JPH03182773A - Image density detector - Google Patents

Abstract

PURPOSE:To always accurately detect the density of a developed image by holding a sensor on a transfer material carrier so that a detection optical path may be held between the surface of an image carrier and the transfer material carrier and detecting the density of a toner image on the image carrier opposed to the sensor on the detection optical path. CONSTITUTION:The sensors 100 and 101 which optically detect the density of the toner image are held and provided on the transfer material carrier 36 so that the detection optical path 50 may be held between the surface of the image carrier 1 and the carrier 36. At the time of detecting the density of the image, a reference pattern is exposed and developed at a specified position on the image carrier 1. Since a transfer sheet is not fed in such a case, the developed images of the reference pattern are opposed some time on the sensors 100 and 101 and the detection optical path 50 by the rotation of the image carrier 1 and the transfer material carrier 36. At such a time, the transfer sheet does not shield the detection optical path 50 and the surface of the transfer material carrier 36 is cleaned at a proper time, so that the detection optical path 50 does not receive the effect of contamination. Thus, the density of the developed image is accurately detected.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention is an image forming apparatus, in particular, a method for developing an electrostatic latent image formed on an image carrier with toner, and transferring the developed toner image. The present invention relates to an image density detection device for an image forming apparatus that forms an image by transferring it to a transfer sheet carried on a material carrier.

(Prior Art) In an image forming apparatus that forms a color image, it is necessary to appropriately control the density of each color toner image in order to improve the reproducibility of color tone.

Conventionally, several methods have been employed to control image density.

The first method is to measure the toner concentration of a two-component developer by measuring the response of the coil to the density of magnetic carriers in the developer, that is, the change in inductance, and adjusting the amount of toner replenishment. Try to keep the mixing ratio at a predetermined value.

In the second method, a developed image of a reference pattern is formed on the image carrier, the density of the developed image is detected, and toner is replenished based on the detection result to maintain the image density at a predetermined value.

The third method employs the first method to keep the toner density constant, then detects the image density from the developed image on the image carrier, and adjusts the toner density so that the density becomes a predetermined value. It is maintained at a predetermined value by manipulating various development conditions such as the development potential unrelated to the development process.

Note that in the second and third methods, the sensor that detects the density of the developed image of the reference pattern formed on the image carrier must be installed around the image carrier, but the sensor that detects the density of the developed image of the reference pattern formed on the image carrier is If there is a transfer carrier or intermediate transfer body,
If it is installed between the transfer section from the image carrier to the image carrier and the cleaning device for the image carrier, the developed image to be detected may be distorted as it passes through the transfer section before reaching the detection position. Detection cannot be performed.

For this reason, it is provided between the developing device and the transfer section (see virtual line IDC3 in FIG. 1).

(Problem to be solved by the invention) The first method simply keeps the toner concentration constant.

Therefore, it is impossible to take into account that the amount of toner charge changes due to changes in humidity or deterioration of the developer, and that the amount of toner adhering to the same image density varies. Furthermore, even if the amount of charge is constant under the same environment, the amount of toner adhesion during toner development may be affected by changes in conditions in other processes, such as changes in the surface potential of the image carrier, sensitivity of the image carrier, exposure amount, etc. cannot be considered.

Furthermore, since the sensor for detecting toner concentration must be in direct contact with or facing the developer, it is susceptible to toner contamination, and a special cleaning means is required to remove this, which is correspondingly expensive.

In the second and third methods, the density of the image formed on the image carrier after development is controlled, so even if the amount of toner adhesion varies due to changes in the amount of charge of the developer, the density of the image formed on the image carrier can be controlled. It is possible to maintain the density of the developed image constant.

However, since the sensor installed in the above position is easily contaminated by toner spilled from the developing device, this problem has also been dealt with by providing a special cleaning means (Japanese Patent Laid-Open No. 62-1
No. 27851), it is correspondingly more expensive.

Furthermore, in the second and third methods, a signal indicating whether or not toner replenishment is necessary is obtained by binary detection of the image density, which is higher or lower than the reference position, and density detection accuracy is not required very much. . However, if you want to control the density of a color image with high precision according to the sensor output,
Differences in the amount of detected light due to differences in the distance between the image carrier and the sensor also pose a problem. In a conventional sensor that is supported independently of the image carrier, the mutual spacing varies due to contact between the image carrier and mounting errors between the image carrier and the sensor, causing detection errors.

Therefore, the present invention solves the problem of toner depletion without any special cleaning means, and also allows the distance between the image carrier and the image carrier to be properly set and maintained without requiring any special structure, and eliminates any of the above-mentioned conventional problems. An object of the present invention is to provide an image density detection device that can solve the problem.

