(12)
`
`United States Patent
`Glasson
`
`(10) Patent N0.:
`(45) Date of Patent:
`
`US 6,234,061 B1
`May 22, 2001
`
`US006234061B1
`
`(54) PRECISION SENSOR FOR A HYDRAULIC
`CYLINDER
`
`(75) Inventor: ?jgglard O. Glasson, Whippany, NJ
`
`5,694,042
`12/1997 Eaton .
`5,701,793
`12/1997 Gardner .
`5,752,811
`5/1998 Petro .
`FOREIGN PATENT DOCUMENTS
`
`(73) Assignee: Control Products, Inc., East Hanover,
`NJ (Us)
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U-S-C- 154(k)) by 0 days-
`
`(21) Appl. N0.: 09/302,701
`(22) Filed:
`Apr. 30, 1999
`
`26 35 614
`38 35 782
`0325787
`0505297
`
`2/1978 (DE).
`4/1990 (DE) .
`8/1989 (EP) .
`9/1992 (EP) .
`
`OTHER PUBLICATIONS
`Murakami, T., M. Kato and M. Ota, “Precision Angle Sensor
`Unit for Construction Machinery,” SAE Technical Paper
`Series 972782, Sep. 1997.
`* cited by examiner
`
`Rehted U_S_ App?cation Data
`(60) Provisional application No. 60/104,866, ?led on Oct. 19,
`1998.
`
`Primary Examiner—F. Daniel Lopez
`(74) Attorney, Agent, 07' Flrm—G1bb0n5, Del D60, Dolan,
`Grif?nger & Vecchione
`
`(51) Int. Cl.7 .................................................... .. F01B 31/12
`(52) US. Cl. ............................................... .. 92/5 R; 33/763
`(58) Field of Search .................... .. 91/ 1' 92/5 R: 33/756
`33/75’9 761 362 763’
`’
`’
`’
`
`(56)
`
`References Cited
`
`Us PATENT DOCUMENTS
`3 403 365 * 9/1968 Richards .............................. .. 92/5 R
`4,121,504
`10/1978 Nowak ................................. .. 92/5 R
`4ZZ31Z7OO
`11/1980 Studebaker_
`4,286,386 * 9/1981 Long .................................... .. 33/759
`4,288,196
`9/1981 Sutton, 11.
`4,319,864
`3/1982 Kaufeldt -
`4,386,552 * 6/1983 Foxwell ............................... .. 92/5 R
`113151156“ et a1‘ '
`
`(57)
`
`ABSTRACT
`_
`_
`_
`_
`_
`A Sensor mountable Wlthm a hydrauhc Cyhnder provldes a
`precision signal indicative of the position of the piston
`utilizing a non-contacting electromechanical transducer. The
`sensor includes a ?exible connector attached betWeen the
`cylinder piston and a converting element for sensing the
`displacement of the cylinder piston. The converting element
`eethpheee a Ptek'hP Speet eehpted to the ether ehd of the
`Connector and rotatable about an 2995- The Spool is under
`tension from a spring coupled to the spool. A lead screW
`engages threads on the interior of the spool, and translates
`along an axis When the spool rotates. A transducer is
`disposed to sense the position of the lead screW, and pro
`Vides an Output Signal proportional to the motion or position
`of the movable element. The transducer may be an LVDT or
`
`7
`
`7
`
`en .
`
`_
`
`.
`
`5,024,250 * 6/1991 Nakamura ............................ .. 92/5 R
`
`other non Contactmg transducer‘
`
`5,341,724 * 8/1994 Vatel .................................... .. 92/5 R
`5,404,661
`4/1995 Sahm et al. .
`
`13 Claims, 9 Drawing Sheets
`
`Page 1 of 15
`
`CATERPILLAR EXHIBIT 1106
`
`

`

`U.S. Patent
`
`May 22, 2001
`
`Sheet 1 0f 9
`
`US 6,234,061 B1
`
`FIG. 1
`
`m
`
`100
`/
`
`110
`POSITION
`/
`0011111011111 -———SIGNAL
`1001111101 SIGNAL
`
`VALVE
`
`—-
`
`——
`
`HYDRAULIC LINES
`PUMP
`HYDRAULIC LINES
`\
`102
`
`105
`011111010 ii
`
`104
`
`Page 2 of 15
`
`

