JPH04146459A - Image forming device - Google Patents

Abstract

PURPOSE:To measure a base reflecting light quantity and a test toner image reflecting light quantity at a place where the surface of an electrostatic latent image carrier is in an almost constant state and to eliminate the variance of a measured value by synchronizing base reflecting light quantity measuring timing and test toner image reflecting light quantity measuring timing with the rotational period of the electrostatic latent image carrier. CONSTITUTION:The density of the surface of a photosensitive body 1, and the toner sticking quantity of a test toner image formed on the surface are optically measured by a reflection type photosensor 15 composed of an LED 16 and a photodiode 17. Respective intervals T1 and T2 of the base reflecting light quantity measuring timing (t1), saturation level test toner image reflecting light quantity measuring timing (t2), and half-tone test toner image reflecting light quantity measuring timing (t3), and the rotational period of the photosensitive drum 1, are synchronized. Thus, a reflecting light quantity from the test toner image is measured at the same position as a base reflecting light quantity measuring position, and the error in the operation of a developing bias voltage is cancelled.

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.

2. Description of the Related Art In general, in image forming apparatuses such as toner image transfer type electrophotographic copying machines and laser blinkers, stabilization control of transferred images (toner concentration in developer, developing bias voltage, voltage applied to the charger) is performed. , exposure light amount control), the amount of test toner adhesion formed 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. 143144/1989, the density of the background of the photoreceptor drum surface is measured as well as the amount of toner adhesion, and the toner adhesion is measured. It has been described that the amount measurement value is corrected by the skin density measurement value.

However, the photoreceptor drum is not necessarily manufactured in a perfect circle, and may be slightly eccentric due to assembly errors. In such a case, the distance between the surface of the photoreceptor drum and the photosensor changes periodically, and the sensor output changes periodically. Alternatively, scratches or dirt may adhere to the surface of the photoreceptor drum, and the condition of the background may change periodically as the photoreceptor drum rotates. In such a state, the measured value of the background density of the photoconductor drum and the measured value of the test toner adhesion amount will vary depending on the timing of each reflected light amount measurement, making it difficult to accurately detect the toner adhesion amount.
As a result, good image stabilization control has been difficult.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus that can accurately detect the amount of attached test toner despite fluctuations in the amount of light reflected from the background of an electrostatic latent image carrier. It's about doing.

In order to achieve the above object, an image forming apparatus according to the present invention includes an electrostatic latent image carrier that is rotationally driven in one direction at a constant speed, and an amount of light reflected from the background of the surface of the electrostatic latent image carrier and this static image carrier. A means for measuring the amount of light reflected from the test toner image formed on the surface of the electrostatic latent image carrier, and a timing for measuring the amount of light reflected from the background by the measuring means and a timing for measuring the amount of light reflected from the test toner image by rotating the electrostatic latent image carrier. It is characterized by comprising a control means for synchronizing with the cycle.

By synchronizing the measurement timing of the background reflected light amount and the measurement timing of the test toner image reflected light amount with the rotation period of the electrostatic latent image carrier, both measurements are performed at a location where the surface of the electrostatic latent image carrier is in a substantially constant state. This eliminates variations in measured values.

Each measurement timing is preferably approximately n times the rotation period of the electrostatic latent image carrier (n is an integer of 1 or more). As a result, both the amount of light reflected from the background and the amount of light reflected from the test toner image are measured at the same location on the surface of the electrostatic latent image carrier.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an image forming apparatus according to the present invention will be described below 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 photosensitive drum (1) is installed so as to be rotatable in the direction of the arrow (a), and around it are a charger (2>) and a developing device using a magnetic brush system installed in four stages in the vertical direction. <3), (4), (5), (6),
Transfer drum (10), residual toner cleaning device (
7) The residual charge eraser lamp (8) is fully placed.

The image league unit (20) includes an exposure lamp (21
), lens array (22), COD line sensor (23)
), etc., and includes an image processing circuit (24). The document placed on the document table glass (25) is placed on the document table 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 color signal of the three primary colors 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), f'θ lens (33)
), a reflecting mirror (34), etc. A laser beam generator (31) generates laser beams for each color based on the Y, M, C, and Bk signals output from the image processing circuit (24), and generates a laser beam for each color on the surface of the photoreceptor drum (1). form an electrostatic latent image.

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 (CI) 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 a fixing device (46) through the toner, where it is fixed, and then transferred to a pair of discharge rollers (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) composed 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 attached color increases, the regular reflection component does not decrease in diameter, but rather the diffuse reflection component increases by a large amount. It uses a reflected light reception method.

