JP2007298450A - Electric potential measuring apparatus and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the possibility of deterioration in the electric potential measurement accuracy in an electric potential measuring apparatus, by approaching and accumulating a particle as a toner, having magnetism near a permanent magnet and its neighbour, even when the apparatus is to be used in an environment where particles like the toner, having magnetism in the electric potential measuring apparatus in which a vibrator is vibrated by a driving means which includes the permanent magnet exist. <P>SOLUTION: The electric potential measuring apparatus comprises a shielding case 2 which has an aperture 3 at the opposite position to an object to be measured 1, the vibrator 7 which is arranged capable of vibration within the shield case 2, a detection electrode 9 which is arranged on the vibrator 7, the driving means which makes the electrostatic capacity between the detection electrode 9 and the object to be measured 1 changed by driving the vibrator 7, and a signal processing means 10 which obtains information about the electric potential of the object to be measured 1 by processing the electrical signal which is generated at the detection electrode 9. The driving means includes the permanent magnet 8 and an electromagnetic coil 9. The permanent magnet 8 is located inside the shielding case 2 and is arranged at the outside of a space, which is formed making the aperture 3 extend vertically, from the aperture 3 of the shielding case 2 to the bottom of the shielding case 2. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a potential measuring device capable of measuring the potential of a measured object (measurement target) in a non-contact manner, and an image forming apparatus having the potential measuring device.

In an image forming apparatus having a photosensitive drum and performing image formation by electrophotography, in order to obtain a stable image quality at all times, the potential distribution on the surface of the photosensitive drum is appropriately (typically uniform) in any environment. ) So that the surface of the photosensitive drum is charged. For this reason, the image forming apparatus is conventionally equipped with a function for measuring the potential of the photosensitive drum surface with a potential measuring device and performing feedback control so as to keep the potential of the photosensitive drum surface uniform using the result. Often done.

One of the functions that are conventionally required for the potential measuring device used for such a purpose is a function of measuring the surface potential of the object to be measured in a non-contact manner. This is because when the potential measuring device comes into contact with the surface of the photosensitive drum, the potential distribution on the surface of the photosensitive drum is not uniform, which causes a disturbance in the formed image. Such a potential measurement method is referred to as “non-contact type” in this specification.

The measurement principle of the non-contact potential measuring device is that the capacitance between the object to be measured and the sensing electrode arranged opposite to the object to be measured is slightly changed, and is proportional to the surface potential of the object to be measured. A method of obtaining a current signal having an amplitude is often used.

The principle of the non-contact potential measuring device will be described below.
Due to the electric field generated between the surface of the object to be measured and the sensing electrode built in the potential measuring device, an electric charge Q of an electric quantity proportional to the surface potential V of the object to be measured is induced on the sensing electrode.
The relationship between Q and V is Q = CV (1)
It is expressed by the formula. Here, C is a capacitance between the detection electrode and the surface of the object to be measured. From equation (1), it is possible to obtain the surface potential V of the object to be measured by measuring the quantity of electricity Q induced on the sensing electrode.

However, it is actually difficult to directly measure the quantity of electricity Q induced on the detection electrode at high speed and accurately. Therefore, as a practical method, the size of the electrostatic capacitance C between the detection electrode and the surface of the object to be measured is periodically changed, and an alternating current signal generated at the detection electrode is measured to measure the object to be measured. The method of obtaining the surface potential of the above is often used.

The following shows that the surface potential of the object to be measured can be obtained by the above method.
Assuming that the capacitance C is a function of time t, the alternating current signal i generated at the detection electrode is a time differential value of the amount of electricity induced at the detection electrode, and the following equation is obtained from equation (1): It is represented by
i (t) = dQ / dt = d (CV) / dt (2)
Here, when the rate of change of the surface potential V of the object to be measured is sufficiently slow with respect to the rate of change of the capacitance C, it can be assumed that V is constant in the minute time dt. Is represented by the following equation.
i (t) = dQ (t) / dt = V · dC (t) / dt (3)

From the equation (3), the magnitude of the alternating current signal i generated at the sensing electrode is a linear function of the surface potential V of the measurement target. Therefore, by measuring the amplitude of the alternating current signal, the surface potential of the measurement target is determined. It is possible to obtain. Further, from the equation (3), if the surface potential V of the measurement target is the same, the magnitude of the alternating current signal i with respect to the surface potential of the measurement target, that is, the sensitivity of the potential measurement device is proportional to the change rate of the capacitance. I understand that.

As one method of periodically changing the capacitance C between the detection electrode and the measurement target surface, the capacitance C is changed periodically by changing the distance between the detection electrode and the measurement target surface. The method of making it include. The capacitance C between the sensing electrode and the surface of the object to be measured is approximately C = A · S / x (4)
It is expressed by the following formula. Here, A is a proportional constant related to the dielectric constant of the substance, S is the area of the detection electrode, and x is the distance between the detection electrode and the surface of the object to be measured. From equation (4), it can be seen that when the distance x changes periodically, the capacitance C also changes periodically.

