Dynamic Modeling and Experimental Verification of A Cable-Driven Continuum Manipulator With Cable-Constrained Synchronous Rotating Mechanisms

The cable-driven segmented manipulator with cable-constrained synchronous rotating mechanisms (CCSRM) is a new type of continuum manipulator, which has large stiffness and less motors, and thus exhibits excellent comprehensive performance. This paper presents a dynamic modeling method for this type of manipulator to analyze the friction and deformation of the cables on the dynamical behaviors of the system. First, the driving cables are modeled based on the ALE formulation, the strategies for detecting stick-slip transitions are proposed by using a trial-and-error algorithm, and the stiff problems of the dynamic equations are released by a model smoothing method. Second, the dynamic modeling method for rigid links is presented by using quaternion parameters. Third, the connecting cables are modeled by torsional spring-dampers and the frictions between the connecting cables and the conduits are considered based on a modified Coulomb friction model. Finally, the numerical results are presented and verified by comparing with experiment results. The study shows that the friction and cable deformation play an important role in the dynamical behaviors of the manipulator. Due to these two factors, the constant curvature bending of the segments does not remain.

Modeling and analysis of the friction in a nonlinear sliding-mode triboelectric energy harvester

Friction plays a pivotal role in the sliding-mode triboelectric energy harvester (TEH), which not only enables the charge transfer between two dielectrics, but also influences the energy harvesting performance by affecting the dynamic response of the TEH. How to evaluate the effects of the friction on TEHs is important for optimizing TEHs in engineering practices. In order to analyze the effects of the friction on the dynamic response and evaluate the energy harvesting performance of TEHs, the paper models the friction of a devised nonlinear TEH based on the Coulomb friction model and the Macro-slip friction theory. The TEH equips a pair of magnets, rendering a switching between the bistability and the monostability by tuning the distance between two magnets. The dynamic model of the nonlinear TEH is established by the extended Hamilton principle. The effects of the friction in sliding-mode TEH are dissected in detail. The influences of parameters on both the mechanical and electrical responses are also systemically studied, to explore an optimal energy harvesting performance in the low-frequency range. This work provides a guideline for designing and accurately analyzing a sliding-mode TEH.

Dynamic Analysis of Hydraulic Support with Single Clearance

Hydraulic support is a complex parallel mechanism composed of multiple kinematic pairs. In the work of hydraulic support, clearances between kinematic pairs are inevitable, which lead to the deterioration of the support’s working performance, and may even affect support’s normal work in serious cases. To study the influence of clearances on hydraulic support and simultaneously avoid the mutual interference between different clearances, the normal and tangential force models of kinematic pairs with clearance are established, based on the Lankarani-Nikravesh contact force model and the Coulomb friction model. Furthermore, the dynamic model of the hydraulic support with single clearance is established by adding a clearance between the rear link and base and, according to the dynamic model of the hydraulic support, the research about the influence of clearance on the movement and force of hydraulic support is carried out, which proves the need to study the clearance of hydraulic support. Moreover, the influence of clearance, clearance size, and different oil inlet drive modes of front and rear columns on the stability of hydraulic support are analysed, and then the change of hydraulic support posture caused by clearance and clearance size is considered. The results show that clearance causes the movement and force of the rear link to fluctuate, which affects the stability of the hydraulic support. The clearance size affects the fluctuation degree of the movement and force, which is an important factor in the instability of hydraulic support. Also, the hydraulic support posture is changed by the clearance and clearance size. Different column oil inlet drive modes have different impacts on the clearance and have different effects on the stability of hydraulic support.

Calculated determination of parameters for Coulomb friction model by simulation of axial joint pressing process

The task for determining of the maximum pressing force at given displacement with acceptable accuracy is urgent in the process of the car axial joint designing. Friction at the interface between the contacting surfaces of the matrix and the body of the axial joint has significant effect on this technological parameter. Modeling of the surfaces contact interaction without taking into account the action of the friction force can lead to high error in the result. The parameters of the Coulomb friction model without carrying out large amount of experimental work using the finite element method is proposed to determine to improve in the accuracy of the maximum pressing force obtained as result of modeling.

