JPH05100517A - Image forming device - Google Patents

Abstract

PURPOSE:To improve service by predicting the residual life of a photosensitive drum and accurately recognizing an exchange time. CONSTITUTION:Electrifiers 2, exposing means 4, surface electrometers 6, and developing units 7, are disposed on the circumferences of four photosensitive drums 1 (1a, 1b, 1c, and 1d) forming the toner images of four colors, respectively. A recording material P is carried by a moving body 12, and to each photosensitive drum 1, sequentially. The potential of the electrosatic latent image of the photosensitive drum 1 is detected by the surface electrometer 6, and a life detecting means 11 detects the residual life of each photosensitive drum 1, base on the result of the detection. An exchange index calculating means for calculating the life of the photosensitive drum 1 packed inside the life detecting means 11, it predicts the residual life of the photosensitive drum 1 via the exchange index calculating means, and judges the exchange time.

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 having a photosensitive drum as an image carrier, and more specifically, an image for predicting the remaining life of the photosensitive drum and accurately determining the replacement time. Forming apparatus

[0002]

2. Description of the Related Art Conventionally, it has been known that an image carrier (photosensitive drum) incorporated in a general image forming apparatus is deteriorated according to a use time by repeating charging, exposure and the like. Then, the photosensitive drum that has reached the end of its life is promptly replaced.

As a means for predicting the life of the photosensitive drum, since the deterioration of the photosensitive drum and the surface potential of the photosensitive drum after charging are correlated with each other, the surface potential of the photosensitive drum is usually measured to measure the photosensitive drum. The degree of deterioration of the drum, that is, whether or not the photosensitive drum has reached the end of its life is determined.

The prediction of the life of the photosensitive drum is as follows.
For example, in a four-color full-color copying machine having four photosensitive drums, each photosensitive drum is independently processed.

[0005]

However, according to the prior art, even if it is possible to determine whether the life of the photosensitive drum has reached the replacement time, if it has not reached the end of life, how much remaining life will remain in the future. Until then, it could not be accurately determined, and it was difficult to predict the replacement time, so there was a service problem such as missing the replacement time.

In particular, in a four-color full-color copying machine having a plurality of photosensitive drums, the characteristics of the photosensitive drums are individually detected for each of the four photosensitive drums and the image forming conditions are individually changed. In some cases, it is not possible to find a relationship regarding the life of the photosensitive drums. As a result, when one photosensitive drum needs to be replaced, it is better to continue to use the other photosensitive drum. In many cases, it was not possible to determine whether or not it was better to replace them at the same time.

Therefore, the present invention provides an image forming apparatus capable of appropriately predicting the replacement time of the photosensitive drum by accurately determining the remaining life of the image carrier (photosensitive drum) by the life predicting means. The purpose is.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and a charging device for charging an image carrier, and an exposure for exposing the image carrier to form an electrostatic latent image. An image forming apparatus including a developing device for developing the electrostatic latent image, an electric potential detecting device for detecting an electric potential of the electrostatic latent image, and an output of the electric potential detecting device for detecting the electric potential of the image carrier. And a life prediction means for determining the remaining life.

At this time, the life predicting means has an exchange index calculating means for the image carrier, and at least one of the dark attenuation characteristic of the image carrier, the grid control potential of the charging device, and the γ characteristic. The exchange index may be calculated based on the total charging time of the image carrier.

The total charging time of the image carrier may be converted from the number of copies.

[0011]

According to the above construction, by detecting the electrostatic latent image formed on the image bearing member by the potential detecting means, the photosensitive characteristic of the image bearing member at that time can be known. Based on this photosensitive characteristic, the life predicting means determines the remaining life of the photosensitive drum.

When the life predicting means has an exchange index calculating means, this exchange index is used as at least one of the dark attenuation characteristic of the image carrier, the grid control potential of the charging device, and the γ characteristic.
In addition, if the calculation is performed based on the total charging time of the image carrier, the remaining life of the image carrier can be accurately calculated. That is, in general, the value of the dark attenuation characteristic or the like changes in correlation with the photosensitive characteristic of the image carrier, and therefore, the data of the dark attenuation characteristic or the like is processed by an appropriate exchange index calculation means to obtain the image carrier. It is possible to almost predict when the remaining life of the body will be exhausted.

