JPH08211669A - Image density detecting device - Google Patents

Abstract

PURPOSE: To provide an image density detecting device excellent in productivity, having low production cost and capable of detecting accurate image density. CONSTITUTION: This image density detecting device is provided with a light emitting diode LED1 being a light emitting element, a phototransistor PT1 being a light receiving element, and diffusing members at the part of the light emitting window LW of the light emitting diode LED1 and the part of the light receiving window PW of the phototransistor PT1 . Then, a sheet-like diffusing film DF is used as the diffusing member and a sticky layer is formed on the sheet-like diffusing film DF.

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 having a developing device containing a developer, and in particular, a plurality of test patch images are formed on an image carrier and are developed by the developing device. The present invention relates to an image density detecting device used in an image forming apparatus that performs development by changing the linear velocity of a developer carrier and then fixes the developer carrier linear velocity at which a test patch image of a set density is obtained to form an image.

[0002]

2. Description of the Related Art In a conventional image forming apparatus, in order to correct a change in the density of a copy image caused by a change in the toner density of a developer and other changes in conditions, it is necessary to correct the change in the density of a copy image.
A test patch latent image is formed on the image carrier with a laser writing unit of constant brightness, or a standard patch plate is provided near the edge of the document table, and the test patch latent image of the standard patch image is formed by the scanning optical system. After the test patch latent image is formed on a carrier and developed by a developing device to form a test patch image, the test is performed by an image density sensor of an image density detection device provided upstream of the rotation of the image carrier of the cleaning device. The reflection density of the patch image is measured, and if the reflection density is higher than a specified value, toner is not replenished, but if the reflection density is lower than the specified value, toner is replenished.

Alternatively, a magnetic permeability sensor is provided at the bottom of the developing device to monitor the toner concentration of the developer, and when the toner concentration becomes lower than a prescribed toner concentration, the toner image is replenished to keep the copy image concentration at an appropriate value. After that, a plurality of test patch latent images are formed by exposure with different brightness, and the test patch latent images are developed with a developer carrier having a constant linear velocity,
An image forming apparatus is known in which the densities of a plurality of developed test patch images are detected by an image density sensor and control is performed to create a gradation correction curve based on a series of detected density data. In this apparatus, the image density may be lowered or the gradation may be deteriorated due to a decrease in developing performance while continuing image formation or a change in the potential of the photosensitive layer of the image carrier.
It is necessary to perform maximum density correction and gradation correction of an image for every fixed number of copies. Therefore, the image forming apparatus is provided with an image density detecting device for measuring the maximum density of an image and for performing gradation correction.

It has been necessary to provide a diffusing member in the light emitting window part of the light emitting element and the light receiving window part of the light receiving element of the image density sensor used in the image density detecting device in order to take in diffused light from the surface to be detected.

FIG. 11 is a sectional view showing the structure of a conventional image density sensor DS ₃ , for example, a light emitting diode LED and a light receiving element in a casing CK made of a synthetic resin opaque to emitted light and detected light. A hole for accommodating the phototransistor PT is formed, and the light emitting diode L is inserted in this hole.
After inserting the ED and the phototransistor PT, a diffuser plate DP in which a light diffusing material is dispersed in an acrylic resin having a thickness of about 2 mm is provided at positions corresponding to the light emitting window and the light receiving window. . In the figure, 110 is an image carrier, and p is a detection surface, for example, a test patch image in which toner is attached to the image carrier 110. When a thick diffuser plate DP is used as shown in FIG. 11, the diffused light generated inside the diffuser plate DP enters the phototransistor PT of the light receiving part together with the reflected light from the surface to be detected, and the correct reflection density is obtained. There was a problem that was not obtained. This problem becomes larger as the diffusivity of the diffuser plate DP is higher and as the plate thickness is thicker.

In order to solve this problem, the applicant has
An image density sensor having the configuration shown in 12 (hereinafter, this image density post-sensor is referred to as a conventional improved image density sensor)
Is proposed. The image density sensor shown in FIG.
The diffuser plate DP is divided into a diffuser plate DPA and a diffuser plate DPB at a position between the light emitting diode LED and the phototransistor PT, and a light shielding plate SP is provided between the diffuser plate DPA and the diffuser plate DPA so that diffused light generated in the diffuser plate DPA is generated. It is designed so as not to spread to the side. Further, in the image density sensor shown in FIG. 12B, a partition CKA is provided between the hole for housing the light emitting diode LED and the hole for housing the phototransistor PT of the casing CK, and the diffusion plate DP is opposed to the partition CKA. A diffusing plate DP is provided so that the partition CKA is fitted in the groove provided in the portion.
Is provided on the casing CK, and the diffused light generated in the diffusion plate DP on the light emitting diode LED side is shielded so as not to reach the phototransistor PT side.

The diffusing plate DP which is a diffusing member is, for example, N-610 (thickness: 2 mm, transmittance: 88%) manufactured by Mitsubishi Rayon Co., Ltd.
Was used.

