Biomechanical loading of the shoulder complex and lumbosacral joints during dynamic cart pushing task

The primary objective of this study was to quantify the effect of dynamic cart pushing exertions on the biomechanical loading of shoulder and low back. Ten participants performed cart pushing tasks on flat (0°), 5°, and 10° ramped walkways at 20 kg, 30 kg, and 40 kg weight conditions. An optoelectronic motion capturing system configured with two force plates was used for the kinematic and ground reaction force data collection. The experimental data was modeled using AnyBody modeling system to compute three-dimensional peak reaction forces at the shoulder complex (sternoclavicular, acromioclavicular, and glenohumeral) and low back (lumbosacral) joints. The main effect of walkway gradient and cart weight, and gradient by weight interaction on the biomechanical loading of shoulder complex and low back joints was statistically significant (all p < 0.001). At the lumbosacral joint, negligible loading in the mediolateral direction was observed compared to the anterioposterior and compression directions. Among the shoulder complex joints, the peak reaction forces at the acromioclavicular and glenohumeral joints were comparable and much higher than the sternoclavicular joint. Increased shear loading of the lumbosacral joint, distraction loading of glenohumeral joint and inferosuperior loading of the acromioclavicular joint may contribute to the risk of work-related low back and shoulder musculoskeletal disorder with prolonged and repetitive use of carts.     

Antagonistic muscle-like actuator and its application to multi-d.o.f. forearm prosthesis

It is first clarified through simulational analysis that co-activation between agonist an muscle and its antagonist both having nonlinear elasticity is indispensable for the stiffness adjustment on an articulator movement. An antagonistic muscle-like actuator (AMA) is then proposed as an approach of imitating a skeleto-muscular articulation system. The AMA has two nonlinear springs which drive one joint antagonistically and provides the joint with the feasibility of stiffness adjustment. The development of the forearm prosthesis which has 6 d.o.f. is developed as an application of the AMA. Two d.o.f. for the wrist and 4 d.o.f. for the two fingers are driven by only one DC motor and one stepping motor for exchanging the driving mode. The whole mechanism is designed as almost the same volume as an adult's forearm. A shape fit mechanism for the finger is proposed, by which the three joints of one finger automatically adjust their angle according to the shape of the object to be grasped.     

Multibody modeling of human body for the inverse dynamics analysis of sagittal plane movements

A multibody methodology for systematic construction of a two-dimensional biomechanical model of a human body is presented, aimed at effective determination of the muscle forces and joint reaction forces in the lower extremities during sagittal plane movements such as vertical jump, standing long jump or jumping down from a height. While the hip, knee and ankle joints are modeled as enforced directly by the muscle forces applied to the foot, shank, thigh and pelvis at the muscle attachment points, the actuation of the other joints is simplified to the torques representing the respective muscle action. The developed formulation is applicable to both the flying and support phases, enhanced by an effective scheme for the determination of reaction forces exclusively in the lower extremity joints. The determination of reactions from the ground is also provided. The problem of muscle force redundancy in the lower extremities is solved by applying the pseudoinverse method, with post-processing procedures used to assure the muscle being tensile. Results of the inverse dynamics analysis of vertical jump are reported.     

Motion analysis of articulated objects from monocular images

This paper presents a new method of motion analysis of articulated objects from feature point correspondences over monocular perspective images without imposing any constraints on motion. An articulated object is modeled as a kinematic chain consisting of joints and links, and its 3D joint positions are estimated within a scale factor using the connection relationship of two links over two or three images. Then, twists and exponential maps are employed to represent the motion of each link, including the general motion of the base link and the rotation of other links around their joints. Finally, constraints from image point correspondences, which are similar to that of the essential matrix in rigid motion, are developed to estimate the motion. In the algorithm, the characteristic of articulated motion, i.e., motion correlation among links, is applied to decrease the complexity of the problem and improve the robustness. A point pattern matching algorithm for articulated objects is also discussed in this paper. Simulations and experiments on real images show the correctness and efficiency of the algorithms.     

