JPH04149573A - Image forming device - Google Patents

Abstract

PURPOSE:To accurately detect an adhering toner quantity by calculating an adhering half-tone testing toner quantity based on the measured value of the quantity of light reflected on the basic surface of an electrostatic latent image carrier, a measured value of the quantity of light reflected on a saturation level testing toner image and the measured value of the quantity of light reflected on a half-tone testing toner image, and also controlling an image forming condition based on the calculation value. CONSTITUTION:A sensor output voltage Vs0 at the basic surface level of a photosensi tive body is measured. The saturation level testing toner image is formed, and then, the quantity of the light reflected on the saturation level testing toner image is mea sured by the sensor 15 so as to obtain the output voltage Vs2. When a basic surface level measuring point on the photosensitive drum 1 reaches a toner image forming position C1 again, the half-tone testing toner image is formed while impressing a developing bias voltage Vb1. The quantity of the light reflected on the half-tone testing toner image is measured by the sensor 15, and then, the output voltage Vs1 is obtained. Vs1 - Vs0/Vs2 - Vs0 is calculated every color toner, and the adhering toner quantity which is obtained when the developing bias voltage Vb1 is impressed is obtained. Then, the developing bias voltage Vb of every color toner is calculated.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an electrophotographic toner image transfer type image forming apparatus, and more particularly to a control mechanism for measuring the amount of toner adhering to an electrostatic latent image carrier.

In general, in image forming apparatuses such as toner image transfer type electrophotographic copying machines and laser printers, stabilization control of transferred images (toner concentration in developer, development bias voltage, application to charger) As a premise for controlling the voltage and exposure light amount, the amount of test toner deposited on the surface of the photoreceptor is measured using a reflective photosensor. Conventionally, various methods have been provided for such image stabilization control. For example, in Japanese Patent Application Laid-open No. 143144/1984, the density of the background on the surface of the photoreceptor drum is measured as well as the amount of toner adhesion, and the toner adhesion is determined by It is described that the quantity measurement value is corrected by the skin density measurement value.

However, the amount of toner adhering to the photoreceptor changes over time based mainly on changes in the charging characteristics of the toner caused by environmental conditions such as humidity. Further, the surface of the photoreceptor may also be stained or scratched with toner, which tends to cause errors in the measured value of the amount of reflected light. Of course, the output voltage of the photosensor also fluctuates due to variations in its own sensitivity and toner contamination.6 Therefore,
Conventionally, it has been difficult to accurately detect the toner adhesion amount by dealing with these various fluctuation factors, and furthermore, it has been difficult to perform good image stabilization control.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an image forming apparatus that can accurately detect the amount of attached test toner despite the presence of various fluctuation factors in the detection of the amount of attached toner. It is about providing.

In order to achieve the above object, an image forming apparatus according to the present invention includes means for forming a test toner image on the surface of an electrostatic latent image carrier in which the amount of reflected light reaches a saturation level, and a means for forming a test toner image on the surface of an electrostatic latent image carrier, means for forming a halftone test toner image under image forming conditions; means for measuring the amount of light reflected from the background of the surface of the electrostatic latent image carrier and the amount of light reflected from the test toner image;
The halftone test toner adhesion amount is calculated based on the measured value of the reflected light amount on the background, the measured value of the reflected light amount of the saturation level test toner image, and the measured value of the reflected light amount of the halftone test toner image, and the image forming conditions are determined based on this calculated value. The invention is characterized by comprising means for controlling.

In image stabilization control, what needs to be accurately detected is the amount of halftone test toner that has been formed under certain image forming conditions. In the present invention, the output characteristics of the measuring means itself are corrected by forming a saturation level test toner image and measuring the amount of reflected light, and the amount of light reflected from the background on the surface of the electrostatic latent image carrier is measured. Corrects for changes in conditions and achieves accurate toner adhesion amount detection.

