JPS6037570A - Control device for copying machine - Google Patents

Abstract

PURPOSE:To maintain always a copied image at adequate density by detecting the quantity of the light reflected from an original and the surface condition of a photosensitive body and controlling selectively a mode for setting automatically the density of the copied image and a mode for setting manually said density according to the two detection signals. CONSTITUTION:The detection signal from a potential sensor which detects the surface condition of a photosensitive body is inputted from a terminal P1 and the potential of the photosensitive body is measured by a Miller integrator consisting of a resistor R3, an operational amplifier Q3 and a capacitor C1. The quantity of the light reflected from an original is detected via a photodetecting sensor 9 by Miller integrator consisting of a resistor R4, an operational amplifier Q2 and a capacitor C2. The output from the Q3 is inverted and amplified by an operational amplifier Q5 and is compared with the output from the Q2 by an operational amplifier Q6. When the difference between the two outputs is a prescribed value or above, a switch element Q10 is turned off and a switch element Q11 is turned on to change over automatic setting to manual setting. The output voltage from a variable resistor VR for manual setting of density is then outputted to a terminal P5. The copied image is thus always maintained at the adequate density.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a control device for a copying machine, in particular, to measuring the density of a document using two types of detection means with different detection characteristics, and adjusting the density of a copied image to an appropriate density. This invention relates to a control device for a copying machine.

[Prior art]

Generally, copying machines are equipped with a manual density setting mode in which the density of the copied image is manually set to a desired density, and some are also equipped with an original density detection means to detect the density of the original. The amount of exposure to the photoreceptor is controlled based on the signal from the detection means, and the density of the copied image is automatically adjusted to an appropriate density.

Conventionally, as a control device for a copying machine equipped with this type of document density detection means, for example, the following has been proposed.

That is, the document is irradiated by an exposure lamp for document irradiation, the amount of light reflected from the document is detected by a light receiving element, the density of the document is measured, and the amount of exposure to the photoreceptor is controlled based on this measurement result. An automatic exposure (AH) control device is known.

However, the control device configured in this manner has the disadvantage that it is not always possible to accurately control the amount of exposure to the photoreceptor due to the effects of temperature drift of the light receiving element, temperature characteristics of the photoreceptor, humidity characteristics, etc. .

In addition, the density of the original is measured by detecting the potential of the photoreceptor using a potential sensor, and the amount of exposure to the photoreceptor is controlled based on the measurement results, and the density of the copied image is automatically adjusted to the appropriate density. However, with a control device configured in this way, the portion of the photoconductor where the potential can be detected by the potential sensor is limited, and the density of only a portion of the document can be measured. Therefore, there were drawbacks such as not being able to obtain an appropriate density for some originals.

[Purpose of the invention]

The present invention has been made to eliminate the above-mentioned drawbacks of the conventional art. and a second detection means for detecting the surface condition, and by selectively controlling the automatic density setting mode and the manual density setting mode according to the detection signals from these two detection means, the fog light amount of the exposure lamp can be controlled. optimally control
It is an object of the present invention to provide a control device for a copying machine that always maintains the proper density of copied images.

〔Example〕

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

FIG. 1 is a schematic diagram showing the basic configuration of an electrophotographic copying machine according to the present invention. In the figure, 1 is a contact glass which is a document table on which a document is placed; Exposure lamp for irradiation (halogen lamp)
, 3, 4, 5.6H A mirror constituting an optical system for projecting the reflected light from the original onto the drum-shaped rotating photoreceptor 7;
8 is an imaging lens, and 9.10 is a light receiving sensor (first detection means) constituting the document density detection means for detecting the density of the document.
, a potential sensor (second detection means), the light receiving sensor 9 is arranged near the optical system, and the potential sensor "!7"10
It is arranged near the surface of the photoreceptor 7. This is a control circuit that inputs detection signals from the 11 light receiving sensors 9 and the potential sensor 10, and is a control circuit that inputs detection signals from the 11 light receiving sensors 9 and the potential sensor 10.
The exposure amount is being adjusted. 12 is a developing device installed around the photoreceptor 7, 13 is a transfer electrode, 14.15.16
is a charger.