A perioral dynamic model for investigating human speech articulation

A multibody system called the perioral dynamic model for investigating dynamic behavior of human speech articulator is presented. The model is based on the biomechanical architecture of human speech articulators, consisting of the soft tissue around the lips, the related muscles, and the jaw bone structure. The dynamic consequence of human speech articulation is revealed as a sequential perioral motion induced by the selectively activated muscle actions. As an anatomically consistent biomechanical platform, the perioral dynamic model is designed to represent the rigid jaw motion as well as the perioral soft tissue deformation interacting with each other. The perioral soft tissue in the model is approximated as a discrete particle system consisting of lumped point masses interconnecting with adjacent ones via viscoelastic elements. To ensure continuum-compatible static deformation in the discrete particle system, we introduce a method of adjusting element stiffness. We also present a new method for determining the effective forces acting on the jaw-bone-attached nodes that transforms jaw dynamics in the rigid body system into the one defined in the discrete particle system, keeping dynamic equivalency and equipollency between two systems. To derive muscle activations which let the developed dynamic model produce a simulated perioral motion mimicking an actual human speech behavior, we present an inverse dynamics technique driven by visual observation-based feedback of an actual lip motion.     

Kinematic Data Consistency in the Inverse Dynamic Analysis of Biomechanical Systems

Inverse dynamic analysis is used in the study ofhuman gait to evaluate the reaction forces transmittedbetween adjacent anatomical segments and to calculate thenet moments-of-force that result from the muscle activityabout each biomechanical joint. The quality of theresults, in terms of reaction and muscle forces, is greatlyaffected not only by the choice of biomechanical model butalso by the kinematic data provided as input. This three-dimensional data is obtained through the reconstruction ofthe measured human motion. A biomechanical model isdeveloped representing human body components with acollection of rigid bodies interconnected by kinematicjoints. The data processing, leading to the spatialreconstruction of the anatomical point coordinates, usesfiltering techniques to eliminate the high frequencycomponents arising from the digitization process. Thetrajectory curves, describing the positions of theanatomical points are obtained using a form of polynomialinterpolation, generally cubic splines. The velocities andaccelerations are then the polynomial derivatives. Thisprocedure alone does not ensure that the kinematic data isconsistent with the biomechanical model adopted, becausethe underlying kinematic constraint equations are notnecessarily satisfied. In the present work, thereconstructed spatial positions of the anatomical pointsare corrected by ensuring that the kinematic constraints ofthe biomechanical model are not violated. The velocity andacceleration equations of the biomechanical model are thencalculated as the first and second time derivatives of theconstraint equations. The solution to these equationsprovides the model with kinematically consistent velocitiesand accelerations. The procedures are demonstrated throughthe application to a normal cadence stride period and theresults discussed with respect to the underlying principlesof the techniques used.     

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.     

Biomechanical Model with Joint Resistance for Impact Simulation

Based on a general methodology using naturalco-ordinates, a three-dimensional whole body responsemodel for the articulated human body is presented inthis paper. The joints between biomechanical segmentsare defined by forcing adjacent bodies to share commonpoints and vectors that are used in their definition.A realistic relative range of motion for the bodysegments is obtained introducing a set of penaltyforces in the model rather than setting up newunilateral constraints between the system components.These forces, representing the reaction momentsbetween segments of the human body model when thebiomechanical joints reach the limit of their range ofmotion, prevent the biomechanical model from achievingphysically unacceptable positions. Improved efficiencyin the integration process of the equations of motionis obtained using the augmented Lagrange formulation.The biomechanical model is finally applied indifferent situations of passive human motion such asthat observed in vehicle occupants during a crash orin an athlete during impact.     

Modeling and analysis of planar rigid multibody systems with translational clearance joints based on the non-smooth dynamics approach

The main purpose of this paper is to present and discuss a methodology for a dynamic modeling and analysis of rigid multibody systems with translational clearance joints. The methodology is based on the non-smooth dynamics approach, in which the interaction of the elements that constitute a translational clearance joint is modeled with multiple frictional unilateral constraints. In the following, the most fundamental issues of the non-smooth dynamics theory are revised. The dynamics of rigid multibody systems are stated as an equality of measures, which are formulated at the velocity-impulse level. The equations of motion are complemented with constitutive laws for the normal and tangential directions. In this work, the unilateral constraints are described by a set-valued force law of the type of Signorini’s condition, while the frictional contacts are characterized by a set-valued force law of the type of Coulomb’s law for dry friction. The resulting contact-impact problem is formulated and solved as a linear complementarity problem, which is embedded in the Moreau time-stepping method. Finally, the classical slider-crank mechanism is considered as a demonstrative application example and numerical results are presented. The results obtained show that the existence of clearance joints in the modeling of multibody systems influences their dynamics response.     

