Static Contact Force Research Articles

Study on calculation method for dynamic load distribution of thread pair of planetary roller screw mechanism

To reveal the dynamic load distribution characteristics of planetary roller screw mechanism under the high-speed operating conditions, based on the spiral surface equation and deformation coordination relationship, a static contact force calculation method of the roller-screw and roller-nut thread at the contact point is proposed, and a formula for calculating the contact angle after bearing is derived. On this basis, further considering the inertial force generated by using high-speed operation, a dynamic load distribution model for planetary roller screw mechanism thread was established. By comparing with the finite element contact model of planetary roller screw mechansim, the error is below 5%, which verifies the correctness of the model established. Finally, the influence of the parameters such as screw speed, axial load, pitch, and tooth flank angle on the distribution of dynamic load was analyzed. The results show that the inertia force causes the roller to have a tendency to move closer to the nut and away from the screw resulting in a decrease in dynamic contact force on the roller screw side and an increase in dynamic contact force on the roller nut side. The degree of uneven distribution of dynamic load is positively correlated with the screw speed and pitch, and negatively correlated with the tooth side angle. The size of axial load has a significant impact on the distribution of dynamic load.

Development of a Contact Force Model Suited for Spherical Contact Event

The stiffness coefficient suited for a spherical contact body is developed by means of a contact semi-angle based on Steuermann’s theory. The new static contact force model is close to the results of FEM when the index of the polynomial is equal to 2. The strain energy is derived according to the contact stiffness coefficient. Taylor expansion is used in the dissipated energy integration process to obtain a more accurate hysteresis damping factor. The new dynamic contact force model consists of the new stiffness coefficient and new hysteresis damping factor, which is suitable for the spherical-contact event with a high coefficient of restitution.

Design and Calibration of a Tri-Directional Contact Force Measurement System

In low pressure turbine stages, adjacent blades are coupled to each other at their tip by covers, called shrouds. Three-dimensional periodic contact forces at shrouds strongly affect the blade vibration level as energy is dissipated by friction. To validate contact models developed for the prediction of nonlinear forced response of shrouded blades, direct contact force measurement during dynamic tests is mandatory. In case of shrouded blades, the existing unidirectional and bi-directional contact force measurement methods need to be improved and extended to a tri-directional measurement of shroud contact forces for a comprehensive and more reliable validation of the shroud contact models. This demands an accurate and robust measurement solution that is compatible with the nature and orientation of the contact forces at blade shrouds. This study presents a cost effective and adaptable tri-directional force measurement system to measure static and dynamic contact forces simultaneously in three directions at blade shrouds during forced response tests. The system is based on three orthogonal force transducers connected to a reference block that will eventually be put in contact with the blade shroud in the test rig. A calibration process is outlined to define a decoupling matrix and its subsequent validation is demonstrated in order to evaluate the effectiveness of the measurement system to measure the actual contact forces acting on the contact.

Experimental investigation of cold adhesion failure physical mechanism of gold plated contact within the Micro-Electromechanical-Relay

Gold plated contacts are widely used in the Micro-Electromechanical-Relay to improve electric contact reliability. However, the cold adhesion phenomenon between gold plated surfaces is prone to cause normally closed contacts operating failure. In this paper, a novel test rig for measuring dynamic force and contact resistance between spring contact and rod shape contact during breaking process is introduced. The dynamic contact force, displacement and contact resistance during contact breaking process are obtained. From these waveforms, the adhesion force between two contacts in each break is estimated. In order to reveal the failure phenomena occurred in the mechanical vibration screening tests, fretting between the closed contact pairs is generated with different amplitudes and cycles by using the motorized stage. Subsequently, the effects of fretting behaviors on cold adhesion of gold plated contact pairs are investigated explicitly. Next, the associated failure physical model is built with the help of mechanical adhesion theory to explain the nature of surface adhesion. Furthermore, surface quality of gold coating and static contact force are also verified as the key factors influencing the adhesion phenomena. Surface morphologies of contacts prove the substantial increase of adhesion force correlates closely with the features of micro asperities.