FIG. 13 shows a photo when the light-emitting diode LED is repeatedly turned off, turned on, and turned off by covering the diffusion plate DP of the image density sensor DS ₃ of the conventional image density detecting device shown in FIG. 11 with black paper. 6 is a graph in which the output of the transistor PT is plotted on the vertical axis as a sensor output after passing through an amplifier circuit having a predetermined amplification factor. Light emitting diode LED
When is turned on, the diffused light in the diffuser plate DP reaches the phototransistor PT, and the sensor output increases. In contrast,
FIG. 14 is a graph in the case where the image density sensor DS ₄ of the conventional improved image density detection device shown in FIG. 12 is used, the diffusion plate DP is covered with black paper, and the same experiment as above is performed. . As shown in Fig. 14, the sensor output does not change regardless of whether the light emitting diode LED is off or on, and is a minute value (0.02V).
Therefore, it can be seen that the diffused light in the diffuser plate DP does not adversely affect.

[0009]

However, in the image density detecting device having the above-mentioned conventional improved image density sensor, the number of parts is increased, the number of assembling steps is increased, the productivity is lowered, and the manufacturing cost is reduced. There was a problem that it would be expensive.

The object of the present invention is to solve the above-mentioned problems,
An object of the present invention is to provide an image density detecting device which is excellent in productivity, has a low manufacturing cost, and can detect an accurate image density.

[0011]

An object of the present invention is to provide an image density sensor including at least a light emitting element, a light receiving element, a light emitting window of the light emitting element, and a diffusion member provided in a light receiving window portion of the light receiving element. In the image density detecting device having the above, the diffusion member is a sheet-shaped diffusing film.

A preferred embodiment of the image forming apparatus is characterized in that the sheet-like diffusion film is provided with an adhesive layer.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior to describing the structure and operation of the present invention, the structure and operation of an embodiment of an image forming apparatus equipped with the image density detecting apparatus of the present invention as a suitable image density detecting apparatus will be described with reference to FIG. explain.

The image forming apparatus includes an image signal generating means 20 such as a scanner or a personal computer.
It adopts an electrophotographic method that has an exposure process that performs gradation recording by changing the light emission time of the semiconductor laser with a signal obtained by pulse-width modulating (PWM) the density signal from 0, and turns on the main switch of the power supply. If so, a fixing temperature setting program for warming up the fixing unit 160, and a charging stabilization program for rotating the stirring screws 133A to 133C for setting the charge amount of the developer to a predetermined value during the warming up period, Further, in order to stabilize the charge potential of the image carrier 110, a program for stabilizing the charge potential that performs a pre-charging process for applying a charge to the image carrier before image formation, and in parallel with the execution of these programs. a plurality of test patches exposed with maximum exposure on the image carrier 110 based on the test patch signal S _G to be read from RAM340 Forming an image, which was developed by the developing device 130 for changing the rotational speed of the developing sleeve 131, and detects the maximum image density by one of the image density sensor DS ₂ of the image density detecting device test patch image was visualized After that, a program for fixing the number of rotations of the developing sleeve 131 to fix the developing characteristic, and a test patch latent image for a plurality of gradation correction are formed, and the developing device 130 with the fixed developing characteristic visualizes the image. And gray scale, a program for detecting the density by another image density sensor DS _{1 of} the image density detecting device to detect the printer characteristic, and a program for gradation correction control for correcting the gradation of the recording signal from the printer characteristic It is equipped with MPU500 having the above.

The main structure of the image forming apparatus will be described below.

The image processing unit 300 includes a LOG 310 and an LUT 32.
0, RAM 330, 340 and selector 350, which corrects the gradation by fixing the maximum image density to a predetermined value and then normalizing the printer characteristics obtained from the grayscaled test patch image based on the maximum image density. Is.

The LOG 310 is a table in which density-density pair table data is written, and is selected by a density selection button provided on the operation panel 600. L
The UT 320 writes table data in which a pair of PWM-density for obtaining the inverted density data detected is written, and sends a recording signal indicating a PWM level to the writing unit 400 or the RAM 330.

The RAM 330 has the following correction curve for backup written therein. This correction curve may be a common curve created by taking into account the characteristic changes of the developer or the photoconductor due to environmental changes, or a plurality of correction curves may be prepared taking into consideration deterioration with time due to the number of copies, etc. for each environment. This backup correction curve is read out by the image density sensor DS ₁
The output can be read out when an output abnormality from the device is detected, or can be selectively read out by an operation from the operation panel 600. Here, the output abnormality is, for example, PW.
The case where the output of the image density sensor DS ₁ does not decrease, becomes constant, increases, or has no output even if the M level increases.

The RAM 340 is either a test patch expressing 256 gradations of 8 bits, a density patch showing the maximum image density according to the printer characteristics under normal temperature and normal humidity (eg, 20 ° C., 50%), and a density patch showing intermediate density. The test patch data indicating that is written.

The selector 350 selects and outputs either the test patch signal S _G from the RAM 340 or the density signal from the LUT 320 or the density signal from the RAM 330 based on the select signal from the MPU 500.

