JP2008166055A - High-frequency oscillation type proximity sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-frequency oscillation type proximity sensor capable of setting a detection distance long enough with not only a ferromagnetic metal but a non-magnetic metal, and that, with stable detection characteristics. <P>SOLUTION: The sensor is provided with a two-thread coil with one of the two coil conductors having one end connected with each other and twisted together as a coil for a resonance circuit, and the other as a coil for copper resistor compensation, a capacitor connected in parallel with the two-thread coil to form a resonance circuit, a driving circuit driving the resonance circuit at a constant frequency, a series circuit of an inductance of the two-thread coil and its inner resistor, and a copper resistor compensation circuit virtually grounding a connection point of each copper resistor at an equivalent circuit of the two-thread coil shown as each copper resistor of the coil for resonance circuit and the coil for copper resistor compensation, and the above series circuit. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  In the present invention, not only a ferromagnetic metal such as iron but also a non-magnetic metal such as aluminum, for example, in a general M18 size cylindrical proximity sensor, the detection distance can be set to 10 mm or more. The present invention relates to an oscillation type proximity sensor.

  The high-frequency oscillation proximity sensor changes the inductance and loss of the detection coil due to electromagnetic induction when the object to be detected approaches the detection coil that forms part of the high-frequency oscillation circuit. The approach of the detection object is detected by utilizing the change in the oscillation frequency and oscillation amplitude of the circuit. In general, this type of high-frequency oscillation proximity sensor is required not only to have stable detection characteristics but also to be able to set its detection distance sufficiently long. ing.

  Therefore, the present inventors first focused on the fact that the detection characteristics of the proximity sensor are exclusively affected by the copper resistance (copper loss) contained in the detection coil, and connected the two ends connected to each other. In a self-excited high-frequency oscillation proximity sensor using a two-wire coil in which one of the coil conductors is a resonance circuit coil and the other is a copper resistance compensation coil as a detection coil, the inductance L of the two-wire coil and its induction In the equivalent circuit of the two-yarn coil shown as each copper resistance Rcu of the resonance circuit coil and the copper resistance compensation coil respectively connected to one end of the series circuit. It was proposed that each copper resistor Rcu itself is canceled by virtually grounding the connection point between each copper resistor and the series circuit, and the detection characteristic is stabilized (for example, Patent Document 1). Reference).

On the other hand, the high-frequency oscillation type proximity sensor has a lower detection sensitivity for nonmagnetic metals such as aluminum and copper than a ferromagnetic metal such as iron, and its detection distance is about 30% of that of a ferromagnetic metal. Therefore, a so-called separately excited high-frequency oscillation proximity sensor that can detect not only ferromagnetic metals but also nonmagnetic metals with high sensitivity by driving a resonance circuit composed of a coil and a capacitor at a constant frequency is provided. Has been proposed (see, for example, Patent Document 2).
JP 2003-298403 A JP-A-3-29415

  However, even if a separately excited high-frequency oscillation proximity sensor as shown in Patent Document 2 described above is used, the detection distance for a nonmagnetic metal can only be made as long as that for a ferromagnetic metal. Specifically, the detection distance of a detection object made of a ferromagnetic metal and / or a non-magnetic metal in a conventional general excitation type high-frequency oscillation proximity sensor is, for example, a general M18 size cylindrical proximity sensor. It is at most about 7 mm, and it is difficult to say that a sufficiently long detection distance is practically secured. Therefore, in order to reliably prevent a collision with a detection target, development of a high-frequency oscillation type proximity sensor whose detection distance is set to 10 mm or more is strongly desired.

  The present invention has been made in view of such circumstances, and the object thereof is not only to a ferromagnetic metal such as iron but also to a nonmagnetic metal such as aluminum, for example, a general M18 size cylindrical proximity. An object of the present invention is to provide a high-frequency oscillating proximity sensor that can sufficiently increase the detection distance of the sensor to 10 mm or more and that has stable detection characteristics and is easy to use.

