You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND OF THE INVENTION 
   Progressing cavity pumps are in increasingly common use in the oil field for production of formation fluids to the surface. The pumps comprise a fixed outer body usually referred to as a stator which connects to the production tubing in the well. Within the stator is a rotating inner component called a rotor which in cooperation with the stator pumps the formation fluids. 
   The rotor is rotated by a string of drive rods that transmit torque from a prime mover at the well head. The prime mover is normally an electric motor that produces up to 100 horsepower and also generates very substantial torque. The drive rods extend from a drive head at the top of the well head down through the production tubing to the rotor. 
   The inside of the stator is rubber and friction is generated as the rotor spins. If the stator is not properly anchored, it will rotate in the clockwise direction (to the “right” when viewed from above) and if not checked, the tubing joints will eventually loosen and part, allowing the tool to fall to the bottom of the well. Production must then be halted until the pump is fished out. To prevent this, pump anchors are used which, when engaged against the well casing, restrict right-handed rotation of the pump. 
   The problem however is that the drive rods themselves store a considerable amount of energy in the form of twist. In fact, after the motor is turned on the rods might twist as many as 50 times before the stator begins to turn. 
   When the motor is stopped, the rods untwist to release their stored torque, and the release can be violent, made worse by the weight of the oil in the tubing from the pump to the surface, resulting in speeds approaching 20,000 rpm. Because the pump anchor has become unset in response to the counterclockwise (to the “left”) unwinding of the rods, the pump is unrestrained and whips around inside the well casing causing major damage to the pump and everything in its vicinity. The torque can also wildly spin the sheaves and pulleys that deliver torque from the motor to the drive rods which can cause additional failures and endanger anyone close by. 
   There are some anchors that are intended to restrain both left and right handed torque but these are typically “one set” or limited set devices and are usually referred to as “tension set anchors”. They must be recovered to the surface then refaced or redressed after each use, which limits their utility. 
   SUMMARY OF THE INVENTION 
   It is therefore a feature of the present invention to provide a torque anchor which obviates and mitigates from the disadvantages of the prior art. 
   It is a further feature of the present invention to provide an anchor that restrains torque in both the left and right handed directions. 
   It is yet another feature of the present invention to provide an anchor that can be used repeatedly between rebuilds. 
   According to one exemplary embodiment of the present invention, there is provided an anchor to inhibit rotation of a device relative to an oil well casing, comprising a tubular mandrel adapted for direct or indirect connection to the device; a cylindrical housing to receive at least a portion of said mandrel concentrically therethrough, said housing being rotatable relative to said mandrel and having a plurality of circumferentially spaced apart apertures formed in an outer surface thereof; a plurality of spaced apart anchoring slips disposed between said housing and said mandrel in registry with respective ones of said apertures in said housing&#39;s outer surface; first biassing means associated with said mandrel for rotation therewith in the clockwise or counterclockwise directions to engage and then move respective ones of said anchoring slips radially towards and then into temporarily anchoring contact with the casing to prevent further rotation of said mandrel and the device connected thereto in either of said clockwise or counterclockwise directions; and one or more drag block means disposed in said housing in registry with respective ones of said apertures in said housing&#39;s outer surface to extend radially outwardly therefrom, each of said drag block means being normally biassed into frictional contact with said casing to inhibit rotation of said housing relative to the casing. 
   According to another aspect of the present invention, there is provided a torque anchor for use in an oil well to temporarily prevent rotation of a device connected to the anchor in the clockwise or counterclockwise directions, or both, comprising a tubular mandrel operatively connected to the device to be anchored; a plurality of casing gripping anchor members disposed in spaced apart relationship about the circumference of said mandrel; a housing mounted concentrically around at least a portion of said mandrel to be rotatable thereon and to at least partially contain said anchor members therein, said anchor members being mounted in said housing for rotation therewith around the mandrel and for radial movement towards and away from said mandrel; cam means on said mandrel for operatively engaging respective ones of said anchor members to bias them towards and into gripping contact with said casing upon rotation of said mandrel in one direction, and to operatively engage another of said anchor members upon rotation of said mandrel in the opposition direction, whereby gripping of the casing by said anchor members effectively stops the rotation of said mandrel; and a plurality of friction members supported by said housing normally biassed into contact with the casing to stop rotation of said housing relative to the casing. 
