a with an opening (the inner bottom surface of the shield on the opposite side of the portion substantially facing the magnetic body 9). FIG. 7B shows a state where the shield 12 with opening is mounted on the electromagnetic coil 10. As shown in FIG. 7 (b), the top surface of the core 11 is aligned with the upper surface of the electromagnetic coil 10 and is below the level of the opening of the shield 12, and the opening is completely formed in FIG. 9 (b). As shown, a leakage magnetic flux is generated, and the magnetic field generation efficiency of the electromagnetic coil with respect to the magnetic body 9 is improved.

In the above configuration, when a current is supplied to the electromagnetic coil 10 from a driving power source (not shown), a magnetic field having an intensity proportional to the magnitude of the current is generated, and the movable magnetic body 9 magnetized in accordance with this generates the magnetic coil 9. The diaphragm 1 receives the attractive force from 10 and bends downward in FIG. When the current supply from the drive power supply is interrupted in this state, the magnetic field and magnetization disappear, the attractive force received by the movable magnetic body 9 from the electromagnetic coil 10 disappears, and the diaphragm 1 is shown in FIG. Curve upward. By periodically repeating the current supply and interruption from the drive power source, the diaphragm 1 periodically vibrates in the vertical direction in FIG. 1, and the distance between the detection electrode 3 on the diaphragm 1 and the measurement object 2 is also increased. It changes with the same period. As a result, a current signal proportional to the surface potential of the measuring object 2 is obtained from the detection electrode 3. By performing signal processing such as detection and rectification on the current signal using the signal processing circuit unit 13, a potential measurement signal of the measurement target 2 is obtained (the wiring connecting the detection electrode 3 and the signal processing circuit unit 13 is not connected). Not shown in FIG. 1).

In this embodiment, due to the presence of the shield 12 with the opening, the magnetic field generation efficiency of the electromagnetic coil 10 with respect to the movable magnetic body 9 is improved, and at the same time, the magnetic noise received by the signal processing circuit 13 is reduced. Therefore, the presence of the shield 12 with the opening makes it possible to obtain both the effects of reducing the power consumption and improving the potential measurement accuracy at the same time. Further, since the core 11 made of a magnetic material is inserted into the air core portion of the electromagnetic coil 10, it is possible to further improve the magnetic field generation efficiency of the electromagnetic coil and reduce the power consumption of the electromagnetic coil. This configuration responds to the demand for reducing the power consumption of the electromagnetic coil when the power supply unit needs to be downsized due to the downsizing of the potential measuring device and the power that can be supplied to the electromagnetic coil is limited.

(Example 2)
As a second embodiment of the present invention, an example of a potential measuring device that vibrates a cantilever type diaphragm having an electromagnetic coil mounted with an opening shield by facing a magnetic body fixed to the substrate will be described. .

FIG. 2 shows the potential measuring apparatus of this example. One end of the diaphragm 1 is fixed to a spacer 4 disposed on the substrate 8. And the detection electrode 3 is arrange | positioned at the surface facing the measuring object 2 of the diaphragm 1, and the electromagnetic coil 10 is arrange | positioned at the surface on the opposite side. A core 11 made of a magnetic material is inserted into the air core portion of the electromagnetic coil 10, and the surface around the electromagnetic coil 10 has an opening at a portion facing the fixed magnetic body 14 disposed on the substrate 8. Covered by the shield 12 with the opening. The other points are the same as in the first embodiment.

Also in this embodiment, when a current is supplied to the electromagnetic coil 10 from a drive power source (not shown), a magnetic field having an intensity proportional to the magnitude of the current is generated, and the electromagnetic coil 10 receives an attractive force from the fixed magnetic body 14. The diaphragm 1 is bent downward in FIG. When the current supply from the drive power supply is interrupted in this state, the attractive force received by the electromagnetic coil 10 from the fixed magnetic body 14 disappears, and the diaphragm 1 is bent upward by the elastic force of the diaphragm 1. By periodically repeating the current supply and interruption from the drive power source, the diaphragm 1 periodically vibrates in the vertical direction of FIG. 2, and the distance between the detection electrode 3 on the diaphragm 1 and the measurement object 2 is also increased. It changes with the same period. As a result, a current signal proportional to the surface potential of the measuring object 2 is obtained from the detection electrode 3. The current signal is subjected to signal processing such as detection and rectification using the signal processing circuit unit 13 to obtain a potential measurement signal of the measurement object 2 (the wiring connecting the detection electrode 3 and the signal processing circuit unit 13 is shown in FIG. 2). Not shown).