The writing unit 400 includes a pulse width modulation circuit 4
10, LD driver 420, writing optical system 430,
Perform the exposure process.

The pulse width modulation circuit 410 compares the reference wave with an analog recording signal obtained by D / A converting the recording signal consisting of predetermined bits, and performs pulse width modulation of the recording signal to make it multi-valued. The modulation signal thus obtained becomes the drive signal for the LD driver 420.

The LD driver 420 oscillates and emits a semiconductor laser by the modulation signal, and has a light quantity stabilizing means for feeding back a signal proportional to the emitted light quantity of the semiconductor laser and driving it so that the light quantity becomes constant. are doing. As a result, the electric current for driving the semiconductor laser can be changed to adjust the latent image potential. Further, an index sensor 439 and an index detection circuit 440 are provided as a synchronization system. In this synchronous system, when the laser beam from the deflection optical system immediately before the start of scanning enters the index sensor 439 through the mirror Mi, the index detection circuit 440 converts the current generated by the index sensor 439 into a current / voltage and outputs it as an index signal. To do. By using this index signal, the surface position of the polygon mirror rotating at a predetermined speed can be detected, and raster scanning synchronized with the rotation of the polygon mirror can be performed.

The writing optical system 430 oscillates a semiconductor laser by a modulation signal obtained by pulse-width modulating a recording signal for one scanning line, deflects a laser beam emitted thereby by a polygon mirror rotating at a predetermined speed, and fθ lens Also, line scanning (main scanning) is performed by narrowing to a minute spot on the image carrier 110 by the first cylindrical lens and the second cylindrical lens, and raster scanning is performed by sub-scanning by rotation of the image carrier 110 to form a latent image. To do. The first cylindrical lens and the second cylindrical lens are optical systems that correct the spot position due to the surface tilt of each mirror surface of the polygon mirror, and the fθ lens is the entire scanning speed of the spot on the image carrier 110 by the polygon mirror. It is a lens that keeps it constant. The recording signal is, for example, an image recording signal, a test patch signal S _G read from the RAM 340, a density signal of the RAM 330, or the like.

The MPU 500 is equipped with a RAM (not shown) in which a program for executing the electrostatographic process and a program constituting the developing property fixing means of the developing device 130 are written, and various output signals from the operation panel 600 are processed. It has a function to do. Further, a paper discharge sensor PS for detecting the discharge of the recording paper and a temperature sensor ThS ₁ for detecting the surface temperature of the fixing roller 161 are connected. The MPU 500 also includes a sleeve driving unit 131M that drives the developing sleeve 131 of the developing device 130 at an arbitrary speed under the control of the MPU 500.
A solenoid for switching between driving and stopping the stirring screws 133A to 133C is connected via a driver (not shown).

The MPU 500 further includes a RAM in which a program used for the printer characteristic detecting means and the maximum image density converting means is written.

The printer characteristic detecting means R which has written the image density sensors DS ₁ and DS ₂ and the test patch signal S _G.
The actual printer characteristics and maximum image density are detected using AM340. This program also includes a program corresponding to the maximum image density conversion means.

The program corresponding to the image density detecting means is an image density sensor DS ₁ and D for the output voltage normalized to 256 gradations by A / D converting the luminance signal.
The image carrier 11 has a value obtained by logarithmically converting the ratio of the rated maximum output of S ₂ (output when nothing is attached on the image carrier 110).
A signal is obtained by adding a value in consideration of the difference between the density of 0 and the density of the recording paper, and a predetermined process is performed on the luminance signal obtained from the test patch images of a plurality of rows visualized on the image carrier 110. Then, an average value is calculated (see JP-A-1-41375). As a result, the MPU 500 can detect the printer characteristics and the maximum image density by eliminating the detection error caused by the vibration of the image carrier 110.

The MPU 500 has a function of controlling the toner concentration of the developer to be constant regardless of the developing property by a signal from the magnetic permeability sensor TS, and the developing property is controlled by changing the rotation speed of the developing sleeve 131. You can select a value.

The toner concentration control means for the developer is a developing device.
The magnetic permeability of the developer loaded in the 130 is detected by the magnetic permeability sensor TS, and a toner replenishing unit (not shown) is driven by this to replenish the toner to the developing device 130, thereby making the toner concentration of the developer almost uniform. It is a constant control.

The program constituting the developing property fixing means is
By controlling the number of rotations of the developing sleeve 131, it is possible to obtain the developability in which the photosensitive characteristics of the photosensitive layer of the image carrier 110 are corrected, and the toner concentration of the developer closely related to the developability is kept constant. The maximum image density is adjusted by controlling the number of revolutions of the developing sleeve 131 to change the amount of the developer conveyed to the developing area on the surface of the image carrier 110.

In this embodiment, a single MPU is used.
Although it was explained in 500 that the above-mentioned various programs are started, the present invention is not limited to this, and two or more MPs are executed.
U may be used for parallel processing.

The operation panel 600 is composed of, for example, a touch display, and is used for instructing the copy magnification, the number of copies, the start of copying, etc., and displays the contents of the operation.

