JPS63187519A - High frequency oscillation type proximity switch - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (a) Industrial Application Field This invention provides a high-frequency oscillation type proximity switch that prevents magnetic flux leakage from a sensor coil and eliminates variations in detection distance due to the influence of surrounding metal bodies to which the sensor unit is attached. Regarding.

(b) Conventional technology In general, a high-frequency oscillation type proximity switch is equipped with a high-frequency oscillation circuit including a sensor coil, and for example, it oscillates when no object to be sensed arrives, and when the object to be sensed approaches, the oscillation circuit oscillates. The conductance changes and the oscillation weakens,
Or stop.

The weakening or stopping of this oscillation is level-discriminated to output the arrival of a detected object. In this type of proximity switch, a detection section including at least a sensor section is embedded in a desired location by screwing or the like.

In the operating state after installation, leakage magnetic flux is generated outward from a side surface of the sensor section other than the detection surface of the sensor section, for example. Therefore, if the mounting member (mounting wall surface) on which the sensor unit is mounted is a metal body, the leakage magnetic flux will have a magnetic effect on the metal body (surrounding metal), which will have a large effect on the detection distance of the sensor unit. It is known that there is a disadvantage in that the detection distance varies depending on whether the mounting member is a metal body or a non-metal body.

Therefore, conventionally, a high frequency oscillation type proximity switch has been implemented in which the outer cover that covers the detection surface of the sensor section is made of non-magnetic metal such as brass.

In this f74 proximity switch with an integrated yellow body outer cover, if the sensor part is attached to a metal mounting member (surrounding metal), the brass cover will be damaged due to leakage magnetic flux generated from the sensor part (sensor coil). An eddy current corresponding to the leakage magnetic flux is generated, and the leakage magnetic flux is canceled by the magnetic flux caused by this eddy current. In other words, leakage magnetic flux can be kept low. Therefore,
The sensor part is not strongly affected by surrounding metal.

(c) Problems to be Solved by the Invention In the above-mentioned proximity switch in which the detection part is covered with an integral brass outer cover, eddy currents generated by leakage magnetic flux are generated in the non-magnetic (brass) cover integrally. This type uses current to cancel leakage magnetic flux.

Therefore, in the case of a proximity switch with a small detection diameter (sensor coil diameter), leakage magnetic flux is considerably reduced, and the influence of surrounding metal on the sensor portion can be eliminated.

However, the method of canceling leakage magnetic flux using eddy current naturally has its limits. For example, in the case of a proximity switch with a large detection diameter, the leakage magnetic flux cannot be sufficiently canceled by eddy current, and surrounding metals due to leakage magnetic flux Therefore, it is not possible to maintain an appropriate detection distance. In other words, there is a disadvantage in that the detection distance of the sensor portion varies due to the difference in the surrounding material, such as when the mounting member is a metal body (surrounding metal) or a non-metal body.

SUMMARY OF THE INVENTION An object of the present invention is to provide a high-frequency oscillation type proximity switch that is not affected by surrounding metal and can maintain an appropriate detection distance even if the proximity switch has a large detection diameter.

(d) Means and operation for solving the problem In order to achieve this object, the high frequency oscillation type proximity switch of the present invention has the following configuration.

A high-frequency oscillation type proximity switch has an auxiliary coil wound around the outer periphery of the detection surface side end of a core equipped with a sensor coil, and the auxiliary coil and the sensor coil are connected in series so that the mutual inductance is negative. The magnetic flux of the auxiliary coil is configured to interlink with the leakage magnetic flux of the sensor coil.

In a high-frequency oscillation type proximity switch having such a configuration, a sensor coil and an auxiliary coil are connected in series, and the connection direction is set in a direction that can cancel the leakage magnetic flux of the sensor coil, that is, the winding direction of the auxiliary coil is different from that of the sensor coil. It's in the opposite direction. Furthermore, the number of turns of the auxiliary coil is set to the optimum number of turns that can sufficiently cancel leakage magnetic flux.

