JPH09204120A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect the thickness of the film of a photoreceptor with high accuracy an to accurately inform a user of the exchange periods of a photoreceptor drum and a process cartridge by calibrating a current detecting circuit and then, executing actual measurement, at the time of measuring the thickness of the film of the photoreceptor. SOLUTION: Before a sequence of the operations of measuring the thickness of the film of the photoreceptor drum, an amplifier A is always calibrated. At this time, a reference voltage value Vth is inputted to the amplifier A by a reference voltage generating means 14. The reference voltage value Vth is set to be equal to a voltage value inputted to the amplifier A, at the time of measuring the thickness of the film of the photoreceptor drum used to the limit. The inputted reference voltage value Vth is amplified by the amplifier A and then, processed by A/D conversion and a digital signal Sth ' is inputted to a CPU 11 and held in a memory 12. A signal Sth when a current flowing when the photoreceptor drum is used to the limit in the thickness of the film is inputted is updated to the signal Sth '. Thus, just after calibrating, the thickness of the film of the photoreceptor drum is measured.

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 using an electrophotographic method, and more particularly to an apparatus capable of accurately measuring the film thickness of a photoconductor.

[0002]

2. Description of the Related Art Copiers, printers and the like are generally used as image forming apparatuses utilizing the electrophotographic method which has been conventionally used.

FIG. 5 is a diagram for explaining the structure of the image forming portion of the image forming apparatus in this prior art, which will be described below.

Reference numeral 1 denotes a photosensitive drum. An organic photosensitive member (OP) is provided on the outer peripheral surface of a drum base made of a conductive material such as an aluminum cylinder.
C) is applied. The photosensitive drum 1 is driven in the direction of the arrow in the figure by a driving unit (not shown), and is uniformly charged to a predetermined potential by the roller charger 2.

Laser exposure 8 according to the image pattern
Is irradiated onto the surface of the photosensitive drum 1, and a latent image is formed on the photosensitive drum 1. Further, the photosensitive drum 1 advances in the direction of the arrow,
The toner image is visualized (developed) by the developing device 3.

The developed toner image is transferred onto the transfer paper 7 by the transfer charger 5. Further, the transfer paper 7 is melted and fixed by a conventionally known fixing device 6 that performs heating and pressurization to obtain an image.

The transfer residual toner on the photosensitive drum 1 is cleaned by a cleaning device 4 having a known blade means. Furthermore, since contamination such as toner melting or paper dust adhesion that occurs on the surface of the photoconductor due to a large amount of paper passing significantly damages the image, it is necessary to positively polish the surface of the photosensitive drum with a cleaning blade to refresh the surface. Maintains a good image. But as a result,
The film thickness of the photoreceptor (OPC), which is the surface layer of the photosensitive drum 1, decreases as a large amount of paper is passed.

The photosensitive drum 1 is integrally arranged in the process cartridge U together with the roller charger 2, the developing device 3, the cleaning device 4 and the like. Since the process cartridge U is a consumable item, it must be replaced due to its life, and it is necessary to provide a function of notifying the user of the cartridge life by some means.

In this prior art, the replacement of the cartridge is determined by the film thickness of the photoconductor, and the film thickness of the photoconductor is determined when the charge is removed from the state where the photoconductor is charged (or from the state where the charge is removed). It can be calculated from the current flowing through the photoconductor when charged).

Regarding this film thickness detection method, Japanese Patent Application No. 04-0
Although detailed description is given in Japanese Patent No. 56914, the surface potential of the photoconductor is increased from 0 to V _d , or V _d
DC current I _dc flowing through the photoconductor when it is lowered from 0 to 0
Is expressed by Equation 1 below.

[0011]

[Number 1] _{| I dc | = ε · ε} 0 · L · v p · V d / d where, d the thickness of the photosensitive member, the dielectric constant epsilon, the dielectric constant in vacuum epsilon _0, 1 primary The effective charging width of the roller charger is L and the process speed is v _p .

