Determination Of Contact Forces Research Articles

The study of rolling stock wheels impact on rail switch frogs

Studies of stress distribution across cross sections by polarization-optical method made it possible to propose a relatively simple experimental method of determining contact forces. Experimental determination of contact forces on crossbars of switches is possible by means of sensors located in places of stress concentration (at core base). Analysis of oscillations during impact-pulse loading makes it possible to determine design parameters of the path. Typically, single circuits with four to five degrees of freedom produce quite satisfactory results and may be recommended for the calculated determination of contact forces on the crossbars of the switches.

Determination of contact force by compression testing of cylindrical specimens

This paper presents a method for determining values of dynamic parameters of the Hunt and Crossley model in order to estimate the amount of force generated at the point of contact (contact force) in an impact. A two-degree-of-freedom lumped-mass-system based on a non-linear visco-elastic model as proposed by Hunt and Crossley has been widely used to accurately model contact force. The primary difficulty associated with the Hunt and Crossley contact force model is the need to determine the unknown dynamic parameters of the model, which can be obtained by calibrating the model against results from high-speed impact experiments. Spherical impactors have to be placed in the gas-gun barrel for accelerating onto the target specimen. An innovative and inexpensive method proposed in this paper describes the use of compression testing on a test rig employing cylindrical specimens of colliding bodies to obtain the dynamic parameters thereby waiving away the need of costly and time-consuming impact experiments.

Numerical Determination of Contact Forces in Radial Roller Bearings with Flexible Rings

Four different approaches have been proposed to account for flexibility of the bearing rings and the neighboring parts of the shaft and the housing in computing the radial contact forces acting onto the rolling elements. A numerical example is presented to demonstrate efficacy and performance of the developed models. Their applicability is estimated for various conditions.

Micro-Vibration-Based Slip Detection in Tactile Force Sensors

Tactile sensing provides critical information, such as force, texture, shape or temperature, in manipulation tasks. In particular, tactile sensors traditionally used in robotics are emphasized in contact force determination for grasping control and object recognition. Nevertheless, slip detection is also crucial to successfully manipulate an object. Several approaches have appeared to detect slipping, the majority being a combination of complex sensors with complex algorithms. In this paper, we deal with simplicity, analyzing how a novel, but simple, algorithm, based on micro-vibration detection, can be used in a simple, but low-cost and durable, force sensor. We also analyze the results of using the same principle to detect slipping in other force sensors based on flexible parts. In particular, we show and compare the slip detection with: (i) a flexible finger, designed by the authors, acting as a force sensor; (ii) the finger torque sensor of a commercial robotic hand; (iii) a commercial six-axis force sensor mounted on the wrist of a robot; and (iv) a fingertip piezoresistive matrix sensor.

Simulation of Interaction of a Pipe Conveyor Belt with Moulding Rolls

Abstract Interaction of a pipe conveyor belt with moulding rolls is a very interesting problem for producers and also for users of pipe conveyors. There are created high resistances and deformations in this part of pipe conveyor. The determination of contact forces is difficult. The paper deals with problem of computation of contact forces generated by action of a conveyor belt on moulding rolls. Analysed is moulding part of the belt during ifs transformation from flat to tubular form. Analyses were performed by means of the Finite Element Method.

Measurement of the mechanical properties of granular packs by wavelength-scanning interferometry

A wavelength-scanning interferometer has been constructed to observe both the normal and in-plane displacements particle by particle at the base of a model granular pack. The pack comprised 25 000 steel beads supported by a thick glass substrate and was subjected to local disturbing forces on its upper surface. The system allows measurement of normal displacements of the beads to a precision of ca 0.1 nm, thereby providing highly accurate determination of contact forces while minimizing artefacts due to substrate and grain compliance. The probability distribution of the normalized contact force was found to be approximately independent of the applied load on the upper surface of the granular pack and has an exponential tail. The probability distributions of the normalized response force and lateral displacement have similar power-law tails. The interactions between contact forces and lateral displacements suggest that significant internal rearrangement occurs in the granular pack as the load is increased, and particle displacement plays an important role in the mechanics of the granular material.

