Inverse Dynamics Simulation Research Articles

Feasibility of EMG-Based Neural Network Controller for an Upper Extremity Neuroprosthesis

The overarching goal of this project is to provide shoulder and elbow function to individuals with C5/C6 spinal cord injury (SCI) using functional electrical stimulation (FES), increasing the functional outcomes currently provided by a hand neuroprosthesis. The specific goal of this study was to design a controller based on an artificial neural network (ANN) that extracts information from the activity of muscles that remain under voluntary control sufficient to predict appropriate stimulation levels for several paralyzed muscles in the upper extremity. The ANN was trained with activation data obtained from simulations using a musculoskeletal model of the arm that was modified to reflect C5 SCI and FES capabilities. Several arm movements were recorded from able-bodied subjects and these kinematics served as the inputs to inverse dynamic simulations that predicted muscle activation patterns corresponding to the movements recorded. A system identification procedure was used to identify an optimal reduced set of voluntary input muscles from the larger set that are typically under voluntary control in C5 SCI. These voluntary activations were used as the inputs to the ANN and muscles that are typically paralyzed in C5 SCI were the outputs to be predicted. The neural network controller was able to predict the needed FES paralyzed muscle activations from "voluntary" activations with less than a 3.6% RMS prediction error.

Musculoskeletal Model-Guided, Customizable Selection of Shoulder and Elbow Muscles for a C5 SCI Neuroprosthesis

Individuals with C5/C6 spinal cord injury (SCI) have a number of paralyzed muscles in their upper extremities that can be electrically activated in a coordinated manner to restore function. The selection of a practical subset of paralyzed muscles for stimulation depends on the specific condition of the individual, the functions targeted for restoration, and surgical considerations. This paper presents a musculoskeletal model-based approach for optimizing the muscle set used for functional electrical stimulation (FES) of the shoulder and elbow in this population. Experimentally recorded kinematics from able-bodied subjects served as inputs to a musculoskeletal model of the shoulder and elbow, which was modified to reflect the reduced muscle force capacities of an individual with C5 SCI but also the potential of using FES to activate paralyzed muscles. A large number of inverse dynamic simulations mimicking typical activities of daily living were performed that included 1) muscles with retained voluntary control and 2) many different combinations of stimulated paralyzed muscles. These results indicate that a muscle set consisting of the serratus anterior, infraspinatus and triceps would enable the greatest range of relevant movements. This set will become the initial target in a C5SCI neuroprosthesis to restore shoulder and elbow function.

Efficient Drive Cycle Simulation

Drive cycle simulations of longitudinal vehicle models are important aids for the design and analysis of power trains, and tools currently on the market mainly use two different methods for such simulations: the forward dynamic and quasi-static inverse simulations. Here, a known theory for the stable inversion of nonlinear systems is used to combine the fast simulation times of the quasi-static inverse simulation with the ability of the forward dynamic simulation to include transient dynamics. The stable inversion technique and a new implicit driver model together form a new concept: inverse dynamic simulation. This technique is demonstrated to be feasible for vehicle propulsion simulation and specifically for three power train applications that include important dynamics that cannot be handled using quasi-static inverse simulation. The extensions are engine dynamics, driveline dynamics, and gas flow dynamics for diesel engines, which are also selected to represent important properties, such as zero dynamics, resonances, and nonminimum-phase systems. It is shown that inverse dynamic simulation is easy to set up, gives short simulation times, and gives consistent results for design space exploration. This makes inverse dynamic simulation a suitable method to use for drive cycle simulation, particularly in situations requiring many simulations, such as optimization over design space, power train configuration optimization, or the development of power train control strategies.

Flexible multibody simulation approach in the analysis of tibial strain during walking

Strains within the bone tissue play a major role in bone (re)modeling. These small strains can be assessed using experimental strain gage measurements, which are challenging and invasive. Further, the strain measurements are, in practise, limited to certain regions of superficial bones only, such as the anterior surface of the tibia. In this study, tibial strains occurring during walking were estimated using a numerical approach based on flexible multibody dynamics. In the introduced approach, a lower body musculoskeletal model was developed by employing motion capture data obtained from walking at a constant velocity. The motion capture data were used in inverse dynamics simulation to teach the muscles in the model to replicate the motion in forward dynamics simulation. The maximum and minimum tibial principal strains predicted by the model were 490 and −588 microstrain, respectively, which are in line with literature values from in vivo measurements. In conclusion, the non-invasive flexible multibody simulation approach may be used as a surrogate for experimental bone strain measurements and thus be of use in detailed strain estimations of bones in different applications.

