Abstract:
A hybrid linear actuator features a central load shaft on which a plurality of solid-state magnetostrictive thrusters are positioned in operative relation to electric motors of a permanent magnet synchronous type to impart linear thrust force to the load shaft through clutch units also positioned thereon and under control of force and stroke amplification of output force from motor shafts projecting from the motors.

Description:
The present invention relates to a high thrust force producing actuator. 
   BACKGROUND OF THE INVENTION 
   High powered, long stroke linear actuators as generally known in the art involve use of solid-state thrusters, motors, self-activating clutches and compliant gearing. Such actuators are disclosed for example in U.S. Pat. Nos. 5,705,863 and 6,294,849, featuring methods of enhancing operation of a magnetostrictive type of motor to minimize and limit stroke impact. 
   Because hydraulic cylinder type linear actuators heretofore utilized have a low power density, attempts have been made to replace such hydraulic actuators with electromechanical types of linear actuators with higher power density without success because of reliability and scaling problems with power screws. Controllability problems have also occurred with respect to the clutch units associated with linear actuators, while stroke limiting problems were heretofore associated with the use of solid-state thrusters in such linear actuators. It is therefore an important object of the present invention to provide a linear force applying actuator involving the beneficial use of electric magnetostrictive types of motors and solid-state thrusters with clutch units having associated facilities to deal with load inertia and control stroke while avoiding the other aforementioned problems heretofore associated with linear actuators. 
   SUMMARY OF THE INVENTION 
   Pursuant to the present invention, a hybrid actuator capable of imparting a linear drive force to a load is provided with both solid-state thrusters and electric linear motors through which such drive force is generated and applied in opposite directions to the load through sets of clutch units under control of compliant stroke and force amplification devices. The arrangement and construction of components forming the hybrid actuator is such as to accommodate control over drive force speed and stroke length in accordance with cyclic variations in clutch operation. As to the component constructions, the solid-state thrusters may feature use of magnetostrictive rods and stacks and high force generating linear electric motors of a permanent magnet synchronous type. 

   
     DESCRIPTION OF DRAWING 
     A more complete appreciation of the invention and many of its attendant advantages will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing wherein: 
       FIG. 1  is a side elevation view of a hybrid linear actuator constructed in accordance with one embodiment of the present invention; 
       FIGS. 2 and 3  are transverse section views taken substantially through planes indicated by section lines  2 — 2  and  3 — 3  in  FIG. 1 ; 
       FIG. 4  is a side elevation view of the actuator illustrated in  FIG. 1 , with outer housing sections thereof removed; 
       FIG. 5  is a longitudinal section view taken substantially through a plane indicated by section line  5 — 5  in  FIG. 3 ; 
       FIG. 6  is an enlarged partial section view taken substantially through a plane indicated by section line  6 — 6  in  FIG. 5 ; and 
       FIG. 7  is a partial section view taken substantially through a plane indicated by section line  7 — 7  in  FIG. 2 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring now to the drawing in detail,  FIG. 1  illustrates a hybrid actuator  10  having an axially elongated housing section  12  adapted to be fixedly anchored at one axial end by a mounting piece  14 . A pair of elongated, parallel-spaced bolts  16  with nuts  17  on the ends thereof interconnect the housing section  12  with a somewhat larger housing section  18  at the other axial end of the hybrid actuator  10  from which an actuating shaft  20  projects for attachment to a load to be driven. 
   As shown in  FIGS. 2 and 3 , the shaft  20  is of a dimensionally constant, six-sided cross-sectional shape extending throughout the actuator  10  between axial shaft end  22  and axial shaft end  24  at which the shaft  20  is attachable to the load for imparting a drive force thereon. Positioned within the actuator housing section  12 , which is of rectangular cross-sectional shape as shown in  FIG. 3 , are six tubular motors  26  of a linear synchronous permanent magnet type. Such motors  26  are disposed in radially spaced relation to the shaft  20  on opposite lateral sides thereof within the housing section  12 . Also disposed within the housing section  12  about the shaft  20  are sets of sixteen magnetostrictive thrusters  32  as shown in  FIG. 3 . 
   Referring now to  FIG. 2 , disposed within the housing section  18  in engagement each of the six (6) planar sides of the shaft  20  are clutch units  34 . Also located within the housing section  18  are gear boxes  40  within which a force and stroke magnification mechanism is provided for engagement with the clutch units when driven by the motors  26  as hereinafter explained. 