Embodiment Hereinafter, an embodiment of an image forming apparatus according to the present invention will be described with reference to the accompanying drawings. This embodiment is a copying machine that outputs a document image read by an image reader using a laser beam scanning optical system to form a full-color image.

In FIG. 1, a photoreceptor drum (1) is installed so as to be rotatable in the direction of arrow (a), and around it is a charger (2) and magnetic brush developing devices arranged in four vertical stages. (3), (4), (5), (6),
Transfer drum (10), residual toner cleaning device (
7) A residual charge eraser lamp (8) is arranged.

The image league unit (20) includes an exposure lamp (21
), lens array (22), CCD line sensor (23)
), etc., and the original placed on the 0M platen glass (25), which is equipped with an image processing circuit (24), is placed on the 0M platen glass (25).
20) moves to the left in FIG. 1, the line sensor (23) sequentially displays R (red), G (green),
It is read as a 3i color signal of B (blue). The R, G, and B color signals are converted by an image processing circuit (24) into signals corresponding to four colors: Y (yellow), M (magenta), C (cyan), and Bk (black).

The laser optical system (30) includes a laser beam generating section (31)
, scanning polygon mirror (32), fθ lens (3
3), a reflecting mirror (34), etc. The laser beam generator (31) is connected to the image processing circuit (24).
A laser beam for each color is generated based on the Y, M, C, and Bk signals output from the photoreceptor drum 1).
An electrostatic latent image of each color is formed on the surface of the

Each developer (3), (4), (5), and (6) contains developer containing yellow, magenta, cyan, and black color toners in order from the top, and can be moved vertically as a unit. Each time an electrostatic latent image of each color is formed, the corresponding developing device (3), (4>, (5), (6)
One of them is set at the development position (C1) to perform development.

On the other hand, for copy paper, use the automatic paper feed cassette (40) or (41)
One sheet at a time is fed from either one of the transfer drums (10
), and is wound around the surface of the transfer drum (10) with its tip chucked by the claw (11).

Then, the transfer drum (10) rotates in the direction of arrow (b) in synchronization with the photosensitive drum (1), and the toner image is transferred onto the copy paper for each color.

That is, the process of charging, exposing, developing, and transferring is performed four times for each color, and when all the toner images have been transferred, the copy paper is peeled off from the transfer drum (10) and transferred to the conveyor belt (45). The toner is sent to the fixing device (46) through the toner, and after being fixed there, the toner is sent to the ejection roller pair (47).
from there onto the tray (48).

By the way, in this embodiment, in order to keep the image density and chromaticity constant at all times, each developing device (3), (4), (5), (
6) Developing sleeves (3a), (4a), (5a)
, (6a) The power supply unit for the developing bias applied to (6a)
The output (voltage value) of 55) is controlled, and the premise is that the density of the surface (background) of the photoreceptor drum (1) and the toner adhesion amount of the test toner image formed on the surface are determined by L as shown in Fig. 2.
Optical measurement is performed using a reflective photosensor (15) consisting of an ED (16) and a photodiode (17).

The measurement in this embodiment employs a method in which a photodiode (17) receives diffused (dispersion) reflected light from the LED (16) on the surface of the photoreceptor drum (1). Reflected light has a regular reflection component and a diffuse reflection component, but with color toner, even if the amount of adhered toner increases, the regular reflection component does not decrease that much, but rather the amount of increase in the diffuse reflection component is large, so the diffuse reflection It uses a light reception method.

Figure 3 shows the relationship between the amount of toner adhering to the photoreceptor drum (1) after development (<M) per unit area and the output voltage (Vs) of the photosensor (15). )
The surface of the LED (16) is not completely mirror-finished, and even if the amount of toner adhered is zero, all the light from the LED (16) is not specularly reflected, but is reflected somewhat diffusely and is reflected off the photodiode (17).
) output voltage (vS) becomes (VsO).

