JP2006003130A - Electric potential measuring apparatus and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric potential measuring apparatus capable of extracting detection signals by almost completely preventing or suppressing the occurrence of reductions in signals due to parasitic capacitance between a detecting electrode and a supporting substrate even in the case that the vibration frequency of a capacitance changing means is high. <P>SOLUTION: The potential measuring apparatus has both the capacitance changing means for changing electrostatic capacitance between a surface to be measured and the detecting electrode 101 and a detecting mean for detecting the amount of charge electrostatically induced to the detecting electrode 101 by the capacitance changing means. The detecting means includes the detecting electrode 101; an insulating film 102 for holding the detecting electrode 101; and a frame member 104 for holding the insulating film 102. In the insulating film 102, a region in contact with the detecting electrode 101 and a region in contact with the frame member 104 do not overlap each other at least at any part in a direction in parallel with the insulating film 102. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a non-contact type potential measuring device and an image forming apparatus using the same.

When forming a high-quality image in an electrophotographic image forming apparatus using a photoreceptor, it is necessary to control the image forming apparatus while measuring the potential of the photoreceptor using a non-contact potential measuring device. . As a non-contact potential measuring device, a small charge is induced to the detection electrode by electrostatic induction by bringing the detection electrode close to the charged photoconductor and mechanically changing the capacitance between the photoconductor and the detection electrode. There is an example to measure.

FIG. 11 shows a conceptual configuration diagram of a non-contact potential measuring apparatus. In FIG. 11, reference numeral 501 denotes an object to be measured, 502 denotes capacitance changing means, and 503 denotes charge detecting means. As the capacity changing means 502 that mechanically changes the capacity, a method of periodically changing the electric lines of force incident on the detection electrode 101 from the measurement object 501 or a method of periodically moving the detection electrode 101 is used. There is something that adopts. As an example of the former, a fork-shaped shutter is inserted between the measurement object (photosensitive member) and the detection electrode, and the shutter is periodically moved in a direction parallel to the surface of the measurement object, so that the measurement object is placed on the detection electrode. There is a configuration in which the capacitance between the measurement object and the detection electrode is changed by periodically blocking the reaching potential line and changing the effective area of the detection electrode viewed from the measurement surface (see Patent Document 1). .

In addition, a metal shield material with an opening is placed at a position facing the measurement object, a detection electrode is provided at the tip of the fork-shaped vibration element, and the position of the detection electrode moves in parallel under the opening Thus, there is a configuration in which the number of potential force lines reaching the detection electrode is changed to change the capacitance (see Patent Document 2).

As an example of the latter, the sensing electrode is arranged at the tip of a cantilever-shaped vibrator, and the cantilever is vibrated to periodically change the distance between the measurement target and the sensing electrode, thereby increasing the capacitance. There is a configuration to change (see Patent Document 3).
U.S. Pat.No. 4,720,682 U.S. Pat.No. 3,852,667 U.S. Pat.No. 4,763,078

If the minute charge electrostatically induced in the detection electrode in the non-contact type potential measuring device is Q,
Q = CV (1)
(C: effective capacity between measurement object and detection electrode, V: potential of measurement object). The capacitance formed by the measurement target (photoconductor, etc.) and the detection electrode changes periodically due to mechanical vibration, etc.
C = C _O · sin (ω · t) (2)
(C _O : capacitance change coefficient). From these equations, if a minute charge Q induced in the sensing electrode is taken out as a minute current I,
I = dQ / dt
= Ω · C _O · V · cos (ω · t) = 2π · f · C _O · V · cos (ω · t) (3)
(Where f is the vibration frequency). From the equation (3), it can be seen that the detection signal from the potential measuring device is determined by the capacitance change coefficient _C0 and the vibration frequency f.

On the other hand, the vibration frequency of the potential measuring device is drastically improved (for example, several tens of kHz) by producing a potential measuring device using a micromachining technique called micromachining technology applying a semiconductor process. be able to. Therefore, there is a possibility that a device for measuring a potential of a large output signal can be realized. However, when a semiconductor substrate or conductor substrate often used in micromachining technology is used as a support substrate for the detection electrode, a parasitic capacitance is generated between the detection electrode and the support substrate, and the output signal can be reduced due to this parasitic capacitance.

