U.S. patent application number 13/487186 was filed with the patent office on 2012-12-06 for drilling rig system with self-elevating drill floor.
This patent application is currently assigned to NATIONAL OILWELL VARCO, L.P.. Invention is credited to Donald Leonard BURLET, Kameron Wayne KONDUC.
Application Number | 20120304553 13/487186 |
Document ID | / |
Family ID | 47258210 |
Filed Date | 2012-12-06 |
United States Patent
Application |
20120304553 |
Kind Code |
A1 |
KONDUC; Kameron Wayne ; et
al. |
December 6, 2012 |
DRILLING RIG SYSTEM WITH SELF-ELEVATING DRILL FLOOR
Abstract
A transportable drilling rig having a self-elevating drill floor
includes a base structure comprising multiple base towers that can
be transported to a wellsite and positioned around an intended
wellbore location. A horizontal base frame is installed between
lower regions of the towers to form a stable rig base structure,
and a drill floor can then be constructed over the base frame and
between the base towers. A suitable rig mast can then be erected on
the drill floor. Floor-lifting cables are anchored to upper regions
of the base towers and disposable around corresponding sheave
assemblies associated with the drill floor. The free ends of the
floor-lifting cables can be engaged by the traveling block in the
rig mast, whereupon the rig's drawworks can be actuated to elevate
the drill floor and mast as required and then locked to the base
towers.
Inventors: |
KONDUC; Kameron Wayne;
(Edmonton, CA) ; BURLET; Donald Leonard;
(Edmonton, CA) |
Assignee: |
NATIONAL OILWELL VARCO,
L.P.
Houston
TX
|
Family ID: |
47258210 |
Appl. No.: |
13/487186 |
Filed: |
June 2, 2012 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61492786 |
Jun 2, 2011 |
|
|
|
Current U.S.
Class: |
52/112 ;
52/126.5; 52/745.18 |
Current CPC
Class: |
E04B 1/34384 20130101;
E04B 1/34331 20130101; E04H 12/344 20130101; E21B 15/00 20130101;
E04H 12/345 20130101; E04H 12/18 20130101 |
Class at
Publication: |
52/112 ;
52/126.5; 52/745.18 |
International
Class: |
E04H 12/34 20060101
E04H012/34; E04H 12/00 20060101 E04H012/00; E04B 1/343 20060101
E04B001/343 |
Claims
1. A drilling rig system comprising: (a) a plurality of base towers
spaced apart in a selected layout; (b) a horizontal base frame
interconnecting lower regions of the base towers to form a base
structure; (c) a drill floor overlying the base frame and
vertically movable relative thereto; and (d) floor-lifting means,
for elevating the drill floor above the base frame.
2. A drilling rig system as in claim 1 wherein: (a) the drill floor
incorporates a plurality of floor-lifting sheave assemblies, each
said floor-lifting sheave assembly being associated with one of the
base towers; (b) a plurality of floor-lifting cables, each said
floor-lifting cable being anchored to an upper region of one of the
base towers; and (c) the floor-lifting means comprises a drawworks
and traveling block associated with a rig mast erected on the drill
floor; such that the floor-lifting cables can be threaded around
the associated floor-lifting sheave assemblies and extended upward
to engage the traveling block, whereupon actuation of the drawworks
will cause the traveling block to move upward within the rig mast,
thereby elevating the drill floor relative to the base
structure.
3. A drilling rig system as in claim 1, further comprising locking
means for locking the drill floor to the base towers to maintain
the drill floor at a desired elevation.
4. A drilling rig system as in claim 3 wherein the locking means
comprises hydraulic latches.
5. A drilling rig system as in claim 1, further comprising guide
means associated with the base towers, to promote uniform upward
movement of the drill floor and to provide lateral stability to the
drill floor during drill floor raising operations.
6. A drilling rig system as in claim 1, further comprising
adjustment means for adjusting the vertical and lateral positions
of the base towers.
7. A drilling rig system as in claim 1 wherein the floor-lifting
means comprises a plurality of worm gear drive mechanisms and a
plurality of mating rack gears, with each rack gear being
incorporated into one of the base towers and one worm gear drive
being incorporated into the drill floor adjacent to an associated
rack gear.