Dynamic Analysis of a Macro–Micro Redundantly Actuated Parallel Manipulator

In this paper the dynamic analysis of a macro–micro parallel manipulator is studied in detail. The manipulator architecture is a simplified planar version adopted from the structure of the Large Adaptive Reflector (LAR), the Canadian design of next-generation giant radio telescopes. In this structure it is proposed to use two parallel redundant manipulators at the macro and micro level, both actuated by cables. In this paper, the governing dynamic equation of motion of such a structure is derived using the Newton–Euler formulation. Next, the dynamic equations of the system are used in the open-loop inverse dynamics simulations, as well as closed-loop forward dynamics simulations. In the open-loop dynamic simulations it is observed that the inertial forces of the limbs contribute only 10% of the dynamic forces required to generate a typical trajectory and, moreover, the total dynamic forces contribute only 10% of the experimentally measured disturbance forces. Furthermore, in the closed-loop simulations using decentralized PD controllers at the macro and micro levels, it is shown that the macro–micro structure results in a 10 times more accurate positioning than that in the first stage of the macro–micro structure. This convincing result promotes the use of the macro–micro structure for LAR application.

Inverse dynamics of wire-actuated parallel manipulators with a constraining linkage

The inverse dynamics of wire-actuated parallel manipulators with a constraining linkage and redundancy in actuation is investigated. To resolve the problem of having infinite solutions for inverse dynamics, a wire deactivation methodology based on Lagrangian equations is proposed and two approaches are developed to detect the counteracting wires. The methodology results in lower actuator forces/torques by reducing the counteracting wire tensions. The robustness of the methodology in avoiding negative wire tensions is verified in the inverse dynamic simulation of an example manipulator.

Efficient forward dynamics simulation and optimization of human body dynamics

AbstractThe modeling of the time dependent, dynamic behavior of the human musculoskeletal system results in a large scale mechanical multibody system. This consists of submodels for the skeleton, wobbling masses, muscles and tendons as redundant actuators. Optimization models are required for the simulation of the muscle groups involved in a motion. In contrast to the inverse dynamics simulation the forward dynamics simulation enables to consider very general problem statements in principle. The paper presents a new approach to the forward dynamics simulation and optimization of human body dynamics which overcomes the enormous computational cost of current approaches for solving the resulting optimal control problems. The presented approach is based on a suitable modeling of the dynamics of the musculoskeletal system in combination with a tailored direct collocation method for optimal control. First numerical results for a human kick demonstrate an improvement in computational time of two orders of magnitude when compared to standard methods.

Experimental verification of a computational technique for determining ground reactions in human bipedal stance

We have developed a three-dimensional (3D) biomechanical model of human standing that enables us to study the mechanisms of posture and balance simultaneously in various directions in space. Since the two feet are on the ground, the system defines a kinematically closed-chain which has redundancy problems that cannot be resolved using the laws of mechanics alone. We have developed a computational (optimization) technique that avoids the problems with the closed-chain formulation thus giving users of such models the ability to make predictions of joint moments, and potentially, muscle activations using more sophisticated musculoskeletal models. This paper describes the experimental verification of the computational technique that is used to estimate the ground reaction vector acting on an unconstrained foot while the other foot is attached to the ground, thus allowing human bipedal standing to be analyzed as an open-chain system. The computational approach was verified in terms of its ability to predict lower extremity joint moments derived from inverse dynamic simulations performed on data acquired from four able-bodied volunteers standing in various postures on force platforms. Sensitivity analyses performed with model simulations indicated which ground reaction force (GRF) and center of pressure (COP) components were most critical for providing better estimates of the joint moments. Overall, the joint moments predicted by the optimization approach are strongly correlated with the joint moments computed using the experimentally measured GRF and COP ( 0.78 ⩽ r 2 ⩽ 0.99 , median , 0.96 ) with a best-fit that was not statistically different from a straight line with unity slope (experimental=computational results) for postures of the four subjects examined. These results indicate that this model-based technique can be relied upon to predict reasonable and consistent estimates of the joint moments using the predicted GRF and COP for most standing postures.