FIG. 10 is a schematic diagram illustrating parasitic capacitance generated between the detection electrode and the support substrate. FIG. 10A is a schematic diagram showing a plane, and FIG. 10B is a schematic diagram of a cross section taken along a cross section A in FIG. In FIG. 10, 101 is a detection electrode, 102 is an insulating film, and 103 is a support substrate. An insulating film 102 is formed on one surface of the support substrate 103, and the detection electrode 101 is formed on the insulating film 102 and is galvanically insulated from the support substrate 103.

Here, parasitic capacitance exists between the detection electrode 101 and the support substrate 103. The capacity C _P of generally parallel plate capacitors,
C _P = ε _P S _P / d _P (4)
(Ε _P : dielectric constant, S _P : capacitor area, d _P : capacitor distance). Assuming that the parasitic capacitance between the detection electrode 101 and the support substrate 103 can be regarded as the same as that of the parallel plate capacitor, the parasitic capacitance is the dielectric constant of the insulating film 102, the area of the detection electrode 101, and between the detection electrode 101 and the support substrate 103. Determined by the distance.

The dielectric constant of the insulating film 102 varies slightly depending on the film formation conditions, but is almost uniquely determined by the material used for the insulating film 102. As an example, the relative dielectric constant is about 7 for a silicon nitride film and about 3.9 for a silicon oxide film. Area of the detection electrode 101 is proportional to the change coefficient C _O of the capacitance of the formula (2), it is uniquely set in terms of the output signal. In addition, the distance between the detection electrode 101 and the support substrate 103 is determined by the thickness of the insulating film 102 formed using a semiconductor process (micromachining technology). The thickness of the insulating film 102 can be changed by the film forming method and the film forming time of the insulating film. However, since a semiconductor process is used, only a very thin thickness can be realized in consideration of the production reality. Can not.

For this reason, in the potential measurement device manufactured using the micromachining technology, the parasitic capacitance between the detection electrode and the support substrate increases because the insulating film is thin. This parasitic capacitance reduces the output signal. This decrease in the output signal increases as the vibration frequency increases. For this reason, in an electric potential measurement device with improved vibration frequency produced using micromachining technology, the increase in the output signal due to the vibration frequency f in equation (3) is canceled out, and the high performance is maintained as it is. Cannot be realized.

In view of the above problems, the potential measuring device of the present invention includes a capacitance changing means for changing the capacitance between the surface to be measured and the detection electrode, and an amount of charge electrostatically induced in the detection electrode by the capacitance changing means. Detecting means, and the detecting means includes the detection electrode, an insulating film holding the detection electrode, and a member holding the insulating film, and the insulating film includes the detection electrode The region in contact with the member and the region in contact with the member do not overlap at least partially in the direction parallel to the insulating film. Here, whether or not they overlap is considered when the thickness of the insulating film is ignored.

In view of the above problems, the potential measuring device of the present invention is electrostatically induced to the detection electrode by the capacitance changing means for changing the capacitance between the surface to be measured and the detection electrode, and the capacitance changing means. Charge detecting means for detecting the charge to be detected, the detecting means comprising the detection electrode and a support member that supports the detection electrode in contact with the detection electrode, and a surface of the support member that contacts the detection electrode Is an insulator, comprising a recess on the opposite side of the contacting surface, and the insulator being exposed in the space in the recess.

In this configuration, as the capacity changing means, in addition to the structure using mechanical vibration as described in the above background art, the temperature of the air around the detection electrode and the temperature of the dielectric are periodically changed using a heater or the like. This is a term that expresses how the capacitance between the measurement target surface and the detection electrode changes because the dielectric constant between the measurement target surface and the detection electrode is periodically changed. For example, it should be called a vibration frequency or a change frequency, but in this specification, it is simply called a vibration frequency for the sake of simplicity.

In view of the above problems, an image forming apparatus according to the present invention includes the above-described potential measuring device and an image forming unit, and the surface on which the detection electrode of the potential measuring device is formed is a surface on which the potential of the image forming unit is to be measured. The image forming units are arranged to face each other, and image formation is controlled using a signal detection result of the potential measuring device.