As one means for periodically changing the distance between the detection electrode and the surface of the measurement object, the detection electrode is arranged at the tip of the vibrating body, and the detection electrode is vibrated in a direction substantially perpendicular to the surface of the measurement object. Means are mentioned. As drive means for causing such vibration, means for vibrating a vibrating body using a permanent magnet and an electromagnetic coil is often used. Advantages of vibrating the vibrating body with the permanent magnet and the electromagnetic coil include that the vibrating body can be vibrated with relatively low power consumption and that the manufacturing and mounting costs are relatively low.

It is also possible to periodically change the capacitance C by periodically changing the exposed area (corresponding to S) of the detection electrode with respect to the object to be measured. Also in this case, as the driving means, means for vibrating a vibrating body such as a shutter member using a permanent magnet and an electromagnetic coil is often used. The principle of potential measurement is basically the same as described above.

As a conventional example of a potential measuring device that drives a vibrating body with a permanent magnet and an electromagnetic coil, the potential measuring device shown in FIG. 9 will be described below (see Patent Document 1).

In the configuration of FIG. 9, a support member 54 is fixed to the bottom of the shield case 52 having an opening 53 on the surface facing the object to be measured 51, and the end of the vibrating body is fixed to the support member 54. . The vibrating body includes two diaphragms 55, and one end of each diaphragm 55 is fixed to the support member 54. The electromagnetic coil 56 is an air core, and is fixed to the other end of the diaphragm 55 so as to be located immediately below the opening 53 of the shield case 52. The permanent magnet 58 is fixed to the bottom of the shield case 52 so as to penetrate the air core of the electromagnetic coil 56. Here, the arrangement positions of the electromagnetic coil 56 and the permanent magnet 58 may be reversed. Further, the symbols N and S in FIG. 9 indicate the magnetization direction of the permanent magnet 58, and the positions of N and S may be reversed. A detection electrode 59 is disposed on the surface of the electromagnetic coil 56 facing the opening 53, and a wiring 61 that transmits an electric signal to the signal processing means 60 is connected to the detection electrode 59.

The principle of potential measurement by the potential measuring device described in Patent Document 1 will be described below.
When a periodic drive current is input to the electromagnetic coil 56 from a drive signal source (not shown in FIG. 9), an attractive force or a repulsive force acts periodically between the electromagnetic coil 56 and the permanent magnet 58, and the diaphragm 55 Vibrates in the bending direction. Thereby, the electromagnetic coil 56 is periodically displaced in the direction perpendicular to the surface of the object 51 to be measured. Thus, since the distance between the surface of the object to be measured 51 and the detection electrode 59 changes periodically, the capacitance between the surface of the object to be measured 51 and the detection electrode 59 also changes periodically, and the above formula According to (3), an alternating current signal proportional to the surface potential of the object to be measured 51 is generated at the detection electrode 59. This alternating current signal is input to the signal processing means 60 via the wiring 61, and after being subjected to processing such as conversion to a voltage signal, amplification, and rectification in the signal processing means 60, it is output as a potential measurement signal.
JP-A-8-110361

By the way, in an image forming apparatus that has a photosensitive drum and forms an image by electrophotography, a latent image formed as a static electricity distribution on the photosensitive drum has fine particles called toner adhered to the photosensitive drum by electrostatic force, and the object to be printed To form an actual image. The toner includes magnetic toner and non-magnetic toner, and both toners are conventionally used. Here, when a conventional potential measuring device having a permanent magnet as described above is mounted on an image forming apparatus using magnetic toner and used for a long time, the potential is measured by the magnetic toner that has entered the potential measuring device. The potential measurement accuracy of the device may deteriorate. The reason is described below.

When the toner having magnetism enters the potential measuring device from the opening of the shield case of the potential measuring device for some reason, the toner having magnetism may be attracted to the permanent magnet. The magnetic toner once attracted to the permanent magnet tends to remain attracted unless it is intentionally removed by disassembly and cleaning. Therefore, as the usage time increases, the number of particles of toner having magnetism deposited in the vicinity of the permanent magnet tends to increase. The toner having magnetism deposited in the vicinity of the permanent magnet in this manner causes a blockage of the space between the electromagnetic coil and the permanent magnet, a change in the resonance frequency of the vibrating body, and the like, which causes a decrease in the amplitude of the vibrating body. There is a possibility. If the vibration amplitude of the vibrating body is reduced, the amplitude of the current signal obtained from the detection electrode may be reduced, and the S / N ratio of the potential measurement signal may be lowered.