An effective approach for dynamic analysis of rovers

In this paper a novel approach to dynamic formulation of rovers has been presented. The complexity of these multi-body systems especially on rough terrain, challenged us to use the Kane's method which has been preferred to others in these cases. As an example, symbolic equations of a six-wheeled rover, named CEDRA Rescue Robot which uses a shrimp like mechanism, have been derived and a simulation of forward and inverse dynamics has been presented. Due to the clear form of equations, each term defines a physical meaning which represents the effect of each parameter, resulting in a frame-work for performance comparison of rovers. Although the method has been described for a 2-D non-slipping case, it is also very useful for dimensional and dynamical optimization, high speed motion analysis, and checking various control algorithms. Furthermore, it can be extended to 3-D cases and other complicated mechanisms and rovers while conserving its inherent benefits and adding to the ease of handling nonholonomic constraints.

A Method to Extend Inverse Dynamic Simulation of Powertrains with Additional Dynamics

Inverse dynamic powertrain simulation, like in Advisor or the QSS-toolbox, has proven to be an efficient and successful approach to simulate vehicles during drive cycles. The approach is based on back-calculation of accelerations and torques from the prescribed velocities in the drive cycle, and the differentiation requirements in this simulation process limits the possibility to include additional states in the powertrain models. The main objective here is to extend the simulation with additional dynamics like e.g. mean value models of the engine. This is achieved using stable inversion of nonlinear systems that can handle such additional dynamics. Computer algebra can be used to perform the necessary model transformations. A key step in obtaining sufficient differentiation properties is to smooth the drive cycle using a kernel with interpretation as an implicit driver model. The proposed method is demonstrated using Mathematica for model transformation and Matlab for simulation.

Contact Modeling and Identification of Planar Somersaults on the Trampoline

This paper presents an extensive study on the trampoline-performed planar somersaults. First, a multibody biomechanical model of the trampolinist and the recurrently interacting trampoline bed are developed, including both the motion equations and the determination of joint reactions. The mathematical model is then identified –the mass and inertia characteristics of the human body are estimated, and the stiffness and damping characteristics of the trampoline bed are measured. By recording the actual somersault performances the motion characteristics of the stunts, i.e. the time variations of positions, velocities and accelerations of the body parts are also obtained. Finally, an inverse dynamics formulation for the system designated as an under-controlled system, is developed. The followed inverse dynamics simulation results in the torques of muscle forces in the joints that assure the realization of the actual motion. The reaction forces in the joints during the analyzed evolutions are also determined. Using the kinematic and dynamics characteristics, the nature of the stunts, the way the human body is maneuvered and controlled, can be studied.

An approach for developing an experimentally based model for simulating flight-phase dynamics.

This paper presents an approach for developing an experimentally validated dynamic multisegment model to simulate human flight-phase dynamics and multijoint control. Modeling and experimental techniques were integrated to systematically examine the contribution of multiple error sources to the accuracy of the model and to determine the complexity of a model that adequately emulates the dynamic behavior at the total-body and multijoint levels during flight. The accuracy of the model and of the experimental data was assessed using an inverse dynamics simulation of flight-phase motion for two representative cases: (i) a physical model released from a bar and (ii) a gymnast performing a layout dismount from a bar. Multijoint models with varying numbers of segments were assessed in order to determine the complexity of the model that adequately simulates the flight-phase task. A five-segment model was found to adequately simulate the layout dismount performed by the gymnast. The error introduced during modeling and digitizing contributed to an apparent violation of the conservation law manifested as large external forces acting on the nonactuated joints. These results demonstrate the need to reduce sources of error prior to testing hypotheses regarding feedforward and feedback components of the multijoint control system. The proposed approach for quantifying sources of error provides a crucial step that is required in the development of experimentally based dynamic models designed to examine and test hypotheses regarding multijoint control logic.