The image carrier 110 is, for example, a (-) electrified coating type OPC on the surface of a conductive substrate made of aluminum or the like.
And a conductive base material is grounded. The image carrier 110 is a drum-shaped photosensitive member that rotates in the direction of the arrow at a linear velocity of 280 mm / sec. The image carrier 110 is provided with an encoder 115 for detecting the phase on the rotation axis of the image carrier 110. A phase signal indicating the phase of 110 is sent to the MPU 500.

A charger 1 to be described later is provided on the peripheral portion of the image carrier 110.
20, a developing device 130, a transfer device 143, a separator 144, a cleaning unit 150, and a paper feed system including a paper feed tray, registration rollers 142, and a conveyor belt 145.

The charger 120 is composed of, for example, a scorotron charger, and uniformly charges the image carrier 110.

The developing device 130 has a developing sleeve 131 which is a developer carrying member driven by a sleeve driving portion 131M, stirring screws 133A, 133B and 133C for stirring the developer, and the stirring screws 133A, 133B and 133C are Eg 1
The developer is adhered to the outer circumference of the developing sleeve 131 that rotates after stirring the developer by rotating at 20 rpm to form a magnetic brush, and a predetermined bias voltage is applied to the developing sleeve 131 to cause the image carrier 110 to rotate. The latent image in the developing area is developed by the magnetic brush to visualize the toner image.

The developer is a polyester type and has a weight average particle size.
A two-component developer comprising a 8.5 μm toner and a carrier having a resin coating on ferrite and a weight average particle size of 60 μm and having a toner concentration of 4 to 6% is used.

The transfer unit 143 superimposes the recording paper on the toner image electrostatically carried on the image carrier 110 and injects electric charges from the back side of the recording paper to electrostatically form the toner image on the recording paper. The material to be transferred is preferably a scorotron charger, but a corotron charger or charging roller can also be used.

The separator 144 discharges the recording paper electrostatically attracted to the image carrier 110 to remove the recording paper from the image carrier 11.
It is separated from 0, and a scorotron charger, a corotron charger, a charging roller, or the like is used.

The cleaning unit 150 brings a blade or the like into contact with the surface of the image carrier 110, scrapes off the toner and dust adhering to the surface of the image carrier 110 after the transfer of the toner image, and stores them in the waste toner box.

The fixing unit 160 is a unit for permanently fixing the toner image on the recording paper by applying heat or heat and pressure to the recording paper carrying the toner image, and is a pair of heating rollers which are rotating bodies for fixing. 161 and pressure roller 1
It has 62.

A heating heater composed of a halogen lamp or the like is provided on the inner cores of the heating roller 161 and the pressure roller 162. The heater for the pressure roller 162 may not be provided. The ambient temperature of the heating roller 161 is detected by a temperature sensor ThS ₁ including a thermistor, and this detection signal is sent to the MPU 500. Based on this detection signal, the MPU 500 controls energization of the heater of the heating roller 161 to keep the ambient temperature of the heating roller 161 within a predetermined temperature range. The pressure roller 162 is pressed against the heating roller 161 by a biasing member such as a spring (not shown). The heating roller 161 rotates clockwise in the drawing, and the pressure roller 162 is pressed against the heating roller 161 and driven to rotate.

The paper discharge sensor PS is provided in the paper path on the paper discharge side of the fixing unit 160, sends a detection signal for detecting the trailing edge of the recording paper to the MPU 500, and counts the number of recording papers discharged (the number of copies). To do.

FIG. 1 is a plan view and a side view showing the structure of the image density sensor DS ₁ provided on the upstream side of the rotation of the image carrier 110 of the transfer unit 143, and FIG. 2 is the image carrier 110 of the cleaning unit 150. FIG. ₃ is a diagram showing an image density sensor DS ₂ provided on the upstream side of rotation, and is a plan view and a side view showing the configuration of image density sensors DS ₁ and DS ₂ for detecting the density of a toner image on an image carrier 110. . In the figure, LED ₁ , LED ₂ and LED ₃ are light emitting diodes, PT ₁ and P
T ₂ is a phototransistor which is a light receiving element, BP is a substrate,
CK is a casing, LW is a light emitting window, PW is a light receiving window, DF
Is a sheet-like diffusion film that is a diffusion member that also serves as a dustproof plate and covers the light emitting window LW and the light receiving window PW.
SK is a socket for electrical connection, 531 is a casing C
A set screw for fixing K to the substrate BP.

In the image density sensor DS ₁ shown in FIG. 1, the central axis of the light emitting diode LED ₁ is perpendicular to the center of the surface to be detected on the image carrier 110, and the central axis of the phototransistor PT ₁ is Two holes are formed in the casing CK so that the angle is 40 ° from the center of the surface to be detected, and the light emitting diode LED ₁ and the phototransistor PT ₁ are inserted into these holes. Since only the diffused reflected light from the detection surface is received to detect the reflection density, the output from low density to high density becomes almost linear, which is suitable for gradation correction (γ correction).

