JP2000352849A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an abnormal image caused by the adhesion of toner and the adhesion of carrier of an image carrier because of the secular change of the electrifying amount of developer. SOLUTION: This device has a two-component developing means 4 developing an electrostatic latent image on the image carrier 1 with two-component developer so as to form a toner image, a transfer means 6 transferring the toner image on the image carrier 1 to transfer material while coming in contact with the image carrier 1 with specified pressing force, and a sensor 12 detecting the rate of the toner and the carrier of the two-component developer in the two-component developing means 4. Then, it is provided with a time zone to add a transfer voltage value or a transfer current value in a non-image area to a default value in accordance with the output value of the sensor 12.

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 such as a copying machine, a facsimile, and a printer.

[0002]

2. Description of the Related Art In recent market conditions of image forming apparatuses such as copiers, facsimile machines and printers, miniaturization and cost reduction are required. Accordingly, in the image forming apparatus, a contact / separation mechanism for contacting / separating the photoconductor as an image carrier and the contact transfer unit in the machine main body cannot be provided in terms of space and cost. In many cases, the photosensitive member is always brought into contact with the photosensitive member. In general, in a two-component developing system, a magnetic detection sensor (hereinafter, referred to as a T sensor) that detects the ratio of toner and carrier (toner concentration) of a two-component developer in a two-component developing system is used as the toner density detecting sensor. I have. However, this T sensor has poor followability with respect to a change in the amount of charge of the developer, causing erroneous detection of the ratio of the toner and the carrier, and sometimes causes problems such as background contamination and a decrease in image density.

Along with this, recently, a toner density detection method of optically detecting the density of a toner pattern image formed on an image carrier by a density sensor called a P sensor has been performed. As is generally known, P
In order to detect the density of a toner pattern image by a sensor, a toner pattern image must be created. Therefore, in the case of the type in which the contact transfer unit is always in contact with the image carrier as described above, the toner pattern image adheres to the contact transfer unit, and in this state, the transfer material is in contact with the contact transfer unit and the image carrier. When the paper passes through the gap, toner stains are generated on the back surface of the transfer material.

Therefore, when the toner pattern image comes into contact with the contact transfer means, a bias having the same polarity as that of the toner is applied to the contact transfer means to reduce the amount of toner electrically attached to the contact transfer means, and Transfer cleaning for returning toner adhered to the contact transfer means to the image carrier by continuously applying a bias having the same polarity as the toner to the contact transfer means even after the toner pattern image passes between the contact transfer means and the image carrier. There is a method.

In general, as described in JP-A-3-69998b, a bias is applied to a transfer member and toner on the applied member is adhered to a photoreceptor (same as the developing principle). Cleaning the transfer member. However, the method of controlling the toner concentration using only the P sensor as the sensor is somewhat unreasonable in view of the contamination of the contact transfer unit and the time required to clean the transfer member as described above.

Therefore, in an image forming apparatus including a normal electrophotographic apparatus, toner concentration control is performed using both a T sensor and a P sensor. That is, the output value of the T sensor is compared with a predetermined control reference value, and the result is compared with the value in the developing device.
The toner is replenished so that the toner concentration of the component developer is kept constant, a toner pattern image is formed on the image carrier at predetermined time intervals or every time a predetermined number of images are formed, and the density of the toner pattern image is measured by a P sensor. Detected and corrected by changing the control reference value according to the detection result, and also predetermine a control reference value corresponding to the upper and lower limits of the toner density. The control is performed so that the control reference value is not shifted out of the range of the control reference value corresponding to the upper and lower limits of the toner density even if it deviates. By employing this technique, an electrophotographic apparatus capable of obtaining a stable image density without any trouble can be realized (see Japanese Patent Application Laid-Open No. 2-3877b).

[0007]

FIG. 2 shows timings of a charging voltage and a developing bias in an image forming apparatus including an electrophotographic apparatus. The charging voltage of the photoconductor and the developing bias of the developing device rise to the target potential just before the image area on the photoconductor as the image carrier, and the charging voltage of the photoconductor and the developing bias of the developing device are turned off after the image area is completed. Fall. Needless to say, it is ideal to design the timing of the rise and fall of the charging voltage and the developing bias so that the toner or carrier does not adhere to the photoconductor.