`

`U.S. Patent
`US. Patent
`
`May 22, 2001
`May 22, 2001
`
`Sheet 2 0f 9
`Sheet 2 0f 9
`
`US 6,234,061 B1
`US 6,234,061 B1
`
`
`
`Page 3 0f 15
`
`Page 3 of 15
`
`

`

`U.S. Patent
`
`May 22, 2001
`
`Sheet 3 0f 9
`
`
`
`Page 4 of 15
`
`

`

`
`
`Page 5 of 15
`
`

`

`U.S. Patent
`US. Patent
`
`May 22, 2001
`May 22, 2001
`
`Sheet 5 0f 9
`Sheet 5 0f 9
`
`US 6,234,061 B1
`US 6,234,061 B1
`
`
`
`Page 6 0f 15
`
`Page 6 of 15
`
`

`

`U.S. Patent
`
`May 22, 2001
`
`Sheet 6 6f 9
`
`US 6,234,061 B1
`
`
`
`Page 7 of 15
`
`

`

`U.S. Patent
`US. Patent
`
`May 22, 2001
`May 22, 2001
`
`Sheet 7 0f 9
`Sheet 7 0f 9
`
`US 6,234,061 B1
`US 6,234,061 B1
`
`FIG. 5
`
`
`
`Page 8 0f 15
`
`Page 8 of 15
`
`

`

`U.S. Patent
`US. Patent
`
`May 22, 2001
`May 22, 2001
`
`Sheet 8 0f 9
`Sheet 8 0f 9
`
`US 6,234,061 B1
`
`
`
`Page 9 of 15
`
`

`

`U.S. Patent
`US. Patent
`
`May 22, 2001
`May 22, 2001
`
`Sheet 9 0f 9
`Sheet 9 0f 9
`
`US 6,234,061 B1
`US 6,234,061 B1
`
`FIG. 7
`FIG. 7
`
`
`
`Page 10 of 15
`
`Page 10 of 15
`
`

