Method and apparatus using a closed loop controlled actuator for surface profilometry

• US 6,901,677 B2
• Filed: 05/05/2004
• Issued: 06/07/2005
• Est. Priority Date: 05/05/2003
• Status: Expired

• Current Assignee: Insitutec LLC
• Original Assignee: University of North Carolina At Charlotte (University of North Carolina System)
• Inventors: Jain, Pavan, Smith, Stuart T., Bauza, Marcin B., Woody, Shane C.
• Primary Examiner(s): BENNETT, GEORGE B
• Application Number:
  US10/839,384
• Publication Number:
  US 20040221465A1
• Time in Patent Office: 398 Days
• Field of Search: 335/03, 335/04, 335/51, 335/56, 335/58, 335/59, 335/61
• US Class Current: 33/551
• CPC Class Codes: G01B 5/0002 Arrangements for supporting, fixing or guiding the measuring instrument or the object to be measured
• CPC Class Codes: G01B 5/20 for measuring contours or curvatures

Abstract

An apparatus for profiling the surface of a workpiece, including a probe adapted to make contact with the surface of a workpiece, a sensor for determining or deriving the force between the probe and the workpiece surface, an actuator that adjusts the position of the probe along an axis, which is generally perpendicular to the surface of the workpiece, in order to maintain a constant force between the probe and the surface, and a closed control loop, including a controller that controls the operation of the actuator based on information from the sensor.

Claims

1. An apparatus for profiling the surface of a workpiece, the apparatus comprising:

a probe adapted to make contact with the surface of a workpiece;

at least one sensor that determines the current interaction force between the probe and the surface of the workpiece;

an actuator that adjusts the future position of the probe along an axis that is generally perpendicular to the surface of the workpiece in order to maintain the future interaction force between the probe and the surface of the workpiece generally constant; and

a closed feedback loop that controls the actuator to adjust the future position of the probe along the generally perpendicular axis at least partially on the basis of the current interaction force between the probe and the surface of the workpiece.

2. The apparatus of claim 1, wherein the at least one sensor determines the interaction force between the probe and the surface of the workpiece by determining the current position of the probe along the generally perpendicular axis.

3. The apparatus of claim 2, wherein the probe, the at least one sensor and the actuator are supported on a platform, wherein at least one of the platform and the workpiece may be translated with respect to the other such that the probe moves across the surface of the workpiece.

4. The apparatus of claim 3, wherein the at least one sensor generates a signal representative of the current position of the probe along the generally perpendicular axis, wherein the signal generated by the at least one sensor is compared to a reference signal, and wherein the actuator adjusts the future position of the probe along the generally perpendicular axis based on the comparison.

5. The apparatus of claim 4, wherein the at least one sensor includes a contact-based sensor.

6. The apparatus of claim 5, wherein the contact-based sensor is selected from the group consisting of:

resonant probes based on contact interactions or flexure probes that utilize distortion under applied loads in which distortions are measured using capacitance sensors, inductance sensors, strain gages, optical sensors, piezoelectric sensors, piezoresistive sensors, linear variable differential transformers (LVDT) and ultrasonic-based sensors.

7. The apparatus of claim 4, wherein the at least one sensor includes a non-contact-based sensor.

8. The apparatus of claim 7, wherein the non-contact-based sensor is selected from the group consisting of:

capacitive sensing sensors, interferometers, optical interferometers, ultrasonic, tunneling and resonant probes and the like sensing near-contact phenomena such as air squeeze films, eddy currents, magnetic waves, gas or liquid pressures or electrostatic charges.

9. The apparatus of claim 4, wherein the result of the comparison of the signal generated by the at least one sensor to the reference signal is combined with a signal representative of movement by the actuator along the generally perpendicular axis.

10. The apparatus of claim 3, further comprising a controller that controls the actuator at least partially on the basis of the current position of the probe along the generally perpendicular axis.

