Line wrap power tongs

A power tong has two powered rings mounted on the tong frame for independent rotation, one ring, a reel carrier, carries a plurality of spring rewind line storage reels. Independent lines extend from each reel and each line is anchored to the second powered ring. An open gap, or throat, extends to the tong center to receive pipe when the lines are all recovered into the reels. The reel carrier ring is rotated to wrap the lines in a spiral pattern around pipe. The second ring is driven to pull the lines and the reel carrier ring is braked to apply tailing tension to the lines but does then turn in sympathy with the second ring to turn pipe. To recover the lines, the second ring is stopped and the reel carrier ring is driven in the direction to allow lines to return to the reels as they unwrap from the pipe.

Apparatus of this invention is definable as a powered pipe tong to be used 
by drilling and workover rigs to manipulate threaded connections of pipe 
strings suspended in earth boreholes or wells. 
RELATED ART 
Conventional power tongs used to accomplish the same purpose as apparatus 
of this invention by different means are typified by the following U.S. 
Pat. Nos. 4,084,453; 4,273,010; 4,404,876; 4,089,240; 4,290,304; 
4,445,403; 4,266,450; 4,350,062; 4,487,092. 
There are no known prior patents related to balanced spiral line wrap power 
tongs. The word "tong" suggests the use of pipe gripping dies, which are 
not present in the apparatus of this invention. 
BACKGROUND OF THE INVENTION 
The use of a spiral wrap of a line of rope or chain to spin a pipe in the 
first stages of pipe thread make-up in pipe string assembly is old art. In 
well drilling practice, the line is wrapped several turns around the pipe, 
and the tailed end is held with some tension as the other end is pulled by 
a capstan, usually a powered capstan. The greater the number of turns 
around the pipe to be rotated, the less tension is required on the tailed 
end. 
In well drilling, the powered line has not been used to apply final torque 
to the pipe, because the side loads are too great and the tensioned line 
becomes dangerous to personnel. Tongs are used to apply final torque. 
Pipe spinners of the chain and wheel type, and combinations of the two, 
have come into common use to spin pipe at low torque. Tongs, some powered, 
have been used to apply high torque as required. 
Conventional power tongs used to apply high torque loads to pipe have pipe 
gripping dies. The dies cause surface damage to pipe. Efforts to minimize 
the damage has continued for years and it has been reduced to some extent. 
All tubular goods used in well drilling and well completion have become 
more expensive. Pipe used in wells with hydrogen sulfide is very expensive 
and has sensitive surfaces. Damage to the surface defeats the chemical 
attack resistant surface treatment. In recent years, there has been an 
increasing sense of urgency associated with pipe surface protection. 
OBJECTS 
It is therefore an object of this invention to provide apparatus to 
mechanically wrap line around pipe to rotate the pipe, and to unwrap and 
recover the line. 
It is another object of this invention to provide apparatus to mechanically 
wrap a plurality of lines around pipe fed from bias retracting reels, and 
to recover the lines into the reels when the pipe turning operation is 
completed. 
It is still another object of this invention to provide apparatus to 
mechanically wrap lines around pipe to be rotated apparatus to 
mechanically wrap lines around pipe to be rotated by feeding the line from 
reels that collectively rotate as required around the pipe centerline, as 
line is paid out from or recovered into the reels. 
It is yet a further object of this invention to provide apparatus to 
mechanically wrap lines around pipe to be rotated, the pulled ends of the 
lines to be powered by a ring capable of being rotated around the pipe 
centerline to apply torque to the pipe, with a cooperating but 
independently rotatable ring also capable of rotation around the pipe 
centerline to carry reels to pay out and to recover the lines. 
It is still another object of this invention to provide a line wrapping 
power tong with a gapped side to allow pipe to move laterally to and from 
the operational center of the apparatus. 
It is yet another object of this invention to provide apparatus to spiral 
wrap a plurality of lines around pipe to be rotated, the lines further 
controlled by level wind axial advance controls related to the amount of 
line wrapped on pipe to assure a reasonably uniform, closely spaced, helix 
pattern of lines applied to pipe. 
It is still a further object of this invention to provide directional 
choice to level wind controls, so that line will advance axially along the 
pipe periphery whether the pipe is to be rotated to make up or break out 
threads. 
These and other objects, advantages, and features of this invention will be 
apparent to those skilled in the art from a consideration of this 
specification, including the attached drawings and appended claims. 
