JP2008128981A - Potential measuring apparatus and method, and image forming apparatus - Google Patents

Abstract

Disclosed is a potential measuring apparatus and method that can perform potential measurement with a relatively high responsiveness by eliminating distance dependency with a measurement object.
An electric potential measurement apparatus includes a detection electrode, a capacitance changing unit, a detection unit, a storage unit, and a correction unit. The capacitance changing means changes the capacitance between the measuring object 1 and the detection electrode 3 and takes out an electric signal from the detection electrode 3. The detection means 4 and 6 obtain a signal of the potential of the measuring object 1 using an electric signal. The storage means 9 corrects the distance fluctuation data of the fluctuation value of the distance between the potential measuring device and the measuring object 1 and the relationship between the fluctuation value of the distance and the correction amount to be applied to the potential signal due to the change of the factor that can be obtained during the potential measurement. Store quantity data. The correction unit 10 corrects the potential signal from the detection units 4 and 6 based on the distance variation data and the correction amount data from the storage unit 9 and the factor information at the time of measuring the potential of the measurement target 1.
[Selection] Figure 1

Description

The present invention relates to a potential measuring apparatus and method capable of measuring a potential of a measurement target, and an image forming apparatus having the potential measuring apparatus.

Conventionally, for example, in an image forming apparatus that has a photosensitive drum and forms an image by electrophotography, in order to always obtain a stable image quality, the potential distribution on the surface of the photosensitive drum is appropriately (typical) under any environment. It is necessary to charge the surface of the photosensitive drum so as to be uniform. For this reason, a potential element on the surface of the photosensitive drum is measured using a potential measuring device, and a functional element that performs feedback control so as to keep the potential on the surface of the photosensitive drum uniform using the result is mounted on the image forming apparatus. Has been done.

One of the required functions for the potential measuring apparatus used for such a purpose is a function of measuring the surface potential of the measurement object 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 disorder in the formed image.

The measurement principle of the non-contact potential measurement device is that the amplitude proportional to the surface potential of the measurement target is changed by minutely changing the capacitance between the measurement target and the detection electrode arranged opposite to the measurement target. A method of obtaining a current signal having the following is used.

The principle of potential measurement of the non-contact potential measuring device will be described below.
Due to the electric field generated between the surface of the measurement target having a certain potential and the detection electrode built in the potential measurement device, a charge of an electric quantity Q proportional to the surface potential of the measurement target is induced in the detection electrode. The relationship between Q and V is expressed by the following equation (1).
Q = CV (1)
Here, C is a capacitance between the detection electrode and the surface of the measurement object. From equation (1), it can be seen that the surface potential of the object to be measured can be obtained by measuring the quantity of electricity Q induced in the sensing electrode.

However, it is actually difficult to directly measure the quantity of electricity Q induced in the sensing electrode at high speed and accurately. Therefore, as a practical method, by periodically changing the size of the capacitance C between the detection electrode and the surface of the measurement object, and measuring the alternating current signal generated at the detection electrode, A method for obtaining a surface potential is used.

It will be shown below that the surface potential of the measurement object can be obtained by the above method. When the capacitance C is expressed as a function of time t, the alternating current signal generated at the detection electrode, that is, the potential detection signal current i is a time differential value of the amount of electricity induced in the detection electrode. Based on the above, it is expressed by the following formula (2).
i (t) = dQ / dt = d (CV) / dt (2)
Here, when the change rate of the surface potential V of the measurement target is sufficiently slow with respect to the change rate of the capacitance C, V can be regarded as being constant in the minute time dt. Therefore, Formula (2) is expressed by the following Formula (3).
i (t) = dQ (t) / dt = V · dC (t) / dt (3)

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

As described above, in order to accurately measure the charge amount Q appearing on the detection electrode when measuring the surface potential V of the measurement target, the size of the capacitance C between the detection electrode and the measurement target is periodically changed. It is better to modulate. As a method of modulating the capacitance C, there are the following methods.

The first method is to effectively modulate the area S of the detection electrode.
The second method is to periodically change the distance x between the detection electrode and the measurement object.
This is because the capacitance C between the detection electrode and the surface of the measurement object is approximately in the relationship represented by the following equation (4).
C = A ・ S / x (4)
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 measurement object. From equation (4), it can be seen that when the distance x or the area S changes periodically, the capacitance C also changes periodically.

