JP2872716B2 - Document density detector - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a document density detecting apparatus such as an electrophotographic apparatus, and more particularly, to a document density detecting apparatus having a simple circuit configuration and an automatic adjustment range for a change in light amount expanded. It relates to a detection device.

[Prior Art] Conventionally, a document density detecting device having a circuit configuration as shown in FIG. 6 has been proposed. In other words, this is the two operational amplifiers 601 and 602, the MCU (A / D converter built in the microcomputer unit) 603, a photodiode D, a capacitor C _1, C _2, a resistor R _1, R _2, R ₃ And a variable resistor VR.

In such a circuit configuration, the reflected light is detected by the photodiode D. As a result, the photocurrent flowing through the diode D is defined as _ID, and this photocurrent _ID is used as the operational amplifier 60.
It converted into a voltage by 1 and resistor R _1.

Voltage V _a that is converted at a point of this time is expressed by _{V a = I D · R 1} .

Thereafter, the voltage Va at the point a is further _added to the operational amplifier 60.
2 to amplify to a voltage value required by the resistor R ₂ and the variable resistor VR.

Voltage V _b at the point b at this time, when the resistance value of the variable resistor VR and V _R, It can be expressed as.

It should be noted that in a light amount detecting device such as a document density detecting circuit and a document size detecting circuit provided in the electrophotographic apparatus, it is necessary to make an adjustment so that a predetermined output can be secured when a predetermined light amount is received. in the document density detecting circuit shown, a document as a reference, enter the reflected light when irradiated with reference made light intensity, the resistance value V _R of the variable resistor VR so that it can output a predetermined voltage value adjust.

However, the above-mentioned variable resistor VR is generally provided on a printed circuit board behind the electrophotographic apparatus, and it is necessary to work around the rear of the electrophotographic apparatus at the time of manufacturing or adjustment at a user's site. Was very bad.

To solve the above problems, it was proposed that
This is a document density detecting device shown in FIG. This original density detecting circuit is obtained by adding a DAC (multiplying D / A converter) 705 to the original density detecting circuit shown in FIG. 6, and the amount of light from an MCU (microcomputer unit with a built-in A / D converter) 703. The data is fed back to the DAC 705, compared with a preset reference value, and a necessary coefficient is set.

However, in the original density detection circuit shown in FIG. 7, the V _REF terminal of the DAC 705 functions as an input and the OUT terminal functions as an output, and the DAC 705 outputs a current. Therefore, the operational amplifier 7
It is necessary to convert to a voltage output in 02, and a positive output is given to the AN terminal of the MCU 703 for use as an inverting amplifier. Therefore, two positive and negative power supplies are required. Also,
An additional operational amplifier is required, resulting in a problem that the device becomes complicated and the manufacturing cost increases accordingly.

In order to solve the drawback of the original density detecting circuit shown in FIG. 7, an original density detecting device shown in FIG. 8 has been proposed.

The original density detecting circuit shown in FIG. 8 has a structure in which a DAC (multiplying D / A converter) 805 is used in a voltage switch mode.

[Problems to be solved by the invention]

However, when a high voltage is input to the OUT terminal of the DAC 805, there is a problem that the linearity of the DAC 805 deteriorates.

Specifically, the DAC 805 in the light amount detection circuit of FIG.
And the output from the V _REF, the relationship between the input voltage V _a, However, when the input voltage Va exceeds _a certain input voltage range (1.2 V or more), the output change with respect to the input becomes non-linear, and the linearity of the output V _REF with respect to the photodiode D also deteriorates.

Therefore, in the original density detecting circuit shown in FIG.
There is a problem that it can be used only in a specific light amount change range.

The present invention has been made in view of the above, and an object of the present invention is to improve the workability and to expand the automatic adjustment range for a change in light amount with a simple circuit configuration while avoiding a complicated device.

[Means for solving the problem]

In order to achieve the above object, the present invention provides a converting means for converting a light amount into a current and a voltage, a control means for programmably controlling the voltage converted by the converting means,
It is an object of the present invention to provide a document density detecting device provided with an amplifying means for amplifying a signal controlled by the control means and a detecting means for detecting a peak value of a light amount.

[Action]

In the document density detecting apparatus according to the present invention, the received light amount is converted into a current and a voltage, and the converted voltage is amplified by a gain computer in a programmable manner, and the peak value of the light amount is detected as the background density of the document.

