CA2621570A1 - Power tong - Google Patents

Abstract

The power tong according to the present invention continuously rotates tubulars for spinning and torquing threaded connections. Continuous rotation is achieved through a rotating jaw that grips the tubular and can continuously rotate it. Hydraulic and electrical power necessary for actuating the actuators or grippers must be generated on board since the continuous rotation does not allow for external connections, neither hydraulic nor electrical ones. A serpentine belt system turns the motors of the on board hydraulic power unit and DC
generators to supply the gripper jaws with the necessary hydraulic and electrical power.

Description

POWER TONG
Field of the Invention This invention relates to the field of devices for rotating tubular members so as to make up or break out threaded joints between. tubulars including casing, drill pipe, drill collars and tubing (herein referred to as pipe or drill pipe), and in particular to a power tong for the improved handling and efficient automation of such activity.

Background of the Invention In applicant's experience, on conventional rotary rigs helpers, otherwise known as roughnecks, handle the lower end of the pipe when they are tripping it in or out of the hole.
They also use large wrenches commonly referred to as tongs to screw or unscrew, that is make up or break out pipe. Applicant is aware that there are some other tongs that are so called power tongs, torque wrenches, or iron roughnecks wlaich replace the conventional tongs. The use of prior art conventional tongs is illustrated in Figure Ia. These other tongs are described in the following prior art descriptions.

In the prior art applicant is aware of United States Patent No. 6,082,225 which issued February 17, 1997 to Richardson for a Power Tong Wrench. Richardson describes an power tong wrench having an open slot to accommodate a range of pipe diameters capable of making and breaking pipe threads and spinning in or out the threads and in which hydraulic power is supplied with a pump disposed within a rotary assembly, which pump is powered through a non-mechanical coupling, preferably magnetic, to a motor disposed outside the rotary assembly.

In the present invention the rotary hydraulic and electrical systems are powered at all times and in all rotary positions via the serpentine belt drive, unlike Richardson #6,082,225 in which they are powered only in the home position. The pipe can thus be gripped and ungripped repeatedly in any rotary position with no dependence on stored energy and the unit can be more compact because of the reduced hydraulic accumulator requirements for energy storage (the present invention uses hydraulic accumulators for energy storage only to enhance gripping speed).

Applicant is also aware of United States Patent No. 5,167,173 which issued December 1, 1992 to Pietras for a Tong. Pietras describes that tongs are used in the drilling industry for gripping and rotating pipes, stating that generally pipes are gripped between one or more passive jaws and one or more active jaws which are urged against the pipe. He states that normally the radial position of the jaws is fixed and consequently these jaws and/or their jaw holders must be changed to accommodate pipes of different diameters.

Applicant is also aware of United States Patent No. 6,776,070 which issued August 17, 2004 to Mason et al. for an iron Roughneck. Mason et al. describes an iron roughneck as including a pair of upper jaws carrying pipe gripping dies for gripping tool joints where the jaws have recesses formed on each side of the pipe gripping dies to receive spinning rollers. By positioning the spinning rollers in the upper jaws at the same level as the pipe gripping dies the spinning rollers are able to engage the pipe closer to the lower jaws and thus can act on the tool joint rather than on the pipe stem.

Mason et al. describe that in running a string of drill pipe or other pipe into or out of a well, a combination torque wrench and spinning wrench are often used, referred to as "iron roughnecks". These devices combine torque and spinning wrenches and are described in U.S. Pat. No. 4,023,449, U.S. Pat. No. 4,348,920, and U.S. Pat. No. 4,765,401, all to Boyadjieff.

In the prior art iron roughnecks, spinning wrenches and torque wrenches are commonly mounted together on a single carriage but are, nevertheless, separate machines (with the exception of the prior art of Mason Patent 6,776,070 which combines the spinner wrench rollers and torque jaws in a common holder, nevertheless, they still work independent of each other). When breaking-out, or loosening, connections between two joints of drill pipe, the upper jaw of the torque wrench is used to clamp onto the end portion of an upper joint of pipe, and the lower jaw of the torque wrench clamps onto the end portion of the lower joint of pipe.

Drill pipe manufacturers add threaded components, called "tool joints", to each end of a joint of drill pipe. They add the threaded tool joints because the metal wall of drill pipe is not thick enough for threads to be cut into them. The tool joints are welded over the end portions of the drill pipe and give the pipe a characteristic bulge at each end. One tool joint, having female, or inside threads, is called a "box". The tool joint on the other end has male, or outside threads, and is called the "pin".

