Multipoint Contact Research Articles

A novelty mandrel supported thin-wall tube bending cross-section quality analysis: a diameter-adjustable multi-point contact mandrel

The mandrel plays a vital role in metal tube bending limit improvement and high-quality achievement. For the bending forming process of metal tubes with different diameters, the corresponding mandrel needs to be customized, which has the disadvantages of a long design cycle, high manufacturing cost, and low reuse rate. Therefore, a novelty concept of diameter adjustable mandrel (DAM) based on the multi-point contact was proposed to adapt different diameter tube bending processes. Since the point-contact characteristics of the DAM can lead to irregular cross-section deformation, the cross-sectional full profile radial error (FP-RE) model was proposed. As a more comprehensive evaluation model, the FP-RE model is used to measure the deformation degree of the whole bending cross-section. A diameter-adjustable DAM was adopted in the AISI 304L tubes (the inner diameter = 40–56 mm) bending experiments. The maximum absolute error of FP-RE was 0.11% compared with the ones obtained from FEA in Abaqus/explicit. In addition, the effects of the DAM characteristic parameters, viz., the support blocks amount, the effective magnification, and the effective support diameter, on the tube forming quality were discussed. The results indicated that (a) an even number of support blocks could prevent the collapse of the outer convex tube wall and improve the quality of the inner concave tube wall. (b) When the DAM was used in the larger inner diameter tube bending, the larger non-contact area would cause an increase in the roundness section distortion. (c) A larger DAM diameter would lead to a more minor cross-section deformation degree for the tubes with the same diameter, while the wall thinning was just the opposite. Finally, the result also proved that the DAM (the minimum effective diameter is 40 mm with six support blocks) could be used for tubes with an inner diameter of about 40–56 mm, and the forming quality was acceptable.

Static aeroelastic instability analysis of an inverted plate in ground effect and comparison with a wind-tunnel test

This paper visits the static instability of an inverted cantilevered plate in axial flow with the ground effect. This plate model is clamped at the trailing edge, and its leading-edge is allowed to move freely. A theoretical analysis strategy and corresponding convergent numerical solutions are reported and compared with a wind-tunnel experiment. In theory, we try a new way to study such an instability problem. We derive the instability equation by operator theory in state-space formulation and model such an instability problem as a mathematical function approximation problem. Glauert’s expansion and the least square method are applied for the numerical solutions of vorticity in ground effect using the mirror image method. The unknown function of the plate slope is expanded as a series of essential polynomial functions based on the Weierstrass theorem, and the least square method is applied for its numerical solutions. The experimental study develops a multi-point contact method using a control rod to preload the tested plate with a slight static deformation close to its natural modal shape. The contact state change between the initially deformed tested plate and the control rod is reflected by the evolution of the voltage output of a designed circuit. A criterion for determining the critical condition of plate instability is established based on such voltage change, and it has a better anti-interference ability to the flow. Results show that the present theoretical analysis agrees well with the experiment and other archived theories. The critical plate slopes (i.e., the plate instability modes) are not dependent on the ground confinement. This conclusion allows us to establish an analytical approximation between the critical dynamic pressure and the ground confinement. The present study and results can successfully predict the plate instability in the ground effect.

A Multi-Point Contact Model Considering Rough Surface for Linear Ultrasonic Motors: Validation and Simulation.

The performance and wear life of linear ultrasonic motors are directly determined by the stator-mover frictional contact behaviors. A complete contact model is important to clearly understand the stator-mover contact mechanism and accurately estimate the motor performance. In this paper, a multi-point frictional contact model considering the roughness of contact interfaces is presented based on a finite model of the stator and an analytical model of the mover. The static/dynamic contact behaviors and output performance of the motor can be simulated efficiently. A quantitative measuring methodology for the dynamic contact forces between the stator and mover is developed. The effectiveness of the contact model for simulating the stator-mover contact forces is first evaluated by experiment. Based on the developed model, several dynamic characteristics of a linear ultrasonic motor are discussed: (a) the static force transferred between contact interfaces under pre-pressure; (b) the transient forces and energy exchange between contact interfaces; (c) the steady-state output performance of motor under different electric excitation parameters; (d) the effects of micro-topography parameters on the output performance of the motor and the force transmission of the contact interface.

