Analysis Of Contact Forces Research Articles

Signal Feature Analysis of Contact Force at the Tip of a Flexible Ureteroscope.

This paper presents a signal analysis approach to identify the contact objects at the tip of a flexible ureteroscope. First, a miniature triaxial fiber optic sensor based on Fiber Bragg Grating(FBG) is devised to measure the interactive force signals at the ureteroscope tip. Due to the multidimensional properties of these force signals, the principal components analysis(PCA) method is introduced to reduce dimensions. The signal features are then extracted from the representative principal component signals using the wavelet transform(WT) method. Experimental results show that the contact objects at the tip of a ureteroscope are readily discriminated from the measured force signals with the proposed approach.Clinical Relevance-This work commits to analyze the contact force signals at the tip of a flexible ureteroscope for the purpose of contact objects identification.

Dynamic Performance of High-Speed Railway Overhead Contact Line Interacting With Pantograph Considering Local Dropper Defect

The local dropper defect is the most common fault in the early service stage of the overhead contact line (OCL) system. The plastic deformation and loose of a dropper may cause the variation of the contact line height, which has a direct effect on the contact performance of the pantograph-OCL system. This paper proposes a methodology to model the OCL with local dropper defect using a nonlinear finite element approach. Employing a developed TCUD (Target Configuration under Dead Load) method, which takes the vertical defective dropper position in the contact line as additional constraints, the local dropper defect is exactly added in the initial configuration of the OCL model. Several simulations of pantograph-OCL interaction are run with different positions of the defective dropper. The effect of local dropper defect on the pantograph-OCL contact forces is analysed. The results show that the increase of the defect degree causes the increment of the contact force peak around the defective dropper point. The defect on the first or last dropper within a span is the most detrimental to the current collection quality, as it directly causes the increase of maximum contact force, which challenges the safe operation of the pantograph-OCL system, and should be strictly restricted. The PSD (Power Spectral Density) analysis of contact force indicates that the dropper defect distorts the frequency characteristics of the contact force. The energy of contact forces decreases at the dropper-interval related frequencies due to the presence of dropper defect. Similarly, a significant `break' of the dropper-interval frequency component can be observed in the time-frequency representation of the contact force. This phenomenon has the potential to be used to identify and locate the defective dropper from the measured contact force.

Contact force modeling and analysis for robotic tilted-disc polishing of freeform workpieces

This paper investigates the tool-workpiece contact mechanism in the disc polishing process, where the soft polishing disc touches the rigid freeform workpiece with a small tilt angle. The developed contact force model can explain how the contact parameters, including the disc contact depth, the disc tilt angle, the radii of curvature of the disc and the workpiece, affect the normal contact force. Under some reasonable geometric and mechanical assumptions of the disc and the workpiece, an approximated contact force equation is derived in a simple power-law form similar to the Hertzian contact model. The contact force is found to be positively related to the disc contact depth and the disc radius, while negatively related to the disc tilt angle and the workpiece normal curvature that is orthogonal to the feed direction. Both finite element simulations and experiments verify the effectiveness of the proposed contact force model. Furthermore, the material removal process is analyzed and a model-based process parameter planning method is developed to achieve uniform material removal considering the variation of workpiece curvatures.

Spectral and informational analysis of pedestrian contact force in simulated overcrowding conditions

In this paper, the time series of contact force among pedestrians in two different crowding conditions is analyzed by using the correlogram-based periodogram and the Fisher–Shannon method to investigate their spectral and informational properties, respectively. The overcrowding was simulated by controlled experiments carried out at University of Science and Technology of China, Hefei in three different walking styles. Our results show that: (1) the contact force is characterized by a significant periodic behavior; (2) a clear discrimination in the Fisher–Shannon information plane is found between contact forces measured in the two conditions of lower and higher pedestrian density.

