JP2003345072A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To adjust an image forming condition by removing noises caused by damages picked up in measuring the density of the surface of an image carrier so as to measure the density of a reference toner image for control, highly precisely measuring the density and using a highly precise measured value. <P>SOLUTION: The image forming apparatus is provided with a density sensor by which the photodetecting signal of the reference toner image is outputted by receiving reflected light diffused and reflected by a reference toner image for measuring the density carried on an image carrier and also the photodetecting signal is outputted by receiving reflected light diffused and reflected by the surface of the image carrier, a minimum light detecting means to detect a photodetecting signal equivalent to the minimum value of the reflected light received by the density sensor and reflected by the image carrier and a controlling means by which the photodetecting signal of the reference toner image is corrected based on the photodetecting signal detected by the minimum light detecting means so as to obtain the density of the reference toner image and the image is formed by using the density. <P>COPYRIGHT: (C)2004,JPO

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 which controls image forming conditions based on a detected density value of an output image.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus using an electrophotographic method, image forming conditions are changed due to changes in environmental conditions such as temperature and humidity or deterioration of a photoconductor and a developer over time, so that an image is reproduced. Since the image quality is impaired, it is common to maintain the image quality, especially the image density, optimally by performing feedback control. Therefore, a control reference toner image is formed, the density of the reference toner image is measured by a density sensor, the density is compared with the target density, and if there is a difference, the difference is multiplied by a feedback gain to control the toner. The correction amount of the actuator set value is calculated.

However, when the density of the reference toner image is measured by a density sensor, if the sensitivity of the density sensor changes due to individual differences, fluctuations in environmental temperature and humidity, and deterioration over time, the measured values will vary. Further, the amount of the reflected light reflected by the toner image also varies depending on the state of the surface of the image carrier on which the toner image to be measured is formed, so that the measured value varies.

Therefore, in order to correct variations in measured values and obtain an accurate density, an output voltage (hereinafter referred to as Vp) obtained by measuring a reference toner image with a density sensor and an image carrier on which the reference toner image is formed. The toner image density is obtained from the difference or ratio between the output voltage (hereinafter referred to as Vc) measured on the surface with the density sensor and the output voltage measured with the density sensor on the reference plate (hereinafter referred to as Vr).

For example, Japanese Patent Publication No. 5-29908 discloses that
A technique for obtaining a deviation between a detection value obtained by detecting a reference patch density of an image portion at least once and a detection value obtained by detecting a density of a non-image portion a plurality of times is disclosed, and JP-A-2-916
In Japanese Patent Laid-Open No. 67-67, there is further disclosed a technique of sampling the reference image density and the background density of the photoconductor a predetermined number of times to obtain an average value, and correcting the output of the light emitting element based on the ratio of the average values. No. 289,465 discloses AD
Each of the technologies for controlling the image forming conditions to maintain the ratio of the average value of the output of the C sensor on the surface of the photosensitive drum and the output of the toner patch in the initial state is disclosed.

Using the disclosed technique, the density of the reference toner image is measured by receiving the diffused light reflected by the reference toner image formed on the image carrier having a black surface or a mirror surface or gloss. When the density of the image carrier surface without scratches is measured using the density sensor, the illumination light emitted from the density sensor is absorbed or specularly reflected by the surface of the image carrier, and the light is received by the light receiving element of the density sensor. Since almost no light enters, the error caused by the sensitivity fluctuation of the density sensor can be corrected by obtaining the average value of the voltage output from the light receiving element.

[0007]

However, while the image forming apparatus is continuously used, the surface of the image carrier is often scratched due to deterioration over time, and foreign matter such as fog toner is often adhered to the density sensor. A part of the illumination light emitted from the device is diffused and reflected by the scratches, etc., and the diffused light is incident on the light receiving element.Therefore, the output voltage of the light receiving element is superposed with noise due to the scratches on the image carrier. Will end up.

FIG. 1 is a diagram showing an example of a density sensor which receives the reflected light diffusely reflected by the object to be measured and measures the density.

