Excess Degrees Of Freedom Research Articles

Efficient and Stable Simulation of Inextensible Cosserat Rods by a Compact Representation

AbstractPiecewise linear inextensible Cosserat rods are usually represented by Cartesian coordinates of vertices and quaternions on the segments. Such representations use excessive degrees of freedom (DOFs), and need many additional constraints, which causes unnecessary numerical difficulties and computational burden for simulation. We propose a simple yet compact representation that exactly matches the intrinsic DOFs and naturally satisfies all such constraints. Specifically, viewing a rod as a chain of rigid segments, we encode its shape as the Cartesian coordinates of its root vertex, and use axis‐angle representation for the material frame on each segment. Under our representation, the Hessian of the implicit time‐stepping has special non‐zero patterns. Exploiting such specialties, we can solve the associated linear equations in nearly linear complexity. Furthermore, we carefully designed a preconditioner, which is proved to be always symmetric positive‐definite and accelerates the PCG solver in one or two orders of magnitude compared with the widely used block‐diagonal one. Compared with other technical choices including Super‐Helices, a specially designed compact representation for inextensible Cosserat rods, our method achieves better performance and stability, and can simulate an inextensible Cosserat rod with hundreds of vertices and tens of collisions in real time under relatively large time steps.

Efficient Memory-Bounded Optimal Detection for GSM-MIMO Systems

We investigate the optimal signal detection problem in large-scale multiple-input multiple-output (MIMO) system with the generalized spatial modulation (GSM) scheme, which can be formulated as a closest lattice point search (CLPS). To identify invalid signals, an efficient pruning strategy is needed while searching on the GSM decision tree. However, the existing algorithms have exponential complexity, whereas they are infeasible in large-scale GSM-MIMO systems. In order to tackle this problem, we propose a memory-efficient pruning strategy by leveraging the combinatorial nature of the GSM signal structure. Thus, the required memory size is squared to the number of transmit antennas. We further propose an efficient memory-bounded maximum likelihood (ML) search (EM-MLS) algorithm by jointly employing the proposed pruning strategy and the memory-bounded best-first algorithm. Theoretical and simulation results show that our proposed algorithm can achieve the optimal bit error rate (BER) performance, while its memory size can be bounded. Moreover, the expected time complexity decreases exponentially with increasing the signal-to-noise ratio (SNR) as well as the system’s excess degree of freedom, and it often converges to squared time under practical scenarios.

A Novel QP-Based Kinematic Redundancy Resolution Method With Joint Constraints Satisfaction

Kinematically redundant manipulators are advantageous for their increased dexterity and ability to fulfill some secondary requirements along with their primary task to follow the prescribed trajectory. The redundancy results in a non-trivial inverse kinematics problem (IK). Standard methods of redundancy resolution are based on the pseudoinverse of the Jacobian matrix of the manipulator. The excessive degrees of freedom are utilized to perform secondary tasks that are projected onto the null space of the Jacobian matrix. However, the joint constraints satisfaction cannot be easily ensured in this way—even though methods that account for the joint position limits are known, the constraints for joint velocities and especially accelerations are not straightforward to include. In this paper, a novel redundancy resolution method based on a less common quadratic programming (QP) approach is described. The proposed velocity-level IK method allows fulfilment of the joint constraints at the position, velocity, and acceleration levels. In the derived formulas, accelerations instead of the usual velocities are used—the discretized joint state equations allow the use of joint accelerations as decision variables in the QP problem. The developed algorithm is investigated in a series of numerical tests in which the kinematics of the KUKA LWR4+ redundant 7-DOF manipulator is exploited. The newly elaborated QP-based IK method is firstly compared with the classic pseudoinverse-based approach and then tested for its ability to keep the joint accelerations within the prescribed bounds. The prospects of the proposed approach are discussed in the concluding section.

