Abstract:
A cable drawworks for a drilling rig has an electric motor and a primary drive transmission which connects the motor to a drum shaft that passes through the hub of a cable drum. The drum shaft is rotatably mounted on the drawworks frame whereas the cable drum is rotatably mounted on the drum shaft. The drum shaft connects to a secondary drive transmission that connects the drum shaft to the cable drum. The secondary drive transmission has a planetary gear transmission set. Each end of the cable drum has a brake drum and a brake band wrapped around thereon. A brake actuating system is used to selectively tighten the bands and includes an equalization linkage system resulting in equal braking forces being applied to each brake drum. The simplified cable drawworks system is compact enough to be mounted on the drilling rig floor and eliminates the need for liquid cooling of the braking mechanism.

Description:
FIELD OF THE INVENTION 
   The present invention relates to the field of drawworks mechanisms for use in raising and lowering traveling blocks within drilling rigs. 
   BACKGROUND OF THE INVENTION 
   Drawworks mechanisms have been used in drilling rigs for decades. Drawworks are, typically, motor-driven drums used to reel in or pay out a cable used on the drilling rig to raise or lower a traveling block within the rig. The cable will typically be used with pulleys and pulley blocks attached to the top of the rig and the traveling block, respectively. The traveling block is used for tripping pipe in and out a drill string, as well known to those skilled in the art. Various methods and devices have been developed for this purpose. However, conventional arrangements require excessive physical space to house such a mechanism on a drilling rig platform. 
   It is, therefore, desirable to have a drawworks mechanism that is compact enough so that it may be located directly on a drilling platform yet having sufficient power and braking ability to safely reel in and pay out cable for raising and lowering a traveling block within a drilling rig. 
   SUMMARY OF THE INVENTION 
   One embodiment of the present invention involves a drawworks mechanism for a drilling rig that overcomes the shortcomings identified in the prior art. The drawworks mechanism comprises a frame that has a footprint compact enough to allow it to be located on a drilling rig platform. The frame comprises at least a floor member having opposing sidewall members. 
   The frame has a motor mounted on it with a drive shaft, preferably, configured in a horizontal position. A drum shaft having first and second ends is rotatably mounted on the frame sidewalls such that it is substantially parallel to the motor&#39;s drive shaft. A primary drive means couples the drive shaft to the first end of the drum shaft. The primary drive means may be any suitable coupling mechanism such as a chain and sprockets, a belt and pulleys, a set of intermeshed gears or any other means as well known to those skilled in the art. Preferably, the primary drive means is a triplex chain and sprockets system having a gear ratio in the range of 1.5:1 to 2:1. A cable drum is rotatably mounted on the drum shaft and is concentrically disposed about the drum shaft between the first and second ends. In one embodiment, a secondary drive means can directly and rotatably couple the drum shaft to the cable drum on the second end side of the drum shaft. Preferably, the secondary drive means is a planetary gear transmission having a sun gear, a ring gear and a planetary gear set as well known to those skilled in the art. The sun gear is disposed about the second end of the drum shaft whereas the ring gear is operatively coupled to the frame and the planetary gear set is operatively coupled to the cable drum. In this configuration, when the drum shaft rotates, the sun gear rotates the planetary gear set that, in turn, rotates the cable drum. In the preferred embodiment, the planetary gear transmission has a 4:1 gear ratio such that the overall gear ratio from the motor to the cable drum is in the range of 6:1 to 8:1. 
   The cable drum also comprises brake means for controlling and braking the rotation of the cable drum. The brake means can comprise at least one band brake mechanism disposed at one end of the cable drum, as well known to those skilled in the art. In a further embodiment, there is a band brake mechanism on each end of the cable drum. A mechanism controlling the brake bands is used to release the bands from the brake drums. The brake control mechanism can be activated to allow the cable drum to rotate. The mechanism is released or deactivated in order for the brake bands to engage the brake drums. In one embodiment, a pneumatically-operated air pot is used although other mechanisms may be used to operate the brake mechanism as well known to those skilled in the art. The use of band brakes, and their inherent nature to be self-actuating, provides a safe braking mechanism that offers superior protection against the cable drum entering into a runaway condition. While one embodiment uses band brakes, it should be apparent to one skilled in the art that other types of braking mechanisms may be used to control the brake drum rotation. These would include disc brakes and drum brakes among others. 