SUMMARY OF THE INVENTION 
Apparatus of this invention utilizes the general concept of conventional 
power tongs adapted to control, manipulate, and drive a plurality of 
spiral wrap lines to rotate pipe both for spinning at low torque and to 
apply the required high torque loads. 
A balanced array of lines is situated around the pipe periphery to extend 
some distance parallel to the pipe axis with each end anchored to 
structure capable of independent rotation. Rotation of one end of the 
array of lines, relative to the other end and about the pipe axis, causes 
the lines to wrap the pipe in a spiral of lines. The lines are fed from 
biased rewind reels as the wrap takes place. The undriven (or tailed) ends 
of the lines are restrained, both in tension and in rotation, about the 
pipe centerline by a reel carrier ring. The resistance is limited, and the 
tailed ends of the lines eventually rotate with the reel carrier, 
reluctantly, as the pipe is rotated by the powered ring pull on the lines. 
When rotation is complete, the reel carrier is powered to overrun the 
driving ring to unwrap the spiral and recover, into the reels, the 
individual lines, until the lines are again parallel the pipe axis. A 
throat may be used in the side of the body and the rotating assemblies to 
allow the pipe to be moved laterally in and out of the tong open, 
generally central, area. An alternate embodiment includes an arrangement 
to advance the free end of the reel supplied lines axially along the pipe, 
as spiral winding evolves, to prevent the lines sliding on the pipe 
surface as the helix angle of the lines changes.

DETAILED DESCRIPTION OF DRAWINGS 
In FIGS. 1, 2, and 3 the general structure for all subsequent figures is 
described. In FIG. 1, body 1 provides support and general enclosure for 
the primary machinery. Partial ring 2 has a throat 2a and an opening 2b. 
The vertical axis VCL is perpendicular to the plane of the drawing. Axis 
VCL is the center of rotation of pipe to be rotated by the tong and the 
center of rotation of partial ring 2 and partial ring 3, which is 
invisible below partial ring 2, as will be described later. Body 1 is 
often referred to as a frame on conventional tongs. 
Gear 4a is the primary input gear for driving ring 2. Gears 4b and 4c are 
idler gears which engage gear 4a and ring gear 2c. Gear 2c is affixed to 
partial ring 2. The spread of gears 4b and 4c provide continuous power 
transmission from gear 4a to gear 2c as the throat 2c is negotiated during 
each revolution of gear 2c. This is conventional power tong gearing. Gears 
5a, 5b, and 5c invisible below gears 4a, 4b, and 4c have a similar layout, 
as will be described later. Partial rings 2 and 3 are each capable of 
independent continuous rotation in either direction. 
Four independent line reels 6 are mounted on partial ring 2, and this ring 
will be referred to as a reel carrier ring. 
Six posts 7 stand vertically on ring 2 near the throat, and will be 
referred to as line tailing posts for reasons to be explained later. The 
principal purpose of posts is to extend structure to make slots available 
for lines. 
In FIG. 2, partially cutaway, taken along line 2--2 of FIG. 1, the two 
partial rings 2 and 3 are shown. Ring 3 is supported for rotation on body 
1 by bearing ring 1b, and secured by retaining ring 3a, which is rigidly 
attached to ring 3. Ring 2 is mounted for relatively independent rotation 
on ring 3 by support ring 3b. Ring 2 is secured on support ring 3b by 
confining ring 2d, which in turn is rigidly attached to ring 2. Fasteners 
that secure the rings 1b, 3a, 3b, and 2d and lend maintenance utility to 
the assembly are omitted for clarity of points of novelty, since such 
fasteners are well established in the art. 
Motor M2 is mounted on the body 1 and drives gear 5a, which in turn drives 
idler gears 5b and 5c. These gears have the same general layout as gears 
4b and 4c for reasons already described, to negotiate the throat 3d in 
ring 3, which corresponds to throat 2a in ring 2 as seen in FIG. 1. 
Motor M1 drives ring 2 through the gears 4a, 4b, and 4c as previously 
described. Motor M1 is mounted on body 1. 
Line driving posts 8 are part of ring 3 and may be intrinsic or attached by 
convenient structural means. In the positions shown, posts 7 and posts 8 
are in general registry. These posts are to manipulate flexible elements 
to wrap and drive pipe, but this function is best described after the 
structure is defined. 
