Compliant contact force models in multibody dynamics : evolution of the Hertz contact theory

Over the last decades, several compliant contact force models have been proposed. However, no complete and systematic comparison has been done on these models, which provides information on their range of application and accuracy for use in different contact scenarios. Thus, the selection of an appropriate model for a given contact problem is still an important and challenging issue to be addressed. The Hertzian contact theory remains the foundation for almost all of the available force models, but by itself, it is not appropriate for most impacts in practice, due to the amount of energy dissipated during the impact. A good number of contact force models have been offered that augment the Hertzian law with a damping term to accommodate the energy loss during the impact process for small or moderate impact velocities. In this work, the main issues associated with the most common compliant contact force models of this type are analyzed. Results in terms of the dynamic simulations of multibody systems are presented, which allow for the comparison of the similarities and differences among the models considered.Fundação para a Ciência e a Tecnologia (FCT) - DACHOR - Multibody Dynamics and Control of Hybrid Active Orthoses (MIT-Pt/BSHHMS/0042/2008), BIOJOINTS - Development of advanced biological joint models for human locomotion biomechanics (PTDC/EMEPME/ 099764/2008), SFRH/BD/40164/2007, SFRH/BD/64477/200

A review of friction models in interacting joints for durability design.

This paper presents a comprehensive review of friction modelling to provide an understanding of design for durability within interacting systems. Friction is a complex phenomenon and occurs at the interface of two components in relative motion. Over the last several decades, the effects of friction and its modelling techniques have been of significant interests in terms of industrial applications. There is however a need to develop a unified mathematical model for friction to inform design for durability within the context of varying operational conditions. Classical dynamic mechanisms model for the design of control systems has not incorporated friction phenomena due to non-linearity behaviour. Therefore, the tribological performance concurrently with the joint dynamics of a manipulator joint applied in hazardous environments needs to be fully analysed. Previously the dynamics and impact models used in mechanical joints with clearance have also been examined. The inclusion of reliability and durability during the design phase is very important for manipulators which are deployed in harsh environmental and operational conditions. The revolute joint is susceptible to failures such as in heavy manipulators these revolute joints can be represented by lubricated conformal sliding surfaces. The presence of pollutants such as debris and corrosive constituents has the potential to alter the contacting surfaces, would in turn affect the performance of revolute joints, and puts both reliability and durability of the systems at greater risks of failure. Key literature is identified and a review on the latest developments of the science of friction modelling is presented here. This review is based on a large volume of knowledge. Gaps in the relevant field have been identified to capitalise on for future developments. Therefore, this review will bring significant benefits to researchers, academics and industrial professionals

A comparative study of the viscoelastic constitutive models for frictionless contact interfaces in solids

The nature of the constitutive contact force law utilized to describe contact-impact events in solid contact interfaces plays a key role in predicting the response of multibody mechanical systems and in the simulation of engineering applications. The goal of this work is to present a comparative study on the most relevant existing viscoelastic contact force models. In the sequel of this process, their fundamental characteristics are examined and their performances evaluated. Models developed based on the Hertz contact theory and augmented with a damping term to accommodate the dissipation of energy during the impact process, which typically is a function of the coefficient of restitution between the contacting solids, are considered in this study. In particular, the identified contact force models are compared in the present study for simple solid impact problems with the sole purpose of comparing the performance of the various models and examining the corresponding system behavior. The outcomes indicate that the prediction of the dynamic behavior of contacting solids strongly depends on the selection of the contact force model.Fundação para a Ciência e a Tecnologia (FCT

A comprehensive survey of the analytical, numerical and experimental methodologies for dynamics of multibody mechanical systems with clearance or imperfect joints

"Available online 19 December 2017"A comprehensive survey of the literature of the most relevant analytical, numerical, and experimental approaches for the kinematic and dynamic analyses of multibody mechanical systems with clearance joints is presented in this review. Both dry and lubricated clearance joints are addressed here, and an effort is made to include a large number of research works in this particular field, which have been published since the 1960′s. First, the most frequently utilized methods for modeling planar and spatial multibody mechanical systems with clearance joints are analyzed, and compared. Other important phenomena commonly associated with clearance joint models, such as wear, non-smooth behavior, optimization and control, chaos, and uncertainty and links’ flexibility, are then discussed. The main assumptions procedures and conclusions for the different methodologies are also examined and compared. Finally, future developments and new applications of clearance joint modeling and analysis are highlighted.This research was supported in part by the China 111 Project (B16003) and the National Natural Science Foundation of China under Grants 11290151, 11472042 and 11221202. The work was also supported by the Portuguese Foundation for Science and Technology with the reference project UID/EEA/04436/2013, by FEDER funds through the COMPETE 2020 – Programa Operacional Competitividade e Internacionalização (POCI) with the reference project POCI-01-0145-FEDER-006941.info:eu-repo/semantics/publishedVersio

