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| United States Patent | 5198761 |
| Link to this page | http://www.wikipatents.com/5198761.html |
| Inventor(s) | Hashimoto; Hisayoshi (Ushiku, JP);
Tamura; Morio (Tsuchiura, JP);
Ichiryuu; Ken (Ibaraki, JP) |
| Abstract | A piston cylinder device having a piston stroke measurement includes a
cylinder tube (1) having an inner tube (2) made of a nonmagnetic material
and an outer tube (3) formed on the outer peripheral surface of the inner
tube and made of a fiber-reinforced resin material. A piston (76) fixed to
a rod (75) is disposed slidably inside the cylinder tube. A stroke
detector is composed of a position indicating magnet (80) disposed in the
piston and an elongated sensor (81) disposed in the cylinder tube. The
elongated sensor includes a thin elongated pipe (82) extending along the
cylinder tube between both of its ends and holds at least one
magnetostriction line (87) having a large magnetostriction coefficient, a
driving coil (84) wound on at least one of the ends of the thin elongated
pipe. A pulsed input current to the drive coil causes magnetostriction
phenomenon on the magnetostriction line generating an ultrasonic wave. A
detecting coil (86) wound on the thin elongated pipe in a predetermined
length separately from the driving coil induces a detection signal
generated by reverse magnetostriction when the ultrasonic wave passes by
the position of the magnetostriction line corresponding to the position
indicating magnet. Also, at least one pin-like magnet (20A, 42A) for
correcting a measurement error due to a temperature change of the stroke
detector, and disposed at a position adjacent to the detecting coil (86)
and more inward in the axial direction than both ends of the detection
coil are fixed to both ends of the cylinder tube (1). |
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Title Information  |
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| Publication Date |
March 30, 1993 |
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| Filing Date |
February 28, 1991 |
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Title Information |
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Claims |
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What is claimed is:
1. A cylinder apparatus made of a composite material comprising a cylinder
tube having an inner cylinder made of a non-magnetic material and an outer
cylinder formed on the outer periphery of said inner cylinder and made of
a fiber-reinforced resin material, a piston slidably disposed in said
cylinder tube, a rod having one end fixed to said piston and the other end
outwardly projecting from said cylinder tube, a stroke sensor for
detecting the stroke of said piston, said stroke sensor comprising a
position indicating magnet provided on said piston and elongated sensor
means provided on said cylinder tube, said elongated sensor means having a
thin elongated tube extending along said cylinder tube between both ends
thereof and containing at least one magnetostriction string having a large
coefficient of magnetostriction, a drive coil wound on at least one of
both ends of said thin elongated tube for producing magnetostriction
phenomenon in said magnetostriction string for generating an ultrasonic
wave when a pulsatile input current is applied thereto, a detection coil
wound over a predetermined length of said thin elongated tube separately
from said drive coil for detecting as a detection signal the induced
electromotive force generated by the inverse magnetostriction phenomenon
when said ultrasonic wave is passed through the position of said
magnetostriction string corresponding to said position indicating magnet,
and
at least one pin-like magnet for correcting a measurement error due to a
change in temperature of said stroke sensor, said at least one pin-like
magnet being provided at each of positions axially inward of both ends of
said detection coil and adjacent both ends of said cylinder tube.
2. A composite material cylinder apparatus according to claim 1, wherein
said pin-like magnet is provided as a radial protrusion on each of two
mount members fitted to the opposite axial ends of said inner cylinder,
and said outer cylinder is formed by winding a fibrous material
impregnated with a resin on the outer periphery of said inner cylinder
while guiding it by said radial protrusion.
3. A cylinder apparatus made of a composite material according to claim 1,
wherein said elongated sensor means is interposed between said inner
cylinder and said outer cylinder.
4. A cylinder apparatus made of a composite material according to claim 1,
wherein said elongated sensor means is disposed on the outer periphery of
said outer cylinder, and a protective layer made of an elastic material is
further coated on the outside of said sensor means.
5. A cylinder apparatus made of a composite material according to claim 2,
wherein at least one other radial protrusion is further provided on at
least one of said two mount members for guiding said fibrous material,
said other protrusion comprising electrode means for leading out lead
wires of said drive coil and said detection coil to the outside.
6. A cylinder apparatus made of a composite material according to claim 1,
wherein said magnetorestriction string contains a plurality of amorphous
wires.
7. A cylinder apparatus made of a composite material according to claim 2,
wherein said elongated sensor means is interposed between said inner
cylinder and said outer cylinder.
8. A cylinder apparatus made of a composite material according to claim 2,
wherein said elongated sensor means is disposed on the outer periphery of
said outer cylinder, and a protective layer made of an elastic material is
further coated on the outside of said sensor means.
9. A cylinder apparatus made of a composite material according to claim 2,
wherein said magnetostriction string contains a plurality of amorphous
wires. |
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Claims |
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Description |
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TECHNICAL FIELD
The present invention relates to a cylinder apparatus made of a composite
material comprising a cylinder tube made of a nonmagnetic material
consisting of a fiber-reinforced resin material, and particularly to a
cylinder apparatus made of a composite material comprising a stroke sensor
for detecting the stroke of a piston.
