JPH05346713A - Electrophotographic device - Google Patents

Abstract

PURPOSE:To control voltage only in order to compensate the lowering of the real copying sensitivity of an original image, to stably control it by a feedback system and to obtain a copied image having optimum density. CONSTITUTION:This device is provided with the feedback system calculating the duty ratio of a PWM signal for controlling the voltage of a copying lamp 3 or an image forming unit based on the sensor output value of a toner amount detecting sensor 54. It is provided with a master CPU 40 which stores a calculated duty ratio beta in a RAM 47, and controls the voltage of the lamp 3, etc., by using the duty ratio beta in the case the duty ratio beta is larger than the duty ratio alpha stored in the RAM 47. Therefore, the master CPU 40 controls the voltage of the copying lamp 3, etc., by using the duty ratio alpha in the case the sensor output value rises because of a factor other than the voltage of the lamp 3 and the duty ratio beta gets larger than the duty ratio alpha.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention PWMs the voltage of a copy lamp and an image forming device for changing the amount of toner on a photoconductor.
The present invention relates to an electrophotographic apparatus controlled by a signal.

[0002]

2. Description of the Related Art Generally, an electrophotographic apparatus transfers toner attached to an electrostatic latent image formed on a photoconductor by exposing a document image onto a transfer paper, heats and melts the transferred toner, and fixes the toner on the transfer paper. By doing so, a copied image is obtained. At this time, the density of the copied image has a close relationship with the amount of toner attached to the photoconductor, and this amount of toner is
The voltage can be arbitrarily adjusted by the voltage of a copy lamp and an image forming device such as a charger or a developing device.

Therefore, the conventional electrophotographic apparatus has a PWM
The voltage of the copy lamp and each of the image forming devices is formed by a voltage generating unit whose output voltage can be arbitrarily changed according to the duty ratio of the (Pulse Width Modulation) signal. The output voltage of the voltage generation unit is controlled by reading the latent image potential of the photoconductor or the toner image density of the toner patch using a toner amount detection sensor such as a potential sensor or an optical sensor. If it is lower than the value, it is judged that the toner amount is low,
This is performed by a feedback system that controls the output voltage by increasing the duty ratio of the PWM signal. And this feedback system
By controlling the voltage of the copy lamp and the voltage of each image forming device so that the read value matches the target value, the density of the copied image is stabilized.

The correction of the read value on the low density side of the toner image, which is so-called fog density correction, is performed by the contamination of the optical system such as the copy lamp and the reflecting mirror, the abrasion and deterioration of the photosensitive layer of the photoconductor, and the number of copies. This is performed in order to compensate for a decrease in the actual image pickup sensitivity of the original image due to an increase or a change over time. Therefore, the control on the low density side of the toner image by the feedback system is usually performed in the direction of increasing the duty ratio of the PWM signal to increase the output voltage of the voltage generating unit.

[0005]

However, in the above-mentioned conventional electrophotographic apparatus, the read value of the toner amount detection sensor on the low density side is, for example, a toner amount detection sensor failure, or toner due to eccentricity or uneven rotation of the photoconductor. The output voltage of the voltage generating unit is controlled by the above-mentioned feedback system even when the voltage rises contrary to the normal due to factors other than the voltage of the copy lamp and the image forming device such as image density unevenness. That is, the duty ratio of the PWM signal is reduced by the feedback system to control the output voltage of the voltage generating unit to be lowered, and the voltage of the copy lamp and each image forming device is adjusted so that the read value matches the predetermined target value. It is designed to be controlled. In this case, since the output voltage of the voltage generating unit is controlled by factors other than the voltage of the copy lamp and the image forming device, the stability of the control by the feedback system is lacking, and the copy image of the optimum density is obtained. You will not be able to get it.

Therefore, in the present invention, due to factors other than the voltage of the copy lamp and the image forming device, such as failure of the toner amount detection sensor, density unevenness of the toner image due to eccentricity of the photosensitive member and uneven rotation of the photosensitive member, the reverse of the normal state. It is an object of the present invention to provide an electrophotographic apparatus capable of performing a stable control by a feedback system and obtaining a copy image with an optimum density even when the temperature is rising.