   The motor used in the present invention may be an electric motor, an internal combustion motor or a hydraulic motor. In one specific embodiment, a 3-phase AC electric motor is used. The motor is coupled to a motor control means for controlling the operation of the motor. A variable frequency drive motor controller mechanism can be used to control the operation of the motor although other control means may be used as well known to those skilled in the art. The motor control means is used to control the rotation direction and rotational speed of the motor so that the motor can operate the cable drum to either reel in or pay out a cable attached to the cable drum. The cable is fed to a pulley mounted on top of a drilling rig and then downward within the rig to a traveling block which is raised or lowered when the cable drum reels in or pays out the cable. 
   It is an aspect of the present invention to provide a cable drawworks that is compact in size so that it can be mounted on the drilling rig floor. 
   It is another aspect of the present invention to provide a cable drawworks that does not require a clutch mechanism to couple power from a motor to the cable drum. 
   It is another aspect of the present invention to provide a cable drawworks that does not require a liquid cooling system for the braking mechanism for the drawworks. 
   It is yet another aspect of the present invention to provide a cable drawworks that is simpler in design and operation than the prior art. 
   Broadly stated, one embodiment of the present invention includes a cable drawworks for a drilling rig, comprising a frame adapted for mounting on a drilling rig, the frame having a floor member and two opposing sidewall members; motor means for operating a cable drum mounted on said frame, said motor means having a drive shaft; a drum shaft having first and second ends, each of said ends rotatably mounted on a sidewall of said frame; said drum shaft having first and second ends; primary drive means for rotatably coupling said drive shaft to the first end of said drum shaft; a cable drum rotatably mounted on said drum shaft, said cable drum located between said first and second ends on said drum shaft; secondary drive means for rotatably coupling the second end of said drum shaft to said cable drum; brake means for braking the rotation of said cable drum; and motor control means for operating said motor means whereby said drawworks is capable of reeling in or paying out a cable attached to said cable drum. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective cutaway view of the front of a drawworks mechanism in accordance with one embodiment of the present invention. 
       FIG. 2  is a perspective cutaway view of the rear of the drawworks mechanism of  FIG. 1 . 
       FIG. 3  is a top plan cutaway view of the drawworks mechanism of  FIG. 1 . 
       FIG. 4  is a perspective cutaway view of the front of the drawworks mechanism of  FIG. 1  revealing the planetary gear transmission. 
       FIG. 5  is a perspective view of the front of the drawworks mechanism of  FIG. 1  illustrating the planetary gear transmission attached to the frame of the present invention. 
       FIG. 6  is a cross-sectional view of the drawworks mechanism taken along section lines A-A in  FIG. 5 . 
       FIG. 7  is a cross-sectional end elevational view of the planetary gear transmission taken along section lines B-B in  FIG. 6 . 
       FIG. 8  is a front elevational view of the main brake shaft of the drawworks mechanism of  FIG. 1 . 
       FIG. 9  is a front elevational view of the equalizer brake linkage of the drawworks mechanism of  FIG. 1 . 
   

   DETAILED DESCRIPTION OF EMBODIMENTS 
   Referring to  FIGS. 1 to 5 , one embodiment of a drawworks mechanism (sometimes herein referred to as “drawworks” or “cable drawworks”) in accordance with the teachings of the present invention is shown. Drawworks  10  comprises of frame  12  having floor  9 , right sidewall  8  and left sidewall  7 . Motor  32  is mounted on floor  9 . Motor  32  can comprise a three-phase AC electric motor such as manufactured by Oilfield-Electric-Marine Inc. of Houston, Tex., U.S.A., Model No. TT600 series, although other types of similar power capability may be used. In one embodiment, motor  32  operates at 600 volts AC and produces up to 5,000 ft.-lb. of torque. Drawworks  10  can have approximate overall dimensions of 69″ wide by 86″ long by 50″ tall. These dimensions permit drawworks  10  to be mounted on a drilling rig floor instead of being situated in a location near the drilling rig thereby reducing the physical space required for drilling operations. 
