.webp){kind=icon}
.svg){kind=icon}
Roughness measurement close to production with the WM | RS-T Sensor on WENZEL coordinate measuring machines.
The measurement of roughness close to production is becoming increasingly important. In connection with the measurement of gears, roughness parameters are of great interest, for example, as they not only describe the surface topography in the micro and nanometer range, but also help to characterize the running behavior of gears.
In addition to roughness, waviness also plays a role. This differs from the roughness primarily in the spatial frequency range under consideration. The spatial frequency ranges are separated in accordance with DIN EN ISO 21920 (formerly DIN EN ISO 4287 and DIN EN ISO 13565) by using profile-based Gaussian filters.
The question is to what extent classic coordinate measuring devices can also be used to measure waviness and roughness as well as the corresponding parameters.
In addition to tactile measurement applications, CMMs have been reinforced in recent years, particularly for optical measurement tasks. As a result, the already solid machine base was further optimized to meet increasing requirements in terms of accuracy, measurement speed and multi-sensor technology.
This created a basis that can basically be extended to include roughness as an additional feature.
Tactile, profile-based roughness measurement systems generally differentiate between two types of systems:
With the glider system, the object surface is morphologically pre-filtered using a skid (see roughness measurement on WENZEL measuring machines with the RFP2 REVO sensor from the manufacturer Renishaw). The roughness measuring tip is supported against the roughness measuring blade, which results in a very small measuring circle.
By using glider systems, the requirements for the basic positioning measurement system are drastically reduced. The control behavior of the machine and external vibration influences are less relevant, as a slight temporal deviation of the position can be averaged out by the referenced skid.
The shape of the surface is already removed by the morphological filter (the gliding blade). The roughness measurement tip thus follows the contour of the profile to be measured. The prerequisite is that KMG is able to carry out sufficiently accurate pre-positioning.
A standard-compliant evaluation of common roughness parameters such as ra or Rz is possible, for example.
However, the interaction is associated with an undesired falsification of the measurement result, particularly in the medium and long-wave spatial frequency range. The filter effect falsifies the recording of waviness and shape, so that standard-compliant evaluation, such as the W and P parameters in accordance with DIN EN ISO 21920, is no longer fully possible.
However, the W parameters in particular are decisive for noise behavior (see FFT analysis by WENZEL Metrology GmbH). Also an evaluation of Abbott-based parameters such as Rv, Rp, and Rk (formerly DIN EN ISO 13565) is no longer readily possible.
In order to be able to represent these parameters as unfalsified as possible, the use of skids should therefore be avoided and self-supporting roughness measurement systems should be used.
For this reason, WENZEL Metrology GmbH — as an alternative to the glider system — uses a self-supporting measurement system in the form of a sensor WM | RS-T.
The self-supporting roughness sensor dispenses with the use of a skid and reproduces the measurement profile of the surface as unfalsified as possible. The only deviations result from the unavoidable interaction of the roughness measuring tip with the measurement object and the control behavior of the machine.
The primary profile, as the basis for the measurement, can result from the coordinate measuring machine or the sensor itself. When the machine is moving, the requirements placed on the machine base are disproportionately higher and depend in particular on its design.
The quality of the machine base and the interaction of machine (mechanics) and controller (controller) are therefore decisive.
When taking measurements with the WM | RS-T sensor, the machine is held in an invariable, controlled position. The requirements for the control behavior of CMMs are thus reduced, which is why CMMs with a large measurement circuit are also suitable for measurements with this type of sensor.
The required feed movement to measure the primary profile (as a basis for waviness and roughness analysis) is carried out by a feed axis integrated in the sensor. This ensures a high level of position quality through a homogeneous movement of the roughness measurement tip.
In contrast to competitor systems, the use of a sensor-side reference sphere to support the measurement system is deliberately avoided.
The support provided by such balls is intended to reduce the measurement circuit and minimize machine influences. To a certain extent, it represents a compromise between a self-supporting system and a skid.
However, WENZEL Metrology GmbH does not see the need to use such an aid, especially as there is a decisive point against its use: Accessibility.
Left figure: WM | RS-T on a GT 450 gear measuring machine
Right image: Roughness measuring tip during tooth flank surgery
By dispensing with the use of a sensor-side reference sphere, the sensor system can also be used to detect measurement objects under difficult, geometric boundary conditions.
Such geometric difficulties arise, for example, when measuring radial waviness and roughness on gear flanks with particularly small modules (module 2 or smaller).
In such a measurement task, the measurement range is further limited by the laterally attached reference spheres, taking into account the required stroke of the roughness needle.
There is also a decisive criterion that is particularly important for WENZEL Metrology GmbH:
The WM | RS-T roughness sensor has two rotational axes (R & T axis), which can be moved continuously in the range of 0° to 360° or -90° to +90° in order to achieve the best possible positioning with respect to the workpiece.
Combined with a rotary table axis (C) and the standard available coordinate axes (XYZ), the result is a total 6 positioning axes, which cover all degrees of spatial freedom — perfect, among other things, for gear-related measurement tasks on GT machines.
On the software side, the WM | RS-T sensor is not used as a sensor, but as measuring head , which, thanks to a specially developed interchangeable interface, can also be automatically replaced by a scanning probe (e.g. Renishaw SP600).
In order to be able to measure such a measuring head into the coordinate system of the measuring machine, it is necessary to measure the system with various swivel positions on a calibration sphere. The procedure is completely analogous to already known measuring heads such as the Renishaw PH10-M or PHS-2.
For this purpose, the WM | RS-T sensor has, among other things, the option of recording individual measurement points.
With the WM | RS-T, a coordinate measuring machine is easily converted into a roughness measuring machine. Integration into user software World Cup | Quartis R2025-2 This goes without saying and opens up a wide range of options for roughness-based measurement tasks in the near future.
Dr.-Ing. François Torner
Head of System Development
Set new standards together!
Become part of an innovative company that has remained young despite 50 years of tradition.
.webp){kind=small}
