JP2000321011A - Magnetic detector, thickness detector and level detector of magnetic body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic detector or the like which detects the size of a magnetic field of a weak magnetic body even with a very simple structure. SOLUTION: This magnetic detector is provided with coils L1 and L2 (first and second coils) which are magnetically connected to each other while arranged so that inductance changes according to dislocation of a mobile core 10, an resonance circuit 100 which oscillates at a fixed oscillation frequency to output a signal to the coil L1, a capacitor C1 (first capacitor) composing a first resonance circuit 121 between it and the coil L1, a capacitor C2 (second capacitor) composing a second resonance circuit 122 between it and the coil 2, a trimmer capacitor VC1 (fine adjustment circuit) connected in parallel to the capacitor C2 and a detection circuit 130 to detect a signal outputted from the second resonance circuit 122. A tuning circuit 120 is made of the first resonance 121 and the second resonance circuit 122, the resonance frequency of the first resonance circuit 121 is set smaller than the oscillation frequency of the oscillation circuit 100 and the resonance frequency of the second resonance circuit 122 is set larger than the oscillation frequency of the oscillation circuit 100.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to, for example, LBP (Lase
The present invention relates to a magnetic detection device used for an image recording device such as an r Beam Printer) and a PPC (Plain Paper Copier). More specifically, the present invention relates to, for example, a thickness detecting device for detecting the thickness of a sheet or the like as an object, and a magnetic material level detecting device for detecting the presence or absence or the amount of a magnetic material such as toner without contact.

[0002]

2. Description of the Related Art In a printer of the electrophotographic process system, if the toner fixing temperature is controlled at a fixed value irrespective of the thickness of a sheet, the fixing property of the toner is deteriorated and the quality of image quality is deteriorated. Some have a function of detecting the thickness of the toner and changing the toner fixing temperature in accordance with the detection result. This type of printer is provided with a thickness detecting device for detecting the thickness of the sheet.

A conventional thickness detector irradiates a sheet with laser light generated by a semiconductor laser light emitting element, and receives the laser light reflected at this time by a semiconductor laser light receiving element.
This is a basic configuration in which the thickness of a sheet is detected based on a change in the wavelength of the laser light (this is a first conventional example of a thickness detecting device). There is also a configuration in which the thickness of a sheet is detected by using a potentiometer (this is a second conventional example of a thickness detecting device).

In a printer not provided with such a thickness detecting device, when data on the type of paper and its thickness is input, the toner fixing temperature is changed according to the input data.

In an ink-jet printer, if recording is not performed in a state where the distance between the nozzle head and the paper is always constant, the pixels become wider or narrower, and the shape of the pixels is deformed. Therefore, an adjustment lever for adjusting the distance between the nozzle head and the sheet is provided. When the type of paper is changed, the thickness of the paper changes and the distance between the nozzle head and the paper changes slightly. Therefore, in this case, it is necessary to check the thickness of the paper and finely adjust the adjustment lever.

On the other hand, as a conventional example of a magnetic substance level detecting device for detecting the presence or absence or the amount of a magnetic substance such as toner without contact, Japanese Utility Model Laid-Open Publication No. 6-76961 and Japanese Utility Model Laid-Open Publication No. 64-43365 disclose a conventional apparatus. There is a disclosed toner concentration detection device. Where,
An oscillation circuit is formed by a sensor coil and a capacitor arranged near the toner box. When the amount of toner in the toner box changes, the inductance of the sensor coil changes and the oscillation frequency changes. The basic circuit configuration detects the presence or absence or the amount thereof in a non-contact manner.

[0007]

However, in the case of the first conventional example of the thickness detecting device, the configuration of the peripheral circuits of the semiconductor laser light emitting element and the semiconductor laser light receiving element is complicated, and it is difficult to reduce the cost. There is a disadvantage that.
Further, in the case of the second conventional example of the thickness detecting device, since it is necessary to use mechanical parts such as a potentiometer, there is a disadvantage that the detecting accuracy is low.

In a printer not equipped with such a thickness detecting device, the cost can be reduced by the omission of the device, but data of the type of paper and its thickness can be input. It becomes necessary or it is necessary to finely adjust the distance between the nozzle head and the paper using an adjustment lever, and it is pointed out that the usability is poor in this respect.

On the other hand, in the conventional example of the magnetic substance level detecting apparatus for detecting the presence or absence or the amount of a magnetic substance such as toner without contact, the amount of toner changes because the toner is a weak magnetic substance. However, there is an essential disadvantage that the change in the oscillation frequency generated at this time is extremely small. When the sensor coil of about 30 μH was buried in the toner and the inductance of the sensor coil was measured, it changed only about several nH. Since the change in inductance is very small, the change in oscillation frequency is very small,
Since a high-precision frequency change detection circuit is not used, it is difficult to detect the presence or absence or the amount of toner as a practical problem. Such a high-precision frequency change detection circuit is very complicated and expensive, and thus poses a major problem in reducing the overall cost.

Further, Japanese Utility Model Application Laid-Open No. 63-187160 and
As disclosed in Japanese Patent Application Laid-Open No. 5-94857, it has been proposed to detect the presence or absence of toner by combining three or four coils in order to increase sensor sensitivity. However, since a high-precision phase detection circuit and the like are required, the same problem as in the above-described conventional example has been pointed out.

There is a method in which a piezoelectric element is arranged outside the toner box and the presence or absence of toner is detected as a change in the vibration state of the piezoelectric element. However, a special electrode structure increases the cost. However, there is a drawback that a tone is generated in an audible band when there is no toner. In particular, even if the presence or absence of toner can be detected, it is extremely difficult to detect the analog amount.

