Abstract:
An actuator (A) includes a body (10) in which a plurality of chambers or bores (34) are defined. The bores are interconnected at an inner end by an elongated passage (30). A heater element (32) extends along the elongated passage. The elongated passage and the inner portion of each chamber or bore are filled with a polymeric material which expands and flows on heating, preferably undergoing a solid to liquid phase change. Extensible members (12), such as pistons, diaphragms, bellows, or the like, are mounted in the bores or wells. When the heater heats the polymeric material causing it to expand and flow, the extensible elements (12) extend under high force with limited travel. In one embodiment, the extension of the extensible members moves a thrust bearing (B) causing frictionally engageable plates (18, 22) of a friction member assembly (C) to engage.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to mechanical power actuators. It finds particular application in conjunction with high force, low travel extensible actuators for brakes, clutches, and the like, and will be described with particular reference thereto. However, it is to be appreciated that the invention will also find application in conjunction with tension control mechanisms, automated chuck mechanisms, chain tension mechanisms, presses, drum brakes, collar brakes, and the like. 
     Applicant&#39;s prior U.S. Pat. Nos. 5,025,627, 5,177,969, and 5,419,133 illustrate a mechanical actuator which provides forces equal to and exceeding the forces that are readily available from hydraulics. Heat is applied, typically in the form of an electrical current through a resistance heater, to a wax or polymer material within a confined chamber. Heating causes expansion of the wax or polymer material, causing a piston or other mechanical member to extend. Selecting a wax or polymer which goes through a phase change during the heating accentuates the expansion of the polymer and the force/travel of the extensible member. At relatively short travels, these prior actuators achieve forces on the order of 10,000-20,000 psi, and higher. 
     Although successful, one drawback of these prior thermochemical/mechanical actuators resides in coordinating the movement of multiple actuators. Through the use of feedback control circuitry, the applicant has been able to control the extension of these actuators with high precision. However, such feedback control circuits tend to be relatively expensive and bulky. 
     The present invention contemplates a new and improved sealed chamber actuator which overcomes the above-referenced problems and others. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the present invention, a new and improved electromechanical actuator is provided. An elongated passage contains polymeric material which expands and flows when heated. A heater element is disposed along the elongated passage. A plurality of chambers are disposed in fluid communication with the elongated passage. An extensible member is mounted in each chamber such that as a polymeric material expands and flows, a common force is exerted on each of the extensible members urging each to extend. 
     In accordance with a more limited aspect of the present invention, the elongated passage is annular. 
     In accordance with another more limited aspect of the present invention, extension of the extensible members causes engagement of a thrust bearing which urges frictional contact between selectively mating friction members, such as a clutch or brake. 
     In accordance with another aspect of the present invention, a brake or clutch assembly is provided. First and second clutch or brake friction members are selectively movable between a frictional engaging relationship and a spaced, disengaged relationship. An actuator selectively moves the friction plates between the spaced, disengaged relationship and the frictional engaging relationship. The actuator includes a housing which defines at least one chamber therein. An extensible member is mounted at least partially within the chamber for selective movement between a retracted position and an extending position. A polymeric material is disposed in the chamber below the extensible member. A heater disposed in thermal communication with the polymeric material selectively heats the polymeric material, causing it to flow and expand. 
     In accordance with a more limited aspect of the present invention, the housing includes a plurality of the chambers each containing the polymeric material and an extensible member. An elongated passage interconnects the chambers. 
     One advantage of the present invention is that it enables a plurality of extensible members to extend with like extension and force characteristics. 
     Another advantage of the present invention resides in its relative simplicity. 
     Other advantages of the present invention reside in its low cost and high reliability. 
     Still further advantages of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating a preferred embodiment and are not to be construed as limiting the invention. 