Design of a Novel Locking Ratcheting Mechanism for a Body-Powered Underactuated Hand

AbstractAs affordable and efficient three-dimensional (3D) printers became widely available, researchers are focusing on developing prosthetic hands that are reasonably priced and effective at the same time. By allowing anyone with a 3D printer to build a body-powered prosthetic hand, many people could build their own prosthetic hand. However, one of the major problems with the current designs is the users must bend and hold their wrist in an awkward position to grasp an object. The primary goal of this work is to present the design process and analysis of a body-powered underactuated prosthetic hand with a novel ratcheting mechanism that locks the finger automatically at a desired position. To estimate how a compliant finger behaves on the actual system with the ratcheting mechanism, the preshaping analysis and the preshaping experiment were conducted. From the experiment, the presence of elastic hysteresis was observed. Additionally, the contact force analysis was performed to see the effects of joint angles and applied tension force. To test how well the hand can grasp, a cup with various weights was lifted and various objects with different shapes were grasped to prove how well the compliant finger can adapt to the shape of the objects. Based on the experiment, the hand had a higher success rate of grasping objects that are lightweight (less than 500 g) and cylindrical or circular shaped.

Contact analysis for dual peg-in-hole assembly of automobile alternator frame

The modeling and analysis of the assembly contact problems in the picking and placement of the automobile alternator frame are carried out in the multi-station processing. According to the three-dimensional assembly characteristics of the actual alternator frame and the fixture, the assembly model in the drilling and milling station is simplified. The alternator frame and fixture assembly problem as a whole is simplified to a dual peg-in-hole assembly problem. All possible one-point contact states and two-point contact states during the assembly process are proposed(L-1)∼(R-10). The contact force analysis is carried out on the typical one-contact state L-1 and the typical two-point contact state L-5, and the relationship between the corresponding assembly forces Fx, Fy, Fz and the assembly moments Mx, My, Mz is obtained. According to the relationship between these assembly forces and assembly moments, the corresponding jamming diagrams are obtained. Finally, according to the three-dimensional size of the actual alternator frame, the experimental verification was carried out by using a 6-DOF force/moment sensor. The experimental results confirmed the validity of the analysis. Technical support is provided for the assembly of automobile alternator frames based on force sensing control for the follow-up work.

Contact force analysis in a planar mechanism with translational clearance joint considering complex contact modes

A translational joint model with clearance was established. A contact mode identification method was derived on the basis of the classification of contact modes. The positional relationships were classified into three different contact modes. The identification method was applied to a planar mechanism with translational joint. The influences of clearance size and velocity on dynamic characteristics between them were studied. The mean square error value of contact force can be used to evaluate the influence of the clearance on the dynamic characteristics of the mechanism.

Dynamic analysis of varus knee using a subject-specific multibody model of the knee before and after osteotomy

Varus misalignment of the hip-knee-ankle angle causes greater loads on the medial compartment of the knee and increases the risk of developing knee osteoarthritis. High tibial osteotomy is a surgical method where the load-bearing axis is shifted laterally. The purpose of this study is to define a subject-specific three-dimensional multibody model of the knee to investigate the effect of osteotomy on cartilages and menisci during the stance phase of gait. It is assumed that osteotomy transfers load-bearing to the lateral parts of the knee. Magnetic resonance images of a patient with varus alignment were used to generate the geometries of the bones, cartilages, and menisci. Then, an experimental approach was used to determine the parameters for the stiffness matrices and compliant contact models of the tibio-menisco-femoral articulations with the use of finite element solutions. As indicated by the research findings, the contact force at the medial cartilage decreased as the load-bearing axis was transferred to the lateral parts. This subject-specific noninvasive analysis of contact force can be considered as a preoperative assessment tool for the surgeon. to predict the effects of high tibial osteotomy and the shifting of the load-bearing axis to the soft tissues of the knee.

Mechanical evaluation of aggregate gradation to characterize load carrying capacity and rutting resistance of asphalt mixtures

The gradation and mechanical properties of aggregates impressively affect the load carrying capacity and rutting resistance of asphalt mixtures. They are able to provide some fundamental parameters that are linked to mixture performance. In order to accurately detect critical controlled sizes and obtain more fundamental parameters that can characterize load carrying capacity and rutting resistance of asphalt mixtures, this paper aims to develop a mechanics-based approach to evaluate aggregate gradation, which contains the theoretical packing analysis and discrete element simulation.An extended theoretical morphology framework is developed by checking the local and global interlock of graded aggregates in the theoretical packing analysis. The sieve size range of primary structure which has an interactive interlock can be determined in the local interlock check model. The relationship between the transferred force and the induced force is proposed in the densest and loosest packing arrangements, respectively. The morphological parameters of disruption factor and weighted average size for the global scale are also proposed in theoretical packing analysis.Then the discrete element method is used to validate the theoretical framework. The advanced gradation input algorithm procedure is established in the discrete element simulation to simulate the compression test of graded aggregates. The mechanical parameters of contact force, contact points and stress–strain curves are extracted from the simulation results.The results show that the discrete element method can validate the theoretical framework and output the performance related parameters. The contact force analysis shows that the aggregates retaining on sieve sizes of 2.36 and 4.75 mm provide more than 50% contribution to resist load, and the aggregates retaining on sieve sizes of 1.18, 0.6 and 0.3 mm provide more than 50% contribution to stabilize the structure. The coordination number analysis suggests that the gradation with more fine aggregates might lead to a greater number of voids but smaller air-void size when the asphalt content and porosity remain constant. The stress–strain curve analysis shows that the modulus and secondary strain are highly related to the rutting performance of an asphalt mixture.

