JPH0561304A - Image forming apparatus and potential detection method - Google Patents

Abstract

(57) [Summary] [Purpose] Eliminates changes in characteristics of individual potential sensors over time due to variations in characteristics and dirt. Makes handling such as sensor positioning easier. [Structure] A known reference voltage is applied to a conductor having a distance equivalent to that of a photoconductor with respect to a sensor, the potential is measured, and an actual sensor detection characteristic is obtained. A mechanism for switching the orientation of the sensor is provided when the conductor is provided at a position different from that of the photoconductor, and a relay that releases the ground of the photoconductor is applied when a reference voltage is applied to the roller that supports the photoconductor. Set up. The detection characteristics are calibrated immediately after the power is turned on and after every predetermined number of copies. When the amount of correction becomes large, a message prompting you to clean the sensor is displayed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly to detection of a photosensitive member potential.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine,
Generally, the surface of a photoconductor is uniformly charged to a high potential, and the surface is irradiated with light reflected from a document to form a potential distribution corresponding to a document image, that is, an electrostatic latent image is formed. A toner is attached according to the above conditions to form a visible toner image. Therefore, in this type of image forming process, it is very important to accurately know the charging potential of the photoconductor in order to obtain a high quality copy image.

A potential sensor capable of detecting the charging potential of the photosensitive member has been conventionally known, but this potential sensor is conventionally expensive, the sensor and its control device are large, and the potential sensor is measured with respect to the distance from the detection target. Since the results are highly dependent and difficult to handle, they were rarely used in conventional copiers.

[0004]

Recently, an inexpensive potential sensor has become available, and it can be used in a copying machine to detect the actual charged potential of the photoconductor to control the image forming process. It is desired to do. However, since the detection characteristics of each sensor vary widely and the detection characteristics of the potential sensor are highly dependent on the distance, a special jig is used to accurately measure the distance between the mounting position of the potential sensor and the surface of the photoconductor. If not adjusted, the detection characteristics of the potential sensor deviate from the expected characteristics, and the detection characteristics vary between devices. Also, the potential sensor is several mm from the surface of the photoconductor.
Since it is necessary to place it at a position of a certain distance, if the detection surface of the potential sensor becomes dirty due to toner scattered in the vicinity, the detection sensitivity of the sensor tends to be lower than usual due to changes with time. Detection error occurs.

Therefore, according to the present invention, it is possible to reduce the detection error based on the variation in the detection characteristics of the individual potential sensors, and to reduce the detection error based on the variation in the detection characteristics caused by the difference in the distance between the photoconductor and the potential sensor. , Eliminating the need for precise positioning of the photoconductor and potential sensor,
It is an object to reduce the change over time in the detection characteristics due to dirt on the detection surface of the potential sensor.

[0006]

In order to solve the above-mentioned problems, in the first invention of the present application, the surface of a photosensitive member charged to a uniform potential is irradiated with light corresponding to an image to form an electrostatic latent image. In an image forming apparatus for forming an image, visualizing the electrostatic latent image with a developer, and transferring the formed visible image to a predetermined recording medium: a potential detecting means arranged at a predetermined distance from the photoconductor. From the potential detecting means to a predetermined position at a distance substantially equal to the distance between the potential detecting means and the position to be measured on the photoconductor,
Reference potential generating means for generating a predetermined reference potential; Detection direction switching for selectively directing the direction of the detection surface of the potential detecting means to both the measurement target position on the photoconductor and the position where the reference potential appears Means; and a detection surface of the potential detection means toward a position where the reference potential appears, and a detection surface of the potential detection means faces a measurement target position on the photoconductor in accordance with the potential detected by the detection means. A potential correcting means for correcting the detected potential is provided.

