JPH11119538A - Toner concentration detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the detecting accuracy of toner concentration by installing a conductor on an opposite-side surface to the concentration detecting surface of a base plate and setting the thickness of the conductor within a specified range. SOLUTION: A detection coil 12 formed to be plane is provided on the base plate 11. The coil 12 is a plane coil pattern formed by providing a silver foil on the surface of the base plate 11 and etching it, and is formed to be a vortex having 50 to 100 μm width and about 100 to 200 μm pitch. The conductor 13 made of metal or the like having a shielding effect is provided on the back side of the base plate 11. However, the expected effect is not obtained if the conductor 13 does not have the specified thickness. Then, the thickness d[m] of the conductor 13 is set to satisfy a relational expression d>=503×√(ρ/f×μs). Provided that ρ is the resistivity [Ω.m], μs is the relative permeability of the conductor and (f) is the oscillation frequency [Hz]. By providing the conductor 13 having the specified thickness as a shielding member, influence associated with temperature change is decreased and the detecting accuracy is enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a toner density detecting device which uses an LC oscillation circuit for detecting a toner density in a developing device and is used in an image forming apparatus such as a copying machine. More specifically, the present invention relates to a toner concentration detection device having a detection coil formed thereon.

[0002]

2. Description of the Related Art In an image forming apparatus for forming an image by an electrophotographic method, an electrostatic latent image is formed on a photoreceptor, developed by a developing device to form a toner image, and then transferred to a recording paper. And fixation is performed.

[0003] Conventionally, there are two types of toner and carrier.
Since the developing device having the component developer consumes toner during development, the toner concentration is detected by a toner concentration detecting device, and when it is determined that the amount of toner is low, the toner is supplied from the toner replenishing section to the developing device. In addition, the image density was prevented from lowering. Several methods for detecting the toner density have been proposed, and one of them is a method for detecting the toner density using a change in the oscillation frequency of an LC oscillation circuit. The apparent magnetic permeability of the developer, which is a mixture of iron powder as a carrier and toner, changes depending on the toner concentration. When the coil is brought close to the developer by, for example, embedding the coil in the developer, the inductance of the coil changes depending on the magnetic permeability of the atmosphere. The oscillation frequency of the LC oscillation circuit is f = 1
/ (2π√ (LC)), a change in toner density can be detected by measuring the frequency f. Various types of toner concentration detecting devices that detect the toner concentration using this LC oscillation circuit have been proposed.
For the purpose of reducing the size and reducing the cost, a toner concentration detecting device for detecting the concentration by a detecting coil formed planarly on a substrate has been proposed by the present applicant (Japanese Utility Model Laid-Open No. 6-79661, JP-A-7-248676, etc.). Further, in order to improve the detection sensitivity of the toner concentration in this toner concentration detecting device, it has been proposed by the present applicant to provide a magnetic material for shielding a flat coil on the back surface of the substrate provided with the detecting coil ( Actual Kaihei 7
-29553). In this proposal, the purpose of installing a magnetic material on the back surface of the substrate is to change the output of the planar coil when the distance from the planar coil changes due to the movement of the screws and other magnetic materials around the detection device due to the vibration of the equipment etc. The purpose of the present invention is to prevent the detection accuracy from deteriorating due to fluctuation.

[0004]

The inventor of the present invention detects the concentration of the toner component in the developer by changing the frequency of the resonance circuit due to the inductance and capacitance of the detection coil formed planarly on the substrate. Further research was conducted on the toner concentration detection device to improve the detection accuracy. As a result, it has been found that if the magnetic material provided on the back surface of the substrate does not have a predetermined thickness, the shielding effect is reduced, and the above-described object of preventing the lowering of the detection accuracy cannot be achieved. Regarding the thickness of the substrate, if the substrate is thick and the distance between the detection coil and the magnetic material is large, the distance between the detection coil and the magnetic material will fluctuate due to the thermal expansion of the substrate, which will affect the inductance change. The effects of this were clarified by experimental research. vice versa,
It has also been found that when the substrate is thin and the distance between the detection coil and the magnetic material is short, the inductance is small, that is, the oscillation frequency is large, making it difficult to measure, and the influence of the oscillation frequency is exerted on the outside. Therefore, to avoid the above effects,
It is also necessary to set the thickness of the substrate within a predetermined range.

The present inventor has an object to provide a toner density detecting device which does not lower the detection accuracy based on the above research results.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to detect a toner concentration in a developer by detecting a change in the frequency of a resonance circuit due to the inductance and capacitance of a detection coil formed planarly on a substrate. A toner density detecting device, wherein a conductor is provided on a surface of the substrate opposite to a density detecting surface, and a thickness d [m] of the conductor satisfies the following relational expression. apparatus.

D ≧ 503 × √ (ρ / f × μ _S ) where ρ: Conductivity [Ω · m] μ _S : Relative permeability of conductor f: Oscillation frequency [Hz] (the invention of claim 1) and A toner concentration detection device that detects the concentration of a toner component in a developer by a frequency change of a resonance circuit due to inductance and capacitance of a detection coil formed planarly on a substrate, wherein a concentration detection surface on the substrate and The present invention is attained by a toner concentration detecting device (invention of claim 2), wherein a conductor is provided on the opposite surface, and the thickness of the substrate is set between 0.8 and 2 mm.

