Contact Force Characteristics Research Articles

Research status and prospect of flexible optimization design methodology of propeller CNC polishing machines.

Among the components of high-tech ships, the structural complexity of the propeller profile requires a high degree of flexibility in the CNC polishing machine. In addressing this requirement, the study formulates the flexible optimization problem pertaining to research on the propeller CNC polishing machine. A comprehensive analysis is undertaken to scrutinize the geometric features of the propeller and the phenomenon of polished contact. The propeller profile-polishing head dynamic contact mechanism is revealed, and the contact force characteristics of propeller polishing are obtained. It is suggested that the propeller configuration-process-polishing machine structure coupling mechanism be explored under the influence of polishing contact force. Subsequently, a dynamic model of the propeller CNC polishing process is formulated. Based on the above model, a simulation of the motion personification and structural flexibility of the propeller CNC polishing machine is proposed to obtain dynamic personification and flexibility rules. Integrating polishing contact force characteristics with dynamic personification and flexibility rules, the dynamic flexible collaborative optimization principle of the propeller CNC polishing machine is revealed. On this basis, multi-objective optimization modeling and solving are carried out, forming a new method for the flexible optimization design of propeller CNC polishing machines.

Difference between running tests and laboratory experiments using twin-disc rolling machine regarding to wheel/rail tangential contact force characteristics

Difference between running tests and laboratory experiments using twin-disc rolling machine regarding to wheel/rail tangential contact force characteristics

A Novel Hybrid Gripper Capable of Grasping and Throwing Manipulation

Throwing motion is known for phenomenally fast rearrangement, sorting tasks, and placing the object outside the limited workspace with less effort. However, in the robotics domain, despite many simple yet versatile, mechanically intelligent grippers reported earlier, they focus primarily on achieving robust grasping and dexterous manipulation. This article presents a novel design of a single actuator driven hybrid gripper with mechanically coupled rigid links and elastic gripping surface; this arrangement provides the dual function of versatile grasping and throwing manipulation. The gripper comprises a latching mechanism (LM) that drives two passive rigid fingers by elongating/releasing the coupled elastic strip. Elongating the gripping surface enables the gripper to adapt to objects with different geometries, vary surface contact force characteristics, and store the energy in the form of elastic potential. A mechanism to discharge the stored potential energy gradually or instantaneously is essential when the intended task is to place the object free from impact or away from the limited reachable workspace. The proposed LM can swiftly shift from a quick release to a gradual release of the stored elastic potential for greater object's acceleration during throwing and no acceleration while placing. By doing so, the object can be placed at the desired location even farther than the manipulator's reachable workspace. We report the proposed gripper's design details, development, and experimentally demonstrate the versatile grasping, impact-free placing, and throwing capabilities.

On topology design of compliant constant output/input force mechanisms with contact interactions

We seek monolithic topologies for constant output (CoFM) and input (CiFM) force mechanisms using topology optimization. We capture large displacements, buckling, contact interaction between members and external surfaces, and importantly, interaction of the mechanism with flexible workpieces to accurately simulate force transfer. Features of constant force characteristics, e.g., magnitude(s) of the desired force(s), range of input displacement over which slope of the force–displacement curve is near zero, and distance between workpiece and the mechanism are controlled individually. Two constant output and constant input force mechanisms each, are synthesized using stochastic optimization ensuring ready manufacturability. We observe that (a) accurate modeling of the mechanism-workpiece interaction is important. (b) Fixed external surfaces may not necessarily contribute to contact force characteristics though interesting alternative solutions are possible in their presence. (c) It behooves to model self contact between members than to reject viable solutions wherein members intersect in intermediate configurations. We finally fabricate the synthesized mechanisms and find that the desired constant force characteristics are by-and-large retained qualitatively, even when the mechanisms may undergo plastic deformation.