In the second aspect of the invention, the surface of the photoconductor charged to a uniform potential is irradiated with light corresponding to an image to form an electrostatic latent image, and the electrostatic latent image is visualized with a developer. Then, in the image forming apparatus for transferring the formed visible image to a predetermined recording medium: a potential detecting means arranged at a position of a predetermined distance from the photoconductor; at a position near an axis supporting the photoconductor,
Reference potential generating means for applying a predetermined reference potential; grounding means for releasing charges on the photoconductor; grounding state switching means for switching the electrical connection state of the grounding means between a grounded state and a non-grounded state; and the grounded state switching The grounding means by the grounding state switching means in accordance with the potential detected by the potential detecting means while the reference potential generating means applies the reference potential in the vicinity of the photoconductor. There is provided a potential correcting unit for correcting the photoconductor potential detected by the potential detecting unit with the unit grounded.

In the third aspect of the invention, light corresponding to an image is irradiated on the surface of the photoconductor charged to a uniform potential to form an electrostatic latent image, and the electrostatic latent image is visualized with a developer. Then, in the method of detecting the potential of the photoconductor in the image forming apparatus for transferring the formed visible image to the predetermined recording medium: the reference potential appearing at the predetermined position is read by the potential sensor, and then the potential of the photoconductor is read by the potential sensor. , The read potential of the photoconductor is automatically corrected according to the value of the read reference potential.

Further, in the fourth aspect of the invention, light corresponding to the image is irradiated onto the surface of the photoconductor charged to a uniform potential to form an electrostatic latent image, and the electrostatic latent image is visualized with a developer. Then, in the method of detecting the potential of the photoconductor in the image forming apparatus that transfers the formed visible image to a predetermined recording medium: a reference that appears at a predetermined position by the potential sensor immediately after the apparatus is turned on and after every predetermined number of image formations. The potential is read, and when each image is formed, the potential of the photoconductor is read by the potential sensor,
The read potential of the photoconductor is automatically corrected according to the value of the read reference potential.

In the fifth aspect of the invention, light corresponding to an image is irradiated onto the surface of the photosensitive member charged to a uniform potential to form an electrostatic latent image, and the electrostatic latent image is visualized with a developer. Then, in the method of detecting the potential of the photoconductor in the image forming apparatus that transfers the formed visible image to a predetermined recording medium: a reference potential appearing at a predetermined position is read by a potential sensor, and the read reference potential and a predetermined characteristic value are set. When the correction amount obtained by the difference of is greater than a predetermined value, a predetermined abnormal signal is output,
When the correction amount is less than the predetermined value, the potential sensor then reads the potential of the photoconductor, and the potential of the read photoconductor is automatically corrected according to the value of the read reference potential.

[0011]

If a constant reference potential having a predetermined potential is generated in the vicinity of the photoconductor and the potential is detected by the potential sensor,
The value of the reference potential detected at this time depends on the detection characteristics of the potential sensor. Therefore, for example, a correction value is generated based on the difference between the detected reference potential and the value of a predetermined standard detection characteristic, and when the potential of the photoconductor is detected, the correction value is added to the detection value. By doing so, it is possible to compensate for variations in the detection characteristics of the individual potential sensors. In the present invention, basically, the potential of the photoconductor is measured after the potential sensor is calibrated in this manner.

In the first aspect of the invention, an electrode or the like for generating a reference potential is arranged at a position slightly deviated from the surface of the photoconductor to be detected, and the direction of the detection surface of the potential detection means (corresponding to the potential sensor) is set. By changing it, it is possible to detect both the reference potential and the photoreceptor surface potential.

In the second aspect of the invention, the voltage is applied to the member near the shaft supporting the photosensitive member so that the reference potential is generated. Since the base (or center) of the photoconductor is normally grounded so that a current flows by corona discharge, the potential detection means detects a predetermined reference potential even if a voltage is applied to a member near the axis in the grounded state. You cannot do it. Therefore, in the present invention, the grounding state switching means is provided so that the photoreceptor is grounded during the normal image forming process, but when the reference potential is generated, the grounding means is switched to the non-grounded state. In the present invention, the value of the reference potential detected by the potential detection means changes according to the detection characteristics of the potential detection means and the distance between the means and the photoconductor, so that calibration should be performed based on the detected reference potential. For example, it is possible to compensate not only for variations in the characteristics of the individual potential detecting means, but also for deviations from the standard characteristics of the detection characteristics based on the installation position of the means, that is, the difference in the distance between the means and the photosensitive member, The positioning of the potential detecting means becomes simple.