Since ε, ε ₀ , L, v _p and V _d can be regarded as constants, it is understood that the DC current I _dc is inversely proportional to the film thickness d of the photosensitive member. Therefore, the film thickness of the photoconductor can be detected by measuring the DC current I _dc with the detection circuit 9. A similar method is also disclosed in Japanese Patent Laid-Open No. 5-53488.

[0013]

However, since the DC current I _dc in the above-mentioned conventional example has a very weak value, the output voltage of the high-voltage power supply circuit for charging the photosensitive member and the amplification factor of the amplifier means of the current detection circuit. It is conceivable that the detected value will vary depending on the temperature characteristics of 1), and therefore the film thickness of the photosensitive drum will not be accurately measured.

The present invention has been made in order to improve the situation of the above-mentioned prior art, and an object thereof is to detect the film thickness of a photoconductor in an image forming apparatus with high accuracy and to provide a photoconductive drum or a process cartridge. An object of the present invention is to provide an image forming apparatus capable of accurately notifying the user of the replacement time of the.

[0015]

In order to achieve the above object, the present invention provides a current detection circuit for measuring the value of current flowing when changing the charging state of a photoconductor as an image carrier for image formation. In the image forming apparatus for measuring the film thickness of the photoconductor from the detected current value, a calibration means for calibrating the current detection circuit, and the current detection circuit before measuring the film thickness of the photoconductor. And a control means for performing calibration.

Therefore, the current value of the photoconductor can be accurately measured by the calibrated current detection circuit, and the film thickness can be detected with high accuracy.

Further, the current detection circuit includes a conversion means for converting the detected DC current value flowing through the photosensitive member into a voltage value, and an amplifier means for inputting the converted voltage value, and the calibration is performed. The means includes a reference voltage generating means for inputting a reference voltage value obtained when measuring a reference film thickness of the photoconductor to the amplifier means, and the control means has the amplifier means to which the reference voltage value is input. Storage means for storing the output voltage value as the reference output voltage value, and comparison means for comparing the reference output voltage value stored in the storage means with the actually measured output voltage value. It is also preferable that

Further, the current detecting circuit comprises a converting means for converting the detected DC current flowing through the photosensitive member into a voltage value, and an amplifier means for inputting the converted voltage value, and the calibrating means. Includes a reference DC current generating means for inputting to the conversion means a reference DC current value obtained when the film thickness serving as a reference of the photoconductor is measured, and the control means receives the reference DC current value. It is provided with storage means for storing the output voltage value of the amplifier means as a reference output voltage value, and comparison means for comparing the reference output voltage value stored in the storage means with the actually measured output voltage value. Is also preferable.

Further, the calibrating means includes a reference capacitor having the same electrostatic capacity as that of the photoconductor having a reference film thickness, and the current detection circuit flows when the charged state of the reference capacitor is changed. The control means includes a converting means for converting the DC current value into a voltage value and an amplifying means for inputting the converted voltage value of the reference capacitor, and the control means for the amplifying means for receiving the voltage value of the reference capacitor. It is characterized by further comprising storage means for storing the output voltage value as a reference output voltage value and comparison means for comparing the reference output voltage value stored in the storage means with the actually measured output voltage value. It is also preferable to do.

In the configuration as described above, the reference output voltage value of the amplifier means corresponding to the reference voltage value, the reference DC current value and the current value of the reference capacitor is compared with the actually measured output voltage value. Therefore, the film thickness can be detected with high accuracy regardless of the variation in the amplification factor of the amplifier means.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) FIGS. 1 and 2 show the present invention applied to the conventional image forming apparatus described with reference to FIG. 5, and show only the characteristic configuration. In this embodiment, members having the same configurations and functions as those of the conventional image forming apparatus are designated by the same reference numerals, and the description thereof will be appropriately omitted.

First, the method for measuring the film thickness of the photosensitive drum will be described with reference to FIG. 1, and then the circuit of the circuit first performed when measuring the film thickness of the photosensitive drum, which is a feature of the present invention, will be described with reference to FIG. The calibration method will be described.

