US20160231148A1 - Floating optical sensor mount - Google Patents

Abstract

A piston-cylinder actuator (20) includes a unique mount (36) for an absolute-position sensor (30). The mount (36) is made from a bearing material provides a flexible connection between the sensor mount (36) and the cylinder housing (40). This flexible connection allows the piston rod (32) to deflect naturally, under its own weight or under other laterally-directed forces, while maintaining the distance and perpendicularity between the sensor (30) and the rod surface (34), within acceptable limits. The sensor mount (36) is made from a bearing material that will allow it to float directly on the rod surface (34) without scuffing or otherwise damaging the rod surface (34), particularly the markings or other indicia on that surface (34). Due to the flexible connection between the sensor mount (36) and the cylinder housing (40), the proper distance between the sensor (30) and the rod surface (34) can be maintained at all times.

Description

RELATED APPLICATIONS
• This application claims the benefit of U.S. Provisional Application No. 61/444,478 filed Feb. 18, 2011, which is hereby incorporated herein by reference.
FIELD OF THE INVENTION
• The present invention relates to a piston-cylinder assembly having a sensor for detecting the position of a piston rod relative to a cylinder housing, and more particularly to a mounting arrangement for the sensor relative to the cylinder housing.
BACKGROUND OF THE INVENTION
• Piston-cylinder assemblies are used in various actuator applications throughout industry, such as in construction equipment. Often it is advantageous for an operator to be aware of the specific position of a piston rod in a fluid pressure-operated cylinder since the working member being actuated is generally physically connected to the end of the piston rod.
• U.S. Pat. No. 7,047,865, for example, discloses a known actuator with a cylinder housing and a rod that is axially movable relative to the cylinder housing. The actuator also has sensor for absolute position sensing in which light from a light source illuminates a pattern on the rod. The sensor is attached to the cylinder housing and detects light reflected from an adjacent portion of the pattern. The position of the rod relative to the housing is determined from the known position of the sensor relative to the housing and the portion of the pattern detected by the sensor.
• In contrast to absolute-position sensors, relative-position sensor systems also are known, but they require periodic “zeroing” to maintain accurate position information. In the event of a power failure, for example, the rod generally must be retracted to a “home” position before being extended again. Depending on the circumstances when the hydraulic cylinder lost power, this might not be practical or even possible. An absolute position sensor always knows the position of the rod, even after a power failure. Knowing absolute position also can be used to more accurately control the actuator extension/retraction.
SUMMARY OF THE INVENTION
• While absolute position sensors for piston-cylinder type actuators provide some advantages over relative position sensors, existing methods of mounting the sensors on piston-cylinders generally do not compensate for lateral rod deflection due to the rod's weight or other forces acting transverse to the axial or longitudinal dimension of the rod. This failure to account for lateral deflection results in poor sensor signal data, particularly for long rods, or large diameter rods.
• The present invention provides a unique mounting apparatus for an absolute position sensor. Accordingly, the present invention provides a piston-cylinder actuator that includes a unique mount for an absolute-position sensor. The mount, made from a bearing material, provides a flexible connection between the sensor mount and the cylinder housing. This flexible connection allows the piston rod to deflect naturally, under its own weight or under other laterally-directed forces, while maintaining the distance and perpendicularity between the sensor and the marked rod surface, within acceptable limits. The sensor mount is made from a bearing material that will allow it to float directly on the rod surface without scuffing or otherwise damaging the rod surface, particularly the markings or other indicia on that surface. Due to the flexible connection between the sensor mount and the cylinder housing, the proper distance between the sensor and the rod surface can be maintained at all times.
• More particularly, the present invention provides a piston-cylinder actuator that includes a cylinder assembly with a cylinder housing. The cylinder housing has a longitudinal axis. The actuator also includes a piston assembly that is generally movable relative to the cylinder assembly along the longitudinal axis. The piston assembly includes a piston rod having indicia extending longitudinally on the rod. The actuator further includes a sensor capable of reading the indicia on the piston rod, and a mount for supporting the sensor relative to the piston rod. The sensor mount is flexibly connected to the cylinder housing to allow the sensor mount to move relative to the cylinder housing to allow the sensor mount to remain in registration with the rod, while maintaining the sensor at a substantially constant position along the longitudinal axis relative to the cylinder housing.
