JPH0648410B2 - Developer concentration controller - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a developing device for visualizing an electrostatic latent image formed on a recording medium, and more particularly to a device for controlling a developer concentration.

<Outline of the Invention> A developer concentration control device according to the present invention is a developing device of an image forming apparatus using a two-component developer in which a carrier and a toner are mixed, and a mixing ratio of the carrier and the toner is set to a magnetic permeability. It is used to keep the developer concentration substantially constant by replenishing the toner based on the output of the detection device. In particular, the present invention eliminates the influence of the instability factor of the developer concentration detecting device at the time of starting the operation of the developing device, and always keeps the current agent concentration at a predetermined value.

<Prior art and its drawbacks> Electrophotographic copying machines, electrostatic recording devices, laser beam printers, etc. form electrostatic latent images according to image information on recording media, and develop them to visualize the latent images. It is equipped with a device. In this developing device, toner is selectively attached to the electrostatic latent image to form a visible image. In this case, the developing device normally uses a two-component developer composed of a carrier and a toner.

When the electrostatic latent image is visualized by using the two-component developer, if the concentration of the two components, that is, the mixing ratio of the carrier and the toner is not appropriate, the image density is low and it is difficult to see, or Problems such as excessive fog and increased fog occur. Therefore, the developer concentration automatic control device that keeps the developer concentration at a predetermined value by detecting the concentration of the developer so that the mixing ratio is appropriately maintained and replenishing the toner when the concentration drops to some extent Has been proposed and implemented.

As a method for automatically controlling the development density, a method of detecting and controlling the magnetic permeability that changes according to the mixing ratio of the carrier and the toner, and a color that changes according to the mixing ratio of the carrier and the toner colored in different colors are detected. There is also a method of controlling by controlling the change in the amount of toner with respect to a fixed amount of carrier as a volume change.

Of these, the method of detecting a change in toner amount as a volume change is often used because it is easy to detect a reference value, but the amount of carrier must always be constant, and stable operation is always required. Was hard to get.

On the other hand, if the physical characteristics such as magnetic permeability that changes according to the mixing ratio of the carrier and the toner are detected and controlled, there is an advantage that the mixing ratio of the toner can be kept constant even if the carrier decreases. However, in the method of detecting the change in magnetic permeability, if the operation of the developing device is stopped for a certain period of time,
Although the developer concentration does not change due to the sinking of the developer due to its own weight, the slight movement of the developer near the sensor that detects the magnetic permeability, and the change in the fluidity of the developer, the operation of the developing device At the start, a phenomenon occurs in which the apparent magnetic permeability of the sensor changes. As a result, at the start of the operation of the normal developing device, the developer concentration is detected to be lower than it actually is, and there is a problem that more toner than necessary is replenished.

<Object of the Invention> The first object of the present invention is to detect the developer concentration by, for example, detecting the magnetic permeability of the developer and maintain the concentration substantially constant. The purpose is to eliminate the influence of an unstable element of the developer concentration detecting device and stabilize the control of the developer concentration.

<Structure of the Invention> The developer concentration control device of the present invention is provided in a developing tank containing a two-component developer in which toner and carrier are mixed, and the developer is formed on a photoreceptor by an electrostatic charge. A developing roller for developing the latent image, a stirring roller for mixing the toner and the carrier and supplying the stirred developer to the developing roller, and a mixing ratio of the carrier and the toner depending on physical characteristics such as magnetic permeability. A developing device for an image forming apparatus, comprising: a developer toner concentration detecting means for detecting; and a toner replenishing means for replenishing toner based on an output of the toner concentration detecting means to maintain a constant toner concentration of the developer. At the end of the operation of the developing device, a means for storing the detection state of the toner concentration detecting means, and at least the agitating roller of the developing device in front of the initial setting state of the image forming apparatus when the power is turned on. Preliminary rotation means for preliminarily rotating for a certain period of time regardless of the stored contents of the detection state storage means; and, during the preliminary rotation of the stirring roller, when the detection state storage means stores the proper toner concentration state, Even if the replenishment signal due to the toner shortage based on the detection output of the toner concentration detection means is output only by rotating the stirring roller for a certain time, the toner replenishment means prohibits the toner replenishment,
When the detection state storage means stores an improper density, in response to the stored content, the toner replenishment means outputs toner and the toner density detection means outputs a signal for detecting the proper toner density state. It is characterized in that it is provided with control means for performing up to.