In the second embodiment in which the arrangement relationship between the electromagnetic coil and the magnetic body is reversed as compared with the first embodiment, the same effect as in the first embodiment can be obtained.

(Example 3)
As a third embodiment of the present invention, a diaphragm having a permanent magnet having magnetic poles is supported by a torsion spring, and the diaphragm is rotated by an electromagnetic coil having a shield with an opening around the torsion spring as a central axis. An example of a potential measuring device that vibrates in the following manner will be described.

FIG. 3 shows a top view of the potential measuring apparatus of this example, and FIG. 4 shows a cross-sectional view taken along A-A ′ in FIG. 3. The diaphragm 15 is connected to a support plate 18 via two torsion springs 17 a and 17 b arranged on the same straight line, and the support plate 18 is fixed to the substrate 8 via a spacer 4. Two detection electrodes 16a and 16b are arranged on the surface of the diaphragm 15 facing the measurement object 2, and a movable permanent magnet 21 is arranged on the opposite surface. The detection electrodes 16a and 16b are arranged so as to be symmetric with respect to a straight line passing through the two torsion springs 17a and 17b. Further, the magnetization direction of the movable permanent magnet 21 may be either N pole as long as it is parallel to the diaphragm 15 and substantially perpendicular to a straight line passing through the two torsion springs 17a and 17b (here, as shown in FIG. 4). The right end of the movable permanent magnet 21 is magnetized so as to be an N pole). As a form of the permanent magnet 21, there are a flat magnet, a plurality of (for example, two) bar magnets arranged in parallel, and the like. The electromagnetic coil 10 is disposed on the substrate 8, and a core 11 made of a magnetic material is inserted into the air core portion of the electromagnetic coil 10. The surface around the electromagnetic coil 10 is covered with an opening shield 12 having an opening in a portion facing the movable permanent magnet 21.

In the above configuration, a current is supplied from a drive power source (not shown) to the electromagnetic coil 10 so that the surface of the electromagnetic coil 10 facing the diaphragm 15 has an N pole. Then, a magnetic field having an intensity proportional to the magnitude of the current is generated, and the N pole side of the movable permanent magnet 21 receives a repulsive force from the electromagnetic coil 10 and simultaneously the S pole side of the movable permanent magnet 21 receives an attractive force from the electromagnetic coil 10. Thus, the diaphragm 15 rotates in the counterclockwise direction in the figure with the torsion springs 17a and 17b as the central axis. In this state, if the direction of the current supplied from the drive power supply to the electromagnetic coil 10 is reversed, the N-pole side of the movable permanent magnet 21 receives the attractive force from the electromagnetic coil 10 and the S-pole side of the movable permanent magnet 21 at the same time. Receives repulsive force from the electromagnetic coil 10. Thereby, the diaphragm 15 rotates in the clockwise direction in the drawing with the torsion spring 17 as the central axis. By periodically reversing the direction of the current supplied from the drive power source to the electromagnetic coil 10, the diaphragm 15 periodically vibrates in the rotational direction about the torsion springs 17a and 17b. Therefore, the distance between each of the detection electrodes 16a and 16b on the vibration plate 15 and the measurement object 2 changes periodically and in opposite directions. As a result, current signals having amplitudes proportional to the surface potential of the measuring object 2 and periodically changing in opposite directions can be obtained from the detection electrodes 16a and 16b. A current signal generated by the detection electrodes 16a and 16b is input to the signal processing circuit unit 20 on the support plate 18 via the wirings 19a and 19b, respectively, and is converted by using the signal processing circuit unit 20, thereby measuring object 2. Is obtained.

Examples of signal processing means in the signal processing circuit unit 20 include the following. That is, a DC voltage signal proportional to the surface potential of the measuring object 2 obtained by performing synchronous detection, amplification, and rectification after calculating the difference between the current signals generated at the detection electrodes 16a and 16b is output as a potential measurement signal. . Here, by calculating the difference between the current signals that change in opposite directions, the intensity of the obtained signal is almost doubled, and the transmission noise in phase with each other received by the current signals in the wirings 19a and 19b cancels each other out to almost zero. Therefore, the S / N ratio of the obtained measurement signal increases. Therefore, the effect of further improving the potential measurement accuracy can be obtained by this signal processing means.