Wheelchair propulsion biomechanics: implications for wheelchair sports.

The aim of this article is to provide the reader with a state-of-the-art review on biomechanics in hand rim wheelchair propulsion, with special attention to sport-specific implications. Biomechanical studies in wheelchair sports mainly aim at optimising sport performance or preventing sport injuries. The sports performance optimisation question has been approached from an ergonomic, as well as a skill proficiency perspective. Sports medical issues have been addressed in wheelchair sports mainly because of the extremely high prevalence of repetitive strain injuries such as shoulder impingement and carpal tunnel syndrome. Sports performance as well as sports medical reflections are made throughout the review. Insight in the underlying musculoskeletal mechanisms of hand rim wheelchair propulsion has been achieved through a combination of experimental data collection under realistic conditions, with a more fundamental mathematical modelling approach. Through a synchronised analysis of the movement pattern, force generation pattern and muscular activity pattern, insight has been gained in the hand rim wheelchair propulsion dynamics of people with a disability, varying in level of physical activity and functional potential. The limiting environment of a laboratory, however, has hampered the drawing of sound conclusions. Through mathematical modelling, simulation and optimisation (minimising injury and maximising performance), insight in the underlying musculoskeletal mechanisms during wheelchair propulsion is sought. The surplus value of inverse and forward dynamic simulation of hand rim stroke dynamics is addressed. Implications for hand rim wheelchair sports are discussed. Wheelchair racing, basketball and rugby were chosen because of the significance and differences in sport-specific movement dynamics. Conclusions can easily be transferred to other wheelchair sports where movement dynamics are fundamental.

The use of inverse dynamics solutions in direct dynamics simulations.

Previous attempts to use inverse dynamics solutions in direct dynamics simulations have failed to replicate the input data of the inverse dynamics problem. Measurement and derivative estimation error, different inverse dynamics and direct dynamics models, and numerical integration error have all been suggested as possible causes of inverse dynamics simulation failure. However, using a biomechanical model of the type typically used in gait analysis applications for inverse dynamics calculations of joint moments, we produce a direct dynamics simulation that exactly matches the measured movement pattern used as input to the inverse dynamic problem. This example of successful inverse dynamics simulation demonstrates that although different inverse dynamics and direct dynamics models may lead to inverse dynamics simulation failure, measurement and derivative estimation error do not. In addition, inverse dynamics simulation failure due to numerical integration errors can be avoided. Further, we demonstrate that insufficient control signal dimensionality (i.e., freedom of the control signals to take on different "shapes"), a previously unrecognized cause of inverse dynamics simulation failure, will cause inverse dynamics simulation failure even with a perfect model and perfect data, regardless of sampling frequency.

Does Elastic Energy Enhance Work and Efficiency in the Stretch-Shortening Cycle?

This target article addresses the role of storage and reutilization of elastic energy in stretch-shortening cycles. It is argued that for discrete movements such as the vertical jump, elastic energy does not explain the work enhancement due to the prestretch. This enhancement seems to occur because the prestretch allows muscles to develop a high level of active state and force before starting to shorten. For cyclic movements in which stretch-shortening cycles occur repetitively, some authors have claimed that elastic energy enhances mechanical efficiency. In the current article it is demonstrated that this claim is often based on disputable concepts such as the efficiency of positive work or absolute work, and it is argued that elastic energy cannot affect mechanical efficiency simply because this energy is not related to the conversion of metabolic energy into mechanical energy. A comparison of work and efficiency measures obtained at different levels of organization reveals that there is in fact no decisive evidence to either support or reject the claim that the stretch-shortening cycle enhances muscle efficiency. These explorations lead to the conclusion that the body of knowledge about the mechanics and energetics of the stretch-shortening cycle is in fact quite lean. A major challenge is to bridge the gap between knowledge obtained at different levels of organization, with the ultimate purpose of understanding how the intrinsic properties of muscles manifest themselves underin-vivo-like conditions and how they are exploited in whole-body activities such as running. To achieve this purpose, a close cooperation is required between muscle physiologists and human movement scientists performing inverse and forward dynamic simulation studies of whole-body exercises.

