WO2003081169A1

WO2003081169A1 - Apparatus and method for determining the spatial relationship between two surfaces

Info

Publication number: WO2003081169A1
Application number: PCT/GB2003/001240
Authority: WO
Inventors: John Cameron
Original assignee: ORCAM ENGINEERING Ltd
Current assignee: ORCAM ENGINEERING Ltd
Priority date: 2002-03-22
Filing date: 2003-03-24
Publication date: 2003-10-02
Anticipated expiration: 2004-09-22
Also published as: EP1492993A1; AU2003219290A1; GB0206951D0

Abstract

An apparatus and a method are described for facilitating the fabrication of a closing spool for installation between two pipe end sections. The apparatus comprises a positional offset measurement instrument suitable for connecting to, and determining the spatial relationship between, two end cap flanges of the pipes. In an alternative embodiment the apparatus further comprises a centre finder flange suitable for connecting a flexible arm of the instrument to an open flanged pipe. A simulation rig is also described which allows for the positional offset measurement instrument to reproduce the recorded measurement data at a location suitable for fabrication of the closing spool. Thereafter, the positional offset measurement instrument can test and verify the dimensions of the closing spool such that these dimensions can be confirmed to lie within predetermined tolerance levels.

Description

Apparatus and Method for Determining the Spatial Relationship Between Two Surfaces

The present invention relates to a measuring device, and in particular, though not exclusively, to a device for measuring the position and orientation of two surfaces with respect to each other.

The measurement of a volume or space occupied by a physical body is not a new physical concept. However, in many applications there is a requirement to be able to determine the relative position and orientation of objects with respect to each other.

An example of such an application is the position and orientation of two pipe end sections, between which a custom manufactured closing spool is required to be installed. The dimensions of the closing spool relate directly to the position and orientation of the respective flanges on the end of the pipe sections.

Traditionally such closing spools were manufactured through a process of trial and error. Such a method is both time consuming and requires a highly skilled individual. In addition there is a tendency to force a poorly fitting closing spool into the space between the two pipe end sections. Forcing a poorly fitting closing spool results in undue stress and strain being applied to the associated pipes that acts to increase the likelihood of fracturing and hence leaks.

There are a number of Prior Art documents that teach of measurement systems based on the employment of theodolites.

An alternative solution to this problem presented in the Prior Art is a measurement system based on a gimbal assembly, as taught by Lebourg in US Patent US No. 4,120,095. Here the position and orientation of the relevant surfaces are measured as a set of horizontal and vertical angles with respect to a single point, origin or horizon at some distance from the surfaces. However, the need for a reference point or horizon acts to limit the use of such systems.

A further alternative solution presented in the Prior Art is a measurement system based on a linear transducer and inclinometer that are employed to define a common axis between the two surfaces. Angular transducers are then employed to measure the orientation of each surface with respect to the commonly defined axis. Additional measurement systems such as theodolites and laser systems involve considerable set-up times and a significant amount of post measurement processing of the captured data. Therefore, such systems are known to be cumbersome and require additional support in order to maintain the device in position while the required readings are taken. Such characteristics are an obvious disadvantage when the measurement system is required to be deployed at remote locations.

It is an object of at least one aspect of the present invention to provide apparatus that can be employed to facilitate bespoke fabrication of a closing spool for installation between two pipe end sections.

According to a first aspect of the present invention there is provided a positional offset measurement instrument for determining the spatial relationship between two surfaces comprising a first and a second end connector and a flexible arm, wherein the flexible arm comprises a plurality of joints each joint providing a degree of freedom such that the flexible arm acts to move the first and second end connectors within a set volume of space.

Most preferably the flexible arm comprises at least six joints.

Most preferably the first and second end connectors enable the positional offset measurement instrument to be connected to the surfaces, between which the spatial relationship is to be determined, such that they mechanically support the weight of the instrument.

Preferably the positional offset measurement instrument further comprises a computer processing unit. Most preferably the positional offset measurement instrument further comprises a housing unit suitable for calibrating and storing the flexible arm.

