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CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the priority of U.S. Provisional patent application Ser. No. 60/336,757 filed Dec. 4, 2001. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to rotating drilling head systems in which an elastomer seals around and grips a rotating drill pipe during drilling operations. 
   2. Description of the Related Art 
   Oil and gas wells are typically drilled by use of a rotating drill pipe with a drill bit at the lower end. Drilling fluids are pumped down the drill pipe and out the drill bit. The drilling fluid returns to the surface, along with cuttings, through the annulus around the drill pipe. In many cases, the pressure at the upper end of the drill pipe annulus is atmospheric. The weight of the drilling fluid is controlled to provide a hydrostatic pressure at the earth formations that is greater than the formation pressure to prevent blowouts. 
   In some cases, however, it is advantageous to isolate the pressure at the upper end of the column from atmospheric pressure. For example, in highly deviated well, a lightweight drilling fluid may be used that is not heavy enough to prevent upward flow in the well due to formation pressure. A drilling head at the upper end of the well controls the pressure. Drilling head systems use an elastomeric element to seal the drilling head against the rotating drill pipe during drilling operations. In some rotating drilling head systems, the seal is formed by the natural resiliency of the elastomeric element against the drill pipe while others use hydraulic pressure to deform the seal element. In U.S. Pat. No. 6,016,880, hydraulic pressure is applied to a bladder that surrounds an elastomeric gripper element that is located above an elastomeric primary seal. The bladder forces the gripper inward to grip the drill pipe to cause the gripper and primary seal to rotate with the drill pipe. The gripper also serves as a secondary seal in the event of leakage of the primary seal. Furthermore, the gripper has to continue gripping and sealing around the drill pipe as it moves downward while drilling. The tool joints at the end of each drill pipe are larger in diameter than the drill pipe and must pass through the gripper while it continues to seal and grip the drill pipe. 
   While the system of the &#39;880 patent is workable, improvements in the gripper are desirable. As the bladder forces the gripper element inward, the gripper deforms, but does not compress. The deformation results in high stress and strain. 
   SUMMARY OF THE INVENTION 
   The rotating drilling head of this invention has an outer housing that is stationarily mounted above the well. An inner housing is rotatably mounted in the outer housing. An annular bladder is mounted in the inner housing. An annular resilient member is mounted in the bladder. The inner housing has a passage for delivering hydraulic fluid pressure to an outer surface of the bladder to cause the bladder to deform inwardly, thereby forcing the resilient member to deform inwardly to grip and rotate with a drill pipe. The resilient member has a first end secured to the inner housing for rotating the inner housing as the drill pipe rotates and a second end that is free to move axially in response to the deformation against the drill pipe. The deformation results in the resilient member elongating, reducing stress and strain. 
   Preferably, the resilient member is elastomeric and has at least one rigid reinforcing ring imbedded within it. Also, preferably, the bladder has rigid seal rings at its upper and lower ends. The seal rings contain seals that slidingly engage an inner wall of the inner housing. The seal rings allow the bladder to contract in length when pressurized. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     So that the manner in which the described features, advantages and objects of the invention, as well as others which will become apparent, are attained and can be understood in detail, more particular description of the invention may be had by reference to the embodiments thereof that are illustrated in the drawings, which drawings form a part of this specification. It is to be noted, however, that the appended drawings illustrate only typical preferred embodiments of the invention and are therefore not to be considered limiting of its scope as the invention may admit to other equally effective embodiments. 
     In the Drawings: 
       FIG. 1A  is a sectional view of an upper portion of a rotating drilling system subassembly having a rotating drilling gripper constructed in accordance with the present invention. 
       FIG. 1B  is a sectional view of a lower portion of the rotating drilling system subassembly of FIG.  1 A. 
       FIG. 2  is an orthogonal view of the bladder assembly of the rotating drilling gripper of FIG.  1 A. 
       FIG. 3  is an enlarged sectional view of the bladder assembly of the rotating drilling gripper of FIG.  1 A. 