In order to achieve the above-described object, the high-frequency oscillation type proximity sensor according to the present invention includes:
<a> A two-filament coil in which one end of two coil conductors connected together and wound together is a resonance circuit coil and the other is a copper resistance compensation coil;
<b> a capacitor that is connected in parallel to the two-thread coil to form a resonance circuit;
<c> a drive circuit for driving the resonant circuit at a constant frequency;
<d> Shown as a series circuit of the inductance of the two-wire coil and its inductive internal resistance, and each copper resistance of the resonance circuit coil and the copper resistance compensation coil respectively connected to one end of the series circuit And a copper resistance compensation circuit that virtually grounds a connection point between each of the copper resistors and the series circuit in the equivalent circuit of the two-thread coil.

  Preferably, the copper resistance compensation circuit is connected to the other end of the resonance circuit coil and the copper resistance compensation coil in the two-thread coil, and inverts and amplifies the voltage generated at the other end of the copper resistance compensation coil. An inverting amplifier that negatively feeds back to the other end of the resonance circuit coil is included. In addition, the drive circuit includes an oscillator that generates a voltage having a constant frequency slightly lower than the natural vibration frequency in the vicinity of the natural vibration frequency of the resonance circuit, and the resonance frequency by converting the voltage of the constant frequency output by the oscillator. A V-I converter applied to the circuit is included.

  Furthermore, an adjustment means for finely adjusting the capacitance of the capacitor according to a phase difference between a voltage output from the oscillator and an output voltage obtained from the resonance circuit is provided.

  According to the high-frequency oscillation type proximity sensor having the above-described configuration, a ferromagnetic circuit such as iron is used by adopting a separately-excited configuration in which a resonance circuit including a two-thread coil and a capacitor is driven at a constant frequency from the outside. The detection distance can be increased not only for metals but also for non-magnetic metals such as aluminum, and the copper resistance (copper loss) of the above-described two-thread coil is compensated, and the copper resistance itself is substantially cancelled. As a result, it is possible to suppress the change in the detection characteristic depending on the temperature characteristic of the copper resistance and to make the resonance condition sharp. In other words, the resonance condition (Q switch characteristic) of the resonance circuit composed of the two-filament coil and the capacitor in which the copper resistance is compensated (cancelled) is narrow in the frequency band and the peak level is increased. Therefore, the change in the output of the resonance circuit due to the presence or absence of the detection target can be increased. As a result, the detection distance can be made sufficiently long regardless of whether the detection target is a ferromagnetic material or a non-magnetic material. For example, in a general M18 size cylindrical proximity sensor, the detection distance can be set to about 12 mm.

Hereinafter, a high-frequency oscillation type proximity sensor according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of a high-frequency oscillation type proximity sensor according to this embodiment, and 1 is a two-thread coil in which one ends of two coil conductors are connected to each other and wound together. This high-frequency oscillation type proximity sensor has a capacitor 2 connected in parallel to the two-thread coil 1, and a resonance circuit 3 is constructed in which one of the two coil conductors is a resonance circuit coil and the other is a copper resistance compensation coil. The resonance circuit 3 is configured to be driven at a constant frequency from the outside. For example, the two-thread coil 1 is formed by winding coils L1 and L2 in which two high-frequency litz wires having one end connected in common are wound around a resin bobbin, and inserting a ferrite core into the bobbin. Become.

  The drive circuit for driving the resonance circuit 3 composed of the two-yarn coil 1 and the capacitor 2 described above is composed of a crystal oscillator and oscillates and outputs a pulse signal (voltage) with a constant frequency, and the output of the oscillator 4 is divided. A frequency divider 5 that generates a signal having a frequency that is in the vicinity of the resonance frequency of the resonance circuit 3 and slightly lower than the resonance frequency by turning, and an output (voltage) of the frequency divider 5 is converted into a current. And a VI converter 6 applied to the resonance circuit 3. By driving the resonant circuit 3 with such a drive circuit, a separately excited high frequency oscillation proximity sensor is configured. Basically, the level detector 7 determines a change in the output (amplitude) of the resonance circuit 3 that changes as the detection target M approaches the two-thread coil 1, thereby detecting the detection target M. It detects the proximity (presence) of.

