JPH03296036A - Original density detecting device - Google Patents

Abstract

PURPOSE:To always obtain an optimum copying density without especially performing a manual adjustment by automatically changing digital data for setting a gain which is given to a gain commanding means so that the light reflected on a standard surface may become a value within a prescribed extent in the case that a light quantity is beyond a reference extent. CONSTITUTION:A device is provided with photoelectric conversion means Da and OP1 for receiving the light reflected on an original by an illuminating means 2a and outputting an electrical signal at a level in accordance with a received light quantity and a light quantity detecting means 40 and the gain setting means 20. And whether or not the light quantity which is detected by the light quantity detecting means 40 is within the reference extent is decided by the gain setting means 20, and in the case that the light quantity is beyond the reference extent, by referring the digital data which is converted by an A/D converting means 20 when the light reflected on the standard surface is converted to the electrical signal by the photoelectric conversion means Da and OP1, the digital data for setting the gain which is given to the gain commanding means 10a so that the digital data can become the value within the prescribed extent is automatically changed. Thus, the optimum copying density can be always obtained without especially performing the manual adjustment.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image processing apparatus that projects an original image onto a photoreceptor by optical scanning, and particularly relates to an original density detection apparatus that detects the background density of an original.

[Conventional technology]

Image processing device 1 that projects an original image onto a photoreceptor by optical scanning 1 For example, in copying machines, facsimile machines, image editing devices, etc., it is used to record and reproduce images with high contrast to the original background, or to record and reproduce images with high contrast to the original background (color etc.). In order to generate a copy with the background dirt removed (that is, without background stains), the original density detection circuit detects the amount of light reflected from the background of the original, and in response to this, a copy without toner on the background is generated. Imaging parameters such as charger voltage or developing bias are adjusted so as to obtain the desired results.

By the way, if the light amount of the document illumination light source, such as an exposure lamp, changes, the detection level of the document density detecting circuit for the density of the document background changes, so that the above-mentioned adjustment of the image forming parameters will result in an error. Conventionally, a sheet of standard density (usually white) is placed on a contact glass plate, and the amplification gain of the original density detection circuit is adjusted so that the density detection level falls within the reference range.

[Problem to be solved by the invention]

Since such gain adjustment is a manual adjustment, the operation is cumbersome.

An object of the present invention is to automatically adjust the amplification gain of a document density detection circuit.

[Means for solving 1!111i] The document density detection device of the present invention includes an illumination means (2a) that illuminates the document; receives light reflected from the document by the illumination means (2a) and adjusts the level according to the amount of received light. photoelectric conversion means (
Da, 0PI); amplification means (OF2) that amplifies the electrical signal of the photoelectric conversion means (Da, 0PI) with a gain corresponding to the gain instruction signal
; A/D conversion means (20) that converts the electrical signal amplified by the amplification means (OF2) into digital data; Generates a gain instruction signal corresponding to the digital data for gain setting and supplies it to the amplification means (OF2); gain indicating means (10a); light amount detecting means (40) for detecting the amount of light emitted from the illumination means (2a); and determining whether the light amount detected by the light amount detecting means (40) is within a reference range and determining whether the amount of light detected by the light amount detecting means (40) is within the reference range. If it is outside nine, the photoelectric conversion means (D
Referring to the digital data of the A/D conversion means (20) when the A/D conversion means (20) is converting the reflected light from the standard surface into an electrical signal, the gain indication means (0PI) is directed in a direction where the value falls within a predetermined range. gain setting means (20) for changing digital data for gain setting given to 10a); 9. Symbols in parentheses indicate corresponding elements in the embodiments shown in the drawings and described later.

[Effect]

The gain setting means (20) determines whether the light amount detected by the light amount detection means (40) is within a reference range, and if it is outside the range, the photoelectric conversion means (Da, DPI) Referring to the digital data converted by the A/D conversion means (20) when converting the reflected light into an electric signal,
The gain indicating means (1
Since the digital data for gain setting given to 0a) is automatically changed, there is no need for manual adjustment, and the optimum copy density can always be obtained.

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

〔Example〕

A mechanical outline of the optical system of a copying machine incorporating an embodiment of the present invention is shown in FIG. 2a, and a perspective view of its appearance is shown in FIG. 2b.

To explain with reference to FIG. 2a, below the contact glass 1 on which an original (not shown) is set is a.