The basic structure of the image density sensor DS ₂ shown in FIG. 2 is almost the same as that of the image density sensor DS ₁ shown in FIG. However, the casing CK has a light emitting diode LED ₂
The center axis of the image carrier 1 and the center axis of the phototransistor PT ₂ are
Two holes are formed in the casing CK so as to be, for example, 40 ° with respect to the normal line standing in the center of the surface to be detected and including the center of the surface to be detected on 10. The LED ₂ and the phototransistor PT ₂ are inserted, and this type of image density sensor detects the reflected density by directly receiving the reflected light in addition to the diffused light from the surface to be detected. Is suitable for determining the maximum image density because it can increase the resolution. The image density sensor DS ₂ has a light emitting diode LED ₃ provided so that its central axis is perpendicular to the center of the surface to be detected.
The light emitting diode LED ₃ and the phototransistor PT ₂ detect an increase in reflectance when a jam occurs when the recording paper is wound around the image carrier 110 without being separated from the image carrier 110. It has two functions of density detection and jam detection.

Diffusion which is a diffusion member provided so as to cover the light emitting windows LW of the light emitting diodes LED ₁ , LED ₂ and LED _{3 and} the light receiving windows PW of the phototransistors PT ₁ and PT ₂ of the image density sensor DS ₁ shown in FIG. For the film DF, for example, a light diffusion film MTN-W4 with an adhesive manufactured by Kimoto Co., Ltd.
Is used. As shown in FIG. 5, the structure of this diffusion film is such that a surface light diffusion layer DF1 is provided on one side of a polyester film DF2 and an adhesive layer DF3 is provided on the other side thereof, and further an adhesive layer DF3 is provided to prevent adhesion before use. A separator SL is provided on the side. Light diffusion film MTN-
W4 (transmittance 86%) is used for the conventional image density sensor DS made by Mitsubishi Rayon Co., Ltd. N-610 Thickness 2 mm (transmittance 8
8%) and almost the same diffusivity, and a thickness of 120 μm
Is thin. Since the light emitted from the light emitting diode LED is diffused in the diffusion film DF, the light emitted from the light emitting diode LED does not directly reach the phototransistor PT but is diffused / reflected many times and is mostly absorbed. Since it reaches the phototransistor PT later, the amount of light becomes so small that it can be ignored.

Further, in the image density sensors DS ₁ and DS ₂ using the diffusion film DF, like the conventional improved image density sensor DS ₄ , the diffusion plate DP is divided or grooved, the light shielding plate SP is prepared, or the casing CK. No additional parts or processing such as formation of the partition wall CKA is required, and after assembling the light emitting diode LED and the phototransistor PT in the casing CK at the time of assembly, the adhesive layer DF3 surface of the diffusion film DF is pressed and adhered to the casing CK. Since the assembly can be completed only by itself, the number of assembling steps can be significantly reduced.

FIG. 6 shows a case in which the diffusion film DF of the image density sensors DS ₁ and DS ₂ of the image density detection device is covered with black paper and the light emitting diode LED ₁ or LED ₂ is repeatedly turned off, turned on, and turned off. 6 is a graph in which the value after the output of the phototransistor PT ₁ or PT ₂ has passed through the concentration detection circuit 520 described below is taken as the sensor output on the vertical axis. As shown in FIG. 6, the sensor output is constant and has a small value (0.02 V) regardless of whether the light emitting diode LED is turned off or on, and it can be seen that the diffused light in the diffusion film DF does not adversely affect. In this embodiment, a light emitting diode LN66 manufactured by Kagoshima Matsushita Electronics Co., Ltd. was used as the light emitting diode LED, and a phototransistor PN101 manufactured by Kagoshima Matsushita Electronics Co., Ltd. was used as the phototransistor PT.

FIG. 4 is a circuit diagram showing an example of the density detecting circuit 520 of the image density detecting apparatus of this embodiment. It is possible to change the variable DC power supply V _ref is connected emitted light quantity of the light emitting diodes LED ₁ of the maximum output 10 (V) to the anode terminal T of the light emitting diodes LED _1. Light emitting diode LE
D ₁ is a resistance element R ₁₀ for current control and a semi-fixed resistance element V
It is connected in series with R _3, and can be fixed after adjusting the variation in the resistance value of the light emitting diode LED ₁ by the semi-fixed resistance element VR ₃ . Light emitting diode L
ED ₁ lights up when the terminal T ₆ is grounded. Further, the anodes of the light emitting diodes LED ₂ and LED ₃ are connected to the terminal T ₄ , a voltage of 12 (V) is applied from the DC power supply, and when the terminal T ₇ is grounded, the light emitting diode LED ₂ is turned on and the terminal T ₈ is turned on. When grounded, the light emitting diode LED ₃ lights up.

The cathode of the phototransistor PT ₁ is connected to the GND terminal T ₉ via the load resistance elements R ₈ and R ₉ and is grounded, and the cathode of the phototransistor PT ₂ is connected to the GND via the load resistance elements R ₂ and R _6. Connected to terminal T ₉ and grounded. Phototransistor PT ₁ and phototransistor P
The anode of T ₂ is connected to the terminal T ₄ and 12 (V) from the DC power supply
Is being applied.