In the method of measuring the film thickness of the photosensitive drum, an alternating voltage is applied by the roller charger 2 so that the surface potential of the photosensitive drum 1 becomes 0V. Reference numeral 13 is a high-voltage circuit for generating a voltage in which an alternating current and a direct current are superimposed on the roller charger 2.
Then, a voltage obtained by superimposing the DC voltage V _d on the AC voltage is applied to charge the surface of the photoconductor to a constant potential V _d . Reference numeral 14 is a reference voltage generating means described later.

Then, while the AC voltage is applied to the roller charger 2, the photosensitive drum 1 is rotated once to remove the charge on the surface of the photosensitive member, and the DC current I _dc is measured. At this time, the DC current I _dc flowing through the photosensitive drum 1 is such that the film thickness of the photosensitive member is d, the relative permittivity is ε, the permittivity in vacuum is ε ₀ , the effective charging width of the roller charger 2 is L, and the process speed is _Let v _p be represented by the following mathematical formula 2.

[0025]

[Number 2] _{I dc = ε · ε 0 ·} L · v p · V d / d where DC current I _dc is replaced by the voltage value _{V dc (V dc = I dc} · R) by a resistor R by the conversion means , Amplifier A
Amplified by The amplified voltage value V _dc is then converted into a digital signal S _dc by the analog-digital converter (A / D converter) 10 and sent to the CPU 11 as control means.

The CPU 11 is provided with a comparison means for comparing the value of S _dc with the value S _th at the end of the cartridge life, which is held in the memory 12 as a storage means. Send a warning signal to prompt you to replace the cartridge. Here, S _th is a signal when the current I _th that flows when the film thickness of the photosensitive drum reaches the end of its life is input.

Next, the features of this embodiment will be described with reference to FIG. That is, the amplifier A is constantly calibrated before the sequence for measuring the film thickness of the photosensitive drum.

The calibration method will be described. First, the reference voltage generator 14 inputs the reference voltage value V _th to the amplifier A. At this time, the value of the reference voltage value V _th is V _th = I _th · R, and is set equal to the voltage value input to the amplifier A when the film thickness of the photosensitive drum that has reached the end of its life is measured.

The input reference voltage value V _th is amplified by an amplifier A and then A / D converted to _obtain a digital signal S _th ′.
Is input to the CPU 11. Then, S _th held in the memory 12 is updated to this S _th ′.

Immediately after the calibration is performed in this manner, the film thickness of the photosensitive drum is measured so that the actual measurement result of the photosensitive drum can be compared even if the amplification factor of the amplifier A changes due to temperature characteristics or the like. Value S stored in the memory 12
_{Since th'is} measured immediately before, the life of the photosensitive drum can be detected with high accuracy with almost no influence.

(Embodiment 2) FIG. 3 is a diagram showing the characteristics of the second embodiment of the present invention, and a circuit calibration method in the present embodiment will be described below.

First, the reference DC current generator 15 inputs the reference DC current value I _th to the circuit. At this time, the value of the reference DC current value I _th is equal to the DC current value I _th input when measuring the film thickness of the photosensitive drum which has reached the end of its life.

The input reference DC current value I _th is converted into a voltage value V _th ′ by the resistor R and input to the amplifier A.
Then, the digital signal S _th ′ that has been amplified and then A / D converted is input to the CPU 11. And the memory 12
The S _th held at is updated to S _th ′.

Immediately after the calibration, the film thickness of the photosensitive drum is measured, so that the actual measurement result of the photosensitive drum can be compared with the amplifier A even if the amplification factor changes due to temperature characteristics or the like. Value S stored in the memory 12
_{Since th'is} measured immediately before, the life of the photosensitive drum can be detected with high accuracy with almost no influence.

(Embodiment 3) FIG. 4 is a diagram showing the feature of the third embodiment of the present invention, and a circuit calibration method in the present embodiment will be described below.

First, the high voltage circuit 13 applies an AC voltage to the reference capacitor C to eliminate the charge on the capacitor C. Then, a voltage obtained by superimposing the DC voltage V _th on the AC voltage is applied. The capacitor C has the same capacitance as that of the photoconductor having the reference film thickness, but the reference film thickness may be the film thickness of the photoconductor that has reached the end of its life.

