JPS5833271A - Automatic toner density adjusting device of electrophotographic device - Google Patents

Abstract

PURPOSE:To correct a variation of environmental humidity, and also to prevent generation of background fog, by constituting a device so that a variation of a toner charged quantity is reduced, in order to maintain developing performance of a developer in a desirable state. CONSTITUTION:A toner density detecting element measures a reflection factor of a developer by a photoelectric detecting element TR consisting of a light diode DL and a phototransistor. An amplification output signal by an amplifier IC2 for receiving a detecting signal from the photoelectric detecting element TR is compared with a reference signal applied by resistances R3, R4 and R5, and a humidity detecting element R6, and a control signal is generated. For instance, when toner density in a developer drops and a reflection factor of the developer increases, a toner density detecting signal increases, a signal generated by being amplified from the amplifier IC2 also becomes large, becomes large than a reference signal voltage value applied to a connecting point of the resistances R3 and R4, and an amplifier IC3 executing a comparator operation is set to an on-state. When an output signal from the amplifier IC3 is received, a transistor TR1 is operated, a driving means M of a toner supplying device connected to a collecting circuit, that is to say, a solenoid, a clutch, a motor, etc. are operated, and a toner is supplied.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic toner concentration adjustment device configured to maintain the toner concentration of a dry two-component developer used in an electrophotographic apparatus at a predetermined value in response to changes in humidity.

In general, in electrophotographic copying, iron powder or granular ferrite whose surface is oxidized or coated with resin, or resin particles or glass beads with magnetic particles dispersed therein are used as a developer to make the electrostatic latent image visible. A dry two-component developer formed by mixing and stirring carrier particles formed by the above and toner particles is widely known.

By the way, there are various factors that determine the development performance of this dry two-component developer, that is, the image density and pack ground density, but among them, the mixing ratio of carrier and toner, that is, the toner density, and the electric charge held by the charged toner. It is known that the amount of toner charge, that is, the amount of toner charge, greatly influences the development performance of the developer.

Conventionally, in order to stabilize the development performance of this dry two-component developer, automatic developer density was developed that detected the toner mixture ratio in the developer and controlled the amount of toner replenishment based on the detection signal. Adjustment devices are known, but they simply keep the mixing ratio of toner and carrier constant, so even if the mixing ratio can be adjusted to a constant value, the image density will change if the toner charge amount changes. There was a drawback. In addition, as another means of stabilizing the developing performance, a latent image for monitoring is formed on the off-screen area of the photoreceptor and this is developed.
There is also known an apparatus configured to photoelectrically detect the density of the developed toner image and determine the toner mixing ratio based on the detection signal. However, in this device, changes in factors other than the development performance of the developer itself, such as deterioration of the photoreceptor and fluctuations in the corona charging device, can be corrected by adjusting the toner mixing ratio of the developer. Therefore, the amount of correction may exceed the toner mixing ratio allowed for the developer, and in such cases, image quality may deteriorate (reduction in contrast, etc.), and furthermore, significant toner scattering may occur. This was extremely inconvenient.

As mentioned above, the conventional means of stabilizing development performance is
In either case, little consideration was given to the amount of toner charge, and these methods were extremely inadequate as stabilizing means.

Among the factors that change the developing performance of the developer,
Although the toner mixing ratio is an important factor as it tends to increase the image density and pack ground fog as it increases, changes in the toner charge amount are extremely important. For example, when the toner charge amount is small, As the image density increases, some toner is not sufficiently captured by the carrier due to insufficient charging, and the pack ground capri also increases. On the other hand, as the toner charge amount increases, the image density decreases and strongly charged toner increases. The amount of carrier that is strongly captured by the carrier and does not have toner attached decreases.
This may inhibit the charging of newly replenished toner, resulting in insufficiently charged toner, resulting in packed ground capri. As described above, whether the toner is charged too much or too little, it adversely affects the developing performance. Furthermore, even though this toner charge varies greatly due to changes in environmental humidity even under a constant toner mixing ratio and constant developer agitation conditions, conventional methods have been able to effectively compensate for this variation and stabilize development performance. No method was proposed to do so.

This invention was made to solve this problem, and in order to maintain the developing performance of the developer in a desirable state,
It is an object of the present invention to provide an automatic toner concentration adjustment device configured to reduce fluctuations in toner charge amount, correct changes in environmental humidity, and prevent pack ground capri from occurring.