8. A drilling rig system comprising: (a) a plurality of base towers
spaced apart in a selected layout; (b) a horizontal base frame
interconnecting lower regions of the base towers to form a base
structure; and (c) a drill floor overlying the base frame and
vertically movable relative thereto; and (d) floor-lifting means,
for elevating the drill floor above the base frame; wherein: (e)
the drill floor incorporates a plurality of floor-lifting sheave
assemblies, each floor-lifting sheave assembly being associated
with one of the base towers; (f) a plurality of floor-lifting
cables, each floor-lifting cable being anchored to an upper region
of one of the base towers; and (g) the floor-lifting means
comprises a drawworks and traveling block associated with a rig
mast erected on the drill floor; such that the floor-lifting cables
can be threaded around the associated floor-lifting sheave
assemblies and extended upward to engage the traveling block,
whereupon actuation of the drawworks will cause the traveling block
to move upward within the rig mast, thereby elevating the drill
floor relative to the base structure.
9. A drilling rig system as in claim 8, further comprising locking
means for locking the drill floor to the base towers to maintain
the drill floor at a desired elevation.
10. A drilling rig system as in claim 9 wherein the locking means
comprises hydraulic latches.
11. A drilling rig system as in claim 8, further comprising guide
means associated with the base towers, to promote uniform upward
movement of the drill floor and to provide lateral stability to the
drill floor during drill floor raising operations.
12. A drilling rig system as in claim 81, further comprising
adjustment means for adjusting the vertical and lateral positions
of the base towers.
13. A method for assembling a drilling rig structure, comprising
the steps of: (a) positioning a plurality of base towers in spaced
relationship in a selected layout at a wellsite; (b) erecting a
horizontal base frame interconnecting lower regions of the base
towers to form a base structure; (c) erecting a drill floor
overlying the base frame and vertically movable relative thereto,
said drill floor incorporating a plurality of floor-lifting sheave
assemblies, each said floor-lifting sheave assembly being
associated with one of the base towers; (d) erecting a rig mast on
the drill floor, including a drawworks and a traveling block; (e)
anchoring a floor-raising cable at an upper region of each base
tower; (f) threading the floor-raising cables around their
associated floor-lifting sheave assemblies and engaging the free
ends of the cables with the traveling block; (g) actuating the
drawworks so as to raise the traveling block and the drill floor
relative to the base structure, until the drill floor is at a
desired elevation; and (h) engaging locking means to lock the drill
floor to the base towers.
14. A method as in claim 13 wherein the locking means comprises
hydraulic latches.
15. A method as in claim 13, further comprising the step of
providing guide means in association with the base towers, to
promote uniform upward movement of the drill floor and to provide
lateral stability to the drill floor during drill floor raising
operations.
16. A method as in claim 13 wherein the base towers are provided
with adjustment means for adjusting the vertical and lateral
positions of the base towers.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 61/492,786, filed on Jun. 2, 2011, and said earlier
application is incorporated herein by reference in its entirety for
continuity of disclosure.
FIELD OF THE DISCLOSURE
[0002] The present disclosure relates in general to rig structures
for drilling wells such as oil and gas wells. In particular, the
disclosure relates to rig structures that can be readily
transported, rapidly erected, and rapidly disassembled, and further
relates to methods for erecting such rig structures.
BACKGROUND
[0003] Wells for the recovery of hydrocarbons or minerals from a
subsurface formation are commonly drilled by connecting a drill bit
onto the lower end of an assembly of drill pipe sections connected
end-to-end (commonly referred to as a "drill string"), and then
rotating the drill string so that the drill bit progresses downward
into the earth to create the desired wellbore. The drill string is
typically rotated by means of a "rotary table" or a "top drive"
associated with a drilling rig erected at the ground surface over
the wellbore.
[0004] The primary components of a typical drilling rig include a
base support structure, a drill floor, and a mast (also called a
derrick) supported on and extending upward from the drill floor.
The drill floor is typically elevated well above the ground surface
to provide space to accommodate and allow access to various
equipment required for drilling operations. An arrangement of
pulleys (sheaves) called a crown block is mounted to the top of the
rig mast. Hoisting apparatus called a drawworks, comprising a cable
drum, a cable winch, and ancillary equipment, is provided in
association with the drill floor. Wire-rope cable is fed from the
cable drum up to the crown block and threaded over the various
sheaves in the crown block, and then down to a "traveling block",
which is an assembly of sheaves that is free to move vertically
within the mast structure as the wire-rope cable ("drill line") is
played out or taken up by the cable winch and drum of the
drawworks. The traveling block has a lifting hook to support
equipment used to raise and lower the drill string, and to add pipe
sections during drill string assembly (or "make-up") and to remove
pipe sections during drill string disassembly ("break-out"). For
drilling operations using a top drive instead of a rotary table to
rotate the drill string, the top drive is suspended from the
traveling block hook.