According to the third aspect of the invention, the result of reading the reference potential with the potential sensor is utilized to correct the detection characteristic when the potential sensor reads the potential of the photoconductor to detect the correct potential of the photoconductor. You can

In the fourth aspect of the invention, the reading of the reference potential by the potential sensor is repeated immediately after turning on the power of the apparatus and every time a predetermined number of times of image formation is performed, so that the detection characteristic is calibrated each time. It is possible to reduce the change over time in the detection characteristics of the potential sensor caused by dirt on the detection surface, temperature change, or the like.

In the fifth aspect of the present invention, when the required correction amount of the detection characteristic of the potential sensor due to aging or the like becomes large to some extent, an abnormal signal is output. It is possible to output a message prompting the operator to clean the machine.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the structure of a mechanical section of a copying machine of one type for carrying out the present invention. This will be described with reference to FIG. Documents are fed by the automatic document feeder (A
DF) 1 is stacked on a tray 1a provided inside, and is automatically fed sheet by sheet and positioned automatically on a contact glass 31 at a document reading position. The exposure lamp 2 is arranged below the contact glass 31. The light emitted from the exposure lamp 2 is reflected by the first mirror-3 and simultaneously exposes the entire surface of the document placed on the contact glass 31. The reflected light from each part of the document is reflected by the second mirror.
OPC through the lens 32, the lens 33, and the third mirror 34.
It is incident on the surface of the belt photoconductor 5 and forms an optical image corresponding to the original image on the photoconductor 5.

On the other hand, the OPC belt photosensitive member 5 is neutralized by the pre-cleaning static eliminator 9 and cleaned by the cleaning unit 4, and then the surface of the OPC belt photosensitive member 5 is uniformly raised by the corona discharge of the charger 8. It is charged to a potential. When the surface of the charged OPC belt photoreceptor 5 is irradiated with light,
Since the surface potential changes according to the intensity of the irradiated light, when a light image from a document is irradiated, a potential distribution corresponding to the image, that is, an electrostatic latent image is formed on the surface of the photoconductor 5. It When passing through the developing device 7, this electrostatic latent image is visualized by adsorbing toner according to its potential distribution. The visualized electrostatic latent image, that is, the toner image is fed from one of the plurality of paper feed trays (10, 14, 15) at a predetermined timing according to the image forming process on the OPC belt photosensitive member 5. The image is transferred onto the transfer paper that is fed so as to overlap the photoconductor 5 when passing through the transfer unit 13. The transfer paper on which the toner image is transferred is separated from the OPC belt photosensitive member 5, the toner image is fixed by the fixing device 12, and the transfer paper is conveyed along a predetermined paper discharge path. The OPC belt photosensitive member 5 on which the toner image has been transferred is neutralized again by the pre-cleaning static eliminator 9 and cleaned by the cleaning unit 4 to prepare for the next image formation.

By the way, generally, in a copying machine, various characteristics of the image forming portion are changed after long-term use. This change occurs due to repeated stress on the photoconductor, developer, etc., toner stains on parts such as toner and paper dust, and environmental changes such as temperature and humidity. Specifically, the charging potential of the photoconductor, the sensitivity of the photoconductor, and the residual potential of the photoconductor change due to the repeated stress of the photoconductor and the influence of temperature and humidity. Changes the charging potential, and the surface potential of the photoconductor immediately after passing through the pre-cleaning charge eliminator changes according to the dirt and temperature and humidity in the cleaning part. Any of these changes affects the image formation, causing changes in the image density and background stains on the copy paper.