The prior art moat and the invention of this application will be described in detail below with reference to the drawings.

FIG. 1 is a diagram showing the relationship between the toner charge amount and the image density of the solid area, where the horizontal axis shows the toner charge amount and the vertical axis shows the image density. This is based on data obtained by stirring a developer prepared by mixing 5 parts by weight in a developing device, and changing only the amount of charge while keeping the toner concentration constant. As can be seen from FIG. 1, even if the toner density of the developer is kept constant, the image density changes due to changes in the toner charge amount, resulting in an extremely inconvenient situation. That is, as described above, when the toner charge amount is a little low, the image density f is high, and as the toner charge amount increases, the image density decreases. The reason why this kind of development occurs is that when an electrostatic latent image is developed, the latent image charge is apparently neutralized by the toner charge. This is thought to be because a small amount of toner is required to neutralize a toner with a large amount of charge.

On the other hand, the amount of toner charge in the developer changes depending on various factors. For example, the amount of charge increases as the agitation action of the developer increases. However, under constant agitation conditions, the charged toner is consumed and uncharged toner is replenished, so that the amount of charge does not increase beyond a single level.

In addition, when the toner concentration decreases, the amount of contact friction between the carrier and the toner increases, and the amount of toner charge increases.However, if an automatic toner concentration adjustment device that adjusts the toner mixing ratio is applied, the toner concentration can be kept constant. Since the toner is retained, changes in the amount of charge due to changes in toner concentration can be prevented.

Furthermore, as mentioned above, it is observed that the toner charge amount varies greatly depending on the change in soil humidity. In other words, Figure 2 shows the change in the amount of charge (song #a) when developer with the same toner concentration (8.5%) is stirred in a low humidity environment (20C, 30%), and the situation in a high humidity environment. (28℃, 85
%) and shows the state of change in charge amount (track #b) when stirring.The horizontal axis is the time (minutes) during which the developing device was operated for stirring, and the vertical axis is the toner charge amount (μQ /g) 0 This tJ2 diagram song! As can be seen from (a) and (b), the toner charge amount tends to increase and stabilize within a few minutes under a low humidity environment (→), whereas under a high temperature environment (BL), the toner charge amount tends to increase and stabilize within a few minutes. Toner charge The toner charge decreases once and then gradually increases, and it takes several tens of minutes before it shows a stable charge amount equivalent to (a).For devices in which this type of developer is used, such as copying machines, etc. Considering its usage, it is often found that several to several dozen copies are made at a time, and the time required for this is within a few minutes. In this case, the charge amount of the toner does not increase and is maintained at a low level (approximately 8 μQ/g).

On the other hand, even with low-humidity agitation, the charge increases reliably, and a stable high charge amount (
approximately 12 μQ/g). Therefore, when using a developing device whose developer toner concentration and stirring time are set so as to obtain appropriate image density in a medium humidity environment (for example, 25C155%), the toner Image density becomes excessive due to insufficient charge amount,
Also, in a low-humidity environment, the toner charge amount becomes excessive and the 111g1 concentration decreases.Such a phenomenon can be avoided simply by using an automatic toner concentration adjustment device that keeps the toner mixing ratio constant. This is often observed in built-in copying devices.

Figure 3 shows how the solid image density changes when a copying machine is placed in environments with different relative humidity using a developer with a predetermined concentration (8.5%, stirred for 5 minutes). As is clear from this figure, the image density maintains a relatively stable value in a low humidity environment even when the relative humidity is 50X.
When the temperature is higher than this, the image density sharply increases, and this increase in image density is due to a decrease in the amount of toner charge.

As is clear from the above description, in an electrophotographic apparatus equipped with a conventional toner density automatic adjustment device that does not take into account changes in the toner charge amount and simply keeps the toner mixing ratio constant, it is difficult to produce significant images due to fluctuations in environmental humidity. Fluctuations in density were unavoidable, and in order to eliminate the drawbacks of the above-mentioned conventional devices, the present invention improves the toner mixing ratio (toner'af) in the developer in response to fluctuations in environmental humidity conditions. The structure is such that a stable toner charge amount is always maintained and a desired image density is obtained by changing the toner charge amount.

