A dynamical systems analysis of assisted and unassisted anterior and posterior hand-held load carriage

Load carriage is recognised as a primary occupational factor leading to slip and fall injuries, and therefore assessing balance maintenance during such tasks is critical in assessing injury risk. Ten males completed 55 strides under five carriage conditions: (1) unassisted anterior, (2) unassisted posterior, (3) assisted anterior, (4) assisted posterior and (5) unloaded gait (UG). Kinematic data were recorded from markers affixed to landmarks on the right side of each participant, in order to calculate segment angles for the foot, shank, thigh and pelvis. Continuous relative phase (CRP) variability was calculated for each segment pair and local dynamic stability was calculated for each segment in all three movement planes. In general, irrespective of the assistive device or movement plane, anterior load carriage was most stable (lower CRP variability and maximum finite-time Lyapunov exponents). Moreover, load carriage was less dynamically stable than UG, displaying the importance of objectively investigating safe load carriage practices.     

Neural-net-based control of dynamical systems: A case study

Multilayer perceptrons trained with the generalized delta rule or backpropagation procedure have been extensively applied in areas such as phoneme and image recognition and synthesis. Recently, many authors have reported interesting results on the application of these structures to the modeling and control of dynamical systems. In this article, we analyze the use of neural nets in a Model Reference adaptive Controller (MRAC) scheme for hydroturbine control. Several simulation results are provided, showing the feasibility of this approach and the factors involved in its design.     

Carry-over effects of backpack carriage on trunk posture and repositioning ability

Immediate effects of backpack carriage on spinal curvature and motor control in adults have been reported. However, there is a scarcity of evidence whether the effects would persist or not after the carrying load is removed. This study aimed to investigate the carry-over effects of backpack carriage on trunk posture and repositioning ability. Thirteen healthy adults were recruited and instructed to walk on a treadmill for 30 min with backpack (10% body weight) followed by 30-min unloaded walking. Participant’s trunk posture and repositioning ability were measured at different time points. During backpack carriage, reduction in lumbar lordosis and posterior pelvic tilt with significant increased cervical lordosis, thoracic kyphosis and trunk forward lean were observed. There was also a significant increase in repositioning errors in all spinal curvatures and trunk forward lean. After removal of the carrying load, there was a tendency for restoration of trunk posture and repositioning ability. However, the cervical lordosis and the repositioning error of all spinal curvatures could not be fully returned to the levels of the preload condition (all p < 0.05). The persistent changes in both spinal curvature and repositioning ability revealed an increased risk of spinal injury even after the backpack was removed, and the effects on the neck and back pain warrant future study.

Relevance to Industry

The effects of backpack carriage (10% body weight for 30 min) on the spine could not be fully restored after 30-min unloaded walking. The persistent changes in both spinal curvature and repositioning ability revealed an increased risk of spinal injury even after the backpack was removed. Proper postural reminder might be given to backpack users to alleviate the adverse effects induced after prolonged backpack carriage.     

The metabolic cost of backpack and shoulder load carriage.

Eleven healthy male volunteer soldiers (mean [SD] age 24.0 [2.8] years, stature 174.1 [5.2] cm, body weight 73.2 [10.8] kg, body fat 14.2 [5.0]% and maximal oxygen uptake 4.1 [0.4] 1 min-1) walked at 4.8 km h-1 on a motor driven treadmill for 5 min at each of three gradients (0, 2.5 and 5%) whilst carrying a two-part 26 kg load either on each shoulder or strapped to a backpack frame. The load was made up of two cylinders, one weighing 18.4 kg and the other weighing 7.6 kg. For all treadmill gradients the mean (SD) backpacking heart rates and oxygen uptakes (0% gradient, 122 [10] beats min-1, 1.51 [0.11] 1 min-1; 2.5% gradient, 135 [10] beats min-1, 1.81 [0.13] 1 min-1; 5% gradient, 155 [7] beats min-1, 2.21 [0.11] 1 min-1) were significantly (p less than 0.001) lower than for shoulder load carriage (0% gradient, 130 [9] beats min-1, 1.70 [0.12] 1 min-1, 2.5% gradient, 147 [8] beats min-1; 2.01 [0.10] 1 min-1; 5% gradient 164 [9] beats min-1, 2.39 [0.11] 1 min-1). The relative oxygen cost of backpacking was 4.3-4.7% VO2 max lower than for shoulder load carriage. It is concluded that the metabolic cost of backpacking an asymmetric two part 26 kg load was significantly less than for shoulder load carriage when walking at 4.8 km h-1 on a treadmill over gradients of 0-5%.(ABSTRACT TRUNCATED AT 250 WORDS)     