Therefore, in this embodiment, the potential sensor 6 arranged in the vicinity of the OPC belt photosensitive member 5 is used to measure the potential on the photosensitive member 5 under various conditions, and the potential corresponding to the measurement result is measured. -Dubbing control is performed so that the image density formed by compensating for the above change is constant.

However, since the potential sensor 6 itself has variations in its detection characteristics among the individual sensors, and the detection characteristics change when the detection surface becomes dirty due to a change with time, the detection characteristics of the potential sensor 6 are changed. Precise compensation control cannot be realized unless it is calibrated from time to time. In order to enable the calibration of the potential sensor 6, in this embodiment, an electrode plate (copper plate) 21 is arranged in the vicinity of the potential sensor 6 as shown in FIG. 2, and a reference voltage Vr can be applied to it. .. Further, the potential sensor 6 is supported so that its detection surface can change its direction between the direction facing the OPC belt photoreceptor 5 (solid line in the figure) and the direction facing the electrode plate 21 (two-dot chain line in the figure). An electric motor 22 is connected to the shaft 6b. Since the detection characteristic of the potential sensor 6 changes according to the distance between it and the detection target, in order to eliminate the influence of the distance, the distance L to the OPC belt photosensitive member 5 and the distance L to the electrode plate 21 on the detection surface 6a. Are the same.

FIG. 3 shows an outline of the configuration of the electrical equipment section of the copying machine shown in FIG. This will be described with reference to FIG. The overall control of the copying machine is processed by the copying process control unit 100 having a built-in microcomputer. The copy process control unit 100 includes an operation board 300, AD.
F1, sorter 17, heater control unit 45, lamp control unit 46, reference voltage generator 47, lens / mirror
The motor 48, clutch and solenoid 49, sensor unit 50, high voltage power supply unit 200 and motor control unit 51 are connected. Lamp control unit 46
Controls the voltage applied to the exposure lamp 2 so that the exposure lamp 2 is turned on / off in accordance with an instruction from the copying process control unit 100 and the brightness becomes constant when turned on. The reference voltage generator 47 uses a predetermined accurate reference voltage Vr (in this example, 50V and 100V).
Are generated according to an instruction from the copying process control unit 100, and the voltage Vr is applied to the electrode plate 21. The high-voltage power supply unit 200 is connected to the charger 8, the transfer unit 13, and the roller 7a of the developing device, and generates a voltage or current applied to each of them. These voltages and currents are automatically corrected by feedback control based on various voltage information detected by the potential sensor 6.

The sensor unit 50 also includes a potential sensor 6. The analog voltage output by the potential sensor 6 at the time of detection is the A / D in the copy process control unit 100.
It is converted to a digital quantity by a converter (which has a resolution of 8 bits in this example). The 8-bit value obtained by this A / D conversion has a correspondence relationship with the detected voltage as shown in the graph of FIG. 4, but the actual detection characteristic Sd of the potential sensor 6 deviates from the reference characteristic Sr. In many cases. This shift occurs due to variations in the characteristics of the individual potential sensors, changes over time, and changes in the environment.

Therefore, in order to accurately measure the potential on the OPC belt photosensitive member 5 by the potential sensor 6, for example, the conversion table corresponding to the actual detection characteristic Sd is used to convert the detected value into a voltage. There is a need. This conversion table is generated by the calibration process of the potential sensor described later. In this embodiment, the electrode plate 21 is placed at a position equivalent to the detection target position on the OPC belt photosensitive member 5 with respect to the potential sensor 6.
Since a known accurate reference voltage can be applied to the electrode plate 21, the detection characteristics should be calibrated based on the result of detecting the potential of the electrode plate 21 to which the reference voltage is applied by the potential sensor 6. You can That is, assuming that the detection characteristic Sd is linear, the 8-bit value Vd1 and the electrode plate 2 detected when the reference voltage of 50V is applied to the electrode plate 21.
The actual characteristic Sd can be calculated from the two points of the 8-bit value Vd2 detected when a reference voltage of 100 V is applied to 1 and their inclinations.

