Abstract:
Disclosed is an actuator capable of imparting a linear, rotary, or combined roto-linear force. In one embodiment, the actuator has a rotor and a stator, each having helical grooves with a thrust ball occupying the grooves. A nose piece is situated at the end of the actuator and can be attached to other equipment. The actuator is electrically controlled and can be used in applications requiring high forces or other specialized environments.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a 35 U.S.C. 371 US national phase application of PCT international application serial number PCT/US2014/065191, entitled “DOWN-HOLE ROTO-LINEAR ACTUATOR” filed on Nov. 12, 2014, incorporated by reference herein in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to actuators. More specifically, the invention relates to electrically-controlled actuators that can impart a linear or a rotary force through an angular displacement. 
       BACKGROUND OF THE INVENTION 
       [0003]    There is a need for an actuator in down hole drilling to control mud flow to a drill head which is down hole 8,000 to 15,000 feet. However, it is generally very difficult to control such devices from the surface so as to accurately control the drill bit mud valve. The reason for that is that the pressure at such depths is about 30,000 PSI. In addition to the pressure, the temperature is generally quite extreme (about 280° F.) and silicon based electronic control devices generally do not operate at such temperatures. While some silicon carbide devices are available, they are highly specialized and extremely expensive, and must be used judiciously. In addition to the high pressure, high temperatures become an increasingly greater issue. The operating temperatures are about 320° F. in the bore hole. Finally, at those distances, it becomes very difficult to send high-power electrical signals down the wire and accurately control from 8,000 to 15,000 feet below the controller. The control signals tend to change from where they originate to the location where they are needed and the final wave shape becomes unacceptable. Accordingly, it is preferable to have the power-electronics portion of the control means located directly behind the drill head with the control means being able to accept low-power control signals from the top-side surface. 
       BRIEF SUMMARY OF THE INVENTION 
       [0004]    The present invention relates to the use of actuators to provide force through an angular displacement which is less than a complete revolution of a rotor turning around a stator. This force can be either an angular-linear (roto-linear) displacement or, when combined with a ball screw assembly and a force-transfer element, becomes a linear force displacement or an angular force displacement. The present invention can provide a short stroke and high force roto-linear phase-modulated actuation for use in down-hole drilling-mud valves and the like. Alternatively, the actuator of the present invention can provide only angular displacement 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1A  is an elevation of the stator subassembly of an actuator according to one embodiment of the present invention showing the integrated-threaded mounting tube, stator frame body, internally embedded stator magnetic elements, external helical ball grooves, and lead wires. 
           [0006]      FIG. 1B  is an end-view of the actuator stator subassembly showing the radial location of the stator core embedded in the stator frame. 
           [0007]      FIG. 1C  is a side elevation of the actuator external rotor subassembly showing the internal helical ball grooves, the internal magnetic rotor elements (or permanent magnets), the linear/torsional transfer element, and the output shaft. 
           [0008]      FIG. 1D  is a side elevation of the structures depicted in  FIGS. 1A, and 1C  assembled into a single unit representing the actuator. 
           [0009]      FIG. 1E  is an isometric exploded view the actuator shown in  FIG. 1D . 
           [0010]      FIG. 1F  is a side elevation of the actuator in partial section showing electrical control means connected to a topside control means. 
           [0011]      FIG. 2A  is an elevational side view of a preferred rigid configuration of a force-transfer element which is used in a roto-linear actuator. 
           [0012]      FIG. 2B  is an elevation view with a cut away side view of the linearly-rigid configuration of the force transfer element of the actuator. 
           [0013]      FIG. 2C  is an elevational side view detail with a cut-away showing a torsionally-rigid configuration of the force transfer element. 
           [0014]      FIG. 3A  is a side-view of an angular displacement actuator stator subassembly, according to one embodiment of the present invention, showing the integrated-threaded mounting tube, stator frame body, internal-embedded asymmetric stator element(s), rotation stop and return-spring tang, and lead wires. 
           [0015]      FIG. 3B  is an end-view of the angular displacement actuator stator subassembly showing the radial location of the asymmetric stator core embedded in the stator frame, the return spring, and the rotation stop and spring tang. 
           [0016]      FIG. 3C  is a perspective side-view of the angular displacement actuator external rotor subassembly showing the internal magnetic rotor elements (or permanent magnets), the return spring and the rotation stop. 
