JPH03110576A - Copying device - Google Patents

Abstract

PURPOSE:To obtain a copy free of off-setting by providing a means of varying copying density based on the detected transmittance of transfer paper. CONSTITUTION:Transmittance detecting means 1 detects and outputs the transmittance of the transfer paper to a control means 2. The control means 2 sends an instruction signal based on the transmittance information to the density varying means 3, which varies copying density according to the instruction signal. The transmittance detecting means 1 has a photodiode PD 1a and an LED 1b;, for instance, and light transmitted from the LED 1b via the transfer paper D is photoelectrically converted by the photodiode 1a, and fetched to the control means CPU 2 as digital data via a current-voltage converting part 1c, a voltage amplifying part 1d and an A/D converting part 1e. In such a way, the transmittance of the transfer paper is directly detected, and copying density is changed in accordance with the detected result, whereby a copy free of offset can be obtained.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a copying device that reads an original image and copies it onto transfer paper using an electrophotographic method, and particularly relates to a copying device that is characterized by show-through control. .

[Conventional technology]

When copying, the density of the original and the density of the background vary widely, so it is essential to have a way to manually change the density. It is also known to control copy density by changing conditions. These copy density controls are disclosed in Japanese Patent Application Laid-open No. 56-92547 and Japanese Patent Application Laid-open No. 56-9.
5253, JP 57-204061, JP 57-210336, and JP 58-76
No. 862 is publicly known.

Among these, the method described in JP-A-56-92547 detects the spectral characteristics of the reflected light from the non-image area of the original, and controls at least one of the exposure amount and the developing bias voltage according to the detected characteristics. It looks like this.

Moreover, what is described in JP-A-56-95253 is not limited to the surface potential of the background part of the manuscript; The surface potential of a reference density object having a dark region and a light region of la is measured and calculated, and an appropriate developing bias voltage is set.

Further, the device described in Japanese Patent Application Laid-open No. 57-204061 is configured to measure the density of an original image and correct the image recording conditions according to the measurement results.

In addition, in the apparatus described in Japanese Patent Application Laid-Open No. 57-210336, the density of the original is detected over the entire length in the feeding direction while the original is being fed, and the brightness of the exposure lamp is set based on this detected value.

In addition, the method described in Japanese Patent Application Laid-open No. 58-76862 uses a sensor to read a plurality of reference density portions of a document with different densities, and based on the read values, corrects the read value of the document information by the sensor. , the document information is corrected by taking into account the slope of the output characteristics.

On the other hand, recently, most of the publications and printed materials, e.g.
More than 85% of printed matter of A4 size or smaller is printed on both sides, and automatic duplex copying machines have been developed to reduce the amount of files, and the opportunities to copy these double-sided copies as manuscripts on both sides have increased in particular. There is.

[Problem to be solved by the invention]

However, in the case of thin transfer paper, the back side is reflected on the front side (see-through), making it difficult to see.

SUMMARY OF THE INVENTION An object of the present invention is to provide a copying apparatus that can automatically reduce or eliminate bleed-through on transfer paper during double-sided copying and obtain good copies.

(Means for solving the problem) The above purpose is to provide a transmittance detection means for detecting the transmittance of transfer paper, a density variable means for varying the copy density, and a means for varying the copy density based on the detected transmittance of the transfer paper. This is achieved by a first means comprising:

Further, a second means includes a paper thickness detection means for detecting the paper thickness of the transfer paper, a density variable means for varying the copy density, and a control means for varying the copy density based on the detected paper thickness of the transfer paper. It is also achieved by

[Effect]

In the first method, the transmittance of the transfer paper is directly detected and the copy density is changed based on the detection result, thereby obtaining a copy that cannot be seen through the front side.

In addition, in the second means, the transmittance of the transfer paper is determined indirectly from the thickness of the transfer paper, and a copy that cannot be seen through is obtained in the same manner as the first means.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a control block diagram of a copying apparatus according to the first means, in which reference numeral 1 denotes transfer paper transmittance detection means, 2 a control means, and 3 a density variable means for varying copy density.

