JP4877683B2 - Electrophotographic equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrophotographic apparatus using a two-component developer, and more particularly to an electrophotographic apparatus using a two-component developer capable of controlling the toner density to an optimum state.
[0002]
[Prior art]
Conventionally, in an electrophotographic apparatus using a two-component developer, when controlling the toner density, a test toner image is created, its reflection density is measured, and the amount of developed toner is calculated. The mainstream method was to replenish the oil and not replenish it when it was not. Image base black on paper transfer is reflection density is 1.4 position, then the reflectivity of a toner image on the image bearing member is small, a low detection accuracy of the reflection density sensor. Therefore, in creating a test toner image, the developing electric field strength is reduced, the toner development amount is reduced, and the detection sensitivity is improved.
[0003]
FIG. 3 is a diagram for explaining an outline of conventional toner density control, in which the horizontal axis represents latent image potential-developing roller potential (hereinafter referred to as development potential), and the vertical axis represents the output value of the reflection density sensor ( Relative value). Curves (A), (B), (C), and (D) show the relationship between the development potential and the sensor output value under the four development conditions. As the development potential increases, the amount of toner adhesion increases, so the output value of the reflection density sensor decreases. Furthermore, as the development potential increases, every curve shows a saturated state. This is because the total amount of toner that can be used at the time of development is determined, and when that amount is reached, the sensor output value also reaches a saturated state.
[0004]
A curve (A) is a standard development condition. When the curve (A) deviates from this curve, the toner supply is mainly turned ON / OFF. For example, the curve (C) is an example in which the gradient of the sensor output value with respect to the development potential becomes gentle as a result of the friction with the carrier being promoted and the toner charge amount being increased because the toner concentration is low. Although the development potential that corresponds to the image base black is P2, the sensor output value at the P2 is a value close to the sensor output value of the curve (A). Therefore, assuming that the development potential is P1, the sensor output values of the curves (C) and (A) are q3 and q1, respectively, and the difference is amplified. When such a difference is detected, toner is supplied, and the curve (C) approaches the curve (A). A curve (B) is an example when the toner density is similarly increased. In this case, the toner is not replenished and is consumed.
[0005]
Although the case where the test toner image is formed on the image carrier has been described above, the object for forming the test toner image is not limited to the image carrier. An image forming apparatus disclosed in Japanese Patent Laid-Open No. 2000-356902 that forms a toner image on a dedicated electrode roller instead of an image carrier is also proposed. The principle is similar to the example described above.
[0006]
[Problems to be solved by the invention]
When controlling the toner density in such a conventional electrophotographic apparatus, there are the following problems. In spite of the fact that the toner concentration is not high, for example, the charge amount of the toner may greatly decrease in the following cases.
(1) When the developer has condensed (2) When left in a high-temperature and high-humidity environment (3) When exposed to a gas that dissolves in water such as ammonia or hydrogen chloride and becomes an acid or alkali Conventional electrophotography Since the apparatus detects the sensor output value at the development potential P1, in the cases (1) to (3), the sensor detects a high toner density as indicated by the curve (B). Consume without replenishing. Over time, the toner density decreases and the toner charge amount also increases, and the sensor output value at the development potential P1 becomes equivalent to the curve (A). However, since the toner density is lower than the target value at that time, the saturation output when the development potential is P2 becomes high as shown by the curve (D). Although the sensor detects a proper output, the image becomes thin.
[0007]
The present invention has been made in view of the above circumstances, and in the electrophotographic apparatus using a two-component developer having a sensor for detecting toner concentration, the detection sensitivity of the sensor is improved as described above. Therefore, an object of the present invention is to provide an electrophotographic apparatus capable of detecting toner density with high sensitivity without causing improper control by reducing the development potential. It is.