After clamping onto the tool joints, the upper and lower jaws are turned relative to each other to break the connection between the upper and lower tool joints.
The upper jaw is then released while the lower jaw (back-up) remains clamped onto the lower tool joint. A
spinning wrench, which is commonly separate from the torque wrench and mounted higher up on the carriage, engages the stem of the upper joint of drill pipe and spins the upper joint of drill pipe until it is disconnected from the lower joint. When making up (connecting) two joints of pipe the lower jaw (back-up) grips the lower tool joint, the upper pipe is brought into position, the spinning wrench (or in some cases a top drive) engages the upper joint and spins it in. The torque wrench upper jaws clamp the pipe and tightens the connection.

Applicant is furtlaer aware of United States Published Patent Application entitled Power Tong, which was published April 5, 2007 under Publication No.
US
2007/0074606 for the application of Halse. Halse discloses a power tong which includes a drive ring and at least one clamping device with the clarnping devices arranged to grip a pipe string. A driving mechanism is provided for rotation of the clamping device about the longitudinal axis of the pipe string. The clamping device communicates with a fluid supply via a swivel ring that encircles the drive ring of the driving mechanism. Thus Halse provides for three hundred sixty degree continuous rotation combining a spinner with a torque tong.
The Halse power tong does not include a radial opening, the tong having a swivel coupling surrounding the tong for transferring pressurized fluid from an external source to the tong when the tong rotates about the axis of the pipe. Halse states that having a radial opening in a power tong complicates the design of the power tong and weakens the structure surrounding the pipe considerably, stating that as a result, the structure must be up-rated in order to accommodate the relatively large forces being transferred between the power tong and the pipe string. Halse further opines that a relatively complicated mechanical device is required to close the radial opening when the power tong is in use, and in many cases also to transfer forces between the sides of the opening.

Summary of the Invention The power tong according to the present invention continuously rotates tubulars for spinning and torquing threaded connections. Continuous rotation is achieved through a rotating jaw that grips the tubular and can continuously rotate it. Hydraulic and electrical power necessary for actuating the actuators or grippers must be generated on board since the continuous rotation does not allow for external connections, neither hydraulic nor electrical ones. A serpentine belt system turns the motors of the on board hydraulic power unit and DC
generators to supply the gripper jaws with the necessary hydraulic and electrical power.

The present invention includes a main drive, rotary jaw and back-up jaw, the rotary jaw is supported and held into position by the use of opposed helical pinions/gears which support the rotary jaw vertically. The rotary jaw gripper cylinders are held in position by a linkage assembly that can withstand the torque parameters of the wrench and the rotary cylinders can be moved in a range of travel by an eccentric, this provides for a tong that can accommodate a large range of pipe diameters (3.5-in drillpipe to 9-5/8 in casing). This large range can be accomplished without changing gripping jaws or jaw holders. The tong does not require a mechanical device to close the radial opening, nor does it need to be upsized, the on-board power source allows the new invention to be compact, can develop high torque for making and breaking and can spin at high speeds. The current invention also overcomes the limitation of the spinning wrench engaging the stem area of the drillpipe (this will over time cause fatigue in the stem area) as the spinning and torquing is accomplished with the same jaw that engages the pipe on the tool joint.

Brief Description of the Drawings Figure 1 is, in exploded perspective view, the power tong according to one embodiment of the present invention.

Figure l a is a depiction of the use of prior art conventional tongs.
Figure 2 is, in partially cut away view, the rotary drive section and serpentine drive belt of the power tong of Figure 1.

Figure 2a is a plan view of Figure 2.
Figure 3 is, in plan view, the power tong of Figure 1 in an assembled view.
Figure 4 is, in front elevation view, the power tong of Figure 3 with the thread compensator cylinders extended.
Figure 4a is, in side elevation view, the power tong of Figure 4 with the thread compensator cylinders retracted.

Figure 5 is a section view along line 5-5 in Figure 4.

Figure 6 is a partially cut away section view along line 6-6 in Figure 4.
Figure 7 is a partially cut away view along line 7-7 in Figure 4.

Figure 8 is, in partially cut away perspective view, the back-up jaw section of the power tong of Figure 1.

Figure 9 is, in partially cut away plan view, the drive unit fixed stage of Figure 8.

