JPH0619318A - Method for preventing image density from lowering - Google Patents

Abstract

PURPOSE:To prevent image density from lowering in the case of operating a developing device again after stopping it under the environment of high temperature and high humidity by sticking toner in the develoing device to an electrostatic latent image carrier, recovering it and supplying new toner to the developing device until an image can be formed after turning on a power source. CONSTITUTION:As soon as the main switch of a copying machine is turned on, the developer is started to be stirred in the developing device 4, and the electrostatic latent image of a specified pattern formed on a photosensitive drum 1 is developed by the developing device 4. When the toner image of this pattern arrives at an image density sensor DS, the density of the pattern is read, and whether or not the toner must be replaced is judged based on information on the image density. In the case of judging that the toner must be replaced because the image density is lowered, a replacing amount is calculated in accordance with the lowered image density. Based on the replacing amount, the toner is stuck to the surface of the photosensitive drum 1 from the developing device 4, it is recovered by a cleaning device 72, and the new toner is supplied to the developing device 4 from a toner supply part 40 so that the toner consumed by being stuck may be compensated.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus, when the apparatus is rested for a long time (for example, overnight or more) in a high-temperature and high-humidity environment and then restarted, dozens of initial sheets or more There is a phenomenon that the image density is lowered in copying or printing up to several hundred sheets.
It is considered that this is because water molecules intervene in the charging mechanism of the carrier and the toner in the developer in the developing device, which disturbs the balance of the exchange of electrons and causes the toner charge amount to be higher than usual.

Even when such a decrease in image density occurs, the image density is restored by repeating copying or printing, and thereby repeating toner consumption and replenishment. This is because the average value of the toner charge amount distribution is lowered to a normal value by adding the uncharged toner (however, the highly charged toner remains), and when the uncharged toner contacts the highly charged toner, the charge is not There are two possible causes: transfer to charged toner and reduction of highly charged toner.

Therefore, conventionally, with respect to the decrease in the image density in the re-operation after the image forming apparatus is stopped, the image formation is usually repeated until the image density is restored to the normal one.

[0005]

However, the method of waiting for the recovery of the image density by repeating the image formation wastes a lot of toner image transfer paper and wastes the image density recovery time. However, there is a problem that you cannot get a copy or print immediately when you are in a hurry.

Therefore, according to the present invention, even when the electrophotographic image forming apparatus is restarted after being suspended in a high temperature and high humidity environment, an image having a normal image density can be obtained from the initial copy or print. It is an object of the present invention to provide a method capable of preventing a decrease in image density as described above.

[0007]

According to the above-mentioned object, the present invention is a method for preventing a decrease in image density in an electrophotographic image forming apparatus, which is provided between the time when the image forming apparatus is turned on and the time when it is ready to form an image. Characterized in that the toner in the developing device is attached to the electrostatic latent image carrier, the attached toner is collected by a cleaning device, and new toner is replenished to the developing device so as to supplement the consumed toner. An image density reduction preventing method is provided.

The "image formable state" means, for example, a printable state in a printer and a copyable state in a copying machine. More specifically, for example, the warm-up of the fixing device is completed, or the photosensitive drum heater is used. Therefore, it is possible that the photosensitive drum reaches a predetermined temperature. This method consumes the existing toner by repeating copying or printing even if the image density decreases when the image forming apparatus is restarted after being stopped for a long time in a high temperature and high humidity environment. The image density is recovered by the addition of new uncharged toner.

Regarding how to determine the amount of toner adhered to the electrostatic latent image carrier (toner consumption amount) after the power is turned on and before the image forming state is established, the preliminary operation of the image forming apparatus is started and the developing operation is started. After stirring the developer for a certain time in a container, a method for reading the image density detection sample pattern (AIDC pattern) formed on the electrostatic latent image carrier and determining the consumption amount from the degree of decrease in the image density, humidity sensor A method of pre-determining the consumption amount according to the humidity level, a method of pre-determining the consumption amount according to the time from when the image forming apparatus is powered off until the next power is turned on, etc. Conceivable.

It is also conceivable to use two or more of the above three methods together or to always consume a certain amount. Regarding the new toner replenishment amount, a method of replenishing the same amount as the consumption amount, a method of replenishing more than the consumption amount and intentionally increasing the toner concentration, and the like are considered.

[0011]

According to the method of the present invention, if it is predicted that a decrease in image density will occur, or if a decrease in image density is recognized from the AIDC pattern, the apparatus is turned on until the image is ready to be formed. Is preliminarily operated, electric charges are applied to the electrostatic latent image carrier by the charger,
Toner adheres to the carrier from the developing device. The attached toner is collected by the cleaning device.

