JPH11223620A - Toner concentration detecting device and manufacture of toner concentration detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a detecting device capable of showing constant performance, reducible in size and hardly causing an error by a change in an environmetal temperature by finding an oscillation frequency of an LC oscillation circuit according to a specific expression, and setting inductance, capacitance and a circuit constant of a resistance of a coil to a specific condition. SOLUTION: An oscillation frequency (f) of an LC oscillation circuit is found according to an expression in detecting the toner concentration of a developer from the oscillation frequency of the LC oscillation circuit. In the expression, L is inductance of the LC oscillation circuit, and C is capacitance, and RL is a reistance of a coil. A circuit constant is respectively set so that a change in these circuit constants in an operating temperature range does not bring about a change in the frequency (f) larger than an allowable value. In the case of the LC oscillation circuit constituted of a coil having inductance formed of a print, a resistance value of the coil is set to 2 to 20 Ω, and the fact that a resistance value of the coil falls within a predetermined range is confirmed in manufacturing a tonner concentration detecting device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a toner concentration detecting device for detecting a toner concentration of a developer in a developing device of an electrophotographic apparatus.

[0002]

2. Description of the Related Art An electrophotographic apparatus is equipped with an automatic toner replenishing control device so that an image having a constant density is always formed by replenishing toner consumed during image formation. As such an automatic control device, a toner concentration detecting device is used. As the toner concentration detecting device,
A so-called L detection type toner concentration detection device (hereinafter, referred to as an L detection device) that detects a change in magnetic permeability of a developer caused by a change in density as a change in an oscillation frequency of an oscillation circuit is widely used.

As a conventional L detecting device, there is a core type L detecting device in which a coil is wound around a magnetic core to form a magnetic field in a space containing a developer to be detected and an LC oscillation circuit is formed by the coil. in use.

[0004] Such a conventional core-type L detector has a high manufacturing cost and is a component in which the core is formed by sintering. There is a problem in that there is a problem in quality control due to variations in the performance of the device, and it is difficult to reduce the size.
In order to solve such a problem of the conventional core type L detecting device, the present applicant disclosed in Japanese Patent Application Laid-Open No. 7-248676 a printed coil type L detecting device in which the inductance of an LC oscillation circuit is constituted by a coil formed by printing. The device was proposed.

[0005] The print coil type L detector has an inductance, and a coil for generating a magnetic field is formed by printing.
This has a remarkable advantage over an equal-core L detection device that can be miniaturized.

[0006]

In the L detection device, a change in the toner concentration in the developer is detected as a change in the oscillation frequency of the LC oscillation circuit. In the print coil type L detection device described, the oscillation frequency f is obtained by the following equation (1).

[0007]

(Equation 2)

In designing the toner concentration detecting device, the inductance and the capacitance, which are the circuit constants of the LC oscillation circuit, are determined based on the above equation (1).

However, as a result of research conducted by the inventor of the present invention, in a printed coil type L detecting device in which a coil that generates inductance of an LC oscillation circuit is formed by printing, it is necessary to ignore the resistance component of the circuit to obtain the oscillation frequency. It was found that it was necessary to design the circuit in consideration of the resistance component. The reason is as follows.

[0010] The toner concentration detecting device is required to operate normally in an environment where the electrophotographic device is installed, particularly, within a predetermined temperature range. In the print coil type L detector, the influence of the resistance of the circuit on the oscillation frequency cannot be ignored, and the oscillation frequency changes due to the temperature change of the resistance value. It was found that the difference between the oscillation frequencies at the upper and lower limits of the operating temperature range exceeded the allowable value.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems in a printed coil type L detecting device, which exhibits constant performance, can be miniaturized, and has an error caused by a change in environmental temperature. It is an object of the present invention to provide a toner density detecting device which has a small amount of toner.

[0012]

The object of the present invention is as follows.
(1) In a toner concentration detecting device for detecting a toner concentration of a developer from an oscillation frequency of an LC oscillation circuit, an oscillation frequency f of the LC oscillation circuit is calculated by the following equation (2).