(Means for Solving the Problems) The present invention develops an electrostatic latent image formed on an image carrier with toner, and transfers the visualized toner image to a transfer material carried on a transfer material carrier. In an image forming apparatus that forms an image by transferring it to a sheet, a sensor that optically detects the density of a toner image is held on a transfer material carrier so that a detection optical path is provided between the sensor and the surface of the image carrier. The present invention is characterized in that the density of the toner image on the image carrier facing the sensor on the detection optical path is detected.

(Function) According to the above configuration, the transfer material carrier is normally maintained at a predetermined distance from the image carrier, and supports the transfer sheet fed during normal image formation on its surface and transfers it from the image carrier. can be subjected to transfer to form an image on a transfer sheet.

When detecting image density, a reference pattern is exposed and developed at a predetermined position on the image carrier. At this time, since the transfer sheet is not fed, the developed image of the reference pattern on the image carrier is rotated by the rotation of the image carrier and the transfer material carrier, so that the developed image is located between the sensor on the transfer material carrier and its detection optical path. When they face each other, the detection optical path is not blocked by the transfer sheet, and the surface of the transfer material carrier is cleaned in a timely manner to remove fogged toner outside the transfer sheet size, so the detection optical path is not affected by dirt. The sensor can detect the density of the developed image without any interference.

(Embodiment) FIG. 1 shows an example of a color copying machine to which the present invention is applied.

In Figure 1 of Section 1, the original placed on the original glass 18 is
CC by exposure lamp 17 and convergent light lens array 15
The D line sensor 16 is exposed to light, and these act as an image league unit 14 as a scanner, and are read as color signals of the three primary colors of R (red), G (green), and B (blue). These R, G, and B color signals are processed by the image processing circuit to produce Y, (yellow), M (magenta), and C.
(cyan) or these plus Bk (black), which is converted into a ternary or quaternary signal, and is given to the laser optical system 11 as an output signal. The copying machine of this embodiment does not have image memory for three colors. For this reason, the image league unit 14 scans each time when forming an image of each color, and based on this, sequentially Y, M, C or Y, M, C, Bk
is applied to the laser optical system 11.

The laser optical system 11 includes a scanning polygon mirror 12 fθ lens 13, a reflection mirror 51, etc.
The photosensitive drum 1 is irradiated with image-forming laser light for each color based on the C or Y, M, C, and Bk signals,
Perform exposure.

The photosensitive drum 1 is driven to rotate in the direction of the arrow.

The surface portion of the photosensitive drum 1 includes an organic photoreceptor in which a charge generation layer and a charge transport layer are laminated on an electrodynamic substrate, and is particularly sensitive to a laser emission wavelength of around 780 nm. . Further, in this embodiment, the photoreceptor is negatively charged by the charger 2.

The image forming system using this device is a so-called N-, P-based system that obtains a positive image from a negative image, in which the photosensitive drum 1 is image-exposed with laser light, and the electrostatic latent image formed thereby is negatively charged. The image is developed using the toner.

A drum cleaner 4, a toner collection roll 5, an eraser lamp 3, and the charger 2 are arranged around the photosensitive drum 1, as well as four types of developing devices. The first developing device 6 transfers the yellow toner to the second developing device 7.
supplies magenta toner, the third developer 8 supplies cyan toner, and the fourth developer 9 supplies blank toner. Toner is supplied to each of these developing devices 6.7.8.9 using toner hoppers lO5, 101, and 10.
The toners of each color individually stocked in 8, 10, and 8, 10, are transferred to each developing device 6, 7, 8, and 9 at appropriate times by a transfer pipe (not shown) based on a replenishment signal.

Transfer sheets such as plain paper and OHP film are stored in paper feed cassettes 9a and 19b in a stacked state.
Paper sheets are fed into the apparatus one by one by paper feed rollers 52a and 52b. The tip of the transfer sheet to be fed comes into contact with the stopped timing roller 20 to form a loop so that the skew is corrected, and the subsequent feeding timing is determined by the drive timing of the timing roller 20. ing. 21 is a vapor sensor used for this purpose.

A transfer drum 36 is provided between the timing roller 20 and the photosensitive drum l. The transfer drum 36 is rotationally driven in the direction of the arrow, holds the transfer sheet fed via the timing roller 20, and uses it to transfer the image from the photosensitive drum 1.

Therefore, as shown in FIG. 3, the transfer drum 36 is mainly composed of a drum frame 54 and a dielectric film 55 supported by the drum frame 54 and stretched into a cylindrical shape. A claw 38 for kinging is provided. This pawl 38 is opened and closed in a timely manner by the operation of a cam (not shown) provided within the transfer tram 36. The dielectric film 55 is a polyester film with a thickness of about 100 to 200 μm. However, it is not limited to this.

