Inverse dynamics

The current, system-specific countermeasures to space deconditioning have limited success with the musculoskeletal system in long duration missions. Artificial gravity (AG) that is produced by short radius centrifugation has been hypothesized as an effective countermeasure because it reintroduces an acceleration field in space; however, AG alone might not be enough stimuli to preserve the musculoskeletal system. A novel combination of AG coupled with one-legged squats on a vibrating platform may preserve muscle and bone in the lower limbs to a greater extent than the current exercise paradigm. The benefits of the proposed countermeasure have been analyzed through the development of a simulation platform. Ground reaction force data and motion data were collected using a motion capture system while performing one-legged and two-legged squats in 1-G. The motion was modeled in OpenSim, an open-source software, and inverse dynamics were applied in order to determine the muscle and reaction forces of lower limb joints. Vibration stimulus was modeled by adding a 20 Hz sinusoidal force of 0.5 body weight to the force plate data. From the numerical model in a 1-G acceleration field, muscle forces for quadriceps femoris, plantar flexors and glutei increased substantially for one-legged squats with vibration compared to one- or two-legged squats without vibration. Additionally, joint reaction forces for one-legged squats with vibration also increased significantly compared to two-legged squats with or without vibration. Higher muscle forces and joint reaction forces might help to stimulate muscle activation and bone modeling and thus might reduce musculoskeletal deconditioning. These results indicate that the proposed countermeasure might surpass the performance of the current space countermeasures and should be further studied as a method of mitigating musculoskeletal deconditioning.► Musculoskeletal deconditioning is a serious risk during long duration space missions. ► A countermeasure combining artificial gravity, squats, and vibration is analyzed. ► Numerical model developed to get muscle and joint dynamics during the countermeasure. ► Countermeasure provided higher muscle activation and joint forces than using iRED.

Some iterative matrix relations for the geometric, kinematic and dynamic analysis of a Delta parallel robot are established in this paper. The prototype of this manipulator is a three degree of freedom spatial mechanism, which consists of a system of parallel chains. Supposing that the position and the translation motion of the platform are known, an inverse dynamic problem is solved using the virtual powers method. Finally, some recursive matrix relations and some graphs for the moments and the powers of the three active couples are determined.

The context of this PhD thesis is the modelling and design of mechatronic systems. The study is positioned in the early design stage of the conception cycle (V-Cycle), where the main efforts have to be produced in terms of methodology, to enhance the quality and the functionality of the products, and based on virtual prototyping (modelling and simulation). One of the possible methodology is to reformulate the design problem as an inverse problem, in order to directly use the design specification of the product, usually given in terms of the system outputs, and then solve the design problem. In this context, the Ampere laboratory of INSA Lyon has developed a conception and design methodology, based on inverse approach and using the bond graph formalism, to propose a step-by-step method based on dynamic and energetic criteria, with a structural analysis phase that allows hierarchical analysis steps, depending on the structural physical layout of the model (topological, phenomenological, parameter set). The aim of the present works is to contribute to the development of this methodology, by enhancing it to the class of descriptor systems. This choice is led by the aim to apply the methodology in the context of chassis design and vehicle dynamics, where, among other, multi-body models represented as a differential-algebraic equation (DAE) system could occur. The contributions are proposed at the level of the topology of the model, as well as at the level of the phenomenological / behavioral aspects. A preliminary step is to enhance the existing algebraic framework to support graphical extension (in term of digraph and bond graph). The overall methodological extensions allow, firstly, a generalization of the approach to the class of descriptor systems, and, secondly, to reach a standardization of the procedures, previously dedicated to direct or inverse models, so as no mandatory differences between those models have to be done anymore.