When the density of the test patch image for gradation correction (γ correction) is detected, the light emitting diode LED ₁ is turned on when the terminal T ₆ is grounded by the control of the MPU 500.
The output current of the phototransistor PT ₁ that receives the reflected light from the test patch image on the image carrier 110 irradiated with the light changes according to the intensity of the reflected light, and the load resistance element R ₉ has both ends of the output current. A voltage proportional to the output current of the phototransistor PT ₁ is generated. This voltage is input to the (+) input terminal of the output detection circuit composed of the operational amplifier IC ₁ and the fixed resistance elements R ₁₁ and R ₁₂ , is amplified, and becomes a signal for gradation correction (γ correction), and the output terminal T Output from ₁ .

When the density of the test patch image for maximum density correction is detected, the light emitting diode LED ₂ is turned on when the terminal T ₇ is grounded by the control of the MPU 500, and the image carrier 110 irradiated with the light is illuminated. The voltage generated between the resistance element R ₂ and the resistance element R ₆ by the output of the phototransistor PT ₂ which receives the reflected light from the test patch image of the operational amplifier I.
The signal is amplified by C ₂ and output from the output terminal T ₂ as a signal for maximum density detection.

When the jam detection is performed, the light emitting diode LED ₃ is controlled by the control of the MPU 500 when the terminal T ₈ is grounded.
Lights up, and the voltage generated at the upper end of the resistance element R ₂ by the output of the phototransistor PT ₂ which receives the reflected light from the image carrier 110 illuminated by the light is amplified by the operational amplifier IC ₃ and output from the output terminal T ₃ . It is output as a signal for jam detection. C ₁ is a smoothing capacitor, C _2, C ₃ is a bypass capacitor for surge voltage or other noise.

The outputs of the various sensors described above are aligned through a voltage conversion circuit (not shown) so that the maximum voltage becomes a voltage suitable for the MPU 500 and input to the MPU 500.

Next, the fixing of the rotational speed (linear velocity) of the developing sleeve 131 for keeping the maximum density of the copy image constant in the image forming apparatus of FIG. 3 will be described.

During warming up at the start of copying,
First, the output voltage of the variable DC power supply V _ref is increased from 0 to 0.2 V by the control of the MPU 500, and the image density sensor DS ₁
Then, the light emitting diode LED ₁ is lit to detect the density of the image carrier 110 in a state where no toner adheres, and the output voltage of the density detection circuit 520 at this time is adjusted to be 9V, for example. The output voltage of the variable DC power supply V _ref is fixed when the output voltage reaches a predetermined voltage (for example, 9 V ± 0.1 V). The image carrier 110 may or may not be rotated during the adjustment of the output voltage, but it is preferable to rotate the image carrier 110 to prevent deterioration of the image carrier 110. As a result, the output change due to the dirt and performance deterioration of the image density sensor DS ₁ is corrected. After this M
The PU 500 performs maximum density correction and gradation correction.

The maximum density correction is performed as follows.
The image carrier 110 is charged by the control of the MPU 500 with no toner on the image carrier 110 as in the case of the image formation. The MPU 500 sends a select signal to the selector 350 of the image processing unit 300, and the test pattern S _G signal of the maximum density correction patch image is sent to the writing unit 400. As a result, on the image carrier 110, almost 3 pixels as shown in FIG.
Latent image p ₁ of the plurality of maximum density correction test patches _{0mm × 20mm, p 2 ···· p} n is written to about 2mm intervals in the sub-scanning direction. At this time, the exposure level is constant, and for example, in the case of an 8-bit digital signal by pulse width modulation (PWM), the level PWM255 corresponding to solid black is used. MPU500
Is the image carrier 1 according to the phase signal from the encoder 115.
After detecting the phase of 10, the developing device 130 is driven at the position synchronized with the latent image to perform reverse development. Development device 1 for this development
The rotation speed of the developing sleeve 131 of 30 can be changed for each test patch latent image as shown in FIG. 7B (developed view) by controlling the sleeve driving unit 131M that drives the developing sleeve 131 by the MPU 500. Is developed and visualized. The rotation speed of the developing sleeve 131 is increased from 100 rpm to 450 rpm every 25 rpm. Thus, the latent images of the test patch p ₁ , p ₂ ·
... p _n is a plurality of test patch images p _{1A having} different densities,
p _2A ... P _nA . The test patch image for maximum density correction passes through the retracted positions of the transfer unit 143 and the separator 144, and the light emitting diode LED _{2 of} the image density sensor DS ₂ provided upstream of the rotation of the image carrier 110 of the cleaning unit 150. Is turned on to detect the amount of reflected light, which is amplified by the density detecting circuit 520 shown in FIG. 4 and then sequentially sent to the MPU 500 as patch density data. After that, the test patch images p _{1A to} p _32A are cleaned by the cleaning unit 150.