A scanner optical system 2 is provided, and an image formed by reflected light from a document is formed on a drum-shaped photoreceptor 3 via the scanner optical system 2.

The scanner optical system 2 includes an illumination light source 2a, a reflector 2b, a first
A first carriage 51 consisting of a mirror 20, etc., and a second carriage 52 consisting of a second mirror 2d, a third mirror 28, etc.
and the imaging lens 2f.

It consists of a fourth mirror 2g, etc. 2h is dustproof glass.

Note that the first carriage 51 and the second carriage 52 are
2 = so that the reflected optical path length from the original does not change during scanning.
It is designed to be driven for reciprocating scanning by a DC motor M7 at a speed ratio of 1.

This will be explained with reference to FIG. 2b.

A drive wire 61 coupled to the scanner optical system 2 is wound around a pulley 60 fixed to the shaft of a DC motor M7. The drive wire 61 is connected from one end 61a to a stud pulley 62. Drive pulley 63 coupled to second carriage 52 . Turn pulley 64. blanket pulley 66
, a blanket 67 coupled to the first carriage 51, a drive pulley 63 . The other end 61b passing through the tightener pulley 68
is connected to form a closed loop.

HPI shown in FIG. 2b is a switch (photo sensor) that detects the home position of the scanner. Similarly, RP
I is a limit switch that detects one forward scanning end position of the scanner, and RP2 is a limit switch that detects another forward scanning end position.

Although not shown in this drawing, there is also a photo sensor HP that detects the home position in the variable magnification mechanism (i.e. lens).
2 is a provision. This switch is turned on when the lens is in the home position and the magnification position. The reason why the forward scanning end position is detected by two limit switches is because when the scanner performs full scanning, the position of the variable magnification mechanism, especially the lens, changes and the scanner collides with it. This is to protect the shins.

The RPI switch is provided at the forward scanning end position, and the RP2 switch is provided at the variable magnification mechanism.

In such a configuration, the scanner optical system 2 is driven rightward from the HP state as schematically shown in FIG. 2a to expose and scan the document surface.

After completing the exposure scan, the scanner optical system 2 moves back toward the home position again. During the backward movement of the scanner optical system 2, it is generally driven faster than during the forward movement, and deceleration control is performed when the scanner optical system 2 approaches the home position HP. Then, when the HPI detects the home position HP, the rotation direction of the motor M7 is reversed (scanner backward movement direction).
By switching from forward rotation (scanner forward direction),
This is to return to the home position HP from the overrun position.

Next, FIG. 2c is a vertical sectional view centering on the first carriage 51 shown in FIG. 2a, and FIG.
A perspective view of the exterior is shown.

In FIG. 2c, 25 is a pressure plate and 26 is an original. 2
7 is an optical fiber with one end facing the vicinity of the illumination lamp 2a, and 28 is a guide rod for moving the carriage. Further, below the contact glass 1 and in front of the original scanning start edge, there is a reference pattern 4 for detecting the reference density.
is provided.

As shown in FIG. 2d, optical fibers 27a and 27b are provided in the longitudinal direction of the illumination lamp 2a, and the reflected light irradiated onto the original 26 by the illumination lamp 2a is transmitted through the optical fiber 27a to an original density detection circuit 30, which will be described later. Furthermore, the light from the illumination lamp 2a is guided to the light amount detection circuit 40 by the optical fiber 27b.

Further, the photodiodes corresponding to the optical fibers 27a and 27b have a peak at a wavelength of about 58 nm.

The output from the optical fiber 27a is used as the 1M document density, and when the voltage corresponding to the light amount changes with respect to the set voltage during exposure scanning of the document, this output is checked and the peak value of the output is determined as the document density. The charger voltage or developing bias voltage is determined based on this background density in order to optimize the density of the copy.

FIG. 1 shows an electric control section that controls each of these constituent elements.

The electric control unit is a microcomputer (hereinafter referred to as MCU) 20. which controls the entire copying machine. A ROM 21 that is connected to the address bus, control bus, data bus, etc. of the MCU 20 and stores fixed data and control programs;
RAM 22 for reading and writing copy data, various flags, etc.
j! X original density detection circuit 30. It is composed of a light amount detection circuit 40 and the like.

The document density detection circuit 30 will be explained.