As described above, by changing the distance or area of the sensing electrode to the measurement target, the potential measurement device that detects the change in the charge excited by electrostatic induction as a current is sensitive to the distance to the measurement target. This distance strongly affects the measurement accuracy and resolution. FIG. 6 is a graph showing, for example, how the relative potential measurement accuracy changes due to the variation in the distance between the potential measurement device and the measurement target. The horizontal axis represents the distance between the potential measuring device and the measurement object, and the vertical axis represents the relative potential measurement accuracy. As shown in FIG. 6, even if the distance to the measurement object is changed by ± 50 μm at 2.5 mm, the measurement accuracy changes by ± 2%.

Therefore, in the potential measuring device according to the prior art, a booster circuit is used and feedback control is performed in order to eliminate the distance dependency with the measurement target (see Patent Document 1). In such a conventional configuration, the potential information to be measured is detected by the detection circuit unit including the detection electrodes, and then the signal is amplified by the amplification circuit unit. Then, the signal obtained from the amplifier circuit section is detected and boosted through the detection circuit and the boost circuit section, and the voltage is applied as a feedback voltage to the shield case through the shield line. In this way, by obtaining an equilibrium point with the potential of the measurement object, the voltage applied to the shield case is made the potential of the measurement object, and the dependence of distance is eliminated.
Japanese Patent Publication No.62-56985

In the potential measuring apparatus as described above according to the prior art, a booster circuit is used and feedback control is performed in order to eliminate the dependency on the distance to the measurement object, but high-speed response is difficult due to the influence of the time constant of the booster circuit. It is. Further, since the booster circuit which is a special circuit is included, the potential measuring device is expensive.

In view of the above problems, the potential measuring device of the present invention includes a detection electrode to be arranged for a measurement target, a capacitance changing unit, a detecting unit, a storage unit, and a correcting unit. The capacitance changing means is means for changing a capacitance between the measurement object and the detection electrode. The detection means is means for obtaining the potential of the measurement object using an electrical signal output from the detection electrode. The storage means is a means for storing distance fluctuation data relating to a fluctuation value of the distance between the detection electrode and the measurement object obtained in advance. The correction means is means for correcting the potential from the detection means based on the distance variation data.

As described above, according to the present invention, how the distance fluctuation occurs is obtained in advance by experimental data, simulation, or the like, and the measured value of the potential is corrected based on the distance fluctuation data. In order to correct the potential more accurately, it is preferable to measure the distance variation in real time when measuring the potential, or to eliminate the influence on the distance variation (feedback control) as in the past. However, the manner in which the distance fluctuation occurs can be predicted in advance with no practical problem. Therefore, the present invention does not use the actual measurement value in real time as the distance fluctuation data, but uses the value of the distance fluctuation data obtained in advance by experiment or simulation, thereby reducing the accuracy of the potential measurement value. The feature is that it can be greatly simplified.

In a simple manner, the present invention can obtain a correction effect by fixing the distance fluctuation data to a predetermined value obtained in advance and correcting the data based on the fixed value. Furthermore, in order to correct with high accuracy, the distance fluctuation data standards and changes in the distance fluctuation data itself (time lapse, usage environment (change due to temperature or vibration, change due to distance), equipment fatigue, etc.) Can be followed based on the following information (factor that can be acquired at the time of potential measurement). That is, even when the potential correction value itself changes due to a change in the distance variation data, the accuracy can be improved by predicting the way of the change and correcting (recorrecting) the correction value over time. it can. For this purpose, it further comprises information acquisition means for acquiring information serving as a reference for the distance variation data, and correction can be performed based on the distance variation data and information serving as a reference for the distance variation data. . For example, when correcting the fluctuation of the surface potential caused by the distance fluctuation due to the eccentric rotation of the photosensitive drum of the image forming apparatus, the correction can be made more precisely based on the information of the distance fluctuation for each rotation phase. However, in a simple manner, correction can be made based on information on several points on the photosensitive drum or information on the average value of one round.

When more precise correction is performed, a correction value for correcting the distance variation data based on information (factors that can be acquired during potential measurement) that is a reference for the distance variation data, and the potential signal based on the correction value. A storage means is provided for storing potential correction amount data for correcting. In this case, the correction means corrects the potential signal from the detection means based on distance variation data and potential correction amount data from the storage means and information on the factor at the time of measuring the potential of the measurement target. It is. The factors include, for example, the phase, temperature, and elapsed time from the reference time (for example, when the device is manufactured and when the device is installed) in the rotation of the rotating measurement object.

