JPS60242479A - Method for stabilizing electrification of electrophotographic sensitive body - Google Patents

Abstract

PURPOSE:To compensate the fluctuation of potential in the dark part of a photosensitive body without requiring a costly surface potential sensor, etc. by determining the total compensation quantity of electrification intensity from the fluctuation quantity, decrease quantity and residual quantity of the surface potential on the photosensitive body and adjusting the electrification intensity of the succeeding operation cycle for forming latent images according to the total compensation quantity. CONSTITUTION:The decrease quantity of electrification in one cycle is handled as a function of temp. with regard to the temp. dependency of fatigue and the temp. dependency of the decrease quantity of the electrification in one cycle is expressed in certain simple function on assumption that the function for restoration of the fatigure does not depend on temp. The temp. change of the initial potential in the dark part can also be approximated by the equation and the potential in the dark part can be expressed by the equation as the potential in the dark part with the number of cycles as a variable. The difference (total compensation quantity of electrification) of the potential in the dark part with respect to the potential in the reference dark part is thereupon determined. The total compensation quantity of electrification is calculated by a compensator 1 and is applied as a compensation signal 1a to a DC high- voltage power source 2. The potential in the dark part (the electrification in the dark part) is thus always stabilized even if there is a temp. elevation in the copying machine or a change in environmental temp.

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention relates to electrophotographic devices such as PPC copiers and optical printers that use photoreceptors made of selenium, etc. The present invention relates to a method for stabilizing the charging strength of a photoreceptor in order to prevent uneven image density due to fatigue during operation.

[Prior art and its problems]

This type of electrophotographic photoreceptor is made by vapor deposition of selenium, etc.
A photosensitive layer is formed. In an electrophotographic photoreceptor using selenium (hereinafter also referred to as a selenium photoreceptor or drum), high sensitivity can be achieved by doping the selenium photosensitive layer with Te or As.

On the other hand, if a large amount of Te or Asi is doped, the potential of the dark area (non-exposed area) in the electrostatic latent image on the photosensitive surface that comes to the developing unit during repeated operations (hereinafter referred to as developing dark area potential 1 or simply dark area potential) The degree to which this decreases increases. In this case, the decrease in potential can be compensated for by increasing the corona current of the corona charger to increase the amount of charge.

For this purpose, attempts have already been made to provide a sensor (potential sensor) for detecting the surface potential of the photoreceptor between the corona charger and the developer, and to make the potential at the detection point constant. With selenium photoreceptors, the decrease in image density due to repeated operations is not due to a decrease in the potential (receptive potential) that the photoreceptor surface can take on immediately after charging, but is a phenomenon that occurs after the photoreceptor surface is charged. It is known that this is caused by an increase in the attenuation of the dark potential (dark attenuation) until the dark area potential is removed. Therefore, depending on where the potential is detected from the corona charger to the developer, there will be a difference in the accuracy of compensating for the potential drop.If the potential sensor is not close to the developer, the potential difference between the detection point and the developer will be large. Therefore, the compensation accuracy decreases.

Several methods for measuring surface potential have already been proposed, and one that can withstand continuous use for long periods of time is a vibrating sector type sensor.The disadvantage of this sensor is that it is expensive. In addition, as mentioned above, since the sensor is placed close to the developer, it is easily contaminated with toner, and it is necessary to devise a means to remove the toner by blowing air, etc., and the potential of the photoreceptor in the detection part and the non-detection part Since the potentials of the photoreceptors are not at the same fatigue level, there is the problem of how much they can be matched, and while the cost is high, there are many problems before they can be used effectively.

There have been many proposals for low-cost potential measurement methods other than traps and vibration sectors for surface and potential measurements, but it can be said that very few of them have been put into practical use.