In the above means, the transmittance of the transfer paper is detected by the transmittance detecting means 1, and the result is inputted to the control means 2. The control means 2 sends a command signal to the density varying means 3 based on this transmittance information, and the density varying means 3 varies the copy density based on this command signal.

FIG. 2 is a control block diagram of a copying apparatus according to the second means, in which a paper 17 detecting means 4 for detecting the paper thickness of the transfer paper is provided instead of the transmittance detecting means 1. ing.

Then, similarly to the first means shown in FIG. 1, the copy density is varied based on the thickness of the transfer paper detected by the paper thickness detection means 4.

FIG. 3 is a block diagram showing a control circuit of one embodiment of the transmittance detection means, in which 1a is a photodiode (PD),
lb is an LED, and the transmitted light from LED lb through the transfer paper is photoelectrically converted by a photodiode 1a, and then digitally converted via a current-voltage converter 1c, a voltage amplifier 1d, and an A/D converter 1e. The above control means (
(CPU) 2. This digital data is then used as adjustment data for double-sided copying.

As a specific example, when the amount of transmitted light is larger than a certain reference value, the developing bias voltage is lowered by about -40V from the standard value. In this embodiment, the transmittance detection means l was provided at a position close to the photoreceptor and used commonly for all paper feed cassettes, so the density cannot be changed by exposure or charge amount due to the timing of image formation. , which was fed back to the developing bias voltage.

Furthermore, with transfer paper that has a high amount of transmitted light, such as OHP paper or second original paper, this method cannot reduce the density, so if this is detected, copying on both sides is prohibited, and after copying only one side, , eject the transfer paper. At this time, a warning is displayed on the operation panel that double-sided copying is not possible.

FIG. 4 is a characteristic diagram showing an example of the detection results of the transmittance detection means, and the maximum value of the detection value is generally at the background portion of the transfer paper, and this value is peak-held and used for density control. In other words, the higher the transmittance of the background, the lower the copy density.

Note that the LED lb of the transmittance detection means 1 used in this example
is preferably equal to or has the same peak wavelength as the wavelength of the exposure light source within the sensitivity wavelength range of the photoreceptor of the copying device, and it is assumed that PDla is also sensitive in the wavelength range of the LED 1b.

In general, it is most suitable to control the copying degree based on the transmittance of the transfer paper as described above, but when the transfer paper is chromatic paper, the emission wavelength of the LEDlb of the transmittance detection means 1 and the PDla Due to spectral sensitivity, etc., there is a possibility that control based on the detected value is not appropriate.

Therefore, as shown in FIG. 2, the density may be controlled by estimating the transmittance based on the thickness of the transfer paper. This utilizes the property that, with the exception of some special papers, the paper thickness is generally proportional to the light transmittance (the light transmittance depends on the paper thickness).

FIG. 5 is a configuration diagram of an embodiment of the paper thickness detection means, FIG. 6 is a perspective view of the paper thickness detection state, and FIG. 7 is an explanatory diagram of an example in which two displacement sensors are arranged, 4a and 4b. 4. rollers that nip and convey the transfer paper; c and tct are displacement sensors.

In FIGS. 5 and 6, a roller 4a and a displacement sensor 4c are fixed to an ARDF body, which will be described later, and a force is applied to the roller 4b in the direction in which it is pressed against the roller 4a by a spring.

When the transfer paper passes between the rollers 4a and 4b, the roller 4b is displaced downward in the figure, and the axial position of the roller 4b is detected by the displacement sensor 4c. The displacement sensor 4c irradiates the roller shaft with laser light, receives the returned light, and converts the delay time into distance. The difference between the value in a steady state when the transfer paper is not passing through and the value when the transfer paper is passing is the thickness of the transfer paper, which is detected in units of 10 microns.