The total charging time of the image carrier at this time may be determined, for example, in proportion to the number of copies with reference to the number of copies.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

As a first embodiment of the image forming apparatus according to the present invention, FIG. 1 shows an image forming portion of a four-color full-color copying machine. The image forming unit includes image forming units I, II, III, and IV, which are configured by disposing image forming means around four photosensitive drums 1a, 1b, 1c, and 1d, which are image carriers.
Four image forming units I, II, III, I
The image formed on the photosensitive drums 1a to 1d by V is transferred to the recording material P carried and conveyed by the moving body 12 which moves and passes adjacent to these.

The image forming units I, II, III, and IV are image forming units for forming images of magenta, cyan, yellow, and black colors, respectively, and image formation by these is performed in the following procedure.

The surface of each of the photosensitive drums 1a, 1b, 1c, 1d is a charger (charging device) 2a, 2b, 2c,
It is uniformly charged by 2d. Next, the photosensitive drum 1a,
The exposure means 4a, 4b, 4c, and 4d controlled on the basis of the image signal to be recorded irradiate on 1b, 1c, and 1d, thereby forming an electrostatic latent image. The electrostatic latent image is visualized by developing devices (developing devices) 7a, 7b, 7c, and 7d with magenta, cyan, yellow, and black color toners. The toner image is supplied from a sheet feeding cassette (not shown) and is transferred and transferred onto the recording material P carried on the moving body (carrying and carrying device) 12 by the transfer chargers 8a, 8b, 8
It is transferred by the discharge from c and 8d. The recording material P is successively conveyed to the image forming units I, II, III and IV, and the above process is repeated to form a full-color image of magenta, cyan, yellow and black, and then these toners are fixed by a fixing device (not shown). The image is fixed. On the other hand, the photosensitive drums 1a to 1d that have finished transferring the toner image onto the recording material P remove the toner remaining on the photosensitive drums 1a to 1d by the cleaner 9
After being removed by a, 9b, 9c and 9d, the static elimination lamp 10
After the surface potentials of a, 10b, 10c, and 10d are uniformly discharged to near 0 V, they are uniformly charged again by the chargers 2a to 2d.

Next, each photosensitive drum 1a, 1b, 1c, 1d
The remaining life calculation procedure and the life comparison with other drums will be described.

FIG. 2 shows the photosensitive drum 1 (photosensitive drums 1a, 1
When it is not necessary to distinguish between b, 1c, and 1d, they are simply referred to as the photosensitive drum 1. In addition, chargers 3a, 3b, 3c, 3
d, the developing units 7a, 7b, 7c, 7d, etc.) is a constant surface potential, for example, the change of the dark attenuation amount V _DD per one rotation of the photosensitive drum 1 from 500 V is the total charging time T of the photosensitive drum 1. FIG. Although this figure shows various characteristics in the structure of the photosensitive drum 1, this figure can be obtained for the same kind of drum by a durability test or the like. The dark attenuation amount V _DD described above increases in proportion to the total charging time T of the photosensitive drum 1. The photosensitive drum 1 has a maximum allowable dark attenuation amount V
_DD Limit is set. The V _DD Limit means that if the dark attenuation amount V _DD increases above that value, high image quality will be impaired.

The dark attenuation amount V _DD of the photosensitive drum 1 is measured as follows. The photosensitive drum 1 is charged by the charger 2 to the above-mentioned constant V _S , for example, V _SO = 500V. In this step, the exposure by the exposure unit 4, the development by the developing unit 7, and the transfer by the transfer charger 8 are not performed, and the surface potential V of the photosensitive drum 1 is set by the surface potential meter (potential detection unit) 6.
_S0 is measured, the photosensitive drum 1 is further rotated once, the surface potential V _S1 at the same position is measured, and V _S0 −V _S1 is calculated. This V _S1 −V _S0 is the dark attenuation amount V of the photosensitive drum 1 at this time.
_{It's DD} . Here, the dark decay amount when the charging time T of the photosensitive drum 1 is zero, that is, when the photoconductor drum 1 is new, is V _DD S, and the dark decay limit amount at the preset drum life is V _DD Limit.
The relationship between both numerical values V _DD S, V _DD Limit and the total charging time T is stored in the memory judgment circuit incorporated in the life detecting means 11 shown in FIG. Here, a new dark decay measurement step was performed, and the result V _DD N, for example, 52 V was obtained. Dark decay characteristic diagram of V _DD N when V _DD N measurements on a storage determination circuit calculates a ride on Figure 2 Total charging time of the photosensitive drum 1 T, for example 590 hours. The total charging time T calculated here is V _DD Limi
life of the photosensitive drum 1 set by t, for example, 90
It is compared with 0 hours and informs that 900 hours-590 hours = 310 hours.