In addition to the method of actually detecting the surface potential of the photoreceptor and feeding back the deviation from the set potential to the corona charger, it is also possible to use a curve that shows the property that such potential fluctuations depend on the copy operation cycle and do not change. Methods have already been proposed in which the amount of charge is adjusted by storing the amount in a digital memory, or by approximating the curve using a simple exponential function generator and calculating the amount of compensation from that curve. This cycle compensation method that compensates for the charge voltage according to the operating cycle does not require a surface potential sensor and has the advantage of being able to compensate for the charge at low cost. However, the conventional method has limitations due to usage conditions. It has the disadvantage that it only works effectively within the specified range. For example, in the case of a high-sensitivity selenium photoreceptor, in addition to the decrease in density caused by repeated copying, the decrease in density becomes more pronounced when copies are repeatedly made in a high temperature environment than at room temperature. Therefore, with simple cycle compensation, it is difficult to keep the dark potential on the surface of the photoreceptor constant over a wide temperature range.

[Purpose of the invention]

Except for the above-mentioned drawbacks, the present invention does not require an expensive surface potential sensor or the like, and can detect fluctuations in the dark potential of the photoreceptor caused by repeated operations over a wide range of practically conceivable copying machine usage modes and environmental temperatures. It is an object of the present invention to provide a method of charging compensation that can compensate for charging.

[Key points of the invention]

The main point of the present invention is that the charging strength (development dark area potential,
In a method of compensating for the amount of decrease in dark area potential (charging decrease amount) by increasing the corona current of a corona charger, including the influence of temperature change on the latent image carrier, the charging strength in a state where no fatigue remains. Assume that the initial charge amount changes with the temperature of the latent image carrier according to a predetermined first function (for example, a function that decreases with a predetermined first temperature coefficient as the drum temperature rises), and the repetitive operation including intermittent operation Latent image forming operation (intermittent copying, continuous copying, etc.)
After entering K, the temperature of the latent image carrier is lowered to the same temperature. A predetermined second function (for example, a function that increases with a predetermined second temperature coefficient as the drum temperature rises, an l-cycle charge reduction amount) and a plurality of time constants (for example, two for each) and a time variable. It consists of an exponential function (for example, two exponential functions corresponding to the copying operation and the copying stop) that attenuates as The amount of change in the charging intensity with respect to a predetermined value is estimated in advance during the latent image forming operation, and the charging intensity is compensated for in accordance with the amount of change. be.

[Embodiments of the invention]

The present invention will be explained below based on FIG. FIG. 1 is a diagram showing an example of the configuration of an electrophotographic copying machine to which the present invention is applied.

In FIG. 1, D is a drum-shaped photoreceptor (hereinafter referred to as drum), which has a photosensitive surface made of a selenium photosensitive layer that forms an electrostatic latent image on its outer peripheral surface, and is rotated in the direction of arrow AXR in the figure. CHI is a corona charger that preliminarily applies a positive charge to the drum D by corona discharge in order to form the latent image; EX is an exposure unit having a semiconductor laser light source that exposes the drum DK and forms a latent image such as a character pattern; DV is a developing device that develops the latent image by adhering a developer such as toner to the latent image, P is a transfer device such as co-material paper that transfers the developed image, and CH2 is a transfer device that transfers the developed image to a transfer material. CL is a cleaning means for removing the developer remaining on the drum D, and DCH is a cleaning means for removing the residual charge on the drum D by irradiation with blue light or the like (referred to as photostatic charge removal). It is a static eliminator. Further, 2 is a DC high-voltage power supply that supplies a corona current IC to the corona charger C) 11, and 6 is a temperature sensor that measures the environmental temperature of the drum D and thus the temperature of the drum D. Reference numeral 1 denotes a charge compensating device (hereinafter referred to as a compensator) consisting of a CPU, etc., which receives copy commands 3a, etc. of a copy control device (hereinafter referred to as a control device) 3, and A (not shown).
The figure shows a compensation signal 1a as a signal that instructs the DC high-voltage power supply 2 to increase the amount of corona current to compensate for the decrease in the amount of charge while inputting the temperature detection signal 6a of the temperature sensor 6 via the /D converter. Provided via an external D/A converter. Reference numeral 5 indicates a DC power source for the exposure means EX, and a control device 3 issues on/off commands 3C to the DC high voltage power supply 2, and the copy command 3a to the compensator 1.
etc., as well as a DC power supply 5 and a transfer corona charger CH2.
control etc.

Next, the present invention will be explained in detail in advance. The compensator”
・Measure the count value of a counter (not shown) that counts how many times ``9'' has been used consecutively (number of cycles N) and the stopping time from when copying stops until when copying starts again. Two pieces of information are sent: the count value of a stop time timer (not shown) (copy stop time t'l).

