WO2017123400A1

WO2017123400A1 - Optical sensor mounting interface with integrated hydraulic vent

Info

Publication number: WO2017123400A1
Application number: PCT/US2016/068189
Authority: WO
Inventors: Ronald Roth; Stuart MEURER
Original assignee: Parker-Hannifin Corporation
Priority date: 2016-01-11
Filing date: 2016-12-22
Publication date: 2017-07-20

Abstract

There is a piston-cylinder actuator including a sensor for reading indicia on a linearly movable piston rod of the actuator for determining relative position of the piston rod relative to a cylinder assembly of the actuator. The sensor is mounted to the cylinder assembly adjacent a sensor chamber of the cylinder assembly that receives a portion of the piston rod for being read by the sensor. The actuator has a primary seal for sealing the piston rod to the cylinder assembly, and a secondary seal for sealing about the piston rod to reduce contamination of the sensor chamber, where the a secondary seal is disposed between the sensor chamber and the primary seal. A leakage path configured for directing fluid leaked past the primary seal away from the sensor chamber extends from an interior to an exterior of the cylinder assembly.

Description

OPTICAL SENSOR MOUNTING INTERFACE WITH

INTEGRATED HYDRAULIC VENT

Related Applications

This international application claims the benefit of U.S. Provisional

Application No. 62/277,070, filed January 1 1 , 2016, which is herein incorporated by reference in its entirety.

Field of Invention

The present invention relates to a piston-cylinder actuator, such as a hydraulic actuator, 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. The mounting arrangement is configured to vent hydraulic fluid leaked from the cylinder housing to the environment.

Background

Linear actuators, such as piston-cylinder actuators, are used in various applications throughout industry, such as in construction equipment, aerospace equipment, naval equipment, etc. Often it is advantageous for an operator to be aware of the specific position of a linearly movable member of the linear actuator, such as a piston rod in a fluid pressure-operated cylinder, since the working member being actuated is generally physically connected to the end of the linearly movable member.

In the case of a piston-cylinder actuator, a sensor such as an absolute- position sensor may be mounted relative to the cylinder housing of the piston- cylinder actuator. The sensor may be positioned to sense the position of the rod that is axially shiftable relative to the cylinder housing. For example, the absolute position sensor may be an optical sensor that includes a light source to illuminate and read an indicia pattern on the rod as the rod passes through a reading chamber of the actuator. The reading may include detecting 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 from the portion of the pattern detected by the sensor.

Such sensors can be subject to providing defective readings or failing to read a relative pattern on a piston rod altogether when debris or other contaminants enter the reading chamber. The other contaminants may include oil or other hydraulic fluid that has leaked from the respective cylinder housing into the reading chamber. Summary of Invention

The present invention provides a piston-cylinder actuator including a sensor for reading indicia on a linearly movable piston rod of the actuator for determining relative position of the piston rod relative to a cylinder assembly of the actuator. The sensor is mounted to the cylinder assembly adjacent a sensor chamber of the cylinder assembly that receives a portion of the piston rod for being read by the sensor. The actuator has a primary seal between the piston rod and the cylinder assembly to seal pressure inside the cylinder assembly, and a secondary seal, such as a scraper, for sealing about the piston rod to reduce or all together prevent contamination of the sensor chamber, where the secondary seal is disposed between the sensor chamber and the primary seal. A leakage path configured for directing fluid leaked past the primary seal away from the sensor chamber extends from an interior to an exterior of the cylinder assembly.

In some embodiments, the leakage path may be disposed along the longitudinal axis between the primary seal and the secondary seal. In some embodiments, the cylinder assembly of the piston-cylinder actuator may be constructed with minimal seals at a head end adjacent the sensor which may reduce part count and which may reduce complexity of the tolerance stackup between the piston rod, cylinder assembly, and seals of the cylinder assembly. This construction consequently may simplify manufacturing of the rod and the indicia pattern disposed on the rod for being read by the sensor. The construction may also allow for weight and size reduction of the actuator and/or provide for a leakage path in the case of seal wear over time.

In some embodiments, the sensor may be coupled to a sensor mount that is coupled to the head end of the cylinder housing. The mount may include the sensor chamber and be configured to receive the piston rod. Accordingly, the mount may be constructed to direct hydraulic fluid leaked from the cylinder housing away from the sensor chamber of the mount. In some cases a small amount of hydraulic fluid in the sensor chamber can affect accurate reading of the pattern on the rod by the sensor. The mount may include the secondary seal and the leakage path.