Three-dimensional FEM–DEM coupling simulation for analysis of asphalt mixture responses under rolling tire loads

As traffic grows by leaps and bounds, deterioration of asphalt surface layers emerges as the primary cause of road network costs. A deep understanding of the tire–pavement interaction is essential for optimizing the surface design of asphalt pavements in the context of aging infrastructure and limited maintenance resources. Most of the current tire–pavement interaction studies have been conducted in the continuum mechanics framework using Finite Element Methods (FEM), which shows limitations in modeling the discontinuity nature of asphalt mixtures. Discrete Element Methods (DEM) offer a promising way to examine the mechanical properties of asphalt mixtures at the particle level, but it is inadequate for modeling deformable tire structure and capturing realistic tire contact forces on the pavement surface. In this study, a FEM–DEM coupling strategy was developed for the modeling of tire–pavement interaction by implementing a DEM model of asphalt mixtures with rolling tire loads from a FEM model. Based on simulations with realistic rolling tire load conditions, this coupling algorithm allows the investigation of particle force chain network evolution, particle displacement and velocity distributions, movements of individual particles, and particle contact force characteristics inside an asphalt mixture. This study offers an enriching expansion of both continuum and discrete mechanics methods for analyzing asphalt mixture responses under rolling tire loads, which can provide insight into pavement surface design.

Review on Load Transfer Mechanisms of Asphalt Mixture Meso-Structure.

Asphalt mixture is a skeleton filling system consisting of aggregate and asphalt binder. Its performance is directly affected by the internal load transfer mechanism of the skeleton filling system. It is significant to understand the load transfer mechanisms for asphalt mixture design and performance evaluation. The objective of this paper is to review the research progress of the asphalt mixture load transfer mechanism. Firstly, this paper summarizes the test methods used to investigate the load transfer mechanism of asphalt mixtures. Then, an overview of the characterization of load transfer mechanism from three aspects was provided. Next, the indicators capturing contact characteristics, contact force characteristics, and force chain characteristics were compared. Finally, the load transfer mechanism of asphalt mixtures under different loading conditions was discussed. Some recommendations and conclusions in terms of load transfer mechanism characterization and evaluation were given. The related work can provide valuable references for the study of the load transfer mechanism of asphalt mixtures.

A consideration of difference in wheel/rail tangential contact force characteristics between in running tests and laboratory experiments using three-dimensional multi-body dynamics model

A consideration of difference in wheel/rail tangential contact force characteristics between in running tests and laboratory experiments using three-dimensional multi-body dynamics model

Radiofrequency Pulmonary Vein Isolation without Esophageal Temperature Monitoring: Contact-Force Characteristics and Incidence of Esophageal Thermal Damage

Esophageal thermal lesions following pulmonary vein isolation (PVI) for atrial fibrillation (AF) potentially harbor lethal complications. Radiofrequency (RF)-PVI using contact force-technology can reduce collateral damage. We evaluated the incidence of endoscopically detected esophageal lesions (EDEL) and the contribution of contact force to esophageal lesion formation without esophageal temperature monitoring. One hundred and thirty-one AF patients underwent contact force-guided RF-PVI. Contact force, energy, force-time-integral, and force-power-time-integral were adopted. During PVI at the posterior segment of the wide antral circumferential line, limits were set for energy (30 W), duration (30 s) and contact force (40 g). Ablations were analyzed postero-superior and -inferior around PVs. Endoscopy within 120 h identified EDEL in six patients (4.6%). In EDEL(+), obesity was less frequent (17% vs. 68%, p = 0.018), creatinine was higher (1.55 ± 1.18 vs. 1.07 ± 0.42 mg/dL, p = 0.016), and exclusively at the left postero-inferior site, force-time-integral and force-power-time-integral were greater (2973 ± 3267 vs. 1757 ± 1262 g·s, p = 0.042 and 83,547 ± 105,940 vs. 43,556 ± 35,255 g·J, p = 0.022, respectively) as compared to EDEL(-) patients. No major complications occurred. At 12 months, arrhythmia-free survival was 74%. The incidence of EDEL was low after contact force-guided RF-PVI. Implementing combined contact force-indices on the postero-inferior site of left-sided PVs may reduce EDEL.

Research on time–frequency characteristics of contact force based on wavelet transform

When a train runs at high speed, affected by the structural characteristics of the catenary, the contact force changes periodically with span and dropper spacing. However, as the running speed of the train increases, the periodic signal of the contact force changes owing to the fluctuation of the catenary and the vibration of the pantograph, which directly affects the stable contact between the pantograph and catenary. Therefore, based on the simulation research method, this study uses the time–frequency transformation method to investigate the influence of changes in the catenary structure on the periodic signal of the contact force. First, the structural design of the catenary structure of the existing railway line is carried out by changing the length of the stitch wires and the dropper spacing, and the stiffness and stiffness curvature variation when the arrangement of the stitch wires and dropper varies are analysed. Then, the relationship between the stiffness, stiffness curvature variation, and contact force variation is analysed. Finally, the wavelet transform method is used to transform the contact force, and variations in the key amplitude component of the contact force are analysed when the structural parameters are changed, and the relationship between the period and the key amplitude component is obtained. By analysing the time–frequency characteristics of the contact force, technical support for improving the speed of the train can be provided.