<Operation> According to the developer concentration control device having the above configuration, the detection state storage unit stores the toner concentration state of the developer by the toner concentration detection unit at the end of the operation of the developing device due to the end of the image forming operation. . Then, in the initial setting of the image forming apparatus when the power is turned on, at least the stirring roller of the developing device is driven by the preliminary rotating means for a certain period of time regardless of the storage of the proper density state in the detection state storage means.

At this time, if the detection state storage means stores the proper state of the toner density, the toner density detection means runs out of toner,
In other words, the toner replenishing operation is prohibited and only the stirring roller is rotated even if a signal for detecting an inappropriate density is output.

On the other hand, when the detection state storage means stores an improper toner density state, the toner is replenished based on the stored contents. Then, the toner replenishment is continuously performed until the toner concentration detecting means brings the toner concentration into an appropriate state, and at the same time, the stirring roller of the developing device is also rotating.

Therefore, for example, if the proper state of the toner concentration of the developer is stored at the end of the operation of the developing device, the developer sinks due to the stopping of the developing device for a predetermined time or more, and the developer near the toner concentration detecting means of the developer is developed. Due to a slight movement of the developer, a change in the fluidity of the entire developer, etc., the apparent detection state of the toner concentration detection means during the preliminary rotation operation related to the initial setting after the power is turned on is incorrect (the toner concentration is lowered due to lack of toner. ) Is detected, the toner replenishment control is not executed because the toner density is in an appropriate state based on the stored contents.

On the other hand, contrary to the above, if the detection state storage means stores that the toner density is improper, the toner replenishing means is driven during rotation of the stirring roller of the developing device in response to the stored content. Replenishment is performed until the toner concentration detecting means detects the proper state of the toner concentration. By this operation, even if the toner concentration detection means does not detect the toner concentration normally due to the sinking of the developer, the movement of the developer, the change of the fluidity of the developer, etc., the toner is in a state of being insufficient as a whole, and the toner concentration is low. It does not significantly exceed the specified value. In addition, since toner is replenished during preliminary rotation at the time of initial setting when the power is turned on, development can be performed in an appropriate state from the start of the copy operation after initial setting, and the toner concentration is kept constant by toner replenishment control. I can keep it. In this case, since the sufficient stirring operation is performed even when storing the proper state in which the toner is not replenished, the development can be performed in the proper state from the beginning of the copy operation after the initial setting, and the toner density control can be performed.

<Embodiment> FIG. 1 is a block diagram of a control unit of a copying machine provided with a developer concentration control device of the present invention.

The entire control is performed by the program processing of the CPU 30, and the control program is written in the ROM 31 in advance. The RAM 32 is used as a working area such as a counter and a flag when executing the control program. Various input / output circuits are connected to the I / Os 33 and 37. The developer concentration detecting circuit 34 detects the concentration of the developer and outputs a binary output signal. The CPU 30 controls the toner motor controller 39 based on the signal output from the developer concentration detection circuit to replenish the toner. The key matrix / sensor 35 is a key input device and other sensors, and the CPU 30 reads its state via the I / O 33. The display device 36 displays each state of the copying machine. The main motor controller 38 is a circuit that controls the main motor of the copying machine.

FIG. 2 is a sectional view of a developing device portion provided in the copying machine.

