JP2011216256A - Proximity switch - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable inexpensive and easy mass production of proximity switches having a constant detecting performance.SOLUTION: Detection distance stabilizing members 20 making a magnetic body ring-shaped, varying inductances L of a coil part 6 and enabled to be endowed with characteristics of offsetting changes of resistances R of the coil part 6 in accordance with changes of gaps A' are fixed on an inner wall 9 of a detection face, so that a detection distance is stabilized irrespective of displacement, if any, of the coil part 6.

Description

  The present invention relates to a proximity switch that determines the approach of a detected object by detecting loss of a magnetic field due to the approach of the detected object such as metal.

  For the purpose of improving the impact resistance and wear resistance of a proximity switch, there is a case in which a stainless material is used for a housing that houses a coil (see, for example, Patent Document 1). FIG. 7 is a cross-sectional view showing a configuration of a conventional proximity switch 1, and the entire housing is made of nonmagnetic stainless steel. In FIG. 7, the coil 2 is wound around the bobbin 3 and accommodated in the annular groove of the ferrite core 4, and the substrate 5 on which various electronic components are mounted is connected to the back surface of the ferrite core 4, 6 is constituted. The coil portion 6 is accommodated in a bottomed cylindrical cap 7, and the coil portion 6 is accommodated together with the cap 7 in a bottomed cylindrical casing 8 and filled with a filler 10. Further, the cable holder 11 is attached to the opening of the housing 8, and the cable 12 is pulled out from the hole of the cable holder 11.

  The proximity switch 1 configured as described above forms a magnetic field in front of the detection surface as the coil unit 6 oscillates. When the detected object enters the magnetic field, an eddy current is generated in the detected object. Therefore, it is possible to detect the eddy current loss of the coil unit 6 and determine the proximity of the detected object. However, the oscillation frequency is set low so that the AC magnetic flux from the coil unit 6 passes through the stainless steel detection surface. In addition, eddy currents are generated on the detection surface in the same manner as eddy currents are generated on the detection target.

For example, the coil unit 6 is caused to function as a self-excited LCR resonance circuit having an inductance (L) component, a capacitance (C) component, and a resistance (R) component, and a change in the resonance impedance Zosc of the LCR resonance circuit is detected. To determine the proximity of the detected object. Here, the resonance impedance is expressed by the following equation (1).
Zosc = L / CR (1)

Japanese Patent Laid-Open No. 9-320422

  When the conventional proximity switch 1 is assembled, an insulating cap 7 that houses the coil portion 6 is temporarily fixed in the housing 8 and sealed with a filler 10 such as an epoxy resin. Therefore, depending on the properties of the filler 10 and the conditions at the time of curing, deformation due to curing shrinkage or stress may occur, and the temporarily fixed coil portion 6 may shift in the X-axis direction. Even if the positional deviation between the casing 8 and the coil unit 6 is slight, the resistance R of the coil unit 6 greatly changes due to the influence of eddy current loss generated on the detection surface. Then, the resonance impedance Zosc also fluctuated from the above equation (1), and there was a problem that the detection distance fluctuated greatly. For example, when the gap A between the casing 8 and the coil portion 6 is shifted in the direction of decreasing, the resistance R increases and the resonance impedance Zosc decreases, so that the actual detection distance extends beyond the set detection distance.

  Further, since it is difficult to prevent a slight misalignment between the housing 8 and the coil portion 6 during assembly, it has been difficult to easily mass-produce proximity switches having a certain detection performance at low cost.

  The present invention has been made to solve the above-described problems, and an object thereof is to enable mass production of a proximity switch having a certain detection performance at low cost and easily.

  According to a first aspect of the present invention, a proximity switch includes a metal casing, a coil unit that is housed in the casing and detects the proximity of the detected object to the casing detection surface, and the inner wall side of the casing detection surface. Change in resistance of the coil portion in response to a change in the gap between the magnetic member and the coil portion by changing the inductance of the coil portion. And a magnetic member having a characteristic of canceling out.

In a proximity switch according to a second aspect of the present invention, the casing is made of a metal having a relative permeability of substantially 1 and a volume resistivity of 45 × 10 ⁻⁸ [Ωm] or more.