[0008]
[Means for Solving the Problems]
The electrophotographic apparatus of the present invention uses a two-component developer, and has an image carrier, a device for forming an electrostatic latent image on the image carrier, and a developing roller that develops the electrostatic latent image. An apparatus, an electrode roller installed in the vicinity of the developing roller, a motor for variably driving the electrode roller, a sensor for measuring the reflection density of the test toner image attached to the electrode roller, and calculating the output of the sensor The test toner image is a solid black image, and the test toner image is developed in an electrophotographic apparatus having an arithmetic device for determining toner replenishment conditions and a toner replenishment device for appropriately replenishing toner in the developer. sometimes to, without changing the rotational speed of the developing roller, a bias voltage is applied as an electric field corresponding to a developing electric field of the previous SL test toner image is generated on the electrode roller, the surface speed of the electrode roller By measuring the reflection density of the test toner image by increasing the sensitivity of the reflection density sensor by making it larger than the surface speed of the image carrier, based on the result calculated by the arithmetic unit using the reflection density, It is characterized by detecting the total amount of toner necessary for development .
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Example 1
Figure 1 is a Ru fragmentary sectional view der for explaining an embodiment of an electrophotographic apparatus according to the invention. The electrophotographic apparatus of Example 1 includes an image carrier 1, a charging device 2 for charging the image carrier 1, an exposure device 3 for forming an electrostatic latent image on the image carrier 1, and developing the electrostatic latent image. A developing device 4, a developing roller 5 in the developing device 4 used for development, a toner replenishing device 6 for replenishing toner, a toner replenishing roller 7 for replenishing toner from the toner replenishing device 6 to the developing device 4, and a developing roller 5 By a developing roller driving motor 8 for driving, a toner replenishing roller driving motor 9 for driving the toner replenishing roller 7, a toner concentration sensor 10 for detecting toner density, a paper feeding device 11 for supplying transfer paper to the transfer region, and a paper feeding device 11 The transfer belt 12 that sandwiches the transfer paper together with the image carrier 1 to convey the fed transfer paper to the transfer area, the transfer belt drive roller 13 that drives the transfer belt 12, and the transfer belt drive roller 3 transcription driven by the belt driven roller 14, a bias roller 15 for transferring the toner to the transfer paper by applying a voltage from the back side of the transfer sheet, the reflection density sensor 16 for detecting the reflection density of the test toner image on the image carrier 1 , A cleaning device 17 that cleans the toner on the image carrier 1, an output value of the reflection density sensor, and a calculation / control device 18 that controls the developing roller drive motor 8 and the toner supply roller drive motor 9. .
[0010]
Hereinafter, the operation of the electrophotographic apparatus shown in FIG. 1 during image formation will be described. The image carrier 1 is uniformly charged by the charging device 2, and then the image carrier 1 is scanned by light from the exposure device 3 to form an electrostatic latent image on the image carrier 1. The electrostatic latent image formed on the image carrier 1 is made into a toner image by being attached with toner by the developing roller 5 of the developing device 4. The transfer paper is fed into the transfer region by the paper feeding device 11, is sandwiched between the image carrier 1 and the transfer belt 12, is applied with a bias voltage by the bias roller 15, and is transferred by the transfer belt driving roller 13 and the transfer belt driven roller 14. The toner image is transferred under the conveying force. The transfer paper onto which the toner image has been transferred leaves the transfer roller 12 and the image carrier 1 and reaches a fixing device (not shown). On the other hand, the image carrier 1 is cleaned by the cleaning device 17, that is, the residual toner is removed, and is uniformly charged again by the charging device 2. The toner replenishing roller 7 is driven by the toner replenishing roller driving motor 9 controlled by the arithmetic / control device 18, and the toner is replenished from the toner replenishing device 6. The developer composed of the replenished toner and carrier is adsorbed by the developing roller 5, and the adsorbed toner is transferred to the image carrier 1 by electrostatic force to form an electrostatic latent image on the image carrier 1.
