Nonmetallic Patents (Class 168/DIG1)
  • Patent number: 6076607
    Abstract: A horseshoe having adjustable flexibility 100 provides a body formed of left and right body portions 200, 300. In a preferred embodiment, forward ends of the body portions are connected by one of three or more alternative center pieces, each resulting in greater or lesser flexibility of the overall horseshoe. A rigid center piece 400 provides very little flexibility; a composite center piece 500 provides a greater degree of flexibility; and a flexible center piece 600 provides the greatest flexibility. The three may be easily interchanged. The horseshoe having adjustable flexibility 100 allows control over the degree to which a horse's hoof splays on impact, and other factors. A plurality of anti-splay flanges 700 allow control over the degree to which the hoof is allowed to splay or flex outwardly, by adjusting the rigidity of the connection to the horse's hoof. An elastic cross-member 800 may be attached between the rear end portions of the left and right body portions.
    Type: Grant
    Filed: September 8, 1998
    Date of Patent: June 20, 2000
    Inventor: Lyle E (Bergy) Bergeleen
  • Patent number: 6056062
    Abstract: A surgical block for attachment to a healthy claw of a cleft-footed animal is made of a blend of polyvinyl chloride and calcium carbonate. The block has parallel faces which are mirror images of each other. The faces are joined by a planar sidewall extending the full length of the block, and a second side wall having a planar section parallel to the first side wall and a forwardly disposed curved section forming the forward end of the block. A planar end wall is perpendicular to the planar portions of the two side walls. Each of the faces has a plurality of longitudinally extending zigzag grooves to receive an acrylic adhesive to attach the block to the animal's claw.
    Type: Grant
    Filed: October 7, 1998
    Date of Patent: May 2, 2000
    Inventor: Travis L. Robison
  • Patent number: 6021851
    Abstract: Horse hoof protection is obtained by incorporating a urethane resin reaction product of low viscosity sides A and B which react rapidly to gel in a few seconds while filling the interstices of the horse's hoof and have when reacted a low hardness of 40 to 80 Shore A to cushion the hoof.
    Type: Grant
    Filed: August 31, 1998
    Date of Patent: February 8, 2000
    Inventor: Richard L. Jacobs
  • Patent number: 5871054
    Abstract: A hoof/shoe attachment device (10) attaching a shoe (14) for a hoofed animal to the animal's hoof without the use of nails. The shoe (14) and an adapter (12) are held together by a adaptor fastener (12C) such as rivets. The hoof/shoe attachment device (10) comprises materials that prevents the rivet heads from pulling through. At least two fabric layers (adaptor cloth retainer upper layer (12BA) and adaptor cloth retainer lower layer (12BB) are embedded in the adaptor (12). The adaptor cloth retainer upper layer (12BA) is made from an arimid fiber known for abrasion resistance. The adaptor cloth retainer lower layer (12BB) is made from fiberglass. The hoof/shoe attachment device (10) when bonded to a hoof (16) results in a long wearing nailess shoe.
    Type: Grant
    Filed: May 22, 1996
    Date of Patent: February 16, 1999
    Inventor: Stephen E. Bloom
  • Patent number: 5842523
    Abstract: An ambulation-protection structure for equine hoof including a layer of plastic affixed the outside surface of the hoof's horn wall. The plastic layer is made of a material of several mixed components and hardens in a rigid, dimensionally stable manner on the surface to which it is firmly affixed, this layer, which is 2 to 20 mm thick, running at least over the front half of the periphery of the outside surface of the hoof.
    Type: Grant
    Filed: December 23, 1996
    Date of Patent: December 1, 1998
    Inventor: Peter Stuebbe
  • Patent number: 5699861
    Abstract: A kit which can be used to form a horseshoe, which can be assembled by a farrier in the field, and which can be applied to a horse using adhesives. Specifically, a kit is provided including a rigid cast polymeric sole or a horseshoe, and a rigid planar member for attachment to the sole. A hoof contacting layer (cuff) including a skirt extending therefrom is also provided. The sole, planar member, and hoof contacting layer all include a heat activated thermoplastic urethane adhesive. The kit can also include layers of shock-attenuating material also coated with the adhesive. Such shock-attenuating material may be wedge shaped. Alternatively, additional layers of rigid wedge-shaped material may be added as necessary to produce a shoe with the desired shape. Since the adhesive is heat activated thermoplastic urethane adhesive, a farrier can heat the layers in the field to activate the adhesive and glue the shoe together.