Detailed Desci~tion of Embodiments of the Invention The power tong according to the present invention may be characterized in one aspect as including three main sections mounted vertically one on top of the other. Each of the sections contains actuators as better described below. With the reference to the drawings which are not intending to be limiting, uppermost is the drive section 10 which includes speed reduction unit 12, each including a number of motors, gearing coupling devices and belts enclosed in housings 14 as better described below, main drive hydraulic motors 16 and serpentine drive hydraulic motors 18. Also included within drive section 10, and although shown exploded in Figure 1, is a serpentine belt drive 20 better described below.

The second main section is the rotary jaw section 22, mounted below and within the drive section 10 and above the back-up jaw section 24. The rotary jaw section 22 is cylindrical in shape with an opening slot 38 allowing the tong axis Z to be selectively positioned concentric with the pipe 8. The rotary jaw section 22 has three gripper actuators 44a, 44b, and 44c arranged radially around axis Z and mounted between two rotary jaw gears 30a and 30b.

Serpentine belt 20 is driven by two serpentine drive hydraulic inotors 18 with drive sprockets 26a, rotating serpentine belt 20 about the idler sprockets 26 which are mounted on drive section 10 and six serpentine drive node sprockets 32 which are double-grooved and which are mounted on the rotary jaw section 22. The serpentine drive node sprockets 32 are comprised of two generator drive sprockets 32a and 32b, two pump drive sprockets 32c and 32d and two rotary jaw idler sprockets 32e and 32f. In the illustrated embodiment, the generator drive sprockets, 32a and 32b, transmit rotary power to generators 34 and the pump drive sprockets, 32c and 32d, transmit rotary power to hydraulic pumps 36 by the action of serpentine belt 20 engaging the upper groove of sprockets 32a, 32b, 32c and 32d. Three synchronization belts, 28a, 28b, and 28c, connect the lower grooves of the rotary-jaw double-groove sprockets 32, specifically synchronization belt 28a connects pump drive sprocket 32c and generator drive sprocket 32a, synchronization belt 28b connects generator drive sprocket 32b and rotary jaw idler sprocket 32e and synchronization belt 28c connects rotary jaw idler sprocket 32f and pump drive sprocket 32d. Thus as the rotary jaw section 22 rotates about axis of rotation Z within a three hundred sixty degree rotational range of motion about axis of rotation Z, even though serpentine belt 20 on corresponding idler sprockets 26 cannot extend across the opening slot 38 because it would restrict selective access of the pipe, the serpentine belt 20 wraps in a C-shape around the rotary jaw section 22 to provide for continual contact between serpentine belt 20 and a minimum of five of the rotary jaw sprockets 32. The synchronization. belts 28 maintain rotation of the individual rotary-jaw double-groove sprockets 32 as they pass through the serpentine gap 29, that is the opening between idler pulleys 26a and 26b, and synchronize the speed and phase of the rotation of rotary jaw drive sprockets 32 to allow them to re-engage the serpentine belt 20 after passing through the serpentine gap 29. As an example, when the rotary jaw section 22 rotates in direction B, pump drive sprocket 32c will reach the serpentine gap 29 and the pump will then be driven by synchronization belt 28a rather than the serpentine belt 20. When rotation continues such that pump drive sprocket 32c passes beyond (farther counter-clockwise) idler sprocket 26b then pump drive sprocket 32c will re-engage with the serpentine belt 20. The process repeats as each of the six rotary jaw drive sprockets 32 passes through the opening between idler sprockets 26a and 26b.

Idler 26d is spring-mounted to maintain minimum tension in the serpentine belt 20 regardless of the rotational position of the rotary jaw section 22. There is a small variation in the length of the path of the serpentine belt 20 as the rotary jaw section 22 rotates.

The sezpentine belt is preferably a toothed synchronous drive belt in order to minimize belt tension requirements, to allow small sprocket diameters and to avoid dependence on friction which could be compromised by fluid contaminants.

The serpentine belt may be double-toothed (teeth on both sides) or single-toothed with the teeth facing inward on the inside of the `C' and outward on the outer side of the `C' and with the serpentine drive motors 26 positioned outside the loop and with two additional idlers as shown in Figure YY. The serpentine drive may be split into two or more separate `C' sections as shown in Figure YY. A continuous synchronization belt may be used instead of the separate synchronization belts 28 as shown in Figure YY. A
roller chain could alternately be used instead of the belt for the serpentine drive but would add lubrication requirernents, would be noisier and would have a lower life.
The number of serpentine drive nodes may be increased or decreased and the number of idlers 26 may also vary.

