Noise evaluation of a point autofocus surface topography measuring instrument

Abstract

In this work, the measurement noise of a point autofocus surface topography measuring instrument is evaluated, as the first step towards establishing a route to traceability for this type of instrument. The evaluation is based on the determination of the metrological characteristics for noise as outlined in draft ISO specification standards by using a calibrated optical flat. The static noise and repeatability of the autofocus sensor are evaluated. The influence of environmental disturbances on the measured surface topography and the built-in software to compensate for such influences are also investigated. The instrument was found to have a measurement noise of approximately 2 nm or, when expressed with the measurement bandwidth, 0.4 nm/√Hz for a single-point measurement.

Any-degrees-of-freedom (anyDOF) registration for the characterization of freeform surfaces

“…1. The target surface is first subjected to outlier removal to remove spurious points due to measurement noise, dirt on the surface and/or measurement artefacts often present in optical measurement instruments [15][16][17]. The surface is subsequently transformed using a priori knowledge, such as removing tilt or pre-alignment using reference features.…”

Performance Evaluation of a Robot-Mounted Interferometer for an Industrial Environment

“…Different methods of noise evaluation have been proposed throughout literature [26,30,34,35]. In an attempt to compare these methods and identify the one best suited in a robotic sensor deployment, a flat surface was measured 11 times and the noise along the instrument Z axis were evaluated using these methods: M1-3 (see below).…”

Reduction of Influence of the High-Frequency Noise on the Results of Surface Topography Measurements

“…However, optical instruments applied for measurements of areal topographies can be particularly sensitive to noise presence when scanning is required. Furthermore, the noise has different sources, including those internally generated and external sources from the environment [ 12 ]. It was also assumed that profilometer after thermal stabilization shows 90% less noise than in the case of an unstable profilometer when thermal sources of errors in surface texture imaging were considered [ 13 ].…”

“…To simplify, the measurement noise can be defined as the noise added to the output signal occurring during the normal use of measuring instrument [ 26 ]. Measurement noise is a “dynamic phenomenon”, which is affected by both the motion of the drive unit and instrument internal noise or environmental disturbances [ 12 ]. To create a standard reference frame for describing measurement noise, it is necessary to describe it along with the associated measurement bandwidth, expressing it in terms of noise equivalent height, in nm, divided by the square root of the data acquisition rate in height points per second [ 11 ].…”