A main object of the present invention is to provide a magnetic detection device which has a very simple structure and detects the magnitude of a magnetic field of a weak magnetic substance. In addition, using this magnetism detection device, a thickness detection device that can achieve high accuracy with a very simple configuration, and the presence or amount of a weak magnetic material with a very simple configuration is detected. It is an object of the present invention to provide a magnetic substance level detecting device capable of performing the above-mentioned operations.

[0013]

According to a first aspect of the present invention, there is provided a magnetic sensing device for detecting the magnitude of a magnetic field, wherein the magnetic sensing devices are magnetically coupled to each other. A first and a second coil arranged so that the inductance changes according to the magnitude of the magnetic field; an oscillation circuit that oscillates at a constant oscillation frequency and outputs a signal to the first coil; A first capacitor that forms a first resonance circuit with the second coil, a second capacitor that forms a second resonance circuit with the second coil, and an output from the second resonance circuit. A tuning circuit is configured by the first resonance circuit and the second resonance circuit, and the resonance frequency of the first resonance circuit is lower than the oscillation frequency of the oscillation circuit. The resonance frequency of the second resonance circuit is set It is configured to be set larger than the oscillation frequency of the circuit.

According to a second aspect of the present invention, there is provided a magnetic sensing device comprising:
A fine adjustment circuit provided so as to finely adjust the resonance frequency of the second resonance circuit and / or the first resonance circuit.

According to a third aspect of the present invention, there is provided a magnetic sensing device comprising:
3. The magnetic sensing device according to claim 1, wherein each of the first coil and the second coil has one end connected to a common terminal. 4.

According to a fourth aspect of the present invention, there is provided a thickness detecting device comprising:
A movable magnetic body that is displaced in accordance with the thickness of the object, and a thickness detection device including a magnetic detection device that detects the magnitude of a magnetic field created by the movable magnetic body as the thickness of the object, The magnetic sensing device includes first and second coils that are magnetically coupled to each other and that are arranged so that the inductance changes according to the displacement of the movable magnetic body, and oscillates at a constant oscillation frequency. An oscillation circuit that outputs a signal to the first coil, a first capacitor that forms a first resonance circuit with the first coil, and a second capacitor that forms a first resonance circuit with the second coil.
And a detection circuit for detecting a signal output from the second resonance circuit. The first resonance circuit and the second resonance circuit constitute a tuning circuit. The resonance frequency of the first resonance circuit is set lower than the oscillation frequency of the oscillation circuit, and the resonance frequency of the second resonance circuit is set higher than the oscillation frequency of the oscillation circuit.

According to a fifth aspect of the present invention, there is provided a magnetic substance level detecting apparatus for detecting presence or absence of a magnetic substance such as toner or the amount thereof in a non-contact manner. A first and a second coil which are coupled and arranged so that the inductance changes in accordance with the amount of the magnetic substance; and an oscillation circuit which oscillates at a constant oscillation frequency and outputs a signal to the first coil. A first capacitor forming a first resonance circuit with the first coil, a second capacitor forming a second resonance circuit with the second coil,
A detection circuit for detecting a signal output from the second resonance circuit; a tuning circuit is configured by the first resonance circuit and the second resonance circuit; and the resonance frequency of the first resonance circuit is oscillated. The configuration is such that the oscillation frequency is set lower than the oscillation frequency of the circuit, and the resonance frequency of the second resonance circuit is set higher than the oscillation frequency of the oscillation circuit.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a case where a thickness detecting device according to an embodiment of the present invention utilizing a magnetic detecting device of the present invention is provided in an electrophotographic process type laser printer, see FIGS. It will be explained while doing. FIG. 1 is a circuit diagram of a magnetic detecting device used in a thickness detecting device according to an embodiment of the present invention, and FIG. 2 is a schematic description showing a thickness detecting device and a peripheral mechanism of the laser printer according to the embodiment of the present invention. FIGS. 3 and 3 are schematic explanatory views showing a coil body used in the thickness detecting device according to the embodiment of the present invention. FIG. 3A is an example thereof, and FIG. Embodiment, FIG. (C) shows still another embodiment, and FIG.
4A to 4C are circuit diagrams, FIG. 4 is an impedance characteristic diagram of a tuning circuit of the thickness detecting device according to the embodiment of the present invention, and FIG. 5 is a thickness detecting device according to the embodiment of the present invention. FIG. 6 is a characteristic diagram of a paper thickness and a detection output voltage in FIG.

A laser printer (see FIG. 2) is provided with a sheet A in a sheet supply cassette (not shown) arranged on the left side in the figure.
Is taken out by a feed roller 40, and a base plate B is attached to a recording head (not shown) arranged on the right side in the figure.
It has a basic configuration in which an image is recorded on a sheet A by a recording head unit by sending it out along the top. This laser printer is provided with a thickness detecting device for controlling the toner fixing temperature and the like according to the thickness of the paper A.

This thickness detecting device is a device for detecting the thickness of the sheet A as an object on the surface of the base plate B. The thickness detecting device is provided between the above-described paper supply cassette and the recording head unit, is disposed at a position where it comes into contact with the surface of the sheet A, and is movable so as to be displaced by the contact. Movable core 10 provided in
(Corresponding to a movable magnetic body) and a magnetic detector 20 fixed around the movable core 10 and detecting the magnitude of the magnetic field generated by the movable core 10 as the thickness of the paper A. ing.

