JP3135690B2 - Automatic image density adjustment device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic image density adjusting device suitable for a copying machine or the like.

[0002]

2. Description of the Related Art In a copying machine, an automatic image density adjusting device is provided so that even when the density of an original is lower or higher than normal, the original is transferred at an optimum density as in the case of a normal density original. That is common. In such a copying machine, for example, when the background density of the document is high, a slightly lower transfer density is automatically set as a whole, thereby preventing transfer fog and the like, and making the transferred image easier to see.
The transfer density is adjusted by changing the exposure amount or changing the bias voltage of the developing sleeve as described below.

FIG. 5 shows a configuration of a copying machine to which a conventional automatic image density adjusting device is applied. In this copying machine, the light of the exposure lamp 2 reflected on the original 1
Is projected on the drum 11 via the. As a result, a latent image of the document 1 is formed on the drum 11, and the toner 12 adheres to the latent image and is developed. Then, the toner 12 on the drum 11 is separately transferred to transfer paper, and the copying is completed.

The amount of toner 12 adhering to drum 11 is
The adjustment can be performed by changing the bias voltage applied to the developing sleeve 10, thereby making it possible to adjust the transfer density. That is, when the bias voltage of the developing sleeve 10 is high, the amount of the toner 12 adhering to the drum 11 decreases, and the transfer density decreases. Conversely, when the bias voltage of the developing sleeve 10 is low, the transfer density increases. For example, when the background density of the original document 1 is high, the bias voltage is set to a high value because it is easy to see if the entire image is transferred as described above.

On the other hand, in this copying machine, the following EE scan is performed to detect the density of the original 1. In addition,
In the following description, the reflection density OD is used as the density.
Now, assuming that the light reflectance of the original 1 is R, the reflection density OD
Is represented by OD = log10 (1 / R). The reflection density OD = 0.0 (R = 1) represents white data, and the reflection density OD = ∞ (R = 0) represents black data.

In the EE scan, the exposure lamp 2 is moved along the original 1. At this time, light reflected from a plurality of measurement points on the original 1 is received by the sensor 4 and the light is photoelectrically converted. An electric signal (hereinafter referred to as an EE signal) corresponding to the density at the measurement point is output. A predetermined number of EE signals are sampled in this EE scan, and are sampled through a gain selection circuit 5 and an offset adjustment circuit 6 to be A.
/ D converter 7.

In the gain selection circuit 5, the reflection density OD =
When the EE signal corresponding to 0.0 to ∞ is amplified, a gain is selected such that all the EE signal is taken into the A / D converter 7. That is, EE corresponding to the reflection density OD = 0.0
The level when the signal is amplified becomes the maximum input level of the A / D converter 7, and the level when the EE signal corresponding to the reflection density OD = ∞ is the minimum input level of the A / D converter 7. Is selected. Therefore, A
Assuming that the resolution of the / D converter 7 is, for example, 64 steps, a signal corresponding to the reflection density OD = 0.0 to ∞ is decomposed into 64 steps.

By selecting the gain in this manner, all of the sampled EE signals can be converted into A / D converters 7.
In addition to the above, it is possible to eliminate the influence of variations in the read density due to the accuracy error of the sensor 4 and the resistance value error of the resistors constituting the circuit. That is, when an image of the same density is read by a plurality of copying machines of the same specification, even if the level of the EE signal differs for each copying machine due to an error in accuracy of each unit or the like, the gain is appropriately selected for each copying machine. It is possible to copy at the same density with a copying machine of the same type.

The output signal of the A / D converter 7 is supplied to the CPU
(Central processing unit) 8, where a density histogram as shown in FIG. 6 is created. Based on the density histogram, the density of the document 1 is determined by a procedure described later. In this figure, the horizontal axis represents the reflection density OD = 0.0 to ∞.
And the reflection density OD = 0.0 to ∞ is the resolution of the A / D converter 7, in this example, the density of the original document which is divided into 64 steps and is represented by a number from 0 to 63. Frequency in density. Here, the output of the A / D converter 7 and the density of the document correspond one to one.