[0008]

FIG. 1 is a perspective view showing an embodiment of a toner concentration detecting device according to the present invention, and FIG. 2 is a circuit diagram. On the substrate 11, a detection coil 12 formed in a plane is provided. The detecting coil 12 is, for example, a planar coil pattern formed by providing a copper foil on the surface of the substrate 11 and etching the same, and has a width of 50 to 100 μm and a pitch of 100.
It is formed in a spiral shape of about 200 μm. The upper surface of the detection coil 12 is covered with a protective layer such as an insulating resin, and the toner concentration detecting device 10 is provided in the developing device so as to approach the developer to be detected via the protective layer. I have.

The circuit according to the present embodiment comprises an inductance L by the detection coil 12, capacitors C ₁ and C ₂ , and a resistor R.
The resonance circuit 10A is configured by the connection shown in the drawing, and is input to the counter 21 via the inverter C-MOS. In the CPU 20, the gate generation circuit 22
The gate is opened for a predetermined time, and the number of pulses during that time is counted by the counter 21. The CPU 20 compares this counter number with a preset count number, and when the difference is equal to or larger than a predetermined value, replenishes the toner.

In a toner concentration detecting device, it is necessary to accurately measure a change in inductance due to a change in developer concentration. However, as shown in the explanatory diagram of FIG. 3, the developer to be detected exists on the front side of the detection coil 12, but there is an object not to be detected on the back side. Aside from maintaining a fixed condition for the object that the user does not want to detect, the detection accuracy greatly decreases when the object fluctuates. In the present invention, as shown in FIG. 1, a conductor 13 made of metal or the like having a shielding effect is provided on the back side of the substrate 11. However, the desired effect cannot be obtained unless the conductor 13 has a predetermined thickness. The present inventor found that conductor 1
The thickness d [m] of No. 3 is represented by the following relational expression d ≧ 503 × √ (ρ / f × μ _S ), where ρ: Conductivity [Ω · m] μ _S : Relative permeability of conductor f: Oscillation frequency It was confirmed experimentally that it was necessary to satisfy [Hz].

As an example, the present inventor has set an oscillation frequency f = 3.5 MHz used for toner concentration detection, and made the conductor 13 an electric copper (conductivity ρ = 1.69E-8Ω · m, relative magnetic permeability μ _S ≒ 1). ) And by setting the thickness of the conductor 13 to d ≒ 35 μm or more, a sufficient shielding effect is obtained.

Further, the present inventor has found that providing the shield member alone is not sufficient, and that the substrate 11 is important for stably and accurately detecting the toner density. FIG. 4 is a graph when the distance between the detection coil 12 and the conductor 13 as a shield member is plotted on the horizontal axis and the oscillation frequency is plotted on the vertical axis. As shown in FIG. 4, when the distance between the detection coil 12 and the conductor 13 changes, the oscillation frequency changes. Therefore, if the thickness of the substrate 11 corresponding to the distance between the detection coil 12 and the conductor 13 is large, the distance variation becomes large due to the influence of thermal expansion. Therefore, the thickness of the substrate 11 is preferably thin. On the other hand, when the plate thickness is 0.8 mm, the oscillation frequency f = 4M
Hz, and the plate thickness is 0.8 mm or less, the transmission frequency becomes higher, the measurement counter becomes higher in counting, causing difficulty, and high-frequency radiated radio waves are generated by wiring inside the machine. But not preferred. The inventor conducted an experiment on the thickness of the substrate 11 that is allowed for a generally used printed circuit board. In consideration of the effects of thermal expansion and the oscillation frequency due to temperature changes in environmental conditions, it was found that the thickness of the substrate 11 was desirably set to 0.8 to 2 mm.

Furthermore, various investigations were made on the substrate material of the substrate 11, and as a result, it was concluded that glass epoxy or ceramic was suitable as a material having low thermal expansion and appropriate strength. If glass epoxy or ceramic is used as the substrate material of the substrate 11,
More accurate toner density detection is possible.

[0014]

According to the present invention, a detection coil formed two-dimensionally on a substrate is used, and the concentration of the toner component in the developer is detected by a frequency change of a resonance circuit due to inductance and capacitance. With respect to the toner concentration detecting device, a target having a predetermined thickness is shielded by providing a conductor having a predetermined thickness as a shield member for an object that the user does not want to detect (claim 1). (2) and (3), a toner density detecting device which is stable and has high detection accuracy is provided.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an embodiment of a toner concentration detecting device according to the present invention.

FIG. 2 is a circuit diagram showing one embodiment of a toner concentration detection device.

FIG. 3 is an explanatory diagram of detection accuracy of toner density.

FIG. 4 is a graph showing a relationship between a distance between a coil and a shield and an oscillation frequency.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Toner density detection apparatus 10A Resonant circuit 11 Substrate 12 Detection coil 13 Conductor

Claims (3)

[Claims] 1. A toner concentration detecting device for detecting a concentration of a toner component in a developer by a frequency change of a resonance circuit due to an inductance and a capacitance of a detection coil formed planarly on a substrate, wherein A toner density detecting device, wherein a conductor is provided on a surface opposite to the density detecting surface, and the thickness d [m] of the conductor satisfies the following relational expression. d ≧ 503 × √ (ρ / f × μ _S ) where ρ: Conductivity [Ω · m] μ _S : Specific magnetic permeability of conductor f: Oscillation frequency [Hz] 2. A toner concentration detecting device for detecting a concentration of a toner component in a developer by a frequency change of a resonance circuit due to an inductance and a capacitance of a detection coil formed planarly on a substrate, wherein A toner density detecting device, wherein a conductor is provided on a surface opposite to the density detecting surface, and the thickness of the substrate is set to 0.8 to 2 mm. 3. The toner concentration detecting device according to claim 1, wherein the substrate is made of glass epoxy or ceramic.