US20190070708A1

US20190070708A1 - Grinding machine calibration

Info

Publication number: US20190070708A1
Application number: US16/104,268
Authority: US
Inventors: Martin S. Suckling
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2017-09-05
Filing date: 2018-08-17
Publication date: 2019-03-07
Also published as: EP3450100A2; EP3450100A3; GB201714185D0

Abstract

A device and method for the setup, alignment and calibration of grinding machines is disclosed. A tool (42 c) is described, comprising a bar (44) and a first location feature (48) located on the bar (44) and configured to engage with a first location of a machine. The tool also provides a datum (66) located at a known but variable distance parallel to the bar (44) from the first location feature (48). A method for calibrating a grinding machine using the tool (42 c) is also described.

Description

The present disclosure concerns the set up and calibration of grinding machines. More specifically, it relates to a device and method for aligning and calibrating a Blade Tip Grinding Machine (BTG) for use on compressor rotor blades of a Gas Turbine engine.
In order to obtain optimum performance from a Gas Turbine engine, it is necessary to control the tip clearance between the tips of both intermediate pressure (IP) and high pressure (HP) compressor rotor blades and their corresponding rotor paths in their respective casings. Optimum tip clearance can be achieved by grinding the blades of the IP and HP rotors on a purpose-built Blade Tip Grinding Machine (BTG) following their assembly into the rotor drum.
BTG machines are known, and are manufactured by several different companies. Typically, they incorporate some form of measurement system to determine the radii of rotor blade tips during and post grinding. Some of the typical measurement systems used on BTG's are not particularly accurate, temperature stable or reliable, and hence some BTG machines now incorporate an optical measurement system to improve the accuracy and reliability of measurements made during use of the machine.
Blade Tip Grinding Machines (BTG) grind rotors to a finished size in a manually or automatically controlled closed loop grinding cycle, where the tip radii determined by the optical gauge “in process” controls the in-feed of the grinding wheel on the machine as part of the control system.
However, in order for rotors to be ground to the correct size it is essential that the measurement plane and direction of travel of the optical gauge and the slide system on which it is mounted are aligned and positioned correctly to the axis of rotation and the datum features of the grinding machine. This can be difficult to achieve with conventional measurement and alignment equipment.
It is an aim of the present invention to address, mitigate, or overcome some or all of these difficulties.
According to a first aspect there is provided a machine calibration tool, the tool comprising a bar which has a longitudinal axis; a first location feature which is located on the bar and configured to engage with a first location of the machine; and, a datum having a location adjacent to the bar at a known but variable distance parallel to the longitudinal axis from the first location feature.
The tool is intended to be used with an optical sensor such as a ZIMMER gauge or alternative measuring system or device to determine the location of machine mounted datums, for example knife-edge datums, on a grinding machine relative to machine datums, such as a rotating axis of the machine and/or a spindle face.
The perpendicular distance of the datum from the longitudinal axis of the bar may be known at all distances of the datum parallel to the longitudinal axis from the first location feature.
The datum may comprise one or more reference features.
One or more of the reference features may be tapered along the longitudinal axis of the bar and/or parallel to the longitudinal axis of the bar, and/or perpendicular to the longitudinal axis of the bar.
One or more of the reference features may comprise one or more knife-edges, for example provided on a knife-edge square plate.
A thin knife-edge can be used to represent a typical blade tip which is to be ground. A tapered interface, for example a knife-edge square plate, allows a very precise and accurate measurement.
A plate with two perpendicular sides can be provided to form a square edge. The two perpendicular sides allow the accurate/precise measurement of both axial and radial positions of the cutting edge of a grinding wheel of a grinding machine with respect to the reference point, for example corresponding to the axis of rotation.
The edge can be used to get an accurate position of the edge by a camera/Laser projecting a beam of light into/onto the edge. The resulting shadow of the tapered interface can be used as the measurement. The two faces of the plate may be tapered over a distance of around 2 mm.
The bar may comprise a reference face which is parallel to the longitudinal axis of the bar, to which the datum is engaged.
The bar may be comprised of one or more of a metal, alloy, ceramic, stone (such as granite) or polymer.
The datum may be fixedly attached to the bar at any one of two or more locations parallel to the longitudinal axis of the bar.
Alternatively, the datum may be slidably attached to the bar and be selectively movable parallel to the longitudinal axis of the bar. The datum may be fixable in any desired position parallel to the longitudinal axis of the bar, for example by a clamping arrangement comprising a T-slot provided in a face of the bar.
The datum may be configured within an arm arrangement.
The datum may be configured to pivot about a pivotable attachment feature within the arm arrangement.
The arm arrangement may be comprised of one or more of a metal, alloy, ceramic, stone (such as granite) or polymer.
The machine calibration tool may further comprise a clocking mandrel located on the bar and aligned with the first location feature. Providing a clocking mandrel, or a tube or other extension from a front face of the bar, provides an accessible reference point to measure the radial distance to the datum.
The clocking mandrel may be movable relative to the bar. In particular, the clocking mandrel may be adjustable for alignment with the working axis of a grinding machine.
A method of calibrating a grinding machine is also provided, comprising the steps of securing the first location feature of a machine calibration tool according to any preceding claim to a grinding machine, setting a datum of the machine calibration tool at a known position relative to a fixed machine datum feature, and using a measurement device and the datum of the machine calibration tool to determine the position of one or more further datum features mounted to the grinding machine relative to the machine datum feature.
The measurement device comprises an optical sensor, possibly associated with or mounted on the grinding machine. Alternatively, the measurement device may comprise a triangulation probe or a physical measurement device.
The one or more further datum features mounted to the grinding machine may comprise machine mounted datum knife-edges.
The grinding machine may be a blade tip grinding (BTG) machine, and the machine datum feature may comprise a rotational axis of the BTG machine, for example the rotational axis of a machine workhead spindle and/or spindle face. Other possible machine datum features such as a tailstock spindle or spindle face may alternatively, or additionally, be included in the calibration.
It is envisaged that the invention will be used during the installation of new gauges, following refurbishment, and for the routine calibration of optical sensors such as ZIMMER systems or similar/derivatives on BTG machines.
The skilled person will appreciate that except where mutually exclusive, a feature described in relation to any one of the above aspects may be applied mutatis mutandis to any other aspect. Furthermore, except where mutually exclusive any feature described herein may be applied to any aspect and/or combined with any other feature described herein.