The movable core 10 is made of a nickel-zinc ferrite material, and is attached to a frame C of a laser printer via a spring 11. The movable core 10 is pressed against the base plate B with the weight F by the spring 11. When there is no paper A, the lower surface of the movable core 10 is in direct contact with the base plate B. The magnitude of the weight F is set to a value such that the paper A enters between the movable core 10 and the base plate B, and the movable core 10 is displaced upward without difficulty according to the thickness of the paper A. . In order to allow the paper A to smoothly enter between the movable core 10 and the base plate B, curved surfaces 101 as shown are formed at both ends of the lower surface of the movable core 10.

The magnetic sensing device 20 is arranged at a position facing the movable core 10 and is fixed to the back side of the base plate B. The output signal of the magnetic detection device 20 is input to a control circuit (not shown) of the laser printer. In addition,
The control circuit includes a CPU for processing a control program for controlling the entire laser printer, an A / D converter connected to an input side of the CPU, and a fixing temperature adjustment connected to an output side of the CPU. And a circuit. The CPU calculates the amount of displacement of the movable core 10 based on an output signal of the magnetism detecting device 20, which will be described later, and outputs this to the fixing temperature adjustment circuit as a signal. The fixing temperature adjustment circuit is a heater energization control circuit that adjusts the toner fixing temperature, and is configured to perform negative feedback control on the toner fixing temperature using a signal output from the CPU as a target value.

The magnetic sensing device 20 includes coils L1 and L2 that are magnetically coupled to each other and that are arranged so that the inductance changes according to the displacement of the movable core 10.
(Corresponding to the first and second coils) and an oscillation circuit 1 that oscillates at a constant oscillation frequency and outputs the signal to the coil L1.
00 and a capacitor C1 (corresponding to a first capacitor) constituting a first resonance circuit 121 between the coil L1.
A capacitor C2 (corresponding to a second capacitor) constituting a second resonance circuit 122 between the coil L2 and a trimmer capacitor VC1 (corresponding to a fine adjustment circuit) connected in parallel to the capacitor C2; A detection circuit 130 for detecting a signal output from the second resonance circuit 122 is provided, and the tuning circuit 120 is configured by the first resonance circuit 121 and the second resonance circuit 122. The magnitude of the magnetic field generated by the movable core 10 is output from the detection circuit 130 as a voltage.

FIG. 1 shows a detailed circuit configuration of the magnetic sensing device 20.
This will be described with reference to FIG. Note that Vcc is the magnetic sensing device 20
Shows the power supply voltage supplied to the power supply.

The oscillation circuit 100 includes a ceramic oscillator CO,
It comprises resistors R2, R3, capacitors C3, C4, and a transistor Q1, oscillates at a constant oscillation frequency fr, and outputs a signal to the tuning circuit 120 via a coupling capacitor C5. The oscillation circuit 100 is roughly divided into a negative resistance circuit (resistance R2,
R3, capacitors C3 and C4 and transistor Q1) and a resonator (ceramic oscillator CO).

The oscillation frequency fr is selected from several MHz to several tens MHz for economical reasons. That is, when the frequency is reduced, the inductance of the coils L1 and L2 of the tuning circuit 120 and the capacitance of the capacitors C1 and C2 are increased and it is necessary to use a dimensionally large one. This is because handling becomes difficult and cost increases.
The reason why the ceramic resonator CO is used as the resonator is that it is inexpensive as compared with a crystal resonator or the like, and that the oscillation frequency can be easily stabilized.

The tuning circuit 120 includes a first resonance circuit 121 in which a coil L1 and a capacitor C1 are connected in parallel;
Coil L2, capacitor C2, and trimmer capacitor VC1
Are connected in parallel with each other.

In order to improve the stability with respect to the change of the ambient temperature, here, the coil L2 and the capacitor C2 having the opposite temperature characteristics are used.
Temperature compensation is performed. The reason why the parallel resonance circuit is used as the first and second resonance circuits 121 and 122 is as follows.
This is for simplifying the circuit configuration. That is, since the voltage output method is used, additional circuits such as a current / voltage conversion circuit become unnecessary when a parallel resonance circuit is used.

The trimmer capacitor VC1 is provided so that the resonance frequency fd2 of the second resonance circuit 122 can be finely adjusted. The reason for providing the trimmer capacitor VC1 is as follows.

Since the coils L1 and L2 do not always have uniform windings in manufacturing, their inductance varies. Therefore, the resonance frequency fd1 of the first resonance circuit 121 varies due to the variation of the coil L1. Also, due to the variation of the coil L2, the second
The resonance frequency fd2 of the resonance circuit 122 varies. As a result, the mutual inductance of the first resonance circuit 121, the second resonance circuit 122, and the tuning circuit 120 varies, and the output of the tuning circuit 120 varies.
In addition, the sensitivity of the tuning circuit 120 varies. That is, variations in the inductance of the coils L1 and L2 result in variations in the output and sensitivity of the magnetic detection device 20. Therefore, by providing the trimmer capacitor VC1 as described above and adjusting the trimmer capacitor VC1, the resonance frequency fd2 of the tuning circuit 120 is adjusted, and the variation in the output and sensitivity of the magnetic sensing device 20 can be eliminated. It was done.

Incidentally, the resonance frequency fd1 of the first resonance circuit 121 is set lower than the oscillation frequency fr of the oscillation circuit 100, and the resonance frequency fd1 of the second resonance circuit 122 is set.
2 is set higher than the oscillation frequency fr of the oscillation circuit 100. This is set for the following reason.