[0007]

In order to solve the above-mentioned problems, the electrophotographic apparatus of the present invention uses the duty ratio of the PWM signal for controlling the voltages of the copy lamp and the image forming device as the sensor output of the toner amount detection sensor. In an electrophotographic apparatus having a feedback system that calculates based on a value, a storage unit that stores the duty ratio of the PWM signal and a duty ratio that is newly calculated based on the sensor output value are stored in the storage unit. When a value larger than the duty ratio is displayed, the newly calculated duty ratio is stored in the storage means, and the voltage of the copy lamp and the image forming device is controlled by the newly calculated duty ratio. When the calculated duty ratio does not show a value larger than the duty ratio stored in the storage means, In the duty ratio stored in the storage means it is characterized in that a control means for controlling the voltage of the copy lamp, and an image forming device.

[0008]

According to the above construction, the sensor output value of the toner amount detection sensor on the low density side is such that the toner amount detection sensor is out of order, and the copy lamp has uneven density of the toner image due to eccentricity or uneven rotation of the photoconductor. When the voltage rises contrary to the normal due to factors other than the voltage of the image forming device, the duty ratio newly calculated based on this sensor output value is higher than the duty ratio stored in the storage unit. Since it does not show a large value, the control unit does not use the newly calculated duty ratio, but instead uses the duty ratio stored in the storage unit to control the voltages of the copy lamp and the image forming device.

Therefore, the correction of the output voltage of the voltage generating unit based on the sensor output value on the low density side is performed by the contamination of the optical system such as the copy lamp and the reflecting mirror, the abrasion and deterioration of the photosensitive layer of the photoconductor, and the number of copies. Since it is done only to compensate for the decrease in the actual shooting sensitivity of the original image due to increase or change with time,
The feedback system enables stable control, and makes it possible to obtain a copy image with optimum density.

Also, the magnitude of the newly calculated duty ratio and the duty ratio stored in the storage means are compared by the control means, and the newly calculated duty ratio is compared with the duty ratio stored in the storage means. Also does not require a highly accurate sensor output value because the feedback system corrects the output voltage of the voltage generating unit only when the value also shows a large value. Therefore, even if the toner amount detection sensor is composed of an inexpensive sensor, the feedback system can stably control the output voltage of the voltage generation unit,
It is possible to simplify the structure and reduce the cost.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following will describe one embodiment of the present invention with reference to FIGS. In this embodiment, a copying machine will be described as an example of the electrophotographic apparatus.

As shown in FIG. 4, the copying machine as the electrophotographic apparatus according to the present embodiment has a transparent original placing table on the upper surface of the copying machine main body 1, and the original placing table is used for copying. An automatic document feeder 27 and a document cover 26 for supplying a target document onto the document table are provided. An optical system 2 is arranged below the document table. The optical system 2 includes a copy lamp 3 including a halogen lamp or the like.
And a plurality of reflecting mirrors 4, 5, 6, 7 and a zoom lens 8, which are installed on an optical system mounting table (not shown). And a plurality of reflecting mirrors 4, 5, 6, 7
Is a photoconductor 2 to be described later, which is light reflected from the original placed on the original table by the light emitted from the copy lamp 3.
1 and is arranged so as to expose the photoconductor 21 to light, as shown by the one-dot chain line, and the zoom lens 8 is
It has a function of refracting and condensing the reflected light so that the reflected light forms a clear image on the photoconductor 21.

A standard white plate 53, which is used at the time of forming a toner patch, which will be described later, is disposed outside the front end image area on the side of the optical system 2. Further, below the optical system 2, a cylindrical photoconductor 21 to which the above-mentioned reflected light is irradiated is disposed, and around the photoconductor 21, as is well known, a predetermined photoconductor 21 is provided. A charger 22 for applying a voltage to form an electrostatic latent image, a developing unit 23 for making toner visible on the electrostatic latent image so as to be visualized as a copy image, a transfer unit 24 for transferring the copy image onto a transfer paper, and a photoconductor. A static eliminator 25 that removes the residual charge of 21, a toner amount detection sensor 54, which will be described later, and the like are arranged at predetermined positions.