That is, when the above-described potential measuring device having a permanent magnet is used in an environment where magnetic particles such as toner exist, such particles are easily attracted to the permanent magnet and the vicinity thereof, and the weight change of the member and the space portion Undesirable situations may occur due to clogging. This is not limited to the potential measuring device as described above, and the electrostatic capacity between the detection electrode and the surface to be measured is periodically changed by driving a shutter member or the like with a driving means such as an electromagnetic comb type including a permanent magnet. It can also occur in an electric potential measuring device that changes to However, the above-described conventional potential measuring device does not consider such a problem at all.

In view of the above problems, the potential measuring device of the present invention has the following elements.
That is, a shield case having an opening in a portion facing the measurement object;
A vibrating body disposed in the shield case so as to vibrate;
On the vibrating body, a detection electrode disposed at a position corresponding to the opening of the shield case;
Drive means for driving the vibrator;
Signal processing means for processing an electrical signal generated at the detection electrode;
Have
The drive means includes a permanent magnet and an electromagnetic coil, and the permanent magnet is formed inside the shield case and extending vertically from the opening of the shield case to the bottom of the shield case. Placed outside the space to be.

Furthermore, it is preferable that a shielding wall for separating an opening of the shield case and a space where the detection electrode is present from a space where the permanent magnet is present may be disposed inside the shield case.

Moreover, in view of the said subject, the electric potential measuring apparatus of this invention has the following elements.
That is, a shield case having an opening in a portion facing the measurement object;
A detection electrode fixedly arranged at a position facing the opening in the shield case;
A shutter;
Driving means for driving the shutter;
Signal processing means for processing an electrical signal generated at the detection electrode;
Have
The drive means includes a permanent magnet and an electromagnetic coil, and the permanent magnet is formed inside the shield case and extending vertically from the opening of the shield case to the bottom of the shield case. And a shielding wall for separating the space where the opening of the shield case and the detection electrode are present from the space where the permanent magnet is present.

In view of the above problems, a potential measuring device 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. A portion where the detection electrode of the potential measuring device is formed is disposed to face a potential measurement target of the image forming means, and the image forming means uses the signal detection result of the signal processing device to perform image formation. Take control.

According to the potential measuring device of the present invention, the permanent magnet is inside the shield case and outside the space formed by extending the opening vertically from the shield case opening to the bottom of the shield case. At least a structure to be arranged. Therefore, the possibility that particles such as magnetic toner entering the potential measuring device from the opening of the shield case reach the vicinity of the permanent magnet and is attracted to the permanent magnet is reduced. Therefore, it is possible to reduce the possibility that normal operation of the potential measuring device having a permanent magnet is hindered by particles such as magnetic toner. Furthermore, this effect can be improved when the shielding wall as described above is arranged.

Further, by using the potential measuring device having the permanent magnet of the present invention for an image forming apparatus using magnetic toner or the like, it is possible to stabilize the image quality over a relatively long period of time.

Hereinafter, embodiments of the present invention will be described. One embodiment of a potential measuring device is a shield case having an opening at a portion facing a measurement object, a vibrating body arranged to be vibrated in the shield case, and facing the opening of the shield case on the vibrating body. It has a sensing electrode arranged at a position. Then, a driving means including a permanent magnet and an electromagnetic coil for driving the vibrating body to change the capacitance between the detection electrode and the measurement target, and an electric signal generated at the detection electrode to process the potential of the measurement target Signal processing means for acquiring the information. Furthermore, the shielding case has a shielding wall disposed in order to separate the space where the opening of the shielding case and the detection electrode are present from the space where the permanent magnet is present. Here, the permanent magnet is disposed inside the shield case and outside the space formed by extending the opening from the shield case to the bottom of the shield case substantially perpendicularly.

When the vibrating body is configured as a cantilever type, the vibrating body is a vibration in which, for example, the end opposite to the side where the detection electrode is arranged is fixed to the support member arranged at the bottom inside the shield case. Configured as a plate. The shielding wall has a through-hole through which the diaphragm is penetrated and is disposed at a position between the detection electrode and the permanent magnet. Thereby, it is possible to provide a shielding wall so as not to disturb the vibration of the vibrating body.

The vibrating body can also be configured as a structure having a torsion hinge connecting two diaphragms. In this configuration, there are at least one support member disposed on the bottom inside the shield case. In this case, the vibrating body includes a detection diaphragm on which the detection electrode is disposed and a driving diaphragm on which at least a part of the driving unit is disposed. And a torsion spring having both ends fixed to the detection diaphragm and the driving diaphragm, and at least one torsion having both ends fixed to at least one of the detection diaphragm and the driving diaphragm and the support member. Provide a spring.