An alternative serpentine system consists of split serpentine belt drive (as opposed to a continuous belt as described above). This may require a different arrangement of sprockets and idlers.

Upper rotary jaw gear 30a and lower rotary jaw gear 30b are parallel and spaced apart so as to carry therebetween hydraulic pumps 36, generators 34, hydraulic tank 42, the rotary jaw hydraulic system 53, rotary jaw electrical controls 54 and the set of three radially disposed hydraulic gripper actuators 44a, 44b, and 44c, all of which are mounted between the upper and lower rotary jaw gears 30a and 30b for rotation as part of rotary jaw section 22 without the requirement of external power lines or hydraulic lines or the like. Thus all of these actuating accessories, which are not intended to be limiting, may be carried in the rotary jaw section 22 and powered via a nested transmission such as described herein as including serpentine belt 20, idler sprockets 26, one of which may act as a belt tensioner, synchronization belts 28 and serpentine drive node sprockets 32.

The serpentine belt 20 and paired drive pulley transmission is herein referred to generically as a form of nested transmission. Without intending to be limiting, a nested transmission may also include planetary gear seginents or other rigid, flexible or resilient iiiteracting rotational drive elements such as gears, belts, etc. wherein for example, such as with respect to the flexible serpentine belt 20, a circumferentially spaced and radially spaced apart array of rotational drive elements are mounted around one of the fixed stages for example the first or upper actuating stage so as to interact with a second set of rotational drive elements mounted on the rotating or second actuating stage and nested within the circumferential array of rotational drive elements mounted to the fixed stage.
The nested transmission transfers power from the fixed stage to the rotational stage in a continuous fashion as, sequentially, one eleinent after another of the rotational drive elements on the rotating stage 'are rotated through and across the opening allowing selective access of the tubular 8. It is also equally intended herein that the use of a nested transmission is intended to also capture the reverse case where the rotatable drive elements mounted on the rotating stage are mounted around the outer circumference of the adjacent rotary jaw and continuously driven as the rotating stage is rotated by the rotatable drive elements which are mounted on the fixed stage nested inwardly of the drive elements on the rotating stage. These and other nested transmissions as would be known to one skilled in the art are intended to be included herein so long as the drive from the fixed stage to the rotating stage is substantially continuous as the rotating stage rotates sequentially one after another of the rotatable drive elements mounted on the rotating stage across the opening into the yoke in which is mounted the tubular.

In the preferred embodiment, the rotary jaw hydraulic system 53 is a dual (high/low) pressure system or infinitely variable pressure system which produces high pressures (in the order of 10,000 psi) necessary for adequately gripping large and heavy-duty tubulars for applying make-up or break-out torque and lower pressures (5000 psi or less) to avoid crushing. smaller or lighter-duty tubulars. Hydraulic pumps 36, rotationally driven as described above, are fixed-displacement, gear or piston pumps. In the idle state, hydraulic pumps 36 charge one or more gas-filled accumulators 55 mounted in or on the rotary jaw section 22 to store energy to enable rapid extension of the gripper actuators 44. In this way, extremely fast gripping speeds can be achieved while keeping the power transmitted by the serpentine belt 20 drive very low, Referring to the hydraulic schematic of Figure 10, unloading relief valve 58 acts as a safety pressure relief for the pumps and also unloads the flow from the fixed-displacement hydraulic pumps 36 to tank at low pressure when the accumulator(s) are fully charged (approximately 5000 psi). Return filter 60 cleans contaminants from the hydraulic oil as it returns to tank 42 and pressure filter 61 provides emergency filter protection for the of the system coinponents. Check valve 62 maintains pressure (approximately 5000 psi fully charged) in the accumulator(s) 55 even when the hydraulic pumps 36 are unloaded to tank 42 at low pressure as desciibed above. Directional control valve 63 is a three-position valve which directs flow to either extend or retract the gripper actuators 44 or hold them in any intermediate position when the valve is unactuated. Directional control valve 63 is hydraulic pilot actuated by pilot directional control valve 64 which is electric solenoid actuated. Manual directional control valve 65 functions the saine as directional control valve 63 described above except it is manually actuated for emergency back-up in the event of electrical failure or during periods of deliberate shutdown of wireless communications (described later) for sensitive operations such. as perforating. Sequence valve 66 blocks flow to the accumulator(s) when it is demanded by the grip circuit and includes a reverse-free-flow check valve to allow flow out of the accumulators at all times. Pressure reducing valve 67 regulates the grip pressure according to the characteristics of the pipe connection, providing high pressures necessary for adequately gripping large and heavy-duty tubulars for applying make-up or break-out torque and lower pressures to avoid crushing smaller or lighter-duty tubulars.
Pressure reducing valve 67 is remote-controlled by proportional pressure relief valve 68 of alternately by a discrete two or three step pressure control. Intensifier 69 boosts the grip pressure by a factor of 4.3 (typical), providing a maximum grip pressure in the order of 10,000 psi without the need for high-pressure pumps or valves. Shuttle valves 70 allow high flow rates directly into the grip cylinders, by-passing intensifier 69, for rapid extension of the gripper cylinders to the point of contact with the pipe connection. Pressure-compensated flow control valves 71 equalize the rapid-advance flow between the cylinders for centering purposes, regardless of any load pressure variations.

