JPH0578837B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a toner concentration detection device, and more particularly to a device for detecting the toner concentration in a two-component developer in which carrier and toner are electrostatically adsorbed.

(Prior Art) In order to obtain stable image quality in a two-component developer, it is necessary to stabilize the toner concentration in the developer. That is, the toner particles in the developer are
The electrostatic latent image formed on the photoreceptor adheres to the image area and is consumed by the electrostatic force. Therefore, the amount of toner contained in the developer is consumed and gradually reduced each time copying is performed, and the toner concentration in the developer decreases. Therefore, it is necessary to stabilize the image quality by appropriately replenishing toner and maintaining the optimum toner density.

Against this background, techniques have been proposed that attempt to control the toner concentration and toner charge amount by utilizing various characteristics of the developer. Special Public Service 1986
In Japanese Patent No. 18062, changes in toner concentration are detected by utilizing the change in inductance of the coil when a carrier passes near the detection coil. In Japanese Patent Publication No. 58-49867, fluctuations in toner concentration are detected by an electrical resistance method, taking advantage of the fact that when the toner concentration is low, the current is large, that is, the resistance is small. In Japanese Utility Model Publication No. 57-22182, fluctuations in the amount of toner are detected by mechanically detecting a decrease in the surface level of the developer.

(Problems to be Solved by the Invention) However, none of the above-mentioned conventional techniques is fully satisfactory, and in some cases there are problems in that the configuration is complicated and reliability is low.

Furthermore, for example, in Japanese Patent Application Laid-open No. 53-92138,
A toner density control device has been disclosed that collects developer returned from a development position in a funnel-shaped sensor, detects a voltage generated in a capacitor due to the charge in the sensor, and controls the toner density accordingly.
However, in this prior art, not all of the developer returned from the development position is collected in the funnel-shaped sensor, but only a portion of it is collected in a sampling manner. Therefore, it cannot be said that the detected toner concentration necessarily accurately reflects the overall toner concentration, and the reliability is still insufficient.

Therefore, a main object of the present invention is to provide a toner concentration detection device that has a simple configuration and is highly reliable.

(Means for Solving the Problems) Simply put, this invention arranges a mesh conductor in the developing chamber so that all the developer returned from the developing position can pass therethrough. This toner concentration detection device is grounded and detects toner concentration based on the amount of charge flowing into the mesh conductor when the developer returned from the development position passes through the mesh conductor.

(Operation) All the developer returned from the development position comes into contact with the mesh conductor. Therefore, the charge on the developer flows to ground through this mesh conductor. When the amount of toner is large, the charge becomes small, and conversely, when the toner concentration is low, the amount of charge becomes large. Therefore, the amount of charge flowing into the mesh conductor is closely correlated with the toner concentration, and therefore, the toner concentration in the developer is detected by detecting the amount of charge flowing into the mesh conductor.

(Effects of the Invention) According to the present invention, since the amount of charge of the developer during development is directly detected using a mesh conductor, there is no correlation with the actual developing method as in the blow-off method. It is more reliable than other methods. Furthermore, since all the developer returned from the development position passes through the mesh conductor, the average amount of toner charge in the developer can be detected. 53−92138
Compared to the method that detects toner concentration by sampling as disclosed in the issue, there is less error.
Even more reliable.

Furthermore, in this invention, since the mesh conductor is grounded, the charge on the carrier of the developer returned from the development position is discharged to the ground, weakening the adhesion between the carrier and the toner, and releasing both. Ru. In other words, according to the present invention, all the carrier charges of the developer returned from the development position are neutralized, so that it is possible to prevent the influence of changes in the developer over time and environmental conditions on the developer. In other words, even if the developer is used repeatedly, the carrier will not be covered with toner, preventing the developer from becoming fatigued or spent, extending the life of the developer, and providing stable copy image quality over a long period of time. . Furthermore, the influence of environmental conditions such as temperature and humidity on developer characteristics can be alleviated.

The above objects, other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.

(Example) Generally, when the toner concentration in the developer increases, the copy density increases, but a phenomenon called "fogging" occurs in which toner adheres to areas that should be white in the copy image, resulting in a decrease in copy image quality. do. On the other hand, when the toner density is low, the entire image becomes thinner, and fine details and solid black areas cannot be faithfully reproduced.Furthermore, the phenomenon of "fogging" is observed, just as when the toner density is high. As described above, in the development process of an electronic copying machine, the amount of toner carried to the photoreceptor by the carrier is largely influenced by the toner concentration.