Some Exploration of the Path-Dependence in the Contact Analysis

One of the most frustrating features of joint mechanics is that all the important processes take place precisely where they cannot be seen or measured directly — the interface between contacting bodies. In order to achieve some insight into the mechanisms that give rise to the nonlinearities of joints one naturally turns to analytic or numerical models of interface mechanics. With such models, one can explore the significance of different assumptions of kinematics or surface mechanics and compare those with laboratory experiments on the integrated joints. Among the limitations of such modeling strategies are the twin problems of 1) employing suitable models for friction and 2) solving the resulting equations. There is evidence that the commonly used Coulomb friction model is inconsistent with the experimentally observed behavior of lap joints; it is necessary to explore the use of more complex models. Additionally, even when computing contact and sliding with the relatively simple Coulomb friction model, capturing the evolution of traction fields from one load set to the next in a physically plausible manner has been a continuing challenge. Obtaining fidelity to such path dependence for more complex models would be consequently more difficult. This issue has motivated the research reported here on the source of the difficulty in modeling path-dependent contact and possible solutions. A two-parameter Coulomb friction model is used to test a conventional contact algorithm and a newer one devised specifically to capture path dependence correctly. The evolution of lateral traction during cyclic loading is used to illustrate how the shear traction distribution at each load step evolves from that of the previous.

Dynamic Responses of Planar Multilink Mechanism considering Mixed Clearances

Translational and revolute joints are the main kinds of joints in planar multilink mechanisms. Translational and revolute clearance joints have great influence on dynamical responses of planar mechanisms. Most research studies mainly focused upon revolute clearance of planar mechanisms based upon the modified Coulomb friction model, some studies investigated clearance of the pin-slot joint, and few studies researched mixed clearances (considering both translational clearance and revolute clearance) based on the LuGre friction model. Dynamic response of the 2-DOF nine-bar mechanism considering mixed clearances based on the LuGre model is investigated in this work. The dynamic model with mixed clearances is built by the Lagrange multipliers. Dynamic responses including motion output of the slider, driving torques, contact forces, shaft center trajectories at revolute clearance pairs, and slider trajectory inside the guide are analyzed, respectively. Influences of different friction models on dynamic responses are studied, such as LuGre and modified Coulomb’s friction models. Effects of different clearance values and different driving speeds on dynamic responses with mixed clearances are both analyzed. Virtual prototype model considering mixed clearances is carried out through ADAMS to verify correctness.

Mitigation Effect of Perforation Drilling on the Sliding Risk during Spudcan Installation Close to Footprints

Perforation drilling is a promising technique to mitigate the sliding risk of jack-up units installed around footprints. Based on the coupled Eulerian–Lagrangian (CEL) method, a 1/2 finite element model, including a rigid Lagrangian spudcan and a Eulerian soil part, was established, and the contact interface was modelled with the Coulomb friction model. Validated against an indoor perforation test, the model was adopted to investigate the mitigation mechanism and effects of the borehole diameter, number, depth, and the drilling range. The simulations reveal that the mitigation efficiency increases with the borehole diameter, number, and depth. However, it shows little improvement if the borehole depth increases beyond double footprint depth. The semi-drilling at the outer side of the footprint is a little more effective than the full-drilling at both the inner and outer sides of the footprint. The present work emphasizes the effects of perforation drilling parameters on the mitigation efficiency, which are of great significance to guide the engineering practice and guarantee the safe operation of the jack-up reinstallation close to existing footprints.

Investigation on Dynamic Interaction of Multiple Clearance Joints for Flap Actuation System

A dynamic simulation model of the flap actuation system is developed in this paper to analyze the dynamic interaction behaviours of multiple clearance joints. The nonlinear contact force model and modified Coulomb friction model are adopted in the four clearance joints to capture their motion modes, including free flight mode, impact mode and continuous mode. The results show that there exists a strong dynamic interaction between different clearance joints and one impact motion mode in a joint will immediately affect other joints. And when the system reaches a stable state, the four clearance joints almost appears the similar tendency due to the rigid connection. Therefore, in order to accurately predict the dynamic responses of multibody system, it is essential for all joints to be modelled as imperfect ones.

Comparison of numerical simulation results of sheet metal parts’ production for AutoForm and TriboForm friction models

The results of numerical simulations with two friction models are studied. The fi rst model corresponded the Coulomb friction model and used in AutoForm on default. The second friction model took into account the quality of surface treatment, its roughness and amount of the lubricant and the effect of the asperities’ height evolution. It is used in TriboForm. The results obtained for the second friction model are used to simulate sheet metal forming processes in AutoForm. It is found that the TriboForm friction model affected the results of the drawing operation. The difference in the results increased due to bigger deformation values of the technological operation.