However, in the two-component developing system in which the toner is charged by friction between the toner and the carrier to perform development, the developer concentration depends on the toner concentration in the developer, the temperature and humidity of the environment around the machine, the use conditions of the developer, and the like. The charge amount changes over time. Therefore, even if the timing of the rise and fall of the charging voltage and the developing bias is designed so that the toner and the carrier do not adhere to the photoconductor at the initial stage, for example, the charge amount of the developer is increased. Sometimes, a positively charged carrier easily adheres to the photoreceptor. Conversely, when the charge amount of the developer is low, the negatively charged toner tends to adhere to the photoconductor.

If the positively charged carrier adheres to the photoreceptor, the toner adhered to the photoreceptor adheres to a transfer member as a contact transfer means, and is transferred at the next transfer of the toner image to a transfer material. This causes a defect and causes an abnormal image such as a white spot. Further, when the negatively charged toner adheres to the photoconductor, the toner on the photoconductor directly adheres to the transfer member. There is a problem that an abnormal image such as the above is generated.

In particular, when a foamed sponge roller is used as a transfer member as a contact transfer means, the surface of the foamed sponge roller has irregularities. It adheres to the contact surface with the material. In other words, the foamed sponge roller has a roller diameter different from that of the part in contact with the photoconductor and the other part because it is in pressure contact with the photoconductor,
At the portion in contact with the photoreceptor, there is a problem in that the shape of the concave portion changes and the toner is discharged, and the toner adheres to the back surface of the transfer material to cause toner contamination.

Since the timing and the falling speed of the charging voltage and the developing bias are generally harder to design than the rising timing and the rising speed of the charging voltage and the developing bias, the charging voltage The above problem is likely to occur when the developing bias is started.

The present invention is directed to an image and a transfer material having an abnormal image such as a white spot due to transfer failure due to a change over time in the charge amount of the developer due to the toner concentration in the developer, the temperature and humidity of the environment around the machine, and the use conditions of the developer. It is an object of the present invention to provide an image forming apparatus capable of preventing occurrence of an abnormal image such as back stain.

[0013]

Means for Solving the Problems To achieve the above object, the invention according to claim 1 comprises an image carrier, an electrostatic latent image forming means for forming an electrostatic latent image on the image carrier, and Two-component developing means for developing the electrostatic latent image on the image carrier with a two-component developer to form a toner image, and a toner image on the image carrier while contacting the image carrier with a predetermined pressing force And a sensor for detecting the ratio of the toner and the carrier of the two-component developer in the two-component developer, and the output value of this sensor is compared with the toner of the two-component developer. In the image forming apparatus used for controlling the ratio of the carrier, a time zone is provided in which a transfer voltage value or a transfer current value in a non-image area is added to a default value in accordance with an output value of the sensor.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, a time for subtracting a transfer voltage value or a transfer current value in a non-image area from a default value in accordance with an output value of the sensor. A band is provided.

According to a third aspect of the present invention, in the image forming apparatus of the first or second aspect, a value for adding or subtracting a transfer voltage value or a transfer current value from a default value is changed.

[0016]

FIG. 1 schematically shows an embodiment of the present invention. This embodiment is an embodiment of the invention according to claims 1 and 2, and is an example of an image forming apparatus including an electrophotographic apparatus. As the photoconductor 1 as an image carrier, for example, a drum-shaped photoconductor is used, and the photoconductor 1 is driven to rotate in a direction indicated by an arrow by a driving unit (not shown). The photoreceptor 1 is uniformly charged by a charger 2 and is exposed to exposure light 3 modulated with image information by a writing device as an exposure unit, thereby forming an electrostatic latent image corresponding to the image information. . Here, the charger 2 is, for example, a contact charger composed of a charging roller, and the charger 2 and the writing device constitute an electrostatic latent image forming unit that forms an electrostatic latent image on the photoconductor 1.

The electrostatic latent image on the photosensitive member 1 is turned into a visible toner image by a developing device 4 as a developing means. Further, transfer paper as a transfer material is fed from a paper feeding device (not shown) to the registration rollers 5.
The registration roller 5 feeds the transfer sheet with the leading end of the transfer sheet aligned with the electrostatic latent image on the photoconductor 1. The transfer paper sent from the registration roller 5 transfers the toner image on the photoreceptor 1 by a transfer unit 6 as a transfer unit.
As a result, the toner image is fixed by a fixing device (not shown) and discharged to the outside.