FIG. 4 is a diagram comparing the relationship between the toner concentration on the horizontal axis and the toner charge amount on the vertical axis. Toner charge amount is 25
C1 The value is shown after stirring for 5 minutes in a developing device in an environment of 55% relative humidity. As is clear from this figure, within the toner concentration range of 4% to 10%, the relationship between toner concentration and band amount is almost linear, and in the region of toner concentration of 4% or less, the toner charge amount is approximately linear. It can be seen that the concentration dependence is greater. As can be read from Figure 2, using a developer with a toner concentration of 8.5%,
When stirring for minutes, the environmental humidity ranges from 30% to 85%.
%, the change in toner charge amount caused by changing the toner concentration is about 4 μQ/g.
Referring to the figure, the degree of rotation is 3% ◎ In reality, changes in toner density itself have the effect of changing image density. For example, when toner density is reduced, the reduction in image density due to the reduction in toner density is Since this is added to the effect of reducing image density due to an increase in the amount, the necessary effect can be obtained even if the adjustment range of toner density is less than 3%. Therefore, the toner density is adjusted according to the environmental humidity conditions. By doing so, a constant image density can be obtained.

Next, a specific example of the toner density automatic adjustment device according to the invention of this application will be described in detail while comparing it with a conventional example. W
FIG. t5 is a block diagram of a conventional automatic developer-toner concentration adjustment device that maintains a constant toner mixing ratio. The detection element 1 that detects the toner concentration in the developer takes various forms depending on the detection principle. That is, a coil is used to determine the toner concentration based on the magnetic permeability of the developer, and a photosensor is used to determine the toner concentration by measuring the reflectance of the developer. The signals from these sensing elements 1 are applied to the control circuit, but normally these signals cannot be used as control signals as they are, and must be amplified or converted into a form suitable for creating control signals by the signal amplification and shaping circuit 2. needs to be formatted. Next, the control signal generation circuit 3 to which this amplified and shaped detection signal is input is usually constituted by a comparator having a reference signal generation circuit 4 that determines the control level, and the control signal generation circuit 3 is composed of a comparator that has a reference signal generation circuit 4 that determines the control level, and the reference signal and the amplified and shaped toner concentration detection signal are inputted. and generates a control signal. The drive circuit 5 receives the control signal and the toner replenishing device 6
The toner replenishing device 6 is a circuit for controlling the operation of the toner replenishing device 6.
When driven by a DC solenoid, DC electromagnetic clutch, DC motor, etc., a DC control element such as a transistor or 80R is used, and when the drive device of the toner replenishing device 6 is driven by AC, a triac, etc. is used. AC elements are used. Normally, the toner replenishing device 6 is configured to replenish toner to the developing device by driving and rotating a porous roller, a roller provided with grooves or irregularities, etc. at the bottom of the toner hopper by the drive circuit 5.

FIG. 6 is a block diagram of an embodiment of an automatic toner concentration adjusting device according to the present invention. toner concentration detection element,
The configurations of the signal amplification and shaping circuit, drive circuit, and toner supply device are the same as those of the conventional device shown in FIG. 5, and the configuration of the control signal generation circuit 3 is different. That is, in the conventional apparatus shown in FIG. 5, the control signal was formed by comparing a preset reference signal with an amplified and shaped toner concentration detection signal, whereas in the present invention, , as shown in Figure 6, the magnitude of the reference signal itself is changed in response to changes in environmental humidity.
It is configured to Various types of elements can be used as the environmental humidity sensing element used in this reference signal changing means, but a humidity-resistance change element whose resistance value changes in response to changes in humidity is preferable. Examples of elements with such characteristics are Hi-Temi-Milight (trade name, Tokyo Cosmos Electric) and Sera-Hatsuku Humidity Sensor H10.
4 (trade name, Marcon Electronics), etc., and these elements have a characteristic that the resistance value decreases as the humidity increases. In some cases, the signal from the humidity sensing element can be applied as is to the reference signal generation circuit, but it may be necessary to perform impedance matching or signal amplification to make the signal suitable for control.
In some cases, it may be configured to be applied via a shaping circuit.

The humidity sensing element measures the environmental humidity in the area where the developer is placed, so it is placed near the developing device.

However, considering the prevention of contamination of the detection element with toner and the ease of electrical wiring, there is little difference in humidity depending on the location, so there is no need to limit the location. Good too. In addition, instead of the humidity detection element, a toner concentration adjustment terminal consisting of something like a variable resistor and displaying the adjustment position corresponding to the humidity can be installed on the outside of the device or inside a cover designated to be opened and closed by the user. If the humidity level is set in the humidity range, the user can make manual adjustments according to the humidity.