Copy process control unit 10 shown in FIG.
The outline of the processing of 0 is shown in FIG. This will be described with reference to FIG. When the power is turned on, first, initialization of the control unit 100 itself (RAM clear, various mode settings, output port status setting, etc.) is performed, and then various initial settings for enabling the copier to operate. (Copy mode setting, timer setting, etc.)
To execute. Next, the potential sensor calibration process is executed. This process will be described in detail later. Then, a standby mode process is executed. In the standby mode processing, the signals output from various sensors and the state of the key switch of the operation board are read, the on / off control of various output devices is executed, and the abnormality check is executed and read. The signal discrimination process is executed, and the timer process and the display process are further executed. The standby mode processing is repeatedly executed until the copying becomes possible, and the copying machine continues the standby state. Copy
When the print key on the operation board is pressed after the operation is ready, the process proceeds to the pre-copy mode process. In the pre-copy mode processing, preparation is made before starting the copy process, for example, cleaning of the surface of the photoconductor is executed. When the number of copies is input by the numeric keypad, the value NK is stored in the number register Nset.

When the pre-copy mode process is completed, the process proceeds to the next copy mode process to actually execute the copy process.
Paper transport processing, toner replenishment processing, abnormality check processing, etc. are also executed at the same time. In the copy process, after the photoconductor is uniformly charged to a high potential as described above, the surface thereof is irradiated with light reflected from the original to form an electrostatic latent image on the photoconductor surface, and the electrostatic latent image is formed. The image is visualized with a toner in the developing unit 5, the toner image is transferred onto a transfer paper, the transfer paper is separated from the photoconductor and conveyed, and the fixing device 12 fixes the toner image onto the transfer paper to transfer the transfer paper. Eject the paper. The copy mode process is repeatedly executed until one copy cycle is completed. When one copy cycle ends, a copy number counter Ccopy
Is incremented by 1 and the content of the counter is compared with the content of the number register Nset. If the two values do not match, the copy mode process is repeated again and a plurality of copy cycles are executed substantially continuously. When the copy cycle for the number of sheets set in the number of sheets register Nset is completed, after adding the value of the copy total number counter Ct and the copy number counter Ccopy,
The copy number counter Ccopy is cleared, and the process proceeds to the post-copy mode processing. In the post-copy mode process, a paper carrying process, an abnormality check, a copy post-process, etc. are executed. The post-copying mode process is repeatedly executed until all paper discharge is completed. Next, the value of the copy total number counter Ct is set to a predetermined number N.
Compare with t. The number Nt of sheets is set to 100 sheets, for example, in association with the number of copies corresponding to the time when the detection characteristic of the potential sensor 6 changes with time. If the value of the copy total number counter Ct is Nt or more, the potential sensor calibration process is executed.

Potential sensor calibration process (step S in FIG. 5)
The specific contents of (1, S2) are shown in FIG. First, in step 10, the electric motor 22 is driven for calibration, and the potential sensor 6 is controlled so that its detection surface faces the electrode plate 21. In the next step 11, the reference voltage generator 47 is controlled to apply a voltage of 50 V to the electrode plate 21. In the following step 12, the electric signal Vd output from the potential sensor 6 is input, and the digital amount obtained by A / D conversion is set to the first value.
It is stored as the measured value Vd1. In the next step 13,
The reference voltage generator 47 is controlled to switch the output voltage to 100V, and 100V is applied to the electrode plate 21. Then, in the next step 14, the electric signal V output from the potential sensor 6
d is input, and the digital amount obtained by A / D conversion is stored as the second measurement value Vd2. In the next step 15, the electric motor 22 is driven again to switch the direction of the potential sensor 6 so that its detection surface faces the predetermined position of the OPC belt photosensitive member 5.