Whole-Body Compliant Control of Robot Arms Based on Distributed Flexible Tactile Electronic Skin

Robots are now working outside of industrial fences more and more closely with humans. Safety is the primary requirement for intimate human–robot interactions. Contacts could happen at any and multipoints of robot. Tactile sensors have great potentials for contact sensing. However, their implementation for the whole-body compliance of robots upon unknown contacts is still challenging. In this work, a systematic solution is proposed. A dual-arm humanoid platform is constructed with distributed tactile sensors on its arms and body. Cheap and easy accessed resistive flexible tactile sensors are used. A data collection and signal processing system is developed for the sensing system with scalable capabilities. External contacts on the robot can be monitored by a visualized system. The multipoint contact force is calculated with the sensor positions taken into consideration. A PD controller-based compliant force control algorithm is proposed in the joint space of the robot. Particularly, a geometry-based force propagation method is introduced in order to achieve overall whole-body compliance of the robot. Experiments verified the whole-body compliance of the robot arms. Safety could then be maintained for frequent human–robot interactions.

See You in Your Backyard: Multipoint Contact, Firm’s Capacity and Capability, and Technological Expansion

Past studies of multipoint competition have mainly focused on the effect of multipoint contact in product markets on firm competitive behaviors in those markets only. Our study advances this literature by examining how multipoint contact in product markets affects a firm’s expansion into a rival’s technological areas. We further investigate the factors that moderate the proposed effect. Our analyses suggest that the degree of multipoint contact between a firm and a rival in product markets has an inverted U-shaped relationship with the degree of the firm’s expansion into the rival’s technological areas (patent classes). Furthermore, the firm’s capacity (market share) and capability (status in terms of technological development) relative to the rival’s have different moderating effects on the relationship between multipoint contact in product markets and the firm’s expansion into the rival’s technological areas. Our findings contribute to the literatures on multipoint contact, competitive dynamics, and firm technology strategies.

Sintering-Induced Failure Mechanism of Thermal Barrier Coatings and Sintering-Resistant Design

Thermal barrier coatings (TBCs) have been developed to protect superalloys against high-temperature heat fluxes, which are required for the development of high-performance gas turbines. TBCs have porous structures, which are densified by sintering. The resulting stiffening is a major cause of TBC failure in service. Therefore, there is a need to reduce the negative sintering effect on the life span of TBCs. In this study, the sintering mechanism and the dominant factors causing changes in stiffening and mechanical properties were revealed experimentally. The experimental results show that the multiscale undulation of the originally smooth two-dimensional (2D) pore inner surface triggers multipoint contact between the upper and lower inner surfaces, resulting in pore healing during thermal exposure. The healing of 2D pores is the main structural characteristic change in TBCs after thermal exposure and the main reason for the stiffening and changes in mechanical properties. Then, the sintering effect on TBCs with vertically cracked structures was designed and simulated. We found that implanting vertical cracks in the topcoat can reduce the sintering effect and driving force for cracking by 87.9% and 79.9%, respectively. The degree of reduction depends on the space between vertical cracks. Finally, the mechanism responsible for the sintering-resistant TBCs was analyzed and discussed. Vertically cracked structures exhibited scale-sensitive stiffening, indicating that macroscopic stiffening is much lower than microscopic stiffening. In other words, the macroscopic sintering effect was lowered, and the TBCs remained highly resistant to global strain during thermal exposure. The resulting strain energy release rates are much lower than those of conventional TBCs. The results of this study contribute to the long-life thermal protection of superalloy-based components used in advanced gas turbines.

