JPH04344401A - Variable inductance converter - Google Patents

Abstract

PURPOSE: To obtain the variable inductance type transducer which is in simple structure, small in the number of components, and easily assembled. CONSTITUTION: The linear variable inductance type transducer whose spring load type plunger containing a magnetic core is axially movable in a stationary type housing containing a coil assembly has the external surface of a plunger made of a ceramic material. The plunger 1 is linearly guided only by sliding in a ceramic sleeve 2 in the housing. A bobbin for the coil assembly can be formed by forming a flange 3 on the sleeve 2 itself.

Description

[Detailed description of the invention]

0001

TECHNICAL FIELD The present invention relates to a variable inductance transducer, and more particularly, the present invention relates to a variable inductance transducer, and more particularly, it includes a housing supporting a coil, in which a movable core connected to a probe head is disposed. This invention relates to a variable inductance transducer of the type used for sensing small linear displacements.

0002

BACKGROUND OF THE INVENTION Transducers as described above are used in engineering measurements, for example in the detection and measurement of very small movements of a tool feed in a machine tool or in the measurement of the dimensions of a workpiece to be machined or ground. It will be done. The motion to be detected is on the order of microns.

[0003] A common and conventional transducer of the above type has a diameter of 8 mm to 10 mm and a length of 35 mm to 70 mm.
It is a cylindrical body of mm. Such a converter has the following main elements:

(1) a hardened tip that engages the surface to be measured; (2) a plunger that supports the tip and slides longitudinally; (3) a foreign material shield, usually a bellows of rubber or plastic. ,(4)
Extremely low friction, long life and no lateral play for positioning and guiding the plunger.
(5) pins and slots or equivalent devices for preventing rotation of said longitudinally moving parts; (6) attached to said plunger; Soft iron (
(7) a stationary coil surrounding said core; (8) a ferromagnetic cylindrical housing supporting said element and forming a mount; and (9) securely attached to said housing. Flexible multicore cables that need to be secured.

[0005] Since the moving elements, usually the tip, plunger, ball bearing and core, are arranged in series, it is difficult to reduce the overall length of the transducer to less than about 30 mm. This severely limits the application of the transducer and prevents its use in many situations where space is at a premium. The user is
Sometimes it is necessary to rely on bifurcated displacement transmission levers or bell crank type levers, which have a clear risk of error.

Furthermore, from (1) to (9) above, it is clear that these known transducers contain a number of elements that have to be separately fabricated and assembled with very high precision. Accurate positioning of the core relative to the chip may require multiple assembly and disassembly of the device. All of these factors make it expensive to achieve the desired quality and precision of the final product, but these factors were previously thought to be necessary to obtain satisfactory results.

In the applicant's UK Patent No. 2,065,891 an improved construction is disclosed in which the core is within the axial length of the bearing, which construction significantly reduces the overall length of the device. Although this product has been very successful, it remains difficult to assemble and contains many separate components.

[0008]

TECHNICAL PROBLEM TO BE SOLVED BY THE INVENTION An object of the present invention is to provide a transducer probe that is simple in structure, has a small number of parts, and is easy to assemble while maintaining the accuracy and durability of the existing structure. That's true.

[0009]

SUMMARY OF THE INVENTION According to an aspect of the invention in its broadest concept, there is provided a variable inductance transducer in the form of a sleeve of ceramic material, within which said sleeve is also formed of ceramic material. The plunger moves and slides directly within the sleeve material without the need for any intervening ball bearings or other separate rotational bearing mechanisms.

Further, according to the present invention, the ceramic sleeve in which the probe slides is configured such that the sleeve itself forms a bobbin and the coil is wound on the bobbin, thereby forming a separate bobbin. Therefore, the number of parts can be reduced.

Furthermore, the tip or head of the plunger can be formed integrally with other parts of the plunger.

Previously, it was thought that some type of ball bearing or other linear bearing would have to be provided and that metal could be the only material of choice for the main elements of the transducer. Plastic is clearly an unsuitable material because it has insufficient dimensional stability, is thermally sensitive and in fact absorbs some moisture. Unexpectedly, it has been found that a ceramic plunger sliding directly within a ceramic sleeve performs completely satisfactorily.

The virtually zero gaps between the relatively moving parts, achieved by the dimensional stability and low thermal expansion of ceramics, means that there is no ingress of foreign matter, and in known constructions This makes it possible to eliminate the bellows or equivalent foreign material shield that was required to protect the ball bearings.

Since the plunger is non-metallic, the core can be placed directly inside the plunger, and if a well-known commercially available ferrite type material with external thread is selected as the core material, The core is mounted inside a female-threaded plunger, making it very easy to adjust the axial position of the core during probe assembly; this can be done using a screwdriver from the rear end of the assembly or from the tip. If it is removable, it can be done from the front end.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the converter of the present invention will be described below with reference to the drawings.

The transducer shown in FIG. 1 basically consists of a cylindrical composite plunger and tip 1 made of ceramic material, which plunger and tip are connected to a bearing sleeve 2 also made of ceramic material. As shown, said sleeve has an outer surface formed with a flange 3, whereby the sleeve forms a bobbin on which a coil (not shown) can be directly wound. are doing. Due to the very high dimensional stability of ceramic and its negligible thermal expansion, the gap between plunger and sleeve can be made extremely small without any risk of jamming or friction. , there is no need to provide a foreign matter shield.

The front flange 3 forms the front wall for the housing defined by the cylindrical outer steel casing 4 and defines the rear end cap, and the housing is protected against external magnetic fields. Provides the necessary coil shielding.