If the toner concentration is relatively high, the carrier particles will be covered with a large amount of toner. the result,
The individual toners have less chance of frictional contact with the carrier and are not as strongly charged. As a result, a large amount of toner moves to the photoreceptor during development, but the charge density of the moved and adhered toner is small. Therefore, although the copy density is high, the electrostatic attraction between the toner and the carrier is too low.
During mixing, agitation, and transportation of developer, toner may scatter inside the machine or adhere to non-image areas of the latent image surface, causing "fogging."

Conversely, when the toner concentration is relatively low, there is a high chance that the carrier will charge the toner.
As a result, the amount of charge that the toner obtains increases, the quality of the copied image is poor, and a phenomenon of insufficient toner density is observed. This is because if the amount of charge held by the toner is large, the electrostatic attractive force between the toner and the carrier becomes too large, making it difficult for the toner to transfer toward the electrostatic latent image. That is, since the amount of toner per unit charge is small, the copy density becomes low. Moreover, the toner that easily separates from the carrier, that is, the weakly charged toner or non-charged toner in the developer appears to be developed, and the image density is low and "fogging" is observed.

For these reasons, the amount of charge applied to toner has an upper limit and a lower limit as shown in FIG.
In order to obtain good image quality, it is necessary to maintain this charge amount within a certain range. The present invention detects the amount of charge, detects the toner concentration based on it, and replenishes toner as necessary.

FIG. 1 is an illustrative view showing the main parts of an embodiment of the present invention. FIG. 2 is a conceptual diagram mainly explaining the flow of charges in the embodiment shown in FIG.

The developing device 10 includes a developer chamber 14 arranged near the photoreceptor drum 12 . This developer chamber 14
Inside, there is a 2 tube consisting of a carrier 16 and a toner 18.
Contains component type developer. That is, the carrier 16 and the toner 18 are agitated by the agitator 22, whereby the carrier 16 and the toner 18 are frictionally charged and attracted to each other by electrostatic force, so that the toner 18 adheres to the surface of the carrier 16. . The developer in this state is conveyed to the latent image surface of the photosensitive drum 12 by the magnetic brush 22 and the sleeve 24. At this time, the height of the spikes of developer adhering to the surface of the sleeve 24 is adjusted by the blade 26.

Toner 1 conveyed to the surface of photoreceptor drum 12
8 is attached to the surface of the photoreceptor drum 12 by latent image charges, while the charges of opposite polarity on the carrier 16 are partially discharged to the ground via the sleeve 24. However, most of the carrier 16 and toner 18, that is, the developer, remains in the original developer chamber 1.
4 and used again.

A scraper 2 is provided near the sleeve 24 to scrape off developer attached to the sleeve 24.
8 is provided. This scraper 28 is integrally provided with a mesh conductor 30. The sleeve 24 has a width about the same as the width of the photoreceptor drum 12, and the scraper 28, that is, the mesh conductor 30, also has a width about the same as the sleeve, so that all the developer returned from the development position is transferred to the mesh conductor. 3
brought to 0. The mesh conductor 30 is a resistor 32
connected to ground through. A detection circuit 34 is provided in association with this resistor 32. The toner replenishment motor 36 is controlled in accordance with the detection by the detection circuit 34.

A toner replenishment motor 36 supplies toner 18 from a toner hopper 38 provided above the developer chamber 14.
The replenishment roller 40 is driven to replenish the developer into the developer chamber 14.

The developer scraped off from the surface of the sleeve 24 by the scraper 28 passes through the mesh portion of the mesh conductor 30, but at this time it comes into contact with the mesh conductor 30, so that the charge on the carrier 16 of the developer is transferred to the mesh. It flows into the conductor 30. This electric charge flows to the ground through the resistor 32. Therefore, a voltage is generated in the resistor 32 in accordance with the amount of charge flowing into the conductor 30.