Research on Tire/Road Peak Friction Coefficient Estimation Considering Effective Contact Characteristics between Tire and Three-Dimensional Road Surface

In the field of transportation, the accurate estimation of tire–road peak friction coefficient (TRPFC) is very important to improve vehicle safety performance and the efficiency of road maintenance. The existing estimation algorithms rarely consider the influence of road roughness and road texture on the estimation results. This paper proposes an estimation method of TRPFC considering the effective contact characteristics between the tire and the three-dimensional road. In the longitudinal and lateral directions of tire–road contact, the model is optimized by incorporating the effective contact area ratio coefficient into the LuGre tire model. The optimized model characterizes the road texture by road power spectrum and establishes the relationship between road texture and tire force. In the vertical direction of tire–road contact, the force transfer between tire and road is represented by a new multi-point contact method. By combining the above models with the normalization method and the unscented Kalman filter (UKF), the timely and accurate estimation of the peak friction coefficient of the tire and the 3D road is realized. Simulation and real vehicle experiments verify the effectiveness of the estimation algorithm.

‘Delayed Forbearance’: Multipoint contact and mutual forbearance in inaugural and subsequent competitive actions

One strand of theoretical development in the multimarket competition literature examines whether mutual forbearance applies uniformly to all types of competitive actions. For example, scholars have shown that mutual forbearance takes effect for exploitation, but not exploration-based actions. Extending this line of research, we study how the dominance of mutual forbearance also differs across inaugural and subsequent competitive actions. The key difference between the two lies in the identity of the initiator – inaugural actions are by firms new to the market domain, and subsequent ones are by existing incumbents. We argue that mutual forbearance has a delayed dominance for subsequent competitive actions (relative to inaugural ones), propose moderating conditions, and test our predictions using product launch decisions of automobile firms in the US between 1980 and 2015.

Discrete element simulation of particles defined by cardioids

Discrete element method with different shapes has attracted considerable research attentions because particle shapes affect dynamic properties of the system. Although convex particles have been extensively investigated, studies on concave particles are limited. Cardioid particles are constructed in this study using parametric equation. Multi-point contact detection algorithm and calculation methods of geometric parameters, such as normal vector, curvature, and overlapping at the contact point, are provided. Two-dimensional (2D) and three-dimensional (3D) systems are simulated by using the discrete element method. Convergence of energy in falling process under gravity verifies the stability and correctness of the algorithm. On this basis, shear curves of simple shear tests with different shapes are calculated and propagation processes of elastic waves in uniaxial compression systems with periodic boundary conditions are simulated. Results showed that the particle shape affects not only shear strength of the simple shear system but also elastic wave velocity in the uniaxial compression system. The particle shape will cause anisotropies of normal vector of contact force, branch vector, and contact force distributions. Influence of shape on the wave velocity is explained from the perspective of anisotropy. The proposed method in this study is universal and suitable for other shapes defined by different parametric equations and can be used to investigate dynamic properties of particle systems with various shapes.

A study on the dynamic contact feature of four-contact-point ball bearing

Four-contact-point ball bearing (FCPBB), with a special double half inner ring structure, presents dynamic multi-point contact characteristics in service. The dynamic contact feature, such as 2-point, 3-point or even 4-point contact phenomena between balls and bearing raceway, lead to completely different bearing friction, heat generation and wear rates. Considering the oil film traction effect, the traction and contact equations for ball and four raceways were proposed, and the changes of bearing dynamic contact feature with complex operating conditions, such as high speed-slight load, combined axial-radial load, were investigated. As bearing preload increases, the interaction between the ball and raceway gradually changes from 3-point to 2-point contact. In this process, the PV factor in outer sub-contact area first increases and then decreases, which is the key factor in bearing friction loss. In case of combined load, the ball may experience 2-point contact, 3-point contact and 4-point contact in one revolution. Besides, when two-point contact occurs, the main-contact area has the largest PV value; when four-point contact occurs, the sub-contact area has the largest PV value.

Tactile Super-Resolution Model for Soft Magnetic Skin

Tactile sensors of high spatial resolution can provide rich contact information in terms of accurate contact location and force magnitude for robots. However, achieving a high spatial resolution normally requires a high density of tactile sensing cells (or taxels), which will inevitably lead to crowded wire connections, more data acquisition time and probably crosstalk between taxels. An alternative approach to improve the spatial resolution without introducing a high density of taxels is employing super-resolution technology. Here, we propose a novel tactile super-resolution method based on a sinusoidally magnetized soft magnetic skin, by which we have achieved a 15-fold improvement of localization accuracy (from 6 mm to 0.4 mm) as well as the ability to measure the force magnitude. Different from the existing super-resolution methods that rely on overlapping signals of neighbouring taxels, our model only relies on the local information from a single 3-axis taxel and thereby can detect multipoint contact applied on neighboring taxels and work properly even when some of the neighbouring taxels near the contact position are damaged (or unavailable). With this property, our method would be robust to damage and could potentially benefit robotic applications that require multipoint contact detection.

