JP3060845B2 - Displacement detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a displacement detecting device, and more particularly, to a displacement detecting device for detecting a displacement using a magnetostriction phenomenon.

[0002]

2. Description of the Related Art Conventionally, there is a displacement detecting device for detecting a displacement amount using a magnetostriction phenomenon. For example, JP-A-55-66
No. 710 discloses a structure in which a permanent magnet is displaced with respect to a magnetostrictive wire. An excitation pulse is applied to the magnetostrictive wire, and two flip-flops are set. The ultrasonic waves are detected by a pair of receiving means provided at both ends of the magnetostrictive wire, and the two flip-flops corresponding to each are separately reset, and the magnetostriction is detected from the difference between the pulse widths of the pulses output from the two flip-flops. The displacement of the permanent magnet with respect to the line is detected.

[0003]

The conventional device requires a pair of detecting means and two flip-flops in order to compensate for a change in the magnetostriction propagation speed depending on the ambient temperature. There was a problem.

[0004] The present invention has been made in view of the above points,
Provided is a displacement detection device that requires a small number of circuit components and has a simple configuration by detecting a magnetostriction signal due to an interaction between a current pulse supplied to a magnetostrictive wire, a permanent magnet, and a current pulse with a single detection coil. With the goal.

[0005]

According to the first aspect of the present invention,
It is made of magnetostrictive material and heated to cover the outer peripheral surface with an oxide film for insulation.
A film is formed, a magnetostrictive wire disposed in a cylinder formed of a conductive material, a current pulse generator that supplies a current pulse to the magnetostrictive wire, and a relative displacement with respect to the magnetostrictive wire. A permanent magnet that intersects the magnetostrictive wire with a static magnetic field, a detection coil disposed at a predetermined position of the magnetostriction wire, a current pulse detected by the detection coil, and an interaction between the permanent magnet and the current pulse. And a detection circuit that detects a time difference between the detection coil and the permanent magnet and detects a displacement of a distance between the detection coil and the permanent magnet.

[0006]

[0007] In the second aspect of the present invention, the cylindrical body is
The permanent magnet is provided inside an absorber rod of the shock absorber, and the permanent magnet is fixed to an absorber cylinder of the shock absorber, has a soft magnetic material sandwiching both poles of the permanent magnet, and measures the vehicle height of the vehicle.

[0008]

According to the first aspect of the present invention, since the detection coil detects the current pulse of the magnetostrictive wire and the magnetostriction signal, only one detection coil is required and the number of circuit components is small.
The configuration becomes simple. Also, an oxide film is formed on the magnetostrictive wire.
By doing so, insulation from the cylinder can be achieved, and the magnetic
The space for disposing the strain wire can be reduced, and the
Heating can also reduce the processing strain of the magnetostrictive wire.

[0009]

According to the second aspect of the present invention, by sandwiching both poles of the permanent magnet with the soft magnetic material, the magnetic flux from the permanent magnet is intensively emitted toward the cylinder, and the absorber rod is made of a magnetic material. Also, the magnetic field of the permanent magnet can effectively cross the magnetostrictive line.

[0011]

FIG. 2 is a block diagram showing an embodiment of the apparatus according to the present invention. In this embodiment, a displacement detecting device is applied to a shock absorber of an air suspension as a vehicle height sensor.

In FIG. 1, a main air chamber 12 and a sub air chamber 13 for filling high-pressure air are formed between an absorber cylinder 11 and a suspension tower (not shown). Since the absorber cylinder 11 moves up and down,
The main air chamber 12 and the absorber cylinder 11 are connected by a diaphragm 15 formed of a flexible resin.

The damping force control of the shock absorber is performed by switching a variable orifice provided in the piston 20. Oil in the upper and lower chambers in the absorber cylinder 11 partitioned by the piston 20 moves through the variable orifice as the absorber cylinder 11 moves up and down, thereby generating a damping force. Therefore, the diameter of the orifice is varied to increase or decrease the damping force.

The damping force switching mechanism includes an absorber rod 22
The diameter of the orifice is switched by rotating the control rod 23 disposed therein. For this reason, a damping force switching actuator 25 is provided above the absorber rod 22.

A cylindrical body 27 having a magnetostrictive wire 26 is provided inside the absorber rod 22. Cylinder 2
7, a current pulse generator 28 is provided, and the generated current pulse is supplied to the magnetostrictive wire 26. A ring-shaped permanent magnet 30 is disposed and fixed above the absorber cylinder 11 in a state of being inserted into the absorber rod 22. Further, a detection coil 31 is disposed around the magnetostrictive wire 26 at an end of a cylindrical body 27 having a magnetostrictive wire 26 on the side where the current pulse generator 28 is provided.

