JP4071515B2 - Permeability detector - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic permeability detecting device that detects the presence or amount of a magnetic material such as toner used in an image forming apparatus using a dry electrophotographic method in a non-contact manner, and is used, for example, in a toner concentration sensor of the image forming apparatus. It is what
[0002]
[Prior art]
In an image forming apparatus such as a copying machine using an electrophotographic technology, the surface of a photosensitive drum is uniformly charged by a charger, and an electrostatic latent image is formed by exposing the photosensitive member according to image information. Then, the electrostatic latent image is developed with toner attached thereto, and the toner image is transferred onto a sheet and fixed to obtain a final image.
[0003]
In such an image forming apparatus, it is necessary to always maintain the toner contained in the developing device in a predetermined level range. For this reason, a toner concentration sensor called a T sensor that detects the toner concentration in the developer is used. Is provided.
This toner density sensor forms a resonance circuit with a coil and a capacitor, and this resonance circuit is connected to an oscillator and placed in the vicinity of the developing device, and oscillates so as to resonate when the amount of toner as a magnetic material is within a predetermined range. The toner can be detected by setting the frequency.
[0004]
[Problems to be solved by the invention]
However, the conventional toner density sensor has a digital circuit portion including an oscillator and an analog circuit portion, and the analog circuit may be affected by the high frequency radiation of the oscillator. Further, the conventional sensor does not necessarily have a good detection accuracy.
[0005]
The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain a magnetic permeability detecting device with high detection accuracy while reducing digital / analog interference.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the magnetic permeability detecting device for toner concentration detection used in the developing device of the image forming apparatus according to the present invention has an impedance that changes in accordance with the magnetic permeability and electric conductivity in a spatially close region. A digital circuit including a coil arranged to be connected, a capacitor connected in series or in parallel with the coil to form a resonance circuit, and a digital oscillation circuit that generates an alternating voltage of a specific frequency and drives the resonance circuit; A magnetic permeability detecting device for detecting a toner concentration used in a developing device of an image forming apparatus in which an analog circuit that takes out a voltage or current in the resonant circuit and generates an analog signal is arranged on the substrate, and sandwiches the coil on the substrate The analog circuit is arranged on one side and the digital circuit is arranged on the other side.
[0007]
DETAILED DESCRIPTION OF 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 detector according to a first embodiment relating to claims 1 to 3.
In FIG. 1, a coil 2 is attached almost at the center 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 disposed between the connector 3 and the coil 2. A digital circuit 6 including a CMOS digital IC (IC1) 5 including four ceramic oscillators and four XOR logic circuits is arranged on the opposite side of the connector 3 with the coil 2 interposed therebetween.
[0008]
FIG. 2 is a circuit diagram showing the configuration of the digital circuit 6 and the analog circuit 4. Here, an outline will be described.
One end of the XOR logic circuit (1/4 IC1) input is pulled up to Hi level, and a ceramic oscillator OSC is arranged between the other input and output of the XOR logic circuit, thereby forming an oscillation circuit. Yes. Here, it oscillates at a fundamental frequency of 4 MHz and the waveform is rectangular. This oscillation output voltage is inputted 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 in the second stage is merely an inversion of the output of the logic circuit 1 / 4IC1 in the first stage. It plays a role that is not conveyed to the stage. However, oscillation may stop when the capacitive component of the load increases.
[0009]
The output of the logic circuit 2/4 IC1 is input to the primary coil L1 via the resistor R3. The end of the primary coil is short-circuited with the end L23 of the secondary coil and is substantially connected to one capacitor (referred to as a stem capacitor) C3. The other ends of the logic IC 1 and the stem capacitor C3 are grounded. The other end of the secondary coil is grounded via a small sensitivity adjusting resistor. Therefore, both the primary coil and the secondary coil form a resonance circuit with the stem capacitor C3.
[0010]
The voltage of the stem capacitor C3 is input to the logic circuit 3 / 4IC1 through the cut-off capacitor C4. This input terminal is connected to a midpoint T4 in which two resistors R15 and R16 having the same resistance value are connected in series so that a half voltage of the digital power supply voltage is applied as a bias. Since the threshold value for turning on / off the CMOS transistor is just half of the power supply voltage, a small change in voltage input to the logic circuit 3/4 IC1 through the cut-off capacitor C4 is converted into a rectangular wave by doing so. can do. The output of 2/4 IC1 and 3/4 IC1 is input to 4/4 IC1, and the phase difference between these two signals is extracted.
[0011]
Since the oscillation waveform of these digital circuits is a clean (pointed) rectangular wave, it contains many harmonic components. Harmonic radiation is quite high and there is a high probability of interference if there is an analog circuit nearby. Accordingly, the digital circuit 6 is all disposed on one side of the coil 2 (the side opposite to the connector 3) as shown in FIG. That is, only the analog circuit 4 is arranged on the connector 3 side of the coil 2.
[0012]
Next, a second embodiment relating to claim 4 will be described.
In FIG. 2, the power supply circuit of the digital circuit 6 includes a resistor R14, a Zener diode ZD, and a capacitor C7 arranged on the digital side (the side opposite to the connector 3). Therefore, an analog power supply line passes under the coil 2. The ground on the digital circuit side must also pass under the coil 2. In general, the ground pattern and the power supply pattern should have a larger area on the substrate 1.
[0013]
However, if there is a pattern with a large solid area near the coil 2, an eddy current is generated there, and the magnetic field generated by the eddy current works to cancel the magnetic field of the coil 2, thereby degrading the sensitivity of the sensor. Therefore, it is necessary to break the general rule in the vicinity of the coil. According to experiments, if the area of the pattern passing through the coil region becomes 1/2 or more of the coil area, the sensitivity is greatly hindered.
[0014]
FIG. 3 shows a wiring pattern for 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. Further, there are three thin signal lines 9, 10, 11 passing under (near) the coil 2, which are as follows.
[0015]
The signal from which the phase difference is extracted by the signal line 10: 4 / 4IC1 is averaged by the CR integration circuit arranged on the digital side, and then transmitted under the coil to the analog circuit side.
Signal line 11: A control voltage line for biasing the varicap D and changing the capacitance enters the digital circuit 6 from the connector 3 under the coil 2.
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 digital voltage line is connected to the analog circuit 4 (as a signal line = almost no power consumption) of the coil 3 I passed down.
[0016]
Next, a third embodiment relating 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 great because it is close to the coil 2, and the substrate surface that supports the coil has irregularities, so the angle of the coil 2 is not stable. For this reason, in this embodiment, as shown in the figure, the wiring pattern is eliminated in the vicinity of the coil.
[0017]
【The invention's effect】
According to the first to third aspects of the invention, the interference between the digital circuit and the analog circuit can be reduced, and the detection accuracy can be increased.
In addition, according to the fourth and fifth aspects of the present invention, eddy currents generated in the wiring pattern of the substrate can be reduced, and detection accuracy can be increased.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing component arrangement on a substrate of a magnetic permeability detection device according to an embodiment of the present invention.
FIG. 2 is a circuit diagram showing a configuration of a digital circuit and an analog circuit.
FIG. 3 is a configuration diagram showing wiring patterns other than circuit components on a substrate.
FIG. 4 is a configuration diagram showing a wiring pattern for connecting circuit components on a substrate.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Board | substrate 2 Coil 3 Connector for power supply 4 Analog circuit 6 Digital circuit 7 Power line 8 Ground line 9, 10, 11 Signal line

