JPS61137001A - Apparatus for detecting position of piston rod of hydraulic cylinder - Google Patents

Abstract

PURPOSE:To enhance detection accuracy by increasing the change width of a secondary output voltage level, by detecting the change in the quantity of the eddy current at the conductor part provided to the peripheral surface of a piston rod generated with the movement of the piston rod. CONSTITUTION:Magnetic fluxes by primary coils 1A-1D having different phases are passed through magnetic cases 4, 5 and a piston rod 6. An eddy current is flowed to the conductor parts 6b and the change in magnetic resistance due to the loss of said eddy current is generated in a magnetic circuit. An Ac signal corresponding to this magnetic resistance is induced to each secondary coils 2A-2D having different phases.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a piston rod position detection device for a fluid pressure cylinder, and in particular to a piston rod position detection device for a fluid pressure cylinder. Regarding an inductive type piston rod position detection device that changes the current and obtains an output signal in accordance with the change in the position of The present invention relates to a piston rod position detection device capable of obtaining an induction coefficient change using at least eddy current loss as a parameter.

[Conventional technology]

U.S. Pat. No. 3,956,973 discloses that a ring-shaped or spiral groove is provided in iron or magnetic metal around a piston rod, and an electric current is generated in response to passage of the groove as the piston rod moves. A piston rod position detection device is disclosed in which a transducer that generates a pulse signal is fixed to a cylinder body side.

In Utility Model Application No. 59-23609, a plurality of magnetic rings are provided around the piston rod at predetermined intervals, primary windings and secondary windings of multiple phases are provided on the cylinder body side, and the primary winding of each phase is The wires are individually excited by a plurality of phase-shifted AC signals so that an AC signal whose phase is shifted according to the position of the piston rod is obtained on the side of the secondary winding, and the amount of this phase shift is digitally calculated. A piston rod position detection device has been disclosed that can detect the position of a piston rod in an absolute manner by counting the number of piston rods.

In Utility Model Application No. 59-23610, a stator consisting of a primary winding and a secondary winding wound around a plurality of magnets is fixed to the cylinder body side, and a plurality of protrusions are formed on the magnetic body around the piston rod. The primary winding of each phase is individually excited by a plurality of phase-shifted AC signals, so that an AC signal whose phase is shifted according to the position of the piston rod is obtained on the secondary winding side. First, a piston rod position detection device has been disclosed which is capable of detecting the position of a piston rod in an absolute manner by digitally counting the amount of phase shift.

[Problem that the invention seeks to solve]

The detection device shown in the above-mentioned U.S. patent is configured to simply generate a pulse signal in response to passage of a groove provided in the bisto shield, so it must be configured to count this pulse signal in order to obtain position data. First, it becomes a de facto incremental pulse generation and counting method. Therefore, there is a problem that the piston rod position cannot be detected absolutely. Furthermore, in order to provide the grooves on the piston rod, cutting or the like must be performed, which poses a problem in that the machining is troublesome.

The above-mentioned 22 utility model registration applications are based on the absolute method, so they do not have the above-mentioned drawbacks.

In addition, in all of the above-mentioned conventional techniques, the induction coefficient of the winding is changed only by the presence or absence of grooves or protrusions made of iron or magnetic metal, so the depth of the grooves or the height of the protrusions must be adjusted to a sufficient level. There is also the problem that detection accuracy cannot be improved unless it is taken into account.

An object of the present invention is to provide a piston rod position detection device that can solve the various problems mentioned above.

[Means and effects for solving the problem] The piston rod position detection device according to the present invention is provided on the open end side of the cylinder body, and includes a coil that is excited by a primary alternating current signal and takes out a secondary output. and a conductor portion provided in a predetermined range on the circumferential surface of the piston rod so as to form an eddy current path for the magnetic flux generated by the coil portion. The conductor portion is made of a weakly magnetic or non-magnetic material and is a relatively better conductor than the material of the other portions of the piston rod. The amount of eddy current flowing through the conductor portion changes in accordance with the relative displacement of the conductor portion with respect to the coil portion as the piston rod moves, and the amount of eddy current flowing through the conductor portion changes accordingly.
A next output signal is obtained at the coil section.

When a conductive portion of the piston rod enters the magnetic field produced by the coil portion, eddy currents flow in that portion, and eddy current losses substantially increase the reluctance of the magnetic circuit passing through the coil portion. The amount of eddy current changes depending on the degree of penetration of the conductor portion, and the magnetic resistance changes accordingly. Therefore, a voltage is induced on the secondary side of the coil portion depending on the relative linear position of the conductor portion of the piston/rod with respect to the coil portion.