Contact Force Analysis of a Rotor-Brush Seal System With Eccentricity and Airflow

The mechanics properties of brush seals are usually very complicated. Here, the contact force of a rotor-brush seal system was analyzed based on the bending deformation theory considering the interaction of eccentricity and flow induced force. The seal force expression was established by using the Bernoulli-Euler beam equation and superposition method, and the effects of eccentricity, friction coefficient, bristle lay angle, and uniform force of flow on the acting force of rotor system was analyzed. An experimental test rig of a Stodola-Green rotor-brush seal system was set up, and the effect of seal force on vibration characteristics of the rotor system was evaluated by the experiment. The results showed that with a flow induced force, the contact force of the rotor decreases with the increase of eccentricity. The contact force increased with the increase of flow induced force as well. The theoretical results were in accordance with the experimental results and, thus, validate the seal force of the brush seal.

Agreement of measured and calculated muscle activity during highly dynamic movements modelled with a spherical knee joint

The inclusion of muscle forces into the analysis of joint contact forces has improved their accuracy. But it has not been validated if such force and activity calculations are valid during highly dynamic multidirectional movements. The purpose of this study was to validate calculated muscle activation of a lower extremity model with a spherical knee joint for running, sprinting and 90°-cutting. Kinematics, kinetics and lower limb muscle activation of ten participants were investigated in a 3D motion capture setup including EMG. A lower extremity rigid body model was used to calculate the activation of these muscles with an inverse dynamics approach and a cubic cost function. Correlation coefficients were calculated to compare measured and calculated activation. The results showed good correlation of the modelled and calculated data with a few exceptions. The highest average correlations were found during walking (r = 0.81) and the lowest during cutting (r = 0.57). Tibialis anterior had the lowest average correlation (r = 0.33) over all movements while gastrocnemius medius had the highest correlation (r = 0.9). The implementation of a spherical knee joint increased the agreement between measured and modelled activation compared to studies using a hinge joint knee. Although some stabilizing muscles showed low correlations during dynamic movements, the investigated model calculates muscle activity sufficiently.

The friction effects for contact force analysis of three-axes CNC machine tool

PurposeThe purpose of this paper is to study the influence of friction on static and dynamic characteristics, as well as the strength and lifetime of a flexible three-axes computer numerical control (CNC) machine tool.Design/methodology/approachThe machine tool is first modeled by using finite element method to analyze static structure with frictionless surface-to-surface contact type. Because the machine tool structure is becoming more and more sophisticated over time, the significant influence of contact conditions between structural elements on the dynamic characteristics of the whole structure must be considered. To examine the dynamic effects caused by inertia forces and displacement of moving bodies on contact stress, the coefficient of friction between two contact bodies is added to perform dynamic simulation and compare the results with the static analysis results.FindingsDistribution of stress and contact forces in solid-flexible contact is also studied by using the fundamental dynamic characteristics of a bushing joint.Originality/valueFinally, the influence of dynamic structure, cutting conditions and material properties on the strength and lifetime of the CNC machine tool is discussed by using fatigue analysis. Consequently, this research can be used for efficient simulation of structural dynamics, lifetime assessment and interactions of the real CNC machine with the machine tool structure in a virtual environment.