Claims (5)

Coil arranged so that impedance changes according to the magnetic permeability and electric conductivity in a spatially close region, a capacitor connected in series or in parallel to the coil to form a resonance circuit, and an alternating frequency of a specific frequency A digital circuit including a digital oscillation circuit that generates a voltage and drives the resonance circuit, and an analog circuit that generates an analog signal by extracting the voltage or current in the resonance circuit is used for a developing device of an image forming apparatus arranged on a substrate. In the magnetic permeability detecting device for toner concentration detection, the analog circuit is arranged on one side of the coil and the digital circuit is arranged on the other side of the substrate . Permeability detecting device for toner concentration detection used in the above . At least the power supply line ( Vcc ) and ground line ( GND ) that supply power to the sensor, and the signal line ( Vout ) that sends the sensor detection signal are connected to the main unit itself. 2. The developing device of an image forming apparatus according to claim 1, wherein the sensor circuit board is connected at one end (short portion), an analog circuit is disposed on a side close to the connection portion, and a digital circuit is disposed on a far side. Magnetic permeability detection device for toner concentration detection to be used .   3. The magnetic permeability detecting device according to claim 1, wherein a Zener diode constituting the power supply circuit of the digital circuit or a capacitor connected in parallel thereto is disposed on the digital circuit side of the coil.   4. The magnetic permeability detection device according to claim 1, wherein a wiring pattern having an area of ½ or more of the area of the coil does not exist on a surface of the substrate facing the coil. 5.   4. The magnetic permeability detecting device according to claim 1, wherein no wiring pattern exists on a surface of the substrate facing the coil. 5.

Images