  In the proximity switch according to claim 3 of the present invention, the magnetic member is formed in a shape protruding from the inner wall of the casing detection surface.

  In the proximity switch according to claim 4 of the present invention, the magnetic member is formed flush with the inner wall of the housing detection surface.

  The proximity switch according to claim 5 of the present invention is formed by coating or printing on the inner wall of the casing detection surface.

  According to this invention, the magnetic member is provided on the inner wall side of the metal casing detection surface to change the inductance of the coil portion, and the change in the resistance of the coil portion according to the change in the gap between the magnetic member and the coil portion is changed. Since the cancellation is made, it is possible to easily mass-produce proximity switches having a constant detection performance at low cost.

It is sectional drawing which shows the structure of the proximity switch which concerns on Embodiment 1 of this invention. It is a graph which shows the change rate of the resistance of the coil part with respect to the variation | change_quantity of a clearance gap between the proximity switch which concerns on Embodiment 1, and the conventional proximity switch. It is a graph which shows the change rate of the inductance of the coil part with respect to the variation | change_quantity of the clearance gap of the proximity switch which concerns on Embodiment 1, and the conventional proximity switch. It is a graph which shows the change rate of the resonant impedance of a coil part with respect to the variation | change_quantity of the clearance gap of the proximity switch which concerns on Embodiment 1, and the conventional proximity switch. It is a graph which shows the change rate of the detection distance with respect to the variation | change_quantity of a clearance gap between the proximity switch which concerns on Embodiment 1, and the conventional proximity switch. It is a graph which shows the change of the detection sensitivity with respect to the variation | change_quantity of a clearance gap of the proximity switch which concerns on Embodiment 1, and the conventional proximity switch. It is sectional drawing which shows the structure of the conventional proximity switch.

Embodiment 1 FIG.
FIG. 1 is a cross-sectional view showing the configuration of the proximity switch 1a according to the first embodiment. The same or corresponding parts as those in FIG. The proximity switch 1a has a detection distance stabilizing member (magnetic member) 20 as a detection surface in order to minimize the change in the resonance impedance Zosc caused by the positional deviation between the coil portion 6 and the nonmagnetic stainless steel casing 8. It is fixed at a predetermined position on the inner wall 9. A cap 7 accommodating the coil portion 6 is temporarily fixed therein, and a filler 10 is injected and sealed.

The housing 8 is made of nonmagnetic stainless steel. The characteristic of nonmagnetic stainless steel is that the relative permeability (ratio of the permeability of the substance at the same electric field strength to the permeability of the vacuum) is substantially 1, and the volume resistivity at 20 ° C. is 45 × 10. It is preferably ^-8 [Ωm] or more.
Further, the detection distance stabilizing member 20 is a magnetic body having a relative permeability higher than that of the housing 8 and a higher volume resistivity. Here, the relative magnetic permeability of the detection distance stabilizing member 20 is 50, and it has the same shape as the coil 2 and a ring shape with a thickness of 0.3 mm.

  Hereinafter, the characteristics of the proximity switch 1a according to the first embodiment will be described in comparison with the characteristics of the conventional proximity switch 1 (FIG. 7) described above. Note that the gap A of the conventional proximity switch 1 is a gap between the detection surface inner wall 9 and the coil portion 6 as shown in FIG. 7, and on the other hand, the gap A of the proximity switch 1a according to the first embodiment. 'Is a gap between the detection distance stabilizing member 20 and the coil portion 6 as shown in FIG.

  FIG. 2 is a graph showing the rate of change ΔR of the resistance R of the coil section 6 with respect to the amount of change in the gaps A and A ′. The horizontal axis represents the distance [mm] between the gaps A and A ′, and the vertical axis represents the rate of change ΔR [ %]. The rate of change ΔR was calculated based on the resistance R when the gaps A and A ′ were 0.57 mm. From FIG. 2, the resistance R increases as the clearances A and A ′ of both the proximity switches 1 and 1 a are reduced. Compared to Note that when the thickness of the detection distance stabilizing member 20 is changed, the resistance R of the coil portion 6 changes.