     FIG. 4  illustrates the hybrid actuator  10  corresponding to that shown in  FIG. 1  with the housing sections  12  and  18  removed together with their associated attachment bolts  16  and mounting piece  14 , thereby exposing the motors  26  and the gear boxes  40 . Also shown exposed are two clutch plates  36  and  38  through which motor output shafts  42  from the motors  26  extend into the gear boxes  40  to control the clutch units  34 . 
   With reference to  FIGS. 3 and 5 , the two sets of eight magnetostrictive thrusters  32  are shown positioned along the shaft  20  with associated thrust plates  28  and  30  at the axial ends of each set of thrusters  32  through which thrust forces are transmitted to the clutch plates  36  and  38 . The thrusters  32  are located on the planar surfaces of the shaft  20 , radially spaced from the motors  26  so that the motor output shafts  42  may transfer forces to the clutch units  34  amplified by mechanisms  70  within the gear boxes  40  as shown in  FIG. 7 . 
   Referring now to  FIG. 6 , one embodiment of the magnetostrictive thrusters  32  is illustrated, which may be utilized in the hybrid actuator  10  as hereinbefore described. Such a thruster  32  includes two magnetostrictive rods  44  respectively disposed within a pair of excitation coils  46  extending axially between magnetic yokes  48  and  50  to complete a magnetic circuit. The two coils  46  are wound so that the magnetic flux therefrom is additive to reduce the required coil size. A positioning screw nut  52  holds the yoke  48  attached to the thrust plate  28  which is electrically grounded through the housing section  16 , while a positioning screw nut  54  holds Belleville spring  56  in position abutting the yoke  50  to pre-stress the thruster rods  44  between the electrically grounded plates  28  and  30 . A thruster piston  58  extends from the yoke  50  through the thrust plate  30  to the clutch plate  36  interconnected by links  60  as shown in  FIG. 5  to the other clutch plate  38 . 
   Each of the motors  26  as shown in  FIG. 5  includes permanent ring magnets  62  positioned in axially spaced relation to each other on the motor shaft  42  within an outer non-magnetic tubular body  64 . Multi-phase windings  66  are positioned within the motor body  64 . Operation of such motor  26  occurs in response to electrical current supplied to the windings  66  from an external power source through cable  68  as shown in  FIG. 2 , for transmission of electrical energy to the excitation coils  46  of the thrusters  32  and motor windings  66  for imparting linear drive forces through the clutch units  34  to the shaft  20  under control of mechanisms within the gear boxes  40 . 
   According to the embodiment as illustrated in  FIG. 7 , the force and stroke amplification mechanism  70  enclosed within the gear box  40  embodies a pair of lever links  72  and  74  interconnected with each other by a flexural pivot  76 . The link  72  is connected at one end by a flexural pivot  78  to an anchor  80  fixed to the gear box  40  housing so as to act as a force amplifying lever. The link  74  is also anchored to the gear box housing through a flexure pivot  84  and is connected by the flexural pivot  76  and an output link  82  to the input lever link  72 . The link  74  thereby operating as an output lever is connected through an output flexure pivot  86  and an output element  88  to the clutch unit  34  to transmit output force thereto. Input force is applied from the motor shaft  42  through a flexure pivot  90  to the input lever  72 . The foregoing configuration of the mechanism  70  magnifies force or stroke without changing direction of the input force transmitted from the motors  26  to the clutches  34  in the arrangement of the present invention as hereinbefore described. 
   From the foregoing description it will be apparent that speed of load displacement by the actuator  10  may be controlled by adjustment of both the total thrust force applied to the shaft  20  from the magnetostrictive thrusters  32  and the linear motors  26  by change in the number of operational cycle phases and cycle length associated with the drive clutch units  34 . By imposition of more stress on the clutch units  34 , length of their operational cycle may be further increased to increase load speed. 
   In the embodiment of the present invention hereinbefore described, two sets of six drive clutch units  34  are associated with the six motors  26  of the tubular linear permanent magnet synchronous type so that forces derived from each set of three motors  26  will evenly drive both set of six clutch units  34 , through the mechanisms  70  in the gear boxes  40  under control of the linear motors  26 . When such motors  26  are driven by the load, they become generators to provide regenerative braking or energize the magnetostrictive thrusters  32  to assist in controllable reactions of the shaft  20 . 
   Obviously, other modifications and variations of the present invention may be possible in light of the foregoing teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.