As described above, by repeatedly providing a plurality of conductive portions in which eddy currents are generated at predetermined intervals, it becomes possible to detect a linear position over a long range. Further, by providing a plurality of conductive portions, it becomes possible to give periodicity to the function of magnetic resistance change with respect to linear displacement, and position detection using a phase shift method becomes possible.

Since eddy currents have the property of flowing near the surface of the conductor, the conductor portion to be provided around the piston/rod is not required to be very thick. Accordingly, the conductor portions can be deposited in a predetermined pattern on the base material of the piston/rod. This means that it is extremely easy to form a conductive portion on the circumferential surface of the piston mouth and throat. That is, such a pattern of relatively thin conductor portions can be relatively easily formed on the base material of the piston rod by plating, thermal spraying, pattern baking, etching, or other suitable surface treatment techniques. Therefore, it is possible to omit troublesome machining and assembly, and it is expected that manufacturing costs will be significantly reduced. However, of course, the scope of the present invention does not exclude electrically conductive portions formed by machining or assembly, and there is no problem even if such electrically conductive portions are used.

There is no particular problem if the conductor portion can be attached in a predetermined pattern on the base material of the rond part from the beginning, but this may be difficult depending on the surface processing technology employed (for example, with plating).

In such a case, first, a predetermined conductive material is deposited on the entire surface of the base material of the piston rod, and then the unnecessary portion is removed, leaving the conductive material deposited on the base material in a predetermined pattern. Preferably, a predetermined pattern of conductor portions is formed by the conductive material. - By way of example, attachment is carried out by plating and removal is carried out by etching. In this way, it is possible to efficiently form the conductor portion on the circumferential surface of the piston/rod. Note that when removing unnecessary conductive material by etching, there is a risk that the etching agent may also attack the base material surface of the piston rod. To address such problems, first apply a coating (e.g., a resin coating) that is resistant to etching chemicals around the entire circumference of the base material of the piston/rod, and then apply a conductive coating over it. The substance may be attached by plating or the like. In this way, the piston rod O base material is protected by the resin coating during etching.

Another piston/rod position detection device according to the present invention includes a coil portion as described above, and a piston rod that is provided so as to protrude in a predetermined range along the moving direction of the rod on the circumferential surface of the piston rod. a magnetic part that changes the magnetic resistance of the magnetic circuit according to the relative position of the magnetic part with respect to the coil part; and a part of the circumferential surface of the piston rod from which the magnetic part does not protrude;
It is provided to form an eddy current path for the magnetic flux, and includes a conductor part that is relatively weakly magnetic or non-magnetic than the magnetic part and made of a relatively good conductor. There is.

Regarding the part of the piston/rod circumferential surface where the magnetic part protrudes, when the part of the magnetic part enters the magnetic field of the coil part, the magnetic resistance of the magnetic circuit passing through the coil part decreases (in other words, the magnetic part is transparent). magnetism or permeance increases). On the other hand, magnetic resistance increases (permeance decreases) in areas where the magnetic material part does not protrude.
. The conductor portions are provided at locations where the magnetic resistance increases in this way. Therefore, when the conductive part of the piston rod (in other words, the part where no magnetic part protrudes) enters the magnetic field generated by the coil part, eddy current loss occurs in that part, which further increases the effective magnetic resistance. It will be done.

In this way, the induction coefficient changes (because the number of coil windings and other conditions are fixed, (substantially equivalent to a change in magnetoresistance) is obtained synergistically. That is,
The range in which the magnetic resistance is relatively reduced by the intrusion of the magnetic part of the piston rod into the magnetic circuit of the coil part (
In the range where the permeance is relatively increased), the influence of eddy current loss due to the conductor portion does not reach, and therefore a voltage of a relatively sufficiently high level can be induced on the secondary side. On the other hand, in a range where magnetic resistance is relatively increased due to detachment of the magnetic part of the piston rod from the magnetic circuit of the coil, the conductive part of the rod enters the magnetic circuit of the coil, causing eddy current loss. In addition to the relative increase in magnetic resistance due to the detachment of the magnetic body part, the relative increase in magnetic resistance due to eddy current loss in the conductive body part is added,
Therefore, the voltage level induced on the secondary side can be further reduced. In this way, the difference between the high level and low level of the secondary side induced voltage, that is, the change width of the secondary output with respect to displacement, can be made sufficiently large, which allows accurate linear displacement detection of the piston rod. be able to do it.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