`

`US 6,234,061 B1
`
`1
`PRECISION SENSOR FOR A HYDRAULIC
`CYLINDER
`
`RELATED APPLICATIONS
`
`This application claims the bene?t of United States Pro
`visional Application Ser. No. 60/104,866, ?led on Oct. 19,
`1998.
`
`FIELD OF THE INVENTION
`
`The invention generally relates to position sensors, and
`more particularly to linear position sensors for use on poWer
`cylinders.
`
`BACKGROUND
`Equipment implementing hydraulic cylinders for
`mechanical movement, such as excavators and other heavy
`construction equipment, depend upon operators to manually
`control the moveable elements of the equipment. The opera
`tor must manually move control levers to open and close
`hydraulic valves that direct pressuriZed ?uid to hydraulic
`cylinders. For example, When the operator lifts a lift arm, the
`operator actually moves a lever associated With the lift arm,
`causing a valve to release pressuriZed ?uid to the lift arm
`cylinder. The use of levers to control hydraulic equipment
`depends upon manual dexterity and requires great skill.
`Improperly operated equipment poses a safety haZard, and
`operators have been knoWn to damage overhead utility
`Wires, underground Wiring, Water mains, and underground
`gas lines through faulty operation of excavators, bucket
`loaders or like equipment.
`In addition to the safety haZards caused by improperly
`operated equipment, the machine’s operating ef?ciency is
`also a function of the operator’s skill. An inexperienced or
`unskilled operator typically fails to achieve the optimum
`performance levels of the equipment. For instance, the
`operator may not consistently apply the force necessary for
`peak performance due to a concern over striking a haZard.
`Ef?ciency is also compromised When the operator fails to
`drive a cylinder smoothly. The operator alternately over
`drives or underdrives the cylinder, resulting in abrupt starts
`and stops of the moveable element and thereby derating
`system performance. As a result, the skill level necessary to
`properly and safely operate heavy equipment is typically
`imparted through long and costly training courses and
`apprenticeships.
`There have been various attempts at implementing an
`automated control system for use on heavy equipment. One
`such system is disclosed in US. Pat. No. 4,288,196. The
`system described therein provides for a computer program
`mable system for setting the loWermost point of a backhoe
`bucket. In US. Pat. No. 4,945,221, a control system for an
`excavator is disclosed. The system attempts to control the
`position of the bucket cutting edge to a desired depth.
`Another position locating system for heavy equipment is
`disclosed in US. Pat. No. 5,404,661.
`These systems and others like them share a common
`feature in that they implement a position sensor. Typically,
`these sensors are rotary potentiometers as, for instance,
`suggested in Murakmi, Kato and Ota, Precision Angle
`Sensor Unit for Construction Machinery, SAE Technical
`Paper Series 972782, 1997. This sensor relies upon a poten
`tiometer Which changes a voltage or current in relation to the
`position of a bucket or boom. Other types of sensors rely
`upon optical, conductive plastic, or metal-in-glass technolo
`gies.
`
`15
`
`25
`
`35
`
`55
`
`65
`
`2
`It is a disadvantage of these sensors that they mount to the
`outside of the machinery, thereby exposing them to the
`environment. In the case of heavy equipment, this environ
`ment includes severe temperatures, excessive moisture, and
`air-borne particulate matter Which may infect the sensor. In
`the case of optical, conductive plastic and metal-in-glass
`technologies, the sensors Would rapidly degrade if used on
`construction equipment. Furthermore, some of these sensors
`use contacting components that are susceptible to Wear,
`vibration and temperature. As a result, no sensor mountable
`to the outside of heavy equipment or relying upon contacting
`elements has gained Widespread use in the industry.
`There have been attempts to overcome the limitations of
`contacting sensors by using electromagnetic energy. For
`example, the system disclosed in US. Pat. No. 4,945,221
`discloses using lasers for sensing position. Others suggest
`using RF energy or the like to provide a feedback signal.
`These systems, hoWever, have not replaced the less expen
`sive potentiometers due to their complexity of use and their
`expense.
`As the demands placed upon actuated machinery
`increases, so does the demand for a loW cost, long-life sensor
`operable in a harsh environment. Despite the development
`of highly sophisticated control systems, computer proces
`sors and application speci?c softWare, the implementation of
`this technology in electrohydraulic equipment has been
`curtailed by the failure to provide a long-life, cost-effective
`precision sensor operable in harsh environments.
`
`SUMMARY OF THE INVENTION
`
`A sensor according to the principles of the invention
`provides a precision signal utiliZing a non-contacting trans
`ducer. In an exemplary embodiment, the sensor mounts
`inside a hydraulic cylinder, aWay from the harsh
`environment, and provides a voltage or current signal
`indicative of the position of the piston. The sensor provides
`a connector, attached betWeen a cylinder piston and a
`converting element, for sensing the displacement of the
`piston. The converting element converts the cylinder dis
`placement to a proportional displacement of a translating
`member. Aprecision transducer senses the displacement of
`the translating member and provides an electrical output
`signal proportional to the piston movement or to the piston’s
`position.
`In one exemplary sensor according to the principles of the
`invention, a ?exible connector such as a cable is attached to
`the movable element (a piston). The converting element
`comprises a pick-up spool coupled to the other end of the
`connector and rotatable about an axis. The spool is under
`tension from a recoil mechanism, such as a spring, coupled
`to the spool. A translating member, Which can be a lead
`screW, engages threads on the interior of the spool, and
`translates along an axis When the spool rotates. Atransducer
`is disposed to sense a position or motion of the translating
`member, and provides an output signal proportional to, and
`therefore indicative of, the position (or motion) of the
`translating member. The transducer can be a linear variable
`differential transformer (LVDT), Which is a non-contacting
`transducer. Of course, other transducers, including those
`using contacting components, can be used.
`For use in a hydraulic cylinder, the sensor’s operation is
`like this. The converting element is attached to a cylinder
`end cap. As the cylinder piston moves Within the cylinder,
`the spool feeds out or draWs in cable, thereby tracking the
`piston’s linear displacement. As the cylinder moves toWard
`the spool, the spring causes the spool to Wind the cable.
`
`Page 11 of 15
`
`