The output of the image density sensor DS ₂ after the amplification inputted to the MPU 500 becomes a graph shown in FIG. Of these, for example, the voltage V _sr (broken line) corresponding to an image density of 1.35
The number of rotations (linear velocity) of the developing sleeve 131 of the test patch image when it first drops below is detected, and this number of rotations is stored in the built-in RAM. At the time of subsequent image formation, a designation signal is sent to the sleeve driving unit 131M so that this rotation speed (linear speed) is used to fix the rotation speed (linear speed) of the developing sleeve 131. As a result, changes in the maximum density of the copy image caused by changes in environmental conditions, deterioration of the photosensitive layer of the image carrier 110, and the like are corrected. Usually the maximum specified concentration is set to 1.4.
This is because if the density is 1.35 or higher, the quality of the copied image is sufficient. The maximum density can be corrected by changing the toner density (mixing ratio) of the developer or changing the amount of the developer conveyed on the developing sleeve 131, but the method of changing the rotation speed of the developing sleeve 131 is the developing sleeve 131. Since the above developer is not excessively large, it is excellent in that it does not generate toner stains or fog.

After the maximum density of the copy image is corrected to the specified density as described above, the gradation is corrected. In the same manner as described above, the gradation correction is performed by controlling the MPU 500 in the state where the toner is not present on the image carrier 110, and the image carrier 110 is charged in the same manner as the image formation described above, and the writing unit 400 performs gradation from the image processing unit 300. A test pattern signal for correction is sent to the semiconductor laser of the writing unit 20. This test pattern is, for example, 256 of 0 to 255 of 8-bit digital signal.
When the level is used, PWM signals of 8 levels are sent to the semiconductor laser of the writing unit 400, and latent images of a plurality of test patches of about 30 mm × 20 mm as shown in FIG. It is written about every 2 mm in the sub-scanning direction. This latent image is reversely developed by the developing device 130 in which the rotation speed of the developing sleeve 131 is fixed, and a plurality of tone-correcting test patch images p _{0 B} , p _1B , p _2b.
・ ・ ・ P _nB・ ・ ・ ・ p _32B , which is reflected by the image density sensor DS ₁ installed upstream of the rotation of the image carrier 110 of the transfer device 144 in which the light emitting diode LED ₁ is turned on by the control of the MPU 500. The amount of light is detected. The detected series of density data is sent to the MPU 500 as gradation correction data. The test patch images p _{0B to} p _32B pass through the retracted positions of the transfer unit 143 and the separator 144 and are cleaned by the cleaning unit 150.

A method of converting the output value of the reflected light amount of the test patch image detected into the density of the patch image will be described.

The latent image formed by sending the PWM signal for every 8 levels for gradation correction to the semiconductor laser of the writing unit 400 was reversely developed by the developing device 130 in which the rotation speed of the developing sleeve 131 was fixed. Patch image p _0B ,
p _1B , p _2b ... p _nB ... p _32B concentration detection circuit 5
The voltage output from the terminal T _{1 of} 20 is V ₀ , V ₈ , V ₁₆ , V ₂₄
· · · · Vn when the · · · · V _255, the concentration of each provisional When _{D Pn D P0 = -logV 0 /} V 0 D P1 = -logV 8 / V 0 D P2 = -logV 16 / D _Pn is obtained with V ₀ D _Pn = −log Vn / V ₀ , and D _P32 = −log V ₂₅₅ / V ₀ is normalized so that the maximum concentration is 1.4. Further, since the density of the white background of a typical recording paper is 0.08, 0.08 is added to all D _Pn . By doing so, the density of the patch image fixed on the recording paper is converted.

Under the control of the MPU 500, the gradation correction data is interpolated to have continuous printer characteristics. As the interpolation method, an interpolation method such as linear spline, Lagrange, or least square method can be used. Here, interpolation was performed using a cubic spline function (see Educational Publishing: Spline functions and their applications).

The test patch image is formed in the image area of the image carrier 110 because it is desired to directly obtain the printer characteristics. However, the test patch image is not limited to this and may be formed in a non-image area.

As described above, in the image forming apparatus shown in FIG. 3 having the image density detecting device, the maximum density of the copy image is corrected to the specified density during the warming-up period of the fixing unit 160, and then the gradation property is changed. Correction is performed.

However, no gradation correction is performed during the subsequent copying. The reason is that after repeated experiments, the maximum density and gradation are corrected first, and if the maximum density is corrected after every tens or hundreds of copies, the gradation hardly changes. Because I discovered it.

The operations of the maximum density correction and the gradation correction are about
Since it takes 20 seconds, performing only maximum density correction every 50 copies greatly improves copy productivity compared to the case where maximum density and gradation correction is performed every 1 copy operation or 50 copy operations. Can be made.

There are two causes for the decrease in the image density of the copied images when the image forming apparatus having the reversal developing system is continuously copied: (a) a decrease in the developing performance and (b) an increase in the potential of the exposed portion of the photoconductor. is there.