In step 16, a conversion table corresponding to the actual characteristic straight line Sd shown in FIG. 4, for example, is created based on the two detected voltage values Vd1 and Vd2. That is, the input value Vd1 corresponding to the converted voltage of 50 V
And the input value Vd2 corresponding to the converted voltage of 100V, the slope of the characteristic straight line Sd is obtained by calculating (Vd2-Vd1) / (100-50), and this slope and Vd1 or Vd2 are obtained. Based on each input value (0
0, 01, 02, 03, ..., FD, FE, FF), and calculates the converted voltage corresponding to each of the input values and the converted voltage so that the correspondence relationship becomes clear ( For example, in order of increasing input value), each calculation result is written in a predetermined memory area as the contents of the table.

In the next step 17, the difference in inclination between the standard characteristic straight line Sr and the actual characteristic straight line Sd is corrected by the correction amount DV.
Ask as. The slope of the straight line Sr is stored as a fixed value in the memory in advance, and the slope of the straight line Sd is obtained from the above-described calculation formula. Therefore, the absolute value of the difference between these slopes is calculated and the result is stored in DV. To do. The correction amount obtained here corresponds to the variation in the characteristics of the standard potential sensor and the characteristics of the potential sensor 6 actually used, and the change over time due to stains on the detection surface, environmental changes, and the like. Therefore, when it is used for a long time, the degree of dirt on the detection surface advances, and the value of the correction amount DV increases. Therefore, in the next step 18, the correction amount DV is compared with a predetermined threshold value D1. When the correction amount DV is larger than the threshold value D1, the display "Please clean the potential sensor" on the operation board 300 is turned on in step 19, and if the correction amount DV is within the threshold value D1. , In step 20, turn off the display of "clean the potential sensor". Last step 2
At 1, the copy total number counter Ct is cleared.

Next, one modified embodiment will be described. In this embodiment, the potential sensor 6B is fixed, and the position for applying the standard voltage is different from that in the previous embodiment. That is, in this embodiment, the structure is changed so that the reference voltage is applied to the roller 23 supporting the OPC belt photosensitive member 5 instead of the electrode plate 21. The roller 23 is made of conductive rubber. Since the thickness of the OPC belt photoreceptor 5 is very small, the OPC belt
It can be considered that the surface of the belt photosensitive member 5 and the surface of the roller 23 are present at substantially the same position. That is, in this embodiment, it is not necessary to adjust the position of applying the standard potential and the position of the OPC belt photosensitive member 5 to match the distance with the potential sensor 6B, and the position of the potential sensor 6B does not need to be accurately aligned. .. Further, a driving means for changing the direction of the potential sensor 6B is unnecessary.

However, since the OPC belt photosensitive member 5 is normally grounded for the image forming process, the grounded OPC belt photosensitive member 5 is located between the potential sensor 6B and the roller 23. Arranged and potential sensor 6
Since B detects the ground potential, the standard potential applied to the roller 23 cannot be detected. Therefore, in this embodiment, as shown in FIGS. 7 and 9, the wiring connected to the ground brush 54 for grounding the OPC belt photosensitive member 5 is grounded via the relay 53, and is controlled by the relay 53. It is configured so that it can be switched to the grounded state.

As shown in FIG. 8, the OPC belt photosensitive member 5
Is a polyester layer P1, an aluminum vapor deposition layer P2, C
It has a four-layer structure of a GL layer P3 and a CTL layer P4,
During the charging and exposure processes, the aluminum vapor deposition layer P
It is necessary to ground 2 to allow the charge that has flowed into this layer to escape. The ground brush 54 is configured by sandwiching a conductive fiber bundle between aluminum sheet metals, and the brush portion is in contact with the surface of the aluminum vapor deposition layer P2.

Referring to FIG. 9, the reference voltage Vr output from the reference voltage generator 47 is passed through the conductive leaf spring 55 and the bearing (conductive) 59, and the metal shaft 23a at the center of the roller 23. And appears on the surface of the roller 23. Reference numeral 57 is a supporting frame of the roller 23, and 56 and 58 are insulators. Further, as shown in FIG. 10, the relay 53 for switching the ground / non-ground of the ground brush 54 is connected to the copying process control unit 100 via the driver 52.

