JPH1010856A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent image-quality deterioration by keeping an amount of toner which is attached to a printing medium at a preset value and making an amount of toner attached onto the printing medium according to switch between the printing mediums (paper and OHP sheet) proper. SOLUTION: The amount of attached toner is detected by an attached-toner quantitative sensor on an intermediate transfer drum 9 and the number of the rotations of a developing roll is controlled based on the result of comparison between the information and the preset information in a CPU. A printing- medium detection sensor 16 capable of identifying the material of the printing mediums 13 is arranged on the stack of printing mediums 13 stored in a sheet feed cassette 15, the output of the sensor is captured into the CPU, and the number of the rotations of the developing roller of each of the developing units 5-8 is controlled based on the information.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using a non-magnetic one-component developer.

[0002]

2. Description of the Related Art In a developing device using a granular developer, the amount of the developer adsorbed and charged on the surface of a developing roll changes due to a change in diameter or an environment due to a change in the fluidity of the developer in the developing device. And the image density fluctuates. JP-A-5-204236
In this publication, the amount of toner adhering to the photosensitive belt is detected by a sensor, and the rotation speed of the developing roller and the conveying roller is changed based on the information, and the peripheral speed ratio between the photosensitive belt and the developing roller and the ratio between the developing roller and the conveying roller are changed. The peripheral speed ratio is kept constant to control the amount of toner adhered on the photosensitive belt. In order to stabilize the image quality due to the difference between print media (paper and OHP sheet), the user operates a key on the front panel of the apparatus to rotate a transfer voltage table or rotate a fixing roller of a fixing unit. The speed table is selected and optimized to stabilize the image quality.

[0003]

SUMMARY OF THE INVENTION The above-mentioned prior art is
Although effective for controlling the density of a developing device using a two-component developer, it is not effective for controlling the density of a developing device using a one-component developer. Another object of the present invention is to provide an image forming apparatus which constantly prints high-quality images stably without the user being conscious of the printing medium.

[0004]

According to the present invention, a change in print density caused by an environmental change or a change with time is detected by a toner adhesion amount sensor on an intermediate transfer drum to detect a toner adhesion amount.
Based on the result, the number of rotations of the developing roll is controlled, or the transfer voltage between the photosensitive drum and the transfer drum is controlled to keep the print density constant. A print medium discrimination sensor capable of discriminating the type of the uppermost print medium stacked and housed in the sheet cassette is installed at the top end of the sheet cassette and the OHP is provided.
The sheet and plain paper are distinguished from each other, and the number of rotations of the developing roller is controlled based on the signal to automatically set the image density according to the type of print medium.

According to the image forming apparatus, the toner adhesion amount on the intermediate transfer drum is detected by the toner adhesion amount sensor, the sensor output is taken into the CPU, and the CPU is developed so that the toner adhesion amount is always constant. Controls the number of rotations of the roller. Also, when the print medium is paper or OHP sheet,
The print medium discriminating sensor discriminates with the CPU, and based on the result, the developing roller rotational speed is controlled by a preset developing roller rotational speed table.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A practical example of the present invention will be described below with reference to FIG. FIG. 1 is an overall explanatory view showing an embodiment of the present invention. Exposure device 1 for optically converting image information
Belt 3 that forms an electrostatic latent image by receiving the laser beam 2 from the printer, a charger 4 that performs charging processing on the surface of the photosensitive belt 3 prior to the exposure processing, and removes the charged potential of a non-image portion on the photosensitive belt 3. A plurality of developing devices 5 for attaching toner 14 to the eraser 21 and the electrostatic latent image formed on the photosensitive belt 3;
6, 7, 8 and an intermediate transfer drum 9 for transferring the toner 14 as needed, a toner adhesion amount sensor 10 arranged near the intermediate transfer drum 9, and an output of the sensor 10 are taken into a CPU 11, and the information and a preset toner The number of rotations of the developing rollers 25 of the developing units 5, 6, 7, and 8 is controlled via the developing unit driving device 12 based on the amount of adhesion. The toner 14 on the intermediate transfer drum 9 is transferred to the transported printing medium 13.
A print medium detection sensor 16 capable of identifying the material of the print medium 13 is disposed above the print medium 13 stacked and housed in the stack 5, and the output of the sensor 16 is taken into the CPU 11, and the information and print medium information set in advance are obtained. Based on the developing device 5,
The number of rotations of the developing rollers 16, 7, and 8 is controlled via the developing device driving device 12. The sheets are taken out one by one from the paper feed cassette 15 by the feed roller 17 and the separation pad 18, guided to the registration roller pair 20 through the paper guide guide 22, and transferred by the roller pair 22 to the transfer unit 2.
3 to be sent. A separation charger 24 for separating the print medium 13 after the transfer processing from the intermediate transfer drum 9, a cleaning unit 19 for removing the residual toner 14 on the intermediate transfer drum 9 after the transfer processing, and a fixing processing on the toner 14 on the print medium 13 And a fixing device 22 that performs the following.