Hybrid dynamical systems: robust control synthesis problems

The paper presents a new approach to robust control synthesis problems for hybrid dynamical systems. The hybrid system under consideration is a composite of a continuous plant and a discrete event controller. State and output feedback problems are considered. The main results are given in terms of the existence of suitable solutions to a dynamic programming equation and a Riccati differential equation of the H^∞ filtering type. These results show a connection between the theories of hybrid dynamical systems and robust and nonlinear control.     

A note on the control of uncertain linear dynamical systems with constrained control input

A method is presented to design a stabilizing saturated state feedback controller for linear continuous-time systems with bounded uncertainty acting via the input channel.     

A control problem for affine dynamical systems on a full-dimensional polytope

Given an affine system on a full-dimensional polytope, the problem of reaching a particular facet of the polytope, using continuous piecewise-affine state feedback is studied. Necessary conditions and sufficient conditions for the existence of a solution are derived in terms of linear inequalities on the input vectors at the vertices of the polytope. Special attention is paid to affine systems on full-dimensional simplices. In this case, the necessary and sufficient conditions are equivalent and a constructive procedure yields an affine feedback control law, that solves the reachability problem under consideration.     

Multi-objective analysis for assessing simultaneous changes in regional spinal curvatures under backpack carriage in young adults

Change in sagittal spinal curvature from the neutral upright stance is an important measure of the heaviness and correctness of backpack use. As current recommendations, with respect to spinal profile, of backpack load thresholds were based on the significant curvature change in individual spinal region only, this study investigated the most critical backpack load by assessing simultaneously the spinal curvature changes along the whole spine. A motion analysis system was used to measure the curvature changes in cervical, upper thoracic, lower thoracic and lumbar regions with backpack load at 0, 5, 10, 15 and 20% of body weight. A multi-objective goal programming model was adopted to determine the global critical load of maximum curvature change of the whole spine in accordance with the maximum curvature changes of the four spinal regions. Results suggested that the most critical backpack load was 13% of body weight for healthy male college students.

Practitioner Summary: As current recommendations of backpack load thresholds were based on the significant curvature change in individual spinal region only, this study investigated the backpack load by considering simultaneously the spinal curvature changes along the whole spine. The recommendation, in terms of the global critical load, was 13% of body weight for healthy male college students.     

On the control of discrete-event dynamical systems

We study a class of problems related to the supervisory control of a discrete-event system (DES), as formulated by Ramadge and Wonham, and we focus on the computational effort required for their solution. While the problem of supervisory control of a perfectly observed DES may be easily solved by dynamic programming, the problem becomes intractable (in the sense of complexity theory) when imperfectly observed systems are considered. Research supported by the Army Research Office (Grant No. DAAL03-86-K-0171) and by an NSF PYI award, with matching funds from Bellcore Inc.     