In the potential measurement device of the present invention, even when the vibration frequency of the capacitance changing means is high, the detection signal is extracted with little or no reduction in output signal due to parasitic capacitance between the detection electrode and the support substrate. Can do.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(First embodiment)
In the present invention, attention is paid to the structure of the detection electrode and the substrate holding the detection electrode in order to realize a potential measuring device in which the decrease in the output signal due to the parasitic capacitance between the detection electrode and the support substrate is hardly suppressed. Specifically, as a structure having a detection electrode, an insulating film for holding the detection electrode, and a frame member for holding the insulating film, as described above, the region where the insulating film is in contact with the detection electrode, and the insulating film is the frame member The region in contact with is not overlapped at least partially in the direction parallel to the insulating film.

FIG. 1 is a schematic diagram for explaining a detection electrode and a structure for holding the detection electrode of the potential measuring device according to the present embodiment. FIG. 1A is a schematic diagram showing a plane, and FIG. 1B is a schematic diagram in a cross section B of FIG. In FIG. 1, 101 is a detection electrode, 102 is an insulating film, and 104 is a frame member having a cavity 104a.

The detection electrode 101 is connected to a first-stage amplifier (not shown) that performs current-voltage conversion as detection means for detecting the amount of charge that is electrostatically induced in the detection electrode. In addition, a charge corresponding to the potential of the measurement target is electrostatically induced on the detection electrode 101 by a capacitance changing unit (not shown) that changes the capacitance between the surface of the measurement target and the detection electrode by mechanical vibration or the like. Is done. The charge induced at this time is supplied through the internal resistance of the first stage amplifier.

The detection electrode 101 is held by an insulating film 102. The insulating film 102 is held by the frame member 104. In the present embodiment, the material portion of the frame member 104 does not exist in the region in which the detection electrode 101 is in contact with the insulating film 102 in the direction parallel to the insulating film 102, and the lower direction of the detection electrode 101 ( In the direction perpendicular to the insulating film 102, the frame member 104 is a hollow portion 104a.

In this structure, the detection electrode 101 and the frame member 104 are insulated by air having a relative dielectric constant of 1, and the distance between them can be made orders of magnitude greater than that of the thin insulating film 102. Therefore, the parasitic capacitance is extremely small compared to the structure of FIG. This structure can be easily realized by etching the lower surface of the structure shown in FIG. 10 using micromachining technology.

In this embodiment, since the detection electrode 101 is thin, it can be held by the insulating film 102. In addition, since the frame member 104 exists so as to surround the detection electrode 101, a strong physical strength can be obtained.

As described above, according to the present embodiment, the parasitic capacitance between the detection electrode and the support substrate (frame member) can be reduced only by using a simple structure called a frame member having a hollow portion. 2 and 3, the frame member 104 has a direction in which the region where the insulating film 102 contacts the detection electrode 101 and the region where the insulating film 102 contacts the frame member 104 are parallel to the insulating film 102. However, it may be configured such that a part thereof overlaps or a form such that the bottom part 104b is present at least partially under the cavity part 104a. In the former, the parasitic capacitance increases somewhat, but it can be made smaller than the structure of FIG. In the latter case, production is somewhat troublesome, but physical strength can be increased.

Since the potential measuring device obtains an output signal by changing the capacitance between a measurement object (photosensitive member, etc.) having a certain distance of several millimeters or more and the detection electrode, the electrostatic charge induced on the detection electrode is very small. It becomes. Therefore, it is necessary to convert the detected change in the minute current into a voltage signal. For this purpose, the first-stage amplifying unit that performs current-voltage conversion connected to the detection electrode 101 needs to perform current-voltage conversion (A / V) with a high gain equal to or higher than Meg.

FIG. 4 is a diagram illustrating a circuit example of a first stage amplifier that performs current-voltage conversion. FIG. 4A shows an FET source follower circuit using a high resistance. Here, VCC indicates a power supply voltage. The circuit of FIG. 4A is an FET source follower circuit having a high input impedance that converts the voltage at both ends of the resistor R _IN generated by a minute current flowing through the high resistor R _IN into a voltage output VOUT. Yes.

In general, when the support substrate is grounded to GND, if a large parasitic capacitance exists between the detection electrode 101 and the frame member 104, a capacitance component exists in parallel with the high resistance _RIN . The impedance at the vibration frequency of the high resistance R _IN and the parasitic capacitance portion decreases as the vibration frequency f of the potential measuring device increases, and the voltage generated across the resistor R _IN decreases.