FIG. 3 is a projection of a selected area of FIG. 2. Line driving posts 8 
are shown near the throat. There are six such posts, three shown, the 
other three are similarly situated on the opposite side (not shown) of the 
opening 3e. Line clamp 9 and retaining bolts 9a will retain the driven end 
on the two lines (flexible elements). A similar arrangement (not shown) is 
on the opposite side of opening 3e, and is similarly disposed relative to 
axis VCL. 
FIG. 4 is a cutaway taken along line 4--4 of FIG. 2. The profile of line 
slide grooves 2e and 3f is typical of the profiles each side of the 
central posts of post groups 7 and 8. The overall assembly is designed, in 
this case, for four independent lines, but any multiple of two can be used 
if space is available for reels. The number of slide paths and slots can 
be changed to accommodate the preferred plurality of lines. 
Line clamps and bolts 9 and 9a secure the driven end of the lines to ring 
3. Reels 6, only one shown, control the tailed end of the line in a manner 
to be described later. As shown, posts 7 and 8 appear intrinsic to their 
related partial rings. The post sets, with slide grooves in place, are 
expendables and bolt to recesses in the associated partial rings. This 
attachment feature is not a point of novelty, and is within the machine 
construction art and not shown in detail, to preserve functional clarity 
of drawings. 
All line tailing reels, one for each line, are of the spring biased line 
retracting type. The spring return reel is a common purchase item usable 
to support heavy power tools on assembly lines. They can be purchased for 
various sizes of lines, flat web straps, hoses, and the like with a 
variety of line length capacity and various spring strengths for applying 
line recovery tension. Some embodiment choices require modification for 
the purpose disclosed. The modifications are detailed where used, but the 
common retract mechanism is considered well established in the art: 
Addressing now the flexible elements to use on the structures described, it 
should be noted that the flexible element referred to herein as a line may 
have a variety of forms. For rotating smooth, clean pipe, nylon rope has 
been found quite effective. Oily pipe responds well to steel cable of the 
very flexible type. The very flexible steel cable has small individual 
wires, however, and existing burrs on used pipe seem to damage cable too 
often. We are still searching for a general purpose line and may yet 
construct the appropriate special purpose line. The line type is subject 
to change from time to time. The descriptive material herein is oriented 
to the artificial fiber line but should not be considered in any way 
restrictive. 
FIG. 5 is identical to FIG. 4, with line 10 shown in the recovered 
position. In initial installation of lines, the individual line is 
installed on the related spring retract reel. The driven end of the line 
is pulled from the reel, laid in the appropriate slide way, and clamped by 
clamp 9, while rings 2 and 3 are positioned with the ring throats 2a and 
3d in registry. In this position, with throat 1a in the frame, throat 2a 
in ring 2, and throat 3d in ring 3 in registry, pipe may be moved 
laterally into the openings. The arrangement of FIG. 5 is on one side of 
the throat. A similar arrangement (not shown) is on the opposite side, as 
shown in FIG. 6. 
In FIG. 6, ring 2 has been rotated two turns relative to ring 3. Only two 
lines are shown for simplicity. If viewed from above, ring 2 has made two 
turns to spiral wrap lines, clockwise in this case, around the pipe. More 
turns are commonly made before ring 3 is driven counterclockwise, in this 
case, to rotate pipe. The number of turns of line depends upon 
circumstance, but when enough turns are on the pipe, ring 3 is driven 
counterclockwise to drive pipe. Ring 2 is allowed to turn in sympathy with 
ring 3, but a restraining force is kept on the tailed end of the lines by 
braking ring 2. Reel tension and the braking action on ring 2 prevents 
line slippage. Should slippage occur, more turns of line are applied to 
the pipe. To turn pipe in the opposite direction, the directions described 
above are reversed. 
The line applies torque to the pipe in accordance to the equation T.sub.t 
(e.sup.fa -1)r where T.sub.t is the line tailed end tension, f is the 
coefficient of friction between line and pipe, a is the amount of line in 
contact with the pipe in radians, and r is the pipe radius. The equation 
defines the point of slippage for one line. 
The ratio of driven end tension T.sub.d to tailed end tension T.sub.t is 
expressed by the equation T.sub.d /T.sub.t =e.sup.fa. The line driven end 
is attached to ring 3 by clamps 9. 
With five wraps of line with a friction coefficient of 0.1, the T.sub.d 
/T.sub.t ratio becomes 23. 
