JPH0664402B2 - Developer detection device - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a device for controlling toner concentration and the like by detecting the presence or absence of a developer on the surface of a piezoelectric element.

[Prior Art] FIG. 3 is a vertical sectional view showing an example of a main part of a developing device.

The drawing shows a developing device provided on the developing roll 1 to regulate the developer 3 to a constant thickness by a doctor blade 2, and a piezoelectric element 4 is provided as a sensor for detecting the amount of the developer 3. ing. As shown in the figure, the piezoelectric element 4 is set in a posture in which it is opposed to the flow direction of the developer 3 and is inclined by a predetermined angle. When the developer 3 is a two-component developer composed of toner and carrier, the developer 3
If the toner is sufficiently present in the developer 3, the ratio of the carrier having good fluidity in the developer 3 is small, and the developer 3 exhibits a fluid state in which a large arc is drawn as indicated by an arrow P, while the toner in the developer 3 is Is insufficient, the ratio of the toner having poor fluidity in the developer 3 is large, so that the developer 3 exhibits a small turning flow state as indicated by an arrow Q.

Further, for example, only the magnetic toner is used as the developer 3 1
In the same manner as the component developing method, the developer 3 is sufficiently present in the flow state of the arrow P, and the developer 3 is in a small amount in the arrow Q. Toner is replenished by the control circuit of FIG.

FIG. 2 is a circuit diagram of a toner concentration control device including a conventional piezoelectric element 4.

Here, this control circuit will be briefly described. The piezoelectric ceramics constituting this piezoelectric element 4 has the characteristic that when an alternating voltage is applied, it expands and contracts according to the polarity of the electric field. In this case, the figure shows a positive feedback oscillation circuit using the piezoelectric element 4 itself as an oscillator. is there. Therefore, the piezoelectric element 4 also serves as an oscillator and a sensor that detects the fluidity of the developer 3 as pressure. Here, for example, if the coupling rate of the piezoelectric element 4 is -α ₂ and the attenuation rate by the resistor R ₁ from the amplifier 7 having an amplification rate of -A is α ₁ as shown in the same figure, the transmission condition is (-A)・ Α ₁・ (-α ₂ )> 1 ・ ・ ・ ・ ・ ・ (1), and R ₁ and R ₂ : expressed as resistance. Therefore, if the amplification factor -A and the attenuation factor α ₁ are set appropriately, the oscillation circuit is established.

Therefore, when the toner density of the toner is consumed in the developer 3 decreases, the pressure to the piezoelectric element 4 becomes good fluidity of the developer 3 as described above is reduced, coupling ratio-.alpha. ₂ of the piezoelectric element 4 Becomes larger and the oscillation of the piezoelectric element 4 continues strongly.

Therefore, the oscillation output from the amplifier 7 is compared with the reference value in the detection comparison circuit 8, and at this time, since the oscillation output is larger, the transistor 9 is turned on and the replenishment signal 10 is generated. This replenishment signal 10 causes the toner replenishment roller 5
To drive the toner replenishment operation. On the other hand, if the toner is sufficiently present in the developer 3, as described above, the developer 3
Fluidity deteriorates, the pressure on the piezoelectric element 4 increases, and the coupling rate −α ₂ decreases, so that the oscillation output is small and becomes unstable, or oscillation is stopped. In this case, the transistor 9 is turned off, the replenishment signal 10 is not generated, and the toner replenishing roller 5 is not driven to replenish the toner.

As described above, in the conventional toner replenishment operation, when the pressure of the developer 3 applied to the piezoelectric element 4 increases, the toner replenishment by the toner replenishing roller 5 is stopped, and the pressure of the developer 3 decreases or the pressure is applied. When the toner runs out, toner supply starts. That is, the toner density of the developer 3 is kept constant by this operation.