Even when the support substrate is in a floating state, if the parasitic capacitance is large and the vibration frequency is high, the support substrate and the detection electrode 101 are coupled in an AC manner, and the semiconductor or conductor support substrate is equivalent to the detection electrode. Therefore, the signals cancel each other and the output signal is reduced. In addition, when there are a plurality of detection electrodes 101 having different output signal phases, if the parasitic capacitance is large and the vibration frequency is high, the signals cancel each other due to signal leakage between the detection electrodes, and the output signal becomes small.

According to the present embodiment, since the parasitic capacitance between the detection electrode 101 and the support substrate (frame member 104) can be greatly reduced, the FET source follower using a high resistance as shown in FIG. In a potential measuring device using a current-voltage conversion circuit, high-gain current-voltage conversion can be realized even when the vibration frequency is high.

As described above, according to the present embodiment, the parasitic capacitance between the detection electrode and the support substrate (frame member) can be reduced by using a simple structure. Therefore, in a potential measurement device having a high vibration frequency, it is possible to provide a high-performance potential measurement device that can suppress a decrease in the output signal at the first stage amplification unit due to parasitic capacitance and obtain a large output.

In addition, a semiconductor substrate or a conductive substrate can be used for the support substrate (frame member), so that the degree of freedom in design and manufacturing processes is increased, and a potential measuring device that can achieve high performance and low cost can be provided. Furthermore, in the form in which the support substrate (frame member) is mechanically vibrated, the frame member can be reduced in weight, so that a high vibration frequency can be realized.

In the present embodiment, as shown in FIG. 1, the insulating film 102 is in contact with a part of the frame member 104. However, the insulating film 102 covers the entire surface of the frame member 104. Also good. Thereby, the manufacturing process can be simplified, and a relatively low-cost potential measuring device can be provided.

Further, as shown in FIG. 1, the surfaces on which the detection electrode 101 and the frame member 104 are in contact with the insulating film 102 are different surfaces on the insulating film 102. May be. In practice, a wiring for taking out a signal from the detection electrode 101 to the first stage amplifier is formed on the insulating film 102, and a parasitic capacitance is generated between the frame member 104, but the wiring area is small and large. There is no impact.

(Second Embodiment)
The potential measuring device according to the present embodiment is different from the first embodiment in the circuit configuration of the first stage amplifier. Others are the same as in the first embodiment. In the circuit configuration of FIG. 4A in the first embodiment, when the vibration frequency becomes high, the gain in the current-voltage conversion unit may be reduced due to the capacitance of the gate portion of the FET itself. FIG. 4B shows a transimpedance conversion circuit using the operational amplifier according to the second embodiment. The circuit in FIG. 4B is a circuit that can realize high-speed and high-gain current-voltage conversion by using a wide-band operational amplifier.

In general, in a transimpedance circuit, if an input capacitance _CP exists in an input terminal portion, the frequency characteristics are deteriorated. Therefore, by inserting the parallel phase compensation capacitor C _f to the feedback resistor R _f, it is necessary to stabilize the negative feedback circuit. However, the amount of feedback decreases in the high frequency range due to the inserted phase compensation capacitor _Cf , and the output signal decreases. As described above, when the input capacitance exists (here, the parasitic capacitance between the detection electrode and the support substrate), the current-voltage conversion gain that can be realized by the transimpedance may be reduced.

By using the potential measuring apparatus according to the second embodiment, it is possible to reduce the parasitic capacitance C _P, the lowering of the gain is also possible to reduce the phase compensation capacitor C _f required for the circuit to operate stably occur Absent. That is, in the first embodiment, by using the first-stage amplifying unit as a transimpedance circuit, it is possible to realize a potential measuring device that can perform high-gain current-voltage conversion even at a higher vibration frequency.

In the present embodiment, the support substrate (frame member) is grounded to GND as shown in FIG. 4B. However, the present embodiment is not limited to this, and various configurations are used. Can do.

(Third embodiment)
The potential measuring apparatus according to the present embodiment relates to a form using capacitance changing means for changing capacitance by parallel mechanical vibration. Others are the same as in any of the above embodiments.