In FIG. 1, 11 is a cylinder body, 12 is a piston, and 6 is a piston rod. As is well known, an opening is provided at one end of the cylinder body, and the piston rod 6 passes through the opening. This cylinder body 11
A coil portion 10 is provided on the side of the open end. The coil section 10 includes primary coils 18 to 1i) and a secondary coil 2A.
~2D, and is fixed to the open end side of the cylinder body 11 with the rondro slidably penetrating the coil space so that the cylindrical space of these coils is concentric with the rod 6. . The piston rod 6 includes a base material, that is, a center rod 6a, a conductor portion 6b provided in a ring shape around the center rod 6a, and a coating 6C covering the entire outer periphery. The width of this conductor portion 6b is i (where P is an arbitrary number), and the rod 6
A plurality of conductor portions 6b are repeatedly provided at predetermined intervals i along the relative linear displacement direction (the arrow L direction in the figure). This conductive portion b is made of a weakly magnetic or non-magnetic material and is made of a relatively better conductor than the material of the center rod 6a, for example copper, aluminum, brass, or other good conductive materials. It is possible to use a mixture or combination of and other substances. The center rod 6a may be made of either a magnetic material or a non-magnetic material, and in short, a material having a higher electrical resistivity (poor conductivity) than the conductive portion 6b is used as the center rod 6a. This is to allow more eddy current to flow only in the intermittently provided conductor portions 6b, and to obtain periodic magnetic resistance changes with respect to displacement. Note that if the center rod 6a is made of a magnetic material such as iron, the magnetic flux will pass through it better, so the corresponding amount of eddy current will also increase, and detection accuracy can be improved.

In this example, the coil is arranged to operate in four phases, these phases being designated A and B for convenience.

They are distinguished using the codes C and D. The magnetic resistance generated in each phase A-D is shifted by 90 degrees depending on the relative position of the ring-shaped conductor portion 6b with respect to the coil.
For example, if the human face is a cosine phase, phase B is a sine phase, and phase C is a sine phase.
The arrangement of each coil and the size and shape of the conductor portion 6b are determined so that the phase is a minus cosine phase and the D phase is a minus sine phase.

In the example shown in Fig. 1, the corresponding primary coils 1A to 1D and secondary coils 2A to 2D of each phase A to D are wound at the same position, and the coil length of each coil is approximately "1D". ”. Then, the A-phase and C-phase coils IA, 2A, IC,
2C are installed next to each other, and the B-phase and D-phase coils I
B, 2B, ID, and 2D are also provided next to each other, and A,
O A phase and C phase coils IA, 2A, IC, 2C where the interval between the C phase coil group and the B and D phase coil groups is rp(n±-1)J (n is any natural number) is housed in a cylindrical case 4 made of a magnetic material such as iron, and B
Phase and D phase coils IB and 2B.

The ID and 2D are also housed in a similar cylindrical case 5, and the entire coil section 10 is further housed in an outer case 13. These iron cases 4 and 5 are used to prevent crosstalk between the coils and to concentrate the lines of magnetic force of the coils to improve the coupling of the magnetic circuits.

In the above configuration, the magnetic flux generated by the primary coils 1A to 1D of each phase passes through the magnetic cases 4, 5 and the piston rod 6, and when the conductor portion 6b enters the magnetic field, the magnetic flux is Eddy currents flow along the links of the conductor portion b.

In a state in which the conductor portion 6b penetrates more into the coil (for example, in a state corresponding to phase A in FIG. 1 at the maximum), more eddy current flows.

On the other hand, when the conductor portion 6b does not penetrate into the coil at all (for example, the C phase state in FIG. 1), almost no eddy current flows. In this way, an eddy current flows through the conductor portion 6b according to the degree of penetration of the conductor portion 6b into the coil of each phase, and a change in magnetic resistance due to this eddy current loss is caused in the magnetic circuit of each phase. An alternating current signal having a level corresponding to this magnetic resistance is induced in the secondary coils 28 to 2D of each phase.

Coating 6C provided on the outer periphery of the piston rod 6
The conductor part b is made of a non-magnetic or weakly magnetic substance that has relatively lower conductivity or non-conductivity than the conductor part b. For example, chrome plating may be used.

In the embodiment shown in FIG. 1, the coils of each phase are housed in cylindrical magnetic cases 4 and 5, and these cases 4 and 5 can form a magnetic conduction path. It is also possible to implement the present invention without providing.

Although the above embodiment has a structure in which the piston rod is inserted into the space within the coil, the structure is not limited to this, and the design can be changed as necessary.

FIG. 3 shows a modification of the coil portion 10, and FIG. 4 is a sectional view taken along line IV-IVil. Primary and secondary coils 1A-ID corresponding to each phase A-D.

2A to 2D are respectively wound around both legs of U-shaped magnetic cores 7A to 7D provided for each phase. Each phase A,
The cores 7A to 7D of D are mutually fixed in a predetermined arrangement so that the cycles of magnetoresistance change are shifted by one cycle (90 degrees) between adjacent phases. For example, the distance between the cores 7A to 7D between adjacent phases is set to .- (P (, 1±1) is sufficient for wide width). The piston rod 6 is of similar construction to that shown in FIG. The interval between both ends of each U-shaped core 7A to 7D approximately corresponds to the width i of the conductor portion 6b, and in each phase, the U-shaped core 78 to 7D passes from one end to the piston rod 6 to the other end. A magnetic circuit is formed extending through each section. Although the cores 7A to 7D of each phase are aligned in a straight line in the linear displacement direction in FIG. 3, they are not limited to this, and may be appropriately shifted in the circumferential direction as shown by broken lines 7B' to 7D' in FIG. May be placed. In that case, between adjacent phases (for example, P
−) can be done. In FIG. 3B'll, the eddy current path created in the conductor portion 6b is formed around the magnetic flux path perpendicular to the end of each core 7A-7D, rather than along the ring shape. Ru.

Therefore, in this case, the conductor portion 6b of the piston rod B
does not necessarily have to be in the shape of a ring surrounding the circumference,
It suffices if it has an area as large as (i to the extent that an eddy current path can be formed) at the portion facing the end portions of the cores 7A to 7110, or it may form a ring-shaped pattern.

In the embodiment shown in FIG. 5, the piston rod portion 6 includes a conductive portion 14 spirally arranged around a central rod 6a. The spiral conductor portions 14 are arranged in a single thread pattern with a pitch width of P. In FIG. 5 the piston rod 6 is shown in side view. FIG. 6 is a cross-sectional view taken along the line ■-■ in FIG. Each core 8A ~
8D has primary coils 1A to 1D and secondary coils 28 to 21.
] is wound.

In the embodiment shown in FIG. 7, the piston rod 6 is provided with a spiral conductor portion 15 around a center rod 6a in a double thread pattern with each pitch being 2P.

FIG. 8 is a cross-sectional view taken along the line VIII-VIII in FIG.
8D, 8A/ to 8D/ are provided. The two cores facing each other at an interval of 180 degrees are in phase,
There are four core pairs each consisting of two cores, and six pairs correspond to phases A to D, respectively. Cores 8A to 8D' of each phase A-D include primary coils 1A to 1D and secondary coils 2A to 2A, as described above.
2D are wound respectively. The in-phase secondary coil outputs are added together.

In FIGS. 5 to 8, a coating 6C is provided on the outer periphery of the rond O, similar to the embodiment shown in FIG.

In the embodiment of FIGS. 5 to 8, as in the embodiment of FIG. formed around. Therefore, in this case as well, the conductor portion 14.15 of the piston rod 6 does not necessarily have to have a continuous spiral shape, but has an area corresponding to the portion facing the ends of the cores 8A to 8D'. or a ring-shaped pattern.

Electric conductor portion 6b in piston rod 6, 14.15
The formation can be carried out, for example, by the following procedure.

(2) Apply a resin coating that is resistant to etching agents over the entire circumference of the center rod 6a.

(2) A predetermined conductive substance is applied over the entire circumference of the resin-coated center rod 6a by a predetermined surface processing technique (for example, plating, thermal spraying, baking, painting, etc.).

■ Next, remove unnecessary portions of the conductive material from the surface of the center rod 6a using a removal technique such as etching.
A pattern of predetermined conductor portions 6b, 14.15 is formed.

(2) Next, coating 6C is applied all around the piston rod 6 to protect and smooth the surface.

The above step (2) serves to prevent the removal agent from attacking not only the conductive substance but also the material of the center rod 6a in the step (2). If such preventive measures are not required, step (2) can be omitted.

Note that, of course, if a surface treatment technique is employed that allows the conductive substance to be deposited in a desired pattern from the beginning, etching or the like is not necessary.

FIG. 9 shows another embodiment of the piston rod 9, and the coil portion 10 has the same structure as that shown in FIG.

The center portion 9a of the piston rod 9 is made of a magnetic material, and a ring-shaped magnetic portion 9d protrudes around the center portion 9a in the linear displacement direction (arrow L). A plurality of conductor parts 9b are filled in the ring-shaped recesses, respectively.Each ring-shaped conductor part 9b is made of iron or other ferromagnetic material, and the conductor part 9b is made of a magnetic material part 9d. It is also made of a material that is relatively weakly magnetic or non-magnetic and has a relatively good conductivity (eg, copper, aluminum, brass, etc., or a mixture of such good conductive materials and other materials). The entire outer periphery of the piston rod 9 is provided with a coating 9C of chrome plating or the like, as described above.This coating 9C may be a sleeve made of synthetic resin.

In the above configuration, the magnetic flux generated by the primary coils 1A to 1D of each phase passes through the magnetic cases 4 and 5 and the center portion 9a of the piston rod 9. A gap between the inner circumferential ends of the cases 4 and 5 and the protruding magnetic portion 9d of the rod 9 is defined as a gap between the inner circumferential ends and the surface of the lower central portion 9a of the conductor portion 9b of the rod 9. narrower than the gap in Also,
The width i of the magnetic portion 9d and the conductive portion 9b approximately corresponds to the length of each coil. Therefore, when the rod 9 is linearly displaced relative to the coil portion 10, the magnetic resistance of the magnetic circuit of each phase changes depending on the relative position of the magnetic body portion 9d with respect to each phase coil. As is well known, in a state in which more of the magnetic material portion 9d enters the coil (for example, in the C phase state in FIG. 9 at the maximum), the magnetic resistance is small, and therefore the permeance is large. As is clear from this, the conductor portions 9b provided between the magnetic portions 9d are located at locations where the magnetic resistance of the rod 9 is relatively increased (locations where the permeance is relatively decreased). It will be set up accordingly.

Further, the conductive portion 9b has a ring shape with respect to the central portion 9a forming a magnetic path, and functions as a so-called short ring, and can form an eddy current path for magnetic flux.

Therefore, in a state where more of the conductor portion 9b penetrates into the coil (for example, at the maximum state of A phase in Fig. 9), more eddy current flows, and the actual magnetic resistance increases due to eddy current loss. I am forced to do it.

On the other hand, as described above, the magnetic resistance of the conductive portion 9b is relatively increased due to the lack of the magnetic portion 9d. Therefore, the magnetic resistance is increased synergistically, and the level of the secondary side induced voltage is synergistically attenuated.

In the above embodiment, the center portion 9a of the rod 9 is the magnetic material portion 9.
Although it is made of the same magnetic material as d, it is not limited to this and may be made of an appropriate non-magnetic material. An example is shown in FIG. 11, and this piston rod 9 is
Non-conductive and non-magnetic material portions 9d and conductive portions 9b are alternately formed. The mandrel 93t may be made of the same magnetic material as the magnetic part 9d, in which case the ninth
It is substantially the same as the figure. Further, the mandrel 9a' may be made of a weakly magnetic or non-magnetic highly conductive material like the conductor portion 9b.

A coil portion similar to that shown in FIG. 3 can be used for the piston rod 9 shown in FIG. 9. Further, as shown in FIGS. 5 to 8, as shown in FIGS. 12 to 15, the conductor portion 9b and the magnetic portion 9d on the circumferential surface of the piston rod 9 may be provided in a spiral shape. .

In the embodiment shown in FIG. 12, magnetic portions 9d and conductive portions 9b are alternately provided in a spiral shape in the rod portion 9 in the arrangement of a single thread having a pitch width of P. The crests of the screws correspond to the magnetic portions 9d, and the conductive portions 9d correspond to the troughs of the screws.
b is provided.

In FIG. 12, for convenience of illustration, the crest of the screw (magnetic part 9
d) and the valley are shown in a side view, and the conductor portion 9b filled in the valley is shown in cross section. FIG. 13 is a cross-sectional view taken along the line 1-1 in FIG.
It is similar to the figure.

In the embodiment shown in FIG. 14, magnetic portions 9d and conductive portions 9b are alternately provided in a spiral shape in the rod 9 in a double-threaded screw arrangement with a pitch width of 2P. As described above, the crests of the screws are the magnetic portions 9d, and the troughs are provided with the conductive portions 9b. Similar to FIG. 12, the peaks (magnetic material portions 9d) and valleys are shown in a side view, and the conductive material portions 9b are shown in a cross-sectional view. FIG. 15 is a sectional view taken along the line V--■ in FIG. 14, and the cores 88 to 8D' are arranged in the same manner as in FIG. 8. Further, the magnetic portion 9d and the conductive portion 9b may be provided only at positions corresponding to the cores 8A to 8D/ of each phase.

Note that the conductor portion 9b around the piston rod 9
An example of a method for forming the magnetic material portion 9d is to machine a ring-shaped groove or a threaded groove on the shaft of a rod made of a magnetic material in correspondence with the position of the conductive material portion 9b, and then to form a ring-shaped groove or a threaded groove. It is preferable to attach a predetermined conductive material to the surface of the round bar by thermal spraying, pattern baking, or other appropriate surface treatment, and then polish the surface of the round bar so that the conductive portion 9b remains only within the groove. Of course, surface treatment (
It may also be applied by thermal spraying or pattern baking), in which case final surface polishing is not necessary.

In each of the embodiments described above, an output signal corresponding to the linear position of the piston rod can be obtained by a phase shift method. That is, in each phase A-D, the linear displacement amount P of the piston rod is shifted by one rotation. Therefore, if the phase angle corresponding to the linear displacement is represented by φ, each phase A
The level of the voltage induced in the secondary coils 2A to 2D of -D is approximately cosφ in the human phase, sinφ in the B phase, and -co in the C phase, depending on the linear position (that is, φ) of the piston rod.
sφ, −sinφ in D phase (however, 2π corresponds to P)
It can be expressed in the following abbreviation. The primary coils IA and IC of A and C phases are excited by the sine wave signal sinωt, and the B
, D-phase primary coil IB, ID are cosine wave signals cosω[
Excite by. Then, for the A and C relative, the output signals of the secondary coils 2A and 2C are differentially added, and for the B and D relative, the output signals of the secondary coils 2B and 2D are also differentially added. The final output signal Y is obtained by adding and combining the differential output signals.

Then, the output signal Y can be substantially expressed in the following informal formula.

Y = sinωt cosφ−(−5inωt co
sφ) + cosωt sinφ−(−cosωt s
inφ)=2sinωt cosφ+2CO5ωt
SInφ=2sin(ωt+φ) If we replace the coefficient indicated as “2” in the above formula with a constant determined according to various conditions, then Y=K sin (
It can be expressed as ωt+φ). Here, φ corresponds to the linear position of the piston rod, so the piston rod position can be detected by measuring the phase shift φ of the output signal Y corresponding to the primary AC signal sinωt (or cosωt). .

Secondary coil output composite signal Y and reference AC signal sinωt
(or cosωt) can be configured as appropriate. FIG. 16 shows an example of a circuit in which the phase shift φ is determined as a digital quantity. still,
Although not particularly shown, the reference AC signal si is calculated using an integrating circuit.
nωt and output signal Y = K sin (ω[+φ)
The phase shift φ can also be determined as an analog quantity by determining the time difference at a phase angle of 0 degrees.

In FIG. 16, the oscillator 62 generates a reference sine signal sin
A circuit for generating ωt and a cosine signal cosω[, and a phase difference detection circuit 37 is a circuit for measuring the phase shift φ. The tough lock pulse C generated by the clock oscillator 33
P is counted by the counter 60. The counter 60 is, for example, modulo M (M is any integer), and its count value is given to the C input of the register. The pulse Pb from the Q output of this flip-flop 64 is applied to the flip-flop 65, the pulse P from the Q output is applied to the flip-flop 66, and the outputs of these 65 and 36 are applied to the low-pass filter 38, 39 and the amplifier 40. 41, a cosine signal cosωt and a sine signal sinωt are obtained and applied to the primary coils 18 to 1D of each phase A to D. M counts in the counter 60 correspond to these reference signals c
This corresponds to a phase angle of 2π radians of osωt and sinωt. In other words, one count value of the counter 60 is
It shows the phase angle in radians.

The composite output signal Y of the secondary coils 2A to 2D is applied to a comparator 43 via an amplifier 42, and a square wave signal corresponding to the positive or negative polarity of the signal Y is output from the comparator 43. In response to the rise of the output signal of the comparator 43, the rise detection circuit 44 outputs a pulse T, and the count value of the counter 60 is loaded into the register 61 in response to this pulse T5. As a result, a digital value Dφ corresponding to the phase shift φ is taken into the register 61. In this way, it is possible to obtain data Dφ that absolutely indicates the piston rod position within the predetermined range P.

The signal processing method is not limited to the phase shift method mentioned above.
Like a normal differential transformer, the differential output of the secondary coil may be rectified to obtain an analog voltage with a level corresponding to the linear position. In that case, the coil portion may be only one of the A and C phases or the B and D phases.

It should be noted that the primary coil and the secondary coil do not necessarily need to be provided separately, and are
It may also be common as shown in No. 8-39507. Further, the patterns of the conductive portions 6b and 9b are not limited to those shown in the drawings, but may be of any shape as long as they can form an eddy current path.

〔Effect of the invention〕

As described above, according to the present invention, it is sufficient to attach the conductive substance to the circumferential surface of the piston rod in a predetermined pattern.
Easy to process and form. In addition, since the conductive part can fully demonstrate its function even if it is thin, the structure is simpler than simply providing grooves in the magnetic material (in this case, the grooves need to be sufficiently deep). be converted into However, the combination of the protrusion of the magnetic part and the conductive part makes it possible to increase the range of change in the secondary output voltage level with respect to displacement, thereby improving detection accuracy.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view showing an embodiment of the piston rod position detection device according to the present invention, FIG. 2 is a cross-sectional view taken along line...-■ in FIG. 1, and FIG. 3 is a modification of the coil section in FIG. 1. FIG. 4 is a sectional view taken along the line IV-TV in FIG. 5 is a sectional view taken along the line VI-VI in FIG. 5, FIG. 7 is a partially sectional side view showing another modification of the coil portion and piston rod in FIG. 1, and FIG. 8 is a sectional view taken along the line VIII-VIII in FIG. 7. , FIG. 9 is a longitudinal sectional view showing another embodiment of the piston rod position detection device according to the present invention, FIG. 10 is a sectional view taken along the line X-X in FIG.
Fig. 1 is a partially sectional side view showing a modification example of the piston port and rod in Fig. 9; Fig. 12 is a partially sectional side view showing a modification example of the coil part and piston rod in Fig. 9;
3 is a sectional view taken along the line -1 in FIG. 12, FIG. 14 is a partially sectional side view showing another modification of the coil portion and piston rod in FIG. 9, and FIG. 15 is a sectional view taken along the line -1 in FIG. FIG. 16 is an electrical block diagram showing an example of a circuit for operating the detection device of the present invention by a phase shift method and measuring the amount of electrical phase shift according to the piston rod position. be. 11... Cylinder body, 12... Piston, 6, 9
...Piston rod, 6a...Center rod, 6b,
9b, 14.15... Conductor portion, 6c, 9c...
・Coating, 9d...Magnetic material part, 10...Coil part, IA~1D...Primary coil, 28~2D...
・Secondary coil.

Claims (1)

[Claims] 1. A coil section provided on the open end side of the cylinder body and excited by a primary alternating current signal and for taking out a secondary output; and an eddy current path for the magnetic flux generated by the coil section. a conductor portion provided in a predetermined range on the circumferential surface of the piston rod so that the piston rod can be It is made of a relatively good conductor, and the amount of eddy current flowing through the conductor portion changes depending on the relative displacement of the conductor portion with respect to the coil portion as the piston rod moves. A piston rod position detecting device for a fluid pressure cylinder, characterized in that a secondary output signal corresponding to the above is obtained in the coil portion. 2. The conductor portion is composed of a ring that is closed around the piston rod, and a plurality of ring-shaped conductor portions are provided at predetermined intervals along the moving direction of the piston rod. The piston rod position detection device according to scope 1. 3. The piston rod position detection device according to claim 1 or 2, wherein the piston rod is inserted into a coil space of the coil portion. 4. The piston rod position detection device according to claim 1, wherein the conductor portions are arranged in a spiral shape at a predetermined pitch around the piston rod. 5. The coil portion includes a magnetic core around which a coil is wound, and a magnetic pole end of the magnetic core faces the circumferential surface of the piston rod with a gap in between. The piston rod position detection device according to item 4. 6. The coil portion includes a magnetic core around which a coil is wound, and a magnetic pole end of the magnetic core faces the circumferential surface of the piston rod with a gap therebetween; The piston rod position according to claim 1, wherein the piston rod is formed of a ring-shaped or planar pattern corresponding to the size of the end so as to form an eddy current path for the magnetic flux from the end of the magnetic pole. Detection device. 7. The electric conductor portion is formed by depositing a predetermined conductive material in a predetermined pattern on the base material of the piston rod, according to any one of claims 1 to 6. Piston rod position detection device. 8. The piston rod position detection device according to claim 7, wherein the conductive substance is attached by plating. 9. The piston rod position detection device according to claim 7, wherein the conductive substance is attached by thermal spraying. 10. The piston rod position detection device according to claim 7, wherein the conductive substance is attached by pattern baking. 11. A resin coating is applied over the entire circumference of the base material of the piston rod, a predetermined conductive substance is applied over the entire circumference of the rod, and then the conductive substance is removed in a predetermined pattern. 8. The piston rod position detection device according to claim 7, wherein a predetermined pattern of conductive material is left behind to form the conductor portion. 12. A predetermined conductive substance is attached all around the base material of the piston rod, and then a process is performed to remove the conductive substance in a predetermined pattern, so that a predetermined pattern of the conductive substance is left behind and the conductive substance is removed. 8. The piston rod position detection device according to claim 7, wherein a conductor portion is formed. 13. According to any one of claims 1 to 12, the piston rod having the conductor portion on its circumferential surface is coated with a predetermined non-magnetic and non-conductive material over the entire circumference. piston rod position detection device. 14. The coil unit includes a plurality of primary coils and a secondary coil corresponding to the primary coil, and each primary coil is excited using a plurality of primary alternating current signals whose phases are shifted. According to any one of claims 1 to 13, wherein a signal obtained by shifting the phase of the primary AC signal according to the relative linear position of the rod portion is obtained on the secondary coil side. The piston rod position detection device described. 15. The primary and secondary coils are composed of four-phase coil groups, and these coils are arranged so that the phase of magnetic resistance change of each phase magnetic circuit is shifted by approximately 90 degrees in accordance with the relative linear position of the rod portion. The secondary coil output is extracted differentially by exciting two phases whose magnetic resistance changes are separated by 180 degrees with a sine wave signal, and another phase whose magnetic resistance changes are separated by 180 degrees. The two phases are excited by a cosine wave signal and the secondary coil output is extracted differentially.
15. The piston rod position detection device according to claim 14, wherein the phase-shifted output signal is obtained by adding and combining secondary coil differential output signals. 16. A coil part provided on the open end side of the cylinder body and excited by the primary alternating current signal and for taking out the secondary output; a magnetic material portion that is provided and changes the magnetic resistance of a magnetic circuit passing through the coil portion according to a relative position of the magnetic material portion with respect to the coil portion; and the magnetic material portion on the circumferential surface of the piston rod. A conductor is provided at a non-protruding portion so as to form an eddy current path for magnetic flux, and is made of a relatively weak magnetic or non-magnetic material and a relatively good conductor than the magnetic material portion. a body portion, wherein the amount of eddy current flowing through the conductor portion changes according to relative displacement of the magnetic portion and the conductor portion with respect to the coil portion as the piston rod moves, and the coil 1. A piston rod position detection device for a fluid pressure cylinder, characterized in that the magnetic resistance of a magnetic circuit of the coil section changes, and a secondary output signal corresponding to the change is obtained at the coil section. 17. The piston rod position detection device according to claim 16, wherein a plurality of the magnetic portions and the conductive portions are provided alternately. 18. The conductor portion is constituted by a ring closed around the piston rod, and the piston rod is inserted into the coil space of the coil portion. piston rod position detection device. 19. The piston rod position detection device according to claim 17, wherein the piston rod is formed by alternately arranging the magnetic portion and the conductive portion in a spiral shape. 20. The coil portion includes a magnetic core around which a coil is wound, and a magnetic pole end of the magnetic core faces the circumferential surface of the piston rod with a gap in between. The piston rod position detection device according to item 17 or 19. 21. The magnetic portion is formed as a protrusion in a magnetic member forming the base of the piston rod, and the conductive portion is provided within a recess of the magnetic member. The piston rod position detection device according to any one of Item 20. 22. The conductor portion is formed by attaching a substance that is relatively weakly magnetic or non-magnetic than the magnetic member and is a relatively good conductor to the recesses of the magnetic member in a predetermined pattern by surface treatment. 22. The piston rod position detection device according to claim 21, wherein 23. The piston rod position detection device according to any one of claims 16 to 22, wherein the piston rod is coated with a predetermined non-magnetic and non-conductive material over the entire outer periphery of the piston rod. 24. The coil unit includes a plurality of primary coils and a secondary coil corresponding to the primary coil, and each primary coil is excited using a plurality of primary alternating current signals whose phases are shifted. Claims 16 to 23, wherein a signal obtained by shifting the phase of the primary AC signal according to the relative linear position of the rod portion is obtained on the side of the secondary coil.
The piston rod detection device according to any one of paragraphs. 25. The primary and secondary coils are composed of four-phase coil groups, and these coils are arranged so that the phase of the change in magnetic resistance of each phase magnetic circuit according to the relative linear position of the rod section is shifted by approximately 90 degrees. The secondary coil output is differentially extracted by exciting two phases whose magnetic resistance changes are separated by 180 degrees with a sine wave signal, and another phase whose magnetic resistance changes are separated by 180 degrees. The two phases are excited by a cosine wave signal and the secondary coil output is extracted differentially.
25. The piston rod position detecting device according to claim 24, wherein the phase-shifted output signal is obtained by adding and combining secondary coil differential output signals.