   Motor  32  has a motor shaft  36  whose longitudinal axis is generally horizontal when motor  32  is mounted on frame  12 . Motor  32  is controlled by motor controller  34 . Motor controller  34  controls the direction and rotational speed of motor  32 . Motor controller  34  may be any type of 3-phase AC motor controller but in one specific embodiment can comprise a variable frequency drive motor controller. Motor controller  34  can be manufactured by Oilfield-Electric-Marine Inc. of Houston, Tex., U.S.A. and can be designed to operate with their TT600 series of AC electric motors. 
   Referring to  FIG. 4 , motor shaft  36  is coupled to encoder  70  by belt  71 . Encoder  70  is used to provide information to motor controller  34  such as motor speed, in revolutions per minute, and motor direction. Encoder  70  can be provided as model HS35 as manufactured by BEI Technologies Inc. of Goleta, Calif., U.S.A. An additional encoder (not shown) might also be operatively coupled to cable drum  16 . These encoders provide information to motor controller  34  that enables drawworks  10  to operate in a number of modes. These include automated drilling operations, hoisting up or down operations, and emergency stopping operations. 
   Rotatably mounted on frame  12  between sidewalls  7  and  8  is drum shaft  42  that has right end  17  and left end  19 . Preferably, drumshaft  42  is positioned such that it is generally parallel to motor shaft  36 . Cable drum  16  is rotatably mounted on drum shaft  42  between right end  17  and left end  19  via roller bearings  76  as shown in  FIG. 6 . This configuration allows cable drum  16  to rotate on drum shaft  42 . 
   Primary drive  37  couples motor shaft  36  to left end  19  of drum shaft  42 . In one embodiment, primary drive  37  comprises drive sprocket  38  mounted on motor shaft  36 , sprocket  46  mounted on left end  19  of drum shaft  42  and chain  40  coupling drive sprocket  38  to sprocket  46 . In this embodiment, chain  40  is a triple row or triplex chain and sprockets  38  and  46  are triplex chain sprockets. Primary drive  37  is covered by primary drive cover  48 . Cover  48  has inspection points  49  and  50  to permit the visual inspection of chain  40 . It should be appreciated by those skilled in the art that other means may be used in the primary drive transmission such as a primary drive belt and sprockets or intermeshed gears. In one embodiment of the present invention, primary drive  37  provides a primary gear reduction from motor  32  to drum shaft  42 . The gear reduction ratio is in the range of 1.5:1 to 2:1. In one embodiment of the present invention, drive sprocket  38  has 28 teeth and sprocket  46  has 52 teeth resulting in a gear reduction ratio of 1.86:1. 
   Referring to  FIGS. 6 and 7 , right end  17  of drum shaft  42  is coupled to cable drum  16  by secondary drive  59 . Right end  17  of drum shaft  42  comprises a pair of tapered roller bearing sets  86  that are supported by bearing cover  88  and cover plate  22  that is bolted to right sidewall  8  of frame  12 . Reinforcing plates  11  strengthen sidewalls  7  and  8  to support the rotation of cable drum  16  in frame  12  when drawworks  10  is being operated. Secondary drive  59  comprises ring gear housing  60  having ring gear  62  attached thereon, planetary gear sub-assembly  64  having four planetary gears  66  rotatably attached thereto and sun gear  68 . Sun gear  68  is fitted to drum shaft  42 . In the preferred embodiment, drum shaft  42  and sun gear  68  have intermeshing splines  69  whereby sun gear  68  is securely coupled to right end  17  of drum shaft  42 . 
   Ring gear housing  60  is operatively coupled to right sidewall  8  of frame  12  via planetary gear cover  84  and cover plate  22 . Planetary gear sub-assembly  64  is fastened to the end of cable drum  16  nearest right sidewall  8  via mounting bolts  65 . Drum shaft  42  passes through roller bearing  76 , seal  82  and spacer  80  which are all supported by bearing housing  75  which, in turn, is fastened to the right-hand side of cable drum  16  and hub  15 . On the left-hand side of cable drum  16 , drum shaft passes through spacer  80 , seal  82  and roller bearing  76  which are secured to the left-hand side of cable drum  16  and hub  15  by cover plate  79 . Drum shaft  42  then passes through spacer  73  before passing through seal  77  and roller bearing  76  which are supported by bearing housing  78  and secured by cover plate  83 . Bearing housing  78  is fastened to sidewall  7  of frame  12 . Drum shaft  42  then passes through spacer  81  and seal  77 . Left-hand end  17  of shaft  42  then is coupled to sprocket  46  by key  44 . 