Embodiments will now be described by way of example only, with reference to the Figures, in which:

FIG. 1 is a sectional side view of a gas turbine engine;

FIG. 2 is a schematic view of a compressor drum in a BTG machine;

FIG. 3 is a schematic view of a calibration tool held in the chuck of a BTG machine;

FIG. 4 is a schematic view of the calibration tool of FIG. 3 in isolation;

FIG. 5 is a schematic view of an alternative calibration tool;

FIG. 6 is a schematic view of a further alternative calibration tool;

FIG. 7 is a schematic view of a further alternative calibration tool; and

FIG. 8 is a schematic view of a further alternative calibration tool.

With reference to FIG. 1, a gas turbine engine is generally indicated at 10, having a principal and rotational axis 11. The engine 10 comprises, in axial flow series, an air intake 12, a propulsive fan 13, an intermediate pressure compressor 14, a high pressure compressor 15, combustion equipment 16, a high pressure turbine 17, an intermediate pressure turbine 18, a low pressure turbine 19 and an exhaust nozzle 20. A nacelle 21 generally surrounds the engine 10 and defines both the intake 12 and the exhaust nozzle 20.
The gas turbine engine 10 works in the conventional manner so that air entering the intake 12 is accelerated by the fan 13 to produce two air flows: a first air flow into the intermediate pressure compressor 14 and a second air flow which passes through a bypass duct 22 to provide propulsive thrust. The intermediate pressure compressor 14 compresses the air flow directed into it before delivering that air to the high pressure compressor 15 where further compression takes place.
The compressed air exhausted from the high pressure compressor 15 is directed into the combustion equipment 16 where 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 turbines 17, 18, 19 before being exhausted through the nozzle 20 to provide additional propulsive thrust. The high 17, intermediate 18 and low 19 pressure turbines drive respectively the high pressure compressor 15, intermediate pressure compressor 14 and fan 13, 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.
FIG. 2 shows an intermediate pressure (IP) compressor drum, generally indicated 14, in a blade tip grinding (BTG) machine, which is generally designated 24. The IP compressor drum 14 is mounted on a central axis 26 between a headstock spindle 28 and a tailstock spindle 30 of the BTG machine 24. A grinding wheel 32 and an optical sensor 34 are aligned with one stage 36 of the compressor drum 14. As the compressor drum 14 is rotated about the axis 26, the grinding wheel 32 is moved into contact with the ends of individual compressor blades in a particular stage 36, while the optical sensor 34 measures the location of the blade tips, and thereby determines their radii from the axis 26.
It will be understood that in order for the BTG machine 24 to ensure that the rotor/blades are machined to the required finished size, and thus ensure the correct tip clearance when the drum 14 is received in its compressor casing, the optical sensor 34 must be aligned and positioned correctly relative to the axis of rotation 26 and other datum features of the BTG machine 24.
Machine mounted calibration edges such as datum knife- edges 38, 40 are also provided at known radial and axial distances from the datum features forming part of the BTG machine 24 structure, such as the rotational axis 26 of the workhead spindle 28 and/or the tailstock spindle 30, and are used during machining of blades on the rotor/drum 14.
FIG. 3 shows a calibration tool 42 mounted in the BTG machine 24 of FIG. 2. The calibration tool 42 will be described more fully below, but briefly comprises a gauge bar 44, a gauge arm 46 extending at right angles to the gauge bar 44, and a mounting spigot 48 via which the calibration tool 42 can be mounted to the headstock spindle 28. The optical sensor 34 is aligned with a free end portion of the gauge arm 46, which represents the position of the tip of a machined compressor blade.
The optical sensor 34 is capable of measuring in the plane perpendicular to its optical axis, which is into the page as shown, so can detect datum features provided on the gauge arm 46. Through use of the calibration tool 42, the position of the machine mounted datum knife- edges 38, 40 may be reliably established relative to the datum features forming part of the BTG machine structure.
