JPS63191165A - Copying device compensating for fatigue of photosensitive body - Google Patents

Abstract

PURPOSE:To prevent copy images from being changed in density even when a copying device is continuously used by forming plural correcting functions depending upon a copying time and finding out a correction value based on a function selected on the basis of the degree of fatigue at the time of ending the preceding copy and a halting time from the end of the preceding copy and the copying time to control the copying operation. CONSTITUTION:Plural correcting functions depending upon the copying time are formed, one function is selected from the plural functions on the basis of the degree of fatigue at the time of ending the preceding copy and the halting time from the end of the preceding copy and a correction value is found out based on the selected function and the copying time to control the copying operation. Thus, the fatigue of the photosensitive body can be compensated and a copy image with proper density can be obtained. Since the plural correcting functions are formed and correction and control can be executed by the function selected on the basis of the degree of fatigue and the halting time, the correction of density can be extremely accurately executed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a copying apparatus that can compensate for photoreceptor fatigue and appropriately control the density of a copied image.

[Background of the invention]

FIG. 10 is a diagram schematically showing a general copying apparatus. An original set on a platen glass 1 is exposed by a light source 2 that performs exposure scanning in the direction of an arrow a, and the image light is guided to a photosensitive drum 8 via mirrors 3 to 6 and a lens 7. The photosensitive drum 8 is charged with high DC voltage by a charging electrode 9 in advance and rotates in the direction of the arrow. When image light arrives at the charged portion, a latent image corresponding to the image light is formed there. Ru. Then, when the latent image reaches the developing section 10, toner is attached thereto and developed. On the other hand, the transfer paper set in the paper feed section 11 is conveyed to the registration roller 12, and is sent out from the roller 12 after being tamped with the leading edge of the image of the original. The developed toner of the photoreceptor drum 8 is transferred to this transfer paper by the transfer scraper 13, and the next separation pole 14 is transferred to the transfer paper.
It is separated from the photoreceptor drum 6 by the conveyor belt 15.
The sheet is sent to a thermal fixing section 16, where the toner image is fixed, and the sheet is discharged to a sheet discharge section 17.

In the copying apparatus described above, the surface of the photosensitive drum 8 is formed of a photoconductor such as selenium, and high-voltage charging, latent image formation, etc. are performed on the surface of the photosensitive drum 8, but this part becomes fatigued due to cumulative use. Due to accumulation, the charging potential changes, the density of the latent image formed changes, and the density of the finally obtained transferred image deteriorates.

For example, areas that should be completely black may not have sufficient toner adhesion and become white, areas that should be halftone may not be able to express sufficient gradation, or even capri may appear on areas that should be white. arise.

Therefore, if copying operations are always continued under the same conditions, the above-mentioned disadvantages will become more noticeable. However, it is known that when the user stops using the device, fatigue recovers depending on the period of inactivity.

[Purpose of the invention]

An object of the present invention is to prevent the density of copied images from changing even with continued use.

[Structure of the Invention] The present invention is a copying apparatus that controls the charging current of a charging electrode and/or the voltage of an exposure lamp depending on the degree of fatigue of a photoreceptor and copying time, and which controls a correction function that depends on the copying time. A plurality of correction functions are provided, one function is selected from the plurality of correction functions according to the degree of fatigue at the end of the previous copy and the pause time since the end of the previous copy, and a correction value is obtained from the selected function and the copy time, The system was configured to perform the above control.

〔Example〕

Examples of the present invention will be described below. First, the principle of copy density control will be explained. As mentioned above, fatigue of the photoreceptor appears as a phenomenon in which the charged potential thereof changes. For example, in a photosensitive drum on which a latent image is formed, the relationship between the exposure amount E and the charging potential Vs is as shown in Figure 1 (fa) if fatigue has occurred.
This results in characteristics as shown by the broken line, and the dynamic range decreases.

