Patent ID: 12235185

DETAILED DESCRIPTION OF EMBODIMENTS

With reference toFIG.1, a gas turbine engine is generally indicated at10, having a principal and rotational axis X-X. The engine10comprises, in axial flow series, an air intake, a propulsive fan12, an intermediate pressure compressor13, a high-pressure compressor14, combustion equipment16, a high-pressure turbine17, an intermediate pressure turbine18, a low-pressure turbine19and an exhaust nozzle20. A nacelle23generally surrounds the engine10and defines both the intake and the exhaust nozzle.

The gas turbine engine10works in the conventional manner so that air entering the intake is accelerated by the fan12to produce two air flows: a first air flow into the intermediate pressure compressor13and a second air flow which passes through a bypass duct22to provide propulsive thrust. The intermediate pressure compressor13compresses the air flow directed into it before delivering that air to the high pressure compressor14where further compression takes place.

The compressed air exhausted from the high-pressure compressor14is directed into the combustion equipment16where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive the high, intermediate and low-pressure turbines17,18,19before being exhausted through the nozzle20to provide additional propulsive thrust. The high17, intermediate18and low19pressure turbines drive respectively the high pressure compressor14, intermediate pressure compressor13and fan12, each by suitable interconnecting shaft.

Other gas turbine engines to which the present disclosure may be applied may have alternative configurations. By way of example such engines may have an alternative number of interconnecting shafts (e.g. two) and/or an alternative number of compressors and/or turbines. Further the engine may comprise a gearbox provided in the drive train from a turbine to a compressor and/or fan.

Gas turbine engines such as those shown inFIG.1typically have a number of spaces which are inaccessible to human operators or mechanics, or which have very restricted access. In particular, the combustion chamber(s)16of the gas turbine engine10may have no practical access by a mechanic, except by “stripping down” the engine and removing various components in order to permit access. Such “stripping down” (and the subsequent rebuilding) is a lengthy and complex process and is not suitable for routine inspection or maintenance tasks. Nevertheless, it is important that areas of the engine such as the combustion chamber(s) are regularly inspected for any wear or irregularities.

FIG.2shows, schematically, a hyper-redundant manipulator30forming part of a probe system according to an embodiment of the present invention. The hyper-redundant manipulator30has four main parts: an arm32, an end-effector34, an actuation mechanism36and a feed-in mechanism38.

The end-effector34is located at the distal end of the arm32and is chosen depending on the scenario for which the probe is to be used. For example, the end-effector34may include one or more of a vision system (e.g. a camera device or similar and, optionally, an illumination device), a gripper, a high-speed spindle, etc. The end-effector34may be interchangeable so that the same probe system can be used for a variety of purposes.

The actuation mechanism36is located at the proximal end of the arm32. This mechanism drives the movement of the arm32either by sending drive signals to individual actuators located on and/or between each section, or by operating actuators which are physically connected to each section (e.g. pneumatically, hydraulically or by cables). By mounting the actuation mechanism36at the proximal end, the actuation mechanism36(or least part of it) can be kept off the moving part of the arm32thereby reducing the weight of the arm and making its motion easier.

The feed-in mechanism38allows advancement (and retraction) of the arm32. The feed-in mechanism38provides accurate linear advancement of the arm along the initial trajectory (the orientation of the arm shown inFIG.2). A range of feed-in mechanisms are known in the art and will not be discussed further here.

The arm32is split into a number of distinct sections33. Each section has two degrees of freedom and can be formed into a curve of any angle (referred to as θ) up to a predetermined maximum angle (usually limited by the design of the sections33to a maximum of around 90° or π/2) from the straight-line axis. Further, the section can form this arc such that the tip of the section subtends any desired angle (referred to as q) from an axis perpendicular to the straight-line axis.

The arm32depicted inFIG.2may be either a discrete design or a continuum design. As the details of the specific designs of arms are well-known in the art they are not described further here.

FIG.3shows a schematic cut-away view of a combustion chamber16of a gas turbine engine such as that shown inFIG.1. For simplicity, the outer and inner walls forming the main sides of the torus shape of the combustion chamber16are shown as a pair of angled rings16a,16b. The arm32is shown extending into the combustion chamber16from an entry port40in the outer wall16a.

In order to perform a general inspection of the combustion chamber16, it is desired to pass the arm of the probe (which may have, for example, a light source and a camera located at its distal end or tip in order to perform this inspection) around a circular path C which is mid way between the outer and inner walls,16a,16b. Due to the torus shape of the combustion chamber16, the path is well-defined and has a constant curvature.

Thus, as shown inFIG.4, the path of the arm32can be divided into two segments. A first segment enters through the entry port40in the outer wall16aand bends through an initial angle of 84.4° to reach an initial point p1where it intersects the path C. The second segment, being the remainder of the arm32, follows the path C with a constant curvature (in this case in the opposite sense to the curvature of the first segment) such that each section bends through an angle of 9.12°.

The initial angle and initial point p1will be dependent on a number of factors, including the location of the entry port40, the distance between the entry point and the path C and the direction of the subsequent second section of the arm. However, for an entry port40on the inner or outer wall of a toroidal space, it is likely to be slightly under or over 90°. The initial angle can be determined manually, or can be computed from inputs of the relevant factors.

