JPH0211906B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a charge control device for an electrostatic recording device, and in particular, has a function of correcting environmental changes and changes over time of a recording medium (photosensitive drum), and controls static electricity while controlling the amount of charge on the recording medium. The present invention relates to a charge control device for an electrostatic recording device that performs electrostatic recording.

Conventional electrostatic recording devices such as electronic copying machines have the drawback that the charging characteristics of the photosensitive drum change due to environmental changes such as humidity and temperature, and are also affected by changes over time such as mechanical fatigue due to use. be.
Conventionally, as a method of correcting such environmental fluctuations and changes over time, the latent image potential of the photosensitive drum is detected and recording conditions such as charging conditions, exposure conditions, and development conditions are changed to form an optimal image. A method of controlling the charging condition and changing the charging condition and exposure condition according to the charging time so that optimum image recording can be performed has been considered. In general, humidity resistance accounts for an overwhelmingly large amount of environmental changes compared to other factors, and most conventional methods have been aimed at improving humidity resistance. Furthermore, after long-term use, there is mechanical fatigue of the photosensitive drum and changes over time due to deterioration of the photosensitive characteristics themselves.In addition, there are changes in charging characteristics for a short period of time immediately after charging starts, and changes in charging characteristics after charging is stopped. Therefore, changes in these charging characteristics must also be taken into account. That is, by repeating charging and exposure, the charging characteristics recover to a steady state, so if the same corona current is applied, the above-mentioned charging characteristics are not compensated for, and the amount of charging changes. As described above, since the magnitude of the change in the amount of charge immediately after the start of charging exhibits a characteristic that changes depending on the degree of moisture absorption of the photosensitive drum, optimal image recording cannot be performed unless this is taken into consideration.

The present invention has been made in view of the above points, and an object thereof is to provide a charge control device that can accurately compensate for changes in the charging characteristics of a photoreceptor at the start of charging.

That is, the present invention provides an image forming apparatus that forms an image by forming an electrostatic latent image by charging and exposing a photoreceptor and developing the electrostatic latent image. and a compensation means for compensating for the charging characteristics of the photoreceptor at the time of starting charging, and the compensation means changes the amount of charge on the photoreceptor according to the charging characteristics specific to the photoreceptor after the start of charging. to converge to a predetermined convergence value, and set the difference between the initial value of the charge amount and the convergence value based on the output of the humidity detection means, and when the humidity detected by the humidity detection means is high. provides a charge control device for an electrostatic recording device, characterized in that the difference between the initial value and the convergence value of the charge amount is set smaller than when the humidity is low.

Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 illustrates the principle of controlling the charging corona current by detecting humidity and charging history to compensate for the moisture absorption characteristics of the photosensitive drum. When charging starts at t ₀ , the charging corona current, that is, the high voltage output current f(t) that charges the entire surface of the photosensitive drum, has an initial value that changes from 300 μA to 400 μA depending on the detected humidity (30 to 80%). It converges from f(t ₀ ) to the final value of 300 μA using an exponential function with a time constant τ ₁ . When charging is stopped at t ₃ , the charging current becomes zero, but the starting current f of the charging current
(t) returns to the initial value f(t ₀ ) with a time constant τ ₂ . In this case, τ ₁ is selected to be around 40 seconds based on the charge recovery characteristics when the photosensitive drum is charged, while τ ₂ is selected to be around 5 minutes depending on the moisture absorption deterioration characteristics when the photosensitive drum is stopped. . When charging is started at t= _t4 before returning to the initial value, the charging current f(t) converges from the starting current value f( _t4 ) to a final value of 300 μA by an exponential function of time constant _τ1 . In other words, the broken line in Figure 1 shows the charge recovery characteristic based on the decrease in water absorption during charging, and as the charge recovers, the high-voltage output current can be reduced. It is understood that when charging is stopped, the amount of water absorbed increases and the charging characteristics deteriorate accordingly, so it is necessary to increase the high voltage output current.

In this way, in the present invention, the initial value f of the charging corona current is determined according to the detected humidity near the photoreceptor drum.
(t ₀ ), and the amount of charge finally applied to the charger is controlled by taking into consideration changes in charging characteristics based on changes in moisture absorption during charging or when charging is stopped.

