Scattered light measuring device tests joint surfaces on hip implants

A large medical technology manufacturer in Germany is now using a scattered light measuring device for surface inspection. The company, which does not wish to be named, manufactures in particular medical products for surgery, such as hip joint implants, for which quality is a top priority. For this purpose, the first such device from OptoSurf was purchased back in 2008, an OptoSurf OS 500. A second followed in 2012. "The decisive factor for investing in our products was the USP's that it offers," reports OptoSurf Managing Director Dr. Rainer Brodmann, listing: "For example, non-contact measurements are made of the entire surface, not just of cutouts, and both polishing quality and defects are detected. The geometry/shape measurements and the short cycle times are also impressive."

Scattered light measuring machine replaces coordinate measuring machine

The scattered light measuring device is used in the last work step in production, directly before packaging in the clean room. In this environment, the goal of the OS 500 is to move away from the visual 'good/bad' evaluation to a traceable measurement. In the past, a visual inspection of the highly polished surfaces was also carried out by two independent persons. However, this was very tiring for humans, so there was a significant risk in terms of reliability in defect detection. With the OptoSurf system, it was also possible to replace the time-consuming tactile form measurement with a coordinate measuring machine with optical form measurement.

Surface quality as a critical factor

The surface of a prosthesis head is of great importance in the manufacture of artificial hip joints. It should have an ideal spherical shape, no scratches or other defects and the roughness should be in the range of a few nanometers. Excessive roughness of the polished ball and even the slightest deviations in the macrogeometry lead to increased wear. Even the finest scratches can significantly promote abrasion. These substances penetrating the body are potential allergy and disease triggers.

The scattered light measuring machine from OptoSurf is capable of measuring the entire surface of the prosthetic head in the range of seconds. The measuring machine consists of a swivel and rotation module that guides the scattered light sensor over the surface, recording 2,000 measurements per second. Comparative measurements with a confocal microscope have demonstrated that the scattered light sensor can be used to repeatably measure the finest polishing quality differences in the nanometer range and scratches that are no longer visible to the eye. Shape deviations above the pole and equator are detected with an accuracy of < 0.2 μm.

Measurement according to ISO 17025

The roughness and form measurement with the scattered light technique is a traceable measuring method, which is secured with standards and ISO 17025 certificates. Both metal and ceramic heads can be measured. "In addition, in the first step we further developed the OS 500 based on the customer's extensive requirements profile. This was followed by various subsequent technical as well as normative requirements, which we also implemented," summarizes Dr. Rainer Brodmann. "After we fulfilled all the wishes of the medical technology manufacturer, the result is absolutely impressive: A significant increase in productivity thanks to our scattered light measuring device."

Source and further information: OptoSurf GmbH