Daniel Dopico

A combined penalty and recursive real-time formulation for multibody dynamics

The continuously improved performance of personal computers enables the real-time motion simulation of complex multibody systems, such as the whole model of an automobile, on a conventional PC, provided the adequate formulation is applied. There exist two big families of dynamic formulations, depending on the type of coordinates they use to model the system: global and topological. The former leads to a simple and systematic programming while the latter is very efficient. In this work, a hybrid formulation is presented, obtained by combination of one of the most efficient global formulations and one of the most systematic topological formulations. It shows, at the same time, easiness of implementation and a high level of efficiency. In order to verify the advantages that the new formulation has over its predecessors, the following four examples are solved using the three formulations and the corresponding results are compared: a planar mechanism which goes through a singular position, a car suspension with stiff behavior, a 6-dof robot with changing configurations, and the full model of a car vehicle. Furthermore, the last example is also analyzed using a commercial tool, so as to provide the readers with a well-known reference for comparison.

Adaptive neurofuzzy ANFIS modeling of laser surface treatments

This paper introduces a new ANFIS adaptive neurofuzzy inference model for laser surface heat treatments based on the Green’s function. Due to its high versatility, efficiency and low simulation time, this model is suitable not only for the analysis and design of control systems, but also for the development of an expert real time supervision system that would allow detecting and preventing any failure during the treatment.

Determination of Holonomic and Nonholonomic Constraint Reactions in an Index-3 Augmented Lagrangian Formulation With Velocity and Acceleration Projections

Index-3 augmented Lagrangian formulations with projections of velocities and accelerations represent an efficient and robust method to carry out the forward-dynamics simulation of multibody systems modeled in dependent coordinates. Existing formalisms, however, were only established for holonomic systems, for which the expression of the constraints at the position-level is known. In this work, an extension of the original algorithms for nonholonomic systems is introduced. Moreover, projections of velocities and accelerations have two side effects: they modify the kinetic energy of the system and they contribute to the constraint reaction forces. Although the effects of the projections on the energy have been studied by several authors, their role in the calculation of the reaction forces has not been described so far. In this work, expressions to determine the constraint reactions from the Lagrange multipliers of the dynamic equations and the Lagrange multipliers of the velocity and acceleration projections are introduced. Simulation results show that the proposed strategy can be used to expand the capabilities of index-3 augmented Lagrangian algorithms, making them able to deal with nonholonomic constraints and provide correct reaction efforts.

Efficient and accurate simulation of the rope–sheave interaction in weight-lifting machines

This article presents different approaches that can be used for modelling wire ropes in weight-lifting machines. It is shown that modelling the rope as a linear spring, although very simple and efficient, is energetically inconsistent and produces spurious terms in the equations of motion if the rope deformation along the segment in contact with the sheave is not considered. In order to overcome this problem and obtain an efficient yet accurate method for the simulation of such systems, a semi-analytical method is derived by introducing an analytical model of the rope–sheave interaction in the system, and the obtained results are compared with a finite-element numerical model. The semi-analytical model is based on a continuum mechanics approach of the rope; it assumes Coulomb friction between the sheave and the rope and neglects the centrifugal force of the segment of rope in contact with the sheave while accounting for tangential inertia forces in the rope. The numerical model is based on the Absolute Nodal Coordinate Formulation, and accounts for both the inertia forces and the bending and axial deformation of the rope.

On the Stabilizing Properties of Energy-Momentum Integrators and Coordinate Projections for Constrained Mechanical Systems

Several considerations are important if we try to carry out fast and precise simulations in multibody dynamics: the choice of modeling coordinates, the choice of dynamical formulations and the numerical integration scheme along with the numerical implementation. All these matters are very important in order to decide whether a specific method is good or not for a particular purpose.

An optimum synthesis for gripping mechanisms by using natural coordinates

Abstract In this paper a simple and efficient procedure for optimum dimensional synthesis of gripping mechanisms is presented. The proposed design method is based on a suitable formulation of grasping performance of gripping mechanisms and makes use of a description of mechanisms by means of natural (fully Cartesian) coordinates. The optimization design problem is formulated by an objective function describing the main grasping performance and constraints prescribing practical design requirements and mechanism peculiarities. A numerical example is reported and discussed to illustrate the engineering feasibility of the proposed design procedure.

