This paper presents a design of multi-axis tactile force sensor using the fringe effect of an electric field between stationary patterned electrodes. The unique configuration of the electrodes ...consisting of four separate square-shaped sensing electrodes, with each encircled by excitation electrodes, allows to achieve enhanced fringe field effect and hence sensitivity. The proposed sensor can decouple the normal, shear and angular shear applied forces. The sensor is fabricated using low-cost rapid prototyping techniques with flexible Ecoflex 00–30 and silicone rubber RTV-528 as the elastomers for contact with the environment. An analytical model is developed that correlates the nominal capacitance of the sensor with that of the geometric dimensions of the stationary electrodes and air cavity height between the electrodes and elastomer. The force measurement ranges in the normal, shear, and angular axis are 5 N, 1.5 N, and 1 N respectively. The sensor shows a perfectly linear response, repeatability, and a low hysteresis error, thermal stability and robustness to the environmental interferences that makes it suitable to be used for force feedback in minimally invasive robotic surgery.
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•The fringing field effect based tactile force sensor is presented.•High sensitivity is achieved by optimizing electrodes geometric configuration.•The sensor can decouple normal, shear and angular shear forces.•The sensor is fabricated using rapid prototyping techniques for low cost.•The sensor is designed for application in robotic surgical systems.
Random vibration testing is traditionally performed by means of single-axis testing. However, real operational environment are in general characterized by multi-axis vibration. As a consequence, ...single-axis testing is incapable of reproducing the actual damaging process of a component in the laboratory. In this work the damage inflicted to a cantilever beam by multi-axis and sequential single-axis random excitation is compared. A fatigue testing campaign is carried out to establish the fatigue properties of the specimen under different types of vibration environment. The results of the fatigue testing campaign are used to define a relationship between the damage inflicted by multi-axis and sequential single-axis excitations. In particular, a correction factor is defined that allows to calculate the fatigue damage under multi-axis vibration environment knowing the damage inflicted by single-axis excitations. The correction factor takes into account the different activation of the vibrating modes of the specimen caused by different types of excitations. The correction factor for multi-axis vibration environments may allow to estimate the damage caused by multi-axis vibration with the use of a single-axis shaker, as well as allowing to calculate the required testing time for a multi-axis test starting from single-axis testing procedures, improving laboratory testing in terms of costs and realism.
•The review focuses on the FDM of discontinuous fiber/polymer composites (FRPC).•The entire FDM-FRPC system (i.e. materials, mechanism and process) is summarized.•As an indispensable technique for ...FDM, hot-melt extrusion process is discussed.•Large-scale FDM and multi-axis FDM are included as the latest advance.•The main challenges and outlook for the future development of FDM is identified.
Fused deposition modeling (FDM) is one of the most widely utilized additive manufacturing techniques by virtue of its numerous merits, such as easy operation, low cost, low energy consumption and little-to-no waste. Based on its simple configuration and extrusion-assisted process, the research and development of this technique is gradually shifting from traditional prototype printing to high-performance composite fabrication. This review provides a panorama for the recent progress of FDM technology in the manufacturing of discontinuous fiber reinforced thermoplastic composites. The entire production chain from the very beginning of FDM filament preparation to the latest stage in large-scale manufacturing process is discussed. The enlightening strategy in multi-axis FDM field is highlighted as it possesses a great potential to manufacture the next-generation composites with superior geometric complexity and flexible fiber alignment. This review also identifies the main challenges and outlook for the future development of this 3D printing technology in fiber reinforced composites.
Density functional calculations with a plane-wave basis set are widely used in materials science. Due to recent developments in high-performance computers, the number of nodes equipped in such ...computers greatly exceeds the number of atoms included in a typical simulation. Thus, it is becoming difficult to perform calculations efficiently even when only a portion of all nodes are used (e.g., 10%). We have developed a multi-axis decomposition scheme in which both G-vectors and band axes are decomposed and 3D-FFT communicators are folded compactly. This proposed scheme retains the inner-most do-loop lengths sufficiently long and restrains the increased MPI communication costs as the number of nodes increases. In an investigation of a wide-gap semiconductor material (SiC), our PHASE/0 DFT code exhibits efficient and strong scaling (up to 82,944 nodes) even for a relatively small system with 3848 atoms, and demonstrates maximum peak performance of 2.25 PFLOPS for a 25,200-atom system despite employing 3D-FFT.