Also in this embodiment, due to the presence of the shield 12 with the opening, the magnetic field generation efficiency of the electromagnetic coil 10 is improved, and at the same time, the magnetic noise received by the signal processing circuit 20 is reduced. Therefore, even in the potential measuring apparatus having the configuration as in the present embodiment, it is possible to simultaneously obtain both the effects of reducing the power consumption and improving the potential measuring accuracy due to the presence of the shield 12 with the opening. The effect of the core 11 inserted in the air core part of the electromagnetic coil 10 is also as described in the first embodiment.

Example 4
Next, a fourth embodiment of the present invention will be described. Here, a diaphragm having an electromagnetic coil on which a shield with an opening is mounted is supported by a torsion spring, and the diaphragm is centered on the torsion spring by making the electromagnetic coil face a permanent magnet fixed to the substrate. This is a potential measuring device that vibrates in the rotating direction.

FIG. 3 shows a top view of the potential measuring device of this example, and FIG. 5 shows a cross-sectional view taken along A-A ′ in FIG. 3. The arrangement of the diaphragm 15 and the two torsion springs 17a and 17b, the support plate 18, the spacer 4, the substrate 8, the two detection electrodes 16a and 16b, the wirings 19a and 19b, and the signal processing circuit unit 20 is the third embodiment. This is the same as the potential measuring apparatus.

In the present embodiment, the electromagnetic coil 10 is disposed on the surface of the diaphragm 15 opposite to the surface facing the measurement target 2, and two fixed permanent magnets 22 a, directly below the electromagnetic coil 10 on the substrate 8. 22b is arranged. The fixed permanent magnets 22a and 22b are arranged at intervals of about the diameter of the electromagnetic coil 10, and the line segments connecting them are arranged so as to be substantially orthogonal to the straight line obtained by projecting the straight line passing through the torsion springs 17a and 17b onto the substrate 8. ing. The magnetization directions of the fixed magnetic bodies 22a and 22b are substantially perpendicular to the diaphragm 15 and opposite to each other. Here, as shown in FIG. 5, the left fixed permanent magnet 22a is magnetized so that the surface facing the electromagnetic coil 10 is an S pole, and the right fixed permanent magnet 22b has a surface facing the electromagnetic coil 10. Magnetized so as to be an N pole. A core 11 made of a magnetic material is inserted into the air core portion of the electromagnetic coil 10, and the surface around the electromagnetic coil 10 is covered with an opening shield 12 having openings at portions facing the fixed magnetic bodies 22 a and 22 b. It has been broken.

In the above configuration, when a current is supplied from a driving power source (not shown) to the electromagnetic coil 10 so that the surfaces of the electromagnetic coil 10 facing the fixed permanent magnets 22a and 22b are N poles, the current is proportional to the magnitude of the current. A magnetic field of the specified strength is generated. As a result, the portion of the electromagnetic coil 10 on the right side of the figure receives a repulsive force from the fixed permanent magnet 22b and the portion of the electromagnetic coil 10 on the left side of the drawing receives an attractive force from the fixed permanent magnet 22a. Accordingly, the diaphragm 15 rotates in the counterclockwise direction in the figure with the torsion springs 17a and 17b as the central axis. In this state, when the direction of the current supplied from the drive power source to the electromagnetic coil 10 is reversed, the left portion of the electromagnetic coil 10 in the drawing receives the attractive force from the fixed permanent magnet 22b and the left side of the electromagnetic coil 10 in the drawing, contrary to the above. This part receives a repulsive force from the fixed permanent magnet 22a. Therefore, the diaphragm 15 rotates in the clockwise direction in the figure with the torsion spring 17 as the central axis.

By periodically reversing the direction of the current supplied from the drive power source to the electromagnetic coil 10, the diaphragm 15 periodically vibrates in the rotational direction about the torsion springs 17a and 17b. Therefore, the distance between each of the detection electrodes 16a and 16b on the vibration plate 15 and the measurement object 2 changes periodically and in opposite directions. As a result, similar to the potential measuring device of the third embodiment, current signals having amplitudes proportional to the surface potential of the measuring object 2 and periodically changing in opposite directions can be obtained from the detection electrodes 16a and 16b. . By converting these current signals using the signal processing circuit unit 20, a potential measurement signal of the measurement object 2 is obtained.

In this embodiment, the same effect as that of the third embodiment can be obtained.

(Example 5)
As a fifth embodiment of the present invention, a configuration example of an image forming apparatus using the potential measuring device of the present invention will be described.

