JPH07261477A - Electrophotographic image forming device - Google Patents

Abstract

PURPOSE:To provide an electrophotographic image forming device capable of properly correcting image process conditions by precisely detecting both of low and high image densities with one density detecting means. CONSTITUTION:In the correction of image forming process conditions for the correction control of an objective image density, high and low density reference toner images of a different image density are formed on a photoreceptor 5 and each toner image density is detected by one density detecting sensor 19. At this time, the irradiating light quantity of the light emitting element 19a of the sensor 19 or the sensitivity of a light receiving element 19b is switched over in accordance with the image density of the toner image subject to the detection of the density, to correct the image forming process conditions according to the value of the detection of the sensor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus such as a copying machine or a printer.

[0002]

2. Description of the Related Art According to an image forming apparatus such as an electrophotographic copying machine or a printer, the surface of a photosensitive member is usually charged by a charging device, and the charged area is exposed with an image corresponding to a document image from an optical system. An electrostatic latent image is formed, and the electrostatic latent image is developed by a developing device to form a visible toner image (visual image).
Then, this is transferred onto the transfer material by the transfer device and fixed by the fixing device. After the transfer of the toner image, the developer remaining on the photoconductor is cleaned and removed by the cleaning device, and the residual charge is erased by the eraser.

Further, such an image forming apparatus is usually provided with a means for making the density of an intended image to be proper. Particularly in an apparatus that reproduces an image having a density with gradation, a plurality of reference image patterns having different image densities are formed on a photoconductor, the densities of the patterns are detected by a density detecting means, and the detected values are detected. The image forming process conditions on the photoconductor, such as the grid potential of the charging device and the exposure lamp voltage in the optical system, are corrected based on the above.

The plurality of reference image patterns are generally a high-density pattern and a low-density pattern, and the process conditions that tend to affect the image density in high-density image formation are corrected by detecting the density of the high-density pattern. In addition, by detecting the density of the low density pattern, process conditions that tend to affect the image density in low density image formation are corrected, thereby achieving good image density in a wide image density range from low density to high density. I am trying.

What is often adopted as the detecting means includes a light emitting element for irradiating the pattern for density detection with light, and a light receiving element for detecting the amount of reflected light from the pattern due to light irradiation from the light emitting element. It is a detection sensor.

[0006]

However, it is extremely difficult or impossible to provide one detection means mainly composed of the light emitting element and the light receiving element with good detection sensitivity in a wide concentration range from low concentration to high concentration. It was possible. That is, as shown in FIG. 16A, the output change of the detection sensor with respect to the change in the density of the detection target pattern (toner image) has a slope of the sensor output change in the low density range in order to increase the detection sensitivity of the low density pattern. On the other hand, if it is set to a large value, the inclination of the sensor output change in the high concentration range becomes small, and a large sensitivity cannot be obtained in the high concentration range. Conversely, if a large sensor output sensitivity is set for the high concentration range,
As shown in FIG. 6 (b), the sensitivity in the low density region disappears or decreases. When the sensitivity is set near the middle of these, as shown in FIG. 16C, a large sensitivity cannot be obtained in both the high density region and the low density region.

As a method for solving such a problem, it is conceivable to provide each of the reference patterns having different densities with a detection sensor having a high detection sensitivity for the density. Inconvenience also occurs in terms of space and the like. Therefore, the present invention, means for forming a plurality of reference visible image patterns having different image densities on the photoconductor, means for detecting the image density of the reference visible image pattern formed on the photoconductor by the pattern forming means, A light emitting element for irradiating the reference image pattern formed on the photoconductor with light, the means for correcting an image forming process condition on the photoconductor based on a detection value of the detection unit. And an electrophotographic image forming apparatus including a light receiving element for detecting the amount of reflected light from the reference visible image pattern by light irradiation from the light emitting element, wherein the detecting means is one and low image density is also provided. It is an object of the present invention to provide an electrophotographic image forming apparatus capable of accurately detecting a high image density and thereby appropriately correcting image processing conditions.

[0008]

As described above, the electrophotographic image forming apparatus of the present invention for solving the above-mentioned problems includes a means for forming a plurality of reference visible image patterns having different image densities on a photoreceptor, and A means for detecting the image density of the reference visible image pattern formed on the photoconductor by the pattern forming means, and means for correcting the image forming process conditions on the photoconductor based on the detection value of the detection means, The detection means includes a light emitting element that irradiates the reference visible image pattern formed on the photoconductor with light, and a light receiving element that detects the amount of light reflected from the reference visible image pattern by the light irradiation from the light emitting element. It is one that includes.

