Patent Publication Number: US-7895935-B2

Title: Toroidal ram actuator

Description:
The present invention relates to a ram actuator that operates under fluid pressure to produce rotary motion. 
     BACKGROUND OF THE INVENTION 
     In fields of engineering rotary motion of an actuator or mechanism is obtained by the use of a linear acting hydraulic or pneumatic ram acting on a linkage or mechanical arm about a pivoting axis. 
     Several problems exist with this means of obtaining rotary motion. Firstly, the space required to package the open-close movement of a linear acting ram is often large and undesirable. Secondly, the mechanical linkages involved limit the output rotation angle about the pivoting axis. Thirdly, the corresponding output torque about the pivoting axis varies dramatically depending upon the perpendicular component of force applied by the linear ram acting about the pivoting axis. And fourthly there are undesirable force vectors acting on the pivoting axis and surrounding components, requiring additional strengthening of such surrounding components. 
     The present invention provides a means of producing useful rotary motion in a compact manner and with a consistent and potentially high output torque. 
     SUMMARY OF INVENTION 
     According to the present invention there is provided a toroidal ram actuator comprising a part toroidal shaped cylinder mounted to a first member and a part toroidal piston reciprocally movable within the cylinder, a free end of the piston being mounted to a second member, wherein the first and second members are pivotally attached along an axis and the relative movement between the cylinder and piston produces rotary motion of the first or second member about the axis. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An embodiment, incorporating all aspects of the invention, will now be described by way of example only with reference to the accompanying drawings in which: 
         FIG. 1   a  is an isometric view of a toroidal ram actuator in accordance with an embodiment of the present invention, illustrating a first ram in a fully extended position; 
         FIG. 1   b  is the same view as  FIG. 1   a  but illustrating the first ram and a second ram at intermediate positions; 
         FIG. 1   c  is the same view as  FIG. 1   a  but illustrating the second ram in a fully extended position; 
         FIG. 2   a  is a side elevation of the toroidal ram actuator; 
         FIG. 2   b  is a plan view of the toroidal ram actuator illustrated in  FIG. 2   a;    
         FIG. 2   c  is a front elevation of the toroidal ram actuator illustrated in  FIG. 2   a;    
         FIG. 3  is a side sectional view taken at section A-A of  FIG. 2   b;    
         FIG. 4  is a side sectional view taken at section B-B of  FIG. 2   b;    
         FIG. 5  is an exploded isometric view of the toroidal ram actuator; and 
         FIG. 6  is an exploded isometric view of a second embodiment of the toroidal ram actuator. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
     In the preferred embodiment of the invention shown in the drawing, a toroidal ram actuator  10  consists of two opposing single acting toroidal rams  11 . It is understood however that the principle of the actuator may operate with a double acting toroidal ram. 
     In this specification the definition of toroidal is ‘geometry of, or resembling a torus’ and the definition of torus is ‘a surface or solid formed by rotating a closed curve, especially a circle, about a line which lies in the same plane but does not intersect it’, for example, a ring doughnut. 
     The device consists of two identical, but axially offset toroidal rams  11  which are inverted, namely rotated by 180°, relative to each other such that a first ram appears ‘upside down’ to a second ram. The toroidal rams  11  each comprise a toroidal cylinder  12  and a toroidal piston, or rod,  13  moveable within the cylinder  12 . The cylinders have an enclosed, internal toroidal surface  15  that is circular in cross-section. The cylinders are approximately semi toroidal, namely approximately half a revolution in length. A toroidal axis  17  is defined by the common central axis of the toroidal cylinders. The toroidal cylinders are rigidly attached to one another forming a single body referred to as a toroidal cylinder housing  16 . 
     Each toroidal cylinder is closed at one end, the tail end  19 , and the rod  13  is adapted to extend from the other end which is open and referred to as the open head end  18 . An internal chamber  20  between the head end and tail end is adapted to hold fluid for actuating the rod hydraulically or pneumatically. The fluid used may, for example, be hydraulic oil or compressed air. 
     The head end  18  of each cylinder  12  is provided with seal gland(s)  21  for supporting pressure seal(s)  22 . The tail end  19  of each cylinder is closed off by means of an end cap  25  attached by welding or otherwise. The housing  16  which houses both cylinders  12  is rigidly attached to a static member, or fixed link  30 . The opening of the head end  18  of each cylinder  12  allows the insertion of the toroidal rod  13  which reciprocally extends and retracts within the cylinder. 