Ankle controls that produce a maximal vertical jump when other joints are locked

Recently, there have been a number of attempts to apply optimal control theory to the analysis of human and animal movement. Because normal movements are very complicated and difficult to analyze, an experimental task that is easier to model and analyze has been chosen. Experimental subjects were instructed to jump as high as possible while keeping their knee and hip joints fully extended and their arms above their heads. The experiment is modeled by a two-segment inverted pendulum that is to be propelled as high as possible by a torque exerted at the joint. This torque is created by a simplified model of joint torque production by muscle and is controlled by a muscle "activation." The resulting optimal control problem is solved and the solution compared to the experimental results.     

Manufacture of a mechanical test rig to simulate the movements of forces within the shoulder

The shoulder complex, also known as the glenohumeral joint is the most manoeuvrable and one of the most well used joints of the human body. Over time problems can occur with the glenohumeral joint and surrounding muscles, cartilage, tendons and ligaments caused by ageing or by over stressing the shoulder complex. This work examines the design of a new innovative glenohumeral test rig. The test rig was required to imitate the movement of the humerus in the human body and replicate all the ranges of motion, which it can move in when combined with the relevant bones, muscles, ligaments and tendons in the shoulder complex. A variable force also had to be applied to the glenoid in all ranges of motion. Research had to be undertaken in the ranges of motion of the shoulder complex and the forces acting on the glenoid. Concept designs were initially created to mimic specific ranges of motion; adduction, flexion, internal (medial) and external (lateral) rotation for example. The concepts were evolved and combined to develop a test rig that would replicate any axial movement of the shoulder. Research determined the most appropriate manufacturing processes and materials so that the test rig could be manufactured in the material laboratories.     

Joint space trajectory planning for flexible manipulators

A trajectory planning approach for controlling flexible manipulators is proposed. It is demonstrated that choosing actual joint angles as the generalized rigid coordinates is the key to applying the proposed approach. From the observation of the special structure of the input matrix, the concepts of motion-induced vibration and inverse dynamics under a specified motion history of the joints are formed naturally. Based on the above concepts, trajectory planning in joint space is proposed by using the optimization technique to determine the motion of joints along a specified path in joint space or work space and for general point-to-point motion. The motion for each joint is assumed to be in a class consisting of a fifth-order polynomial and a finite terms of Fourier series. This parameterization of motion allows the optimal trajectory planning to be formulated as a standard nonlinear programming problem, which avoids the necessity of solving a two-point-boundary-value problem and using dynamic programming. Setting the accelerations to zero at the initial and the final times is used to obtain smoother motion to reduce the spillover energy into unmodeled high-frequency dynamics. A penalty term on vibration energy contained in the performance index is used to minimize the vibration of the system modeled by lower frequency only. The final simulation results show the effectiveness of the proposed approach and the advantage for proper trajectory planning. © 2995 John Wiley & Sons, Inc.     

A novel formulation for determining joint constraint loads during optimal dynamic motion of redundant manipulators in DH representation

The kinematic representations of general open-loop chains in many robotic applications are based on the Denavit–Hartenberg (DH) notation. However, when the DH representation is used for kinematic modeling, the relative joint constraints cannot be described explicitly using the common formulation methods. In this paper, we propose a new formulation of solving a system of differential-algebraic equations (DAEs) where the method of Lagrange multipliers is incorporated into the optimization problem for optimal motion planning of redundant manipulators. In particular, a set of fictitious joints is modeled to solve for the joint constraint forces and moments, as well as the optimal dynamic motion and the required actuator torques of redundant manipulators described in DH representation. The proposed method is formulated within the framework of our earlier study on the generation of load-effective optimal dynamic motions of redundant manipulators that guarantee successful execution of given tasks in which the Lagrangian dynamics for general external loads are incorporated. Some example tasks of a simple planar manipulator and a high-degree-of-freedom digital human model are illustrated, and the results show accurate calculation of joint constraint loads without altering the original planned motion. The proposed optimization formulation satisfies the equivalent DAEs.     