АНАЛИЗ ПРОБЛЕМ ТОЧНОСТИ ПРЕЦИЗИОННЫХ ПРОМЫШЛЕННЫХ РОБОТОВ

The article highlights the issues of compliance of the mechanics of manipulators of precision industrial robots (PIRs) with the highest accuracy standards specified in the normative technical documentation and practically achieved in the fields of machine-building, instrument-making and electronic industries. In the spotlight there are the possibilities of systems of multi - connected control of complex spatial mechanisms with excessive degrees of freedom (including manipulators of PIRs), the possibilities of systems of multi-circuit control of PIR drives with precision sensors of linear and angular displacements, velocities, accelerations, acceleration gradients (in the future), the issues of matching these parameters with the parameters of the computational part of control systems — the bit depth of digital sensors (more than 20 digits) with an resolution of less than an arc second. PIR manipulators are used in systems of multi-connected and multi-circuit regulation and control with elements of artificial intelligence, such as automatic adjustment systems (AASs), automatic control systems (ACSs) and artificial intelligence systems (AISs). These problems are considered in a wide range, including the transition to the fields of nanotechnologies, specifically: for linear (nanometers) and angular (hundredths of arc seconds) measurements, as well as the measurements of velocities, accelerations, and acceleration gradients (in the future — for systems with a human operator in the loop, i.e. human-machine systems (HMSs)).

Game as a psychological program of the subject’s life activity

Modern features of human life activity are characterized by the accumulation of risks of critical uncertainty, lack of predictability and rational basis for productive decision-making and social interaction. It actualizes the large-scale problems of various genesis. In particular, it is talked about global problems of the military-political, medical-social and cultural-economic context. The hybrid geopolitical confrontation, the COVID-19 sanitary crisis, the precariat-movements Gilets jaunes and BLM and others are the examples of this. Therefore, a modern person is faced with the critical urgency to find and use reliable means of life activity in such conditions. Scientific psychology has the task of creating and providing practical effective mental tools for a person’s life in the complex social conditions of everyday life. The development of such tools should be carried out on a multidisciplinary methodological basis. It is argued that the most important tool of human life under these circumstances is the phenomenon of the game which is in the subject field of philosophical, psychological, mathematical, sociological, cultural and political discourses. Comparative scientific analysis confirms that the game is a universal onto-phenomenal form and a productive program of subject’s rational life activity; a way of the person’s and a society’s being in difficult conditions. In the field of scientific methodology, the game becomes a canonical multidisciplinary basis for research of this range of problems. This opportunity is given to the game by its ability to ensure the processes of systemgenesis of human and social group, because it is the game as a metaprogram of the subject’s life activity that optimally ensures the implementation of the fundamental principles of systemgenesis: a) ordered integrity; b) self-stabilization; c) self-organization, d) hierarchization and e) interaction of system components. Among these principles, the leading role is played by the principle of mutual cooperation, which is provided by the mechanisms of releasing the components of the system from excessive degrees of freedom, creating a model of useful results for it. These principles are axiomatically and isomorphically implemented both at the level of personality and at the level of social communication. This is due to the game programming of the subject, which exactly corresponds to the situation relevant to him. A universal system-forming factor in the genesis of a personal game program here is usefulness. The game combines time-space indicators, indicators of the result quality, and the mechanisms of its verification. The game introduces a program-genetic context of influence on the formation of human behavior from the mode of imitation to the mode of full-fledged action in moments of uncertainty. The full-fledged application of the game as a metaprogram of activity in difficult conditions spreads in society the priorities of intersubjective communicative rationality. The canonicity of the game here is manifested in the isomorphism of its content and participation with the mechanisms of Pareto-optimality (mathematical game theory), communicative rationality (philosophy), and taxonomy of the types of leading human activity (psychology of activity).