[Problems of conventional technology]

However, in such a conventional toner concentration control device, the developer 3 is not used when the carrier becomes worn and the fluidity deteriorates due to high temperature and high humidity or long-term use, or after a long period of non-use. When the fluidity becomes worse than that at the time of setting and the developer 3 sticks to the surface of the piezoelectric element 4 which is a detection sensor in particular, the piezoelectric element 4 produces different vibrations when the developer 3 is present and when it is not present. Will not be done,
Even if the toner is consumed and the toner concentration is lowered, the lack of toner cannot be detected, and not only the image quality is significantly deteriorated, but also in the two-component developing method, even a carrier pulling phenomenon occurs, It's a big problem.

[Object of the Invention]

In view of the above-mentioned conventional drawbacks, the present invention oscillates (vibrates) a detection unit including a piezoelectric element for a certain period of time when a piezoelectric element detects a pressure change due to fluidity of a developer and controls toner concentration.
After the output is increased and the developer on the surface of the piezoelectric element is shaken off once, the original normal detection operation is performed on the piezoelectric element to keep the toner concentration in the developer constant and obtain a good reproduced image. It is an object of the present invention to provide a toner density control device that enables the above.

[Main points of the invention]

In order to achieve the above object, the present invention sets a detection timing for detecting the presence or absence of the developer in a developer detecting device for detecting the presence or absence of the developer on the surface of the piezoelectric element using a piezoelectric element, A control unit is provided to make the oscillation output of the piezoelectric element different between the detection timing and the non-detection timing, and the control unit controls the oscillation output of the piezoelectric element to be smaller at the detection timing than at the non-detection timing. It is characterized by doing.

Example of Invention

An embodiment of the present invention will be described below with reference to FIGS. The same members as those in the conventional example are designated by the same reference numerals, and the description thereof will be omitted.

First, the configuration will be described.

FIG. 4 is a sectional view of a developing device having the toner concentration control device of the present invention, and FIG. 5 is a sectional view of the developing device.
The state in which the toner in the developing device is low is shown.

The developing device 26 used in the present invention includes a developing hopper 27.
Inside, a sleeve 28, a stirring roll 29, a doctor blade as a regulating member, a piezoelectric element 4 as a detection sensor are arranged, and a toner storage portion 6a for storing replenishment toner 6 is formed above the developing hopper 27. The toner supply roller 5 is provided below the toner storage portion 6a.

The sleeve 28 is made of a non-magnetic cylinder such as aluminum and rotates in the direction of the arrow, and the magnet roll 1 magnetized with a large number of poles is fixedly arranged inside the sleeve 28.
Are adsorbed on the surface of the sleeve 28. The developer 3 is formed by mixing a carrier whose main component is a magnetic material and having a particle size of 20 to 200 μm, and a toner whose main component is a resin. As the carrier, a magnetic material having a main component coated with a resin or a resin mixed with a resin is also used. Piezoelectric element 4
Is for detecting the fluidity of the developer 3.

Next, the operation of the developing device 26 based on the above configuration will be briefly described. The photoconductor 30 passes through a charging / exposure area (not shown) and holds the electrostatic latent image corresponding to the original image while the developing device 26 and It enters the developing area 30b which faces.

The developer 3 including the carrier and the toner is a stirring roll 29.
Photosensitive member 3 that is agitated by friction and charged by friction
It has a charge of the opposite polarity to that of the electrostatic latent image formed on 0. Then, the developer 3 is adsorbed on the surface of the sleeve 28, conveyed in the direction of the arrow by the rotation of the sleeve 28, and the thickness of the developer 3 is regulated by passing the doctor blade 2 to the developing area 30b with the photoconductor 30. Sent.

In the developing area 30b with the photoconductor 30, the developer 3 forms a brush by the main pole N ₁ of the developing roll 1 and contacts the surface of the photosensitive layer 30a, and the electrostatic latent image is visualized by the toner. The developer 3 after development is agitated by the agitating roll 29 and sent again onto the sleeve 28.

By the way, the developer 3 conveyed on the sleeve 28 is
Although the doctor blade 2 regulates the spike height to a certain level, the surplus developer 3 that is conveyed collides with the doctor blade 2 and rises along the doctor blade 2 due to the conveying force of the sleeve 28. Occurs. Then, after rising, the developer 3 which has reached a position where it is not affected by the magnetic field of the developing roll 1 flows down so as to collapse while coming into contact with the surface of the piezoelectric element 4 as shown by an arrow S. Here, two flows of the developer 3 are generated, one that is conveyed to the doctor blade 2 and the other that flows down.