Although an amplifier circuit is generally provided between the oscillation circuit 100 and the tuning circuit 120, the magnetic detection device 20 does not intentionally provide this amplifier circuit. what if,
When the amplifier circuit is provided, the oscillation circuit 100 and the tuning circuit 120
Is good, and the signal level of the first resonance circuit 121 is constant regardless of the presence or absence of the movable core 10. In this case, the stability of the signal is good, but only the amount of change in the mutual inductance of the tuning circuit 120 is the amount of change in the signal. In the magnetic sensing device 20, this amplifier circuit is omitted for simplification of the circuit and cost reduction. The coupling capacitor C5 is simply provided without an amplification circuit.
If the oscillation circuit 100 and the tuning circuit 120 are connected via only the oscillation circuit 100, the oscillation circuit 100 becomes unstable due to poor isolation between the oscillation circuit 100 and the tuning circuit 120. To solve this problem,
The resonance frequencies fd1 and fd2 and the oscillation frequency f
r. Details will be described below.

First, the reason why the resonance frequency fd1 of the first resonance circuit 121 is set lower than the oscillation frequency fr of the oscillation circuit 100 is as follows. Resonance frequency fd1 =
When the oscillation frequency is fr, the Q becomes maximum, but the impedance changes greatly due to a slight change in the inductance of the coil. As a result, the oscillation circuit 100 becomes unstable. Oscillation circuit 100
It is better for the load impedance to be constant. Therefore, the oscillation circuit 100 operates stably by setting the resonance frequency fd1 lower than the oscillation frequency fr.

When the movable core 10 comes close to a level that affects the tuning circuit 120 from the state where the movable core 10 is not present, the inductance of the coil L1 and the coil L2 increases. As a result, the resonance frequency fd1 of the first resonance circuit 121 also decreases. This is at the oscillation frequency fr
This means that the load impedance to the oscillation circuit 100 decreases. Therefore, the voltage of the first resonance circuit 121 decreases, but the current flowing into the first resonance circuit 121 increases. Since the voltage excited in the coil L2 of the second resonance circuit 122 also increases, the output voltage of the detection circuit 130 also increases, and the sensitivity of the magnetic detection device 20 is improved as compared with the case where the amplification circuit is provided. The impedance of the first resonance circuit 121 at the oscillation frequency fr is desirably approximately several hundreds Ω.

Next, for the same reason as described above, the resonance frequency fd of the second resonance circuit 122 is increased as shown in FIG.
2 is set to be higher than the oscillation frequency fr of the oscillation circuit 100. At this time, it is desirable to set the resonance frequency fd2 so that Q does not decrease at the oscillation frequency fr.
This is to improve the sensitivity of the magnetic detection device 20. The second resonance circuit 12 at the oscillation frequency fr
The impedance of 2 is desirably about several kΩ.

Further, in the magnetic sensing device 20, since the amplifier circuit is not provided, the first resonance circuit 121 can be directly connected to the ground. If the amplification circuit is provided, the high-frequency current flowing through the first resonance circuit 121 flows to the ground through a coupling capacitor connected to the collector of the oscillation circuit 100, but the coupling capacitor has a capacitance. Is big. Therefore, when the environmental temperature changes, the amount of change in impedance is large. Therefore, if the current of the amplifier circuit does not flow to some extent (several mA), the detection output voltage of the magnetic detection device 20 will be affected. In the case of the magnetic sensing device 20, since the amplifier circuit is not provided, the high-frequency current flowing through the first resonance circuit 121 flows directly to the ground without passing through the coupling capacitor. As shown in the magnetic sensing device 20
Does not affect the detected output voltage.

Therefore, here, the first resonance circuit 121 is directly connected to the ground, but this allows the second resonance circuit 122 to be directly connected to the ground.
And one end of the first resonance circuit 121 can be connected to a common terminal (that is, ground). Therefore, one end of each of the first coil L1 and the second coil L2 can be connected to a common terminal (that is, ground).
Thus, the first coil L1 and the second coil L2 can be so-called center tap coils (see FIG. 3D).

FIGS. 3A to 3C show that the first coil L1 and the second coil L2 are so-called center tap coils, which are wound around a bobbin 810, and the end portions of the coils are formed. (Lead wire) is connected to a substrate 820, and these and a core (eg, a nickel-zinc ferrite core) 830 provided at the center of the bobbin 810 are connected to a housing 850.
9 shows a coil body 800 stored in FIG. First coil L
1 is wound below the bobbin 810 in the figure, and the second coil L2 is wound above the bobbin 810. As a result, at the time of installation, the second coil L2 side is closer to the movable core 10 than the first coil L1, and contributes to improvement in detection sensitivity.

The coil body 800 shown in FIG.
This is a type in which the core 830 protrudes from 10 and is also exposed from the housing 850, and can have higher sensitivity than the coil body 800 of FIGS. 3B and 3C. The coil body 800 in FIG. 3B does not allow the core 830 to protrude from the bobbin 810, and the housing 850
The coil body 800 shown in FIG.
It is easier to manufacture and a lower cost type. The coil body 800 shown in FIG. 3C includes a first coil L1 and a second coil L2 wound around a bobbin 810 and a substrate 820.
The ends of the first coil L1 and the second coil L2 are soldered to the leads of the bobbin 810 that are drawn out in the lateral direction of the bobbin 810, and the leads are soldered to the substrate 820. Connected. In the coil body 800 of FIGS. 3A and 3B, the first
The ends of the coil L1 and the second coil L2 are
10 leads are soldered to the substrate 820
Are soldered by being inserted into the pattern lands provided in the pattern.

Such a coil body 800 is a conventional coil body (for example, a coil wound directly around a core, and each of the first coil L1 and the second coil L2 has two terminals. The following advantages are obtained.