Optionally an end connector comprises a centre finding flange adapter suitable for connecting one end of the flexible arm to an open flange pipe.

Preferably the centre finding flange adapter comprises a central locator, a main body and two or more arms.

Preferably the main body connects the central locator to the arms wherein rotation of the central locator acts to move centre finding flange adapter between an unsecured position and a secured position.

Most preferably with the centre finding flange adapter in the secured position the arms are fastened about the pitch centre diameter of the open flange pipe whilst the central locator is positioned at the centre of the open flange pipe.

Preferably the joints comprise a rotational spindle, a mechanical coupling means and a transducer.

Optionally the joints further comprise a thermistor or a similar device for measuring temperature.

Preferably the positional offset measurement instrument further comprises a power source and a microprocessor unit. Preferably the microprocessor receives and processes information from each of the transducers relating to the physical environment of the associated joint thereafter transmitting the information to the computer processing unit .

Preferably the microprocessor relays information transmitted by the computer processing unit to the transducers thus enabling the flexible arm to position the first and second end connectors at a pre determined spatial relationship.

According to a second aspect of the present invention there is provided a centre finding flange adapter suitable for connecting to an open flange pipe comprising a central locator, a main body and two or more arms.

Preferably the main body connects the central locator to the arms wherein rotation of the central locator acts to move the centre finding flange adapter between an unsecured position and a secured position.

According to a third aspect of the present invention there is provided a simulator for aiding in the reproduction of the spatial relationship between two surfaces comprising a rig and a positional offset measuring instrument in accordance with the first aspect of the present invention.

Most preferably the positional offset measuring instrument provides a calibration means for the simulator.

Preferably the rig comprises a base frame on which is mounted one or more guides, two or more posts, two or more adjustable arms, two or more pivotal mounts and two or more flange plates.

Preferably a first post is fixed to the base frame while a second is mounted on the one or more guides such that the lateral position of the second post relative to the first can be altered.

Preferably the adjustable arms provide a means for altering the relative distance between the flange plates.

Preferably the pivotal mounts provide a means for altering the relative angle between the flange plates.

According to a fourth aspect of the present invention there is provided a method of determining the spatial relationship between two surfaces comprising: 1) Setting a flexible arm of a Positional Offset Measuring Instrument in accordance with the first aspect of the present invention to a known reference position; 2) Connecting one end of the flexible arm to a first surface; 3) Connecting the second end of the flexible arm to a second surface; 4) Recording a data set that defines the relative spatial relationship between the surfaces.

Preferably the known reference position is defined by a housing means suitable for storing and transporting the Positional Offset Measuring Instrument.

Preferably the flexible arm of the Positional Offset Measuring Instrument connects directly to the centre of the first and second surfaces. Alternatively the flexible arm connects to a surface via a Centre Finding Flange Adapter employed to locate the centre of said surfaces.

Most preferably the data set that defines the relative spatial relationship between the surfaces comprises five or more vectors measured relative to the known reference position.

Preferably the vectors are measured by transducers of the Positional Offset Measuring Instrument that each relay information to a computer processing unit via an internal microprocessor unit.

Optionally the data set further comprises temperature measurements recorded by one or more thermistors.

Most preferably the information relayed to the computer processing unit defines the physical environment of the associated joints. In particular the information relates to the mechanical position and temperature of the joint. Preferably the computer processing unit calculates and displays the data set from the relayed information.

Preferably the data set comprises average readings taken over a predetermined length of time such that temperature and mechanical vibrations effects experienced by the flexible arm are accounted for.

Optionally the computer processing unit relays the calculated data set to a remote location.

According to a fifth aspect of the present invention there is provided a method for manufacturing a closing spool for connection with two pipe ends comprising: 1) Determining the spatial relationship between two surfaces in accordance with the method of the fourth aspect of the present invention; 2) Employing a simulator in accordance with the apparatus of the third aspect of the present invention to reproducing the spatial relationship between the two surfaces; 3) Constructing the closing spool in situ within the simulator.