In this density histogram, a bias (= 3.5 to 7) is set corresponding to a predetermined range of document density. The bias is set in one-to-one correspondence with the bias voltage applied to the developing sleeve 10. For example, Bias 4 corresponds to a bias voltage of 250 V (volts), and Bias 5 corresponds to a bias voltage of 330 V.

The bias voltage corresponding to the bias 7 is the highest, and the transfer density at this time is the lowest. The threshold values between the biases are symbolized as determination levels J2D to J4, and are used as a reference for determining the overall density of the document 1 as described later. In this example, for example, the judgment level J2D is the document density 7 and the judgment level J4 is the document density 27.

In order to transfer the image of the original 1 to the transfer paper at an optimum density based on the density histogram created in this manner, that is, to transfer the image at an easy-to-see density while preventing transfer fog and the like, the following will be described. The bias voltage to be applied to the developing sleeve 10 is determined by such a procedure.

In determining the bias voltage, first, the lightest original density (hereinafter, referred to as the lightest density) and the darkest original density (hereinafter, referred to as the highest density) from the density histogram.
Is calculated, and then the spread density (= darkest density−lightest density) is calculated. In this example, the lightest density = 5, the darkest density = 14, and the spread density = 14−5 = 9.

Next, the frequency of each document density is added in order from the lightest density, and the density of the document when the sum exceeds half of the sampling number for the first time is defined as the average density. In this example, the total sampling number is 640, and the total frequency at each density exceeds half, that is, exceeds 320 for the first time when the document density is 10, and this is the average density.

Next, a bias for the document 1 is determined by a bias determination process 30 shown in FIG. In the bias determination process 30, first, the average density and the judgment level J2
Are compared, and if the average density is smaller, the average density is then compared with the judgment level J2D. When the average density is lower, the bias is determined to be 3.5, and when the average density is higher, the bias is determined to be 4 (steps 31 to 34).

If it is determined in step 31 that the average density is larger than the judgment level J2, the spread density and the reference spread density (for example, set in the middle to distinguish a line image from a photographic image) are set next. If it is determined that the spread density is higher, the average density is compared with the determination levels J3D, J3, and J4, and the biases 4.5 to 7 are determined based on the magnitude relation (step). 3
6-42).

If it is determined in step 35 that the spread density is smaller than the reference spread density, then the lightest density is compared with the judgment levels J2 to J4, and the biases 4 to 7 are determined based on the magnitude relation ( Steps 43 to 51).
The density histogram shown in FIG.

When the bias is determined in this way,
Next, the CPU 8 instructs the bias circuit 9 to generate a bias voltage corresponding to the bias. As a result, the bias voltage generated by the bias circuit 9 is applied to the developing sleeve 10, and the image of the original 1 is transferred at the optimum transfer density.

[0019]

In the above-described bias determination method, the criterion for determining whether to select the bias 7 having the lightest transfer density is the determination level J4.
This is, as described above, the document density 27, that is, the reflection density O
D = 0.2 is set. In other words, the bias 7 is selected for a document density that is half or more of the entire document density range of 0 to 63.

FIGS. 8 and 9 show another example of a conventional density histogram. FIG. 8 shows the case where the bias becomes 6, and FIG. 9 shows the case where the bias becomes 7. As can be seen from the figure, even when the maximum class biases 6 and 7 are selected, the lightest density and average density are near the judgment level J4. This is because the density of the original 1 is equal to the reflection density OD = 0.
This is because if it is 2 or more, it will be too dark as a whole and it will be difficult to see it.

Therefore, even though the reflection density OD = ∞ is set as a possible density of the density histogram, only half of the reflection density OD = 0.2 is actually detected. Will be. Therefore, only about half of the input level width of the A / D converter 7 (FIG. 5) is used.