Robust control of set-valued discrete-time dynamical systems

This paper presents results obtained for the control of set-valued discrete-time dynamical systems. Such systems model nonlinear systems subject to persistent bounded noise. A robust control problem for such systems is introduced. The problem is formulated as a dynamic game, wherein the controller plays against the set-valued system. Both necessary and sufficient conditions in terms of (stationary) dynamic programming equalities are presented. The output feedback problem is solved using the concept of an information state, where a decoupling between estimation and control is obtained. The methods yield a conceptual approach for constructing controlled-invariant sets and stabilizing controllers for uncertain nonlinear systems     

Discrete dynamical systems with symmetries: Computer analysis

Discrete dynamical systems and mesoscopic lattice models are considered from the standpoint of their symmetry groups. Universal specific features of deterministic dynamical system behavior associated with nontrivial symmetries of these systems are specified. Group nature of soliton-like moving structures of the “spaceship” type in cellular automata is revealed. Study of lattice models is also considerably simplified when their symmetry groups are taken into account. A program in C for group analysis of systems of both types is developed. The program, in particular, constructs and investigates phase portraits of discrete dynamical systems modulo symmetry group and seeks dynamical systems possessing special features, such as, for example, reversibility. For mesoscopic lattice models, the program computes microcanonical distributions and looks for phase transitions. Some computational results and observations are presented.     

Sensitivity analysis of stochastic dynamical systems

A new, efficient algorithm is developed for the sensitivity analysis of a general class of stochastic dynamical systems. The algorithm is based on an idea of the likelihood ratio method that utilizes a probability density information for the sensitivity analysis, and on the Fokker-Planck or Kolmogorov's forward equation for computing the evolution of probability densities. The ideas of stochastic sensitivity analysis and likelihood ratio method are presented and combined to derive the sensitivity of average values of the performance functional with respect to system parameters. The present algorithm avoids the time consuming Monte Carlo or stochasic simulations, and, instead, sensitivity gradients of the probability density function and performance functional are directly computed during single-run simulation.     

Stability analysis of non-linear dynamical systems

This paper examines the possibility of using non-linear comparison systems in the stability analysis of non-linear dynamical systems. Stability criteria and estimates of the stability region of non-linear comparison systems are established. It is shown that the use of non-linear comparison systems may lead to less conservative results than those obtained by linear ones.     

Comments on "Decentralized control of interconnected dynamical systems"

In this note it is pointed out that in the above paper Proposition 2 quoted is not exact and Corollary 1 is incorrect. Improvements on Theorem 7, Theorem 8, ii) of Theorem 9, and Corollary 4 in the paper are also made.     

Adaptive control for nonlinear nonnegative dynamical systems

Nonnegative and compartmental models are widespread in engineering systems and life sciences and play a key role in the understanding of these systems. In this paper, we develop a direct adaptive control framework for nonlinear uncertain nonnegative and compartmental dynamical systems. The proposed framework is Lyapunov-based and guarantees partial asymptotic set-point regulation; that is, asymptotic set-point regulation with respect to part of the closed-loop system states associated with the plant. In addition, the adaptive controller guarantees that the physical system states remain in the nonnegative orthant of the state space.     

On the decentralized control of interconnected dynamical systems

It is shown that rise fixed modes of an interconnected dynamical system under decentralized control are precisely the uncontrollable and unobservable states of the individual system components. As such, the system can be stabilized by decentralized controllers if and only if its individual system components can be stabilized. Moreover, these conditions are shown to be equivalent to the conditions for stabilizing the system using a global controller.     

Identification and control of dynamical systems using neuralnetworks

It is demonstrated that neural networks can be used effectively for the identification and control of nonlinear dynamical systems. The emphasis is on models for both identification and control. Static and dynamic backpropagation methods for the adjustment of parameters are discussed. In the models that are introduced, multilayer and recurrent networks are interconnected in novel configurations, and hence there is a real need to study them in a unified fashion. Simulation results reveal that the identification and adaptive control schemes suggested are practically feasible. Basic concepts and definitions are introduced throughout, and theoretical questions that have to be addressed are also described.     

A modified variable structure control algorithm for stabilization of uncertain dynamical systems

A modified VS feedback is suggested for robust stabilization of continuous-time dynamical systems in the presence of parametric and external time-varying disturbances satisfying the ‘matching conditions’. The main feature of the proposed algorithm is that it contains additional switching ‘integral’ terms which track the unknown disturbances and make it possible to achieve the typical VSS robustness by using switching terms in the control law with arbitrarily small amplitude. This result can be achieved only if the derivatives of the disturbances are bounded.