Note that the manual density setting mode, in which the density of the copying iron is manually set to a desired density, is not shown because it is well known, but for example, the density setting is set in five stages, and the exposure lamp 2 can be set to any density regardless of the density of the original. Adjusting the exposure meter.

FIG. 2 is a block diagram showing the basic configuration of the control device of the copying machine, and numeral 11 in the figure is a light amount control circuit that controls the amount of exposure of the exposure lamp 2 in accordance with a signal from the control circuit 11 described above.

Based on the above configuration, the operation will be explained below. Note that since the normal copying process is well known, detailed explanation will be omitted.

The surface of the photoreceptor 7 is uniformly charged by corona discharge by the chargers 14, 15, 16, and then an electrostatic latent image corresponding to the original is formed by light reflected from the original. This latent image is
Next, a developer is applied in the developing device 12 to visualize the image. Although not shown, the transfer electrode 13 transfers the image to a copy paper wrapped around a transfer drum, and the toner is fixed by a fixing device (not shown) to obtain a copy of the document.

Here, the process of forming an electrostatic latent image of a document on the photoreceptor 1 will be described in detail.

The electrophotographic copying machine shown in FIGS. 1 and 2 is equipped with an original density detection means for detecting the density of the original.
An automatic density setting mode is provided in which the density of the copied image is automatically adjusted to an appropriate density based on a detection signal from the detection means. That is, a light receiving sensor 9 that detects the amount of reflected light from the original and a potential sensor 1O that detects the surface condition of the photoreceptor 1 are arranged, and these two sensors 9, 1
Automatic concentration setting mode and manual concentration setting mode are selectively controlled according to the detection signal from 0. For example, sensor 9. This is to adjust the density of the copied image by switching to manual setting when an error occurs in the original density measurement using IO.In this way, two sensors 9 with different detection functions are used.
, 10 are used to perform optimal AE control.

FIG. 3 shows the input/output voltage characteristics of the light amount control circuit 11 shown in FIG. It's in control. Further, FIG. 4 is a diagram showing the relationship between the amount of exposure to the photoreceptor 7, the surface potential of the photoreceptor 1, and the density of the original. For example, if the voltage applied to the exposure lamp 2 that irradiates the original is 60V, and the density of the original is 0.07 (same density as a standard white plate), the potential on the surface of the photoreceptor 7 will be -Ov, and the density of the original will be If is 0.3 (gray), the potential on the surface of the photoreceptor 7 is 300V.

FIG. 5 shows each of the above-mentioned sensors 9. FIG. 3 is a diagram illustrating the position of a document whose density is detected by lO. The potential sensor 10 detects the width of the document placed on the contact gas 2l, which is the document table, and the light receiving sensor 9 detects the width 8 portion.
It is configured to be detected by a potential sensor!
This indicates that the range detected by the light receiving sensor 9 is wider than the range detected by the light receiving sensor 9.

FIG. 6 is a circuit diagram showing a specific example of the control circuit 11 shown in FIG. 2. In the figure, R1 to R15 are resistors, 0□ and 02 are capacitors, Ql to Q7 HOPAMP (operational amplifier), Tr, or Tr4 FET) transistor, Q8 is an inverter, Q.

Driver 1. Q+o and Qs+ are analog switch elements for switching from automatic setting to manual setting,
VR indicates a variable resistor for manual concentration setting, and Ll'i indicates a lamp for manual setting display.

The detection signal from the potential sensor 10 is input from the terminal P1, and is connected to the resistor R8, OPAMPQ3 and capacitor 01.
The potential of the photoreceptor 1 is measured by the first mirror integrator Za.

The amount of reflected light from the original is measured by a light receiving sensor 9 such as a photodiode.
A second Miller integrator 11 is detected by the resistor R4, OPAMPQ2 and the capacitor C2.
b.

Before measuring the density of the original, a reset signal is input to the terminal P2, and the density of the original is reset to 0 by the FET transistor Tr4 of the first integrator 11a and the resistor R7. Once the measurement has been made, the exposure lamp 2 scans the document with an amount of light according to the measurement result, and a copied image with appropriate density is obtained.

Miller integrator +18. llb is each FET? transistors Tr2 and Trl are connected, and only when measuring the density of the original, the gate potential of each is set to H (fT i g h ) by the measurement timing signal from terminal P3.
) level, and the resistance between the drain and source becomes small. Then, integration is performed using an integration constant determined by the values of the respective resistors R, 8, n, 4 and the capacitor 01.0□.

