JPS6291969A - Electronic copying machine - Google Patents

Abstract

PURPOSE:To eliminate the need for a device, which moves a density detecting means by fixing the density detecting means on an original carrying path so that this means faces an original and detecting the original density when the original passes the density detecting means. CONSTITUTION:A density detecting means 41 consisting of an optical sensor or the like is attached under one end of a platen glass 2 on the carrying path of an original 4. This detection signal 42 is processed by a copy density determining circuit 43. With respect to the density detecting means 41, a light emitting element 51 and a photodetector 52 are stored in one package 53. When the light emitting element 51 is lit, the light is reflected on the original 4 and is detected by the photodetector 52. The intensity of this reflected light is converted to an electric signal to detect the density. Carrying and density detection are performed simultaneously to quicken the timing of exposure start in comparison with conventional successive execution of carrying, density detection, and exposure of the original 4.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to an electronic copying machine equipped with an automatic document feeder.

``Prior Art'' Generally, in an electronic copying machine, an original is placed on a platen glass and an operator presses a print start button to copy the original onto copy paper. However, it is not only time-consuming for an operator to repeat this process for a large number of documents, but it is also bad for office efficiency. An automatic document feeder has been developed that automatically starts printing, ejects the document after copying, and supplies the next new document.

FIG. 8 shows a longitudinal sectional view of the automatic document feeder 1.

This device is supported by three legs (not shown) and placed at a predetermined position above the platen glass 2. On the top surface of this device, there is a document tray 3 that accommodates the document 4 to be copied.
is provided. A feed belt 5 is provided at the lower right of the document tray 3 to sequentially feed the documents 4 from the bottom layer. This feed belt 5 is equipped with an air suction mechanism 5', which sucks the leading edge of the lowest document 4 and sends it out in the direction of arrow 6.

A guide plate 7, a feed roller 8 and two pinch rollers 9 are provided in front of the guide plate 7. Further, the claw 11 is in an open state as shown by the broken line.

After the document 4 is pulled out by the feed belt 5, it advances along the guide plate 7, and is conveyed onto the platen glass 2 below by the feed roller 8 and the pinch roller 9.

A conveyor belt 12 is provided directly above the platen glass 2 to convey the original to a final copying position. This conveyor belt 12 conveys the original in the direction of arrow 16.

A registration gate 13 is provided at the left end of the platen glass 2 to stop the progress of the transported original 4 and stop the original 4 at a predetermined copying position.

Further, a registration sensor 14 is installed adjacent to this, which detects when the leading edge of the original 4 reaches this registration gate 130 portion and outputs a detection signal for operations such as starting exposure.

After exposure, the registration gate 13 is opened and the conveyor belt 12 conveys the document in the direction of arrow 16, and the document is discharged to the outside via the guide plate 17 and the discharge roller 18.

If the original has images to be copied on both sides, after the exposure is completed, the conveyor belt 12 is reversed and conveys the original 4 in the direction of arrow 21. The original 4 is reversely fed along the guide plate 7, and at this time, the feed roller 8 is also reversely rotated in the same direction. The claw 11 now enters the conveyance path as shown by the solid line in the figure, advances the document 4 along the guide plate 22, and sends it under the conveyance belt 12 again.

At this time, the document 4 is just turned over, and the side opposite to the previous side is exposed.

In order to synchronize the feeding of the document 4 of such an automatic document feeder, the opening/closing of the register gate 13, and the timing of exposure, this device and the main body of the electronic copying machine are connected by a signal cable (not shown).

FIG. 9 shows a longitudinal sectional view of a conventional electronic copying machine equipped with this automatic document feeder.

The automatic document feeder 1 is placed above the platen glass 2, and the optical system 26 is placed below.

The image drawn on the original document 4 is configured to be focused on the upper surface of a belt-shaped photoreceptor 27 by the optical type 26.

Exposure is instantaneously performed by a flash light source (not shown).

The photoreceptor 27 rotates in the direction of an arrow 28, is developed by a developing device 29, passes through a transfer device 31, passes through a charger 32, and returns to the exposure section again.

The copy sheets 33 are stored in two paper feed devices 34, and are pulled out one by one, pass through the path indicated by the broken line arrow 36 in the figure, are transferred by the transfer device 31, and are fixed by the fixing roller 37. Thereafter, the paper is discharged onto a discharge tray 40 by a discharge roller 38, but in the case of double-sided copying, it is fed into an auxiliary tray 39 and turned over. Then, copying of the back side is performed again along the path of arrow 36.

Normally, in such an electronic copying machine, when an operator first sets a predetermined number of originals 4 on the original tray of the automatic document feeder 1 and presses a print start button on a console panel (not shown), the originals start as shown in FIG. The paper is fed to a copying position above the platen glass 2 by the feed belt 5, the feed roller 8, and the conveyor belt 12.