[0013]

(Equation 3)

The inductance L of the LC oscillation circuit, the capacitance C, and the resistance R of the coil
_L is set such that a change in these circuit constants in the operating temperature range of the toner concentration detecting device does not cause a change in the frequency f larger than an allowable value. (3) Inductance in a toner concentration detecting device, wherein a resistance value of the coil is set to 2 to 20 Ω, and (3) inductance. When manufacturing a toner concentration detecting device using a LC oscillation circuit constituted by a coil formed by printing as a detecting member, it is confirmed that the resistance value of the coil is within a predetermined range. The manufacturing method of the detection device is achieved.

Hereinafter, the above-mentioned problem in the printed coil type L detecting device will be specifically described, and the operation of the present invention will be described.

In an example of the core type L detecting device, when the lower limit of the environmental temperature at which the device is used is 10 ° C. and the upper limit is 50 ° C., the difference between the oscillation frequencies at the upper and lower limits is about 140 Hz. On the other hand, the toner concentration of the developer is required to be measured up to a change of 1%. An experimental result was obtained in which the fluctuation of the oscillation frequency corresponding to the change of the toner concentration of 1% in the core type L detecting device was about 1 KHz. That is, 1
KHz is a control target, but a fluctuation of 140 Hz at maximum, which is a fluctuation due to temperature, is a sufficiently small value with respect to the control target of 1 KHz, and it is a value that can be ignored in measuring the toner density. it can.

On the other hand, in the example of the print coil type L detecting apparatus, the fluctuation of the oscillation frequency in an environment of 10 to 50 ° C. is 4.2 KHz, and the fluctuation of the oscillation frequency corresponding to the change of 1% of the toner density is about 5 KHz. Experimental results were obtained respectively. For a control target of 5 KHz, a fluctuation of 4.2 KHz at the maximum is not a negligible value for control.

Usually, in order to compensate for such fluctuations due to temperature, a method is adopted in which a temperature compensating capacitor having appropriate temperature characteristics is selected and the temperature characteristics of the toner density detecting device are suppressed to a desired range.

However, in the printed coil type L detecting device, a capacitor considered to be appropriate was selected, and the fluctuation of the oscillation frequency was confirmed. As a result, a value different from the expected value was obtained. As a result of investigating the cause, it was found that the resistance component generated in the print coil affected the oscillation frequency. It is considered that the reason is that in the printed coil type L detection device, a large inductance cannot be obtained due to its structure, and the resistance component has a large influence on the oscillation frequency.

From such considerations, in the printed coil type L detecting device, the oscillation circuit is represented as shown in FIG. 2 in consideration of the resistance component R _L of the printed coil, and the oscillation frequency is represented by the equation (2). You.

[0021]

(Equation 4)

In FIG. 2, the oscillation circuit is a typical Colpitts oscillation circuit comprising a coil L having a predetermined inductance, capacitors C1 and C2, a transistor Q and a resistor R. It is composed of coils. R _L is a resistance generated in the coil portion.

When a voltage V is applied to this circuit, an oscillation signal is output from the source of the transistor Q. R _L is a resistance of the coil L. The oscillation circuit is not limited to the Colpitts oscillation circuit.

On the other hand, in the case of the core type L detector, the value of the inductance can be much larger than that of the printed coil type L detector due to its structure.
The oscillation frequency is within an error range that does not normally cause a problem even when approximated by the equation (1).

[0025]

(Equation 5)

In the present invention, by selectively adjusting the circuit constant of the oscillation circuit based on the above equation (2), the error caused by the temperature change can be sufficiently suppressed within the environmental temperature range in which the toner density detecting device is used. Printed coil type L
The detection device was successfully realized.

As described above, in the printed coil type L detecting device, the resistance of the coil cannot be ignored.
In the production of the toner concentration detecting device of the present invention,
Quality control is performed according to a different method.

In the manufacture of a conventional toner concentration detecting device, at the quality inspection stage, an inspection is performed to determine whether or not the oscillation frequency is within a predetermined range. No test was performed to determine if the values were within the range.

In the present invention, an inspection is performed to determine whether or not the resistance of the coil portion of the oscillation circuit is within a predetermined range.