11. The apparatus of claim 10, wherein the controller is a proportional-integral-differential controller.

12. The apparatus of claim 3, wherein the at least one sensor is at least one first sensor, and the apparatus further comprises at least one second sensor that detects movement by the actuator along the generally perpendicular axis.

13. The apparatus of claim 12, further comprising a stage connecting the probe to the actuator, wherein the at least one second sensor detects displacement of the stage and produces an output, corresponding to the detected displacement of the stage, that is representative of a characteristic of the surface of the workpiece at a given point.

14. The apparatus of claim 13, further comprising a device that produces a trace of the outputs of the at least one second sensor in conjunction with the respective relative positions of the probe as the probe moves across the surface of the workpiece and the at least one second sensor detects the displacement of the stage at a plurality of given points on the workpiece.

15. The apparatus of claim 13, wherein the actuator is interconnected with the stage via a flexure-based guiding mechanism.

16. The apparatus of claim 3, wherein the actuator is a fine actuator, having a narrow range of motion, and is selected from the group consisting of:

a piezoelectric actuator device, a linear motor, and a voice coil actuating device.

17. The apparatus of claim 2, wherein the actuator is a first actuator, and wherein the apparatus further comprises a second actuator, under the control of the closed feedback loop, that adjusts the future position of the probe along the generally perpendicular axis.

18. The apparatus of claim 17, wherein the first actuator is a fine actuator, having a narrow range of motion, and the second actuator is a coarse actuator, having a long range of motion.

19. The apparatus of claim 18, further comprising first and second controllers that control the first and second actuators, respectively, at least partially on the basis of the current position of the probe along the generally perpendicular axis, and wherein the second controller further controls the second actuator at least partially on the basis of the output of the first controller.

20. The apparatus of claim 18, wherein the at least one sensor is at least one first sensor, and the apparatus further comprises at least one second sensor and at least one third sensor that detect movement by the first and second actuators, respectively, along the generally perpendicular axis.

21. A method of gathering data related to the surface of a workpiece, comprising:

placing a probe in contact with the surface of a workpiece;

determining, via at least one sensor, the current interaction force between the probe and the surface of the workpiece; and

at least partially on the basis of the current position of the probe, adjusting, via an actuator, the future position of the probe along an axis that is generally perpendicular to the surface of the workpiece in order to maintain the future interaction force between the probe and the surface of the workpiece generally constant.

22. The method of claim 21, wherein determining the interaction force between the probe and the surface of the workpiece includes determining the current position of the probe along the generally perpendicular axis.

23. The method of claim 22, further comprising:

supporting the probe, the at least one sensor and the actuator on a platform; and

translating at least one of the platform and the workpiece with respect to the other such that the probe moves across the surface of the workpiece.

24. The method of claim 23, further comprising:

generating, via the at least one sensor, a signal representative of the current position of the probe along the generally perpendicular axis;

comparing the signal generated by the at least one sensor is to a reference signal; and

adjusting, via the actuator, the future position of the probe along the generally perpendicular axis based on the comparison.

25. The method of claim 23, wherein the at least one sensor is at least one first sensor, the method further comprising:

detecting, via at least one second sensor, movement by the actuator along the generally perpendicular axis.

26. The method of claim 25, wherein detecting includes detecting movement of a stage connecting the probe to the actuator, the method further comprising:

detecting, via the at least one second sensor, displacement of the stage; and

producing, via the at least one second sensor, an output, corresponding to the detected displacement of the stage, that is representative of a characteristic of the surface of the workpiece at a given point.

27. The method of claim 26, further comprising:

producing a trace of the outputs of the at least one second sensor in conjunction with the respective relative positions of the probe as the probe moves across the surface of the workpiece and the at least one second sensor detects the displacement of the stage at a plurality of given points on the workpiece.

28. The method of claim 25, wherein the surface of the workpiece is a planar surface.

29. The method of claim 25, wherein the surface of the workpiece is a curvilinear surface such as a cylindrical or elliptical surface.

30. The method of claim 25, further comprising:

based on the translating step, maintaining the actuator within its operating range.