Therefore, if the overall charge amount of the photoreceptor drum is increased using a charging electrode and at the same time the amount of exposure from the exposure lamp is decreased, the charging potential Vs of the portions with a small amount of exposure will increase due to the former, and the charging potential Vs of the portions with a high amount of exposure will increase due to the latter. The same potential Vs of the parts increases, the entire dynamic range becomes wider, and the characteristics of the copy density with respect to the charged potential Vs become good from white to solid black, as shown in FIG. 1 fbl.

In this way, fatigue can be compensated for by correcting the amount of charge or the amount of exposure. This fatigue level is the fatigue level up to the end of the previous copy operation (starting idling after power off or power on), the down time from the end of that copy to the start of the current copy (time to recover from fatigue, and power off). (There is downtime due to idling, or downtime during idling), and the current copying time (in the case of continuous copying, the number of sheets copied so far, that is, charge-on time, or exposure time) as a factor. Therefore, the correction amount can be controlled by taking these factors into consideration.

For example, when a copying apparatus is used in the manner shown in FIG. 2, if the photoreceptor is not used at all at time t1, the photoreceptor fatigue level at this time is "0". Then,
At time t2, the photoreceptor has not yet been used, so the fatigue level is also "0", and therefore, in this case, fatigue accumulates only in accordance with the copying time from time t2. Therefore, as shown in FIG. 3, correction can be made by controlling the amount of exposure, amount of charging, etc. according to the copying time. The correction value at time t3 is Dl.

At time t4 when copying starts again, the fatigue level is at time t3.
The fatigue level at time t2, that is, the value determined by the fatigue level "0" at time t2 and the copy time (tz~t3), and the
4, the new fatigue level, that is, the correction value, is determined from time t4 onward based on the fatigue level, the pause time, and the copying time from time t4.

Since the fatigue level was "0" at time t2, the correction characteristic was a single curve starting from the fatigue level "0", but at time t4, the fatigue level and rest time at time t3 (tz~t4
), multiple fatigue levels are possible, so prepare multiple characteristic curves as correction functions as shown in Figure 4, and adjust one of them according to the fatigue level at time t4. Then, a correction value is determined according to the copy time along the selected characteristic curve.

Note that the rest time, which is a factor that determines the degree of fatigue, should not be measured within a certain period of time. Also, when measuring copy time, there are continuous copies and intermittent copies, so these are also taken into consideration. In this case, continuous intermittent copying performed at intermittent times within a predetermined period of time is treated as continuous copying without any downtime. The determination of continuous copying or intermittent copying is made by counting the number of continuous copies and the number of stops (including stopping of continuous copying and stopping of intermittent copying). In this case, the rotation time of the photoreceptor drum and the charge-on time or exposure-on time are also taken into consideration.

Although not related to fatigue, when changing the magnification, the linear velocity of the photosensitive drum changes depending on the magnification of enlargement or reduction, so the amount of exposure light and the amount of charge are corrected accordingly.

This will be explained in detail below. FIG. 5 is a block diagram showing a hardware configuration for the control, in which a density control unit 22 is provided for a main CPU 21 for copy control provided on the main body of the copying apparatus. This unit 22 is a sub CPU 2 that exchanges data with the main CPU 21.
3. It has a nonvolatile memory 24 for storing correction data, a high voltage transformer 25 that applies high voltage to the charging electrode 9, and an exposure power source 26 that applies voltage to the exposure lamp 2. Note that the high voltage transformer 25 and the exposure power supply 26 have a built-in D/A converter that converts digital data from the sub CPU 23 into analog data. The correction method will be explained below.

(1) Correction of charging amount This correction is performed by correcting the charging current. High voltage transformer 2
5, by adding data of a predetermined digital signal thereto, the value of the charging current can be changed from 450 to 1 in 5 μA steps.
, 085μ8 in 128 steps. Parameters that determine this charging current include the initial charging value, temperature, and the aforementioned fatigue and magnification.

FIG. 6 is a diagram showing a flowchart for obtaining the charging current by this correction, and the initial charging value is determined by selecting one of, for example, five types by a low-reswitch (not shown) depending on the film thickness of the photoreceptor.
Select and do this. The temperature charge correction takes in the photoreceptor drum temperature and corrects the initial charge value. The fatigue charge correction is performed by determining the fatigue correction data for the first copy immediately after the copying machine is powered on, taking in the subsequent copy time, and correcting the above-mentioned temperature charge correction value. The variable magnification charge correction corrects the fatigue charge correction value according to the variable magnification ratio. The value obtained thereby becomes the value that ultimately determines the charging current.