On the side where the transfer paper is supplied to the photosensitive member 21, there is provided a paper feed unit consisting of a registration roller 31 for setting the transfer paper supply timing and a plurality of paper feed cassettes capable of accommodating the transfer paper of each size. 30 are provided. Also,
On the side where the transfer paper is unloaded from the photoconductor 21, a belt-shaped transfer device 32 for placing and transferring the transfer paper, a fixing unit 33 for heating and melting the toner transferred to the transfer paper, and a copy image are displayed. A plurality of discharge trays 34 and the like on which the formed transfer sheets can be placed in units of a plurality of sheets are arranged. Further, below the photoconductor 21, the intermediate tray 36, the paper feed roller 38, and the reversing unit 3 which are used when performing double-sided copying or composite copying.
7 are disposed via the paper transport path 35.

As shown in FIG. 3, the copying machine described above has a master CPU 40 which also serves as a control device (control means) for a copy lamp and an image forming device, which will be described later, and a slave which controls the optical system 2 and the like. It is controlled by a control system having a CPU 41. Slave C
The PU 41 receives a signal from a rotary encoder (RE) 45 that detects the rotation speed of the motor 18 that drives the optical system mounting table and the like and a signal from a home position sensor (not shown) according to a program stored in advance in the ROM 44. The motor 18 via the driver 46
In addition to controlling the rotation of the sheet, a signal for instructing the timing of supplying the transfer paper to the photoconductor 21 is transmitted to the registration roller 31 of FIG.

The master CPU 40 has a built-in arithmetic unit for calculating the duty ratio of each PWM signal from the sensor output value described later. Further, for example, a charging unit 50, which constitutes an image forming device with the charger 22, The developing unit 23 which is an image forming device shown in FIG. 4, a copy lamp lighting circuit 43 for setting the light amount of the copy lamp 3, and the like are connected. The copy lamp lighting circuit 43 and the image forming device have a voltage generating unit such as the charging unit 50 described above.
It has an integrating circuit that outputs a DC voltage proportional to the duty ratio of the PWM signal. Therefore, as shown in FIG. 6, the output voltage of each of the copy lamp lighting circuit 43 and the image forming device is controlled by increasing or decreasing the duty ratio of each PWM signal output from the master CPU 40.

As shown in FIGS. 3 and 5, the master CPU 40 has an LED (light emitting diode).
A toner amount detecting sensor 54 having a light emitting element 51 such as a light receiving element 52 such as a photodiode or a phototransistor is also connected. The light emitting element 51 is connected to the output terminal of the master CPU 40 via a resistor 55, a NOT circuit 56, etc., and the master CPU 40 controls light emission and light extinction. The light receiving element 52 is connected to an analog port which is an input terminal of the master CPU 40 via an amplifier circuit 58 such as a voltage follower, and outputs a sensor output value proportional to the amount of received light.

The sensor output value is adjusted by the variable resistor 57 or the like so that the analog port of the master CPU 40 is not saturated, that is, within the upper and lower limit values of the analog port, and then input to the analog port of the master CPU 40. Then, an analog value is converted into a digital sensor output value by an A / D converter built in the master CPU 40. The duty ratio of each PWM signal is calculated from the sensor output value by the arithmetic unit built in the master CPU 40. When the sensor output value input to the analog port is not adjusted, the master CPU 40 determines that the toner amount detection sensor 54, the copy lamp lighting circuit 43, the image forming device, and the like have failed and, for example, turns on the maintenance lamp. An alarm operation such as turning on the light is performed. The toner amount detection sensor 54
May consist of a potential sensor.

The toner amount detecting sensor 54 is shown in FIG.
As shown in, the density of the toner patch 59 formed on the photoconductor 21 is read in the measurement mode such as the duty ratio correction routine, which is arranged near the photoconductor 21, and the sensor output value corresponding to this density is obtained. It is installed in.