  FIG. 3 is a graph showing the rate of change ΔL of the inductance L of the coil section 6 with respect to the amount of change in the gaps A and A ′. The horizontal axis indicates the distance [mm] between the gaps A and A ′, and the vertical axis indicates the rate of change ΔL [ %]. As shown in FIG. 3, in the proximity switch 1a, the magnetic flux actively passes through the detection distance stabilization member 20, and the detection distance stabilization member 20 passes through the detection distance stabilization member 20 because its magnetic resistance is smaller than that of air. As a result, the magnetic resistance decreases, and the magnetic flux increases and the inductance L increases.

Therefore, if the shape (thickness, diameter, etc.) and relative permeability of the detection distance stabilizing member 20 are determined so that the inductance L and the resistance R change at the same ratio, the resonance impedance Zosc is substantially as shown in FIG. It becomes constant.
FIG. 4 is a graph showing the rate of change ΔZosc of the resonance impedance Zosc of the coil section 6 with respect to the amount of change of the gaps A and A ′. The horizontal axis indicates the distance [mm] between the gaps A and A ′, and the vertical axis indicates the rate of change ΔZosc. [%] Is shown. As described above, in the conventional proximity switch 1, when the gap A is reduced, the resistance R is increased with respect to the substantially constant inductance L, so that the resonance impedance Zosc is reduced as shown in FIG. On the other hand, in the proximity switch 1a according to the first embodiment, when the gap A ′ is reduced, the inductance L and the resistance R increase at the same ratio, so that the resonance impedance Zosc hardly changes.

FIG. 5 is a graph showing the change rate ΔOP of the detection distance OP of the proximity switches 1 and 1a with respect to the amount of change in the gaps A and A ′. The rate ΔOP [%] is shown. From FIG. 5, the detection distance of the proximity switch 1a when the detection distance stabilizing member 20 is provided is substantially constant regardless of the change in the gap A ′. In this example, when the gaps A and A ′ are changed by 0.05 mm from 0.55 to 0.60 mm, the detection distance of the proximity switch 1 is changed by 46%, whereas the detection distance of the proximity switch 1a is changed by 4%. It becomes.
However, the amount of change in the detection distance of the proximity switch 1a can be further suppressed by adjusting the shape and relative permeability of the detection distance stabilizing member 20, and theoretically, the detection distance can be set regardless of the change in the gap A ′. It is also possible to make it constant.

  FIG. 6 is a graph showing the detection sensitivity of the proximity switches 1 and 1a with respect to the amount of change in the gaps A and A ′. When the horizontal axis indicates the distance [mm] between the gaps A and A ′ and the vertical axis indicates the object to be detected. The resonance impedance Zosc ratio [%] when there is no. From FIG. 6, it can be seen that the proximity switch 1a has a lower Zosc ratio than the proximity switch 1, so that the detection sensitivity is improved.

  Since the detection distance stabilizing member 20 has the above-described effects, the detection distance does not change even if the casing 8 and the coil portion 6 are misaligned when the proximity switch 1a is assembled. Therefore, the proximity switch 1a The detection performance can be kept constant when mass-produced. Further, since it is only necessary to provide the detection distance stabilizing member 20, it is low cost and simple.

  As a material for forming the detection distance stabilizing member 20, a plastic magnet (hereinafter referred to as a plastic magnet) which is a molded product obtained by kneading magnetic powder in plastic is preferable. This is because the degree of freedom in shape and electromagnetic properties is high. The detection distance stabilizing member 20 may be formed using a material such as permalloy and amorphous tape and ferrite in addition to the plastic magnet.

  Although the detection distance stabilizing member 20 formed of these materials is fixed to the detection surface inner wall 9, it is desirable to fix the detection distance securely because the above-described effects are drastically reduced when a positional shift occurs. The positional deviation of the detection distance stabilizing member 20 needs to be at least smaller than the positional deviation of the coil portion 6.

  In order to prevent displacement of the detection distance stabilizing member 20, the thickness of the detection distance stabilizing member 20 is reduced so as not to be affected by the sealing filler 10, and is fixed to the inner wall 9 of the detection surface in advance with an adhesive. . Alternatively, the detection distance stabilizing member 20 is applied or printed as a magnetic paint on the inner surface 9 of the detection surface to be in close contact, and a coating agent is applied thereon. Alternatively, the housing 8 and the detection distance stabilizing member 20 may be integrally formed by a metal powder injection molding method (MIM).