The temperature charging correction described above is a correction that increases the potential in proportion to the temperature, since the charging potential tends to decrease as the temperature of the drum increases.

In the fatigue charge correction described above, the correction value is determined by the flow shown in FIG. First, from the previous charge correction values (fatigue correction value and rest time) stored in the memory 24, when the power is turned on, the data of the rest time (the time from the end of the previous copy to the current power-on) is retrieved and the start is started. (when the copy button is operated), the previous fatigue charge correction value is taken out, and the correction function, that is, the charge correction mode is determined based on both of them.

Regarding this correction mode, there are a plurality of modes (correction characteristics) as shown in FIG. 4, and a specific mode is selected from among them. Then, according to the characteristics of the selected mode, as shown in Figure 3, the fatigue charge correction value that changes sequentially from the initial fatigue correction value depending on the charge-on time is determined.Table 1 below is for determining the charge correction mode. This is a table of

T on the vertical axis is the rest time, and X on the horizontal axis is the previous fatigue charge correction value.

Table 1 The following Table 2 shows the charge correction mode (vertical axis) determined in Table 1.
and charge-on time data t as copy time (horizontal axis)
This is a table for determining the fatigue charge correction value to be output.

Table 2 When copying the second continuous sheet, a new fatigue charging correction value is determined based on the data of the charging on time value up to that point in accordance with the mode determined for the first sheet in Table 1. That is, in the case of continuous copying, once the charge correction mode is determined at the time of copying the first sheet, it is fixed thereafter. At this time, the charge-on time is counted up as the time during which the photosensitive drum continues to rotate, and is reset to "0" when the drum stops rotating.

On the other hand, in the case of intermittent copying, that is, when copying starts after idling, a new charge correction is made based on the fatigue charge correction value from the previous copy and the downtime from the previous copy to the current copy. Decide on the mode and
A new fatigue charge correction value is determined based on this mode and the charge-on time t during the current copy. At this time, since the drum has stopped rotating due to the completion of the previous copy, the charge-on time starts from "0".

As described above, the charge correction mode is set only at the start after power-on or after idling, and is otherwise fixed. That is, in the case of continuous copying, it is set and fixed at the time of the first copy, and in the case of intermittent copying, it is set each time.

At the end of copying (power-off), the fatigue charge correction value data that has been output is stored in the memory in a compressed form (8 bits - 4 bits). The reason why the data is compressed in this way is that the data to be stored has a 1-byte (8-bit) structure, of which 4 bits are allocated to pause time data (updated every moment by a clock).

As described above, in the case of intermittent copying, if the intermittent time, that is, the downtime is within a predetermined time, the downtime is treated as 'OJ' and the process is treated as continuous copying.

Therefore, in this case, the charge correction mode is the same as the previous one.

In addition, since the charging on time t measurement is reset to O when the drum rotation stops due to the end of the previous copy, you can use it as is and re-count that time from 0, or you can restore the previous count value. Then, a new count value may be accumulated on the count value.

The above-mentioned charge-on time t is determined in principle by the number of copies, but if the size of the transfer paper is different, the charge-on time t required for large size sheets is longer, so it is corrected. The following Table 3 is a table from which data for correction can be obtained.

Table 3 Next, the magnification/charging correction shown in FIG. 6 is performed as follows. When changing the magnification, the linear velocity of the photoreceptor changes depending on the magnification, so first, the magnification is converted into a linear velocity as shown in Table 4 below. The linear velocity ratio is a ratio based on the linear velocity at the same magnification.

Table 4: (1) is the charging current value before the scaling correction, (2) is the charging current value after the scaling correction, n is the number of correction steps before the scaling correction, and n' is the number of correction steps after the scaling correction. As mentioned above, the minimum charging current is 450 μ8, so the following equation holds true. The correction step interval is 5 μA.