Energetically consistent simulation of simultaneous impacts and contacts in multibody systems with friction

This paper presents a methodology for treating energy consistency when considering simultaneous impacts and contacts with friction in the simulation of systems of interconnected bodies. Hard impact and contact is considered where deformation of the impacting surfaces is negligible. The proposed approach uses a discrete algebraic model of impact in conjunction with moment and tangential coefficients of restitution (CORs) to develop a general impact law for determining post-impact velocities. This process depends on impulse–momentum theory, the complementarity conditions, a principle of maximum dissipation, and the determination of contact forces and post-impact accelerations. The proposed methodology also uses an energy-modifying COR to directly control the system’s energy profile over time. The key result is that different energy profiles yield different results and thus energy consistency should be considered carefully in the development of dynamic simulations. The approach is illustrated on a double pendulum, considered to be a benchmark case, and a bicycle structure.

Experimental and Analytical Studies of the Connector Insertion Phase

Studies of connectors for electric and electronic automotive systems have been and still are being pursued. The electrical connector reliability mainly depends on the connector insertion force. This force is related to the contact force which is imposed by the connector design. A nonintrusive technique for contact force determination by deflection measurement of the contact spring during insertion phase using a laser device has been developed. The following insertion parameters during the insertion stroke can be measured: contact deflection which yields the contact force, insertion force, and contact resistance. Regarding the results for real connectors, an experimental sample of a connector based on a cylindrical pin crossed with a cylindrical spring is proposed in this paper. With this simple setup, an mathematical model was developed and permits analysis of the influence of each parameter (width, spring radius, etc). Based on analysis of the influence of the spring width and of the gap, this study offers the possibility of optimizing the design of such connectors for use in the automotive industry.

An Algorithm for Compliant Contact Between Complexly Shaped Bodies

A new contact algorithm designed for multibody dynamics is presented. It is based on representation of the body surfaces by polygon meshes and contact force determination by the elastic foundation model. Areal discretisations of the contact patches are constructed using methods closely related to computer graphics, e.g. collision detection based on bounding volume hierarchies and generation of subdivision surfaces by means of boundary representation data structures. Two examples prove the robustness of the method for complexly shaped bodies causing multiple and multiply bordered contact patches and conforming contacts.

NUMERICAL INVESTIGATION OF A ROTOR SYSTEM WITH DISC-HOUSING IMPACT

This paper presents a computer modelling investigation of the dynamic behaviour of rotors supported by hydrodynamic bearings. The rotor is discretized into finite elements. The fluid-film bearings are represented by non-linear forces that are linearized in the neighbourhood of the static equilibrium position. Particular emphasis is given to the modelling of impacts between rotor discs and their casings, for which two approaches are used, namely (i) Newton's impact theory and (ii) direct determination of contact forces using a contact stiffness. In the first approach, the discs are assumed to be connected to the shaft by spring elements. The discs and the stationary part are considered to be absolutely rigid. Velocity components of the discs after the impact are calculated using the law of conservation of the momentum and moment of momentum. Dissipation of mechanical energy during impact is taken into account through the coefficient of restitution. In the second approach local flexibility and damping in the contact area are assumed. Local deformation produces impact forces and moments acting on the shaft at the disc location. In both cases, Coulomb friction is assumed to act in the contact area. A modified form of the Newmark method was applied to solve the resulting non-linear equations of motion. Both approaches make it possible to characterize the steady state forced vibration behaviour (periodic, quasi-periodic, chaotic). In addition, the second approach provides further information on the likely magnitude and time history of the impact forces, duration of impacts, etc. The two approaches are illustrated by examples involving imbalance excitation and kinematic excitation of the baseplate.

The influence of the radial basis function training strategy on the performance of a neural gripper

In this article, a neural network-based grasping system that is able to collect objects of arbitrary shape is introduced. The grasping process is split into three functional blocks: image acquisition and processing, contact point estimation, and contact force determination. The paper focuses on the second block, which contains two neural networks. A competitive Hopfield neural network first determines an approximate polygon for an object outline. These polygon edges are the input for a supervised neural network model [radial basis function (RBF) or multilayer perceptions], which then defines the contact points. Tests were conducted with objects of different shapes, and experimental results suggest that the performance of the neural gripper and its learning rate are significantly influenced by the choice of supervised training model and RBF learning algorithm.