The density sensor 30 shown in FIG. 1 has a light emitting element (LED) 31 and a light receiving element (PD) 32, and a light emitting element (L) is added to a reference toner image 34 formed on a belt surface 33.
The measurement light is emitted from the ED) 31, the measurement light diffusely reflected by the reference toner image 34 is received by the light receiving element (PD) 32, and a light reception signal is output.

FIG. 2 is a diagram showing the output voltage of the light receiving signal when the density of the reference toner image formed on the belt surface and the density of the belt surface are measured.

In FIG. 2, the vertical axis represents the output voltage of the concentration sensor, and the horizontal axis represents the elapsed time.

When the belt moves and the reference toner image passes the measurement position, the density level Vp of the reference toner image is output, and before and after the passage, the density level of the belt surface is output. However, if scratches or foreign substances are attached to the surface of the belt, noise diffusely reflected by the scratches or the like is superimposed and output, so that the output level becomes high.

Therefore, if there is a scratch on the surface of the image bearing member, Japanese Patent Publication No. 29908/1993 and Japanese Patent Laid-Open No. 9166/1990.
Even if the average value obtained by measuring Vc a plurality of times is obtained by the technique disclosed in Japanese Patent Laid-Open No. 7-52965 and Japanese Patent Laid-Open No. 5-289465, high-precision concentration measurement cannot be performed because noise is superimposed.

In view of the above circumstances, the present invention eliminates noise picked up due to scratches on the surface of an image carrier when measuring the density of an image carrier surface when measuring the density of a control reference toner image with a density sensor. However, it is an object of the present invention to provide an image forming apparatus that performs highly accurate reference toner image density measurement and adjusts image forming conditions by using the highly accurate measurement value.

[0015]

An image forming apparatus of the present invention which achieves the above object carries a toner image and carries the toner image on an image carrier which moves in a predetermined process direction.
In an image forming apparatus for forming an image composed of a fixed toner image on the recording medium by finally fixing the toner image on a predetermined recording medium, the density measurement carried on the image carrier is measured. A density sensor that receives the reflected light diffusely reflected by the reference toner image and outputs a reference toner image light reception signal, and also receives the reflected light diffusely reflected by the surface of the image carrier and outputs a light reception signal, and the density sensor The minimum light detecting means for detecting a light receiving signal corresponding to the minimum value of the reflected light from the image carrier, and the reference toner image light receiving signal output from the density sensor are detected by the minimum light detecting means. A control unit that performs correction based on the light reception signal, obtains the density of the reference toner image based on the corrected reference toner image light reception signal, and adjusts the image forming conditions for forming the image using the density. Characterized by comprising a.

As described above, the minimum light detecting means detects the light receiving signal on the surface of the image carrier which carries the reference toner image for density measurement in the state where there is no scratch or foreign matter attached, and thereby the light receiving signal of the reference toner image is detected. Since the density of the reference toner image is obtained by correcting the above, it is possible to obtain a highly accurate density measurement value and accurately adjust the image forming condition by the highly accurate density measurement value.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the image forming apparatus of the present invention will be described below.

FIG. 3 is a schematic block diagram showing the image forming apparatus of this embodiment.

The image forming apparatus shown in FIG. 3 is a xerographic engine which forms an electrostatic latent image by irradiating a laser beam after charging the surface of the photoconductor with a scorotron charger and develops the electrostatic latent image with toner. , Y, magenta M, cyan C, black K, and an image output unit (I) of a tandem color electrophotographic image forming apparatus provided for each color.
OT) is shown, and the image reading unit and the image processing unit are omitted.