If the toner concentration is constant, the amount of charge applied to the toner 18 is constant, and therefore the resistance 32
The current flowing through the resistor 32, that is, the voltage across the resistor 32 is constant. Since this voltage is a function of the toner charge amount, that is, the frictional charge applied to the developer, from FIGS. 4 and 5, which show the relationship between the toner concentration and the toner charge amount, the voltage across the resistor 32 is Becomes a function. Therefore, if the toner concentration is detected by detecting this voltage and the motor 36 is controlled according to the toner concentration, the amount of toner charge in the developer chamber 14 will eventually become constant and stable. You can obtain high image quality.

This will be explained in more detail with reference to FIG. As described above, the amount of charge imparted to the developer is expressed as the voltage generated across the resistor 32 connected to the mesh conductor 30 when it is discharged to the ground via the mesh conductor 30 connected to the ground. can be detected. The voltage across this resistor 32 is
It is amplified by the operational amplifier 42 constituting the detection circuit 34 and applied to the (+) input of the comparator 44 . A reference voltage Vo determined by a variable resistor 46 is applied to the (-) input of the comparator 44. The output of comparator 44 is applied to the base of transistor 48. The drive motor 36 is connected to the current path of the transistor 48 .

When the toner concentration is low, the amount of toner charge is large, and therefore the voltage across the resistor 32 is large. Conversely, as the toner concentration increases, the voltage decreases. Therefore, if the amount of developer passing through the mesh conductor 30 is constant, it can be determined that when the voltage across the resistor 32 is high, the toner concentration is low, and when the voltage is low, the toner concentration is high.

If the toner density is greater than the predetermined reference density,
Operational amplifier 4 applied to comparator 44 (+) input
The voltage Vtc of No. 2 is smaller than the reference voltage Vo. Therefore, the output of this comparator 44 remains at a low level, transistor 48 is turned off, and motor 3
6 is deactivated.

Conversely, when the toner density is lower than the predetermined standard density, the voltage across the resistor 32, that is, the output voltage Vtc of the operational amplifier 42 becomes larger than the reference voltage Vo. Therefore, the output of the comparator 44 becomes high level, the transistor 48 is turned on, and the motor 3
6 is energized. In response, the replenishment roller 40 provided in the toner hopper 38 is rotated, so that the toner 18 is transferred from the toner hopper 38 to the developer chamber 14.
It is replenished inside.

Note that the desired toner concentration can be arbitrarily set by adjusting the variable resistor 46 for setting the reference voltage Vo.

Furthermore, the charge density of the toner is formed by friction with the carrier, and this triboelectricity is significantly affected by relative humidity and there is a risk of leakage of the charge held by the developer. Since the degree varies depending on various conditions such as the material of the device and the environmental conditions, it is difficult to always expect the toner to have a constant charge density.

For example, when the relative humidity is low, triboelectric charging properties become better and the charge density of the toner increases, causing a phenomenon of toner shortage in the copied image. This is because when the charge density of the toner is large, the Coulomb force between the toner and the carrier becomes large, and as a result, it becomes difficult for the toner to migrate toward the electrostatic latent image.

On the other hand, when the relative humidity is high, the triboelectric charging properties deteriorate, and even if the toner concentration is appropriate, an overtoning phenomenon occurs, and "fogging" and in-machine scattering are observed. If the humidity increases further and a state of dew condensation occurs, conventional methods using electrical resistance such as those disclosed in Japanese Patent Publication No. 58-49867 or methods utilizing development characteristics such as those disclosed in Japanese Patent Application Laid-open No. 54-143144 In the methods disclosed in publications and the like, it is determined that the toner concentration is insufficient and toner is replenished, which may end up causing problems such as overtoning.

On the other hand, according to this embodiment, the toner concentration can be controlled by following the change in the charge density of the toner regardless of the change in the toner consumption amount. Good developed image quality and constant image density can be expected from beginning to end.

If the mesh conductor 30 is connected to the ground as in the above embodiment, the following advantages can be expected.

The toner particles in the developer adhere to the image area due to the electrostatic force of the electrostatic latent image and are consumed, but the carrier particles are not consumed and are used repeatedly as they are. As a result, when the developer is used for a long period of time, toner that does not contribute to development, so-called spent toner, becomes stuck or fused to the surface of the carrier, reducing the ability of the carrier to triboelectrically charge the toner. This adversely affects the image quality, such as a decrease in the density of the developed image and the occurrence of "fogging".
Therefore, it is necessary to periodically replace such a developer with a new one well in advance of such adverse effects occurring. That is, stabilization and long life of the developer are major issues in the maintenance of electronic copying machines.