According to one aspect, there is a piston-cylinder actuator including a cylinder assembly having a cylinder housing, the cylinder housing having a longitudinal axis, and 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 along the length of the piston rod. The actuator includes a sensor capable of reading the indicia on the piston rod and a sensor chamber defined by the cylinder assembly along the longitudinal axis and receiving the piston rod, wherein the sensor is mounted to the cylinder assembly adjacent the sensor chamber for reading indicia on a portion of the piston rod in the sensor chamber. The actuator also includes at least one primary seal for sealing the piston rod to the cylinder assembly and at least one secondary seal for sealing about the piston rod to reduce contamination of the sensor chamber, the at least one secondary seal disposed along the longitudinal axis downstream of the at least one primary seal and upstream of the sensor chamber. Further included is a leakage path configured for directing fluid leaked from the cylinder housing to an exterior of the cylinder assembly and away from the sensor chamber.

The leakage path may extend from an interior of the cylinder assembly adjacent a pressurizable cylinder chamber of the cylinder housing to an exterior surface of the cylinder assembly.

The leakage path may be disposed along the longitudinal axis between the at least one primary seal and the at least one secondary seal. One opening of the leakage path may be provided at an exterior surface of the cylinder assembly, and a second opening of the leakage path may be provided along a rod path of the cylinder assembly along which the piston rod travels in the cylinder assembly.

The piston-cylinder actuator may include only one primary seal for sealing the piston rod to the cylinder assembly to maintain pressure within the cylinder housing.

The piston-cylinder actuator may further include another secondary seal for sealing about the piston rod to reduce contamination of the sensor chamber, the another secondary seal disposed along the longitudinal axis downstream of the sensor chamber.

The at least one primary seal may be disposed along the longitudinal axis upstream of the leakage path and upstream of the at least one secondary seal.

The at least one secondary seal may be a wiper for wiping the outer surface of the portion of the piston rod being received into the sensor chamber.

The sensor may be an optical sensor.

The cylinder assembly may further include a mount coupled to the cylinder housing, the mount being configured for receiving the piston rod extending from the cylinder housing, wherein the mount includes the sensor chamber, and wherein the sensor is coupled to the mount adjacent the sensor chamber.

The mount may include the at least one secondary seal and the leakage path.

The mount may further include another secondary seal such that the two secondary seals are disposed along the longitudinal axis at opposite sides of the sensor chamber.

The cylinder assembly may further include a cylinder head coupled to the cylinder housing for maintaining pressure in the cylinder housing, and wherein the mount is integral with the cylinder head.

A method of reducing contamination of the sensor chamber of the piston- cylinder actuator may include the steps of: (a) engaging the piston rod via the at least one secondary seal to reduce passage of contaminant from the cylinder housing into the sensor chamber, and (b) directing contaminant leaked from the cylinder housing to an exterior surface of the cylinder assembly via the leakage path disposed upstream of the at least one secondary seal and downstream of the at least one primary seal along the longitudinal axis.

According to another aspect there is a sensor mount for supporting a sensor relative to a head end of a cylinder housing and relative to a piston rod movable within the cylinder housing. The sensor mount includes a mount body, a housing- coupling surface at an exterior of the mount body for fixedly coupling to the head end of the cylinder housing, a central passage internally defined by the mount body for receiving the piston rod, a sensor chamber disposed along the central passage for allowing optical sensing of the piston rod by the sensor, a sensor-coupling surface at an exterior of the mount body adjacent the sensor chamber for coupling to the sensor to arrange the sensor relative to the sensor chamber, and a leakage path extending from the central passage to an exterior surface of the sensor mount for directing fluid leaked from the cylinder housing to an exterior of the sensor mount and away from the sensor chamber.

The leakage path may be disposed along the central passage between the housing-coupling surface and the sensor chamber.

The sensor mount may further include at least one seal for sealing about the piston rod to reduce contamination of the sensor chamber, the at least one seal disposed along the central passage between the leakage path and the sensor chamber.

The sensor mount may further include another seal such that the another seal and the at least one seal are disposed along the central passage at opposite sides of the sensor chamber.