• An exemplary embodiment of the actuator provided by the invention further includes one or more of the following features. An exemplary cylinder assembly includes a seal gland mounted in the cylinder housing. The seal gland has a central aperture for receipt of the piston rod. The seal gland is separate from the sensor mount. In an exemplary actuator, clearance between the sensor mount and the piston rod is less than clearance between the seal gland and the piston rod.
• An exemplary sensor mount is connected to the cylinder housing with a retaining wire that forms a wire lock. The retaining wire provides a flexible connection between the seal gland and the sensor mount. The flexible connection between the sensor mount and the cylinder housing is provided by ensuring sufficient clearances between the retaining wire, the seal gland, and the sensor mount.
• An exemplary sensor mount includes a bearing surface for interfacing with the piston rod and an aperture transverse the bearing surface to provide the sensor with access to the indicia. The mount is made of a bearing material. The mount includes a collar that defines a passage therethrough for receipt of the piston rod. The mount includes a collar that extends around the piston rod. An exemplary sensor is an optical sensor.
• The present invention also provides a piston-cylinder actuator including a cylinder assembly with a cylinder housing that defines a cylindrical volume, the cylinder housing having a longitudinal axis. The actuator also includes a piston assembly generally movable relative to the cylinder assembly along the longitudinal axis. The piston assembly includes a piston rod having indicia extending longitudinally on a surface of the rod. The actuator further includes a sensor capable of detecting the indicia on the piston rod, and means for supporting the sensor relative to the piston rod. The support means is flexibly connected to the cylinder housing to pivot relative to the cylinder housing while maintaining the sensor at a substantially constant position along the longitudinal axis relative to the cylinder housing. The support means includes a sensor mount made of a bearing material.
• Finally, the present invention provides a method of providing a flexible connection for a sensor mounted on a piston-cylinder actuator. The method includes the steps of: a) separating an optical sensor mount assembly from a seal gland assembly; b) providing less clearance between the sensor mount and a rod than the clearance between a seal gland and the rod; c) providing a wire lock connection between the seal gland and sensor mount; and d) building in sufficient clearances between the wire lock, seal gland, and sensor mount to allow flex between the seal gland and sensor mount.
• Further features of the invention will become apparent from the following detailed description when considered in conjunction with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a perspective view of an exemplary piston-cylinder actuator provided in accordance with the invention.
• FIG. 2 is a longitudinal cross-sectional view of the actuator ofFIG. 1 as seen along lines2-2.
• FIG. 3 is an enlarged view of an aperture-end portion of the actuator shown inFIG. 2.
DETAILED DESCRIPTION
• Referring now to the drawings and initially toFIGS. 1 and 2, an exemplary embodiment of an actuator provided by the invention is shown generally at20. Theactuator20 includes acylinder assembly22, apiston assembly24 that is movable relative to thecylinder assembly22, and asensor assembly26 with asensor30 for detecting the absolute position of thepiston assembly24 relative to thecylinder assembly22. Thepiston assembly24 includes anelongated piston rod32 that has indicia markings (not shown) provided on at least a so longitudinal portion of itsperipheral surface34. These markings include patterns that vary along the length of therod32, enabling thesensor30 to identify the position of therod32 from a portion of the pattern adjacent thesensor30. Thus the indicia can be formed in thesurface34 of therod32, embedded in therod32, etched, carved, formed, or printed on therod32, or otherwise provided by other devices that function to identify the position of the indicia relative to therod32. Thesensor30 is supported by supporting means in the form of asensor mount36 that is made of a bearing material that floats on thepiston rod32 as therod32 moves, allowing thesensor mount32 to remain in registration with therod32 without damaging the markings on therod32. Thesensor mount36 is flexibly coupled to thecylinder assembly22 to accommodate transaxial displacement of therod32 relative to alongitudinal axis38 of thecylinder assembly22 while maintaining a substantially constant position along theaxis38. The flexible connection enables thesensor mount36 to maintain a proper relationship between thesensor30 and thesurface34 of thepiston rod32, even when thepiston rod32 is deflected from alignment with thelongitudinal axis38 of thecylinder assembly22 due to the weight of therod32 or other laterally-acting forces on therod32, sometimes referred to as side load conditions.
• Although the illustrated piston-cylinder actuator20 is designed for axial movement of thepiston assembly24, thesensor mount36 provided by the present invention is applicable to other types of actuators, such as actuators with piston assemblies that rotate relative to the cylinder assembly.