An optical sensor, such as a ZIMMER gauge, may be aligned axially and radially relative to datum features on the BTG machine using the described calibration tool. Some blade stages have “Hade” angles ground on their tips, and therefore any axial positioning error can affect the measured radii of individual blade stages.
The calibration tool 42 from FIG. 3 is shown in greater detail in FIG. 4.
The gauge bar 44 is flat and straight, with the sides square to each other, and is of sufficient rigidity and stability such that it does not distort under its own weight and that of the gauge arm 46. The gauge bar 44 is provided with a number of discrete mounting points, stops or other fixings to allow location of the gauge arm 46 at a number of discrete/defined radial distances 60 from the mounting spigot 48. The gauge bar 44 and arm 46 as illustrated are steel components, but it should be understood that either or both could instead be constructed from an alternative thermally and dimensionally stable material, such as a suitable metal, alloy, ceramic, stone (such as granite) or polymer, or from a combination of such materials.
The gauge bar 44 is fastened onto the mounting spigot 48. The function of the mounting spigot 48 is to locate the gauge bar 44 and arm 46 onto the spindle face of the BTG machine 24 in place of the hydraulic chuck used during machining operations, and assist with stability and alignment. However, it would be possible instead to provide the gauge bar 44 with suitable features to allow it to be mounted into a chuck, collet or similar work holding feature, or for the mounting spigot 48 to be integrally formed with the gauge bar 44.
A rear engagement face 50 of the mounting spigot 48 abuts to the front face of the spindle of the BTG machine 24, and a calibrated dimension 52 between the plane of the rear face 50 of the mounting spigot 48 and the front face 54 of the gauge bar 44 can then be established via a suitable measurement method.
The function of the gauge arm 46 is to provide datum features in known geometric alignment to the face 54 of gauge bar 44 and the rotational axis 26 of the BTG machine workhead spindle 28. For example, taking a corner 56 of the gauge arm 46 as a datum, the axial distance 58 from the face 54 is known, and the radial distance from the rotational axis 26 is the sum of the distance 60 and the radius of the mounting spigot 48, both of which are known.
Levelling screws may be provided to set the gauge bar 44 parallel to the direction of travel of the optical sensor 34 and the base of the BTG machine. This operation may be performed using an engineer's spirit or electronic level, mounted onto the horizontal surface of the gauge bar 44. The centring of the mounting spigot 48 on the rotational axis 26 can be checked using a Dial Test Indicator (DTI) or similar to measure the runout on its outside diameter (OD).
In order to account for possible misalignment of the tool 42 when secured to the BTG machine, a clocking mandrel 51 is provided concentrically with the mounting spigot 48 on the opposite side of the gauge arm 44. The alignment of the clocking mandrel 51 can be adjusted independently of the gauge arm 44, and can thus be made precisely coaxial with the rotational axis 26 of the BTG machine. This could be achieved by measuring the runout on the outside diameter of the clocking mandrel 51, for example with a Dial Test Indicator (DTI), and adjusting the alignment of the clocking mandrel 51 so that the runout is minimised. A Total Indicated Runout (TIR) of less than 5 μm, for example, would indicate that the outside diameter of the clocking mandrel 51 is concentric to the rotational axis 26 of the machine.
The clocking mandrel 51 gives greater certainty of the position of the datum point 56 relative to the rotational axis 26. The distance 61 from the outer diameter of the clocking mandrel 51 to the datum point 56 can be readily determined, either by direct measurement or by measurement to a known reference point on the gauge arm 46. The radius of the clocking mandrel 51 is known and, because of the possibility of fine adjustment, is known to precisely correspond to additional distance to the rotational axis 26 of the machine.
The inclusion of the clocking mandrel 51 additionally provides a readily accessible reference for the machine axis 26, which is an important datum of the BTG machine that is largely obscured or inaccessible once the tool 42 is attached.