Further, by setting the resistance of the printed coil type L detection device within the range of 2 to 20 Ω, the inductance and the capacitance are selectively adjusted together with the selection and adjustment of the resistance value. A printed coil type L detecting device having a high sensitivity could be manufactured. When the resistance value is smaller than 2Ω, the length of the coil formed by the printing pattern cannot be made large, so that the inductance becomes small and the required sensitivity cannot be obtained. If the resistance value exceeds 20Ω, the fluctuation of the oscillation frequency due to the temperature change of the resistance value becomes large, the error due to the temperature change exceeds the allowable value, and if this temperature error is to be corrected by inductance and capacitance, the Q value And the object of the present invention cannot be achieved.

[0031]

FIG. 3 is a plan view of a developing device in which the toner density detecting device of the present invention is used, and FIG. 4 is a sectional view taken along line AA in FIG.

In these figures, reference numeral 10 denotes a housing of a developing device for accommodating a two-component developer composed of toner and carrier, 11 denotes a lid for closing an upper opening of the housing 10, and 12 denotes a developer to be conveyed to a developing area. Developing sleeve,
Reference numeral 13 denotes a magnet body composed of a plurality of magnets that generate a magnetic field that forms a developer layer on the developing sleeve 12, reference numeral 14 denotes a paddle wheel that supplies a developer to the developing sleeve 12, and reference numeral 15 denotes a developer on the developing sleeve 12. The developer layer thickness regulating member regulates the layer thickness to a predetermined amount.

Reference numerals 16 and 17 denote agitating screws for agitating and transporting the developer. The first agitating screw 16 is provided in the vicinity of an opening 18 for receiving the replenishment toner, and the second agitating screw 17 is a paddle wheel 14. Is provided in the vicinity.

The first stirring screw 16 and the second stirring screw 17 are provided in a first stirring chamber 10B and a second stirring chamber 10C formed on both sides of a partition wall 10A standing upright from the bottom of the housing 10. 4 and are driven and rotated by drive sources (not shown) in opposite directions indicated by arrows, as shown in FIG.

The first stirring screw 16 conveys the developer in the direction of the arrow shown in FIG. 1 by its rotation. Further, a paddle portion 16A is integrally formed on the most downstream side of the first stirring screw 16 in the developer conveying direction. The developer conveyed by the rotation of the first stirring screw 16 passes through the opening 10 </ b> D at the end of the partition wall 10 </ b> A, and is conveyed to the upstream side of the second stirring screw 17.

The second stirring screw 17 has substantially the same shape as the first stirring screw 16, and is supported by the housing 10 in a position opposite to the front and rear. That is, the paddle portion 17A is also formed integrally with the second stirring screw 17 at the downstream end in the developer conveyance direction. By the rotation of the second stirring screw 17, the developer is transported as shown by the arrow,
It is supplied to the paddle wheel 14 side. The developer conveyed to the downstream side of the second stirring chamber 10C by the second stirring screw 17 passes through the opening 10E at the other end of the partition wall 10A, and the first stirring screw in the first stirring chamber 10B. 1
Reflux upstream of 6.

In a longitudinal space where the photosensitive drum 1 and the developing sleeve 12 are closely opposed to each other, an electrostatic latent image formed on the photosensitive drum 1 is developed by the developer conveyed by the developing sleeve 12. This is a development area E.

Reference numeral 18 shown in FIG. 3 denotes a toner replenishing opening formed on the top of the lid 11, which is provided near the uppermost stream in the developer conveying direction of the second stirring screw 17, and stores toner from a toner cartridge (not shown). The toner replenished through the means, the toner conveying means and the opening 18 is received and introduced into the first stirring chamber 10B.

From the toner cartridge to the toner storage means,
The newly supplied toner supplied to the opening 18 of the developing device via the toner conveying means is conveyed in the direction indicated by the arrow while being stirred and mixed with the developer by the first stirring screw 16 rotating in the first stirring chamber 10B. The paddle 16C is fed into the second stirring chamber 10C through the opening 10D at the end of the partition wall 10A. The developer sent into the second stirring chamber 10 </ b> C is moved by the second stirring screw 17.
Further, the toner is supplied to the paddle wheel 14 while being stirred, and is supplied onto the developing sleeve 12 by the paddle wheel 14.

