Composite fluid actuated cylinder
A fluid actuator having a honed metallic sleeved inner liner assembled with fitted end caps. The inner liner and end caps are wound with carbon reinforced fiber filaments in both longitudinal and hoop orientations so as to withstand increased fluid pressure over traditional metallic designs. The fluid actuator of the present invention is lightweight and had an extremely stiff piston and rod assembly, which may also be fabricated from high flexural modulus composite materials so as to allow for a very stiff, lightweight, hydraulic cylinder which is particularly resistant to column buckling at long extensions and comprises an economical, non-rebuildable design.
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This invention relates generally to hydraulic cylinders used for actuation which permits a substantial weight reduction without sacrificing strength and allows for greatly longer actuation strokes due to the use of high modulus composite fiber for both the cylinder and piston rod assemblies. To provide actuator cylinders having lighter weight than those constructed with a monolithic metal piece but at the same time providing adequate strength, the use of a composite cylinder has been suggested. Typical of such composite cylinders are those disclosed in prior art U.S. Pat. Nos. 5,415,079, 4,685,384, 4,697,499, 4,802,404, and 4,773,306 which are hereby incorporated in their entirety by this reference. The composite cylinders disclosed in these patents include a metal liner which is wound with hoop windings made of a suitable composite fiber such as a graphite filament impregnated with a suitable resin. The filaments, in addition to being hoop wound, have also been helically wound, and in some instances, disposed in longitudinal winding form. The combination of the hoop, helical and longitudinal windings provide the ability for the composite cylinder to react to circumferential loads, axial loads and compressive loads generated in the cylinder during the operation of the hydraulic actuator. Heretofore, in order that the cylinder had the necessary strength and resistance to buckling under fully loaded and extended conditions, it was necessary to greatly oversize the rod diameter to meet the Euler buckling criteria. Such a diameter increase not only increases weight, but also subtracts from the available hydrostatic area developed by the opposing piston face in the generation of net usable pressure.
SUMMARY OF THE INVENTIONIn accordance with one aspect of the invention, a composite wound hydraulic cylinder assembly utilizes pre-assembled sleeve and end caps. A piston and rod may be inserted into the sleeve, and the sleeve and end caps become a mandrel for filament winding operations.
According to other aspects of the invention circumferential or hoop stress windings are provided around the sleeve, which may be a honed metal sleeve to minimize diametral expansion and stresses. The mandrel may also include longitudinal windings at a small wind angle to constrain the pair of end caps against hydrostatic forces acting to push them away from the honed sleeved cylinder.
Also, in accordance with another aspect of the invention, the rod and piston elements are fabricated from high modulus composite fiber so as to provide significant bending moment stiffness and resistance to column buckling over traditional steel rod designs.
A composite cylinder constructed in accordance with the present invention is adapted for use in a wide variety of applications requiring lightweight components, large force, and long strokes. Such hydraulic actuators are particularly well suited for robust, high load robotics, special purpose manipulators, aircraft flight control actuators, or the like. Typically, dual acting capability is required, meaning that pressure can be applied to either side of the piston to effect outward and inward movement on a piston rod. According to some embodiments of the present invention, appropriate fluid inlet and outlet passages and mounting means are included. Although not shown in the embodiments below, composite cylinders including those made according to principles of the present invention may include linear travel indicators, such as linear variable differential transducers (LVDT), or digital or optical encoders. A full implementation of a hydraulic apparatus is not illustrated herein, since such is well known to those skilled in the art.
Referring to
The thin walled liner 1 is receptive of a piston and rod assembly. A piston 3 of the piston and rod assembly shown in
The piston 3 is attached to a rod 9 as shown in
Pcr=n π2 E I/12
-
- where: Pcr is the critical buckling load,
- n is the type of end constraints applied, and can range from 0.24 to 1.2,
- E is Young's Modulus,
- I is the moment of inertial of the cross section, and
- l is the column length.
Thus it can be seen that for a given cross section and length, the composite rod construction of the present invention can sustain 2.7 times the loading without buckling than can an equivalent steel rod, and such a composite rod would weigh 6 times less than steel of the same dimensions.
The elements of the composite hydraulic cylinder 20 may be respectively first fitted and assembled, and subsequently the thin walled liner 1 and the end caps 5 and 7 may be over-wound with a plurality of layers of impregnated carbon fiber material to provide the overall additional strength required for a hydraulic actuators while at the same time providing a substantial weight reduction. By using composite materials, such as by filament winding the combination of the thin walled liner 1 and the end caps 5, 7, an overall composite hydraulic actuator 20 weight reduction of approximately 75 percent (75%), as compared to metal actuators, may be realized.
In addition, the buckling strength of the rod 9 may also be greatly increased by employing fiber reinforced composite materials. A comparative estimation of the increase in load carrying capability can be seen by referring to
As mentioned above, the thin walled liner 1 is preferably constructed of a hardenable stainless steel (15-5 PH) or other metal capable of having a high surface hardness, and may include a central hollow barrel with the separate end fittings 5, 7, which are assembled and become a mandrel for filament winding. The filament used in winding is preferably a carbon fiber which has been impregnated with an epoxy resin, and preferably includes an appropriate curing agent and a curing accelerator as is well known to those skilled in the art having the benefit of this disclosure.