Computer-aided configuration of modular robotic systems

A system has been developed to interactively assemble modular and reconfigurable robotic systems in a computer animation environment. The modular robot is based on a set of one, two and three degree of freedom joint modules and generic links. These modules may be assembled into a large class of robotic systems that include serial, parallel, mobile and hybrid configurations. A model of the configured robotic system is immediately available for use in a wide variety of robotics research areas, including: obstacle avoidance, redundant inverse kinematics, dynamic simulations, mobile platforms and world model databases.

Finite element vibration analysis of a helically wound tubular and laminated composite material beam

Finite element stiffness and consistent mass matrices are derived for helically wound, symmetrical composite tubes. The tubular element is considered to have constant cross-section and small deformations restricted to a plane. Each node has three degrees of freedom: axial and transverse displacement and rotation (slope of transverse displacement). Shell theory and lamination theory are used to formulate element stiffness matrices. The stiffness and mass matrices derived from the helically wound tubular composite material are reduced to symmetrically laminated composite beam. The free vibration and natural frequency are investigated for five different materials: steel, aluminum, carbon/N5280, Kevlar-49/epoxy and graphite/epoxy composites and various layup configurations. One application of a rotating flexible beam is investigated. The dynamic model of the flexible rotating beam includes the coupled effect between the rigid body motion and the flexible motion. The inverse dynamic simulation is performed by a prescribed driving torque in the numerical simulation. The influence of flexibility on rigid body motion are presented and discussed. From the numerical results, the composite material strongly possesses the lower power consumption and the passive control in damping the vibration of the structure.

A useful matrix form of Kane's equations

Cranes are systems highly used in industrial applications to transport heavy loads. The nonlinear behavior, and the crane own dynamic produce vibrations during the motion. In order to improve the system performance and specifically to ensure stability and a control with minimum vibrations, this work proposes a new strategy based on IDCS (Inverse Dynamic Control Simulation) using machine learning with Artificial Neural Networks ANN that gives the possibility to learn the inverse dynamic model of the crane and apply the feedback information based on the inverse dynamic control simulation. IDCS allows a suitable signal control avoiding noise and need for extra sensors in the feedback loop. The ANN creates the inverse dynamic model of the crane. The training architecture is developed to learn the inverse dynamic model of the crane in different operational points, and is used as feedforward control with the feedback dynamic in the IDCS scheme. Simulations and experiments are conducted with an industrial crane, and results show that the proposed method decreases vibration and position error. The proposed ANN-IDCS showed suitable performance compared to other controllers such as analytical inverse model control (AIC), Dual Matching Control (DMM) and shaped reference in feedforward (FRC).

Mixed methods for complex kinematic constraints in dynamic figure animation

Advances for achieving user control of a dynamic simulation of linked figures is presented. The formulation integrates forward and inverse kinematics specification within a mixed method of forward and inverse dynamics simulation. Kinematic specifications can be imposed through kinematic constraints embedded within the dynamics framework. Kinematic constraints may be simple (functions of one degree of freedom), or complex (functions of multiple interrelated degrees of freedom). Thus, keyframed paths, closed loops, point-to-path constraints, and collisions between links and the environment can be simulated. A simultaneous solution for unknown motion and forces of constraint is performed. A Lagrange multiplier method is outlined for incorporating these general constraints into the mathematical formulation of the equations of motion. Results from three example simulations are presented and discussed.

Inverse dynamic analysis and simulation of a platform type of robot

AbstractThis article presents an algorithm to solve the inverse dynamics for platform type of manipulators using Newton‐Euler equations of motion. We found that the inverse dynamics of the system is governed by thirty‐six linear equations. The number of these simultaneous equations can be reduced to six, if a proper sequence is taken. The relationships between the actuating forces and the shape of the structure are analyzed. Based on the algorithm, computer code for simulation was developed. Three cases were studied. As a result, configurations which minimize the actuating forces are suggested. It is also found that the fluctuation of the driving forces is lesser when the path is closer to the center of the base. These results are believed to be useful in the design and control of this type of manipulating devices.