More specifically, when a carrier is used repeatedly in a development cycle, a charge of opposite polarity to that of the consumed toner remains on the carrier, ie, a positive charge in a development system where the toner is negatively charged. If this state is repeated, it becomes difficult for the residual charge on the carrier to be neutralized by spent toner, etc., and the residual charge gradually accumulates.
If development is continued in this state, the residual charge makes it difficult for the toner to adhere to the latent image area.
The resulting copy has poor contrast. In other words, developer fatigue is caused by an increase in the amount of charge on the carrier, and as the amount of charge on the carrier increases, the attractive force due to the electrostatic Coulomb force between the toner and the carrier increases, and as a result, Toner becomes difficult to separate from the carrier. Therefore, not only is it difficult to develop, but the carrier surface is covered with toner, and new toner is not sufficiently charged by friction, resulting in an unstable charging state, resulting in poor copy image quality.

Also, even if the carrier surface and toner come into contact,
Not only is frictional charging less likely to occur, but the charge of the carrier is transferred to the toner, resulting in the generation of reversely charged toner.

However, according to the embodiment shown in FIG. 1, such developer fatigue can be effectively prevented. That is, the developer returned to the developer chamber 14 passes through the mesh conductor 30 by the scraper 28 while being in contact with it. Since this mesh conductor 30 is connected to the ground through a resistor 32, when the developer comes into contact with the mesh conductor 30, the charge on the developer, that is, the carrier, is discharged, and the residual charge on the carrier is almost eliminated. Therefore, when the collected developer passes through the mesh conductor 30, the charge on the carrier is discharged to the ground, the amount of charge on the carrier is reduced, the adhesion between the carrier and the toner is weakened, and the two are It will be released. Therefore, there is no state in which toner remains attached to the surface of the carrier, and the carrier and toner can always come into contact with each other in an uncharged state at the next friction stage. Therefore, even if the developer is used repeatedly, it is possible to prevent the developer from becoming fatigued or spent. That is, there is no reduction in image quality density, increase in density in the background area, or scattering inside the machine, and stable high-quality images can be obtained over a long period of time.

This is illustrated in FIGS. 6 and 7. That is, according to the embodiment shown in FIG. 1, an increase in the amount of charge of the developer with respect to the copy volume and the generation of spent toner are suppressed compared to the conventional method (here, the one that detects the surface level of the developer) is suppressed. Therefore, it can be used stably for a long period of time. Therefore, maintenance cycles and developer replacement cycles can be lengthened.
Maintenance becomes easier.

Furthermore, since the mesh conductor 30 is used, it is possible to filter out dust, paper scraps, or aggregated toner particles mixed in the developer, suppressing disturbances in the developer layer, and providing even more stable image quality.

It goes without saying that the mesh size of the mesh conductor 30 must be larger than the particle size of the carrier 16. Furthermore, if removal of dirt and the like is also considered, the size of such a mesh would have to be smaller than the gap between the sleeve 24 and the scraper 28.

[Brief explanation of drawings]

FIG. 1 is an illustrative view showing an embodiment of the present invention. FIG. 2 is a schematic diagram mainly for explaining the flow of charges in the embodiment shown in FIG. FIG. 3 is a graph showing the relationship between toner concentration and toner charge amount. FIGS. 4 and 5 are graphs showing the correlation between toner concentration and voltage generated across the resistor. FIG. 6 is a circuit diagram showing a preferred embodiment of the invention.
FIG. 7 and FIG. 8 are graphs showing a comparison between the amount of charge with respect to copy volume and the amount of spent toner with respect to copy volume, respectively. In the figure, 30 is a mesh conductor, 32 is a resistor, 34 is a detection circuit, 36 is a replenishment motor, and 40
indicates a replenishment roller.

Claims (1)

[Scope of Claims] 1. A developer chamber in which the developer to which the carrier and toner are electrostatically adsorbed is stored, such that all the developer returned from the development position passes through the developer chamber while being in contact with each other. established in
and a grounded mesh conductor; and a detection means for detecting the toner concentration in the developer based on the amount of charge flowing into the mesh conductor.