JPS6359143B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for forming images. Images formed by electrophotography are easily affected by environmental conditions and the like, and stabilizing the electrostatic latent image is extremely important in practice.

First, the main factors that contribute to the characteristics of images formed based on general electrophotography are listed: photoreceptor characteristics, charging means characteristics for photosensitization, exposure source characteristics and exposure amount, development characteristics, transfer characteristics, These include transfer material characteristics, residual developer cleaning characteristics, etc. Since each of these characteristics is influenced and fluctuated by temperature, humidity, contamination such as dust, changes over time, etc., complex changes in the image characteristics occur. Conventionally, in order to stabilize this image change, a method has been adopted in which each of the above characteristics is stabilized independently, but this method has not yet reached a state that can be called fully satisfactory.

As a method for stabilizing electrophotographic images, the so-called Carlson process is used to form an electrostatic latent image on a xerographic photoreceptor by charging and exposing it to light. The potential of the electrostatic latent image or the density of the developed image is detected and fed to the charging/exposure means of the process. For example, U.S. Pat. No. 2,956,487 describes the method of back-up and stabilization.
Factors that make an electrostatic latent image unstable include fluctuations in charging voltage, foreign matter adhering to charged electrodes, changes over time due to oxidation of charged electrodes, corona discharge characteristics due to temperature and humidity,
Examples include changes in image exposure, fatigue of the photoreceptor, and changes in temperature and humidity characteristics of the photoreceptor. If each of these instability factors is within a certain range, measure the potential of the exposed and non-exposed areas of the electrostatic latent image, and change the charging voltage, exposure amount, etc. using the feedback system to stabilize the image. It is possible to stabilize the electrolatent image.

The above US patent controls the potential of an electrostatic latent image formed based on the Carlson process, but when the photoreceptor etc. deteriorates, its residual potential increases and the potential of the exposed area changes. Stabilization becomes difficult. On the other hand, methods that require two or more types of charging processes to form an electrostatic latent image (for example, Japanese Patent Publication No. 19748, No. 42-23910, Japanese Patent Publication No. 24748, No. 43-1973 proposed by the applicant, etc.) ), by controlling the charging means that performs each charging step, it is possible to change the exposed and non-exposed part potentials of the electrostatic latent image formed, thereby realizing stable image formation. I found something suitable for this. However, even if feedback is applied from the latent image potential measuring means to each charging means, there is a drawback that it takes a long time to converge and stabilize the latent image potential to a reference value.

The present invention provides an image forming apparatus that can reduce the time required to stabilize an image and always obtain a proper image.

The details of the present invention will be explained below based on embodiments and with reference to the drawings.

FIG. 1 is a side view of an apparatus for carrying out an electrostatic latent image formation process. The electrostatic latent image formation process is
This is an application of the process described in Japanese Patent Publication No. 42-23910, which uses a photoreceptor whose basic structure is a photoconductive layer and an insulating layer laminated on a conductive support.

Photosensitive drum 1 made by molding this photosensitive member into a drum shape
is rotationally driven in the direction of the arrow by a driving means (not shown). The photoreceptor is subjected to uniform corona discharge by the primary charger 2, and then subjected to AC charger 3 by the AC charger 3.
At the same time as the corona static elimination is applied, the light image of the original image on the platen 30 is exposed by the exposure light source 4, and then the entire surface is uniformly exposed by the lamp 5. In this way, a high contrast electrostatic latent image is obtained on the surface of the photosensitive drum 1. Exposure is performed by scanning (forward movement) by the reciprocating movement of the mirror 31 and lamp 4. This electrostatic latent image is developed in a developing device 7 using a developer consisting of colored charged particles (toner) and a magnetic carrier. The developed toner image is transferred to the transfer paper by feeding a transfer paper between the photosensitive drum 1 and the transfer charger 8 in synchronization with the photoconductor drum, and applying corona discharge from the transfer charger 8.