As shown in FIGS. 1 and 2, the frame 22 supporting the transfer drum 36 is supported by the main body of the apparatus so as to be movable about a pivot 41, and is biased counterclockwise by a spring 4o. Solenoid SQL is connected. Normally, the solenoid SQL is turned off, and the transfer drum 36 is pressed against the positioning roller 39 arranged on the photosensitive drum l side by the bias of the spring 40, and the distance between the photosensitive drum l and the transfer drum 36 is set to 0.1 to 0. It is kept constant at around .5 lungs.

The transfer sheet fed to the transfer drum 36 via the timing roller 20 is held only at its leading edge by chatter tong claws 38, and is then charged from the inner surface of the transfer drum 36 by a negatively charged suction charger 24, and at the same time is charged from the surface of the transfer sheet by an opposing electrode. 23 is brought into contact, the dielectric film is charged, and the surface of the transfer sheet is electrically grounded, whereby the transfer sheet is electrostatically attracted to the dielectric film and held on the transfer drum 3G.

Thereafter, the toner image on the photosensitive drum 1 developed by the first color yellow developer 6 is transferred from the inner surface of the photosensitive drum 1 to a transfer sheet held on a transfer drum 36 by a transfer charger 25 . At this time, the yellow developer 6
The other developing devices 7 to 9 are in a non-developing state so as not to disturb the image developed by the yellow developing device 6.

The electrical film after the transfer is positively charged and electrostatically attracts the transfer sheet. Such development and transfer steps are performed by selecting and using a predetermined developing device as many times as necessary according to the color information and color designation of the image to be formed.

When the final transfer process is completed, the static elimination charger 26.2
7 works, and the chucking claw 3 is activated by a cam (not shown).
8 is opened and the electrostatic holding and chucking of the transfer sheet to the transfer drum 36 are released, so that the transfer sheet is reliably separated from the transfer drum 36 by the separating claw 28 and sent to the succibon conveying section 29. . Here, the separate charger 26 mainly functions to reduce the electrostatic adhesion force between the dielectric film and the transfer sheet by using AC output to eliminate static from the dielectric film. The charger 27, which faces the charger 26 with a dielectric film in between, mainly eliminates the charge on the surface of the transfer sheet when the transfer sheet is separated from the transfer drum 36, and also prevents the discharge caused by the separation, thereby preventing the transferred image from flying off. This prevents damage.

Thereafter, the transfer sheet is fixed by a heat fixing roll in a fixing device 30, and is discharged to a paper discharge tray 32 via a paper discharge roller 35. The image on the ejected transfer sheet can be any color image depending on the number of times of development and transfer and the color of the toner used for development.

Of course, monochrome images can also be obtained.

In the above, the toner concentration of the developer used for development is controlled to a predetermined value using a method similar to the conventional method, and in order to further control the image density to a predetermined value, transfer is performed as shown in FIGS. 3 and 4. The dielectric film 55 of the drum 36 is made transparent, and a light projector 100 and a light receiver 101 for image density detection are embedded in the connecting portion 56 of the drum frame 54 covered by the transparent dielectric film 55,
These are arranged to face the surface of the photosensitive drum 1 with a detection optical path 50 passing through a dielectric film 55. As a result, the developed image of the reference pattern exposed and developed at a predetermined position on the photosensitive drum 1 is irradiated with light from the light projector 100, and the image density of the developed image is detected by receiving the reflected light from the developed image with the light receiver 101. Based on this detected value, the density of the developed image formed on the photosensitive drum 1 can be controlled to a predetermined value.

Since the detection and control of toner density cannot be performed in parallel with image formation, it is performed at an appropriate time when the conditions for forming an image on the photosensitive drum 1 may be changing. Appropriate times include various cases such as when the copying machine is turned on, when image formation is completed, when a predetermined number of images have been formed, or when human operations are performed as necessary. is possible.

When a signal for detecting and controlling image density is received, a reference pattern set in advance is output from the laser optical system 11 at a predetermined timing to expose the photosensitive drum l, and the resulting electrostatic latent image is transferred to a predetermined developing device. For example, the image is developed using a black developing device 9.

At this time, feeding of the transfer sheet is omitted, and the developed image on the photosensitive drum l is transferred to the light emitter 100 and the light receiver 101 on the transfer drum 36.
and are opposed to each other on the detection optical path 50 with a dielectric film 55 interposed therebetween. The density of the developed image can be detected from the output of the light receiver 101 at this time, and the density can be controlled to a predetermined value.