Here, when the vehicle height changes and the capacity of the main air chamber 12 changes, the piston 20 moves up and down in the absorber cylinder 11 at the same time.
The length of the magnetostrictive line 26 from 1 to the permanent magnet 30 changes.

The magnetostrictive wire 26 is made of a soft magnetic material whose main component is Fe-Ni or Fe-Co and whose density change with temperature is extremely small. In particular, Ni45-50-Fe is -1.
The coefficient of thermal expansion is substantially constant in the temperature range of 00 to 400 ° C., and the change in the magnetostriction transmission speed is extremely small.

As shown in FIG. 3A, the magnetostrictive wire 26 is disposed in a cylinder 27 made of a conductive non-magnetic material, and connects one end 26a of the magnetostrictive wire 26 and one end 27a of the cylinder 27 to each other. The pulse generator 28 is connected between the other end 26b of the magnetostrictive wire 26 and the other end 27b of the cylindrical body 27 to supply a current pulse to the magnetostrictive wire 26. It is necessary to provide insulation between the two parts except for one ends 26a and 27a.

For this reason, as shown in FIG.
An oxide film 40 is formed on the outer peripheral surface of 6 to perform insulation. If cold working is performed at the time of manufacturing the magnetostrictive wire 26, working strain is generated, and the magnetostrictive effect is reduced. The oxide film 40 is simultaneously formed at the time of annealing to remove the processing strain, and the processing strain is also reduced.
Since it is not necessary to separately provide an insulating material for the magnetostrictive wire 26 on which the oxide film 40 is formed, the space for accommodating the magnetostrictive wire of the cylindrical body 27 can be reduced, and as shown in FIGS. It is also possible to adopt a structure in which 26 is embedded in a part of the cylindrical body 27.

The permanent magnet 30 is provided to cross the static magnetic field with the magnetostrictive wire 26.
As shown in FIG. 1A, an absorber rod 2 made of a magnetic material is provided between a permanent magnet 30 and a cylindrical body 27 having a magnetostrictive wire 26 therein.
There are two. In this case, most of the magnetic flux from the permanent magnet 30 along the longitudinal direction of the absorber rod 22 forms a magnetic loop passing through the absorber rod 22 having a small magnetic resistance. You just have to.

Therefore, as shown in FIG.
0 are sandwiched between the soft magnetic materials 33 and 34. As a result, most of the magnetic flux of the permanent magnet 30 exits from the soft magnetic materials 33 and 34 in the axial direction of the absorber rod 22 and forms a magnetic loop passing through the absorber rod 22 facing the soft magnetic materials 33 and 34. 34, a large amount of magnetic flux leaks and the magnetic field of the permanent magnet is effectively
7 can be crossed. Thereby, the magnetostrictive wire 26
Can be increased, and the level of the magnetostriction signal detected by the detection coil 31 increases.

When the current pulse generated by the current pulse generator 28 is supplied to the magnetostrictive wire 26, a local magnetic field in the circumferential direction is formed on the magnetostrictive wire 26 by the current pulse.
As the current pulse instantaneously propagates below the magnetostrictive line 26 in the axial direction, the circumferential magnetic field is generated in the axial direction. When the current pulse passes through the installation position of the detection coil 31, an electromotive force is generated in the detection coil 31.

When the circumferential magnetic field collides with the axial magnetic field generated by the permanent magnet 30, a combined magnetic field is formed in the direction in which the magnetostrictive wire 26 is twisted. The magnetostrictive material has a physical property that, when a magnetic field is applied, a strain is generated in a direction of a magnetic force line, and when a mechanical strain is applied, the material is magnetized in the strain direction. For this reason, a mechanical torsion occurs in the magnetostrictive wire 26 at the position where the permanent magnet 30 is arranged, and the mechanical torsion propagates on the magnetostrictive wire 26 in the vertical direction of the absorber rod 22 along with the magnetization of the magnetostrictive wire 26, and the detection coil 31 is reached. An electromotive force is generated in the detection coil 31 by magnetization accompanying the mechanical torsion of the magnetostrictive wire 26.

FIG. 1 shows a circuit diagram of an embodiment of the detection circuit. In the figure, in parallel with the detection coil 31 resistance R ₁ and a capacitor C ₁ are connected to form an oscillation circuit. When a current pulse is applied to the magnetostrictive wire 26, an induced electromotive force of the first derivative of the current pulse is generated in the detection coil 31, and the magnetostrictive wire 2
An induced electromotive force is generated due to the mechanical torsion of No. 6.

The induced electromotive force of the detection coil 31 is expressed by the following equation.

[0026]

(Equation 1)

Here, a ₁ and a ₂ are the inner radius and the outer radius of the coil, L is the coil length, N is the total number of turns, m is the magnetization amount, and V is the magnetostriction transmission speed.