Composite windings are placed around the outer surface of the thin walled liner (
Referring next to
Although the invention has been shown and described with respect to certain preferred embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of the specification. The present invention includes all such equivalent alterations and modifications, and is limited only by the scope of the claims.
Claims
1. A fluid actuator, comprising:
- a fiber reinforced composite cylinder assembly;
- a piston disposed in the fiber reinforced composite cylinder assembly;
- a fiber reinforced composite rod connected to the piston and extending through an end of the cylinder assembly, the rod being rigid and comprising longitudinally oriented fibers to enhance buckling resistance in the longitudinal direction,
- wherein the fiber reinforced composite cylinder assembly includes fiber reinforcement along the cylinder body and end caps forming a substantially permanently assembled fluid actuator.
2. A fluid actuator according to claim 1, wherein the piston comprises a fiber reinforced composite.
3. A fluid actuator according to claim 2, further comprising a hardened metallic coating disposed over the piston.
4. A fluid actuator according to claim 2, wherein the fiber reinforced composite piston and fiber reinforced composite rod comprise a single-piece integral unit.
5. A fluid actuator according to claim 4 wherein the fiber reinforced composite rod and fiber reinforced composite piston comprises a carbon fiber molded structure.
6. A fluid actuator according to claim 4, further comprising a hardened metallic coating disposed over the fiber reinforced composite piston and rod.
7. A fluid actuator according to claim 1, wherein the piston is adhesively connected to the fiber reinforced composite rod.
8. A fluid actuator according to claim 1, wherein the fiber reinforced composite cylinder assembly further comprises:
- a metal liner;
- first and second end fittings attached to ends of the metal liner;
- a carbon fiber impregnated with an epoxy resin wound about the metal liner and end fittings.
9. A fluid actuator according to claim 8, wherein the carbon fiber is layered in helical and hoop windings.
10. A fluid actuator according to claim 8 wherein the first and second end fittings overlap associated end portions of the metal liner and comprise external domed surfaces.
11. A fluid actuator according to claim 1, wherein the fiber reinforced composite cylinder assembly further comprises:
- a liner;
- first and second end fittings attached to ends of the liner;
- helical and hoop windings about the liner and first and second end fittings as a single unit.
12. A hydraulic actuator, comprising:
- a mandrel, the mandrel comprising:
- a hollow tube including a hardened metallic interior cylindrical surface;
- semi-spherical end caps disposed at each end of the hollow tube;
- carbon fiber wound about the mandrel and reinforcing the hollow tube and semi-spherical end caps of the mandrel;
- a piston and rod assembly comprising carbon fiber reinforcement disposed in the hollow tube, wherein the rod comprises a carbon fiber composite having longitudinally oriented fibers.
13. A hydraulic actuator according to claim 12, wherein the piston and rod are adhesively attached to one another.
14. A hydraulic actuator according to claim 12, wherein the piston and rod comprise a single, integrated piece.
15. A hydraulic actuator according to claim 14, wherein the piston and rod comprise a carbon fiber mold.
16. A hydraulic actuator according to claim 12, further comprising a hardened metallic coating disposed over the piston.
17. An assembly, comprising:
- a piston having a central cavity;
- a rod inserted into the central cavity, wherein the rod comprises a carbon fiber composite having longitudinally oriented fibers; and
- an adhesive disposed in an annulus between the central cavity and the rod.
18. An assembly according to claim 17, wherein the adhesive comprises an epoxy.
19. An assembly according to claim 17, wherein the piston comprises a carbon composite and a hardened metallic over layer.
20. A method of making a hydraulic cylinder, comprising:
- providing a cylinder;
- inserting a fiber reinforced composite piston and rod into the cylinder, wherein the rod comprises a carbon fiber composite having longitudinally oriented fibers; and
- winding filament around the cylinder to reinforce substantially all of the surface area of the cylinder and enclose the piston and rod within the cylinder.
21. A method of making a hydraulic cylinder according to claim 20, wherein the cylinder comprises a metallic liner.
22. A method of making a hydraulic cylinder according to claim 21, further comprising attaching end caps to ends of the metallic liner, and wherein the winding comprises winding the end caps and the cylinder as a single unit.
23. A method of making a hydraulic cylinder according to claim 20, further comprising adhesively bonding the piston to the rod.
24. A method of making a hydraulic cylinder according to claim 20, further comprising molding the fiber reinforced composite piston and rod as a unitary piece.
25. A method of making a hydraulic cylinder according to claim 20, further comprising overlaying the piston with a hardened metallic coating.
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Type: Grant
Filed: Jul 26, 2004
Date of Patent: Mar 6, 2007
Patent Publication Number: 20060016329
Assignee: S.A. Robotics (Loveland, CO)
Inventor: Samuel A. Johnson (Loveland, CO)
Primary Examiner: Michael Leslie
Attorney: Holland & Hart LLP
Application Number: 10/899,342
International Classification: F16J 10/00 (20060101);