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Abstract Friction force of the linear motion ball guide (LMBG) with preload is important to predict the mechanical efficiency, thermal deformation, and stiffness variation in optimal design processes of the precision machinery. In this paper, an explicit friction force model of the LMBG with a two-point ball contact structure has been formulated in terms of the material and geometric parameters as well as the assembly and operating conditions. Contrary to the LMBG maker's model with accuracy 63%, the prediction accuracy over 90% is verified through experiments. It is confirmed that the friction force depends upon the ball size, conformity factors of the grooves, lubricant viscosity, and ball contact angles. Sliding and viscous frictions are significantly influenced by operating conditions as well. Highlights • Hysteresis, sliding and viscous friction components are formulated explicitly. • Friction force model is a function of geometric, assembly and operating conditions. • The sliding and viscous frictions are dominant at low and high speeds. • Precision measurements confirm the accuracy of the formulated friction model. • High efficient LM guides with good stiffness are designed easily via the model. [ABSTRACT FROM AUTHOR]

Measuring friction on the human body is challenging on areas where the surface of the skin is curved. Handheld devices for measuring friction may make it easier to rapidly measure from hard-to-reach areas, however, the orientation of the probe relative to the surface is often sub-optimal to reliably measure the normal force. Here, the friction on the surfaces of a mannequin and a human body are measured and corrected using a curvature correction technique. This is accomplished by accounting for the shape of the measurement surface and the orientation of the measurement device relative to that surface. Two strategies for constructing the surface shape of the measurement surface are compared. [Display omitted] • Implement a curved surface correction method in 3D with a linear sliding handheld tribometer. • Test methods for capturing the 3D curved surface shape for the surface correction method. • Measure sliding friction on a human body. [ABSTRACT FROM AUTHOR]

This study conducted friction experiments of three elastomer block materials on ice (low pressure injection of polyurethane (PU), injection moulding of a thermoplastic polyurethane (TPU) and vulcanization of rubber (RU)), with a linear tribometer operating under four different ambient air temperatures (−10 to 0 °C) and six different sliding velocities (0.3–5 m/s). At low temperatures (−10 °C and −5 °C), the RU material showed the highest dynamic and static friction. However, at high temperatures (−2 °C and 0 °C) the PU revealed the highest dynamic friction and highest static friction at 0 °C. We discuss the physical phenomena's of elastomer friction on ice and in relation to the application of footwear slipping on ice. • Slipping accidents simulated by biofidelic friction testing of elastomers on ice. • PU outsole material on warm ice provides higher static friction coefficient compared to TPU and RU materials. • RU outsole material revealed higher dynamic friction coefficient on cold (−10 to 5 °C) ice compared to TPU and PU materials. • Hybrid outsole constructions combining materials, composites and design solutions may be able to accommodate slip resistance. [ABSTRACT FROM AUTHOR]

The tribological interaction between patterned running surfaces and an ice track was investigated. The friction coefficient was analyzed according to the patterned running surface type, ambient temperature, and rotational track velocity. The results were analyzed based on the structural characteristics of the patterned running surface in terms of average height and skewness. Generation of the water layer was visualized using transparent replicas of the patterned running surfaces. The water layer ratio was then calculated and compared with the friction coefficient. We found that the water layer either functioned as a lubricant or offered frictional resistance depending on the water layer ratio and the type of patterned running surfaces as the lubricating friction regime changed. • The friction force between the commercially available patterned running surfaces of jumping ski and ice is measured. • The water layer is visualized to elucidate the effect of the surface patterns on ice friction coefficient. • The lubricating friction regime varies by surface patterns , resulting either increases or decreases frictional drag. [ABSTRACT FROM AUTHOR]

In situ measurement of frictional properties, particularly of human skin, is challenging. A major challenge is that the measured surface may be curved and oriented arbitrarily relative to the measurement device, making it difficult to obtain accurate and reliable friction estimates. Here we propose a method to simultaneously estimate the orientation of the surface during friction measurements, using a custom-made hand-held tribometer. The method accounts for the position and orientation of the tribometer relative to the shape of the measured surface. Our simple calibration method allows lightweight tribometers to be built with cheaper materials like plastic, without sacrificing accuracy. [Display omitted] • Propose a general method to measure force data on curved surfaces for sliding contacts and friction analysis. • Implement this curve correction method with a linear sliding handheld tribometer. • Describe the importance of carefully testing and calibrating the outputs of lightweight devices that may have low flexural rigidity. [ABSTRACT FROM AUTHOR]

Abstract: The developers of innovative automotive active systems have recently stimulated new interest toward the analysis of the frictional behaviour of brake and clutch facings. This paper presents the experimental results acquired with a laboratory setup on brake and clutch facing samples in sliding motion for different operating conditions. An artificial neural network has been used to obtain a comprehensive view of the influence of the main sliding parameters. The study has also taken into account the not weak influence of the sliding acceleration to improve the friction coefficient prediction during transient operations of these dry friction based devices. [Copyright &y& Elsevier]

Finger pad friction varies significantly between individuals due to personal differences and environmental effects. For this reason, comparison of the absolute friction values becomes non-informative and is rarely reported in literature. This work investigates whether friction data can be normalised to correlate between individuals. A set of textured samples were tested by 10 volunteers in dry sliding conditions with a range of normal loads up to 4 N. A reference smooth sample was used for each participant to normalise the dataset. The proposed approach allows to eliminate one of the unknown parameters, e.g., finger pad ridge contact area function, and discuss the data with respect to other variables. • Friction measurements from 10 volunteers, 4 samples and 9 normal loads were analysed to propose a normalisation method. • Normalisation reduces one of the personal variables and allows friction comparison between individuals. • Friction measurements normalised by a reference represent a change of contact area fraction with normal load. • Volunteers showed similar fractions of real contact area despite differences in skin properties and friction. [ABSTRACT FROM AUTHOR]

Investigation of friction force induced by seals is important in improving control accuracy and evaluating sealing performance for hydraulic actuators. An experimental apparatus was developed to measure the friction forces for hydraulic cylinders under different operating conditions based on position and chamber pressures measurements only. The effects of velocity, external load, seal diameter, and sealing profiles on steady state friction force of hydraulic cylinders were examined. In addition, the influences of amplitudes of velocity and acceleration on dynamic friction force were also highlighted. It was shown that the hydraulic actuator with combined piston seal demonstrates the highest friction force and is less sensitive to variation of load than that of Glyd ring and U-cup seal. • A friction force test method is proposed for hydraulic actuators using position and chamber pressures measurements only. • Friction behaviors of hydraulic actuators with different sealing profiles have been experimentally investigated. • A novel combined piston seal is evaluated in terms of friction measurement and is compared with commonly used seals. • The effects of velocity, load, seal diameter, seal cross section, and acceleration on friction behaviors are studied. [ABSTRACT FROM AUTHOR]