Next, a description will be given of the operation of the image forming apparatus of the present invention in which the amount of adhered toner is adjusted and developed, and the print medium 13 is automatically determined to produce a stable print image.
The surface of the photosensitive belt 3 is uniformly charged by the charger 4 and is exposed by the exposure device 1 to form a toner adhesion amount detection pattern. When the photosensitive belt 3 rotates and the electrostatic latent image reaches the developing point, the thin toner layer formed on the surface of the developing roll 16 moves to the electrostatic latent image. At this time, the rotation speed of the developing roll 16 is rotating at a preset rotation speed. Photosensitive belt 3
The upper toner 14 is transferred to the intermediate transfer drum 9, the amount of the toner 14 is detected by the toner adhesion sensor 14, and the output of the sensor 10 is input to the CPU 11.
If the output of the sensor 10 is larger than the preset toner adhesion amount, the CPU 11 lowers the difference by the number of rotations of the developing roller 16, and if not, increases the number of rotations of the developing roller 25 to increase the toner of the intermediate transfer drum 9. The adhesion amount is maintained at a preset toner adhesion amount. On the other hand, a print medium detection sensor 16 that can identify the material of the print medium 13 is provided above the print medium 13 stacked and stored in the paper feed cassette 15 so that
3 and the OHP sheet 13 are determined by providing a threshold voltage according to the characteristics shown in FIG. The number of rotations of the developing roller 16 of the developing devices 5, 6, 7, and 8 is controlled via the developing device driving device 12 based on the print medium information thus obtained. For example, if the print medium 13 is O
In the case of the HP sheet, since the color transparency is poor unless the amount of adhered toner is increased as compared with paper, the rotation speed of the developing roller 25 of the developing units 5, 6, 7, and 8 is increased via the developing unit driving device 12. Then, the amount of toner adhered to the OHP sheet is increased to increase the transparency. Then, development is performed on the electrostatic latent image for each of the plurality of developing devices 5, 6, 7, and 8, transfer to the intermediate transfer drum 9 is performed a plurality of times each time, and thereafter, the transfer roller 17 is separated from the paper feed cassette 15 and the delivery roller 17 The sheets are taken out one by one by a pad 18 and passed through a paper guide 22 to a pair of registration rollers 20.
And is sent to the transfer unit 23 by the roller pair 22 and is transferred to the print medium. Further, the print medium 13 after the transfer processing is separated by a separation charger 24 separating from the intermediate transfer drum 9 and fixed through a paper guide 22 to a fixing device 22 for performing a fixing processing.

[0008]

According to the present invention, in order to maintain a predetermined amount of toner adhesion, a toner adhesion amount sensor near the circumference of the intermediate transfer drum detects a toner adhesion amount and controls the number of rotations of the developing roller based on the information. Can be realized automatically, even if the user does not recognize the type of print medium,
It is possible to optimize the amount of toner adhered on the print medium, always maintain the image density at a predetermined value, suppress fogging and toner scattering, and extend the toner consumption life of the developing device.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a main part of a laser printer.

FIG. 2 is a block diagram of a control device.

FIG. 3 is a characteristic diagram of a print medium detection sensor output.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Exposure apparatus, 2 ... Laser beam, 3 ... Photosensitive belt, 5,
6, 7, 8: developing device, 9: intermediate transfer drum, 10: toner adhesion amount sensor, 11: CPU, 12: developing device driving device, 13: printing medium, 14: toner, 15: paper feed cassette, 16 ... Print medium detection sensor, 25: developing roller.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Shoji Shokai 1-1-1 Higashitaga-cho, Hitachi City, Ibaraki Pref.

Claims (4)

[Claims] A developing roller is provided opposite to a surface of a photosensitive belt, and one component charged and adsorbed on the surface of a developing roll is determined by a difference between a peripheral speed of a surface of the developing roller and a peripheral speed of a surface of the photosensitive belt. In a one-component developing device for attaching a developer to an electrostatic latent image on the photosensitive belt and an apparatus for transferring a toner image visualized by the developing device to an intermediate transfer member, a toner attachment amount on the intermediate transfer member is detected. An image forming apparatus in which a toner adhesion amount sensor is disposed as close to the intermediate transfer member as possible, and the number of rotations of the developing roller is controlled based on a signal from the toner adhesion amount sensor. 2. An image forming apparatus in which an electrostatic latent image on a photosensitive member is visualized by a toner layer frictionally charged by a regulating blade of a developing roller. A print medium discrimination sensor that can discriminate the type is installed at the top
An image forming apparatus wherein a P sheet and plain paper are distinguished from each other, and the number of rotations of a developing roller is controlled based on the signal. 3. An image forming apparatus according to claim 1, wherein an output of the print medium discrimination sensor is taken into a CPU, and the development roller is rotated based on an output of the print medium discrimination sensor according to a development roller rotation speed table created in advance. 4. The image forming apparatus according to claim 1, wherein when the printing medium is an OHP sheet, the number of rotations of the developing roller is equal to or more than that when the printing medium is paper.