JP2000075617A - Electrophotographic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely control toner replenishment, to form a proper-density image and to prevent an undesirable phenomenon such as toner splash by finding the stop time and the operation time of a developing device and correcting the control of a toner replenishment device by a control means, based on the stop time and the operation time. SOLUTION: The standstill state of a developer, that means, time in the stop state of a developing unit 20 is calculated by considering the characteristic of an L sensor 40. Based on the calculated time in a stop state of the unit 20, the operation relation of a toner replenishment means with respect to the output of the sensor 40 is corrected. Then, when image forming is started and the unit 20 is operated, the stop state of the unit 20 is interrupted, that means, the progress of the stop time is stopped. Since the developer is stirred by this action, there is the function that the stop time is shortened. Then, the operation of the unit 20 is detected and the stop time and the characteristic recovery time of the unit 20 are calculated from the detected result by a control part. Then, the control part performs the correction based on the stop time and the characteristic recovery time of the unit 20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic apparatus, and more particularly, to control of a toner replenishing device for replenishing a developing device with toner. The electrophotographic apparatus of the present invention is used for a copying machine, a facsimile, a printer, and the like.

[0002]

2. Description of the Related Art A toner replenishing device in an electrophotographic apparatus is configured to always supply an image having an appropriate density and to replenish toner without causing toner scattering. For this purpose, it is required to properly replenish the toner consumed by the image formation, but in order to detect the amount consumed by the image formation, the toner replenishing device needs to detect the toner concentration of the developer. A density sensor is provided, and as the toner density sensor, a sensor that detects a change in toner density by detecting a change in magnetic permeability of a developer (hereinafter, referred to as an L detection sensor) is widely used. .

[0003] The magnetic permeability of a developer depends on the density of a magnetic material in the developer, and when the toner concentration is high, the carrier carrier, which is a magnetic material, has a low concentration and the magnetic permeability decreases. The magnetic permeability also changes when the density of the magnetic material in the developer changes due to factors other than the toner concentration. That is, when the developer is stirred, the density of the developer decreases and the magnetic permeability decreases. Conversely, when the developer is allowed to stand for a long period of time, the density of the developer increases, and as a result, the density of the magnetic material increases and the magnetic permeability increases.

Therefore, the correspondence between the output of the L detection sensor and the toner density as the developing performance is different between the operating state of the electrophotographic apparatus in which the developer is agitated and the stopped state of the electrophotographic apparatus in which the developer is left stationary. The difference is that some correction is required in toner supply using the L detection sensor.

As such a correction, Japanese Patent Laid-Open Publication No. Sho.
In Japanese Patent No. 967, a correction is made such that the level of a threshold value for outputting a toner replenishment signal is increased when the machine is started. Japanese Patent Application Laid-Open No. Sho 59-202474 does not measure the toner concentration of the stored developer.

[0006]

By the way, copiers called so-called low-speed machines of 30 sheets per minute or less are often installed and used in small offices or rooms, and a large number of copies are continuously made. Often, a small copy is taken at rest intervals instead of being taken. In such a mode of use in a low-speed machine, the developer in the copying machine operates with the relatively long standing time, and the developer in the developing device operates with the relatively long standing time. And the stirring is repeated. In such a use situation, the stirring time is also long and short, the density of the developer does not sufficiently decrease, and the copying operation often ends in a process in which the detection result by the L detection sensor does not become stable.

As described above, the developer in a low-speed machine often does not have a constant density at the end of operation of the machine, and often does not have a constant density at the start of operation of the machine.

Therefore, when the toner supply control technology described in Japanese Patent Application Laid-Open No. 64-40967 is applied to a low-speed machine of about 30 sheets per minute or less, proper supply is not performed, and When the toner concentration becomes excessive, fogging and toner scattering easily occur.

This is clear from the following experimental results. FIG. 1A shows the transition of the toner density with respect to the copy amount as a design value, and FIG. 1B shows the toner supply control according to the prior art described in the above-mentioned Japanese Patent Application Laid-Open No. 64-40967. 3 shows the transition of the toner density with respect to the actual copy amount when the image is adopted. As shown,
With a design value set as an ideal value for forming an image with an appropriate density, the toner density changes from an initial value of 5.0% at a copy amount of 0 to 4.0% at the time of copying 20,000 sheets. In actual copying, about 5.3% of the initial value to about 4.4% when copying 20,000 sheets
, Indicating that the toner density is higher than the designed value. By maintaining the toner concentration at a high value, fogging is likely to occur, and toner scattering and toner contamination are likely to occur.