DEM modeling on stress profile and behavior in granular matter

This paper presents a systematic numerical investigation of static stress profile within a confined granular packing using discrete element method. The vertical and horizontal stress profiles are carefully identified within the packing structure, and the effects of container diameter and friction coefficient on the stress distributions are systematically investigated and analyzed. The results show a quantitative agreement between the vertical stress profile gauged at the bottom and the stress profile calculated within the packing structure. I.e. beyond a hydrostatic region, the static vertical stresses saturate exponentially with the packing depth. A positive correlation between the saturation stress and the container size and a negative correlation with the friction coefficient can be observed. Besides, it is also found that the well-known Janssen coefficient (or Janssen constant) is not a constant value; it decreases asymptotically to a constant with the packing depth, which implies a non-constant friction effects existed between the granular assemblies and the boundaries. And the analysis of contact forces within the packing structure also indicates a stabilized condition beyond the hydrostatic region. It is believed that these findings could develop a comprehensive insight on the stress distribution of granular matter.

Transformation of sliding motion to rolling during spheres collision

In this research, we have investigated the three-dimensional elastic collision of two balls, based on friction in the tangential plane. Our aim is to offer analytical closed form relations for post collision parameters such as linear and angular velocities, collision time and tangential and normal impulse in three dimensions. To simplify the problem, stick regime is not considered. In other words, balls have a low tangential coefficient of restitution. Sliding, sliding then rolling, and rolling at the beginning of contact are three cases that can occur during impact which have been considered in our research. The normal interaction force is described by the Hertz contact force and dimensionless analysis is used for investigating normal interaction force; furthermore, Coulomb friction is considered during sliding. Experimental data for collisions show when sliding exists through the impact, tangential impulses can be taken as frictional impulses using the Coulomb law if the dynamic regime is not stick regime. To identify transformation of sliding motion to rolling or sticking during the impact process, linear and trigonometric functions are considered as an approximation for the normal interaction force. Afterwards, we have obtained the condition for the possibility of this transformation; moreover, we can estimate the duration of sliding and rolling or sticking. We have obtained an analytical solution for maximum force and deformation, collision time, impulses and post-collision linear and angular velocities in three dimensions.

The Friction Effects for Contact Force Analysis of Three Axes CNC Machine Tool

In this paper, the influence of friction on static, dynamic characteristics, the strength and lifetime of a 3-axes flexible CNC machine tool are taken into account. The machine tool is first modelled by using finite element method (FEM) to perform static structural analysis. After that, the dynamic effects caused by the inertia forces and the displacement of moving part of the machine on contact stress are considered in this study. Then, the stress and contact force distributions on solid-flexible contact are also obtained. Finally, the influence of dynamic structure, cutting conditions and material properties on strength and lifetime of CNC machine tool are discussed by using fatigue analysis. Consequently, the proposed method can be used for efficient simulation of structural dynamics, lifetime assessment as well as interactions of the real CNC machine with the machine tool structure in a virtual environment.

Online monitoring of pipe conveyors part II: Evaluation of selected operational parameters for the design of expert system

Abstract Online monitoring of pipe conveyors operation is a key condition to their operational reliability. According to Molnar et al. (2016), the parameter to be used for evaluation is the change of contact forces on the idler rolls of hexagonal idler housing of a pipe conveyor. However, the statement itself is not enough for online monitoring purposes. Evaluation criteria in form of evaluation gauge enabling the identification of processes occurring in the conveyor belt need to be set followed by adequate measures taken afterwards. The paper aims to review the courses of contact forces at various tension forces since these are the parameters convenient for tracking of pipe conveyor operation. For better independence of results and conclusions, the measured values are transformed with the use of min/max method of standardization and then modified by moving averages. Experimental tests are evaluated with the use of basic statistics methods, correlation and regression analysis. The outputs include analysis of contact forces and time dependence, contact forces and tension force dependence for two different measurements, with and without material.

Computational analysis of contact forces influence on cold forming processes in the dies with complex surfaces

Interaction forces between the workpiece and the die appear during the cold forming process of metals in dies. Surface forces of high-intensity influence the mesh structure and internal structure of the finished piece by mechanical action. Frictional forces hinder the flow of the material in contact with the die walls, especially on surfaces of complex shape. Under certain conditions, the material can adhere to the wall of the die, leading to the blocking of the cold forming process. In order to highlight the influence of contact forces on cold forming processes in dies with complex surfaces there were used numerical simulation methods with finite elements. Numerical simulations of the process of axial cold forming in the die were carried out for analysis data acquisition necessary, in order to achieve HTD pulleys, for an ordinary range of friction coefficients. The analysis was directed to the gearing area of the HTD pulleys (head, flank and base of the tooth). The analysis highlighted the negative effects of friction forces on the shape and quality of the products and the need to use quality lubricants. Also, using the cold forming process they can be achieved substantial savings by redistribution of the material without removing it.