In other words, the density range is set to be about twice the density range actually detected as a density range that can be taken by the density histogram, and this is divided into 64 steps in the resolution of the A / D converter 7, in this example. Therefore, the document density actually detected is decomposed into 32 steps, which is about half of the original density. That is,
This means that the resolution inherent in the automatic image density adjusting device is reduced by half.

Accordingly, the present invention has been made to solve the above-mentioned problem, and has an automatic image density adjustment capable of improving the resolution of the apparatus by effectively utilizing the resolution inherent in the A / D converter. A device is proposed.

[0024]

In order to solve the above-mentioned problem, an automatic image density adjusting apparatus according to the present invention illuminates a document with light.
When the reflected light is read to form an image,
Image forming density can be automatically adjusted according to the density of the original
The automatic image density adjustment device receives reflected light from the original.
A sensor means for converting the light into an electric signal;
Amplifies the output signal by the sensor means based on the predetermined gain
Gain selection circuit and amplification by the gain selection circuit
Extraction of a signal corresponding to a predetermined density range from a signal
Digital signal and the signal extracted by this
A / D conversion circuit for converting the signal into a signal
Control for adjusting the image forming density based on the output of the conversion circuit.
Control device, this control device is extracted by the cut-off circuit
Signal to be matched with the input range of the A / D conversion circuit.
Command the gain selection circuit to select the appropriate gain.
It is characterized by that.

[0025]

In FIG. 1, when reading an original 1 to form (copy) an image, first, the density of the original 1 is determined by EE scanning. In this EE scan, the exposure lamp 2 is moved along the document 1, and at this time, light reflected from a plurality of measurement points of the document 1 is received by the sensor (sensor means) 4 and photoelectrically converted. The EE signal obtained here is converted into a voltage V1 by an I / V conversion circuit 21 constituting a density discrimination signal extraction means, and then a high-frequency component is removed by a low-pass filter circuit 22 and supplied to a gain selection circuit 5. You.

The signal amplified by the gain selection circuit 5 is supplied to a cut-off circuit 23, where a signal in a range necessary for determining the density of the original 1, for example, a reflection density OD = 0 as shown in FIG. Only signals corresponding to the range of 0.0 to 0.3 are extracted. The gain of the gain selection circuit 5 is selected so as to match the input level width of the A / D converter 7 when a signal in this range is amplified.

Therefore, conventionally, the reflection density OD = 0.0
While the signal corresponding to 信号 is processed by the A / D converter 7, the present invention processes the signal in a narrow range of the reflection density OD = about 0.0 to 0.3 by the A / D converter 7. Therefore, when the A / D converter 7 having the same resolution as the conventional one is used, the resolution of the device can be improved.

The signal A / D-converted by the A / D converter 7 is supplied to the CPU 8, where a density histogram as shown in FIG. 4 is created and the density of the original 1, that is, the average density and the lightest density in this example. , The highest density and the spread density are determined. According to the bias determination process 30 shown in FIG.
The bias is compared with the judgment levels J2D to J4 (= 3.
5-7) are determined.

Here, a bias voltage is set corresponding to each bias, and an instruction is issued from the CPU 8 to the bias circuit 9 to generate the bias voltage. Then, a bias voltage generated by the bias circuit 9 is applied to the developing sleeve 10.

After the bias voltage for the original 1 is determined in this manner, the exposure lamp 2 is moved along the entire surface of the original 1.
Moves, and the light reflected by the original 1 is irradiated on the drum 11 through the slit 20 and the lens 3, whereby a latent image of the original 1 is formed on the drum 11. Next, drum 1
The toner 12 adheres to the latent image formed on the surface 1 and is developed. At this time, the amount of the toner 12 adhering to the drum 11 is
This corresponds to the bias voltage applied to the developing sleeve 10, and the higher the bias voltage, the smaller the amount of toner 12 attached.