           [0017]      FIG. 3D  is an end-view of the angular displacement actuator rotor subassembly showing the outer cylindrical housing, and depicts the radial location of the return spring and the rotation stop. 
           [0018]      FIG. 3E  is a perspective side-view the items depicted in  FIGS. 3A, and 3C  assembled into a single unit representing the angular displacement actuator. 
           [0019]      FIG. 3F  is a side elevation of the angular displacement actuator in partial section showing electrical control means connected to a topside control means. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0020]    The present invention provides means for more accurate control of mud flow to the drill head at even greater depths. Generally the present invention provides an actuator  164  which includes a cylindrical stator assembly  100  which comprises a spaced apart semi annularly spaced thrust groove  116 . In the preferred embodiment, a pair of thrust grooves is provided and each groove is separated by a distance along the length of the stator body. Each of these thrust grooves  116  angularly extends up to about 540 degrees around the exterior of the stator assembly  100 . The stator houses an array of electrically-magnetizeable stator elements  124  positioned around the stator  100 , positioned between the thrust grooves  116 , and serve to interact with the magnetic elements  148  of the rotor assembly  140 . The external helical grooves  116  on the stator assembly  100  provide a channel which partially contains a set of thrust balls  160  that mesh with coextensive matching thrust grooves  144  in the rotor assembly  140 . The stator grooves  116  may be created in the manufacturing process by molding, or machining, or other methods known to a person having ordinary skill in the art. 
         [0021]    The actuator also includes a cylindrical rotor assembly  140  having an inner diameter adapted to rotatably accept the stator  100 . That is, the rotor  140  has an interior space in which the stator  100  resides, as can be seen in  FIGS. 1D and 1E . The rotor  140  has an array of magnetic rotor elements  148  positioned within and adjacent to the stator elements  124  at an application specific spacing, as will be described below. The rotor elements  148  are comprised of either permanent magnet material, or ferrous magnetically-permeable material. The rotor  140  includes a groove  144  that is co-exstensive with the groove  116  of stator  100 . In the preferred embodiment, the rotor  140  has a pair of grooves  144  that align with the grooves  116  of the stator  100 , forming a space that retains thrust balls  160 . When assembled, the thrust balls  160  are placed within the channel of the rotor  140 , and mesh with the co-extensive grooves  116  in the stator  100 , to permit the angular movement of the rotor  140  upon the stator  100  to also impart a linear movement of the rotor  140  upon the stator  100 . In other words, the thrust balls  160  and grooves allow a screw-like motion between the rotor  140  and stator  100 . The internal grooves  144  on the rotor assembly  140  may be created in the manufacturing process by molding, or machining, or any other forming process. The rotor assembly  140  also includes conical nose piece  152  projecting from one end which interfaces with one or more tools used for working at depth. The other end of said rotor  140  provides access for the stator  100  there within. In one preferred embodiment, threads  108  on an end of the stator  100  provides for mounting the actuator  164  to another piece of equipment or a suitable carrier. 
         [0022]    The helical pitch of the external grooves  116  on the stator, and the internal grooves  144  of the rotor  140 , is governed by the linear force that is required from the actuator based upon the application that the actuator is designed for. If a short-stroke high linear-force displacement is required, the helical groove pitch will be shallower than if a high-stroke low linear-force displacement is required. That is, an actuator  164  with a shallow pitch will have a shorter linear displacement for one revolution of the rotor  140  when compared to the linear displacement of an actuator  164  with a steeper pitch over the same revolution. 
         [0023]    As an example of one application-specific variation of the actuator, the linear stroke length is 0.18 inches and the force required is 125 pound-force. In this example, the required helical groove spacing is 3 inches, when the achievable angular displacement is 20 degrees. The achievable angular displacement is a function of the ratio of the number of salient electromagnetic stator elements  124  (12 in this example) to the number of salient magnetic rotor elements  148  (8 in this example). In this case a stroke frequency of 10 Hz leads to a supplied power of 0.032 hp and a device power consumption on the order of 50-150 W. Other variations of the present invention can be specified depending on the application for which it is being used. 
         [0024]      FIGS. 1A-1F  show a presently preferred embodiment of a roto-linear embodiment of the present invention that provides either an angular force displacement, a linear force displacement, or both an angular and linear force displacement to a mechanical load. The type of force applied, linear, angular, or both, will depend on the configuration of the force transfer element  153 , which is shown in  FIGS. 2A-2C . 