`

`US 6,234,061 B1
`
`3
`When the cylinder moves away from the spool, the cylinder
`force overcomes the spring tension and pulls cable off the
`spool. The spool is in threaded engagement With a lead
`screW. As the spool rotates, the spool and lead screW convert
`the rotary motion of the spool to a linear displacement of the
`lead screW. The displacement is proportional to the piston
`displacement. The lead screW is attached to an LVDT core
`that moves Within an LVDT body When the cylinder moves.
`The LVDT delivers an electrical signal at its output, Which
`can be con?gured as a position signal, rate signal or the like.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`A more complete understanding of the invention may be
`obtained from consideration of the folloWing description in
`conjunction With the draWings in Which:
`FIG. 1 is a block diagram of an exemplary feedback
`control system for a hydraulic cylinder;
`FIG. 2 shoWs a perspective of an exemplary cylinder
`according to the principles of the invention;
`FIGS. 3A, B and C shoW an exemplary sensor according
`to the principles of the invention;
`FIG. 4 shoWs another exemplary sensor according to the
`principles of the invention;
`FIG. 5 shoWs another exemplary sensor according to the
`principles of the invention;
`FIG. 6 shoWs another exemplary sensor according to the
`principles of the invention; and,
`FIG. 7 shoWs another exemplary sensor according to the
`principles of the invention.
`
`10
`
`15
`
`25
`
`DETAILED DESCRIPTION
`
`4
`210 and a piston 212. The piston 212 is operable to translate
`in dependence upon hydraulic ?uid pumped into the cylin
`der. The cylinder enclosure 210 further includes a base 214,
`and the piston 212 is a moveable element With respect to the
`base. A precision sensor 218 provides a position related
`signal across the terminals 219 and 222. For instance, the
`sensor delivers a signal across the sensor’s terminals indica
`tive of the position “d” in FIG. 2. A high pressure bulkhead
`connector (not shoWn) provides a mechanism for routing the
`terminals 219 and 222 to the outside of the cylinder enclo
`sure 210. The sensor 218 further comprises a ?exible
`connector 216 attached to the piston 212, a converting
`element 220 attached to the base 214 and a transducer (not
`shoWn). The connector 216 also attaches to the converting
`element 220 and directly imparts the displacement of the
`piston 212 With respect to the base 214 to the converting
`element 220. The converting element 220 converts this
`displacement to a proportional displacement of a translating
`member (not shoWn). The transducer, located remote from
`the piston, senses the position or motion of the translating
`member.
`An exemplary embodiment of the converting element 220
`is described With reference to FIGS. 3A, 3B and 3C. A ?rst
`mounting element 302 is provided for attaching the convert
`ing element 220 to, for instance, the base of the hydraulic
`cylinder. Asecond mounting element 306 and a third mount
`ing element 308 are ?xedly attached to the ?rst mounting
`element 302. The converting element 220 includes a rotating
`element 310 rotatably attached betWeen the second mount
`ing element 306 and the third mounting element 308. An
`anti-backlash spring 312 is mounted to the third mounting
`element 308. Ablock 304 and an anti-rotation spring 305 are
`attached to the ?rst mounting element 302. An arm 320
`attaches to a translating member 324 at one end and engages
`the block 304 at the other. A spring 317 for providing a
`rotary mechanism for the rotating element 310 is housed in
`a spring housing or spring mounting (not shoWn). The
