JPH0226004Y2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field This invention relates to a phase shift type linear position detection device.

Prior Art A differential transformer is a conventionally known linear position detection device, but since it converts a linear position into a voltage level, it has the disadvantage of being easily affected by external disturbances and causing errors. There is.

In view of this, the present applicant has filed an earlier application (in practice) to construct a linear position detection device using a phase shift type detection device, which is capable of accurate detection without being affected by output level fluctuations caused by disturbances, etc. Gansho 57-
32127). The linear position detection device disclosed in this prior application includes a plurality of primary coils arranged in a predetermined arrangement and shifted in a linear displacement direction, a secondary coil corresponding to the primary coil, and a secondary coil of these primary coils. and a core portion disposed so as to be linearly displaceable relative to the secondary coil, and each of the primary coils is excited by a plurality of phase-shifted reference AC signals, whereby the An output signal obtained by shifting the phase of the reference AC signal according to the relative linear position of the core portion is generated in the secondary coil. In this case, the core section has a plurality of cylindrical magnetic cores of a predetermined length arranged at predetermined intervals via non-magnetic spacers, and the reluctance change is determined by one pitch of the core arrangement. is produced in the coil in response to relative linear displacement. A phase shift of one cycle (2π) is performed for each cycle of reluctance change. Therefore, the amount of phase shift in the output signal indicates an absolute value within the range of linear displacement of one period (one pitch of the core).

By the way, in the above-mentioned prior art, the length of one cylindrical core cannot be made longer than the length of the coil, and when the length of the cylindrical core, the length of the spacer, and the coil length are equal, the absolute detection range for one cycle can be maximized. It could only be set to . That is, one cycle of the absolute detectable range is limited to twice the length of the coil, and in order to expand that range, the length of the coil must be extended. However, unnecessarily increasing the coil length is not a good idea in terms of cost and equipment scale.

Purpose of the invention This invention was made in view of the above points.
It is an object of the present invention to provide a phase shift type linear position detection device that can expand one cycle of the absolute linear position detectable range without unnecessarily increasing the coil length.

Summary of the invention The above object can be achieved by using a core whose cross-sectional area increases or decreases continuously or stepwise in the direction of linear displacement.

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

In FIG. 1, the detection head section 1 includes a primary coil and a secondary coil housed in a casing 4 in a predetermined arrangement, and a long rod-shaped core inserted into these coils so as to be relatively linearly movable. Part 2 is included. The core portion 2 includes a non-magnetic sleeve 6 and a magnetic core 3 housed within the sleeve 6. The core 3 is formed by forming a plurality of conical or truncated conical tapered portions 3a, 3b, . . . alternately and in opposite directions at a constant pitch along the axial direction (relative linear displacement direction). A first tapered portion 3a whose cross-sectional area gradually decreases over a constant length P/2 (P is an arbitrary constant), and a second tapered portion 3b whose cross-sectional area gradually increases over a constant length P/2. Together, they contribute to one cycle of trigonometric reluctance change. The length of the pair of tapered portions 3a and 3b is P. Such a length p
A plurality of taper sets are continuously formed in the axial direction as necessary. A linear displacement to be detected is applied to the core portion 2 or a casing 4 including a coil, and the core portion 2 is relatively displaced in accordance with this displacement to be detected.

In this embodiment, the coils are arranged to operate in four phases. For convenience, these phases are distinguished using symbols A, B, C, and D. Primary coils 7, 8, 9, 10 and secondary coils 11, 12, 13, 14 are provided individually for each phase A to D. The secondary coils 11 to 14 of each phase A to D are respectively wound outside (or inside or by bifilar winding) of the corresponding primary coils 7 to 10, respectively. The reluctance generated in each phase A to D is shifted by 90 degrees depending on the position of the core 3. For example, if phase A is a cosine phase, phase B is a sine phase, phase C is a minus cosine phase, and phase D is a sine phase. is becoming a negative sign phase. Therefore, each coil is provided in the order of A, B, C, and D phases at a predetermined interval "P(n+1/4)" (where n is any natural number, preferably 0). The length of each coil is unrelated to one pit P of the tapered core 3 and can be arbitrarily selected.