Further, the master CPU 40 has a ROM
42 and RAM (storage means) 47 are connected,
In the ROM 42, a slave CPU command routine that outputs an operation signal or the like to the slave CPU 41 based on signals from various key switches or sensors (not shown), an initialization routine that sets an initial value on the low concentration side in the initial state, Various programs such as a duty ratio correction routine for controlling the duty ratio of the PWM signal output to the copy lamp lighting circuit 43 and each image forming device based on the sensor output value obtained from the toner amount detection sensor 54. Is written. In addition, RAM4
In 7, a duty ratio storage area used when executing the above-mentioned initialization routine and duty ratio correction routine is formed.

The operation of the copying machine having the above arrangement will be described.

First, after completion of assembly in the factory or replacement of parts such as the photoconductor 21 and the copy lamp 3, after the image quality of the copied image is adjusted, the initialization routine shown in FIG. 2 is executed. The duty ratio of each PWM signal on the low density side in the initial state is set.

That is, when the initialization routine is executed,
As shown in FIG. 4, the copy lamp 3, the reflecting mirror 4 and the like are moved to the outside of the front end image area, and a predetermined lamp voltage is applied to the copy lamp 3. The copy lamp 3 emits light toward the standard white plate 53 with an amount of light corresponding to the applied lamp voltage, and this light is reflected by the standard white plate 53 and then passes through the reflecting mirrors 4 to 7 to the photoconductor 21. The photosensitive layer located at the outermost periphery of is exposed to form an electrostatic latent image on the photoconductor 21. Then, the electrostatic latent image on the photoconductor 21 is made into a low-density toner patch by adhering the toner of the toner amount corresponding to the exposure amount when passing through the developing section 23 (S1).

As shown in FIG. 5, when the toner patch 59 is prepared, the light emitting element 5 is applied with a predetermined voltage and current.
The energization of No. 1 is started, and the toner patch 59 is irradiated with light having a light amount corresponding to this energization amount. The light applied to the toner patch 59 is received by the light receiving element 52.
Light receiving element 52 that receives the reflected light that is reflected in the direction
Outputs a sensor output value having a voltage corresponding to the amount of received light (S2). Then, this sensor output value is adjusted by the variable resistor 57 or the like so that the analog port of the master CPU 40 is not saturated, and then input to the analog port of the master CPU 40 (S3).

When the sensor output value is input to the analog port of the master CPU 40, it is determined whether the sensor output value is adjusted by the variable resistor 57 or the like so that the analog port is not saturated (S4). ). When it is determined that the sensor output value is adjusted, the analog value is converted to a digital sensor output value by the A / D converter built in the master CPU 40, and then the calculation built in the master CPU 40. The device calculates the duty ratio α of each PWM signal from the sensor output value (S5). Each calculated PWM
The duty ratio α of the signal is stored in the duty ratio storage area of the RAM 47 via the master CPU 40 (S
6).

On the other hand, if it is determined in S4 that the sensor output value is not adjusted, the master CPU 40
Toner amount detection sensor 54 and copy lamp lighting circuit 4
3. It is determined that the image forming device or the like has failed, and an alarm operation such as turning on a maintenance lamp is performed to prompt repair of the failed part (S7).

Next, when copying is performed by a copying machine, the duty ratio correction routine shown in FIG. 1 is executed prior to copying. When the duty ratio correction routine is executed, as shown in FIG. 4, the copy lamp 3, the reflecting mirror 4, etc. are moved to the outside of the front end image area, and a predetermined lamp voltage is applied to the copy lamp 3. The copy lamp 3 emits light toward the standard white plate 53 with an amount of light corresponding to the applied lamp voltage, and this light is reflected by the standard white plate 53 and then passes through the reflecting mirrors 4 to 7 to the photoconductor 21. To expose an electrostatic latent image on the photoconductor 21. Then, the electrostatic latent image on the photoconductor 21 is adhered when the toner of the toner amount corresponding to the exposure amount passes through the developing unit 23,
The toner patch has a low density (S11).