As the toner is consumed, the toner density in the developing device decreases. Then, new toner is replenished in the developing device so as to compensate for the lowered toner concentration. When the cleaning device is equipped with a means for recycling the collected toner, the collected toner will be reused eventually, so that the image forming apparatus as a whole consumes a large amount of toner, which is a burden to the user. There is no such thing.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of an example of a copying machine to which the method of the present invention is applied. 2, 3 and 4 each show the procedure of an embodiment of the method of the present invention. The copying machine shown in FIG. 1 has a photosensitive drum 1 in the center thereof, and a charging charger 2, an interimage eraser 3, a developing device 4, a transfer charger 5, a separation charger 6, a cleaning device 7, and a main eraser 30 around the photosensitive drum 1. Has been placed. The developing device 4 includes a toner replenishing section 40 for replenishing new toner, and a recycle duct 70 for returning the toner collected by the cleaning device 7 to the toner replenishing section 40.

An image density detecting sensor DS is arranged below the cleaning device 7 for the photosensitive drum 1, and a humidity sensor HS for detecting the humidity inside the developing device 4 is provided in the developing device 4. An optical system 8 is arranged above the photosensitive drum 1. This optical system includes a lamp 81 for irradiating an original image placed on the original placing glass 89 and a reflection mirror 8.
2, 83, 84, 85, 86 and 87 and lens 88. Although not shown in the drawing, the lamp 81 and the mirror 82, and the mirrors 83 and 84 are mounted on different movable frames, respectively, and by moving the frames, the original image on the original placing glass 89 is scanned. can do.

An image density detecting sample pattern (AIDC pattern) 90 is formed in advance on the edge of the original placing glass 89. Reference numeral 89a is a document cover that can be opened and closed.
A timing roller pair 91, an intermediate roller pair 92, and a sheet feeding cassette 93 are sequentially arranged on one side of the transfer charger 5, and a sheet feeding roller 94 faces the cassette 93. A transfer paper conveyance belt 101, a fixing roller pair 102, and a paper discharge tray 103 are sequentially arranged on one side of the separation charger 6.

According to this copying machine, in a normal copying operation, the photosensitive drum 1 is rotationally driven in the counterclockwise direction CCW in the figure, while the charging charger 2 uniformly charges the surface of the drum 1. Image exposure L is performed from the optical system 8 to the charging area to form an electrostatic latent image. Further, after being subjected to inter-image erase by the inter-image eraser 3 as required, the formed electrostatic latent image is developed in the developing device 4 to become a toner image, and this toner image is sent to the transfer area facing the transfer charger 5. On the other hand, from the paper feeding cassette 93 to the paper feeding roller 94
Transfer paper is pulled out one by one by the intermediate roller pair 92.
After passing through the timing roller pair 91, it is sent to the transfer area in synchronism with the toner image on the photosensitive drum 1. Thus, in the transfer area, the toner image on the photosensitive drum 1 is transferred onto the transfer paper by the action of the transfer charger 5, and then the transfer paper is separated from the drum 1 by the separation charger 6 and is transferred to the fixing roller pair 102 by the conveyor belt 101. The toner image is carried, the toner image is fixed there, and then discharged to the paper discharge tray 103.

The residual toner on the photosensitive drum 1 is cleaned and removed by the cleaning device 7, and the residual charge is erased by the main eraser 30. In such a copying machine, the method of the present invention is carried out according to the procedure shown in FIG. That is, after the main switch of the copying machine is turned on (step S1), the copying machine starts preliminary operation. In this preliminary operation, the photosensitive drum 1, the charging charger 2, the developing device 4, etc. are operated, and the image of the AIDC pattern 90 is exposed from the optical system 8 to the charged area of the photosensitive drum 1.

That is, when the main switch of the copying machine is turned on, the developer is immediately stirred in the developing device 4 (step S2), and the electrostatic latent image of the AIDC pattern formed on the photosensitive drum 1 is continuously developed. It is developed by the container 4. When the toner image of this pattern arrives at the image density sensor DS, the density of the pattern is read here (step S3), and it is determined from the image density information whether toner replacement is necessary (step S4). When it is determined that the replacement is not necessary, in other words, when the reduction in the image density is not substantially recognized, the copying is ready immediately (step 8), and the warming-up of the fixing roller pair 102 is waited for to make the desired copying. Start.

However, if the image density is lowered in step S4 and therefore it is judged that the toner needs to be replaced, the replacement amount is calculated according to the lowered image density (step S5), and the replacement amount is determined. Then, (step S6), toner is attached from the developing device 4 to the surface of the photosensitive drum 1 based on the replacement amount, and new toner is replenished to the developing device 4 from the toner replenishing portion 40 so as to supplement the toner consumed by the adhering. Yes (step S7). Thus, the copyable state is set (step S8). After that, copying is started after waiting for the fixing roller pair 102 to warm up.