       FIG. 4  is an enlarged sectional view of the gripper assembly of the rotating drilling gripper of FIG.  1 A. 
       FIG. 5  is a plan view of the gripper assembly of the rotating drilling gripper of FIG.  1 A. 
       FIG. 6  is an enlarged sectional view of a detailed portion of the rotating drilling system subassembly of  FIG. 1A  showing the input tubing for the control fluid circulated around the bladder assembly of FIG.  1 A. 
   

   DETAILED DESCRIPTION 
     FIGS. 1A and 1B  show a drilling system subassembly  10  comprising a stationary structure  11 , a latch mechanism  12 , and a rotating cartridge subassembly  13 . Rotating cartridge assembly  13  has a rotating drilling gripper  15  constructed in accordance with the present invention. Gripper  15  is used in drilling operations and is typically installed as part of drilling system subassembly  10 . Gripper  15  generally rotates with cartridge assembly  13 , but the present invention would permit a rotational connection between them. In the embodiment of  FIG. 1A , drilling system subassembly  10  is generally located very near the drilling rig floor. A primary function of gripper  15  is to grip a drillstring  14  extending axially through the centers of drilling system subassembly  10  and gripper  15  with a variable, controllable gripping force such that gripper  15  can rotate with drillstring  14  and allow drillstring  14  to move up or down in the axial direction, regardless of the rotation of drillstring  14 . Another function of gripper  15  is to form a secondary or emergency seal to prohibit further upward travel of drilling fluid should it leak past the primary seal or stripper  16 . 
   Gripper  15  comprises a bladder assembly  18  and a resilient member referred to herein as a gripper body assembly  20 .  FIGS. 2 and 3  show bladder assembly  18  corresponding to the embodiment of gripper  15  in FIG.  1 A. Bladder assembly  18  is an open, right circular cylinder comprising a bladder  22 , upper and lower reinforcement rings  24 ,  26 , and upper and lower retention rings  28 ,  30 . Bladder  22  forms the cylindrical wall  32  of bladder assembly  18 , has upper and lower ends  34 ,  36 , respectively, and is preferably made from a flexible elastomer such as urethane or treated natural rubber. 
   Rigid reinforcement rings  24 ,  26  are molded with and integral to ends  34 ,  36 , respectively, of bladder  22  and provide structural rigidity to ends  34 ,  36 . Thus, the nominal diameter of bladder  22  remains essentially constant in the vicinity of reinforcement rings  24 ,  26 , though the diameter may vary along other, more flexible portions of bladder  22 . Reinforcement rings  24 ,  26  preferably have internally threaded holes  38  by which retention rings  28 ,  30  are attached to ends  34 ,  36  respectively, of bladder  22  using mating, externally threaded bolts  40  having hex-socket caps  42 . 
   Retention rings  28 ,  30  form upper and lower limits, respectively, of bladder assembly  18 , and attach to bladder  22  in coaxial alignment with bladder  22 . The uppermost surface  44  of upper retention ring  28  and the lowermost surface  46  of lower retention ring  30  each have circularly distributed countersink holes  48 . Countersink holes  48  extend through the entire thicknesses of retention rings  28 ,  30 , allowing each bolt  40  to pass freely therethrough and engage the threads of corresponding hole  38 . Bolts  40  screw freely into holes  38  until caps  42  engage shoulders  49  of countersink holes  48 . Further tightening of the threaded connection pulls retention rings  28 ,  30  and bladder  22  into secure abutment, creating a metal to elastomer seal. 
   Retention rings  28 ,  30  have inner diameters slightly smaller than the nominal inner diameter of bladder  22  in the vicinity of reinforcement rings  24 ,  26  and the outer diameters of retention rings  28 ,  30  slightly exceed the nominal outer diameter of bladder  22  in the vicinity of reinforcement rings  24 ,  26 . Seats  50  are inset into the outermost cylindrical surface of retention rings  28 ,  30 . Each retention ring  28 ,  30  has a pair of seats  50 . Seats  50  each carry elastomer seals  52 . 