According to the present invention, means for changing the irradiation light amount of the light emitting element according to the image density of the pattern (irradiation light amount changing means) or the sensitivity of the light receiving element according to the image density of the pattern. Means (light receiving element sensitivity changing means) is adopted. Note that both the irradiation light amount changing means and the light receiving element sensitivity changing means may be adopted.

When the irradiating light amount changing means is adopted, in order to optimize the image density correction, for example, it is performed by irradiating light from the light emitting element to the photosensitive member prior to the image density detection of the density detection target pattern. , The amount of light reflected from the background portion where the toner image such as the reference image pattern is not formed is detected by the light receiving element, and the reference irradiation light amount of the light emitting element is adjusted so that the detected value becomes a predetermined value. It is conceivable that after the adjustment, the irradiation light amount of the light emitting element is made different according to the image density of the density detection target pattern.

The image forming process conditions include at least a condition that easily affects the image density of the high density part and a condition that easily affects the image density of the low density part, and the former is the charging charger. Examples of the latter include the voltage applied to the exposure lamp in the optical system (exposure lamp voltage) and the like.

As the light emitting element in the detecting means,
Various types such as light emitting diodes and lamps can be adopted. Further, as the light receiving element, various kinds such as a phototransistor and a phototube can be considered. As a means for changing the amount of light emitted by the light emitting element, there can be mentioned, for example, one that controls the current supplied to the light emitting element to make the light emitting amount of the light emitting element different. Examples include a light emitting circuit for supplying and a means for supplying pulse power to the circuit, the light emitting circuit integrating the pulse input and supplying a current according to the duty ratio of the pulse to the light emitting element. .

As means for changing the sensitivity of the light receiving element,
Output resistance of light receiving element (in other words, output resistance of detection means)
Can be used to change the sensitivity of the light receiving element, and to control the reference voltage applied to the light receiving element to change the sensitivity of the light receiving element. By the way, if the final image density to be obtained is still controlled by the device by the correction of the image process conditions, the user may select a density other than the above-mentioned control density according to his / her preference or as necessary. Even when you want to get the concentration of, you can't do that.
Therefore, so that the user can set the desired density,
It is also possible to provide an image density adjusting means capable of adjusting the image density by the operator, in other words, manually adjusting the image density.

In this case, it is conceivable that when the user sets the image density at the beginning, the density set by the user is maintained when the apparatus automatically controls the density thereafter. That is, as the manually adjustable image density adjusting means, for example, an adjusting means such as an exposure lamp voltage by a user is included, and after adjustment of the voltage or the like, the reference image pattern forming means or another pattern forming means has a low density reference. It is conceivable that a visible image pattern is created, its density is detected by the density detecting means or another detecting means, and the reference condition at the time of correcting the process condition is changed based on the detected value.

[0015]

According to the image forming apparatus of the present invention, a plurality of reference visible image patterns having different image densities are formed on the photoconductor when the image forming process conditions for correcting and controlling the density of the target image are corrected. The density of each pattern is detected by one density detecting means. At this time, when the irradiation light amount changing unit is provided, the irradiation light amount of the light emitting element of the detection unit is switched so as to increase the detection sensitivity according to the image density of the density detection target pattern. When the light-receiving element sensitivity changing means is provided, the detection sensitivity of the light-receiving element is switched according to the image density of the density detection target pattern. Then, the image forming process condition is corrected according to the detected value, and thereby the image density is corrected.

When the irradiation light amount changing means adjusts the irradiation light amount by the light emitting element to the reference irradiation light amount prior to the image density detection of the density detection target pattern, the reference irradiation light amount is set by that, and then the reference irradiation light amount is set. The density of the visible pattern is detected. Further, when the manually operable image density adjusting means is provided, the required image density can be set according to the preference of the user.