The IOT is stretched around four photoconductors 1Y, 1M, 1C and 1K which rotate in the direction of arrow A, and is stretched around a roll 13, and circularly moves in the direction of arrow B while contacting each of the four photoconductors 1. An intermediate transfer belt 6 that receives a toner image transferred from the photoconductor 1, and scorotron chargers 2Y, 2M, 2C, and 2K that charge the surfaces of the four photoconductors 1;
A laser output unit (ROS) that forms an electrostatic latent image on each photoconductor 1 by exposing the surface of each photoconductor 1 that has been charged with exposure light that is modulated based on an image signal that is color-separated for each color.
3Y, 3M, 3C and 3K, and developing devices 4Y, 4M, 4C and 4K that develop the electrostatic latent image on each photoconductor 1 with each color developer to form a toner image on each photoconductor 1. The primary transfer devices 5Y, 5M, 5C, and 5K that transfer the toner images of the respective colors on the photoconductor 1 to the intermediate transfer belt 6, and the toner images of the respective colors that are sequentially superimposed and transferred on the intermediate transfer belt 6 are fed to the paper tray 11.
A secondary transfer device 7 for transferring the paper P sent from the feed roll 12 to the paper P, a fixing device 9 for fixing each color toner image transferred on the paper P to the paper P, and a paper tray 11 for storing the paper P. A cleaner (not shown) that cleans the surface of each photoconductor 1 and a charge eliminator (not shown) that removes residual charges on the surface of the photoconductor are provided. Further, in the circulating direction B of the intermediate transfer belt 6, downstream of the photoconductor 1K,
A density measuring device 20 for measuring the density of the control reference toner image transferred onto the surface of the intermediate transfer belt 6 is provided, and the intermediate position is provided upstream of the photoconductor 1Y in the circulating movement direction B of the intermediate transfer belt 6. A belt cleaner 8 for cleaning the surface of the transfer belt is provided. The concentration measuring device 20
Is the minimum value of the reflected light from the intermediate transfer belt, which is received by the density sensor that receives the reflected light diffusely reflected by the measurement target and outputs a light reception signal, and the density sensor on the surface of the intermediate transfer belt 6. And a minimum light detecting means for detecting the received light signal. The density of the reference toner image is corrected based on the detection value detected by the minimum light detecting means.
Further, the density of the reference toner image measured by the density measuring device 20 is sent to the control unit 14, and the control unit 14 adjusts the image forming condition of the image forming apparatus based on the measured value.

An image signal read from a document by an image reading unit (not shown) or an image signal created by an external computer (not shown) is input to an image processing unit (not shown), and color Conversion processing is performed. The signal modulated by the image signal decomposed for each color is the laser output unit 3.
Input to Y, 3M, 3C, 3K, each laser output unit 3
Irradiates the surface of the photoconductors 1Y, 1M, 1C and 1K uniformly charged by the scorotron chargers 2Y, 2M, 2C and 2K with the laser beam R. By the irradiation of the laser beam R, an electrostatic latent image corresponding to the color-separated image signal is formed on each photoconductor 1, and the electrostatic latent image is formed by the developing device 4Y of each color.
Toners are applied from 4M, 4C, and 4K and developed, and a toner image is formed on each photoconductor 1. The toner image formed on each photoconductor 1 is transferred to the primary transfer devices 5Y, 5M, 5C, 5
By K, the images are sequentially superimposed and transferred onto the intermediate transfer belt 6. After the transfer of the toner image to the intermediate transfer belt 6 is completed, each photoconductor 1 is cleaned of adhering substances such as residual toner by a cleaner (not shown), and residual charges are removed by a static eliminator (not shown).

The toner image on the intermediate transfer belt 6 is transferred onto the paper P sent from the paper tray 11 by the secondary transfer device 7, and then the toner image transferred onto the paper P is fixed. An image is formed on the sheet P by the container 9 to fix the image. After the transfer of the toner image onto the paper P is completed, the belt cleaner 8 cleans the adhering substances such as residual toner on the intermediate transfer belt 6, and the one-time image forming operation is completed.

On the other hand, the density of the control reference toner image formed on the intermediate transfer belt 6 is measured by the density sensor 10, and after the measurement, it is not transferred onto the paper P by the secondary transfer device 7, It is cleaned as it is by the belt cleaner 8.

Next, the formation and density measurement of the reference toner image in this embodiment will be described.

FIG. 4 is a plan view of a control reference toner image formed on the intermediate transfer belt of this embodiment.

As shown in FIG. 4, the size of the control reference toner image PA1 of this embodiment is 2 cm × 2 cm, and the density of the reference toner image PA1 is solid or covered by the surface of the image carrier. What is used is used.