     In the preferred embodiment of the actuator  10 , each cylinder  12  contains a wear sleeve  26  which acts as a wearing and guiding surface for each rod inside the cylinder. The wear sleeve  26  is adapted to evenly guide and fully support the rod as it extends and retracts to thereby prevent the rod from rocking or distorting under a load. The sleeve is made of a wearable material, such as a composite material, for example nickel filled polytetrafluoroethylene or similar, to allow the rod to move smoothly inside the cylinder. 
     The geometry of the sleeve  26  is similar to that of the cylinder in which it is housed such that the sleeve  26  can be inserted into its corresponding cylinder  12  through the open head end  18 . The sleeve  26  is also circular in cross section. A clearance between the sleeve and internal surface of the cylinder  12  compensates for any misalignments of the rod supported inside the sleeve or if the rod does not follow a true toroidal path. The clearance also facilitates sleeve insertion into the cylinder. 
     Each rod  13  is a solid member made of steel or other suitable metal, is a semi-torus in shape and has a circular cross section. The rods may be heat treated/hardened and/or chromed for greater durability and wear characteristics. The rod  13  is guided and can move freely within its corresponding cylinder  12 . Accordingly, the rod has one degree of freedom, that being the circular path the rod partly subscribes about the toroidal axis  17 . 
     A leading end  28  of the rod protrudes from the head end  18  of the cylinder  12  when the rod is fully retracted in the cylinder. The leading end  28  of each rod is attached to and acts against a dynamic member, namely a dynamic link  31 , which is movable relative to the fixed link  30 . The dynamic link  31  is attached to and rotates about fixed link  30 . The dynamic link  31  also has one degree of freedom, that being the same as the rod, namely a part circular path about the toroidal axis  17 . 
     As the two cylinders  12  are in line but axially offset to the toroidal axis  17 , and inverted relative to each other so that the head end  18  of the cylinders are diametrically opposed, the rods  13  act in opposition to each other on the dynamic link  31 . 
     Each rod  13  is rigidly attached to the dynamic link  31  by using a bolt  38  or other similar fastener to fasten the leading end  28  of the rod to a reaction surface  50  on the dynamic link  31 . The first and second rods  13   a ,  13   b  are attached to opposite sides of reaction surface  50 . 
     Reaction surface  50  is machined to allow an accurate relationship between its opposite surfaces on which the rods  13   a ,  13   b  bear against and the toroidal axis  17  about which the rods  13  and dynamic link  31  rotate. 
     Accordingly, actuation of a first ram  11   a  extends a first rod  13   a  in a clockwise direction about the toroidal axis thereby also moving dynamic link  31  in the clockwise direction, whereas actuation of a second ram  11   b  extends the second rod  13   b , and hence the dynamic link, in an anti-clockwise direction. Ram actuation is alternated between the first and second rams. 
     Actuation of the toroidal rams illustrated in the drawings is carried out by a single acting cylinder in the rams such that fluid is introduced into the cylinder through inlet/outlet ports  33   a ,  33   b , to force the rod  13  to move outwardly of the cylinder under the pressure of increasing fluid. During retraction fluid is forced out of the cylinder through the same inlet/outlet port under the pressure of the rod being pushed back into the housing by the force of the opposing rod. 
     The inlet/outlet ports  33   a ,  33   b  are a through hole from the outside of each cylinder to the inside chamber  20 . Each inlet/outlet port may have welded to it on the outside, a suitable hydraulic or pneumatic fitting to allow a corresponding hydraulic or pneumatic hose or fitting to be attached. 
     In operation, hydraulic or pneumatic fluid is fed into the first cylinder  12   a  via its corresponding inlet/outlet port  33   a . The first cylinder  12   a  becomes pressurized. Simultaneously, hydraulic or pneumatic pressure is relieved from the second cylinder  12   b  by fluid discharging from the second cylinder&#39;s inlet/outlet port  33   b . Hydraulic or pneumatic fluid is prevented from leaking beyond the pressure seals  22 , which form a positive seal between each cylinder and its corresponding rod, and O-rings provided at the head end. 
     Pressurizing first cylinder  12   a  forces first rod  13   a  to fully extend from cylinder  12   a . This step is illustrated in  FIGS. 1   a ,  2   a ,  2   b ,  2   c ,  3  and  4 . Force is then transferred to the dynamic link  31  to which the leading end  28  of rod  13   a  is attached. This in turn produces a torque about the toroidal axis  17  and causes the dynamic link  31  to rotate about the toroidal axis in a first direction. Simultaneously, and in direct proportion, as rod  13   a  extends from cylinder  12   a , second rod  13   b  retracts into cylinder  12   b  under the force imparted by the first rod and transferred through dynamic link  31 , to which the second rod is also attached on an opposing side thereof to the first rod.  FIG. 4 , which shows section B-B of  FIG. 2   b , illustrates second rod  13   b  fully retracted inside cylinder  12   b.    