This circuit is a multiplication type D/A converter (hereinafter referred to as DAC) 10a (AD7524 manufactured by Analog Devices, Inc.).
), photodiode Da, anti-phase amplifier ○P1. It consists of a positive phase amplifier ○P2, etc.

When the reflected light guided by the optical fiber 27a hits the photodiode Da, a photocurrent IDa flows. This photocurrent IDa is determined by the gain resistor R5, va=−R5·
...(5) Represented by: This voltage Va is V of DACl Oa, εF
input to the terminal. The approximate expression for the voltage Vc output from the DAC 10a is as follows.

Vc=IDa-R5X (256/D)-(6)(
D is a digital amount determined according to DO to D7 from the MCU 20, and is expressed as a value in the range of 0 to 255).

The OUT terminal of the DAC 10a is connected to the inverting input terminal of the positive phase amplifier OP2. Therefore, the output voltage Vc of DACl Oa is non-inverting amplified by the positive phase amplifier OP2 and resistors R6 and R7, and is amplified by the A of the MCU 20 via the resistor R8.
/D converter input terminal ANI. This AN
The voltage vb input to I is expressed as: Vb=VeX (1+R7/R6) +IDa-R7... (7). From equations (6) and (7), the photocurrent ID
The relationship between a and the voltage vb input to the ANI terminal is Vb=IDa-R5X (256/D)X(1+R7/
R6) 10I Da-R7...The approximate formula is (8),
It can be seen that the gain of this circuit changes depending on the digital data D. Therefore, since the feedback gain can be changed by the digital data D, the OUT terminal voltage of DACloa can also be controlled.

For example, in equation (6), when the amount of light is large and IDa is large, if the digital data D is increased, Vc (D
ACloa's OUT terminal voltage) can be controlled to a small value, and conversely, when the amount of light is small and I Da is small,
By reducing D, Vc can be greatly controlled.

DO to D7 of the DACloa are connected to the data bus DO-D7 of the MCU 20, and a control line (not shown) is further connected to the MCU 20. This allows MCU
20 is the amount of light detected by the optical fiber 27a,
Compare it with preset density information, set the digital data D of DACloa in the direction in which both match, and write that data to the memory.
Give to 0a.

The light amount detection circuit 40 has a circuit configuration similar to that of the original density detection circuit 30, and detects the amount of light emitted from the illumination lamp 2a via the optical fiber 27b, and compares the amount of light with preset density information. D in the direction where both match
Set digital data D of AC10b.

Note that in the light amount detection circuit 40, a circuit including a resistor R9 and a capacitor C6 is a smoothing circuit for removing noise.

Next, the MCU 20 automatically adjusts the gain of the document density detection circuit 30 when the aforementioned light amount detection circuit 40 detects a change in the amount of light from the illumination lamp 2a when the scanner is at the home position.

The operation of the MCU 20 at this time will be explained with reference to the flowchart shown in FIG.

The MCU 20 first checks whether the illumination lamp 2a is on or not (Step 1: Hereinafter, the word "step" will be omitted in parentheses and the number will be referred to as "No.").

If the illumination lamp 2a is on, the scanner is checked at the home position using the home sensor HPI shown in Figure 2b.2) If the scanner is at the home position, the illumination lamp 2a is turned on. The amount of light is read (3), and the aforementioned light amount detection circuit 40 checks whether the amount of light is different from a preset value (4).

When the light amount is changing from the set value, the diode D2. Discharge the voltage of the peak hold circuit consisting of capacitor C3 (
5) Read the reflected light of the reference pattern 4 shown in FIG. 2c (6) and check whether it differs from a preset value (7). The voltage of capacitor C3 of this peak hold circuit is set to MC before starting the exposure scan of the original.
It is discharged by the output from the PORT terminal by U20, and during exposure scanning, the peak value of the output is caused by the diode D2.
charged through. The MCU 20 detects the peak value of this output as the background density of the original. With conventional technology,
This peak value detection was detected by software, but it was a 50Hz ripple of the lamp.

The output changes depending on the black and white state of the original, and software detection is complicated.

Note that the voltage VC of the capacitor C3 is the voltage of the positive phase amplifier OP.
Since it is connected to the non-inverting input terminal of DAC10a
It becomes the same as the OUT terminal voltage Vc of .