[0017]

Embodiments of the present invention will be described below with reference to the accompanying drawings. The image forming apparatus shown in the figure is an electrophotographic copying machine. As shown in FIG. 1, the image forming apparatus has a photosensitive drum 5, and a charger 6 for uniformly charging the surface of the drum 5 and an inter-image eraser. 10, a developing device 7 that visualizes an electrostatic latent image formed by an optical system 20 by attaching toner to the electrostatic latent image, and a transfer charger 28 that transfers the toner image onto a copy sheet P fed from a timing roller pair 30. A separation charger 29 for separating the copy paper P from the photosensitive drum 5, a cleaner 9 for removing the residual toner adhering to the photosensitive drum 5, and a main eraser 8 for erasing the residual charges on the photosensitive drum 5 are provided. ing.

The photosensitive drum 5 can be rotationally driven in the direction of an arrow a in the figure at a constant peripheral speed v, and the optical system 20 is provided above it.
Is provided. The image of the original M placed on the original platen glass 1 of the optical system 20 is exposed to the exposure section X ₂ by the optical system, and an electrostatic latent image corresponding to the original image is formed on the photosensitive drum 5. It The optical system 20 includes an exposure lamp 21 and a mirror 2.
2a to 22d and a projection lens 23. The exposure lamp 21 and the mirror 22a are used for exposing the original image.
Means that the mirrors 22b and 22c can move in the direction of arrow b at a speed of v / m (m = copy magnification), and the mirrors 22b and 22c can move at a speed of v / 2m.

The charging charger 6 is a charger having a grid 61, and uniformly charges the surface of the photosensitive drum 5 at the charging portion X ₁ before the electrostatic latent image is formed by the optical system 20. The inter-image eraser 10 erases electric charges in a portion outside the image forming area corresponding to the original image on the photosensitive drum 5, and is also used for forming reference latent images L _1a and L _1b described later.

The developing device 7 uses a developer composed of a mixture of a magnetic carrier and an insulating toner to adhere toner to the electrostatic latent image passing through the developing portion X ₃ by a known magnetic brush method, that is, so-called. Develop by regular development. Development tank 7
In 0, a developing sleeve 7 having a magnetic roller 72 built-in
1, a height control plate 73, a bucket roller 74, and a screw roller 75 are installed. The developer is attracted to the outer peripheral surface of the developing sleeve 71 by the magnetic force of the magnetic roller 72 based on the rotation of the bucket roller 74 in the direction of arrow c, and the developing sleeve 71 rotates in the direction of arrow d or the direction of the magnetic roller 72 in the direction of arrow d ′. It is conveyed to the developing section X ₃ based on the rotation of the.

On the other hand, a toner replenishing roller 77 rotatably driven by a replenishing motor 78 controlled as described below is provided at the bottom of the toner tank 76 provided above the developing tank 70.
Is installed. The toner in the toner tank 76 is replenished onto the screw roller 75 based on the rotation of the replenishing roller 77, and is agitated and mixed with the developer already existing by the rotation of the roller 75, and is sent to the bucket roller 74. The toner is friction-charged with the magnetic carrier by stirring and mixing the toner to a predetermined charge amount.

This copying machine is equipped with a control unit 100 (see FIG. 5) for controlling the entire operation thereof. Control unit 100
Is the central information processing unit CPU, read-only memory RO
M, a random access memory RAM (hereinafter referred to as "RAM"), a microcomputer MC including an input / output unit, etc.
The operation of each of the above parts is controlled according to the operation (see). That is, a copy sheet including the photoconductor drum 5, the charging charger 6, the developing device 7, the transfer charger 28, the separation charger 29, the cleaner 9, the main eraser 8, the interimage eraser 10, the optical system 20, and the timing roller pair 30. The transport system, the fixing device, and the like operate based on the instructions of this control unit. The control unit 100 also gives an instruction to the operation panel 200 for various displays.

In the copier operation panel 200 shown in FIG. 6, 201 is a print switch, 211 is a numerical value input key used for setting the number of copies, 212 is an input clear key, 2
Reference numeral 13 is an interrupt copy key, and 214 is a reset key. Reference numerals 271 and 272 denote display light emitting diodes that indicate the set number of copies, the set value of the copy magnification, and the like. The light emitting diode is hereinafter referred to as "LED". The exposure adjustment keys 231, 232 are particularly related to the adjustment of the exposure lamp 21 in the optical system 20, and by pressing 231 the exposure amount increases and the image density decreases. By pressing 232, the exposure amount decreases and the image density increases. At this time,
The light amount of the exposure lamp is displayed by the density display LED 273 provided on the display unit. When the exposure amount is automatically adjusted, it is automatically adjusted by pressing the AUTO key 233.
In this case, the exposure amount is adjusted by an exposure amount sensor (not shown here) like other known automatic exposure adjustment control. In this case, the AUTO display LED2 on the display unit
74 is turned on.

