Self positioning fixation system and method of using the same

The present invention has at least one rack chock which is supported pivotally and tiltably at one end by a pin and cross head assembly located at a position between at least one leg rack and the hull of the platform. The other end of the rack chock is connected to the jack foundation with an actuator assembly. The pin and cross head assembly is disposed slidably within a guide for permitting the teeth of the rack chock to engage the leg rack teeth without visual monitoring and manual control. The actuator assembly connected to the other end of the rack chock controls the swinging movement of the rack chock and its engagement and disengagement with the leg rack. A pair of jacks urges upper and lower wedges with tiltable surfaces converging onto the rack chord's upper and lower surfaces, thus obtaining a optimal surface to arrest the relative movement between the rack chock and the leg rack. As such, load from the jack foundation is transferred to the legs, overturning moments on the legs to the jack foundation. Stress to the mating surfaces of the present invention and the leg rack is minimized as the engagement of the present invention takes place under load from the inertia load of the rack chock due to the pivoting action with minimum forcing action from the actuator assembly.

FIELD OF THE INVENTION 
The present invention relates to a fixation system for self elevating 
platform or jackup rig. In particular, the present invention pertains to a 
system for automatically engaging the fixation device to arrest the 
relative movement between the supporting legs and hull of self elevating 
platform while preserving surface integrity of the mating surfaces. 
BACKGROUND OF THE INVENTION 
Various prior art fixation systems are employed to arrest the relative 
motions and transfer the overturning moments and loads between the hull 
and legs of a jackup rig. 
A jackup rig as used herein means any working platform for drilling, work 
over, production, crane work, compressor station, diving support or other 
offshore purpose in an elevated position above the water, and being 
supported on jackable legs to the ocean floor or other water bottom, with 
the inherent capability of relocating from one site to another by lowering 
to a floating position, and after being moved to a new established 
location, raising again to an elevated position. Jackup rigs are equipped 
with rack and pinion jacking systems for raising and lowering the 
platform. The rack is fixed to the leg along its vertical length, and 
pinions and their drives are disposed on the jacking units' structures 
which are connected to the hull. 
The first type of fixation systems use stoppers or lock bolts which 
individually engage with and lock into the tooth spaces or on the tooth 
flanks of the rack on the leg. These stoppers can be moved individually or 
as group by actuators. However, the individual stopper is capable of 
adjusting its position when it meshes with the tooth spaces of the rack. 
Exemplary of the first type of fixation systems are U.S. Pat. Nos. 
4,447,401, 4,813,814, and 5,139,366. Each of these systems requires manual 
intervention during engagement notwithstanding certain automation 
features. Where the movement of stoppers is in a direction substantially 
perpendicular to the leg rack, the stoppers may not engage fully into the 
tooth space in all relative positions of the hull with respect to the leg. 
By rack chock fixation system, the present invention refers to a system for 
aligning and locking a section of rack chock with a profile matching the 
teeth of the rack on the jackable legs. U.S. Pat. No. Re. 32,589 
exemplifies the rack chock fixation system where a series of vertical and 
horizontal screw jacks align a rack chock piece with flat upper, lower and 
lateral surfaces with a matching teeth profile on the leg rack. The 
alignment is accomplished manually and visually. Once aligned, the rack 
chock and the leg rack are locked by screw jacks. 
Another type of locking fixation system for jackup rig is exemplified by 
U.S. Pat. No. 4,389,140 which teaches the use of a rack chock with 
inclined upper and lower surfaces with flange edges held between claws of 
vertically movable wedges with mating surface and matching inclination. 
The wedges are guided to move vertically by nuts fixed into the wedges; 
the rack piece is engaged with mating teeth on the leg rack by independent 
rotating screws. Rotation of the screws with identical speed in the same 
direction moves the wedges as well as the rack vertically. Rotation of the 
screws with identical speed in the opposite direction brings the wedges 
closer and moves the rack piece laterally by sliding along the inclined 
surfaces. Similarly the locking fixation system requires visual monitoring 
for the exact matching of the rack chock with the teeth of the leg rack. 
