JPH01200384A - Copy control method - Google Patents

Abstract

PURPOSE:To eliminate a defect in cleaning by converting the density of a document into a voltage and calculating the ratio of the number of times of sampling of a larger voltage than a predetermined voltage and a small voltage from a voltage level, and controlling a transferring current and a destaticizing current preceding cleaning according to the ratio. CONSTITUTION:A CPU 30 reads a maximum voltage and a minimum voltage from a voltage value held by a peak holding circuit 29 according to the detected quantity of photodetection. The maximum voltage is a voltage based upon the quantity (white part of document) of light which is reflected at the highest frequency and the minimum voltage is a voltage based upon the quantity (black part of document) of light which is reflected at the lowest frequency. Those voltage values are sampled by the CPU 30 at a specific period and the number of times of sampling of the larger voltage than the predetermined voltage level and the number of times of sampling of the smaller voltage are compared with each other to determine the transferring current and destaticizing current preceding cleaning current according to which rate range the rate is in. Consequently, cleaning performance is maintained and improved regardless of the density of a document 2.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a copy control method, and particularly to a copy control method that makes it possible to improve cleaning performance without impairing transfer efficiency.

[Prior art]

In an electrophotographic copying machine, there are originals that consume a large amount of toner, such as pictures and photographs, and originals that do not consume a large amount of toner (for example, general documents and charts).

Conventionally, residual toner has been cleaned by changing the cleaning charger or cleaning bias depending on the document.

In most of these methods, the operator manually changes the cleaning bias level (cleaning level) when the operator looks at the copy image and thinks that cleaning is defective. However, when a -degree cleaning failure occurs, even if the cleaning level is changed manually, there is a high possibility that the same problem will occur again depending on the document, and if this happens, maintenance of the cleaning device will have to be carried out. Additionally, the ability of the cleaning device is limited, and if there is a large amount of residual toner, it cannot be handled manually.

〔the purpose〕

An object of the present invention is to eliminate the drawbacks of the prior art described above and to prevent cleaning failures regardless of the amount of residual toner.

〔composition〕

To this end, the present invention detects the density of the original, converts it into voltage, samples this voltage, and sets the voltage level to a predetermined voltage level, the number of sampling times for a larger voltage and the number of sampling times for a smaller voltage. The present invention is characterized in that the transfer current and the pre-cleaning static elimination current are controlled according to the calculated ratio.

Hereinafter, one embodiment of the present invention will be described based on the drawings.

First, FIG. 2 shows a schematic diagram of the main parts of a copying machine to which the present invention is applied, in which an original 2 set on a contact glass 1 is exposed by a lamp 31, a reflector 4, and a first mirror 5. While scanning the exposure in the direction of the arrow with the unit (scanner) 6, the second. Third mirror 7.8, lens 9 and fourth
An image is formed on a photoreceptor 11 via a mirror IO, and developed by a developing sleeve 12. In the configuration shown in the figure, a document fixing method is used. Then, the transfer paper 13 is fed to the photoreceptor 11 at a predetermined timing by the registration roller 14, and the image is transferred by the action of the transfer charger 15. Thereafter, the transfer paper 13 is separated from the photoreceptor 11 by the separation charger 16.

Here, FIG. 1 is a detailed configuration diagram of the original exposure unit in FIG. 2, and the original exposure unit 6 is guided by a guide shaft 17 and moves back and forth. Further, the reflecting plate 4 has an opening 4 that guides the latent image forming light 18 to the first mirror 5.
a is formed.

In this embodiment, the lamp 3 is also used as the detection light 19 for detecting the density of the original, and the reflection plate 4 receives the latent image forming light 1.
8, an opening 4b is formed to guide this detection light 19 to the document surface. - On the other hand, the fixing part 20 of the copying machine main body
A light receiving element (for example, a photodiode) 21 is provided. Then, a flexible optical fiber 22 is provided, which has an introduction section 22a at one end that takes in light containing density information from the original 2 based on the detection light 19, and whose other end is connected to a position opposite to the light receiving element 21. It is being The light receiving element 21 and the optical fiber 22 constitute a document density detector 23. That is, the reflected light from the document is transmitted to a detection section provided at an arbitrary position via the optical fiber 22, and the light receiving element 21 detects the amount of the transmitted reflected light. Note that the position of the document density detector 23 is represented by the position of the introduction section 22a of the optical fiber 22. The vicinity of this introducing portion 22a is fixed to the document exposure unit 6 by a fixed angle 24.

Further, in FIG. 1, reference numeral 25 denotes a document reference plate provided at the home position.