  In such a separately excited type high frequency oscillation proximity sensor, the present invention further includes a copper resistance compensation circuit 8 for canceling the copper resistance of the two-thread coil 1 and stabilizing the detection characteristics. The copper resistance compensation circuit 8 inverts and amplifies the voltage generated at the other end of the copper resistance compensation coil L2 in the two-wire coil 1, for example, and inverts the output to the other end of the resonance circuit coil L1. This is realized as an amplifier 9.

  Such a copper resistance compensation circuit 8 basically includes a series circuit of an inductance L (= L1 = L2) of the two-filament coil 1 and its inductive internal resistance Ri as shown in FIG. When shown as an equivalent circuit having each copper resistance Rcu of the resonance circuit coil and the copper resistance compensation coil respectively connected to one end of a series circuit, the connection of the copper resistance and the series circuit in the equivalent circuit The point D is virtually grounded. The presence of the copper resistor Rcu itself is canceled by the virtual ground at the connection point D, thereby preventing the detection characteristics from becoming unstable due to the copper resistor Rcu in the resonance circuit 3. The copper resistance compensation circuit 8 that plays such a role is as described in detail in the above-mentioned Patent Document 1.

  By the way, when the copper resistance in the two-thread coil 1 is compensated as described above, the resonance characteristic of the resonance circuit 3 is steep with a narrow resonance frequency width and a large peak level by canceling the copper resistance Rcu. It can be (sharp). That is, the resonance characteristics (x, y, z) when the copper resistance of the two-thread coil 1 in the resonance circuit 3 described above in FIG. 3 is not compensated, and the resonance characteristics (X, Y, Z) when the copper resistance is compensated. As shown by contrast, the resonance characteristic can be made sharp by the copper resistance compensation. The characteristic (x, X) indicates a resonance characteristic when the detection target M does not exist, and the characteristic (y, Y) indicates a resonance characteristic when the detection target M is a ferromagnetic material such as iron. The characteristics (z, Z) indicate the resonance characteristics when the detection object M is a nonmagnetic material such as aluminum or copper.

  More specifically, when the copper resistance Rcu of the two-yarn coil 1 is canceled by the copper resistance compensating circuit 8, the Q value of the resonance circuit 3 constituted by the two-yarn coil 1 and the capacitor 2 is increased. As the substantial resistance component of the two-thread coil 1 decreases, the amplitude (level) at the resonance frequency increases, and the amplitude (level) rapidly decreases with respect to the deviation from the resonance frequency. That is, the resonance characteristics of the resonance circuit 3 can be made sharper by copper resistance compensation.

  When the ferromagnetic material such as iron comes close to the double-threaded coil 1 with respect to the characteristic X of the resonance circuit 3 under such driving conditions, the impedance of the double-threaded coil 1 is reduced, and the amplitude as shown as the characteristic Y in FIG. Since it itself becomes small, the presence of the ferromagnetic material can be detected with high sensitivity by monitoring the change in the resonance frequency. Further, when a non-magnetic material such as aluminum approaches the two-thread coil 1, the magnetic flux is canceled by the eddy current generated in the non-magnetic material, and the inductance of the two-thread coil 1 is reduced. The resonance point (resonance frequency) changes. Therefore, it is possible to detect the presence of the non-magnetic material with high sensitivity by monitoring the amplitude at the drive frequency described above, not the amplitude at the resonance frequency at that time.

  Therefore, as described above, the resonance circuit 3 is driven at a constant frequency in the vicinity of the resonance frequency, and the output (amplitude) of the resonance circuit 3 at this drive frequency is monitored. Alternatively, even if it is a non-magnetic material, its proximity (presence) can be detected with high sensitivity. By the way, according to the experiments by the present inventors, for example, in a general M18 size cylindrical proximity sensor, it is possible to set the detection distance for iron, which is a ferromagnetic material, as long as 7 mm to 12 mm. However, the detection distance for copper and aluminum can be set as long as 2 mm to 12 mm.

  By the way, as described above, when the separately excited high frequency oscillation proximity sensor is configured as described above, the resonance characteristic (Q switch characteristic) becomes sharp as described above. In order to detect the proximity of M, the drive frequency of the resonance circuit 3 and the resonance frequency of the resonance circuit 3 must be matched with high accuracy. As the adjustment method, for example, the oscillation frequency itself of the oscillator 4 may be adjusted, or the frequency division ratio by the frequency divider 5 may be adjusted. In general, the capacitance of the capacitor 2 is finely adjusted. Is.