Generally, the ratio of cause (b) is small and the ratio of cause (a) is large. In the case of the cause (a), the developability can be returned to that before deterioration by changing the linear velocity of the developer carrying member (developing sleeve 131). Since the ratio of the cause (b) is small, a large deviation of the gradation correction curve does not occur. Therefore, the gradation can be maintained in the same state as the initial state by only changing the linear velocity of the developing sleeve 131 for each predetermined number of copies and correcting the maximum density.

FIG. 10 shows an image forming apparatus equipped with the image density detecting apparatus of the present invention and an image forming apparatus equipped with an image density detecting apparatus having a conventional improved image density sensor, both of which are shown in Table 1. Using an image forming apparatus having image forming conditions,
The image density detecting device of the present invention of the PWM signal and the test patch image input to the laser writing device (after fixing the linear velocity of the developing sleeve 131 and correcting the gradation during the warm-up period of the fixing unit 160) and the conventional 4 is a graph showing a relationship between an image density converted from a value detected by using an improved image density detecting device, a PWM signal, and a density of a fixed image obtained by the image forming apparatus of FIG. 3.

The table below shows the image forming conditions of the examples.

[0073]

[Table 1]

As a result, as shown in FIG. 10, the image forming apparatus equipped with the conventional improved image density detecting apparatus and the image forming apparatus equipped with the image density detecting apparatus of the present invention have exactly the same results. It was confirmed that the image quality was good and that the image density of the copy-fixed image coincided.

Although the above embodiments describe the image forming apparatus having the developing device using the two-component developer, the present invention is not limited to this, and the developing device using the one-component developer is provided. It can also be applied to an electrophotographic printer or the like (in this case, the magnetic permeability sensor TS can be eliminated).

[0076]

As described above, in the image density detecting device of the present invention, since the sheet-shaped diffusing film is used as the diffusing member of the image density sensor, it is necessary to provide the light shielding member or the partition as in the conventional device. Therefore, it is possible to prevent the diffused light generated in the diffusing member from reaching the light receiving portion. Furthermore, when using a diffusion film with an adhesive layer, the number of parts of the image density sensor is reduced, assembly becomes extremely easy, productivity is significantly improved compared to conventional image density detection devices, and manufacturing cost is reduced. In addition, the image forming apparatus provided with the image density detecting device of the present invention has an effect of always obtaining a copy image having proper maximum image density and gradation.

[Brief description of drawings]

FIG. 1 is a plan view and a side view showing an example of an image density sensor of an image density detection device of the present invention.

FIG. 2 is a plan view and a side view showing another example of the image density sensor of the present invention.

FIG. 3 is a block diagram showing an example of an image forming apparatus provided with the image density detecting device of the present invention.

FIG. 4 is a circuit diagram showing an example of a density detection circuit of the image density detection device.

FIG. 5 is a cross-sectional view showing the structure of a diffusion film.

FIG. 6 is a graph showing a light-shielding test result of the image density sensor of the present invention.

7A and 7B are a perspective view and an enlarged development view showing a test patch image for maximum density correction.

FIG. 8 is a graph showing the output of the density detection circuit at the time of maximum density correction.

FIG. 9 is a development view showing a test patch image for tone correction.

FIG. 10 is a graph showing the relationship between the PWM signal and the detected image density of a test patch image, and the PWM signal and the density of a copy-fixed image obtained by an image forming apparatus equipped with the image density detection device of the present invention.

FIG. 11 is a sectional view showing a configuration of a conventional image density sensor.

FIG. 12 is a cross-sectional view showing a configuration of a conventional improved image density sensor.

FIG. 13 is a graph showing a light-shielding property test result of a conventional image density sensor.

FIG. 14 is a graph showing the results of a light-shielding test of a conventional improved image density sensor.

[Explanation of symbols]

110 Image carrier 130 Development device 131 Development sleeve (developer carrier) 131M Sleeve drive unit 300 Image processing unit 400 Writing unit 500 MPU 520 Density detection circuit DS ₁ and DS ₂ Image density sensor DF Diffusion film (sheet-shaped diffusion member ) DP Diffusion plate (diffusion member) CK Casing LED, LED ₁ , LED ₂ , LED ₃ Light emitting diode (light emitting element) LW Light emitting window PT, PT ₁ , PT ₂ Phototransistor (light receiving element) p ₁ , p ₂ ...・_Pn test patch latent image p _1A , p _2A ... _PnA test patch image PW light receiving window

Front page continuation (72) Inventor Akira Takahashi 2970 Ishikawa-cho, Hachioji, Tokyo Konica stock company (72) Inventor Hiroshi Akita 2970 Ishikawa-cho, Hachioji, Tokyo Konica stock company

Claims (2)

[Claims] 1. An image density detecting device having an image density sensor comprising at least a light emitting element, a light receiving element, and a light emitting window of the light emitting element and a diffusing member provided in a light receiving window of the light receiving element. An image detection device, wherein the member is a sheet-shaped diffusion film. 2. The image density detecting device according to claim 1, wherein the sheet-like diffusion film is provided with an adhesive layer.