Prediction of Impact Contact Forces of Composite Plates Using Fiber Optic Sensors and Neural Networks

Real-time determination of contact forces due to impact on composite plates is necessary for on-line impact damage detection and identification. We demonstrate the use of fiber optic strain sensor data as inputs to a neural network to obtain contact force history. An experimental and theoretical study is conducted to determine the in-plane strains of a clamped graphite/epoxy composite plate upon low-velocity impacts using surface-mounted extrinsic Fabry-Perot interferometric (EFPI) strain sensors. The plate is impacted with a semispherical impactor with various impact energies using the drop-weight technique. The significant features of the strain and contact force response are contact duration, peak strain, and strain rise time. We have designed and built an instrumented drop-weight impact tower to facilitate the measurement of contact force during an impact event. The impact head assembly incorporates a load cell to measure the contact forces experimentally. An in-house finite-element program is used to establish the validity of the EFPI fiber optic sensor contact force response. The finite-element model is based on a higher-order shear deformation theory and accounts for geometric nonlinearity. Experimental load cell data and finite-element impact-induced contact force responses are in close agreement. The load cell data is used to train a three-layer feed-forward neural network which utilizes the Delta Bar Delta back-propagation algorithm. The output of the neural network simulation is the contact force history and the inputs are fiber optic sensor data in two different locations and time in 10-ms intervals. The efficiency and accuracy of the neural network method is discussed. The neural network scheme recovers the impact contact forces without using any complex signal processing techniques.

Determination of Contact Forces for Two Manipulators Mutually Lifting a Rigid Object using a Technique of Dynamic Load Distribution

Determination of Contact Forces for Two Manipulators Mutually Lifting a Rigid Object using a Technique of Dynamic Load Distribution

Measuring equipment and measurements of adhesive force between gold electrical contacts

This paper describes the apparatus to measure adhesive force between electrical contacts with micro-sliding and the measurements of adhesive force between gold electrical contacts by this measuring equipment. The electrical contact that is concerned in this paper is mounted on a cantilever supporting arm in a small electromagnetic relay. A straight back-and-forth sliding motion occurs on closed contacts when a relay suffers from an externally applied shock, or on contact follow of closing contact operation. Therefore, this apparatus is designed to give a straight back-and-forth sliding motion to closed electrical contacts. We investigated the measuring accuracy of this apparatus and measured the adhesive force between gold electrical contacts. The following results have been confirmed. (1) The error in determination of contact force from 19.6/spl times/10/sup -3/ N to 1.47 N is less than 1%. (2) The error in measurement of adhesive force from 9.8/spl times/10/sup -3/ N to 1.47 N is less than 1%. (3) At gold contacts under conditions of contact force (0.1/spl sim/0.5 N), and the number (1/spl sim/20 times) and the length (50 /spl mu/m and 100 /spl mu/m) of straight back-and-forth sliding motion, the adhesive force measured by this apparatus has been illustrated to be influenced by the contact force, and the number and the length of sliding motion.

Determination of Contact Forces for Two Manipulators Mutually Lifting a Rigid Object Using A Technique of Dynamic Load Distribution

ABSTRACTThis article presents a new technique and approach for dynamically distributing the payload when two serial link manipulators mutually hold and transport a rigid object. A new vector variable which parameterizes the internal stress contact force and torque degrees of freedom (DOF) is introduced and defined as a linear function of the contact forces.” When this equation is combined with the object's dynamical equations, the resulting system yields a well specified solution for the contact forces as a function of the internal stress DOF parameterizing variable. The article investigates two different approaches to selecting the matrix which transforms the contact forces to obtain the internal force parameterizing variable. In one approach the matrix is selected to be orthogonal to the transformation matrix in the object's dynamical equations and in the other it is a function of two constrained scalar parameters which govern the distribution of the payload between the object motion inducing components...