The timing of this detection will be explained. A position sensor 44 shown in FIG. 5 detects the tips of the units of the light projector 100 and the light receiver 101, which are rotated together with the transfer drum 36, at predetermined positions. After the unit tips of the emitter 100 and the receiver 101 are detected by the position sensor 44, the transfer drum 36
The time taken to reach the transfer position T between the photosensitive drum 36 and the photosensitive drum 1 is 11, and the time from the time Q when the reference pattern is exposed on the photosensitive drum 1 until the exposure point reaches the transfer position T facing the transfer drum 36 is 11. When the time is t2, the reference position sensor 44 detects the tip of the light emitter 1001 and the light receiver 101 at a time point P of 1. -1. The following is the exposure time Q, and the timing of each operation for density detection is as shown in FIG.

Since the image on the photosensitive drum 1 that is subjected to the above detection is after development, it is possible to detect and control the image density taking into account the developer and various conditions of development at that time, and to prevent Solerano fluctuations. can be accommodated.

Furthermore, since the distance between the transfer drum 36 and the photosensitive drum 1 is kept constant by the positioning roller 39, the distance between the emitter 100, the receiver 101, and the photosensitive drum 1 is always constant, and this changes, causing the emitter to 100, light receiver 10
The optical path length of the detection optical path 50 formed between the photosensitive drum 1 and the photosensitive drum 1 changes, which causes a change in the amount of light received by the light receiver 101, which eliminates the occurrence of errors in detection.

The transfer drum 36 is also provided with a cleaner 1 as shown in FIG.
02 is provided so as to be detachable. This cleaner 102
is for cleaning the fog toner adhering to the surface of the dielectric film 55 outside the size of the transfer sheet.
When forming an image, the solenoid SQL! When the solenoid 5otz is turned on, the dielectric film 55 is separated from the dielectric film 55 so as not to interfere with image formation.However, when no image is formed, for example, when the copying machine is turned on or when the copying operation is finished, the dielectric film 55 is separated from the dielectric film 55 by turning off the solenoid 5otz. The surface of the dielectric film 55 is cleaned by pressure contact.

Therefore, the surface of the dielectric film 55 is constantly cleaned, and it is also possible to avoid dirt from toner or the like from interfering with the concentration detection.

Note that although the light projector 100 and the light receiver lot are embedded in a part of the transfer drum 36 covered by the dielectric film 55, they may be provided exposed on the surface of the dielectric film 55 if it is a non-image forming part of the transfer drum 36. , in which case the sensor surface is directly cleaned by the cleaner 102.

(Effects of the Invention) According to the present invention, the transfer material carrier is normally maintained at a predetermined distance from the image carrier, and carries the transfer sheet fed during normal image formation on its surface and carries it as an image carrier. An image can be formed on a transfer sheet by transferring it from a body, but when detecting the image density, a reference pattern is exposed and developed at a predetermined position on the image carrier, and the transfer sheet is not fed. Due to the rotation of the image carrier and the transfer material carrier, the developed image of the reference pattern on the image carrier is generated at a certain period of time without the sensor on the transfer material carrier and its detection optical path being blocked by the transfer sheet. The density can be detected by facing the image bearing member and the transfer material carrier, and in particular, this detection is performed with a constant detection optical path length between the image carrier and the transfer material carrier, and in addition, the surface of the transfer material carrier is cleaned in a timely manner. This allows accurate detection at all times without being affected by contamination caused by toner or the like.

Therefore, it is particularly effective for color image forming apparatuses in which it is desired to control image density with high precision.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a color copying machine according to a first embodiment of the present invention, FIG. 2 is a side view of the transfer drum section, FIG. 3 is a perspective view of the transfer drum, and FIG. 4 is a sectional view of the transfer drum. , FIG. 5 is an explanatory diagram showing the relationship between each timing of exposure of the reference pattern and image density detection, and FIG. 6 is a time chart of each operation corresponding to each timing of exposure and detection. 6～9-・-・4 8 4 5 26.27 8 4 100 ・-・-・・・・Photosensitive drum・-・・Developer Image reader unit Original glass Charging During charging Charger Discharge charger Chucking claw position Sensor emitter 101 −・−・・−・−・ Light receiver

Claims (1)

[Claims] (1) An image in which an electrostatic latent image formed on an image carrier is developed with toner, and the developed toner image is transferred to a transfer sheet carried on a transfer material carrier to form an image. In the forming apparatus, a sensor for optically detecting the density of the toner image is provided on the transfer material carrier so as to have a detection optical path between the sensor and the surface of the image carrier, and is opposed to the sensor on the detection optical path. An image density detection device characterized by detecting the density of a toner image on an image carrier.