As described above, the erroneous control caused by the measurement error of the L detection sensor caused in the toner replenishment control using the L detection sensor is described in Japanese Patent Application Laid-Open No. Sho.
Although there is a correction method described in Japanese Patent Application Laid-Open No. 967, it has been found that correction is not sufficient even with this correction method, erroneous control is inevitable, and causes fog and the like. This erroneous control is particularly remarkable in a low-speed machine.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problem in the prior art of toner supply control using an L detection sensor. An object of the present invention is to provide an electrophotographic apparatus which forms an image and prevents undesirable phenomena such as toner scattering.

[0012]

The object of the present invention is as follows.
Operation detecting means for detecting the operation of the developer stirring means in the developing device; toner replenishing means for replenishing the developing device with toner; and toner for detecting the toner density of the developer by detecting the magnetic permeability of the developer. An electrophotographic apparatus comprising: a density detecting unit; and a control unit that controls the toner replenishing unit based on an output of the toner density detecting unit.
The control means determines a stop time and an operation time of the developing device from an output of the operation detection means, and corrects the control by the control means of the toner replenishing device based on the stop time and the operation time. An electrophotographic apparatus,
Achieved by

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (1) Electrophotographic apparatus An embodiment in which the present invention is applied to a copying machine will be described with reference to FIGS. FIG. 2 is a sectional view of a copying machine according to an embodiment of the present invention, and FIG. 3 is a block diagram of the copying machine.

A charger 11, a developing unit 20, a transfer unit 16, a separator 17 and a cleaning device 18 are arranged around the photosensitive drum 10 which rotates clockwise as indicated by an arrow. The toner image is formed on the peripheral surface of the photoreceptor drum 10 by the charging by the charger 11, the imagewise exposure by the exposure light 13 from the light source such as the semiconductor laser, and the development by the developing device 20 according to the rotation in the arrow direction of FIG. .

The toner image on the peripheral surface of the photosensitive drum 10 is transferred onto a recording sheet by a transfer unit 16. Reference numeral 12 denotes a light source for uniformly irradiating the photoconductor drum 10 to erase the history of the photoconductor drum 10, reference numeral 14 denotes an erasing light source for erasing unnecessary charges of the charged photoconductor drum 10, and reference numerals 15A and 15B denote recording. A transport roller that transports the paper between the transfer device 16 and the photosensitive drum 10.

The developing device 20 has a magnet inside, and has a developing sleeve 23 for transporting the developer to the developing area, an impeller 24 for supplying the developer to the developing sleeve 23, and an axially transporting developer. Transfer screw 2 to be supplied to impeller 24
7, 28. The conveying screws 27 and 28 rotate as indicated by arrows, convey the developer in the axial directions opposite to each other, stir the developer, and uniformly mix the toner in the developer. An L detection sensor 40 that detects the toner concentration of the developer is provided below the transport screw 28 on the bottom plate of the developing device 20. The L detection sensor 40 detects the toner concentration of the developer from the magnetic permeability of the developer, and a known sensor can be used.

In FIG. 3, a CPU serving as a control unit operates based on input signals from a main switch MS, a clock CL and an L detection sensor TS to control the toner replenishing means SS. The control unit CPU also controls the operation of the developing device DV. The developing device DV is a general term for the developing sleeve 23, the impeller 24, the conveying screws 27 and 28, and the motor (not shown) for driving them in the developing device 20 in FIG. The control unit CPU outputs operation command signals to the developing device DV to operate them, and together with such control, recognizes the time during which the operation command signal is output as the characteristic recovery time representing the operation time. In addition, an operation of recognizing a time during which the operation command signal is not output as a stop time is also performed.

In the present embodiment, the developing sleeve 23, the impeller 24, and the conveying screws 27 and 28 are driven by the same motor, but are driven by different motors, and the control unit CPU controls these motors. May be controlled separately.

The electrophotographic apparatus according to the present embodiment has a stop memory M1 and an operation memory M2. Stop memory 1
Is a non-volatile memory that stores the stop time, and the operation memory M2 is a non-volatile memory that stores the characteristic recovery time, as described later.