Further, in view of the above problems, the potential measurement method of the present invention includes a step of taking out an electric signal from the detection electrode by changing a capacitance between a measurement target and the detection electrode, and the measurement using the electric signal. A step of obtaining a potential signal related to the potential of the target, and a step of correcting the potential signal based on distance fluctuation data relating to a fluctuation value of a distance between the detection electrode and the measurement target obtained in advance. And Further, the potential measuring method that enables more precise measurement according to the present invention uses a step of taking out an electric signal from the detection electrode by changing a capacitance between a measurement object and the detection electrode, and the electric signal. A step of obtaining a potential signal related to the potential of the measurement object, a data acquisition step, a storage step, a factor acquisition step, and a correction step. In the data acquisition step, the distance fluctuation data related to the fluctuation value of the distance between the detection electrode at the reference position and the measurement object due to the change of the factor that can be obtained at the time of the potential measurement, and the fluctuation value of the distance and the potential signal Correction amount data relating to the relationship of correction amounts to be applied is obtained. The reference position is, for example, the position when the detection electrode is fixed, and the reference position is an intermediate position in the range where the detection electrode reciprocates. In the storing step, the distance variation data and the correction amount data are stored. In the factor acquisition step, information on the factor at the time of measuring the potential of the measurement target is acquired. In the correction step, the potential signal is corrected based on the stored distance variation data and correction amount data and the acquired information on the factor.

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

According to the present invention, based on the distance variation data (for example, based on the distance variation data and the correction amount data, and information on the factor obtained at the time of measurement), the potential signal is corrected and Eliminates the dependency of the distance to the measurement object. This eliminates the need to adopt the potential measurement principle that applies the same potential as the measurement target to the potential measurement device itself, thereby reducing the time for measuring the potential of the measurement target and enabling a high-speed response.

Embodiments of the present invention will be described below. One embodiment of the potential measuring device of the present invention uses a detection unit that is a capacitance changing unit that changes an electrostatic capacitance between a measurement target and the detection electrode and extracts an electric signal from the detection electrode, and an electric signal. And a detection circuit unit which is a detection means for obtaining a potential signal related to the potential of the measurement object. Further, based on the correction data storage unit that is a storage means for storing the distance variation data and the correction amount data, the distance variation data and the correction amount data, and information such as the rotation phase, temperature, and elapsed time that are the factors, A correction circuit unit that is a correction unit that corrects the potential signal is provided. An encoder, a temperature sensor, a clock, etc., which are factor acquisition means for acquiring the factor information, may be provided.

The concept of this embodiment is as follows. It is difficult to directly measure the variation in the distance each time the potential is measured. Therefore, according to the characteristics of the object to be measured and the configuration of the potential measurement device, the information (factor that can be obtained at the time of potential measurement) that can be easily acquired at the time of measurement is found, and the information and the distance fluctuation are determined. Obtain relationship data. Furthermore, data on the relationship between the correction amount of the detected potential signal and the distance variation is also obtained. In this way, an easy-to-acquire factor is acquired at the time of potential measurement, and from this, a distance variation value and further a correction amount are obtained based on data stored in advance, and based on this, a potential signal obtained at that time is obtained. Correction is applied to obtain correct potential information of the measurement object.

The measurement target is an object such as a photosensitive drum that is rotationally driven, and the variation in the distance in the rotation of the measurement target is caused by at least one of the roundness of the measurement target and the eccentric amount of the rotation center. In the potential measuring device, the operation is as follows. The distance variation data is data related to the variation value of the distance at each phase, which is a factor in the rotation of the measurement target, and the correction circuit unit includes the phase information, the distance variation data, and the correction amount data at the time of potential measurement. Based on the above, the potential signal is corrected. This form corresponds to a first example described later.

At least one of the measurement object and the potential measurement device includes a fixing member, and the potential measurement device for a case where the variation in the distance is caused by thermal expansion or contraction due to temperature of the one including the fixing member, It becomes as follows. The distance variation data is data relating to a variation value of the distance at each temperature as a factor, and the correction circuit unit generates a potential signal based on the temperature information at the time of potential measurement, the distance variation data, and the correction amount data. Correct. This form corresponds to a second embodiment described later.

