JP3084074B2 - How to fix permanent magnets - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for fixing a permanent magnet mounted on a piston for position detection or the like.

[0002]

2. Description of the Related Art Conventionally, in order to detect a stroke position of a hydraulic cylinder, a piston is provided with a cylindrical permanent magnet.

FIG. 4 is a view showing a conventional method of fixing a permanent magnet, and shows a state in which a permanent magnet 52 is fixed to a piston 51 of a fluid pressure cylinder 50.

[0004] The hydraulic cylinder 50 has a cylinder tube 61, a piston 62, a piston rod 63 and the like. The piston 62 is composed of two pistons 62a and 62b divided in the axial direction. After the cylindrical permanent magnet 52 is fitted into a groove 64 formed between the pistons 62a and 62b, It is screwed into the piston rod 63 and assembled. 65 is a wear ring,
66 is a switch operated by the permanent magnet 52.

[0005]

As described above, in the prior art, since the permanent magnet 52 was fixed by dividing the piston 62 into two parts in the axial direction, the processing error of the two pistons 62a and 62b was conventionally achieved. Have caused various problems.

That is, the two pistons 62a, 62b
Of outer diameter due to machining error of two pistons 62
Since there are many structurally unstable elements of the piston 62, such as the difference in clearance between the inner diameter spigot portions of the pistons 62a, 62b and the inclination of the end contact surfaces of the two pistons 62a, 62b, the cylinder tube 61 In order to prevent seizure and abnormal wear during sliding with the inner peripheral surface, two sliding wear rings 65 were indispensable.

However, even when such a wear ring 65 is used, the above-mentioned structural instability due to the use of the two pistons 62a and 62b is accompanied by the problem of an increase in cost due to an increase in the number of parts. By
The smooth operation of the piston 62 was impaired, and maintenance problems such as replacement due to wear of the wear ring 65 remained.

On the other hand, there has been proposed a method in which the piston 62 is formed into an integral structure without being divided, and the permanent magnet 52 divided into two in a semicircle is fitted therein and then fixed by bonding with an adhesive. I have.

However, since the same magnetic poles oppose each other and a repulsive force acts on the bonding surface of the permanent magnet 52, a jig for holding down the permanent magnet 52 until the adhesive is completely cured is required. It is necessary and it takes a lot of time to cure the adhesive. Further, it is necessary to perform an operation for removing the adhesive protruding from the groove 64, and furthermore, there is a problem in reliability of the fluid pressure cylinder 50 because an adhesive portion may be damaged by long-time use.

The present invention has been made in view of the above problems, and has as its object to provide a method for easily and reliably fixing a cylindrical permanent magnet divided in a circumferential direction.

[0011]

According to the first aspect of the present invention, there is provided a method for solving the above-mentioned problems, comprising the steps of:
Permanently arranged in a generally tubular shape
Divide the magnet on the outer surface of the piston made of non-magnetic material
To fix in a circular groove provided without
Wherein the permanent magnet is arranged in a tubular shape in the groove.
After location, the outer peripheral surface of the permanent magnet, than the width of the outer peripheral surface of the permanent magnet Ri Do a synthetic resin material having a heat-shrinkable
Place a ring that having a smaller width, by contracting by heating the ring, the permanent magnet in the groove
And fix it.

[0012]

[0013]

The contracted ring is tightly attached to the outer peripheral surface of the permanent magnet to bind the separated permanent magnet. Thereby, the permanent magnet is fixed.

[0014]

FIG. 3 is a sectional front view of a hydraulic cylinder 1 using a permanent magnet 14 fixed by a fixing method according to the present invention.

The fluid pressure cylinder 1 includes a cylinder tube 11 made of a non-magnetic material, a piston 12 made of a non-magnetic material,
And a piston rod 13 and the like. The piston 12 is provided with a cylindrical groove 21 on the outer peripheral surface thereof.
Has been fixed by. In addition, 16 is packing, 17
Is a switch operated by the permanent magnet 14.

FIG. 1 is a front view showing a method of fixing the permanent magnet 14 according to the present invention, and FIG. 2 is a sectional side view of the permanent magnet 14.