Since the conventional coil body is formed by directly winding a coil around a core, when soldering the ends (lead wires) of the coil to a substrate, the ends are fixed to the pattern land by tweezers one by one. I needed to do that. Also, two soldering points were required for each of the first coil L1 and the second coil L2, for a total of four soldering points. Furthermore,
Due to manual work, there was a possibility of solder failure such as short circuit.

On the other hand, the coil 800 has only one winding step in the manufacture of the coil. The end (lead wire) of the coil is wound around a lead of the bobbin 810 and soldered. Since the center tap is used, the connection with the substrate 820 can be completed at three places. Further, the lead of the bobbin 810 has a diameter of about φ0.4 mm, and it is easy to pass the lead through the substrate 820 and to solder it. Further, the surface mounting type such as the coil body 800 in FIG. 3C does not require the leads to pass through the substrate 820, so that the manufacturing is easier.

On the other hand, the detection circuit 130 includes a diode D2,
It comprises a resistor R6, a capacitor C7, and a buffer amplifier OP1, detects a signal output from the tuning circuit 120, and outputs the detected signal as a voltage to the OUTPUT terminal via the buffer amplifier OP1.

The time constant of the resistor R6 and the capacitor C7 is
It is desirable to increase the input level of the buffer amplifier OP1 so as not to fluctuate due to the ripple. However, as the time constant increases, not only does the outer shape of the capacitor C7 increase, but also the cost increases. Therefore, here, the constant value of the resistor R6 is set to about several hundred kΩ to several MΩ, and the capacitance of the capacitor C7 is set to 0. It is selected to be about 0.01 F to several F.

The detection circuit 130 has only one diode, and this one diode D2 is directly connected to the tuning circuit 120 without using a coupling capacitor. On the other hand, a coupling capacitor may be provided between the anode of the diode D2 and the tuning circuit 120, and another diode may be provided between the connection point between the anode of the diode D2 and the coupling capacitor and the ground. is there. However, in this case, Vf of the two diodes is changed due to a change in the environmental temperature.
Will be affected. On the other hand, in the case of the detection circuit 130, since there is only one diode,
The effect that Vf changes due to a change in environmental temperature is half that of the two diodes.

In the detection circuit 130, the diode D
2 is directly connected to the tuning circuit 120 without passing through a coupling capacitor, so that the anode of the diode D2 is biased to ground. Thereby, the diode D2 is not destroyed by the electrostatic surge, and the bias point of the AC voltage is stabilized, so that the detection output is also stabilized. Furthermore, in the detection circuit 130, since the number of components can be reduced as described above, the cost and size of the magnetic detection device 20 can be reduced.

The coil 800 of the magnetic sensing device 20
The above circuit components except for are mounted on a board (not shown),
It is incorporated together with the coil 800 in the housing 21. At this time, the coil body 800 is disposed on the base plate B side such that the second coil L2 side is closer than the first coil L1.
Is exposed from the housing 21 so as to be in contact with the lower surface of the housing.

Although not shown, the housing 2
1 is provided with a connector on the outer surface thereof. The power supply voltage Vcc is input through this connector, while the detection circuit 1
Thirty output signals are output.

The thickness detecting device according to the embodiment of the present invention having the above-described configuration is configured such that the inductance in the tuning circuit 120 depends on the magnitude of the magnetic field generated by the movable core 10 that is displaced in accordance with the thickness of the sheet A. Changes. Thereby, the output voltage of the detection circuit 130 changes as shown in FIG. 5 according to the thickness of the paper A. The characteristics of the thickness of the paper A and the output voltage of the detection circuit 130 include a substantially linear characteristic portion and a subsequent characteristic portion that saturates. Basically use. It has been confirmed that the above configuration enables detection of a sheet as thin as several tens of μm.

As described above, in the thickness detecting device according to the embodiment of the present invention, the displacement amount of the movable core 10, that is, the sheet A
It is possible to stably detect the thickness of the sheet with high accuracy.
In addition, the circuit configuration is very simple compared to a conventional magnetic field sensor of the same type that detects a magnetic body, including the fact that only one oscillation circuit 100 is required, and it is not necessary to use expensive circuit components. Cost reduction can also be achieved.

In the thickness detecting device according to the embodiment of the present invention, the trimmer capacitor VC1 is provided in the second resonance circuit 122. Instead, the same one as the trimmer capacitor VC1 is provided in the first resonance circuit. 121 may be provided. However, it is easier to adjust the trimmer capacitor VC1 if it is provided in the second resonance circuit 122 having a large Q. Of course, a trimmer capacitor may be provided in each of the first resonance circuit 121 and the second resonance circuit 122. Also,
The trimmer capacitors may be connected in series instead of being connected in parallel. Instead of using a trimmer capacitor as the fine adjustment circuit, a coil whose inductance can be changed may be used.

In the thickness detecting device according to the embodiment of the present invention, the coil L1 is arranged at a position away from the sheet A and the coil L2 is arranged at a position close to the sheet A. The circuit configuration is such that the impedance is low and the impedance of the second resonance circuit 122 is high. This is also one of the factors that make the detection accuracy extremely high. This is because the coil L1 is less likely to be affected by the surrounding noise magnetic field, while the coil L2 detects a change in the magnetic field only in the vicinity thereof with high sensitivity.

Note that the coil L having a shielding effect is used.
1, it is more effective to arrange around L2. A coil body 800 'on which the one having the shielding effect is arranged will be described with reference to FIG. FIG. 6 is a schematic explanatory view showing still another example of the coil body used in the thickness detecting device according to the embodiment of the present invention.

