JPH0233247Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a copying machine that visualizes a latent image formed on a photoreceptor by developing it, for example.

In this type of conventional copying machine, the density of the original to be copied is detected by a density detection element and the exposure amount or developing bias voltage of the original is automatically controlled to obtain a copy. However, in such copying machines, when the original is colored other than black and white, the density may be detected incorrectly due to the spectral characteristics of the density detection element, making it impossible to properly control the exposure amount, etc. This was inconvenient because good copies could not be obtained.

This idea was made in view of the above circumstances.
Detects the spectral characteristics of the reflected light from the image area of the original,
By controlling at least one of the exposure amount and the developing bias voltage according to the detection output,
It is an object of the present invention to provide a copying machine that can perform appropriate control according to color even for colored originals and can obtain good copies.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings. In FIG. 1, 1 is a table (original table) on which an original is placed, 2 is an exposure lamp that irradiates light onto the original on the table 1, and a first mirror 3, a lens 4, and a second mirror 5 are used to place an original on the original. This figure shows an optical system for forming an image of the reflected light on the slit plate 6 and on the photosensitive drum 7 near the slit 6', and this drum 7 forms an electrostatic latent image of the incident image. . Note that 8 is a charger that deposits electricity on the drum 7 prior to forming the latent image, 9 is a developer that reversely develops the latent image on the drum 7, 10 is a paper supply unit that supplies copy paper, and 11 is a conveyance guide section that conveys the paper in this supply section 10 and guides it to the transfer section.
2 is a transfer charger that transfers the toner image on the drum 7 onto paper; 13 is a peeling charger that peels the paper from the drum 7; 14 is a conveyance path that conveys the peeled paper to the paper discharge port 15; A fixing device 16 fixes the toner image on the paper conveyed through the conveyance path 14;
7 is a charger for neutralizing electricity that neutralizes the drum 7 after transfer;
18 is a fluorescent lamp for removing the latent image on the drum 7, and 19 is a cleaning device for cleaning the drum 7. These have the same construction as a conventional copying machine, and a detailed explanation of their operation will be omitted.

In the present invention, in order to detect the reflected light from the image area of the document, for example, as shown in FIG. Photodiodes 21 and 22 are provided.

FIG. 3 shows a spectral characteristic detection circuit 30 for detecting the spectral characteristics of reflected light from the image area of a document, and an exposure amount control for controlling the light amount of the exposure lamp 2 according to the detection output of this detection circuit 30. This shows the circuit. That is, in the spectral characteristic detection circuit 30, 31 is a first operational amplifier, 32 is a Zener diode for generating a reference voltage, and the Zener voltage output terminal of this Zener diode 32 connects the first photodiode 21 and resistor 33. The inverting input terminal (-) and the non-inverting input terminal (+) of the first operational amplifier 31 are respectively connected through the inverting input terminal (-) and the non-inverting input terminal (+). A first black level tracking circuit 36 including a diode 34 and a capacitor 35 connected in series is connected to the output terminal of the operational amplifier 31. On the other hand, 37
is a second operational amplifier, whose non-inverting input terminal (+) is grounded via a resistor 38, and whose inverting input terminal (-) is grounded via the second photodiode 22. And this operational amplifier 37
A second black level tracking circuit 41 including a diode 39 and a capacitor 40 connected in series is connected to the output terminal of the black level tracking circuit 41 . Each capacitor 3 of the first and second black level tracking circuits 36 and 41
The terminal voltages of 5 and 40 correspond to resistors 4 and 40, respectively.
2 and 43 to an inverting input terminal (-) and a non-inverting input terminal (+) of a third operational amplifier 44, and this non-inverting input terminal (+) is grounded via a resistor 45. On the other hand, 46 is a first reference voltage setting circuit, which supplies a reference voltage generated using a Zener diode 47 to the output terminal of the first black level tracking circuit 36, and 48 is a second reference voltage generation circuit. can be,
A reference voltage generated using a Zener diode 49 is supplied to the output end of the second black level tracking circuit 41 . On the other hand, 50 is a bridge circuit that rectifies the AC power input, 51 is an integration circuit that integrates the output of this bridge circuit 50, 52 is a zero cross detection circuit that pulses the output of this integration circuit 51, and 53 is this detection circuit 52. is a transistor whose output is supplied to its base via a resistor 54, its emitter is grounded, its collector is connected to the non-inverting input terminal (+) of a fourth operational amplifier 55, and the capacitor 5
6 and is connected to the power supply +V via a variable resistor 57. The fourth operational amplifier 55 has its inverting input terminal (-) connected to the output terminal of the third operational amplifier 44 and its output terminal connected to the input terminal of a photocoupler 59 via a drive circuit 58. . This photocoupler 59 generates a gate pulse for applying a triac when driving is input, and 60 is a triac connected between the AC power source and the exposure lamp 2, and is turned on and conductive by the gate pulse.

