JP2003279544A - Detection device for magnetic permeability - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve detection accuracy by reducing interference between a digital circuit and an analog circuit. <P>SOLUTION: A coil 2 is installed at the center of a substrate 1 and a connector 3 for power supply is connected to one end of the substrate 1. The analog circuit 4 including an operational amplifier is arranged between this connector 3 and the coil 2. The digital circuit 6 with the digital IC (IC1) 5 of a CMOS including an ceramic oscillator and 4 circuits of XOR logic circuits is arranged at the other side of the connector 3 with placing the coil 2 between the circuits 4 and 6. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic permeability detecting device for contactlessly detecting the presence or the amount of a magnetic substance such as toner used in an image forming apparatus using a dry electrophotographic system.
For example, it is used for a toner concentration sensor of the image forming apparatus.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine using electrophotography, the surface of a photoconductor drum is uniformly charged by a charger, and the photoconductor is exposed in accordance with image information so as to be statically charged. An electrostatic latent image is formed, toner is attached to the electrostatic latent image for development, the toner image is transferred to a sheet, and then fixed to obtain a final image.

In such an image forming apparatus, it is necessary to always maintain the toner contained in the developing device within a predetermined level range. Therefore, a toner called a T sensor for detecting the toner concentration in the developer is used. A concentration sensor is provided. This toner concentration sensor has a resonance circuit composed of a coil and a capacitor. The resonance circuit is connected to an oscillator and placed near a developing device to oscillate so as to resonate when the amount of toner as a magnetic material falls within a predetermined range. The toner can be detected by setting the frequency.

[0004]

However, the conventional toner concentration sensor has a digital circuit part including an oscillator and an analog circuit part, and the analog circuit may be affected by the high frequency radiation of the oscillator. Further, the conventional sensor does not always have high detection accuracy.

The present invention has been made to solve the above problems, and it is an object of the present invention to obtain a magnetic permeability detecting device which has a high detection accuracy while reducing digital / analog interference.

[0006]

In order to achieve the above object, the magnetic permeability detecting device according to the present invention is arranged so that the impedance changes in accordance with the magnetic permeability and electric conductivity of spatially adjacent regions. And a capacitor connected in series or in parallel with the coil to form a resonance circuit,
Magnetic permeability detection in which a digital circuit including a digital oscillation circuit that generates an alternating voltage of a specific frequency and drives the resonance circuit, and an analog circuit that takes out the voltage or current in the resonance circuit and generates an analog signal are arranged on a substrate. In the device, the analog circuit is arranged on one side and the digital circuit is arranged on the other side with the coil interposed therebetween on the substrate.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing a magnetic permeability detection device according to a first embodiment of claims 1 to 3.
In FIG. 1, a coil 2 is attached to a substantially central portion of a substrate 1, and a power supply connector 3 is attached to one end of the substrate 1. The coil 2 has a primary coil and a secondary coil. An analog circuit 4 including an operational amplifier is arranged between the connector 3 and the coil 2. On the side opposite to the connector 3 with the coil 2 interposed, a ceramic oscillator or XO
CMOS digital IC with four R logic circuits
A digital circuit 6 including (IC1) 5 is arranged.

FIG. 2 is a circuit diagram showing the configurations of the digital circuit 6 and the analog circuit 4. Here, the outline will be described.
An oscillator circuit is formed by pulling up one end of the input of the XOR logic circuit (1 / 4IC1) to Hi level and arranging the ceramic oscillator OSC between the other input and output of the XOR logic circuit. There is. Here, it oscillates at a fundamental frequency of 4 MHz and the waveform is rectangular. This oscillation output voltage is input to another XOR logic circuit (2 / 4IC1) in which one end of the logic circuit input is pulled up to the Hi level. The output of the logic circuit 2 / 4IC1 of the second stage only inverts the output of the logic circuit 1 / 4IC1 of the first stage. However, the influence of the load connected to the second stage of the oscillation circuit (1 It plays a role that does not convey to (step). However, the oscillation may stop when the capacitance component of the load increases.

The output of the logic circuit 2 / 4IC1 is a resistor R3.
Is input to the primary coil L1 via. The end of the primary coil is short-circuited with the end L23 of the secondary coil, and substantially one capacitor (this is called a stem capacitor)
It is connected to C3. The other ends of the logic IC1 and the stem capacitor C3 are grounded. The other end of the secondary coil is grounded via a small resistance adjusting resistor. Therefore, both the primary coil and the secondary coil form a resonance circuit with the stem capacitor C3.

The voltage of the stem capacitor C3 is input to the logic circuit 3/4 IC1 through the cutoff capacitor C4. A digital power source and a ground are connected to a midpoint T4 in which two resistors R15 and R16 having the same resistance value are connected in series so that a voltage half the digital power source voltage is applied as a bias to this input terminal. Since the threshold value for turning on / off the CMOS transistor is located at about half of the power supply voltage, by doing so, a minute change in voltage input to the logic circuit 3/4 IC1 through the cutoff capacitor C4 is converted into a rectangular wave. can do. 4 / 4I
The outputs of 2 / 4IC1 and 3 / 4IC1 are input to C1, and the phase difference between these two signals is extracted.

