JPH03134678A - Toner image density detector - Google Patents

Abstract

PURPOSE:To execute exact toner image density control by correcting dirt on the detecting surface of a sensor based on difference between a detection output to a photosensitive body part, where there is no toner image, due to density detection sensors for black toner and color toner to be used while being switched, and a reference output due to the sensor without dirt. CONSTITUTION:Detection sensors 15a and 15b are respectively equipped with light emitting elements 16 and 18 and light receiving elements 17 and 19 and receive irregularly reflected light from the color toner of a photosensitive body 6 and regularly reflected light from the black toner image. These sensors are switched and moved to density detection positions and the toner density is detected. Corresponding to the difference between the density detection output due to the regularly reflected light reception from the part of the photosensitive body 6, where there is no toner image caused by these respective sensors 15a and 15b, and the similar detection output in the case that the detecting surfaces of the sensors 15a and 15b are not made dirty, a CPU 26 corrects the dirt on the detecting surfaces of the sensors 15a and 15b and the exact toner image density control can be executed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a device for detecting the density of a toner image on a photoreceptor in an image forming apparatus such as a copying machine or a printer.

[Prior Art] In this type of apparatus, for example, as disclosed in Japanese Patent Application Laid-Open No. 61-209470, a light emitting element irradiates a toner image on a photoreceptor and the reflected light is received by a light receiving element. a detection sensor configured to detect the toner image density by receiving the toner image density; There is a toner image density detection device that includes a second position for detecting toner image density and a means for switching and driving the toner image density.

The toner image density is maintained at a predetermined density by adjusting one or more of the bias voltage in the developing device, the surface potential of the photoreceptor, etc. based on the output from the detection sensor of the apparatus.

[Problem to be solved by the invention]

However, in the optical detection sensor described above, the sensor detection surface gradually becomes dirty due to toner scattering and dust, and as a result, the sensor output deviates from the correct state, making accurate image density control difficult.

As a method to remove such dirt from the sensor detection surface,
As disclosed in Japanese Patent Application Laid-Open No. 58-2861,
A method of electrostatically eliminating adhesion of developer to the sensor detection surface by applying a voltage of the same polarity as the potential of the developer to the sensor detection surface is disclosed in Japanese Utility Model Application No. 58-45547. There are methods such as blowing cleaning air onto the sensor detection surface as shown in the above, and methods of cleaning the sensor detection surface with a cleaning member as disclosed in Japanese Patent Application Laid-Open No. 158656/1980. However, the sensor detection surface may not be completely cleaned.

SUMMARY OF THE INVENTION Therefore, in the toner image density detection device of the above type, the present invention corrects the dirt on the sensor detection surface of the toner image density detection sensor to obtain accurate density information that matches the toner image density. The purpose is to provide control.

[Means to solve the problem]

As a result of research to achieve the above object, the inventor has found that a))
When the toner image density detection sensor is set to the first position for detecting the black toner image density, the sensor output (light receiving element output) is as shown by the solid line in Fig. 5 when the toner density is O. It reaches the maximum and gradually decreases as the toner image density increases, so the sensor output obtained by receiving the specularly reflected light from the area on the photoconductor where there is no toner image and the sensor output from the area on the photoconductor where there is no toner image. b) The sensor output can be easily corrected from the reference sensor output when the sensor detection surface is not contaminated by specularly reflected light, and b) the detection sensor is set at a second position for detecting color toner image density that receives reflected light. In this case, as shown by the solid line in Figure 6, the sensor output (light receiving element output) is the lowest when the color toner density is 0, so it is not possible to obtain a similar standard sensor output, so from this point Although the correction is difficult, the inventors have discovered that the correction for black toner image density detection can also be applied to correction for color toner density detection, and have completed the present invention.