• Turning to further details of the various components, thecylinder assembly22 includes acylindrical housing40, and thepiston assembly24 is movable relative to thecylinder housing40 back and forth along thelongitudinal axis38. The illustratedcylinder housing40 has two opposed ends, oneend42 being closed by acylinder coupling44, while theother end46 is adapted to receive aseal gland50.
• Theseal gland50 has anoutside surface52 that mates and sealingly interacts with a correspondinginside surface54 of thecylinder housing40. Theseal gland50 also has an innerannular surface56 that defines a central axial aperture that receives thepiston rod32. The aperture in theseal gland50 allows reciprocating passage or movement of thepiston rod32. The innerperipheral surface56 of theseal gland50 has a series of spaced circumferential recesses,60-64, which receive peripheral seals66-70, respectively. The peripheral seals66-70 provide a leak-tight seal between theperipheral surface34 of thepiston rod32 and the innerperipheral surface56 of theseal gland50. The diameter of the seal gland aperture and the diameter of thepiston rod32 are dimensioned to permit the smooth passage of thepiston rod32 while preventing pressurized working fluid from migrating outside the pressurized volume of thecylinder housing40. Theseal gland50 generally is flush with theapertured end46 of thecylinder housing40.
• Thepiston assembly24 includes thepiston rod32, which extends through the aperture in theseal gland50, and apiston head72 that is closely received within thecylinder housing40. Thepiston head72 sealingly divides thecylinder housing40 into twochambers74 and76. Thepiston assembly24 also can be referred to as a plunger assembly. Thepiston rod32 is attached to thepiston head72 at one end, and an opposing end of the piston rod includes arod coupling78 for connecting theactuator20 to an object to be moved.
• Thepiston assembly24 generally is movable along an axis of thepiston rod32, which inFIG. 2 is coextensive with thelongitudinal axis38 of thecylinder housing40. Thepiston assembly24 and thecylinder housing40 can reciprocate relative to each other depending upon whichcylinder chamber74 or76 is pressurized. Pressure is supplied to thecylinder housing40 by any desired external pressure source (not shown) to afirst cylinder port80 coupled to thechamber74, and exhausted via asecond cylinder port82 coupled to thecylinder chamber76, and vice versa, depending on the desired direction of movement. Thepiston rod32 cooperates with the central longitudinal aperture in theseal gland50 to close theapertured end46 ofcylinder housing40.
• Thepiston rod32 and the associated indicia on therod32 move relative to both thecylinder housing40 and thesensor30, which reads the indicia adjacent thesensor30 to determine the position of therod32 relative to thecylinder housing40. Thesensor30 preferably is an absolute-position sensor. An exemplary absolute-position sensor is an optical sensor, such as the Intellinder™ sensor from Parker Hannifan Corp. of Cleveland, Ohio U.S., although other non-optical type sensors also may benefit from thesensor mount36 provided by the invention. Theoptical sensor30 typically includes a light source (such as a light-emitting diode, generally referred to as an LED) and a light sensor (generally a charge coupled device or CCD) that are mounted on a circuit board (sometimes referred to as a printed circuit board or PCB). Light guiding elements guide the light from the light source to thesurface34 of therod32, and reflected light from therod32 to the light sensor.
• Maintaining a specific distance between thesensor30 and the surface of therod32 is important to ensure effective sensing accuracy. If the distance is too great or too small, or if thesensor30 does not face squarely (perpendicularly) on the surface of therod32, the position-determining portion of the pattern visible to thesensor30 will be out of focus. Testing has shown that a transverse or side load induced by the weight of therod32 itself or other laterally-acting forces on therod32, deflects therod32 from theaxis38 of thecylinder housing40, forming an angle between the axis of therod32 and the axis of thecylinder40. The greater the distance between thesensor30 and thecylinder housing40, the more exaggerated the problem becomes. This problem is more evident in actuators with larger diameter and longer piston rods.
• The means for supporting thesensor30, such as the illustratedsensor mount36, includes abearing platform100 that is tethered to thecylinder housing40 with a flexible coupling that accommodates deflection of therod32 from alignment of its longitudinal axis with thelongitudinal axis38 of thecylinder housing40. Thebearing platform100 is made of a bearing material. Thesensor30 is mounted directly to the bearing material, rather than being mounted on a support structure that is in turn coupled to a separate bearing material. The flexible coupling allows thesensor mount36 to pivot or rotate about an axis transverse thelongitudinal axis38 of thecylinder housing40 to accommodate the transaxial displacement or bending of therod32, while remaining in contact with therod32 and in a substantially constant position along thataxis38.