The sensor mount may further include a sensor path defined by the mount body and extending from the sensor chamber to an exterior of the mount body for allowing optical reading of the piston rod by the sensor. The sensor mount may be provided in combination with the cylinder housing, the piston rod movable with the cylinder housing, and the sensor, wherein the sensor is coupled to the sensor-coupling surface, and wherein the housing-coupling surface is fixedly coupled to the head end of the cylinder housing.

The foregoing and other features of the invention are hereinafter described in greater detail with reference to the accompanying drawings.

Brief Description of the Drawings

The annexed drawings, which are not necessarily to scale, show various aspects of the disclosure.

Fig. 1 is a partial top view of an exemplary piston-cylinder assembly according to the invention.

Fig. 2 is a partial side view of the exemplary piston-cylinder assembly of Fig.

1 .

Fig. 3 is a partial cross-sectional view of the exemplary piston-cylinder assembly as shown in Fig. 2.

Fig. 4 is another partial cross-sectional view of the exemplary piston-cylinder assembly as shown in Fig. 2.

Fig. 5 is yet another partial cross-sectional view of the exemplary piston- cylinder assembly as shown in Fig. 2.

Detailed Description

The principles of the present application have general application to linear actuators having a sensor for tracking linear movement of a linearly movable member of the linear actuator. The principles of the present application have more specific application to piston-cylinder actuators having a sensor for determining the linear position of a rod of the actuator, such as relative to a cylinder housing of the actuator. A piston-cylinder actuator described herein may be applicable to any type of piston-cylinder actuator, such as a single rod or double rod actuator, or such as a linear-type or rotational-type actuator. As will be appreciated, the principles of the application are generally applicable to any actuator having an internal fluid that may leak causing inaccurate readings by a respective sensor. As used herein, fluids may include liquids, gases, or a combination thereof. Further, the principles are applicable in a multitude of applications including construction, aerospace, naval, marine, etc.

Referring now to the drawings and initially to Figs. 1 -3, an exemplary embodiment of an actuator provided by the invention is shown generally at 20. The actuator 20 is a double-rodded actuator, such as a balanced double-rodded actuator. The double-rodded actuator 20 includes a cylinder assembly 22 and a piston assembly 24 movable relative to the cylinder assembly 22. The actuator 20 also includes a sensor assembly 26 with a sensor 30 for detecting the position, such as the absolute position, of the piston assembly 24 relative to the cylinder assembly 22.

The principles of the present disclosure are equally applicable to unbalanced double-rodded actuators and single-rodded actuators. Additionally, the sensor assembly 26 of an actuator to which the principles are applicable may be provided for detecting relative position of the piston assembly 24 relative to the cylinder assembly 22.

The depicted piston assembly 24 includes an elongated piston rod 32 that has indicia markings 33 (Fig. 3) (also referred to as indicia patterns) provided on at least a longitudinal portion of its peripheral surface 34 (Fig. 3). The piston assembly 24 also includes another elongated rod 35 disposed opposite the piston rod 32. While the illustrated piston rod 35 does not include indicia 33, the rod 35 may include indicia in other embodiments.

The indicia markings 33 include patterns that extend longitudinally along the length of the rod 32. The patterns may vary along the length of the rod 32, enabling the sensor 30 to identify the position of the rod 32 from a portion of the pattern adjacent the sensor 30. The indicia 33 can be formed in the surface 34 of the rod 32, embedded in the rod 32, etched, carved, formed, or printed on the rod 32, or otherwise provided by other devices that function to identify the position of the indicia 33 relative to the rod 32.

The cylinder assembly 22 includes a cylindrical housing 40. The piston assembly 24 is movable relative to the cylinder housing 40 back and forth along a longitudinal axis 38 of the cylinder housing 40, and thus of the cylinder assembly 22. The illustrated cylinder housing 40 has two opposed ends 42 and 46. The primary end 42 is at least partially closed by a primary cylinder head 50 that receives the piston rod 32 of the piston assembly 24, while the secondary end 46 is at least partially closed by a secondary cylinder head 51 that receives the respective piston rod 35 of the piston assembly 24.