On the other hand, FIG. 1 shows a circuit diagram of a toner concentration control device which is an essential part of the present invention. The figure shows a circuit 13 in which a positive feedback circuit 11 including a resistor R ₃ , a piezoelectric element 4 and an amplifier 7 is grounded from a connection point 12 of the resistors R ₃ and R ₄ through resistors R ₄ and R ₅ connected in series. And a switch circuit 16 grounded via a switch 15 from the connection point 14 of the resistors R ₄ and R ₅ to each other. Further, the oscillation output from the amplifier 7 is input to the detection comparison circuit 8 to be detected. At 8, the detection comparison circuit 8 compares a preset reference value with the oscillation output. The comparison result of the detection comparison circuit 8 is input to the base of the transistor 9, the transistor 9 is turned on when the output of the detection comparison circuit 8 is a high signal, and the transistor 9 is turned off when the output of the detection comparison circuit 8 is a low signal. .

The voltage element 4 described in the above-mentioned configuration and the above-mentioned prior art page.
The attenuation factor from the amplifier 7 is
When 5 is ON And when the switch 15 is off, Becomes That is, the switch 15 represented by the equation (4) is turned on.
In the case of FF, since the attenuation rate is larger than that in the case of ON represented by the equation (3), the positive feedback rate is increased and stronger oscillation is performed as can be understood from the oscillation condition of the above equation (1).

FIG. 6 is a diagram showing a waveform of the oscillation output of the piezoelectric element 4 at this time, and a waveform 17 is a vibration mode when the switch 15 is OFF and is a so-called no-load state in which the pressure of the developer 3 is not applied. The waveform 18 shows the oscillation output when the pressure of the developer 3 is applied, so-called load. Even at this time, the oscillation condition is satisfied and the oscillation is continued. On the other hand, the waveform 19 shows the oscillation output when there is no load when the switch 15 is ON, and the waveform 20 shows the time when the load is present. The piezoelectric element 4 receives pressure due to the developer 3 whose fluidity is lowered, Shows the state where oscillation is stopped.

Therefore, the toner or the like adhering to the piezoelectric element 4 is filtered off by using the piezoelectric element 4 in the strong oscillation state shown by the waveform 17, and the developer 3 is produced by using the output of the piezoelectric element 4 in the oscillation state shown by the waveform 19 or 20. It can be seen that it is sufficient to detect the toner density inside. FIG. 7 is a time chart showing the operation timings of the toner sieving operation (hereinafter referred to as a vibration mode) and the toner concentration detection operation (hereinafter referred to as a detection mode) of the piezoelectric element 4. FIG. 6A shows a case where 21 is ON at the timing of a drive motor (not shown), that is, a state in which the photosensitive drum 30 is rotated and a copying operation is being performed. Reference numeral 22 indicates a state in which the drive motor is off, that is, the photoconductor drum 30 stops rotating and the copying operation is not performed. FIG. 2B shows the oscillation output of the piezoelectric element 4, and the vibration mode 23 and the detection mode 24 are alternately performed by switching the switch 15 as described above.

No development is performed during the period of the vibration mode 23, and development is performed during the period of the detection mode 24.
That is, the detection mode 24 is applied only during the ON period of the drive motor (the period during which copying is performed), and the piezoelectric element 4 is always in the vibration mode 23 during the OFF period of the drive motor, and the piezoelectric element 4 adheres to the piezoelectric element 4. The operation of sieving off the remaining toner is performed.

Further, the period (detection period) 25 in which the toner density is actually detected by the control circuit is a part of the period in which the piezoelectric element 4 is in the detection mode 24. That is, the detection timing is set during this period to perform the actual detection operation.