`housing is attached to the ?rst mounting element 302.
`In FIGS. 3B and 3C an exploded vieW of the converting
`element 218 is shoWn. Apress-in hub 316 having a shaft 309
`With internal threads is rotatably attached to a bushing 321.
`The bushing is ?xedly attached to the third mounting
`element 308. For ease of installation, the third mounting
`element can comprise an upper half 308A and a loWer half
`308B. The translating member 324, having threads formed
`thereon, engages the internal threads of the hub 316. The
`rotating element 310 de?nes an internal opening into Which
`the hub is pressed so that it rotates as the rotating element
`310 rotates. On a side opposite the hub 316, a bushing 322
`?xedly mounts in the second mounting element 306 Which
`can also comprise an upper half 306A and a loWer half 306B.
`As shoWn in FIG. 3C, the brackets 306 and 308 de?ne a
`circular opening for attaching the bushings 322 and 321,
`respectively. An axle 323 attaches to the bushing 322, and
`the rotating element 310 rotatably engages the bushing 322.
`In this exemplary embodiment, the transducer is a linear
`variable differential transformer (LVDT), Which has a core
`and a body. The LVDT body acts as the axle 323.
`Alternatively, the LVDT body can be internal to a separate
`axle. The LVDT core 325 is attached to the translating
`member 324 and disposed to translate Within the LVDT
`body.
`Operation of this exemplary sensor is explained With
`reference to FIGS. 2, 3A, 3B and 3C. The ?exible connector
`216 attaches to the piston 212 Which causes the rotating
`element 310 to rotate in a ?rst direction When the piston 212
`moves aWay from the cylinder base 214. When the piston
`
`A feedback sensor for a cylinder according to the prin
`ciples of the invention provides a precision signal indicative
`of a piston position With relation to a cylinder. The sensor is
`durable, maintains a long life, and is con?gured for use in
`harsh environments. An exemplary sensor mounts inside a
`hydraulic cylinder, thereby protecting the sensor, and uses a
`non-contacting transducer to provide the precision signal. A
`converting element converts the motion of the piston to a
`proportional motion of a translating member. The
`transducer, Which can be located remotely from the piston,
`senses the position of the translating member, and provides
`an electrical output signal indicating the piston’s position.
`This signal can be conditioned and used in a feedback
`control system, a user interface, or any system Where such
`a signal is desirable.
`In FIG. 1, a block diagram of an exemplary feedback
`control system 100 is shoWn. The control system 100
`comprises a hydraulic cylinder 104 actuated by a pump 102
`and a valve 108. As is knoWn in the art, the pump 102
`delivers hydraulic ?uid under pressure to the cylinder 104
`Which forces the piston 105 to move With respect to the
`cylinder. The valve 108 controls the ?oW of hydraulic ?uid
`to the cylinder 104. To implement feedback control, a
`feedback sensor 106 senses the position of the piston 105
`and delivers a position signal to a controller 110. The
`controller 110 actuates the valve 108 according to certain
`instructions. The piston 105 may be attached to some other
`apparatus (not shoWn) Whereby a displacement of the piston
`causes a displacement of the apparatus. Although a hydrau
`lic cylinder is shoWn, it should be apparent that other types
`of cylinders, such as pneumatic cylinders, can be used.
`Referring to FIG. 2, a hydraulic cylinder 200 that can be
`used in the feedback control system 100 of FIG. 1 is shoWn.
`The hydraulic cylinder 200 comprises a cylinder enclosure
`
`35
`
`45
`
`55
`
`65
`
`Page 12 of 15
`
`