As shown in FIGS. 4a and 4b, as the amount of toner adhesion increases, the amount of diffusely reflected light increases, and the sensor output voltage (Vs) also increases accordingly. When the adhesion amount (M> exceeds a certain amount), the amount of diffusely reflected light from the toner particles (T) stacked on the photoreceptor drum (1) does not increase and remains almost constant, and the sensor output voltage ( Vs) is the saturation level (Vs2).In full-color copying machines, slight fluctuations in the adhesion amount (M>) due to environmental conditions such as humidity or deterioration of toner and carrier cause changes in image density and chromaticity after transfer. appears.

By the way, in this example, the 55th! As shown in J, a uniform positive charge of potential (VO) is applied to the photosensitive drum (1), and a laser beam is irradiated to the image area to increase the potential (Vi).
to form an electrostatic latent image. This electrostatic latent image is reversely developed in each of the developing devices (3), (4), (5), and (6) while applying a developing bias of voltage value (vb). That is, the positively charged toner adheres to the image area at the potential (Vi), forming a toner image.

Figure 6 shows the development bias voltage (
The relationship between Vb) and toner adhesion amount (M) is shown.

The voltage (Vi) corresponds to the potential of the image area (the surface potential of the photoreceptor attenuated by the laser beam). The solid line (A) in the figure shows the change in the adhesion amount (M>) when the toner charge amount (Qf) maintains the reference value. In this example, the toner concentration in the developer was measured using a magnetic measuring element etc. Toner replenishment is controlled to maintain a constant toner density at all times.

Therefore, it is not necessary to consider changes in the toner charge amount (Qf'') due to fluctuations in the toner concentration in the developer. However, the toner charge amount (Qf) changes due to changes in humidity and deterioration of the printing durability of the developer. In the figure, the dashed line (B) shows the change in the adhesion amount (M) when the toner charge amount (Qf> decreases (at high humidity or deterioration of printing durability), and the broken line (C) shows the change in the toner charge amount (Qf). The amount of adhesion (M
), and when the developing bias voltage (vb) is constant, as the toner charge amount (Qf) decreases, the adhesion amount (M
) increases, and as it increases, it decreases. Therefore, even if the toner adhesion characteristics change, by controlling the voltage value (vb) of the developing bias, it is possible to maintain the toner adhesion amount (M) constant and stabilize the image density and chromaticity. Become. for example,
When the toner adhesion amount when applying a predetermined developing bias voltage (Vbl') is (Ml), in order to obtain the target toner adhesion amount (Mp), the developing bias voltage (Vb
) is because .

It should be controlled so that.

Since (Mp), (Vbl), and (Vi) are values that can be determined in advance, if the toner adhesion amount (Ml) is measured from the output of the photo sensor (15), the toner adhesion amount measurement value (Ml) can be obtained. Development bias voltage (vb) to be controlled
) is automatically determined. By inputting this relationship as a table into the ROM of the microcomputer (50), the developing bias voltage can be automatically controlled based on the measurement of the toner adhesion amount (Ml).

However, the actual measured output voltage value of the photosensor (15) is LE
It fluctuates mainly due to contamination of D (16) and photodiode (17) due to toner powder smoke, etc. Figure 7 shows the toner adhesion amount (M) and the measured output voltage of the photosensor (15) (
Vs). - The dotted chain line (D) shows the case when there is no dirt and the sensor output is 100%, the solid line (E) shows the case when there is little dirt and the sensor output is 80%, and the dashed line (F) shows the case when there is a lot of dirt and the sensor output is 60%. As shown in each figure, when the copying machine is in actual operation, there is some dirt on the photo sensor (15).
As mentioned above, due to fluctuations in toner charge amount (Qf) due to environmental conditions such as humidity and deterioration of developer printing durability, toner adhesion amount (M) when applying a developing bias of a predetermined voltage (Vbl) becomes target adhesion amount < Mp” ) will be a different value.If the sensor output is 8
When a developing bias of 0% and a predetermined voltage is applied, if the amount of toner deposited is (Ml), the actual measured value of the sensor output voltage is (Vsl).