Design, analysis and experiment of a passively adaptive underactuated robotic hand with linkage-slider and rack-pinion mechanisms

This paper presents the design, analysis and experiment of a passively adaptive five-fingered underactuated dexterous hand (UADH).The UADH has the ability to powerfully grasp objects with different shapes and sizes by using linkage-slider and rack-pinion mechanisms. First, a description of the mechanical design of the UADH, including the transmission scheme, finger and thumb mechanisms, and the overall configuration, is presented in detail. Subsequently, the kinematics and statics of the designed UADH during fingertip grasping and adaptive grasping are described. This paper details the modeling of the contact force of each phalanx, followed by several numerical calculations to reveal the effect of the contact position and bending angle on the contact force. Finally, an experimental platform is established, and several experiments are carried out on the UADH prototype. The results demonstrate that the developed UADH has good dexterity, adaptability and strong fingertip grasping ability, and the results also validate the static contact force model.

An obstacle separation method for robotic picking of fruits in clusters

Selectively picking a target fruit surrounded by obstacles is one of the major challenges for fruit harvesting robots. Different from traditional obstacle avoidance methods, this paper presents an active obstacle separation strategy that combines push and drag motions based on 3D visual perception to separate obstacles from the target. We define a region of interest 3D point cloud with a number of sub-blocks around the target to determine the presence or absence of obstacles and generate the separation paths accordingly. A linear push is used to clear the obstacles from the area below the target, while a zig-zag push that contains several linear motions is proposed to push aside more dense obstacles. The zig-zag push can generate multi-directional pushes and the side-to-side motion can break the static contact force between the target and obstacles, thus helping the gripper to receive a target in more complex situations. Moreover, we propose a novel drag operation to address the issue of mis-capturing obstacles located above the target, in which the gripper drags the target to a place with fewer obstacles and then pushes back to move the obstacles aside for further detachment. Furthermore, an image processing pipeline consisting of color thresholding, object detection using deep learning and point cloud operation, is developed to implement the proposed method on a newly developed harvesting robot. Field tests show that the proposed method can improve the picking performance substantially. This method helps to enable complex clusters of fruits to be harvested with a higher success rate than conventional methods.

Simultaneous Kinematic and Contact Force Modeling of a Human Finger Tendon System Using Bond Graphs and Robotic Validation.

This paper aims to use bond graph modeling to create the most comprehensive finger tendon model and simulation to date. Current models are limited to either free motion without external contact or fixed finger force transmission between tendons and fingertip. The forward dynamics model, presented in this work, simultaneously simulates the kinematics of tendon-finger motion and contact forces of a central finger given finger tendon inputs. The model equations derived from bond graphs are accompanied by nonlinear relationships modeling the anatomical complexities of moment arms, tendon slacking, and joint range of motion (ROM). The structure of the model is validated using a robotic testbed, Utah's Anatomically correct Robotic Testbed (UART) finger. Experimental motion of the UART finger during free motion (no external contact) and surface contact are simulated using the bond graph model. The contact forces during the surface contact experiments are also simulated. On average, the model was able to predict the steady-state pose of the finger with joint angle errors less than 6 deg across both free motion and surface contact experiments. The static contact forces were accurately predicted with an average of 11.5% force magnitude error and average direction error of 12 deg.

Optimum Coupling of an Active Middle Ear Actuator: Effect of Loading Forces on Actuator Output and Conductive Losses.

Introduction:The desired outcome of the implantation of active middle ear implants is maximum coupling efficiency and a minimum of conductive loss. It has not been investigated yet, which loading forces are applied during the process of coupling, which forces lead to an optimum actuator performance and which forces occur when manufacturer guidelines for coupling are followed.Methods:Actuator output was measured by laser Doppler vibrometry of stapes motion while the actuator was advanced in 20 μm steps against the incus body while monitoring static contact force. The occurrence of conductive losses was investigated by measuring changes in stapes motion in response to acoustic stimulation for each step of actuator displacement. Additionally, the electrical impedance of the actuator was measured over the whole frequency range at each actuator position.Results:Highest coupling efficiency was achieved at forces above 10 mN. Below 1 mN no efficient coupling could be achieved. At 30 mN loading force, which is typical when coupling according to manufacturer guidelines, conductive losses of more than 5 dB were observed in one out of nine TBs. The electrical impedance of the actuator showed a prominent resonance peak which vanished after coupling.Conclusion:A minimum coupling force of 10 mN is required for efficient coupling of the actuator to the incus. In most cases, coupling forces up to 100 mN will not result in clinically relevant conductive losses. The electrical impedance is a simple and reliable metric to indicate contact.