An image forming apparatus of this embodiment is shown in FIG. Around the photosensitive drum 29, a charger 24 that can be controlled by the charger controller 25, an exposure device 26, a potential measuring device 23 of the present invention, and a toner supplier 27 are installed. A latent image is obtained by charging the surface of the photosensitive drum 29 with the charger 24 and exposing the surface of the photosensitive drum 29 with the exposure device 26. By attaching toner to the latent image by the toner supplier 27, a toner image in which the latent image is developed is obtained. This toner image is transferred to a printing object 30 sandwiched between the feed roller 28 and the photosensitive drum 29, and the toner on the printing object 30 is fixed. Image formation is achieved through these steps. The charger controller 25 constitutes a signal processing device, and the charger 24, the exposure device 26, the photosensitive drum 29, and the like constitute image forming means.

In this configuration, the charged state of the photosensitive drum 29 is measured by the potential measuring device 23 of the present invention, and the surface potential measurement signal of the photosensitive drum 29 is output to the charger controller 25. Based on this measurement signal, the charger controller 25 feedback-controls the charging voltage of the charger 24 so that the surface potential of the photosensitive drum 29 after charging becomes a desired value (measurement signal of the potential measuring device 23 of the present invention). Can be fed back to the exposure unit 26 to control it). Thereby, stable charging of the photosensitive drum 29 is realized, and stable image formation is realized.

Sectional drawing which shows the electric potential measurement apparatus in one Embodiment and 1st Example of this invention. Sectional drawing which shows the electric potential measuring apparatus in the 2nd Example of this invention. The top view which shows the electric potential measurement apparatus in the 3rd and 4th Example of this invention. Sectional drawing in A-A 'of FIG. 3 of the electric potential measuring apparatus in 3rd Example of this invention. Sectional drawing in A-A 'of FIG. 3 of the electric potential measuring apparatus in the 4th Example of this invention. Schematic of an image forming apparatus in a fifth embodiment of the present invention. The perspective view explaining an example of the mounting method of the shield with an opening. It is an intensity distribution diagram of a magnetic field stretched by a coil calculated by numerical analysis, (a) an intensity distribution diagram when a core is inserted into a coil air core, and (b) an intensity when an opening shield is mounted on the coil. Distribution map. Sectional drawing which shows the conventional electric potential measuring apparatus using the cantilever which has a permanent magnet. Sectional drawing which shows the conventional electric potential measuring apparatus using the cantilever which has a coil.

Explanation of symbols

1, 15 ... vibration member (diaphragm)
2, 29 ... Measurement object (photosensitive drum)
3, 16a, 16b ... detection electrode 10 ... electromagnetic coil 9, 21 ... magnetic body (movable magnetic body, movable permanent magnet)
11 ... Core 12 ... Shield (Shield with opening)
14, 22a, 22b ... Magnetic body (fixed magnetic body, fixed permanent magnet)
23 ... Potential measuring device 25 of the present invention ... Signal processing device (charger controller)
24, 26, 29... Image forming means (charging device, exposure device, photosensitive drum)

Claims (8)

A vibrating member having a sensing electrode and a magnetic material;
An electromagnetic coil;
A potential measuring device having
An electric potential measuring apparatus, wherein the periphery of the electromagnetic coil is covered with a shield made of a magnetic material except for a portion facing the magnetic body. A vibrating member having a sensing electrode and an electromagnetic coil;
Magnetic material,
A potential measuring device having
An electric potential measuring apparatus, wherein the periphery of the electromagnetic coil is covered with a shield made of a magnetic material except for a portion substantially facing the magnetic body. 3. The potential measuring device according to claim 1, wherein the shield has an opening that transmits a magnetic field in a portion substantially opposed to the magnetic body. 4. 4. The potential measuring device according to claim 1, wherein the electromagnetic coil has a core made of a magnetic material. 5. 5. The potential measuring device according to claim 1, wherein the vibrating member is supported by a torsion spring. 6. 6. The potential measuring apparatus according to claim 1, wherein the magnetic body is a permanent magnet having a magnetic pole. In the electric potential measuring device according to any one of claims 1 to 6,
The vibration member has a detection electrode disposed on a surface facing a measurement target,
It is a diaphragm in which one of the magnetic body and the electromagnetic coil is arranged on the opposite surface,
An electric potential measuring apparatus in which the other of a magnetic body and an electromagnetic coil is fixedly disposed immediately below a diaphragm. An electric potential measuring device according to any one of claims 1 to 7, a signal processing device for processing an output signal obtained from the electric potential measuring device, and an image forming means,
The sensing electrode of the potential measuring device is arranged facing the potential measurement target,
The image forming apparatus, wherein the image forming unit controls image formation based on a signal detection result of the signal processing apparatus.

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