The output of the L detection sensor TS is discriminated by the control unit CPU, and when the output value exceeds a predetermined value, a toner supply command signal is output from the control unit CPU to the toner supply device SS. Also, the output of the L detection sensor TS is
It is controlled by controlling the control voltage Vc by the PU. That is, the control voltage Vc is a voltage for controlling the output value of the L detection sensor TS. By changing the control voltage Vc, the output of the L detection sensor TS for a certain toner density value changes. Therefore, the correspondence between the output of the L detection sensor TS and the threshold value is changed by the control of the control unit CPU. This control is control performed according to the operation state of the developing device, as described later.

(2) Principle of Toner Replenishment Control in the Present Embodiment In the control of toner replenishment in the present embodiment, various concepts such as a stop time, a developer characteristic change amount, and a characteristic recovery time are used. Before describing the toner supply control, these concepts will be described.

A. Stop Time The stop time indicates the length of time during which the developing device DV, particularly the impeller 24 and the conveying screws 27 and 28 for stirring the developer, are stopped. The power of the copier is turned on, but not in the image forming state, but in a standby state, so that not only when the developing device DV is stopped, but also when the power is turned off and the copier, in other words, the developing device The stop time when the DV is stopped is also counted as the stop time.

The stop time acts on the developer in a direction to increase its density. On the other hand, when the developing device DV is operating, the developer is agitated, so that the operating time of the developing device DV acts on the developer in a direction to decrease the density. Therefore, the operation of the developing device DV is introduced into the calculation of the stop time not only to stop the stop time counting but also to reduce the stop time.

The stop time is counted by the control unit CPU when the power is on. When the power is off, the count is counted by a clock provided in the copying machine. When the power is turned on and the control unit CPU operates, the count value of the clock is read by the control unit CPU. The counting of the stop time when the image forming apparatus is not provided with a clock will be described later.

The stop time is stored in a stop memory M1 constituted by a nonvolatile memory provided in the control unit CPU.

B. Amount of change in developer characteristics A long period of time, for example, when the developer is kept still for 1000 seconds or more, the characteristics of the developer, that is, the amount corresponding to the density is used as a reference of the characteristics, and the amount of change in the characteristics is 0. . As the stop time becomes shorter, the characteristic change amount increases.

As shown in FIG. 4, the developer characteristic change amount is
For example, it takes a value of 0 at a specific stop time of 1000 seconds, and is a quantity that is negatively proportional to the logarithm of the stop time of the developing device DV.

C. As shown in FIG. 5, the characteristic recovery time is an amount that is directly proportional to the amount of change in the developer characteristic, and is an amount corresponding to the operation time of the developing device DV20, in other words, the impeller 24 and the transport screws 27 and 28.

The characteristic recovery time corresponds to, for example, a direct proportional relationship with the operation time of the developing device DV. As the operation time of the developing device DV increases, the characteristic recovery time increases. The specific relationship between the two is determined by the developing device D
It varies variously depending on the structure of V and the developer used. The characteristic recovery time is qualitatively the time required for the characteristics of the developer changed by stirring to recover to the reference characteristics.

The stop time and the characteristic recovery time are mutually converted via the developer characteristic change amount. From the relationship between the characteristic recovery time and the operation time as described above and the relationship between the stop time, the amount of change in the developer characteristic, and the characteristic recovery time shown in FIGS. 4 and 5, the stop time and the operation time are determined from the long stop time. Short operating times are derived and are interconverted in that short operating times lead to long operating times.

Next, the principle of toner supply control in this embodiment will be described.

A change in the relationship between the toner density detected by the L detection sensor and the true toner density, that is, the relationship between the toner content (weight) in the developer, was received from the state in which the developer was allowed to stand. Related to the amount of agitation. Therefore, if the output of the L detection sensor is corrected based on the amount of agitation that the toner has received after being left still for a long time, it is possible to detect the toner concentration without error. If toner replenishment control is performed based on the detected value thus corrected, proper toner replenishment can be performed, and a high-quality image can be stably formed.

In consideration of such characteristics of the L detection sensor,
The state in which the developer is stationary, that is, the time during which the developing device DV is stopped is calculated, and the calculated developing device D
The correspondence between the output of the L detection sensor and the operation of the toner supply unit is corrected based on the stop time of V.