Next, the positional relationship will be explained. First, FIG. 1 shows a state in which the document exposure unit (scanner) 6 has moved a little from the home position and its image formation corresponding portion 26 has reached the leading edge of the document 2. As shown in FIG. Here, the position of the imaging corresponding section 26 when the original exposure unit 6 is located at the home position is Pl,
In the state shown in the figure, the position of the imaging corresponding part 26 (document leading edge position) is Pl, the position of the introduction part 22a of the optical fiber 22 when the original exposure unit 6 is located at the home position is Pl, and the latent image leading edge is Pl. Assuming that the position of the introducing section 22a when it reaches the developing section is P4, the imaging corresponding section 26 is located at the home position from the document 2.

It is set so that it does not face the document 2. On the other hand, the introduction part 22a of the optical fiber 22 is arranged at a position preceding the imaging corresponding part 26 by the distance between the positions PI and P3, and when the original exposure unit 6 is located at the home position, the original 22a is placed at the position P3. are set to face each other.

In this embodiment, during the copying operation, the density of the original is detected by scanning the original between positions Pz and P4 using the detection light 19, and the developing bias voltage is controlled by the maximum value of the detection signal (value corresponding to the background area). A mode is adopted in which the copying operation is executed as is, and pre-scanning for detecting the original density is not performed.

First, until the exposure unit 6 moves from the home position to the state shown in FIG. 1 (current position), the introduction part 22a of the optical fiber 22 faces the original 2 from the beginning.
The surface of the document will be scanned.

That is, based on the detection light 19 of the lamp 3, light containing density information of the original 2 is introduced into the optical fiber 22 from the introduction section 22a and transmitted. The light introduced into the optical fiber 22 is guided to the light receiving element 21 and photoelectrically converted.

FIG. 3 is a configuration diagram of a control circuit, in which a light receiving element (in this embodiment, a photodiode) 21 is connected to two OPs, for example.
It is connected to a peak hold circuit 29 including amplifiers 27 and 28, and a photocurrent corresponding to the amount of light flowing through the light receiving element 21 is converted into a current and a voltage and output as a detection signal (2).

The light-receiving element 21 is connected between + and - of the operational amplifier 27, and is used with no voltage applied so as to prevent dark current from flowing. The detection signal VDE obtained from the OP amplifier 28 in this manner is effectively used as original density information as a signal for determining process conditions when making a copy. However, at the time when the exposure unit 6 starts moving, the light amount of the lamp 3 needs to have already risen.

Thereafter, the exposure unit 6 further scans to the left from the current position shown in FIG. 1, but at this time, the detection of the original density continues using the detection light 19 that precedes the latent image forming light 18. .

Then, in accordance with the scanning of the exposure unit 6, the latent image forming light 1
8, the leading edge of the latent image formed on the photoreceptor 11 will eventually reach the developing position by the developing sleeve 12, but just before that, the detection signal 2 is generated. The developing bias voltage VR corresponding to E is set by the CPU 30 with an A/D converter,
A bias voltage a31 is applied to the developing sleeve 12.

The peak hold circuit 29 operates in the original density detection area P3. shown in FIG. The maximum value between Pa is detected, this is regarded as the original background density, and the developing bias voltage VII corresponding to this maximum value is applied. Here, when controlling the developing bias voltage (8) as in this embodiment, the distance from the current position P3 until the leading edge of the latent image reaches the developing position is 1. is converted to a distance on the document, so this distance changes when zooming in or out. Now, as shown in FIG. 3, if the distance between the exposure section and the development section on the photoreceptor 11 is L2, the document density detector 2 can be effectively used for density adjustment.
The scanning distance of No. 3 can be converted into a distance on the document and expressed as follows.

However, m is an enlargement/reduction ratio of, for example, 0.5≦m≦2.

FIG. 4 is a timing chart showing the operation of this embodiment.

As can be seen from the figures (al and b), the lamp 3 is turned on when the exposure unit 6 starts running.

In addition, L is the concentration detection section, and in Figure 1, =L, +
l, 2').

(C) in FIG. 4 shows the developing bias voltage (■), and this voltage (■8) is the maximum value of the detection voltage that the CPU 30 has keeled by the peak hold circuit 29, as shown in (dl).
Control is performed based on the value sampled at the end of the interval t1.

According to the operation mode of this embodiment, the original density detection area is enlarged because the original density detector 23 faces the original 2 and detects the original density from the time when the exposure unit 6 starts scanning. Therefore, density control can be performed with higher accuracy. Moreover, the means for this purpose is also extremely simple. Also, if the image is at the same size, the image density of a specific area of the document 2 will be detected and used for density control, but if the copy is made at a variable magnification such as reduction or enlargement, the detection area will be automatically adjusted depending on the ratio. It is detected by the change in concentration and is used for good concentration control.