〔Example〕

Hereinafter, a document density detecting apparatus according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram including a document density detecting device according to the present invention. In FIG. 1, a circuit A functions as a document density detecting circuit, and circuits B and C function as a document size detecting circuit.

In Figure 1, the photodiode D ₁ light current I _D flows by receiving light, and an operational amplifier OP _1, which is connected to the photodiode D _1, respectively the connected resistor R _1, R
₂ , R ₃ , R ₄ , R ₅ and the connected capacitors C ₁ , C
₂ , C ₃ , C ₄ , a DAC (multiplying D / A converter) 102, an operational amplifier OP ₂ (circuit A) for non-inverting amplification of the output voltage in cooperation with the resistors R ₁ , R ₂ and an arithmetic Amplifier OP ₃ (Circuit B, Circuit C)
When the peak hold circuit 103 with the capacitor C ₁
And a diode D ₂ (circuit A). The resistor R ₅ and the C ₄ are circuit B, in the circuit C, and constitute a smoothing circuit 106 for eliminating noises.

Further, an MCU (A / D) that inputs various signals from each unit of the light amount detecting device such as the original density detecting circuit and the original size detecting circuit and outputs a control signal to each predetermined unit after a predetermined calculation.
A microcomputer unit with a built-in converter) 101,
A ROM 105 is connected to the MCU 101 and stores a program for executing a control process for each unit, and a RAM 104 stores processing results of the MCU 101, data, and the like.

FIG. 2 is an external perspective view of the entire scanner section of the electrophotographic apparatus. The first carriage 201, the second carriage 202, which moves at a predetermined speed in the document scanning direction, and the first and second carriages are moved. A scanner motor 203, a wire 204 interposed between the scanner motor 203 and the carriages 201 and 202, and light guided to the original by optical scanning, and an exposure process is performed to form an electrostatic latent image on the surface. And a main motor 206 for driving other components such as the photosensitive drum 205.

FIG. 3 is a side view of the optical system shown in FIG. 2, and includes a contact glass 301 on which an original is placed, an illumination lamp 302 constituting the first carriage 201, a reflecting plate 303, a reflecting mirror 304, The second carriage 202 includes reflection mirrors 305 and 306, and an imaging lens 307, a reflection mirror 308, and a lens 309 fixed in the optical path.

In FIG. 4, a document 402 placed on the contact glass 301, a document pressing plate 401 for fixing the document 402, and one end thereof near the illumination lamp 302 are provided. It comprises an optical fiber 403 and a guide rod 404 for moving the carriage.

Further, as for the optical fiber 403, as shown in FIG. 5, three optical fibers 403a, 403b, 403c provided in the longitudinal direction of the illumination lamp 302 are installed. The reflected light illuminating the original 402 placed on the original is transmitted through the plurality of optical fibers 403as, 403b, and 403c to the original density detecting circuit (circuit A) and the original size detecting circuit (circuit B, circuit B, shown in FIG. 1).
C).

In the optical fibers 403a, 403b, and 403c, the corresponding photodiodes have different spectral sensitivities. Optical fiber 40
The photodiode corresponding to 3a has a peak at a wavelength of about 580 nm, and the others have a peak at a wavelength of about 420 nm.

A circuit having a sensitivity peak at a long wavelength uses the output as a document density. At the time of exposure scanning of the document 402, this output is checked, the peak of the output is determined as the background density of the document, and based on this, the document bias voltage is determined so as to optimize the copy density.

Further, a circuit having a peak of sensitivity at a short wavelength is used for document size detection.

That is, in FIG. 4, the original pressing plate 401 is colored yellow and has a very small reflectance with respect to light having a wavelength of 420 nm, but has a high sensitivity to the photosensitive drum 205 with light having a wavelength of 580 nm where the sensitivity of the photosensitive drum 205 is high. Therefore, the reflectance is high. Prior to the exposure scanning of the original 402, a prescan for detecting the original size is executed. When the scanner returns, the original pressing plate 401 and the original 402 are distinguished based on a change in the output of this circuit. Judge.

The optical fiber 403b is for detecting the document length, and the optical fiber 403c is for detecting the document width.

 The operation of the above configuration will be described.

In each of the circuit diagrams in FIG. ₁ , when light guided by the corresponding optical fibers 403a, 403b, and 403c strikes the photodiode D1, a photocurrent _ID flows there. The photocurrent I _D is the gain resistors R _3, is represented by Va = I _D · R _3.

