Note: Descriptions are shown in the official language in which they were submitted.
--1--
POSITION-SENSING CYLINDER
Background of the Invention
This invention relates to a hydraulic cylinder with a poten-
tiometric position-sensing transducer.
In hydraulic controls technology, it is often desirable to
obtain feedback signals representing the operating position of a
hydraulic cylinder. U. S. Patent No. 3,726,191 discloses one
solution to this problem. The '191 cylinder has a resistance and
conductor ele~ent support reciprocally received in a piston rod
bore. A conductive wiper assembly is carried for movement with
the piston and rod. However, the transducer construction of the
'191 patent requires a relatively large transducer cross section
which displaces a large volume of hydraulic fluid as the cylinder
rod moves with respect to the transducer assembly. The bore
required in the cylinder rod to accommodate such a transducer of
large cross section and to provide an e,cape path for displaced
hydraulic fluid is so large as to prevent its use in many hydrau-
lic cylinders where compact size is required. Furthermore, the
wiper contacts of the '191 patent are suspended in the fluid
escape path, allowing flow forces to vibrate or bend the contact
leaf, resulting in operating noise and loss of signal, respec-
tively. Finally, the element support is supported only at one
end by a plastic sealing element which is subject to mechanical
stress and failures.
Summary of the Invention
An advantage of the present invention is that it provides a
position-sensing cylinder with good immunity to electrical noise
caused by hydraulic flow-induced vibxation.
Another advantage of the present invention is that it pro-
vides a position-sensing cylinder with a potentiometer element
support with good rigidity and low cross-sectional area.
Another advantage of the present invention is that it pro-
vides a potentiometer support element which is mechanically
supported along the length of its engagement with the cylinder
rod bore.
A further advantage of the present invention is that it
provides a position-sensing cylinder with an improved fluid
pressure seal which is spaced apart from the potentiometer support
- and thus, not subject to mechanical stress caused by the support
-- 40 of the potentiometer support.
These and other advantages are achieved by the present
invention which provides a position-sensincJ c~linder with a T-
shaped potentiometer support with one end welded or fixed to a
hollow metallic terrninal which is press fitted into a fitting
which is threadably attached to one end of the cylinder housing.
A ceramic plug seals the interior of the terminal, but pro~ides
no support for and is separate from the support. Further support
for the potentiometer support is provided by the sliding engage-
ment between it and the wall of the rod bore within which the
potentiometer support reciprocates. A wiper carrier cooperates
with the bore wall and the potentiometer support to prevent fluid
flow in the ~icinity of the flexible wiper contacts.
Brief Description of the Drawings
FigO 1 is a cross-sectional view of the hydraulic cylinder
for the present invention.
Fig. 2 is a partial sectional view of a portion of appli-
cant's invention.
Fig. 3 is a view taken in the direction of arrows 3-3 of
Fig. 2.
Fig. 4 is a view taken in the direction of arrows 4-4 of
Fig. 2.
Fig. 5 is a top view of the terminal piece and the transducer
support of the invention.
Figs. 6a through 6d are unscaled sectional views taken in
the direction of arrows A-A, B-B, C-C and D-D, respectively, of
Fig. 5.
Fig. 7 is an end view of the wiper carrier of the invention.
Detailed Description
A fluid actuator or hydraulic cylinder 10 includes a housing
12 having a hollow cylindrical barrel portion 14 within which
reciprocates a piston 16 connected to a rod 18. A rod-receiving
cap 20 is threadably connected to an end of the housing 12. A
blind stepped bore 22 extends into the piston 16 and the rod 18.
As best seen in Fig. 2, the bore 22 has a large diameter
portion 24 with a snap ring groove 26 therein and an annular
ridge 28 at one end, a smaller diameter portion 30 and an annular
shoulder 32 extending therebetween.