FIG. 5 shows an alternative calibration tool 42 a. A gauge bar 44, mounting spigot 48 and clocking mandrel 51 are provided as before, but in the alternative tool 42 a the gauge arm 46 has been replaced by a shaped extension 46 a having a surface 47 provided at an oblique angle to the front face 54 of the gauge bar 44. It will be understood that so long as the position and geometry of the shaped extension 46 a and its position relative to the gauge bar 44 are known, the axial position 58 and radial position 60, 61 of any datum point 56 a on the angled surface 47 can be readily determined. In other words, the location of the datum 56 a perpendicular to the longitudinal axis of the gauge bar 44 is known at all distances of the datum 56 a from the rotational axis 26 of the BTG machine 24.
A further alternative calibration tool 42 b is shown in FIG. 6. The tool 42 b comprises a gauge bar 44, gauge arm 46, mounting spigot 48 and clocking mandrel 51 similar to the tool 42 of FIG. 4. However, the alternative calibration tool 42 b of FIG. 6 additionally comprises a knife-edge square plate 62, which provides a radial knife-edge 64 and an axial knife-edge 66.
The radial knife-edge 64 and an axial knife-edge 66 provide features which, when measured by the optical sensor 34, are of the same form as the datum features 38, 40 of the BTG machine 24. Both the radial knife-edge 64 and the axial knife-edge 66 can be aligned in a plane that passes through the rotational axis 26, and is parallel to the top face of the gauge bar 44. The optical sensor 34 is designed to “see” knife-edges, such as the datum knife- edges 38, 40 or compressor blade tips, so the inclusion of the knife-edge square plate 62 helps to ensure that the datum(s) 56 b provided on the calibration tool 42 b is/are reliably detected. The radial and axial knife- edges 64, 66 provide a good approximation to compressor blade tips.
As noted above, the optical sensor 34 is capable of measuring in the plane perpendicular to its optical axis, i.e. along axes perpendicular to the radial and axial knife- edges 64, 66, and also of the machine mounted calibration edges 38, 40.
A further alternative calibration tool 42 c is shown in FIG. 7. The tool 42 c comprises a gauge bar 44, mounting spigot 48 and clocking mandrel 51 as before. The gauge arm 46 c in the tool 42 c of FIG. 7 extends at an oblique angle to the gauge bar 44 and is provided, at its free end, with a knife-edge square plate 62 as described in relation to FIG. 6. The axial knife-edge 66 of the knife-edge square plate 62 is aligned to be parallel with the gauge bar 44.
In this alternative, the radial distance 60 c, 61 c from the mounting spigot 48 to a datum point is made continuously variable. The front face 54 of gauge bar 44 is provided with a T-slot, and the gauge arm 46 c has two ground surfaces which abut to the gauge bar 44. Screws from the gauge arm 46 c are received in T-nuts fitted into the T-slot, allowing the gauge bar 46 c to slide along the gauge bar 44 as shown at 68. Once in the desired radial position, the ground surfaces of the gauge arm 46 c are clamped against the ground surfaces of the gauge bar 44 by tightening the screws into the T-nuts. The sliding adjustment described allows stepless, continuous, adjustment of the gauge arm 46 c in the radial direction. The radial distance 60 c may be set and measured using any suitable measurement system and method.
FIG. 8 shows a further alternative calibration tool 42 d. The gauge arm 46 d in this alternative has a first portion 70 extending from the gauge arm 44, and a second portion 72 mounted to the first portion 70 by a pivot 74, and movable between positions indicated in broken lines. A knife-edge square plate 62, as previously described, is provided on the end of the second portion 72 remote from the pivot 74. The axial and radial positions 58 d, 60 d, 61 d of the datum can both be varied using the pivot 74.
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.
For example, the gauge arm 46, 46 a, 46 b, 46 c, 46 d may be provided with one of more measurement faces and/or levelling pads for mounting an engineer's spirit or electronic level to ensure that the gauge arm 46, 46 a, 46 b, 46 c, 46 d is level relative to the base of the BTG machine 24.