The developer in which the latent image has been developed in the developing area E and the toner has been consumed is removed by the magnet 1 inside the developing sleeve 12.
3 from the surface of the developing sleeve 12 by the repulsive magnetic field,
It is returned to the second stirring screw 17 by the paddle wheel 14. The second stirring screw 17 has its paddle portion 17
A, the reflux developer is passed through the opening 10E to the first stirring chamber 10B.
Transport to

Immediately upstream of the toner supply opening 18, there is provided a toner density sensor 20 for detecting the toner density of the developer. The installation position of the toner density sensor 20 is a position where the developer flowing from the developing unit and before supplying new toner can be measured.

FIG. 5 shows the mounting structure of the toner density sensor 20. In FIG. 5, reference numeral 20 denotes a toner concentration sensor formed of a printed circuit board.
It is arranged below. The first stirring screw 16 is provided with respect to the housing 10 such that a gap D is formed between the inner wall S1 of the housing 10 and the outer periphery S2 of the screw blade of the first stirring screw 16. Smooth rotation is ensured.

In the portion where the toner concentration sensor 20 is provided, a spacer 30 is provided between the inner wall S1 of the developing device housing 10 and the first stirring screw 16 to fill the gap D. This spacer 30 is used for the first stirring screw 1.
No. 6 is provided in order to prevent a gap between the outer periphery S2 of the screw blade 6 and the spacer 30 such that the developer stays there.

The toner density sensor 20 detects the density of the developer by measuring the magnetic permeability of the developer existing in the magnetic field formed by the toner density sensor 20. By disposing the spacer 30 as described above, the developer does not stay in the magnetic field formed by the toner concentration sensor 20, and the developer existing in the magnetic field is removed by the screw blade of the first stirring screw 16. Only the developer filling the space, that is, the developer filling the space S4 in FIG. This developer is not a stagnant developer,
The developer is being conveyed by the stirring screw 16.

With such a configuration of the density detecting section, noise caused by the staying developer is removed, and accurate density detection can be performed.

The toner density sensor 20 employs an L detection method for detecting the magnetic permeability of the developer. The L detection method utilizes the fact that the carrier is a magnetic substance, forms a magnetic field in the developer, and detects the toner density of the developer by measuring the magnetic permeability of the developer.

FIG. 6 is a plan view of a printed circuit board on which the coil L is formed.

[0048]

Embodiment (1) Embodiment 1 A commercially available capacitor that can be used in the oscillation circuit of the printed coil type L detection device is selected, and the optimum value of the resistance _RL of the coil portion for the selected capacitor is calculated by the above equation (2). Were evaluated according to the following formula.

FIG. 7 shows the resistance R of the coil portion in the oscillation circuit.
₅ is a graph showing a temperature change of a circuit constant of an oscillation circuit used for selecting _L and a capacitor C.

Lines PH + RH, PH + PH, RH + RH,
CH + CH, CH + PH, and CH + RH indicate frequency characteristics of the oscillation circuit when various types of capacitors are used. CH is a capacitor having a temperature coefficient (change in capacitance with respect to temperature) of 0 ± 60 (ppm / ° C.).
Is a capacitor having a temperature coefficient of -150 ± 60 (ppm / ° C), and RH is a temperature coefficient of -220 ± 60 (ppm / ° C).
Are respectively shown. For example, PH + RH is equal to the capacitor PH in the capacitors C1 and C2 of the oscillation circuit in FIG.
And RH are used.

In FIG. 7, the frequency fluctuation is ± 175 Hz.
Is an allowable temperature error, and an area between the line m and the line n is an area within the allowable error.

The capacitor is selected under the condition that the frequency fluctuation falls within an allowable range within the fluctuation range of the resistance value of the oscillation circuit at the upper and lower limits of the environmental temperature. In the example of FIG. 7, PH + P
H and PH + RH are selected as capacitors meeting this condition. Thus, the capacitor PH + RH
If the resistance value of the resistor _RL is set to 6 to 12 Ω for the capacitor PH + PH and 4 to 11 Ω for the capacitor PH + PH, an L detector suitable for the purpose can be obtained. Then, it was confirmed that the calculation example shown in FIG. 7 matches the experimental result.

In FIG. 7, the temperature coefficient of the inductance is 25.95 PPM.

