Profile method

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Stylus device: A carrier (1) holds a small tip (2) which is drawn horizontally (3) over the object surface (5). As the tip follows the profile, the boom moves vertically (4). The vertical position is recorded as a light green profile (6).

The profile method is a method for the metrological description of surfaces. In the roughness by mechanical contact stylus (special designs z. B. be Perthometer a probe tip made of diamond is called) moved at constant speed over the surface of a sample (workpiece). The measuring profile results from the vertical position shift of the probe tip, which is usually recorded by an inductive position measuring system. For the metrological description of a surface, standardized roughness parameters are obtained from the measurement profile .

Overview

With a mechanical stylus, the stylus tip comes into direct contact with the surface, which is why this process is also referred to as a tactile or touching measuring process. The schematic picture shows that the shape of the probe tip has a major influence on the measurement result. For example, pores or cracks in a surface can only be shown to the extent that the stylus tip can penetrate them. The probe tip acts like a mechanical filter on the surface to be scanned. In DIN EN ISO 3274, the point angle γ and the point radius rt of diamond stylus tips are specified. Most often, a stylus tip radius of 5 µm and a tip angle of 60 ° are used. However, radii of 2 and 10 µm and angles of 90 ° are also standardized.

The measurement profile contains the short-wave components of the surface roughness , which is superimposed by long-wave features, the waviness and (with a sufficiently long measuring section) the form deviation.

Structure and mode of operation

In the stylus method, a distinction is made between one- and two-step stylus systems and a reference surface stylus system. While the surface is mechanically pre-filtered by the distance between the runners or the distance between the runner and the probe tip with the one and two runners probe system, with the reference surface probe system all wave components are present in the measurement signal.

Reference surface sensing systems

Reference surface probe systems are probe systems that are guided on ideal geometric reference surfaces, are self-aligning or have to be aligned with the surface of the test object. The reference surface can also be outside the touch probe, e.g. B. lie in the feed direction. With the reference surface probe systems, the movements of the probe tip relative to the geometrically ideal reference surface are measured. This means that roughness and waviness can be recorded as a function of the reference distance. Since a reference surface probe system, unlike the skid probe system, does not distort the surface profile, it is also used in arbitration cases. The disadvantage is that the reference surface of the probe system must be aligned parallel to the surface to be measured. Devices with electronic alignment are able to record positional deviations and to compensate for them mathematically.

Skid touch systems

With the skid probe systems, the measuring system must be supported on the surface to be measured with one skid (single-skid probe system) or with two skids (pendulum probe system) and aligned with it. The skid can be arranged both in front of and behind the probe tip and to the side of it. Pendulum probe systems are defined as self-aligning probe systems with two cylindrical or convex skids arranged one behind the other in the feed direction, which are supported on the surface of the test body. With the skid probe system, only the relative movement of the probe tip to the skid is measured. The styli are easy to align, but have the disadvantage that shape deviations cannot be detected at all and undulations can only be detected depending on the distance between the stylus tip and the runner and the distance between the waves in the surface profile. In order to largely rule out profile falsification, random comparative measurements should be carried out with a reference surface probe system.

Examples of a preferred application of the skid touch systems are:

  • Roughness measurements on geometrically complex surfaces such as ball bearing grooves.
  • Measurements on tooth flanks or bores; these are also possible with one-step stylus systems.
  • Measurements for the detection of ripples, e.g. B. on rolls, sheets, milled surfaces. Pendulum probe systems with about 2 mm long cylindrical skids are suitable for this.

Reference plane tracing system

With a reference plane probe system, the probe slides along an almost ideal reference plane (reference plane) over the surface to be tested. The reference plane is built into the perthometer's feed unit and must be aligned approximately parallel to the workpiece surface. The recorded surface profile shows the shape deviations measured against the reference plane and records all measured variables very precisely. It is used to measure waviness and form deviation without falsifying skids

Two runners

With this pendulum probe system, the probe head is guided on two skids on the surface to be tested. Because it is mounted in a joint, the system aligns itself automatically and is very easy to use. Two-runner probe systems are preferred for measuring curved sheets and rolls and are standardized according to SEP1940

Single skid system

The single-skid sensing system is guided by a skid on the workpiece surface and also in the feed device. The button is connected to a joint in the feed device. This probe system can be used to advantage, particularly for small dimensions (flat surfaces, bores and shafts), but with certain undulations the profile will be falsified.

See also

literature

  • H. Bodschwinna: Surface measuring technology for the assessment and optimization of technical functional surfaces. Habilitation thesis Uni Hannover. Shaker Verlag , 2000, ISBN 3-8265-7484-2 .
  • VDI / VDE guideline 2602: Roughness measurement with electrical stylus instruments. VDI-Verlag, Düsseldorf 1983.
  • H. v. Weingraber, M. Abou-Aly: Handbook Technical Surfaces. Vieweg-Verlag, Braunschweig 1989, ISBN 3-528-06318-1 .
  • DIN EN ISO 3274: Geometrical product specifications (GPS) - Surface quality: Profile method - Nominal properties of contact stylus devices. Beuth Verlag, Berlin 1998.
  • V. Raimund: Roughness measurement theory and practice. Beuth Verlag, Berlin 2013, ISBN 978-3-410-23882-9 .