Now, when an alternating current is passed through the sensor coil and the auxiliary coil, the auxiliary coil generates a magnetic flux in the opposite direction that interlinks with the leakage magnetic flux of the sensor coil. As a result, the leakage magnetic flux generated from the sensor coil is canceled by the magnetic flux generated in the opposite direction from the auxiliary coil. Therefore, even if the sensor part of the proximity switch is attached to a mounting member made of a metal plate (surrounding metal), there will be no effect of leakage magnetic flux, and even if the sensor part of the proximity switch is attached to a mounting member made of a non-metallic body such as a resin plate. It becomes possible to maintain the same detection distance as in the case.

(E) Embodiment FIG. 2 is an external view showing a high frequency oscillation type proximity switch according to the present invention, and FIG. 1 is a sectional view.

The high-frequency oscillation type proximity switch is made of non-magnetic metal, and has a mounting screw part 11 on the outer periphery of the upper and lower sides (both end surfaces).
A cylindrical outer case 1 with an opening, an auxiliary coil case 2 fitted inside the opening at one end of the outer case 1, a core 4 fitted inside the auxiliary coil case 2 and equipped with a sensor coil 3, It consists of a coil case 5 that covers one end opening surface (the senna coil 3 exit surface) of the outer case l.

The opening of the outer case 1 is closed by an auxiliary coil case (coil case 5) 2, and the opening at the other end is closed by a cable clamp 12. The printed circuit board 13 is installed, and the printed circuit board 1
3 is fixed with a filling resin 14. The printed circuit board 13 is mounted with an oscillation circuit section, which will be described later, and a lead wire (cable) 15 connected to the printed circuit board 13 is drawn out from the cable clamp 12.

The auxiliary coil case 2 is formed into a cylindrical body with an open bottom at one end (upper end), and an E-shaped core 4 is fitted inside.
The sensor coil 3 is wound around the shaped core 4. The coil case 5 is formed into a bottomed cylindrical body with an opening at one end (lower end), and is fitted into the opening of the outer case l. In other words, the outer circumferential surface of the coil case 5 is fitted in contact with the inner circumferential surface of the outer case 1, and the bottom surface covers the protruding surface of the sensor coil (core 4) 3. The bottom surface of the coil case 5 is set as the detection surface of the sensor.

A feature of the present invention is that the auxiliary coil 6 is wound around the auxiliary coil case 2.

The auxiliary coil case 2 has a pair of flange plates 21 and 21 protruding from the outer periphery of the opening end surface of the cylindrical body with a certain distance between them.
The protruding tip of the coil case 5 is set so as to come into contact with the inner circumferential surface on the bottom side of the coil case 5. And this collar plate 21
．． An auxiliary coil 6 is wound in the groove 22 between the coils 21.

That is, the auxiliary coil 6 is wound around the outer periphery of the core 4 via the auxiliary coil case 2. This auxiliary coil 6
is wound in the opposite direction to the winding direction of the sensor coil 3. The auxiliary coil 6 and the sensor coil 3 are connected in series so that the mutual mR inductance is negative, so that the reverse magnetic flux generated from the auxiliary coil 6 cancels the leakage magnetic flux generated from the sensor coil 3. (See Figure 3).

Figure 3 shows the circuit of the high frequency oscillation type proximity switch +7
．． ? FIG. 2 is a block diagram showing an example.

The sensor coil 3 and the auxiliary coil 6 are connected in series to the oscillation circuit 71.

The oscillation circuit 71 oscillates high frequency waves using the sensor coil 3 and the auxiliary coil 6 in a state where no detection object arrives. Then, the detection circuit 72 converts the high frequency oscillation signal into direct current. Further, the comparator 73 compares the DC signal corresponding to the high frequency oscillation signal outputted from the detection circuit 72 with a preset reference level. If the object to be detected approaches the detection surface of the sensor section, the magnetic flux generated by the sensor coil 3 will be absorbed by the object A, disrupting the oscillation conditions. In other words, detection number 13 becomes below the reference level. Here, the comparator 73 outputs a signal indicating that the detection object A has approached to the output circuit 74, and the output circuit 74 outputs a stop or drive signal to the subsequent actuator drive circuit.

FIG. 4 is an explanatory diagram showing the distribution of magnetic flux generated by the sensor coil 3 and the auxiliary coil 6 when the sensor part of the high-frequency head type proximity switch of the embodiment is mounted on the metal mounting member (surrounding metal) 8. It is.

