Method of and apparatus for scanning the surface of a workpiece

• US 5,189,806 A
• Filed: 08/17/1992
• Issued: 03/02/1993
• Est. Priority Date: 12/19/1988
• Status: Expired due to Term

• Current Assignee: Renishaw PLC
• Original Assignee: Renishaw PLC
• Inventors: McMurtry, David R., Henning, Brian C. R.
• Primary Examiner(s): Will, Thomas B.
• Application Number:
  US07/928,667
• Time in Patent Office: 197 Days
• Field of Search: 33/503, 33/558.01, 33/558.4, 33/553, 33/554
• US Class Current: 33/503
• CPC Class Codes: G01B 21/04 by measuring coordinates of points
• CPC Class Codes: G05B 19/4015 going to a reference at the beginning of machine cycle, e.g. for calibration
• CPC Class Codes: G05B 2219/37207 Verify, probe, workpiece

Abstract

A method of scanning a workpiece surface is disclosed in which a machine carrying a scanning head is moved along a path, preferably at constant velocity, while a surface contacting device is moved by the scanning head to oscillate transversely to the instantaneous path direction to scan an area of the surface. Transducers on the machine, the head, and where necessary the surface contacting device provide data relating to the positions of the surface contacting device to data gathering device under the control of a computer. Apparatus for carrying out the method is also disclosed and includes a scanning head for moving the surface detecting device which may be a stylus or a probe relative to one axis, and preferably orthogonal axes. The head can include a set-up for inertia balancing the head and mass balancing the surface detection device. Also the head may include air bearings on which the stylus or probe are supported for oscillation. Surfaces to be scanned may be flat plates, cones, bores or other surfaces with compound angles.

Claims

1. Apparatus for gathering data relating to a surface of a workpiece, the apparatus including a part of a coordinate positioning machine, and comprising:

a surface detecting device;

support means for mounting the surface detecting device for movement within a three-dimensional reference framework, the support means being supported on the part of the coordinate positioning machine;

means for producing relative movement between the surface detecting device and the surface to bring the surface detecting device into a predetermined spatial relationship with the surface;

means for producing relative movement between the surface detecting device and the surface along a path at constant speed within the reference framework, whereby the surface detecting device passes over the surface;

means for simultaneously producing relative oscillatory movement between the surface detecting device and the surface in a direction transverse to said path such that said surface detecting device moves through a plurality of locations; and

means for determining at said plurality of locations relative to a datum position;

(a) an instantaneous position of the surface detecting device relative to the support means; and

(b) an instantaneous position of the part of the coordinate positioning machine, whereby data in respect to the positions of a plurality of points of the work surface relative to said reference framework may be gathered.

2. Apparatus as in claim 1, wherein the means for producing relative movement between the surface detecting device and the surface includes means for producing said movement at a constant velocity.

3. Apparatus as in claim 1, wherein the means for producing relative movement between the surface detecting device and the surface along the path is provided by the part of the coordinate positioning machine and said support means provides the means for producing the oscillating movements.

4. Apparatus as in claim 1, wherein the surface is a cylindrical surface which has a longitudinal axis and the means for producing relative movement along the path includes means for producing relative movement having at least a component of direction parallel to said longitudinal axis.

5. Apparatus as in claim 1, wherein the support means is a scanning head having at least one axis and the transverse are oscillating pivotal movements about said at least one axis of said scanning head.

6. Apparatus as in claim 1, wherein the support means is a scanning head having at least one axis and the transverse movements of the surface detecting device relative to the surface are oscillating translating movements relative to said at least one axis of the scanning head.

7. Apparatus as in claim 1, wherein the surface detecting device comprises a stylus having a surface contacting tip.

8. Apparatus as in claim 7, wherein the stylus includes transducers for detecting deformation of the stylus resulting from contact of the stylus with the surface.

9. An apparatus as claimed in claim 1, wherein the surface detecting device is a non-contact probe.

10. Apparatus as in claim 1, further comprising:

means for reducing the effect on the apparatus of any forces produced in the support means in reaction to said relative oscillatory movement produced between the surface detecting device and the surface.

11. Apparatus as in claim 10, wherein the means for reducing the effect on the apparatus of the forces produced in the support means comprises a mass within the support means which is rotationally accelerated to produce an equal and opposite reaction to said forces.

12. An apparatus as in claim 10, wherein the means for simultaneously producing relative oscillatory movement is an electric motor having parts mounted for relative rotation in opposite directions.

13. Apparatus as in claim 1, further comprising control means for establishing the predetermined spatial relationship between the surface detecting device and the surface.

14. Apparatus as in claim 13, wherein the apparatus includes position-determining transducers for determining an instantaneous position of the part of the coordinate measuring machine within said reference framework.

15. Apparatus according to claim 14 and further comprising data gathering means controlled by the control means for gathering position data from the position determining transducers on the machine.

16. Apparatus according to claim 15, wherein the support means includes position determining transducers for determining the position of the surface detecting device relative each axis of the support means and the data gathering means additionally receives position data from the position determining transducers in the support means.

17. Apparatus according to claim 15 wherein the surface detecting device is an analogue probe and the data gathering means additional receives position data from the position-determining transducers in the probe.