[0005] For optimal efficiency and economy in well-drilling
operations, it is desirable for drilling rigs to be readily
transportable, rapidly erected, and rapidly disassembled for
transportation to new wellsites. Accordingly, the transportability
of rig components and the speed at which components can be
assembled with the minimum amount of auxiliary equipment are
paramount concerns. Conventional types of transportable rigs may
require auxiliary support equipment to facilitate the erection and
disassembly of large components such as the base, the drill floor,
and the pipe racking board, thereby increasing rig set-up,
take-down, and operational costs.
[0006] Numerous types of transportable rigs may be found in the
prior art. Known transportable rigs commonly feature what is called
a "bootstrap mast". A bottom mast section having a large lower
opening on one side is mounted to the drill floor, using a mobile
crane. The crane then lowers the top section of the finished mast
(housing the crown block) into the bottom mast section, and the top
mast section is temporarily pinned to the bottom mast section.
Next, the crane positions an intermediate mast section through the
opening in the bottom mast section so that the upper end of the
intermediate mast section can be securely connected to the lower
end of the upper mast section. The traveling block is then lowered
to engage and support the intermediate section, the upper mast
section is unpinned from the bottom mast section, the drawworks is
actuated to hoist the upper and intermediate mast sections a
distance corresponding to the height of the intermediate mast
section, and then the partially-constructed mast assembly (i.e.,
upper section plus one intermediate section) is temporarily pinned
to the stationary bottom mast section. This latter process is then
repeated as necessary to install additional intermediate mast
sections until the mast has reached its intended final height,
whereupon the lowermost intermediate mast section is secured to the
bottom mast section so that the rig is ready to be put into
service.
[0007] Drilling sites are often located in remote areas requiring
truck transportation of rig components and equipment required for
rig assembly (or "rig-up"). Further complicating the rig-up process
is the common need to relocate the rig to a more promising site
after a wellbore has been drilled and it has been determined that
the wellbore will not be sufficiently productive to warrant
completion and operation of the well. Wellsite changes can occur
once every several months, and, in response, prior art rig systems
have attempted to increase the mobility of rig components and the
efficiency of rig erection and disassembly procedures in order to
minimize associated costs. However, the need for auxiliary
equipment typically remains necessary for performing steps such as
placing the drill floor.
[0008] Since the variable costs associated with leased support
equipment, such as cranes and the like, are calculated on a per
hour or per day basis, expediting rig take-down, transport, and
set-up operations is crucial for minimizing equipment leasing
costs. Typically, rig take-down and set-up times are in the order
of days, and very large equipment and labor costs can be incurred
for each end of a set-up and take-down operation. Various prior art
drilling rigs are geared towards facilitating rapid set-up,
take-down and transport, but they still require auxiliary equipment
such as external cranes and external winches, which most often need
to be leased and therefor increase overall rig set-up and take-down
costs, particularly for remote wellsites.
[0009] One approach to reducing rig set-up times and costs is to
raise the drill floor to its intended service elevation after
erection of the mast. This results in economies due to the fact
that the mast can be erected with the drill floor close to ground
level rather than in its final position 20 feet or more above
ground. The cranes and other equipment manipulating and positioning
the various drill floor and mast components do not require as high
a reach, and workers have more ready access to the drill floor
during rig-up procedures.
[0010] An example of a transportable drilling rig having a drill
floor that can be raised after mast erection can be seen in U.S.
patent application Ser. No. 12/492,980 (Wasterval), Pub. No. US
2012/0326734A1. Wasterval teaches the construction of a drill floor
over a base structure, which is provided with hydraulic cylinders
for raising the drill floor above the base structure. After the
drill floor has been raised by an increment corresponding to the
stroke of the hydraulic cylinders, a first set of box beams are
disposed between the drill floor and the base structure, and the
box beams are anchored to the drill floor. The lift cylinders on
the base structure can then be retracted to engage lift points on
the box beams. The lift cylinders are then actuated again, this
time to raise both the drill floor and the first box beams anchored
thereto. This allows insertion of a second set of box beams between
the base structure and the first set of box beams, thus elevating
the drill floor a further incremental amount. This procedure is
repeated as necessary to install additional sets of box beams until
the drill floor has reached its intended elevation.