Further, the shielding wall has a through-hole through which a torsion spring having both ends fixed to the detection diaphragm and the driving diaphragm is passed. According to this configuration, the torsion spring has a very small cross-sectional area and displacement compared to the diaphragm, so that the through hole of the shielding wall can be made small. Therefore, the possibility that magnetic toner or the like reaches the vicinity of the permanent magnet and is attracted to the permanent magnet is further reduced. As a result, it is possible to greatly reduce the possibility that normal operation of the potential measuring device having a permanent magnet is hindered by toner having magnetism or the like.

In this configuration, two sensing electrodes are arranged, and a potential measuring device that cancels transmission noise by differentially amplifying signals having opposite phases generated at each sensing electrode can be obtained. Here, the detection diaphragm is provided so as to be able to vibrate in the rotational direction with the torsion spring as the central axis, and the two detection electrodes are positioned on opposite sides of the detection vibration plate across the central axis of the rotational vibration. To be arranged. The signal processing means has a function of calculating and amplifying the difference between the electrical signals generated at the respective detection electrodes. In this configuration, the common-mode noise superimposed on the wiring connecting each detection electrode and the signal processing means is removed, while the intensity of the necessary signal component is doubled, so the S / N ratio of the potential measurement signal Will improve. Therefore, the potential measurement accuracy of the potential measuring device can be improved.

The potential measuring device according to another embodiment includes a shield case having an opening at a portion facing the measurement target, and a detection electrode fixedly disposed at a position facing the opening of the shield case in the shield case. In order to change the capacitance between the detection electrode and the measurement target by driving the shutter and the shutter disposed so as to vibrate in the shield case in order to change the degree of exposure of the detection electrode to the measurement target through the opening. Drive means including a permanent magnet and an electromagnetic coil. In addition, it has signal processing means to process the electrical signal generated at the detection electrode and acquire information on the potential of the object to be measured. Inside the shield case, there is a space where the opening of the shield case and the detection electrode exist and a permanent magnet. A shielding wall is arranged for separating the space to be separated. In this configuration, the shutter is, for example, a shutter member that has an opening at a portion corresponding to the detection electrode and vibrates by moving in parallel, and the shielding wall has a through-hole through which the shutter member passes. It arrange | positions in the position which hits between an opening part and a permanent magnet.

A mechanism for controlling the charge amount of the photosensitive drum is constructed by mounting the above-described potential measuring device having a permanent magnet on an image forming apparatus such as an electrophotographic printer and combining it with a charger and a charger controller. Can do.

Hereinafter, more specific embodiments of the present invention will be described with reference to the drawings.

Example 1
A potential measuring apparatus according to Example 1 of the present invention will be described. FIG. 1 shows the configuration of the potential measuring device in this example. FIG. 1 (a) is a top view of the structure provided in the shield case 2 as viewed from above, and FIG. 1 (b) is a cross-sectional view taken along line A1-A2 of FIG. 1 (a). In FIG. 1, a support member 4 is fixed to the inner bottom of a shield case 2 having an opening 3 on a surface facing an object to be measured (measurement target) 1. One end of the plate 7 is fixed.

The permanent magnet 8 that is a part of the driving means is disposed on the diaphragm 7, and the electromagnetic coil 6 that is also a part of the driving means is directly below the permanent magnet 8 in the bottom part inside the shield case 2. Placed in position. Here, the arrangement positions of the electromagnetic coil 6 and the permanent magnet 8 may be reversed. Further, the symbols N and S in FIG. 1B represent the magnetization direction of the permanent magnet 8, and the positions of N and S may be reversed.

The detection electrode 9 is arranged at a position directly below the opening 3 on the surface of the diaphragm 7 facing the opening 3 of the shield case 2, and an electric signal is transmitted to the signal processing means 10 to the detection electrode 9. Wiring 11 to be connected is connected.

In the configuration described above, the space outside the space formed by extending the opening 3 to the bottom of the shield case 2 in the direction in which the detection electrode 9 exists substantially perpendicular to the surface of the shield case 2 where the opening 3 is located. In addition, a permanent magnet 8 is arranged. That is, the permanent magnet 8 is disposed inside the shield case 2 and outside the space formed by extending the opening 3 from the opening 3 of the shield case 2 to the bottom of the shield case 2 substantially vertically. Yes. Therefore, even in this configuration, magnetic particles such as magnetic toner that enter the potential measuring device from the opening 3 of the shield case 2 can reach the vicinity of the permanent magnet 8 and adhere to the permanent magnet 8 or the like. Sex is reduced. Therefore, even this configuration is an example of the present invention.

In this embodiment, the shielding wall 12 is provided in order to further reduce the possibility that particles having magnetism will reach the vicinity of the permanent magnet 8 and adhere to the permanent magnet 8 or the like. The shielding wall 12 is arranged so as to separate the internal space of the shield case 2 into a space where the opening 3 and the detection electrode 9 of the shield case 2 are present and a space where the permanent magnet 8 is present. At that time, in order to prevent the shielding wall 12 itself from disturbing the vibration of the diaphragm 7, a through-hole 13 is provided at the position of the shielding wall 12 through which the diaphragm 7 penetrates as shown in FIG. The size of the through hole 13 is designed to be larger than the maximum displacement of the diaphragm 7 at the position of the shielding wall 12.