FIG. 7 shows an example in which two displacement sensors 4c and 4a are used facing each other, and the distance between the displacement sensors 4c and 4a! , displacement sensor 4
If the detected values of c and 4d are A and B, the paper thickness P is calculated as follows: P=/-(A+B).

The configuration of a copying apparatus to which the present invention is applied will be described in detail below.

FIG. 8 is a block diagram of the copying system, and FIG. 9 is a block diagram of the main part of the copying machine, in which a photosensitive drum 501 that can be rotated clockwise is arranged approximately in the center of the copying machine body. A static elimination lamp 506 is installed around it. Electrostatic charger 502. Erase lamp 503. First developing device 301
．． Second developing device 302. Pre-transfer static elimination lamp 504. Transfer charger 4042 Separate charger 405. A blade type cleaning device 600 is provided.

The photoreceptor drum 501 has a photoreceptor layer provided on its surface, and this photoreceptor is connected to the static elimination lamps 5o6. Charger 50
2, and receives image exposure from the optical system 100.

The optical system 100 is arranged below a contact glass 101 so as to be able to scan an original image, and includes a light source 102, movable mirrors 105, 106, 107, 109, 110, lenses 113, . It is composed of a fixed mirror 112. The light source 102. The movable mirror 105 is connected to the photosensitive drum 50
The movable mirror 106,
107 is driven by a drive motor (not shown) to move at a speed of (V/2m). The circumferential speed of this photoreceptor is
It remains constant regardless of whether the magnification is the same or variable. Further, when changing the copying magnification, the lens 113 moves on the optical path and the mirrors 109 and 110 move to ensure an optical path length corresponding to the magnification. Note that 114 is a dustproof glass that partitions the optical system and the image forming system.

On the other hand, paper feed units 210 and 220 are installed on the right side of the copying machine body, respectively, and are equipped with call rollers 203 and 222, paper feed rollers 204 and 223, and separation rollers 205 and 224. vs. 402. Suction conveyance roller 407° fixing device 700. Paper ejection intermediate roller 8
012 main body paper ejection roller 802. 21
2.225 is a paper size detection switch.

In front of the registration roller pair 402, there is a registration roller pair 4.
A sensor 401 in front of the registration roller is provided to control the 0N10FF of 02.

A manual paper feed section 201 is provided above the paper feed section 210, and either manual paper feed or cassette paper feed can be used. The manual paper feed section 201 is provided with a size sensor (not shown) that detects the size of paper in the width direction. The manual paper feed section 201 can be opened and closed, and a pressure arm (not shown) that presses the paper in the cassette of the paper feed section 210 when opened is detected by a sensor (not shown) that detects opening/closing. The pressing force is released, and paper feeding from the manual paper feeding unit 201 is enabled.

The manual paper feed section 201 or the cassette paper feed section 210
, 220, the paper is sent to the registration roller pair 402.
The toner image is timed with the toner image on the photoconductor 501, transferred to the upper surface by a transfer charger 404, and peeled off from the photoconductor 501 by a separation charger 405.

The peeled transfer paper is sucked and conveyed by the suction conveyance roller 407 and sent to the guide plate 701 of the fixing device 700, where it is transferred to the fixing roller 704. The pressure roller 705 fixes the toner image on the upper surface. The transfer paper after fixing is peeled off from the fixing roller 704 by a separating claw 707 and transferred to a pair of fixing paper discharge rollers 70.
8 and reaches an intermediate paper discharge roller 801. Here, the gate 803 is at the position indicated by the broken line, and the paper is transported to the re-feeding side.
The trailing edge of the paper is detected by the paper detection sensor 823 when it is held by the reversing rollers 813 and 814, and after a predetermined period of time, the gate 816 moves to the position indicated by the broken line, and the reversing rollers 813 and 81
4 is reversed counterclockwise, and the paper heads toward the main body paper discharge roller 802 along the gate 815. This main body paper ejection roller 8
The sheets sent out from 02 are stacked on the tray 824 with the original surface facing downward. Since the lower end of the gate 815 is made of a flexible film, once the paper passes through it, it does not return to the original conveyance path.