     Hydraulic pressure is then relieved from the first cylinder  12   a  and pressure is applied to the second cylinder  12   b , which actuates second rod  13   b  to extend. Force is transferred to the attached dynamic link in the opposite direction to that of first rod  13   a , and an opposite torque is created about the toroidal axis  17 , resulting in rotation of the dynamic link  31  in the opposite direction.  FIG. 1   b  illustrates dynamic link  31  partially rotated where rods  13   a  and  13   b  are partially extended at an intermediate position.  FIG. 1   c  illustrates link  31  rotated, with first rod  13   a  fully retracted and second rod  13   b  fully extended. 
     This process is repeated to alternate actuation of the first and second rams  11   a ,  11   b , to thereby reciprocally move dynamic link  31  along an arcuate path centred at toroidal axis  17 . 
     A removable cover may be provided over the toroidal ram actuator  10  to cover the moving rods  13  and prohibit these from being damaged. 
     The cylinder housing  11   b  in this embodiment is constructed from a number of separately machined and fabricated components which define the two opposing cylinders  12   a ,  12   b . The housing parts comprise a central part  35 , two outer parts  36 , one to either side of central part  35 , and two cylinder end caps  25  which close off the tail end  19  of the cylinders  12 . The end cap  25  consists of a flat metal plate welded to the tail end of each cylinder. 
     The central part  35  is approximately half a revolution of a solid metal ring of rectangular section, that is machined on each side to form a semi toroidal shaped channel that is semi circular in cross section. The central part forms half of the internal surface of each cylinder. 
     The outer parts are formed from machining mating components to complete the cylinder formation on either side of the central part. The outer parts  36  are aligned and welded concentrically to each side of the said central part  35  to form a complete pair of axially offset and inverted cylinders. Aligning grooves may be machined into the mating surfaces to assist in alignment. 
     Another alternative method of constructing each said toroidal cylinder housing is to machine the internal toroidal surface from a solid metal disc using a special boring tool and boring machine. The boring tool and machine would be set up so that the tool rotates about the said common toroidal axis and cuts the internal toroidal surface in which the said composite channel and said toroidal rod is housed. 
     Machined into the head end  18  of each cylinder  12  is a cylindrical recess  39  of diameter greater than that of the internal cross-sectional diameter of the cylinder and facing inwardly of the cylinder. This recess  39  forms the recess in which the seal gland  21  is housed, which in turn supports the pressure seal  22 . The external end face of the head end  18  is also machined to form a groove to receive a face seal such as an O-ring  40  or similar. The O-ring  40  seals a gland cover  41  against the cylinder  12 . A second O-ring  46  sits in a groove in the seal gland to seal the gland against the end cover. Drilled and tapped holes  43  machined into the end face of the cylinder&#39;s head end  18  allow for fixing of the gland cover  41  to the head end  18  by way of fasteners  45 . 
     The seal gland  21  is a cylindrical ring made of metal and/or composite material that sits, or ‘floats’, in the cylindrical recess  39  between the rod and the cylinder. A clearance between seal gland  21  and cylinder  12  serves a similar function to the clearance between the wear sleeve  26  and cylinder  12  in that the clearance allows for misalignment during movement of the rod. The depth of the cylindrical ring is equal to that of the said cylindrical recess  39  such that the seal gland sits flush with the external end face of the head end  18 . The seal gland  21  extends into the chamber so that the pressure seal  22  contacts the rod. 
     The seal gland may optionally be made of a composite material similar to that of the composite sleeve  26  with material properties that give the gland better wear characteristics. Such composite materials have low porosity which provides good sealing properties. 
     The seal gland cover  41  illustrated in the figures is a machined flat metal plate with a cylindrical opening  42  in the centre through which rod  13  extends. Around the periphery of the plate are holes  44  which align with the drilled and tapped holes  43  on the face of the head end  18  of each cylinder. Fasteners such as cap screws are used to attach the seal gland cover  41  to the head end  18  of each cylinder  12 . The gland cover seals against the O-rings  40  and  46  preventing hydraulic or pneumatic fluid escaping from the cylinder chamber  20 . A wiper seal (not shown) could be attached or housed on the outside of the seal gland cover and concentric with the opening  42  and would bear against the rod  13  to prevent dirt/debris from entering the seal gland  21 . 
     The pressure seals  22  and wiper seals may be standard linear ram seals, have a geometry that adapts to the arcuate surface of the toroidal shaped rods, or may be custom made seals having an arcuate sealing surface to match the arcuate surface of the rods. One example of a suitable pressure seal is U-seal having a depth that will not compromise seal performance and durability in sealing against a toroidal shaped rod. The pressure and wiper seals may be made from a polyurethane/rubber based material or a similar material/s to that used in standard hydraulic or pneumatic rod seals. 