`

`US 6,234,061 B1
`
`5
`travels toward the cylinder base 214, the spring 317 causes
`the rotating element 310 to rotate in a direction opposite to
`the rotation caused by the piston moving aWay from the base
`214. In other Words, the ?exible connector Winds around the
`rotating element 310 When the piston 212 moves toWard the
`base 214, and unWinds from the rotating element 310 When
`the piston moves aWay from the base. The linear motion of
`the piston 212 converts to the angular motion of the rotating
`element 310 via the pulling action of the piston on the
`?exible connector and due to the rotational action of the
`spring 317.
`As the rotating element 310 rotates, the hub 316 rotates
`With it. The hub’s internal threads engage threads on the
`translating member 324. As the rotating element and hub
`rotate, the threaded engagement causes the translating mem
`ber 324 to move linearly along the rotational axis of the
`rotating element 310. The thread arrangement is chosen such
`that the movement of the translating member is proportional
`to the movement of the piston. The threads can be acme,
`square, modi?ed square, buttress, uni?ed, ISO, ball bearing,
`extra-?ne pitch or any other of various knoWn threads.
`Likewise, the position of the translating member 324 With
`respect to the transducer is in a one-to-one correspondence
`With the position of the piston 212. The LVDT 323, 325
`senses a position (or a movement) of the translating member
`and provides a position related signal.
`The precision and performance of the sensor is enhanced
`by providing the previously set forth anti-rotation elements
`320, 304 and 305 and anti-backlash elements 320 and 312.
`When the rotating element 310 rotates, causing the trans
`lating member 324 to translate along an axis, there is a small
`frictional force betWeen the inner threads of the hub and the
`external threads formed on the translating member. This
`small frictional force is overcome before the translating
`member moves. To overcome this force, the arm 320 is
`provided at an end of the translating member 324. The arm
`320 bends substantially perpendicular to a longitudinal axis
`of the translating member and engages the block 304. For
`purposes of illustration, the arm 320 is shoWn engaging the
`block in FIG. 3A such that, When the rotating element 310
`rotates in a counterclockwise direction, the block inhibits the
`arm 320 from turning, thereby overcoming any frictional
`force arising from the threaded engagement.
`The anti-rotation spring 305 applies a force to the arm
`such that it engages the block 304 at substantially all times.
`The force exerted by this spring is perpendicular to the
`longitudinal axis of the translating member 324 and is
`chosen such that it overcomes the frictional force caused by
`the threaded engagement When, With reference to FIG. 3A,
`the rotating element 310 rotates in a clockWise direction. It
`should be apparent that various other equivalent structures
`can be used to inhibit the motion of the arm 320 When the
`rotating element 310 rotates. For instance, instead of the
`spring 305, another block can be used. Thus, the arm 320 can
`be held betWeen tWo blocks or a slot formed in one block.
`In any con?guration, the anti-rotational forces upon the arm
`320 are such that the arm translates When the rotating
`element 310 rotates.
`In addition to the frictional force inherent in the threaded
`engagement, the tolerances of the threads can introduce a
`dead space betWeen the threads. For example, When the
`translating member 324 changes direction, due to a change
`in the direction of motion of the piston 212, the piston can
`move some small distance before the threads engage. In
`other Words, depending upon the thread tolerance, there may
`be play betWeen the threads. This is overcome by the
`anti-backlash spring 312 attached to the bracket 308. The
`
`10
`
`15
`
`25
`