• The flexible coupling is provided by aflexible retaining wire102 andcorresponding grooves104 and106 in themount36 and the inner surface of thecylinder housing40, respectively, that form a wire lock. Thesensor mount36 is thus separate from theseal gland50. Theretaining wire102 prevents movement between themount36 and thecylinder housing40 along theaxis38, but sufficient clearance between the wire lock,seal gland50 andsensor mount36 exists to allow thesensor mount36 to flex relative to thecylinder housing40. In other words, the wire lock permits some rotation of thesensor mount36 about an axis transverse thelongitudinal axis38. The wire lock thus allows thesensor mount36 to pivot relative to thecylinder housing40, thereby maintaining a consistent orientation and spacing between thesensor30 and thesurface34 of therod32. In minimizing or preventing movement along thelongitudinal axis38 of thecylinder housing40, the wire lock also maintains a substantially constant axial position of thesensor30 relative to thecylinder housing40. Other types of flexible coupling also would work, such as a gimbal mount or other arrangement.
• The illustratedsensor mount36 is in the shape of a collar that extends completely around thepiston rod32. The central aperture in thesensor mount36 receives and is substantially filled by thepiston rod32. The axis of the central aperture in themount36 preferably is coextensive with the longitudinal axis of thepiston rod32 at all times. Thesensor mount36 further includes a transverse passage or bore110 that intersects the central aperture, preferably perpendicular to the axis of the aperture, which axis is aligned with the longitudinal axis of therod32 when assembled. Themount36 preferably includes one or more wiper seals adjacent the sensor bore110 to clear debris from therod surface34. In the illustrated embodiment, an inner peripheral surface of themount36 has acircumferential recess112 that receives a peripheral seal orwiper114 that prevents debris on thesurface34 of therod32 that might interfere with the sensor's detection of the pattern on thepiston rod32 from entering the aperture. The opposing side of the sensor bore110 is protected by the seals66-70 in theseal gland50. The sensor bore110 is thus interposed between theouter wiper114 and the peripheral seals66-70 of theseal gland50.
• Accordingly, a method of providing a flexible connection for an absolute-position sensor30 in a piston-cylinder actuator20 comprises the following steps:
• a) separating the optical sensor mount36 from theseal gland50; b) providing less clearance between thesensor mount36 and thepiston rod32 than the clearance between theseal gland50 and therod32; c) providing a wire lock connection between theseal gland50 and thesensor mount36; and d) building in sufficient clearances between the wire lock,seal gland50, and sensor mount36 to allow flex between theseal gland50 andsensor mount36.
• While thesensor mount36 has been shown and described as part of a complete system, theactuator20, thesensor mount36 also could be provided as part of a kit for retrofitting existing actuators. Additionally, although the invention is described with reference to a piston-cylinder actuator, the sensor can be used with hydraulic actuators, pneumatic actuators, rotary actuators, or any other device that requires position sensing. Moreover, the invention is not limited to optical sensors, and the principles of the invention may be applicable to other types of sensors that need to be precisely positioned relative to the moving object being detected, such as a magnetic-type sensor that needs to have a read head closely spaced relative to surface with magnetically-readable indicia.
• In summary, the present invention provides an actuator design with aunique sensor mount36 made from a bearing material and a flexible connection between thesensor mount36 and thecylinder housing40. This flexible connection allows therod32 to deflect naturally, under its own weight or under other laterally-directed forces, while maintaining the distance and perpendicularity between thesensor30 and the marked rod surface, within acceptable limits. This flexible connection is attained by a) separating thesensor mount36 from theseal gland50; b) providing less clearance between thesensor mount36 and therod32 than between theseal gland50 and the rod21; c) providing a wire lock connection between theseal gland50 and thesensor mount36; and d) building in sufficient clearances between the retainingwire102, theseal gland50, and thesensor mount36 to allow ‘flex’ or limited relative non-axial movement between theseal gland50 and thesensor mount36. Thesensor mount36 is made from a bearing material that will allow it to float directly on therod surface34 without scuffing or otherwise damaging therod surface34, particularly the markings or other indicia on that surface. Due to the flexible connection between thesensor mount36 and thecylinder housing40, the proper distance between thesensor30 and therod surface34 can be maintained at all times. The concepts in (a)-(d) above, in conjunction with thesensor mount36, provide a unique solution to the lateral deflection problem.
• Although the invention has been shown and described with respect to a certain preferred embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a “means”) used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.