With five turns of line with a friction coefficient of 0.1 and 100 pounds 
tension on the tailed ends of each of four lines, the torque applied to a 
six inch pipe is 2,200 foot pounds. Six turns of line, under the same 
circumstance, delivers 4,238 foot pounds. 
With the friction increased to 0.2, three turns of line on the same pipe 
delivers 4,237 foot pounds of torque. 
FIG. 7 is a top view of FIG. 6 showing the lines 10 wrapped around pipe in 
preparation for rotating pipe. The mounting of reels 6 on ring 2 has 
already been described, and the reel mounts are not shown. Only two reels 
are shown in position so that both ends of each line can be seen. Line 
tailed end 10a goes to the reel, and end 10b goes to clamp 9, not visible 
in this figure but as shown in FIGS. 5 and 6. 
FIG. 8 shows a modified reel assembly 11, a preferred embodiment, to 
replace reels 6. The apparatus is otherwise unchanged from that previously 
described herein. This embodiment of the reel provides a reasonably 
uniform spiral of line around pipe. 
When line 10 is pulled from reel 14 of the reel assembly 11, control arm 12 
is caused to pivot around reel axis 11a and move in the direction of arrow 
D2. When line 10 is allowed to be recovered into reel 14, control arm 12 
moves in the direction of arrow D1. Control arm 12 is caused to pivot by 
gear axle 12c and gear 12d. Gear 12d runs between annular internal gear 
14a of reel 14 and sector gear 13a, which is cut on mount 13. One control 
arm 12 is situated on each side of the reel assembly. The near side arm is 
cut away to show the gear. In the embodiment used to rotate small pipe, a 
single gear 12d is situated on each side of reel 14 and is mounted for 
rotation by way of axle 12c, one on each control arm 12. For rotating 
small pipe, there is less line pulled out of reel 14 for each turn of line 
on the pipe compared with large pipe, and this simple gearing moves 
control arm 12 an appropriate amount per turn of reel 14. 
When larger pipe is to be rotated, reel 14 turns a greater amount per 
revolution of ring 2 relative to ring 3, and control arm 12 must be geared 
to move a smaller amount per turn of reel 14. 
FIG. 9 is a top view of the reel assembly 11 of FIG. 8. Reduction gearbox 
15 is added to control arm 12. There is only one reduction gearbox, 
because the reel assemblies as mounted on reel carrier ring 2 are too 
close together for gearboxes to clear on both sides. The single gear 12d 
is replaced by gears 12d1 and 12d2; independent but on coaxial axes are 
shafts extending from gearbox 15. The gearbox is fastened to the 
appropriate control arm 12. Both control arms 12 are themselves identical. 
The gearbox reduces the ratio of movement of the control arms relative to 
reels 14. The reduction gearing is not detailed because it is changed for 
various ranges of diameters of pipe to be rotated by the apparatus. Such 
gearing within the gearboxes is common to machine construction art. 
All control arm gearing is driven by gear 14a, and directly, or by 
reduction, drives the control arm through an arc about axis 11a, by 
operating on stationary gear 13a. 
Rollers 12a and 12b only control the vertical position of line 10, because 
peripheral forces on the line are opposed by posts 7. When line 10 is in 
the starting position, as shown in FIG. 5, control arm 12 is in the lowest 
position indicated by arrow D1. Control arm 12 can pivot upward in 
direction D2 about 70 degrees, as line 10 reels out to wrap line around 
pipe. This results in a fairly uniform spiral wrap. 
If flat web belts are used for lines 10, the rollers 12a and 12b will force 
the belts to twist to a horizontal condition for recovery into reel 14. 
FIGS. 10 through 14 apply to an alternate embodiment of the apparatus 
including alternate forms for the reel carrier ring and the powered 
partial ring, formerly rings 2 and 3 respectively. The frame and ring 
drive gearing remains unchanged and conform to those features described 
for FIGS. 1 and 2. Frame, motors, and ring drive gearing are not again 
detailed for FIGS. 10 and 11. 