    Type: Grant
    Filed: September 22, 1995
    Date of Patent: December 23, 1997
    Assignee: Trustees of the University of Pennsylvania
    Inventor: Robert D. Sigafoos
  • Patent number: 5681350
    Abstract: A rigid and permeable prosthesis that fills the debrided portion of the wall of a horse's hoof having white line disease or the like includes a mass of particulate material with individual particles coated with a resin so as to cleave to one another at all contact areas and transfer weight, while leaving interconnected pore spaces that allow air and liquid medications to reach the diseased area during the healing process.
    Type: Grant
    Filed: January 11, 1996
    Date of Patent: October 28, 1997
    Inventor: Thomas J. Stovall
  • Patent number: 5353878
    Abstract: A horseshoe having a shock absorbing layer and a metal frame which are tightly coupled to each other due to protrusions and depressions. The shock absorbing layer has an arc-shaped protrusion formed at its bottom front, a plurality of uniformly spaced small protrusions formed on opposite side arms of the layer, a pair of circular protrusions downwardly formed on both ends of the layer. The metal frame has first and second protrusions downwardly longitudinally extending from its lower surface throughout its length, a center protrusion being formed between the first and second protrusions, a first depression being provided between the first and center protrusions, a second depression provided between the second and center protrusions and having a tapered shape.
    Type: Grant
    Filed: December 11, 1992
    Date of Patent: October 11, 1994
    Assignee: Nova Horseshoe Co., Ltd.
    Inventor: Byung S. Lee
  • Patent number: 5330008
    Abstract: A protective covering for a horse's hoof is provided which comprises a horseshoe having convex and concave edges and a polymeric fiber fabric embedded in a polymeric resin bonded to the horseshoe. The fabric extends beyond the convex edge of the horseshoe. When the shoe is fitted to the horse's hoof, the fabric extends up over the outside of the hoof. The protective covering is secured to the hoof using an acrylic structural adhesive both between the hoof and the shoe and between the polymeric fiber fabric and the outside of the hoof. The polymeric fiber fabric is preferably a polyolefin, and particularly preferred is woven polyethylene. The polymeric resin is preferably polyurethane.
    Type: Grant
    Filed: December 2, 1992
    Date of Patent: July 19, 1994
    Assignee: Trustees of the University of Pennsylvania
    Inventors: Robert D. Sigafoos, William Moyer, Mary Hazzard
  • Patent number: 5222561
    Abstract: Shoes for horses are fabricated from a plastic material which is reinforced by kinked metal wire. The shoes are lightweight, readily formable, have good wear properties and are much easier on the horse than metal shoes. The reinforced plastic material is also useful for fabrication of hoof pads.
    Type: Grant
    Filed: October 9, 1992
    Date of Patent: June 29, 1993
    Assignee: Rostoker, Inc.
    Inventors: Richard A. Fisher, Julius J. Bonini, Michael J. McGuire, Gareth Rostoker
  • Patent number: 5213163
    Abstract: A horseshoe comprised principally of semihard polyurethane capable of being reversibly heated to about F. for hot-attachment with a gap-filling adhesive in accordance with the process of the author's prior patent. The shoe has an angular cross section with one leg of the angle bonded to the sidewall of the hoof and the other leg to the bottom of the hoof. The upper leg is of sufficient rigidity to make the L-beam cross section of the shoe strong enough to withstand bending moments without the addition of metal strengthening members. The hot shoe is pliably fit to the contour of the individual hoof as it is being bonded; precise fitting is not required because the adhesive is gap-filling. Lateral relative motion between the shoe and the hoof is prevented by an anchoring mechanism into the sulci of the frog. Case hardened steel plates in the toe and heel regions of the shoe provide superior wear resistance.
    Type: Grant
    Filed: January 30, 1992
    Date of Patent: May 25, 1993
    Inventor: Allan B. Schaffer
  • Patent number: 5199498
    Abstract: A hoof pad comprising a polymer composition containing at least about 50% by weight of high molecular weight polycaprolactone polymers wherein the composition has a melting point of from about F. to about F.