Three-dimensional finite element (FE) models of a non-pneumatic wheel (NPW) with three different honeycomb cell angles are developed and verified to investigate their multi-axis stiffness and road ...contact characteristics. The experiment designs based on L8(27) and L9(34) orthogonal arrays are subsequently formulated to identify influential design factors affecting the wheel response measures and their nonlinear effects. The multi-axis stiffness of the NPW are strongly influenced by the spokes design parameters, although the yaw stiffness is mostly affected by the tread parameters. The road contact properties, however, are dominantly affected by the annular beam and tread design parameters. The results from these experiment designs are effectively used to establish guidance for design tuning of the NPW for realizing desirable stiffness and road contact properties. A L16(215) orthogonal array experiment is further formulated to study the interactions among the influential design factors in view of the multi-axis stiffness and road contact responses of the wheel. The results showed negligible contributions due to interactions among the design factors. It is shown that the NPW design parameters can be tuned to achieve multi-axis stiffness properties comparable to those of the pneumatic tires.
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A multi-axis force sensor measures forces and moments occurring in more than one spatial direction. In this way, a single multi-axis sensor can perform what is essentially a ...three-dimensional measurement of physical quantities. This feature makes multi-axis sensors popular in a wide range of engineering research including automation, machining processes, aerospace, medical applications and civil engineering. Measurement of multi-directional forces and moments is typically achieved using multiple strain-sensitive elements mounted on an elastic structure. Both the sensitive elements and the elastic structure require careful consideration to design a force sensor for accuracy, reliability and robustness. While the development of multi-axis sensors has been considered extensively in the literature over the past seven decades, a collective resource which collates and examines this information does not exist. This review explores multi-axis force sensor developments across a broad range of disciplines. The salient fundamental sensing techniques adopted for the strain-sensitive elements reported in the literature are discussed and a critical review of elastic structure designs that have featured in the literature is also presented.
Low back pain has been reported to have a high prevalence among occupational drivers. Whole-body vibration during the driving environment has been found to be a possible factor leading to low back ...pain. Vibration loads might lead to degeneration and herniation of the intervertebral disc, which would increase incidence of low back problems among drivers. Some previous studies have reported the effects of whole-body vibration on the human body, but studies on the internal dynamic responses of the lumbar spine under multi-axis vibration are limited. In this study, the internal biomechanical response of the intervertebral disc was extracted to investigate the biomechanical behaviour of the lumbar spine under a multi-axial vibration in a whole-body environment. A whole-body finite element model, including skin, soft tissues, the bone skeleton, internal organs and a detailed ligamentous lumbar spine, was used to provide a whole-body condition for analyses. The results showed that both vibrations close to vertical and fore-and-aft resonance frequencies would increase the transmission of vibrations in the intervertebral disc, and vertical vibration might have a greater effect on the lumbar spine than fore-and-aft vibration. The larger deformation of the posterior region of the intervertebral disc in a multi-axis vibration environment might contribute to the higher susceptibility of the posterior region of the intervertebral disc to injury. The findings of this study revealed the dynamic behaviours of the lumbar spine in multi-axis vehicle vibration conditions, and suggested that both vertical and fore-and-aft vibration should be considered for protecting the lumbar health of occupational drivers.
This paper investigates the effects caused by simultaneous multiple random excitations on the fatigue-life of the specimen under test. In multi-axis accelerated fatigue testing, the test ...specifications are usually provided in terms of PSDs only. However, different combinations of the test specifications can significantly affect the fatigue behaviour of the specimen, resulting in altered failure modes and test durations. In this context, the original contribution of this paper is to provide a novel method for combining the PSD test specifications, which is able to recreate in the laboratory the most severe and damaging vibration environment possible. The aim of the present methodology is to get out the extreme dynamic response of the specimen by fully exploiting the total energy offered by the test specifications. This method avoids the risk of underestimating the fatigue damage to undergo the specimen during laboratory testing. The paper offers the mathematical implementation of the method and its experimental validation achieved throughout an intense test campaign. Fatigue tests have been performed on specially designed specimens, by exploiting a three-axial electro-dynamic shaker.
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