The transfer paper onto which the toner image has been transferred passes through a fixing device 10 consisting of a heating and pressure roller, and the toner image is fixed. A cleaning device 11 cleans the photosensitive drum having residual toner on its surface and prepares it for the next electrostatic latent image forming process.

In the illustrated apparatus, a probe 6 for measuring the surface potential of the photoreceptor drum 1 is disposed at a position following the full-surface exposure lamp 5. The probe may be any of various conventionally used probes, such as a vibratory capacitance probe. This probe 6 is coupled to a surface potential measuring circuit 16 to process the probe signal,
Output the necessary signals from there. The surface potential measuring circuit 16 generates a voltage proportional to the potential measured by the probe, and inputs it to the control section 21 via the AD converter 19. As will be described in detail later, the control section inputs the signal from the drum rotation pulse generator 12b and processes the input signal from the probe 6, while the output is sent to the D-A converter 1.
It is connected to each process means via 7, 18, 23, etc.

In order to facilitate understanding of the method of the present invention, basic procedures for making the surface potential on various commonly considered photoreceptors constant will be explained. (Potential convergence method) First, measure the potential V _D (hereinafter referred to as dark potential) of the non-exposed area of the latent image, compare it with a predetermined standard dark potential V _DR , and calculate the potential difference x = V _DR − V _D is determined, and if the potential difference does not fall within a constant value, a voltage ΔEp proportional to x is applied, for example, superimposed on the voltage Ep currently being applied to the primary charger 2. After waiting for a time until the effect of the change in the voltage applied to the primary charger 2 is detected by the probe, V _D is measured again,
This cycle is repeated until the potential difference |x| reaches a constant value a.

Next, the exposed part potential V _L (hereinafter referred to as the light part potential) of the latent image is measured, and this is set to a predetermined standard bright part potential.
Compare with V _LR to find the potential difference y=V _LR −V _L. If this potential difference |y| does not fall within the constant value b, the voltage △E _AC proportional to y is changed to AC
It is added superimposed on the voltage E _AC currently applied to the charger 3. After waiting for a period of time until the effect of the change in voltage E _AC is detected by the probe, V _L is measured again and repeated until |y| falls within a certain constant value b. Next, even if |y| stays at a constant value, |x| will change again, so the above procedure will be changed to |x|<a, |y|
Repeat until <b can be realized simultaneously.

In order to stabilize the electrostatic image using this method,
This requires relatively long drum rotations (several to dozens of times), and in general electrophotographic equipment,
This has the fatal disadvantage that it takes a long time to copy the first sheet. (Coefficient method) First, the photosensitive drum 1 is rotated while keeping it in a dark state, and then exposed to light to make it in a bright state. probe 1
While the dark state portion of the photosensitive drum passes through the second position, the dark potential V _D is measured, and then the light potential V _L is measured while the bright state portion passes through the second position. These measured values V _D and V _L are compared with each standard potential V _DR and V _LR , and x
= V _DR - V _D , y = V _LR - V _L , and if both are not within the range of constant values a and b, then use a function f with x and y as variables to determine each predetermined applied voltage.
(x, y), g(x, y), △Ep=f
(x, y), ΔE _AC =g(x, y) is determined. The primary voltage Ep and Ac voltage E _AC are changed according to this determined value. This process is repeated until |x|<a and |y|<b. In detail, the exposure is kept in the dark state, the photosensitive drum is rotated, and the dark area potential V _D
Measure. Compare the measured value with the probe with the standard potential, and if the potential difference |x| does not fall within the constant value a,
The primary voltage is changed by △Ep=αx=α(V _DR −V _D ). On the other hand, since the photoreceptor is changing from a dark state to a bright state, the light potential V _L is measured immediately after measuring the dark potential V _D with the probe. This potential difference |y
If | is not within the constant value b, △E _AC =βy=
Change the AC voltage by β(V _DR − V _D ). Next, the surface of the photoreceptor is switched to a dark state, and the probe waits until the effects of the previously changed primary voltage and AC voltage are detected, and the above procedure is repeated |x|<
Converge to a|y|<b. This is effective because the time required in the potential convergence method can be shortened to 1/3 to 1/5. However, the above functions f(x, y) and g(x, y) differ depending on the photosensitive plate, and even with the same photosensitive plate, they change depending on environmental changes such as moisture absorption of the photosensitive plate, so it is not possible to provide accurate high pressure setting conditions. There are drawbacks.