I=450 +nX5. I' = 450 +n
If '

Table 5 (2) Exposure amount correction This correction is performed by the voltage applied to the exposure lamp. The exposure power supply 26 outputs a voltage of AC 110 to 162.6 V by applying a predetermined digital signal thereto. In this embodiment, a lamp with a constant voltage of 8C160V is used, and the voltage is changed at step intervals of 0.66V. Parameters that determine this exposure voltage include the initial exposure value, temperature, fatigue, and variable magnification, as in the case of the charge amount correction described above.

FIG. 8 is a flowchart for obtaining the exposure voltage through this correction, and the initial exposure value is determined by adjusting a variable resistor (not shown). Temperature charge correction incorporates the photoreceptor drum temperature and corrects the initial charge value. Fatigue exposure correction is
The fatigue correction data for the first copy immediately after power-on is determined, the subsequent copy time is taken in, and the above temperature exposure correction value is corrected. The variable magnification charge correction corrects the fatigue charge correction value according to the variable magnification ratio. The value obtained thereby becomes the value that ultimately determines the exposure voltage.

The temperature exposure correction described above tends to reduce the charging potential and the amount of toner adhesion as the temperature of the drum increases.
For example, only when the temperature is 25°C or higher, the exposure lamp voltage is corrected by -0.25v/'C.

In the fatigue exposure correction described above, the correction value is determined by the flow shown in FIG. This is similar to the fatigue charge correction explained in FIG. 7 above, and the charge-on time is also used here as the copy time. The exposure correction mode is set only at the start after power-on or after idling, and is otherwise fixed. In other words, in the case of continuous copying, it is set and fixed at the time of the first copy, and in the case of intermittent copying, it is set each time,
This is exactly the same as the charge correction described above.

This exposure correction mode also has a plurality of modes (correction characteristics) as shown in FIG. 4, and a specific mode is selected from among them. Then, according to the characteristics of this selected mode, as shown in FIG. 3, depending on the cumulative charging time,
Determine the fatigue charge correction value.

The following Table 6 is a table for selecting this exposure correction mode. T is the rest time, and Y is the previous fatigue exposure correction value.

Table 6 Table 7 is a table for obtaining an exposure fatigue correction value using the exposure correction mode (vertical axis) determined in Table 6 and the charge-on time data t (horizontal axis).

Table 7 Also in this fatigue exposure correction, the fatigue exposure correction value to be stored in the memory at power-off is compressed from 8 bits to 4 bits and then stored, as in the case of the charging correction described above.

Next, the magnification/charging correction shown in FIG. 8 is performed as follows.

This is done by converting the magnification into linear velocity as shown in Table 8 below. The light amount ratio is the ratio to the amount of light irradiated onto the photoreceptor at the same linear velocity.

Table 8 (1) is the exposure voltage value before the scaling correction, v' is the exposure voltage value after the scaling correction, m is the number of correction steps before the scaling correction, and m' is the number of correction steps after the scaling correction. As mentioned above, the minimum exposure voltage is 110ν, so the following equation holds true. The correction step interval is 0.66v.

V = 110 + rn Xo, 66 + V'
−110+ m ′ X O,66 Furthermore, the exposure voltage V,
The light intensity ratio at V' is proportional to the 3.38th power in approximation to an incandescent light bulb, so that the following equation holds true.

Therefore, this formula becomes 〕. This formula shows that when the VH exposure voltage (m+1st as a digital value) is set at a magnification of Xo, 71 to X1.55, V' (vl (m' as a digital value) +1st) and performs light intensity correction.If this formula is rewritten in each case, the following Table 9 is obtained.
It becomes as shown in .

Table 9 Here, the actual movement of fatigue level will be explained.

The fatigue charge correction value at the end of the previous copy is '3', the fatigue exposure correction value at the end of the previous copy is '6J, and the pause time is 8.
If it takes ~15 minutes, then transfer 10 sheets of A3 size transfer paper in a row.
An example will be described in which copying is completed by setting 0 copies (the charging on time data is "7" from Table 3).