In FIG. 4, the magnetic flux generated by the sensor coil 3 is shown by a solid line, and the magnetic flux generated by the auxiliary coil 6 is shown by a broken line. The magnetic flux generated from the auxiliary coil 6 is transferred to the sensor coil 3.
The direction is opposite to the magnetic flux generated by the magnetic flux. In this state, the magnetic flux generated by the sensor coil 3 includes a magnetic flux perpendicular to the detection surface (surrounding metal 8) and a leakage magnetic flux flowing in the direction of the surrounding metal 8, and this leakage magnetic flux is , is interlinked with the magnetic flux of the auxiliary coil.

FIG. 5 is an explanatory diagram showing the relationship between the magnetic flux generated by the sensor coil 3 and the auxiliary coil 6, and the inductance and loss of the surrounding metal 8.

In FIG. 5, the symbol L2 indicates the sensor coil 3, and the symbol L2 indicates the auxiliary coil 6. L3 indicates the inductance of the surrounding metal 8 that interlinks with the leakage magnetic flux Φ of the sensor coil L, and L4 indicates the magnetic flux of the auxiliary coil Lz, and the magnetic flux Φ3 that does not interlink with the above L+ and Lz is It shows the inductance of the surrounding metal 8 that intersects. In other words, L4
indicates an inductance that is not affected by Ll, L3, etc. Also, Φ. indicates the magnetic flux emitted from the detection surface of the sensor coil L, and Φ1 is the magnetic flux of the sensor coil L,
It shows the leakage magnetic flux emitted from areas other than the detection surface. Furthermore, Φ2
is the magnetic flux of the auxiliary coil L2, which indicates the magnetic flux interlinking with the aforementioned L3, and φ3 is the magnetic flux of the auxiliary coil L2,
It shows the magnetic flux interlinked with the above mentioned. In other words, it can be explained that the two fluxes generated from the sensor coil 3 and the auxiliary coil 6 and the (assumed) magnetic fluxes derived from the sensor coil 2 and the auxiliary coil 6 have the relationship shown in FIG.

FIG. 6 is an equivalent circuit diagram showing the relationship between the inductance and loss of the sensor coil I21, the auxiliary coil L2, and the surrounding metal 8. That is, the sensor coil Ll, the auxiliary coil L2, the sensor coil L, and the auxiliary coil L2 shown in FIG.
The relationship between the inductances of the four coils R3 and R4 (assumed coils) due to the surrounding metal 8 generated by the magnetic flux is explained.

In FIG. 6, M2 shows the mutual inductance between the beam and R2, that is, the mutual inductance between the sensor coil 3 and the auxiliary coil 6, and M2 shows the mutual inductance between L and the beam 1. Further, M3 indicates mutual inductance between R2 and R3, and M4 indicates mutual inductance between R2 and R4. Furthermore, R1 indicates the loss of the surrounding metal 8 related to the above-mentioned L3, and R2 indicates the loss of the surrounding metal 8 related to the above-mentioned L4.

That is, in the relationship between L and R2, the mutual inductance is -Ml, and in the relationship between L and R3, the mutual inductance is -M2. Further, in the relationship between R2 and R4, the mutual inductance becomes M3, and further, in the relationship between R2 and R4, the mutual inductance becomes -M4.

Here, the reason why the magnetic flux leaking to the surrounding metal 8 can be minimized will be explained below using FIG. 6 above.

Now, if the AC voltage applied to input terminals a and b is ■, and the flowing current is i, then ■ is v−jω(Ll−Ml+I−□−Ml)i+ (RI+
Rz) i−jω(1□−1:+)i+jωmonaiz
......It is represented by (1).

If this equation (1) is modified to find the flowing current 11i2, R4+JωL4 R4+jωL4 is obtained.

Substituting the thus obtained equations (2) and (3) into the above (1) 2, we get “” J ω(L++Lz 2M+) + (R+
+Rz) 1R3-1-jωLI R4+Jω
L4 is obtained. In other words, eliminate currents iI and i2, and i
It is a linear expression of Furthermore, from this equation (4), input terminal a
, the impedance Z when looking at the coil side from b is: -jω(Ll +L2-2Ml) +(R1+R2)R
z+jωLff R, +jωL4 is obtained.