    Type: Grant
    Filed: April 28, 1992
    Date of Patent: April 6, 1993
    Assignee: Michael Diesso
    Inventor: Scott Knudsen
  • Patent number: 5180017
    Abstract: A replaceable horseshoe pad is disclosed for use with a shoe plate. The horseshoe pad comprises a cushioning sole plate and a plurality of ground contacting cleat-like members each jointed to, and extending outwardly from the sole plate. The cleat-like members are adapted to extend through corresponding cleat receiving apertures formed in the shoe plate. The invention further comprises a mechanism for securing the sole and shoe plates to a horse's hoof.
    Type: Grant
    Filed: September 3, 1991
    Date of Patent: January 19, 1993
    Inventor: Samuel M. Alagna
  • Patent number: 5168934
    Abstract: The horseshoe assembly of the present invention comprises a U-shaped pad member having one or more glide clips attached thereto around its outer circumference. Each of the glide clips has a glide surface protruding a short distance below the bottom surface of the pad member. The coefficient of friction of the glide members is less than that of the pad member. A modified form of the invention utilizes a metal plate between the pad member and the horse's hoof. The metal plate has a small roller at its forward edge. A further modification comprises casting a plurality of shoes in various shapes and sizes capable of fitting directly to horses' hooves without further reshaping of the shoes.
    Type: Grant
    Filed: March 5, 1991
    Date of Patent: December 8, 1992
    Inventors: David J. Nebel, Keith L. Hansen
  • Patent number: 5137092
    Abstract: A horseshoe conformed substantially to the U-shaped sole of the hoof and comprising a portion of an elastic friction material and a reinforcing insert of a flexible material, wherein the insert is narrower than the width of the U-shaped sole such that thrust, shock and shear loads are elastically absorbed by the portion. The portion comprises an upwardly open cavity which extends in the longitudinal direction of the portion and in which a separate element of a curable composite material is positioned, the composite material being caused to cure in situ only after the insert has been given its final shape.
    Type: Grant
    Filed: December 7, 1990
    Date of Patent: August 11, 1992
    Inventor: Arne Tuunanen
  • Patent number: 5129461
    Abstract: A plastic shoe for horses to be secured to a hoof in conjunction with exposure to a thermal operation includes a sole part having an upper edge and being constructed substantially in the shape of a horseshoe for placement under an edge of a hoof. A wall part is secured to the sole and protrudes from the upper edge for laminar joining to a conical outer surface of the hoof. At least one of the parts is constructed of material being shrinkable under the effect of heat.
    Type: Grant
    Filed: March 27, 1991
    Date of Patent: July 14, 1992
    Inventor: Sergej Igrow
  • Patent number: 5069289
    Abstract: A new process for attaching a non-metallic shoe to a horse's hoof and for repairing a crack in the hoof. The process involves preheating the hoof and the part to be attached, if any, to about 275 degrees F. and then bonding with a hard paste-type urethane adhesive. The adhesive undergoes a phase change from paste to liquid at the hot surface and thereby produces a highly wetting liquid film that leads to a bond many times stronger than would have otherwise occurred.
    Type: Grant
    Filed: June 18, 1990
    Date of Patent: December 3, 1991
    Inventor: Allan B. Schaffer
  • Patent number: 5048614
    Abstract: A composite horseshoe made of a resilient urethane material and containing therein four separate, spaced apart metal inserts. The first metal insert forms a core in the shape of a horseshoe and lies entirely within the resilient horseshoe. The second and third metal inserts are relatively short elongated plates which lie above the two ends of the first metal insert, with the upper face of each plate lying flush with the surface of the resilient horseshoe. The fourth metal insert is a curved elongated plate called the toe grab which lies along the front of the resilient horseshoe and projects outwardly from the resilient horseshoe.
    Type: Grant
    Filed: July 11, 1990
    Date of Patent: September 17, 1991
    Inventor: John Klimko
  • Patent number: 4993494
    Abstract: A horseshoe (1) conformed substantially to the U-shaped sole of the hoof and having a reinforcing insert (16) of a flexible and, alternatively, partially curable material and a portion (17) which encloses the insert (16) and is made of an elastic friction material. The insert (16) is narrower than the width of the U-shaped sole such that thrust, shock and shear loads generated as the horse moves at a walking, trotting or galloping pace are elastically absorbed by the portion (17) enclosing the insert.