The register gate 13 is closed at this time, and the register sensor 14
detects that a document has been sent here and outputs a detection signal. Next, in FIG. 9, the copy paper 33 is sent out from the paper feeder 34, and the flash light source is turned on at a predetermined timing to perform exposure. After that, the photoreceptor 27
is developed, transferred onto the copy paper 33, and the copy paper 33 is discharged as is.

On the other hand, the automatic document feeder 1 moves the register gate 1 after the exposure is completed.
3 is opened, the document 4 is ejected, the registration gate is closed again, and the feed belt 5 is driven to start feeding the next document 4.

In the manner described above, this device automatically copies the set original 4.

"Problems to be Solved by the Invention" In such an electronic copying machine, the density of the image to be copied of the document fed onto the platen glass 2 is detected, and the copying conditions are automatically set in accordance with this. It is preferable to do so.

Therefore, a method may be considered, such as detecting the density of the image after the original is sent to the copying position, and changing the potential of the developing device 29 (FIG. 9) accordingly.

For this purpose, it is necessary to receive the reflected light from a predetermined portion of the image of the original using an optical sensor, and to detect the density based on the result. At this time, in order to detect the density of the entire image of the original, a method has been developed in which a density detection means such as an optical sensor is moved over a certain range on the lower surface of the platen glass and the average value of the density is taken.

However, such a method requires a certain amount of processing time from when the document reaches the copying position until the density is detected, which is an obstacle to speeding up the copying process.

The present invention has been made with attention to the above points, and an object of the present invention is to provide an electronic copying machine that can improve copying efficiency by detecting the density of an image of a document before it reaches the copying position. It is something to do.

``Means for Solving the Problems'' The electronic copying machine of the present invention is one in which a document is conveyed onto a platen glass by an automatic document feeder to obtain a copy. The detection means is fixed, and when the original passes through a portion facing the density detection means, the density detection means detects the density of the image on the original over a predetermined length, and the copy density is determined based on this detection signal. It is characterized by:

"Function" In this way, if the density detection means is fixed on the document transport path so as to face the document, and the density is detected when the document passes in front of the density detection means, the density detection A device for moving the means is not required.

Further, the density detection work is already completed before the document reaches the copying position, and the copying operation can be quickly started.

Embodiment FIG. 1 is a block diagram showing an embodiment of an electronic copying machine of the present invention.

In the figure, the automatic document feeder 1 has almost the same configuration as that in FIG. 8 for the most part, and the same parts are given the same reference numerals and redundant explanations will be omitted.

In the figure, concentration detection means 41 consisting of an optical sensor etc.
It is attached below one end of the platen glass 2 in the conveyance path of the original 4. This detection signal 42 is transmitted to the copy density determining circuit 4.
3.

The processing result 44 is read by a control circuit 46 that controls the operation of the entire device. This control circuit 46 selectively controls the potential of the developing device 29 based on the read processing result 44.

As the concentration detection means 41, for example, as shown in FIG. 2, a light emitting element 51 and a light receiving element 52 are housed in one puff cage 53. When the light emitting element 51 turns on, the light is reflected by the original 4 and detected by the light receiving element 52. Concentration detection is performed by converting the intensity of this reflected light into an electrical signal.

FIG. 3 is a block diagram of the copy density determining circuit 43.

First, in order to turn on the light emitting element 51 during the concentration detection operation, a driver circuit 57 consisting of a constant voltage power supply 56 and a switch inserted into a circuit 58 connecting this and the light emitting element 51 is provided. There is.

A lighting control signal 61 from the control circuit 46 turns on the switch of this driver circuit 57, and a constant voltage power supply current is supplied to the light emitting element 51, so that the light emitting element 51 is turned on.

On the other hand, the detection signal 42 of the light receiving element 52 is processed by an integrating circuit 62 and a comparing circuit 63, and the result is stored in a latch circuit 64. The light receiving element 52 outputs a detection signal 42 of the density of the image on the original 4 for a certain length while the original 4 is being conveyed. This detection signal 42 fluctuates in accordance with the image density of the original document 4 during the detection operation, but it is manually inputted to the integrating circuit 62 to obtain its average value signal 66.

This average value signal 66 is composed of, for example, three comparison signals 71 to 73.
A 2-bit digital signal is output from the comparator 63 to the latch circuit 64 depending on the range. The data stored in this latch circuit 64 is read by the control circuit 46 as a processing result 44 of this circuit.

By increasing the developing potential of the developing device 29, more toner adheres to the photoreceptor and the copy density can be increased. Therefore, as shown in FIG. 4, four types of development potential can be selected, and the higher the density of the document, the lower the development potential is selected.