Optionally the construction of the closing spool comprises the step of employing the flexible arm of the Positional Offset Measuring Instrument to verify that the dimensions of the closing spool fall within a predetermined tolerance value.

Preferably the closing spool is then transported to and fixed between the two pipe ends. Example embodiments of the present invention, which are given by way of example only, are described with reference to the following figures:

Figure 1 presents a schematic representation of a first embodiment of a positional offset measurement instrument (POMI) in situ between two pipe ends;

Figure 2 presents further detail of a flexible arm of the POMI of Figure 1;

Figure 3 presents a schematic representation of: (a) a first transfer housing; and (b) a second transfer housing employed within the flexible arm of Figure 2;

Figure 4 presents an alternative embodiment of the POMI suitable for deployment with open ended pipes;

Figure 5 presents a schematic representation of a Centre Finder Flange Adapter (CFFA) of the POMI of Figure 4; and

Figure 6 presents a schematic representation of a simulation rig, employed by the POMI, to aid in the construction of a closing spool.

Referring to Figure 1 a schematic representation of an embodiment of a positional offset measurement instrument (POMI) is generally depicted at 1, in situ between two pipes 2 that comprise end cap flanges 3 with central locators. From Figure 1 the POMI 1 can be seen to comprise a flexible arm 4, further detail of which is presented in Figure 2, and a computer processing unit (CPU) 5. To aid the description of the present embodiment of the POMI 1 opposite ends the flexible arm 4 have been labelled A and B, respectively.

With reference to Figure 2, and commencing at A and progressing to B, the flexible arm 4 can be seen to comprise a first end connector 6 that is rigidly connected to a first transfer housing assembly 7. Located perpendicular to the first transfer housing assembly 7 is a second transfer housing assembly 8.

Perpendicular to the second transfer housing 8 there is rigidly attached a first extension member 9. One end of a third transfer housing assembly 10 is thereafter rigidly attached to the opposite end of the first extension member 9 such that, it lies parallel to the second transfer housing 8. The opposite end of the third transfer housing 10 is then attached perpendicularly to one end of a second extension member 11.

The first extension member 9 comprises a hollow tube within which is housed a power source 12 and a microprocessor unit (PCB) 13 employed to control and monitor the flexible arm 4 of the POMI 1, as described below.

At the opposite end of the second extension member 11 is located a fourth transfer housing assembly 14 located so as to have a parallel orientation to the second extension member 11. A fifth transfer housing assembly 15 is thereafter attached at right angles to the fourth transfer housing assembly 14.

One end of a sixth transfer housing assembly 16 is then rigidly attached to the fifth housing assembly 15 such that the sixth housing assembly 16 is orientated perpendicular to the fifth 15. Finally, at the opposite end of the sixth housing assembly 16 is rigidly attached a second end connector 17.

The transfer housing assemblies 7, 8, 10, 14, 15 and 16 all work on a similar principle in that they provide for the rotational displacement of one section of the flexible arm 4 relative to another. Figure 1 outlines the degrees of rotational freedom (Rl - R6) provided by the six transfer housing assemblies 7, 8, 10, 14, 15 and 16, respectively, for the various sections of the flexible arm 4.

A schematic representation of the transfer housing assemblies 7, 8, 14, 15 and 16 is presented in Figure 3(a) while that of transfer housing 10 is presented in Figure 3 (b) . From these figures the transfer housing assemblies 7, 8, 10, 14, 15 and 16 can be seen to comprise a central rotational spindle 18, a transducer 19 and a mechanical coupling 20. The central rotational spindle 18 is mounted within the mechanical coupling 20 so that it connects to the transducer 19. A data cable 21 is also provided in order to relay technical data to and from the microprocessor unit 13. The transducers 19 provide for the taking of high accuracy rotational measurements from the associated transfer housing assemblies 7, 8, 10, 14, 15 and 16. These measurements are then relayed and recorded by the microprocessor unit 13. Thermistors (not shown) can also be incorporated within the transfer housing assemblies 7, 8, 10, 14, 15 and 16 in order to provide temperature information to the microprocessor unit 13. Such information is essential for the accurate reproduction of the spatial relationship between the two pipe ends (as described below) and hence is vital to the production of a high tolerance closing spool.