The housing 12 includes a threaded axial bore 34 for thread-
ably receiving a steel outer transducer fitting 36. Fitting 36
includes a raised annular flange 38 for butting against a corres-
~llB~
1 ponding houslng shoulder 40. An O-ring 42 maintains a fluid~
tight seal be-tween the fitting 36 and the housing 12. Fitting 36
also includes a stepped axial bore 44 extending therethrough.
A steel terminal piece 46 is press fitted into the fitting
bore 44. Terminal 46 includes an annular groove 48 which receives
a back-up ring 50 and an O-ring 52 for maintaining a fluid seal
between the fitting 36 and the terminal 46. A portion of ceramic
material 54 is formed in the hollow interior of the terminal 46
to form a hermakic seal -therein. The terminal 46 is formed as a
separate piece from the ~itting 36 so that when the ceramic
material 54 is heated within the terminal 46, the fitting 36 is
not degraded by the high temperatures to which it would otherwise
be e~posed if the fitting 36 and the terminal 46 were a single
piece.
A steel support element 60 extends into the bore 22 from an
end 62 received by and welded to the terminal 46. Thus, the end
62 of the support 60 is rigidly supported with respect to the
housing 12 by metallic pieces 36 and 46, whereas other position-
sensing cylinders, such as described in U. S. Patent No. 3,726,191,
have supported the transducer support element by press fitting
the support into a plastic insulating sleeve, which is, in turn,received by a metallic threaded fitting. In this arrangement,
the transducer support is less rigidly supported at its supported
end and the plastic insulating material is subject to stress
failures, such as cracking, which then degrades its sealing
properties. Furthermore, in the instant invention, the ceramic
seal 54 is subject to very little mechanical stress caused by
suppoxting the support 60. Instead, the ceramic seal 54 need
only withstand the hydraulic pressures for which it is designed
to withstand, with the result that the instant invention has
increased integrity with respect to fluid pressure sealing.
The support 60 has a substantially T-shaped cross-sec~ion
(as best seen in Figs. 3 and 4) formed by a cross piece 64 away
from which perpendicularly extends a stiEfening ridge 66. The
side of cross piece 64, which is opposite the ridge 66, forms a
- planar support surface 68~ A circular edged notch 70 is formed
in the end 62 of support 60, as best seen in ~igs. 2 and 4.
The cross piece 64 and the ridge 66 divide the bore 22 into
three fluid chambers 65, 67 and 69, of which chambers 65 and 67
are visible in Fig. 2. As best seen in Figs. 2 a~ld 3, the curved
1 outer peripheral surfaces 59, 61 and 63 of the support 60 slidably
engage the wall of the bore 22. This engagement adds rigidity to
the support 60 and helps to prevent deformation of the support 60
and reduces vibration to which the support 60 would be subjec~ if
S it were cantilevered or supported merely at one end.
As best seen ln Figs. 5 and 6a-d, a resistance or potenti-
ometer assembly 72 is placed on the planar support surface 68 of
the cross piece 64. The assembly includes an electrically insu]-
ating base 74 fixed to the support surface 68 and which may be
formed of material such as "Kapton", a trademark material avail-
able from DuPont~
The assembly 72 also includes a conductive plas-tic potenti-
ometer element 76, of which the largest or elongated central
portion thereof is laid directly upon the insulating base 74.
The ends 78 and 80 of the potentiometer element are overlaid onto
portions of copper or metallic electrical conductive ground and
power strips 82 and 84, respectively. The potentiometer element
76 terminates at edges 79 and 81, respectively. Conductive
ground strip 82 terminates at edge 83, under the end 78 of the
potentiometer element 76, as shown in dashed line in Fig. 5. A
conductor 86 is soldered to the other end of ground strip 82.
Conductive power strip 84 terminates at an edge 85 under end 80
of the potentiometer element 76, as also shown in dashed line in
Fig. 5. The overlaps between the conductive strips 82/ 84 and
the potentiometer element ends 78, 80 need only be sufficient to
provide good electrical continuity therebetween. The other end
of power strip 84 is joined via a solder joint to a conductor 88.