A specific device for controlling the amount of charge as described above is shown in FIG. In FIG. 2, the photosensitive drum 1 is composed of three layers, for example, an insulating layer, a photoconductive layer, and a conductive layer from the surface.A primary charger 2 is arranged around the photosensitive drum 1 to charge the entire surface of the photosensitive drum 1. Ru. Next to the primary charger 2, a secondary charger (static eliminator) 3 and a full-surface exposure lamp 5 are arranged adjacent to each other in the direction of rotation of the drum. This secondary charger 3
The photosensitive drum 1 is exposed to a reflected light beam 4 from an original (not shown) illuminated by a light source 9, and at the same time, the charge on the photosensitive drum is removed, thereby forming an electrostatic latent image of the original on the photosensitive drum 1. The electrostatic latent image thus formed is entirely exposed by a full-surface exposure lamp 5 in order to increase the sensitivity, resulting in an electrostatic latent image with even better gradation. Thereafter, the electrostatic latent image on the photosensitive drum is moved to a developing device 7 and developed with toner via a developing roller 8.

Further, a variable resistance humidity sensor 13 is disposed at a suitable location around the photosensitive drum 1, for example, between the developing device 7 and the secondary charger 3. This humidity sensor 1
3 is applied with an AC bias voltage of about 1000 Hz 1 VRMS from the oscillation circuit 11 via a resistor R8 and a capacitor C2. Further, the output from the humidity sensor 13 is input to a rectifier circuit 14, and the signal from the humidity sensor 13 is converted into direct current. A time constant circuit 15 consisting of resistors R1, R2 and a capacitor C1 is connected to the rear stage of the rectifier circuit 14, and this time constant circuit has a time constant of τ ₂ =R1·C1 when the electronic switch 16 is open, and a time constant of τ 2 when the electronic switch 16 is short-circuited. It has two time constants: ₁ = C1・R1・R2/R1+R2. The output of the time constant circuit 15 is taken out from the connection point of R1 and R2, amplified by the amplifier 18, and input to the high voltage generation circuit 19. The output of this high voltage generation circuit is connected to the primary charger 2 to control the amount of charge of the primary charger. electronic switch 16
A synchronizing signal during the charging rotation of the photosensitive drum is applied from the sequence controller (not shown) of the recording apparatus main body to the control input 17 of the recording apparatus.
Ground one end of 2 and set the time constant of the time constant circuit as τ ₁ =
C1・R1・R2/R1+R2, and when charging is stopped, one end of R2 is opened and the time constant of the time constant circuit is set to τ ₂ =C1・R1. We have realized a means to compensate for this. Further, the high voltage generating circuit 19 is controlled to be turned on or off by a timing signal applied to the terminal 17.

FIG. 3 shows specific circuits of the oscillation circuit 11, the rectifier circuit 14, the electronic switch 16, and the amplifier 18. The oscillation circuit 11 is an operational amplifier Q1
This is a positive feedback blocking oscillation circuit having a positive feedback blocking oscillation circuit whose oscillation frequency is the optimum condition for the humidity sensor 13.
The values of C1 and R3 are selected so that the frequency becomes 1KHz. The output of Q1 is input to the switching transistor Q2, and the output of Q2 is input to R8, C2.
is applied as a bias current to the humidity sensor 13 via. The terminal voltage detected from the humidity sensor 13 is converted to a low impedance by an impedance converting amplifier Q3, and then rectified by a linear detection circuit Q4. This rectified output is smoothed by a resistor R4 and a capacitor C3, and then amplified by an amplifier Q5 and connected to a time constant circuit 15. On the other hand, electronic switch 1
6 consists of a transistor Q6, the collector of which is connected to a resistor R2 of a time constant circuit, and the base of which is connected to a terminal 17. Furthermore, time constant circuit 1
The output of 5 is current amplified by Q7 and then sent to limiter D.
After the voltage is limited by voltages 1 and D2, the voltage is input to the high voltage generation circuit 19 via the voltage follower Q8.

Next, the operation of the control device configured as above will be explained. A timing signal synchronized with the charging rotation of the photosensitive drum 1 is applied to the terminal 17 from a sequence controller of the copying machine main body. In this case, if the timing of turning on the power for driving the circuit substantially coincides with the charging rotation of the photosensitive drum 1, a constant voltage, for example +24V, is input to the terminal 17. When this voltage is applied to terminal 17, switching transistor Q6 becomes conductive and capacitor C1 starts charging with time constant τ ₁ =C1・R1・R2/R1+R2, and the voltage at the connection point of R1 and R2 becomes exponential. It decreases functionally. This decrease in voltage is determined in response to the charging recovery characteristic based on the decrease in the amount of moisture absorbed during charging, as explained immediately in connection with FIG. In this case, when the humidity is high and the output voltage from the humidity sensor 13 is high, a small voltage is applied to the time constant circuit from the inverting amplifier Q4, so that the initial value at t ₀ at the start of charging is shown in FIG. The higher the humidity, the smaller the corona current, and in this way correction is performed taking into account environmental conditions, especially humidity conditions.