The primary cylinder head 50 is separable from the cylinder housing 40 and is coupleable to the cylinder housing 40, such as via suitable fasteners 39a. A suitable seal 41 a (Fig. 4) seals between the cylinder housing 40 and the cylinder head 50. In other embodiments, where suitable, the cylinder housing 40 and the primary cylinder head 50 may be integral one another. As used herein coupling may include direct coupling or indirect coupling.

Likewise, the secondary cylinder head 51 is separable from the cylinder housing 40 and is coupleable to the cylinder housing 40, such as via suitable fasteners 39b. A suitable seal 41 b (Fig. 4) seals between the cylinder housing 40 and the cylinder head 51 . In other embodiments, where suitable, the cylinder housing 40 and the secondary cylinder head 51 may be integral one another.

Turning now to Figs. 4 and 5, the actuator 22 is shown in partial cross- section. Referring to the primary end 42, although equally applicable to the secondary end 46, the cylinder assembly 22 includes at least one primary seal 52, such as an annular seal. The illustrated primary seal 52 is disposed along the longitudinal axis 38 of the cylinder assembly 22 adjacent the primary distal cylinder end surface 42a. As shown, the primary cylinder head 50 is adapted to support the primary seal 52. In other embodiments the cylinder housing 40 may instead be adapted to receive the primary seal 52. A single primary seal 52 is included for sealing the illustrated piston rod 32 to the cylinder assembly 22. In this way, part count, manufacturing time and manufacturing tolerances are reduced. Concern for minimal leakage past a single primary seal 52 is accounted for, as further detailed below. In other embodiments, the primary end 42 may include more than one primary seal 52.

The primary seal 52 has an outer portion that mates and sealingly interacts with a corresponding inside surface of the cylinder assembly 22. The primary seal 52 also has an inner annular portion that defines a central axial seal aperture that receives the piston rod 32. The aperture in the primary seal 52 allows reciprocating passage or movement of the piston rod 32. The diameter of the seal aperture and the diameter of the piston rod 32 are dimensioned to permit the smooth passage of the piston rod 32 while maintaining pressure within the cylinder housing 40. This may include reducing, and preferably preventing, pressurized working fluid from migrating outside the pressurized volume of the cylinder housing 40. The

pressurized working fluid may be any suitable fluid, such as a suitable hydraulic fluid.

Turning now to additional components of the piston assembly 24, the piston assembly 24 includes the piston rod 32, which extends through the aperture in the primary seal 52, the opposing piston rod 35, which extends through an aperture in respective seals 58 and 59, and a piston head 60 that is closely received within the cylinder housing 40. The piston rod 32 cooperates with the central longitudinal aperture in the primary seal 52 to close the primary apertured end 42 of cylinder housing 40. Likewise, the piston rod 35 cooperates with the central longitudinal apertures in the seals 58 and 59 to close the secondary apertured end 46 of cylinder housing 40.

The piston head 60 is coupled to each of the piston rods 32 and 35 and sealingly divides the cylinder housing 40 into two chambers 62 and 64. The first chamber 62 is disposed adjacent the primary end 42, and the second chamber 64 is disposed adjacent the secondary end 46. The piston rod 32 is attached to the piston head 60 at one end, and an opposing end of the piston rod 32 includes a rod coupling 66 for connecting the actuator 20 to an object to be moved, such as a suitable working member. The piston rod 35 is attached to the piston head 60 at a second and opposite end, and an opposing end of the piston rod 35 includes a rod coupling 67 for connecting the actuator 20 to an object to be moved, such as a suitable working member.

The piston assembly 24 generally is movable along an axis of the piston rod 32, which in FIG. 2 is coextensive with the longitudinal axis 38 of the cylinder housing 40. The piston assembly 24 and the cylinder housing 40 can reciprocate relative to each other depending upon which cylinder chamber 64 or 66 is

pressurized. Pressure is supplied to the cylinder housing 40 by any desired external pressure source (not shown) to a first cylinder port 70 coupled to the chamber 62, and exhausted via a second cylinder port 72 coupled to the cylinder chamber 64, and vice versa, depending on the desired direction of movement.

Turning now to the sensor assembly 26, the sensor 30 is supported on the cylinder assembly 22. The sensor 30 is capable of reading the indicia 33 on the piston rod 32. As shown, a sensor 30 is disposed only adjacent the primary end 42, though in other embodiments, the actuator 20 may include an additional sensor adjacent the secondary end 46 for detecting the position of the piston rod 35. In even other embodiments, the sensor 30 may be omitted and only the additional sensor may be included.