When the photosensitive drum 1 of any one of the four image forming units I to IV is to be replaced, the remaining life calculation is performed for the remaining three photosensitive drums 1. .. The calculation and comparison means start signal is preferably given by a separate program for a special purpose such as a service mode, and only the comparison means may be used if the remaining life value is stored in the memory or the like. The comparison method is, for example, four photosensitive drums 1a, 1b,
When the remaining lifes of 1c and 1d are a, b, c and d, respectively, and the total life time of each photosensitive drum is L, each photosensitive drum 1
Exchange index of a, 1b, 1c, 1d (exchange index calculation means)
R is represented by the following equation.

R _a = 1 − {(a + b + c + d) / 4L} × (a / L) R _b = 1 − {(a + b + c + d) / 4L} × (b / L) R _C = 1 − {(a + b + c + d) / 4L } × (c / L) R _d = 1-{(a + b + c + d) / 4L} × (d / L). By using the above-described calculation formula, it becomes a standard of which one of the remaining three photosensitive drums 1b, 1c, 1d should be replaced or all of them should be replaced at the same time. When any of the photosensitive drums 1a, 1b, 1c, 1d is damaged and is to be replaced before the end of its life, 0 may be assigned to a variable (for example, a) corresponding to the photosensitive drum. To execute substitution, it is desirable to set the service mode and execute from that mode. By using the above formula, the remaining life of the photosensitive drum 1 can be taken into consideration, and the time for replacing the other three drums can be effectively managed in a well-balanced manner.

FIG. 4 shows the outline of the potential control procedure according to the present invention in the relationship between the elapsed time and the photosensitive drum surface potential V _S.

FIG. 5 shows the potential control according to the present invention.
The change in the intensity of, for example, the laser beam of the exposure unit 4 that irradiates the photosensitive drum 1 is represented by the transition of time.

FIG. 6 shows the potential control according to the present invention.
2 is a graph showing changes in voltage V _G (grid voltage) applied to the grid 3 of the charging device 2 for controlling the surface potential V _S of the photosensitive drum 1 shown in FIG.

FIG. 7 is a graph showing a calculation method for calculating a preset image forming potential from the results of the potential measurement at three points described later.

Next, the potential control method and process in the present invention will be described with reference to FIGS.

