Hardness and Tactile Probing Methods

Development of profile methods

The Working Group deals with the further development of stylus instruments technology by preparing a device study with the following objectives:

• Improved resolution and extended vertical measuring range Measurement
• Uncertainty vertical 1 nm in compliance with the uncertainty calculation in Directive DKD 4-2 Part 1
• Reduction of the contact force with an air-bearing-guided pick-up
• Extensive scanning of the surface by moving the specimen with an air-bearing table
• Use of different scanning techniques (optical, mechanical)

Specifications of the device study: 

- Vertical measurement range 100 µm
- Noise vertical < 1nm
- Vertical resolution 0.01 nm
- Horizontal adjustment range 70 mm x 70 mm
- Contact force 5 µN to 700 µN

Air-bearing-guided pick-up (LUPO)

The air-bearing-guided pick-up was developed in PTB to realise the following specifications:

Linear movement to allow direct calibration with displacement interferometer Adjustable contact force by magnetically generated weight compensation Constant contacting force independent from elongation (until about ± 40 µm) Exchangeable stylus tip High lateral stiffness together with low friction in the direction of motion Low thermal load Measurement with inductive measuring system Measurement with displacement interferometer Range of motion 1mm to prevent overload problems Measuring range 100 µm

A detailed description is presented in the contribution to the International Surface Seminar Chemnitz 2004.

Development of a high-precision xy-table for surface-scanning profile methods

When the surface of a body is to be scanned instead of a single profile, a very large number of profile sections must be realized parallel to each another. Now, the pick-up has no longer to be guided at constant height on a straight line, but at constant height relative to a surface. In order to fulfil this and other extreme requirements (as, for example, low noise, speed constancy, straightness of the profile sections), a set up was realized with a high-precision xy-table which allows an artefact to be scanned below a contacting system, e.g. LUPO-system described above.

The xy-table bearing the specimen is supported on an air bearing pretensioned with vacuum on a plane, high-precision granite surface. For the x-movement, it is laterally guided on the x-ruler with an identical air bearing pretensioned with vacuum. For the y-movement, the x-ruler is again guided with such an air bearing pre-tensioned with vacuum along the y-ruler. In contrast to the “piggy-back” construction, the plane movement of the table here fully benefits from the small flatness deviations of the base. Together with especially low-noise x- and y-drives, this table bearing led to z-noise values for the table movement which, expressed as Rz of a surface, are smaller than 3 nm. This study thus reaches the same noise values as the best commercial profilometers at present available.