[0011] The Wasterval system thus allows the drill floor to be
erected or constructed close to ground level, followed by erection
of the rig mast on the drill floor, whereupon the drill floor (with
erected mast) can be elevated as required. However, this system has
an inherent drawback in that the rig floor raising procedure has to
be carried out in incremental and comparatively complex stages, and
is correspondingly complex and time-consuming. In addition, the
Wasterval system entails the provision of a robust hydraulic
system, which might not otherwise be needed on site during rig-up,
and thus increases rig-up costs. As well, the Wasterval system
requires the use of mobile cranes or other auxiliary hoisting
equipment to manipulate and position the box beams, further adding
to rig-up costs.
[0012] For the foregoing reasons, there is a need for an improved
transportable drilling rig that can be rapidly erected and
disassembled with minimal need for auxiliary equipment. In
particular, there is a need for an improved transportable rig in
which the drill floor can be elevated after erection of the mast,
but without requiring hydraulics or auxiliary hoisting
equipment.
BRIEF SUMMARY
[0013] In general terms, the present disclosure teaches a
transportable drilling rig apparatus having a drill floor that can
be elevated after erection of the rig mast, without requiring a
hydraulic system or auxiliary hoisting equipment. In one
embodiment, the rig's traveling block and drawworks are used to
elevate the drill floor. In alternative embodiments, a worm gear
drive mechanism can be used to elevate the drill floor.
[0014] The rig apparatus includes a rig base structure comprising a
plurality of base towers that can be positioned in a suitable
spaced relationship on a wellsite. In one embodiment, there are
four base towers arranged in a square or rectangular pattern, but
other embodiments could use more than four towers and as few as
three, and possibly in different (i.e., non-rectilinear) patterns.
A generally horizontal base frame is installed between lower
regions of the towers, thus tying the towers together to form a
suitably rigid and stable rig base structure. The towers may be
provided with height adjustment mechanisms (e.g., hydraulic jacks)
to facilitate leveling the base structure over uneven ground
surfaces. As well, the towers may optionally be provided with
"walking" mechanisms whereby the lateral positions of the towers
can be adjusted prior to installation of the horizontal base frame.
The walking mechanisms can be coupled for cooperative actuation to
facilitate lateral movement of the completed rig base
structure.
[0015] A drill floor can then be constructed over the horizontal
base frame of the rig base structure. The drill floor may comprise
multiple slab sections that are anchored to each other after being
positioned over the base frame to form an integral drill floor
structure. Optionally, the horizontal base frame can be
advantageously set at a height above ground corresponding to the
level of a flatbed truck or trailer, thus facilitating unloading of
drill floor sections by shifting them laterally off the trailer bed
onto the base frame. The drill floor is mated to the towers with
suitable guide means such that the drill floor can be uniformly
elevated relative to the towers, with the towers acting to provide
lateral stability to the drill floor at all stages of the
floor-elevating process. When the drill floor has been elevated to
the required elevation, it is locked to the towers by any suitable
means, such as but not limited to hydraulic clamps.
[0016] In a preferred embodiment, the drill floor is elevated using
only the rig's traveling block and drawworks. To enable this mode
of operation, sheave assemblies are mounted to and under the drill
floor adjacent to each tower. Each tower has a floor-lifting cable
anchored to an upper region of the tower and disposable under and
around the corresponding sheave assembly associated with the drill
floor, such that the free (i.e., non-anchored) ends of the
floor-lifting cables converge toward a central area of the drill
floor. After the rig mast has been erected using the traveling
block and drawworks, the free ends of all floor-lifting cables can
be engaged by the traveling block hook. The drawworks can then be
actuated to raise the drill floor in one continuous operation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] Embodiments in accordance with the present disclosure will
now be described with reference to the accompanying figures, in
which numerical references denote like parts, and in which:
[0018] FIG. 1 is an elevation illustrating the unloading of base
towers from a transport truck and positioning of the towers on a
wellsite.
[0019] FIG. 2 is an elevation illustrating a horizontal base frame
interconnecting the rig towers.
[0020] FIG. 3A is a first elevation view of an embodiment of a
drilling rig structure in accordance with the present disclosure,
showing the drill floor installed over the horizontal base frame,
with a rig mast in an early stage of erection upon the drill
floor.