Potential measurement for a case where at least one of the measurement object and the potential measurement device includes a fixed member, and the variation in the distance is caused by a change with time due to an elapsed time from a reference time of the one including the fixed member. In the device, it is as follows. The distance variation data is data relating to a variation value of the distance at each elapsed time which is a factor, and the correction circuit unit is based on the information on the elapsed time at the time of potential measurement and the distance variation data and the correction amount data. Correct the potential signal. This form corresponds to a third embodiment described later. In consideration of a plurality of factors, it is possible to obtain data related to the variation value of the distance due to these changes and perform the same correction as described above. For example, the temperature and elapsed time can be used as factors.

According to the embodiment described above, the dependency of the distance from the measurement object is eliminated from the potential signal by using the correction circuit unit as described above. Thereby, since the same potential as the measurement target is not applied to the potential measurement device itself, the time for measuring the potential of the measurement target is shortened, and high-speed response can be realized. In addition, since a booster circuit which is a special circuit is not necessary, the cost can be reduced.

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

(First embodiment)
A first embodiment of the present invention will be described with reference to FIG. FIG. 1 shows a conceptual configuration of a potential measuring apparatus according to the present embodiment. The potential measuring device includes a detection unit 3 including a detection electrode arranged with respect to the measurement object 1. In the detection unit 3, an electric signal corresponding to the potential of the measurement target 1 is generated in the detection electrode by changing the capacitance between the measurement target 1 and the detection electrode by an appropriate form of capacitance changing means. . Capacitance changing means includes a means for periodically changing the distance between the detection electrode and the measuring object 1 by vibrating a swinging plate that carries the detection electrode around its axis, or a reciprocating shutter on the fixed detection electrode. There are means for periodically moving the exposed area of the detection electrode with respect to the measuring object 1 by moving it. This electrical signal is amplified by the amplification circuit unit 4 and processed by the detection circuit unit 6 to be a potential signal related to the potential of the measurement target 1. The amplification circuit unit 4 and the detection circuit unit 6 constitute detection means for converting the electric signal into the potential signal by impedance conversion, detection, amplification, rectification and the like.

In the above configuration, when the measurement object 1 is a rotationally driven object, the variation in the distance between the potential measurement device and the measurement object 1 is caused by the roundness of the measurement object 1 and the eccentric amount of the rotation center thereof. . This distance variation is one cycle for one rotation of the measuring object 1. Therefore, if the distance fluctuation value at each phase in one rotation is known in advance, if the value is used to correct the potential signal related to the potential of the measurement target 1 from the detection circuit unit 6, the potential due to distance dependence Signal accuracy deterioration can be prevented. For example, correction amount data relating to the relationship between the distance variation value similar to that shown in FIG. 6 and the variation value of the potential signal related to the potential of the measurement object 1 (that is, the correction amount to be applied to the potential signal) is obtained in advance. . This correction amount data is also stored as correction data together with distance variation data related to the distance variation value corresponding to each phase position, and is used when necessary.

In the above configuration, the correction circuit unit 10 performs the following processing on the potential signal related to the potential of the measurement target 1 obtained through the detection unit 3, the amplification circuit unit 4, and the detection circuit unit 6. The correction circuit unit 10 receives these data from the correction data storage unit 9 that stores the previously obtained distance variation data and correction amount data, and the distance variation value and potential corresponding to the current phase position of the measurement target 1 Find the amount of correction to be applied to the signal. Based on these, the correction circuit unit 10 corrects the potential signal from the detection circuit unit 6. In this way, distance compensation becomes possible. At this time, of course, the phase at the present time (at the time of potential measurement) is determined by factor acquisition means as will be described later, and this information is also input to the correction circuit unit 10. When the measurement object 1 is a photosensitive drum, the variation in distance is a shake of the photosensitive drum, and correction data for each rotational phase is saved and stored in the correction data storage unit 9.

A schematic example of this distance variation data graph is shown in FIG. The horizontal axis is the phase, the vertical axis is the distance fluctuation amount, and the distance fluctuation value (variation amount) when the phase is Φ is ± Δd. The distance fluctuation value varies depending on the phase, but has a periodicity of 2π and can be measured relatively easily. In particular, when the measurement object 1 is a photosensitive drum, the roundness and the amount of eccentricity may be measured during inspection of the photosensitive drum, and the data can be used.