On the other hand, when the timing signal applied to terminal 17 is turned off and charging is stopped, transistor Q6 is cut off and the charge that had been charged in C1 until then is R
1 and is discharged with a time constant τ ₂ =C1·R1.
In this case, the time constant τ ₂ is selected to compensate for charging deterioration due to an increase in water absorption when charging is stopped. In this case, differential amplifiers Q3, Q4, Q5, Q7
consists of an operational amplifier with four built-in FET input circuits, and no current flows into R5.

In this way, the output of the time constant circuit is Q7, Q8
The voltage is amplified and input to the high voltage generation circuit 19 and applied to the primary charger 2, thereby controlling the amount of charge on the photosensitive drum 1.

The calibration method is a very difficult problem in humidity detection, but in this example, assuming that variations in the humidity sensor itself can be tolerated at the output stage, the cause of circuit variations is minimized, so calibration is not possible at all. It becomes necessary. In other words, fluctuations in the output of the differential amplifier are standardized to an amplitude of 0V to 12V through one-stage switching of transistor Q2, so fluctuations in the sensor bias current can be prevented, and furthermore, in the forward direction of the rectifier diode, fluctuations in the sensor bias current can be prevented. Since variations in voltage are standardized using the linear detection circuit Q4, fluctuations in the rectified output can be prevented. Furthermore, since the smoothing circuit, time constant circuit, and sensor itself are coupled to the next stage using a FET input differential amplifier, fluctuations can be eliminated.
Also, all differential amplifiers used have an open gain of 80.
Since a high gain amplifier of ~100 dB is used in a closed loop, the gain is determined by the input and feedback resistor values and can compensate for variations in the amplifier gain.

FIG. 4 shows another embodiment of the present invention, in which a standard resistor R having the same resistance value as the resistance value of the humidity sensor 13 at normal humidity is shown.
This is an example in which a changeover switch 6 and a changeover switch 20 are provided, and the other parts are the same as those in the embodiment shown in FIG. 2, and a description thereof will be omitted. In this embodiment, the output level of the amplifier 18 can be easily calibrated by switching the input of the rectifier circuit 14 from the humidity sensor 13 to the resistor R6.

Further, in the case of the embodiment shown in FIG. 4, there is an advantage that difficult work such as keeping the environment (humidity) constant is not required when correcting variations in the circuit or variations in charging characteristics due to moisture absorption of the photoreceptor. is obtained.

In the embodiments described above, the high voltage applied to the primary charger is controlled by detecting the humidity. However, by controlling the corona current for static elimination flowing to the secondary charger, the charging characteristics change due to moisture absorption. It is also possible to control the amount of charge removal so as to compensate for the charging history.

Furthermore, the electrostatic recording device is equipped with a surface potential measurement device that measures the surface potential of the photosensitive drum, and controls recording conditions such as charging, exposure, and development according to the potential of the latent image.A humidity sensor is also installed to measure humidity characteristics and charging history. It is clear that an optimal image can be obtained by performing compensation by .

As described above, according to the present invention, the charging characteristics at the start of charging are changed continuously from the initial value to the convergence value, and the humidity inside the device is also detected, and when the humidity is high, when the humidity is low, Compared to the above, since the initial value is set to a value close to the convergence value, even if the charging characteristics at the start of charging change due to fluctuations in humidity, this can be compensated for with high accuracy.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the principle of control performed by the device of the present invention, FIG. 2 is a block diagram showing the configuration of the first embodiment of the invention, and FIG. FIG. 4 is a circuit diagram showing the detailed structure. FIG. 4 is a block diagram showing the structure of a second embodiment of the present invention. 1...Photosensitive drum, 2...Primary charger, 3...
Secondary charger, 4...Exposure light beam, 5...Full surface exposure lamp, 7...Developer, 8...Developing roller, 9...
...Exposure light source, 16...Electronic switch.

Claims (1)

[Scope of Claims] 1. In an image forming apparatus that forms an image by forming an electrostatic latent image by charging and exposing a photoreceptor and developing the electrostatic latent image, the humidity within the apparatus is detected. and a compensating means for compensating for charging characteristics of the photoreceptor at the start of charging, and the compensating means adjusts the amount of charge on the photoreceptor according to the charging characteristics specific to the photoreceptor after the start of charging. and converge to a predetermined convergence value, and set the difference between the initial value of the charge amount and the convergence value based on the output of the humidity detection means, wherein the humidity detected by the humidity detection means is A charge control device for an electrostatic recording device, characterized in that when the humidity is high, the difference between the initial value and the convergence value of the charge amount is set smaller than when the humidity is low.