In FIG. 10, reels 6 are positioned on and attached to ring 16 as previously 
described herein. Ring 16, the reel carrier, has notch 16a to accept line 
feed horn block 20. Only one arrangement is shown, an identical such 
arrangement is on the opposite side of axis VCL, and only one will be 
described. Guide columns 18 are secured to ring 16, one on each peripheral 
side of notch 16a. Block 20 has bushings 20a slidably situated around the 
columns, and can move vertically up and down the columns. The blocks 20 
also have threaded bushings 20c attached to the blocks and engage the 
threads on lead screw 19. Lead screw 19 is axially affixed to ring 16 for 
relative rotation. The lead screw is rotated by relative rotation between 
ring 16 and ring 17. Ring gear 17b is affixed to ring 17. Lead screw 
pinion 19a is slidably splined and rotationally secured one on each lead 
screw in an annular clearance 17a in ring 17. 
As previously described herein, rings 16 and 17 have throats to admit pipe 
to be rotated and ring gear 17b has a discontinuity at the throat. To 
synchronize the two lead screws 19, and to negotiate the discontinuity in 
ring gear 17b, the lead screws are connected by a gear train including 
gear 21b and mating right angle gear 21a. These are spiral gears. A gear 
21b is affixed to each lead screw, and gear 21a is affixed to shaft 21c. 
Shaft 21c is horizontal, mounted for rotation on ring 16, and extends to a 
similar gear arrangement for the mating lead screw on the opposite side of 
notch 16a. Thus the two lead screws are synchronized, and both continue to 
rotate in unison when one gear 19a is in the discontinuity of ring gear 
17b. (Note FIG. 13 for the situation of shaft 21c.) 
Pipe to be rotated can be rotated in either direction to make up or break 
out threaded connections. The lines must be advanced along the pipe 
periphery in either direction of relative rotation of rings 16 and 17. 
This requires the ability to reverse the gearing driving the lead screws. 
Each pinion 19a is mounted on the operatively related lead screw by mating 
splines, and the gear is pinned to a reverser rod which extends through 
the hollow lead screws. This arrangement will be described in more detail 
later. In FIG. 10, the internal ring gear 17c, attached to ring 17, should 
be noted. When pinion 19a is moved downward, it is briefly engaging both 
ring gear 17b and 17c. All pinions 19a are shifted at once, and the brief 
double engagement preserves synchronization throughout the useful life of 
the assembly. Further downward movement of gears 19a disengages them from 
gear 17b and fully engages them with gear 17c. Lead screw reversal only 
occurs when the throat openings of rings 16, 17, and frame 1 are in 
registry, and selection of make up or break out of pipe threads is made. 
The gearing ratio is slightly changed when the pinions are shifted from 
external ring gear 17b to internal ring gear 17c, but the synchronization 
is assured, and the spiral wrap of lines around pipe to be rotated 
tolerates the resulting slight variation in helix angle. 
FIG. 11 is a projection of FIG. 10 and is viewed from the throat around 
axis VCL. If rings 16 and 17 are rotated 180.degree., a similar view of 
the opposed structure would be identical. Bracing structure 22 is attached 
to columns 18 and contains bearing bushings for the upper end of the feed 
screws 19. When lines are installed, one line will extend through horn 
openings 20b. There are two such openings on the side viewed and four 
openings for the apparatus. Line driving posts 8 and line slide grooves 3f 
are as previously described herein. 
FIG. 12 is the same view as FIG. 10 with less cutaway and less detail 
shown. The single line 10 is representative of the four used on the full 
assembly. The spiral of the single line shown leaves room for the other 
three lines. All four lines result in nearly covering the pipe periphery. 
Ring 16 has completed three revolutions around the pipe relative to ring 
17. Block 20 can normally travel upward on columns 18, forced upward by 
lead screw 19 in engagement with threaded bushing 20c, to allow five 
rotations of ring 16 relative to ring 17. In use, both rings would now be 
rotated counterclockwise viewed from above. As previously described 
herein, ring 16 will be braked to provide line tailing tension as ring 17, 
by way of clamp 9 and driving post 8, applies tension to the driven end of 
the line to rotate pipe. 
FIG. 13 is a view taken along line 13--13 of FIG. 11. This view shows the 
relationship of the line feed horns 20b and notch 16a. Ring 16 is cutaway 
to show shaft 21c and gears 21a. Shaft 21c is mounted on ring 16 for 
rotation around its horizontal axis. No lines or reels are shown. Note 
that lead screws 19 are tubular. 