[0021] FIG. 3B is a second elevation view of the assembly in FIG.
3A.
[0022] FIG. 4A is a first elevation view similar to FIG. 3A, after
complete erection of the rig mast, with the floor-raising cables
engaging the traveling block hook in preparation for elevating the
drill floor.
[0023] FIG. 4B is a second elevation view of the assembly in FIG.
4A.
[0024] FIG. 5A is a first elevation view similar to FIG. 4A, after
the drill floor has been elevated and the rig is ready to be put
into service.
[0025] FIG. 5B is a second elevation view of the assembly in FIG.
5A.
[0026] FIG. 6 is a plan cross-section through the base towers of
one embodiment of a drilling rig structure and drill floor layout
in accordance with the present disclosure, prior to elevation of
the drill floor.
DETAILED DESCRIPTION
[0027] FIGS. 1 through 5B progressively illustrate the steps
involved in assembling one embodiment of a transportable drilling
rig in accordance with present disclosure. FIGS. 1 and 2 depict the
delivery and positioning of a plurality of base towers 10 at a
drill site. Preferably (but not necessarily), towers 10 will be
provided with adjustment means 12 for adjusting their height,
lateral position, and vertical alignment. Persons skilled in the
art will know that such means can be provided in a variety of ways
using known technologies, and such means do not constitute
components of the broadest embodiments of drilling rigs in
accordance with this disclosure.
[0028] After the required number of towers 10 are in their required
positions relative to the centerline CL.sub.W of a wellbore to be
drilled using the rig being constructed, a base frame 20 is
constructed or installed as shown in FIG. 2, interconnecting the
base towers 10. Base frame 20 can be of any suitable layout and
structural configuration. The structure can also be assembled off
the well and "walked" into drilling position if equipped with
adjustment means 12.
[0029] As seen in FIG. 3, a drill floor 30 is then constructed over
and temporarily supported on base frame 20, whereupon a rig mast
structure 100 can be erected upon drill floor 30. The structural
details of the rig mast and the methods by which it is erected are
not directly relevant to the subject matter sought to be protected
hereby. For illustration purposes, however, rig mast 100 is shown
as a bootstrap mast of the type described previously herein,
comprising: [0030] a bottom mast section 110 with support legs 112
and 114 anchored at their lower ends 112L and 114L to corresponding
anchorages 112X and 114X on drill floor 30; [0031] a top mast
section 120 fitted with a crown block 122 and traveling block 124
(as previously described); [0032] one or more intermediate mast
sections 130 adapted for connection to top mast section 120 and
adjacent mast sections 130 (as previously described).
[0033] As seen in FIG. 3A and in greater detail in plan view in
FIG. 6, drill floor 30 is provided with a suitable drawworks
(generally indicated by reference number 40), including a cable
drum 42 which carries wire rope used for a drill line fed up and
through crown block 122 and down to traveling block 124 as
previously described. In the embodiment illustrated in FIG. 6, the
rig structure includes four base towers 10 laid out in a
rectilinear pattern. Drill floor 30 is configured in the general
shape of a cross, with adjacent "arms" of the cross fitted closely
around their associated base tower 10. Reference numbers 35 denote
drill floor guide and anchorage means to facilitate stable and
uniform vertical movement of drill floor 30 relative to base towers
10 during drill floor lifting operations, and for anchoring drill
floor 30 to base towers 10 after drill floor 30 has been elevated
to its intended position for drilling operations. Although
indicated for convenience by a single reference number 35, the
drill floor guide means and the drill floor anchorage means may be
separate and independent mechanisms.
[0034] The location and general configuration of the drawworks
(including cable drum 42) are indicated by reference number 40; in
the illustrated embodiment, drawworks 40 is at least partially
installed on a cantilevered section of drill floor 30. In the
illustrated embodiment, drill floor 30 incorporates a rotary table
135 for rotating a drill string. A driller's control cabin is
indicated by reference number 44. Drill floor 30 may have one or
more cantilevered catwalks 31 for worker access.
[0035] Mounted to (and typically underneath) drill floor 30 are a
plurality of sheave assemblies for use in elevating drill floor 30.