The permanent magnet 14 has two semicircular permanent magnet pieces 14a and 14b divided at two places on the circumference.
Consists of FIG. 1A shows a state in which the permanent magnet pieces 14a and 14b are arranged in a tubular shape in the groove 21.
As shown in FIG. 3, a ring 15 made of a heat-shrinkable synthetic resin material is provided on the outer peripheral surfaces of the permanent magnet pieces 14a and 14b.
Is arranged, and this ring 15 is heated and contracted.

Then, as shown in FIG. 1 (b), the contracted ring 15 comes into close contact with the outer peripheral surface of the permanent magnet pieces 14a, 14b, thereby tightening the permanent magnet pieces 14a, 14b. 14 is fixed in the groove 21.

The ring 15 is made of a heat-shrinkable thin-walled tube (for example, GF tube RC manufactured by Gunze Co.) made of a material such as fluorine resin, and the width (length in the axial direction) of the outer peripheral surface of the permanent magnet 14. Before shrinking, it is slightly larger than the outer diameter of the permanent magnet 14 and is smaller than the outer diameter of the permanent magnet 14 by being heated to about 80 to 200 ° C. Shrink.
For heating the ring 15, a hair dryer or another hot air gun is used.

The outer diameter of the ring 15 after contraction is smaller than the inner diameter of the cylinder tube 11, so that sliding with the inner peripheral surface of the cylinder tube 11 does not occur. However, even if sliding occurs between them, the operation of the piston 12 is not hindered at all because the ring 15 is made of a fluorine resin having good slidability.

According to the embodiment described above, the piston 12 is
The permanent magnet 14 can be easily and reliably fixed to the groove 21 of the piston 12 without being divided into two pieces. Therefore, all of the conventional problems caused by dividing the piston 12 into two parts are solved, and the degree of freedom and reliability of the design of the fluid pressure cylinder 1 are increased, and the cost can be reduced.

In the above embodiment, the permanent magnet piece 14
An adhesive may be applied to the joint surfaces of a and 14b.
Also in this case, since a necessary minimum amount of adhesive that does not protrude from the groove 21 may be used, an operation of removing excess adhesive as in the case of using only the adhesive is performed as in the related art. No need. As the permanent magnet 14, a rubber magnet, a resin magnet, a metal magnet, or the like can be used. The number and shape of the divided portions of the permanent magnet 14, the structure of the piston 12, and the like can be variously changed in addition to the above.

[0023]

According to the present invention, a cylindrical permanent magnet divided in the circumferential direction can be easily and reliably fixed.
This allows for an integrated structure without splitting the piston
The permanent magnet in the groove of the piston easily and securely.
Can be specified.

[Brief description of the drawings]

FIG. 1 is a front view showing a method for fixing a permanent magnet according to the present invention.

FIG. 2 is a sectional side view of a permanent magnet according to the present invention.

FIG. 3 is a sectional front view of a fluid pressure cylinder using a permanent magnet fixed by the fixing method according to the present invention.

FIG. 4 is a diagram showing a conventional method of fixing a permanent magnet.

[Explanation of symbols]

 12 piston 14 permanent magnet 15 ring 21 groove

Continuation of the front page (58) Fields investigated (Int. Cl. ⁷ , DB name) F16B 4/00 F15B 15/14 F15B 15/28 G01B 7/00 H01F 7/02

Claims (1)

(57) [Claims] A permanent magnet which is divided at a plurality of locations on a circumference and which is arranged in a tubular shape as a whole is provided in a tubular groove provided without being divided on an outer peripheral surface of a piston made of a non-magnetic material. In the method for fixing in the above, after arranging the permanent magnet in a tubular shape in the groove, the outer peripheral surface of the permanent magnet is made of a heat-shrinkable synthetic resin material, the outer peripheral surface of the permanent magnet A method of fixing a permanent magnet, comprising: arranging a ring having a width smaller than the width of the permanent magnet, and heating and shrinking the ring to fix the permanent magnet in the groove.