The third type of fixation system for jackup rigs is typified in U.S. Pat. 
No. 4,662,787 which teaches the use of a rack chock with inclined upper 
and lower surfaces having flanged edges held between claws of horizontally 
movable wedges with mating surface and matching inclination. Wedge guides 
in the framework (attached rigidly to the hull) guided the wedges, while 
independent screwjacks acting against the flat end of the wedges provided 
movement to it. Rotation of the screwjacks in opposing directions with the 
same speed moves the rack chock vertically. Rotation of the screwjacks in 
the same direction moves the inclined surfaces of the wedges towards or 
away from each other, thus moving the rack chock toward or away from the 
leg rack by sliding along the inclined faces of the wedges. 
All three types of prior art fixation system employ combinations of rack 
chocks, wedges, and jacks to arrest the relative movements between legs 
and hull as well as to transfer the loads in a self elevating platform. It 
can also be said that all prior art fixation systems require visual 
monitoring for the exact meshing of the teeth of the rack chock with the 
teeth of the leg rack. 
OBJECT OF THE INVENTION 
It is an object of the present invention to provide a new fixation system 
for self elevating platform or jackup rig without relying on visual 
monitoring and manual control to align and engage the rack chock to the 
leg rack. 
It is another object of the present invention to provide a new fixation 
system for self elevating platform which incorporates a rack chock 
supported at one end pivotally and tiltably by at least one pin and cross 
head assembly disposed between the leg rack and the hull of the platform 
for aligning the rack chock with the leg rack without visual monitoring 
and manual control. 
It is yet another object of the present invention to provide a new fixation 
system for self elevating platform having a slidable pin supported within 
a slidable cross head which in combination with the pivotally supported 
rack chock self positions the teeth of the rack chock with the leg rack 
teeth during engagement even when the leg assembly has angular 
misalignment with the rack chock in any direction. 
It is a further object of the present invention to provide a new fixation 
system for self elevating platform which will successfully transfer the 
load from the jack foundation to the leg assembly or vice versa even when 
the leg assembly has angular misalignment with the rack chock in any 
direction. 
It is a further object of the present invention to provide a new fixation 
system for self elevating platform which automatically engages and 
disengages with the leg rack while preserving surface integrity of the 
mating surfaces. 
It is yet a further object of the present invention to provide a new 
fixation system for self elevating platform which incorporates wedges with 
tiltable surface converging onto the mating surfaces of the rack chock to 
enable optimal surface contact for load transfer. 
SUMMARY OF THE INVENTION 
The present invention has at least one rack chock which is supported 
pivotally and tiltably at one end by at least one pin located at a 
position between at least one leg rack and the hull of the platform. The 
other end of the rack chock is connected to the jack foundation with an 
actuator assembly. The pin is disposed rotatably between a pair of cross 
heads which in turn are disposed slidably within a guide. The cross heads 
are maintained in an equilibrium position for the rack chock to engage the 
leg rack teeth by a pair of springs within the guide. Thus, the pin and 
cross head assembly enables the teeth of the rack chock to engage the leg 
rack teeth without visual monitoring and manual control. The actuator 
assembly connected to the other end of the rack controls the swinging 
movement of the rack chock and its engagement and disengagement with the 
leg rack. A pair of opposing jacks urge upper and lower wedges with 
tiltable surfaces converging onto the upper and lower surfaces of the rack 
chock in arresting the relative movement between the rack and the leg 
rack. As such, load from the jack foundation is transferred to the legs, 
overturning moments on the legs to the jack foundation. Stress to the 
mating surfaces of the present invention and the leg rack is minimized as 
the engagement of the present invention takes place without any 
misalignment between the rack chock and the leg rack.

DESCRIPTION OF THE EMBODIMENT OF THE INVENTION 
A method and apparatus for positioning a fixation device automatically and 
arresting the relative movement between the supporting legs and hull of 
self elevating platform is described. In the following description, 
numerous specific details are set forth such as rack, pin and program 
steps, etc. in order to provide a thorough understanding of the present 
invention. It will be obvious to one skilled in the art that the present 
invention may be practiced without these specific details. In other 
instances, well-known parts such as those involved with the rack and 
pinion jacking system are not shown in order not to obscure the present 
invention. 