  In this case, for example, a representative sample is used, and the output of the frequency divider 5 and the resonator that can detect the ferromagnetic metal and the nonmagnetic metal at a long distance and an equal distance by the adjuster 9. The optimum value of the phase difference φ with respect to the output 3 is obtained in advance. In a mass-produced product, the capacitance of the capacitor 2 may be finely adjusted so that the phase difference φ between the output of the frequency divider 5 and the output of the resonator 3 becomes the optimum value of the phase difference. That is, if there is a difference between the drive frequency of the resonance circuit 3 and the resonance frequency of the resonance circuit 3, the frequency division is performed as shown in FIG. 4A depending on the imaginary component of the impedance of the resonance circuit 3 at the drive frequency. A phase shift φ occurs between the output (rectangular wave) V1 of the circuit 5 and the output (sine wave) V2 of the resonance circuit 3. This shift, that is, the phase difference φ includes the influence of the phase rotation in the VI converter accurately. For this reason, the optimum value of the phase difference φ is different for each circuit configuration. However, by referring to this phase difference φ, the capacitance of the capacitor 2 can be adjusted easily and accurately.

  The present invention is not limited to the embodiment described above. For example, for copper resistance compensation of the two-thread coil 1, the output of the resonance circuit 3 can be phase-controlled and negatively fed back to the copper resistance compensation coil. In the embodiment, the output of the oscillator 4 is divided by using the frequency divider 5 to generate a constant frequency voltage signal for driving the resonant circuit 3. However, the constant frequency is generated by using a VCO (frequency variable control oscillator). It is also possible to generate a voltage signal of a constant frequency using a PLL circuit (phase lock loop circuit). Furthermore, it goes without saying that the fine adjustment means of the resonance condition for the resonance circuit 3 is not specified in the embodiment. In short, various modifications can be made without departing from the scope of the present invention.

The schematic block diagram of the high frequency oscillation type proximity sensor which concerns on one Embodiment of this invention. The figure which shows the equivalent circuit of a 2 thread coil. The figure which shows the resonance characteristic of the high frequency oscillation type proximity sensor shown in FIG. The figure which shows the relationship between the drive signal of a resonance circuit, and its output.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 2 Thread coil 2 Capacitor 3 Resonant circuit 4 Oscillator 5 Divider 6 VI converter 7 Level detector 8 Copper resistance compensation circuit 9 Adjuster (resonance frequency adjustment)

Claims (4)

One of two coil conductors connected at one end to each other and wound together is a two-strand coil having a resonance circuit coil and the other being a copper resistance compensation coil;
A capacitor connected in parallel to the two-thread coil to form a resonant circuit;
A drive circuit for driving the resonant circuit at a constant frequency;
A series circuit of an inductance of the two-yarn coil and its inductive internal resistance, the two-yarn shown as each copper resistance of the resonance circuit coil and the copper resistance compensating coil respectively connected to one end of the series circuit A high-frequency oscillation type proximity sensor comprising: a copper resistance compensation circuit that virtually grounds a connection point between each of the copper resistors and the series circuit in an equivalent circuit of a coil.   The copper resistance compensation circuit is connected to the other end of the resonance circuit coil and the copper resistance compensation coil, and inverts and amplifies the voltage generated at the other end of the copper resistance compensation coil, and the other end of the resonance circuit coil The high frequency oscillation type proximity sensor according to claim 1, further comprising an inverting amplifier that performs negative feedback.   The drive circuit includes: an oscillator that generates a voltage having a constant frequency slightly lower than the natural vibration frequency in the vicinity of the natural vibration frequency of the resonance circuit; and the resonance circuit that converts the voltage of the constant frequency output by the oscillator into a current. The high-frequency oscillation type proximity sensor according to claim 1, further comprising a V-I converter applied to the capacitor.   4. The high-frequency oscillation type proximity sensor according to claim 3, further comprising adjusting means for finely adjusting the capacitance of the capacitor according to a phase difference between a voltage output from the oscillator and an output voltage obtained from the resonance circuit. .

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