The voltage of the I _D · R ₃ are input to the V _REF terminal of DACs 102. As a result, the approximate expression of the voltage _Vb output from the OUT terminal of the DAC 102 is represented by the following expression.

In the above formula, D is a digital amount determined according to D0 to D7 of the DAC 102, and is a value in the range of 0 to 255.

The output voltage V _OUT a includes an amplifier OP _2, resistors R _1, is non-inverting amplified by R _2, is input to the A / D converter input terminal AN ₁ of MCU101 via the resistor R _4.

Voltage V _c inputted to the A / D converter input terminal of the noninverting amplifier is amplified by the circuit MCU101 is It is represented by

From the above, after all, the relationship between the V _c inputted to the optical current I _D and the AN pin, It can be seen that the circuit gain changes according to the digital data D.

As described above, since the feedback gain can be changed by the digital data D, the OUT terminal voltage of the DAC 102 can also be controlled.

Also, it can be seen from the following equation that if the light amount is large and I _D is large, if D is reduced, V _D (DACOUT terminal voltage) is also reduced.

Next, the setting of the digital data D will be described.

D0 to D7 of the DAC 102 are connected to data buses D0 to D7 of the MCU 101, and a control line (not shown) is connected to the MCU 101. Thus, the MCU 101 outputs the digital data D to the DAC 102 in the same manner as writing data to the memory.

At the time of voltage adjustment, the optical system shown in FIGS.
The digital data D is detected by the optical fiber shown in the figure, and the digital data D is changed so that the A / D input voltage of the MCU 101 becomes a constant value.
Write to 102.

In addition, as a second embodiment, a standard reflection member (not shown) is installed at a predetermined location, and a change in lamp voltage is automatically detected inside the device, and an automatic correction process is performed. Can also.

Note that the above description can be used commonly in the circuit diagrams A, B, and C.

Next, the circuit diagram A (original density detecting circuit) will be described.

Before starting exposure scanning of the document, the MCU 101 outputs a signal from the PORT to discharge the capacitor voltage of the peak hold circuit 103 composed of the diode D ₂ and the capacitor C ₁ .

Thereafter, the output peak value during exposure scanning is charged through the diode D ₂ to the capacitor C _1, MCU 101 detects the time output of the peak as background density of the document.

In the prior art, this peak value detection was detected by software, but the output was changed due to the 50 Hz ripple of the lamp and the black and white state of the document, and the software detection became complicated, making it difficult to demand high accuracy. There is a problem.

The voltage V _D of the capacitor C _{1 in} the circuit diagram A is an operational amplifier.
Because it is connected to the non-inverting input terminal of the OP _2, it becomes equal to the voltage of V _b (imaginary short). That is, It is represented by

〔The invention's effect〕

As described above, in the original density detecting apparatus according to the present invention, the converting means for converting the light amount into current and voltage, the control means for performing gain control of the voltage converted by the converting means, and the voltage controlled by the controlling means are controlled by the controlling means. Amplifying means for amplifying the received signal, and detecting means for detecting the peak value of the light amount. After converting the received light amount into current and voltage, the converted voltage is amplified by programmable gain control to amplify the peak value of the light amount. Since the value is detected as the background density of the document, the work life can be improved, and the automatic adjustment range for the change in the light amount can be expanded with a simple circuit configuration while avoiding the complexity of the apparatus.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a light amount detecting device including a document density detecting device of the present invention, FIG. 2 is an external perspective view of the entire scanner section of the electrophotographic apparatus, and FIG. 3 is a view of the scanner section shown in FIG. Side view of the optical system, FIG. 4 is a longitudinal sectional view centering on the first carriage unit, FIG. 5 is an external perspective view of the first carriage,
6, 7 and 8 are circuit diagrams of a conventional document density detecting device. EXPLANATION OF SYMBOLS 101: MCU (microcomputer unit with built-in A / D converter) 102: DAC (multiplying D / A converter) 103: peak hold circuit 104: RAM, 105: ROM D ₁ ... photodiode _{OP 1, OP 2, OP 2} ...... operational amplifier R ...... resistance, C ...... capacitor

Claims (1)

(57) [Claims] A converter for converting the amount of light into a current and a voltage; a controller for programmably gain-controlling the voltage converted by the converter; an amplifying unit for amplifying a signal controlled by the controller; A document density detecting device, comprising: a detecting means for detecting a value.