FIG. 5 is a schematic diagram for explaining the potential measuring apparatus according to this embodiment. In FIG. 5, 201 is a shield part, 202 is an opening, 203 is a beam, 204 is a comb electrode on the moving side, 205 is a comb electrode on the fixed side, 206 is a wiring on the insulating film 102, 207 is a wiring 206 It is a connected pad. The shield part 201 is made of a conductive member, has the purpose of forming an electric field spatially, and is fixed at a certain potential. Electric charges are induced on the detection electrode 101 by electric lines of force coming from the measurement object through the opening 202 opened in the shield part 201. The charge induced to the detection electrode 101 is taken out from the pad 207 via the wiring 206 on the insulating film 102 and connected to the charge detection means (first stage amplification unit) (not shown).

By applying an alternating high voltage between the moving comb electrode 204 and the fixed comb electrode 205, an attractive force is generated between the comb teeth of the electrode, and the shield unit 201 reciprocates in the direction C. Do. Due to the reciprocating motion, charges are induced in the detection electrode 101.

FIG. 6 is a schematic cross-sectional view illustrating the detection electrode 101 and a structure for holding the detection electrode 101 of the potential measurement device according to the present embodiment. FIG. 6A is a sectional view taken along a section D in FIG.

As shown in FIG. 6A, on the insulating film 102 supported by the frame member 104 having a plurality of cavities 104a, the detection electrodes 101 are formed in a line shape or a long strip shape corresponding to each of the cavities 104a. It is configured. The downward direction of the line-shaped detection electrode 101 is a cavity portion 104a so that the material portion of the frame member 104 does not exist. By arranging the plurality of material portions of the frame member 104 in a line corresponding to the detection electrode 101, even when the total electrode area of the detection electrode 101 is large, the deflection of the insulating film 102 supporting the detection electrode 101 can be reduced. It can be reduced or the usable strength range can be expanded. Further, by arranging a large number of detection electrodes 101 arranged in a line, the amount of induced charge can be increased.

According to the present embodiment having these characteristics, even in a potential measuring device having a large total electrode area, a structure with less parasitic capacitance can be configured without reducing the output signal, and a highly accurate potential measuring device can be realized.

Further, in the configuration of the potential measuring device having the above-described line-shaped detection electrode 101, since the width of the detection electrode 101 is small, the amount of movement required for the shield part 201 can be reduced, so that the speed of vibration can be increased. Become. This configuration is particularly desirable because it can effectively reduce the influence of parasitic capacitance on the output signal during high-speed vibration.

FIG. 6B is a schematic cross-sectional view showing another configuration of the present embodiment. In FIG. 6B, a plurality of detection electrodes 101 </ b> A and 101 </ b> B are arranged for one opening 202 of the shield part 201 and one cavity 104 a of the frame member 104. By using this embodiment, crosstalk between the signals of the plurality of detection electrodes 101A and 101B is unlikely to occur due to the presence of the cavity 104a, so that different output signals are accurately separated from the plurality of detection electrodes 101A and 101B. Can be taken out. In this way, a plurality of detection electrodes 101A and 101B can be arbitrarily arranged in one opening 202 of the shield part 201 so that a desired signal that can be differentially processed can be output. A high-performance potential measuring device can be realized.

In addition, since the plurality of detection electrodes 101A and 101B are arranged in one opening 202 of the shield part 201 and one hollow part 104a of the frame member 104, the arrangement can be easily made and a small configuration can be achieved. An apparatus for measuring a vibration frequency potential can be provided. In this embodiment, the electrostatic drive type potential measuring device is used. However, the invention is not limited to this drive method, and any method can be used as long as the shield unit 201 can be driven in parallel to the detection electrode 101. Can also be used.

(Fourth embodiment)
The potential measuring apparatus according to the present embodiment relates to a form having capacitance changing means for changing the capacitance by mechanical vibration around the oscillation central axis. Others are the same as the first embodiment or the second embodiment.

FIG. 7 is a schematic diagram for explaining the potential measuring apparatus according to this embodiment. In FIG. 7, reference numeral 301 denotes a shield portion, 302 denotes an opening, 303 denotes a support substrate, 304 denotes a torsion spring, 305 denotes a wiring, 306 denotes a pad, 307 denotes a coil substrate, 308 denotes a coil, and 309 denotes a pad. The shield part 301 is composed of a conductive member, and has the purpose of spatially shaping the electric field from the measurement object, and is fixed at a certain potential. Electric charges are induced to the detection electrode 101 provided on the vibrating frame member 104 via the insulating film 102 through the opening 302 opened in the shield part 301.