Notation and Nomenclature 
The detailed description with respect to the steps of positioning 
automatically the rack to the leg rack are presented partially in terms of 
algorithm and symbolic representation upon operation on data bits within 
the computer memory. These algorithmic descriptions and representations 
are the means used by those skilled in the art in the data processing arts 
to most effectively convey the substance of their work to others skilled 
in the art. 
An algorithm is here, and generally, conceived to be a self-consistent 
sequence of steps leading to a desired result. These steps are those 
require physical manipulation of physical quantities. Usually, though not 
necessarily, these quantities take the form of electrical or magnetic 
signals capable of being stored, transferred, combined, and otherwise 
manipulated. In this case, the physical quantities are voltage signals 
which correspond to the speech signals. It proves convenient at times, 
principally for reason of common usage, to refer to these signals as bits, 
values, elements, symbols, characters, terms, numbers or the like. It 
should be borne in mind, however, hat all of these and similar terms are 
to be associated with the appropriate physical quantities and are merely 
convenient labels applied to these quantities. 
Further, the manipulations performed are often referred to in terms such as 
adding or comparing, which are commonly associated with the mental 
operations performed by a human operator. No such capability of a human 
operator is necessary, or desirable. In most cases, in any of the 
operations described herein which form part of the present invention; the 
operations are machine operations. Useful machines for performing the 
operations of the present invention include general purpose digital 
computers or similar devices such as digital signal processors. In all 
cases, it should be borne in mind that there is a distinction between the 
method operation in operating a computer and the method of computation 
itself. The present invention relates to method steps for operating a 
computer in processing position signals of the rack relative to the leg 
rack teeth to generate other desired physical signals. 
The present invention also relates to an apparatus for performing these 
operations. This apparatus may be specially constructed for the required 
purpose or it may comprise a general purpose computer as selectively 
activated or reconfigured by a computer program stores in the computer. 
The algorithms presented herein are not inherently related to any 
particular computer or other apparatus. In particular, various general 
purpose machines may be used with programs written in accordance with the 
teachings herein, or it may prove more convenient to construct specialized 
apparatus such as digital signal processor to perform the required method 
steps. The required structure for a variety of these machines would appear 
from the description given below. 
PREFERRED EMBODIMENT OF THE PRESENT INVENTION 
FIG. 1 is a side, elevational view of a prior art rack chock fixation 
system for jackup rig. System 10 illustrates a prior art rack chock 
fixation device as taught in U.S. Pat. No. Re. 32,589 where vertical screw 
jacks 12 and horizontal screw jacks 14 align a teeth section 11 of a rack 
chock piece with a matching teeth profile 21 on the leg rack 20. Once 
aligned, the rack chock 10 and the leg rack 20 are locked by screw jacks. 
The alignment is accomplished manually and visually. Furthermore, the 
prior art fixation system described in FIG. 1 arrests primarily two 
degrees of relative movements between the rack chock and leg rack. 
FIG. 2 is a side, elevational view of another prior art locking system for 
jackup rig. Locking system 30 teaches the use of a counter rack with 
inclined upper surface 33 and lower surface 34 with "T" extensions held 
between claws of vertically movable wedges 36 and 38 with mating surface 
and matching inclination. The wedges 36 and 38 are guided to move 
vertically by nuts fixed into the wedges. The counter rack piece is 
engaged with mating teeth 41 on the leg rack 40 by independent rotating 
screws 32. Rotation of the screws with identical speed in the same 
direction moves the wedges as well as the counter rack vertically. 
Rotation of the screws with identical speed in the opposite direction 
brings the wedges closer and moves the counter rack piece laterally by 
sliding along the inclined surfaces. Like the prior art rack chock 
fixation in FIG. 1, the locking fixation system 30 requires visual 
monitoring for the exact matching of the rack chock teeth 31 with the 
teeth 41 of the leg rack. 