For clarity in this patent document, the sheaves used for this
particular purpose will be referred to as drill floor sheaves. One
exemplary drill floor sheave arrangement is illustrated in FIGS. 3A
through 5B, and in greater detail in FIG. 6. In this exemplary
arrangement, an outer drill floor sheave 32A and an inner drill
floor sheave 32B are provided in association with each base tower
10, with the rotational axes of inner and outer drill floor sheaves
32A and 32B being parallel and transverse to a radial line
extending from their associated base tower 10 to well centerline
CL.sub.W. Although drill floor sheaves 32A and 32B in the
illustrated embodiment are actually mounted below or within the
structure of drill floor 30, they are shown in solid outline in
FIG. 6 for purposes of clarity.
[0036] In the illustrated embodiment, there is a set of drill floor
sheaves for each base tower 10, but this is not essential.
Alternative embodiments could have one or more base towers 10 that
do not have an associated drill floor sheave assemblies.
Furthermore, although in the illustrated embodiment each drill
floor sheave assembly includes a pair of drill floor sheaves,
alternative embodiments could use drill floor sheave assemblies
comprising more than two drill floor sheaves or possibly only one
drill floor sheave.
[0037] In FIGS. 3A and 3B, upper mast section 120 has been
positioned and pinned to bottom mast section 110, and a first
intermediate mast section 130 has been positioned within bottom
mast section 110 and connected to upper mast section 120. As seen
with particular clarity in FIG. 3B, mast-raising cables 135
anchored to upper regions of bottom mast section 110 extend around
sheaves 132 at the lower end of the intermediate mast section 130
disposed within bottom mast section 110 and upward for engagement
with traveling block 124. Drawworks 40 is then actuated to raise
traveling block 124 and lift the assembly of upper mast section 120
and intermediate mast section 130 until the lower end of
intermediate mast section 130 has been raised sufficiently to allow
another intermediate mast section 130 to be positioned within
bottom mast section 110, and so on until rig mast 100 has been
constructed to its final intended height as shown in FIGS. 4A and
4B.
[0038] At this stage, the mast-raising cables 135 are disengaged
from traveling block 124. A plurality of floor-raising cables 33,
corresponding in number to the number of drill floor sheave
assemblies, are threaded from anchor points 33X in upper regions of
their associated base towers 10, around drill floor sheaves 32A and
32B and then upward for engagement by traveling block 124, all as
seen in FIGS. 4A and 4B. Drawworks 40 is then actuated to raise
traveling block 124, thereby elevating drill floor 30 to an
intended service elevation as seen in FIGS. 5A and 5B. Drill floor
30 is then anchored to base towers 10 by suitable anchorage means
35 (which by way of non-limiting example could be provided in the
form of hydraulic latches).
[0039] Although the drawworks and traveling block are used to
elevate drill floor 30 for purposes of embodiments illustrated
herein and previously described, alternative embodiments of rig
systems in accordance with the present disclosure could use
different means for elevating drill floor 30. By way of
non-limiting example, a worm gear drive unit could be used to
elevate drill floor 30, with guide rollers, and mating racks built
into base towers 10 at each corner of drill floor 30. The worm gear
drive mechanism could be actuated by any suitable power means, such
as hydraulic or electric motors. In one alternative embodiment, a
worm gear drive could be provided as a supplement or back-up to a
primary cable-implemented floor-raising mechanism.
[0040] It will be readily appreciated by those skilled in the art
that various modifications to embodiments in accordance with the
present disclosure may be devised without departing from the scope
and teaching of the present teachings, including modifications
which may use equivalent structures or materials hereafter
conceived or developed. It is to be especially understood that the
scope of the present disclosure is not intended to be limited to
described or illustrated embodiments, and that the substitution of
a variant of a claimed element or feature, without any substantial
resultant change in functionality, will not constitute a departure
from the scope of the disclosure.
[0041] In this patent document, any form of the word "comprise" is
to be understood in its non-limiting sense to mean that any item
following such word is included, but items not specifically
mentioned are not excluded. A reference to an element by the
indefinite article "a" does not exclude the possibility that more
than one of the element is present, unless the context clearly
requires that there be one and only one such element.
[0042] Relational terms such as "parallel" and "horizontal" are not
intended to denote or require absolute mathematical or geometric
precision. Accordingly, such terms are to be understood in a
general rather than precise sense (e.g., "generally parallel" or
"substantially parallel") unless the context clearly requires
otherwise.
[0043] Wherever used in this document, the terms "typical" and
"typically" are to be interpreted in the sense of representative or
common usage or practice, and are not to be understood as implying
invariability or essentiality.
* * * * *