   Retention rings  28 ,  30  and bladder  22  are sized such that the sum of their lengths in the axial direction equals a desired length, discussed in more detail below. The lengths of bolts  40  and depths of holes  38  in reinforcement rings  24 ,  26  are also carefully sized so that the caps  42  of bolts  40 , which are countersunk into countersink holes  48 , fit flush with or below the uppermost surface  44  or flush with and above lowermost surface  46 . 
     FIGS. 4 and 5  show gripper body assembly  20  is also an open, right circular cylinder. Gripper body assembly  20  comprises a gripper element  54  and upper and lower support or reinforcing rings  56 ,  58 . Gripper element  54  forms the cylindrical wall  60  of gripper body assembly  20 , has upper and lower ends  62 ,  64 , respectively, and is preferably made from a flexible, durable elastomer such as urethane or treated natural rubber. The elastomer used to form gripper element  54  is generally harder than the elastomer used to form bladder  22 . 
   Rigid support rings  56 ,  58  are molded into ends  62 ,  64 , respectively, of gripper element  54 . Upper support ring  56  is embedded in, but its upper surface is preferably flush with, uppermost part of end  62 . Upper support ring  56  has internally threaded holes  66  similar to holes  38  of reinforcement rings  24 ,  26 . Lower support ring  58  is preferably completely embedded in lower end  64 . Similar to reinforcement rings  24 ,  26 , support rings  56 ,  58  provide structural rigidity to ends  62 ,  64  of gripper element  54 . Thus, the nominal diameter of gripper element  54  remains essentially constant in the vicinity of support rings  56 ,  58 . The diameter may vary, however along the more central portion of gripper element  54 . 
   Cylindrical wall  60  of gripper element  54  has a radially inner surface  68  and a radially outer surface  70 . In its natural state, outer surface  70  has a constant diameter, just less than the nominal inner diameter of bladder  22 . Inner surface  68  of gripper element  54  is cylindrically symmetric, but has a variable diameter, even when wall  60  is in its natural state. Tracing the profile of inner surface  68 , beginning just radially inside of upper support ring  56  on upper end  62 , inner surface  68  tapers radially inward and downward some distance until it reaches an upper transition point  72 , preferably downward approximately one-third of the total length of gripper element  54 . From upper transition point  72 , the profile of inner surface  68  extends as a cylinder further downward until it reaches a lower transition point  74 , approximately two-thirds down the total length of gripper element  54 . From lower transition point  74 , the profile of inner surface  68  extends radially outward and downward until it reaches lower end  64  of gripper element  54 . Preferably, the taper angles at upper and lower transition points  72 ,  74  are equal, but they could differ. A bottom surface  76  of gripper element  54  is annular and extends from inner surface  68  to outer surface  70  at lower end  64 . 
   Gripper body assembly  20  fits concentrically within bladder assembly  18 . The length of gripper body assembly  20  in the axial direction, however, is less than the corresponding length of bladder assembly  18 , when both are at their natural lengths. When uppermost surface  44  of upper retention ring  28  of bladder assembly  18  and the uppermost part of upper end  62  of gripper element  54  are aligned, bottom surface  76  of gripper element  54  approximately aligns with lower end  36  of bladder  22 . That is, in the embodiment shown in  FIG. 1A , gripper body assembly  20  is shorter than bladder assembly  18  by approximately the thickness of lower retention ring  30 . 
   Gripper body assembly  20  attaches to a torque plate  78  (FIGS.  1 A and  5 ). Torque plate  78  is an annular member having some thickness and countersink holes  80  therethrough. Bolts  82  pass freely through countersink holes  80  until each cap  84  of bolts  82  abuts a shoulder  86  of countersink holes  80 . Bolts  82  engage threaded holes  66 , and tightening of the threaded connection pulls torque plate  78  and gripper body assembly  20  into secure abutment. 