FIG. 3A is side, elevational view of the rack chock system of the present 
invention. The rack chock system 50 of the present invention comprises a 
rack chock 51, a pin and cross head assembly 60, and an actuator assembly 
70. The rack chock system 50 is coupled to the jack foundation 45 and in 
the vicinity of a leg well 47 for engaging and disengaging a leg rack 80. 
It should be understood by one skilled in the art that the legs are raised 
or lowered through a plurality of leg wells in a jackup rig. Referring 
again to FIG. 3A, the rack chock 51 is coupled pivotally at one end to the 
pin and cross head assembly 60 for engaging and disengaging the leg rack 
80 without visual inspection and manual control. The other end of the rack 
chock 51 is coupled to one end of an actuator assembly 70 for engaging and 
disengaging the rack chock system 50. Along the edge of the rack chock 
closer to the leg rack is a set of matching teeth 55 for mating with the 
teeth 81 of the leg rack 80. 
FIG. 3B is exploded, cross section, elevational view of the pin and cross 
head assembly of the rack chock system according to Section A--A in FIG. 
3A. The pin and cross head assembly 60 comprises a guide casing 61, pin 
62, cross heads 64, spherical bearings 65, push cylinders 66 and springs 
68. As mentioned above in connection with the description of FIG. 3A, one 
end of the rack chock is coupled pivotally with the pin for engaging and 
disengaging in a in-line fashion the leg rack (not shown in FIG. 3B) 
without visual monitoring and manual control. The pin and cross head 
assembly 60 aligns the teeth of the rack chock automatically with that of 
the leg rack. In FIG. 3B one end of the rack chock 51 is coupled pivotally 
to a pin 62 disposed between two cross heads 64. The pin 62 is supported 
and arrested against rotation in the cross heads 64. The pin 62 also acts 
as an axis of rotation for the rack chock 51. The cross heads 64 are 
disposed slidably within the guide casing 61 which in turn is coupled to 
the jack foundation 45. The cross heads 64 slide up and down between the 
guides 63 in a direction parallel with the longitudinal axis of the leg 
rack 80. Push cylinders 66 are disposed in the guide casing 61 to push 
against and position the cross heads 64 when it is necessary. These push 
cylinders 66 are normally in a retracted position. Disposed between the 
cross heads 64 and the guide casing 61 are springs for positioning the 
cross heads 64 in an equilibrium position within the guide casing. 
FIG. 4A shows a side, elevational view of an embodiment of the present 
invention being employed to engage an opposing pinion type leg rack. A 
pair of rack chock systems 50 according to the present invention are shown 
engaging an opposing pinion type leg rack 80. As the leg rack and rack 
chock system is symmetrical, the rest of the description of the present 
invention shall concentrate on elaborating on the rack chock system on the 
right hand side. As mentioned in FIG. 3A, one end of the rack chock 51 is 
coupled pivotally and slidably with the pin and cross head assembly 60 to 
engage the leg rack without visual monitoring and manual control. The 
mechanism for engaging the rack chock 51 to the leg rack is carried out by 
the actuator assembly 70. The end of the rack chock 51 opposite the pin 
and cross heads assembly is coupled to one end of the actuator assembly 
70. The other end of the actuator assembly 70 is coupled to the jack 
foundation 45. In one embodiment of the present invention, the actuator 
assembly 70 comprises a piston and cylinder assembly. It should be 
understood by one skilled in the art that other actuator assemblies may be 
employed to engage and disengage the rack chock system of the present 
invention. 
FIG. 4B is a side, elevational view of the embodiment of the present 
invention being employed to lock an opposing pinion type leg rack. Once 
the teeth 55 of the rack chock engages and matches the teeth 81 of the leg 
rack, wedges 53 and 57 are urged by jacks 52 and 54 respectively to lock 
the rack chock and leg rack assembly. The rack chock 51 has edges 56 and 
58 which matches the profile of the surfaces of wedges 57 and 53 
respectively. The tooth crest of the edge 56 has rounded surfaces to 
cooperate with the inclined surfaces of the wedge 57. As such, the 
relative movement between the rack chock 51 and the leg rack 80 is 
minimized. Although the jacks 52 and 54 are illustrated as opposing each 
other in FIGS. 4A and 4B respectively, it should be understood by one 
skilled in the art that other positions are possible. For example, the 
guide surfaces of the wedges may be altered such that the jacks are 
parallel to each other. 