Claims (14)

1-15. (canceled)

16. A piston-cylinder actuator, comprising:

a cylinder assembly including a cylinder housing that defines a cylindrical volume, the cylinder housing having a longitudinal axis;

a piston assembly generally movable relative to the cylinder assembly along the longitudinal axis, the piston assembly including a piston rod having indicia extending longitudinally on a surface of the rod;

a sensor capable of reading the indicia on the piston rod; and

means for supporting the sensor relative to the piston rod;

where the support means includes a bearing surface for interfacing with the piston rod and an aperture transverse the bearing surface to provide the sensor with access to indicia, and the support means is flexibly connected to the cylinder housing to pivot relative to the cylinder housing while maintaining the sensor at a substantially constant position along the longitudinal axis relative to the cylinder housing.

17. An actuator as set forth inclaim 16, where the support means includes a sensor mount made of a bearing material.

18. An actuator as set forth inclaim 16, where the cylinder assembly includes a seal gland mounted in the cylinder housing, the seal gland having a central aperture for receipt of the piston rod.

19. An actuator as set forth inclaim 18, where the seal gland is separate from the sensor mount.

20. An actuator as set forth inclaim 18, where clearance between the sensor mount and the piston rod is less than clearance between the seal gland and the piston rod.

21. An actuator as set forth inclaim 18, where a wire lock provides a flexible connection between the seal gland and the sensor mount.

22. An actuator as set forth inclaim 18, where the sensor mount is connected to the cylinder housing with a retaining wire that forms a wire lock.

23. An actuator as set forth inclaim 22, where the flexible connection between the sensor mount and the cylinder housing is provided by ensuring sufficient clearances between the retaining wire, the seal gland, and the sensor mount.

24. An actuator as set forth inclaim 16, where the mount is made of a bearing material.

25. An actuator as set forth inclaim 16, where the mount includes a collar that defines a passage therethrough for receipt of the piston rod.

26. An actuator as set forth inclaim 16, where the mount includes a collar that extends around the piston rod

27. An actuator as set forth inclaim 16, where the sensor is an optical sensor.

28. A method of providing a flexible connection for a sensor mounted on a piston-cylinder assembly comprising the steps of:

a) separating an optical sensor mount assembly from a seal gland assembly,

b) providing less clearance between the sensor mount and a rod than the clearance between a seal gland and the rod,

c) providing a wire lock connection between the seal gland and sensor mount

d) building in sufficient clearances between the wire lock, seal gland, and sensor mount to allow ‘flex’ between the seal gland and sensor mount.

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