To advance the arm32along the path C, using a tip-following approach (“curve following” as the tip will always follow the curved path C), an optimisation process is employed which is used to drive the actuation mechanism36and advance the arm32and the tip along the path C.FIG.5shows the parameters for the optimisation. When the arm32is advanced the driving algorithm aims to maintain the curve of the distal section against the desired curvature by adjusting the bend of sections A and B (being the sections of the arm32which are not already following the path C; the distal sections which are already following the path C can be maintained in their existing configuration as they will simply translate circumferentially along the path). This is achieved by minimizing the error in two co-ordinates: the start of the distal section (p1−the initial point), and the end (p2) (although it will be appreciated that, as the arm is following a fixed curve, other points which are in the region of constant curvature could be chosen instead of the end point). Since the curvature of the path C is homogenous throughout the navigation, it is possible to only calculate for one section length's worth of advancement since the process can be repeated throughout the length of the arm.

FIG.6shows a simulation of the initial stages of the progression of the arm using the optimisation process described in more detail below. The heavy line is the desired path of the arm, whilst the lighter path is the actual path of the arm. Joins between sections of the arm are depicted by dots. As in previous figures, the dashed line shows the path C which it is desired to follow.

The starting point is the configuration ofFIG.5in which two sections of the arm are inside the chamber. The figures inFIG.6show the progression of the arm32as the next complete section of the arm is introduced. It can be seen that the distal section (p2) follows the path C closely as it advances along it, but that there is some deviation of the section being introduced into the chamber from the desired path as the section is introduced, with this deviation reducing as the complete section is introduced.

An example optimization process for determining the positioning and orientation of the arm32will now be described. However, it will be appreciated that other optimization processes can be used.

It is well-known that the effectiveness of an optizimation process is largely determined by the definition of the objective function. The main problem with creating objective functions for hyper-redundant manipulators has been that the optimization function has to include both the accuracy of the tip position (which is normally relatively simple) as well as the deviation of the remainder of the arm from the desired path (which is not so simple).

However, in the present embodiment, the objective function can be simplified as it is only reliant on comparison of the path with the points p1and p2. Therefore, for each advancement of the tip op, which results from a linear advancement δb of the arm at the base, the objective function can be written as:
f(δb)=Max [α·|P1(b+δb)−p1|+β·|P2(b+δb)−(p2+δp)|]

Where P1(x) and P2(x) are the calculated positions of points p1and p2for an advancement of x at the base of the arm. α and β are weighting coefficients which are used to tune the performance of the objective function. Usually β will be chosen to be significantly larger (e.g. by an order of magnitude) than a as the position of the tip is much more important than the intermediate arrangement of the arm, but this may vary depending on the circumstances (e.g., in a particularly constrained access situation, deviation in p1may be undesirable and so the weightings may be more even, or even reversed).

The objective function can then be used in a movement algorithm such as the following, which is also depicted schematically inFIG.7. In block “a” the relevant parameters (such as the number of sections in the arm and the initial angle) are initialised. Optionally in blocks “b”, user input is provided which decides whether it is desired to move the arm forward (further into the chamber) or to reverse and withdraw the arm, and how far. In the case of forward motion, this determines the value of op and the optimization proceeds to find a new arrangement of the sections of the arm. Alternatively, if the user wishes to reverse, the previous orientation is retrieved from a store of prior arrangements (such as a memory device). Once a new arrangement has been determined by the optimization function, the appropriate instructions are sent to the actuation mechanism and the position information is recorded in the memory device for future reference (blocks “d”). The system then verifies whether another step is feasible, or if the next section should be added to the arm by the feed-in mechanism (blocks “e”). The cycle then repeats from the initial movement decision point.

The method for guiding the probe inside the combustion chamber16(i.e., the constrained space) is illustrated inFIG.8. The method includes determining an initial point p1where the probe intersects the path C (i.e., a predetermined curve) which defines a circle or part circle within the space (S1); and determining an initial bend for the probe between the entry port40(i.e., entry point) on a surface of the combustion chamber16and the initial point p1(S2). The process then includes repeatedly determining a new orientation of the sections33(i.e., segments) which results in an advancement of the distal end to a new position which is on the path C, the new orientation being determined so as to minimise the deviation between each of: a) the point on the probe where the probe starts to follow the path C and the initial point p1, and b) a point p2on the probe closer to the distal end than the point where the probe starts to follow the path C and the path C (S3); and adjusting the orientation of the sections33to the new orientation and advancing the probe so that the distal end is located at the new position (S4).

As a result of the simplifications to the optimization process that can be made by the reliance on the two points for navigation, the computational load of the optimizing step (which is the rate-limiting step), significant performance improvements were obtained compared to, for example, a similar approach without such constraints as mapped out in Palmer et al.

Performance improvements in the control of hyper-redundant manipulators can take two forms: faster computation can allow faster movement/progression of the tip with the same accuracy; or faster computation can mean that more accurate solutions are searched for by either considering a greater range of possible configurations, or by using smaller incremental advancements (op in the above description).

By comparing the performance of the tip-following approach in Palmer et al. and the approach of the present embodiment, it was found that the optimization step of the present embodiment took approximately 20% of the time taken for the optimization step of Palmer et al. using the same increments.

Further, once a pattern of movements have been determined for the advancement of a whole section of the arm into the target space, the orientations for each partial step of the advancement for a particular op can be stored and used for the insertion of the next segment, rather than calculating afresh.

It will be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the concepts described herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.