FIG. 14 is intended to show the elements involved in changing the direction 
of rotation of the lead screws relative to the relative rotational 
direction of rings 16 and 17. Bracing structure 22 is rotated out of 
normal position around the longitudinal axis of the lead screw to show 
reverser linkage. Ring 17 and gears 17b and 17c, as well as pinion 19a 
have been described. Lead screw splines 19b engage a mating spline in 
pinion 19a, and the pinion can slide axially relative to the lead screw. 
Shift rod 23 extends along the bore 19d of the lead screw. Rod 23 has a 
transverse hole 23b to snugly fit cross pin 24, which is secured in a 
transverse hole in pinion 19a, and is free to move axially in slots 19c 
through the wall of the lead screw. At the top end, rod 23 extends beyond 
the end of the lead screw and has spool 23a to allow rod 23 to rotate but 
engage pin 25a to follow the vertical motion of the pin. Crank throw pin 
25a is part of crank 25. Crank 25 is mounted for rotation about a 
horizontal axis in pollow blocks 26 which, in turn, are secured to 
structure 22. Handle 25b can be manually moved to rotate crank 25 about 
180.degree. to move crank throw pin 25a downward. This moves gear 19a, 
from the position shown, downward to disengage the pinion from gear 17b 
and to engage gear 17c. 
The lead screw 19 is positioned vertically by shoulder 19a abutting an 
opposed surface on ring 16 and shoulder 19f abutting a lower surface of 
structure 22. Each crank 25 controls the rotation of a pair of lead screws 
operatively associated with each line feed horn block 20. 
The weight of handle 25b retains the selected position. 
It is unnecessary to use a throat in the side of power tongs to rotate 
pipe. The throat only allows the tongs to be removed from the pipe and to 
be moved away at any time. Power tongs are often used without the side 
throat and are left in place around the pipe throughout the pipe string 
assembly. Descriptive material in this disclosure is oriented to throated 
tongs because a system that operates with a throat can do quite well 
without the throat and the gearing arrangement peculiar to throated tongs. 
Tongs, however, that were not inteded to use an open throat cannot easily 
be changed to add a throat. 
If back-up tongs are used to hold pipe essentially non-rotational, while 
power tongs rotate a mating pipe section, the powered ring disclosed 
herein can be used and held stationary to serve the back-up function. 
Further, the drive ring can be effectively welded to the body. The driven 
end of the lines will then, consequently, be anchored to the body. 
Having described the essential elements of the more complicated open throat 
power tongs of this invention, it is deemed unnecessary to show in detail 
the version without a throat. Further, having described in detail tongs 
with means to rotate machinery to which the driven ends of lines are 
attached, it is deemed unnecessary to describe in detail the structure 
held non-rotational to which the driven ends of the lines are attached. 
Simpler versions of the tongs of this invention are anticipated by and are 
within the scope of the claims. 
The expression "braking" is used herein with regard to the reel carrier 
ring. The reel carrier ring is necessarily powered and the power is, 
preferably, supplied by a hydraulic motor. Fluid motors are available with 
built-in torque limiting relief valves. Such valves are the equivalent to 
relief valves connecting both motor fluid ports. When common fluid motors 
are reversed, the function of intake and exhaust ports are reversed. A 
bi-directional relief valve is, therefore, required for a general purpose 
motor. The torque limiter valve is usually adjustable. Use of the torque 
limited motor serves as the preferred brake for the reel carrier ring. The 
torque limiting valve serves the braking purpose whether the fluid 
pressure source is on, off, or reversed. A bi-directional relief valve is 
equivalent to two relief valves, oppositely oriented, and commonly 
connected at the flow ends. 
Motors of many types are available with friction brakes directly connected 
to the shafts. Some provide constant drag but most such brakes are 
automatically activated when power to the motor is turned off. Friction 
braked motors of either type are optional drives for the reel carrier 
ring. 
Use of either the torque limited or friction braked motors is anticipated 
by and is within the scope of the claims. 
From the foregoing, it will be seen that this invention is one well adapted 
to attain all of the ends and objects hereinabove set forth, together with 
other advantages which are obvious and which are inherent to the method 
and apparatus. 
It will be understood that certain features and subcombinations are of 
utility and may be employed without reference to other features and 
subcombinations. This is contemplated by and is within the scope of the 
claims. 
As many possible embodiments may be made of the apparatus and method of 
this invention without departing from the scope thereof, it is to be 
understood that all matter herein set forth or shown in the accompanying 
drawings is to be interpreted as illustrative and not in a limiting sense.