The piston rod 32 and the associated indicia 33 on the rod 32 move relative to both the cylinder housing 40 and the sensor 30, which reads the indicia 33 adjacent the sensor 30 to determine the position of the rod 32 relative to the cylinder housing 40. The sensor 30 preferably is an absolute-position sensor. An exemplary absolute-position sensor is an optical sensor, such as the Intellinder™ sensor from Parker Hannifin Corp. of Cleveland, Ohio U.S., although other non- optical type sensors may be used. The optical sensor 30 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 the surface 34 of the rod 32 and guide reflected light from the rod 32 to the light sensor.

The cylinder assembly 22 defines a sensor chamber 80 providing space for projection of light from the sensor 30 to the rod 32 and for reflection of the light from the rod 32 back to the sensor 30. The sensor chamber 80 is defined by the cylinder assembly 22 along the longitudinal axis 38 and receives the piston rod 32 therein. The sensor 30 is generally mounted to the cylinder assembly 22 adjacent the sensor chamber 86 for reading indicia 33 on a portion of the piston rod 32 in the sensor chamber 80.

Maintaining a specific distance between the sensor 30 and the surface 34 of the rod 32 is important to ensure effective sensing accuracy. If the distance is too great or too small, or if the sensor 30 does not face squarely (perpendicularly) on the surface of the rod 32, the position-determining portion of the pattern visible to the sensor 30 will be out of focus.

Turning now to the depicted arrangement of the sensor 30 relative to the cylinder assembly 22, and more particularly relative to the sensor chamber 80 of the cylinder assembly 22, the cylinder assembly 22 includes a sensor mount 86. The sensor mount 86 is coupled to the sensor 30 and is provided to arrange the sensor 30 adjacent the sensory chamber 80. The sensor mount 86 includes a mount body that defines the sensor chamber 80 therein. Coupling of the sensor mount 86 to the remainder of the cylinder assembly 22 aligns the sensor chamber 80 along the longitudinal axis 38 for receiving the piston rod 32 into the chamber 80.

As illustrated, the sensor mount 86 is coupled to the remainder of the cylinder assembly 22, such as to the primary cylinder head 50. The sensor mount 86 couples, such as fixedly couples, the sensor 30 relative to the cylinder housing 40, such that the sensor 30 is fixed relative to the moving piston assembly 24.

Fasteners (not shown), such as bolts, allow for the coupling, although other suitable fastening elements or methods may be used.

In some embodiments, where suitable, elements of the cylinder assembly 22 may be integral with one another. For example, the cylinder head 50 and the cylinder housing 40 may be integral with one another. In another example, the sensor mount 86 and the primary cylinder head 50 may be integral with one another. Consequently, the sensor mount/cylinder head body of such an

embodiment may include elements of each of the sensor mount 86 and the cylinder head 50 described as separate with respect to the depicted embodiment of Figs. 4 and 5.

The depicted sensor mount 86 includes a housing-coupling surface 90 at an exterior of the mount body for coupling, for example fixedly coupling, to the first head end 42 of the cylinder housing 40. The mount 86 also includes a sensor- coupling surface 92 at an exterior of the mount body adjacent the sensor chamber 80 for coupling to the sensor 30 to arrange the sensor 30 relative to the sensor chamber 80. The sensor mount 86 is configured to receive the piston rod 32 via a central passage 94. The central passage 94 is internally defined by the mount body and extends longitudinally through the mount body for receiving the piston rod 32. The sensor chamber 80 is disposed along the central passage 94 for allowing optical sensing of the piston rod 32 by the sensor 30.

An optical passage 96, also referred to as a sensor path, extends through the mount body from the sensor chamber 80 to an exterior of the mount body, such as the sensor-coupling surface 92. The optical passage 96 enables reading of the indicia 33 on the portion of piston rod 32 in the sensor chamber 80 by the sensor 30. In the depicted embodiment, the optical passage 96 is disposed transverse the central passage 94, though may be otherwise suitable arranged in other

embodiments. The sensor 30 may be sealed to the sensor-coupling surface 92 via a suitable seal, such as a seal disposed about the optical passage 96. This seal is provided to reduce, and preferably prevent, contaminant from leaking into the sensor chamber 80.