Effect of Electrical Load on Contact Welding Failure of Silver Tin Oxide Material Used in DC Electromechanical Relays

In order to clarify the contact welding failure mechanism of DC electromagnetic relay, a series of electrical endurance tests are carried out with the use of silver tin oxide material under resistive and capacitive load conditions. The typical waveforms of contact voltage and contact current during making and breaking resistive load and capacitive load (load capacitance of 1mF, 1.5mF, 2mF and 2.5mF) are obtained by the designed model switch. Further, the variations of sensitive electrical parameters such as bounce energy, contact resistance, static contact force and break arc energy during electrical endurance test are analyzed explicitly. It is found that the variations in sensitive electrical parameters is closely related to the electrical load type. In particular, under the capacitive load conditions, the sharp increase of each sensitive electrical parameter in the end of lifetime prognosticates the dynamic welding failure of silver tin oxide contact material. Finally, with the help of SEM (Scanning Electron Microscope) pictures of failed contacts, the surface erosion features of contact materials are mainly determined by the competition between the cathode arc and the anode arc. And the material transfer and distribution are the root reason for the contact welding failure of DC electromechanical relays.

Self-adaptive grasp process and equilibrium configuration analysis of a 3-DOF UACT robotic finger

Self-adaptation is a typical and widespread characteristic in underactuated finger grasp. This paper presents the self-adaptive grasp process and equilibrium configuration of a 3-DOF underactuated finger comprising cable-truss units, which uses a tendon-pulley transmission and parallel four-linkage mechanism to realise grasps. The structure and the self-adaptation at the grasp closing stage are illustrated. On the basis of a situation where one or two phalanges are in contact with the object, fixed-point grasp models and the joint workspaces are discussed, respectively. The corresponding workspace that is formed when the distal phalange contacts the object at a fixed point is assessed through numerical analysis. The expression of general static contact force is established by using the virtual work principle, and expressions reveal that the phalanges’ static statuses are obtained. According to the middle phalange contacting or not contacting with the object, the distributions of every phalange condition are assessed, and the self-adaptive grasp process in complex distribution regions and four equilibrium grasp configurations are analysed from two grasp situations. Valid and adequate self-adaptive grasp experiments are conducted to verify the accuracy of the self-adaptive grasping analysis.

HVSRMS localization formula and localization law: Localization diagnosis of a ball bearing outer ring fault

Abstract The angle position of the outer ring fault has a significant influence on the residual life and the operation performance of ball bearing. Therefore, the realization of the localization diagnosis of the outer ring fault is of great importance to the bearing performance degradation assessment and the life prediction. In this paper, a novel localization diagnosis method, named horizontal–vertical synchronized root mean square (HVSRMS) localization law and localization formula, is developed to diagnose the angle position of outer ring fault accurately. Firstly, based on the established nonlinear contact model of the bearing system, the detailed change law of static contact force when the angle position of the outer ring fault is on both sides of 270° is studied, which lays a theoretical foundation for the discovery of localization law. Subsequently, the vibration acceleration signal and dynamic contact force of the outer ring fault are synchronously analyzed through theoretical research, and the new feature for localization diagnosis is presented as: the prime impact direction of horizontal vibration acceleration (IPDoHVA). Therefore, the outer ring fault localization law of ball bearing is proposed. On this basis, the HVSRMS localization formula is improved by combining it with the localization law. Thus the one-to-one mapping relationship between HVSRMS and outer ring fault angle position is determined. Finally, experiments are carried out to validate the accuracy and feasibility of the proposed localization law and localization formula. The research results provide a new approach and method for localization diagnosis and the residual life prediction of a defective bearing.

Study on Switching Characteristics and Associated Degradation Mechanism of Contact Material Under Capacitive Load

Electrical lifetime and relative dynamic welding failure mechanisms of an electromechanical relay for a capacitive load are interesting topics in the area of switching devices and contact materials. In this paper, a silver tin oxide contact material has been tested with a capacitive load by using our designed novel model switch. The typical waveforms of contact current and contact voltage at making and breaking are presented. Furthermore, the variations in bounce energy, static contact force, dynamic contact force, arc energy, and contact resistance as a function of operation cycles are plotted and analyzed explicitly. In particular, the intermittent long-duration arcing phenomena during breaking are observed and explained with the variations in local contact asperities. Based on the collected sensitive parameters, an associated physical degradation mechanism of contact materials under the capacitive load is proposed.