The combination of the computer processing unit 5 and the microprocessor unit 13 is employed to calibrate the flexible arm 4 at a known physical datum or zero reference position, from which all relative movements can be measured. In the preferred embodiment this zero reference position is defined by a casing unit (not shown) that is employed to safely store and transport the flexible arm 4. The microprocessor unit 13 is further employed to relay information to the computer processing unit 5. Optical or electrical transmitting and receiving devices (not shown) may be employed to achieve this relaying of information.

It should be noted that the computer processing unit 5 may comprise a hand held control device, a lap top computer, a desk top computer or any other suitable computer device. The computer processing unit 5 is employed to store information relating to the position of the flexible arm or alternatively to set the flexible arm to a predetermined position based on co-ordinates stored by or entered into the computer processing unit 5.

In general, the POMI 1 is used to measure the displacement between any two points in three dimensional space. As is known in the art, any two points in three dimensional space can be represented in a Cartesian coordinate system by the vectors (x,y,z) and (x',y'z') . Therefore, to fully describe the system it is required to define six independent variables.

However, the position of the second point (x',y'z') relative to the first (x,y,z) can be achieved by defining a new set of variables a, b, and c where a=(x-x'), b=(y- y' ) and c=(z-z') . A similar argument can be presented irrespective of whether the measurements are made in spherical co ordinates (r, θ, φ) or polar co ordinates (r, θ, z) , three variables are still required to be defined.

For the POMI 1 to operate correctly each of the above points should be the centre points of a plane namely, the centre of the end cap flanges 3. It can be seen that such planes themselves exhibit three degrees of freedom, tilt in two dimensions and rotation (t_h, t_v, r_t) and (t_h' , t_v' , r'_t) respectively. As before these variables can be reduced to a relative displacements by defining a new set of variables d, e and f such that d=(t_h-t_h'), e=(t_v-t_v') and f=(r_t-rt')- Therefore, a full description of the relative system would be contained within the newly defined data set [a,b, c, d, e, f] . As outlined above the POMI 1 is devised around a "reference-displacement" form of measurement. That is a known reference position of the flexible arm 4 is initially measured and thereafter the POMI 1 is "zeroed". The actual displacement measured is therefore a displacement measurement from this reference position. This allows for full temperature compensation, inter instrument variation cancellation and also increases the measurement precision.

Employing such a measurement system allows the r_t value of the master end, namely end A of the flexible arm 4, to be made redundant. This is achieved by employing the "12 o'clock" position of the associated end cap flange 3A as a reference point. Therefore, a measurement of rotation in absolute space is not needed merely the rotation of the second end cap flange 3B relative to the first end cap flange 3A. Furthermore, the design of the POMI 1 is such that the instrument leaves the first end cap flange 3A in a "normal" direction along the z axis as defined in Figure 1. Therefore, by defining the origin of the relative measurement system to coincide with this point means that both the x and y measurements can be set identically to 0. A result of such a definition is that by employing such a relative axis system there is no requirement to make independent physical measurements of the x, y, or r_t co ordinates.

Therefore, the above "reference-displacement" form of measurement provides that the POMI 1 can determine the spatial relationship between two surfaces by recording the five vector data set [x' , y' , z' , z, r ' ] • This sixth vector redundancy is achieved by allowing end A to have an axis aligned with one of the orthogonal axis of end B.

In order to improve the measurement of the spatial relationship between two surfaces the microprocessor unit 13 can be employed to provide an average value over a number of measurements which are thereafter stored by the computer processing unit 5. Such a feature allows the POMI 1 to compensate for any vibrations experienced by the flexible arm 4.