   Rotating cartridge subassembly  13  further comprises an upper housing  88  and a lower housing  90  (FIG.  1 A). Upper housing  88  is a cylindrically symmetric shell having different diameter sections. An upper section  92  of upper housing  88  has an inner diameter d 1  equal to the nominal diameter of the central axial opening of drilling system subassembly  10 : that is, a diameter just large enough to accommodate drillstring  14 , including its joints or collars. A lower section  96  of upper housing  88  has an enlarged inner diameter d 2  that is significantly larger than inner diameter d 1 . Upper section  92  transitions abruptly into lower section  96 , producing an upper ledge  100 . 
   Lower housing  90  is also a cylindrically symmetric shell having different diameter sections. An upper section  102  of lower housing  90  has an inner diameter d 3  just large enough to accommodate bladder assembly  18 . Upper section  102  of lower housing  90  has an outer diameter d 4  just less than inner diameter d 2  of upper housing  88 . A lower section  108  of lower housing  90  has a first inner diameter d 5 , a second inner diameter d 6 , a first ledge  114 , and a second ledge  116 . Viewing lower housing  90  in a downward direction, its inner diameters d 3 , d 5 , d 6  transition abruptly radially inward, forming ledges  114 ,  116 , respectively. 
   The portion of lower housing  90  extending downward from ledge  116 , having inner diameter d 6 , abuts and attaches to an outer surface of a sleeve  118 . Sleeve  118  extends from just below gripper  15  down to a stripper assembly  119  (FIG.  1 B). The uppermost end of sleeve  118  is at the same relative height as first ledge  114 . The inner diameter of sleeve  118  defines the nominal diameter of the central axial opening of drilling system subassembly  10 . 
   First and second rings  120 ,  122 , respectively, are complementary rings that fit together to fill the space between the portion of lower housing  90  extending downward from first ledge  114  to the height of second ledge  116  and the outer surface of sleeve  118 . First ledge  114 , an upper surface of first ring  120 , and the uppermost end of sleeve  118  are coplanar. 
   When gripper  15  is assembled, gripper body assembly  20  is nested inside bladder assembly  18 , as described above. Torque plate  78  sits atop surface  44  of upper retention ring  28 , suspending gripper body assembly  20  inside bladder assembly  18 . Torque plate  78  fastens to upper section  102  of lower housing  90  using conventional means such as pins, through which torque can be transmitted. Bladder  18  locates within lower housing  90 , with its seals  52  ( FIG. 3 ) sealing against the inner surface of lower housing  90 . 
   A portion of upper section  102  of lower housing  90  fits concentrically within lower section  96  of upper housing  88 . As stated above, the uppermost, annular surface of lower housing  90  and the upper surface of torque plate  78  are coplanar and in abutting contact with upper ledge  100  of upper housing  88 . Gripper  15  is concentrically placed within lower housing  90 . Lower retention ring  30  of bladder assembly  18  sits atop and occupies all of first ledge  114  of lower housing  90 . Thus, gripper  15  is constrained between upper housing  88  and lower housing  90 . Because gripper body assembly  20  is shorter than bladder assembly  18 , as described above, there is a gap  124  between the bottom surface  76  of gripper element  54  and the upper surface of first ring  120 . 
   Upper housing  88  and lower housing  90  are themselves constrained by bearings  126 . Bearings  126  allow rotating cartridge assembly  13  to rotate relative to stationary structure  11 . Stationary structure  11  surrounds cartridge assembly  13 , forming a sealed cavity  130  between stationary structure  11  and rotating cartridge assembly  13 .  FIG. 6  shows an inlet tube  132  through which a control fluid  134  can enter cavity  130 . Upper section  102  of lower housing  90  has ports  136  to allow fluid communication of control fluid  134  through lower housing  90 . An outlet tube  138  ( FIG. 1B ) allows control fluid  134  to be circulated. 