That is, the present invention provides a detection sensor that detects toner image density by irradiating a toner image on a photoreceptor with light from a light emitting element and receiving the reflected light with a light receiving element; a toner image comprising means for switching drive between a first position for detecting the density of a black toner image that receives specularly reflected light and a second position for detecting the density of a color toner image that receives diffusely reflected light; In the density detection device, the detection sensor set at the first position receives specularly reflected light from a portion of the photoconductor where there is no toner image, and a sensor output obtained from the detection sensor and the sensor output where there is no toner image on the photoconductor. The method further comprises means for correcting the toner image density detection outputs of the detection sensors placed at the first and second positions from the reference sensor output when there is no stain on the sensor detection surface due to specularly reflected light from the part. The present invention provides a characteristic toner image density detection device.

In addition, means such as a brush may be provided for cleaning the detection surface of the sensor when the detection sensor drive means is driving the detection sensor position switching.

[For production]

According to the toner image density detection device of the present invention, the detection sensor constituting the device is placed in the first position for detecting black toner image density or in the second position for detecting color toner image density by the position switching driving means. be done. When placed at the first position, the light receiving element receives specularly reflected light emitted from the light emitting element constituting the detection sensor. When placed at the second position, diffusely reflected light is received by the light receiving element.

No matter where the detection sensor is placed, the sensor output is corrected according to the dirt on the sensor detection surface, and accurate toner image density information can be obtained.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a schematic configuration of a color copying machine employing an embodiment, FIGS. 2 and 3 show a cross section of a toner image density detection device, and FIG. 4 shows a configuration of the detection device. The detection sensor output correction means is shown.

The copying machine shown in FIG. 1 reads a document on a document table glass 1 with an image reader 2, emits a laser beam from a laser device 40 based on the read data, and transmits the laser beam to a polygon mirror 4 and a folding mirror. 5 and irradiates it onto a photoreceptor 6, thereby forming an electrostatic latent image corresponding to the original image on the photoreceptor. The latent image advances to the developing section according to the rotation of the photoreceptor 6 in the direction of the arrow in the figure, and is transferred to the developing device 7.
The image is developed by the developing device inside. The developing device 7 includes a magenta developer 71, a cyan developer 72, and a yellow developer 73.
, a black developing device 74 are mounted, and by raising and lowering the developing device 7, any one of the developing devices can be moved to a developing position. During full-color copying, development is performed in the order of cyan, magenta, yellow, and black.

On the other hand, the transfer paper sent out from the paper feed tray 9 is sent from the intermediate roller 10 to the timing roller 11 along the conveyance path. The timing roller 11 sends out the transfer paper in synchronization with the toner image on the photoreceptor 6. The transfer paper sent out from the timing roller is held on the transfer drum 8 by a transfer paper holding mechanism (not shown), and advances to a transfer section where it comes into contact with the photoreceptor 6 as the transfer drum rotates in the direction of the arrow in the figure.

A transfer charger 80 in the transfer drum 8 is provided in the transfer section, and the toner image on the photoreceptor 6 is transferred to the transfer paper by the action of the charger.

During full-color copying, magenta, cyan, yellow, and black toner images are transferred, and transfer is performed a total of four times. Thereafter, the transfer paper is separated from the transfer drum 8 and conveyed to a fixing device 13 by a suction belt 12, where the toner image is fixed, and the paper is discharged to a discharge toner 14.

During the process, each time a toner image is formed by one of the developing devices in the developing device 7, a reference pattern image is formed prior to the formation of the image, and the density of this reference pattern image is detected by the toner image density detection sensor. 15, this detected density is compared with a predetermined reference density, and based on the density difference, the developing bias voltage Vl,
The setting of the surface potential v0 of the photoreceptor 6 is changed, and the toner image density is maintained at a predetermined density.

As shown in FIGS. 2 and 3, the toner concentration detection sensor 15 includes a light emitting element 16 and a light receiving element 17 supported by a holder 15a, and a light emitting element 18 supported by a holder 15b.
and a light receiving element 19. This holder 15
a and 15b are connected to each other.

The elements 16 and 17 are provided so that the element 17 can receive specularly reflected light projected from the element 16 onto the photoconductor 6, and these elements are used when detecting the density of the quasi-pattern image using black toner. It will be done.

The elements 18 and 19 are provided so that the element 19 can receive the diffusely reflected light of the light projected from the element 18, and these are used when detecting the density of the reference pattern image made of color toner.