As shown in FIG. 5, when the toner patch 59 is formed, the light emitting element 5 is applied with a predetermined voltage and current.
The energization of No. 1 is started, and the toner patch 59 is irradiated with light having a light amount corresponding to this energization amount. The light applied to the toner patch 59 is received by the light receiving element 52.
Light receiving element 52 that receives the reflected light that is reflected in the direction
Outputs a sensor output value of a voltage corresponding to the amount of received light (S12). Then, this sensor output value is adjusted by the variable resistor 57 or the like so that the analog port of the master CPU 40 is not saturated, and then input to the analog port of the master CPU 40 (S13).

When the sensor output value is input to the analog port of the master CPU 40, it is determined whether the sensor output value is adjusted by the variable resistor 57 or the like so that the analog port is not saturated (S14). ). When it is determined that the sensor output value is adjusted, the analog value is converted to a digital sensor output value by the A / D converter built in the master CPU 40, and then the calculation built in the master CPU 40. The device calculates the duty ratio β of each PWM signal from the sensor output value (S15). When the duty ratio β of each PWM signal is calculated, this duty ratio β
Is determined to be larger than the duty ratio α stored by the above-mentioned initialization routine (S16).

When it is determined that the duty ratio β is larger than the duty ratio α, that is, when the density of the toner patch 59 formed on the photoconductor 21 is determined to be lower than the initial setting value. , Instead of the duty ratio α stored by the initialization routine, the newly calculated duty ratio β is changed to RA via the master CPU 40.
It is stored in the duty ratio storage area of M47 (S1
7). Then, thereafter, until the duty ratio correction routine is newly executed, the master CPU 40 controls the voltage of the copy lamp 3 and each image forming device by the feedback system using the duty ratio β. As described above, when the duty ratio of the PWM signal is increased from α to β, the DC voltage output from the voltage generation unit included in the copy lamp lighting circuit 43 and the image forming device is proportionally increased. The increase in the DC voltage increases the light amount of the light emitted from the copy lamp 3 and the charge amount of the photoconductor 21, and increases the amount of adhered toner (toner amount) supplied from the developing unit 23. Therefore, the toner amount of the photoconductor 21, that is, the density of the copied image is stabilized by the feedback system using the duty ratio β.

In step S17, the duty ratio β is stored in the duty ratio storage area of the RAM 47 instead of the duty ratio α. Therefore, for example, a new duty ratio correction routine is executed and a new duty ratio γ is executed.
Is calculated, this duty ratio γ is compared with the duty ratio β in S16.

On the other hand, if it is determined in S16 that the duty ratio β is not greater than the duty ratio α,
That is, when it is determined that the density of the toner patch 59 formed on the photoconductor 21 is higher than the initial setting value, the newly calculated duty ratio β is discarded (S18). After that, until the duty ratio correction routine is newly executed, the master CPU 40 calls the duty ratio α stored in the duty ratio storage area of the RAM 47, and copies it by the feedback system using this duty ratio α. The voltage of the lamp 3 and each image forming device is controlled to stabilize the toner amount of the photoconductor 21, that is, the density of the copied image.

If it is determined in S14 that the sensor output value has not been adjusted, the master CPU
40 determines that the toner amount detection sensor 54 and the like are out of order, performs an alarm operation such as turning on a maintenance lamp, and prompts repair of the failed portion (S19).

When the duty ratio is corrected by the above duty ratio correction routine and the voltage of the copy lamp 3 and each image forming device is set by this duty ratio,
Subsequently, the copy mode is executed, and the photosensitive layer of the photoconductor 21 is charged to a predetermined potential by the charger 22 which is an image forming device, as shown in FIG. Then, by moving the optical system table on which the optical system 2 is installed in the A direction, the originals covered by the original cover 26 are sequentially irradiated by the copy lamp 3 from the leading end, and the reflected light from the originals is reflected by the optical system. The photoconductor 21 is exposed to light via 2 to form an electrostatic latent image on the photoconductive layer of the photoconductor 21.

When copying is performed using the automatic document feeder 27 arranged above the copying machine main body 1, the drums 29a and 29b and the like are used in the document feeding path 28 of the automatic document feeder 27. While the original is being conveyed, the original is sequentially irradiated from the leading end portion by the copy lamp 3 through slits (not shown) provided at two positions of the original conveying path 28, and the reflected light from the original is reflected by the photoconductor 2 in the same manner as described above.
Exposed to 1.

