For optical roughness measurement of surfaces, a special 3D microscope with high accuracy makes a “print” of the surface by using a vertical scan of the surface. 

The roughness of a surface is essential for many surface characteristics. It defines how well a paint sticks or how much it wears on other surfaces in contact.

An example could be: Does the surface act as a catalyst or what friction is due to liquid fluids?

On surfaces with lubrication, roughness measurement can e.g. be used to measure how much lubricant the roughness can hold and how large the support is.

Many surface specifications have direct requirements for a maximum roughness expressed by one or more roughness parameters.

Therefore, it is also important what exactly we talk about when putting numbers on the rough. This is described in an international standard called ISO 4297: 1997, which describes a number of parameters, all of which are defined by measuring a height profile measured on a line on the surface.

Traditionally, such a profile is measured with an instrument with a diamond tip pickup with a well-defined rounding radius, which runs in a line above the surface and records the profile.

A typical roughness profile

Optical measurement

For optical roughness measurement, a special 3D microscope with high accuracy makes a “print” of the surface by using a vertical scan of the surface. This method has a precision to 1 nm.

The method measures not only a line but an entire area, and not least, the measurement is made completely without physical contact with the surface. Therefore, one can measure on fragile surfaces, such as paper, textiles, plastics and other surfaces where a diamond in direct contact will be able to scratch the surface and thereby destroy it.

The method also makes it possible to measure roughness on curved surfaces with even very small radii of curvature. If you want to measure in hard-to-reach places, you can cast the surface with a special 2 component silicone rubber, which can then be examined in the microscope.

The area measurement also opens for new possibilities for measuring parameters that are not dependent on direction. A surface structure with a dominant direction (texture) can also be investigated with this method.

What does one get with a standard measurement? 

For an optical roughness measurement at FORCE Technology, a roughness measurement according to ISO 4287: 1997 is carried out which includes all lines in the 3D image with the corresponding statistical uncertainty calculation. The parameters Ra, Rq and Rz are calculated. In addition, the surface-based roughness parameters Sa, Sq and Sz are calculated. Other parameters from ISO 4287: 1997 can be calculated if desired and a definition of which parameters may be of interest to the customer can also be performed by our surface characterization experts. 3D images of the surface can also be provided.