  In the example of FIG. 1, the detection distance stabilizing member 20 protrudes from the detection surface inner wall 9, but may be embedded in the detection surface to be flush with the detection surface inner wall 9. Moreover, the detection distance stabilization member 20 should just be a shape which makes the inductance L and resistance R of the coil part 6 large by the same ratio, and may be a disk and a core extension type other than a ring shape. Further, the outer diameter of the detection distance stabilizing member 20 may be larger than the outer diameter of the coil portion 6.

  As described above, according to the first embodiment, the housing 8 made of nonmagnetic stainless steel and the coil unit 6 that is housed in the housing 8 and detects the proximity of the detection target to the detection surface are provided. In the proximity switch 1a, it is a magnetic member provided on the inner wall 9 of the detection surface, has a higher relative permeability than the material of the casing 8, and changes the inductance L of the coil portion 6 to respond to the change of the gap A ′. The detection distance stabilizing member 20 having the characteristic of canceling out the change in the resistance R of the coil unit 6 is provided. For this reason, even if the gap A ′ between the detection surface inner wall 9 and the cap 7 is displaced during assembly of the proximity switch 1a, the detection distance can be stabilized regardless of the displacement, and the proximity having a certain detection performance. Switches can be mass-produced easily at low cost.

  In the first embodiment, the housing 8 is made of non-magnetic stainless steel, but is not limited to this, and is made of titanium having high strength and high volume resistivity, similar to stainless steel. Also good. Alternatively, the housing 8 can be made of magnetic stainless steel.

  In the first embodiment, the detection distance stabilizing member 20 is fixed to the detection surface inner wall 9. However, the detection distance stabilization member 20 is not limited to this and is fixed to the side periphery of the housing 8 on the detection surface inner wall 9 side. Also good.

In the first embodiment, the coil unit 6 is composed of the coil 2, the bobbin 3, the ferrite core 4 and the substrate 5. However, the coil unit 6 includes at least the coil 2 for generating a magnetic field. What is necessary is just to exist and you may abbreviate | omit another member as needed.
Moreover, although the ferrite core 4 is a product made from a ferrite, you may use the core comprised with materials other than this.
Furthermore, although the coil part 6 was accommodated in the insulating cap 7, this cap 7 may be omitted.

In the first embodiment, the proximity switch 1a using the self-excited LCR resonance circuit for the coil unit 6 has been described as an example. However, the proximity switch using the separately excited resonance circuit including a crystal resonator or the like ( It is also possible to apply the detection distance stabilizing member 20 to the all-metal detection impedance element method), which has the same effect. In the case of separate excitation, the resonance impedance is expressed as Zosc = R + (ωL) ² / R (ω: angular frequency), and the detection distance so that the change amount of the inductance L cancels the change amount of the resistance R according to this equation. A stabilizing member 20 may be provided.

DESCRIPTION OF SYMBOLS 1,1a Proximity switch 2 Coil 3 Bobbin 4 Ferrite core 5 Board | substrate 6 Coil part 7 Cap 8 Case 9 Detection surface inner wall 10 Filler 11 Cable holder 12 Cable 20 Detection distance stabilization member (magnetic member)

Claims (5)

In a proximity switch including a metal casing and a coil unit that is housed in the casing and detects the proximity of the detection target to the casing detection surface.
A magnetic member provided on the inner wall side of the housing detection surface, having a relative permeability higher than that of the metal of the housing, and changing an inductance of the coil portion to change a gap between the magnetic member and the coil portion. A proximity switch comprising a magnetic member having a characteristic that cancels a change in resistance of the coil portion in accordance with a change. 2. The proximity switch according to claim 1, wherein the casing is made of a metal having a relative magnetic permeability of substantially 1 and a volume resistivity of 45 × 10 ⁻⁸ [Ωm] or more.   The proximity switch according to claim 1, wherein the magnetic member is formed in a shape protruding from the inner wall of the housing detection surface.   The proximity switch according to claim 1, wherein the magnetic member is formed flush with an inner wall of the housing detection surface.   The proximity switch according to claim 1, wherein the magnetic member is formed by applying or printing on an inner wall of the housing detection surface.

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