The toner 12 adhered to the drum 11
Is separately transferred to transfer paper, and copying is completed. In this way, by changing the bias voltage applied to the developing sleeve 11 and adjusting the amount of the toner 12 adhering to the drum 11, the optimum density according to the density of the original 1, that is, a density that is easy to see without transfer fog or the like. Can be transferred.

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the automatic image density adjusting apparatus according to the present invention is applied to a copying machine will be described in detail with reference to the drawings. The same parts as those described above are denoted by the same reference numerals, and detailed description is omitted.

FIG. 1 shows the configuration of a copying machine to which the automatic image density adjusting device according to the present invention is applied. Referring to FIG. 1, light from an exposure lamp 2 reflected on a copy surface of a document 1 is detected by a sensor 4 disposed near an optical system such as a lens 3.
The sensor 4 converts the received light into an EE signal, which is converted into a voltage V1 by an I / V conversion circuit 21. The high-frequency component of the voltage V1 is removed by the low-pass filter circuit 22, and the high-frequency component is supplied to the A / D converter 7 via the gain selection circuit 5 and the cutoff circuit 23.

In the gain selection circuit 5, according to an instruction from the CPU 8, a signal in a range necessary for judging the density of the original 1 as described later, for example, the reflection density OD = 0.0 to 0.3
When the EE signal corresponding to the range of
A gain that matches the input range of the / D converter 7 is selected.

That is, the level when the EE signal corresponding to the reflection density OD = 0.0 is amplified matches the maximum input level of the A / D converter 7, and the EE signal corresponding to the reflection density OD = 0.3 is obtained. Is amplified by the A / D converter 7
Is selected so as to match the minimum input level of. As a result, all the detected EE signals can be taken into the A / D converter 7 in the same manner as described above, and the effects of the accuracy of the sensor 4 and the resistance value errors of the resistors constituting each unit are eliminated. It becomes possible.

In the cut-off circuit 23, only the signal corresponding to the reflection density OD = 0.0-0.3 is extracted from the output signal of the gain selection circuit 5 and supplied to the A / D converter 7. A / D conversion is performed. In this example, the resolution of the A / D converter 7 is set to 64 steps.

The output of the A / D converter 7 is supplied to the CPU 8, and a density histogram is created based on the output. In this density histogram, OD = 0.0 to 0.3 is set as a possible range of the reflection density OD, and this is A / D
The document density (0 to 63) is set by dividing the document into 64 steps which are the same as the resolution of the converter 7. Therefore, the output of the A / D converter 7 and the document density correspond one to one. The lightest density, the darkest density, the average density, and the spread density are calculated from the density histogram, and are compared with the judgment levels J2D to J4 in the same manner as described with reference to FIG. 7 to determine the bias.

Next, the configuration and operation of each part of the automatic image density adjusting device in the copying machine will be described. The resistance values of the resistor and the thermistor used here are the same as the reference numerals.

FIG. 2 shows a detailed configuration of each part of the automatic image density adjusting apparatus according to the present invention. In the figure, light reflected from a document 1 is photoelectrically exchanged by a sensor 4. The current I output therefrom is proportional to the density of the original 1.

The thermistor TH is connected between the output terminal of the sensor 4 and the ground. This thermistor TH is provided for performing temperature correction in the sensor 4. The current I output from the sensor 4 is
The voltage V1 supplied to the amplifier A2 of the I / V conversion circuit 21
Is converted to A resistor R1 is connected between the non-inverting input terminal of the amplifier A2 and the ground.
1 = I × ((R1 × TH) / (R1 + TH))
That is, the voltage V1 is proportional to the current I, that is, the density of the original 1.