BACKGROUND ART
Conventional stroke sensors of cylinder apparatuses made of a composite
material comprise a stroke sensor disclosed in JP, A, 63-238415 which
employs the magnetostriction effect. This stroke sensor has a cylinder
tube comprising an inner cylinder made of a nonmagnetic material and an
outer cylinder formed by winding a fiber material consisting of a strand
of continuous filaments impregnated with a resin on the outer periphery of
the inner cylinder. A position indicating magnet is provided on the piston
which is slidably disposed in the cylinder tube, and an elongated sensor
body, which employs the magnetostriction effect, is interposed between the
inner and outer cylinders of the cylinder tube. The sensor body comprises
a thin elongated tube containing an amorphous ribbon, a drive coil wound
at one end of the thin elongated tube for inducing the magnetostriction
phenomenon in the amorphous ribbon and generating an ultrasonic wave when
a pulsatile input current is applied to the thin elongated tube, and a
detection coil wound over a predetermined length of the thin tube for
detecting as a detection signal the induced electromotive force generated
by the inverse magnetostriction phenomenon when the ultrasonic wave passes
through a position of the amorphous ribbon, which corresponds to the
position indicating magnet. Because the time taken from the application of
the pulsatile input current to the detection of the detection signal
depends upon the piston stroke, the piston stroke can be detected by
measuring the time.
On the other hand, since the sonic speed of the ultrasonic wave generated
depends upon the temperature of the apparatus, an increase in oil
temperature of the cylinder apparatus causes changes in the sonic speed of
the ultrasonic wave and the above-described time and thus causes error in
the measurement. JP, A, 63-238415 therefore proposes temperature
compensation methods for correcting the measurement error produced. In a
first method, a fixed compensating magnet is embedded at a predetermined
position between the inner and outer cylinders, the induced electromotive
force, which is produced by the inverse magnetostriction phenomenon when
the ultrasonic wave passes through the fixed magnet, is detected as a
second detection signal, and the distance between the drive coil and the
fixed magnet is used as a reference distance for temperature compensation
so that the detection signal generated by the position indicating magnet
is corrected by using the reference distance and the time taken from the
application of the pulsatile input current to the detection of the second
detection signal. In a second method, one of two magnets, which are
disposed at both axial ends of the piston, is also used as a magnet for
indicating the position of the piston, the induced electromotive forces
obtained from the two magnets are detected as detection signals, and the
distance between the two magnets is used as a reference distance for
temperature compensation so that the detection signal generated from the
position indicating magnet is corrected by using the time difference
between the two detection signals and the reference distance.
However, the above-mentioned temperature compensation methods have the
following problems:
In the first method, although the distance between the detection coil and
the fixed compensating magnet is used as the reference distance, the
reference distance cannot be measured unless the positions of the
detection coil and the fixed magnet are determined. Since the drive coil
itself has a certain length, the position of the drive coil cannot be
correctly determined. Further, the fixed compensating magnet is disposed
on the outer surface of the inner cylinder formed, and the outer cylinder
is then formed thereon. However, the position of the fixed magnet is
easily shifted when a fiber material is wound for forming the outer
cylinder. In addition, since both the drive coil and the fixed magnet are
buried in positions between the inner and outer cylinders, the positions
of the drive coil and the fixed magnet cannot be seen from the outside
after the cylinder tube has been completely formed. For the above reasons,
the distance between the detection coil and the fixed magnet cannot be
accurately measured, and the accuracy of temperature compensation thus
deteriorates.
In the second method, although the distance between the two magnets
provided on the piston is used as the reference distance, the two magnets
cannot be seen from the outside after the piston has been incorporated in
the cylinder tube. Further, the accuracy of compensation increases with an
increase in the reference distance. In this method, however, because the
distance between the two magnets is short due to the short length of the
piston itself, it is impossible to ensure that the reference distance has
a sufficient length. For the above reasons, this method also has a problem
with respect to the low accuracy of temperature compensation.
Examples of prior art related to a cylinder, which is formed by winding a
strand of continuous filaments impregnated with a resin, include JP, A,
63-166522 and 63-249628.
It is an object of the present invention to provide a cylinder apparatus
made of a composite material comprising a stroke sensor which enables an
improvement in accuracy of temperature compensation for a change in
environmental temperature such as the oil temperature or the like and
which enables the precise measurement of the piston stroke.
DISCLOSURE OF THE INVENTION
In order to achieve the object, the present invention provides a cylinder
apparatus made of a composite material comprising a cylinder tube having
an inner cylinder made of a non-magnetic material and an outer cylinder
formed on the outer periphery of the inner cylinder and made of a
fiber-reinforced resin material, a piston slidably disposed in the
cylinder tube, a rod having an end fixed to the piston and the other end
outwardly projecting from the cylinder tube, and a stroke sensor for
detecting the stroke of the piston, the stroke sensor comprises a position
indicating magnet provided on the piston and elongated sensor means
provided on the cylinder tube, the elongated sensor means having a thin
elongated tube extending along the cylinder tube between both ends thereof
and containing at least one magnetostriction string having a high
coefficient of magnetostriction, a drive coil wound on at least one of
both ends of the thin elongated tube for producing magnetostriction
phenomenon for generating an ultrasoni | | |