When the phase of the measurement location is known in advance, the phase data may be input to the potential measuring device each time, and correction may be performed by the correction circuit unit 10 using the correction data at that phase. If it is not known in advance, the current phase is determined by measuring with an encoder as a factor acquisition means, input as a signal to a potential measuring device, and correction is performed by the correction circuit unit 10 using correction data at that phase. . Further, in a suitable form of factor acquisition means, the phase at the time of potential measurement may be obtained by calculating the phase from the home position and speed of the photosensitive drum.

As described above, in the present embodiment, the correction circuit unit 10 performs correction based on the distance variation data and correction amount data obtained and stored in advance and the rotational phase at the time of potential measurement that is determined each time. Thus, distance compensation is possible when the variation in the distance between the potential measuring device and the measuring object 1 is caused by at least one of the roundness of the measuring object 1 and the amount of eccentricity of the rotation center thereof. For the sake of simplicity, this distance compensation is not performed for each rotation phase, but is corrected based on several points of distance variation data on the circumference of the photosensitive drum, or the average value of the distance variation data on the circumference of the photosensitive drum. Correction can also be performed based on the above.

(Second embodiment)
Next, a second embodiment of the present invention will be described. The potential measuring apparatus according to the present embodiment also has a configuration as shown in FIG. 1, and is the same as that of the first embodiment. The difference is that, in the first embodiment, the object to be measured is a rotationally driven object, whereas in the second embodiment, the following is true. That is, at least one of the measuring object 1 and the potential measuring device includes a fixing member. And the fluctuation | variation of the distance of an electric potential measuring apparatus and the measuring object 1 originates in the thermal expansion thru | or contraction by the temperature of what contains a fixing member.

Usually, the distance variation is for a specific temperature range. If the temperature at the time of potential measurement is known in advance, the correction circuit unit 10 corrects the potential signal obtained from the detection circuit unit 6 of the potential measurement device based on the value and the distance variation data and the correction amount data as described above. Add By doing so, it is possible to prevent deterioration in the accuracy of the potential signal due to distance dependency. The distance fluctuation value for each temperature can be theoretically obtained from, for example, the material, structure, and thermal expansion coefficient of each member of the measurement target including the fixed member and the potential measuring device including the fixed member. Moreover, you may obtain based on the data from experiment.

In the above configuration, the correction circuit unit 10 performs the following processing on the potential signal related to the potential of the measurement target 1 obtained through the detection unit 3, the amplification circuit unit 4, and the detection circuit unit 6. The correction circuit unit 10 receives the information on the distance variation value and the information on the correction amount to be applied to the potential signal from the correction data storage unit 9 that stores the distance variation data and the correction amount data obtained in advance. Receive temperature information. Based on these, the correction circuit unit 10 corrects the potential signal from the detection circuit unit 6 to compensate for the distance. For example, when the measurement target is a photosensitive drum of a copying machine, correction data for each temperature around the photosensitive drum is saved and stored in the correction data storage unit 9.

A schematic example of this distance variation data graph is shown in FIG. It means that the horizontal axis is temperature, the vertical axis is the distance fluctuation value, and the distance fluctuation value at temperature T is ± Δd. Although the distance fluctuation value varies depending on the temperature, since the guaranteed environmental temperature of the apparatus is in a specific range, it is often only necessary to store a relatively small amount of data. For example, in the case of a copying machine, the guaranteed temperature range is often about 0 ° C. to 60 ° C. Further, if there is a temperature sensor in the vicinity of the measurement object 1 and the potential measurement device, a signal may be received from the temperature sensor. When there is no temperature sensor, a temperature detection unit may be configured inside the potential measurement device.

As described above, in this embodiment, the temperature signal at the time of potential measurement is input to the potential measuring device every time the potential is measured, and the distance variation data and the correction amount data in the correction data storage unit 9 at that temperature are employed. Then, the correction circuit unit 10 performs correction. In this way, distance compensation is possible when the variation in the distance between the potential measuring device and the measuring object 1 is caused by thermal expansion or contraction due to the temperature of the measuring object including the fixing member or the potential measuring device including the fixing member. Become.