`35
`
`45
`
`55
`
`65
`
`6
`spring applies a force to the arm 320 directed along the
`translating member’s longitudinal axis. This force holds the
`translating member in substantially constant threaded
`engagement With the internal threads of the hub 316. The
`force exerted by this spring is chosen such that the trans
`lating member may move against the spring When the piston
`displaces to cause such movement.
`It should be apparent that various materials and con?gu
`rations can be used to implement a sensor according to the
`principles of the invention. For instance, the rotating ele
`ment 310 can be con?gured to enhance the performance of
`the sensor by forming grooves thereon so that the ?exible
`connector 216 Winds up along successive grooves of the
`rotating element 310. In this Way, no portion of the ?exible
`connector 216 lies over another portion. Alternatively, Wind
`guides can be used, or for displacements of large magnitude
`relative to the storage capacity of the rotating element, the
`rotating element can be con?gured such that some portions
`of the ?exible connector overlay other portions of the
`?exible connector.
`LikeWise, various materials can be used for the ?exible
`connector. Aconnector made of Kevlar®, and materials like
`it, provide desirable attributes, including loW stretch, toler
`ance to a hydraulic ?uid environment, and stability over a
`Wide range of temperature (loW coef?cient of thermal
`expansion). For example, Kevlar® is knoWn to have a
`coef?cient of thermal expansion on the order of —0.000002/
`degree Farenheit (-2 parts per million per degree Farenheit).
`The connector can also comprise other types of cable, such
`as metallic cable, Nylon®, or stranded cable, and can be
`coated to provide longer life or to adjust the coef?cient of
`friction. Its diameter can also be adjusted to meet storage
`needs on the rotating element or to decrease Windage.
`Similarly, the connector can be af?xed to the rotating
`element or moveable element by Well-knoWn methods, such
`as a clevis, pin, Weld, bolt or screW, splice, adhesive,
`threaded terminal, sWayed oval, eye, ball and socket,
`thimble, or a strap fork.
`In the embodiment shoWn in FIGS. 2, 3A, 3B and 3C, the
`transducer is a linear variable differential transformer
`(LVDT). It should be apparent to those skilled in the art that
`other types of transducers can be implemented Without
`departing from the principles of the invention, including
`differential variable reluctance transducers (DVRTs®), Wire
`Wound potentiometers, conductive plastic potentiometers,
`inductive or capacitive sensors, Hall-effect transducers, or
`sensors based upon light emitting diodes, or laser light. In
`each case, the target element for the transducer af?xes to the
`translating member. The sensing element is disposed to
`sense the motion or position of the target element. Similarly,
`the rotational spring can be a spiral torsion spring, a volute
`spring, a constant force extension spring, a helical torsion
`spring, a tWisted elastic element, a round tension or com
`pression spring, a cantilever tension or compression spring
`or any other type of spring Which may be usable to impart
`a rotational action on the rotating element. LikeWise, the arm
`320 can also be a pin or other similar structure for engaging
`the block 304 and the anti-backlash spring 312.
`Another exemplary embodiment of a sensor according to
`the principles of the invention is shoWn in FIG. 4. In this
`embodiment, an LVDT core 424 is caused to translate along
`an axis substantially parallel to an axis of rotation for a
`rotating element 410. The ?exible connector 420 af?xes to
`the rotating element 410 and to a movable element (not
`shoWn). A lead screW 415 threadedly engages the rotating
`element 410 at one end. At another end, the lead screW is
`af?xed to an arm 422. The LVDT core 424 af?xes to the
`
`Page 13 of 15
`
`