Dynamic Response Optimization of Complex Multibody Systems in a Penalty Formulation Using Adjoint Sensitivity

Multibody dynamics simulations are currently widely accepted as valuable means for dynamic performance analysis of mechanical systems. The evolution of theoretical and computational aspects of the multibody dynamics discipline make it conducive these days for other types of applications, in addition to pure simulations. One very important such application is design optimization. A very important first step towards design optimization is sensitivity analysis of multibody system dynamics. Dynamic sensitivities are often calculated by means of finite differences. Depending of the number of parameters involved, this procedure can be computationally expensive. Moreover, in many cases, the results suffer from low accuracy when real perturbations are used. The main contribution to the state-of-the-art brought by this study is the development of the adjoint sensitivity approach of multibody systems in the context of the penalty formulation. The theory developed is demonstrated on one academic case study, a five-bar mechanism, and on one real-life system, a 14-DOF vehicle model. The five-bar mechanism is used to illustrate the sensitivity approach derived in this paper. The full vehicle model is used to demonstrate the capability of the new approach developed to perform sensitivity analysis and gradient-based optimization for large and complex multibody systems with respect to multiple design parameters.

A 3D Physics-Based Hydraulic Excavator Simulator

The actuation of hydraulic excavators is a complex and not intuitive task which requires long and costly training periods, since the qualification of the operator has a significant impact in productivity and safety. Simulation-based training combined with virtual reality is becoming a competitive alternative to traditional training to reduce costs and risks in the instruction of excavator operators. Several excavator training simulators have been developed, but none of them features a dynamic model of the machine complete enough to simulate all the maneuvers performed in the daily work of real excavators. The authors have applied real-time simulation techniques from multibody system dynamics to develop a full 3D physics-based excavator simulator made up of 14 rigid bodies with 17 degrees of freedom. The simulation engine includes a custom collision detection algorithm and detailed tire force and contact force models. Terrain excavation and bucket loading and unloading are also simulated. The resulting model delivers realistic real-time behavior and can simulate common events in real excavators: slipping on slope terrains, stabilizing the machine with the blade or the outriggers, using the arm for support or impulsion to avoid obstacles, etc. The simulator console has a semi-immersive virtual reality interface that emulates the excavator cabin. The operator console imitates most of the controls of the real machine cabin using low-cost standard USB input devices: steering wheel, 2 joystiks with the standard excavator functions and 2 pedals. A tactile screen replicates the digital control panel of the excavator, which lets the operator control different machine settings. A hard shell hemispherical dome of 2 m diameter is used to project the subjective view from the operator’s position. The resulting simulator, which can run in a standard PC due to its high computational efficiency, can reproduce almost all the maneuvers performed by real excavators.Copyright

Real-time multi-body formulation for virtual-reality-based design and evaluation of automobile controllers

Abstract Nowadays, modelling and simulation of vehicle dynamics play a great role in the design and evaluation of vehicle control systems, as they reduce costly and time-consuming construction of prototypes and experimentation. Multi-body simulation can be used for controller design, tuning and testing of electronic control units, optimum control, or onboard devices providing driver advice and/or actuation. This article reports on the application of a robust real-time formulation to the development of a low-cost and efficient computational framework for the design and evaluation of automobile motion controllers. The core elements of the tool are the real-time formalism for the dynamics of multi-body systems, a virtual-reality (VR) interface for human-in-the-loop simulation, and Matlab for the controllers. A detailed model of an existing prototype car has been implemented in the Fortran language, and controllers have been designed for several purposes, in order to test the developed framework. It has been demonstrated that the dynamic formalism is fast enough to enable human-in-the-loop simulation, that the VR interface is of great help for both control design and evaluation, and that Matlab algorithms can be efficiently connected to the Fortran computational model of the car.

A Hybrid Global-Topological Real-Time Formulation for Multibody Systems

The continuously improved performance of personal computers enables the real-time motion simulation of complex multibody systems, such as the whole model of an automobile, on a conventional