In this copying system, the automatic duplex document feeder (ARDF), which will be described later, feeds the original in page order, so when copying only one side like this, the copy side will be the bottom side, making it possible to obtain copies in page order. .

From the left side to the center of the lower part of the main body, a paper refeeding section for double-sided copying and its conveying section 800 are arranged.

The conveyance path for double-sided copying corresponds to roughly two cases: one is for A4 horizontal size or smaller, and the other is for relatively larger sizes.

In the case of double-sided copying of A4 landscape size or smaller, the first side of the paper that has been copied passes through a pair of fixing and ejecting rollers 708 before being transferred to an intermediate ejecting roller 8.
It reaches 01. At this time, the game [803] is at the position of the solid line, and the paper heads toward the main body paper ejection roller 802, and when the trailing edge of the paper is detected by the paper detection sensor 823, the paper ejection intermediate roller 801 and the main body paper ejection roller 802 are reversed. Then, the paper heads toward the guide plate 821 with the trailing edge leading. The paper is held by a pair of transport rollers 810, and in the case of A5 landscape size or HLT size (half letter size), the gate 820 is at the position shown by the solid line, and the paper is stacked on the paper refeed tray 808 by the pair of transport rollers 809.

Gate 820 for A4 landscape size or B5 landscape size
is at the position indicated by the broken line, and immediately after passing through the pair of transport rollers 810, it heads toward the paper refeed tray 808. From one manuscript to multiple <
In the case of so-called 1 to N copying, in which N) copies are made, the same operation is repeated and the sheets are stacked one after another on the paper re-feeding tray 808. Incidentally, at this time, the leading edges of each stacked sheet are aligned by a pull-in roller 807.

When copying the second side, the topmost paper is conveyed by the calling roller 804, and the paper feeding roller 805J separation roller 80
6, one sheet of the stacked sheets C is fed. The conveyor roller pair 408 is rotated, and the registration roller pair 402 is rotated.
reach. Here, the C timing is set with the leading edge of the image on the 32nd side (the back side in the case of a double-sided original), and the image is sent to the transfer unit. In step 1, the paper goes through the same process as for single-sided copying and reaches the paper ejecting intermediate roller 801. At this time, the gate 803 remains at the solid line O position, so the paper passes directly to the main body ejecting roller pair 80.
2 and is then stapled onto the tray 824. As a result, the first surface becomes the bottom surface and the second surface l becomes the top surface when stacked.

In the case of double-sided copying of A4 vertical size or larger, when the copied paper passes through the pair of fixing paper discharge rollers 708 and reaches the middle paper discharge roller 801, the gate 803 at this time is at the position indicated by the broken line, and the paper is The rear end of the paper is detected by the paper detection sensor ε23, and after a predetermined period of time has elapsed, the reversing roller ε13. or 1
In the case of a finch (43.18 cm), the gate 817 is at the position indicated by the broken line, and the paper is immediately fed onto the refeed tray 808.

When the paper is B4 size or 14 inches (35,56 cm) size, the gate 818 is in the position shown by the broken line when the paper is A4 portrait size or B5 portrait size, and the gate 811 is at the position indicated by the broken line to feed the paper onto the refeeding tray 808. The operations from paper refeeding to paper ejection are the same as those for A4 landscape size or smaller.

By configuring the conveyance path as described above, in the case of A4 landscape size or smaller, the switchback is performed more quickly, so that the time required to stack the paper on the re-feeding tray can be slightly shortened.