     A number of drilled and tapped holes in the side of housing  16  are used to attach the cylinder housing to the fixed link  30  using fasteners  45  such as bolts or cap screws. 
     In the first embodiment of the actuator illustrated in  FIGS. 1-5  the fixed link  30  includes through holes  47  that align with the toroidal axis  17  to support a pivoting pin  48  used to attach the fixed link  30  to dynamic link  31 . Pivoting pin  48  extends through similar holes  47  in dynamic link  31 . Bearings  49  and/or bushes  52  mounted in the through holes  47  allow dynamic link  31  to rotate relative to fixed link  30 . 
     A pivoting pin plate  53  attached to the end of pin  48  and fixed, in  FIGS. 1   a - 1   c , to the dynamic link  31 , rigidly fixes the pin to the dynamic link or the fixed link, as desired, to prevent undesired rotation of the pin  48 . 
     The above described embodiment which is illustrated in  FIGS. 1-5  is used to drive a member, such as the dynamic link  31 .  FIG. 6  illustrates a second embodiment which is a variation on the actuator of the first embodiment in that it is used to produce rotary output motion of the pivoting pin  48  to harness the reciprocating shaft rotary motion of the pin  48 . The pivoting pin  48  in this embodiment takes the role of an output shaft  58  and the dynamic link  31  takes on the role of a torque arm  51 . This variation may only be suitable for lower torque output applications such as pneumatic applications due to limitations in the torque transmitting capabilities of the output shaft. 
       FIG. 6  shows that cylinder housing  16  comprises an integrated solid plate  54  on each side thereof. The fixed link in the second embodiment is not illustrated in  FIG. 6 . A through hole  47  concentric with the toroidal axis  17  supports output shaft  58 , bearing  49  and bushes  52 . 
     The torque arm  51  is similar in design to the dynamic link  31 , but has no protruding length beyond the point of attachment of the rods  17  because there is no need for the torque arm to drive a member but instead functions to transmit the torque to the said output shaft. 
     The design of the bushes  49  located in holes  47  is such that the output shaft which passes through the bushes  49  is mechanically linked to the torque arm  51  such that when the torque arm is rotated, the output shaft also rotates. The mechanical link may be in the form of a mechanical attachment such as bushes with two internal flats on the side and corresponding flats machined on the output shaft as illustrated in  FIG. 6 , or may involve more complex geometry such as an internal spline on the bushes and a corresponding external spline on the said output shaft. Any other form of matching geometry to mechanically link the said torque arm to the said output shaft may be used. 
     As discussed above, the toroidal ram actuator may use double acting toroidal ram/s in replacement of the two opposing single acting toroidal rams. The single acting toroidal ram only forces the rod outwardly of the cylinder and relies on an external force to push the rod to retract. One double acting ram actuator could be used to actuate both the extension of the rod and its retraction. Hence, only a single, double acting toroidal ram would be required to produce rotation of the output shaft or dynamic link in both directions, replacing two single acting rams. 
     Accordingly, the actuator  10  may consist of two single acting toroidal rams, or a combination of any number of single or double acting rams axially aligned, offset and/or inverted. Single acting toroidal rams are preferably grouped in opposing pairs. 
     The proposed actuator  10  defines each said toroidal cylinder and corresponding said toroidal rod as being circular in cross section. However the toroidal surface of both the cylinder  12  and the rod  13  may be of a cross section that resembles something other than a circle. For example, an elliptical toroidal surface may be used as well as custom elliptical pressure and wiper seals. 
     The above metal components of the toroidal ram actuator  10  have been described as being formed by machining. It is understood, however, that the components may be casted in accurate cast mouldings and then machined as required. 
     Alternatively, it may be suitable in some lighter applications, such as in a pneumatic actuator which may only requires small output torques and hence small loads, to replace the metal components with a suitable plastic material. The plastic parts may be moulded or machined from raw materials. The overall relative geometry of the toroidal ram actuator in plastic would be similar to that of the above described machined and welded embodiments. 
     The size of the toroidal ram actuator varies according to the application in which it is used. For example, a large actuator would be required in applications such as actuating the arms of excavators, cranes and other heavy earth moving equipment, mining equipment or agricultural equipment. Smaller versions of the actuator may be used in manufacturing processes where pneumatic production equipment is used or the like. Essentially, the present toroidal ram actuator can replace linear ram actuators currently used in any application where rotary motion is to be produced. 
     It will be understood to persons skilled in the art of the invention that many modifications may be made without departing from the spirit and scope of the invention.