The contents of the potential sensor calibration processing in this embodiment are shown in FIG. The contents of each step will be described with reference to FIG. In the first step 30, the contact of the relay 53 is opened and the grounding of the OPC belt photosensitive member 5 is released.
In the next step 31, the reference voltage generator 47 is controlled to apply a constant voltage of 50 V to the roller 23 as a reference voltage. In the following step 32, the electric signal Vd output from the potential sensor 6B is input, and the digital amount obtained by A / D conversion is stored as the first measurement value Vd1. In the next step 33, the reference voltage generator 47 is controlled to switch the output voltage to 100V, and 100V is applied to the roller 23. Then, in the next step 34, the potential sensor 6B
The electric signal Vd output by is input, and the digital amount obtained by the A / D conversion is stored as the second measurement value Vd2. In the next step 35, the contact of the relay 53 is closed,
The aluminum vapor deposition layer P2 of the OPC belt photoreceptor 5 is grounded. The process after step 36 is the same as the corresponding step after step 16 in FIG. 6 of the above embodiment. The configuration and operation other than those described are the same as those in the above-described embodiment.

[0035]

As described above, according to the present invention, it is possible to prevent variations in the detection characteristics of the potential detection means (6) and changes with time in the detection characteristics caused by dirt on the detection surface, environmental changes, and the like. Automatically corrects the photoconductor (5)
The surface potential can be accurately detected. By performing feedback control based on the photoconductor potential detected by this, stable image formation is realized.

Further, in the first invention, it is necessary to accurately align the position (21) of the potential detecting means and the electrode to which the reference voltage is applied, but the second invention does not require precise alignment. Easy to handle. Further, according to the fourth aspect of the invention, since the detection characteristic of the potential detecting means is calibrated immediately after turning on the power of the apparatus and every time a predetermined number of times of image formation is performed, a correct potential can always be detected with the calibrated detection characteristic. The influence of aging can be avoided. Further, if the detection surface of the potential detecting means is abnormally soiled and the detection characteristic is largely deviated from the standard characteristic, the detection error may increase even if the detection characteristic is calibrated. According to the fifth invention, an abnormal signal is output at such a time, and accordingly, a message such as "please clean the potential sensor" is displayed to inform the operator of the abnormal condition and cause it. Can be encouraged to disappear.

[Brief description of drawings]

FIG. 1 is a front view showing a component of a copying machine according to an embodiment.

FIG. 2 is a partially enlarged front view showing the configuration of a part of FIG.

FIG. 3 is a block diagram showing a configuration of an electrical component section of the copying machine of FIG.

FIG. 4 is a graph showing an input digital value and a converted voltage value.

5 is a flowchart showing the processing of the control unit shown in FIG.

FIG. 6 is a flowchart showing the contents of processing in steps S1 and S2 in FIG.

FIG. 7 is a perspective view showing the vicinity of a photoconductor in a modified example.

FIG. 8 is a perspective view showing a configuration of a photoconductor.

FIG. 9 is a plan view showing the vicinity of a photoconductor in a modified example.

FIG. 10 is a block diagram showing a configuration of an electrical component section of a modified example.

FIG. 11 is a flowchart showing a potential sensor calibration process in a modified embodiment.