Translational joints with clearance in rigid multibody systems

A computational methodology for dynamic description of rigid multibody systems with translational clearance joints is presented and discussed in this work. Over the last years, extensive work has been done to study the dynamic effect of the revolute joints with clearance in multibody systems, in contrast with the little work devoted to model translational joints with clearance. In a joint with translation clearance there are many possible ways to set the physical configuration between the slider and guide, namely: (i) no contact between the two elements, (ii) one corner of the slider in contact with the guide surface, (iii) two adjacent slider corners in contact with the guide surface, (iv) two opposite slider corners in contact with the guide surfaces. The proposed methodology takes into account these four different situations. The conditions for switching from one case to another depend on the system dynamics configuration. The existence of a clearance in a translational joint removes two kinematic constraints from a planar system and introduces two extra degrees of freedom in the system. Thus, a translational clearance joint does not constrain any degree of freedom of the mechanical system but it imposes some restrictions on the slider motion inside the guide limits. When the slider reaches the guide surfaces an impact occurs and the dynamic response of the joint is modeled by contact-impact forces. These forces are evaluated here with continuous contact force law together with a dissipative friction force model. The contact-impact forces are introduced into the system’s equations of motion as external generalized forces. The proposed methodology is applied to a planar multibody mechanical system with a translational clearance joint in order to demonstrate its features.Fundação para a Ciência e a Tecnologia (FCT

Study of the friction-induced vibration and contact mechanics of artificial hip joints

The main objective of this work is to study the effect of friction-induced vibration and contact mechanics on the maximum contact pressure and moment of artificial hip implants. For this purpose, a quasi-static analysis and a multibody dynamic approach are considered. It is shown that the multibody dynamic model is effective at predicting contact pressure distribution and moment of hip implants from both accuracy and time-consuming points of view. Finally, from the computational simulations performed, it can be observed that the friction-induced vibration influences the contact pressure and the moment in hip implants by introducing an oscillating behaviour in the system dynamics.Fundação para a Ciência e a Tecnologia (FCT

歩行メカニズムにおける粘弾性着地の効果および動力学解析のための計算論的手法に関する研究

Since animal bodies are highly complex to be organized biologically, it is not easy to evaluate the advantage of flexibility in the muscularskeletal system in comparison with mechanical rigid bodies. For the reason, a simplification had been implemented in traditional scheme of the reduced degree of freedom mechanisms with well-designed fixed limb trajectory for real world applications, and the best mechanical structure was explored to minimize its energy consumption known in walking linkage mechanisms. As the possible hypothesis, the advantage of high energy conservation effect can be maximized according to a smooth grounding at the touching moment of the toe on the ground. The smooth trajectory itself can be reproduced by closed-linkage walking models, while the effect of the interaction between the toe and ground is unclear and viscoelastic contact may enhance the effect. For the clarification of the hypothesis, a fine computational framework is needed to be established to provide less computational cost and enough accuracy and stability in the analysis. Traditionally, the rigid-body mechanics and contact force analysis were separately studied and developed. In the present study, multibody dynamics approach based on the analytical mechanics was newly integrated with the viscoelastic contact force model, which is able to implement a hysteresis damping phenomenon simply. By using the linkage mechanisms, the elasticity of the grounding was analyzed through the inverse dynamics based on the proposed computational framework involving the multibody dynamics and contact force model implementation. The proposed method was located in an intermediate position between the discrete contact model for a less frequency attachment of bodies and the continuous model for stable attachment phenomenon. In the sense, the method was appropriate for analyses of walking mechanisms with a consistent frequency of the attachment with the ground, which requires a fine reaction force analysis. In the computer experiment as the comparison of typical and simplified walking linkage mechanisms, the proposed method applied to Chebyshev and Theo-Jansen walking mechanisms and demonstrated the required torque in the driving input when those mechanisms were walking on the ground. In an energy analysis, which is defined as the required input-torque integration in a cycle of the leg motion, the perfectly elastic ground contact commonly reduced the energy consumption significantly in the comparison of the coefficient of restitution in the damping factor model by Lankarani and Nikravesh. The result proved the hypothesis of the positive effect of the smooth grounding in the range of the proposed computational approach. It may contribute to providing an criterion not only for a real walking robot design but also assistive devise configurations to absorb unnecessary ground reaction force to prevent the damage to the leg mechanism and enhance a smooth walking pattern.九州工業大学博士学位論文 学位記番号：生工博甲第407号 学位授与年月日：令和3年3月25日1 Introduction|2 Mathematical formulations in multibody system dynamics|3 Foot-ground contact model|4 An integrated computational framework for the energy analysis of rigid closed-loop walking mechanisms|5 Comparison between the proposed method and the other methods|6 Dynamic modelling of the horse locomotion|7 Discussion and Conclusion九州工業大学令和2年