Application of a Cobot to measure the coefficient of friction of pairs of materials

Abstract

Since the earliest inventions of tools to the development of complex machinery for production lines, humans have consistently pursued the goal of achieving better products with minimal energy consumption. In this quest for efficiency, they began to study physical phenomena such as friction, wear, and lubrication. These studies gave rise to a branch of science known as tribology. Within this field, significant interest emerged in analyzing the behavior of frictional forces and, consequently, the coefficients of friction (CoF) generated between two contacting surfaces in relative motion. Understanding these interactions enables more informed decisions in the selection of materials, coatings, and lubricants to ensure adequate motion transmission, improve system performance, extend component lifespan, enhance efficiency, and reduce energy consumption. To study friction coefficients under specific tribological conditions, specialized machines called tribometers were developed. The wide range of contact configurations, motion types, and wear mechanisms required for testing led to the creation of various tribometer models. However, existing tribometers often require modifications or custom setups to meet the evolving demands of tribological research, especially for tests involving non-standard motion paths. In addition, as research advances the need has grown for faster yet reliable testing methods and for accessible solutions that allow friction measurements to be performed directly at the testing site. This research evaluates the use of the UR5e collaborative robot (Cobot) as a reliable alternative for on-site friction testing under non-conventional motion conditions that are not typically addressed by traditional tribological test benches. The study was divided into two main approaches: the first, conduct standard pin-on-disk tests in dry, room-temperature conditions, following ASTM G99 norm; the second, perform tests using a custom sinusoidal slide path. For both testing approaches, three pairs of materials were tested (steel/aluminum, steel/steel, and steel/wood), a specialized end-effector was designed, and force and velocity data were acquired using the Cobot’s internal sensors. The friction data obtained by Cobot were compared and correlated with those gathered from the parallel pin-on-disk experiments. Additionally, this work discusses the findings, behavioral differences, potential sources of error, limitations, and future perspectives regarding the use of Cobots in tribological testing.