Force Stacking Assembly for Use with a Subterranean Excavating System

Abstract

A force stacking assembly for use with an earth boring system that includes a series of actuators that each generate a force, and that are arranged to create a combined force that is cumulative of all of the actuators. The actuators include members that react in response to an applied stimulus, such as from an electrical current or magnetic field. The members are arranged in series in a hollow housing, planar bulkheads are transversely mounted in the housing. Each of the members have an end axially abutting a corresponding bulkhead. Ends of each member distal from it corresponding bulkhead couple to a ram member, that in turn couples to a drill bit. Energizing the members causes each to exert a force against the ram member, which is transferred to the bit.

What is claimed is: 
     
         1 . A system for excavating within a wellbore comprising:
 a drill string;   a housing having an end that couples to the drill string;   actuators in the housing that are selectively extendable and that each have an end coupled with the housing; and   a ram assembly having an end coupled to a drill bit, and that couples to ends of the actuators opposite from the ends of the actuators that couple with the housing, so that when the actuators are selectively extended, the drill bit selectively extends a distance from the drill string.   
     
     
         2 . The system of  claim 1 , wherein each of the actuators exerts a force onto the ram assembly when selectively extended, and wherein the actuators are arranged in series in the housing such that a sum of the forces is transmitted to the ram assembly. 
     
     
         3 . The system of  claim 2 , wherein when the actuators are selectively extended, the drill bit is axially displaced an amount substantially equal to axial elongation of one of the actuators. 
     
     
         4 . The system of  claim 1 , wherein the actuators comprise members made from an activatable material that elongates in response to applied electricity. 
     
     
         5 . The system of  claim 4 , wherein the activatable material comprises a substance selected from the group consisting of a piezoelectric material, a magnetorestrictive material, and combinations thereof. 
     
     
         6 . The system of  claim 1 , wherein the drill bit comprises an outer bit having an axial bore, and an inner bit that reciprocates within the axial bore in response to the actuators being changed into an activated state. 
     
     
         7 . The system of  claim 1 , wherein the actuators are axially elongated when selectively activated. 
     
     
         8 . The system of  claim 1 , wherein the housing is hollow and bulkheads are formed within the housing at axially spaced apart locations, and wherein outer peripheries of each of the bulkheads couple with an inner surface of sidewalls of the housing. 
     
     
         9 . The system of  claim 8 , wherein the ends of the actuators that couple with the housing are in abutting contact with the bulkheads. 
     
     
         10 . The system of  claim 1 , wherein planar radial walls are provided inside of the ram assembly, and that extend in a direction transverse to an axis of the ram assembly, and wherein ends of the actuators that couple with the ram assembly abut the radial walls. 
     
     
         11 . The system of  claim 1 , wherein the ram assembly coaxially moves within the housing when the actuators are selectively extended. 
     
     
         12 . A method of excavating within a wellbore comprising:
 rotating a drill string in the wellbore that comprises drill pipe, a drill bit coupled to the drill pipe, and actuators disposed between the drill pipe and drill bit;   generating actuating forces with the actuators by selectively elongating each of the actuators a designated distance; and   imparting a summation of the actuating forces against the drill bit to urge at least a portion of the drill bit away from the drill pipe an urged distance that is substantially the same as the designated distance.   
     
     
         13 . The method of  claim 12 , wherein the actuators are elongated at a frequency that comprises a resonant frequency selected from the group consisting of a resonant frequency of the drill string and a resonant frequency of a formation that surrounds the wellbore. 
     
     
         14 . The method of  claim 12 , wherein selectively elongating each of the actuators a designated distance comprises directing electricity to a magnetorestrictive member disposed in an actuator that axially expands and generates one of the actuating forces. 
     
     
         15 . The method of  claim 12 , wherein the portion of the drill bit urged away from the drill pipe comprises an inner bit that is proximate an axis of the drill bit. 
     
     
         16 . The method of  claim 12 , wherein at least a portion of the drill bit comprises all of the drill bit, and when at least a portion of the drill bit is urged away from the drill pipe the urged distance, the drill bit is urged into excavating contact with a bottom of the wellbore. 
     
     
         17 . A system for excavating within a wellbore comprising:
 a bottom hole assembly that selectively couples to a drill string;   actuators in the bottom hole assembly that are selectively extendable a designated distance and that each exert a force when extended;   a drill bit coupled with the bottom hole assembly; and   a means for transferring the combined forces exerted by the actuators to the drill bit, and urging the drill bit a distance away from the drill string that is substantially the same as the designated distance.   
     
     
         18 . The system of  claim 17 , wherein the actuators comprise members having material that is responsive to an application of electricity. 
     
     
         19 . The system of  claim 18 , wherein the bottom hole assembly further comprises a housing that is coupled with the drill string, and wherein members are arranged in series in the housing, and ends of each of the members are coupled with the housing. 
     
     
         20 . The system of  claim 19 , wherein the bottom hole assembly further comprises a ram assembly that couples to the drill bit, and wherein ends of the members opposite from the ends that couple with the housing couple to the ram assembly, so that when the members expand, the ram assembly is urged axially a distance that is substantially the same.