[Explanation of symbols]

1: Automatic document feeder 2: Exposure lamp 3: First mirror 4: Cleaning unit 5: O
PC belt photoconductor 6,6B: Potential sensor (potential detection means) 7: Developer 8: Charger 9: Before cleaning cleaner 10: Paper tray 12: Fixer 13:
Transfer unit 14: Double-sided tray 15: Large capacity tray 16:
Inversion unit 17: Sorter 21: Electrode plate 22: Electric motor (detection direction switching means) 23:
Roller 31: Contact glass 32: Second mirror 33:
Lens 34: Third mirror 47: Reference voltage generator (reference voltage generating means) 53: Relay (grounding state switching means) 54: Earth brush (grounding means) 55: Leaf springs 56, 58: Insulator 57:
Support frame 59: Bearing 100: Copy process control unit (potential correction means)

Claims (5)

[Claims] 1. A visible image formed by irradiating light corresponding to an image on the surface of a photosensitive member charged to a uniform potential to form an electrostatic latent image and visualizing the electrostatic latent image with a developer. In an image forming apparatus that transfers the image to a predetermined recording medium: a potential detecting unit arranged at a position at a predetermined distance from the photoconductor; and a distance from the potential detecting unit to a measurement target position on the photoconductor is substantially Reference potential generating means for generating a predetermined reference potential at a predetermined position of equal distance; the orientation of the detection surface of the potential detecting means is set both at the measurement target position on the photoconductor and at the position where the reference potential appears. Detection direction switching means for selectively directing the detection surface of the potential detection means toward the position where the reference potential appears, and the detection surface of the potential detection means on the photoconductor in accordance with the potential detected by the detection means. Detected toward the measurement target position of Potential correction means for correcting the potential
An image forming apparatus comprising: 2. A visible image formed by irradiating light corresponding to an image on the surface of a photoconductor charged to a uniform potential to form an electrostatic latent image and visualizing the electrostatic latent image with a developer. In an image forming apparatus for transferring the toner to a predetermined recording medium: a potential detecting means arranged at a predetermined distance from the photosensitive member; a reference for applying a predetermined reference potential to a position near an axis supporting the photosensitive member. Potential generating means; grounding means for releasing charges on the photoconductor; grounding state switching means for switching the electrical connection state of the grounding means between grounded state and non-grounded state; and the grounding state switching means for ungrounding the grounding means. Then, according to the potential detected by the potential detecting means in a state where the reference potential generating means applies the reference potential in the vicinity of the photoconductor, the ground state switching means sets the grounding means to the grounding state to detect the potential. To the means An image forming apparatus comprising: a potential correcting unit that corrects the detected photoconductor potential. 3. A visible image formed by irradiating light corresponding to an image on a surface of a photoconductor charged to a uniform potential to form an electrostatic latent image and visualizing the electrostatic latent image with a developer. In the method for detecting the potential of the photoconductor in the image forming apparatus for transferring the image to a predetermined recording medium: a reference potential appearing at a predetermined position is read by a potential sensor, then the potential of the photoconductor is read by the potential sensor, and the potential of the read photoconductor is read. Is automatically corrected according to the value of the read reference potential. 4. A visible image formed by irradiating light corresponding to an image on the surface of a photoconductor charged to a uniform potential to form an electrostatic latent image and visualizing the electrostatic latent image with a developer. In the method of detecting the potential of the photoconductor in the image forming apparatus for transferring the image to a predetermined recording medium: a reference potential appearing at a predetermined position is read by a potential sensor immediately after the power is turned on of the apparatus and every time a predetermined number of image formations are performed, and each image A potential detection method, wherein the potential of the photoconductor is read by a potential sensor at the time of formation, and the potential of the read photoconductor is automatically corrected according to the value of the read reference potential. 5. A visible image formed by irradiating light corresponding to an image on the surface of a photoconductor charged to a uniform potential to form an electrostatic latent image and visualizing the electrostatic latent image with a developer. In the method of detecting the potential of the photoconductor in an image forming apparatus that transfers the image to a predetermined recording medium: A reference potential appearing at a predetermined position is read by a potential sensor, and a correction amount obtained by the difference between the read reference potential and a predetermined characteristic value Is a predetermined value or more, a predetermined abnormal signal is output, and when the correction amount is less than a predetermined value, the potential of the photoconductor is then read by a potential sensor, and the potential of the read photoconductor is the value of the read reference potential. A potential detection method characterized in that it is automatically corrected in accordance with the above.