By using the high density reference toner image in this manner, it is possible to eliminate the influence of the surface state of the intermediate transfer belt when measuring the density of the reference toner image.

The reference toner image Pa1 is formed on the intermediate transfer belt along the measurement line L1 measured by the density sensor.

FIG. 5 shows a density sensor 1 used in this embodiment.
It is a schematic block diagram of 0.

As shown in FIG. 5, the density sensor 10 includes a light emitting diode (LED) 10a for emitting infrared light toward the control reference toner image PA1 on the intermediate transfer belt 6.
And a photodiode (PD) 10b that receives diffused light from the control reference toner image PA1 and outputs a light reception signal.
And a shutter 10c for blocking infrared light directed to the control reference toner image PA1 and diffused light from the control reference toner image PA1 above the control reference toner image PA1, and a reference plate attached to the shutter 10c. 10e and.

Measuring light is emitted from the light emitting diode (LED) 10a to the surface of the intermediate transfer belt 6 at an angle of 45 °,
The diffused light reflected by the control reference toner image PA1 is reflected by the photodiode (P
D) It is arranged in a posture and a position where it is incident on 10b.

FIG. 6 is a schematic view of the shutter 10c provided in the density sensor 10 as seen from the LED / PD side.

In FIG. 6, the shutter 10c is provided with a measurement window 10d and a reference plate 10e for obtaining a reference for the sensitivity of the density sensor 10. Then, it can be moved in the left-right direction in the drawing by a driving mechanism (not shown).
In the shutter 10c, the reference plate 10e is arranged on the optical axis of the light receiving element 10b in the closed state, and the measurement window 10d for measuring the density of the reference toner image is arranged in the optical axis of the light receiving element 10b in the opened state. To move.

FIG. 7 is a schematic configuration diagram of the concentration measuring device.

In FIG. 7, the density measuring device 20 is composed of a density sensor 10 and a minimum light detecting means for detecting the minimum value of a light reception signal received by the light receiving element of the density sensor of the diffuse reflection light reflected on the surface of the intermediate transfer belt. An under peak hold circuit 15 is provided. The output of the concentration sensor 10 is
At the same time as the output (Vo) of the density sensor 10 is input to the under peak hold circuit 15, the detected minimum value is output as the hold output (Vh). The hold output (Vh) of the under peak hold circuit 15 is reset by the reset signal (RESET).

When the diffused light from the control reference toner image PA1 on the intermediate transfer belt is incident on the light receiving surface of the photodiode 10b, the photodiode 10b outputs a current that changes according to the density of the toner image. The current output from the photodiode 10b is current-voltage converted, and the output is input to the control unit 14 and the under peak hold circuit 15. The under peak hold circuit 15 holds the input minimum value of the output voltage of the concentration sensor 10, and inputs the held minimum value to the control unit 14 described later. The RESET signal is sent to the control unit 14
Is output from.

FIG. 8 is a diagram showing a timing chart when the density of the control reference toner image is measured by the density measuring device.

In FIG. 8, the first level shows the density sensor 1.
The operation of the shutter 10c of 0, the second step is the operation of the lighting signal of the light emitting element 10a of the density sensor 10, and the third step is
The output voltage waveform of the concentration sensor 10, the fourth stage shows the operation of the reset signal of the under peak hold circuit 15, and the fifth stage shows the output voltage waveform of the under peak hold circuit 15.

As shown in FIG. 8, first, the shutter 10c in the first stage is closed and the light emitting element (LED) 1 in the second stage is closed.
With 0a turned off, a reset signal is input to the under peak hold circuit 15 of the fourth stage. This allows
The hold voltage of the fifth-stage under peak hold circuit 15 is once reset to the power supply voltage Vcc (maximum value), and then the output voltage Vhdk when the LED 0a of the concentration sensor 10 is turned off is held. Then, in the third-stage density sensor 10, the output voltage (Vodk) when the light is turned off
Is measured.