The main body has two cassette paper feed units 210, 220 and one manual paper feed unit 201, but if you want to feed more paper sizes, a multi-stage paper feeder can be connected to the bottom of the main body. Use 9'00. Multistage paper feeding device 900
are the third paper feed section 901, the fourth paper feed section 910 . It consists of a fifth paper feed section 920 and a sixth paper feed section 930. In particular, the sixth paper feed section 930 can also be used as a mass paper feed device (1, CT) that can feed a large amount of paper. ing. The paper feeding method here is the same as that of the main body, with calling rollers 903, 913, 923, 933 and paper feeding roller 90.
4,914,924,93.4, separation roller 905,9
This is a reverse roller feeding system consisting of 15,925,935 sheets. The roller pair 951 and 952 is for conveyance. Paper size detection switches 906, 916, 926.
6, and the paper size stored in each cassette can be detected. For example, assume that the cassette of the fourth paper feed section 910 is selected, and its operation will be described. First, several sheets of paper are sent out by the rotation of the pick-up roller 913, and by the action of the paper feed roller 914, which rotates counterclockwise, and the separation roller, which is urged to rotate counterclockwise below a certain torque, Only one sheet of paper is sent to the transport roller pair 952. In this way, the paper passes through the pair of transport rollers 951' and 408, and then passes through the pair of registration rollers 4.
Reach 02. Registration roller front sensor 4 in the middle
01 is blocked by the paper, after a predetermined time the transport roller pair 4
08,951,952 will stop. Thereafter, like the sheets fed from other paper feed sections of the main body, the sheets are conveyed again in synchronization with the image on the photoreceptor.

With this multi-stage paper feed, the large paper feed cassette is placed on the left side.
Although it is shown that a small-sized cassette is set on the right side, it is not necessary to do so, but it is shown because it is better balanced in terms of the overall configuration. In the unlikely event that a paper jam occurs in the paper feeding section, the portion indicated by the - dot 81 line 940 is opened to remove the jammed paper from the transportation section.

As shown here, the reason why the four paper feed sections are separated on the left and right is to shorten the conveyance path as much as possible to shorten the paper conveyance time, and to avoid placing the cassettes near the floor, which impairs operability. This is because I tried not to do that.

FIG. 10 is a configuration diagram of an automatic double-sided document feeder, in which a contact glass 101 provided on a copying machine main body 100
An automatic double-sided document feeder (ARDF) 1000 is installed at the top.

The ARDF 1000 includes a document feeding section 1001, a conveyance section 1019. Inversion section 1012. Consists of a paper discharge section 1037,
The document feeding unit 1001 includes a tray 1003, a calling roller 1004. A separation roller 1006 and a blocking roller 1007 are provided, and the document is set in page order from the top with the original surface facing upward. The conveyance unit 1019 includes an endless conveyor belt (1020) driven by a belt drive roller 1021 and a belt fixed roller 1.
022, belt driven roller 1024 and belt pressure roller 1023. Pull-out roller: Pull-out roller: Driven 1026. Conveyance roller 1027,
It consists of conveyance rollers 1028 and the like. The reversing section 1012 includes a reversing roller 1013, a driven roller 1014, and a deflecting claw 101.
It consists of 5 etc. The paper ejection section 1037 is a reversing paper ejection roller 10
29, Reversing paper ejection roller 1030, paper ejection guide roller 1031
, a paper discharge roller 1033, a paper discharge roller 1034, etc.

Further, in FIG. 10, work 002 is the document entrance,
05,1016.1032.1039 is various sensors, 1
008, 1009.1010.1011 are pull-out rollers, 1018 is a document reference scale, 1035 is a document exit, 1036 is a document receiver, and A is a document scanning reference position in the copying machine main body 100.

Next, a case will be described in which a copy is obtained from the most common one-sided original in the ARDFlooO having the above-described configuration. The stacked documents are transferred to a calling roller 1004 and a separation roller 1.
006 and blocking rollers 1007, only one sheet is conveyed to pull-out rollers iooa, i010, passes over the document reference scale 1018, and is conveyed onto the contact glass 101. The length of the fed document in the feeding direction is detected by a sensor 1039, which determines the drive time of the conveyor belt 1020. Further, a sensor 1005 detects the presence or absence of a document.