If the sensor is dirty, for example, the solid line (
In state E), the sensor output voltage at which the amount of diffusely reflected light reaches the saturation level is (Vs2), and the sensor output voltage when the amount of toner adhesion is zero (diffusely reflected light from the surface of the photoconductor) is (Vs2).
sO), and the sensor output voltage of diffusely reflected light from toner having a certain adhesion amount value 1) is (Vsl). In addition, when there is no sensor dirt, that is, in the state shown by the solid line (D), the sensor output voltage at which the amount of diffusely reflected light reaches the saturation level is (Vs
2'), the sensor output voltage when the toner adhesion amount is zero (photoreceptor background diffuse reflection light) is (VsO'), and the sensor output voltage of the diffuse reflection light from the toner with the above adhesion amount (Ml) is ( Vsl″).

In the above cases, The relationship holds true.

In other words, the value obtained by subtracting the sensor output voltage of the diffusely reflected light from the surface of the photoconductor from the sensor output voltage of the diffusely reflected light from the toner with a certain adhesion amount (Ml), and the sensor output voltage at which the amount of diffusely reflected light reaches the saturation level. The ratio of the diffusely reflected light from the surface of the photoreceptor to the value obtained by subtracting the sensor output voltage can be determined by the amount of toner deposited (Ml), regardless of the state of sensor dirt or the state of the surface of the photoreceptor.

Therefore, the toner adhesion amount (Ml) can be determined based on the following equation. The relationship between (α) and (Ml) can be determined in advance depending on the copying machine, and if this relationship is input into the ROM of the microcomputer (50) as a table, the sensor output voltage (VsO), (Vsl), (Vs
From 2), the toner adhesion amount (Ml) can be automatically calculated.

Then, the toner adhesion amount (Hl) with a predetermined developing bias voltage (Vbl) applied is determined as described above, and the developing bias voltage (Vb) for obtaining the target adhesion amount (Mp) is based on the above formula 0. is required.

Table 1 below shows ('v'sl -VsO)/(Vs
2-VsO), toner adhesion amount (Ml), and development bias voltage (vb).
) of the microcomputer (50) to calculate
This is a specific example of a table input to OM.

That is, in this embodiment, the sensor output 1 (ff
l (VsO), the sensor output voltage of the saturation level test toner image (Vs2) and the predetermined bias voltage (vbl)
Halftone test toner image at the time of application (test toner image with lower image density than saturation level test toner image)
The sensor output voltage (Vsl) is measured, and the developing bias voltage (Vb) is calculated from these measured values based on Table 1 above
Calculate. The calculated bias voltage (Vb) is fed back to the developing bias power supply unit (55) and is used for control during actual copying operation. As a result, the toner charge amount (Q
It is possible to calculate the voltage value of the developing bias that accurately corresponds to the variation in f), and to maintain the amount of toner adhesion constant.

Incidentally, the photosensitive drum (1) is not necessarily manufactured in a perfect circle, and may be installed in a copying machine with a slight eccentricity. Alternatively, scratches or dirt may adhere to the surface of the photoreceptor drum (1), and the condition of the background may change periodically in the circumferential direction. In such a case, the output of the sensor (15) fluctuates periodically as the photoreceptor drum (1) rotates as shown in FIG. When the amount of light reflected from a halftone test toner image is measured and the developing bias voltage (Vb) is calculated, an error occurs.

Therefore, in this embodiment, as shown in FIG.
15), the measurement timing (tl) of the amount of reflected light from the background and the timing (tl) of measuring the amount of reflected light from the saturation level test toner image.
) and the halftone test toner image reflected light amount measurement timing (t3).
It was possible to match the rotation period (TO) of 1).

As a result, the amount of light reflected from the test toner image is measured at the same position as the measurement position of the amount of background reflected light, and the calculation error of the developing bias voltage (vb) is eliminated.