Combined Airfoil and Snubber Design Optimization of Turbine Blades With Respect to Friction Damping

A major concern for new generations of large turbine blades is forced and self-excited (flutter) vibrations, which can cause high-cycle fatigue (HCF). The design of friction joints is a commonly applied strategy for systematic reduction of resonance amplitudes at critical operational conditions. In this paper, the influence of geometric blade design parameters onto the damped system response is investigated for direct snubber coupling. A simplified turbine blade geometry is parametrized and a well-proven reduced-order model for turbine blade dynamics under friction damping is integrated into a 3D finite element tool-chain. The developed process is then used in combination with surrogate modeling to predict the effect of geometric design parameters onto the vibrational characteristics. As such, main and interaction effects of design variables onto static normal contact force and resonance amplitudes are determined for a critical first bending mode. Parameters were found to influence the static normal contact force based on their effect on elasticity of the snubber, torsional stiffness of the airfoil and free blade untwist. The results lead to the conclusion that geometric design parameters mainly affect the resonance amplitude equivalent to their influence on static normal contact force in the friction joint. However, it is demonstrated that geometric airfoil parameters influence blade stiffness and are significantly changing the respective mode shapes, which can lead to lower resonance amplitudes despite an increase in static contact loads. Finally, an evolutionary optimization is carried out and novel design guidelines for snubbered blades with friction damping are formulated.

ロボットマニピュレーションにおける接触力の剛体モデルに基づく解析について

This paper discusses points of issue on static analysis of indeterminate contact forces raised by Omata. In summary, 1) Rigid-body-based analysis of static contact forces may have an advantage over elastic-contact-based analysis, which is physically more accurate, from an engineering viewpoint. 2) The elastic-contact-based method for contact force analysis by Rimon et al. is applicable only when preload contact forces are known and therefore it cannot always substitute for the conventional rigid-body model with Coulomb friction. 3) Virtual slidings and their combinations used in rigid-body-based analysis by the authors correspond to actual physical phenomena of contact forces.

The Contact Resistance Performance of Gold Coated Carbon-Nanotube Surfaces under Low Current Switching

Multi-Walled CNT (MWCNT) are synthesized on a silicon wafer and sputter coated with a gold film. The planar surfaces are mounted on the tip of a piezo-electric actuator and mated with a gold coated hemispherical surface to form an electrical contact. These switching contacts are tested under conditions typical of MEMS relay applications; 4V, with a static contact force of 1mN, at a low current between 20-50mA. The failure of the switch is identified by the evolution of contact resistance which is monitored throughout the switching cycles. The results show that the contact resistance can be stable for up to 120 million switching cycles, which are 106 orders of higher than state-of-the-art pure gold contact. Bouncing behavior was also observed in each switching cycle. The failing mechanism was also studied in relation to the contact surface changes. It was observed that the contact surfaces undergo a transfer process over the switching life time, ultimately leading to switching failure the number of bounces is also related to the fine transfer failure mechanism.

The Establishment and Numerical Calculation of Thin Film Lubrication Model

Thin film lubrication (TFL) and elasto-hydrodynamic lubrication (EHL) are different lubrication states, their lubrication mechanisms are different, but the transition from EHL to TFL is a continuous process at the aspect of film thickness change, it is important to establish a physical-numerical model that can be suited for both EHL and TFL. Based on rheological, the change of micro thickness is expressed by the change of viscosity, then the micro problem of TFL can be turn to macro problem. The adsorption layer is divided into two parts formatted by static contact and shear force in the calculation. In a given static adsorption film, other oil film parts will be comprehensive consideration, modified formula of the overall average equivalent viscosity is gained by the method of combining numerical calculation and experiment, then numerical model is established for both EHL and TFL. TFL and EHL typical characteristics and the effectiveness of the model can be obviously shown by the results.

The Separate Neural Control of Hand Movements and Contact Forces

To manipulate an object, we must simultaneously control the contact forces exerted on the object and the movements of our hand. Two alternative views for manipulation have been proposed: one in which motions and contact forces are represented and controlled by separate neural processes, and one in which motions and forces are controlled jointly, by a single process. To evaluate these alternatives, we designed three tasks in which subjects maintained a specified contact force while their hand was moved by a robotic manipulandum. The prescribed contact force and hand motions were selected in each task to induce the subject to attain one of three goals: (1) exerting a regulated contact force, (2) tracking the motion of the manipulandum, and (3) attaining both force and motion goals concurrently. By comparing subjects' performances in these three tasks, we found that behavior was captured by the summed actions of two independent control systems: one applying the desired force, and the other guiding the hand along the predicted path of the manipulandum. Furthermore, the application of transcranial magnetic stimulation impulses to the posterior parietal cortex selectively disrupted the control of motion but did not affect the regulation of static contact force. Together, these findings are consistent with the view that manipulation of objects is performed by independent brain control of hand motions and interaction forces.