Model-based water-flooding optimization using multi-objective approach for efficient reservoir management

The efficient development of an oil field mostly depends on a comprehensive optimization of subsurface flow. To account for several discrete or even contradicting objectives, multi-objective optimization (MOO) approach presents multiple optimum solutions for decision-making processes. There are excessive degrees of freedom in any optimization problem of the life-cycle of water-flooding to optimize the short-term performance during the process. Choosing each strategy has a different impact on the long-term reservoir performance. Thus, in this study, we have utilized two different model-based algorithms based on multi-objective particle swarm optimization (MOPSO) and non-dominated sorting genetic algorithm II (NSGA-II) methods with some modifications to plan the short- and long-term production strategies simultaneously in water-flooded reservoirs. These algorithms are both population-based techniques, in which the Pareto-ranking approach is combined with the inherent search towards the optimal solution for a multi-criterion optimization problem. Maximizing the long-term Net Present Value (LNPV) and short-term (discounted) NPV (SNPV) are the objectives to be met in the investigated MOO problems. To address the imperfect Pareto front obtained in MOO problems, some modifications have been added to the utilized algorithms, including using a modified comparison operator in the NSGA-II method and employing the crowding distance parameter in the leader selection process together with a revised archive controller as well as a dynamic boundary search to MOPSO algorithm. By these means, the entire Pareto fronts are actively generated, which covers the complete solutions area through both algorithms. To validate the developed approaches, two benchmark water-flooded reservoir models have been employed. In the first case, the optimization parameters are the wells injection rates in the Egg benchmark reservoir model. In the second one, we have adjusted the opening values of the inflow control valves (ICV) of smart wells in the water-flooding process of a layered reservoir with a five-spot pattern. The effect of the trading-off between Pareto elitism and diversity on the final results is investigated for both algorithms. Results illustrate that the competitive values of the NPV functions, LNPV and SNPV pairs, lying on the obtained Pareto front, provide a promising criterion to improve the decision-making process. A comparison of various methods shows that for both case-studies, MOPSO can strongly propose a production strategy that more appropriately optimizes SNPV and LNPV compared to the NSGA-II as well as compared to some previous efforts published in the literature. A high rate of convergence, together with the logical Pareto front having enough diversity and uniformity, and also the independency of the final solution on the initial guess, are the main advantages of MOPSO in comparison with other approaches.

Improving technical fitness of race walkers on the basis of special exercises to focus on key parameters of movements

In race walking, the reliability of competitive activity, the risks of disqualification are determined by athlete's stable control of the key motion characteristics at a distance, especially in the face of fatigue. Therefore, the formation of specialized sensations in an athlete to control these movements is an important condition for sports technique improvement. Hypothesis of study: the use of special exercises to increase the analytical perception of motion key parameters will increase the effectiveness of race walking technique, control for fatigue development. Objective of study: to show the possibilities of increasing special fitness in race walking through the use of special exercises, improvement of the analytical perception of motion key parameters. Subjects and methods of study: 10 athletes aged 17-20 years and engaged in sports training for 4-6 years participated in the study. Special exercises, assessment of race walking technique (video shooting) before and after their performance within three weeks (10 sessions) were used. Results: it is shown that the targeted use of special exercises with the analysis of subjective sensations creates conditions for the activation in the athlete of specialized perceptions for the basic sports technique elements. After the use of special exercises, the increase in speed was due to an increase in the stride length - 1.14 m (S = 0.04), relative to the initial one - 1.09 m (S = 0.03) (p < 0.01). The stride length increase in athletes occurred at the expense of the length of the “rear” stride ( = 0.43 м; S = 0.02) at statistically significant differences from the initial indices. This created the prerequisites for improving athletic performance. Conclusions. Special exercises focusing on key parameters of movements contribute to increase of technical fitness of race walkers. The proposed approach creates the prerequisites for further research on the formation of the motor composition of the skill of body position accuracy, the development of sensations of free movement, inertia, liberation from excessive degrees of freedom in the parts of the body with account for the functional state of the athlete.