Study on Shear Mechanical Properties and Microscopic Failure Mechanism of Dentate Joints Based on DEM and Laboratory Tests

The stability control of the surrounding rock is greatly influenced by the rock joint’s shear mechanical characteristics and deformation failure mechanism. A numerical model of the dentate joints was created using a particle flow discrete element method (DEM). To study the shear mechanical behavior and damage evolution characteristics of the joints, a numerical simulation of the joints shear test under the same normal stress was conducted. Additionally, the joints’ shear failure mechanism and failure mode were investigated from a microscopic perspective in conjunction with laboratory tests. The results show that the shear strength steadily increases as the roughness of the rock joints increases and that it rapidly decreases after reaching its peak shear strength, indicating an obvious brittle failure. Varied rock joints exhibit significantly different micro-crack evolution, with rougher rock joints (r = 0.30, r = 0.37) exhibiting greater micro-crack production and crack extension into the model’s interior. Rock joint specimens with lower roughness (r = 0.17) had less concentration and fewer areas of contact force concentration. The shear failure mode of the rock joints gradually shifts from abrasion failure mode to snip failure mode as the roughness rises, which is largely compatible with the failure characteristics shown in the laboratory testing. The pattern of micro-crack development within the model specimen and the failure characteristics of the laboratory tests are in good agreement with the distribution characteristics of contact force on the rock joints.

Experimental evaluation of tangential contact force characteristics between wheel and rail focusing on water flow rate

Experimental evaluation of tangential contact force characteristics between wheel and rail focusing on water flow rate

Analysis of contact force characteristics of vibratory finishing within pipe-cavity

Vibratory finishing realizes the finishing of the workpiece surface by vibrationally-fluidized granular media. Due to the granular media’s fluidized nature, vibratory finishing can be applied to surface finishing in restricted space, such as the cavity of integral casting casing. In this work, taking the typical elongated pipe-cavity inside the casings as the analysis object, based on the discrete element method (DEM), a series of simulations were carried out on the length and diameter of pipe-cavity, the load of media, vibration amplitude, and frequency. The frequency multiplication of the normal contact force between the granular media and the surface in restricted space was discovered. A method of processing contact force data based on the Fourier transform was proposed. And then, the normal contact force, its average, and coefficient of variation at different positions of the slender pipe-cavity were analyzed. It is found that the normal force fluctuates along the axial direction and is symmetric on the circumferential positions. Furthermore, the effects of various variables, including length, diameter, load, amplitude, and frequency on the normal force, have been obtained. The method and results can reference studying the dynamic behavior of granular media in restricted space.

Experimental evaluation of tangential contact force characteristics between wheel and rail under wet condition using twin-disk rolling machine

Experimental evaluation of tangential contact force characteristics between wheel and rail under wet condition using twin-disk rolling machine

Influence of wheel turning trace on wheel/rail tangential contact force characteristics under wet condition

Influence of wheel turning trace on wheel/rail tangential contact force characteristics under wet condition

Characteristics of Contact Force and Muscle Activation During Choreographed Falls With 2 Common Landing Techniques in Contemporary Dance.

This study investigated the contact forces and muscle activation during 2 choreographed fall techniques in contemporary dancers and how these were affected by the fall technique. Ten collegiate-level dancers were instructed in 2 choreographed falls: (1)an anteriorly focused fall involving ankle plantar flexion, knee flexion, and hip flexion with dispersion of forces up the anterior surface of the shank (technique 1) and (2)a laterally focused fall involving inversion at the ankle with dispersion of forces up the lateral aspect of the shank (technique 2). The knee and hip contact forces were 26.3% smaller (technique 1: 1743N vs technique 2: 1284N) and 24.1% greater (technique 1: 1334N vs technique 2: 1656N), respectively, in technique 2 (P < .03). At the time of knee contact, percentage of maximal voluntary isometric contraction (%MVIC) was 45.8% greater for rectus femoris muscle (technique 1: 7.2% vs technique 2: 10.5%) and 96.9% greater for gluteus medius muscle (technique 1: 3.2% vs technique 2: 6.3%) (P < .01) in technique 2. The results provide insight into determining safer landing strategies to avoid knee injuries in individuals who experience a fall (ie,dancers, athletes, and older adults).