FIG. 7 shows a specific example of a circuit configuration based on the block diagram of FIG. 6. In FIG. 7, the toner concentration detection element is configured to measure the reflectance of the developer by a photoelectric detection element TP consisting of a light emitting diode D1 and a phototransistor.An amplifier IC1 receives a detection signal from the photoelectric detection element Tp. connects a feedback resistance ratio of 1 to function as a proportional amplifier circuit. Amplifier■
02 connects a feedback resistor R2 and capacitors C1 and C2 for removing noise components to function as a waveform shaping amplifier circuit. It has a comparator circuit configuration that generates ON/OFF signals without connecting an amplifier IC or μ feedback resistor. The amplified output signal by amplifier IO is compared with a reference signal provided by resistors R3, R4, R5 and humidity sensing element R6 to generate a control signal. For example, when the toner concentration in the developer decreases and the reflectance of the developer increases, the toner concentration detection signal increases, and the signal amplified and generated from the amplifier IC also increases.
The reference signal voltage value applied to the connection point of resistors R3 and R4 is increased, and the amplifier IC, which functions as a comparator, is turned on. Amplifier IO receives the output signal of the spider and turns on transistor Tr! is operated, and the driving means M1 of the toner replenishing device connected to the collector circuit, that is, a solenoid, a clutch, a motor, etc., is operated to replenish toner. When the toner is replenished and the reflectance of the image forming agent decreases, the toner concentration detection signal appears small and the operation mode is opposite to the above operation mode, toner supply is stopped.OR7 detects the environmental humidity. An element whose resistance value changes depending on humidity, such as Huumilite (trade name), which has humidity-resistance characteristics as shown in FIG. 8, is used. As is clear from the circuit that applies a reference voltage to the amplifier IO in FIG. 7, as the environmental humidity increases, the resistance of the humidity detection element, that is, the reference potential increases, and the stability check toner concentration of the circuit shown in FIG. will shift to a decreasing direction.

On the other hand, when the humidity is low, the resistance value of the humidity detection element increases and the stable point of the circuit shifts in the direction of increasing the toner concentration.0Resistors R4 and R5 determine the adjustment range of the toner concentration and the curve of humidity versus toner concentration. In other words, even if the resistance value of the humidity sensing element Re increases significantly, the influence on the reference voltage is limited by the parallel resistance Rs.
Even if the resistance value of sensing element R6 decreases significantly, the series resistance R4
Therefore, the adjustment of the toner concentration is not carried out without limit, but can be configured to be carried out within the range in which the action of the developer normally occurs, thereby preventing toner scattering due to excess toner. It is possible to prevent the occurrence of scattering and carrier adhesion to the photoreceptor due to insufficient toner. Note that manual adjustment can of course be achieved by replacing the humidity sensing element PL in FIG. 7 with a variable resistor that is selectively operated by the user.

FIG. 9 shows another embodiment for changing the toner density adjustment level using the environmental humidity sensing element according to the present invention, in which the negative feedback amount of the amplifier circuit is changed by the humidity sensing signal to adjust the amplifier gain, As a result, the configuration is such that the magnitude of the toner concentration detection signal is changed depending on the environmental humidity. In Fig. 9, the feedback resistance of the proportional amplifier IC is the resistance R11s R,...
and humidity sensing element R1m'. As mentioned earlier, when the humidity decreases, the amount of charge increases and the image density decreases, and to compensate for this, it is necessary to increase the toner density and reduce the amount of charge.
In this embodiment, when the humidity decreases, the humidity sensing element R
When the resistance value of tS is large, the amount of feedback decreases, the amplification degree of the proportional amplifier IC1 increases, and the output increases. Therefore, if the reference voltage applied to the control signal generation circuit is fixed, the toner replenishing device is driven by the control signal to replenish toner, thereby increasing the toner concentration of the developer. As a result, the detection signal from the toner concentration detection element becomes smaller and the control system becomes stable. On the other hand, when the humidity increases, the amount of charge decreases, so it is necessary to adjust the toner concentration. However, in this embodiment, since the resistance value of the humidity detection element RIB is small, the amplification degree of the amplifier I01 decreases. Therefore, the output signal becomes small. Therefore, the control signal is stopped, and the toner replenishing device that had been driven until then is stopped, so the toner concentration becomes a low concentration trap and the control system becomes stable.