This sensor 15 has a window 2 through which irradiated light and reflected light can pass.
It is housed in a case 20 having a diameter of 0a, and can slide inside the case. When the elements 16, 17 move to the right until they hit the right wall of the case in the figure, they can assume the first position facing the window 20a, and when they move to the left until they hit the left wall of the case in the figure, the elements 18. 19 can take a second position facing the window 20a. Note that a protection plate 21 made of transparent synthetic resin or glass with good light transmittance is attached to the window 20a to form a sensor detection surface.

Holder 15a is connected to solenoid 22, and holder 15b is connected to tension spring 23. Therefore, when the solenoid 22 is de-energized, the holder 15a
, 15b assume the first position shown in FIG. 2 by the action of the spring 23, and when the solenoid 22 is energized, the holders 15a, 15
b assumes the second position shown in FIG. 3 against the spring 23.

Although the sensor detection surface 21 becomes dirty with scattered toner and dust as the sensor is used, the sensor output is corrected by the circuit shown in FIG.

The circuit shown in Figure 4 converts the sensor output (light receiving element output) into A/
Microcomputer 26 (
Hereinafter, the sensor 15 is configured to be inputted to the microcomputer 26. When the sensor 15 is set to the first position shown in FIGS. 2 and 4, the output of the light receiving element 17 is When set to the second position shown in FIG. 3, the outputs of the light receiving elements 19 are respectively input to the microcomputer 26.

This input switching is performed by the switching device 24.

The microcomputer 26 operates as follows.

First, prior to detecting the toner image density, the sensor 15 is set to the first position, and a portion of the photoreceptor 6 where there is no toner image is irradiated with light from the elements 1 and 7, and the specularly reflected light is sent to the element 1.
Receives light at 6. The light receiving element output thus obtained is input to the microcomputer 26 via the converter 25. Microcomputer 2
6 stores in advance the output Vl of the light receiving element 16 obtained in the same way when the sensor detection surface 21 is not dirty (see FIG. 5), and the stored value 1 and the output Vl when the sensor detection surface 21 is dirty are stored in advance. The ratio with the element output V2 (see FIG. 5) is calculated, the calculated value (Vl/V2)=k is obtained, and this is stored.

After the above preparations are completed, the image density is detected as the toner image is formed on the photoreceptor. This detection is performed using a reference pattern image formed before the main image corresponding to the original image. When the reference pattern image is a black toner image, the sensor 15 is set to the first position, the light emitting element 16 emits light, the specularly reflected light is received by the light receiving element 17, and the light receiving element output V3 (fifth (see figure) is input to the microcomputer 26.

The microcomputer 26 multiplies this output ■3 by the correction value k to obtain the corrected sensor output k・■3, compares this value with a predetermined and stored reference density value for the black toner image, and calculates the difference. Based on this, the voltage is outputted to the charger high voltage generation transformer 28 via the D/A converter 27, and is also outputted to the high voltage generation transformer 30 for the bias voltage of the developing device via the D/A converter 29. In this way, the photoreceptor surface potential ■ is determined according to the correct toner image density detection value corrected according to the dirt on the sensor detection surface. And the bias voltage (6) in the developing device is set, and a toner image of a predetermined density is obtained.

On the other hand, when the reference pattern image is a color toner image, the sensor 15 is set at the second position, light is irradiated from the light emitting element 18 to the reference pattern image, and the diffusely reflected light is received by the light receiving element 19. The light receiving element output V4 (see Figure 6)
is input to the microcomputer 26. The microcomputer 26 multiplies the input value (4) by the correction (tlfk) to calculate the corrected sensor output k4 (4), and compares this value with a predetermined and stored reference density value for the color toner image. ,
Based on the difference, it is outputted to the high voltage generation transformer 2 for the charger via the D/A converter 27, and
The signal is outputted via the D/A converter 29 to the high voltage generating transformer 30 for bias voltage of the developing device. In this way, the photoreceptor surface potential ■ is determined according to the correct toner image density detection value corrected according to the dirt on the sensor detection surface. Then, the bias voltage VB in the developing device is set, and a color toner image of a predetermined density is obtained.