Each phase A to D according to the relative linear displacement of the core part 2.
The reluctance of the magnetic circuit in the tapered part 3
Change with one pitch length P of a, 3b as one period,
Moreover, since each phase is provided at an interval of P/4, the phase of the reluctance change is shifted by 90 degrees for each phase (therefore, the phase A and C are shifted by 180 degrees, and the phase B
Even the phase and D phase are shifted by 180 degrees).
Therefore, the coil arrangement of each phase A to D is not limited to that shown in FIG. 1 as long as it brings about such a reluctance change.

The connection format of the primary coils 7 to 10 and the secondary coils 11 to 14 in FIG. 1 is as shown in FIG. 2, as an example. In this wiring type, one of the A phase and C phase
The secondary coils 7 and 9 are excited in the same phase by the sine signal sinωt, and the secondary coils 11 and 13 are connected in opposite phases.
In addition, the primary coils 8 and 10 of the B phase and D phase are excited in the same phase by the cosine signal cosωt, and the secondary coil 1
2 and 14 are connected in reverse phase. A, C phase pair and B, D
The sum of the phase pair secondary coil outputs becomes the output signal Y of the detection head section 1. This output signal Y
is obtained by shifting the reference AC signal (sinωt or cosωt) by a phase angle φ corresponding to the relative linear position x of the core portion 2. The reason is that each phase A~
This is because the reluctances of D are shifted by 90 degrees, and the electrical phases of the excitation signals of one pair (A, C) and the other pair (B, D) are shifted by 90 degrees. This point can be expressed briefly as follows.

That is, if the phase corresponding to the relative linear position of the core portion 2 is φ, the function of reluctance change according to the linear position is cosφ for the A phase, sinφ for the B phase,
The C phase can be expressed as -cosφ and the D phase as -sinφ. The A and C phases are operated in opposite phases to each other by a sine signal sinωt, and the B and D phases are operated in opposite phases to each other by a cosine signal cosωt, and the resulting secondary coil output is additively Therefore, the output signal Y can be substantially expressed in the following informal formula.

Y=sinωtcosφ−(−sinωtcosφ) +cosωtsinφ−(−cosωtsinφ) =2sinωtcosφ+2cosωtsinφ =2sin(ωt+φ) If we replace the coefficient indicated as “2” in the above formula with a constant K determined according to various conditions, we get It can be expressed as Y=Ksin(ωt+φ). Here, since the phase φ of the reluctance change is proportional to the relative linear position x of the core part 2 according to a predetermined proportionality coefficient (or function), the reference signal sinωt (or cosωt) in the output signal Y
The linear position x can be detected by measuring the phase shift φ from . However, the phase shift φ
When the full width is 2π, the amount of linear displacement is the aforementioned distance P(1
This corresponds to the length of the set of tapered portions 3a and 3b). That is, according to the electrical phase shift amount φ in the signal Y, an absolute linear position within the range of the distance P can be detected. Tapered parts 3a, 3b
If a plurality of taper sets are formed in succession, absolute linear position detection can be performed within the range of the length P for each taper set. At that time, if you want to find the absolute linear position for one period or more, use any appropriate means (the detection accuracy may be coarse with distance P as one unit) and use the absolute address of each taper set. It is sufficient to determine this by a combination of the absolute address of each taper set and the absolute linear position within one period based on the above-mentioned phase shift φ. By measuring the electrical phase shift φ, it is possible to accurately determine the absolute linear position within the range of distance P with fairly high resolution. It is also clear that fluctuations in the signal level due to disturbances etc. do not affect the phase shift amount φ at all.