In the coil body 800 ', the coil L
1, L2 is directly wound around the core 815. An outer core 870 is provided at intervals around a core 815 around which the coils L1 and L2 are wound, and a shield 880 made of metal or the like is provided therearound. The structure thus configured is fixed to the base 855. In the figure, reference numeral 860 is a lead. For the core 815 and the outer core 870, for example, a ferrite core is used.
Therefore, the coil body 800 'thus configured exhibits a shielding effect between the shield 880 and the outer core 870, is not affected by the noise magnetic field from the side direction, and has only one end surface of the core 815 on the coil L2 side. Have directivity to be the detection surface 890. Note that the shielding effect is exhibited only by providing the external core 870 or the shield 880.

Although the above-described arrangement and the like are preferable for the coils L1 and L2, as long as the coils are magnetically coupled to each other and the inductance is changed according to the displacement of the movable core 10, There is no limitation on the arrangement, positional relationship, connection, etc. of the two.

In the thickness detecting device according to the embodiment of the present invention, any configuration may be used for the oscillation circuit 100 as long as a signal of a constant frequency can be generated and output. An amplifier or the like may be used.

In the thickness detecting device according to the embodiment of the present invention, the movable magnetic body (movable core 10) is brought into direct contact with the sheet A to be sent. Any arrangement may be used as long as it is displaced according to the thickness of the object. That is, the movable magnetic body may be attached to a member (for example, an existing roller) that comes into contact with the sheet A sent in an apparatus such as a laser printer.

Further, for example, a new member (detection member) which comes into contact with the fed sheet A may be provided. This new member may be elongate, for example. In this case, the new member is supported by a rotating shaft, one end of the new member is brought into contact with the sheet A to be sent, and a movable magnetic body is provided at the other end of the new member. Become. And
If the distance between the rotation axis and the other end is made longer than the distance between the rotation axis and the one end, the displacement amount of the movable magnetic body that is displaced in accordance with the thickness of the sheet A is smaller than the movable magnetic body. It is larger than when the sheet is directly brought into contact with the sheet A to be sent. That is, the detection sensitivity of the thickness detecting device is increased. In the above-described case (other than the movable core 10), the magnetic sensing device 20 is provided at a position close to the movable magnetic body. When the other end is heavier than the one end, it goes without saying that, for example, a spring is provided at the other end so that the one end comes into contact with the sheet A to be sent.

In the above embodiment, the laser printer of the electrophotographic process system has been described. However, the present invention can be similarly applied to an ink jet printer.
In this case, the fixing temperature adjustment circuit is not operated by the signal output from the CPU, but the recording head drive time adjustment circuit or the head interval adjustment mechanism is operated by the signal.

The recording head driving time adjusting circuit is a circuit for adjusting the amount of ink discharged from the nozzle head per pixel as the driving time of the recording head. The recording head driving time adjusting circuit adjusts the recording head per pixel according to a signal output from the CPU. Has a basic configuration in which the driving time of the device is changed. In this case, the driving time of the recording head per pixel is automatically adjusted according to the thickness of the sheet A.

On the other hand, the head spacing adjusting mechanism is a mechanism for adjusting the spacing between the nozzle head and the paper by a stepping motor or the like, not by an adjusting lever, and the amount of rotation of the stepping motor or the like in accordance with a signal output from the CPU. Is changed. In this case, the interval between the nozzle head and the paper A is automatically and constantly maintained irrespective of the thickness of the paper A.

The ink jet printer has the same advantages as the electrophotographic laser printer. Also, unlike before,
It is not necessary to finely adjust the distance between the nozzle head and the paper using the adjustment lever, and the usability is also improved in this respect.

The image recording apparatus using the thickness detecting device according to the present invention can be applied not only to a printer such as a laser printer but also to a PPC or the like.

The thickness detecting device according to the present invention can detect not only the thickness of the paper of the image recording apparatus but also any object as long as it is a non-magnetic material. . In addition, the shape and material of the movable magnetic body are not limited to the above embodiment.

Next, a magnetic substance level detecting apparatus according to an embodiment of the present invention will be described with reference to FIG. FIG. 7 is a circuit diagram of the magnetic substance level detecting device according to the embodiment of the present invention.

The level detector of the magnetic material according to the embodiment of the present invention is different from the magnetic detector 20 of the thickness detector according to the embodiment of the present invention in that the comparison circuit 140 is provided on the output side of the detection circuit 130. Is equivalent to the addition of Therefore, the movable core 10 as a movable magnetic body is not provided. Further, the magnetic body level detecting device according to the embodiment of the present invention does not detect the magnitude of the magnetic field of the movable core 10 but detects the presence or absence of toner in a toner tank provided in the laser printer.

For this reason, the magnetic substance level detecting device is mounted on a mounting opening provided at a position below the bottom surface or side surface of the toner tank (not shown). On this occasion,
In the magnetic body level detection device, the portion of the coil body 800 is
It is attached with the coil L2 side facing the inside of the toner tank.

The level detector of the magnetic material mentioned here is as follows.
It is detected whether or not the amount of toner in the toner tank exceeds a preset reference amount. When the amount exceeds the reference amount (a state where it is determined that there is toner), the voltage at the L level is not detected. In a state where it is determined that there is no toner), a basic configuration is used in which an H level voltage is output as a signal to a control circuit (not shown) for controlling the entire laser printer.

The printer operation may be performed without any problem if the amount of toner in the toner tank exceeds the reference amount. However, if the amount is less than the reference amount, the user is informed that the remaining amount of toner is small. Since it is necessary to give a warning in advance or to forcibly stop the operation of the printer, it is necessary to provide such a magnetic substance level detecting device in the laser printer.