Since the oscillation waveforms of these digital circuits are clean (pointed) rectangular waves, they contain a lot of harmonic components. Harmonic radiation is quite large and is likely to cause interference if there are analog circuits nearby.
Therefore, the digital circuit 6 is all arranged on one side of the coil 2 (on the side opposite to the connector 3) as shown in FIG. That is, the analog circuit 4 is provided on the connector 3 side of the coil 2.
Only are placed.

Next, a second embodiment according to claim 4 will be described. In FIG. 2, the power supply circuit of the digital circuit 6 is a resistor R14, a Zener diode ZD, and a capacitor C7 arranged on the digital side (the side opposite to the connector 3).
It is composed of. Therefore, an analog power supply line runs under the coil 2. Further, the ground on the digital circuit side also needs to pass under the coil 2. Generally, on the substrate 1, it is said that the ground pattern and the power supply pattern should have a large area.

However, if there is a pattern having a large solid area near the coil 2, an eddy current is generated there, and the magnetic field created by this eddy current acts so as to cancel the magnetic field of the coil 2, degrading the sensitivity of the sensor. Let Therefore, it is necessary to violate the above general rule near the coil. According to an experiment, if the area of the pattern passing through the coil region becomes 1/2 or more of the coil area, the sensitivity is greatly impaired, so it is necessary to set it to this value or less.

FIG. 3 shows a wiring pattern other than the circuit components formed on the substrate 1. In FIG. 3, the two thick lines are the power line 7 and the ground line 8. Also, there are three thin signal lines 9, 10 and 11 that pass under (in the vicinity of) the coil 2, which are as follows.

The signal of which the phase difference is extracted by the signal line 10: 4/4 IC1 is averaged by the CR integrating circuit arranged on the digital side and then transmitted under the coil to the analog circuit side. Signal line 11: A control voltage line that biases the varicap D and changes the capacitance enters the digital circuit 6 from below the coil 2 from the connector 3. Signal line 9: In order to generate the reference voltage of the final stage of the operational amplifier from the digital power supply voltage stabilized by the Zener diode ZD, the analog circuit 4 is provided with a digital voltage line (as a signal line, power consumption is almost zero) of the coil 3. I passed it down.

Next, a third embodiment according to claim 5 will be described. FIG. 4 shows a wiring pattern for connecting circuit components on the substrate 1. If there is a wiring pattern on the lower surface of the coil 2, the loss is large because it is close to the coil 2, and the angle of the coil 2 is not stable because the surface of the substrate that supports the coil is uneven. Therefore, in the present embodiment, the wiring pattern is eliminated near the coil as shown in the figure.

[0017]

According to the invention described in claims 1 to 3, according to the present invention, it is possible to reduce the interference between the digital circuit and the analog circuit and to increase the detection accuracy. Further, according to the inventions of claims 4 and 5, the eddy current generated in the wiring pattern of the substrate can be reduced and the detection accuracy can be improved.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an arrangement of components on a substrate of a magnetic permeability detection device according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing configurations of a digital circuit and an analog circuit.

FIG. 3 is a configuration diagram showing a wiring pattern other than a circuit component on a substrate.

FIG. 4 is a configuration diagram showing a wiring pattern for connecting circuit components on a substrate.

[Explanation of symbols]

1 substrate 2 coils 3 Power supply connector 4 analog circuits 6 digital circuits 7 power line 8 ground wire 9, 10, 11 signal line

Claims (5)

[Claims] 1. A coil arranged so that its impedance changes in accordance with magnetic permeability and electric conductivity of regions that are spatially close to each other, and a capacitor connected in series or in parallel with the coil to form a resonance circuit. Magnetic permeability detection in which a digital circuit including a digital oscillation circuit that generates an alternating voltage of a specific frequency and drives the resonance circuit, and an analog circuit that takes out the voltage or current in the resonance circuit and generates an analog signal are arranged on a substrate. In the device, the magnetic permeability detecting device, wherein the analog circuit is arranged on one side and the digital circuit is arranged on the other side with the coil interposed therebetween on the substrate. 2. The magnetic permeability detection device according to claim 1, wherein the analog circuit is arranged on a power supply side and the digital circuit is arranged on a side far from a power supply. 3. The magnetic permeability according to claim 1, wherein the Zener diode constituting the power supply circuit of the digital circuit or the capacitor connected in parallel with the Zener diode is arranged on the digital circuit side of the coil. Detection device. 4. The magnetic permeability according to claim 1, wherein a wiring pattern having an area equal to or more than ½ of the area of the coil does not exist on the surface of the substrate facing the coil. Detection device. 5. The magnetic permeability detection device according to claim 1, wherein a wiring pattern is not present on a surface of the substrate facing the coil.