When the image forming is started and the developing device DV is operated, the operation of the developing device DV means that the stop state of the developing device DV is interrupted, that is, the progress of the stop time is stopped. However, since the developer is agitated by this operation, there is an effect of shortening the stop time. If the operation time is short, the amount of reduction in the stop time is small,
If it is long, the reduction amount of the stop time will be large.

As described above, in the control of toner replenishment using the L detection sensor, the operation of the developing unit DV is detected, and the stop time and the characteristic recovery time of the developing unit DV are calculated from the detection result. By performing the correction based on the time and the characteristic recovery time, appropriate toner replenishment is performed.

The stop time and the characteristic recovery time of the developing device DV are as follows.
It is directly counted from the measurement of the stop time and the operation time of the developing device DV, and is calculated based on the characteristic of the developer at the time of calculating the stop time and the characteristic recovery time, that is, the amount of change in the developer characteristic.

(3) Calculation of Stop Time of Developing Unit DV and Characteristic Recovery Time of Developer FIG. 6 is a flowchart showing a program for calculating the stop time and the characteristic recovery time. The calculation of the stop time and the characteristic recovery time shown in FIG.
This is performed in an interrupt routine interrupted every msec.

First, it is determined whether or not the developer is being stirred (S1). This determination is for judging whether to calculate the stop time or the characteristic recovery time by checking whether the developing device DV is stopped or operating, and the control unit CPU operates the developing device DV. When a command signal is being output, YE
S, NO when not outputting.

It is determined that the operation is in progress, and if YES, the routine enters a routine for calculating the characteristic recovery time.

Next, it is determined whether or not the stop flag is ON (S10). This step S10 is a step for checking the history of the developing device DV, and the copying machine, in other words, the developing device DV is in a stopped state. Sometimes, the answer is YES, and when it is in the operating state, the answer is NO. If NO, the operation is continued, and the operation counter counts +1. This count value is stored in the operation memory M2. At the time of YES, since the developing device DV is operating,
The stop flag is turned off and the drive flag is turned on (S12, S13).

Next, the control unit CPU reads the value of the stop memory M1, that is, the stop time. Then, the amount of change in the developer characteristics is calculated from the read stop time. The relationship between the amount of change in the developer property with respect to the stop time is shown in the graph of FIG. 4 and is written in the LUT provided in the control unit CPU. By reading from this, the amount of change in the developer property is calculated ( S14). For example, the stop time is T1s
If ec, the developer characteristic change amount is V1 (V).

Next, the characteristic recovery time is calculated from the developer characteristic change amount (S15). The relationship of the characteristic recovery time to the amount of change in the developer characteristic is shown in FIG. 5, and is read from the LUT in the same manner as described above. For example, a characteristic recovery time of a value of R1 is obtained from the developer characteristic change amount of V1 (V).

The obtained characteristic recovery time is stored in the operation memory M2 (S16).

If it is determined in step S1 that the developer is not being agitated, and if the drive flag is not ON (S20), since the developing device DV is being stopped, the stop flag is turned ON and the stop counter counts +1. (S21, S22).

When the drive flag is ON, the drive flag is turned off (S23), and the characteristic change recovery time is read from the value in the operation memory M2 (S24).

The developer characteristic change amount is calculated from the characteristic change recovery time according to FIG. 5 (S25), and the stop time is calculated from the developer characteristic change amount according to FIG. 4 (S26).
The calculated stop time is stored in the stop memory M1 (S
27).

When the main power of the copying machine is turned on, that is, the main switch is turned on and the control unit CPU is operating, the stop time of the developing unit DV is shown in FIG. Is calculated.
On the other hand, the stop time of the developing unit DV while the main switch is turned off and the control unit CPU operates is measured by a clock (not shown) provided in the copying machine. Then, when the main power is turned on and the control unit CPU operates, the time measured by the clock is read.

When the above-mentioned clock is not provided in the copying machine, the stop time is calculated by the process shown in FIG. When the main switch is turned on, the stop flag is turned on (S41), and it is specified that the copying machine is in the stopped state. Next, in S42, the temperature in the fixing device is read. The temperature inside the fixing device is measured by a temperature sensor (not shown) provided for controlling the fixing temperature. The stop time is calculated from the read fixing temperature using the heat release time constant (S43). The calculation of the stop time from the temperature of the fixing device is supported by the following theory.