A sleeve 5 made of a suitable synthetic material, for example Paxolin (registered trademark), is fixed in the hollow plunger 1 with an adhesive, and the sleeve 5 is formed with an external thread. A female thread is formed for accommodating the ferrite core 6 . A flange 7 provided at the rear end of the sleeve 5 provides a shoulder which engages the rear end of the ceramic sleeve 2 and defines the forward limit position of the plunger. A helical coil type compression spring 8 presses the plunger into the forward position.

It is important that the axial position of the ferrite core 6 with respect to the tip of the plunger is precisely correct; this position is approximately midway between the two coils when the plunger is in the forward position shown. That is required. In the transducer of the invention, this adjustment can be made very easily without disassembling the transducer. Its adjustment can be effected with a screwdriver via an access opening in the end cap, which can then be closed by a threaded plug 9.

[0020] By using a ferrite core,
A larger signal is produced than with a soft iron core. In conventional structures, ferrite could not be used. This is because the sleeve must be hollow to fit the desired shape, and ferrite is too brittle to form a thin sleeve.

A cable 10 making the connection to the coil is provided through the end cap. The rearmost flange 3 of the sleeve 2 has a notch or flat (not shown) to provide an air gap for each wire. According to another feature of the invention, contact pads for the wires can be formed directly on the rear face of said flange by electroplating, which makes it extremely easy to attach the wires of the cable by soldering at this point. do.

In known transducers it has always been necessary to provide some means to prevent rotation of the plunger, usually a radial pin engaging a slot in the housing. This is because it is not possible to have all elements truly concentrically arranged and rotation therefore changes the accuracy of the transducer. The simplicity of the construction of the present invention allows the core to remain truly concentric with the coil, which allows the plunger to remain free to rotate, thus further simplifying construction and can be reduced.

The selection of ceramic material can be determined experimentally to suit the environment in which the transducer operates. Generally speaking, silicon carbide or silicon nitride are suitable. Of course, this material must be non-magnetic.

A particularly suitable ceramic material is the material sold under the registered trademark "Syalon 201". This material is based on silicon nitride and contains aluminum oxide in solid solution, and has very stable properties with virtually zero thermal expansion and high resistance to chemical attack and impact. . The air gap between the plunger and the sleeve can be substantially zero. The reason is that both these elements are both made of the same material and
Therefore, even if the amount of microscopic thermal expansion is the same, they are both equal.

In FIG. 2, elements similar to those in FIG. 1 are given the same reference numerals. Almost the only difference is that the tip, designated 11, is not integral with the ceramic plunger, but is a separately formed element having a spigot 12 at its rear end. The chip is screwed into the sleeve 5 by the insertion portion. Instead of being made of pacrolin, this sleeve can be made of brass.

Since the body of the plunger is separate from the tip, this body is a uniform hollow cylinder of simple shape, without flanges and with no change in diameter, as shown in FIG.
can be more easily formed from ceramic materials than the embodiments of FIG.

Since the tip 11 is removable, the position of the ferrite core 6' in the sleeve 5 can be carried out from the front end by inserting a screwdriver after removing the tip 11, and therefore from the rear. The plug 9 can be omitted. Moreover, in the embodiment of FIG.
The rear end of the spring 8 is seated in the protrusion rather than in the socket. The flange 3' can be the full internal diameter of the casing 4, and the ceramic body can be provided with a flattened portion 13, which is easier to form than a notch, to provide an air gap for the wire to the coil.

[Brief explanation of drawings]

FIG. 1 is a schematic longitudinal sectional view showing an embodiment of the invention.

FIG. 2 is a schematic longitudinal sectional view showing another embodiment of the invention.

[Explanation of symbols]

Claims (10)

[Claims] 1. A housing supports an axially movable plunger, the plunger having a projecting tip for engaging a body, the displacement of the body being measured, and the plunger having a magnetic core. a moving inductance transducer, wherein the housing accommodates a fixed coil assembly surrounding the plunger, the outer surface of the plunger being formed of a ceramic material, and the plunger having a sleeve of ceramic material within the housing. A transducer characterized in that it is movably guided in a linear manner only by direct slidable contact with the transducer. 2. The transducer of claim 1, wherein the ceramic material of the outer surface of the plunger is the same as the ceramic material of the sleeve. 3. A transducer according to claim 1 or 2, characterized in that the body of the plunger, excluding the core, is formed of a ceramic material. 4. The transducer of claim 3, wherein said tip is integral with said plunger. 5. The transducer of claim 4, wherein the body of the plunger is cylindrical and has a closed end forming the integral tip. 6. A transducer according to claim 1, wherein the sleeve forms a bobbin on which the coil assembly is wound. 7. The transducer of claim 6, wherein said sleeve has outer flanges for positioning said coil assembly, and at least one of said outer flanges provides an electrical connection to said coil assembly. A transducer characterized in that it has a flat portion for providing an air gap for making a connection. 8. The transducer of claim 3, wherein the body of the plunger is a simply shaped hollow cylinder made of a ceramic material and substantially without flanges, the cylinder housing an inner sleeve made of a non-ceramic material. A transducer, characterized in that the core is located within the inner sleeve. 9. The transducer of claim 8, wherein the inner sleeve includes an outer flange defining a stop that limits movement of the plunger. 10. The converter according to claim 8 or 9,
The inner sleeve is formed with internal threads and the core is screwed into the internal threads such that the axial position of the core within the plunger is adjusted from the end of the transducer using a tool. A converter characterized by being able to.