If contaminant, such as debris or hydraulic fluid from the cylinder housing 40, or other contaminant from the actuator 20, leaks or otherwise travels into the sensor chamber 80, the indicia 33 may be at least partially obscured. The contamination may cause delay or partially inaccurate or wholly inaccurate readings of the indicia 33 by the sensor 30. The more contamination in the sensor chamber 80, the more exaggerated the problem may become.

To account for this concern, the sensor mount 86 further includes at least one secondary seal 102 for sealing about the piston rod 32 to reduce, and preferably prevent, contamination of the sensor chamber 80. As depicted, the sensor mount 86 includes a pair of opposing secondary seals 102 and 104, such as scrapers, disposed along the central passage 94 at opposite sides of the sensor chamber 80. The sensor chamber 80 is thus interposed between the secondary seals 102 and 104.

When coupled to the remainder of the cylinder housing 22, the secondary seal 102 is disposed along the longitudinal axis 38 downstream of the at least one primary seal 52 and upstream of the sensor chamber 80. As used herein, the upstream direction is defined as a direction from the rod coupling 66 to the cylinder housing 40, while the downstream direction is oppositely defined as a direction from the cylinder housing 40 to the rod coupling 66.

At least one of the secondary seals 102 and 104, and for example both, are wipers for wiping the outer surface of the portion of the piston rod 32 being received into the sensor chamber 80 in a respective upstream or downstream direction. While two secondary seals 102 and 104 are shown, additional seals may be included where suitable.

As will be appreciated, the use of a single primary seal 52 may allow for some leakage of hydraulic fluid from within the cylinder housing 40, such as from the cylinder chambers 62 and 64. In some cases, the indicia 33 on the elongated piston rod 32 may increase a surface finish roughness. Over time, this roughness may increase leakage past the primary seal 52 and/or decrease life of the primary seal 52.

Such leakage while very small may cause contamination of the sensor chamber 80, causing improper readings of the indicia 33 by the sensor 30. In one example, a single drop of hydraulic fluid may leak past the primary seal 52 every approximately fifty cycles of the piston rod 32. This leaked hydraulic fluid may be directed away from the sensor chamber 80 via a leakage path 1 10 that is configured for directing fluid leaked from the cylinder housing 40 to an exterior of the cylinder assembly 22 and away from the sensor chamber 80.

In the depicted embodiment, leakage path 1 10 may direct fluid leaked from the cylinder housing 40 to an external atmosphere at an exterior of the cylinder assembly 22. In other embodiments, the leakage path 1 10 may direct fluid leaked from the cylinder housing 40 to a collection passage that may connect to a collecting tank, such as a fluid supply tank or fluid return tank. In this way, environmental contamination and/or a low-pressure hydraulic oil reservoir in the associated hydraulic system may be reduced. Accordingly, in other embodiments, an exterior of the cylinder assembly 22 at the leakage path 1 10 may include a suitable coupling, such as for connecting a fluid passage tube between the actuator 20 and such a tank.

In the depicted embodiment, the sensor mount 86 of the cylinder assembly 22 includes the secondary seals 102 and 104 and the leakage path 1 10. The leakage path 1 10 extends from an interior of the cylinder assembly, such as at the longitudinal axis 38 adjacent a cylinder chamber 62 of the cylinder housing, to an exterior surface of the cylinder assembly 22. For example, a first opening 1 1 1 of the leakage path 1 10 is provided at an exterior surface of the mount 86 of the cylinder assembly 22, and a second opening 1 12 of the leakage path 1 10 is provided along a rod path of the cylinder assembly 22 along which the piston rod 32 travels in the cylinder assembly 22.

In the depicted embodiment, the leakage path 1 10 extends fully through the mount body between opposing sides of the mount body, such as in a direction generally transverse the longitudinal axis 38 or central passage 94. Thus the leakage path 1 10 has two exterior openings 1 1 1 opposed one another. In other embodiments, the leakage path 1 10 may only extend from an interior of the cylinder assembly 22 to a single opening at the exterior of the cylinder assembly 22. In even other embodiments, more than one leakage path may be included. The leakage path 1 10 is disposed along the longitudinal axis 38 between the primary seal 52 and the secondary seal 102. Put another way, the leakage path 1 10 is disposed along the central passage 94 between the housing-coupling surface 90 and the sensor chamber 80.