This voltage V1 is supplied to the low-pass filter circuit 2
2 is applied to the non-inverting input terminal of the amplifier A3 via the two resistors R2 and R4. A capacitor C1 is connected between the non-inverting input terminal of the amplifier A3 and the ground, and a resistor R2
A capacitor C2 is connected between the connection midpoint of the resistor R4 and the output terminal of the amplifier A3. A resistor R3 is connected between the output terminal of the amplifier A3 and the ground.
R5 is connected, and a connection point between the resistor R3 and the resistor R5 is connected to the inverting input terminal of the amplifier A3.

In the low-pass filter circuit 22, the AC component of the applied voltage V1 is removed. That is, A
When the exposure lamp 2 using the C power source is the light source, the light component emitted from the exposure lamp 2 is superposed on the AC component of the power source, so that the low-pass filter circuit 22 removes the AC component. Now, R2 = R4, C1 =
Assuming that C2, the output voltage V2 of the amplifier A3 is V2 = (1
+ R5 / R3) × V1. This voltage V2 is applied to the non-inverting input terminal of the amplifier A4 of the gain selection circuit 5 via the resistor R6.

In the gain selection circuit 5, the amplifier A4
Analog switch S between the inverting input terminal of
Four types of resistors R20 to R23 are connected in parallel via W1 to SW4. Analog switches SW1 to SW
Reference numeral 4 is turned on / off by an instruction from the CPU 8, and by appropriately switching the analog switches SW1 to SW4, 14 kinds of combined resistors RR can be obtained. Further, a resistor R7 is connected between the output terminal and the inverting input terminal of the amplifier A4.

The gain G in the gain selection circuit 5 is G = (1 + RR / R7). Here, the combined resistance RR
Can be selected as described above, so that the gain G is also 1
For example, it is possible to select a gain in increments of 0.5 from, for example, 1.0 to 8.0. The output voltage V3 of the amplifier A4 is V3 = G × V2 = (1 + RR / R7) × V2
Becomes

The voltage V3 is equal to the value of the resistor R1
2 is applied to the non-inverting input terminal of the amplifier A5.
A resistor R13 is connected between the non-inverting input terminal of the amplifier A5 and the ground, and a resistor R15 is connected between the output terminal of the amplifier A5 and the ground. The power (5 V) divided by the resistors R8 and R9 is input to the inverting input terminal of the amplifier A5 via the resistor R10. Further, a resistor R11 and a resistor R14 are connected between the output terminal and the inverted input terminal of the amplifier A5.

In the cut-off circuit 23, a subtraction circuit is formed using the amplifier A5. Now, R10 = R11
= R12 = R13 = R14, and when the voltage input to the inverting input terminal is the reference voltage VB, the output voltage V4 of the amplifier A5 is V4 = V3-VB. Here, the reference voltage V
B is determined by the voltage division ratio between the resistor R8 and the resistor R10, and is a voltage corresponding to the reflection density OD slightly higher than the density of the document 1 actually detected. In this example, the reflection density OD = 0.
A voltage corresponding to 3 is set.

That is, as shown in FIG. 3, the cut-off circuit 23 changes the output voltage V3 of the gain selection circuit 5 to the reference voltage V3.
By subtracting B, the reflection density OD = 0.0-0.3
, That is, only signals in a range necessary for determining the density of the original 1. Note that the reference voltage VB is appropriately set according to actual use conditions.

In this way, a signal in a relatively narrow range required for density determination is extracted and supplied to the A / D converter 7, where it is A / D converted and then supplied to the CPU 8.
The CPU 8 creates a density histogram as shown in FIG. 4 based on the input data.

In this density histogram, a reflection density OD = 0.0-0.3 is set as a range in which the density can be taken, and the original density is divided into 64 levels.

Based on the density histogram, a bias is determined in the same procedure as described above (FIG. 7), and the CPU 8 issues an instruction to the bias circuit 9 to generate a bias voltage corresponding to the bias. As a result, a predetermined bias voltage is supplied to the developing sleeve 10. By adjusting the bias voltage in this manner, it is possible to clearly copy various images such as a light line drawing, a multi-tone photographic image, and a dark line drawing.