On stability of emulated turning processes in HIL environment

Hardware-in-the-loop (HIL) experimental setup is presented to investigate the stability of turning processes. A dummy workpiece is fixed to a main spindle, which is excited in the radial direction by electromagnetic contactless actuators. The actuators emulate contact force characteristics including surface regeneration effect between the cutting tool and the workpiece with 100 kHz sampling frequency. The cutting force is calculated by a high performance real time target that uses the measured present and previous values of the relative displacements of the dummy workpiece. The loss of linear stability is monitored for various real spindle speeds and virtual chip widths. Measured lobe diagrams are compared with the results of theoretical stability analysis.

Analysis of stress distribution of disc cutter under different tunnelling parameters

ABSTRACTWith the rapid development of China’s undefined economy and the urgent need of underground space engineering, the localisation of road header, especially the cutting tool of road header, is becoming more and more important. Disk cuter is the main tool of hard rock tunnelling machine. Its rock breaking efficiency and service life are directly related to the progress and cost of the project. Based on the contact force characteristics and motion law of disc cutter, a three-dimensional finite element analysis model for the driving process of disc hob is established by using Abaqus. On the basis of friction characteristics, the stress analysis of disc cutter in tunnelling process is carried out. The influence of relevant tool parameters on rock breaking efficiency is obtained by numerical simulation, and the distribution law of stress field in rock breaking process of disc cutter is obtained. And the influence of different penetration and rotation speed on the stress distribution of cutter ring. It is of great significance to analyse the stress field of TBM(Tunnel Boring Machine) disc hob to maximise the tunnelling benefit.

Uneven distribution characteristics of contact force of large-sized non-asbestos brake pad

Large-sized non-asbestos brake pad is used in the brake system of mine hoister. During the braking process, uneven contact force distribution in the contact surface will occur, which accordingly le...

Prior-Information-Based Finite-Frequency $\text{H}_{\infty}$ Control for Active Double Pantograph in High-Speed Railway

The fluctuation in contact force between the pantograph and the catenary severely affects the current collection quality of electric multiple units in high-speed railway. In particular, when double pantographs operate simultaneously, the contact force on trailing pantograph (TP) fluctuates violently due to the passage of leading pantograph (LP). To address this problem, a prior-information-based finite-frequency $\text{H}_{\infty}$ controller, incorporating an adaptive estimator, is proposed for the active control of double pantographs in this paper. As the prior information is of great importance, the frequency characteristics of contact force are analyzed based on power spectrum density and utilized in calculating the control gain matrix. The finite-frequency control is employed to decrease the contact force fluctuation within the concerned frequency range with limited control force. Considering the unknown and time-varying noise statistic, an adaptive cubature Kalman filter is presented to estimate the states of pantographs. The effectiveness and robustness of the proposed control strategy are evaluated with implementations in a nonlinear double-pantograph-catenary system model under different operational conditions. The results show that, for both LP and TP, the control strategy can adequately decrease the contact force fluctuation. Particularly, it has a good capability to reject parameter perturbations and external disturbance.

Nonlinear analysis of a shimmying wheel with contact-force characteristics featuring higher-order discontinuities

In this study, the yaw dynamics of a towed caster wheel system is analysed via an in-plane, one degree-of-freedom mechanical model. The force and aligning torque generated by the elastic tyre are calculated by means of a semi-stationary tyre model, in which the piecewise-smooth characteristic of the tyre forces is also considered, resulting in a dynamical system with higher-order discontinuities. The focus of our analysis is the Hopf bifurcation affected by the non-smoothness of the system. The structure of the analysis is organised in a similar way as in case of smooth bifurcations. Firstly, the centre-manifold reduction is performed, then we compose the normal form of the bifurcation. Based on the Galerkin technique an approximate, semi-analytical method to calculate the limit cycles is introduced and compared with the method of collocation. The analysis provides a deeper insight into the development of the vibrations associated with wheel shimmy and demonstrate how the non-smoothness due to contact-friction influences the dynamic behaviour.