After the trailing edge of the document once passes through the document scanning reference position A, the document conveyed by the conveyor belt 1020 is rotated clockwise by the belt drive roller 1021 to convey the document to the conveyor belt 102.
By moving 0 to the left, the original reference scale 101
8 and is set at the document scanning reference position A.

The conveyor belt) 1020 has a document reference scale of 10.
After it hits point 18, it continues to rotate, correcting the registration and skew of the original, and then stops. At this time, the conveyor belt 1020 and the document tray will slip. When the exposure by the optical system is completed, the belt drive roller 1021 is driven to rotate counterclockwise, and the original document is conveyed rightward and sent to a pull-out roller: drive 1025 located outside the contact glass 101. Here, the document is reversed along the U-shaped guide in the figure, and
Conveying rollers inside 1 0 2 7. Conveyance roller 1028
transported by. The image side of the document is now facing up. Further, the document is reversed by a reversing paper ejection roller 1029 and a paper ejection guide roller 1031.

After passing through the paper ejection roller 1034 and the document ejection port 1035,
The document is discharged onto the document receiver 1036 provided on the ARDF 100O with the image side facing down. By this operation, the originals are stacked in page order with the originals facing down.

FIG. 11 is an enlarged view of the main part of the ARDF, and the case where a copy is obtained from a double-sided original will be explained based on this view.

In this case, the original document is conveyed from the paper feed unit 1001 through the conveyance path P1 onto the contact glass 101, but the length of the original document is detected by the sensor 1039, and the drive time of the conveyance belt 1020 is determined by this. Convey belt 1 so that the document is set exactly at the document reference position.
This is done by stopping 020. Then, when the original tray is set, the front side of the original tray is scanned, and then the original tray is sent to the reversing section 1012 in order to copy the back side. At this time, the document is returned in the direction of the paper feed section 1001, but if it is sent as it is, it will not pass through the conveyance path P2 leading to the reversing section 1012, but will go backwards along the conveyance path P1 and return to the paper feed section 1001.
There is a risk that it will enter 1. - As mentioned earlier, in order to switch the conveyance route for boat fishing, a branch claw or the like is provided midway to switch the conveyance route of the document document. 3
1 convex portion 1041. Recessed portion 1042. Second convex portion] 043
, a conveyance guide-iller 104 between the conveyance paths Pi and P2.
0, and by conveying the document with the leading edge of the document in the document advancing direction along these uneven portions and mimies, the conveyance path is automatically switched 7.

First, when 7 originals are sent from the paper feed section 1001 through the transport path P1, the originals are made of flexible material (once the original passes through, it does not return to its original conveyance state). The tip of the document slips through the conveyance guide Mylar 1040, climbs over the first convex portion 1041, jumps along the concave portion 1040, and jumps over the apex of the second convex portion IC43, which is slightly higher than the surface on the contact glass 101, to the contact glass 101.
It is transported smoothly to the top. When the document on the contact glass 101 is conveyed to the reversing unit 1012 through the conveyance path P2, the document passes over the slope of the second convex portion 1043 that is slightly higher than the surface on the contact glass 101, and
It climbs the slope of the first convex portion 1041 that is continuous with the concave portion 1042 and is conveyed while being guided by the conveyance guide mylar 1040, so that it is smoothly wound around the reversing roller 1013 and enters the reversing portion 1012. Also, since there is a conveyance guide mylar 1040 for original paper, the paper feeding section 100
It never enters 1. The original is reversed by the reversing unit 1012 and sent again through the transport path P3 onto the contact glass 101, but in this case, it is transported smoothly as in the case of the transport path PL.

As mentioned above, if the transfer paper has high transmittance (the transfer paper is thin), show-through will occur.