(Third embodiment)
Next, a third embodiment of the present invention will be described. The potential measuring apparatus according to the present embodiment also has a configuration as shown in FIG. 1, and is the same as that of the first embodiment. The difference is that, in the first embodiment, the object to be measured is a rotationally driven object, whereas in the third embodiment, the following is true. That is, at least one of the measurement object and the potential measurement device includes the fixing member. And the fluctuation | variation of the distance of an electric potential measuring apparatus and a measuring object originates in the time-dependent change by the elapsed time from the reference time of what contains a fixing member.

The above distance variation depends on the elapsed time since the device was manufactured. If the time for potential measurement is known in advance, the potential measurement device is based on the value and the distance variation data and correction amount data as described above. The correction circuit unit 10 corrects the potential signal obtained from the detection circuit unit 6. In this case, it is possible to prevent the deterioration of the accuracy of the potential signal due to the distance dependency. The distance fluctuation value resulting from the change over time due to the elapsed time may be obtained, for example, based on data from an endurance experiment.

In the above configuration, the correction circuit unit 10 performs the following processing on the potential signal related to the potential of the measurement target 1 obtained through the detection unit 3, the amplification circuit unit 4, and the detection circuit unit 6. The correction circuit unit 10 receives information on the distance variation value and information on the correction amount to be applied to the potential signal from the correction data storage unit 9 that stores the distance variation data and the correction amount data obtained in advance, and receives the current time from the timer. Receive the signal. Based on them, the correction circuit unit 10 corrects the potential signal detected by the detection circuit unit 6 to perform distance compensation. For example, when the measurement target is a photosensitive drum of a copying machine, correction data for each elapsed time of the photosensitive drum is saved and stored in the correction data storage unit 9.

A schematic example of this distance variation data graph is shown in FIG. The horizontal axis is time (endurance time), the vertical axis is the distance fluctuation value, and the distance fluctuation value at time t is ± Δd. Although the distance fluctuation value differs for each elapsed time, the guaranteed date of the apparatus is in a specific finite range, and therefore it is often necessary to store relatively little data. For example, in the case of a copying machine, the warranty date is usually in the range of about 5 years. In addition, when there is a clock or a copier counter that measures the current time in the vicinity of the measurement object and the potential measurement device, the time signal may be received. If it does not exist, a timepiece may be configured inside the potential measuring device.

As described above, in this embodiment, the time signal at the time of potential measurement is input to the potential measuring device every time measurement is performed, and the distance variation data and the correction amount data in the correction data storage unit 9 for the elapsed time are employed. Then, the correction circuit unit 10 performs correction. In this way, distance compensation is possible when the variation in the distance between the potential measuring device and the measuring object 1 is caused by the change over time of the measuring object including the fixing member and the potential measuring device including the fixing member.

(Fourth embodiment)
As a fourth embodiment of the present invention, an image forming apparatus using the potential measuring device of the above embodiment will be described below.

The configuration of the image forming apparatus of this embodiment is shown in FIG. Around the photosensitive drum 11, a charger 13 that can be controlled by the charger controller 12, a potential measuring device 14, an exposure device 15, and a developer supplier 16 of the present invention are installed. The mechanism for controlling the charge amount of the photosensitive drum 11 includes a charger control device 12, a charger 13, and a potential measuring device 14 of the present invention. The charger 13 is connected to the charger 13, and The charger control device 12 is connected to the potential measuring device 14 of the present invention.

The basic operation principle of the image forming apparatus of this embodiment will be described below.
A latent image is obtained by charging the surface of the photosensitive drum 11 with the charger 13 and exposing the surface of the photosensitive drum 11 with the exposure device 15. The latent image is developed by attaching a developer to the latent image by the developer supplier 16. After this image is transferred to the printing object 18 sandwiched between the printing object feeding device 17 and the photosensitive drum 11, the developer on the printing object 18 is fixed. An image is formed on the printed object 18 through these steps. In this configuration, the charger controller 12 constitutes a signal processing unit, and the charger 13, the exposure unit 15, the photosensitive drum 11 and the like constitute an image forming unit.

The operation principle of the mechanism for controlling the charge amount of the photosensitive drum 11 in this configuration will be described. The potential measuring device 14 of the present invention measures the surface potential of the photosensitive drum 11 after charging, and outputs a signal related to the surface potential of the photosensitive drum 11 to the charger control device 12. Based on a signal related to the surface potential of the photosensitive drum 11, the charger controller 12 feedback-controls the charging voltage of the charger 13 so that the surface potential of the photosensitive drum 11 after charging becomes a desired value. Thereby, stable charging of the photosensitive drum 11 is realized, and stable image formation is realized.