FIG. 10 is a circuit configuration diagram of a main part of still another embodiment, in which the output signal of the toner concentration detection element is divided into voltages by a voltage dividing circuit, and the voltage division ratio of the voltage dividing circuit is determined by changes in the resistance value of the humidity sensing element. An example is shown in which the configuration is changed according to the following. 10th
In the figure, resistors) Lzt, 'fLus 82M, and humidity sensing element R24 constitute a resistive voltage divider circuit, and the output of the voltage divider circuit is taken out from the connection point of resistors gxt and Rn,
It is configured such that the output voltage of the voltage dividing circuit increases as the resistance value of the humidity sensing element R24 increases during low humidity. If the reference voltage of the control signal generation circuit is maintained at the level of -1, as in the case of Fig. 9, the voltage will be divided when the humidity is low, and the amplified signal will become large, toner will be replenished and the developer will be injected. The toner concentration increases, the detection signal from the toner concentration detection element decreases, and the control system becomes stable. On the other hand, when the humidity becomes high, the resistance value of the humidity detection element R24 decreases, so the amplified signal decreases, the toner replenishment that had been performed until then is stopped, and the toner concentration in the developer decreases. The control system becomes stable at the point where the detection signal from the detection element becomes large. Furthermore, resistance R2! , FLn
act as series and parallel resistors to limit the adjustment level of toner concentration due to humidity changes to within a predetermined range. Note that the humidity sensing element 1' in FIGS. 9 and 10
Lts and R44 can be replaced with variable resistors that are selectively operated by the user in the same way as described for the humidity sensing element R6 in FIG. 7, or can be manually adjusted.

7, 9, and 10, a humidity sensing resistance change element whose output is taken out as a change in resistance value is used as a humidity sensing element, and a developer toner concentration sensing element is used as a humidity sensing resistance change element, and a developer toner concentration sensing element is used as the developer reflectance. Each of the embodiments of the present invention using seven sensors for measuring humidity has been shown, but the circuit configuration of each of the shown embodiments is changed depending on the detection signal form corresponding to the operating principle of each detection element, and the humidity detection signal Various forms other than the above-mentioned embodiments can also be adopted for the circuit configuration for linking the toner density control level to a change in the toner density control level.

As described above in detail based on the embodiments, the present invention provides a toner concentration automatic adjustment device with a humidity detection element for measuring environmental humidity, and automatically adjusts the toner concentration control level based on the detection signal of the detection element. Since the toner density is automatically reduced when the humidity is high and increased when the humidity is low, the toner charge amount does not change even if the environmental humidity changes, so it is always good. The image density can be maintained, and the occurrence of packed ground capri can be prevented.

[Brief explanation of drawings]

Figure 1 is a characteristic diagram showing the relationship between toner charge amount and image density, Figure 2 is a characteristic diagram showing the relationship between developer operating time and toner charge amount, and Figure 3 is a characteristic diagram showing the relationship between humidity and image density. FIG. 4 is a characteristic diagram showing the relationship between toner concentration and toner charge amount, FIG. 5 is a block diagram of a conventional toner concentration automatic adjustment device, and FIG. 6 is a toner concentration automatic adjustment device according to the present invention. FIG. 7 is a diagram showing an example of a circuit configuration based on the block diagram of FIG. 6, FIG. 8 is a characteristic diagram of a humidity sensing element, FIG. FIG. 10 is a diagram showing the main circuit configuration of other embodiments of the present invention. In the figure, DL is a light emitting diode, TP#'i photoelectric detection element (phototransistor), IO, IO, and IC8 are all amplifiers, Tr is a transistor, M is a driving means for the toner replenishing device, R6, R1111, R24 are humidity detection elements, respectively.

Claims (1)

[Claims] A toner concentration detection element for detecting the toner concentration in a dry two-component developer consisting of toner and carrier, a toner replenishment device, and a control circuit for controlling the operation of the toner replenishment device in accordance with a signal from the toner concentration detection element. In the automatic toner concentration adjustment device for an electrophotographic apparatus, the scissor control circuit is further equipped with a humidity detection element, and the toner concentration is corrected according to fluctuations in environmental humidity to stabilize development performance. Automatic toner density adjustment device.