[0011]
Next, the operation when the toner density of the test toner image is detected by the electrophotographic apparatus shown in FIG. 1 will be described. Image bearing member 1 is uniformly charged by the charging device 2, then, is scanned by the light from the exposure device 3, image phases downy black on the image bearing member 1 in question electrostatic latent image is formed. The electrostatic latent image formed on the image carrier 1 is developed by the developing roller 5 of the developing device 4 to become a test toner image. At this time, since the transfer belt 12 is separated from the image carrier 1 by a mechanism (not shown), the reflection density sensor 16 detects the reflection density of the test toner image. At this time, the calculation / control device 18 controls the developing roller drive motor 8 so that the rotation speed of the developing roller 5 is r times (r <1) that during standard image formation. Thereafter, the test toner image on the image carrier 1 is collected by the cleaning device 17, and the image carrier 1 is uniformly charged again by the charging device 2.
[0012]
When the arithmetic / control device 18 calculates the sensor output value of the reflection density sensor 16 and determines that the toner density is “light”, the arithmetic / control device 18 applies the developer having a low toner density that forms a thin test toner image. In order to replenish the toner, a toner replenishment signal is output to the toner replenishment roller drive motor 9, and the toner replenishment roller 7 replenishes the toner from the toner replenishment device 6.
[0013]
As described above, in order to increase the sensor sensitivity, as a method of reducing the toner adhesion amount, the saturation density that cannot be predicted by the conventional method can be predicted by reducing the rotation speed of the developing roller. Further, in combination with the conventional method, the toner density and the toner charge amount can be detected independently, so that appropriate feedback can be performed.
[0014]
(1) When the developer is condensed , (2) When left in a high-temperature and high-humidity environment , (3) Exposed to ammonia , hydrogen chloride, or other gas that dissolves in water and becomes acid or alkali In this case, only the toner charge amount is decreased although the toner concentration is not high. In such a case, for example, it is preferable to apply the following feedback. That is, the toner density is not changed, and the rotation speed of the developing roller 5 is decreased to suppress the toner adhesion amount. Alternatively, the toner density is lowered (for example, waiting for a natural drop without toner replenishment, or a dummy image is taken and forcibly lowered), and then the saturation density is lowered. Increase the rotation speed to compensate for it.
[0015]
(Example 2)
2, Ru fragmentary sectional view der for explaining the second embodiment of the electrophotographic apparatus according to the present invention. Note that the developer in the apparatus is omitted. In the figure, components having the same functions as those in FIG. 1 are given the same numbers as those in FIG. 1. In addition, 19 is a magnetic pole provided inside the developing roller 5 for conveying the developer, 20 Is an electrode roller for developing a test toner image in place of the image carrier 1, 21 is a reflection density sensor for detecting the reflection density of the toner image on the electrode roller 9, and 22 is a developer regulating member for uniformly leveling the developer. It is. The electrode roller 20 may be a metal roller or a metal surface covered with a medium resistance resin or metal oxide. The length in the axial direction may be short, even about 1 cm, and the degree of freedom in the axial direction is also high. In addition, it is preferable that the image can be installed outside the image area because the image is not affected.
[0016]
The operation when the toner density of the test toner image is detected by the electrophotographic apparatus shown in FIG. 2 will be described below. Since the operation until the electrostatic latent image is formed on the image carrier 1 is the same as that in the first embodiment, the description is omitted. The developer is carried along with the rotation of the developing roller 5 by the magnetic force of the magnetic pole 19 disposed inside the developing roller 5, is regulated by the developer regulating member 22, is uniformly leveled, and contacts the image carrier 1. Then, the electrostatic latent image is developed. Next, the developer develops the electrode roller 20. At this time, a bias voltage that generates an electric field corresponding to a developing electric field for a solid image is applied to the electrode roller 20, and the surface speed of the electrode roller 20 is set higher than the surface speed of the image carrier 1 (implementation). This is the same as the rotation speed of the developing roller 5 made slower than the standard speed in Example 1). Next, the reflection density sensor 21 measures the reflection density of the toner image on the electrode roller 20.