In addition, more than one set of readings can be held in the memory of the computer processing unit 5. The recorded data is capable of thereafter being transmitted by the computer processing unit 5 to a remote location in a digital format. Therefore, the recorded data does not degrade with distance and hence can effectively be sent to any required location.

In an alternative embodiment (not shown) the first 9 and second 11 extension members can be adapted so as to incorporate extension lengths (not shown) . Such extension lengths are automatically detected by the microprocessor unit 13 and so are incorporated into the calculation of the spatial relationship between the two surfaces, as required.

The POMI 1 can be further adapted so as to be capable of determining the spatial relationship between two open flange pipes 22, as presented in Figure 4. In this embodiment the POMI 1 further comprises two Centre Finder Flange Adapters (CFFA) 23 as shown in Figure 5, one being employed with each open flange pipe 22. The CFFA can be seen to comprise a central locator 24, a main body 25 and three arms 26. The central locator 24 is suitable for receiving the end connectors 6 and 17 of the flexible arm 4 while the main body 25 is employed to control the relative position of the arms 26.

A CFFA 23 is deployed with an open flange pipe 22 such that it locates with a first bolt hole from the 12 o'clock position via the central locator 24. The arms 26 then rotate through the main body 25 so as to capture the pitch centre diameter (PCB) of the flange face. This process ensures that an accurate pipe centre measurement of the pipe 22 is achieved.

In practice for a 4x Multiple Hole Flange the first bolt hole can be any hole on the flange. Holes two, three and four can then be located at 90°, 180° and 270° positions, respectively, relative to the first hole. For a 3x Multiple Hole Flange the first bolt hole can again be any hole on the flange. Holes two and three are then located at 120° and 240° positions, respectively, relative to the first hole.

In order to aid in the construction of a closing spool a simulator is often employed. The traditional approach to constructing and producing such a simulator is based on the concept of providing an accurately manufactured CNC rig that incorporates expensive transducers to feedback actual positional information to a control system. Data parameters are typically entered into the control system as set points, and the simulator manipulates the axis so as to achieve these set point positions. Employing the POMI 1 allows a simplified simulator 27 to be used in the construction of a closing spool, as depicted in Figure 6. The simulator 27 comprises a base frame 28, a set of parallel runners 29, a first 30 and second 31 post, two adjustable arms 32, two pivotal mounts 33 and two flange plates 34.

The first post 30 can be seen to be fixed to the base frame 28 while the second 31 is mounted on the parallel runners 29 such that it can be moved laterally relative to the first post 30. The adjustable arms 32 allow the relative distance between the flange plates 34 to be altered while the pivotal mounts 33 control the relative angle between these plates 34.

The simulator 27 employs the POMI 1 as the feedback system for positioning the flange plates 34 relative to each other and so provides a mechanical reproduction of the surveyed flange arrangement. This provides the present simulator 27 with several significant advantages over those taught in the Prior Art.

The . simulator 27 described above does not require a high precision manufactured structure or the incorporation of expensive transducers. Also there is no requirement for the simulator 27 to be independently calibrated as the POMI 1 can be employed to calibrate and adjust the simulator 27 as appropriate.

A further advantage of the described simulator 27 occurs if the simulator 27 becomes slightly bent or twisted (as is very possible in a working environment) as these effects can compensated for by the POMI 1. Therefore, the simulator 27 can be used as a physical clamping facility during the fabrication of the required closing spool without the concern of it being damaged.

Once the desired spool piece has been created the flexible arm 4 can be employed as a further check on the required tolerance of the piece. The computer processing unit 5 can be employed to accurately set the orientation of the flexible arm 4 such that the first and second end connectors 6 and 17 are positioned so as to locate with the opposite ends of the manufactured spool piece. Therefore, by bringing the flexible arm 4 into physical contact with the spool piece a check on its dimensions can be made. In order to produce a suitable spool piece these dimensions are required to fall within a predetermined tolerance level before the spool piece will be deemed acceptable for transportation to, and fitting at, the required location.