According to this copying machine, the photosensitive drum 5 is operated by operating the print switch 201 on the operation panel 200.
Is rotated, the surface thereof is charged by the charging charger 6 at the charging portion X ₁ , and the charged area is subjected to image exposure corresponding to the original image from the optical system 20 to form an electrostatic latent image. This latent image is developed by the developing device 7 in the developing section X ₃ and becomes a visible toner image. On the other hand, the copy paper P sent from a paper supply unit (not shown) arrives at the timing roller pair 30 and is sent to the transfer unit X _{4 in} synchronism with the toner image on the drum 5, and is then transferred by the transfer charger 28. The toner image is transferred onto the sheet. The sheet P on which the toner image has been transferred is separated from the drum 5 by the separation charger 29, reaches a fixing device (not shown), where the toner image is fixed, and then discharged to the outside of the machine by a sheet discharge roller (not shown).

Further, in this copying machine, two reference visible image patterns (reference toner images) L are used for stabilizing the image by appropriately setting the density of the finally obtained image.
_2a and L _2b (see FIG. 4) are created. In other words, these reference patterns are used to measure the density of the reference pattern X ₃
In order to indirectly know the surface potential of the image portion on the photosensitive drum 5 in, the process condition of image formation is corrected according to the density measurement value, and the density of the finally obtained image is controlled. Be served. As a pre-process of creating the reference pattern, two reference latent images L _1a and L _1b having different surface potentials are created in the reference pattern creation area L on the photoconductor drum 5 according to an instruction from the control unit 100 (FIG. 2, (See FIG. 3). In this embodiment, the first reference latent image L _1a is created under the same conditions as the image forming conditions for the original image. In particular,
The surface potential of the first reference latent image L _1a is 600 V, which is equivalent to the surface potential of the original image portion because it is not charged by the charging charger 6 and is not exposed to light by the interimage eraser 10 and the optical system 20. The surface potential of the second reference latent image L _1b is the halftone pattern 8 prepared in advance in the optical system 20.
0 (see FIG. 1) is irradiated with light to expose the surface of the photoconductor drum 5 charged by the charging charger 6 to a potential lower than that of the first reference latent image L _1a .

Next, the photosensitive drum 5 in the developing section X ₃ .
The creation of the reference latent images L _1a and L _1b used to detect the upper surface potential will be described. The inter-image eraser 10 used to create the reference latent images L _1a and L _1b has a plurality of LEDs 10a and 10b along the longitudinal direction (rotational axis direction) of the photosensitive drum 5, as shown in FIGS. is doing. The LED 10a is in a position that does not face the area L in which the reference latent images L _1a and L _1b are created, and the LWED 10b is in a position that faces the area L.

First, the area L for forming the first reference latent image L _1a is charged to a surface potential of 600 V by the charging charger 6, and then the photosensitive drum 5 is rotated to the position of the inter-image eraser 10. Moving. On the other hand, interimage eraser 1
0 indicates that all LEDs 1 are
0a and 10b are caused to emit light, and the surface charge of the photosensitive drum 5 is erased so that unnecessary toner does not adhere. When the tip of the region L reaches the position of the inter-image eraser 10, only the LED 10b arranged at the position corresponding to the width W _{2 of the} region L stops emitting light. Further, the region L moves a distance W ₁ , and when the rear end of the region L reaches, the LED 10b is made to emit light again. In this way, the peripheral charges are erased and 600
A reference latent image L _1a charged to V is created.

The area for forming the second reference latent image L _1b is charged to a surface potential of 600 V by the charging charger 6, and then the halftone pattern 8 from the optical system 20 is charged.
The surface potential can be lowered by exposure to zero.
Further, the image-to-image eraser 10 erases the peripheral charges in the same manner as the reference latent image L _1a, and forms the reference latent image L _1b having a lower surface potential than the reference latent image L _1a .

First and second reference latent images L_1a, L_1bIs photosensitive
With the rotation of the body drum 5, the developing unit X ₃Go through the development equipment
The toner is attached by the device 7 and visualized. This present
The developing method by the image device 7 is the regular developing method as described above.
Yes, the portion where the charge is not erased, that is, the reference latent image L
_1a, L_1bToner adheres to the area, and
Semi-toner image) L_2a, L_2b(See FIG. 4).