The present invention eliminates various drawbacks in the potential convergence method and the coefficient method, and the operating conditions of the electrostatic latent image forming means are sequentially changed in n stages during rotation of the photoreceptor prior to the image forming process. (n≧3), forming a bright area and a dark area on the photoreceptor under each operating condition, detecting the surface potential of the bright area and the dark area, and based on the detected value. A characteristic curve of the photoreceptor is determined, and operating conditions of the electrostatic latent image forming means that provide a predetermined contrast potential are determined from this characteristic curve, thereby making it possible to obtain a stable image. .

An example of the present invention will be explained in detail with reference to FIG. A case is shown in which the primary charger 2 and the AC charger 3 are arranged at an angle of 45 degrees, and the angle between the AC charger 3 and the potential detection sensor 6 is arranged at an angle of 30 degrees. When rotating the drum 1 and AC charging, the lamp 13 is simultaneously exposed to the same image.
The uniform light biased by is intensified step by step as E ₁ → E ₂ → E ₃ every time the drum rotates r°.

Bright and dark areas of image exposure are given at each level of uniform light intensity. For example, white paper and black paper corresponding to bright and dark areas of the original are provided in advance at the leading end of the original platen 30.

AC charging, image exposure and uniform bias light are delayed by 45° compared to primary charging, and potential detection is further delayed.
Perform each step with a 30° delay.

Figure 2 shows (uniform light intensity) changing in three stages.
A timing chart for detecting bright and dark potentials in steps of r°/2 is shown.

Regarding each timing, the pulses generated by the pulse generator 12b in FIG. Depending on the situation, the timing is determined by switching between bright and dark exposure and measuring the surface potential. The stepwise change time of the amount of uniform light needs to be a time width that allows the detection sensor to stably measure the bright and dark potentials when the amount of light is changed.

Here, it is desirable to set r° to 0.2 to 0.5 seconds (30° to 90°). The amount of uniform light that is changed in steps is such that even when the latent image potential changes due to environmental changes or deterioration of the photoconductor, a predetermined contrast potential can be obtained. It is preferable to change it within the range of light quantity conditions.

Next, as described above, when surface potential detection is performed, the output voltage of the potential detection sensor 6 according to the bright/dark potential is converted from analog to digital by 19 and input to the calculation unit 20.

The arithmetic unit calculates the light intensity value (digitally converted) by changing the uniform light intensity in a stepwise manner.
The potential contrast between bright and dark potentials is calculated, and a potential contrast curve is output to the control unit 21. The control section 21 determines the voltage applied to the lamp light source 13 that provides uniform light so as to obtain a predetermined potential contrast from the potential contrast curve determined in the calculation section. The output value from the control section 21 is digital-to-analog converted by 17 and inputted to the lamp light source 4.

The bright area potential under a newly set uniform light intensity can be obtained from the bright potential curve obtained by sequentially changing the uniform light intensity in advance, and A bias corresponding to the shortage of the partial potential is applied to the sleeve roller of the developing device 7.

FIG. 3 is a curve of the surface potential V and the amount of light image E when uniform light is irradiated and varied.

Figure 4 shows the changing light amount of uniform light when x ₁ is 0.2 lux sec,
The curves of the potential contrast V _C (V _D −V _L ) of the bright potential V _L and the dark potential V _D are shown when x ₂ is changed to 0.4 lux・sec and x ₃ is changed to 0.6 lux・sec. It is a graph. The bright image exposure amount is 0.8lux·sec. now,
If the standard dark potential V _SD is +450 and the same bright potential V _SL is -50 V, the same potential contrast V _SC is 500 V.
This value exists between x ₂ and x ₃ , and when a linear approximation is made to the potential contrast curve between these points, the amount of light that is further biased to the uniform light amount at point x ₂ as a value proportional to the potential contrast, i.e. A uniform light amount of 0.428 lux·sec to obtain V _SC is determined.