         [0025]    Referring to  FIG. 1A , stator subassembly  100  includes an integrated mounting tube  104  having mounting threads  108 . Stator subassembly  100  is preferably made from a nonmagnetic material, such as a high temperature resin. Mounting tube  104  is preferably a hollow cylindrical member that provides access for stator drive wires  112 . Helical grooves  116  are provided on the outside surface of the stator subassembly  100  to convert an angular motion to a linear motion as more completely depicted by the roto-linear actuator  164  in  FIG. 1D . The stator subassembly  100  is a pressure vessel that is molded around stator winding assembly  120 . In the present embodiment, the stators poles  124  of stator winding assembly  120  are shown as separate stator cores. However, in alternative embodiments a one piece stator core with multiple salient poles  124  can be used. 
         [0026]    As show in  FIG. 1B  the stator winding subassembly  120  is concentrically located within the body of stator subassembly  100 . Stator poles  124  of the stator winding subassembly  120  are preferably encapsulated within a nonmagnetic body of the stator subassembly  100 . 
         [0027]    In  FIG. 1C , a perspective view of the external rotor subassembly  140  of the roto-linear embodiment of the invention is shown. In rotor  140 , the helical grooves  144  are provided on an inside surface of the rotor  140  and are congruent with helical grooves  116  in stator subassembly  100 . When the helical stator grooves  116  and the helical rotor grooves  144  are aligned, with thrust balls  160  disposed in the space created by the overlapping grooves, angular motion is converted to linear motion as more completely depicted by the actuator  164  in  FIG. 1D . The magnetic rotor elements  148  are preferably internal to the rotor, and are made of a magnetically permeable, or permanent magnet, material to produce torque when interacting with the magnetic flux produced by stator poles  124 . The force transfer element  153  transfers only linear motion to output shaft  156  if transfer element  153  is linearly rigid and torsionally free, such as the transfer element shown in  FIG. 2B . However, it can transfer only angular motion to output shaft  156  if transfer element  153  is torsionally rigid and linearly free, as shown in  FIG. 2C . The transfer element  153  can transfer linear and angular motion to output shaft  156  if the transfer element  153  is both torsionally and linearly rigid. 
         [0028]    Referring to  FIG. 1D , a perspective view of an assembled roto-linear actuator  164  is shown. External helical grooves  116  on stator subassembly  100  align with the internal helical grooves  144  on rotor subassembly  140  and include within the formed grooves force transferring thrust balls  160 . The entire assembly  164  is mounted for use via mounting tube  104  and mounting threads  108 . Output linear and/or rotational force, or both, is transferred to the load by threaded output shaft  156 . Output shaft  156  is threaded to allow the actuator to be attached to an additional tool or object. Alternatively, output shaft  156  is provided without threads. 
         [0029]    An isometric exploded view of the major subassemblies—stator subassembly  100  and rotor subassembly  140 —that make up the overall mechanical portion of the actuator  164  ( FIG. 1D ) is shown in  FIG. 1E . External helical grooves  116  of stator subassembly  100  align with the internal helical grooves  144  on rotor subassembly  140  by means of force transferring balls  160 . The entire assembly  164  is mounted for use by means of mounting tube  104  and mounting threads  108 . Output linear and/or rotational force, or both, is transferred to the load by threaded output shaft  156 . 
         [0030]      FIG. 1F  depicts a logical-electronic control means  180  of the roto-linear actuator  164 . Interconnect wiring  112  from actuator  164  electrically connects to connection points  176  of the logical-electronic control means  180 . Electrical power is supplied to the logical-electronic control means  180  via connection point  168 , and logical control signals are passed to the logical-electronic control means via connection point  172 . The control means  180  functions by providing power in the form of electronic drive signals to the stator coils in the actuator to affect the movement of rotor  140  about stator assembly  100 . The instantaneous dynamic current of the stator coils in the stator is monitored by control means  180  in order to ascertain the position of the rotor, and/or the instantaneous-angular-torque/linear-force provided by the actuator to the load. The control means  180  is programmed with appropriated mathematical relations to affect the delivery of the required linear and/or angular force displacement to the load, and to dynamically adjust the drive parameters utilizing feedback resulting from monitoring the dynamic current values of the coils in the stator assembly  120 . The control means  180  can be programmed, and actuated via the logical control port  172 . 
