Areal surface measurement using multidirectional laser line scanning

The overall quality of a machined component has an important association with
the quality of its surface finish. To obtain adequate data for the surface metrology
of machined components, areal scanners are often preferred over stylus based
profile scanners due to their ability to acquire surface data over a relatively large
area. To further improve efficiency, there is a desire to perform on-machine
measurement, and recently, high-resolution areal surface scanners have been
integrated as an on-machine measurement device. Due to the limited areal
coverage, these scanners can require multiple scans to capture data from surfaces
produced on machine tools which requires a sufficient amount of time to
complete a full surface scan. In addition, since these scanners are very sensitive,
scanning delays often cause areal scanners to capture data contaminated with
noise which may arise from within the machining environment such as axes
vibrations, temperature effects, dust, etc. These factors mean such instruments
are typically used in metrology laboratories.
This paper presents a new methodology referred to as multidirectional
scanning (MDS) which is a technique that exploits characteristics of a 2D laser
line scanner (profilometer). The device is used in two directions to scan the
overall component surface ensuring the coverage of a wider surface area
compared to typical areal scanners. Since the scanner is robust and integrated
onto a machine tool, controlled axes feed rates in the orthogonal directions
ensure high spatial resolution which in turn helps to identify and reduce the noise
levels in the data. This methodology has been validated to be both accurate and
rapid to scan the component surface, reducing the cost associated with machine
downtime and also having a wider coverage of 6x6 mm2 for a single scan,
compared to 1 mm2 for most conventional areal surface measurement
instruments having comparable spatial and vertical resolution.