The operating principle of the potential measuring apparatus in this embodiment will be described below.
When a drive current having periodicity is input to the electromagnetic coil 6 from a drive signal source (not shown in FIG. 1), an attractive force or a repulsive force periodically acts between the electromagnetic coil 6 and the permanent magnet 8, and the diaphragm 7 Vibrates in the bending direction (see arrow in Fig. 1 (b)). As a result, the distance between the surface of the object to be measured 1 and the detection electrode 9 changes periodically, so that the capacitance between the surface of the object to be measured 1 and the detection electrode 9 also changes periodically. Therefore, an alternating current signal proportional to the surface potential of the object 1 to be measured is generated at the detection electrode 9 according to the above equation (3). This alternating current signal is input to the signal processing means 10 via the wiring 11, and is converted into a voltage signal, amplified and rectified by the signal processing means 10, and then output as a potential measurement signal. However, the surface potential of the object to be measured can also be measured by a method using a feedback processing circuit unit or the like. In this method, a voltage is applied to an appropriate member (for example, the shield case 2) so that the voltage output signal is adjusted to zero, and the applied voltage at that time is used as the potential of the object to be measured. is there.

The configuration of the first embodiment can be modified as shown in FIG. FIG. 3 (a) is a top view of the structure provided in the shield case 2 as viewed from above, and FIG. 3 (b) is a cross-sectional view along B1-B2 in FIG. 3 (a). In FIG. 3, a portion 37 that penetrates the through-hole 13 of the shielding wall 12 of the diaphragm 7 that is a vibrating body is formed of a material that is less rigid than the other portions. As a result, the vibration amplitude of the portion of the diaphragm 7 on which the detection electrode 9 is disposed can be further increased, so that the sensor output can be increased and the sensitivity of the potential measuring device can be increased. The other points are the same as in the first embodiment.

Further, it can be modified as shown in FIG. FIG. 4 is a top view of the structure provided in the shield case 2 as viewed from above. In FIG. 4, the width of the portion 7a that penetrates the through hole 13 of the shielding wall 12 of the diaphragm 7 that is a vibrating body is smaller than the other portion. This also makes it possible to increase the vibration amplitude of the portion of the diaphragm 7 on which the detection electrode 9 is arranged, thereby increasing the sensor output and further increasing the sensitivity of the potential measuring device. In this configuration, since the size of the through hole 13 can be reduced, the function of the shielding wall 12 becomes more effective. The other points are the same as in the first embodiment.

(Example 2)
A potential measuring apparatus according to Example 2 of the present invention will be described. FIG. 5 shows the configuration of the first type of the potential measuring device according to this example. FIG. 5 (a) is a top view of the structure provided in the shield case 2 as seen from above, and FIG. 5 (b) is a cross-sectional view taken along line C1-C2 of FIG. 5 (a). In FIG. 5, a support member 4 is fixed to the inner bottom portion of the shield case 2 having an opening 3 on the surface facing the object to be measured (measurement target) 1, and the end of the vibrating body 5 is attached to the support member 4. The part is fixed.

The vibrating body 5 includes a detection diaphragm 14, a drive diaphragm 15, a torsion spring 16 that couples the detection diaphragm 14 and the drive diaphragm 15, and a torsion spring 17 that couples the drive diaphragm 15 and the support member 4. Here, the positions where the detection diaphragm 14 and the drive diaphragm 15 are arranged may be switched. In this case, the torsion spring 17 connects the detection diaphragm 14 and the support member 4. In either case, the detection diaphragm 15 is disposed so as to be located immediately below the opening 3 of the shield case 2.

The permanent magnet 8 constituting a part of the driving means is disposed on the driving diaphragm 15, and the electromagnetic coil 6 constituting the other part of the driving means is located directly below the permanent magnet 8 in the bottom part inside the shield case 2. It is arranged at the position corresponding to. Again, the arrangement positions of the electromagnetic coil 6 and the permanent magnet 8 may be reversed. Further, the symbols N and S in FIG. 5 represent the magnetization direction of the permanent magnet 8, and the positions of N and S may be reversed.

The pair of detection electrodes 18 and 19 are arranged on the detection diaphragm 14 so as to be located on opposite sides of a straight line passing through the torsion spring 16. The detection electrodes 18 and 19 are connected to wirings 20 and 21 for transmitting electric signals to the signal processing means 22, respectively.