The circuit configuration of the magnetic substance level detecting device is shown in FIG.
As described above, the magnetic sensing device 20 of the thickness sensing device according to the embodiment of the present invention as described above,
This corresponds to a configuration in which a comparison circuit 140 is added to the output side of the detection circuit 130. Therefore, the configuration and operation of the same circuit portion as in the magnetic sensing device 20 are the same, so that only the comparison circuit 140 will be additionally described below.

The comparison circuit 140 includes resistors R7 and R8 and a comparator OP2, compares the output voltage of the detection circuit 130 with a reference voltage corresponding to the reference amount of toner, and compares the comparison result with the reference amount of toner. Is output to the OUTPUT terminal as a signal indicating whether or not the number has exceeded the limit.

The reference voltage is generated by dividing the power supply voltage Vcc by the resistors R7 and R8. In addition,
Instead of dividing the voltage by the resistors R7 and R8, the reference voltage may be divided and generated by a variable resistor. When the reference voltage is generated by the variable resistor, the reference voltage can be adjusted. However, since the trimmer capacitor VC1 is provided also in the magnetic substance level detecting device, the reference voltage can be adjusted by the resistors R7 and R8 without adjusting the reference voltage by the variable resistor.
This is usually sufficient because the pressure is fixed and the pressure is fixedly generated.
Therefore, it is not necessary to adjust the reference voltage.

As described above, the magnetic substance level detecting device according to the embodiment of the present invention can detect the presence or absence of toner, which is a weak magnetic substance, with a very simple configuration. Further, since it is not necessary to use an extremely simple configuration and expensive circuit components, the cost of the magnetic substance level detecting device can be reduced.

In the magnetic material level detecting device according to the embodiment of the present invention, the comparison circuit 140 is provided for detecting the presence or absence of toner. However, when the amount of toner is detected, the comparison circuit 140 is used. Can be omitted. That is, in this case, the magnetic substance level detecting device is the same as the magnetic detecting device 20. Therefore, in this case, the characteristic diagram of the amount of toner of the magnetic substance level detecting device and the detection output voltage is the same as that of FIG. 5, but only the “paper thickness” on the horizontal axis of FIG.
It simply changes to "toner amount".

The magnetic substance level detecting apparatus according to the embodiment of the present invention can be applied not only to a printer such as a laser printer but also to a PPC or the like.
In addition, magnetic substances other than toner can be detected.

[0076]

As described above, according to the first aspect of the present invention,
The magnetic sensing device according to the first aspect of the present invention is a magnetic sensing device for detecting the magnitude of a magnetic field, wherein the first and second magnets are magnetically coupled to each other and arranged so that the inductance changes according to the magnitude of the magnetic field. An oscillation circuit that oscillates at a constant oscillation frequency and outputs the signal to a first coil;
A first capacitor that forms a first resonance circuit with the second coil, a second capacitor that forms a second resonance circuit with the second coil, and an output from the second resonance circuit. A first resonance circuit and a second resonance circuit, the first resonance circuit and the second resonance circuit forming a tuning circuit.
The resonance frequency of the resonance circuit is set to be lower than the oscillation frequency of the oscillation circuit, and the resonance frequency of the second resonance circuit is set to be higher than the oscillation frequency of the oscillation circuit.

Therefore, in the case of the magnetic detecting device according to the first aspect of the present invention, the magnitude of the magnetic field of the weak magnetic material can be detected with high accuracy. In addition, the overall configuration is very simple, and the cost can be reduced.

The magnetic detecting device according to claim 2 of the present invention is
A fine adjustment circuit provided so as to finely adjust the resonance frequency of the second resonance circuit and / or the first resonance circuit.

Therefore, in the case of the magnetic sensing device according to claim 2 of the present invention, by adjusting the fine adjustment circuit,
Variations in output and sensitivity of the magnetic detection device can be eliminated.

The magnetic sensing device according to a third aspect of the present invention comprises:
3. The magnetic sensing device according to claim 1, wherein each of the first coil and the second coil has one end connected to a common terminal. 4.

Therefore, in the case of the magnetic sensing device according to claim 3 of the present invention, the tuning coil composed of the first coil and the second coil can be a so-called center tap, so that the tuning coil can be used. Is easy to produce and assemble, and the cost of the magnetic sensing device is reduced by reducing the cost of the tuning coil.

The thickness detecting device according to claim 4 of the present invention is
A movable magnetic body that is displaced in accordance with the thickness of the object, and a thickness detection device including a magnetic detection device that detects the magnitude of a magnetic field created by the movable magnetic body as the thickness of the object, The magnetic sensing device includes first and second coils that are magnetically coupled to each other and that are arranged so that the inductance changes according to the displacement of the movable magnetic body, and oscillates at a constant oscillation frequency. An oscillation circuit that outputs a signal to the first coil, a first capacitor that forms a first resonance circuit with the first coil, and a second capacitor that forms a first resonance circuit with the second coil.
And a detection circuit for detecting a signal output from the second resonance circuit. The first resonance circuit and the second resonance circuit constitute a tuning circuit. The resonance frequency of the first resonance circuit is set lower than the oscillation frequency of the oscillation circuit, and the resonance frequency of the second resonance circuit is set higher than the oscillation frequency of the oscillation circuit.

Therefore, in the case of the thickness detecting device according to claim 4 of the present invention, the magnitude of the magnetic field generated by the movable magnetic body is detected as the thickness of the object by the magnetic detecting device. Claim 1 of the present invention relates to an apparatus.
Is used. Therefore, the thickness detecting device according to claim 4 of the present invention is a thickness detecting device that can achieve high accuracy while having a very simple configuration. Further, cost reduction can be achieved.