[0017]
The sensor output value thus obtained enables appropriate feedback as in the case of the first embodiment shown in FIG. Using this electrophotographic apparatus, even when the rotational speed of the developing roller is not variable, as precedent, (1) if the developer is condensation, when left in the (2) high temperature and high humidity environment, ( 3) When ammonia is dissolved in water, such as ammonia or hydrogen chloride, and exposed to an acid or alkali gas, the toner charge amount is decreased despite the fact that the toner concentration is not high. Such feedback is preferred. That is, without increasing the toner density (that is, while controlling so as not to be lower than the current toner density), the developing device 4 is idled and the developer is agitated to wait for the toner charge amount to rise. Alternatively, excessive toner adhesion is suppressed by reducing the development potential without lowering the toner concentration.
[0018]
【Effect of the invention】
Te Sutotona image when developed, to be smaller than the standard speed that predetermined rotational speed of the developing roller, the toner adhesion amount is reduced, it is possible to increase the sensor sensitivity. Further, since the saturation density, which could not be predicted in the past, can be predicted, the total amount of toner used for development can be detected. In addition, since the toner concentration and the toner charge amount can be detected independently in combination with the conventional method, appropriate feedback can be performed to make the toner concentration the target value.
[0019]
Based on the computation result, by controlling the developing roller speed during image development, it is possible to make the total amount of toner supplement a change in toner amount to be used for developing a constant.
[0020]
To be greater than the surface speed of the surface velocity of the image bearing member electrodes roller, it is possible to increase the sensor sensitivity, it is possible to detect the amount of toner used in development, for the target value of the toner density Appropriate feedback can be made. Further, when the test toner image is developed and the toner density of the test toner image is detected, the reflection density can be detected without forming the test toner image on the image carrier. The concentration can be detected, and the degree of freedom in detection timing can be increased.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of an essential part for explaining an embodiment of an electrophotographic apparatus according to the present invention.
FIG. 2 is a cross-sectional view of an essential part for explaining another embodiment of the electrophotographic apparatus according to the present invention.
FIG. 3 is a diagram for explaining an outline of conventional toner density control;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Image carrier 2, 2 Charging device, 3 ... Exposure device, 4 ... Developing device, 5 ... Developing roller, 6 ... Toner supplying device, 7 ... Toner supplying roller, 8 ... Developing roller drive motor, 9 ... Toner supplying roller Drive motor, 10 ... toner density sensor, 11 ... paper feeding device, 12 ... transfer belt, 13 ... transfer belt drive roller, 14 ... transfer belt driven roller, 15 ... bias roller, 16 ... reflection density sensor, 17 ... cleaning device, DESCRIPTION OF SYMBOLS 18 ... Calculation / control apparatus, 19 ... Magnetic pole, 20 ... Electrode roller, 21 ... Reflection density sensor, 22 ... Developer control member.

Claims (1)

An image carrier using a two-component developer, a device for forming an electrostatic latent image on the image carrier, a developing device having a developing roller for developing the electrostatic latent image, and the vicinity of the developing roller An electrode roller, a motor for variably driving the electrode roller, a sensor for measuring the reflection density of the test toner image attached to the electrode roller, and calculating the output of the sensor to determine a toner replenishment condition an arithmetic unit, Te electrophotographic apparatus odor and a toner replenishing device for replenishing the appropriate toner in the developer,
Before Symbol test toner image is Ri solid black image Der,
Sometimes develops the previous SL test toner image, without changing the rotational speed of the developing roller,
Applying a bias voltage such that an electric field is generated corresponding to the developing electric field before Symbol test toner image on the electrode roller, the reflection density by the surface speed of the electrode roller is greater than the surface velocity of the image bearing member Increase the sensitivity of the sensor to measure the reflection density of the test toner image ,
Based on the result of the arithmetic unit is calculated by using the reflection density, electrophotographic apparatus and detecting the amount of toner required for development.

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