The POMI as described in accordance with the various aspects of the present invention exhibits several advantages for the fabrication of a bespoke closing spool. In the first instance many of the problematic features of the iterative trial and error method have been circumvented. Therefore employing the POMI provides a more efficient method for producing a closing spool that does not require the same levels of manual skill.

Secondly the described embodiments of the present invention do not require an origin at a distance from the surfaces, or a common axis between the surfaces to be defined. Instead the POMI employs a "reference- displacement" form of measurement that permits the spatial relationship between the two surfaces to be described in terms of a five vector data sets instead of the previously required six vector data sets.

A further advantage of the described embodiments of the POMI is that it is both light and flexible such that it can be easily deployed while supporting it's own weight between either a set of pipes comprising end cap flanges or open ended pipes when the POMI itself comprises CFFA. Therefore, once deployed the POMI does not require additional external support or the continued presence of an operator.

The POMI also allows a simplified simulator to be employed in the manufacture of the closing spool. Such a simulator reduces the tendency to force a poorly fitting closing spool into a space between two pipe end sections. This reduces the detrimental effects of undue stress and strain being applied to the associated pipes and so lowers the likelihood of unwanted fracturing and leaks.

Although exemplary embodiments of the present invention have been shown and described, it will be apparent to those having ordinary skill in the art that a number of changes, modifications or alterations to the invention described herein may be made, none of which depart from the invention as defined in the appended claims. All such changes, modifications, and alterations should therefore be seen as being within the scope of the present invention.

Claims

1) A positional offset measurement instrument for determining the spatial relationship between two surfaces comprising a first and a second end connector and a flexible arm, wherein the flexible arm comprises a plurality of joints each joint providing a degree of freedom such that the flexible arm acts to move the first and second end connectors within a set volume of space.

2) A positional offset measurement instrument as claimed in Claim 1 wherein the instrument comprises at least six joints.

3) A positional offset: measurement instrument as claimed in Claim 1 or Claim 2 wherein the first and second end connectors enable the positional offset measurement instrument to be connected to the surfaces, between which the spatial relationship is to be determined, such that they mechanically support the weight of the instrument.

4) A positional offset measurement instrument as claimed in any of the preceding claims wherein the instrument further comprises a computer processing unit.

5) A positional offset measurement instrument as claimed in any of the preceding claims wherein the instrument further comprises a housing unit suitable for calibrating and storing the flexible arm. 6) A positional offset measurement instrument as claimed in any of the preceding claims wherein the end connector comprises a centre finding flange adapter suitable for connecting one end of the flexible arm to an open flange pipe.

7) A positional offset measurement instrument as claimed in any Claim 6 wherein the centre finding flange adapter comprises a central locator, a main body and two or more arms.

8) A positional offset measurement instrument as claimed in any Claim 7 wherein the main body connects the central locator to the arms such that rotation of the central locator acts to move centre finding flange adapter between an unsecured position and a secured position.

9) A positional offset measurement instrument as claimed in any Claim 8 wherein when the centre finding flange adapter is in the secured position the arms are fastened about the pitch centre diameter of the open flange pipe whilst the central locator is positioned at the centre of the open flange pipe.

10) A positional offset measurement instrument as claimed in any of the preceding claims wherein the joints comprise a rotational spindle, a mechanical coupling means and a transducer.

11) A positional offset measurement instrument as claimed in any of the preceding claims wherein the joints further comprise a thermistor or a similar device for measuring temperature.

12) A positional offset measurement instrument as claimed in any of the preceding claims wherein the instrument further comprises a power source and a microprocessor unit.

13) A positional offset measurement instrument as claimed in Claim 12 wherein the microprocessor receives and processes information from each of the transducers thereafter transmitting the information to the computer processing unit.

14) A positional offset measurement instrument as claimed in Claim 12 or Claim 13 wherein the microprocessor relays information transmitted by the computer processing unit to the transducers thus enabling the flexible arm to position the first and second end connectors at a pre determined spatial relationship.

15) A centre finding flange adapter suitable for connecting to an open flange pipe comprising a central locator, a main body and two or more arms.