Range of octocopter balancing angles with excessive degrees of freedom

Range of octocopter balancing angles with excessive degrees of freedom

Path Planning of Complex Pipe Joints Welding with Redundant Robotic Systems

SummaryIn this paper, a path planning algorithm for robotic systems with excess degrees of freedom (DOF) for welding of intersecting pipes is presented. At first step, the procedure of solving the inverse kinematics considering system kinematic redundancy is developed. The robotic system consists of a 6 DOF robotic manipulator installed on a railed base with linear motion. Simultaneously, the main pipe is able to rotate about its longitudinal axis. The system redundancy is employed to improve weld quality. Three different simulation studies are performed to show the effect of the robotic system kinematic redundancy to plan a better path for the welding of intersecting pipes. In the first case, it is assumed that robotic manipulator base and main pipe are fixed, and the path is planned only with manipulator joints motion. In the second case, only the robot base is free to move and the main pipe is fixed, and in the third case, the main pipe is free to rotate together with the base of the manipulator. It is seen that kinematic constraints according to the system’s redundancy will help to plan the most efficient path for the welding of complex pipe joints.

Effects of Voluntary Agonist-Antagonist Coactivation on Stability of Vertical Posture.

We explored the effects of voluntary coactivation of agonist-antagonist leg and trunk muscles on stability of vertical posture. Young healthy subjects performed several tasks while standing with no additional muscle coactivation, low coactivation, and high coactivation. Postural stability was estimated using indices of postural sway and of intertrial variance in the space of muscle groups with parallel scaling of activation levels (M-modes). An increase in coactivation led to a significant increase in the postural sway speed reflected in faster rambling and trembling trajectories. Coactivation also led to a relative drop in the variance component that had no effects on the center of pressure coordinate and an increase in the component that shifted the center of pressure. We conclude that additional muscle coactivation does not help to stabilize vertical posture and is more likely to lead to postural destabilization. The results are consistent with an earlier hypothesis on muscle coactivation ensuring abundance (excessive degrees of freedom) at the level of control variables.

Motion planning for an actuated flexible polyhedron manifold

Stepping or crawling translation manoeuvres are computationally complicated when applied to hyper-redundant mechanisms. We introduce a motion planner for a novel polyhedron-shaped Actuated Flexible Manifold (AFM). The AFM is a two-dimensional closed or open surface embedded in . The AFM can reshape itself up to a given radius of curvature at any given location on its surface. Motion can be made possible using a mesh of linear actuators. Our first goal was to calculate the forward and inverse kinematics in the configuration space for a discrete flat AFM. We demonstrate our solution on some actuated flexible grid-shaped manifolds using different actuation methods. We then simulate a translation of a hyper-redundant discrete, polyhedron-shaped AFMs. In addition, we show how the AFM can use its excessive degrees of freedom to avoid obstacles while moving. Our algorithm is applicable for a set of hyper-redundant mechanisms of various geometries.

How well do the muscular synergies extracted via non-negative matrix factorisation explain the variation of torque at shoulder joint?

The way central nervous system manages the excess degrees of freedom to solve kinetic redundancy of musculoskeletal system remains an open question. In this study, we utilise the concept of synergy formation as a simplifying control strategy to find the muscle recruitment based on summation of identified muscle synergies to balance the biomechanical demands (biaxial external torque) during an isometric shoulder task. A numerical optimisation-based shoulder model was used to obtain muscle activation levels when a biaxial external isometric torque is imposed at the shoulder glenohumeral joint. In the numerical simulations, 12 different shoulder torque vectors in the transverse plane are considered. For each selected direction for the torque vector, the resulting muscle activation data are calculated. The predicted muscle activation data are used for grouping muscles in some fixed element synergies by the non-negative matrix factorisation method. Next, torque produced by these synergies are computed and projected in the 2D torque space to investigate the magnitude and direction of torques that each muscle synergy generated. The results confirmed our expectation that few dominant synergies are sufficient to reconstruct the torque vectors and each muscle contributed to more than one synergy. Decomposition of the concatenated data, combining the activation and external torque, provided functional muscle synergies that produced torques in the four principal directions. Four muscle synergies were able to account for more than 95% of variation of the original data.

