Introduction

Analyzing the material’s surface characteristics with precision is very important for mechanical component parts and there are various techniques that are sophisticated and precise. There are various 2D and 3D surface profilometers and optical measurements are mostly used because of their non-destructive and non-contact methods of surface analysis. However, in many industries and in case of the highly reflective materials the conventional method of stylus profilometry is applied [1]. Fig-1 shows the stylus profilometer by RES surface engineering.

Fig-1 Stylus profilometer by RES surface engineering [2].

Definition

A stylus profilometer is a contact-based profilometer that brings its stylus tip into direct contact with the measuring surface and traces the desired path to determine the topography of the surface. This is one of the early profilometry techniques that developed during surface characterization research. A stylus profilometer is mostly used in measuring the step heights and the sample features sizes that have been patterned on the surface [3]. The schematic diagram of the stylus profilometer is shown in Fig-2.

Fig-2 Schematic diagram of stylus profilometer [4].

Working principle

The working principle of the stylus profilometer is to analyze the surface topography using a probe that moves physically along the surface to acquire the surface characteristics such as height. This analysis will be supported by the mechanical feedback loop that monitors the force at which the probe moves over the surface of the sample. The arm of the stylus is controlled by the feedback system at a specific amount of torque known as a set point. The changes in the z direction made during the tracing of the stylus probe over the surface are measured which reconstructs the surface. The stylus profilometer works with the feedback system which physically touches the surface, and the probe is very sensitive toward the surface which might cause the destruction to the cantilever tip [5]. In Fig-3 basic elements of the stylus, profilometer are shown.

Fig-3 Basic elements of the stylus profilometer [6].

Measurement consideration

The most important part of the stylus profilometer is the cantilever tip because this tip makes physical contact with the measuring surface. The dimensions of this tip are very important to be considered where the radius of the stylus tip should be very small with low contact pressure. The materials used in this stylus tip are diamond and sapphire and the shape of the tip is usually a ballpoint tip with a conical shape. The measurement data from this stylus profilometer is very reliable as they make the contact based measurements.

Fig-4 Stylus tip of the profilometer [7].

Advantages and disadvantages

The stylus profilometer is a contact-based and destructive technique for analyzing the topographical characteristics of the material surface. The major advantage of this technique is its capability of long-distance measurement and clear wave profile of the surface roughness.

The disadvantages of this method involve the physical contact of the stylus tip over the surface which leads to stylus wear. The measuring pressure maintained to trace the surface can cause scratches on the samples, however, this technique is unable to measure the topography of the viscous samples. The measurement is very time-consuming and is limited to the radius of the stylus tip. The sample preparation is one of the important steps that has to be considered during this technique where the samples might be cut and processed for tracing the detectors. The initial positioning of the stylus tip over the surface is another difficult task.

Research on stylus profilometer

The stylus profilometer is a traditional method that uses physical contact over the surface for the topographical analysis, there are various researchers who have studied the performance using various calibration techniques. Kyung Joong Kim et.al., studied a new calibration technique for a stylus profilometer using multiple delta layer films [8]. The stylus profilometer technique determines the very accurate wave profile of the surface hence it is mostly used in medical applications. Massimiliano Merloa et.al. studied the tribological characteristics of the hip femoral head affected by metallic debris and found that the surface roughness of the femoral head was the influencing factor [9].

Reference:

[1] Lee, D.H. and Cho, N.G., 2012. Assessment of surface profile data acquired by a stylus profilometer. Measurement science and technology, 23(10), p.105601.

[2] remchem.com/resources/roughness-measurement-tips/

[3] https://lnf-wiki.eecs.umich.edu/wiki/Stylus_profilometry

[4] Lee, D.H. and Cho, N.G., 2012. Assessment of surface profile data acquired by a stylus profilometer. Measurement science and technology, 23(10), p.105601.

[5] https://www.nanoscience.com/techniques/optical-profilometry/stylus/

[6] https://australiasurfacemetrologylab.org/new-page

[7] https://www.keyence.eu/ss/products/microscope/roughness/equipment/line_01.jsp

[8] Kim, K.J., Jung, C.S. and Hong, T.E., 2007. A new method for the calibration of the vertical scale of a stylus profilometer using multiple delta-layer films. Measurement Science and Technology, 18(9), p.2750.

[9] Merola, M., Ruggiero, A., De Mattia, J.S. and Affatato, S., 2016. On the tribological behavior of retrieved hip femoral heads affected by metallic debris. A comparative investigation by stylus and optical profilometer for a new roughness measurement protocol. Measurement, 90, pp.365-371.