In the present embodiment, a frame member 104 having two hollow portions 104a is integrally formed, and the frame member 104 is supported on a support substrate 303 by a pair of torsion springs 304 so as to be able to oscillate. A wiring 305 and a pad 306 are also formed on the insulating film 102 and connected to charge detection means (first stage amplifier) (not shown). A coil 308 and a pad 309 are formed on the coil substrate 307 to swing the integrated frame member 104.

FIG. 8 is a schematic diagram for explaining the detection electrodes 101A and 101B and the structure for holding the detection electrodes 101A and 101B of the potential measuring device according to the present embodiment. FIG. 8A is a schematic diagram showing a plane, and FIG. 8B is a schematic diagram in a section E of FIG. 8A. As shown in the figure, the detection electrodes 101A and 101B are arranged corresponding to the two cavities 104a of the frame member 104, respectively.

In FIG. 8, 310 is a magnet. As shown in FIG. 8B, a magnet 310 having an S pole and an N pole arranged as shown in the drawing is arranged at the lower part of the frame member 104 integrated. By applying an alternating current to the coil 308, a magnetic field is generated, and a tensile force or a repulsive force is generated between the coil 308 and the magnet 310. Thereby, the frame member 104 is swung (twisted) in the direction G around the axis F defined by the pair of torsion springs 304. Since the distance between the measurement object and the detection electrodes 101A and 101B changes, an electric charge is induced on the detection electrodes 101A and 101B. Here, since the two detection electrodes 101A and 101B are arranged as shown in FIG. 8, the respective detection electrodes 101A and 101B are swung in the upside down direction with respect to the measurement target. Therefore, an output signal whose phase is inverted by 180 degrees is output from each of the detection electrodes 101A and 101B. Thus, in this embodiment, since the output signal whose phase is inverted by 180 degrees is obtained separately and differentially processed, it is possible to provide a potential measuring device having a high common-mode noise rejection ratio.

In this configuration, it is easy to increase the torsional vibration frequency by reducing the entire frame member 104. The configuration of this embodiment is also particularly desirable because it can effectively reduce the influence of parasitic capacitance on the output signal due to high-speed vibration.

Further, as shown in FIG. 8B, the lower direction of the detection electrodes 101A and 101B has a structure in which only the insulating film 102 is present and the material portion of the frame member 104 does not exist. Therefore, as in the above embodiment, the parasitic capacitance between the detection electrode 101 and the frame member (support substrate) 104 is small.

Further, since the swinging shaft F is made to coincide with the material part at the center of the frame member 104 integrated, the shaft deflection at the time of swinging can be reduced. Therefore, it becomes easy to design the frequency of torsion, and stable reciprocating motion of torsion can be performed, so that a stable output can be obtained. Therefore, since the output is stabilized in a short time, a highly accurate and high-speed potential measuring device can be provided.

However, if the rigidity is necessary and sufficient, it is not necessary to make the swing axis F coincide with the material portion of the frame member 104, and the frame member 104 may be constituted by only the outer peripheral portion as the material portion. Further, the number of the hollow portions 104a of the frame member 104 is not limited to two, and the frame member 104 having two or more hollow portions 104a may be used.

In addition, since the magnet 310 is disposed under the frame member 104 over the plurality of cavities 104a, the rigidity of the entire frame member 104 can be increased. That is, the rigidity of the frame member 104 itself can be maintained even if the material portion of the frame member 104 is thinned in order to reduce the parasitic capacitance with the detection electrode. Thus, the influence of the parasitic capacitance can be further reduced, and a highly accurate potential measuring device can be provided.

In this embodiment, the two detection electrodes 101A and 101B are arranged as shown in FIG. 8, but the present embodiment is not limited to this, and a plurality of detection electrodes 101 having arbitrary positions and shapes are arranged. It may be a thing. In the present embodiment, an electromagnetic drive type potential measuring device is used. However, the present embodiment is not limited to this, and any method can be used as long as the frame member 104 can be driven to swing. Can be used.