A modified discrete element method for concave granular materials based on energy-conserving contact model

The development of a general discrete element method for irregularly shaped particles is the core issue of the simulation of the dynamic behavior of granular materials. The general energy-conserving contact theory is used to establish a universal discrete element method suitable for particle contact of arbitrary shape. In this study, three dimentional (3D) modeling and scanning techniques are used to obtain a triangular mesh representation of the true particles containing typical concave particles. The contact volume-based energy-conserving model is used to realize the contact detection between irregularly shaped particles, and the contact force model is refined and modified to describe the contact under real conditions. The inelastic collision processes between the particles and boundaries are simulated to verify the robustness of the modified contact force model and its applicability to the multi-point contact mode. In addition, the packing process and the flow process of a large number of irregular particles are simulated with the modified discrete element method (DEM) to illustrate the applicability of the method of complex problems.

Pick position optimization of vacuum suction gripper frame in IRB360 robot using Taguchi analysis and genetic algorithm

ABSTRACT Multi-Point Contact Vacuum Suction Grippers, coupled to an IRB 360 robot mechanical system, are commonly used for performing numerous pick and place operations on flat glass plates. The position of the suction cups over the pick-positions has a key role in defining the self-weight deformation of the flat glass plate when lifted. Now every robotic material handler produces its own inherent mechanical vibrations. In this work, a method is proposed for defining the optimal pick-positions for a flat glass plate of specific dimensions, with a view to minimise the deformation and accordingly the forced vibrations during robotic handling. The results of the above method were then used in designing a three-point vacuum gripper and perform pick and place operations. The above method involves a combination of Taguchi design of experimental techniques on finite element analysis, and genetic algorithm is used to optimise the Robot pick position. Regression analysis is used to develop the predicted model of robot pick position and ANOVA analysis is used to contribute the individual process parameter on robot pick position intervals. The developed mathematical model was further analysed with Genetic algorithm to find out the optimum conditions leading to the maximum pick position accuracy.

MODERN TECHNOLOGIES FOR FINISHING BEARING ROLLWAYS

The most promising methods for improving the quality of the surfaces of the raceways of ball bearing rings with multipoint contact are pulse hardening ultra-sonic treatment and superfinish with an inclined abrasive bar. (Research purpose) The research purpose is studying modern technologies for improving the quality of the surfaces of the raceways of ball bearing rings with multipoint contact; to carry out mathematical modeling of the process of forming a rational geometric shape of a complex raceway surface during the application of ultrasonic treatment and superfin-ish with an inclined abrasive bar. (Materials and methods) It was noted that achieving a rational geometric shape of a complex raceway surface without the use of advanced processing devices is extremely difficult. It was determined that in the case of pulsed hardening ultrasonic treatment, the initial velocity V0 is reported to the steel ball in contact with the oscillating wall of the waveguide. Upon impact with the treated sur-face, the ball penetrates into it to a certain depth ∆сж, as a result, the surface of the treated part is exposed to a short-term compressive force Fсж. It was revealed that dur-ing the superfinish process, the workpiece rotates around its axis with an inclined abrasive bar, and an abrasive bar is pressed against the surface of the rolling track of the workpiece with force P. The oscillation axis of the bar is inclined at an angle to the axis of the workpiece. (Results and discussion) It was shown that the technologies of ultrasonic processing and superfinish with an inclined abrasive bar were tested on thrust-radial rolling bearings and ball bearings with multipoint contact. (Conclusions) In the first variant, during the smoothing process, the surface layer of the raceway of the ball bearing rings is deformed, the part and the tool are heated to higher tempera-tures, which in turn leads to rapid tool wear. In the second variant, the technology of processing the complex profile of the raceway of ball bearing rings requires special control. It is necessary to improve superfinish operations in the direction of increasing their technological capabilities.