Learning how, what, and whether to communicate: emergence of protocommunication in reinforcement learning agents

This paper examines whether and how a primitive form of communication emerges between adaptive agents by using their excess degrees of freedom in action and perception. As a case study, we consider a game in which two reinforcement learning agents learn to earn rewards by intruding into the other’s territory. Our simulation shows that agents with lights and light sensors can learn turn-taking behavior for avoiding collisions using visual communication. Further analysis reveals a variety in the mapping of messages to signals. In some cases, the differentiation of roles into a sender and a receiver was observed. The result confirmed that protocommunication can emerge through interaction between agents having generic reinforcement learning capability.

Generation of natural motions for redundant multi‐joint systems: A differential‐geometric approach based upon the principle of least actions

AbstractThis article challenges Bernstein's problem of redundant degrees of freedom (DOF) that remains unsolved from both the standpoints of physiology and robotics. A rather simpler but difficult control problem of movements of human‐like multi‐joint reaching with excess DOF is analyzed from Newtonian mechanics and differential geometry. It is shown that, regardless of ill‐posedness of inverse kinematics for such a redundant system, a simpler control signal composed of a well‐tuned (synergistic) combination of task‐space position feedback (corresponding to spring‐like forces) and joint velocity feedback (viscous‐like forces) leads to a skilled motion of reaching in a natural way without solving inverse kinematics or dynamics. Fundamental characteristics of human skilled multi‐joint movements such as (1) generation of a quasi‐straight line trajectory of the endpoint and (2) a little “variability” in task space but notable “variability” in joint space are analyzed from the concepts of “stability on an EP (equilibrium‐point) manifold” and “transferability to an EP submanifold.” It is claimed that the control signal exerts torques on joints of the whole arm just like a single virtual‐spring drawing the endpoint of the arm to the target while giving a specified viscosity to each joint. This leads to an interpretation that skilled reaching movements emerge through formation of a set of neuro‐motor signals exerting relevant group of muscles to generate a total potential energy equivalent to that of the spring. Discussions are presented on how such control signals in case of human reaching can be generated in a feedforward manner with capability of anticipatory adjustments of stiffness. © 2005 Wiley Periodicals, Inc.

USING POST-EIGENSTRUCTURE ASSIGNMENT DESIGN FREEDOM FOR THE IMPOSITION OF CONTROLLER STRUCTURE

Recent algorithm developments in the field of output-feedback eigenstructure assignment make use of the available design freedom in a multi-stage assignment process. Depending on the number of degrees of freedom available and the manner in which they are distributed between the stages, it is possible that not all will be used. This paper develops an algorithm by which these excess degrees of freedom may be put to use by nulling individual elements of the gain matrix, thereby imposing structure upon the resulting controller. Consideration is given to the effect of this process on the remaining gain matrix elements.

Psychophysiological Mechanisms of Choice in High School Students and University Students Specializing in Humanities

Elucidation of behavioral reactions of high school and university students in stochastic and deterministic environments is an important problem. Rapidly changeable and unstable social and information environment makes it urgent to raise the problem of decision-making in all areas of human activity [18]. According to the theory of functional systems suggested by P. K. Anokhin, a behavioral act is considered as an aggregate of many physiological processes selected at the stage of decision-making [1-3]. According to V. B. Shvyrkov [25], a behavioral act should be regarded as a component of a functional system, because interaction of external information with internal processes is mediated by the entire operating complex of the functional system. Although it is beyond doubt that the closed circuit of a functional system is cyclic, principles of central mechanisms are a subject of discussion [23]. In the physiological sense the process of decisionmaking is based on selection of certain executive mechanisms and physiological integration of results of afferent synthesis [2]. A decrease in the degree of freedom of the central nervous system neurons and a decrease in their possible involvement in the functional aggregates are neurophysiological characteristics of the stage of decision-making. Excessive degrees of freedom are easily sorted out by the frontal lobes of the brain. A. R. Luriya considered the frontal lobes of the brain as the main nervous substrate of decision-making in goaloriented spontaneous activity [13]. Psychophysiological aspects of this problem are based on mechanisms of decision-making at different levels of sensorimotor and mental activities [7]. According to the physiological concept suggested by Anokhin, psychophysiological mechanisms of choice can be studied from individual manifestation of different forms of behavioral activity under different experimental settings [18]. Studies of behavior under uncertain conditions are of particular interest [17, 22]. Environmental uncertainty implies the absence of objective and subjective determinancy [10]. According to [5, 21], the main behavioral reaction under uncertain conditions is individual prognosis of the probability of future events. According to A. S. Batuev [4], the process of decision-making includes formation of a dynamic constellation of spatially separated brain structures involved in a behavioral act. Adaptive behavior in a variable environment is based on probabilistic prognosis implemented in associative brain systems. For example, thalamofrontal structures are involved in probabilistic prognosis and goal-oriented behavior. According to the contemporary viewpoint, the rates of decision-making and central information processing are determined by nervous system mobility [24]. Decision-making as an object of psychophysiological research can be studied experimentally, providing thereby the opportunity for testing functional systems of different levels of hierarchy and functional systems involved in various psychophysiological processes. There are objective and subjective factors of learning activity. The psychophysiological state of high school and university students depends on these factors [9, 20], Analytical capacity is an important component of successful learning [8, 9]. It should be noted that agerelated psychophysiological mechanisms of making choice remain virtually obscure [9]. The goal of this work was to elucidate age-related dynamics of certain psychophysiological mechanisms of choice in high school students and university students specializing in humanities.