In order to prevent such show-through, the present invention performs transfer paper detection (transmittance detection or paper thickness detection) as described above, and controls copy density based on the result.

FIG. 12 is a process control block diagram of the copying machine, and this circuit includes mode control and timing '11? Sequence controller 11 that performs B and key group 1 of 8 production parts
An operation controller 14 that performs input of 2 and output of display 13
and a process controller 15 that controls the copying process to the condition value. The information is exchanged between these controllers through serial communication. When the sequence controller 11 receives a double-sided key manual input, which will be described later, from the operation controller 14, it transmits a double-sided mode display and changes the process conditions of the process controller 15. When the copying process is started, the setting targets for the exposure lamp I6, the developing bias 17, and the electrification charger 18 are transmitted from the sequence controller 11 to the process controller 15, and the process controller I5 controls each to reach the target values. In the double-sided copy mode, by changing this target setting value from that in the normal mode, a reduction in copy density is realized.

The sequence controller 11, operation controller I4, and process controller 15 are shown in FIG.
This constitutes the control means 2 shown in FIG.

FIG. 13 is a partially enlarged view of the operation panel, in which 41 is a page continuous copying key, 42 is a double-sided key, and 43 is a double-sided document key.

Each time the page continuous copying key 41 is pressed, each LED of the first double-sided original mode, continuous copying variable magnification mode, and first spread original mode
41a, 41b, and 4ic are lit in sequence, and the mode changes. This first double-sided document mode is a double-sided document with 2 pages on each side.
This is the mode for copying sheets. The continuous copy magnification mode is a mode in which two originals are superimposed and copied onto one sheet of transfer paper.

The first spread document mode is a mode in which both pages of a book document in a spread state are copied onto two sheets of transfer paper.

Similarly, when the duplex key 42 is pressed, each LB in the single-sided original mode, second double-sided original mode, and second spread original mode is pressed.
D42a, 42b, and 42c are lit in sequence, and the mode in which they are lit is selected. Here, the single-sided original mode is a mode in which two originals are copied onto the front and back sides of one sheet of transfer paper. The second double-sided original mode is a mode in which a double-sided original is copied onto the front and back sides of one sheet of transfer paper.
When using 0, the original is also automatically reversed and copied.

Furthermore, the second spread document mode is a mode in which both pages of a book document in a spread state are copied onto the front and back sides of one sheet of transfer paper.

When the double-sided document key 43 is pressed, the third double-sided document mode LED 43a lights up. In this mode, a double-sided original is copied onto both sides of one sheet of transfer paper.

Note that the keys 41, 42, and 43 constitute the key group 12 in FIG.

FIG. 14, FIG. 15, and FIG. 16 are explanatory diagrams of the copy density control method. When the double-sided original copy mode is selected by the double-sided original key 43, the copy density is controlled according to the key operation. The mode is input to the control means 2, and the CPU instructs each section to operate according to the preset mode. These known parts constitute the four-degree variable means 3 shown in FIGS. 1 and 2.

The method of varying the copy density will be specifically described below.

(1) Method for changing the amount of exposure light on a document The light source (exposure lamp) 102 in FIG. 8 is phase controlled,
The exposure is normally adjusted to about 62 to 70 (V). Copy density (notch) control is achieved by increasing or decreasing the amount of light reflected from the original by increasing or decreasing the amount of exposure light, and by raising or lowering the surface potential of the photoreceptor.

As shown by the solid line in FIG. 14, the lamp voltage varies depending on each notch, but in the above-mentioned double-sided copying mode, by increasing the lamp voltage at each notch as shown by the broken line, copies are made thinner than usual.