16) A centre finding flange adapter as claimed in Claim 15 wherein the main body connects the central locator to the arms such that rotation of the central locator acts to move the centre finding flange adapter between an unsecured position and a secured position.

17) A centre finding flange adapter as claimed in Claim 16 wherein when the centre finding flange adapter is in the secured position the arms are fastened about the pitch centre diameter of the open flange pipe whilst the central locator is positioned at the centre of the open flange pipe.

18) A simulator for aiding in the reproduction of the spatial relationship between two surfaces comprising a rig and a positional offset measuring instrument in accordance with Claim 1 to Claim 14.

19) A simulator as claimed in Claim 18 wherein the positional offset measuring instrument provides a calibration means for the simulator.

20) A simulator as claimed in Claim 18 or Claim 19 wherein the rig comprises a base frame on which is mounted one or more guides, two or more posts, two or more adjustable arms, two or more pivotal mounts and two or more flange plates.

21) A simulator as claimed in Claim 20 wherein a first post is fixed to the base frame while a second post is mounted on the one or more guides such that the position of the second post relative to the first can be altered.

22) A simulator as claimed in Claim 20 or Claim 21 wherein the adjustable arms provide a means for altering the relative distance between the flange plates.

23) A simulator as claimed in Claim 20 to Claim 22 wherein the pivotal mounts provide a means for altering the relative angle between the flange plates.

24) A method of determining the spatial relationship between two surfaces comprising: 1) Setting a flexible arm of a Positional Offset Measuring Instrument in accordance with Claims 1 to Claims 14 to a known reference position; 2) Connecting one end of the flexible arm to a first surface; 3) Connecting the second end of the flexible arm to a second surface; 4) Recording a data set that defines the relative spatial relationship between the surfaces.

25) A method as claimed in Claim 24 wherein the known reference position is defined by a housing means suitable for storing and transporting the Positional Offset Measuring Instrument.

26) A method as claimed in Claim 24 or Claim 25 wherein the flexible arm connects directly to the centre of the first and second surfaces.

27) A method as claimed in Claim 24 or Claim 25 wherein the flexible arm connects to a surface via a Centre Finding Flange Adapter employed to locate the centre of said surfaces.

28) A method as claimed in Claim 24 to Claim 27 wherein the data set that defines the relative spatial relationship between the surfaces comprises five or more vectors measured relative to the known reference position.

29) A method as claimed in Claim 28 wherein the vectors are measured by transducers of the Positional Offset Measuring Instrument that each relay information to a computer processing unit via a microprocessor unit.

30) A method as claimed in Claim 24 to Claim 29 wherein the data set further comprises temperature measurements recorded by one or more thermistors.

31) A method as claimed in Claim 29 or Claim 30 wherein the information relayed to the computer processing unit defines the physical environment of the associated joints.

32) A method as claimed in Claim 31 wherein the physical environment comprises the mechanical position and temperature of the joints.

33) A method as claimed in Claim 29 or Claim 32 wherein the computer processing unit calculates and displays the data set from the relayed information.

34) A method as claimed in Claim 24 to Claim 33 wherein the data set comprises average readings taken over a predetermined length of time such that temperature and mechanical vibrations effects experienced by the flexible arm are accounted for. 35) A method as claimed in Claim 30 to Claim 34 wherein the computer processing unit relays the calculated data set to a remote location.

36) A method for manufacturing a closing spool for connection with two pipe ends comprising: 1) Determining the spatial relationship between two surfaces in accordance with the method as defined by Claims 24 to Claims 35; 2) Employing a simulator in accordance with the apparatus as defined by Claim 18 to Claim 23 to reproducing the spatial relationship between the two surfaces; 3) Constructing the closing spool in situ within the simulator.

37) A method as claimed in Claim 36 wherein the construction of the closing spool comprises the step of employing the flexible arm to verify that the dimensions of the closing spool fall within a predetermined tolerance value.

38) A method as claimed in Claim 36 or Claim 37 wherein the closing spool is transported to and fixed between the two pipe ends.