FIG. 5 shows the density detection signal of a general original.The detection level (corresponding to the average value signal) is as shown by a curve 81 in the case of a white original, and as shown by a curve 82 in the case of a colored original. It becomes like this. That is, the detection voltage changes by about 1.5 volts between the case where there are no characters and the case where the entire surface is black. Here, the levels of the comparison signals 71 to 73 shown by drawing three lines as shown in the figure are determined and sent to the comparison circuit 63. In the manner described above, the density detection result 44 (FIG. 1) of the original 4 is obtained.

The control circuit 46 includes a microprocessor 83 and a ROM element (read only memory) 8 connected to the microprocessor 83 via a pass line 84 in order to control the operation of each part of the device.
5, and RAM element (random access memory)
86 and an interface (I/F) 87. The ROM element 85 includes this developing device 2.
An operation program for controlling the development potential of No. 9 is also stored. Further, data necessary for various operations is temporarily stored in the RAM element 86.

As shown in FIG. 6, the electronic copying machine of the present invention described above, as shown in FIG. At the same time, the timing of the start of lightning has been accelerated (Figure b).

A more detailed flowchart of such operations is shown in FIG.

First, the light emitting element 51 shown in FIG. 2 is turned on in synchronization with the start of document conveyance (step 1 in FIG. 7).
■). This is to limit the light emitting time of the light emitting element 51 to only the time necessary for concentration detection, thereby extending its lifespan.

Next, it is checked whether the original 4 has arrived at the density detection means 41 (step 2). When the document 4 arrives, the detection signal 42 from the light receiving element 52 (FIG. 2) is input to the integrating circuit 62, and averaging thereof for a certain period of time is started. The arrival of a document can be detected by detecting a sudden change in the detection signal 42 of the light receiving element 52.

Alternatively, the timing may be determined by measuring a certain period of time from the start of transport using a timer.

The time for density detection is also set by a timer, and the density detection signal is output for a certain period of time depending on the size of the original or regardless of the size of the original.

When the detection result 44 corresponding to the average value of this detection signal is read from the latch circuit 64 to the control circuit 46, a development potential is selected. The control circuit 46 sends the selection signal 89 to the developing unit 2.
Send to 9. The developing potential is adjusted, for example, by adjusting the resistance value of a resistor inserted in the power supply circuit of the developing device. Alternatively, the control circuit may send a selection signal to a selection circuit (not shown) that selects and outputs one of several voltages.

As a result, the development potential is adjusted (step (2)), and then the light emitting element 51 is turned off (step (2)).

Since this density detection means 41 operates effectively only when an automatic document feeder is used, this program is exited by ending the ADF mode (step 2). If the document is to be fed in continuously, return to the first step (■).

"Variation" The electronic copying machine of the present invention is not limited to the above embodiments.

The density detection means may be placed anywhere as long as the original passes through it before reaching the copying position. However, the location of the above embodiment is also preferable due to its structure.

Furthermore, the circuit for processing the concentration detection signal may be replaced with various circuits that perform similar operations.

In the above embodiment, the developing voltage of the developing device has a one-to-one correspondence with the output signal of the density determining circuit, so the power supply circuit etc. can be directly controlled by the output signal of this determining circuit. For example, the burden on the control circuit can be reduced.

Conversely, if the output signal of the density detection means is A/D converted, read by the control circuit, and compared with the conditions in the ROM, etc., the copy density determination circuit can be further simplified. You can also do it.

Effects of the Invention J The electronic copying machine of the present invention described above quickly detects the density of the original, thereby making it possible to speed up the copying operation and improve the quality of the copies at the same time.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the electronic copying machine of the present invention, FIG. 2 is a vertical sectional view showing the structure of its density detection means, FIG. 3 is a block diagram of a copy density determining circuit, and FIG. A graph showing the correspondence between the development potential and the density of the image on the original, FIG. 5 is a graph showing the correspondence between the detection level of the density detection means and the density of the image on the original, and FIG. 6 shows the operation of the electronic copying machine of the present invention. FIG. 7 is a flowchart showing the operation of the electronic copying machine of the present invention, FIG. 8 is a vertical sectional view of an automatic document feeder suitable for carrying out the present invention, and FIG. FIG. 1 is a vertical cross-sectional view of a conventional electronic copying machine. 4...Original document, 29...Developer, 41...Density detection means, 46...Control circuit. Applicant Fuji Xerox Co., Ltd.

Claims (1)

[Claims] In an apparatus in which a document is conveyed onto a platen glass by an automatic document feeder to obtain a copy, a density detection means is fixed on the document conveyance path so as to face the document, and the document passes through a portion facing the density detection means. An electronic copying machine characterized in that the density detection means detects the density of an image on a document over a predetermined length, and the copy density is determined based on this detection signal.