When the power switch of the copying machine main body is turned off,
When it becomes N, the photosensitive drum 1 starts to rotate. Next t ₀
The grid voltage V _G, for example, −250 V, is sequentially applied for up to t ₁ seconds, and then the negative charge is applied to the charger 2.
Then, the photosensitive drum 1 is irradiated with the laser light with an exposure amount E _D slightly lower than the maximum exposure amount E _MAX . The surface potential V _a on the photosensitive drum 1 after being charged with the grid voltage V _g1 -250 V and exposed with the exposure amount E _D is the surface potential meter 6 of FIG.
Read in and recorded in graph 7V _a point on the calculation circuit (not shown). The following t ₁ ~t ₂ seconds grid voltage V _g2 -500 V exposure in the step and the step is irradiated to the photosensitive drum 1 by E _L which the laser beam is slightly exposed, the surface potential V _b is graph at that time Recorded at 7V _b point. Taken together time grid voltage laser exposure surface potential _{t 0 ~t 1 -250V E D V} a t 1 ~t 2 -250V E L V b t 2 ~t 3 -500V E D V c t 3 ~t 4 _{-500V E L V d t 4 ~t} 5 -750V E D V e t 5 ~t 6 -750V E L V h becomes, so that six points of all V _a ~V _h in FIG. 7 on a computing circuit To be recorded. On this calculation circuit, V _a , V _c , V
_{2 which is the} straight line connecting the points _e and the straight line connecting V _b , V _d and V _h
Based on the straight line of the book, a point that is equal to a preset image forming potential is obtained, and a grid control voltage V _G at that time is obtained. 8 shows the total charging time T created by the same method as in FIG.
_The dotted line shows the result of the 6-point potential control performed on the photosensitive drum 1 after ₂ = 1000 hours. The solid line is the result of 6-point potential control on the new photosensitive drum 1. R in FIG. 8 indicates the image forming potential of 450 V on the new photosensitive drum 1, and the grid control voltage V _G at this time is 512.5 V. On the other hand, S in FIG. 8 represents the image forming potential of 450 V on the drum after the total charging time of 1000 hours. The grid control voltage V _G at this time is 703.0V. That is, when a constant image forming potential is assumed, as the fatigue of the photosensitive drum 1 progresses, the grid control voltage V _G for securing the image forming potential increases. However, it is not preferable to apply the grid control voltage V _G of the photosensitive drum 1 to the photosensitive drum 1 from the charger 2 because of the configuration of the charger 2 and because the life of the photosensitive drum 1 is accelerated. Therefore, in the example of the present invention, the grid control voltage V _G = 750 V is set as the upper limit and the life of the photosensitive drum 1 is set. Here, the life detecting means 1 of FIG.
The storage calculation circuit of No. 1 stores the relationship diagram between the total charging time T of FIG. 8 and the grid control voltage V _G for securing a constant image forming potential, for example, 450V. This relational diagram can be obtained in advance by a durability test or the like of the photosensitive drum 1. The newly set image forming potential is 600
When it is V, the total charging time T in FIG. 9 is calculated in the memory calculating circuit of the life detecting means 11 in FIG. 1 and 687 hours are calculated. Further, here, the upper limit of the grid control voltage V _G is determined to be 750 V, and the total charging time T at that time is determined.
Is 1050 hours, it is understood that 1050−687 = 363 hours is the remaining usable time of the photosensitive drum 1. The comparative calculation for replacing the photosensitive drum 1 is the same as that in the first embodiment. (Embodiment 3) A video signal 00HE corresponding to a white background of an image is generated by a pattern generator (not shown) as shown in FIG.
Data of X (hexadecimal), video signal FF HEX corresponding to black, and video signal corresponding to halftone, for example, 80 HEX, is generated, and a laser driver (not shown) is driven. At this time, the laser drive current is changed. Let I ₀ . A corresponding latent image is formed on the photosensitive drum 1 by the laser 23.

At this time, the surface potential V _S on the photosensitive drum 1
Is measured by the surface electrometer 6 and input to the life detecting means 11. The surface potentials of the video signals OO, FF, and HEX are V _oo , V _FF , and V ₈₀ , respectively. Next, in FIG. 10, the characteristic coefficient R of the photosensitive drum 1 is obtained. Where k
= A _{(V 00 -V 80) / (} V 00 -V FF), and represents the degree of linearity of the characteristic of the photosensitive drum 1 (E-V characteristic).

In FIG. 10, when k = 0.5, the surface potential of the photosensitive drum 1 changes linearly with respect to the video signal. When the surface potential changes rapidly, k increases. This is mainly due to changes in temperature and humidity around the photosensitive drum and with time.

Although the EV characteristic shows a curve in FIG. 10, even if the characteristic of the photosensitive drum 1 changes, these curves can be uniquely determined by the characteristic coefficient k without intersecting. It can be said that the closer k is to 0.5, the better the gradation of the output image.

The dotted line k = 7.0 on FIG. 10 is the gradation characteristic curve after the total charging time of the photosensitive drum of 1000 hours. As the total charging time T of the photosensitive drum 1 increases, k indicating the magnitude of change in the curve also increases. That is, the limit of the value of k is set and the life of the photosensitive drum 1 is determined.

FIG. 11 is a diagram showing the relationship between the coefficient k and the total charging time T. Also in this embodiment, the remaining life of the photosensitive drum 1 is calculated from the difference between the newly calculated value of k and the preset upper limit value of k. The comparison calculation performed for replacing the photosensitive drum 1 is the same as in the first and second embodiments.