The temperature change in the developing dark area potential (dark area potential) Vd(T) of the photoreceptor can be expressed as in the following equation (10A), where T'C is the drum temperature.

Vd(T)=VO(T)−ΔVs(T)−(IO
A) However, VO(T) is the dark potential in a state without fatigue when the drum temperature is T ''C (called the initial dark potential, and the corresponding amount of charge on drum D is called the initial charge amount)
ΔVs(T) is the amount of potential decrease due to fatigue when the drum temperature is T'C (referred to as fatigue charge decrease amount).On the other hand, when a certain drum temperature T'C is fixed, the fatigue charge decrease amount Δ
Vs can be considered as follows.

Immediately after a selenium photoreceptor without initial fatigue is used for the number of cycles N in continuous copying, the fatigue charge reduction amount (newly referred to as the operation special charge reduction amount) ΔVs(N) is expressed by the following formula (IA).

ΔVs(N) Engineering A+A-C(to)+A-C(2t0)
Ten...Ten people...(1 person) T here. '1 cycle period of the home copy, A is the amount of charge reduction that newly occurs every cycle (referred to as 1 cycle charge reduction amount), and C(t) is the time t for fatigue recovery (attenuation of the charge reduction amount itself). It is a function of the coefficient representing the dependence of .

C(to) is the charge reduction amount A that occurred in the previous cycle (that is, during the (N-1)th cycle), which is N
Similarly, the final term A-C(N-1) to) on the right side is the charge reduction amount t that remains after being attenuated in the cycle (i.e., one cycle period to), which is the charge that occurred in the first cycle. The amount of decrease A is the Nth cycle (i.e. 1
The graph shows the amount of charge reduction that remains while attenuating after a time (N-1) times the cycle circumference XA''o).

The function C(t
), the following equation (2) can be assumed.

(::(t)=Ks-exp(-t/rs)+KJ-e
xp(-t/7ノ) ・・・・・・・・・(2) Here, τS and τE are the operating short time time constant (abbreviated as short time constant) and the operating characteristic long time time constant (long time constant), respectively. omitted)
, Ks, Kl are coefficients.

However, since there is no attenuation of the charge reduction amount at time 1=0 (therefore, C(0)=1), there is a relationship expressed by the following equation (2 people).

E s + KJ = = 1 ... time (2 people) The reason for providing two long and short time constants τS and τ is that 751 short time constants can compensate for the short copy operation of about 500 cycles. It is possible, but it cannot support continuous copying for a longer period of time, there is almost no need to provide three or more time constants, and it takes time to calculate, so the number of time constants is limited to two. This is what I did. However, the number of time constants is not limited to two.

The special charge reduction amount ΔVs(
N) continues to be copied continuously - in the limit, it converges to a certain value. This child is called the maximum compensation amount. It is (1), (
From formula 2), jVs(N-+ω)=A-(Ks-(τS/lo) 10K
l・(τl/1o)) ...(3). Therefore, it can be seen that the maximum compensation amount is proportional to the amount of charge reduction per cycle.

When a certain drum temperature T″G is fixed in this way, the formula (
jA) and (2), the amount of charge reduction required for operation is determined, and the corona current IC is increased via the compensator 1 and the DC high-voltage power supply 2 to compensate for this, thereby performing charge compensation.

However, as a result of detailed investigation of the temperature dependence of repeated fatigue of high-sensitivity selenium photoreceptors, we found that the function C (
, t) does not vary with temperature, but it turns out that the main factor is that the temperature changes and the temperature changes, which is also a proportionality constant of ΔVs (N).

In other words, the temperature dependence of fatigue is expressed as 1 in equation (IA).
The cycle charge reduction A is a function of temperature, and the function C(t) of recovery from handling fatigue does not depend on temperature. 11).

A(T)=a-'f'+b-(11) However, a and b are constants.

By introducing the relationship of equation (11) into (one person), equation (IA) can be expressed as equation (IB) below.

Further, the temperature change in the initial dark potential vo('r) in the formula (IOA) can also be approximated by, for example, the following formula (12).

Customer yo (T) = f −'r0g ・------(
12) However, f and g are constants.