Thus, the output signal of the buffer 40 obtained by amplifying the output voltage of the oscillation circuit becomes as shown in FIG. Here, P1 is a detection signal of a current pulse, and P2 is a detection signal of a mechanical twist.

The detection signal a shown in FIG. 5A is compared with a reference value in a comparator 41 and shaped into a pulse signal b shown in FIG. 5B. The pulse signal b is frequency-divided by 1/2 by a T-type flip-flop configured by feeding back the output of the Q terminal of the D-type flip-flop 42 to the data input terminal D to obtain a pulse signal C shown in FIG. The pulse signal C is a pulse that falls at the time of the detection signal P1 and rises at the time of the detection signal P2.

The pulse signal c is supplied to the base of the transistor 43. The transistor 43 cuts off during the low level period of the pulse signal c, and the capacitor C ₂ is charged with the time constant C ₂ · R ₂ through the resistor R ₂ . Thus, as shown in FIG. 5D, the collector voltage of the transistor 43 increases as the low-level period of the pulse signal c increases. At the same time, the pulse signal c includes the capacitor C ₃ and the diode D ₁
When the resistance R ₃ and are supplied to a differential circuit composed of a rising edge pulse e shown in FIG. 5 (E) detects a rise of the pulse signal c is generated.

The FETs 44 and 45, the capacitor C ₄ ,
Sample-and-hold circuit is constituted by the resistor R ₄ and the buffer 46. At the time of occurrence of the rising edge pulse e, the sample and hold circuit samples and holds the collector voltage of the transistor Q as shown in FIG. That is, the hold voltage is equal to the detection signal P1.
To a detection signal P2.

As described above, in this embodiment, since the detection coil 31 detects the current pulse and the magnetostrictive signal, there is no delay between the supply of the current pulse to the magnetostrictive wire and the generation of the ultrasonic wave, and the circuit The number of components is smaller than before, and the configuration is simplified.

[0033]

As described above, according to the first aspect of the present invention, since the detection coil detects the current pulse of the magnetostrictive wire and the magnetostriction signal, only one detection coil is required, and the number of circuit components is small. And the configuration becomes simple.

According to the second aspect of the present invention, by forming an oxide film on the magnetostrictive wire, it is possible to insulate the magnetostrictive wire from the cylindrical body and to reduce the space for disposing the magnetostrictive wire in the cylindrical body. In addition, the processing distortion of the magnetostrictive wire can be reduced by heating when forming the oxide film.

According to the third aspect of the present invention, by sandwiching both poles of the permanent magnet with the soft magnetic material, the magnetic flux from the permanent magnet is intensively directed toward the cylinder, and the absorber rod is made of a magnetic material. However, the magnetic field of the permanent magnet can effectively cross the magnetostrictive wire, the mechanical distortion of the magnetostrictive wire due to the magnetostriction phenomenon can be increased, and the level of the magnetostrictive signal detected by the detection coil increases. Useful.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a detection circuit of the device of the present invention.

FIG. 2 is a configuration diagram of the device of the present invention.

FIG. 3 is a diagram for explaining a magnetostrictive line of the device of the present invention.

FIG. 4 is a diagram for explaining a permanent magnet and a soft magnetic material of the device of the present invention.

FIG. 5 is a signal timing chart of each section of the circuit of FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Absorber cylinder 12 Main air chamber 13 Sub air chamber 20 Piston 22 Absorber rod 23 Control rod 25 Actuator 26 Magnetostrictive wire 27 Cylindrical body 28 Current pulse generator 30 Permanent magnet 31 Detection coil 33, 34 Soft magnetic material 40 Oxide film

Claims (2)

(57) [Claims] 1. An outer peripheral surface made of a magnetostrictive material and heated to
Oxidation film for insulation is formed and made of conductive material
A magnetostrictive wire disposed in the cylindrical body, a current pulse generator for supplying a current pulse to the magnetostrictive wire, and a permanent displacement relative to the magnetostrictive wire to intersect a static magnetic field with the magnetostrictive wire. A magnet, a detection coil disposed at a predetermined position on the magnetostrictive wire, a time difference between a current pulse detected by the detection coil, and a magnetostriction signal due to an interaction between the permanent magnet and the current pulse. A displacement detection device comprising a detection circuit for detecting a displacement of a distance between a detection coil and a permanent magnet. 2. The shock absorber of claim 1, wherein the cylinder is a shock absorber.
The permanent magnet is provided inside a sober rod,
Fixed to the shock absorber cylinder of the shock absorber
2. The vehicle according to claim 1 , further comprising a soft magnetic material sandwiching both poles of the permanent magnet, and measuring a vehicle height of the vehicle.
Displacement detector.