FIG. 3 shows the relationship between the toner adhesion amount (M) per unit area on the photosensitive drum (1) after development and the output voltage (Vs) of the photosensor (15). Usually, photoreceptor drum (1)
The surface of the LED (16) is not completely mirror-finished, and even if the amount of toner attached is zero, all of the light from the LED (16) is not reflected specularly, but is reflected somewhat diffusely, causing the 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) becomes the saturation level (Vs2). In a full-color copying machine, slight variations in adhesion 1 (M) due to environmental conditions such as humidity or deterioration of toner or carrier appear as changes in image density and chromaticity after transfer.

Incidentally, in this embodiment, as shown in FIG. 5, a uniform positive charge of potential (Vo) is applied to the photoreceptor drum (1), and the image area is irradiated with a laser beam to reduce the potential to ff1). 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). Solid line (A) in the diagram
indicates the change in the adhesion amount (M) when the toner charge amount (Qf) maintains the reference value. In this embodiment, the toner concentration in the developer is measured using a magnetic measuring element or the like, and toner replenishment is controlled so as to maintain a constant toner concentration at all times. Therefore, it is not necessary to consider changes in the toner charge amount (Qf') due to changes 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 dotted line (B) shows the change in adhesion amount (M) when the toner charge amount (Qf) decreases (at high humidity or printing durability deteriorates), and the broken line (C) shows the toner charge amount (Qf). The amount of adhesion increases (at low humidity, etc.)
When the developing bias voltage (vb), which indicates the change in M), is constant, when the toner charge amount (Qf) decreases, the adhesion amount (
M) increases and decreases as it increases. Therefore, even if the toner adhesion characteristics change, the voltage value (Wb) of the developing bias
The toner adhesion amount (M) is kept constant by controlling
It becomes possible to stabilize image density and chromaticity. 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 (Vbl) is
b) is because .

Mp Wb −−(Vbl −Vi ) + Vi
It is only necessary to control it 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) and the developing bias voltage (vb
) 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 L
It fluctuates mainly due to contamination of the E D (16) and photodiode (17) due to toner powder smoke, etc. Figure 7 shows the toner adhesion amount (M) and the measured output voltage (Vs) of the photo sensor (15). - The dashed line (D) shows the sensor output when there is no dirt and the sensor output is 100%, the solid line (E) shows the sensor output when there is little dirt and the sensor output is 80%, and the broken line (F) shows the sensor output when there is a lot of dirt. is 60%. When the copying machine is in actual operation, there is some dirt on the photosensor (15), and as mentioned above, the toner charge amount (Qf ), the predetermined voltage (V
Toner adhesion amount (M
) has a value different from the target adhesion amount (Mp). When the sensor output is 80% and a developing bias of a predetermined voltage is applied,
If the toner adhesion amount is (Ml), the actual measured value of the sensor output voltage is (Vsl).

If the sensor is dirty, for example, the solid line (
In the state of 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 (
VsO), and the sensor output voltage of diffusely reflected light from toner with a certain adhesion amount (Ml) 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 (
Vs2'), the sensor output voltage when the toner adhesion amount is zero (photoreceptor surface 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 (VsO'). 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 is determined by the amount of toner adhesion (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 as a table into the ROM of the microcomputer (50),
Sensor output voltage (VsO), (Vsl), (Vs2
), it is possible to automatically calculate the amount of toner adhesion (Ml).

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

Table 1 below shows (Vsl-VSO)/(Vs2-V
sO), toner adhesion amount (Ml), and developing bias voltage (V
This is a specific example of a table that can be input into the ROM of the microcomputer (50) to calculate the developing bias voltage (Vb).

In Table 1, that is, in this example, the sensor output voltage (V
sO), the sensor output voltage (VS2) of the saturation level test toner image and the sensor output voltage (Vsl) of the halftone test toner image when a predetermined bias voltage (Vbl) is applied are measured, and from these measured values, the first Calculate the developing bias voltage (Vb) based on the table. 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. This makes it possible to calculate the voltage value of the developing bias that accurately corresponds to fluctuations in the toner charge amount (Qf) and maintain the toner adhesion amount constant, regardless of the presence or degree of sensor contamination.

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 photoconductor drum (1) rotates as shown in FIG. Image and Halftone Test Measure the amount of light reflected from the toner/image and set the developing bias voltage (V
If the calculation in b) is performed, an error will occur.

Therefore, in this embodiment, as shown in FIG.
15), the measurement timing (tl) of the amount of reflected light on the background, and the timing (t2) of measuring the amount of reflected light on the saturation level test toner image.
) and halftone test toner image reflected light amount measurement timing (t3), each interval (TI), ('12) was made to coincide with the rotation period (TO) of the photoreceptor drum (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 if the photosensitive drum (1) is formed to have an elliptical cross section and the output of the sensor (15) fluctuates due to this, the period of fluctuation is equal to the drum rotation period (10).In this case, are each measurement timing interval (Step 1), (Step 2)
may be set to (work 0/2).