Next, other embodiments will be described. In this embodiment, as shown in FIG. 7, an element 16.1 is mounted on the holder 15a of the detection sensor.
In addition, the holder 15b is provided with a transparent plate 32 that protects the elements 18 and 19. The holder 15a115b is slidably housed in the case 33, and as shown in FIG. 7, the elements 16.17 are at a first position facing the case window 33a, that is, the position for detecting the black toner image density, and the elements 18. 19 can take a second position facing the window 33a, that is, a position for color toner image density detection. There is a slight gap between the plate 31.32 and the upper wall of the case 33, and brushes 34.34 are provided at the left and right ends of the window 33a, and the holder 15aS
When the brush 15b moves from right to left and from left to right, this brush rubs the surface of the plates 31 and 32 to remove dirt.

This minimizes the decrease in the amount of reflected light that reaches the detection sensor, reduces the range of correction, and enables more accurate detection.

Other points are the same as those of the embodiment described above.

Note that the present invention is not limited to the above-mentioned embodiments, and can be implemented in various other ways.

For example, according to the above embodiment, the sensor 15 includes an element 16.17 for detecting the density of a black toner image and an element 18, 19 for detecting the density of a color toner image.
As disclosed in Japanese Patent Application No. 1-209470, it is equipped with one light-emitting element and one light-receiving element, and these pixel elements are arranged in a posture for detecting black toner image density and a posture for detecting color toner image density. Switching control may also be performed.

In addition, a light-emitting element, a light-receiving element for detecting black toner image density, and a light-receiving element for detecting color toner image density, or a light-emitting element for detecting black toner image density and a light-receiving element for detecting color toner image density. It is conceivable to include a light-emitting element and one light-receiving element.

In either case, means for cleaning the sensor detection surface may be provided, such as by using a brush or blowing compressed air from an air pump driven in conjunction with the sensor drive.

〔Effect of the invention〕

According to the present invention, there is provided a detection sensor that detects toner image density by irradiating a toner image on a photoreceptor with light from a light emitting element and receiving the reflected light by a light receiving element; means for switching drive between a first position for detecting black toner image density, which receives specularly reflected light, and a second position, for detecting color toner image density, which receives diffusely reflected light. In the detection device, it is possible to correct the dirt on the sensor detection surface of the toner image density detection sensor to obtain accurate density information that matches the toner image density, thereby providing accurate toner image density control.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of a color copying machine equipped with an embodiment of the present invention, FIGS. 2 and 3 are cross-sectional views centered on the detection sensor portion of the toner image density detection device shown in FIG. Fourth
The figure is a block diagram of a circuit for correcting the detection sensor output, Figure 5 is a graph showing the relationship between black toner image density and light receiving element output, and Figure 6 is a graph showing the relationship between color toner image density and light receiving element output. , FIG. 7 is a sectional view centered on a detection sensor portion in another embodiment of the present invention. 6...Photoreceptor 15...Detection sensor 16.18...Light emitting element 17.19...Light receiving element 26...Microcomputer Applicant: Minolta Camera Co., Ltd. Figure 5 Figure 6 Toner image density →

Claims (2)

[Claims] (1) A detection sensor that detects toner image density by irradiating light from a light emitting element onto a toner image on a photoconductor and receiving the reflected light by a light receiving element; Toner image density detection comprising means for switching drive between a first position for detecting black toner image density that receives specularly reflected light and a second position for detecting color toner image density that receives diffusely reflected light. In the apparatus, the detection sensor set at the first position receives specularly reflected light from a portion of the photoreceptor where there is no toner image, and a sensor output obtained from the portion where there is no toner image on the photoreceptor. The toner image density detection outputs of the detection sensors placed at the first and second positions are each corrected from the reference sensor output when the sensor detection surface is not contaminated by specularly reflected light. Toner image density detection device. (2) The toner image density detecting device according to claim 1, further comprising means for cleaning the detection surface of the sensor when the detection sensor driving means is driven to switch the detection sensor position.