Performing a process on a workpiece

• US 20090213216A1
• Filed: 11/05/2008
• Published: 08/27/2009
• Est. Priority Date: 02/21/2008
• Status: Active Grant

• Current Assignee: Rolls-Royce PLC (Rolls-Royce Holdings Plc)
• Original Assignee: Rolls-Royce PLC (Rolls-Royce Holdings Plc)
• Inventors: Hastilow, Neil K.
• Granted Patent: US 8,218,001 B2
• Time in Patent Office: Days
• US Class Current: 348/142
• CPC Class Codes: B23K 2101/001 Turbines
• CPC Class Codes: B23K 26/389 of fluid openings, e.g. nozzles, jets laser machining of inkjet nozzles B41J2/1634
• CPC Class Codes: B23P 2700/06 Cooling passages of turbine components, e.g. unblocking or preventing blocking of cooling passages of turbine components
• CPC Class Codes: G05B 19/401 characterised by control arrangements for measuring, e.g. calibration and initialisation, measuring workpiece for machining purposes G05B19/19 takes precedence
• CPC Class Codes: G05B 19/402 characterised by control arrangements for positioning, e.g. centring a tool relative to a hole in the workpiece, additional detection means to correct position G05B19/19 takes precedence
• CPC Class Codes: G05B 2219/45139 Laser drilling
• CPC Class Codes: G05B 2219/49113 Align elements like hole and drill, centering tool, probe, workpiece
• CPC Class Codes: G05B 2219/50296 Tool offset by verifying piece and registrating errors

Abstract

Features such as holes 10 in a component which may be an aerofoil component of a gas turbine engine are re-drilled after initial formation, for example to remove blockages created in a coating process. In order to ensure that re-drilling occurs at the precise location of the initial holes, a selected number of the holes A-F are selected, and their exact positions identified, for example by camera imaging and image processing. The actual positions of the selected features are compared with the nominal positions, and an algorithm is generated and then used to calculate the actual positions of the non-selected holes of the array.

Claims

1. A method of performing a process on an existing array of features on a workpiece supported on a fixture, the method comprising:

i) selecting at least three, but not all, of the features of the array;

ii) identifying the nominal position in a coordinate space of each of the selected features, and generating a nominal position data set for the selected features;

iii) identifying the actual position in the coordinate space of each of the selected features, and generating an actual position data set for the selected features;

iv) generating an algorithm to transform the nominal position data set to the actual position data set;

v) applying the algorithm to the nominal positions of the non-selected features of the array to generate actual positions of the non-selected features;

vi) performing the process on the selected and non-selected features at the respective identified and generated actual positions.

2. A method as claimed in claim 1, characterised in that the nominal positions of the selected features are obtained from data stored in a memory of a coordinate measuring machine.

3. A method as claimed in claim 1, characterised in that the actual positions of the selected features are obtained by capturing and analysing a camera image of each selected feature.

4. A method as claimed in claim 3, characterised in that the process is performed by means of a laser, the camera image being obtained through the optical system of the laser.

5. A method as claimed in claim 3, characterised in that, in step (iii), the camera is initially directed at the nominal position of the respective selected feature and is displaced to the actual position of the respective selected feature on the basis of the output of the analysis of the cameras image.

6. A method as claimed in claim 3, characterised in that analysis of the image is performed by a computer.

7. A method as claimed in claim 1, characterised in that the algorithm is generated by performing a best fit alignment of the actual position data set with the nominal position data set, and calculating the offset between the actual and nominal position data sets.

8. A method as claimed in claim 7, characterised in that the algorithm includes a scaling factor.

9. A method as claimed in claim 1, characterised in that the workpiece is an aerofoil component of a gas turbine engine.

10. A method as claimed in claim 9, characterised in that the features are cooling air holes in the aerofoil component.

11. A method as claimed in claim 10, characterised in that the process comprises the re-drilling of the cooling air holes.

12. A method as claimed in claim 10, characterised in that the process comprises the formation of shaped features at the cooling air holes.

13. Apparatus for performing a method in accordance with claim 1, the apparatus comprising:

i) a memory for storing the nominal position data set and the actual position data set;

ii) a camera;

iii) a coordinate measuring machine for displacing the camera to camera positions corresponding to the nominal positions of the respective selected features;

iv) image analysis means for receiving images from the camera and identifying the actual positions of the respective features;

v) processing means for generating the algorithm and subsequently calculating the actual positions of the non-selected features;

vi) processing means for performing the process on the features at the respective actual positions.