     FIG. 1 is a cross-sectional view of an annular thermochemical mechanical actuator in accordance with the present invention in combination with a thrust bearing and a clutch or brake plate; 
     FIG. 2 is a top view of the annular actuator of FIG. 1; 
     FIG. 3 is a detailed view of one embodiment of a heater for the annular actuator of FIGS. 1 and 2; 
     FIG. 3A is a cross-sectional view through section 3A--3A of FIG. 3; 
     FIG. 4 is another embodiment of the heater of FIG. 3; 
     FIG. 4B is a sectional view through section 4A-4A of FIG. 4; 
     FIG. 5 is an alternate, annular piston embodiment of the thermochemical/mechanical actuator; 
     FIG. 5A illustrates a cross-section of one embodiment of the actuator of FIG. 5; 
     FIG. 5B illustrates a cross-section of another embodiment of the actuator of FIG. 5; 
     FIG. 6 illustrates another alternate embodiment of the thermochemical/mechanical actuator in which force is transmitted radially; 
     FIG. 7 illustrates an alternate, linear embodiment of the actuator; and, FIG. 8 illustrates an alternate, triangular version of the actuator. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A thermochemical/mechanical actuator A which includes a body portion 10 is fixed against longitudinal, and preferably rotational movement. A plurality of axial, longitudinally extensible members 12 extend from the body during actuation. The extensible members 12 press against a longitudinally movable, but preferably rotationally stationary, plate 14 of a thrust bearing B, a hydrodynamic bearing, or other actuation mechanism. Ball or roller bearings 16 connect the first plate 14 of the thrust bearing with a second or output plate 18 which is connected with a shaft 20. When the longitudinally extensible members 12 extend, pressure on the first thrust bearing plate moves the whole thrust bearing assembly, including the output plate and the shaft 20 longitudinally, engaging a brake or clutch plate 22 of a friction member assembly C. 
     In the clutch embodiment, the clutch plate 22 is connected with a second shaft 24. One of shafts 20 and 24, preferably shaft 24, is connected with a source of motive power, such as an engine or motor. The other shaft, preferably shaft 20, is connected with associated equipment that is selectively connected to the motive power source and disconnected from the motive power source. Extension of the members 12 moves the thrust bearing and friction member assembly into locking frictional engagement such that the shafts 20 and 24 are frictionally locked to rotate together. 
     In a brake embodiment, one of the shafts 20, 24, preferably shaft 24, is connected with a rotating member, e.g., the wheel of a vehicle. The output plate 18 of the thrust bearing is locked against rotational movement. Actuation of the actuator presses the thrust bearing, or an associated braking surface, against the brake plate 22, causing frictional braking. It will be appreciated that in this embodiment, the shaft 20 is locked against rotation or can be eliminated. 
     In a tension control embodiment, a sensor 26 senses the rotational speed of the output shaft, e.g., shaft 20, the tension on a web that is driven by rotation of shaft 20, or the like. In response to the sensed condition, an actuator control 28 adjusts the degree of extension and/or amount of force of the longitudinal extension members 12 to adjust the degree of frictional engagement between the thrust bearing B and the friction member assembly C which is connected to the source of motive power. 
     With continuing reference to FIG. 1 and further reference to FIG. 2, the body member 10 of the thermochemical/mechanical actuator A defines an elongated, preferably annular channel 30 which extends around the body member. For manufacturing simplicity, the body is preferably constructed of two steel members which are welded. An electrical heater 32 is mounted in the annular channel 30 for selectively heating a polymer, wax, metal alloy, or other phase change or thermally expansible material therein. The housing further defines a plurality of bores 34, three in the preferred embodiment, in communication with the annular channel 30. The pin or other longitudinally extensible member 12 is disposed in each bore. Other suitable extensible members include snap domes, bellows, differential pistons, and the like. More specifically to the preferred embodiment, each bore receives a bearing and seal 36 about an upper portion of the bore. A compression sleeve 38 compresses a gasket, such as an O-ring 40, sufficiently to provide an effective seal to prevent the polymer from flowing along the sides of the longitudinally extensible member and escaping. Other gasket or seal mechanisms, such as a diaphragm, bellows, other gasket configurations, or the like, are also contemplated. 
     In operation, the control 28 causes the heater element 32 to commence heating the polymer material, melting and expanding it. Polymer along the heater element melts first, establishing a fluid reservoir of the polymer extending along the heating element. With continued heating, more of the polymer melts and expands, causing the elements 12 to extend. The fluid path between the bores 34 defined by the flowable polymer surrounding the heater element provides a pressure equalization path such that the same pressure is developed in each bore. Equalized pressure in the bores causes the extension members 12 to extend with like force. When the heater is turned off, the polymer cools and contracts, causing a like contraction of the members 12. Preferably, a spring force is provided which urges the extension members to return to their initial position. 