Reference numeral 5 is a drum-shaped photoconductor, and 15 is a developing device for developing the electrostatic latent image formed on the photoconductor. In the developing device 15, a developing roller 3 including a cylindrical non-magnetic sleeve 10 and a magnet 11 provided in the sleeve is provided in a developing tank 19. The sleeve 10 is rotated clockwise in the drawing, and the magnet 11 is fixed so that the N ₁ pole (main pole) is opposed to the developing position of the photoconductor 5 in particular. Therefore, the developer 2 is adsorbed on the sleeve 10 by the magnetic force of the magnet 11,
This developer is conveyed to the developing position facing the photoconductor 5 as the sleeve 10 rotates, and after this conveyance, the developing tank 1
It is returned to 9 and stirred by the stirring roller 4. Sleeve 10
The amount of the developer 2 adsorbed on the developer 2 is regulated by the doctor 12 to be constant while being conveyed to a position facing the photoconductor 5.

In the developing device configured as described above, the sensor 20 for detecting the toner concentration of the developer 2 is the S of the magnet 11.
It is arranged at a position facing between the _first pole and the N ₂ pole.

When the sleeve 10 is rotated, the developer 2 attracted by the magnetic force of the magnet 11 is conveyed onto the sleeve according to the rotation of the sleeve 10. The developer that has passed through the developing area of the photoconductor 5 during the transportation passes through the sensor 20. At this time, the sensor 20 detects a change in magnetic permeability in order to detect the density of the developer 2 passing through. Here, when the sensor 20 detects that the developer concentration is below the reference, the toner supply roller 8 is rotated and the toner 7 in the hopper 9 is supplied into the developing tank 19. The supplied toner is sufficiently stirred with the developer 2 by the stirring roller 4 and sent to the developing roller 3. As a result, the concentration of the developer gradually increases, and the sensor 2
When it is detected that 0 is a constant developer concentration, the rotation of the toner supply roller 8 is stopped and the toner supply is stopped.

FIG. 3 is a diagram showing a developer concentration detecting circuit using the sensor 20.

As shown in the figure, the sensor 20 has a ferrite core 21
A coil L ₁ for applying a reference signal, a coil L ₂ for detecting the magnetic permeability of the developer _2, and a coil L for reference adjustment.
₃ is wound around, and in particular, it faces the developer ₂ for detecting the coil L ₂ side, and the developer 2 and the ferrite core 21 form a closed magnetic circuit. A ferrite core 21 and a screw-shaped reference adjustment core 22 forming another closed magnetic circuit are provided on the coil L ₃ side, and the core 22 adjusts the magnetic flux passing through the coil L ₃ . Coil L ₂ and coil L
₃ is wound in the opposite direction and connected in series. Further, one end of the coil L ₃ is grounded, and one end of the coil L ₂ is connected to one terminal of the phase detector 23.

An oscillator 24 that outputs a reference signal is connected to the coil L ₁ and is supplied with the reference signal. Oscillator 24
The inversion signal of the reference signal of is supplied to the other terminal of the phase detector 23. The phase detector 23 outputs a signal whose pulse width is modulated according to the phase difference between the two signals, and this output signal is supplied to the smoothing circuit 25. Here, for example, if the concentration of the developer 2 is reduced, the magnetic permeability is increased, and the induced voltage of the coil L ₂ is also increased and the phase is shifted accordingly. Then, the composite signal of the induced voltage of the coil L ₃ and the voltage of the coil L ₂ that hardly changes is supplied to the phase detector 23, so that the phase relationship with the reference signal is compared and the pulse width of the output signal is growing. The smoothing circuit 25 supplies a high voltage to the voltage comparator 26 as the pulse width increases. As a result, the voltage comparator 26 outputs an "H" level signal.

FIG. 4 is a circuit diagram showing details of FIG.

In the figure, V _D is a power supply voltage, which is made constant by a constant voltage circuit using a Zener diode ZD1.
In the oscillator 24, the exclusive OR circuit EX1 is used as an amplifier circuit, and the coil L ₁ and the capacitors C2 and C3 form a positive feedback circuit. In the phase detector 23, the combined induced voltage of L ₂ and L ₃ of the sensor 20 is supplied to the base of the amplifying transistor Q1 after the direct current component is cut off via the capacitor C5. The signal amplified by the transistor Q1 is waveform-shaped by the exclusive OR circuit EX2 and supplied to one terminal of the exclusive OR circuit EX3 for phase detection. The inverted output signal of the oscillator 24 is supplied to the other terminal of the circuit EX3 to output a pulse signal having a width corresponding to the phase difference between the reference signal and the detection signal due to the change in permeability.