   According to a further aspect of the present invention, there is provided a method for anchoring a device against rotation in a well bore, comprising the steps of non-rotatably connecting the device to a mandrel disposed either above or below the device; surrounding at least a portion of the mandrel with a cylindrical housing that is rotatable relative to said mandrel, said housing having associated therewith a first set of anchor members normally biassed into frictional contact with the well bore to hold the housing stationary relative thereto, and a second set of anchor members actuatable in response to rotation of said mandrel for movement between a first retracted position and a second well bore gripping position, wherein gripping of the well by said second set of anchor members prevents further rotation of said mandrel. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Exemplary embodiments of the invention will now be described in greater detail and will be better understood when read in conjunction with the following drawings in which: 
       FIG. 1  is a perspective view of the torque anchor of the present invention; 
       FIG. 2  is a side elevational cross-sectional view of the anchor of  FIG. 1 ; 
       FIG. 3  is a cross-sectional view of the tool of  FIG. 2  along the line  3 — 3 ; 
       FIG. 4  is a cross-sectional view of the tool of  FIG. 2  along the line  4 — 4 ; 
       FIG. 5  is a perspective view of one end of a slip housing forming part of the tool of  FIG. 1 ; 
       FIG. 6  is an end view of the other end of the slip housing shown in  FIG. 5  with a drag block therein; and 
       FIG. 7  is a perspective view of a center mandrel forming part of the tool of  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE EMBODIMENTS 
   Referring initially to  FIG. 1 , the principal components of the present torque anchor  1  include a longitudinally extending tubular mandrel  10 , one or more cylindrical rotatable anchoring slip assemblies  20  that can be biassed against the well casing by the mandrel to prevent rotation of the anchor, frictional drag blocks  45  that are continuously biassed against the casing and a rotatable slip housing  75  that retains the slip assemblies and drag blocks in their operational positions. 
   With reference to  FIGS. 2 and 7 , mandrel  10  is a hollow tubular member threaded at its opposite ends  5  and  6  for respective connection at one end to the stator of the progressing cavity pump (not shown), and at the other end to any tubing below the anchor (again not shown). At a point intermediate along its length the mandrel includes a section  9  serrated with longitudinally extending teeth  11  the configuration of which will be seen most clearly in  FIG. 3 . The cross-sectional shape of toothed section  9  is generally trochoidal including three longitudinally symmetrical lobes  12  spaced apart by webs  13 . As will be seen most clearly in  FIG. 3 , the teeth on lobes  12  extend radially above the outer surface  8  of mandrel  10 , whereas the teeth on webs  13  peak below surface  8  except where they transition into the lobes. As will be described in greater detail below, lobes  12  convert the rotating movement of mandrel  10  into linear movement of anchor slips  25  forming part of assemblies  20  to bias them against the well casing to set the anchor against rotation. The action of the lobes is therefore cam-like. 
   Ideally, the lobes and teeth of section  9  are machined into the mandrel&#39;s parent metal but the section can be formed as a discrete component and welded into place between sections of mandrel. 
   With reference to  FIGS. 2 ,  3  and  5 , anchor slip assemblies  20  include anchor slips  25  which are generally cylindrical in shape formed with longitudinally extending teeth  26  that extend around their entire circumference. Each slip is formed with an axially extending bore  27  therethrough to receive a spindle  28  about which the slip can rotate freely. The diameter of the bore preferably exceeds the diameter of the spindle so that there is some radial “play” between the two. This allows the slips to self-adjust a bit for small irregularities in the casing or small misalignments between the mandrel and the casing, and it also ensures that the slips can continue to rotate even if some sand or dirt works its way into bore  27 . The slips can also move a bit in the axial direction of the spindles if desired. 
   The slip&#39;s teeth  26  are shaped to engage teeth  11  on mandrel  10 . In a typical anchor, there will be as many slips  25  as there are lobes  12  on the mandrel. Although the present anchor could function with only a single slip assembly, as a practical matter there should be two or three slip assemblies and the use of more than three is also possible. 
   With reference to  FIGS. 2 ,  4  and  6 , the present anchor also includes at least one and more typically a plurality of drag blocks  45 . Each drag block is generally rectangular in shape with champhers  46  at their opposite ends to facilitate movement of the anchor up and down through the well bore. Each drag block may be a single metal block drilled on the underside to retain springs  52  used to continuously bias the drag blocks outwardly into contact with the well casing as will be described below. Each drag block is additionally formed with longitudinally extending flanges  44  that will bear against the edges of apertures  87  in slip housing  75  to prevent the drag blocks from being completely extruded by springs  52 . The embodiment shown includes three drag blocks but fewer or more can be used. 
   Slip assemblies  20  and drag blocks  45  are retained in place relative to mandrel  10  by slip housing assembly  75 . As will be seen most clearly in  FIGS. 2 and 5 , slip housing  75  is cylindrical in shape for a concentric fit around mandrel  10 . The end of the housing that encloses slips  25  is internally hollowed out to provide a cavity  77  for the slips, lobes  12  and spring clips  30  that can optionally be used to normally bias the slips against mandrel teeth  11 . 
   The inner end of cavity  77  is machined out to accommodate a guide ring  80 . Ring  80  is itself formed with a plurality of grooves  81  to capture the axially extending ends of spindles  28  so that they can rotate freely as well as move up and down in the grooves. A plurality of bolts  83  extending through the outer surface of housing  75  connect the ring to the housing and prevent its rotation relative to the housing. The outer end of cavity  77  is formed with axially aligned grooves  86  similar in size and shape to the grooves in ring  80  and which similarly function to capture the other ends of spindles  28  for rotation and for up and down movement. 