18. Apparatus according to claim 15 wherein the surface detecting device comprises a stylus which carries transducers whereby any deformation of the stylus due to contact with the surface may be measured and the data gathering means additionally receives data from the transducers carried by the stylus.

19. Apparatus according to claim 1, wherein said support means further comprises a fixed part, a movable part and an air bearing in said fixed part supporting said movable part, the air bearing defining a first axis of movement for the support means.

20. Apparatus according to claim 19, wherein the movable part includes a second part, said second part having an axis of movement transverse to said first axis of movement of the support means, wherein said second part is supported on an air bearing and mounts said surface detecting device.

21. Apparatus as in claim 20, wherein said support means includes at least one position determining transducer for determining the position of the surface detecting device relative to the first axis of movement of the support means.

22. Apparatus as claimed in claim 20, wherein said support means includes at least one position determining transducer for determining the position of the surface detecting device relative to the axis of movement of the second part.

23. Apparatus according to claim 1, wherein said support means comprises a fixed part and a movable part, said movable part capable of rotation around an axis passing through said fixed part and said movable part, the rotation being facilitated by an air bearing.

24. Apparatus according to claim 1, wherein the means for producing relative oscillatory movement is an electric motor and further comprising a second electric motor to operate the support means to produce relative movement in a direction substantially normal to the path and normal to a local plane of the surface of the workpiece and a control means, wherein each electric motor is operable either in a positioning mode or a constant torque mode and said control means being provided to selectively switch the electric motors between the different modes of operation.

25. A method of gathering data relating to a surface of a workpiece with a surface detecting device, the device being supported on a part of a coordinate positioning machine in a three-dimensional reference framework by a scanning head providing movement of said surface detecting device with 2 degrees of freedom relative to said machine part, the workpiece being support on a table of the machine relative to which said part is movable, the method comprising the steps of:

bringing the surface detecting device into a surface detecting relationship with the surface;

operating the machine to produce relative movement between the scanning head and the workpiece surface at constant speed along a path adjacent the workpiece surface whereby the surface detecting device passes over the workpiece surface;

simultaneously operating the scanning head to produce relative oscillatory movements between the surface detecting device and the workpiece surface in a direction transverse to the instantaneous path and substantially parallel to the local plane of the workpiece surface;

maintaining the surface detecting relationship between the surface detecting device and the workpiece surface at a plurality of locations as the surface detecting device passes over the surface; and

determining at said locations relative to a datum position;

(a) the instantaneous position of the surface detecting device relative to the machine part, and

(b) the instantaneous position of the machine part relative to the table, and

using the results of said determination to determine the positions relative to said reference framework of a plurality of points on the workpiece surface.

26. A method as claimed in claim 25 and in which the surface detecting relationship between the surface detecting device and the workpiece surface is maintained by operating the scanning head additionally to produce relative movement between the surface detecting device and the surface in a direction substantially normal to the instantaneous path and normal to the local plane of the workpiece surface.

27. A method as claimed in claim 26 and in which the relative movements between the surface detecting device and the workpiece surface in a direction substantially normal to the instantaneous path and normal to the local plane of the workpiece surface provided by said scanning head are oscillating movements.

28. A method as claimed in claim 27 and wherein the surface to be scanned is a cylindrical surface in or on the workpiece and which has a longitudinal axis, and the path has at least a component of direction parallel to said longitudinal axis.

29. A method as claimed in claim 25 and in which said relative movement between the scanning head and the workpiece surface take place in a straight line at constant velocity.

30. A method as claimed in claim 25, wherein the scanning head has at least two axes and the transverse movements of the surface detecting device relative to the surface are oscillating pivoting movements about at least one of said axes of the scanning head.

31. A method as claimed in claim 25, wherein the scanning head has at least two axes and the transverse movements of the surface detecting device relative to the surface are oscillating translating movements to at least one of said axes of the scanning head.

32. A method as claimed in claim 25 and wherein the surface detecting device comprises a stylus having a surface-contacting tip, and the surface detecting relationship thereof with the surface is a relationship in which the surface contacting tip is in contact with the surface.

33. A method as claimed in claim 32 and wherein the stylus carries transducers whereby any deformation of the stylus due to contact with the surface may be determined, the method further comprising the steps of:

determining from the transducers on the stylus the amount by which the stylus may be deformed, and,

using the results of such determination in determining the positions of points on the surface in said coordinate framework relative to said datum position.

34. A method as claimed in claim 25 and wherein the surface detecting device is a touch trigger probe having a stylus with a surface-contacting tip, and the surface detecting relationship thereof with the surface is a relationship in which the surface contacting tip is in contact with the surface.

35. A method as claimed in claim 25 and wherein the surface detecting device is an analogue probe having a stylus with a surface-contacting tip, the surface detecting relationship thereof with the surface being a relationship in which the surface contacting tip is in contact with the surface, the probe having transducers whereby the positions of the stylus relative to the probe may be determined, the method comprising the further steps of:

determining from the transducers of the analogue probe the position of the stylus relative to the probe at each one of said plurality of locations, and,

using the results of such determination in determining the positions of points on the surface in said co-ordinate framework relative to said datum position.

36. A method as claimed in claim 25 and wherein the surface detecting device is a non-contact probe and the surface detecting relationship thereof with the surface is a relationship in which the probe is positioned at a pre-determined distance from the surface.