The configuration of the present embodiment described above is also formed by extending the opening 3 to the bottom of the shield case 2 in the direction in which the detection electrodes 18 and 19 exist substantially perpendicularly to the surface of the shield case 2 where the opening 3 is provided. The permanent magnet 8 is disposed in a space outside the space to be stored. That is, the permanent magnet 8 is disposed inside the shield case 2 and outside the space formed by extending the opening 3 from the opening 3 of the shield case 2 to the bottom of the shield case 2 substantially vertically. Yes. Therefore, even in this configuration, magnetic particles such as magnetic toner that enter the potential measuring device from the opening 3 of the shield case 2 can reach the vicinity of the permanent magnet 8 and adhere to the permanent magnet 8 or the like. Sex is reduced. Therefore, even this configuration is an example of the present invention.

Also in this embodiment, the shielding wall 12 can be provided in order to further reduce the possibility that particles having magnetism will reach the vicinity of the permanent magnet 8 and adhere to the permanent magnet 8 or the like. The shielding wall 12 is separated from the detection diaphragm 14 so that the internal space of the shield case 2 is separated into a space where the opening 3 and the detection electrodes 18 and 19 of the shield case 2 are present and a space where the permanent magnet 8 is present. It is arranged at a position between the drive diaphragms 15. At this time, a through-hole 13 is provided at the position of the shielding wall 12 through which the torsion spring 16 penetrates so that the shielding wall 12 itself does not disturb the vibration of the vibrating body 5. The size of the through hole 13 is designed to be larger than the cross-sectional shape of the torsion spring 16.

The operating principle of the potential measuring apparatus in this embodiment will be described below.
When a periodic drive current is input to the electromagnetic coil 6 from a drive signal source (not shown in FIG. 5), an attractive force or a repulsive force periodically acts between the electromagnetic coil 6 and the end of the permanent magnet 8, The drive diaphragm 15 vibrates in the rotational direction with the torsion spring 16 as the central axis. The vibration of the drive diaphragm 15 is transmitted to the detection diaphragm 14 via the elastic force of the torsion spring 16, and the detection diaphragm 14 also vibrates in the rotation direction with the torsion spring 16 as the central axis. As a result, the distance between the surface of the object to be measured 1 and the detection electrodes 18 and 19 changes so as to be in opposite phases, and the capacitance between the surface of the object to be measured 1 and the detection electrodes 18 and 19 Also change to be in opposite phase to each other. As a result, according to the above equation (3), alternating current signals having opposite phases proportional to the surface potential of the object 1 to be measured are generated on the detection electrodes 18 and 19. These current signals are input to the signal processing means 22 via the wirings 20 and 21. The signal processing means 22 converts each input current signal into a voltage signal, calculates the difference between them, and outputs a potential measurement signal obtained by amplifying and rectifying the result. Again, the surface potential of the object to be measured can be measured by a method using the feedback processing circuit unit or the like.

The configuration of the first type of the second embodiment can be changed as shown in FIG. FIG. 6 shows the configuration of the second mold in this example. FIG. 6 (a) is a top view of the structure provided in the shield case 2 as viewed from above, and FIG. 6 (b) is a cross-sectional view taken along the line D1-D2 of FIG. 6 (a). Here, the first and second support members 23 and 24 are fixed to the bottom inside the shield case 2 having the opening 3 on the surface facing the object 1 to be measured. The ends of 5 are fixed respectively.

The vibrating body 5 includes a detection diaphragm 14, a drive diaphragm 15, a torsion spring 16 that couples the detection diaphragm 14 and the drive diaphragm 15, a torsion spring 17 that couples the drive diaphragm 15 and the second support member 24, A torsion spring 25 that connects the detection diaphragm 14 and the first support member 23 is provided. Also here, the detection diaphragm 15 is arranged so as to be located immediately below the opening 3 of the shield case 2. The arrangement of other components is the same as that of the first mold. The operation is also the same as that of the first type configuration.

The features of the two types of configurations are described below.
The configuration of the first type is a configuration suitable for further reducing the power consumption of the potential measuring device because it is relatively easy to design the spring constant of the vibrator 5 to be small. In the configuration of the second type, the vibrating body 5 is supported on both sides of the first and second support members 23 and 24, and the vibration in the rotational direction of the vibrating body 5 is relatively stable. Therefore, the configuration is suitable for further downsizing the through-hole 13 of the shielding wall 12 and further stabilizing the potential measurement signal of the potential measuring device.

(Example 3)
A potential measuring apparatus according to Example 3 of the present invention will be described. FIG. 7 shows the configuration of the potential measuring apparatus in this example. FIG. 7 (a) is a top view of the structure provided in the shield case 2 as viewed from above, and FIG. 7 (b) is a cross-sectional view taken along line E1-E2 of FIG. 7 (a). In this embodiment, the electromagnetic comb tooth type driving means 39 including the permanent magnet 38 is used to drive the shutter portion 33 to change the exposed area of the detection electrode 36 with respect to the object to be measured (measurement target) 1. The capacitance between the surface of the object to be measured 1 is periodically changed.