In this automatic image density adjusting device, as described above, a signal in a range necessary for determining the document density, for example, an analog signal corresponding to a range of reflection density OD = 0.0 to 0.3 is converted into an analog signal. The resolution of the D converter 7 is divided into 64 steps in this example. When the same A / D converter 7 as that of the related art is used, the resolution of the device is greatly improved. Become. In the case where the same resolution as the conventional one is sufficient, it is possible to use an A / D converter simpler than the conventional one, thereby making it possible to reduce the cost.

[0052]

As described above, according to the present invention, the original
The electrical signal that depends on the reflected light from the
Gain selection circuit for amplifying the amplified signal
A cut-off circuit for extracting a signal corresponding to a certain concentration range,
A / A that converts the extracted signal into a digital signal
A D conversion circuit and an image based on the output of the A / D conversion circuit.
A control device for adjusting and controlling the image forming density.
The device converts the signal extracted by the cut-off circuit into an A / D conversion signal.
Select a gain that matches the input range of the road
The instruction control of the gain selection circuit is performed.

With this configuration, the reflection density is higher than in the prior art.
Signal in a narrow range of, for example, a reflection density of 0.0 to 0.3
Since it becomes possible to A / D convert a signal corresponding to the range, when an A / D converter having the same resolution as that of the related art is used, the resolution of the automatic image density adjusting device can be improved. Become. Further, if the resolution of the device is the same as that of the conventional device, an A / D converter having a low resolution can be used, so that the cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a copying machine to which an automatic image density adjusting device according to the present invention is applied.

FIG. 2 is a configuration diagram of an automatic image density adjustment device according to the present invention.

FIG. 3 is an explanatory diagram for explaining outputs of a gain selection circuit 5 and a cut-off circuit 23;

FIG. 4 is an explanatory diagram illustrating an example of a density histogram created by the automatic image density adjustment device according to the embodiment.

FIG. 5 is a configuration diagram of a copying machine to which an automatic image density adjusting device according to a conventional example is applied.

FIG. 6 is an explanatory diagram illustrating an example of a density histogram created by a conventional automatic image density adjusting device.

FIG. 7 is an explanatory diagram illustrating a procedure of a bias determination process.

FIG. 8 is an explanatory diagram for explaining a density histogram when the conventional bias is 6.

FIG. 9 is an explanatory diagram for explaining a density histogram in a case where a conventional bias is 7.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Original 2 Exposure lamp 3 Lens 4 Sensor 5 Gain selection circuit 6 Offset adjustment circuit 7 A / D converter 8 CPU 9 Bias circuit 10 Developing sleeve 11 Drum 12 Toner 21 I / V conversion circuit 22 Low-pass filter circuit 23 Cut-off circuit TH Thermistor

Continuation of front page (72) Inventor Seicho Nakagama 2970 Ishikawacho, Hachioji-shi, Tokyo Konica Corporation (56) References JP-A-63-60461 (JP, A) JP-A-3-41484 (JP, A) JP-A-59-67527 (JP, A) JP-A-63-123061 (JP, A) JP-A-60-218639 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 15/00 303 G03B 27/72 G03G 15/04

Claims (1)

(57) [Claims] An original is irradiated with light and the reflected light is read.
When forming an image with
Automatic image density adjustment device that can automatically adjust the density
There are, converting this by receiving reflected light from the document into an electric signal
And an output signal from the sensor means based on a predetermined gain.
A gain selection circuit for amplifying the signal, and a predetermined density range from the signal amplified by the gain selection circuit.
Digital signal and cutback circuit for extracting a signal corresponding, the signal extracted by the cutback circuit
An A / D conversion circuit for converting the image forming density, and adjusting the image forming density based on the output of the A / D conversion circuit.
And a control device for controlling an integer, the control device, the signals extracted by the cutback circuit the A / D converter
Choose a gain that matches the input range of the circuit
Automatically controlling the gain selection circuit .