    Type: Grant
    Filed: December 5, 1988
    Date of Patent: February 19, 1991
    Inventor: Arne Tuunanen
  • Patent number: 4972909
    Abstract: This invention is to disclose and claim an open ended light weight molded plastic horseshoe having a core segment of 60% glass fiber reinforced polyurethane plastic molding compound, encapsulated in clear polyurethane having treads and caulks formed on the earth side of the horseshoe. The core segment provides the rigidity for the horseshoe while the encapsulating clear polyurethane provides cushioning and wear properties. The core segment has integrally molded button protrusions on the hoof side surface, the earth side surface, and on the inner and outer edges of the legs.
    Type: Grant
    Filed: January 23, 1989
    Date of Patent: November 27, 1990
    Assignee: Rose Plastics & Machinery, Inc.
    Inventor: Allen J. Rose
  • Patent number: 4957168
    Abstract: A horseshoe molded of a new high impact, high temperature resistant polyphenylene sulfide resin that possesses the unique property of possessing a metallic sound indistinguishable from metal horeshoes. The metallic-sounding plastic horseshoes may be attached to a hoof either by nails or by means of a newer species of super-adhesives. The new metallic-sounding polymer horseshoes have a special advantages over regular metal horseshoes. The new horseshoes are about one-sixth the weight of equivalent size metal horseshoes. They can be adjusted in size and shape by means of heating at or about F. and adjusting of the size and shape to fit the hoof. They possess unique chemical, abrasion, and shock resistance. Their lightweight, metal appearance, and metallic sound make them most suitable for sportswear; also, children and the elderly may now enjoy this healthful sport.
    Type: Grant
    Filed: May 3, 1989
    Date of Patent: September 18, 1990
    Inventor: Orlando A. Battista
  • Patent number: 4896727
    Abstract: A medium and a method for filling or replacing the horn wall or horny parts of the coffin of the hoof of an animal, particularly a horse, the medium consisting of a mixture of a plurality of components, of which one is a synthetic resin and another consists of filler particles such as wood, rubber, cork or a combination of filler particles, the mixture being adapted to be cured by the addition of a hardening catalyst and optionally an accelerator, and the method comprising first freeing the horse's hoof of the parts which are to be replaced, whereupon the shoe is placed under the hoof with the nails already in the correct desired positions, the whole area there being degreased, for example with acetone, thereupon all holes being liberally filled with a medium which hardens in the course of time, the outer surface then being finished after the filling medium has become touch-hard.
    Type: Grant
    Filed: June 15, 1988
    Date of Patent: January 30, 1990
    Inventor: Wilhelmus G. H. M. Busser
  • Patent number: 4892150
    Abstract: A horseshoe including an arcuate elastomeric shoe body having an upper hoof engaging surface and a lower surface. The upper surface is generally flat and has an arcuate force-bearing recess along the internal periphery disposed to receive a trimmed ridge of the keratinous portion of a hoof. The shoe is thermofit to the animal hoof in order to conform the shoe to the irregularities of the hoof. Upwardly extending tabs from the shoe body contact the outer side wall of the hoof and a quick setting adhesive is applied to the tabs. A non-setting adhesive is applied to the force-bearing recess and the upper surface of the shoe body. The non-setting adhesive is also applied to a sole protective flange which extends inwardly from the shoe body. A tough wear member, resembling an iron horseshoe may be adhered to the elastomeric shoe body.
    Type: Grant
    Filed: May 2, 1988
    Date of Patent: January 9, 1990
    Inventor: Owen E. Thoman
  • Patent number: 4888225
    Abstract: The present invention relates to orthopedic splinting articles and methods for forming orthopedic splints at least part way around an animal body part. The splinting articles comprise a unitary blank formed of an open-celled foam sheet impregnated with a water curable, isocyanate functional, polyurethane prepolymer resin. The blank is dimensioned to extend the length of the body part to be immobilized and to partially, but preferably not completely, extend around the circumference of the body part. Upon activation of the resin impregnated foam sheet and molding the same around the body part, an orthopedic splint is formed. The present invention further relates to the use of such resin-impregnated foam materials as walking heels or laminates betweeen casts and walking heels, as supports for orthotic devices such as arch supports for foot orthotics, and as protective coverings for animal hoofs.