Here, the transfer unit 6 uses a contact transfer unit using a transfer roller formed of a foamed sponge, for example, ruby cell of Toyo Polymer, etc., and presses the photosensitive member 1 with a predetermined pressure by a pressing unit (not shown). Contact by pressure. Further, the photoreceptor 1 from which the transfer paper has been separated is cleaned by a cleaning device having a blade 8 to scrape off the untransferred toner, and the charge is erased by a discharging lamp (not shown), and then the charging device 2 is rotated.

The developing device 4 has a developing roller 9 as a developer carrier rotatably driven by a driving unit (not shown) and stirring members 10 and 11, and the two-component developer contained therein is stirred by the stirring member 10 , 11 to supply the toner to the developing roller 9. The developing roller 9 is applied with a developing bias from a developing bias power source, carries and transports the two-component developer, and develops the electrostatic latent image on the photoconductor 1 with the two-component developer.

The developing device 4 is supplied with toner from a toner supply unit (not shown) as a toner supply unit.
The toner concentration detecting means 12 including a magnetic detection sensor (T sensor) detects the ratio (toner concentration) of the toner and the carrier of the two-component developer in the developing device 4. Further, a toner pattern image is created on the photoconductor 1 at a predetermined timing,
The density of the toner pattern image is detected by a density sensor 18 called a P sensor.

FIG. 2 shows the timing of charging and developing in this embodiment, and FIG. 3 shows the timing of transfer in this embodiment. The charging voltage and developing bias of the photoconductor 1
Immediately before the upper image portion, the target potential (charging voltage is -900 V,
The developing bias rises to -600 V) and the photosensitive member 1
After the upper image section ends, it turns off and falls. The rise and fall timings of the charging voltage and the developing bias are designed so that toner and carrier do not adhere to the photoconductor 1 as much as possible.

For example, when the charging voltage and the developing bias rise and fall, the charging voltage is always lower than the developing bias by about 200 V to 300 V, so that the carrier adhesion to the photosensitive member 1 and the Try to prevent toner adhesion. The value of 200 V to 300 V differs depending on the type of the carrier, and is substantially determined by the type of the developer.

However, in the two-component developing system in which the toner is charged by friction between the toner and the carrier to perform the development, the charge amount of the developer changes with time due to the temperature and humidity of the peripheral environment of the machine, the use condition of the developer, and the like. I will. Therefore, for example, when the charge amount of the developer has been increased, the positively charged carrier is applied to the photosensitive member 1 from the developing roller 9 as the developer carrier, the voltage of which is lower than the developing roller 9 by about 200 V to 300 V. And the toner is likely to adhere to the photoconductor 1. On the other hand, when the charge amount of the developer is low, the negatively charged toner tends to adhere to the photoconductor 1.

FIG. 4 shows the correlation between the Q / M representing the charge amount per unit weight of the developer and the output value of the T sensor 12. Generally, when the toner concentration is constant, T / M
The output value of the sensor 12 tends to be lower, and conversely, Q /
As M decreases, the output value of T sensor 12 tends to increase. That is, by detecting the output value of the T sensor 12 for each image formation, it is possible to sequentially detect whether the T / M of the developer at that time is high or low. In other words, at the time of the rise and fall of the charging voltage and the developing bias before and after the image area, whether the carrier easily adheres to the photoconductor 1 or the toner easily adheres to the photoconductor 1 Can be detected sequentially.

FIG. 5 shows a circuit section of this embodiment. The CPU 13 as control means takes in the output value of the T sensor 12 and outputs the toner replenishment unit 14, the transfer high-voltage power supply 15,
The charging high-voltage power supply 16 is controlled. In this case, the CPU 13
Compares the output value of the T sensor 12 with the control reference value, and controls the toner replenishing unit 14 so that the ratio of toner and carrier (toner density) of the developer in the developing device 4 becomes constant based on the result.