A detection signal from the potential sensor lO that detects the potential of the photoreceptor 1 is integrated by the first mirror integrator 11a, and
It is inverted and amplified by AMPQ5.

This inverted and amplified output voltage of OPAMPQfi and the output voltage of OPAMPQ2 corresponding to the amount of reflected light from the original measured by the second mirror integrator 11b are
PQ6, and when the difference in output voltage is less than a predetermined value, that is, both sensors 9. If the difference in density of the original document detected by lO is equal to or greater than a predetermined value, as described above, the automatic density setting is switched to the manual density setting, and the density of the copied image is set to the manually set density. In the example shown in Figure 6,
OPA
The output of MPQ6 turns off analog switch element QIO and turns on analog switch element Q11. Then, the output ('NIt pressure) set by the variable resistor VR for manual concentration setting is transmitted from the terminal P5 to the light amount control circuit 17.
At the same time, the lamp L lights up to display the manual setting. In this way, if a detection error occurs in the sensor that measures the density of the document, it is possible to switch to manual setting.

FIG. 7 shows the integrator 118. FIG. 3 is a diagram showing the relationship between the density integration amount (voltage) according to the density of the original, which is integrated by Ilb, and the density of the original. When the density of the original detected by the potential sensor 10 and the light receiving sensor 9 is the same value, the output of the integrator 11b is 01, and the output of the integrator 11a is D.
The respective integral constants are set in advance so that when originals with the same density are detected, the integrator +18 of the potential sensor 10 always has a lower output voltage, and the detection signal from the potential sensor 10 The exposure amount of the exposure lamp 2 is controlled based on. ! ! In addition, as shown in FIG. 5, although the detection position of the document that can be detected by the potential sensor IO has a small area, the density of the detected document differs from the density of the document detected by the light receiving sensor 9 by more than a predetermined value. In such cases, errors in document density measurement can be prevented by switching from automatic density setting to manual density setting.

〔Effect of the invention〕

As described above, according to the present invention, the document density detection means for detecting the density of the document is divided into the first detection means for detecting the reflected light from the document and the second detection means for detecting the surface condition of the photoreceptor. Since the automatic density setting mode and the manual density setting mode are selected and controlled according to the detection signals from these two detection means, for example, when in the automatic density setting mode, it is possible to If a measurement error occurs during detection, it is possible to switch to manual density setting mode and appropriately control the amount of exposure to the photoreceptor, which has the effect of always obtaining a copy image with an appropriate density.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the basic configuration of an electrophotographic copying machine according to the present invention, FIG. 2 is a block diagram showing the basic configuration of a control device according to an embodiment of the present invention, and FIG. 3 is an input/output diagram of a light amount control circuit. Figure 4 is a diagram showing the voltage characteristics; Figure 4 is a diagram showing the relationship between the amount of exposure to the photoreceptor, the surface potential of the photoreceptor, and the density of the original; Figure 5 is a diagram showing the position of the original where the density is detected by each sensor. ,
FIG. 6 is a circuit diagram showing a specific example of the control circuit, and FIG. 7 is a diagram showing the relationship between the density integral amount depending on the density of the original and the density of the original. 2...Exposure lamp...Photoreceptor 9...Light receiving sensor (first detection means) 1
0... Potential sensor (second detection means) 11...
. . . Control circuit 11-11 . . . Light amount control circuit Q + o s Qu . . . Analog switch element as switching means Note that the same reference numerals in the drawings indicate the same or corresponding parts. 12- Yoruchi/-W Tsua Kokaku Gokon 1+ W Usuri Knee->Funami sucking 3-Q Boshuutai

Claims (1)

[Claims] There is an automatic density setting mode in which the density of the copied image is automatically adjusted to the appropriate density based on the detection signal from the original density detection means that detects the density of the original, and a manual density mode in which the density of the copied image is manually set to the desired density. In the control device for a copying machine having a setting mode, the original density detection means is configured by a first detection means for detecting the amount of light reflected from the original and a second detection means for detecting the surface condition of the photoreceptor. A control device for a copying machine, characterized in that selection control between the two modes is performed according to detection signals from these two detection means.