The back-up jaw section 24 is typically mounted to a tong positioning system (outside the scope of this invention) capable of holding the tong assembly level and enabling vertical and horizontal positioning travel. It could be pedestal-mounted on the rig floor, mast-mounted, track-mounted on the rig floor or free hanging froxn the mast structure. The back-up jaw section 24 includes a parallel spaced apart array of planar jaw frames and in particular an upper backup jaw plate 48a and a lower backup jaw plate 48b. Backup jaws plates 48a and 48b may be maintained rigidly in their parallel spaced apart aspect by means of thread compensator cylinders 50. Apart from providing spacing between backup jaws plates 48a and 48b, thread compensator cylinders 50 actuate so as to extend bolts 46 on rods 50a in direction C so as to selectively adjust the spacing between the second actuating stage 22 and third actuating stage 24. Thus with the cylindrical threaded joint 8eb of tubular 8 held within cylinders 52a-52c in third actuating stage 24, and with the threaded tapered female end or box (not shown) extending upwardly from the tubular portion 8b held within cylinders 52a-52c, as the rotating or second actuating stage 22 is rotated relative to the fixed or third actuating stage 24 so as to rotate tool joint pin 8c relative to tubular portion 8b, the second and third actuating stages 22 and 24 respectively may be drawn towards one another by the retraction of rods 50a into cylinders 50 in direction C thereby threadably engaging threaded box 8c onto the pin (not shown). Cylinders 50 maintain a spacing which defines cavity between the backup jaws in which is rigidly mounted the array of radially spaced apart hydraulic cylinders 52a, 52b and 52c. Hydraulic cylinders 52a-52c are radially spaced apart around axis of rotation A and disposed radially inwardly so that the operative ends of the actuators which may be selectively actuated telescopically into the distal end 40b of yoke 40 so as to clamp therein a tubular 8 and in particular a lower portion 8b of tubular 8 while an upper portion 8a of tubular 8 is clamped within cylinders 44a-44c and rotated in second actuating stage 22 in direction B about axis of rotation A relative to the fixed first and third actuating stages 10 and 24 respectively.

The rotary jaws 30a and 30b of seoond actuating stage 22 are maintained in alignment interleaved between the first and third actuating stages 10 and 24 respectively by means of guide rollers 54 which are rotatably mounted in a radially spaced apart array circumferentially around the outer circurnference of the rotary jaws and also aligned orthogonally relative to backup jaw 48a and parallel to one another, The rotary jaw guide rollers 54 centralize the rotary jaws preventing radial loading of the drive pinions 56.
Interspersed circumferentially around the rotary jaws 30a and 30b are a further radially spaced apart parallel array of rotary jaw driving pinions 56 which interniesh and engage helical teeth 56a with corresponding gear teeth on the outer circumference of rotary jaws 30a and 30b so that as driving pinions 56 are driven by main drive hydraulic motors 16 via reduction gear system 58 rotary jaws 30a and 30b are simultaneously rotatably driven in direction B about axis of rotation A. Pinions 56 and gear teeth are helical to ensure proper meshing thus even torque splitting between top and bottom plates. All of the components in the first and third actuating stages are mounted on a frame 60.

As will be apparent to those skilled in the art in the ligbbt of the foregoing disclosure, many alterations and inodifications are possible in the practice of this invention without departing from the spirit. or scope thereof. Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.