Claims

1. A machine calibration tool, the tool comprising:

a bar which has a longitudinal axis;

a first location feature which is located on the bar and configured to engage with a first location of the machine; and,

a datum having a location adjacent to the bar at a known but variable distance parallel to the longitudinal axis from the first location feature.

2. A machine calibration tool according to claim 1, wherein the perpendicular distance of the datum from the longitudinal axis of the bar is known at all distances of the datum parallel to the longitudinal axis from the first location feature.

3. A machine calibration tool according to claim 1, wherein the datum comprises one or more reference features.

4. A machine calibration tool according to claim 3, wherein one or more of the reference features are tapered along the longitudinal axis of the bar.

5. A machine calibration tool according to claim 3, wherein one or more of the reference features are parallel to the longitudinal axis of the bar.

6. A machine calibration tool according to claim 3, wherein one or more of the reference features are perpendicular to the longitudinal axis of the bar.

7. A machine calibration tool according to claim 3, wherein one or more of the reference features comprise one or more knife-edges.

8. A machine calibration tool according to claim 1, wherein the bar comprises a reference face which is parallel to the longitudinal axis of the bar, to which the datum is engaged.

9. A machine calibration tool according to claim 1, wherein the bar is comprised of one or more of a metal, alloy, ceramic, stone or polymer.

10. A machine calibration tool according to claim 1, wherein the datum is fixedly attached to the bar at any one of two or more locations parallel to the longitudinal axis of the bar.

11. A machine calibration tool according to claim 1, wherein the datum is slidably attached to the bar and is selectively movable parallel to the longitudinal axis of the bar.

12. A machine calibration tool according to claim 1, wherein the datum is configured within an arm arrangement.

13. A machine calibration tool according to claim 12, wherein the datum is configured to pivot about a pivotable attachment feature within the arm arrangement.

14. A machine calibration tool according to claim 12, wherein the arm arrangement is comprised of one or more of a metal, alloy, ceramic, stone or polymer.

15. A machine calibration tool according to claim 1, further comprising a clocking mandrel located on the bar and aligned with the first location feature. 25

16. A machine calibration tool according to claim 15, wherein the clocking mandrel is movable relative to the bar.

17. A method of calibrating a grinding machine comprising the steps of:

securing the first location feature of a machine calibration tool according to claim 1 to a grinding machine,

setting the datum of the machine calibration tool at a known position relative to a fixed machine datum feature, and

using a measurement device and the datum of the machine calibration tool to determine the position of one or more further datum features mounted to the grinding machine relative to the machine datum feature.

18. A method according to claim 17, wherein the measurement device comprises an optical sensor associated with the grinding machine.

19. A method according to claim 17, wherein the one or more further datum features comprise machine mounted datum knife-edges.

20. A method according to claim 17, wherein the grinding machine is a blade tip grinding (BTG) machine, and wherein the machine datum feature comprises a rotational axis of the BTG machine.