Next, the second stage LED 10a is turned on. As a result, the output voltage of the third-stage density sensor 10 becomes a voltage corresponding to the reference plate 10e when the shutter 10c is closed, and the reference plate output voltage (Voref) of the density sensor 10 is measured. Also, before and after this,
The under peak hold circuit 15 of the fifth stage is reset. As a result, the under peak hold circuit 15
Hold voltage is reset to the power supply voltage Vcc (maximum value), and then the output voltage corresponding to the reference plate 10e of the density sensor 10 is held.

Subsequently, the first-stage shutter 10c is opened before the control reference toner image PA1 passes through the measurement position of the density sensor 10. As a result, the third-stage density sensor 10 outputs a voltage corresponding to the surface of the intermediate transfer belt 6. After that, when the reference toner image PA1 passes the measurement position, the output of the density sensor 10 once increases, and then the voltage corresponding to the surface of the intermediate transfer belt 6 is output again. At this time, the density sensor 10 causes the reference toner image P
The output voltage (Vop) corresponding to A1 is measured.

Intermediate transfer belt 6 used in this embodiment
Has a black surface, or has a mirror surface or gloss, so that the density sensor 10 of a type that receives diffused light and outputs a light reception signal is used. Therefore, when the background of the surface of the intermediate transfer belt 6 and the density of the toner image are measured and the surface is not scratched and no foreign matter is attached, the output voltage of the density sensor 10 becomes the minimum value. . However, if it is scratched or foreign matter is attached, the output voltage of the density sensor 10 becomes large, which causes noise.
However, since the density measuring device 20 of the present embodiment uses the under peak hold circuit and holds the minimum value of the light receiving signal output from the density sensor 10, the voltage level corresponding to the surface of the intermediate transfer belt 6 is temporarily changed. When the voltage is held, it is not affected even if a large voltage is output from the density sensor 10 due to a scratch or a foreign substance after that.

Here, since the reference toner image PA1 is formed every time the density is measured, the reference toner image PA1 itself is not deteriorated, and the reference toner image PA1 has a defect, a scratch or a foreign substance. Even if noise is picked up, it is possible to remove the noise by re-forming and measuring the reference toner image PA1. Meanwhile, the intermediate transfer belt 6
The output voltage of the concentration sensor 10 increases and noise is superimposed on the surface due to deterioration over time and adhesion of foreign matter. This noise cannot be removed even if the measurement is performed again like the reference toner image PA1. Therefore, when measuring the background of the surface of the intermediate transfer belt 6, it is necessary to obtain the minimum value for the purpose of noise removal. Of the outputs from the density sensor 10, Vp is directly output from the density sensor 10 and Vc is under. The output is made via the peak hold circuit.

The control reference toner image PA1 is the density sensor 1
After passing the measurement position of 0, the background of the surface of the intermediate transfer belt 6 is measured, and the first-stage shutter 10C is closed. As a result, the output voltage of the density sensor 10 is
The voltage corresponds to e.

Since the output voltage of the fifth stage under peak hold circuit continues to hold the voltage corresponding to the surface of the intermediate transfer belt 6, the peak hold circuit holds the voltage on the surface of the intermediate transfer belt 6. The corresponding voltage (Vhb) is measured.

Next, the control unit 14 defines and calculates the density of the reference toner image PA1 as the relative reflectance with respect to the density of the reference plate 10e based on the measured voltage according to the following equation. Relative reflectance = normalization coefficient × {(Vop−Vodk) −
(Vhb-Vhdk)} / (Voref-Vodk) As described above, by obtaining the relative reflectance with respect to the reference plate output, even if the density sensor 10 becomes dirty, or changes in sensitivity due to a change with time or a change in temperature, The density of the reference toner image can be measured with high accuracy.

Next, the operation of the control unit for controlling the image forming conditions using the reference toner image density measured with high accuracy by the density measuring device 20 will be described.

FIG. 9 is a block diagram of the control unit in this embodiment.

In FIG. 9, the control unit 14 is connected to the concentration measuring device 20 having the concentration sensor 10 and the under peak hold circuit 15 and the drive circuit 3a for driving the laser output unit of the IOT.