Here, an embodiment of an image forming apparatus using the potential measuring apparatus of the present invention will be described with reference to FIG. FIG. 9 is a view showing the arrangement of the photosensitive drum 401 on a plane perpendicular to the rotation axis H. FIG. In FIG. 9, 401 is a photosensitive drum, 402 is paper, 403 is a cleaner, 404 is charging means, 405 is exposure means, 406 is a potential measuring device of the present invention, and 407 is development means.

The photosensitive drum 401 rotates about the axis H in the direction I. The photosensitive drum 401 is charged by the charging unit 404 and is exposed by the exposure unit 405 to form a charged pattern. The potential measuring device 406 measures the potential of the charging pattern on the photosensitive drum 401. In the developing unit 407, only the charged pattern portion (or only other than the charged pattern portion) is developed by adsorbing toner or the like, and the image is transferred onto the paper 402 scanned in the direction J. Thereafter, the photosensitive drum 401 is cleaned by the cleaner unit 403. Using the measurement result of the potential measuring device 406, the charging unit 404 and the exposure unit 405 are controlled to adjust the image.

In this example, the potential measuring device described in the third embodiment (FIGS. 5 and 6A) is used as the potential measuring device 406. The frame member 104 uses a silicon substrate, and the insulating film 102 is a silicon oxide film (thickness: 200 nm). Gold is used for the detection electrode 101. The shield part 201, the beam 203, and the comb-tooth electrodes 204 and 205 are made of Ni. Further, the shield part 201, the beam 203, and the comb electrode 204 are grounded to GND.

In the shield portion 201, 50 openings 202 of 10 μm × 100 μm are arranged in a line shape (long strip shape) at intervals of 20 μm. A detection electrode 101 of 20 μm × 100 μm is arranged in a line corresponding to each opening 202 immediately below the opening 202. The detection electrodes 101 arranged in a line are connected by a wiring 206 and are connected to the first stage amplification unit (not shown). In the first-stage amplifier, current (charge) -voltage conversion is performed using a transimpedance circuit using a high resistance of 50 MegΩ and an operational amplifier (unity gain frequency: 500 MHz).

This potential measuring device can be easily formed by performing film formation, etching, plating, or the like using micromachining technology. By applying an alternating voltage having a resonance frequency (around 10 kHz) between the comb electrodes 204 and 205, the shield part 201 moves by about ± 10 μm. Along with this vibration, a signal corresponding to the potential of the photosensitive drum 401 can be output from the first-stage amplifier connected to the detection electrode 101.

Since the potential measuring device 406 in the image forming apparatus according to the present embodiment can extract a signal without attenuation even when the total area of the detection electrodes 101 is large at a high vibration frequency, the potential measuring device 406 can perform high speed and high output (high accuracy). ) Signal output can be obtained. Therefore, the image forming apparatus of the present embodiment can grasp the potential distribution of the photosensitive drum 401 accurately at high speed and perform image control, so that a high-quality image can be formed.

This example differs from Example 1 in that the potential measuring device (FIG. 7, FIG. 8) of the fourth embodiment is used as the potential measuring device 406. Others are the same as in the first embodiment.

In the potential measuring device 406 of the present embodiment, the shield 301 is iron, and an opening 302 of 1 mm × 1 mm is formed. The support substrate 303 is silicon, and the detection electrode 101, the wiring 305, and the pad 306 are made of gold. The coil substrate 307 is made of silicon, and the coil 308 and the pad 309 are made of copper. The two detection electrodes 101A and 101B disposed on the insulating film 102 (thickness 200 nm), which is a silicon nitride film, have a size of 400 μm × 900 μm. The frame member 104 disposed immediately below the opening 302 of the shield 301 has a size of 1 mm × 1 mm. This potential measuring device can be easily formed by performing film formation, etching, or the like using micromachining technology.

By passing an alternating current having a resonance frequency (30 kHz) of the frame member 104 through the coil 308, the frame member 104 mechanically swings about ± 3 degrees around the torsion spring 304. Thereby, each output from the first stage amplifier (not shown) connected to each of the two detection electrodes 101A and 101B has a waveform in which the phase is shifted by 180 degrees (positive and negative electrodes are inverted). Here, in the first-stage amplifier, current (charge) -voltage conversion is performed using a transimpedance circuit using a high resistance of 100 MegΩ and an operational amplifier (unity gain frequency: 2 GHz).