Claims (5)

1. A power tong for threading and unthreading a threaded coupling in a tubular, the tong comprising:

first, second and third actuating stages, said first and third actuating stages mounted to each other, in fixed relation to one another, said second actuating stage rotatably mounted interleaved between said first and third actuating stages and adapted for three hundred sixty degree rotation relative thereto, said third actuating stage having a fixed yoke, said fixed yoke having an open end for receiving a tubular into said fixed yoke and an opposite distal end, said third actuation stage containing opposed third stage gripping means cooperating with said fixed yoke for selectively gripping the tubular when positioned in said distal end of said fixed yoke between said third stage gripping means, said second actuating stage having a corresponding second stage yoke, said second stage yoke having an open end for receiving the tubular into said second stage yoke and an opposite distal end, said second actuating stage containing opposed second stage gripping means cooperating with said second stage yoke for selectively gripping the tubular when positioned in said distal end of said second stage yoke between said second stage gripping means, said second stage yoke alignable, by selective rotation of said second actuating stage, with said fixed yoke for simultaneous receipt into said fixed yoke and said second stage yoke of the tubular, said first actuating stage containing drive means for selectively rotating said second actuating stage relative to said first and third actuating stages about an axis of rotation substantially coaxial with the tubular when positioned into said distal ends of said fixed yoke and said second stage yoke and gripped by said third stage gripping means and said second stage gripping means respectively, wherein with the tubular thereby gripped by said second and third stages gripping means, and with a threaded coupling of the tubular positioned and gripped in either said second or third actuating stages by respectively said second or third stage gripping means, said rotation of said second actuating stage about said axis of rotation and driven by said drive means urges relative rotation between oppositely disposed ends of the tubular oppositely disposed on either side of the threaded coupling, wherein second stage actuating accessories are mounted to said second actuating stage for simultaneous rotation therewith, and wherein said actuating accessories cooperate with said second stage gripping means whereby said second actuating stage is a substantially self-contained three hundred sixty degree rotatable gripping system for gripping the tubular and rotation thereof about said three hundred sixty degrees of rotation relative to said first and third actuating stages, at least one of said actuating accessories requiring at least one accessory drive take-off from said drive means, wherein said at least one accessory drive take-off includes a nested transmission.

2, The apparatus of claim I wherein said reest.ed transmission includes a first set of transmission elements mounted to so as to cooperate with said drive means, and a second set of transmission elements mounted to so as to cooperate with said second actuating stage and said at least one of said actuating accessories, wherein said first and second sets of transmission elements engage and are nested relative to one another to thereby transfer motive power from said first actuating stage to said second actuating stage during said rotation of said second actuating stage, and wherein at least one pair of transmission elements of said second set of transmission elements are spaced apart sufficiently so as to at least span a distance substantially equal to the opening of said open end of said second stage yoke during said rotation of said second actuating stage and corresponding simultaneous rotation of said at least one pair of transmission elements of said second set of transmission elements, and wherein at least one pair of transmission elements of said first set of transmission elements are spaced apart sufficiently so as to span a distance substantially equal to the opening of said open end of said second stage yoke during said rotation of said second actuating stage, and wherein during said rotation at least one of said at least one pair of transmission elements of said first set of transmission elements remains in driving engagement with at least one of said at least one pair of transmission elements of said second set of transmission elements at all times during said three hundred sixty degree rotation of said second actuating stage.

3. The apparatus of claim 1 wherein said nested transmission includes a serpentine belt rotatably mounted on one of said first or second actuating stage and wherein at least one pair of pulleys is mounted to the other of said first or second actuating stage and cooperates with said serpentine belt so as to continuously transfer power to said second actuating stage during rotation thereof for actuation of said actuating accessories.

4. The apparatus of claim 2 wherein said first set of transmission elements include rollers or pulleys spaced around said first actuating stage and wherein a continuous serpentine drive belt is tensioned therearound, and wherein said second set of transmission elements include at least one pair of pulleys mounted to said second actuating stage and having a drive belt tensioned therearound, wherein said serpentine drive belt does not cross said open end of said second stage yoke, and wherein said pair of pulleys on said second actuating stage are spaced apart so as to only sequentially cross only one at a time across said open end of said third stage yoke.

5. The apparatus of claim 1 further comprising a first stage yoke of said first actuating stage aligned with said third stage yoke.