A metallic or electrical conductive commutator strip 90 is also
positioned on the insulating base 74. Commutator strip 90 extends
from an edge indicated by reference numeral 92 to an end 94 to
which is soldered to a conductor 96. An overlay strip 98 of
conductive plastic material is positioned on top of the commutator
strip 90 and extends from edge 99 to an edge also indica~ed by
reference numeral 92. The major portion of the power strip 84 is
separated -from the commutator strip 90 by the middle or potenti-
ometer strip 76 to reduce the possibility of metallic particles
forming undesirable short circuit connections between the power
strip 84 and the commutator strip 90. Also note that the trans-
ducer element 72 is not received in a recess or channel in the
support 60, but rather is positioned on top of the planar support
surface 68. The absence of a recess or channel reduces the
likelihood of metallic particles forming undesirable short circuit
connections between the support 60 and the outer edges of the
power strip 84 and the commutator strip 90. For clarity, the
thicknesses of the various strips in Figs. 6a-d are exaggerated.
The conductors 86, 88 and 96 extend from their solder joints,
through the notch 70, the terminal member 46 and the ceramic seal
54 to respective connector terminals 100, 102 and 104, two of
which are visible in Fig. 2. A conventional ~emale plug-t~pe
connector may be coupled to the connector terminals 100, 102 and
104 so that electrical signals may be extracted therefrom.
A wiper carrier 110 is received by bore portion 24 of the
bore 22, as best seen in Fig. 2. The wiper carrier 110 has a
generally cy]indrical body 112 of an insulating material such as
glass-reinforced nylon with an annular rabbet 114 in one end
thereof. The rabbet 114 registers with the ridge 28 only when
the carrier 110 is properly mounted in the bore portion 24,
otherwise, the annular ridge 28 will prevent the carrier 110 from
being inserted far enough into bore portion 24 to allow insertion
of snap ring 126 into snap ring groove 26. A wiper support
flange 116 extends inwardly from a portion of the body 112. A
two-pronged conductive wiper 118 is embedded in and supported by
the flange 116 so that prongs 120 and 122 resiliently and slid-
ably engage the surfaces of plastic conductive strip 98 above
commutator strip 90 and the potentiometer element portion 76,
respectively. The wiper 118 is exposed to the fluid in chamber65. As best seen in Fig. 7, the prongs 120 and 122 have multiple
fingers. A rectangular recess 124 is formed in the inner surface
125 of the carrier flange 116 so that the inner surface 125
closely registers with the surface 68 of the support element 60
and with the transducer element 72. The carrier 110 is coupled
for movement with the rod 18 and piston 16 between snap ring 126
and a resilient wave washer 128.
When the piston 16 and rod 18 move back and forth with
respect to the housing 12 and the support 60, fluid flows into
and out of chamber 65, around the end 129 of the support 60 and
via chambers 67 and 69. However, the close sliding fit between
the inner surface 1~5 and surface 68 and element 72 substantially
prevents fluid flow into or out of chamber 65 via the wiper
c~rrier 110, thus reducing flow-induced turbulence in the vicinit~
L6
. .
of the wiper 118. Thls reduced turbulence prevents turbulence~
induced vibrat.ions in the wiper 118 which could otherwise intro
duce noise into the signals picked up by the wiper 118.
Mode of Operation
In operation, a voltage potential is applied across terminals
102 and 100 to apply a corresponding voltage potential across the
resistance element 760 As the piston 16 and rod 18 move back and
forth within the housing 12, the wiper 118 moves with the piston
16 and rod 18 and with respect to the support 60 and the trans-
ducer element 72. Thus, the voltage or potential to which the
wiper 118 is subjected varies from ground potential to approxi-
mately the voltage at the power strip 84, depending upon the
longitudinal position of the wiper 118 relative to the resistance
element 76. The voltage on wiper 118 is communicated to the
exterior of the cylinder housing 12 via con~utator strips 98 and
90, conductor 96 and connector terminal 104, from where it can be
monitored to indicate the position of the cylinder 10.
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