Next, the operation of FIG. 3 with the above configuration will be explained. When reflected light from the image area of the document enters the first photodiode 21 during a copying operation, this diode 21 detects it as a current change, and this detected current is converted into a current/voltage by the first operational amplifier 31. . This conversion output changes in accordance with the intensity of the reflected light from the image area, and this level change is tracked by the first black level tracking circuit 36 and the third black level tracking circuit 36.
is applied to the inverting input terminal (-) of the operational amplifier 44. Similarly, the reflected light from the image area is detected as a current change by the second photodiode 22,
This detected current is converted into current and voltage by the second operational amplifier 37. This conversion output changes in accordance with the intensity of the reflected light from the image area, and this level change is tracked by the second black level tracking circuit 41 and the non-inverting input terminal (+ ) is applied to The differential amplification output by the third operational amplifier 44 is the difference between the output of the first black level tracking circuit 36 and the output of the second black level tracking circuit 41. Note that during copy standby, the input levels in the first and second black level tracking circuits 36 and 41 do not change, and therefore no tracking output is generated.
At this time, the first and second reference voltage setting circuits 46,
Each setting output of 48 is directly transmitted to the third operational amplifier 4.
4 inputs.

By the way, as shown in FIG. 4, the spectral sensitivity characteristics of the first and second photodiodes 21 and 22 have peak sensitivities corresponding to the low and high wavelength regions of the incident light, respectively, and Photodiode 21 has a lower peak sensitivity and a wavelength of about 6700 Å.
When , the sensitivities of both photodiodes 21 and 22 become the same. Therefore, assuming that the amounts of light incident on the first and second photodiodes 21 and 22 are the same and the amplification factors of the first and second operational amplifiers 31 and 37 are the same, the third operational amplifier 44 has the same amount of light. The output has a value corresponding to the wavelength of the reflected light from the image area. In other words, when the wavelength is about 6700 Å, the detection values of photodiodes 21 and 22 are equal, so
The respective outputs of the first and second black level tracking circuits 36 and 41, which track the output levels of the first and second operational amplifiers 31 and 37, respectively, are canceled out by the third operational amplifier 44. However, in this case, the first operational amplifier 3
Since the reference voltage input of No. 1 is the Zener voltage of the Zener diode 32, the third operational amplifier 4
The output voltage of No. 4 is an amplified value of the Zener voltage, and is not zero volt. This is to prevent the inverted input voltage of the fourth operational amplifier 55 at the subsequent stage from becoming negative. Also, photodiode 2
If the wavelength of the incident light of 1 and 22 is less than 6700 Å,
The output of the first operational amplifier 31 increases, and the first
Since the output of the black level tracking circuit 36 becomes larger, the output voltage of the third operational amplifier 44 becomes larger. Further, when the wavelength of the incident light is 6700 Å or more, the output of the second operational amplifier 37 increases,
Since the output of the second black level tracking circuit 41 becomes larger, the output voltage of the third operational amplifier 44 becomes smaller. In this way, the third operational amplifier 44
The spectral characteristics of the incident light, that is, the spectral characteristics of the reflected light from the image area, are determined by the output voltage of the .

