Haptic Rendering and Human Stabilization in Presence of Structural Flexibility

Unstable behaviour is a significant problem in many haptic applications. The sampled-data nature and time delays induce complex dynamic behaviours in such systems. Structural flexibility may further reduce the stable domain of operation. This is illustrated via the systematic modeling and analysis of an impedance type haptic device with typical design elements such as closed-loop mechanisms and cable/capstan drives. The role of the operator in the dynamics of these systems is also demonstrated. The present work provide stability analysis, experimental validation and derive conditions for the range of parameters in which the operator can significantly contribute to the stabilization of the system

The discretized coulomb friction model in a non-singular complementarity formulation for multibody systems with contacts

Postprint (published version

Use of performance indicators in the analysis of running gait impacts

Foot-ground impact is a critical event during the running cycle. In this work, three performance indicators were used to characterize foot-ground impact intensity: the effective pre-impact kinetic energy, representative elements of the effective mass matrix, and the critical coefficient of friction. These performance indicators can be obtained from the inertial properties of the biomechanical system and its pre-impact mechanical state, avoiding the need to carry out force measurements. Ground reaction forces and kinematic data were collected from the running motion of an adult that adopted both rear-foot and fore-foot strike patterns. Different running cycles were analysed and statistical tests performed. Results showed that the three proposed indicators are able to illustrate significant differences between fore-foot and rear-foot strike impacts. They also support the hypothesis that fore-foot strike reduces impact intensity. On the other hand, a higher likelihood of slipping during the contact onset is associated with fore-foot strike pattern.Postprint (author's final draft

Dynamics of Mechanical Systems Part 1: Concepts, Geometry and Kinematic Considerations

This document summarizes some important concepts, geometric and kinematic considerations for the dynamics of mechanical systems

Dynamic considerations of heel-strike impact in human gait

Based on the impulsive-dynamics formulation, this article presents the analysis of different strategies to regulate the energy dissipation at the heel-strike event in the context of human locomotion. For this purpose, a seven-link 2D human-like multibody model based on anthropometric data is used. The model captures the most relevant dynamic and energetic aspects of the heel-strike event in the sagittal plane. The pre-impact mechanical state of the system, around which the analysis of the heel impact contribution to energy dissipation is performed, is defined based on published data. In the context of the proposed impulsive-dynamics framework, different realistic strategies that the subject can apply to modify the impact dynamics are proposed and analyzed, namely, the trailing ankle push-off, the torso configuration and the degree of joint blocking in the colliding leg. Detailed numerical analysis and discussions are presented to quantify the effects of the mentioned strategies.Postprint (author's final draft

Use of Penalty Formulations in Dynamic Simulation and Analysis of Redundantly Constrained Multibody Systems

[Abstract] The determination of particular reaction forces in the analysis of redundantly constrained multibody systems requires the consideration of the stiffness distribution in the system. This can be achieved by modelling the components of the mechanical system as flexible bodies. An alternative to this, which we will discuss in this paper, is the use of penalty factors already present in augmented Lagrangian formulations as a way of introducing the structural properties of the physical system into the model. Natural coordinates and the kinematic constraints required to ensure rigid body behaviour are particularly convenient for this. In this paper, scaled penalty factors in an index-3 augmented Lagrangian formulation are employed, together with modelling in natural coordinates, to represent the structural properties of redundantly constrained multibody systems. Forward dynamic simulations for two examples are used to illustrate the material. Results showed that scaled penalty factors can be used as a simple and efficient way to accurately determine the constraint forces in the presence of redundant constraints

Energy-Consistent Haptic Rendering of Contact Forces

Abstract-Enhancing the realism of the perceived contact force is a primary challenge in haptic rendering of virtual walls (VWs) and objects (VOs). For VOs, this goal directly translates into accurate rendering of not only stiffness, but also mass. The most challenging situation arises when the stiffness of the object is large, its mass is small, and sampling is slow. To address this challenge, a framework entitled highfidelity haptic rendering (HFCR) has been developed. The HFCR framework is composed of the following three main strategies: an energy-consistent rendering of the contact force, smooth transition between contact modes, and remaining leak dissipation. The essence of all these strategies is to make the energy of the VO emulate its continuous-time counterpart. This is achieved through physically meaningful modifications in the constitutive relations to suppress artificial energy leaks. This paper reports simulation and experiments involving the onedimensional canonical model of a VO to illustrate the HFCR framework and compare it to the existing methods. Results demonstrate the promising stability and force rendering fidelity of this framework

Kinematic Modelling and State Estimation of Exploration Rovers

This is a post-peer-review, pre-copyedit version of an article published in IEEE Robotics and Automation Letters. The final authenticated version is available online at: http://dx.doi.org/10.1109/LRA.2019.2895393.[Abstract] State estimation is crucial for exploration rovers. It provides the pose and velocity of the rover by processing measurements from onboard sensors. Classical wheel odometry only employs encoder measurements of the two wheels in the differential drive. As a consequence, input noise can lead to large uncertainties in the estimated results. Also, the estimation models used in classical wheel odometry are nonlinear, and the linearization process that propagates the mean and covariance of the estimated state introduces additional errors in the process. This letter puts forward a novel wheel odometry approach for six-wheeled rovers. A kinematic model is formulated to relate the velocity of the wheels and the chassis, and later used to develop the corresponding estimation model. The components of the velocity of the chassis, decomposed in the chassis-fixed coordinate frame, are selected as the system state in the estimation, which results in a linear model. The motions of all wheels are fused together to provide the measurements. Wheel slip is considered random Gaussian noise in this kinematic model. The continuous-time Kalman filter is employed to process the model. Experimental validation with six-wheeled rover prototypes was used to confirm the validity of the proposed approach.MINECO; RYC-2016-2022

Energy-leak monitoring and correction to enhance stability in the co-simulation of mechanical systems

[Abstract] Non-iterative co-simulation is an increasingly important technique for the simulation of complex mechanical systems. Adopting co-simulation schemes enables the simultaneous use of computational resources and makes it possible to select the most appropriate modelling techniques and algorithms to describe and solve the dynamics of each system component. However, it inherently requires the coupling of different subsystems at discrete communication times, which may compromise the stability of the overall integration process. One of the negative effects of discrete-time communication is the introduction of artificial energy in the system dynamics, which can render the simulation unstable if it accumulates over time. Excess energy can be dissipated introducing virtual damping elements in the subsystem models. The actual amount of damping must be adjusted as the simulation progresses to ensure that all the artificially generated energy is removed from the system while keeping the dynamics realistic. In this paper, we introduce a monitoring framework to keep track of this excess energy, and put forward a dissipation methodology to eliminate it. The ability of this framework to achieve stable non-iterative co-simulation was tested with several mechanical system examples.Ministerio de Economía y Competitividad (MINECO); RYC-2016-2022

Some aspects of heel strike impact dynamics in the stability of bipedal locomotion

Postprint (published version