The more times the amount of uniform light is changed stepwise, the more effectively the amount of uniform light can be determined using the above-mentioned linear approximation to achieve the predetermined V _{SC .} Since there will be some error in the linear approximation, it is better to use quadratic or cubic
The following curve approximation can determine the uniform light amount more effectively.

For example, if x is the variable when the amount of uniform light is changed in steps, then the brightness detected at each step is
The potential contrast V _C of the dark potential can be expressed as V _C =ax ² +bx+c, and the unknowns a, b, and c are obtained by changing the amount of uniform light in three steps, and a quadratic curve can be determined. 3 step change x ₁ to 0.2luxsec, x ₂
Assuming that is 0.4luxsec and x ₃ is 0.6luxsec, the uniform light amount can be determined by substituting 500V for the predetermined potential contrast V _SC to the obtained quadratic curve. That is, when V _C is 500V, xsc is obtained by solving the well-known formula (-b+√ ² -4(-500))/2a. Similarly, 3
When performing the following curve approximation, it can be obtained by changing the light amount in four steps.

As described above, by continuously changing only the amount of uniform light and performing a series of potential detections accordingly, it is possible to determine the amount of uniform light so as to obtain a predetermined potential contrast. Therefore, unlike the conventional convergence method, there is no need to repeat the operation of changing the high voltage once and then detecting the potential several to dozens of times, and the process time lost between the charger and the potential detection sensor is reduced. less,
Compared to commercial copy machines, the time required for potential detection can be reduced.

Further, in the coefficient method, if the characteristics of the photosensitive plate change, the predetermined coefficients will change, so the control cannot be carried out correctly, but this problem can be adequately addressed.

Furthermore, the light source that biases uniform light to form brightness and darkness when measuring the potential in bright and dark areas may be a light source for image exposure, or a light source provided separately for measurement.
Further, the amount of light from the lamp may be mechanically applied using a shutter so that the rise and fall characteristics of the lamp do not cause measurement errors and loss time. Note that the amount of uniform light can be changed not only by changing the lamp power supply voltage that provides uniform light, but also by several methods.
It is also possible to use an ND filter or change the aperture of the lamp light.

[Brief explanation of drawings]

Fig. 1 is a sectional view of the stable image forming device according to the present invention, Fig. 2 is a timing chart showing the operation of Fig. 1, and Fig. 3 is a V-E when uniform light is irradiated.
The characteristic diagram, Figure 4, is a potential contrast characteristic diagram when the amount of uniform light is changed stepwise.
15 is an exposure light source, 15 is a bias light source, 16 is a surface electrometer, and 22 is a developing bias power source.

Claims (1)

[Scope of Claims] 1. An electrostatic latent image forming means for forming an electrostatic latent image on a photoreceptor, a developing means for developing the electrostatic latent image formed on the photoreceptor, and an electrostatic latent image formed on the photoreceptor. a detection means for detecting surface potentials in bright and dark regions; and a control means for controlling operating conditions of the electrostatic latent image forming means in accordance with the output of the detection means, the control means being used in the image forming step. During the rotation of the photoreceptor prior to this, the operating conditions of the electrostatic latent image forming means are sequentially changed in n steps (n≧3), and a bright area and a dark area are formed on the photoreceptor for each operating condition. forming a region, detecting the surface potential of the bright region and the dark region by the detecting means, determining a characteristic curve of the photoreceptor based on the detected value, and obtaining a predetermined contrast potential from the characteristic curve. An image forming apparatus characterized in that operating conditions of an electrostatic latent image forming means are determined.