It is said that the prior art fixation systems described in FIGS. 1 and 2 
arrest all possible degrees of relative movements between the rack chock 
and leg rack. FIG. 5 is a cross section, elevational view of a locking 
wedge of the present invention for arresting more than two degrees of 
relative movements between the rack chock and leg rack. Accordingly, the 
flat surface of a hemisphere 71 is disposed slightly raised above the 
inclined surfaces of the locking wedges 53 and 57. The hemisphere 71 is 
secured to a bearing housing 75 with a fastener 72. The curved surface of 
the hemisphere and the curved interior of the bearing housing 78 form a 
pair of mating surfaces. These surfaces function as a bearing assembly 
within locking wedges 53 and 57 and permit them to engage with the flat 
surface 79 tilting. These surfaces also provide maximum surface contact 
with the inclined surface of rack chock on which they converge, regardless 
of the rack chock's position. As such, the locking wedges 53 and 57 
transfer the loads from the jack foundation to the leg assembly or vice 
versa even when the leg chock assembly and consequently the inclined 
surface of the engaged rack chock are mis-aligned with inclined surfaces 
of the locking wedges. 
FIG. 6 is a flow chart illustrating the steps under which the present 
invention aligns and engages a leg rack of a self elevating platform 
automatically. The followings steps are carried out without visual 
monitoring and manual control. Feedback and corrective action only occur 
when the landing of the teeth of rack chock make contact with the crest of 
the leg rack teeth. Referring again to FIG. 6, the process of engagement 
begins in step 90 with the actuator assembly 70 in a fully retracted 
position initially. Then in step 92 the process determines whether the 
flanks of rack chock teeth 55 allows proper mating with those of the leg 
rack teeth 81 when the rack chock is parallel with the leg rack. If yes, 
then no further alignment is needed and the rack chock may engage with the 
leg rack in step 94. If no, the actuator assembly extends in step 96 to 
the point of contact of rack chock teeth with that of the leg rack teeth. 
From the displacement of the actuator assembly 70, the process determines 
in step 98 whether the crest radius of the rack chock teeth 55 is over the 
bottom crest fillet or bottom flank of the leg rack teeth 81. In such a 
case, the process extends the actuator assembly 70 further in step 100 
such that the rack chock teeth 55 is urged to follow the path of least 
resistant along the flank contours of the teeth 55 and 81 to the 
engagement position. In step 102 the process determines whether the crest 
radius of the rack chock teeth 55 contacts the top crest fillet or top 
flank of the leg rack teeth 81. If so, the process extends the actuator 
assembly 70 further in step 104 such that the rack chock teeth 55 is urged 
to follow the path of least resistant to the engagement position. 
Otherwise in step 106, the rack chock teeth 55 presses against the leg 
rack teeth 81 on the crest landing and no further movement of the rack 
chock is possible regardless of how strongly the actuator assembly 70 is 
extended. This feedback signal is passed in step 108 to the push cylinders 
66 which are then activated to push the pin and cross head assembly 60 
upwards. As a result, the point of contact between teeth 55 and 81 is 
shifted to the position in step 102 where the actuator assembly can extend 
the rack chock system to an engagement position. 
While the present invention has been described particularly with reference 
to FIGS. 1 to 6 with emphasis on a system for automatically engaging and 
arresting the relative movement between the supporting legs and jack 
foundation of self elevating platform, it should be understood that the 
figures are for illustration only and should not be taken a limitation on 
the invention. In addition, it is clear that the method and apparatus of 
the present invention has utility in many applications where 
self-positioning system is required. It is contemplated that many changes 
and modifications may be made by one of ordinary skill in the art without 
departing from the spirit and the scope of the invention as described.