After that, the photosensitive drum 5 passes through the transfer portion X ₄ , but at this time, the transfer operation is not performed, so that the copy paper P
It is not transferred to the upper side and remains on the photosensitive drum 5. The surface potential of the first reference latent image L _1a is 600 as described above.
V, and the surface potential of the second reference latent image L _1b is lower than that. Therefore, the first reference toner image L _2a obtained by developing them has a large toner adhesion amount and a high density, and the second reference toner image L _2b has a low toner adhesion amount and a low density (see FIG. 4). ). Therefore, in this embodiment, the densities of the reference toner images L _2a and L _2b are detected by the image density detecting means, and the reflection type photosensor 19 is used as the detecting means to optically measure the density.

As shown in FIGS. 1 and 3, the reflection type photo sensor 19 detects a light emitting element 19a for irradiating the reference toner image with light and the amount of light reflected from the toner image due to light irradiation from the light emitting element. The reference toner images L _2a and L ₂ which are formed in the area L and which are formed of the light receiving element 19b and face the surface of the photosensitive drum 5 from the transfer portion X ₄ to the cleaner 9.
It is installed at the position corresponding to _2b . Therefore, the photosensor 19 can measure the densities of the reference toner images L _2a and L _2b . In this embodiment, the light emitting element 19a is LE
D, and the light receiving element 19b is a phototransistor.

The output voltage Vs of the light receiving element 19b is input to the A / D port of the controller 100 as shown in FIG. The input sensor output voltage Vs is converted into a digital signal by the A / D converter, and the R of the microcomputer MC is backed up by the battery through the data bus.
The data is stored in the AM, taken out as appropriate, processed for data, and used for correction of image forming process conditions as described later.

Next, the density measurement of the reference toner image by the photo sensor 19 will be described in detail. In this embodiment, as described above, two reference visible image patterns (reference toner images) L _2a and L _2b used to control the density of the formed image and stabilize the image are created. By detecting the low density toner image L _2b and detecting the high density toner image L _2a , the current flowing through the LED 19a of the photo sensor 19 is switched to detect the low density toner image L _2b. The toner image L _2a can be detected with high accuracy.

More specifically, as shown in FIG.
When current is small to flow in ED19a, low density toner image L _2b is a toner image density (ID) of about 0.2 to 0.3
Can detect the concentration of, but ID1.3
When the density of the high density toner image L _2a , which is about the same, is detected, I
At the level of D1.0, the sensor output (output of the phototransistor 19b) has already become constant at 5.0V, and the density of the toner image L _2a cannot be detected. On the contrary, LED19a
When the current supplied to the high density toner image L _2a is large, the density of the high density toner image L _2a can be detected.
_When the density of _2b is detected, the sensor output is already constant at 0.2V at the level of ID 0.7, and the density of the toner image L _2b cannot be detected (the measured ID is Macbeth reflection manufactured by Macbeth Co.). Measured with a densitometer RD918.). Therefore, in this embodiment, the current flowing through the LED 19a is set to be large when the density of the high density toner image L _2a is detected, and is small when the density of the low density toner image L _2b is detected. If so, the amount of irradiation light to the toner image is switched.

In this embodiment, in order to switch the light emission amount of the LED 19a of the sensor 19, the pulse input from the microcomputer MC in the control unit 100 is integrated so that a current corresponding to the duty ratio of the pulse flows through the LED 19a. The light emitting circuit of the sensor 19 and the LED 19a and the sensor output (phototransistor 19b output) circuit are as shown in FIG. Here, the LED light emitting circuit changes the energy emission amount according to the duty ratio of the pulse.

Although the output of the LED 19a is changed by changing the pulse duty here, it is also possible to change the supply current amount and control the output by using another light emitting circuit configuration. Further, in order to increase the inclination of the sensor output with respect to the toner image density for both the low-density toner image and the high-density toner image, in addition to switching the light emission amount of the LED 19a, the light receiving element (here, the phototransistor 19b) of It is possible to switch the sensitivity. This can be achieved by switching the sensor output resistance according to an instruction from the control unit 100. The sensor characteristics and circuit configuration at that time are as shown in FIGS. As can be understood from the circuit of FIG. 10, sensor output resistance (large, small)
The sensitivity of the phototransistor 19b is switched by switching, and the same effect as when the output of the LED 19a is changed is obtained. In this case, the LED output is changed only by changing the pulse input value, but the configuration is complicated, but the sensor output can be switched depending on the concentration without being limited by the light emission performance of the LED. In the circuit of FIG. 10, the sensor output resistance is switched by switching the relay contact, but it can also be achieved by switching with a transistor or the like.