In the present embodiment including the high-performance potential measuring device 14 of the present invention compensated for the distance as described above, the charger control device 12 which is a signal processing means for processing the output signal from now on, and the image forming means, image formation is performed. The unit controls image formation based on the signal processing result of the signal processing device 12. Thus, by using the potential measuring device of the present invention for the image forming apparatus, it is possible to stabilize the image quality accurately and stably.

FIG. 3 is a configuration diagram of an image forming apparatus according to first to third embodiments of the present invention. The graph which shows the schematic example of the distance fluctuation value in each phase in rotation when distance fluctuation | variation arises due to at least one of the roundness of a measuring object and the eccentric amount of a rotation center. The graph which shows the schematic example of the distance fluctuation value in each temperature when distance fluctuation | variation arises due to the thermal expansion thru | or shrinkage | contraction by the temperature of at least one of the measuring object containing a fixing member, and the electric potential measurement apparatus containing a fixing member. The graph which shows the schematic example of the distance fluctuation | variation value in each elapsed time when distance fluctuation | variation arises resulting from the time-dependent change of at least one of the measuring object containing a fixing member, and the electric potential measurement apparatus containing a fixing member. FIG. 10 is a configuration diagram of an image forming apparatus according to a fourth embodiment of the present invention. The graph which shows the change of the relative electric potential measurement precision by the distance fluctuation | variation between an electric potential measuring apparatus and a measuring object.

Explanation of symbols

1, 11 Measurement target (photosensitive drum)
3 Detection unit (including detection electrode and capacitance changing means)
4 Detection means (amplifier circuit part)
6 Detection means (detection circuit part)
9 Storage means (correction data storage)
10 Correction means (correction circuit)
12 Signal processing means (charger controller)
13 Image forming means (charger)
14 Potential measurement apparatus of the present invention
15 Image forming means (exposure unit)
16 Image forming means (developer supply unit)

Claims (7)

A sensing electrode;
Capacitance changing means for changing the capacitance between the measurement object and the detection electrode;
Detection means for obtaining the potential of the measurement object using an electrical signal output from the detection electrode;
Storage means for storing distance variation data relating to a variation value of the distance between the detection electrode and the measurement object obtained in advance;
Correction means for correcting the potential from the detection means based on the distance variation data;
A potential measuring device comprising: An information acquisition means for acquiring information serving as a reference for the distance variation data;
2. The potential measuring apparatus according to claim 1, wherein the correction is performed based on the distance variation data and information serving as a reference for the distance variation data. The measurement target is a rotationally driven object, and the variation in the distance in the rotation of the measurement target is caused by at least one of the roundness of the measurement target and the eccentric amount of the rotation center. An electric potential measuring device comprising:
3. The potential measuring device according to claim 2, wherein the distance variation data is data related to a variation value of the distance at each phase which is the information in the rotation of the measurement target. The potential measurement device is intended for a case where at least one of the measurement object and the potential measurement device includes a fixing member, and the variation in the distance is caused by thermal expansion or contraction due to temperature of the material including the fixing member. And
3. The potential measuring device according to claim 2, wherein the distance variation data is data relating to a variation value of the distance at each temperature as the information. Potential measurement for a case where at least one of the measurement object and the potential measurement device includes a fixed member, and the variation in the distance is caused by a change with time due to an elapsed time from a reference time of the one including the fixed member. A device,
3. The potential measuring device according to claim 2, wherein the distance variation data is data relating to a variation value of the distance at each elapsed time as the information. Changing the capacitance between the measurement object and the detection electrode and taking out an electric signal from the detection electrode;
Obtaining a potential signal related to the potential of the measurement object using the electrical signal;
Correcting the potential signal based on distance variation data relating to a variation value of the distance between the detection electrode and the measurement target obtained in advance;
A method for measuring an electric potential, comprising: A potential measuring device according to any one of claims 1 to 5, a signal processing means for processing an output signal obtained from the potential measuring device, and an image forming means,
The image forming apparatus is characterized in that the potential measuring device is disposed opposite to a potential measurement target of the image forming unit, and the image forming unit controls image formation using a signal processing result of the signal processing unit. apparatus.

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