Note that the photosensitive drum (1) is formed to have an elliptical cross section, and when the output of the sensor (15) fluctuates due to this, the period of the fluctuation is equal to the drum rotation period (step 0). In this case, each measurement timing interval (TI), (T
2) may be set to (τ0/2).

FIG. 10 shows the control circuit of this copying machine.

The microcomputer (50) has a built-in A/D converter, and when the Hunsen (Sl) is connected to the AClooV power supply, the power switch (62) is turned on and off by the DC5Q: source of the power supply circuit (61). Start regardless. 'When the source switch (62) is turned on, the
(63) turns on the main switch (70) of the switch matrix (64). Matrix (64)
is equipped with numerous input means such as a copy switch (71) and various display sections (65). Input signals from various switches of the MADROX (64) are input to the microcomputer (50) in a time-sharing manner via a dehooder (66).

The analog boat of Microfunpyuta (50) has
Signals from the photosensor (15), thermistor of the fixing device (46), etc. can be input. Each output boat can output drive signals to the main motor, various clutches, etc. inside the copying machine body.

Next, only the portions related to the present invention regarding the control procedure by the microcomputer (50) will be described.

Figure 11 shows the main routine. When the microcomputer (50) is reset and the program starts, step (Sl) clears the RAM, sets various registers, and initializes various devices to initial modes. be done.

Next, in step (S2) start the internal timer (
The timer value can be set in step (Sl)), it is determined that the main switch (62) is turned on in step (S3), and the copy switch (71) is turned on in step (S4).
) is turned on, a subroutine for calculating the developing bias voltage (vb) is called in step (S5). The vb calculation subroutine here will be described in detail below. Subsequently, in step (S6), a copy operation subroutine is called. The copy operation here is performed by setting the developing bias voltage (vb) to the value calculated in step (S5). Finally, in step (57), the process waits for the internal timer to end and returns to step (S2).

FIG. 12 shows a subroutine for calculating vb executed in step (S5).
At step 20), the main motor is turned on to rotate the photosensitive drum (1) and to start each element necessary for image formation. Subsequently, step (521) measures the sensor output voltage (VsO) at the skin level of the photoreceptor, and step (521)
22) starts the timer (T).

Next, in step (523), it is determined whether the count value of the timer (T) has become equal to (T6-6).

Here, (T, ) is the time required for one rotation of the photoreceptor drum (1), and (ΔT) is the exposure time from the toner image forming position (C1) to the position (C2) where the amount of reflected light of the toner image is measured by the sensor (15). This is the time during which the body drum (1) rotates. Therefore,
In step (523), the count value of the timer (T) is changed to (r
e-6 guns), step (5
Step 24) forms a saturation level test toner image.

Next, when it is confirmed in step (525) that the count value of the timer (T) is equal to (T, ), that is,
The photoreceptor drum (1) is 1 from the time of step (521).
When it rotates, the amount of light reflected from the saturation level test toner image is measured by the sensor (15) in step (526), and its output voltage (Vs2) is obtained. Next, step (527
), the timer (T) is reset to "0", and at the same time, the timer (T) is started at step (528), and at step (529), the count value of the timer (T) becomes equal to (L - 6th). Determine whether or not. Step (529
), that is, if the background level measurement point on the photosensitive drum (1) reaches the toner image forming position (C1) again, the developing bias voltage (Vb
A halftone test toner image is formed while applying l'). Next, in step (531), when it is confirmed that the count value of the timer (T) has become equal to (r-),
In step (532), the amount of reflected light from the halftone test toner image is measured by the sensor (15), and its output voltage (
Vsl).

The above control is performed on the developing device (3) containing yellow toner, and in step (533'), the above-mentioned step (
527) to (532) are performed on each developing device (4>, (5) containing magenta toner, cyan toner, and black toner.
).

(6) is executed. Note that this processing order is arbitrary.

Next, in step (534), for each color toner (V
Calculate sl - VsO)/(Vs2 - VsO),
The toner adhesion amount (Ml) when the developing bias voltage (Vbl) is applied is determined. And step (535)
Then, the developing bias voltage (vb) is calculated for each color toner based on the above equation 0.