Then, by calculating the loss (real number) by subtracting the imaginary number from this (5) 2, we obtain R4'' + (ωL4)2.

In this (6) 2, M3, M 2 >> M 4
Therefore, if the equation related to M4 is ignored, the loss is expressed by the following equation.

On the other hand, mutual inductance M2, M is expressed by the following equation.

M2 = kl B] - 2 "T ...... (8) M
3- to 2 jL2 ・L, ......(9
) where k, , and 2 are the coupling coefficients between self-inductances.

Here, if the number of turns of the auxiliary coil L2 is selected appropriately, ! VI2=M3 (10
) can be done. Therefore, equation (7) is expressed as IZ
lit =R+ +Rz (11). In other words, by appropriately selecting the number of turns of the auxiliary coil L2, it is possible to eliminate the influence of leakage magnetic flux generated from the sensor coil L.

Note that when the material of the surrounding metal 8 changes, only the value of R3 changes, so from the above equations (8) and (9), equation (10) holds regardless of the material. The t position at that time is also as shown in equation (11). In other words, by appropriately selecting the number of turns of the auxiliary coil 6, it is possible to reduce the loss (coloring of R3 and R4) due to leakage magnetic flux of the sensor coil 3, and reduce the influence of the metal body (surrounding metal) 8 on which the sensor section is attached. It is possible to eliminate it.

Therefore, irrespective of whether the mounting member 8 in which the sensor section is buried is made of metal or non-metal, the magnetic flux leaking from the sensor coil 3 is completely canceled by the reverse magnetic flux generated from the auxiliary coil 6. Therefore, a detection distance of a certain length can be always ensured, and the difference in detection distance due to the difference in the mounting member (surrounding material) 8 can be explained.

(F) Effects of the Invention In this invention, as described above, the auxiliary coil is wound around the outer periphery of the detection part of the sensor, and the auxiliary coil and the sensor coil are connected in series, so that the magnetic flux of the auxiliary coil is of! It interlinks with the ii+52 magnetic flux in the opposite direction, canceling out the leakage magnetic flux.

As a result, the leakage magnetic flux generated from the sensor coil is reduced to nearly 0, and even if the mounting member to which the large-diameter sensor section is attached is a metal body (surrounding metal), the detection distance C will not be affected by the leakage magnetic flux at all. do not have. Therefore, as in the past, depending on whether the mounting member is a metal body or a non-metal body,
There is no disadvantage such as a difference in detection distance, and an appropriate detection distance can always be maintained regardless of the material of the mounting member.

Further, even when the sensor section is attached to a surrounding metal body, the present invention has the advantage of being able to extend the detection distance compared to the conventional eddy current method, and has excellent effects that achieve the purpose of the invention.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing an embodiment of the high frequency oscillation type proximity switch, Fig. 2 is an external view of the embodiment of the high frequency oscillation type proximity switch, and Fig. 3 shows an example of purchasing a circuit for the same high frequency oscillation type proximity switch. The block diagram, FIG. 4, is an explanatory diagram of the magnetic flux generated when the high-frequency oscillation type proximity switch of the embodiment is placed on the surrounding metal body (mounting member), and FIG. is an explanatory diagram showing the relationship between the inductance and loss of the bundle and the surrounding metal, and Fig. 6 is an equivalent circuit diagram showing the relationship between the inductance and loss of the sensor coil, auxiliary coil, and surrounding metal.■=Outer case, 2: Auxiliary coil case, 3: sensor coil, 4: core, 5: coil case, 6: auxiliary coil. Patent applicant: Tateishi Electric Co., Ltd. Agent
Patent Attorney Shigeru Nakamura Ikuchi Figure 2 Figure 4 Figure 5

Claims (1)

[Claims] (1) An auxiliary coil is wound around the outer periphery of the detection surface side end of the core provided with the sensor coil, and the auxiliary coil and the sensor coil are connected in series so that the mutual inductance is negative, and the auxiliary coil A high frequency oscillation type proximity switch configured to link the magnetic flux of the sensor coil with the leakage magnetic flux of the sensor coil.