The application of scanning probe microscopy in materials science studies

The family of techniques known as scanning probe microscopy (SPM) was invented in 1981 by Binnig and Rohrer. The most common methods are scanning-tunneling microscopy, atomic-force microscopy (AFM), and near-fi eld scanning optical microscopy, although hundreds of other variants have since been developed. Regardless of the specifi c version, each applies the same basic concept: detecting interactions between a scannable nanoscale probe and a nearby surface in order to measure and/or map local surface properties. Atomic-force microscopy was designed for detecting and mapping tipsample forces. These include repulsive and attractive interactions such as van der Waals, electronic, and magnetic forces, though applications to detect chemical, thermal, acoustic, and a host of other properties have since been implemented. The concept also extends to lithography, whereby the probe is used to modify a surface through physical, electronic, chemical, or thermal means. The probe itself in AFM is generally a microfabricated tip at the end of an integrated cantilever. Static or intermittent contact forces between the tip apex and a surface are measured as corresponding shifts in the lever defl ection or the resonant frequency, respectively. Although the lever motion is generally nanoscale, it is nearly always amplifi ed by refl ecting focused light off of the lever The Application of Scanning Probe Microscopy in Materials Science Studies

Influence of hand forces and handle size on power absorption of the human hand–arm exposed to zh-axis vibration

The effect of handle size and hand forces, on the power absorbed by the hand–arm system, was investigated in a laboratory study using seven healthy male subjects exposed to two levels of broadband random vibration in the 8–1000 Hz frequency range along the z h-axis. The measurements were performed with three instrumented cylindrical handles of different diameter (30, 40 and 50 mm). The influence of hand forces applied by the subjects holding the vibrating handles was investigated under nine different grip/push force combinations. The posture adopted by the subjects consisted of the bent forearm with elbow angle of 90° and neutral wrist position, as described in the ISO 10819 standard. The pressure distribution at the hand–handle interface was also measured to quantify the static contact force corresponding to each combination of grip force, push force and handle size. The hand–handle coupling force, as defined in ISO/WD 15230, was further evaluated by summing the grip and push forces. The measured total absorbed power revealed relatively low inter-subject variability (generally less than 12%). Total absorbed power was found to be better correlated with coupling force than the contact force, while most of the absorbed power occurred in the low-frequency range, below 200 Hz. The magnitude of power absorbed within the hand and arm was observed to be strongly dependent upon the handle size; larger handles cause higher absorption of energy. The results also suggested that the power absorption is influenced by the grip as well as push force. The results attained from ANOVA confirmed the significance of all studied factors, i.e. vibration magnitude, handle diameter, and the grip and push forces on the power absorbed into the human hand and arm exposed to vibration.

On entropy estimates of contact forces in static granular assemblies

As an extension of previous work by others, this articles deals with maximum-entropy estimates for the statistics of static contact forces in assemblies of nearly rigid grains. As found in the previous works, the constraint of mean stress leads provisionally to a distribution of contact force that is exponential at large force. This behavior, found in various experiments and numerical simulations, does not depend on special models of force propagation postulated in the contemporary physics literature. Following K. Bagi [Behringer, R. Jenkins, J.T. (Eds.), Powders and Grains, Balkema, 1997, p. 251] consideration is also given to entropy maximization under the constraint of constant mean strain, which leads to a similar exponential tail in the distribution of particle displacements. In contrast to the previous works, it is emphasized that the exact form of the probability density depends on the statistical weight (a priori probability) assigned to elementary volumes in the state-space of contact forces or displacements. This leads to the conclusion that the large-force exponential is a general representation of maximum-entropy statistics arising from global constraints, whereas the state-space measure is dictated by local mechanics. A few examples of state-space measure are considered, and the resulting distributions are compared to previous experiment and simulation. A striking analogy is revealed between the force distribution in a static sphere assembly and the Maxwell–Boltzmann velocity distribution for gases. Based on the methods of statistical thermodynamics, a virtual-thermodynamic formalism is presented for complementary strain energies in granular statics. This involves no direct appeal to the concept of (static) granular temperature favored in certain statistical-physics literature. As a possible test of the general validity of the entropy principle in granular statics, the question is raised as to whether it can describe the heterogeneous two-phase structure found in photoelastic experiments and numerical simulations of granular assemblies.