Analysis of contact rates and force of infection of Hand-foot-mouth disease in Chongqing, China

Hand-foot-mouth disease (HFMD) is primarily caused by enterovirus 71 and coxsackieviruses A16, and usually transmitted among children under five years old. HFMD has been a significant public health challenge in China. In 2015, there were 1767931 cases and 114 deaths reported in China. To understand the transmission of the disease, we examined the age-specific force of infection (FOI) and the transmission rate of HFMD in Chongqing using data from May 2008 to December 2011. Chongqing is the only municipality in the southwest part of China. It has the largest population density compared with other cities in the area, and its has a typical seasonality pattern of HFMD that was found in the southeastern part of China. The FOI of HFMD for Chongqing might be different between age groups, because we had an observation that the FOI of HFMD was identical among age groups before the 2008 outbreak, but was heterogeneity after the outbreak in Fuyang, Anhui Province. Regard to the transmission rate, we studied whether it changed during the year and studied the possible connection of changing in transmission rate with school closure and with holidays. Data of HFMD reported cases were obtained from the Data-center of China Public Health Science; demography data and meteorological data were obtained from the National Bureau of Statistics of China. We used catalytic model to estimate the age-specific FOI of HFMD for Chongqing, and used Time Series Susceptible Infectious Recovered (TSIR) model to estimate the time varied transmission rate of HFMD. In the TSIR model, the serial interval was assumed to be two weeks based on the fact that the incubation period of HFMD was 3–5 days and the infectious period was about 7–10 days. We calculated the proportion of HFMD incidence for each age group. Our results show that: the incidence of HFMD in Chongqing had two peaks, one in spring and one in winter; proportion of cases among children under six years old were 93%, with the largest fraction of cases among 2–3 years old; the FOIs in different age groups were different, FOI of 3–4 years old age group was the highest, and FOI of 35–39 years old was relatively higher than that of other adults; transmission rate among individuals changed during the year; transmission rate increased during summer and winter vocations, meaning that in China the transmission rate of HFMD in community was higher than the transmission rate in school. Control measures of HFMD should focus on young children, especially 3–4 years old, in community during summer and winter vocations.

Digital analysis of occlusion using T-Scan III in orthodontics

Disclusion Time Reduction (DTR) is an objective treatment protocol using T-Scan III (Digital Analysis of Occlusion) for Force Finishing in Orthodontics. Chronic Occluso-muscle Disorder is a myogenous subset of Temporomandibular Disorder symptoms (TMD) can occur to most of post orthodontic cases, if they are not force finished. These muscular symptoms are induced within hyperactive masticatory muscles due to prolonged Disclusion Time, occlusal interferences, and occlusal surface friction that occurs during mandibular excursive movements. This article describes a gadget T-Scan III which can be used for this purpose; whereby measured pretreatment prolonged Disclusion Time can be reduced to short Disclusion Time using the ICAGD enameloplasty, guided by T-Scan occlusal contact time and force analysis.

Design and performance analysis of a rotary traveling wave ultrasonic motor with double vibrators

This paper presents the development of a rotary traveling wave ultrasonic motor, in which a vibrating stator and vibrating rotor are combined in one motor. The stator and rotor are designed as similar structures an elastic body and a piezoelectric ceramic ring. In exciting of the piezoelectric ceramics, the elastic body of the stator and rotor will generate respective traveling waves, which force each other forward in the contact zone. Based on the elliptical rule of particle motion and matching principle of vibration, the design rules of two vibrators are determined. The finite element method is used to design the sizes of vibrators to ensure that they operate in resonance, and the simulation is verified by measuring the vibration with an impedance analyzer. It is found out that to maintain an appropriate contact between the stator and rotor, two vibrators need to be designed with close resonance frequencies, different vibration amplitudes, and be driven by an identical driving frequency. To analyze this innovative contact mechanism, particle velocity synthesis theory and contact force analysis using Hertz contact model are carried out. Finally, a prototype is fabricated and tested to verify the theoretical results. The test results show that the output performance of the motor driven by the two vibrators is significantly improved compared to the motor driven by a sole stator or rotor, which confirms the validity of the double-vibrator motor concept.