The sensitivity of the light receiving element (here, phototransistor) may be switched by another method such as changing the reference voltage applied to the light receiving element in addition to the method of switching the sensor output resistance. In any case, the output of the sensor 19 is input to the control unit 100 as described above, and is used for correction of the image forming process conditions as described below.

With reference to the flow charts shown in FIGS. 11 to 15, the function of the microcomputer in the control unit 100, the correction of the sensor 19 itself prior to the detection of the density of the reference toner images L _2a and L _2b , and the two reference toners will be described. Preparation of images L _2a and L _2b , density detection thereof, switching of LED light emission amount of the sensor 19 in the density detection, correction of image forming process conditions based on the density detection value, initial correction for image density correction by the user, etc. explain.

FIG. 11 shows the main routine of the copying operation. When the program starts and the print switch 201 is pressed in step S10 (hereinafter "step" is omitted), copying is performed (S20). The correction count is counted in S30, and the copying operation is repeated until the final copy is determined in S40. After the final copying, it is determined in S50 whether or not the correction counter is equal to or more than the set number, and if so, the image forming process condition is corrected in S60, the correction counter is cleared in S70, and the process returns.

The correction operation of S60 is as shown in FIG. When the correction counter counts up in the main routine shown in FIG. 11 and the correction timing comes, first the photosensitive member 5 or the like is driven (S80), and in order to correct the density detection sensor 19, exposure by light irradiation from the LED 19a is performed. The phototransistor 19b detects the amount of light reflected from the surface of the body drum 5, and the LE is adjusted so that the sensor output becomes 1V.
The current flowing through D19a is controlled and adjusted (S90, S10).
0). With this, the irradiation light amount by the LED 19a is adjusted to the reference irradiation light amount. The sensor output 1V is not limited to this, and may be changed according to the model or the like.

Next, the current is multiplied by A (usually 3 to 4 times).
(S110), and then a high density toner image _L2a is created (S110).
120), and the density level is detected by the sensor 19 (S130). When the sensor output is below a certain level (4.5V in this case) (S140), the process condition that greatly affects the image density of the high density portion is controlled. Here, the potential of the grid 61 of the charger 6 is selected as the process condition, and the potential is raised until YES in S140 (S150).

Next, the current passed through the LED 19a of the sensor 19 is returned to the original (S160), the low density toner image L _2b is created (S170), and the density level is detected by the sensor 19 (S180). If the sensor output is less than or equal to the predetermined lower limit value (S190), the process condition that affects the image density of the low density portion is controlled. Here, the voltage applied to the exposure lamp 21 in the optical system 20 (exposure lamp voltage)
Is selected, and the voltage is reduced until YES in S190 (S200). When the sensor output is equal to or higher than the predetermined upper limit value (S210), the voltage is set to S210.
In step S220, increase until YES. In this embodiment, 2.3V is adopted as the predetermined lower limit value and 2.7V is adopted as the predetermined upper limit value, and the exposure lamp applied voltage is adjusted in 1V units with 60V as a reference. However, the values are not limited to these values, and may be different depending on the model, for example.

When the initial correction is performed in S221, the initial correction subroutine is entered, the initial correction is executed, and the process returns to the main routine. In the above description, the correction operation that is performed in order of the density detection of the high density toner image → the high density portion image correction operation → the density detection of the low density toner image → the low density portion image correction operation is described. The low / density toner image may be detected first, and the process conditions may be corrected based on the output calculation result. The sequence in that case is as shown in FIG.

The present invention can be applied to other process control as long as the process conditions are controlled using two or more reference patterns having different densities. The contents of the initial correction (S221) are shown in FIG. The determination as to whether or not to perform the initial correction (S410) is made by inputting the initial setting code when the copying machine is shipped. When the initial correction is performed, the initial correction code is reset (S47
0), so that it is not performed again. Also, the initial correction code may be inserted later so that the correction can be added later.