This work is focused on impedance control of robot manipulators performing six-degree-of-freedom interaction tasks. An energy-based formulation leads to formally deriving the dynamic equation characterizing a mechanical impedance at the end effector. An inverse dynamics strategy with contact force and moment measurement is adopted to obtain a configuration-independent desired impedance. For given contact force and moment, an impedance control scheme is proposed acting on both translational displacement and rotational displacement where end-effector orientation is described using a singularity-free representation in terms of a unitary quaternion. Experimental results on an industrial robot with open control architecture are presented

Constrained multibody systems typically feature multiple closed kinematic loops that constrain the relative motions and forces within the system. Typically, such systems possess far more articulated degrees-of-freedom (within the chains) than overall end-effector degrees-of-freedom.Thus, actuation of a subset of the articulations creates mixture of active and passive joints within the chain.The presence of such passive joints interferes with the effective modular formulation of the dynamic equations-of-motion in terms of a minimal set of actuator coordinates as well the subsequent recursivesolution for both forward and inverse dynamics applications. Thus, in this paper, we examine the development of modular and recursive formulations of equations-of-motion in terms of a minimal set of actuated-joint-coordinates for an exactly-actuated parallel manipulators. The 3 RRR planar parallel manipulator, selected to serve as a case-study, is an illustrative example of a multi-loop, multi-degree-of-freedom system with mixtures of active/passive joints. The concept of decoupled natural orthogonal complement (DeNOC) is combined with the spatial parallelism inherent in parallel mechanisms to develop a dynamics formulation that is both recursive and modular. An algorithmic approach to the development of both forward and inverse dynamics is highlighted. The presented simulation studies highlight the overall good numerical behavior of the developed formulation, both in terms of accuracy and lack of formulation stiffness.

This paper presents the modeling, identification and control of the 7 degrees of freedom (DoFs) Mitsubishi PA-10 robot arm. The backdrivability, high accuracy positioning capabilities and zero backlash afforded by its harmonic drive transmission, make the PA-10 ideal for precise manipulation tasks. However, the lack of any technical knowledge on the dynamic parameters of its links and the non linear characteristics of friction at its joints, make the development of an accurate dynamic model of the robot extremely challenging. The innovation of this research focuses on the development of the full dynamic model of the PA-10 robot arm, the development of a new non linear model for the friction at its joints, the estimation of the stiffness characteristics of its joints and finally the full identification of the dynamic parameters of the robot arm. The accuracy of the full dynamic model identified is proved by an end-effector trajectory tracking task using a model-based inverse dynamic controller.

In this article the results of the application of a flexible structure artificial neural network for controlling the angular velocity of a servo-hydraulic rotary actuator are discussed. A mathematical model for the system is derived, and a flexible artificial neural network (ANN)-based controller with the feedback error learning method as a learning algorithm is applied to the system. The neural network-based controller has a feed-forward structure and three layers. The flexible bipolar sigmoid function was used as the activation function of the network. The simulation and experimental results show good performance of the developed method in learning the inverse dynamic of the system and controlling the angular velocity of the rotary hydro motor. The advantages of the developed method for servo-hydraulic actuators over other traditional approaches are discussed.

SUMMARY In this paper, a novel algorithm is formulated and implemented for optimum path planning of parallel manipulators. A multi-objective optimisation problem has been formulated for an efficient numerical solution procedure through kinematic and dynamic features of manipulator operation. Computational economy has been obtained by properly using a genetic algorithm to search an optimal solution for path spline-functions. Numerical characteristics of the numerical solving procedure have been outlined through a ...

Body segment inertial parameters (BSIPs) are important data in biomechanics. They are usually estimated from predictive equations reported in the literature. However, most of the predictive equations are ambiguously applicable in the conventional 3D segment coordinate systems (SCSs). Also, the predictive equations reported in the literature all include two assumptions: the centre of mass and the proximal and distal endpoints

Link segment models are extremely useful for increasing the comprehension of joint overload. The aim of the present study was to analyze proximal joint reaction forces and moments during different movements performed with and without external load. One subject performed shoulder flexion, extension and abduction, and elbow flexion movements
(with and without external load) Kinematic data were obtained
by videogrammetry (frequency sample 50 fields/s). One link segment model was used to obtain kinetic data. The model is governed by Newton/Euler movement equations. The results suggested a not proportional increasing of proximal joint reaction forces and moments. The proximal joint reaction force longitudinal component was the only one that increased proportionally to the external load. Proximal joint reaction force shearing components and proximal moments presented
increasing values of different magnitudes. The use of external load promoted increased magnitudes of proximal joint reaction force and moment, although it was not proportional. Proximal joint reaction force and moment are influenced in different ways by the external load. This suggests the need of a strict control of the prescribed exercises for different shoulder dysfunctions.