     Various heat removal techniques may be employed to accelerate cooling and retraction. The housing body 10 may simply have sufficient heat capacity or be thermally connected with other structures which do. Alternately, air or other gaseous fluids may be passed over the housing body 10 to cool it. As another embodiment, liquids may be passed over or through passages in the housing body 10 to cool it. For example, the entire body may be immersed in a coolant bath such as oil or water. Alternately, passages can be defined within the body 10 through which a coolant fluid is circulated. The coolant circulation may be controlled by a pump connected with the output shaft. In this manner, if the unit starts to overheat, the extension members 12 extend engaging the clutch and commencing the pumping of the coolant. 
     With reference to FIGS. 3 and 3A, the heater element 32 of the preferred embodiment is a cable or tube type heater. A resistive heating element 50 extends along the center of the heater, such as an Imonel, nichrome, nickel, or other resistance wire. The wire is surrounded by a magnesium oxide or other electrical insulator 52 which has good thermal conductive properties. A sheath, such as a stainless steel sheath 54 surrounds the assembly. In DC applications, the sheath 54 provides a current return path for the current flowing through the resistive element 50. In AC applications, a grounded return is provided within the sheath. Alternately, the coil could extend in a full loop such that both ends of the resistance wire pass through a high pressure fitting 56, that provides a high pressure seal with the housing body. 
     With reference to FIGS. 4 and 4A, other heaters are also contemplated. For example, an annular carrier 60 of insulating material defines a multiplicity of openings 62 therethrough, at least adjacent the chambers 34. The opening provides transverse passages to permit the polymer to flow across the carrier and into the bores 34. Inner and outer annular edges 64 and 66 provide clamping edges for clamping the carrier 60 centered within the annular passage 30. An adhesive layer 68 fixes the position of each of a plurality of windings of resistive wires 70, such as copper, nichrome, nickel, or the like. optionally, other wire mounting mechanisms, such as a series of clips or guides, may also be utilized. optionally, another adhesive or mounting layer may be mounted to the opposite face of the polymeric carrier 60 to accommodate a second set of heater wires. Moreover, a plurality of these units can be stacked. In a direct connection embodiment, ends of the windings 70 are connected through a high pressure feedthrough and are connected with the heater control 28. In an inductive embodiment, the ends of the windings 70 are connected to each other in a loop to function as the secondary winding of a transformer. A primary winding is disposed adjacent the housing and the power is conveyed by induction from the primary to the secondary winding. In this manner, high pressure feedthroughs are eliminated. 
     In FIGS. 5 and 5A, the plurality of individual pistons are replaced with a single, annular piston 80. The annular piston 80 is disposed in an annular bore 82 with appropriate seals (not shown). The annular bore 82 connects with the annular passage 30 within which the heater element 32 is disposed. 
     In the embodiment of FIG. 5B, the annular passage 30 is connected with a plurality of bores 34. A piston, bellows, diaphragm, or other movable member 84 is slidably disposed in each bore with appropriate seals (not shown). The bores 34 extend between the annular path 30 and an annular groove in the housing in which the annular piston member 80 is slidably disposed. In this manner, a plurality of piston or other extensible elements 84 are disposed between the polymer ring 30 and the annular piston 80. 
     With reference to FIG. 6, it is to be appreciated that the extensible members 12 need not extend longitudinally. Rather, the members can extend radially outward from the housing member 10, radially inward, or both. A member with outward radially moving extension members can be utilized as a drum brake element, a clutch which engages a surrounding clutch cylinder, or the like. The embodiment with radially inward extending members can be utilized as a collar brake or clutch to engage a shaft extending therethrough. The inward, radially extending members may also engage elements of a chuck for engaging tools or workpieces, or the like. 
     With reference to FIG. 7, it is to be appreciated that the passage 30 need not be a full annulus, and need not be annular. Rather, an elongated passage 30&#39; of another shape, such as linear, extends between a plurality of bores 34&#39;. Extensible members 12&#39; are disposed within each of the bores with appropriate seals. The extensible members can extend from a common side of the body to provide a linear pressing movement. Alternately, the extensible members 12&#39; can extend from opposite sides of the body member to create force in two directions to increase the effective travel of the actuator. 
     The elongated passage may have other shapes than linear and circular. In general, the passage may extend between any two or more points at which extensible members are to be extended with like force characteristics. For example, as shown in FIG. 8, the elongated path may extend along a triangular shape. Bores with extensible members can be located at various points along the triangle such as at the midpoints, the corners, or the like. Other patterns such as square, rectangular, hexagonal, irregular, and the like are also contemplated. 
     The invention has been described with reference to the preferred embodiment. obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.