The voltage comparator 26 comprises an exclusive OR circuit EX4, and the detected signal is applied to one input terminal of this circuit EX4. The resistor R6 is provided to give the voltage comparator a hysteresis characteristic.

FIG. 6 is a diagram showing the detection output (level of the output point of the smoothing circuit) with respect to the weight percentage of the toner of the density of the developer. In the figure, when the developer concentration increases, A → B
→ C → D → F → G → H, and when descending, H → G
→ F → E → C → B → A changes. By providing the voltage comparator with the hysteresis characteristic in this way, the output signal of the developer concentration detecting circuit is prevented from repeating inversion at a minute time interval when the developer concentration is near the proper concentration.

FIG. 7 shows the detection output (smoothing circuit 25
Is a diagram illustrating an example of the output signal of FIG. As is clear from the relationship with FIG. 6, the developer concentration decreases and the detection output becomes 2.
When it exceeds 5 V (t1), it reaches the voltage V _C. As a result, the voltage comparator outputs "H" level, and toner supply is started. When the developer concentration rises and the detection output falls below 2.5 V (t2), the voltage reaches V _F. As a result, the voltage comparator outputs "L" level, and the toner supply is stopped.

In this way, the developer concentration is maintained at an appropriate value. However, as shown in the figure, by leaving it for a time of ta to tb, the developer sinks due to its own weight, the flow of the developer near the magnetic permeability sensor, Furthermore, the detection output immediately after the start of operation increases by the voltage υ due to changes in the fluidity of the developer.

FIGS. 5 (A) and 5 (B) are flowcharts showing the processing procedure of the control unit shown in FIG. 1 for eliminating the adverse effect of the voltage rise of the detection output.

After the copying machine is set to the initial state when the power is turned on, the rotation of the photosensitive drum and the preliminary rotation of the stirring roller provided in the developing device are started (n10). Then, the value of the toner counter is determined (n11). The toner counter is a counter that stores the number of copies made when the developer density falls below the reference value (under toner state), and this value is stored in the RAM even when the developing device is not operating. If the toner counter is 0, it means that the developer density was proper at the end of the operation of the developing device, and a certain time is waited until the preliminary rotation is completed (n11 → n16 → n1).
7).

After that, when the copy start is performed, it is determined whether the under toner state is present or not based on the output signal of the developer concentration detection circuit (n19). In the under toner state, the toner motor that drives the toner supply roller is turned on (n2
0). When the density of the developer reaches an appropriate value during the copy cycle, the toner motor is turned off and the toner counter is reset (n25 → n26). If the developer concentration does not reach the reference value by the end of one copy cycle, the toner counter is incremented (n22).
As a result, when the value of the toner counter exceeds 30, it is in a state where the toner cannot be replenished, and the operation of the copying machine is forcibly stopped (n23 → n24).

At the start of the operation of the developing device (during preliminary rotation of the stirring roller), if the value of the toner counter is 1 or more, the toner motor is turned on until the developer concentration detected by the developer detection circuit is not under toner ( n11 → n12 →
n13 → n12). When the density of the developer is not under toner, the toner motor is turned off and the toner counter is reset (n14 → n15). When toner is replenished according to the output of the developer concentration detection circuit while preliminarily rotating the stirring roller, the sinking of the developer is relieved during the toner replenishment and the abnormality detection output of the developer concentration detection circuit is eliminated. The toner is replenished in accordance with the normal output of the developer concentration detection circuit, so that the developer has an almost proper toner mixing ratio. When the toner is replenished, the toner mixing ratio is originally low, so that the toner is hardly over-replenished. Moreover, when the toner mixing ratio is significantly reduced (when the toner counter value is close to 30), the toner supply is started at the same time as the preliminary rotation is started, so that the time until the completion of the toner supply is shifted backward. (If the toner supply is started after a certain period of time, the time until the toner supply is completed becomes longer by that much), and the time until the copy start can be shortened.