In the fixing device, when the main switch of the copying machine is turned off, the power of the heating source is turned off. As a result, the temperature is reduced by the heat radiation time constant peculiar to each fixing device. Therefore, the temperature in the fixing device is specified by the elapsed time from the time when the main switch is turned off and the heat radiation time constant, and the time elapsed from the time when the main switch is turned off is specified by measuring the temperature.

(4) Control of toner replenishment Control of toner replenishment in the present embodiment is periodically performed during the operation of the copying machine, such as once for each image formation. The toner supply control is performed according to the flowchart of FIG.

At S30 in FIG. 7, the characteristic recovery time is read from the operation memory M2. The correction amount of the control voltage Vc for the characteristic recovery time is also stored in the LUT provided in the control unit CPU, and the correction amount Vc of the control voltage Vc is calculated from this LUT in S31 (S32). Similarly, the control voltage Vc is obtained from the correction amount, and the toner supply control is performed (S34, S35).

The toner replenishment is performed by driving the toner replenishing device SS according to a toner replenishment command signal from the control unit CPU when the output of the toner density detecting means TS exceeds a predetermined threshold value. The toner density detecting means is configured so that the output level of the toner density detecting means TS can be changed by controlling the control voltage Vc, and the control voltage Vc can be changed to, for example, 64 levels.

In step S34 in FIG. 7, the control voltage Vc is set to one of 64 levels.

Incidentally, such a toner concentration detecting means TS
It is also possible to perform a correction for changing the threshold value instead of the correction for changing the control voltage Vc.

As described above, the control of the control voltage Vc of the L detection sensor TS is obtained from the calculation based on the characteristic recovery time. However, it can be said that this control is based on the stop time. That is, FIG.
As can be seen, the stop time and the characteristic recovery time are mutually converted via the developer characteristic change amount. If the characteristic recovery time increases, the stop time decreases.If the characteristic recovery time decreases, the stop time decreases. Is related to say that increases.

FIG. 1C shows the transition of the toner concentration of the developer in the developing device according to the toner supply control described above with respect to the copy volume of the copying machine.

As shown in FIG. 1C, the toner concentration in the present embodiment is from the initial value of about 5.0% to 20%.
It changes to about 3.9% at the time of copying 000 sheets, and almost coincides with the design value shown in FIG.

It is illuminated that there is almost no control deviation as compared with the conventional example shown in FIG.

Further, in the conventional example shown in FIG. 1B, the toner density greatly fluctuates at each copy as indicated by the deep valley of the curve, whereas in the present embodiment,
The valleys and peaks are small, and the fluctuation of the toner density during each copy is small.

The correspondence between the formed image density and the toner density changes depending on the developing performance of the developer. Even if the toner density is the same, the obtained image density will be different due to the difference in the developing performance of the developer.Therefore, it is necessary to change the toner density in accordance with the difference in the developing performance. Correction is needed.

Examples of changes in the developing performance include deterioration of the developer, changes in environmental temperature, changes in environmental humidity, and the like.

In the present embodiment, the correction of the toner supply control for such a change in the developing performance of the developer is performed.

The deterioration of the developer is caused by the stress applied to the developer.
Is added to the developer by the rotation of. Therefore, the actual state of the deterioration degree of the developer can be substantially grasped by integrating the rotation of the developing sleeve 23. The control unit CPU calculates the degree of deterioration of the developer by integrating the time during which the operation command signal of the developing device DV is output.

Incidentally, the degree of stirring of the developer which affects the density of the developer corresponds to the rotation of the conveying screws 27 and 28. Therefore, the control unit CPU detects the operation of the developing device and the degree of deterioration of the developer from the output of the operation command signal of the developing device DV.

In this embodiment, the developing sleeve 2
3 and the transport screws 27 and 28 are driven by the same motor, but they may be configured to be driven by separate motors. In such a case,
The control unit CPU separately controls each motor, and detects the operation of the developing device and the degree of deterioration of the developer from each operation command signal.

A temperature sensor and a humidity sensor are provided in the electrophotographic apparatus shown in FIG. 2 to detect the environmental temperature and correct toner supply control.

The above-described various corrections for the above-described various toner replenishment controls are performed by the above-described correction, that is, by changing the control voltage Vc that changes the output of the L detection sensor or changing the threshold value. be able to.