With the above control, halftone test toner can be accurately measured without being affected by variations or fluctuations in the output voltage of the photosensor (15) or the condition of the surface of the photoreceptor, and in spite of changes in environmental conditions such as humidity. The amount of adhesion can be detected, and the developing bias voltage (Vb) can be calculated accurately. In addition, the background measurement timing, the saturation level test toner image measurement timing, and the halftone test toner image measurement timing are synchronized with the rotation of the photosensitive drum (1), making the calculation of the developing bias voltage (Wb) more accurate.

Note that the image forming apparatus according to the present invention is not limited to the above-mentioned embodiments, and can be variously modified within the scope of the gist thereof.

For example, the configuration of the copying machine itself may be arbitrary, and in particular, it may be a monochrome copying machine instead of a full color copying machine, or one that uses a normal visible light optical system instead of a laser beam scanning optical system. Alternatively, as image stabilization control, there is not only a method of controlling the developing bias voltage value based on the detection of the amount of toner adhesion, but also a method of controlling the initial surface potential of the photoconductor (■, ) based on the output of the band macharger (2), The image portion potential (Vi) based on the emission intensity of the beam and furthermore, the amount of toner replenishment may be controlled. Furthermore, the detection of the amount of toner adhesion by the photosensor may be performed not by the diffuse reflection light reception method but by the specular reflection light reception method.

As is clear from the above description, according to the invention, the measured value of the amount of reflected light from the background of the electrostatic latent image carrier, the measured value of the amount of reflected light from the saturation level test toner image, and the halftone test toner image. Since the amount of halftone test toner deposited is calculated based on the measured value of the amount of reflected light from the surface, and the image forming conditions are controlled based on this calculated value, changes in the surface of the electrostatic latent image carrier and dirt on the measuring means can be avoided. In spite of variations in characteristics and characteristics, it is possible to accurately detect the amount of toner adhering to the surface of the electrostatic latent image carrier, and as a result, it is possible to perform good image stabilization control.

[Brief explanation of the drawing]

The drawings show an embodiment of an image forming apparatus according to the present invention, in which Fig. 1 is a schematic diagram of the configuration of a copying machine, Fig. 2 is an explanatory diagram of the arrangement of a photosensor, and Fig. 3 shows sensor output voltage with respect to toner adhesion amount. Figures 4a and 4b are illustrations of diffusely reflected light by toner particles, Figure 5 is an illustration of the reversal phenomenon, and Figure 6 is the amount of toner adhesion versus developing bias voltage when the amount of toner charge varies. FIG. 7 is a graph showing the sensor output voltage versus toner adhesion amount when the sensor is dirty, FIGS. 8 and 9 are graphs showing the sensor output when the photosensitive drum is rotating, and FIG. The control circuit diagram of the micro combi coater, FIG. 11, and FIG. 12 are flowcharts showing the control procedure, respectively. <1)... Photosensitive drum, (2)... Charger, (3), (4), (5), (6)... Developing device, (10)... Transfer drum, ( 15)... Photo sensor, (30)... Laser beam scanning optical system, (5
0>...Microcomputer, (55)...Development bias power supply unit.

Claims (1)

[Claims] 1. In an image forming apparatus that forms a toner image on the surface of an electrostatic latent image carrier and transfers this toner image onto a sheet, a test in which the amount of light reflected on the surface of the electrostatic latent image carrier reaches a saturation level. means for forming a toner image; means for forming a halftone test toner image on the surface of an electrostatic latent image carrier under certain image forming conditions; a means for measuring the amount of light reflected from the surface; and a means for calculating the amount of attached halftone test toner based on the measured value of the amount of reflected light from the background, the measured value of the amount of reflected light of the saturation level test toner image, and the measured value of the amount of reflected light of the halftone test toner image. , and means for controlling image forming conditions based on the calculated value.