In FIG. 7, a support member 37 is fixed to the bottom inside the shield case 2 having an opening 3 on the surface facing the object to be measured (measurement target) 1, and the support member 37 includes a permanent magnet 38. An electromagnetic comb type drive means 39 is arranged. The permanent magnet 38 is connected to one end of the shutter support member 35, and the inner ends of the pair of beams 31 are attached to the shutter support member 35. The outer end of each beam 31 is fixedly supported by a support member 37 by a beam stator 32. The other end of the shutter support member 35 is integrally provided with a shutter portion 33 having a plurality of (three in the illustrated example) openings 34. The shutter unit 33 and the shutter support member 35 constitute a shutter or shutter member. Therefore, when a driving force is applied to the permanent magnet 38, the beam 31 is bent, and the shutter support member 35 and the shutter portion 33 are integrally translated in the direction of the arrow in FIG. In FIG. 7, the shape of the electromagnetic comb-type drive means 39 including the permanent magnet 38 is not important and is therefore simplified. In FIG. 1 and the like, the signal processing means and wiring illustrated are omitted.

Further, the same number of detection electrodes 36 as the openings 34 are provided on the support member on the bottom inside the shield case 2 so as to face the shutter portion 33. Therefore, when the shutter portion 33 vibrates in parallel, the positional relationship between the corresponding opening 34 and the detection electrode 36 changes, and the exposed area of each detection electrode 36 with respect to the object 1 to be measured changes. In this way, the electrostatic capacitance between the detection electrode 36 and the surface of the object 1 to be measured changes periodically, and the potential of the object 1 to be measured is measured according to the measurement principle. In the present embodiment, since the exposed areas of the plurality of detection electrodes 36 change in phase, all signals from the detection electrodes 36 are added and processed. However, for example, it is possible to adopt a configuration in which the exposed areas of the two detection electrodes facing the object to be measured 1 are changed in reverse phase by the shutter unit. The differential amplification process as described above is performed.

Also in the present embodiment, the shielding wall 12 is provided in order to reduce the possibility that magnetic particles reach the vicinity of the permanent magnet 38 and adhere to the permanent magnet 38 or the like. The shielding wall 12 is located at the position of the shutter support member 35 so as to separate the internal space of the shield case 2 into a space where the opening 3 and the detection electrode 36 of the shield case 2 are present and a space where the permanent magnet 38 is present. Be placed. At this time, a through-hole 13 is provided at the position of the shielding wall 12 through which the shutter support member 35 penetrates so that the shielding wall 12 itself does not hinder translational vibration of the shutter support member 35. The size of the through hole 13 is designed to be larger than the cross-sectional shape of the shutter support member 35. In the type using the shutter, the permanent magnet is often arranged away from the portion facing the opening even in the conventional example. However, in this embodiment, a shielding wall as described above is further provided to further reduce the possibility that particles having magnetism will reach the vicinity of the permanent magnet and adhere to the permanent magnet, thereby reducing the potential measurement accuracy. It is preventing.

(Example 4)
As Example 4 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 40, a charger 42 that can be controlled by a charger controller 41, a potential measuring device 43 of the present invention, an exposure device 44, and a toner supplier 45 are installed.

The mechanism for controlling the charge amount of the photosensitive drum 40 includes a charger control device 41, a charger 42, and a potential measuring device 43 of the present invention. The charger 42 is connected to the charger 42. Further, a potential measuring device 43 of the present invention is connected to the charger control device 41.

The basic operation principle of the image forming apparatus in this embodiment will be described below.
A latent image is obtained by charging the surface of the photosensitive drum 40 with the charger 42 and exposing the surface of the photosensitive drum 40 with the exposure device 44. By attaching toner to the latent image by the toner supplier 45, a toner image in which the latent image is developed is obtained. This toner image is transferred to a printing object 47 sandwiched between a feeding roller 46 as a printing object feeding device and the photosensitive drum 40, and the toner on the printing object 47 is fixed. Image formation is achieved through these steps. The charger controller 41 constitutes a signal processing device, and the charger 42, the exposure device 44, the photosensitive drum 40, and the like constitute image forming means.

The operation principle of the mechanism for controlling the charge amount of the photosensitive drum 40 of the image forming apparatus in this embodiment is as follows. The potential measuring device 43 of the present invention measures the surface potential of the photosensitive drum 40 after charging, and outputs a measurement signal of the surface potential of the photosensitive drum 40 to the charger control device 41. The charger controller 41 receives the measurement signal of the surface potential of the photosensitive drum 40, and feedback-controls the charging voltage of the charger 42 so that the surface potential of the photosensitive drum 40 after charging becomes a desired value. Thereby, stable charging of the photosensitive drum 40 is realized, and stable image formation can be achieved. At this time, the measurement signal of the potential measuring device 43 of the present invention can also be used so as to be fed back to the exposure unit 44 and controlled, for example.