(2) Embodiment 2 An oscillation circuit is formed by creating a printed coil so that the resistance value of the resistance _RL of the coil portion falls within the range of 7 ± 3Ω, and the oscillation frequency of the completed oscillation circuit is adjusted. Temperature characteristics and resistance values were measured. FIG. 8 shows the measurement results. The vertical axis (temperature characteristic) in the graph of FIG. 8 indicates a fluctuation frequency value with respect to a change in temperature of 1 ° C. The oscillation circuit has an inductance and a capacitance of about 3 μH, respectively, and C1 = C
2 = 1500 PF.

In FIG. 8, the line at -175 Hz is the upper limit of the temperature characteristic (in absolute value) of the allowable oscillation frequency in this embodiment.

As is clear from the figure, the temperature characteristics of each sample are all smaller than -175 ° C., and the temperature characteristics of the oscillation frequency corresponding to the resistance value within the target value of 7 ± 3Ω are within the allowable range. It has been proved that the oscillation circuit having the temperature characteristics shown in the figure can be sufficiently used for the toner concentration detecting device.

(3) Embodiment 3 As in Embodiment 2, the resistance value of the resistance R _L of the coil portion is set to 7 ±
It was set to 3Ω. The inductance and the capacitance were 3 μH and Cl = C2 = 1500 PF, respectively.

FIG. 9 shows the temperature characteristics (H
z / ° C.), FIG. 10 shows the distribution of the number of samples as a variation value of the oscillation frequency corresponding to a change in toner concentration of 4%, and FIG. 11 shows the distribution of the number of samples as seen at the oscillation frequency. Each distribution is shown.

As in the second embodiment, the allowable value of the temperature characteristic is −
175 Hz. As is clear from FIG. 9, the largest absolute value of the temperature characteristic is in the range of -140 to -149 ° C., and these are values within the allowable range. The samples shown in FIGS. It shows that it can be used sufficiently for a concentration detector.

[0060]

According to the printed coil type L detecting device,
Frequency fluctuation of the oscillation circuit due to a change in environmental temperature can be suppressed within an allowable range. As a result, it is possible to manufacture a toner density detecting device having a constant performance, and a small-sized toner density detecting device having high detection sensitivity is realized.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an LC oscillation circuit for a toner concentration detection device described by a conventional expression method.

FIG. 2 is a circuit diagram of an LC oscillation circuit for a toner density detection device described by an expression method used in the present invention.

FIG. 3 is a plan view of a developing device in which the toner concentration detecting device of the present invention is used.

FIG. 4 is a sectional view taken along line AA in FIG. 3;

FIG. 5 is a sectional view taken along line BB in FIG. 1;

FIG. 6 is a plan view of a printed circuit board on which the circuit shown in FIG. 2 is created.

FIG. 7 is a graph showing temperature changes of inductance, capacitance, and resistance in the toner concentration detecting device according to the first embodiment of the present invention.

FIG. 8 is a graph showing a distribution on temperature characteristics of a sample according to Example 2 of the present invention.

FIG. 9 is a graph showing a distribution on temperature characteristics of a sample according to Example 3 of the present invention.

FIG. 10 shows a sensitivity distribution of a sample according to Example 3 of the present invention.

FIG. 11 shows an oscillation frequency distribution of a sample according to the third embodiment of the present invention.

[Explanation of symbols]

20 Toner density sensor L coil C1, C2 Capacitor R Resistance of _L coil

Claims (4)

[Claims] In a toner concentration detecting device for detecting a toner concentration of a developer from an oscillation frequency of an LC oscillation circuit, an oscillation frequency f of the LC oscillation circuit is determined by the following equation (2). And the inductance L of the LC oscillation circuit,
Wherein the capacitance C and the resistance _RL of the coil are set such that a change in these circuit constants in the operating temperature range of the toner density detection device does not cause a change in the frequency f larger than an allowable value. apparatus. 2. A toner density detecting device using an LC oscillation circuit constituted by a coil having an inductance formed by printing as a detecting member, wherein the resistance value of the coil is set to 2 to 20Ω. . 3. When manufacturing a toner concentration detecting device using an LC oscillation circuit constituted by a coil having an inductance formed by printing as a detecting member, it is necessary to confirm that the resistance value of the coil is within a predetermined range. A method for manufacturing a toner concentration detecting device, comprising: 4. The method according to claim 3, wherein the oscillation frequency of the LC oscillation circuit is confirmed to be within a predetermined range.