In this way, the dark potential Vd(T
) is expressed by the following formula (10
).

Vd ('1', N) = VO ('f') - jVs (T, N
)...(10) Then, by substituting the difference (#; called charge compensation amount) Δ■C between the reference dark potential Vd0JC and the dark potential Vd(T, N) in equation (1o), the following equation (13) is obtained. become that way.

jvc=Vdo-Vd(T,N)=Vdo-VO('J
”)+jVs (T, N)...Song (13) This total charge compensation amount is calculated by the compensator 1, and D as the compensation signal 1a.
By supplying C to the high-voltage power supply 2, the dark area potential (charging in the dark area) can always be stabilized even if the temperature inside the copying machine increases or the environmental temperature changes.

-Next, Table 1 describes the measurement results of changes in the dark area potential of the drum D when an operation equivalent to an actual copying operation is performed using the copying machine shown in FIG. In this measurement, the developing device D in Fig.
In place of the developer DVK, a surface electrometer glove (not shown) is installed in place of the developing device DVK to measure the potential of the photosensitive surface of the drum D, and the developing dark area potential (dark area potential) is measured with the surface electrometer. be.

The carrier transport layer (CT
L) K pure setzysoμm'g, carrier generation layer (CG
L) 8eTe110.6 with high concentration of KTe40wt%
A photosensitive layer having a multilayer structure in which 2 μm of pure selenium was sequentially laminated as a surface protective layer was used. This photoreceptor is approximately 4 times more sensitive than a normal selenium photoreceptor to white light, and has a half-attenuation exposure dose of 0.6μJ/cIl for a semiconductor laser light source with a wavelength of 780nm. .

The conditions for fatigue operation are as follows: After the copying machine is stationary for at least 12 hours to remove fatigue from the photoreceptor (drum D), one cycle period t0 is 5 seconds, and the first cycle is performed using the semiconductor as exposure means EX. Laser exposure 4OFFl
, the initial dark potential was measured after charging in a state of Measure the dark potential after fatigue (referred to as post-SOO cycle dark potential),
The difference between both potentials was investigated. These tests were conducted at three temperatures: 5° C., 20° C., and 35° C., while changing the environmental temperature, and in two cases: with and without charge compensation according to the present invention. Table 1 shows the case of no charging compensation (5
), at each drum temperature T, the above-mentioned initial dark area potential VO (T), fatigue charge reduction amount (total amount of poetry reduction during III production) ΔVs (T , N), dark area potential after 500 cycles t
In the case of charging compensation, the compensated initial dark potential at each corresponding drum temperature T is the same (50
The dark potential after 0 cycles is shown. In addition, here is the ceremony (Tayuso x
2), each constant in (13) is set as follows.

That is, coefficient Ks=0.9346, K l =0
．． 0654.

Short time constant rs=25sec, long time constant 71=5000s
ec, constant a = 0.0667 (v/"c), constant b = 0.667V, constant f = -4 (V/"C), constant g = 890V, reference dark potential Vd O = 810V C
As an example, this value is expressed as the initial dark potential vo('I'
).

As can be seen from Table 1, in the case (5) without charging compensation, the temperature change in the initial dark potential VO(T) is approximately 11
00V/30℃・810V=-0.41cm/℃, the amount of change due to temperature constant width and fatigue is 300V (however, the reference voltage is 810■), whereas charging compensation ), the initial dark potential (7) temperature change is approximately -15V/30℃-810V=-0.06%/
``C1 Also, the range of the amount of change combining temperature change and fatigue is ±IO
V, which is significantly improved.

For the sake of simplicity, the above explanation is based on the case where the copying operation is continuous. However, even in a case where intermittent copying or continuous copying is repeated intermittently, the operation poetry charge in equation (13) or (IB) can be used. The present invention can be applied to a one-cycle charge reduction change in the amount of charge reduction (in the following description, simply referred to as fatigue charge reduction amount for convenience) ΔVs (T, N).