In summary, what has been described above, the piezoelectric element 4 operates as a vibrator in the vibration mode 23, and the strong vibration of the piezoelectric element 4 shown by the waveforms 17 and 18 sifts out toner and the like. Prevents adhesion of toner, etc. on the surface of the piezoelectric element 4 and its vicinity, which is a problem
Next, the switch 15 is turned on to lower the oscillation output to the detection level, and the toner concentration is detected by the piezoelectric element 4 vibrating like the waveform 19 or 20 in the detection period 25 after a fixed time and the toner concentration is controlled. It does.

Therefore, according to the toner concentration control device of this embodiment,
When the developer concentration of the developer 3 is relatively high, the fluidity of the flowing developer 3 is poor, the contact resistance with the surface of the piezoelectric element 4 is high, and the output of the control circuit is not performed so that the toner is not replenished.

On the other hand, if the toner density of the developer 3 decreases as the above-described development cycle is repeated, the fluidity of the developer 3 becomes good, the contact resistance with the surface of the piezoelectric element 4 also decreases, and the toner supply roller 5 is rotated from the control circuit. A signal for causing the toner is output and the toner replenishing operation is performed. As a result, the toner density of the developer 3 is always kept constant. That is, the developer 3
The toner replenishment control is always performed accurately by changing the fluidity of the developer 3 on the surface of the piezoelectric element 4 according to the toner concentration.

Although the above description has been made of the case of controlling the toner density using the two-component developer, it is needless to say that the present invention can be applied to the replenishment control of the one-component developer and the toner hopper detection of the two-component toner.

〔The invention's effect〕

As described above, according to the present invention, after the oscillation output of the toner concentration control circuit including the piezoelectric element is increased to eliminate the adhesion of the developer on the piezoelectric element, the detection level of the toner concentration control circuit is lowered, Since the apparatus for controlling the toner concentration by detecting the presence / absence of the developer by providing the detection timing is provided, even when the developer fluidity is deteriorated such as at the time of high temperature and high humidity, the presence / absence of the developer toner 4 is detected.
Since the surface of the piezoelectric element does not adhere to the developer or the like, it is possible to accurately detect the presence or absence of the developer (toner) with high reliability. Therefore, the reproduced image developed by the developing device having a constant amount of developer is a good reproduced image without carrier pulling.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a toner concentration control circuit diagram which is an essential part of the present invention, FIG. 2 is a control circuit diagram used for conventional developer presence detection, and FIG. 3 is a detection device. 4 is a sectional view of the developing device showing the flow state of the developer in FIG. 4, FIG. 4 and FIG. 5 are sectional views showing an embodiment of the present invention, and FIG. 6 is a waveform of an oscillation output to the piezoelectric element in the present invention. Similarly, Fig. 7 and Fig. 7 are time charts for detecting the presence or absence of the developer. 1 ... Development roll, 2 ... Doctor blade, 3 ... Developer, 4 ... Piezoelectric element, 5 ... Toner supply roller, 6 ... Toner, 7 ... Amplifier, 8 ... Detection comparison circuit, 9 ... ... Transistor, 10 ... Supply signal, 11 ... Positive feedback circuit, 12 ... Connection point, 13 ... Circuit, 14 ... Connection point, 15 ... Switch, 16 ... Switch circuit, 17 ... Waveform, 18 ...... Waveform, 19 ...... Waveform, 20 ...... Waveform, 21 ...... Timing when drive motor is ON, 22 ...... Timing when drive motor is OFF, 23 ...... Vibration mode, 24 ...... Detection mode, 25 ... … Detection period, −α ₂ …… Coupling rate, −A …… Amplification rate, α ₁ …… Attenuation rate (conventional example), α ₁ ′ …… Attenuation rate (when switch is ON), α ₁ ″ …… Attenuation rate (when the switch is _{OFF), R 1, R 2} ...... resistance, _{3, R} 4, _{R 5} ...... resistance,

Claims (1)

[Claims] 1. A developer detecting device for detecting the presence or absence of a developer on the surface of the piezoelectric element using a piezoelectric element, wherein detection timing for detecting the presence or absence of the developer is set,
A control unit is provided which makes the oscillation output of the piezoelectric element different between the detection timing and the non-detection timing, and the control unit makes the oscillation output of the piezoelectric element smaller at the detection timing than at the non-detection timing. A developer detecting device characterized by controlling.