Thus, it will be understood that the secondary seal 102 is disposed along the central passage 94 between the leakage path 1 10 and the sensor chamber 80. It will also be understood that the primary seal 52 is disposed along the longitudinal axis 38 upstream of the leakage path 1 10 and upstream of the at least one secondary seal 102.

The construction of the cylinder assembly 22, and particularly of the sensor mount 86, including the secondary seals 102 and 104 and the leakage path 1 10, may provide numerous benefits. Even if debris, hydraulic fluid, or other

contaminant are on the surface of the piston rod 32, the leakage path vent 1 10 and wipers 102 and 104 are provided to maintain cleanliness of the sensor chamber 80. As previously mentioned, these benefits also may include reduced part cost, reduced assembly time and cost, and reduced stackup tolerancing between the piston assembly 24 and the cylinder assembly 22. Other benefits may include reduced weight via elimination of parts and material, and reduced adder length by reducing the number of seals, allowing the actuator 20 to be used for space- conscious applications.

Although the illustrated piston-cylinder actuator 20 is designed for axial movement of the respective piston assembly 24, the sensor mount 86 provided by the present disclosure is applicable to other types of actuators, such as actuators with piston assemblies that rotate relative to the respective cylinder assembly and relative to the sensor mount.

A method of reducing contamination of the sensor chamber 80 of the piston- cylinder actuator 20 includes the steps of: (a) engaging the piston rod 32 via the at least one secondary seal 102 to reduce passage of contaminant from the cylinder housing 40 into the sensor chamber 80, and (b) directing contaminant leaked from the cylinder housing 40 to an exterior surface of the cylinder assembly 22 via the leakage path 1 10 disposed upstream of the at least one secondary seal 102 and downstream of the at least one primary seal 52 along the longitudinal axis 38.

In summary, there is a piston-cylinder actuator 20 including a sensor 30 for reading indicia 33 on a linearly movable piston rod 32 of the actuator 20 for determining relative position of the piston rod 32 relative to a cylinder assembly 22 of the actuator 20. The sensor 30 is mounted to the cylinder assembly 22 adjacent a sensor chamber 80 of the cylinder assembly 22 that receives a portion of the piston rod 32 for being read by the sensor 30. The actuator 20 has a primary seal 52 for sealing the piston rod 32 to the cylinder assembly 22, and a secondary seal 102 for sealing about the piston rod 32 to reduce, and preferably prevent, contamination of the sensor chamber 80, where the a secondary seal 102 is disposed between the sensor chamber 80 and the primary seal 52. A leakage path 1 10 configured for directing fluid leaked past the primary seal 52 away from the sensor chamber 80 extends from an interior to an exterior of the cylinder assembly 22.

Although the invention has been shown and described with respect to a certain 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

Claims What is claimed is:

1 . A piston-cylinder actuator, comprising;

a cylinder assembly including a cylinder housing, 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 along the length of the piston rod;

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

a sensor chamber defined by the cylinder assembly along the longitudinal axis and receiving the piston rod, wherein the sensor is mounted to the cylinder assembly adjacent the sensor chamber for reading indicia on a portion of the piston rod in the sensor chamber;

at least one primary seal for sealing the piston rod to the cylinder assembly; at least one secondary seal for sealing about the piston rod to reduce contamination of the sensor chamber, the at least one secondary seal disposed along the longitudinal axis downstream of the at least one primary seal and upstream of the sensor chamber; and

a leakage path configured for directing fluid leaked from the cylinder housing to an exterior of the cylinder assembly and away from the sensor chamber.

2. The piston-cylinder actuator of claim 1 , wherein the leakage path extends from an interior of the cylinder assembly adjacent a pressurizable cylinder chamber of the cylinder housing to an exterior surface of the cylinder assembly.

3. The piston-cylinder actuator of claim 1 or of any preceding claim, wherein the leakage path is disposed along the longitudinal axis between the at least one primary seal and the at least one secondary seal.

4. The piston-cylinder actuator of claim 1 or of any preceding claim, wherein one opening of the leakage path is provided at an exterior surface of the cylinder assembly, and a second opening of the leakage path is provided along a rod path of the cylinder assembly along which the piston rod travels in the cylinder assembly.