         [0031]      FIGS. 2A through 2C  show different configurations of force-transfer-element  153 . Force-transfer-element  153  may be configured to transfer both linear and angular motion displacement, transfer only linear displacement, or transfer only angular displacement. The selection of which element  153  to use is done in the initial configuration before being placed into service. 
         [0032]      FIG. 2A  shows a rigid configuration for force-transfer-element  153 . In this embodiment of the element, collar  152  is rigidly connected, or is a monolithic structure with shaft  156 . In this embodiment, the rotational and/or linear displacement that collar  152  is subjected to is transferred directly to shaft  156 . 
         [0033]      FIG. 2B  shows the linearly rigid configuration for force transfer element  153 . In this embodiment of the element, collar  152  is shaped in a manner that allows shaft  156  to rotate within collar  152 , but permits any linear displacement imparted on collar  152  to be transferred to shaft  156 . 
         [0034]      FIG. 2C  shows the torsionally-rigid configuration for force-transfer-element  153 . In this embodiment of the element, collar  152  is shaped in such a fashion which allows shaft  156  to stroke within collar  152 , but allows any angular displacement imparted on collar  152  to be transferred to shaft  156  via keyways and keys  232 . 
         [0035]      FIGS. 3A through 3F  show an alternative embodiment of the present invention that provides angular force displacement to a mechanical load. The actuator in this embodiment provides powered angular displacement in one angular sense and utilizes a spring to return the angular displacement to the rest position and utilizes a multi-salient stator with a single winding. As shown in  FIGS. 3A-3F , thrust grooves  116  and  144  are not present. Consequently, rotation of the rotor assembly  340  does not result in linear motion in this particular embodiment. 
         [0036]    Referring to  FIG. 3A , a perspective view of the stator subassembly  300 , integrated mounting tube  304 , and mounting threads  108 . Mounting tube  304  is a hollow member and provides access to stator drive wires  112 . The multi-salient single winding stator  320  is shown and spring return stop tab  324  is also displayed. 
         [0037]    As show in  FIG. 3B  the stator winding subassembly  320  is concentrically located within the body of the device  300 , and the salient poles  328  of the stator winding subassembly  320  are totally encapsulated within the non-magnetic body of the stator subassembly  300 . 
         [0038]      FIG. 3C  is a perspective view of the external rotor subassembly  340  of the device. The salient magnetic rotor elements  348  are internal to the rotor, and are made of a magnetically permeable material in order to produce torque when interacting with the magnetic flux produced by the stator poles  328 . The ridged-threaded output shaft  352  is shown at the drive end of the external rotor subassembly  340 . The return spring  356  is shown as well as the return spring retaining tang and stop tab  344 . 
         [0039]    As shown in the end view of rotor subassembly  340  in  FIG. 3D , the housing is visible and the return spring  356 , the return spring retaining and stop tab  344  are shown. 
         [0040]      FIG. 3E  is an elevation of the angular displacement actuator according to the alternative embodiment of the present invention. The multi-salient stator poles  320  and magnetic rotor elements  348  are shown in their assembled state. The entire assembly is mounted for use by means of mounting tube  304  and mounting threads  108 . Output rotational force is transferred to the load by threaded output shaft  352 . 
         [0041]      FIG. 3F  shows the logical-electronic control means  180  of the angular-displacement actuator. Interconnect wiring  312   a  and  312   b  from the actuator connects to connection points  372   a  and  372   b  of the logical-electronic control means  180 . Electrical power is supplied to the logical-electronic control means  180  via connection point  168 , and logical control signals are passed to the logical-electronic control means via connection point  172 . The control means  180  functions by providing power-electronic drive signals to the multi-salient stator coil  120  of the angular-displacement actuator to affect the movement of the rotor  340  about the stator assembly  300 . The instantaneous dynamic current of the stator coils  320  in the stator  300  is monitored by the control means  180  in order to ascertain the position of the rotor  340 . Alternately the angular displacement actuator may contain flux sensing windings, or other position sensors, as part of stator coils  320  to provide highly accurate rotor  340  position feedback to the control means  180 . 
         [0042]    The feedback provided by said position sensor is connected to points  372   b , and shown on  FIG. 3F  as ‘Sense, Se’. The control means  180  is programmed with appropriated mathematical relations to affect the delivery of angular force displacement to the load, and to dynamically adjust the drive parameters by utilizing feedback resulting from monitoring the dynamic current values of the coils  320  in the stator  300 , and/or the position sensor. The control means  180  can be programmed, and actuated via the logical control port  172 .