Analysis of isometric cervical strength with a nonlinear musculoskeletal model with 48 degrees of freedom

Background: Musculoskeletal models served to analyze head–neck motion and injury during automotive impact. Although muscle activation is known to affect the kinematic response, a model with properly validated muscle contributions does not exist to date. The goal of this study was to enhance a musculoskeletal neck model and to validate passive properties, muscle moment arms, maximum isometric strength, and muscle activity. Methods: A dynamic nonlinear musculoskeletal model of the cervical spine with 48 degrees of freedom was extended with 129 bilateral muscle segments. The stiffness of the passive ligamentous spine was validated in flexion/extension, lateral bending, and axial rotation. Instantaneous joint centers of rotation were validated in flexion/extension, and muscle moment arms were validated in flexion/extension and lateral bending. A linearized static model was derived to predict isometric strength and muscle activation in horizontal head force and axial rotation tasks. Results: The ligamentous spine stiffness, instantaneous joint centers of rotation, muscle moment arms, cervical isometric strength, and muscle activation patterns were in general agreement with biomechanical data. Taking into account equilibrium of all neck joints, isometric strength was strongly reduced in flexion (46 %) and axial rotation (81 %) compared to a simplified solution only considering equilibrium around T1–C7, while effects were marginal in extension (3 %). Conclusions: For the first time, isometric strength and muscle activation patterns were accurately predicted using a neck model with full joint motion freedom. This study demonstrates that model strength will be overestimated particularly in flexion and axial rotation if only muscular moment generation at T1–C7 is taken into account and equilibrium in other neck joints is disregarded.     

Modeling of the condyle elements within a biomechanical knee model

The development of a computational multibody knee model able to capture some of the fundamental properties of the human knee articulation is presented. This desideratum is reached by including the kinetics of the real knee articulation. The research question is whether an accurate modeling of the condyle contact in the knee will lead to reproduction of the complex combination of flexion/extension, abduction/adduction, and tibial rotation observed in the real knee. The model is composed by two anatomic segments, the tibia and the femur, whose characteristics are functions of the geometric and anatomic properties of the real bones. The biomechanical model characterization is developed under the framework of multibody systems methodologies using Cartesian coordinates. The type of approach used in the proposed knee model is the joint surface contact conditions between ellipsoids, representing the two femoral condyles, and points, representing the tibial plateau and the menisci. These elements are closely fitted to the actual knee geometry. This task is undertaken by considering a parameter optimization process to replicate experimental data published in the literature, namely that by Lafortune and his coworkers in 1992. Then kinematic data in the form of flexion/extension patterns are imposed on the model corresponding to the stance phase of the human gait. From the results obtained, by performing several computational simulations, it can be observed that the knee model approximates the average secondary motion patterns observed in the literature. Because the literature reports considerable inter-individual differences in the secondary motion patterns, the knee model presented here is also used to check whether it is possible to reproduce the observed differences with reasonable variations of bone shape parameters. This task is accomplished by a parameter study, in which the main variables that define the geometry of condyles are taken into account. It was observed that the data reveal a difference in secondary kinematics of the knee in flexion versus extension. The likely explanation for this fact is the elastic component of the secondary motions created by the combination of joint forces and soft tissue deformations. The proposed knee model is, therefore, used to investigate whether this observed behavior can be explained by reasonable elastic deformations of the points representing the menisci in the model.     

Motion planning for mobile manipulators with a non-holonomic constraint using the FSP (full space parameterization) method

The efficient utilization of the motion capabilities of mobile manipulators, i.e., manipulators mounted on mobile platforms, requires the resolution of the kinematically redundant system formed by the addition of the degrees of freedom (DOF) of the platform to those of the manipulator. At the velocity level, the linearized Jacobian equation for such a redundant system represents an underspecified system of algebraic equations, which can be subject to a varying set of contraints such as a non-holonomic constraint on the platform motion, obstacles in the workspace, and various limits on the joint motions. A method, which we named the Full Space Parameterization (FSP), has recently been developed to resolve such underspecified systems with constraints that may vary in time and in number during a single trajectory. In this article, we first review the principles of the FSP and give analytical solutions for constrained motion cases with a general optimization criterion for resolving the redundancy. We then focus on the solutions to (1) the problem introduced by the combined use of prismatic and revolute joints (a common occurrence in practical mobile manipulators), which makes the dimensions of the joint displacement vector components non-homogeneous, and (2) the treatment of a non-holonomic constraint on the platform motion. Sample implementations on several large-payload mobile manipulators with up to 11 DOF are discussed. Comparative trajectories involving combined motions of the platform and manipulator for problems with obstacle and joint limit constraints, and with non-holonomic contraints on the platform motions, are presented to illustrate the use and efficiency of the FSP approach in complex motion planning problems. © 1996 John Wiley & Sons, Inc.     