Next, a description will be given of an operation for controlling the amount of exposure to a document according to the above-mentioned spectral characteristics. If the spectral sensitivity characteristics of the photoreceptor drum (Fig. 1, 7) are as shown in Fig. 5, then the exposure amount must be increased because the sensitivity decreases for light with long wavelengths. . Assume that it is detected from the output of the third operational amplifier 44 according to the spectral characteristics as described above that the reflected light from the image area has a long wavelength. In this case, the inverting input voltage of the first operational amplifier 55 is small as described above. Further, the AC power input is rectified by a bridge circuit 50, and the output thereof is applied to the base of a transistor 52' of a zero cross detection circuit 52 through an integration circuit 51. This transistor 52' performs a zero cross detection operation,
A pulse of "1" level (power supply level) is generated at zero cross, and the output becomes "0" level (ground level) at other times. This transistor 5
When the output of transistor 2' is at the "1" level, the transistor 53 is turned on, discharging the charge in the capacitor 56, and when the output of the transistor 52' is at the "0" level, the transistor 53 is turned off, and the capacitor 56 is charged. Start. Along with this, the non-inverting input voltage of the fourth operational amplifier 55 also increases,
When the voltage exceeds the inverted input voltage, the fourth operational amplifier 55
The input comparison operation inverts its output. At this time, the drive circuit 58 drives the photocoupler 59, the gate pulse is applied to the triac 60 and it becomes conductive, and the exposure lamp 2 is turned on. Then, when the zero cross occurs again, the transistor 53 becomes conductive to discharge the charge in the capacitor 56, the non-inverting input voltage of the fourth operational amplifier 55 becomes zero volts, the output is inverted, and the drive circuit 58 is turned off. Therefore, the photocoupler 59 is also turned off.

Through this operation, control is performed so that the longer the wavelength of the reflected light from the image area of the original, the larger the conduction angle of the exposure lamp 2 and the larger the exposure amount, and vice versa. .

In the above description, the exposure amount was controlled by the detection output of the spectral characteristics, but in addition to (or in place of) this control, a case will be described in which the developing bias voltage is controlled by the detection output of the spectral characteristics.
FIG. 6 shows an example of a developing bias voltage switching control circuit, and 61 is a spectral characteristic detection voltage input terminal, from which the output voltage of the third operational amplifier 44 of FIG. 3 is guided. This input terminal 61 is connected to each inverting input terminal (-) of the fifth and sixth operational amplifiers 62 and 63, and each non-inverting input terminal (+) of the operational amplifiers 62 and 63 is connected to a reference voltage. V ₅ , V ₆ (V ₅ < V ₆ )
is being guided. Each output terminal of the operational amplifiers 62 and 63 corresponds to the first and second relay drive circuits 6.
4 and 65, and first and second relays 66 and 67 are connected to the relay drive circuits 64 and 65, respectively.

On the other hand, the AC power input is supplied to the primary side of a transformer 68, and a series circuit of a diode 69, a resistor 70, and a capacitor 71 is connected to the secondary side of the transformer 68. And this capacitor 71
A series circuit of resistors 72, 73, 74, and 75 is connected in parallel to. 76 is the second relay 67
The off-side contact is connected to the connection point of the resistors 72 and 73, the on-side contact is connected to the connection point of the resistors 73 and 74, and the movable contact is connected to the connection point of the first relay 66. relay contact 7
It is connected to the off-side contact of 7. The on-side contact of this relay contact is connected to the connection point of the resistors 74 and 75, and the movable contact is connected to the developing device (FIG. 1, 9).

If the spectral sensitivity characteristics of the photoreceptor drum (Fig. 1, 7) are as shown in Fig. 5, then the developing bias voltage must be increased because the sensitivity decreases for light with long wavelengths. need to be lowered. Assume that a small voltage is introduced to the input terminal 61 as a spectral characteristic detection output when the reflected light from the image area of the original has a long wavelength. At this time, the outputs of the fifth and sixth operational amplifiers 62 and 63 are both at the "1" level without being inverted. At this time, each transistor 78 of the first and second relay drive circuits 64 and 65,
79 are both in a conductive state, relays 66 and 67 are both driven, and relay contacts 76 and 77 are both connected to on-side contacts. Therefore, transformer 68
The output is rectified by a diode 69, and the lowest voltage among the outputs divided by resistors 72, 73, 74, and 75 is applied to the developing device. Then, when the voltage at the input terminal 61 increases and becomes greater than V ₅ ,
Only the output of the fifth operational amplifier 62 is inverted and becomes “0”
level, the transistor 78 of the first relay drive circuit 64 is turned off, and the first relay 6
6 is not driven and the relay contact 77 is connected to the off-side contact, so the voltage applied to the developer increases. Furthermore, when the voltage at the input terminal 61 increases and becomes higher than _V6 , the output of the sixth operational amplifier 63 is also inverted and becomes the "0" level, and the transistor 79 of the second relay drive circuit 65 is also turned off. , second
Since the relay 67 is also not driven and the relay contact 76 is connected to the off-side contact, the voltage applied to the developer further increases.