   In operation, drillstring  14  is passed through the central axial opening of drilling system subassembly  10 . Drillstring  14  is driven to rotate about the central axis and caused to move up and down. Rotating cartridge assembly  13  is designed to rotate with drillstring  14 , but not translate. Cartridge assembly  13  is not separately driven, but is instead caused to rotate when gripper  15  grips rotating drillstring  14 . 
   To cause the gripping to occur, control fluid  134  is injected under pressure through inlet tube  132  into cavity  130 . Control fluid  134  passes through ports  136 , bearing on the outer surface of wall  32  of bladder assembly  18 . Seals  52  stop the upward and downward travel of control fluid  134 , restricting the application of control fluid  134  onto bladder  22 . However, seals  52  are free to slide on the inner wall of lower housing  90 , thus bladder  22  is free to contract in length as it undergoes pressure. Bladder  22 , in response to the pressure of control fluid  134 , deforms into the outer surface of wall  60  of gripper body assembly  20 , thereby transferring the pressure from control fluid  134  to gripper element  54 . Gripper element  54  responds to that pressure by pressing harder onto drillstring  14 , thereby increasing the normal force between gripper element  54  and drillstring  14  and both sealing and gripping drillstring  14 . 
   Gripper element  54 , being deformable, flattens out somewhat against drillstring  14 , increasing the surface area of gripper element  54  in contact with drillstring  14 . The increased surface area and increased normal force both serve to increase the frictional (gripping) force between gripper element  54  and drillstring  14 . Thus, the gripping force can be varied by varying the pressure of control fluid  134 . Outlet tube  138  provides a return path for control fluid  134 . In this way, gripper  15  grips drillstring  14  with a variable, controllable gripping force such that gripper  15  can either hold drillstring  14  in place or it can allow drillstring  14  to move up or down in the axial direction, regardless of the rotation of drillstring  14 . 
   The radial inward pressure of bladder  18  causes gripper element  54  to elongate. To prevent excessive deformation into the central axial opening of drilling system subassembly  10 , gripper element  54  is also allowed to deform axially into gap  124 . This allows some of the stress in gripper element  54  to be relieved by strain in the axial direction. This helps to prevent clipping or lopping off an expanded portion of gripper element  54  as drillstring  14  translates up or down. This is particularly a potential problem when the larger diameter collars, that is, where the individual sections of drillstring  14  join, pass gripper element  54 . The tapered portions of inner surface  68  also help in that regard. Rings  120  and  122  provide a stop to limit elongation, if necessary. 
   The present invention offers many advantages over the prior art. Placing gripper body assembly  20  inside bladder assembly  18  allows for the pre-assembly of grippers  12  having variously sized gripper assemblies  20  and bladder assemblies  18  to accommodate different drilling environments. It allows for regulating the amount of gripping force by controlling fluid pressure and surface area exposed to that pressure. Grippers  12  can be optimally sized to accommodate expected drilling loads. Different elastomers can be used to produce desired deformations. The useful lifetime of gripper element  54  is increased by incorporating a gap  124 , thereby reducing the extent to which gripping element  54  deforms into the region where it is likely to be lopped off or torn by the passing drillstring  14  or collar. 
   While the invention has been particularly shown and described with reference to a preferred and alternative embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.

Summary:
A rotating drilling head seals around drill pipe while drilling. The drilling head has an outer housing that mounts to the rig floor. An inner housing is rotatably mounted in the outer housing. An annular bladder is mounted in the inner housing. An annular elastomeric gripping member is mounted in the bladder. The inner housing having a passage for delivering hydraulic fluid pressure to the outer surface of the bladder to cause the bladder to deform inwardly, thereby forcing the gripping member to deform inwardly to grip and rotate with a drill pipe. The gripping member has a first end secured to the inner housing for rotating the inner housing as the drill pipe rotates and a second end that is free to move axially to allow the bladder to elongate in response to the deformation by the bladder.