(2) Method of changing the developing ability Similar to (1), this method involves increasing or decreasing the developing bias voltage. Since the organic photoreceptor is negatively charged, by increasing the negative developing bias voltage, the amount of toner adhering to the photoreceptor 501 decreases and the density becomes thinner. The solid line in FIG. 15 is the developing bias when copying a normal single-sided original, and in the double-sided original copying mode at each notch, the copy density is reduced by increasing the bias voltage as shown by the broken line.

+3+ Method of changing the amount of charge on the photoreceptor A scorotron charger 502 is used to charge the photoreceptor 501, and a high voltage (-5.0 to -7.5KV) is applied to the charge wire in the dark to charge the photoreceptor 501. This is done by causing a discharge (drum potential #-7
50V). And by varying the grid voltage,
Conventionally, a decrease in sensitivity (increase in residual potential) of a photoreceptor is corrected to maintain an appropriate image density. Also,
At this time, the lamp voltage and developing bias are also corrected at the same time. Each time the negative grid voltage is increased, the amount of charge increases and the copy density increases. Therefore, as shown by the broken line in FIG. 16, the grid voltage can be lowered (lower than the normal correction value) to achieve a reduction in concentration.Also, by changing the voltage applied to the charger 502 and the charging distance, it is possible to easily reduce the amount of charge. can be controlled and the copy density can be lowered.

In addition, the copy density can be reduced by changing the transfer rate, limiting the amount of toner replenishment, etc. Similar effects can also be obtained by combining the above methods.

In this embodiment, as shown in FIGS. 14 to 16, the density variable means 3 was switched to two stages according to the detected data, but the density variable means 3 was switched to two stages based on the thickness of the transfer paper and the detected level of transmittance. It will be more effective if you change it. The optimum copy density for the type of transfer paper can then be obtained.

In the present invention, the transmittance detecting means 1 and the paper thickness detecting means 4 are provided at appropriate locations in the copying machine shown in FIGS. 8 and 9.

〔Effect of the invention〕

As explained above, the invention according to claim 1 directly detects the transmittance of the transfer paper, and the invention according to claim 2 indirectly detects the transmittance of the transfer paper, and based on this result, the copy density is determined. Since it is variable, it is possible to provide a copying apparatus that can obtain copies without show-through.

[Brief explanation of drawings]

FIG. 1 is a control block diagram of a copying apparatus according to a first means;
FIG. 2 is a control block diagram of a copying apparatus according to a second means;
FIG. 3 is a block diagram showing a control circuit of an embodiment of the transmittance detecting means, FIG. 4 is a characteristic diagram showing an example of transmittance detection results, and FIG. 5 is a block diagram of an embodiment of the paper thickness detecting means. , FIG. 6 is a perspective view of the paper thickness detection state, FIG. 7 is an explanatory diagram of an example of displacement sensor arrangement, FIG. 8 is a configuration diagram of the copying system, and FIG. 9 is a configuration diagram of the copying machine, which is the main part thereof. , FIG. 10 is a block diagram of the automatic duplex document feeder, FIG. 11 is an enlarged view of the main parts of the automatic duplex document feeder, FIG. 12 is a block diagram showing a control circuit for process control of the copying device, and FIG. The figure is a partially enlarged view of the operation panel, and FIGS. 14, 15, and 16 are explanatory views of the copy density control method. 1... Transmittance detection means, 2... Control means, 3...
Density variable means, 4... Paper thickness detection means. No.! Fig. 2 Fig. 3 Fig. 4 Conveying direction reading position □ Fig. 5 Fig. 7 Fig. II Fig. 12 Fig. 3 Fig. 13 Fig. 1

Claims (2)

[Claims] (1) It is characterized by comprising a transmittance detection means for detecting the transmittance of the transfer paper, a density variable means for varying the copy density, and a control means for varying the copy density based on the detected transmittance of the transfer paper. A copying device that uses (2) It is characterized by comprising a paper thickness detection means for detecting the paper thickness of the transfer paper, a density variable means for varying the copy density, and a control means for varying the copy density based on the detected paper thickness of the transfer paper. A copying device that uses