When an electrostatic latent image is formed on the photosensitive layer of the photoconductor 21, subsequently, the toner supplied from the developing unit 23 adheres to the electrostatic latent image to form a copy image. Thereafter, a transfer sheet (not shown) is sent to the registration roller 31 from the paper supply unit 30 including a plurality of paper supply cassettes, and is temporarily stopped by the registration roller 31 if necessary, and then the photoconductor 21 is moved at a predetermined timing. Is supplied to.

The copy image on the photoconductor 21 is transferred by the transfer device 24 onto the supplied transfer paper. After that, the transfer paper is peeled off from the photoconductor 21 and conveyed to the fixing unit 33 by the conveyance device 32, where the copy image is fixed on the transfer paper, and if it is a single-sided copy, the discharge tray 34 is used as it is.
Is discharged to. On the other hand, in the case of synthetic copying and double-sided copying, the transfer paper discharged from the fixing unit 33 is the paper transport path 35.
Sent to the intermediate tray 36 if it is a composite copy.
On the other hand, in the case of double-sided copying, the front and back sides are reversed by the reversing unit 37, and then the sheets are discharged to the intermediate tray 36.
Then, after a plurality of transfer papers are accumulated in the intermediate tray 36, the transfer papers on the intermediate tray 36 are sequentially fed from the uppermost one by the paper feed roller 38 and sent to the photoconductor 21.
Copying will continue.

As described above, in the copying machine of this embodiment, the sensor output value of the toner amount detection sensor 54 on the low density side is, for example, a toner amount detection sensor 54 failure, or toner due to eccentricity or uneven rotation of the photoconductor 21. In the case where the voltage is rising contrary to the normal due to factors other than the voltage of the copy lamp 3 and the image forming device such as image density unevenness, the duty ratio β newly calculated based on this sensor output value is RA.
The master CP does not show a value larger than the duty ratio α stored in the duty ratio storage area of M47.
U40 discards the newly calculated duty ratio β and instead controls the voltage of the copy lamp 3 and the image forming device by using the duty ratio α stored in the duty ratio storage area of the RAM 47.

Therefore, the correction of the output voltage of the voltage generating unit based on the sensor output value on the low density side is performed by the dirt on the optical system 2 such as the copy lamp 3 and the reflecting mirrors 4 to 7, the photoconductor 21.
This is done only to compensate for the wear and deterioration of the photosensitive layer, and the decrease in the actual image pickup sensitivity of the original image due to the increase in the number of copies and the change over time, etc., so stable control can be performed by the feedback system, and the optimum density It is possible to obtain a copy image.

In controlling the output voltage of the voltage generating unit by the above feedback system, the RAM 47 is used.
It is performed by comparing the magnitude of the duty ratio α stored in the duty ratio storage area of the and the newly calculated duty ratio β with the duty ratio correction routine.
Does not require highly accurate sensor output values. Therefore, even if the toner amount detection sensor 54 is composed of an inexpensive sensor,
The feedback system can perform stable control of the output voltage of the voltage generating unit, which simplifies the structure and reduces the cost.

In the above duty ratio correction routine, the duty ratio β of each PWM signal is calculated from the sensor output value input from the light receiving element 52, and this duty ratio β and the duty ratio storage area of the RAM 47 are stored. Although the duty ratio is corrected by comparing the magnitude with the duty ratio α that has been set, the present invention is not limited to this. That is, in the initialization routine, the light receiving element 5
After converting the sensor output value of analog value input from 2 into the sensor output value a of digital value, this sensor output value a is stored in the storage area of the RAM 47, and in the duty ratio correction routine, the newly obtained sensor The duty ratio may be corrected by comparing the output value b with the sensor output value a stored in the storage area of the RAM 47. In this case, when it is determined that the sensor output value b is larger than the sensor output value a, the duty ratio of each PWM signal is calculated from the sensor output value b, while the sensor output value b is calculated as the sensor output value b. When it is determined that the value is not larger than the value a, the duty ratio of each PWM signal may be calculated from the sensor output value a.