A magnetic substance level detecting apparatus according to a fifth aspect of the present invention is a magnetic substance level detecting apparatus for detecting the presence or absence or the amount of a magnetic substance such as toner in a non-contact manner. A first and a second coil which are coupled and arranged so that the inductance changes in accordance with the amount of the magnetic substance; and an oscillation circuit which oscillates at a constant oscillation frequency and outputs a signal to the first coil. A first capacitor forming a first resonance circuit with the first coil, a second capacitor forming a second resonance circuit with the second coil,
A detection circuit for detecting a signal output from the second resonance circuit; a tuning circuit is configured by the first resonance circuit and the second resonance circuit; and the resonance frequency of the first resonance circuit is oscillated. The configuration is such that the oscillation frequency is set lower than the oscillation frequency of the circuit, and the resonance frequency of the second resonance circuit is set higher than the oscillation frequency of the oscillation circuit.

In the case of the magnetic substance level detecting apparatus according to the fifth aspect of the present invention, the magnetic substance level detecting apparatus for detecting the presence or absence or the amount of a magnetic substance such as toner without contact is basically used. The magnetic detection device according to claim 1 of the present invention is used. Therefore, the magnetic substance level detecting device according to claim 5 of the present invention can detect the presence or absence or the amount of a weak magnetic substance with a very simple configuration. Also,
Cost reduction can also be achieved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a magnetic detector used in a thickness detector according to an embodiment of the present invention.

FIG. 2 is a schematic explanatory view showing a laser printer and a thickness detecting device according to an embodiment of the present invention and a peripheral mechanism thereof.

FIGS. 3A and 3B are schematic explanatory views showing a coil body used in the thickness detecting device according to the embodiment of the present invention. FIG. 3A is an example of the coil body, and FIG. For example,
FIG. 9C is a circuit diagram of still another embodiment, and FIG. 9D is a circuit diagram of FIGS.

FIG. 4 is an impedance characteristic diagram of a tuning circuit of the thickness detecting device according to the embodiment of the present invention.

FIG. 5 is a characteristic diagram of a thickness of a sheet and a detection output voltage in the thickness detecting device according to the embodiment of the present invention.

FIG. 6 is a schematic explanatory view showing still another example of the coil body used in the thickness detecting device according to the embodiment of the present invention.

FIG. 7 is a circuit diagram of a magnetic substance level detecting device according to the embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 100 oscillation circuit 120 tuning circuit 121 first resonance circuit 122 second resonance circuit 130 detection circuit C1 capacitor (first capacitor) C2 capacitor (second capacitor) L1 coil (first coil) L2 coil (second coil) VC1 Trimmer capacitor (fine adjustment circuit)

Claims (5)

[Claims] 1. A magnetic detecting device for detecting the magnitude of a magnetic field, wherein the first and second coils are magnetically coupled to each other and arranged so that the inductance changes according to the magnitude of the magnetic field. An oscillation circuit that oscillates at a constant oscillation frequency and outputs the signal to a first coil; a first capacitor that constitutes a first resonance circuit between the first coil and the second coil; , A second capacitor constituting a second resonance circuit, and a detection circuit for detecting a signal output from the second resonance circuit, wherein the first resonance circuit and the second resonance circuit are provided. And a tuning circuit is configured, the resonance frequency of the first resonance circuit is set lower than the oscillation frequency of the oscillation circuit, and the resonance frequency of the second resonance circuit is set higher than the oscillation frequency of the oscillation circuit. A magnetic sensing device, comprising: 2. The second resonance circuit and / or the first resonance circuit.
2. The magnetic sensing device according to claim 1, further comprising a fine adjustment circuit provided so as to finely adjust the resonance frequency of the resonance circuit. 3. The first coil and the second coil,
3. The magnetic sensing device according to claim 1, wherein each end is connected to a common terminal. 4. A thickness detection device comprising: a movable magnetic body that is displaced in accordance with the thickness of an object; and a magnetic detection device that detects the magnitude of a magnetic field generated by the movable magnetic body as the thickness of the object. The first and second coils, which are magnetically coupled to each other and arranged so that the inductance changes in accordance with the displacement of the movable magnetic body, include a constant oscillation device. An oscillation circuit that oscillates at a frequency and outputs the signal to a first coil;
A first capacitor forming a second resonance circuit between the first capacitor and the second coil; and a detection circuit detecting a signal output from the second resonance circuit. A tuning circuit is formed by the first resonance circuit and the second resonance circuit, the resonance frequency of the first resonance circuit is set lower than the oscillation frequency of the oscillation circuit, A thickness detecting device, wherein the resonance frequency is set to be higher than the oscillation frequency of the oscillation circuit. 5. A level detecting device for a magnetic material for detecting the presence or absence or the amount of a magnetic material such as a toner in a non-contact manner, wherein the devices are magnetically coupled to each other and have an inductance corresponding to the amount of the magnetic material. First and second coils arranged so as to change, an oscillation circuit which oscillates at a constant oscillation frequency and outputs the signal to the first coil, and a first resonance circuit between the first coil And a second capacitor forming a second resonance circuit between the first capacitor and the second coil, and a detection circuit for detecting a signal output from the second resonance circuit. A tuning circuit is formed by the first resonance circuit and the second resonance circuit. The resonance frequency of the first resonance circuit is set to be lower than the oscillation frequency of the oscillation circuit.
Wherein the resonance frequency of the resonance circuit is set to be higher than the oscillation frequency of the oscillation circuit.