Output signal Y of detection head section 1 and reference AC signal
The means for determining the phase shift φ from sinωt (or cosωt) can be constructed as appropriate. Figure 3 shows the phase shift φ
This figure shows an example of a circuit in which the equation is calculated using a digital quantity. Although not particularly shown, an integration circuit is used to generate a reference AC signal sinωt and an output signal Y=Ksin(ωt+
By finding the time difference of 0 phase with φ),
It is also possible to obtain the phase shift φ using an analog quantity.

In FIG. 3, the oscillation unit 32 is a reference sine signal.
A circuit for generating sinωt and a cosine signal cosωt, and a phase difference detection circuit 37, is a circuit for measuring the phase shift φ. Clock pulses CP generated by a clock oscillator 33 are counted by a counter 30. The counter 30 is, for example, Modillo M,
The count value is given to register 31. From the 4/P frequency-divided output of the counter 30, a pulse Pc obtained by dividing the clock pulse CP by 4/M is taken out and applied to the C input of a flip-flop 34 for 1/2 frequency division. The pulse Pb output from the Q output of this flip-flop 34 is applied to the flip-flop 35,
The pulse Pa from the Q output is the flip-flop 3
6, and the outputs of these 35 and 36 pass through low-pass filters 21, 22 and amplifiers 23, 24 to obtain a cosine signal cosωt and a sine signal sinωt. The M count in the counter 30 corresponds to the phase angle of 2π radians of these reference signals cosωt and sinωt. That is, one count value of the counter 30 indicates a phase angle of 2π/M radians.

The output signal Y of the detection head section 1 is applied to a comparator 26 via an amplifier 25, and the positive and negative signals of the signal Y are
A square wave signal corresponding to the negative polarity is applied to the comparator 26.
is output from. In response to the rise of the output signal of the comparator 26, the rise detection circuit 28 outputs a pulse Ts, and the count value of the counter 30 is loaded into the register 31 in response to this pulse Ts. As a result, the digital value according to the phase shift φ
Dφ is taken into register 31.

Note that the shape of the core 3 is not limited to a tapered shape in which the cross-sectional area gradually decreases and increases gradually, but may be a shape in which the cross-sectional area gradually decreases and increases gradually. Moreover, the core part 2 may be located between the coil ends of the primary coil and the secondary coil, without arranging the coils concentrically with the core part 2.

Effects of the invention As explained above, according to this invention, a core with a shape in which the cross-sectional area gradually decreases and gradually increases is repeated one or more times, so that the phase shift type linear position can be adjusted without increasing the coil length unnecessarily. This provides an excellent effect in that one cycle of the absolute detection range of the detection device can be expanded.

[Brief explanation of the drawing]

FIG. 1 is an axial sectional view showing an embodiment of the detection head used in the linear position detection device according to this invention, FIG. 2 is a circuit diagram showing an example of the coil connection type in the same embodiment, and FIG. 2 is a block diagram showing an example of a circuit for supplying a reference AC signal to the detection head section of FIG. 1 and a circuit for measuring a phase shift of an output signal; FIG. DESCRIPTION OF SYMBOLS 1...Detection head part, 2...Core part, 3...Core, 3a, 3b...Tapered part, 4...Casing, 6...Sleeve, 7-10...Primary coil,
11-14... Secondary coil, 32... Oscillation section, 3
7...Phase difference detection circuit.

Claims (1)

[Claims for Utility Model Registration] A core arranged so as to be relatively displaceable in a linear direction and whose cross-sectional area gradually decreases and gradually increases by the same distance (P/2) along the linear direction. A magnetic core having a predetermined pitch P and a predetermined phase difference other than 180° or 360° (360°/D)
individually excited by a reference AC signal having
A predetermined distance P×{n±(1/
D) At least two primary coils provided around the magnetic core and separated from each other by a distance n (where n is an arbitrary integer); A phase shift type linear position detection device comprising: a secondary coil that detects an output signal whose phase is shifted by a change in reluctance that occurs in response to the relative displacement of the core in the linear direction.