First, regarding charge correction, the previous fatigue charge correction value is
Since the pause time is 8 to 10 minutes in "3", the charge correction mode is determined to be "3" from Table 1.

From Table 2, the fatigue charging correction value is '5J' based on the charging correction mode "3J" and the charging on time data "7". In other words, as the number of copies increases, the fatigue charge correction value changes from "2" to "3" to "4" on charge correction mode '3J.
When 100 sheets have been copied, the value changes to "5" and stops.

On the other hand, regarding exposure compensation, the previous fatigue exposure compensation value is
Since the pause time is 8 to 15 minutes in "6", the exposure correction mode is determined to be "3" from Table 6.

Then, from this exposure correction mode "3" and the charge-on time data r7J, the fatigue exposure correction value becomes "10j" according to Table 7. In other words, as the number of copies increases, the fatigue exposure correction value exceeds that of mode "3". Changes to "6", "8",
After copying the 100th sheet, step "rlo".

The memory for storing data such as the charging fatigue correction value, exposure fatigue correction value, rest time, etc. described above does not necessarily need to be provided in the unit 22, and may be provided in the main body of the copying machine, or may be provided within the main body of the copying machine. It may also be stored in non-volatile memory, such as non-volatile RAM or battery-backed RAM. Therefore, data is saved even when the power is turned off, and fatigue correction is performed accurately even when the power is turned on next time and copying is started.

Further, in the embodiments, the correction was performed using the charge-on time as the copy time, but it is also possible to perform the correction using the exposure-on time, which is a value proportional to the number of copies, instead.

In addition, the contents of the above-mentioned initial charging values, initial exposure values, Tables 1 to 9, etc. are based on the R of the non-volatile RAM or the
It is stored in nonvolatile memory such as AM in advance according to the characteristics of materials such as photoreceptor drums, charging electrodes, and exposure lamps, but when those materials are replaced or changed, the contents corresponding to them are stored. The preset will be reset.

In addition, although we have explained charge correction and exposure correction separately above and have not explained in detail the timing of their correction, if the number of operating bits of the CPU is small, it will be difficult to control them simultaneously, so it is necessary to correct both. If commands are issued at the same time, each correction is performed separately at different timings by a predetermined period of time.In this way, sudden changes in copy density can also be prevented.

〔Effect of the invention〕

As described above, according to the present invention, fatigue of the photoreceptor can be compensated for, and a copied image with appropriate density can be obtained. In particular, since a plurality of correction functions can be provided and correction control can be performed using the functions selected according to the degree of fatigue and downtime, concentration correction can be performed extremely accurately.

[Brief explanation of the drawing]

Fig. 1 is a diagram for explaining photoreceptor fatigue, Fig. 2 is an explanatory diagram of the operation mode of the copying machine, Fig. 3 is an explanatory diagram of fatigue correction for fatigue starting from fatigue level O, and Fig. 4 is a diagram for explaining fatigue level. FIG. 5 is a block diagram showing the hardware configuration of the image density control part of this embodiment. FIG. 6 is a flowchart of charge correction of this embodiment.
FIG. 7 is a flowchart of charging fatigue correction in FIG. 6, FIG. 8 is a flowchart of exposure correction of this embodiment, and FIG.
This figure is a flowchart of the exposure fatigue correction in FIG. 8, and FIG. 10 is a schematic configuration diagram of a general copying apparatus. Agent Patent Attorney Tsuneaki Nagao Figure 1 (a) (b) tl ℃2 T: 3 i4 -time Figure 3 Figure 4 → Copy time (copy sand

Claims (1)

[Claims] (1) A copying apparatus that controls the charging current of the charging electrode and/or the voltage of the exposure lamp according to the degree of fatigue of the photoreceptor and the copying time, which provides a plurality of correction functions that depend on the copying time, and One function is selected from the plurality of correction functions based on the degree of fatigue at the end of copying and the downtime since the end of the previous copying, and a correction value is obtained based on the selected function and the above-mentioned copying time, and the above-mentioned control is performed. A copying apparatus characterized in that it is configured as follows.