   With reference to  FIGS. 2 and 6 , the end of the slip housing that retains the drag blocks  45  is generally solid with the exception of rectangular notches  90  which house the drag blocks and springs  52 . The width of notches  90  is substantially equal to the width of flanges  44  on the drag blocks for a reasonably close fit allowing the drag blocks to move up and down in the notches. The drag blocks will extend outwardly through apertures  87  with which they are in registry in the slip housing&#39;s outer surface. As will be seen most clearly in  FIG. 6 , the width of the apertures is less than the width of flanges  44  so that springs  52  don&#39;t completely extrude the drag blocks. 
   The outer surface of housing  75  is formed with additional apertures  88 , one in registry for each of slips  25 . 
   End caps  95  are connected to slip housing  75  such as by means of bolts  98  to close the ends of the housing and to hold the drag blocks and slips in place. When assembled, slip housing  75  and end caps  95  are free to rotate about mandrel  10 . Axial movement of the slip housing relative to the mandrel is prevented by means of the major diameter of lobes  12  being greater than the inner diameter of guide ring  80  and the end  74  of housing  75 . 
   In operation, the assembled torque anchor is connected below or occasionally above the pump and the combination is connected to the end of the production tubing and lowered into the well. When the pump is properly positioned in the well, the motor is turned on to transmit torque to the rotor via the drive rods extending down the interior of the production tubing. As the rotor begins to turn to the right, the stator also begins to turn to the right due to the friction of the rotor against the stator&#39;s internal rubber lining. 
   As the stator begins to turn, so too does mandrel  10 . Housing  75  however remains relatively stationary due to the frictional contact between drag blocks  45  and the well casing which also assists to center the anchor in the well bore. As the mandrel rotates, lobes  12  engage the teeth on slips  25  to cam or force the slips radially outwardly until the teeth on the slips extend above the surface of the slip housing to contact and engage the inner surface of the casing by biting into the casing&#39;s metal. This stops any further rotation of the mandrel and the pump stator connected thereto. The more torque transmitted to the mandrel, the tighter the anchoring contact engagement of the slips against the casing. 
   If the motor stops turning the pump for any reason, the tendency will be for the unwinding rods to torque the stator to the left. When that happens, the mandrel will also turn to the left but the drag blocks will continue to hold the slip housing relatively stationary. Lobes  12  will rotate to the left but will then quickly, within a fraction of a rotation, engage slips  25  to again force them outwardly against the casing, thereby preventing any destructive counter-rotation of the pump until the stored torque in the rods is dissipated. The trochoidal cross-sectional shape of toothed section  9  assures that slips  25  will have adequate space to retract inwardly towards mandrel  10  to completely disengage the well casing. As will be appreciated, the trochoidal cross-sectional shape of section  9  and the presence of teeth or webs  13  are preferred aspects. Other shapes are possible and the teeth on the webs can be reduced or even eliminated with the key aspect being that there is sufficient space between the mandrel and housing  75  to allow the slips to back off from anchoring contact with the well casing. 
   If any of the teeth on the slips are worn down, the slips can be rotated at surface, until fresh teeth are exposed to the lobes and to the casing. In this way, the present anchor enjoys an extended operational life compared to conventional anchors before major redressing or replacement of parts is required. Again, because of the trochoidal shape of toothed section  9 , the slips can be pulled away from mandrel  10  enough to clear the teeth on webs  13  which allows the slips to be rotated to expose fresh teeth without having to disassemble housing  75 . 
   Although the present anchor has been described for use to prevent rotation of a progressing cavity pump, it will be appreciated that it can be used with any downhole tool, device or installation that needs to be anchored against rotation in either the clockwise or counterclockwise directions, or both. 
   The above-described embodiments of the present invention are meant to be illustrative of preferred embodiments and are not intended to limit the scope of the present invention. Various modifications, which would be readily apparent to one skilled in the art, are intended to be within the scope of the present invention. The only limitations to the scope of the present invention are set forth in the following claims appended hereto.

Summary:
An anchor to inhibit rotation of a device relative to an oil well casing, comprising a tubular mandrel adapted for direct or indirect connection to the device; a rotatable cylindrical housing with a plurality of apertures and able to receive at least a portion of the mandrel concentrically therethrough; a plurality of spaced apart anchoring slips disposed between the housing and the mandrel in registry with respective ones of the apertures in the housing&#39;s outer surface; a rotation mechanism associated with the mandrel to engage and then move respective ones of the anchoring slips radially towards and then into temporarily anchoring contact with the casing; and one or more drag blocks disposed in the housing in registry with respective ones of the apertures in the housing&#39;s outer surface to extend radially outwardly therefrom, each of the drag blocks being normally biased into frictional contact with the casing.