Through such an operation, the developing bias voltage is controlled so that when the wavelength of the reflected light from the image area of the document is long, the developing bias voltage is low, and conversely, when the wavelength is short, the developing bias voltage is high.

In the above explanation, the spectral characteristics of the image area of the document are detected using two photodiodes 21 and 22 as shown in FIG. 2, but as shown in FIG. One photodetection element 70 may be used. As an example of this element 70, FIG. 8 and FIG. 9 show one in which equivalently two sets of photodiodes having different spectral sensitivities are assembled into one package. FIG. 8 shows its structure, in which two photodiodes with different sensitivities to light wavelengths are fabricated in the same semiconductor substrate in the depth direction of the semiconductor substrate, and 81 is an insulating film;
82, 83, and 84 are electrodes, respectively. In this case, one photodiode has increased short wavelength sensitivity, and the other photodiode has increased long wavelength sensitivity, and their characteristics are similar to those shown in Figure 4, and the equivalent circuit is shown in Figure 9. The result will be as shown in the figure.

Further, in the above embodiment, the photodetecting element is provided on the slit plate near the photoreceptor drum, and an exposure lamp is used as the irradiation light source for the original. It is also possible to provide a light source separately from the exposure lamp and detect the reflected light emitted from the light source. Further, as a method of changing the exposure amount, instead of changing the light amount of the exposure lamp, the aperture of the lens may be changed or the width of the slit of the slit plate may be changed.

As mentioned above, the present invention provides a copying machine that develops a latent image formed on a photoreceptor into a visible image.
The document to be copied is irradiated with light, the spectral characteristics of the reflected light from the image area of the document are detected using a photodetection element, and at least one of the exposure amount to the document and the developing bias voltage is determined according to the detection output. It is designed to control the following.

Therefore, even for colored originals, it is possible to accurately detect the spectral characteristics of the image area and automatically control the appropriate exposure amount or developing bias voltage according to the image color, resulting in good copying. can be obtained.

[Brief explanation of the drawing]

1 to 6 show an embodiment of the copying machine according to the present invention, FIG. 1 is a sectional view showing the main parts of the mechanism, and FIG. 3 is a circuit diagram showing an example of a spectral characteristic detection circuit and an exposure amount control circuit; FIG. 4 is a characteristic diagram showing the spectral sensitivity of the photodiode shown in FIG. 2; Fig. 5 is a characteristic diagram showing the spectral sensitivity of the photosensitive drum shown in Fig. 1, Fig. 6 is a circuit diagram showing an example of a developing bias voltage switching control circuit, and Fig. 7 is a photodetection diagram on the slit plate shown in Fig. 1. A plan view for explaining a modification of the arrangement of elements, No. 8
This figure is a sectional view showing the structure of the photodetector element shown in FIG. 7, and FIG. 9 is an equivalent circuit diagram of the photodetector element shown in FIG. 8. 2... Exposure lamp, 7... Photosensitive drum, 9...
...Developer, 21, 22...Photodiode, 3
0...Spectral characteristic detection circuit.

Claims (1)

[Scope of utility model registration request] The first and second parts each have different spectral characteristics and detect the reflected light from the image area of the original to be copied.
a light-receiving means, a detection means for detecting the spectral characteristics of the original by comparing the outputs of these light-receiving means, and at least one of the exposure amount for the original and the bias voltage for development is controlled according to the output of the detection means. A copying machine characterized by comprising: a control means for controlling the copying machine;