Note that the peak hold circuit 29 shown in FIG. 3 has an added function of applying a reset signal to the reset terminal in order to eliminate the previous history before detecting the concentration. This reset signal is applied before the lamp 3 is turned on, as shown in FIG. 4(d).

Furthermore, in the operating mode of this embodiment, the developing bias voltage 8 is controlled based on the detection of the original density, but the amount of light exposing the original by the lamp 3 may also be controlled.

These may be used alone or in combination. When controlling the exposure light amount, the light amount of the lamp 3 is kept at a constant value from the home position to the current position shown in Fig. 1, and the light amount of the lamp 3 is adjusted according to the document density detection output during that time. It is necessary to switch at the current position. However, if the response speed of the lamp 3 is a problem, the acquisition of the density signal and the switching of the light amount of the lamp 3 will be performed at a position closer to the home position than the current position in FIG.

Next, the image density control method of the present invention will be explained.

In FIG. 3, the CPU 30 reads the maximum voltage and minimum voltage from the voltage value held by the peak hold circuit 29 based on the detected amount of received light. The maximum voltage is a voltage based on the amount of light that is reflected the most (white portion of the document), and the minimum voltage is a voltage that is based on the amount of light that is reflected the least (black portions of the document).

These voltage values are sampled at a predetermined period in the CPtJ30, and the number of samplings of voltages larger than a predetermined voltage level is compared with the number of samplings of voltages smaller than a predetermined voltage level, and it is determined in which range of the predetermined ratio the ratio falls. Accordingly, the transfer current and the pre-cleaning static elimination current are determined.

Now, the amount of reflected light from the original is converted into voltage, and if the voltage is higher than a predetermined voltage level, a comparator (
(It may be built into the CPU 30 or may be provided externally.) Since the output becomes "L" and becomes "H" if the voltage is small, the ratio N of the number of samplings for each is calculated.

FIG. 5 is a diagram showing the relationship between the sampling frequency ratio, the pre-cleaning static elimination current, and the transfer current. As shown in the figure, in this example, the transfer efficiency was set to t] so that N < 0.2 aμA 0, 2≦N<0.4 bμA 0.4≦N<0.6 cμA 0. It is determined that 6≦N dμA.

In addition, to make it easier to remove toner with a cleaning device, the current for pre-cleaning static elimination, which applies the same polarity as the toner polarity before cleaning, is set to N<0.2 eIJA 0, 2≦N<0.4 f μA 0.4≦ N<0.5 gμA 0.5≦N<0.6 hμA 0.6≦N <0.7 rμA0.7≦N
It is determined to be 3ttA.

FIG. 6 is a flowchart illustrating the operation of determining the pre-cleaning static elimination current and transfer current described above. For example, in step 1, the calculated value of N is N < 0.
In case 2, that is, when the density of the original is compared to a predetermined level (density) (step 2), the ratio of dark parts is approximately 2.
If it is 0% or less, the transfer current is set to aμA, and the pre-cleaning static elimination current is set to eμA.

Depending on the document, if it is judged that 0.2≦N<0.4, that is, the dark part is about 20 to 40% (step 3), the transfer efficiency will decrease slightly, so change to bμA,
Since there are many dark areas, a lot of toner remains on the photoreceptor after transfer, so in order to improve cleaning performance, the pre-cleaning static elimination current is changed to fμA.

Thereafter, by controlling the transfer current and the pre-cleaning static elimination current according to steps 4 to 7 depending on the density of the original, cleaning performance can be improved without impairing transfer efficiency.

〔effect〕

As described above, according to the present invention, (11) maintaining cleaning performance regardless of the density of the original;
You can improve.

(2) Maintenance intervals can be extended.

It has the following effects.

[Brief explanation of the drawing]

FIG. 1 is a detailed configuration diagram of a document exposure unit of a copying machine showing an embodiment of the present invention, FIG. 2 is a schematic side view of the copying machine, and FIG.
4 is a timing chart for explaining the operation, FIG. 5 is a diagram showing the ratio N of sampling times according to the present invention, and FIG. 6 is a control flowchart. 23... Original density sensor, 30... cpu. Figure 1 Figure 2 ¥4 Figure (e) Cl-'U sampling Figure 5 Figure 6

Claims (1)

[Claims] The density of the original is detected and converted into a voltage, this voltage is sampled at a predetermined period, and the voltage level is calculated as the ratio of the number of samplings of a voltage larger than the predetermined voltage level and the number of samplings of a voltage smaller than the predetermined voltage level. A copying control method characterized by calculating and controlling a transfer current and a pre-cleaning static elimination current according to the calculated ratio.