Analysis of the musculoskeletal system of the hand and forearm during a cylinder grasping task

Musculoskeletal disorders of the hand are mostly due to repeated or awkward manual tasks in the work environment and are considered a public health issue. To prevent their development, it is necessary to understand and investigate the biomechanical behavior of the musculoskeletal system during the movement. In this study a biomechanical analysis of the upper extremity during a cylinder grasping task is conducted by using a parameterized musculoskeletal model of the hand and forearm. The proposed model is composed of 21 segments, 28 musculotendon units, and 20 joints providing 24 degrees of freedom. Boundary conditions of the model are defined by the three-dimensional coordinates of 43 external markers fixed to bony landmarks of the hand and forearm and tracked with an optoelectronic motion capture system. External marker positions from five healthy participants were used to test the model. A task consisting of closing and opening fingers around a cylinder 25 mm in diameter was investigated. Based on experimental kinematic data, an inverse dynamics process was performed to calculate output data of the model (joint angles, musculotendon unit shortening and lengthening patterns). Finally, based on an optimization procedure, joint loads and musculotendon forces were computed in a forward dynamics simulation. Results of this study assessed reproducibility and consistency of the biomechanical behavior of the musculoskeletal hand system.     

On the optimal layout of multi-purpose trusses

This paper provides a solution to the problem of minimum mass design of multi-purpose trusses for which the design variables are not only the areas of the bars but also the positions of the joints. Displacement constraints and non-constant stress constraints (stability) are taken into account.

With multiple loading systems, the optimal structure is normally statically indeterminate and generally not even ·fully stressed”. The solution is obtained by successive iterations, using a gradient method with move-limits. For each iteration only the critical forces and displacements are considered and trusses with up to 40 joints have been optimized.

Analytical expressions are derived for the necessary gradients, i.e. for the partial derivatives of the displacements and forces with respect to the bar areas and joint coordinates.     

Kinematics for the whole arm of a serial-chain manipulator

This paper provides a viewpoint for kinematics for the whole arm of a serial-chain manipulator with 2-d.o.f. rotational joints. An in-depth understanding of the duality between a rigid link and a 2-d.o.f. joint allows us to derive simple and geometric equations describing the manipulator kinematics. The obtained kinematic equations are analyzed in two ways compared with the Frenet-Serret formula of a spatial curve which is utilized for a reference shape of the manipulator. One way is based on limit analysis where we increase the number of joints while the total length of the manipulator remains constant. The other way utilizes an extended mechanism through the link-joint duality. The information presented in this paper is useful for mechanism design dynamic analysis, control design and motion planning of the manipulators in whole-arm manipulation.     

A constrained assumed modes method for dynamics of a flexible planar serial robot with prismatic joints

In the present study, for the first time, flexible multibody dynamics for a three-link serial robot with two flexible links having active prismatic joints is presented using an approximate analytical method. Transverse vibrations of flexible links/beams with prismatic joints have complicated differential equations. This complexity is mostly due to axial motion of the links. In this study, first, vibration analysis of a flexible link sliding through an active prismatic joint having translational motion is considered. A rigid-body coordinate system is used, which aids in obtaining a new and rather simple form of the kinematic differential equation without the loss of generality. Next, the analysis is extended to include dynamic forces for a three-link planar serial robot called PPP (Prismatic, Prismatic, Prismatic), in which all joints are prismatic and active. The robot has a rigid first link but flexible second and third links. To model the prismatic joint, time-variant constraints are written, and a motion equation in a form of virtual displacement and virtual work of forces/moments is obtained. Finally, an approximate analytical method called the “constrained assumed modes method” is presented for solving the motion equations. For a numerical case study, approximate analytical results are compared with finite element results, which show that the two solutions closely follow each other.