On One Generalization of the Multipoint Nonlocal Contact Problem for Elliptic Equation in Rectangular Area

Nonlocal contact problem for two‐dimensional linear elliptic equations is stated and investigated. The method of separation of variables is used to find the solution of a stated problem in the case of Poisson’s equation. Then, the more general problem with nonlocal multipoint contact conditions for elliptic equation with variable coefficients is considered, and the iterative method to solve the problem numerically is constructed and investigated. The uniqueness and existence of the regular solution are proved. The iterative method allows reducing the solution of a nonlocal contact problem to the solution of a sequence of classical boundary value problems.

Multi-point Contact Stability Prediction Considering Force-induced Deformation Effect in Milling Thin-Walled Parts

Multi-point Contact Stability Prediction Considering Force-induced Deformation Effect in Milling Thin-Walled Parts

Design of a Multi-Point Kinematic Coupling for a High Precision Telescopic Simultaneous Measurement System.

This paper covers the design of a new multi-point kinematic coupling specially developed for a high precision multi-telescopic arm measurement system for the volumetric verification of machine tools with linear and/or rotary axes. The multipoint kinematic coupling allows the simultaneous operation of the three telescopic arms that are registered at the same time to a sphere fixed on the machine tool spindle nose. Every coupling provides an accurate multi-point contact to the sphere, avoiding collisions and interferences with the other two multi-point kinematic couplings, and generating repulsion forces among them to ensure the coupling’s fingers interlacing along the machine tool x/y/z travels in the verification process. Simulation presents minimal deformation of the kinematic coupling under load, assuring the precision of the sphere-to-sphere distance measurement. Experimental results are provided to show that the multi-point kinematic coupling developed has repeatability values below ±1.2 µm in the application.

Chatter prediction in flank milling of thin-walled parts considering force-induced deformation

The deformation and chatter that occur in flank milling thin-walled parts are key factors affecting the machining quality. To solve the above problems, this paper systematically studies the force-induced deformation and chatter. Predictive models that are consistent with the actual cutting process are proposed based on a deep understanding of the process. First, the continuity principle of deformation along a continuous toolpath is revealed. Based on that, a flexible deformation prediction model with accelerated convergence rate is proposed. In predicting the deformation of the next tool location, the proposed model takes the deformation value of the previous adjacent tool location as the initial iteration value. It reduces the iteration space of the prediction process and greatly improves the prediction efficiency. Then, according to the dynamic characteristics of the tool and the thin-walled part in the milling process, a multi-mode dynamic model of the tool and a multipoint contact dynamic model of the thin-walled part are established, and the milling dynamic model is obtained by coupling the above two models in modal space. Considering deformation and the removed material, dynamics of thin-walled parts and cutting parameters are modified in the milling dynamic model. To improve the chatter prediction accuracy, the milling dynamic model is solved via a method based on the extended Newton-Cotes rules. Finally, deformation and chatter experiments of flank milling thin-walled parts are performed. The experimental results validate the correctness of the proposed models.

Pomegranate-type Si/C anode with SiC taped, well-dispersed tiny Si particles for lithium-ion batteries

Severe volume expansion and inherently poor lithium ion transmission are two major problems of silicon anodes. To address these issues, we proposed a pomegranate-type Si/C composite anode with highly dispersed tiny silicon particles as the core assisted by small amount of SiC. Skillfully exploiting the high heat from magnesiothermic reduction, SiC can assist the good dispersion of silicon and provide good interface compatibility and chemical stability. The silicon anchored to the carbon shell provides multipoint contact mode, that together with the carbon shell frame, significantly promoting the transfer of dual charge. Besides, the pomegranate-type microcluster structure also improves the tap density of the electrode, reduces the direct contact area between active material and electrolyte, and enhances the electrochemical performance.

Numerical investigation of impact of non-spherical particles with spin and multi-point contact

Numerical investigation of impact of non-spherical particles with spin and multi-point contact