[0042]

As described above, the electrophotographic apparatus of the present invention has the function of controlling the voltage of the copy lamp and the image forming device.
The present invention has a feedback system for calculating the duty ratio of the WM signal based on the sensor output value of the toner amount detection sensor, and a storage means for storing the duty ratio of the PWM signal, and a new one based on the sensor output value. When the calculated duty ratio shows a value larger than the duty ratio stored in the storage means, the newly calculated duty ratio is stored in the storage means, and the copy is performed with the newly calculated duty ratio. While controlling the voltage of the lamp and the image forming device, when the newly calculated duty ratio does not show a value larger than the duty ratio stored in the storage means, the above-mentioned copy is performed with the duty ratio stored in the storage means. And a control means for controlling the voltage of the lamp and the image forming device.

As a result, the sensor output value of the toner amount detection sensor on the low density side is, for example, a failure of the toner amount detection sensor, or a copy lamp or image forming device such as toner image density unevenness due to eccentricity or uneven rotation of the photoconductor. When the voltage rises contrary to the normal due to factors other than the voltage of, the duty ratio newly calculated based on this sensor output value shows a value larger than the duty ratio stored in the storage means. Therefore, the control unit can control the voltages of the copy lamp and the image forming device by using the duty ratio stored in the storage unit instead of using the newly calculated duty ratio.

Therefore, the correction of the output voltage of the voltage generating unit based on the sensor output value on the low density side is performed by the contamination of the optical system such as the copy lamp and the reflecting mirror, the abrasion and deterioration of the photosensitive layer of the photoconductor, and the number of copies. Since it is done only to compensate for the decrease in the actual shooting sensitivity of the original image due to increase or change with time,
With the feedback system, stable control can be performed, and it is possible to obtain a copy image with an optimum density.

The control means compares the magnitude of the newly calculated duty ratio with the duty ratio stored in the storage means, and the newly calculated duty ratio is calculated from the duty ratio stored in the storage means. Also does not require a highly accurate sensor output value because the feedback system corrects the output voltage of the voltage generating unit only when the value also shows a large value. Therefore, even if the toner amount detection sensor is composed of an inexpensive sensor, the feedback system can stably control the output voltage of the voltage generation unit,
It is possible to simplify the structure and reduce the cost.

[Brief description of drawings]

FIG. 1 is a flowchart showing a duty ratio correction routine in a copying machine which is an electrophotographic apparatus according to an exemplary embodiment of the present invention.

FIG. 2 is a flowchart showing an initial setting routine.

FIG. 3 is a block diagram of a copying machine showing an embodiment of the present invention.

FIG. 4 is a schematic configuration diagram of a copying machine.

FIG. 5 is a circuit diagram of a toner amount detection sensor.

FIG. 6 is an explanatory diagram of a duty ratio of a PWM signal.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Copier main body 3 Copy lamp 21 Photoconductor 22 Charging device (image forming device) 23 Developing unit (image forming device) 40 Master CPU (control means) 41 Slave CPU 43 Copy lamp lighting circuit 44 ROM 47 RAM (storage means) 50 Charging unit 51 Light emitting element 52 Light receiving element 53 Standard white plate 54 Toner amount detection sensor

Claims (1)

[Claims] 1. An electrophotographic apparatus having a feedback system for calculating a duty ratio of a PWM signal for controlling a voltage of a copy lamp and an image forming device based on a sensor output value of a toner amount detection sensor. Storage means for storing the ratio,
When the duty ratio newly calculated based on the sensor output value shows a value larger than the duty ratio stored in the storage means, the newly calculated duty ratio is stored in the storage means and The voltage of the copy lamp and the image forming device is controlled by the calculated duty ratio, and when the newly calculated duty ratio does not show a value larger than the duty ratio stored in the storage means, it is stored in the storage means. An electrophotographic apparatus, comprising: a control unit that controls the voltage of the copy lamp and the image forming device with a specified duty ratio.