This initial correction is performed for the following reason. That is, as described above, after the reference toner image is created, its density is detected and the image forming process condition is corrected, the density of the image formed by the copying machine is determined only by the state of the copying machine. At this time, for example, when the density preferred by the user is different from the density controlled by the copying machine, even if the exposure lamp voltage is changed initially to set the density preferred by the user, the process condition correction operation described above is performed thereafter. When the process is performed, the density returns to the level controlled by the copying machine, which is different from the user's preference. Therefore, the density required by the user can be maintained by the following procedure. First, in S420 and S430, the exposure lamp voltage is adjusted so that the density is desired by the user. The copying machine recreates the low-density reference toner image L _2b under the process conditions at that time (S440), the sensor 19 detects the density (S450), and is used in S190 and S210 in the correction operation routine (FIG. 12). The reference condition for correcting the process condition (here, the upper limit value and the lower limit value of the sensor output) is changed (S460).

The upper and lower limits of the sensor output value in S460 are changed according to the following table in this embodiment. Sensor output reference value (V) Lower limit value (V) Upper limit value (V) 3.5 3.3 3.7 3.0 2.8 3.2 2.5 2.3 2.7 2.7 2.0 1.8 2.0 1.5 1.3 1.7 For example, when the detection value of S450 is 2.9V, the lower limit value and the upper limit value of the sensor output reference value of 3.0V are 2.8V,
It is changed to 3.2V. In this way, the value in the corresponding column of the detected value is changed. These values may be further subdivided or may be changed steplessly to improve accuracy. The numerical values in the table are only one example, and may be different depending on the model or the like.

Further, instead of the initial correction shown in FIG.
The initial correction shown in 5 may be performed. In the initial correction shown in FIG. 15 as well, it is determined in S480 whether or not to perform the initial correction. When performing the initial correction, first, in S490 and S500, the exposure lamp voltage is adjusted so as to obtain the density desired by the user. After this adjustment, change amount of exposure lamp voltage (adjustment amount) Δ
V is stored (S510), the changed exposure lamp voltage is returned to the copier setting (S520), the initial correction code is reset (S530), and the change amount ΔV is added to or subtracted from the exposure lamp voltage, To return. After the process conditions shown in FIG. 12 or FIG. 13 are corrected thereafter, the density required by the user can be maintained by adding or subtracting the change amount ΔV stored in S510 (S540). The exposure lamp voltage in the initial correction has a total of 9 steps in increments of 2V with respect to the initial center value of 60V. However, these values are not limited to those values and may be different depending on the model or the like.

Next, step S in the initial correction of FIG.
The exposure lamp voltage adjustment by the user in steps S490 and S500 in the initial correction of 420, S430, and FIG. 15 will be described. When the initial correction mode is entered, a display indicating that the initial correction mode is set is displayed on the display unit on the operation panel 200. Here, "C1" or "S3" is displayed on the LED 271. Next, in this state, the user presses the exposure lamp adjustment keys 231 and 232 to select an appropriate value, puts the user's favorite original on the original table, and presses the print switch 201 to perform copying. Repeat this,
When the density becomes appropriate, the reset switch 214 is pressed and the process proceeds to step S510.

According to the copying machine described above, the density of the high density reference toner image L _{2a and} the density of the low density reference toner image L _2b are accurately detected by one density detection sensor 19 so that the image forming process conditions are appropriate. It is possible to perform various corrections, and thereby obtain a target image having an appropriate density. Further, in the above-described embodiment, the image forming process conditions are corrected when the copy operation is performed more than the set number of times. However, it is performed before the copy operation is started after the power is turned on or after a predetermined time has elapsed. The image forming process condition may be corrected.

Further, according to the above copying machine, the irradiation light amount by the LED 19a of the detection sensor 19 is adjusted to the reference irradiation light amount prior to the detection of the reference toner image density, so that the image process condition correction is optimized accordingly. It is also possible to obtain the image density requested by the user according to his or her preference.

[0051]

According to the present invention, the means for forming a plurality of reference image patterns having different image densities on the photoconductor and the image density of the reference image pattern formed on the photoconductor by the pattern forming means are And a means for correcting an image forming process condition on the photoconductor on the basis of a detection value of the detection means, wherein the detection means applies light to the reference visible image pattern formed on the photoconductor. An electrophotographic image forming apparatus comprising: a light emitting element for irradiating light; and a light receiving element for detecting the amount of light reflected from the reference visible image pattern due to light irradiation from the light emitting element, wherein the detecting means is one. Thus, it is possible to provide an electrophotographic image forming apparatus capable of accurately detecting both low image density and high image density, and thereby performing appropriate correction of image process conditions.