The toner attached to the photosensitive drum 1 in step S7 is collected by the cleaning device 7 and returned to the toner replenishing section 40 by the recycling duct 70. As described above, one embodiment of the present invention has been described.
The method of the present invention may be carried out by the embodiments shown in FIGS.

In the embodiment shown in FIG. 3, after the main switch of the copying machine is turned on (step S10), the humidity inside the developing device 4 is detected by the humidity sensor HS (step S20). It is determined whether or not the image density is lowered, in other words, it is necessary to replace the toner (step S30), and when the toner replacement is not necessary, the copy ready state is immediately set (step S70). Waiting for the fixing roller pair 102 to warm up, the target copying is started. However, when it is determined that the toner needs to be replaced, the replacement amount is calculated according to the detected humidity (step S40), the replacement amount is determined (step S50), and the developing device 4 detects the exposure amount based on the replacement amount. Toner is attached to the body drum 1, and new toner is replenished from the toner replenishing section 40 to the developing device 4 so as to supplement the toner thus consumed (step S60), and thus the copy ready state is obtained (step S70).

Further, in the embodiment shown in FIG. 4, after the main switch is turned on (step S100), the time from the last power-off to the main switch on is integrated (step S200), and the integrated time indicates that the image density has decreased. It is determined whether or not there is a risk, in other words, whether or not toner replacement is required (step S300). If toner replacement is not required, the copying is ready immediately (step S700). Waiting for the warm-up of the pair 102, the target copying is started. However, when it is determined that the toner needs to be replaced, the replacement amount is calculated based on the accumulated time (step S400),
The replacement amount is determined (step S500), toner is made to adhere from the developing device 4 to the photosensitive drum 1 based on this replacement amount, and the toner replenishing section 40 is transferred to the developing device 4 so as to replenish the toner thus consumed. New toner is replenished (step S600), and the copy is ready (step S700).

In any of the above-described embodiments, it is determined in step S4, S30, S300 whether toner replacement is necessary, calculation of toner replacement amount in steps S5, S40, S400, steps S6, S50,
Toner replacement amount determination in S500, step S
The toner consumption and replenishment in S7, S60, and S600, and the setting of the copyable state in steps S8, S70, and S700 can all be realized by a control unit including a computer (not shown).

Image density information from the image density sensor DS and humidity information from the humidity sensor HS are input to this control unit. Also, toner consumption in order to prevent image density reduction,
When replenishing, the photosensitive drum 1, the charger 2, the developing device 4 and the like may be operated based on an instruction from the controller. FIG. 5 is a graph showing how much toner should be replaced with respect to the drop in the image density of the AIDC pattern in the case of the embodiment shown in FIG. 2, for example, the image density (ID) of the pattern. If Y% falls, it means that X% needs to be replaced.

[0025]

As described above, according to the image density reduction preventing method of the present invention, even when the electrophotographic image forming apparatus is restarted after being suspended in, for example, a high temperature and high humidity environment, an initial copy is performed. Alternatively, it is possible to prevent the image density from being lowered so that the image having a normal image density can be obtained from the print.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of an example of a copying machine to which the method of the present invention is applied.

FIG. 2 is a flowchart showing the procedure of one embodiment of the method of the present invention.

FIG. 3 is a flowchart showing the procedure of another embodiment of the method of the present invention.

FIG. 4 is a flowchart showing a procedure of still another embodiment of the method of the present invention.

5 is a graph showing a required toner replacement amount with respect to an image density drop amount in the case of the embodiment shown in FIG.

[Explanation of symbols]

 1 Photoreceptor Drum 2 Charging Charger 3 Image Eraser 30 Main Eraser 4 Developer 40 Toner Replenisher 5 Transfer Charger 6 Separation Charger 7 Cleaning Device 70 Recycle Duct 8 Optical System 90 AIDC Pattern 91 Timing Roller Pair 92 Intermediate Roller Pair 93 Paper Feed Cassette 94 Paper feed roller 101 Transfer paper transport belt 102 Fixing roller pair 103 Paper ejection tray DS Image density sensor HS Humidity sensor

Claims (1)

[Claims] 1. A method for preventing a decrease in image density in an electrophotographic image forming apparatus, wherein toner in a developing device is converted into an electrostatic latent image after the power of the image forming apparatus is turned on and before an image can be formed. A method for preventing a decrease in image density, which is characterized in that the toner adhered to a carrier is collected by a cleaning device, and new toner is replenished to the developing device so as to supplement the toner consumed thereby.