The output of the density sensor 10 and the density sensor 10
Together with the output of the under peak hold circuit that holds the minimum value of the output, it is sent to the error calculator 24 of the controller 14 and the density of the reference toner image PA1 is calculated.

The control unit 14 stores the target density value of the control reference toner image (a value converted from the relative reflectance of the output value of the density sensor 10 with respect to the reference plate output) to a target value memory 2
3, an error calculator 2 for calculating an error between the concentration target value stored in the target value memory 23 and the concentration measurement value during the control operation.
4 and a control rule memory 26 that stores a control rule that defines the correspondence relationship between the image quality of the reference image and the operation amount setting value,
The control amount is stored in the operation amount correction calculator 25 for calculating the correction amount of the operation amount such that the error of the measured value with respect to the target density value becomes zero by using the control rule, and the calculated correction amount. The operation amount set value at the time of output image formation is calculated from the operation amount set value at the time of creating the reference image, and the operation amount memory 21 for storing the operation result and the operation amount set value stored in the operation amount memory 21 are output. The operation amount output circuit 22 for supplying to the IOT drive circuit is provided.
The operation amount of the image forming apparatus at the time of forming the reference image and at the time of forming the output image is stored.

Here, the operation amount is an adjustment amount of a parameter for changing the output value of the controlled object, that is, a set value of the charging voltage of the charger, a set value of the exposure amount of the exposure light, a developing bias voltage of the developing device. And the transfer current of the transfer device.

In this embodiment, a laser power set value (hereinafter, abbreviated as LP set value) of the laser output unit (ROS) 3 is used as an operation amount for controlling the image quality of an output image. In addition,
The LP set value is standardized to a value from 0 to 255.

The LP set value is selected as the manipulated variable because there is a high correlation between the LP set value and the output image quality. Furthermore, the exposure amount can be instantaneously changed by changing the LP set value, and high responsiveness can be obtained.

The LP set value read out from the manipulated variable memory 21 is supplied to the laser drive circuit 3a of the IOT via the manipulated variable output circuit 22, whereby the laser drive circuit 3 is driven.
a supplies laser power according to the LP set value to the laser output unit (ROS) 3.

On the other hand, the reference image signal generator 13 outputs the reference image signal to the drive circuit 3a of the IOT in synchronization with the reference image forming timing, and the reference toner image PA1 is formed on the photosensitive member.
Is formed.

FIG. 10 is a flow chart showing the operation of the control unit.

In FIG. 10, first, the reference toner image PA1 is formed on the intermediate transfer belt (S1), and then the density (relative reflectance) of the reference toner image PA1 is measured by the density measuring device 20. (S2). Then, the concentration target value stored in the target value memory 21 and the concentration measuring device 20
The error from the measurement value output from is calculated by the error calculator 25 (S3). Next, the operation amount correction calculator 25 calculates the correction amount of the operation amount (S4).

Here, the manipulated variable correction calculator 25 determines the correction amount ΔLP of the LP set value as follows.

ΔLP = ΔD / A1 where ΔD is the error calculated by the error calculator 25,
A1 is a control rule stored in the control rule memory 26, and is a coefficient indicating the correspondence between the LP setting value and the reflected light amount measurement value of the reference toner image. This coefficient can be obtained in advance by experiments or the like.

The calculated ΔLP is the LP when the reference toner image is formed.
The LP set value after correction is obtained by subtracting from the set value. The obtained LP setting value is stored in the operation amount memory 21 as the operation amount setting value at the time of image formation.

Next, the LP set value for image formation stored in the manipulated variable memory 21 is supplied to the drive circuit 3a of the IOT via the manipulated variable output circuit 22 (S5).
The drive circuit 3a supplies laser power according to the LP set value to the laser output unit (ROS) 3.

With the above operation, one control operation is completed. After that, by repeating this operation periodically, the density of the output image is kept constant.

Although the present embodiment has been described based on the intermediate transfer type image forming apparatus using the intermediate transfer belt, the present invention is also applicable to the direct transfer type image forming apparatus. Further, the image forming apparatus is not limited to the tandem type and may be, for example, a 4-cycle type.

