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Hardness and Tactile Probing Methods

Working group 5.11

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 Opens external link in new windowDKD 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.