    Type: Grant
    Filed: June 3, 1988
    Date of Patent: December 19, 1989
    Assignee: Minnesota Mining and Manufacturing Company
    Inventors: Timothy C. Sandvig, Dennis C. Bartizal, Matthew T. Scholz, Anthony J. Campagna, Chris J. Libbey
  • Patent number: 4765411
    Abstract: A method of shoeing a hoofed animal is provided and includes the step of forming a mold (12) having a general configuration of a shoe for the hoof (80). The mold (12) is filled with a liquid acrylic material (64). The hoof (80) of the animal is placed within the mold (12). The acrylic material is cured utilizing ultraviolet light (50, 52), such that the liqid acrylic material solidifies and is integrally joined to the hoof (80) without any intervening adhesive or mechanical attachment. The hoof (80) is then removed from the mold (12).
    Type: Grant
    Filed: January 20, 1987
    Date of Patent: August 23, 1988
    Inventor: Jerald L. Tennant
  • Patent number: 4690222
    Abstract: A nailless horse shoe comprising a resilient material is disclosed. The horse shoe comprises a curved body, an upwardly projecting tab and downwardly depending projections and gripper. Additional strength is provided by use of a curved member embedded in the body having a high strength to weight ratio.
    Type: Grant
    Filed: December 27, 1985
    Date of Patent: September 1, 1987
    Inventor: Kenneth A. Cameron
  • Patent number: 4580637
    Abstract: This horseshoe has segment 1A joining segments 1B, 1C which have first portions 2B, 2C for connection with segment 1A and second portions 3B, 3C which, in use, overlie a heel region. When assembled segments 1B, 1C are secured fast to segment 1A. Second portions 3B, 3C are formed to cover a range of different feet and adapted to be shaped to the foot to which the shoe is fitted. Segment 1A to 1C are formed from plastics material injection moulded onto steel inserts 4A, 4B, 4C. The inserts 4B, 4C within the second portions 3B, 3C are so contoured as to permit the shaping of the plastics material.
    Type: Grant
    Filed: August 20, 1984
    Date of Patent: April 8, 1986
    Inventor: Stephen J. King
  • Patent number: 4513824
    Abstract: A screw-on horseshoe formed from a plastic material is disclosed. A flex joint is provided that allows the horseshoe to expand and contract as pressure is applied to the horse's hoof, thereby reducing friction between the hoof and the shoe. The horseshoe also provides a lip portion projecting upwardly from a horseshoe base portion to protect the horse hoof wall from obstacles encountered during the movement of the horse. A novel screw having a double helix thread pattern including a high thread pattern and a low thread pattern is used to fasten the horseshoe to the horse's hoof without piercing the hoof wall. The screw includes a keyed recessed self-holding head that is complementary to, and therefore readily driven by, a power drill. A lightweight, yet wear-resistant, horseshoe that is readily attached to a horse's hoof with a minimum amount of labor and a minimum amount of damage to the hoof that can be constructed in many styles and sizes to match a large variety of horse uses is thus described.
    Type: Grant
    Filed: November 18, 1983
    Date of Patent: April 30, 1985
    Inventor: Donald F. Ford
  • Patent number: 4496002
    Abstract: Shoes for horses are fabricated from ultra-high molecular weight ethylene polymers having a molecular weight of at least 1 million. Such shoes are light weight, have good wear properties, and are much easier on the horse's feet than metal shoes.
    Type: Grant
    Filed: July 21, 1983
    Date of Patent: January 29, 1985
    Inventors: Joseph W. Jones, Edward W. Bishop
  • Patent number: 4420046
    Abstract: Horse hoof wear appliance of thermoplastic elastomer, preferable polyurethane, made of two parts, one a strip conforming to the contour of the horny hoof portion of the hoof, with its rear ends united near the hoof buttresses by a connecting strap to form an annulus, the other a closure plate removably attachable for completely closing the free space inside the annulus. The ground bearing surfaces of annulus and the ground bearing surface of closure plate are coplanar and each has longitudinal and transverse anti-skid relief sculptures, divided into four separate regions, forward, rearward, and lateral, and all extending mainly parallel to the adjoining edges of the appliance.