   In operation, as motor  32  rotates drum shaft  42  via primary drive  37 , sun gear  68  rotates planetary gear sub-assembly  64  thereby turning cable drum  16 . In the one embodiment, sun gear  68  and planetary gear  66  each have 28 teeth. Ring gear  62  has 112 teeth thereby resulting in a secondary gear reduction ratio of 4:1. Combined with the gear reduction provided by primary drive  37 , the overall gear reduction from motor  32  to cable drum  16  is in the range of 6:1 to 8:1. In one specific embodiment, the overall gear reduction ratio is 7.43:1. A cable (not shown) is attached to cable drum  16  and passes over roller  14  before ascending to cable pulleys mounted on top of a drilling rig (not shown). The cable is reeled in or paid out to raise or lower a traveling block within the drilling rig by operating the controls (not shown) of motor controller  34 . 
   Referring to  FIGS. 1 to 9 , the braking mechanism of the present invention is shown. Attached to each end of cable drum  16  are brake drums  18 . Surrounding each brake drum  18  are brake bands  20 . Each brake band  20  has a “live end” and a “dead end”. Each live end has a lug  51  affixed to brake band  20 . Link  29  is attached to lug  51  at one end via pin  27 . The other end of link  29  is pivotally attached to brake shaft crank  23  via pin  27 . Brake shaft cranks  23  are attached to main brake shaft  26  which is rotatably mounted on frame  12  substantially parallel to the axis of cable drum  16 . Main brake shaft  26  may be made into two sections having coupling  26 A joining the two sections together into a single shaft. Each end of main brake shaft  26  passes through a sidewall (e.g.,  8 ) of frame  12 , such as through flange bearings  94 , to permit rotation of main brake shaft  26 . On each end of main brake shaft  26  are actuator cranks  28 . Attached to each actuator crank  28  is a brake actuator  24 . In one embodiment, brake actuators  24  are spring-loaded, pneumatically-operated devices coupled to pneumatic control lines (not shown) such as Maxibrake® model no. MA15623 as manufactured by Haldex Commercial Vehicle Systems of Kansas City, Mo., U.S.A. It should be appreciated by those skilled in the art, however, that other types of mechanisms may be used to operate main brake shaft. 
   The dead end of each brake band  20  has a dead end lug  52  mounted thereon. Equalizer rods  54  are pivotally attached at one end to each dead end lug  52  via pins  53 . The other ends of equalizer rods  54  pass through pivot blocks  56 . Equalizer rods  54  are threaded and are secured to pivot blocks  56  with lock nuts  58 . Each pivot block  56  is pivotally attached to an L-shaped equalizer link  90  that is, in turn, pivotally attached to equalizer lugs welded to floor  9  of frame  12 . Equalizer bar  30  is pivotally attached at each end to an equalizer link  90 . 
   In operation, brake actuators  24  are activated or pressurized to turn brake shaft  26  thereby loosening tension on brake bands  20  so that cable drum  16  may turn freely. When braking is to be applied to cable drum  16 , brake actuators  24  are relieved of their pressure allowing the internal spring of the actuators to cause actuators  24  to operate actuator cranks  28  and rotate brake shaft  26  thereby causing brake bands  20  to tighten around brake drums  18 . As brake bands  20  contact brake drums  18 , the frictional forces on brake bands  20  cause equalizer rods  92  to pull up on pivot blocks  56 . The mechanical relationship caused by equalizer bar  30  connected to equalizer links  90  results in an automatic equalization of the braking forces on brake drums  18  so that each brake drum  18  experiences the same braking force. This prevents cable drum  16  from twisting along its axis during braking conditions. 
   Although a few preferred embodiments have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention. The terms and expressions used in the preceding specification have been used herein as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the clams that follow.