Then, with the AC voltage applied to the capacitor C, the capacitor C is discharged to measure the DC current value I _th ′. The DC current I _th has a voltage value V _th ′ (V
_th = I _th ′ · R), amplified by the amplifier A, converted into a digital signal S _th ′ by the A / D converter 10 and sent to the CPU 11. And the memory 12
The S _th held at is updated to this S _th ′. After calibrating in this way, the film thickness of the photosensitive drum is measured, so that the value S _th ′ held in the memory 12 is measured immediately before, even if the amplification factor of the amplifier A changes due to temperature characteristics or the like. Therefore, the life of the photosensitive drum can be accurately measured with almost no influence. Further, since the high-voltage circuit 13 is also calibrated in the method of the present embodiment, it becomes possible to measure the life of the photosensitive drum with higher accuracy.

[0038]

The present invention has the above-described structure and action. When measuring the film thickness of the photoconductor, the current detection circuit is calibrated before the actual measurement is performed, so that the film thickness can be accurately measured. Therefore, it is possible to accurately inform the user of the replacement time of the photosensitive drum or the process cartridge.

Further, a means for generating a reference voltage value or a reference current value or a reference capacitor is provided, and the reference voltage or current is added to the current detection circuit immediately before the actual measurement of the film thickness of the photosensitive member. Since the actual measured film thickness of the photoconductor is compared with the output value of the current detection circuit at the time point, the film thickness is highly accurate even if the output value changes due to temperature characteristics in the current detection circuit. It is possible to detect.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a current detection circuit and a calibration unit according to the first embodiment.

FIG. 3 is a configuration diagram of a current detection circuit and a calibration unit according to the second embodiment.

FIG. 4 is a configuration diagram of a current detection circuit and a calibration unit according to the third embodiment.

FIG. 5 is a configuration diagram of a conventional image forming apparatus.

[Explanation of symbols]

 1 Photosensitive Drum (Photosensitive Member) 2 Roller Charger 10 A / D Converter 11 CPU (Control Means) 12 Memory (Storage Means) 13 High Voltage Circuit 14 Reference Voltage Generating Means 15 Reference DC Current Generating Means A Amplifier R Resistance C Capacitor

Claims (4)

[Claims] 1. A film is provided with a current detection circuit for measuring a value of a current flowing when a charged state of a photoconductor as an image carrier for forming an image is changed, and a film thickness of the photoconductor is measured from the detected current value. The image forming apparatus according to claim 1, further comprising: a calibrating unit that calibrates the current detection circuit, and a control unit that calibrates the current detection circuit before measuring the film thickness of the photoconductor. 2. The current detection circuit includes a conversion unit that converts a detected DC current value flowing through the photosensitive member into a voltage value, and an amplifier unit that receives the converted voltage value. The means includes a reference voltage generating means for inputting a reference voltage value obtained when measuring a reference film thickness of the photoconductor to the amplifier means, and the control means includes the amplifier means to which the reference voltage value is input. And a comparison means for comparing the reference output voltage value stored in the storage means with the actually measured output voltage value. The image forming apparatus according to claim 1. 3. The current detection circuit includes a conversion unit that converts the detected DC current flowing through the photoconductor into a voltage value.
An amplifier unit to which the converted voltage value is input is provided, and the calibration unit inputs a reference DC current value obtained when measuring a reference film thickness of the photoconductor to the conversion unit. A storage means for storing the output voltage value of the amplifier means to which the reference DC current value is input as a reference output voltage value; and the reference output voltage value stored in the storage means. The image forming apparatus according to claim 1, further comprising a comparison unit that compares an actually measured output voltage value. 4. The calibration means includes a reference capacitor having the same capacitance as that of a photoconductor having a reference film thickness, and the current detection circuit flows when changing the charging state of the reference capacitor. The control means includes a conversion means for converting the DC current value into a voltage value and an amplifier means for inputting the converted voltage value of the reference capacitor, and the control means for the amplifier means to which the voltage value of the reference capacitor is input. It is characterized by further comprising storage means for storing the output voltage value as a reference output voltage value and comparison means for comparing the reference output voltage value stored in the storage means with the actually measured output voltage value. The image forming apparatus according to claim 1.