A toner pattern image is formed on the photoreceptor 1 at predetermined time intervals or every time a predetermined number of images are formed.
The density of the toner pattern image is detected by the P sensor 18. The CPU 13 changes and corrects the control reference value according to the output value result of the P sensor 18 and determines a control reference value corresponding to the upper and lower limits of the toner density in advance. Control is performed so that the control reference value is not shifted out of the range of the control reference value corresponding to the upper and lower limits of the toner density even if the value deviates from the target value. The transfer high-voltage power supply 15 applies a high voltage to the transfer device 6, and the charging high-voltage power supply 1
6 applies a high voltage to the charger 2. Also, the CPU 13
Developing device (developing unit) 4, writing device (writing system) 1
7 is controlled.

The CPU 13 determines the output value V of the T sensor 12
It is determined whether or not t 'is lower than an appropriate value (default value) Vt in which neither carrier adhesion nor toner adhesion of the photoconductor 1 is likely to occur, and the output value Vt' of the T sensor 12 is adjusted to an appropriate value (default value). ) When the shift is lower than Vt, the transfer high-voltage power supply 15 is controlled so that the transfer current or the transfer voltage before and after the image portion becomes higher than the default value. As a result, it is possible to prevent the carrier from adhering to the photoconductor 1 when the charging voltage and the developing bias rise and fall before and after the image area. FIG. 7 shows, in the present embodiment, the case where the transfer current or the transfer voltage is controlled to be higher than the default value indicated by the solid line in the non-image portion fall section that falls from the image section to the non-image section. .

Further, the CPU 13 determines whether or not the output value Vt 'of the T sensor 12 is higher than an appropriate value (default value) Vt in which the toner adheres to the photosensitive member 1 and the toner does not easily adhere. Output value Vt ′ of sensor 12
Is higher than an appropriate value (default value) Vt, the transfer high-voltage power supply 15 is controlled so that the transfer current or the transfer voltage before and after the image portion becomes lower than the default value. Thus, the photosensitive member 1 at the time of rising and falling of the charging voltage and the developing bias before and after the image area is formed.
Can be prevented from adhering to the toner.

According to this embodiment, the image carrier 1, the charger 2 as an electrostatic latent image forming means for forming an electrostatic latent image on the image carrier 1 and the writing system 17, A two-component developing means 4 for developing an electrostatic latent image on the body 1 with a two-component developer to form a toner image, and a toner on the image carrier 1 while contacting the image carrier 1 with a predetermined pressing force It has a transfer means 6 for transferring an image to a transfer material, and a sensor 12 for detecting the ratio of the toner and the carrier of the two-component developer in the two-component developing means 4. In the image forming apparatus used for controlling the ratio of the toner and the carrier of the developer, a time period is provided in which a transfer voltage value or a transfer current value in a non-image area is added to a default value according to an output value of the sensor 12. Therefore, the toner concentration in the developer Border of temperature and humidity, that the abnormal image white spots due transfer defective carrier adhesion of the image bearing member is generated by the temporal change of the charge amount of the developer by use conditions of the developer is generated can be prevented.

According to this embodiment, a time period is provided in which the transfer voltage value or the transfer current value in the non-image area is subtracted from the default value in accordance with the output value of the sensor 12. Temporal changes in the charge amount of the developer due to the toner concentration in the medium, the temperature and humidity of the surrounding environment of the machine, the use conditions of the developer, etc., cause toner adhesion to the image carrier, causing abnormal images such as back contamination of the transfer material. Can be prevented.

Another embodiment of the present invention is an embodiment according to the third aspect of the present invention. In this embodiment, in the above embodiment, when the CPU 13 controls the transfer current or the transfer voltage before and after the image portion to be higher or lower than the default value, the CPU 13 determines the output value Vt ′ of the T sensor 12 and the default value Vt. The difference (Vt−Vt ′ = Z) is calculated, and the value of the transfer current or the transfer voltage to be controlled to be higher or lower before and after the image portion corresponding to the difference Z is determined using, for example, a table as shown in FIG. I do.

This table is a matrix for increasing the control width of the transfer current or the transfer voltage when Z is large. When the CPU 13 controls the value of the transfer current or the transfer voltage by using such a matrix, it is possible to add or subtract the transfer current or the transfer voltage value before and after the image portion without excess or deficiency. At the time of rise and fall of the voltage / developing bias, there is an effect that defects of carrier adhesion and toner adhesion of the photoconductor 1 are more unlikely to occur. At this time, the values of x and α in the matrix may be fixed values or variable values. Further, since the present invention does not limit the form of the matrix, another matrix may be formed.

