Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
2000-08-09
2002-08-20
Williams, Hezron (Department: 2856)
Measuring and testing
Vibration
By mechanical waves
C073S662000, C073S668000, C310S321000
Reexamination Certificate
active
06435031
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a lift cylinder (a hydraulic cylinder) in a fork lift, and in particular to a technology for detecting a position of a piston in the lift cylinder.
2. Description of the Related Art
In general, a lift cylinder (a hydraulic cylinder) is installed in a fork lift to move a fork upwardly and downwardly. By reciprocating a piston rod in the lift cylinder, the fork is moved upwardly and downwardly. Hence, in a case where various controls are applied to the fork in the fork lift having the lift cylinder, the upwardly and downwardly moved positions and upwardly and downwardly moving speeds of the fork are detected by measuring a position and a moving speed of the piston rod (the piston) of the lift cylinder,
As means for detecting the position or the moving speed of the piston of the lift cylinder, an ultrasonic wave sensor is typically used. An example of the lift cylinder using such ultrasonic wave sensor is described in Japanese Patent Laid-Open No. 10-238513. An arrangement of the lift cylinder described in this publication will be briefly described with reference to FIG.
10
.
As shown in
FIG. 10
, a lift cylinder (a single action type piston cylinder)
50
is provided with a cylinder tube
52
, a cylinder block
53
, a piston rod
51
, a piston
54
movable integrally with the piston rod
51
, and so on. A hydraulic oil is filled in the lift cylinder
50
as a power medium for the piston rod
51
.
A ultrasonic wave sensor
55
is disposed so that a transmitter and receptor side thereof is confronted with a bottom surface
54
a
of the piston
54
. The ultrasonic wave sensor
55
is provided with a vibration element
60
, a case member
61
supporting the vibration element
60
and a cap member
62
covering the vibration element
60
. The cap member
62
is made of metal such as iron,aluminum or the like for the purpose of protecting the vibration element
60
. The vibration element
60
is generally provided with a backing member
63
for absorbing vibration generated in its back side.
The ultrasonic wave sensor
55
is designed to be a single device for conducting both of transmission and reception of the ultrasonic wave. Accordingly, the ultrasonic wave generated from the vibration element
60
is transmitted from a surface of the cap member
62
, for example, along a passage indicated by two-dotted chain line
70
in
FIG. 10
(hereafter, referred to as “transmitted wave”), reflected by the bottom surface
54
a
of the piston
54
, and thereafter received along a passage indicated by two-dotted chain line
71
(hereafter, referred to as “received wave”). An electric signal corresponding to the ultrasonic wave received by the vibration element
60
is outputted through a wiring
58
to a transmission/reception circuit
56
and a control device
57
.
The position of the piston
54
of the lift cylinder
50
is detected by measuring a time period required for reciprocating the ultrasonic wave between the ultrasonic wave sensor
55
and the bottom surface
54
a
of the piston
54
, i.e., a delayed time of the received wave with respect to the transmitted wave (hereafter, referred to as “a measurement time length”). The position of the piston
54
thus detected can be used, for instance, for various controls regarding the fork of the fork lift.
The lift cylinder
50
provided with the ultrasonic wave sensor
55
for detecting the position of the piston
54
as described above is hardly affected by an environment use condition, and is remarkably effective in consecutively detecting the position of the piston
54
with ease.
However, the ultrasonic wave generated from the vibration element
60
contains an indirectly transmitted wave, i.e. a surface wave, (for example, a wave that is transmitted through an inner wall surface of the cylinder tube
52
along a passage indicated by two-dotted chain line
72
or
73
in FIG.
10
). Since the surface wave indirectly transmitted through the inner wall of the cylinder tube
52
in this manner is detected as a reverberation by the ultrasonic wave sensor
55
, the measurement accuracy of the measurement time length may be lowered. This phenomenon is explained in more detail with reference to
FIGS. 10 and 11
.
FIG. 11
shows an example of wave forms of the transmitted wave and the received wave.
In
FIG. 10
, it is known that the surface wave transmitted along the passage indicated by the two-dotted chain line
72
or
73
is generally faster than the transmitted and received waves transmitted along the passages of the two-dotted chain lines
70
and
71
. For this reason, as shown in
FIG. 11
, the surface wave faster in transmission is detected as the reverberation prior to the received wave transmitted along the passage
71
indicated by the two-dotted chain line
71
to interfere with the received wave. Accordingly, it is difficult to obtain an accurate measurement time length.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a position detecting device for a hydraulic cylinder and an industrial vehicle equipped with the position detecting device, which can obtain an accurate measurement time length by reducing a reverberation that may interfere with transmitted and received waves transmitted directly.
A position detecting device for a hydraulic cylinder according to the present invention is a hydraulic cylinder position detecting device for detecting a position of a piston with a ultrasonic wave, the piston being movable within a cylinder, the detecting device including a ultrasonic wave sensor provided within the cylinder for transmitting the ultrasonic wave toward the piston and receiving the ultrasonic wave reflected by the piston, and an anti-vibration member for suppressing a vibration caused by an ultrasonic wave transmitted indirectly between the ultrasonic sensor and the piston.
Here, terms used in claims and the detailed description of the invention are interpreted as follows:
(1) The “piston” includes not only a type in which a movable member is slid within a cylinder (a so-called piston type cylinder) but also a type in which a clearance is formed between a movable member and an inner surface of a cylinder, such as a ram (protruded bar) of a ram type cylinder.
(2) The “indirectly” means using a medium other than a power medium (such as a hydraulic oil) of a cylinder during process in which a transmitted wave generated from an ultrasonic wave sensor is reflected by a piston and then received by the ultrasonic wave sensor. For example, the transmission along the passages indicated by the two-dotted chain lines
72
and
73
in
FIG. 10
used for the explanation of the conventional lift cylinder is encompassed by the definition of the “indirectly” since the transmitted and received waves use the inner wall surface of the cylinder tube as a medium. In contrast, the transmission along the passages indicated by the two-dotted chain lines
70
and
71
is defined as the “directly” and is not encompassed by the “indirectly”. The detection of the transmitted and received waves transmitted along a passage encompassed by the “directly” makes it possible to obtain an accurate measurement time length.
(3) The “anti-vibration member” is met as long as it suppresses a vibration caused by a ultrasonic wave (i.e., it is high in attenuation effect or absorbing effect), and includes not only members made of resin (such as polyphenylene sulfide (PPS) resin) but also members of various materials (such as FRP (fiber-reinforced plastic) material).
(4) The “grooved portion” is met as long as it has a recessed portion or a protruded portion, and includes various recesses or protrusions other than a planar surface. For example, not only linear, spiral and circular recesses but also protruded shapes or the like fall within the “grooved portion”.
(5) The “industrial vehicle” means a vehicle which is provided with a hydraulic cylinder and which is provided with a member moved by driving of the hydraulic cylinder, and includes not only a for
Kabushiki Kaisha Toyoda Jidoshokki Seisakusho
Morgan & Finnegan , LLP
Saint-Surin Jacques
Williams Hezron
LandOfFree
Position detecting device for hydraulic cylinder, and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Position detecting device for hydraulic cylinder, and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Position detecting device for hydraulic cylinder, and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2952028