Further, although the density measuring apparatus of this embodiment detects the minimum value of the density on the surface of the image carrier by using the under peak hold circuit, it is not necessarily limited to the under peak hold circuit. Find the minimum value,
Any circuit may be used as long as it has a function of holding. Further, when the control unit can perform high-speed sampling of the voltage output from the concentration sensor 10, the output voltage (Vo) of the concentration sensor 10 is directly sampled by the control unit without using the under peak hold circuit. The minimum value can be obtained by processing the sampling data.

[0066]

According to the image forming apparatus of the present invention, even if there are scratches or foreign matter on the surface of the image carrier, the density of the surface of the image carrier can be measured without being affected by noise due to the scratches or foreign substances. Since the density of the corrected reference toner image becomes highly accurate, and the image forming conditions are controlled by using the highly accurate density measurement result, it is possible to maintain the image density reproducibility with high accuracy.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an example of a density sensor that receives reflected light diffusely reflected by a measurement target and measures the density.

FIG. 2 is a diagram showing an output voltage of a light receiving signal when the density of a reference toner image formed on the surface of the belt and the density of the surface of the belt are measured.

FIG. 3 is a schematic configuration diagram showing an image forming apparatus of the present embodiment.

FIG. 4 is a plan view of a control reference toner image formed on the intermediate transfer belt of the present embodiment.

FIG. 5 is a schematic configuration diagram of a concentration sensor 10 used in this embodiment.

FIG. 6 shows the shutter 10c included in the density sensor 10 at L
It is the schematic seen from the ED / PD side.

FIG. 7 is a schematic configuration diagram of a concentration measuring device.

FIG. 8 is a diagram showing a timing chart when the density of a control reference toner image is measured by a density measuring device.

FIG. 9 is a block diagram of a control unit in the present embodiment.

FIG. 10 is a flowchart showing the operation of the control unit.

[Explanation of symbols]

1, 1Y, 1M, 1C, 1K Photoreceptor 2, 2Y, 2M. 2C, 2K Scorotron charger 3, 3Y, 3M. 3C, 3K laser output (RO
S) 3a Drive circuit 3b Reference image signal generator 4, 4Y, 4M. 4C, 4K developing device 5, 5Y, 5M. 5C, 5K Primary transfer device 6 Intermediate transfer belt 7 Secondary transfer device 8 Belt cleaner 9 Fixing device 10, 30 Density sensor 10a, 31 Light emitting diode (LED) 10b, 32 Photodiode (PD) 10c Shutter 10d Measurement window 10e Reference plate 11 Paper tray 12 Feed roll 13 Roll 14 Control unit 15 Under peak hold circuit 20 Density measuring device 21 Manipulation amount memory 22 Manipulation amount output circuit 23 Target value memory 24 Error calculator 25 Manipulation amount correction calculator 26 Control rule memory 33 Belt surface 34 Toner image

Continued front page    F-term (reference) 2H027 DA09 DA10 DE02 DE07 DE10                       EA01 EA02 EA03 EA05 EB04                       EC03 EC06 EC20

Claims (2)

[Claims] 1. A recording medium, which carries a toner image and is carried on an image carrier which moves in a predetermined process direction, and finally fixes the toner image on a predetermined recording medium. In an image forming apparatus for forming an image composed of a fixed toner image thereon, the reflected light diffusely reflected by the reference toner image for density measurement carried on the image carrier is received to output a reference toner image reception signal. A density sensor that receives the reflected light diffusely reflected on the surface of the image carrier and outputs a light reception signal, and a light reception signal that is received by the density sensor and corresponds to the minimum value of the reflected light from the image carrier is detected. Minimum light detecting means for correcting the reference toner image light receiving signal output from the density sensor based on the light receiving signal detected by the minimum light detecting means, and using the corrected reference toner image light receiving signal Determine the density of the reference toner image, an image forming apparatus characterized by comprising a control means for adjusting the image forming conditions for forming the image by using the density. 2. The image according to claim 1, wherein the minimum light detecting means has a peak hold circuit for holding a light reception signal corresponding to the minimum value of the reflected light from the image carrier. Forming equipment.