[0068]

According to the present invention, erroneous control in toner replenishment control using the L detection sensor is prevented, proper toner replenishment control is performed, an image having a proper density is obtained, and toner scattering is prevented.

[Brief description of the drawings]

FIG. 1 is a graph showing a change in toner density with respect to a copy amount in a conventional technique and an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a copying machine according to an embodiment of the present invention.

FIG. 3 is a block diagram of a control system of the copying machine shown in FIG.

FIG. 4 is a graph showing a relationship between a stop time and an amount of change in developer characteristics.

FIG. 5 is a graph showing a relationship between a developer characteristic change amount and a characteristic recovery time.

FIG. 6 is a flowchart of a process for calculating a stop time and a characteristic recovery time.

FIG. 7 is a flowchart illustrating a toner supply control process.

FIG. 8 is a flowchart illustrating a process of calculating a stop time.

[Explanation of symbols]

 CPU control unit M1, M2 Memory TS, 40 L detection sensor SS Toner replenishing means 20, DV developer

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H027 DA11 DA14 DA31 DA39 DA40 DA45 DD02 DD07 DE04 DE09 ED08 ED10 EE06 EF06 EG04 2H077 AB02 AB14 AB15 AC02 AC03 AD06 DA10 DA18 DA20 DA24 DA42 DA52 DA78 DB02 DB22 EA13

Claims (13)

[Claims] An operation detecting unit for detecting an operation of a developer stirring unit in a developing device, a toner replenishing unit for replenishing toner to the developing device, and a toner of the developer by detecting a magnetic permeability of the developer. An electrophotographic apparatus comprising: a toner density detecting unit for detecting a density; and a control unit for controlling the toner replenishing unit based on an output of the toner density detecting unit. An electrophotographic apparatus wherein a stop time and an operation time of the apparatus are obtained, and the control by the control unit of the toner replenishing device is corrected based on the stop time and the operation time. 2. The electrophotographic apparatus according to claim 1, wherein the stop time and the operation time are correlated. 3. The method according to claim 1, wherein the stop time and the operation time are related to each other such that when the stop time increases, the operation time decreases. Electrophotographic equipment. 4. The electrophotographic apparatus according to claim 1, wherein the stop time and the operation time are related to each other via a parameter representing a characteristic of the developer. 5. The electrophotographic apparatus according to claim 1, wherein the correction by the control unit is performed by changing a control voltage for changing an output of the toner density detecting unit. apparatus. 6. The apparatus according to claim 1, wherein said correction by said control means is performed by changing a threshold value for discriminating an output of said toner density detecting means. Electrophotographic equipment. 7. The electrophotographic apparatus according to claim 1, wherein the correction is changed according to a degree of deterioration of the developer. 8. The electrophotographic apparatus according to claim 6, wherein the degree of deterioration of the developer corresponds to a length of operation time of a developer conveying unit in the developing device. 9. The apparatus according to claim 1, further comprising a sensor for detecting temperature and / or humidity in the electrophotographic apparatus, wherein the correction is changed based on an output of the sensor.
The electrophotographic apparatus according to any one of the above. 10. The electrophotographic apparatus according to claim 1, wherein the stop time is read when the operation of the electrophotographic apparatus is started. 11. A main switch for turning on / off a main power supply of the image forming apparatus, and a clock which operates independently of on / off of the main switch, wherein the main switch is turned off from an output of the clock. The electrophotographic apparatus according to claim 10, wherein the stop time during the stay is acquired. 12. A main switch for turning on / off a main power supply of an image forming apparatus, a fixing device for fixing a toner image on recording paper, and a fixing device temperature sensor for detecting a temperature in the fixing device, wherein the main switch is provided. 11. The electrophotographic apparatus according to claim 10, wherein the stop time while the mason switch is turned off is obtained based on an output of the fixing device temperature sensor immediately after turning on. 13. A stirring and conveying means for conveying the developer, stirring the developing sleeve and the developer forming a layer of the developer in the developing area, and supplying the developing sleeve to the developing sleeve. Wherein the degree of deterioration of the developer is detected from the operation time of the developing sleeve, and the operation detecting unit detects the operation of the developing device from the operation of the stirring and conveying unit. An electrophotographic apparatus according to claim 7.