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

The microcomputer (50) has a built-in A/D converter, and when the outlet (51) is connected to the AClooV power supply, the DC5V power supply of the power supply circuit (61)
It starts regardless of whether the power switch (62) is on or off. When the power switch (62) is turned on, the relay (
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 in the matrix (64) are input to the microcomputer (50) in a time-division manner via a decoder (66).

The analog boat of the microcomputer (50) has
Signals from the photosensor (15), thermistor of the fixing device (46), etc. are input. Each output port outputs drive signals to the main motor, various clutches, etc. within the copying machine main 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. Ru.

Next, in step (S2) an internal timer is started (
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).
If it is determined that χ is turned on, a subroutine for calculating the developing bias voltage (Vb) is executed in step (S5). The 5vb 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 (S7), the process waits for the internal timer to end and returns to step (S2).

FIG. 12 shows a subroutine for calculating vb that can be executed in step (S5). Here, first, step (5)
At step 20), the main motor is turned on to rotate the photosensitive drum (1) and to start each element necessary for image formation. Next, in step (521), the sensor output voltage (VsO) at the surface level of the photoconductor is measured, and in step (52)
2) Start the timer (T).

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

Here, (EVA is the time for the photoconductor drum (1) to rotate once, and (Δt) is the time from the toner image forming position (C1) to the position (C2) where the amount of light reflected from the toner image is measured by the sensor (15). This is the time during which the drum (1) rotates. Therefore, in step (523), the count value of the timer (T) is changed to (to
-ΔT), 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, in step (526) the amount of reflected light from the saturation level test toner image is measured by the sensor (15) and its output voltage (Va2) is obtained. Next, step (527
), the timer (T) is reset to "0", and at the same time, the timer (T) is started at step (52B), and at step (529), the count value of the timer (T) becomes (T, -Δ
T). Step (52
If YES in step 9), 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 (V
Next, in step (531), when it is confirmed that the count value of the timer (T) has become equal to (T, ), step (532 ), the amount of reflected light from the halftone test toner image is measured by the sensor (15), and its output voltage (Vsl) is obtained.

The above control is performed on the developing device (3) containing yellow toner, and in step (533), the
27) to (532) are carried out by each developer (4) and (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
sl-VsO)/(Va2-VsO) to determine the toner adhesion amount (Ml) when the developing bias voltage (Vbl) is applied. Then, in step (535), the developing bias voltage (vb) is calculated for each color toner based on the above formula 0.

Through the above control, 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), and the developing bias voltage (Vb) is accurately calculated.

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, not only the method of controlling the developing bias voltage value based on the detection of the toner adhesion amount, but also the initial surface potential (Va) of the photoreceptor based on the output of the charger (2), and the method of controlling the laser beam The image portion potential (Vi) based on the light emission intensity and furthermore, the toner replenishment amount may be controlled. In addition, in such control, it is not necessarily necessary to form a saturation level test toner image and a halftone test toner image and compare the amount of reflected light from each, but to stabilize the image by measuring the amount of reflected light from only one of them. Control may also be performed. Furthermore, the detection of the toner adhesion amount 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 explanation, according to the present invention, the timing of measuring the amount of light reflected from the background of the electrostatic latent image carrier and the timing of measuring the amount of reflected light of the test toner image are set to the rotation period of the electrostatic latent image carrier. Because of the synchronization, even if the output of the measuring means fluctuates periodically due to changes in the distance between the electrostatic latent image carrier surface and the reflected light amount measuring means, or due to dirt or scratches on the electrostatic latent image carrier surface, , 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 diagrams of the microcomputer, FIG. 11, and FIG. 12 are flowcharts showing control procedures, respectively. (1)...Photosensitive drum, (2)...Charger, (3), (4), (5), (6)...Developer, (10)...Transfer drum, ( 15)...Photo sensor, (30)...Laser beam scanning optical system, (
50)...Microcomputer, (55)...
Development bias power supply unit. 11i6 Figure 11 bias voltage, Vb (V) Figure 8 Figure 91Z Figure 11

Claims (1)

[Scope of Claims] 1. An image forming apparatus that forms an image on a sheet by an electrophotographic method, comprising: an electrostatic latent image carrier that is rotationally driven in one direction at a constant speed; and a background surface of the electrostatic latent image carrier. means for measuring the amount of light reflected from the electrostatic latent image carrier and the amount of light reflected from the test toner image formed on the surface of the electrostatic latent image carrier; and the timing of measuring the amount of light reflected from the background by the measuring means and the timing of measuring the amount of light reflected from the test toner image by the measuring means. An image forming apparatus comprising: a control means for synchronizing the rotation period of an electrostatic latent image carrier.