In all the three embodiments, the photosensitive drum 1
Was calculated by the total charging time T. Further, in order to predict the life of the photosensitive drum to a realistic value, it is effective to convert the total charging time T into the number of copies. For example, if the life of the photosensitive drum 1 is 1000 hours, the current number of copies is 35,000, and the current total charging time after calculation is 650 hours, the number of copies per 1 hour of total charging time is 35000/650 = 53.4. Sheets / hour. Therefore, when the remaining life is 350 hours, 350 × 53.8 = 1883
Can be calculated as 0 sheets. By converting the life from time to the number of copies, the photosensitive drum 1 depending on the usage environment of the main body
The difference in service life will be corrected naturally.

In the present invention, three criteria for determining the life of the photosensitive drum 1 are described in the first three embodiments, but these criteria may be used alone or in combination. Is. Further, when a plurality of combinations are combined, a calculation circuit may be added such as which reference the priority is set to. Further, the surface potential V _S , the grid control voltage V _{G, and the} like used in the respective embodiments are merely examples, and the numerical values are not limited, and may be set individually depending on the situation. Further, in the chart used for determining the life of the photosensitive drum 1 and predicting it, the basic characteristics and numerical values change depending on the structure of the photosensitive drum 1 used, but the calculation method of the photosensitive drum does not change.

[0036]

As described above, by mounting the life predicting means for calculating the exchange index regarding the life of the image bearing member (photosensitive drum), the remaining life of the image bearing member is accurately grasped, and It is possible to properly know the replacement time and improve serviceability such as maintenance.

In particular, in the case of having a plurality of image bearing members, when one image bearing member is replaced, it is better to replace them at the same time by calculating this exchange index for the rest. It is possible to accurately judge whether or not to use it.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing an outline of an image forming unit of an image forming apparatus according to the present invention.

FIG. 2 is a diagram showing a relationship between a dark decay amount of a photosensitive drum and a total charging time.

FIG. 3 is a diagram showing the relationship between the surface potential of the photosensitive drum and the number of revolutions.

FIG. 4 is a diagram showing a state of a photosensitive surface potential when performing potential control.

FIG. 5 is a diagram showing a state of an exposure amount when performing potential control.

FIG. 6 is a diagram showing a state of a grid control potential when performing potential control.

FIG. 7 is a diagram showing a state of an image forming potential when performing potential control.

FIG. 8 is a diagram showing a relationship between a surface potential and a grid control potential.

FIG. 9 is a diagram showing a relationship between a grid control potential and a total charging time.

FIG. 10 is a diagram showing characteristic coefficients of a photosensitive drum.

FIG. 11 is a diagram showing a relationship between a characteristic coefficient of a photosensitive drum and a total charging time.

[Explanation of symbols]

1, 1a, 1b, 1c, 1d Image carrier (photosensitive drum) 2, 2a, 2b, 2c, 2d Charging device (charger) 4, 4a, 4b, 4c, 4d Exposure means 6, 6a, 6b, 6c, 6d potential detection means (surface electrometer) 7,7a, 7b, 7c, 7d developing device (developing unit) 11 lifetime prediction unit _{R, R a, R b,} R c, R d exchange index calculating means (exchange換指number) V _G Grid control potential T Total charging time

Claims (3)

[Claims] 1. An image forming apparatus comprising: a charging device for charging an image bearing member; an exposing unit for exposing the image bearing member to form an electrostatic latent image; and a developing device for developing the electrostatic latent image. An image forming apparatus, comprising: an electric potential detection unit that detects the electric potential of the electrostatic latent image; and a life prediction unit that determines the remaining life of the image carrier based on the output of the electric potential detection unit. .. 2. The life predicting means includes exchange index calculating means for the image carrier, and at least one of a dark decay characteristic of the image carrier, a grid control potential of the charging device, and a γ characteristic, The image forming apparatus according to claim 1, wherein the exchange index is calculated based on a total charging time of the image carrier. 3. The image forming apparatus according to claim 2, wherein the total charging time of the image carrier is converted from the number of copies.