In other words, the amount of fatigue charge reduction ΔVsl (T, , Nl) immediately after N1 cycles of continuous copying and stopping the subsequent copying from a state without fatigue is calculated by the following formula by setting the cycle number N1kN1 in the above formula (IB). (20) % Formula % Next, the fatigue charge reduction amount jVs2(0) that remains while attenuating after the copy stop time t1 is calculated by adding new fatigue to equation (20).
It is expressed by multiplying by a function C1 (tl) representing the time dependence of recovery, and is expressed by the following equation (21).

Here, the function CI (t 1 ) can be expressed, for example, by the following equation (22).

CI(tl) = 1s-exp(-tl/Tl5) 1K
II!・exp(-tl/τIJ) ・−・・(22)
Here, τIS is the short-time time constant at stop, τ17! is the long time constant at stop, Kls, KIJ are coefficients Klj + KIJ
There is a relationship of =1. Note that the number of time constants in equation (22) is generally not limited to two.

Next, when the second continuous copy is restarted, the fatigue charge reduction amount ΔVs (T, N) after N cycles is calculated using the formula (21)
The amount of fatigue charge reduction (therefore, the value of (IB)) when it is assumed that there is no initial fatigue charge reduction amount due to
The amount of fatigue charge reduction remaining while attenuating after o time), that is, ΔVs2(0)-C(N-1o)=A(T)-C(N-
to)-C1(tl)J:υ. In other words, fatigue charge reduction amount jVs(
T, N)H is represented by the following formula (23) or (23A).

ΔVs(T,N)=A(T)-C(N-to)-CI(
tl)・=A(T)−[C(N−to)−C1,(tl
) It should be noted that the fatigue charge reduction amount ΔVs (T, IN) in the second continuous copying shown in equation (23A) is expressed as a product of a predetermined function.

By repeating the same procedure for any subsequent copy operations, the amount of fatigue charge reduction can be estimated, but in any case, the fatigue charge reduction amount in such general copy operations is equal to one cycle charge reduction. Amount A (
T), and a predetermined function consisting of exponential functions c(t) and cl(1) having a plurality of time constants and decaying with time, and determined from the time history of the copy operation including the stop time after thermal fatigue; It can be easily inferred that it is expressed as the product of .

〔Effect of the invention〕

As is clear from the above description, according to the present invention, the initial charge amount when the photoreceptor is not fatigued is
The amount of charge reduction due to fatigue, which is the difference between the initial charge amount and the charge amount after continuous or intermittent copying when the drum temperature is fixed, is calculated as a function of the second drum temperature. It is composed of an exponential function that has multiple time constants and decays over time, and can be calculated as the product of a predetermined function determined from the history of the copying operation from the time of no fatigue and the time of stopping. Since we decided to perform charge compensation by estimating the amount of change in the drum's charge for a predetermined amount, it is possible to minimize changes in the dark area of the selenium photoreceptor over a wide temperature range and usage mode (continuous copying, intermittent copying). It became possible to stabilize it to the point where it could be ignored. Further, since such potential compensation is performed by a microprocessor built into the copying machine, there is an advantage that the increase in hardware cost is relatively small.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of the configuration of a copying machine to which the present invention is applied. D: Electrophotographic photoreceptor (selenium photoreceptor, drum), CHI: Corona charger, EX:
...Exposure means, l) V...Developer, P...
...Transfer material, CH2...Transfer corona charger, 1
)CH... Static eliminator, 1... Charge compensator (compensator), 2... DC high voltage power supply, IC...
...Corona current, 3...Copy control device (
control device), 1a...compensation signal, 3a...
...Copy command, 6...Temperature sensor. spear 1 figure

Claims (1)

[Scope of Claims] 1) In an electrophotographic apparatus having a photoconductor that forms a latent image by repeating the steps of charging, exposing, and removing static electricity, the temperature of the photoconductor is read at the start of the latent image forming operation, and The amount of decrease in the surface potential of the photoconductor per operation cycle and the decrease in surface potential up to the relevant operation cycle, which is calculated based on the amount of variation in the surface potential of the photoreceptor due to temperature, and is corrected by the temperature read for each latent image forming operation cycle. In addition to determining the remaining amount of charge, calculate the total compensation amount of the charging strength from the above fluctuation amount, decrease amount, and remaining amount, and adjust the charging intensity of the next latent image forming operation cycle according to this total compensation amount. A method for stabilizing the charge on a photoreceptor of an electrophotographic device.