As described above, according to the present embodiment, the value of adding or subtracting the transfer voltage value or the transfer current value from the default value is changed. This has the effect of making it less likely to occur. In this embodiment and the above embodiment,
The time for adding or subtracting the transfer voltage value or the transfer current value from the default value may be fixed, or may be made variable according to the rise / fall performance of the charging high-voltage power supply 16 and the transfer high-voltage power supply 15. No problem.

[0034]

As described above, according to the first aspect of the present invention, the charge amount of the developer depending on the toner concentration in the developer, the temperature and humidity of the peripheral environment of the machine, the use condition of the developer, and the like. It is possible to prevent the occurrence of abnormal images such as white spots due to transfer failure due to carrier adhesion of the image carrier due to the aging change.

According to the second aspect of the present invention, with the above-described structure, the image bearing is carried out by the change of the charge amount of the developer with time due to the toner concentration in the developer, the temperature and humidity of the peripheral environment of the machine, the use condition of the developer, and the like. It is possible to prevent the occurrence of an abnormal image such as a back stain on the transfer material due to the adhesion of the toner to the body.

According to the third aspect of the present invention, with the above-described configuration, there is an effect that the problem of carrier adhesion and toner adhesion of the image carrier is more unlikely to occur.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing one embodiment of the present invention.

FIG. 2 is a timing chart showing timings of a charging voltage and a developing bias in the electrophotographic apparatus.

FIG. 3 is a timing chart showing transfer timing of the embodiment.

FIG. 4 is a diagram showing a correlation between Q / M representing a charge amount per unit weight of a developer and an output value of a T sensor in the embodiment.

FIG. 5 is a block diagram showing a circuit unit of the embodiment.

FIG. 6 is a diagram showing a table used in another embodiment of the present invention.

FIG. 7 is a diagram indicated by a dotted line in the case where the transfer current or the transfer voltage is controlled to be higher than a default value in the non-image portion falling section in the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Charging device 4 Developing device 6 Transfer device 12 T sensor 13 CPU 14 Toner supply unit 15 High voltage power supply for transfer 16 High voltage power supply for charging

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masaru Tanaka 1-3-6 Nakamagome, Ota-ku, Tokyo, Ricoh Co., Ltd. (72) Inventor Jiji Mizuishi 1-3-6 Nakamagome, Ota-ku, Tokyo・ Ricoh Co., Ltd. (72) Inventor Kenzo Tatsumi 1-3-6 Nakamagome, Ota-ku, Tokyo ・ Ricoh Co., Ltd. (72) Toshitaka Yamaguchi 1-3-6 Nakamagome, Ota-ku, Tokyo ・ Stock Inside the Ricoh Company (72) Inventor Ken Amamiya 1-3-6 Nakamagome, Ota-ku, Tokyo, Inc. Inside the Ricoh Company (72) Inventor Hiroshi Mizusawa 1-3-6, Nakamagome, Ota-ku, Tokyo Ricoh Inc. (72) Inventor Mayumi Ohori 1-3-6 Nakamagome, Ota-ku, Tokyo F-term in Ricoh Co., Ltd. (reference) 2H027 DD07 EA03 EA06 EC06 EC09 ED24 EE02 FC08 2H032 AA05 BA 03 CA02 CA15 2H077 AD06 AE06 DA10 DA42 DA54 DB02 DB15 EA01

Claims (3)

[Claims] 1. An image carrier, an electrostatic latent image forming means for forming an electrostatic latent image on the image carrier, and developing the electrostatic latent image on the image carrier with a two-component developer. Two-component developing means for forming a toner image; transfer means for transferring the toner image on the image carrier to a transfer material while contacting the image carrier with a predetermined pressing force; An image forming apparatus having a sensor for detecting the ratio of the toner and the carrier of the component developer, and using the output value of the sensor to control the ratio of the toner and the carrier of the two-component developer, according to the output value of the sensor A time zone in which a transfer voltage value or a transfer current value in a non-image area is added to a default value. 2. The image forming apparatus according to claim 1, wherein a time period is provided for subtracting a transfer voltage value or a transfer current value in a non-image area from a default value in accordance with an output value of the sensor. Characteristic image forming apparatus. 3. The image forming apparatus according to claim 1, wherein a value for adding or subtracting a transfer voltage value or a transfer current value from a default value is changed.