As described above, when the value of the toner counter is 0 during the preliminary rotation of the stirring roller, only the stirring roller is rotated regardless of the output state of the developer concentration detection circuit. Therefore, the abnormality detection output of the developer concentration detection circuit during the preliminary rotation of the stirring roller is ignored, and the actual developer concentration can be appropriately maintained.

The above embodiment detects a change in the magnetic permeability of the developer by a phase detection circuit as a developer concentration detection circuit.By adding a hysteresis characteristic to the detection output of this phase detector, the output level of the voltage comparator is increased. Stabilizes so as not to repeat inversion at a minute time interval, but by reducing the width of this hysteresis to some extent,
It is possible to suppress a rise in the detection output voltage at the start of operation of the developing device after being left for a long time. FIG. 8 is a diagram showing an example in which the hysteresis width is set to be smaller than that in the case of the detection output characteristics shown in FIG. As shown in the figure, when the developing device is left unattended from time ta to time tb, the rising voltage ν ′ becomes small. Therefore, after the operation of the developing device is started, the time during which the output of the phase detector can be regarded as stabilized can be substantially shortened. In this way, the toner concentration of the developer can be controlled efficiently and with high responsiveness by appropriately setting the certain period of time during which the toner replenishing means should be prohibited according to the voltage increase width.

<Effects of the Invention> According to the present invention, since toner is not replenished more than necessary when the operation of the developing device is started by the start of image formation, the toner for always maintaining an appropriate toner concentration from the beginning of the image formation operation. Replenishment control can be performed, the density can be kept constant, and development can be performed without fogging.

[Brief description of drawings]

FIG. 1 is a block diagram of a control unit of a copying machine using a developer concentration control device of the present invention, FIG. 2 is a sectional view of a developing device portion of the copying machine, and FIG. 3 is a developer concentration detection circuit. FIG. 4 is a block diagram, FIG. 4 is a detailed circuit diagram thereof, FIGS. 5 (A) and 5 (B) are flowcharts showing a processing procedure of the control unit, and FIG.
FIG. 7 is a diagram showing the relationship between the output of the smoothing circuit and the developer concentration, and FIGS. 7 and 8 are diagrams showing the fluctuation state of the output level of the smoothing circuit due to the control of the developer concentration.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Tatsuya Ito 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Within Sharp Corporation (56) References JP-A-62-105172 (JP, A) JP-A-56 -119156 (JP, A)

Claims (1)

[Claims] 1. A developing roller provided in a developing tank for containing a two-component developer containing a mixture of a toner and a carrier, the developing roller for developing the electrostatic latent image formed on a photoreceptor.
An agitating roller for supplying the developer, in which the toner and the carrier are mixed and agitated, to the developing roller, and a toner concentration detecting means of the developer for detecting a mixing ratio of the carrier and the toner by physical characteristics such as magnetic permeability, A developing device of an image forming apparatus, comprising: a toner replenishing device for replenishing toner based on an output of the toner concentration detecting device to keep the toner concentration of a developer constant, wherein the toner concentration is A means for storing the detection state of the detection means, and a pre-rotation means for preliminarily rotating at least the stirring roller of the developing device for a certain period of time regardless of the stored contents of the detection state storage means when the image forming apparatus is initialized when the power is turned on. During the preliminary rotation of the stirring roller, when the detection state storage means stores the proper toner concentration state, Prohibits toner replenishment by the toner replenishing means be replenished signal is output by the toner shortage based on the detection output of the toner concentration detecting means by simply rotating a certain period of time,
When the detection state storage means stores an improper density, in response to the stored content, the toner replenishment means outputs toner and the toner density detection means outputs a signal for detecting the proper toner density state. A developer concentration control device, comprising: