JPH0665961B2 - Fluid pressure cylinder piston rod position detector - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piston rod position detecting device for a fluid pressure cylinder, and particularly to an induction coefficient depending on the relative displacement of the piston rod with respect to a winding fixed on the cylinder body side. For an inductive type piston rod position detecting device for obtaining an output signal in accordance therewith. More specifically, a relatively good conductor part such as copper is provided around the piston rod. The present invention relates to a piston rod position detecting device capable of obtaining an induction coefficient change with at least an eddy current loss as a parameter.

[Conventional technology]

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

In Japanese Utility Model No. 59-23609, a plurality of magnetic rings are provided around the piston rod at predetermined intervals, and a primary winding and secondary winding of multiple phases are provided on the cylinder body side. The wires are individually excited by a plurality of AC signals having a phase shift so that an AC signal phase-shifted according to the position of the piston rod is obtained on the side of the secondary winding. There is disclosed a piston rod position detecting device capable of absolutely detecting the position of the piston rod by counting.

In Japanese Utility Model No. 59-23610, a stator composed of a primary winding and a secondary winding wound around a plurality of magnetic poles 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 AC signals having a phase shift so that an AC signal phase-shifted according to the position of the piston rod can be obtained on the secondary winding side. There is disclosed a piston rod position detecting device capable of absolutely detecting the position of a piston rod by digitally counting the amount of phase shift.

[Problems to be solved by the invention]

Since the detection device shown in the above-mentioned U.S. Pat. However, the method of generating and counting incremental pulses is actually used. Therefore, there is a problem that the position of the piston rod cannot be detected absolutely. Further, in order to form the groove in the piston rod, a cutting process or the like must be performed, which is a problem that the process is troublesome.

Since the above two utility model registration applications are of the absolute type, they do not have the above-mentioned drawbacks, but they also have the problem that it takes time to assemble or process the magnetic ring or projection around the piston rod.

Further, in any of the above-mentioned conventional techniques, the change in the induction coefficient of the winding is caused only by the presence or absence of the groove or the protrusion of iron or magnetic metal, so that the depth of the groove or the height of the protrusion is sufficient. There is also a problem that the detection accuracy cannot be improved unless the above is satisfied.

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

[Means and Actions for Solving Problems]

The piston rod position detecting device according to the present invention is provided on the opening end side of the cylinder body, and is excited by this excitation and at least two primary coils which are respectively excited by primary AC signals whose phases are shifted from each other. 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 made of a conductor relatively better than the material of the other portion of the piston rod, and the conductor portion is predetermined along the moving direction of the piston rod. The conductor portion having the same pattern is repeatedly provided at a repeating cycle of, and the conductor portion is formed on the piston rod by a surface treatment. A pattern is formed by adhering a predetermined conductive material, and the primary coil is arranged so that the correspondence between the primary coil and the conductor portion of the piston rod is deviated between the primary coils. By doing so, the primary AC signal is phase-shifted according to the relative linear position of the piston rod.
The next output AC signal is obtained from the coil section,
The arrangement of the coil portion is determined so that the phase shift amount corresponds to an electrical angle of 360 degrees for a linear displacement amount corresponding to one repeating cycle of the arrangement of the conductor portions in the piston rod. It is a thing.

When the conductor portion of the piston rod enters the magnetic field of the coil portion, an eddy current flows in that portion, and the magnetic resistance of the magnetic circuit passing through the coil portion is substantially increased by the eddy current loss. The amount of eddy current changes according to the degree of penetration of the conductor portion, and the magnetic resistance changes accordingly. Therefore, a voltage corresponding to the relative linear position of the conductor portion of the piston rod with respect to the coil portion is induced on the secondary side of the coil portion.

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

Since the eddy current has a property of flowing near the surface of the conductor, the conductor portion to be provided on the peripheral surface of the piston rod does not need to have a large thickness. Therefore, the conductor portion can be attached on the base material of the piston rod in a predetermined pattern. This means that it is very easy to form the conductor portion on the circumferential surface of the piston rod. That is, the pattern of such a relatively thin conductor portion can be relatively easily formed on the base material of the piston rod by other suitable surface processing technique such as plating, thermal spraying, pattern baking or etching. Therefore, it is possible to omit troublesome machining and assembly, and it is expected that the manufacturing cost will be significantly reduced.

There is no particular problem if the conductor portion can be adhered from the beginning on the base material of the rod portion in a predetermined pattern, but it may be difficult depending on the surface processing technique used (for example, plating). In such cases, first
A predetermined conductive material is attached to the entire surface of the base material of the piston rod, then the conductive material attached to the base material is left in a predetermined pattern to remove unnecessary portions, and the remaining conductive material is used to determine a predetermined value. It is preferable that the conductor portion of the pattern is formed. As an example, the deposition is performed by plating and the removal is performed by etching. By doing so, it is possible to efficiently perform the work of forming the conductor portion on the circumferential surface of the piston rod. When the unnecessary conductive substance is removed by etching, the base material surface of the piston rod may be attacked by the etching agent. In order to deal with such a problem, first, a coating (for example, a resin coating) that is resistant to an etching agent is applied to the entire circumference of the base material of the piston rod, and then the conductive material is applied on the coating. The substance may be attached by plating or the like. Then, the base material of the piston rod is protected by the resin coating during etching.

Another piston rod position detection device according to the present invention is provided with a coil portion as described above and a magnetic field that passes through the coil portion and 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. In a magnetic body portion that changes the magnetic resistance of the circuit according to the relative position of this magnetic body portion with respect to the coil portion, and in a portion where the magnetic body portion on the peripheral surface of the piston rod does not project,
A conductor portion that is provided so as to form an eddy current path for the magnetic flux and that is relatively weakly magnetic or non-magnetic than the magnetic body portion and that is made of a relatively good conductor. There is.

Regarding the portion of the piston rod circumferential surface where the magnetic portion projects, when the portion of the magnetic portion enters the magnetic field of the coil portion, the magnetic resistance of the magnetic circuit passing through the coil portion decreases (in other words, the magnetic permeability). That is, permeance increases). On the other hand, the magnetic resistance increases (the permeance decreases) at the portion where the magnetic material portion does not project. The conductor portion is provided at the place where the magnetic resistance increases in this way. Therefore, when the conductor part of the piston rod (in other words, the part where the magnetic part does not project) enters the magnetic field generated by the coil part, eddy current flow loss occurs at that part, which further increases the substantial magnetic resistance. Be increased.

In this way, not only the magnetic resistance change (permeability change) due to the displacement of the magnetic body part but also the induction coefficient change with the eddy current loss due to the displacement of the conductor part as the parameter (the number of coil windings and other conditions are fixed, (Substantially equivalent to the change in magnetic resistance) is synergistically obtained. That is,
In the range where the magnetic resistance is relatively decreased by the penetration of the magnetic part of the piston rod into the coil magnetic circuit (the range where the permeance is relatively increased), the effect of the eddy current loss due to the conductor part is not exerted. Therefore, a relatively sufficiently high level voltage can be induced on the secondary side. On the other hand, in the range where the magnetic resistance is relatively increased by the detachment of the magnetic body portion of the piston rod from the coil magnetic circuit, the conductor portion of the rod enters the coil magnetic circuit to cause eddy current loss. Therefore, in addition to the relative magnetic resistance increase due to the detachment of the magnetic body portion, the relative magnetic resistance increase due to the eddy current loss of the conductor portion is added, so that it can be further lowered by the voltage level induced on the secondary side. In this way, the difference between the high level and the low level of the secondary side induced voltage, that is, the width of change in the secondary output with respect to the displacement can be made sufficiently large, which enables accurate linear displacement detection of the piston rod. You will be able to do it.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In FIG. 1, 11 is a cylinder body, 12 is a piston, 6
Is the 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. The coil 10 is provided on the open end side of the cylinder body 11. The coil unit 10 is 1
A cylinder body including secondary coils 1A to 1D and secondary coils 2A to 2D, with the rod 6 slidably penetrating the coil space so that the cylindrical space of these coils is concentric with the rod 6. It is fixed to the open end side of 11. The piston rod 6 includes a base material, that is, a center rod 6a, and a conductor portion provided in a ring shape around the center rod 6a.
6b and a coating 6c covering the entire outer circumference. The width of this conductor portion 6b is P / 2 (where P is an arbitrary number)
And the relative linear displacement direction of the rod 6 (arrow L in the figure,
Direction)) and multiple conductor parts 6b
Are repeatedly provided. The conductor portion 6b is made of a weakly magnetic or non-magnetic material and is made of a good conductor relatively to the material of the center rod 6a, for example, copper or aluminum or brass or a good conductive material such as them. A mixture or mixture of other substances can be used. The center rod 6a may be made of either a magnetic substance or a non-magnetic substance, and in short, a substance having a larger electric specific resistance than the conductor portion 6b (having a poor conductivity) is used as the center rod 6a. This is because the conductor portion 6b is intermittently provided.
This is to allow more eddy current to flow only in the area of, and to obtain a periodic magnetoresistive change with respect to displacement. If the central rod 6a is made of a magnetic material such as iron, the passage of the magnetic flux is improved, so that the corresponding eddy current amount is increased and the detection accuracy can be improved.

In this embodiment, the coils are provided so as to operate in four phases, and these phases are distinguished by using symbols A, B, C and D for convenience. According to the relative position of the ring-shaped conductor portion 6b with respect to the coil, the magnetic resistance generated in each of the phases A to D is shifted by 90 degrees. For example, when 4 phases are cosine phases, B phase is a sine phase, The arrangement of the coils and the size and shape of the conductor portion 6b are determined so that the C phase is the minus cosine phase and the D phase is the minus sine phase.

In the example of FIG. 1, those corresponding to the primary coils 1A to 1D and the secondary coils 2A to 2D of the respective phases A to D are wound at the same position, and the coil length of each coil is approximately “P”. / 2 ".
A-phase C-phase coils 1A, 2A, 1C and 2C are provided adjacent to each other, and B-phase and D-phase coils 1B, 2B, 1D and 2D are also provided adjacent to each other. The spacing between the C phase coil group and the B and D phase coil groups (N is an arbitrary natural number).

The A-phase and C-phase coils 1A, 2A, 1C and 2C are housed in a cylindrical case 4 made of a magnetic material such as iron, and the B-phase and D-phase coils 1B, 2B, 1D and 2D are also similar cylinders. It is housed in the case 5, and the entire coil portion 10 is further housed in the outer case 13. These iron cases 4 and 5 prevent the crosstalk between the coils and concentrate the magnetic lines of force of the coils to enhance the coupling of the magnetic circuit.

In the above configuration, the magnetic flux generated by the primary coils 1A to 1D of each phase passes through the magnetic material cases 4 and 5 and the piston rod 6, and when the conductor portion 6b enters the magnetic field, it depends on the amount of penetration. Eddy currents flow along the ring of the conductor portion 6b. The more the conductor portion 6b penetrates into the coil (for example, the maximum state corresponding to the phase A in FIG. 1), the more eddy current flows. On the contrary, almost no eddy current flows in the state where the conductor portion 6b does not penetrate into the coil at all (for example, the state of phase C in FIG. 1).
In this way, an eddy current flows in the conductor portion 6b according to the penetration degree of the conductor portion 6b into the coil of each phase, and a magnetic resistance change due to this eddy current loss is generated in the magnetic circuit of each phase. An AC signal having a level corresponding to the magnetic resistance is induced in the secondary coils 2A to 2D of each phase.

Coating 6c provided on the outer circumference of the piston rod 6
Is a non-magnetic or weakly magnetic substance that has a relatively low conductivity or non-conductivity relative to the conductor portion 6b. For example, chrome plating may be used.

In the embodiment of FIG. 1, each phase coil is a cylindrical magnetic body case.
Although the cases 4 and 5 are housed in the cases 4 and 5 so that the magnetic paths can be formed, the present invention can be implemented without providing such a magnetic case.

Although the piston rod is inserted into the space in the coil in the above-described embodiment, the present invention is not limited to this, and the design can be appropriately changed as necessary.

FIG. 3 shows a modification of the coil portion 10, and FIG. 4 is a sectional view taken along line IV-IV thereof. Primary and secondary coils 1A to 1D and 2A to 2D corresponding to the respective phases A to D are respectively wound around both legs of a U-shaped magnetic core 7A to 7D provided for each phase. The cores 7A to 7D of the phases A to D are fixed to each other in a predetermined arrangement so that the cycles of magnetoresistance change are deviated by 1/4 cycle (90 degrees) between adjacent phases. For example, the interval between cores 7A to 7D between adjacent phases is 3P / 4 (in a broad sense, It is good). Piston rod 6 is first
The structure is similar to that shown in the figure. Each U-shaped core 7A
The distance between both ends in ~ 7D corresponds approximately to the width P / 2 of the conductor portion 6b, and in each phase, a magnetic circuit that goes from one end of the U-shaped core 7A to 7D through the piston rod 6 to the other end. Are formed respectively. In FIG. 3, the cores 7A to 7D of each phase are aligned in a straight line in the linear displacement direction. You may. In that case, the interval in the linear displacement direction between the adjacent phases is not limited to 3P / 4 and can be made shorter (for example, P / 4). In the example of FIG. 3, the eddy current path generated in the conductor portion 6b is formed around the magnetic flux path perpendicular to the end of each core 7A to 7D, rather than being formed along the ring shape. Therefore, in this case, the conductor portion 6b of the piston rod 6 does not necessarily have to have a ring shape surrounding the peripheral surface, and a certain amount of (eddy current) may be present at a position facing the end portions of the cores 7A to 7D. It only has to have an area (so that the path can be formed) or form a ring-shaped pattern.

In the embodiment shown in FIG. 5, the piston rod portion 6 comprises a conductor portion 14 provided in a spiral shape around the center rod 6a. The spiral conductor portion 14 has a pitch width of 1
The threads are arranged in a pattern. In FIG. 5, the piston rod 6 is shown in a side view. FIG. 6 is of FIG.
FIG. 6 is a cross-sectional view taken along the line VI-VI and, as shown in the figure, a U-shaped core of each phase A to D around the piston rod 6 at intervals of 90 degrees.
8A to 8D are provided, and each core 8A to 8D has a primary coil
1A to 1D and secondary coils 2A to 2D are wound.

In the embodiment of FIG. 7, the piston rod 6 is the central rod.
A helical conductor portion 15 is provided around 6a in a double thread pattern with one pitch of 2P. FIG. 8 is a sectional view taken along the line VIII-VIII in FIG. 7, in which eight cores 8A to 8D and 8A 'to 8D' are provided around the rod 6 at intervals of 45 degrees. Two cores facing each other at an interval of 180 degrees are in phase with each other, and there are four pairs of cores each consisting of two cores, and each pair corresponds to phases A to D, respectively. The primary coils 1A to 1D and the secondary coils 2A to 2D are wound around the cores 8A to 8D 'of the respective phases A to D, as described above. In-phase secondary coil outputs are added together.

5 to 8, the coating 6c is provided on the outer circumference of the rod 6 as in the embodiment of FIG.

In the embodiment shown in FIGS. 5 to 8, the eddy current paths in the conductor portions 14 and 15 are the same as in the embodiment shown in FIG.
It is formed around the magnetic flux path perpendicular to the ends of A to 8D '. Therefore, also in this case, the conductor portions 14, 1 of the piston rod 6 are
5 does not necessarily have to be a continuous spiral, core 8
It suffices to have a certain area or to form a ring-shaped pattern at the portions facing the ends of A to 8D '.

The conductor portions 6b, 14 and 15 on the piston rod 6 can be formed by the following procedure as an example.

A resin coating having resistance to an etching agent is applied to the entire circumference of the center rod 6a.

A predetermined conductive material is attached to 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, an unnecessary part of the conductive material is removed from the surface of the center rod 6a by a removal technique such as etching to form a pattern of predetermined conductor parts 6b, 14 and 15.

Next, the coating 6c is applied to the entire circumference of the piston rod 6 to protect and smooth its surface.

The above process is useful for preventing the removing agent from invading not only the conductive substance but also the material of the center rod 6a in the process of. If such a preventive measure is unnecessary, the process can be omitted. When a surface processing technique capable of depositing a conductive substance in a desired pattern is adopted from the beginning, of course, etching or the like is unnecessary.

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

A central portion 9a of the piston rod 9 is made of a magnetic material, and a magnetic material portion 9d protruding in a ring shape around the central portion 9a is provided with a predetermined width P / 2 in the linear displacement direction (arrow L, direction). This magnetic material part 9d is spaced at a predetermined interval in the linear displacement direction.
A plurality is provided for each P / 2. A plurality of conductor portions 9b are filled in a ring shape in the ring-shaped recesses between the magnetic body portions 9d. The width of each ring-shaped conductor portion 9b is also P / 2. The central portion 9a and the magnetic material portion 9d are made of a ferromagnetic material such as iron, and the conductive material portion 9b is relatively weakly magnetic or non-magnetic than the magnetic material portion 9d and has a relatively good conductive material (for example, Copper, aluminum, brass, etc., or a mixture of a good conductor material such as these and other materials). The entire outer circumference of the piston rod 9 is coated by chrome plating or the like as described above.
9c is provided. The coating 9c may be a synthetic resin sleeve.

In the above configuration, the magnetic flux generated by the primary coils 1A to 1D of each phase passes through the magnetic material cases 4,5 and the central portion 9a of the piston rod 9. The gap between the inner peripheral ends of the cases 4 and 5 and the protruding magnetic body portion 9d of the rod 9 is between the inner peripheral end portion and the surface of the lower central portion 9a of the conductor portion 9b of the rod 9. Narrower than the gap. Further, the width P / 2 of the magnetic body portion 9d and the conductor portion 9b substantially corresponds to the length of each coil. Therefore, when the rod 9 is linearly displaced relative to the coil portion 10, the magnetic material portion 9d for each phase coil is
The magnetic resistance of the magnetic circuit of each phase changes in accordance with the relative position of the. As is well known, a state in which a large number of magnetic material portions 9d penetrates into the coil (for example, C at the maximum in FIG. 9)
The smaller the magnetic resistance, the larger the permeance. As is clear from this, the conductor portion 9b provided between the magnetic body portions 9d is located at a portion where the magnetic resistance of the rod 9 is relatively increased (a portion where the permeance is relatively reduced). It will be provided correspondingly. Further, the conductor portion 9b has a ring shape with respect to the central portion 9a forming the magnetic path, functions as a so-called short ring, and can form an eddy current path for the magnetic flux. Therefore, the more the conductor portion 9b penetrates into the coil (for example, the maximum state of the phase A in FIG. 9), the more eddy current flows, and the substantial magnetic resistance increases due to the eddy current loss. To be On the other hand, as described above, the magnetic resistance of the conductor portion 9b is relatively increased due to the lack of the magnetic body portion 9d. Therefore, the magnetic resistance is synergistically increased and the level of the secondary side induced voltage is synergistically attenuated.

Although the central portion 9a of the rod 9 is made of the same magnetic material as the magnetic portion 9d in the above embodiment, the present invention is not limited to this and may be an appropriate non-magnetic material. An example thereof is shown in FIG. 11. This piston rod 9 has a ring-shaped magnetic body portion 9d and a conductor portion 9b having a width P / 2 around a mandrel 9a 'made of a non-conductive and non-magnetic material. Are formed alternately. The mandrel 9a 'may be made of the same magnetic material as the magnetic part 9d, in which case it is substantially the same as that shown in FIG. Further, the mandrel 9a 'may be made of a weakly magnetic or non-magnetic material having good conductivity, 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. Further, similarly to FIGS. 5 to 8, as shown in FIGS. 12 to 15, the conductor portion 9b and the magnetic portion 9d on the peripheral surface of the piston rod 9 may be provided in a spiral shape. .

In the embodiment shown in FIG. 12, in the rod portion 9, the magnetic substance portion 9d and the conductor portion are formed by the arrangement of the single thread having one pitch width of P.
9b are alternately provided in a spiral shape. The thread portion of the screw corresponds to the magnetic material portion 9d, and the conductor portion 9b is provided at the root portion of the screw. In FIG. 12, for convenience of illustration, the thread crests (magnetic material portions 9d) and troughs are shown in a side view, and the conductor portions 9b filled in these troughs are shown in cross section. Fig. 13 shows Fig. 12
It is a III-III line sectional view, and the arrangement | positioning of core 8A-8D is the same as FIG.

In the embodiment shown in FIG. 14, one pitch width of the rod 9 is 2P.
9d of magnetic material and 9b of conductive material in the arrangement of double thread
Are alternately provided in a spiral shape. Similar to the above, the thread portion of the screw is the magnetic body portion 9d, and the conductor portion 9b is provided in the valley portion. As in FIG. 12, the peaks (magnetic material portions 9d) and valleys are shown in a side view, and the conductor portions 9b are shown in a sectional view. FIG. 15 is a sectional view taken along the line VV of FIG. 14, and the cores 8A to 8D 'have the same arrangement as that of FIG. Also,
The magnetic material portion 9d and the conductive material portion 9b may be provided only at the positions corresponding to the cores 8A to 8D 'of each phase.

An example of a method of forming the conductor portion 9b and the magnetic body portion 9d around the piston rod 9 will be described. A ring-shaped groove or screw is formed on the mandrel of the rod made of a magnetic body in correspondence with the position of the conductor portion 9b. The groove is machined, and then a predetermined conductive material is attached to the surface of the round bar by plating, thermal spraying, pattern baking, or other suitable surface treatment, and then the surface of the round bar is polished to form a conductor portion 9b only in the groove. You should leave it. Of course, a predetermined conductive material may be attached by a surface processing treatment (for example, thermal spraying or pattern baking) only along a predetermined pattern for forming a conductor portion, in which case the last surface polishing is not necessary. Become.

In each of the above-described embodiments, an output signal according to the linear position of the piston rod can be obtained by the phase shift method. That is, in each of the phases A to D, a periodical magnetic resistance change occurs with the linear displacement amount P of the piston rod as one cycle, and the phase of this magnetic resistance change is 90 between adjacent phases.
Deviated by degrees (P / 4). Therefore, if the phase angle corresponding to the linear displacement is represented by φ, the level of the voltage induced in the secondary coils 2A to 2D of the respective phases A to D is approximately A according to the linear position of the piston rod (that is, φ). In phase, cosφ,
Sin phase for B phase, -cos phase for C phase, -sin phase for D phase
(However, 2π corresponds to P). The A and C phase primary coils 1A and 1C are excited by the sine wave signal sinωt, and the B and D phase primary coils 1B and 1D are cosine wave signal co.
Excited by sωt. The output signals of the secondary coils 2A, 2C are differentially added in the A, C relative direction, and the outputs of the secondary coils 2B, 2D are also differentially added in the B, D relative directions. The differential output signals are added and synthesized to obtain the final output signal Y. Then, the output signal Y can be substantially expressed by the following simplified formula.

Y = sinωt cosφ − (− sinωt cosφ) + cosωt sinφ − (− cosωt sinφ) = 2sinωt cosφ + 2cosωt sinφ = 2sin (ωt + φ) A constant that is conveniently determined by the above equation as “2” according to various conditions. If replaced by K, it can be expressed as Y = Ksin (ωt + φ). Here, since φ corresponds to the linear position of the piston rod, the primary AC signal sinωt (or cos)
The piston rod position can be detected by measuring the phase shift φ of the output signal Y corresponding to ωt).

Secondary coil output composite signal Y and reference AC signal sinωt
The means for obtaining the phase shift φ from (or cosωt) can be appropriately configured. FIG. 16 shows an example of a circuit in which the phase shift φ is calculated by a digital amount. Although not shown in the drawing, the reference AC signal sinωt
It is also possible to obtain the phase shift φ by an analog amount by obtaining the time difference between the output signal Y and the output signal Y = Ksin (ωt + φ) at a phase angle of 0 degree.

In FIG. 16, the oscillator 32 is a circuit for generating the reference sine signal sinωt and the cosine signal cosωt, and the phase difference detection circuit 37 is a circuit for measuring the phase shift φ. The clock pulse CP oscillated from the clock oscillator 33 is the counter 30.
Is counted in. The counter 30 is, for example, modulo M (M
Is an arbitrary integer), and the count value is given to the register 31. From the 4 / M frequency-divided output of the counter 30, a pulse Pc obtained by frequency-dividing the clock pulse CP by 4 / M is extracted and applied to the C input of the 1/2 frequency-division flip-flop 34. The pulse Pb output from the Q output of the flip-flop 34 is added to the flip-flop 35, the pulse Pa output from the output is added to the flip-flop 36, and the outputs of these 35 and 36 are supplied to the low-pass filters 38, 39 and the amplifiers 40, 41. A cosine signal cosωt and a sine signal sinωt are obtained via 1
Applied to the next coils 1A-1D. The M count in the counter 30 corresponds to the phase angle of 2π radians of these reference signals cosωt, sinωt. That is, one count value of the counter 30 is The phase angle in radians is shown.

The combined output signal Y of the secondary coils 2A to 2D is applied to the comparator 43 via the amplifier 42, and a square wave signal according to the positive / 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 Ts, and the count value of the counter 30 is loaded into the register 31 in response to the pulse Ts.
As a result, the digital value D _φ corresponding to the phase shift φ is taken into the register 31. In this way, the data D _φ indicating the piston rod position within the predetermined range P as an absolute value can be obtained.

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

Incidentally, the primary coil and the secondary coil do not necessarily have to be provided separately, and are not put into practical use No. 58-2621 or 58-3950.
It may be common, such as the one shown in No. 7. Further, the patterns of the conductor portions 6b and 9b are not limited to those shown in the figure, and may have any shape as long as they can form an eddy current path.

〔The invention's effect〕

As described above, according to the present invention, the conductive material may be attached to the peripheral surface of the piston rod in a predetermined pattern.
Easy to process and form. Also, even if the conductor part is thin, its function can be sufficiently exhibited, so the structure is simpler than when only the groove is formed in the magnetic body (in this case, the groove needs to be deep enough). Be converted. Further, by combining the protrusion of the magnetic body portion and the conductor portion, it is possible to increase the change width of the secondary output voltage level with respect to the displacement, and it is possible to improve the detection accuracy.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view showing an embodiment of a piston rod position detecting device according to the present invention, FIG. 2 is a sectional view taken along line II-II of FIG. 1, and FIG. 3 is a modification of a coil portion in FIG. A sectional view showing an example, FIG. 4 is a sectional view taken along the line IV-IV in FIG. 3, FIG. 5 is a partial sectional side view showing a modified example of the coil portion and the piston rod in FIG. 1, and FIG. VI-VI line sectional view of FIG.
FIG. 7 is a partial cross-sectional side view showing another modified example of the coil portion and the piston rod in FIG. 1, and FIG. 8 is a VI of FIG.
II-VIII sectional view, FIG. 9 is a longitudinal sectional view showing another embodiment of the piston rod position detecting device according to the present invention, FIG. 10 is a sectional view taken along line XX of FIG. 9, and FIG. FIG. 9 is a partial sectional side view showing a modified example of the piston rod in FIG. 9, FIG. 12 is a partial sectional side view showing a modified example of the coil portion and the piston rod in FIG. 9, and FIG. 13 is a III in FIG. -III sectional view, FIG. 14 is a partial sectional side view showing another modification of the coil portion and piston rod in FIG. 9, FIG. 15 is a sectional view taken along line VV of FIG. 14, and FIG. FIG. 4 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 an electrical phase shift amount according to the piston rod position. 11 …… Cylinder body, 12 …… Piston, 6,9 …… Piston rod, 6a …… Center rod, 6b, 9b, 14,15 …… Conductor part, 6c, 9c …… Coating, 9d …… Magnetic body Part, 10
…… Coil part, 1A to 1D …… Primary coil, 2A to 2D …… Secondary coil.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-49-107758 (JP, A) Real-life Sho 55-1712 (JP, U) Real-life Sho 59-23609 (JP, U) Real-life Sho 59- 23610 (JP, U) JP47-27268 (JP, B1)

Claims (24)

[Claims] 1. At least two primary coils, which are provided on the open end side of a cylinder body and are excited by primary AC signals having mutually shifted phases, and a secondary output AC signal induced by this excitation. 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. It is made of a weakly magnetic or non-magnetic material and is made of a conductor that is relatively better than the material of the other parts of the piston rod, and has the same pattern in a predetermined repeating cycle along the moving direction of the piston rod. The conductor portion is repeatedly provided, and the conductor portion is provided with a predetermined conductive substance in a predetermined pattern on the piston rod by a surface treatment. The primary AC signal is provided by arranging the primary coils such that the correspondence between the primary coil and the conductor portion of the piston rod is deviated between the primary coils. Phase shifted according to the relative linear position of the piston rod 2
The next output AC signal is obtained from the coil section,
The arrangement of the coil portion is determined so that the phase shift amount corresponds to an electrical angle of 360 degrees for a linear displacement amount corresponding to one repeating cycle of the arrangement of the conductor portions in the piston rod. A fluid pressure cylinder piston rod position detector. 2. The conductor portion comprises a ring 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 claim 1. 3. The piston rod position detecting 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 detecting device according to claim 1, wherein the conductor portions are arranged in a spiral pattern around the piston rod at a predetermined pitch. 5. The coil portion includes a magnetic core wound with a coil, and a magnetic pole end portion of the magnetic core faces a peripheral surface of the piston rod with a gap interposed therebetween. The piston rod position detection device according to item 1 or 4. 6. The coil portion includes a magnetic core wound with a coil, and a magnetic pole end of the magnetic core faces a peripheral surface of the piston rod with a gap, and the conductor portion is formed. 2. The magnetic recording medium according to claim 1, wherein the magnetic field is formed of a ring-shaped or plane-shaped pattern corresponding to the size of the magnetic pole end so as to form an eddy current path for the magnetic flux. Piston rod position detector. 7. The piston rod position detecting device according to claim 1, wherein the conductive substance is attached by plating. 8. The piston rod position detecting device according to claim 1, wherein the conductive substance is attached by thermal spraying. 9. The piston rod position detecting device according to claim 1, wherein the conductive substance is attached by pattern printing. 10. A resin coating is applied over the entire circumference of the base material of the piston rod, and a predetermined conductive material is adhered over the entire circumference of the rod, and then the conductive material is removed in a predetermined pattern. The piston rod position detecting device according to claim 1, wherein the piston rod position detecting device is subjected to a treatment so that a conductive material having a predetermined pattern is left to form the conductor portion. 11. A predetermined conductive material is attached to the entire circumference of the base material of the piston rod, and then the conductive material is removed in a predetermined pattern to leave the conductive material in the predetermined pattern. The piston rod position detecting device according to claim 1, wherein the conductor portion is formed by being formed. 12. The method according to any one of claims 1 to 11, wherein the entire circumference of the piston rod having the conductor portion on its peripheral surface is coated with a predetermined nonmagnetic and nonconductive substance. The piston rod position detection device described in (1). 13. The coil section according to claim 1, wherein the coil section includes the plurality of primary coils and a secondary coil provided corresponding to each primary coil. The piston rod position detector described in. 14. The primary and secondary coils are composed of four-phase coil groups, and the phase of the magnetic resistance change of each phase magnetic circuit according to the relative linear position of the piston rod is approximately 90.
These coils are arranged so as to be shifted by degrees, and two phases whose magnetic resistance changes are separated by 180 degrees are excited by a sine wave signal, and the secondary coil output is taken out differentially.
The other two phases whose magnetic resistance changes are separated by 180 degrees are excited by the cosine wave signal to differentially extract the secondary coil output, and the relative secondary coil differential output signals are added and combined to form the phase. 14. The piston rod position detecting device according to claim 13, wherein a shifted output signal is obtained. 15. A cylinder body is provided on the open end side, and
A coil portion that is excited by the next alternating current signal and that extracts a secondary output, and is provided so as to project in a predetermined range along the moving direction of the rod on the circumferential surface of the piston rod, An eddy current path with respect to the magnetic flux at a magnetic material portion that changes the magnetic resistance according to the relative position of this magnetic material portion with respect to the coil portion, and at a location on the circumferential surface of the piston rod where the magnetic material portion does not project. And a conductor part that is relatively weakly magnetic or non-magnetic than the magnetic part and that is composed of a relatively good conductor. The amount of eddy current flowing through the conductor portion changes according to the relative displacement of the magnetic body portion and the conductor portion with respect to the coil portion, and the magnetic circuit of the coil portion changes. Magnetic resistance changes, the piston rod position detection device of a fluid pressure cylinder, characterized in that the second output signal corresponding thereto is to be obtained at the coil portion. 16. The piston rod position detecting device according to claim 15, wherein a plurality of the magnetic material portions and the conductive material portions are provided alternately. 17. The method according to claim 15, wherein the conductor portion is a ring closed around the piston rod, and the piston rod is inserted into the coil space of the coil portion. The piston rod position detection device according to item 16. 18. The piston rod position detecting device according to claim 16, wherein the piston rod is formed by alternately arranging the magnetic body portions and the conductor portions in a spiral shape. 19. The coil portion includes a magnetic core wound with a coil, and a magnetic pole end of the magnetic core faces a peripheral surface of the piston rod with a gap interposed therebetween. 15. A piston rod position detection device according to item 15, item 16 or item 18. 20. The magnetic material portion is formed as a protruding portion in a magnetic member forming a base portion of the piston rod, and the conductive material portion is provided in a concave portion of the magnetic material portion. 20. The piston rod position detection device according to any one of items 15 to 19. 21. The conductor portion is surface-treated with a material having a relatively weak magnetic property or a non-magnetic property as compared with the magnetic member and made of a relatively good conductor in a recess of the magnetic member in a predetermined pattern. 21. The piston rod position detection device according to claim 20, which is attached by processing. 22. The piston rod position detecting device according to claim 15, wherein the entire outer circumference of the piston rod is coated with a predetermined non-magnetic and non-conductive substance. 23. The coil portion includes a plurality of primary coils,
A secondary coil corresponding to the primary coil is included, and each primary coil is excited by using a plurality of primary AC signals having a phase shift, whereby the primary AC signal is relatively linear to the rod portion. 23. The piston rod position detecting device according to claim 15, wherein a signal phase-shifted according to the position is obtained on the side of the secondary coil. 24. The primary and secondary coils are composed of four-phase coil groups, and the phase of the magnetic resistance change of each phase magnetic circuit according to the relative linear position of the rod portion is shifted by about 90 degrees. These coils are arranged, and the two phases whose magnetic resistance changes are 180 degrees apart are excited by a sine wave signal and the secondary coil outputs are taken out differentially, and the magnetic resistance changes are separated by 180 degrees. Another two phases are excited by a cosine wave signal to differentially take out the secondary coil output, and the relative secondary coil differential output signals are added and synthesized to obtain the phase-shifted output signal. The piston rod position detecting device according to claim 23.