When the means for changing the irradiation light quantity of the light emitting element in the density detecting means is adopted, it adjusts the irradiation light quantity by the light emitting element to the reference irradiation light quantity prior to the image density detection of the density detection target pattern. Sometimes, the image process condition correction is optimized accordingly. Further, when the manually operable image density adjusting means is provided, the required image density can be obtained according to the user's preference.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a main part of a copying machine that is an embodiment of the present invention.

FIG. 2 is a perspective view showing an inter-image eraser and a state in which a reference latent image is formed on a photosensitive drum by the eraser.

FIG. 3 is an explanatory diagram showing a positional relationship between an inter-image eraser and a sensor for detecting the density of a reference latent image and a reference toner image formed thereby.

FIG. 4 is an explanatory diagram of a high density reference toner image and a low density reference toner image.

5 is a block diagram showing an outline of a control circuit of the copying machine shown in FIG.

FIG. 6 is a plan view of an operation panel of the copying machine shown in FIG.

FIG. 7 is a graph showing the relationship between toner image density and sensor output depending on the magnitude of light emitting element (LED) current.

FIG. 8 is a diagram showing a concentration detection sensor and a circuit related thereto.

FIG. 9 is a graph showing the relationship between toner image density and sensor output depending on the magnitude of sensor output resistance.

FIG. 10 is a circuit diagram when switching the sensor output resistance.

FIG. 11 is a flowchart showing a main routine of operation of a control unit.

FIG. 12 is a flowchart showing a correction operation subroutine.

FIG. 13 is a flowchart showing another example of the correction operation.

FIG. 14 is a flowchart showing an initial correction subroutine.

FIG. 15 is a flowchart showing another example of initial correction.

FIG. 16 is a graph showing a relationship between a conventional density detection sensor output and a toner image density.

[Explanation of symbols]

5 Photoreceptor Drum 6 Charging Charger 61 Grid 7 Developing Device 28 Transfer Charger 29 Separation Charger 8 Main Eraser 9 Cleaner 10 Image Eraser 10a, 10b Light Emitting Diode in Eraser 30 Timing Roller Pair 20 Optical System 21 Exposure Lamp 80 Halftone Pattern 19 Density detection sensor 19a Light emitting diode 19b Phototransistor 100 Control unit 200 Operation panel 201 Print switch 214 Reset switch 231, 232 Exposure adjustment key 273 Density display LED L _1a , L _1b Reference latent image L _2a High density toner image L _2b Low density toner image

Claims (4)

[Claims] 1. A means for forming a plurality of reference visible image patterns having different image densities on a photoconductor, and a means for detecting the image density of the reference visible image patterns formed on the photoconductor by the pattern forming means, A light emitting element for irradiating the reference image pattern formed on the photoconductor with light, the means for correcting an image forming process condition on the photoconductor based on a detection value of the detection unit. And an electrophotographic image forming apparatus including a light receiving element that detects a reflected light amount from the reference visible image pattern due to light irradiation from the light emitting element, the irradiation light amount of the light emitting element to an image density of the pattern. An image forming apparatus provided with a means for changing it accordingly. 2. The means for changing the irradiation light amount of the light emitting element, prior to detecting the image density of the density detection target pattern, determines the amount of light reflected from the background portion of the photoconductor by the light irradiation from the light emitting element. The reference light amount of the light emitting element is adjusted so that the light receiving element detects it and the detected value becomes a predetermined value, and after the adjustment, the irradiation light amount of the light emitting element is changed according to the image density of the density detection target pattern. Claim 1
The image forming apparatus described. 3. The image forming apparatus according to claim 2, further comprising a manually operable image density adjusting unit. 4. A means for forming a plurality of reference image patterns having different image densities on a photoconductor, and a means for detecting the image density of the reference image patterns formed on the photoconductor by the pattern forming means, A light emitting element for irradiating the reference image pattern formed on the photoconductor with light, the means for correcting an image forming process condition on the photoconductor based on a detection value of the detection unit. And an electrophotographic image forming apparatus including a light receiving element that detects the amount of reflected light from the reference visible image pattern due to light irradiation from the light emitting element, the sensitivity of the light receiving element depending on the image density of the pattern. An image forming apparatus provided with means for changing.