Since the potential measuring device in the image forming apparatus according to the present embodiment can easily extract a high-speed differential signal output with a simple configuration, a signal output excellent in noise resistance can be obtained. Therefore, the image forming apparatus according to the present embodiment can quickly and accurately grasp the potential distribution of the photosensitive drum and perform image control without being greatly affected by noise, so that a high-quality image can be formed.

It is a schematic diagram explaining the detection electrode of the electric potential measuring device which concerns on 1st Embodiment, and the structure holding it. It is sectional drawing explaining the detection electrode of the electric potential measuring device which concerns on a modification, and the structure holding it. It is sectional drawing explaining the detection electrode of the electric potential measuring device which concerns on another modification, and the structure holding it. It is a figure explaining the circuit example of the first stage amplifier part which performs current-voltage conversion of the electric potential measuring device which concerns on this invention. It is a schematic diagram explaining the electric potential measurement apparatus which concerns on 3rd Embodiment. It is a cross-sectional schematic diagram explaining the detection electrode of the electric potential measuring device which concerns on 3rd Embodiment, and the structure holding it. It is a schematic diagram explaining the electric potential measurement apparatus which concerns on 4th Embodiment. It is a schematic diagram explaining the detection electrode of the electric potential measuring device which concerns on 4th Embodiment, and the structure holding it. FIG. 3 is a diagram showing an arrangement of an image forming apparatus using the potential measuring device of the present invention on a plane perpendicular to a rotation axis of a photosensitive drum. It is a schematic diagram explaining the parasitic capacitance which generate | occur | produces between a detection electrode and a support substrate. It is a notional block diagram of a non-contact potential measuring device.

Explanation of symbols

101, 101A, 101B Detection electrode 102 Insulating film (insulator)
104 Member for holding an insulating film (frame member, support member)
104a Concavity (cavity of frame member)
201-205, 308, 310 Capacity changing means

Claims (10)

Capacitance changing means for changing the capacitance between the surface to be measured and the detection electrode, and detection means for detecting the amount of charge electrostatically induced in the detection electrode by the capacitance changing means, The detection means includes the detection electrode, an insulating film that holds the detection electrode, and a member that holds the insulating film. The insulating film is in contact with the region that is in contact with the detection electrode and the member. The potential measuring device is characterized in that at least a part of the region does not overlap in a direction parallel to the insulating film. The potential measuring apparatus according to claim 1, wherein the detection unit includes a plurality of detection electrodes with respect to a single frame member. The potential measuring device according to claim 1, wherein the detection unit has a circuit configuration in which current-voltage changes using a high resistance and impedance is changed by an FET source follower circuit to output a voltage. The potential measuring apparatus according to claim 1, wherein the detection unit has a circuit configuration that outputs a voltage by a transimpedance circuit including a high resistance and an operational amplifier. The potential measuring device according to claim 1, wherein the capacitance changing unit changes a capacitance between a surface to be measured and the detection electrode by mechanical vibration. The potential measuring device according to claim 1, wherein the capacitance changing unit changes the capacitance by vibrating a shield having an opening in a direction parallel to the detection electrode. The detection means includes a torsion spring for swinging the frame member, and the capacity changing means changes the capacity by torsionally reciprocating the frame member around the torsion spring. A potential measuring device according to claim 1. The potential measuring device according to claim 1, wherein the capacitance changing unit and the detecting unit are formed by a micromachining technique. 9. The electric potential measuring device according to claim 1 and an image forming unit, wherein a surface on which the detection electrode of the electric potential measuring device is formed is opposed to a surface of the image forming unit which is a target of potential measurement. An image forming apparatus, wherein the image forming unit controls image formation using a signal detection result of a potential measuring device. A capacitance changing means for changing the capacitance between the surface to be measured and the detection electrode; and a charge detection means for detecting a charge electrostatically induced in the detection electrode by the capacitance changing means,
The detection means includes a support member that supports the detection electrode and the detection electrode in contact with the detection electrode,
The surface of the support member that contacts the detection electrode is an insulator,
A potential measuring device comprising a concave portion on the opposite side of the contacting surface and exposing the insulator in a space in the concave portion.

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