`

`US 6,234,061 B1
`
`7
`other end of the arm 422 and is disposed to translate in an
`LVDT body 426. When the ?exible connector is pulled such
`that it unWinds from the rotating element 410, the threaded
`engagement causes the lead screW 415 to translate. This, in
`turn, causes the LVDT core 424 to translate Within the LVDT
`body 426. A recoil mechanism 428 causes the rotating
`element 410 to Wind the connector 420 When the moveable
`element (not shoWn) moves such that there is no tension on
`the connector 420. This also causes the LVDT core 424 to
`translate Within the LVDT body 426. The LVDT thereby
`provides a position related signal for the movable element
`(not shoWn).
`Of course, the sensor can also be affixed in various
`locations Within a cylinder. For instance in FIG. 5, a sensor
`500 is shoWn attached to the cylinder end cap 503 de?ning
`the piston shaft aperture. The ?exible connector 502 is
`af?xed to the same side of the piston as the shaft. Operation
`of this con?guration is the same With respect to FIGS. 2, 3A,
`B, and C.
`It should also be apparent that various mechanical con
`nections can be made betWeen the transducer and the
`converting element of the sensor. In FIG. 6, an actuated cam
`602 is shoWn engaged With an LVDT core 604 and With the
`sensor’s converting element 606. In FIG. 7, a mechanical
`connection betWeen the converting element 702 and the
`transducer 704 is made via an extension cable 706.
`Likewise, the converting element can be con?gured in
`various Ways Without departing from the principles of the
`invention. For instance, gears instead of threads can convert
`the linear displacement of the movable element to the linear
`displacement of the translating member. It should also be
`apparent that for applications With relatively large displace
`ments of the movable element or Where an obstruction is
`located betWeen the converting element and the movable
`element, various pulleys, guides or blocks and tackle can be
`provided to route the connector from the movable element to
`the sensor’s converting element.
`It is to be understood that the invention is not limited to
`the illustrated and described forms of the invention con
`tained herein. It Will be apparent to those skilled in the art
`that various changes may be made Without departing from
`the scope of the invention and the invention is not consid
`ered limited to What is shoWn in the draWings and described
`in the speci?cation.
`What is claimed is:
`1. A sensor for providing a position related signal for a
`?rst element in relation to a second element, the sensor
`comprising:
`a ?exible connector having a ?rst end attached to the ?rst
`element;
`a rotating element attached to the second element and
`coupled to a second end of the ?exible connector;
`a translating member in threaded communication With the
`rotating element, Wherein a displacement of the ?rst
`element causes a displacement of the translating mem
`ber; and
`a transducer disposed to sense a position of the translating
`member, Wherein the transducer provides the position
`related signal;
`the sensor further including:
`a mounting element attached in ?xed relation to the
`second element, the rotating element rotatably
`attached to the mounting element;
`a block attached to the mounting element, the trans
`lating member having an arm extending substan
`
`15
`
`25
`
`35
`
`45
`
`55
`
`65
`
`8
`tially perpendicular to a longitudinal axis of the
`translating member; and
`an anti-rotational spring attached to the mounting
`element and engaged With the arm, Wherein the
`anti-rotational spring exerts an anti-rotational
`force on the arm.
`2. The sensor of claim 1 further including an anti-backlash
`spring attached to the mounting element and disposed to
`exert an anti-backlash force along the longitudinal axis of
`the translating member.
`3. A sensor for providing a position related signal for a
`piston in relation to a cylinder, the cylinder having a cylinder
`bore, the sensor comprising:
`a ?exible connector having a ?rst end attached to the
`piston;
`a rotating element attached to the cylinder and coupled to
`a second end of the ?exible connector;
`a translating member in dependence With the rotating
`element, Wherein a displacement of the piston causes a
`displacement of the translating member; and
`a transducer disposed to sense the translating member for
`providing the position related signal,
`the sensor being disposed in the cylinder bore.
`4. The sensor of claim 3 further comprising hydraulic
`?uid contained Within the cylinder so that the transducer is
`exposed to the hydraulic ?uid.
`5. The sensor of claim 3 Wherein said rotating element is
`a spool having an outer periphery With Wind guides.
`6. The sensor of claim 3 further including an anti-backlash
`force exerted along a longitudinal axis of the translating
`member.
`7. The sensor of claim 3 further comprising a recoil
`mechanism coupled to the rotating element for imparting a
`rotational action on the rotating element.
`8. The sensor of claim 3 Wherein the translating, member
`is in threaded communication With the rotating element.
`9. The sensor of claim 3 Wherein the translating member
`displaces along an axis of rotation of the rotating element.
`10. The sensor of claim 3 further including a mounting
`element attached in ?xed relation to the cylinder, the rotating
`element rotatable attached to the mounting element.
`11. The sensor of claim 3 further including an anti
`rotational force exerted on the translating member.
`12. A device comprising:
`a cylinder containing a Working ?uid;
`a piston slidingly engaged With the cylinder and respon
`sive to the Working ?uid; and
`a sensor disposed Within the cylinder for providing a
`position related signal, the sensor including:
`a ?exible connector having a ?rst end coupled to the
`piston,
`a rotating element coupled to a second end of the
`?exible connector;
`a translating member coupled translate in response to
`rotation of the rotating element, Wherein a displace
`ment of the piston causes a displacement of the
`translating member; and
`a transducer exposed to the Working ?uid and respon
`sive to the translating member, the transducer pro
`viding the position related signal.
`13. The system of claim 12 Wherein the cylinder is a
`hydraulic cylinder and the transducer is operable in a
`hydraulic ?uid.
`
`Page 14 of 15
`
`

`

`UNITED STATES PATENT AND TRADEMARK OFFICE
`CERTIFICATE OF CORRECTION
`
`PATENT NO. : 6,234,061 B1
`DATED
`: May 22, 2001
`INVENTOR(S) : Richard O. Glasson
`
`Page 1 of 1
`