Contact area

About: Contact area is a research topic. Over the lifetime, 12358 publications have been published within this topic receiving 256401 citations. The topic is also known as: contact patch & contact region.

Highly sensitive flexible three-axis tactile sensors based on the interface contact resistance of microstructured graphene

Abstract: The lack of high-performance tactile sensors, especially for pressure/force, is a huge obstacle for the widespread application of intelligent robots. Current pressure sensors are often operated in the high range of pressure and normal direction, showing a little ability in the low range of pressure and three-axis direction simultaneously. Herein, a highly sensitive flexible tactile sensor with three-axis force sensing capacity is presented by combining microstructured polydimethylsiloxane (PDMS) arrays and a reduced graphene oxide (rGO) film. The deformation of microstructured rGO/PDMS results in a change in the contact area between the rGO film and electrode, leading to a high sensitivity of -1.71 kPa-1 in the low range pressure of 0-225 Pa with a fast response time of 6 ms at a large feature size of 100 μm. To realize three-axis sensing, a sensing unit was built up, which was composed of the adjacent four parts of patterns and electrodes underneath a bump. A mechanical model of the exerted spatial force was established to calculate each axis force component via the deformation of the rGO/PDMS pattern. The experimental results show that the current difference between the adjacent two parts has a strong relationship with the applied force. As a proof of concept, we have demonstrated a 3 × 3 array sensor for arbitrary force sensing. Our tactile sensor would be used in transmitting information from a gentle spatial force and would exhibit broad applications as e-skin in integrated robots.

Experimental Characterization of Wheel-Rail Contact Patch Evolution

Abstract: The contact area and pressure distribution in a wheel/rail contact is essential information required in any fatigue or wear calculations to determine design life, re-grinding, and maintenance schedules. As wheel or rail wear or surface damage takes place the contact patch size and shape will change. This leads to a redistribution of the contact stresses. The aim of this work was to use ultrasound to nondestructively quantify the stress distribution in new, worn, and damaged wheel-rail contacts. The response of a wheel/rail interface to an ultrasonic wave can be modeled as a spring. If the contact pressure is high the interface is very stiff, with few air gaps, and allows the transmission of an ultrasonic sound wave. If the pressure is low, interfacial stiffness is lower and almost all the ultrasound is reflected. A quasistatic spring model was used to determine maps of contact stiffness from wheel/rail ultrasonic reflection data. Pressure was then determined using a parallel calibration experiment. Three different contacts were investigated; those resulting from unused, worn, and sand damaged wheel and rail specimens. Measured contact pressure distributions are compared to those determined using elastic analytical and numerical elastic-plastic solutions. Unused as-machined contact surfaces had similar contact areas to predicted elastic Hertzian solutions. However, within the contact patch, the numerical models better reproduced the stress distribution, as they incorporated real surface roughness effects. The worn surfaces were smoother and more conformal, resulting in a larger contact patch and lower contact stress. Sand damaged surfaces were extremely rough and resulted in highly fragmented contact regions and high local contact stress.

Grasping without squeezing: Shear adhesion gripper with fibrillar thin film

Abstract: Nearly all robotic grippers have one trait in common: they grasp objects with normal forces, either directly, or indirectly through friction. This method of grasping is effective for objects small enough for a given gripper to partially encompass. However, to grasp larger objects, significant grip forces and a high coefficient of friction are required. We present a new grasping method for convex objects, using almost exclusively shear forces. We achieve shear grasping with a gripper that utilizes thin film gecko-inspired fibrillar adhesives that conform to the curvature of the object. We present a verified model for grasping a range of curvatures and results that demonstrate the thin film fibrillar adhesives' increased contact area on textured surfaces when loaded in shear. Finally, the gripper is implemented on a robotic arm and grasps a variety of convex objects (at rest and ballistic).

On the debris-level origins of adhesive wear.

Abstract: Every contacting surface inevitably experiences wear. Predicting the exact amount of material loss due to wear relies on empirical data and cannot be obtained from any physical model. Here, we analyze and quantify wear at the most fundamental level, i.e., wear debris particles. Our simulations show that the asperity junction size dictates the debris volume, revealing the origins of the long-standing hypothesized correlation between the wear volume and the real contact area. No correlation, however, is found between the debris volume and the normal applied force at the debris level. Alternatively, we show that the junction size controls the tangential force and sliding distance such that their product, i.e., the tangential work, is always proportional to the debris volume, with a proportionality constant of 1 over the junction shear strength. This study provides an estimation of the debris volume without any empirical factor, resulting in a wear coefficient of unity at the debris level. Discrepant microscopic and macroscopic wear observations and models are then contextualized on the basis of this understanding. This finding offers a way to characterize the wear volume in atomistic simulations and atomic force microscope wear experiments. It also provides a fundamental basis for predicting the wear coefficient for sliding rough contacts, given the statistics of junction clusters sizes.