5. The piston-cylinder actuator of claim 1 or of any preceding claim, wherein the piston-cylinder actuator includes only one primary seal for sealing the piston rod to the cylinder assembly to maintain pressure within the cylinder housing.

6. The piston-cylinder actuator of claim 1 or of any preceding claim, wherein the piston-cylinder actuator further includes another secondary seal for sealing about the piston rod to reduce contamination of the sensor chamber, the another secondary seal disposed along the longitudinal axis downstream of the sensor chamber.

7. The piston-cylinder actuator of claim 1 or of any preceding claim, wherein the at least one primary seal is disposed along the longitudinal axis upstream of the leakage path and upstream of the at least one secondary seal.

8. The piston-cylinder actuator of claim 1 or of any preceding claim, wherein the at least one secondary seal is a wiper for wiping the outer surface of the portion of the piston rod being received into the sensor chamber.

9. The piston-cylinder actuator of claim 1 or of any preceding claim, wherein the sensor is an optical sensor.

10. The piston-cylinder actuator of claim 1 or of any preceding claim, wherein the cylinder assembly further includes a mount coupled to the cylinder housing, the mount being configured for receiving the piston rod extending from the cylinder housing, wherein the mount includes the sensor chamber, and wherein the sensor is coupled to the mount adjacent the sensor chamber.

1 1 . The piston-cylinder actuator of claim 10, wherein the mount includes the at least one secondary seal and the leakage path.

12. The piston-cylinder actuator of claim 10 or any of claims 10 or 1 1 , wherein the mount further includes another secondary seal such that the two secondary seals are disposed along the longitudinal axis at opposite sides of the sensor chamber.

13. The piston-cylinder actuator of claim 10 or of any of claims 10-12, wherein the cylinder assembly further includes a cylinder head coupled to the cylinder housing for maintaining pressure in the cylinder housing, and wherein the mount is integral with the cylinder head.

14. A method of reducing contamination of the sensor chamber of the piston-cylinder actuator of claim 1 or of any preceding claim, the method including the steps of:

(a) engaging the piston rod via the at least one secondary seal to reduce passage of contaminant from the cylinder housing into the sensor chamber; and (b) directing contaminant leaked from the cylinder housing to an exterior surface of the cylinder assembly via the leakage path disposed upstream of the at least one secondary seal and downstream of the at least one primary seal along the longitudinal axis.

15. A sensor mount for supporting a sensor relative to a head end of a cylinder housing and relative to a piston rod movable within the cylinder housing, the sensor mount comprising:

a mount body;

a housing-coupling surface at an exterior of the mount body for fixedly coupling to the head end of the cylinder housing;

a central passage internally defined by the mount body for receiving the piston rod;

a sensor chamber disposed along the central passage for allowing optical sensing of the piston rod by the sensor;

a sensor-coupling surface at an exterior of the mount body adjacent the sensor chamber for coupling to the sensor to arrange the sensor relative to the sensor chamber; and

a leakage path extending from the central passage to an exterior surface of the sensor mount for directing fluid leaked from the cylinder housing to an exterior of the sensor mount and away from the sensor chamber.

16. The sensor mount of claim 15, wherein the leakage path is disposed along the central passage between the housing-coupling surface and the sensor chamber.

17. The sensor mount of claim 15 or of any of claims 15 or 16, further including at least one seal for sealing about the piston rod to reduce contamination of the sensor chamber, the at least one seal disposed along the central passage between the leakage path and the sensor chamber.

18. The sensor mount of claim 15 or of any of claims 15-17, further including another seal such that the another seal and the at least one seal are disposed along the central passage at opposite sides of the sensor chamber.

19. The sensor mount of claim 15 or of any of claims 15-18, further including a sensor path defined by the mount body and extending from the sensor chamber to an exterior of the mount body for allowing optical reading of the piston rod by the sensor.

20. The sensor mount of claim 15 or of any of claims 15-19, in combination with the cylinder housing, the piston rod movable with the cylinder housing, and the sensor, wherein the sensor is coupled to the sensor-coupling surface, and wherein the housing-coupling surface is fixedly coupled to the head end of the cylinder housing.