Neutron excess in analytical expressions for fusion barrier parameters

The neutron excess dependence of heavy-ion fusion barriers is investigated, guided by predictions of different ion-ion potentials. We develop phenomenological expressions for the fusion barrier radii and heights, involving both the entrance channel mass asymmetry and neutron excess of the projectile and target. Compared to commonly used formulas, the developed expressions reproduce theoretical barrier parameters with a higher accuracy. Furthermore, they provide a means to assess the importance of the neutron excess degree of freedom implied by each potential.

Finite element modeling discretization requirements for the laser forming process

Due to high efficiency and accuracy, 3D finite element modeling has been an effective tool to analyze the laser forming process. The discretization of a given finite element model has a significant effect on the results of simulation. To reduce the lengthy computational time caused by excessive degrees of freedom while insuring an accurate solution, the minimum discretization requirements of finite element modeling of the laser forming process need to be determined. This paper investigates the effects of temporal and spatial discretization on the final angular deformation of the plate. Numerical results under different discretization conditions are examined. The minimum requirements for discretization of 3D finite element models for laser forming are established by examining the convergence of the numerical solutions with increased discretization. The numerical results are in good agreement with the experimental measurements.

Self-Organizing Feature Maps for Modeling and Control of Robotic Manipulators

This paper presents a review of self-organizing feature maps (SOFMs), in particular, those based on the Kohonen algorithm, applied to adaptive modeling and control of robotic manipulators. Through a number of references we show how SOFMs can learn nonlinear input–output mappings needed to control robotic manipulators, thereby coping with important robotic issues such as the excess degrees of freedom, computation of inverse kinematics and dynamics, hand–eye coordination, path-planning, obstacle avoidance, and compliant motion. We conclude the paper arguing that SOFMs can be a much simpler, feasible alternative to MLP and RBF networks for function approximation and for the design of neurocontrollers. Comparison with other supervised/unsupervised approaches and directions for further work on the field are also provided.

Interplay of Biomechanical Constraints and Kinematic Strategies in Selecting Arm Postures

In this study, the authors examined the interplay between biomechanics and control strategies in the resolution of excess degrees of freedom at the joint level. Seven participants made aimed arm movements from 30 starting points and several starting postures to targets. Final arm postures for movements to a target exhibited substantial joint angle variation. Through regression modeling and by comparing observed final arm postures with biomechanically plausible postures, the authors identified 3 kinematic strategies: (a) Maintain deviations from the average angle at the starting point to the joint's final posture; (b) make torso rotations that are a fixed proportion of shoulder rotations; and (c) adopt a characteristic combination of 4 wrist-positioning approaches. The results demonstrated that kinematic strategies can account for substantial variance in final arm postures, if one takes into account 2 types of individual differences—those that arise inevitably from biomechanical constraints and those that reflect choices in movement strategy.