    Type: Grant
    Filed: July 20, 1981
    Date of Patent: December 13, 1983
    Inventor: Jean-Pierre R. Choplin
  • Patent number: 4346762
    Abstract: A two part plastics material horseshoe has a relatively flexible plastics strip part of generally L-shaped cross-section, shaped so as to be suitable for adhering to the side wall of a hoof, and a relatively inflexible plastics shoe-part adapted for bonding to the strip-part once the latter has been adhered to the hoof. The two parts are pre-united in the toe region, to set the relative dispostion thereof prior to adhering the strip part to the hoof. Attachment of the strip-part to the hoof is enhanced by providing a liner having a rough texture within the strip-part, and the shoe-part may be affixed to the strip-part by a heat-welding technique.
    Type: Grant
    Filed: July 1, 1980
    Date of Patent: August 31, 1982
    Inventor: Igal Tovim
  • Patent number: 4235292
    Abstract: A hoof covering for horses comprises a horseshoe-shaped plastic body made integrally of wear-resistant plastic material and having a generally acute-angled cross section. The plastic body has a lower side with a substantially planar tread surface and a planar upper surface which serves as a support for a hoof of a horse, and an upwardly extending side in the form of a side wall capable of being bent into the desired shape for mounting the hoof covering on the hoof by adhesive means. The lower side of the plastic body defines a horseshoe-shaped groove opening into the substantially planar tread surface. A horseshoe-shaped steel yoke is retained in the groove and has a plurality of spaced-apart steel calks which project through the horseshoe-shaped groove and beyond the tread surface of the plastic body. This groove is in the cross-sectional region of its opening slightly narrower than the steel yoke. Screwable connection elements may be provided between the steel yoke and the calks.
    Type: Grant
    Filed: April 11, 1979
    Date of Patent: November 25, 1980
    Inventor: Helmuth Dallmer
  • Patent number: 4206811
    Abstract: A hoof covering for horses comprises a horseshoe-shaped plastic body which has a generally acute-angled cross section so as to form a lower side with a flat upper surface and an upwardly extending side in the form of a conical side wall. The flat upper surface serves as a support for a hoof of a horse. The conical side wall is capable of being bent into the desired shape for mounting the hoof covering on the hoof by an adhesive.
    Type: Grant
    Filed: August 26, 1977
    Date of Patent: June 10, 1980
    Inventor: Helmuth Dallmer
  • Patent number: 4189004
    Abstract: A horseshoe of molded composition having a sole and walls which substantially conform to the shape of a horse's hoof, the shoe is generally slipper-shaped with the front wall being high enough to cover a substantial area of the front wall of the hoof, and the rear wall is limited in height to avoid interference with the cartilage heel of the hoof, the top edge of the side walls slope downward from the upper edge of the front wall to upper edge of the rear wall, at least one reinforcing protuberance on each side wall for admitting self-threading screws for anchoring the horse boot to the side wall of the horse's hoof.
    Type: Grant
    Filed: January 20, 1978
    Date of Patent: February 19, 1980
    Assignee: Les-Kare Inc.
    Inventor: Neel W. Glass
  • Patent number: 4155406
    Abstract: This plastic protection and wearing device for equidae hooves comprises a sole element attached to an upper element engaging the outer surface of the hoof and characterized in that the upper is open at its rear end, the rear end covered with a heel-piece notched to permit the passage of the horny heel plates of the hoof, the heel-piece having a front extension in the form of a pair of wing portions guided in relation to the sole and upper assembly in order to prevent any tilting of the heel-piece in relation to the said assembly when the hoof is enclosed therein.
    Type: Grant
    Filed: July 15, 1976
    Date of Patent: May 22, 1979
    Inventor: Leon Hourlier
  • Patent number: 3961668
    Abstract: A correctional pad for use on the hoof of an animal such as a horse or the like is disclosed comprising a resilient body member having a side wall with a bottom wall extending laterally therefrom. The body member is comprised of a material such as Neoprene or the like so that the side wall member may be adhesively secured to the side of the animal's hoof so that the bottom wall member will be selectively positioned beneath the hoof to alter the flight of the animal's foot. One of the embodiments is substantially straight and is L-shaped in cross-section. A further embodiment is also L-shaped in cross-section but it is curved along its length so as to conform to the curvature of the animal's hoof. The thickness of the bottom wall member may be increased by laminating additional thicknesses thereon.
    Type: Grant
    Filed: January 31, 1974
    Date of Patent: June 8, 1976
    Inventor: Robert A. Sirles