If the voltage value corresponding to the reflected light read from the reference pattern 4 in step 7 is different from the voltage corresponding to the set value, check the magnitude relationship between the two (8).
When the voltage value corresponding to the reflected light read from is larger than the voltage corresponding to the set value, the digital data D of DACloa is incremented by 1, and the voltage value corresponding to the reflected light is lowered according to equation (9)1 (8). .

Conversely, when the voltage value corresponding to the reflected light read from the reference pattern 4 is less than the voltage corresponding to the set value, the digital data D is decremented by 1 (10) and the voltage value corresponding to the reflected light is increased. The digital data D is output as follows (11).

Then, step 11 is performed until the voltage corresponding to the reflected light read from the reference pattern 4 matches the voltage of the set value.
→ 6 → 7 → 8 → 9 (or 10) → IJ... repeat the loop.

The above is an outline of the control flowchart in the MCU 20.

That is, in this embodiment, the amount of light from the illumination lamp 2a before the exposure scan of the original is compared with the amount of light set in advance by the light amount detection circuit 40, and if the two are different, the amount of light emitted from the illumination lamp 2a is compared with the amount of light that is set in advance by the light amount detection circuit 40. The reference density is read by the reflected light from the reference pattern 4 provided in the document density detection circuit 30, and the digital data D of DACloa is controlled so that the density matches a preset density.

At this time, the DAC is adjusted so that the amount of light from the illumination lamp 2a also matches the amount of light set in advance by the light amount detection circuit 40.
The digital data D of 10b is controlled.

〔Effect of the invention〕

As described above, according to the present invention, the gain setting means (20) determines whether the light amount detected by the light amount detection means (40) is within the reference range, and if it is outside the range, the gain setting means (20) determines whether the light amount detected by the light amount detection means (40) is within the reference range. When the means (Da, DPI) converts the reflected light from the standard surface into an electrical signal, refer to the digital data converted by the A/D conversion means (20), and the value will be within a predetermined range. Since the digital data for gain setting given to the gain indicating means (10a) is automatically changed in the direction, there is no need for manual adjustment and the optimum copy density can always be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an electrical control section of a copying machine that embodies the present invention by way of example. FIG. 2a is a side view schematically showing the mechanism of the optical system of the copying machine, and FIG. 2b is an external perspective view thereof. FIG. 2c is a vertical sectional view centered on the first carriage 51 shown in FIG. 2a, and FIG. 2d is a vertical sectional view. FIG. 5 is an external perspective view of the first carriage 51. FIG. FIG. 3 is a flowchart showing the operation contents of the MCU 20 shown in FIG. 1: Contact glass 2: Scanner optical system 2a
: Illumination light source (illumination means) 2b: Reflector plate 2c: First mirror 2d: Second mirror 2e: Third mirror
2f: Imaging lens 2ε: Fourth mirror
2h: Dustproof glass 4: Reference pattern 10a: DAC (gain indicating means) 10b
: DAC20: MC1l (A/D conversion means, gain setting means) 21: ROM
22: RAM 27: Optical fiber 30: Original density detection circuit 40: Light amount detection circuit (light amount detection means) 51: First carriage 52: Second carriage Da, Db: Photodiode OPI to OP4: Amplifier (Da, OPI: Photoelectric conversion Means) (OP2 Two-increase two-hand width Means Applicant Rico Co., Ltd.

Claims (1)

[Scope of Claims] Illumination means for illuminating the document; Photoelectric conversion means for receiving reflected light from the document by the illumination means and outputting an electrical signal at a level corresponding to the amount of received light; Gain instruction for the electrical signal of the photoelectric conversion means Amplifying means for amplifying the signal with a gain corresponding to the signal; A/D converting means for converting the electrical signal amplified by the amplifying means into digital data; Generating a gain instruction signal corresponding to the digital data for gain setting to perform the amplification. gain instruction means for providing a gain indication to the means; light amount detection means for detecting the amount of light emitted from the illumination means; and determining whether the amount of light detected by the light amount detection means is within a reference range, and if it is outside the range, the photoelectric The A/D when the conversion means converts the reflected light from the standard surface into an electrical signal.
A document density detection device comprising: gain setting means for referencing the digital data of the conversion means and changing the digital data for gain setting given to the gain instruction means in a direction such that the digital data becomes a value within a predetermined range.