1A is a top view of a potential measuring device according to Embodiment 1 of the present invention, and FIG. 2B is a side sectional view taken along a broken line A1-A2. FIG. 2 is a perspective view showing a shielding wall and a diaphragm of the potential measuring device in Example 1. 5A is a top view of a potential measuring device according to a modification of Embodiment 1 of the present invention, and FIG. 5B is a side sectional view taken along a broken line B1-B2. FIG. 6 is a top view of a potential measuring device according to another modification of Example 1 of the present invention. (a) A top view of a potential measuring device according to a second embodiment of the present invention, and (b) a side sectional view taken along a broken line C1-C2. (a) A top view of another configuration of the potential measuring device according to the second embodiment of the present invention, and (b) a side sectional view taken along a broken line D1-D2. (a) A top view of a potential measuring device according to a third embodiment of the present invention, and (b) a side sectional view taken along a broken line E1-E2. FIG. 10 is a diagram illustrating a configuration example of an image forming apparatus according to Embodiment 4 of the present invention. It is side surface sectional drawing which shows the example of the electric potential measuring apparatus which has the conventional permanent magnet.

Explanation of symbols

1, 40 ... Measurement target (object to be measured, photosensitive drum)
2 ... Shield case
3 ... Opening of shield case
5, 7 ... Vibrating body (diaphragm)
6 ... Electromagnetic coil
6, 8, 38, 39 ... Driving means
8, 38 ... Permanent magnet
9, 18, 19, 36 ... detection electrode
10, 22 ... Signal processing means
12 ... Shielding wall
13 ... Through hole in the shielding wall
14 ... Detection diaphragm
15 ... Drive diaphragm
16, 17, 25 ... Torsion spring
33, 35 ... Shutter (shutter part, shutter support member)
40, 42, 44 ... Image forming means (charger, exposure device, photosensitive drum)
41 ... Signal processing device (charger controller)
43 ... Potential measuring device of the present invention

Claims (9)

A shield case having an opening in a portion facing the object to be measured;
A vibrating body disposed in the shield case so as to vibrate;
On the vibrating body, a detection electrode disposed at a position corresponding to the opening of the shield case;
Drive means for driving the vibrator;
Signal processing means for processing an electrical signal generated at the detection electrode;
Have
The driving means includes a permanent magnet and an electromagnetic coil, and the permanent magnet is formed inside the shield case and extending vertically from the opening of the shield case to the bottom of the shield case. An electric potential measuring device arranged outside a space. 2. The shielding wall according to claim 1, wherein a shielding wall for separating a space in which the opening of the shielding case and the detection electrode are present and a space in which the permanent magnet is present is disposed inside the shielding case. Potential measurement device. The vibrating body is a diaphragm whose end is fixed to a support member disposed in the shield case, and
3. The potential measuring device according to claim 2, wherein the shielding wall has a through-hole through which the diaphragm is passed, and is disposed at a position between the detection electrode and the permanent magnet. 4. The portion of the vibrating body that penetrates the through hole is formed of a material that is less rigid than the other portion so as to increase the vibration amplitude of the portion where the detection electrode is disposed. The potential measuring device according to 1. 4. The potential measuring device according to claim 3, wherein a width of a portion of the vibrating body that penetrates the through hole is smaller than another portion. The vibrator is
A detection diaphragm in which the detection electrode is disposed;
A driving diaphragm on which the driving means is disposed,
The detection diaphragm and the drive diaphragm are connected by a torsion spring,
and,
3. The potential measuring device according to claim 2, wherein the shielding wall has a through-hole through which the torsion spring is passed. A shield case having an opening in a portion facing the object to be measured;
A detection electrode fixedly arranged at a position facing the opening in the shield case;
A shutter;
Driving means for driving the shutter;
Signal processing means for processing an electrical signal generated at the detection electrode,
The driving means includes a permanent magnet and an electromagnetic coil, and the permanent magnet is formed inside the shield case and extending vertically from the opening of the shield case to the bottom of the shield case. An electric potential measuring apparatus, characterized in that a shielding wall is arranged outside the space and for separating a space where the opening of the shield case and the detection electrode are present and a space where the permanent magnet is present. The shutter is a shutter member that translates and vibrates; and
8. The potential measuring device according to claim 7, wherein the shielding wall has a through-hole through which the shutter member passes, and is disposed at a position between the opening and the permanent magnet. The potential measuring device according to any one of claims 1 to 8, a signal processing device that processes an output signal obtained from the potential measuring device, and an image forming unit,
The portion where the detection electrode of the potential measuring device is formed is arranged opposite to the potential measurement target of the image forming means, and the image forming means controls image formation using the signal detection result of the signal processing device. An image forming apparatus.

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