Optimization of Joint Torques of Robot Using Dynamic Redundant Degrees of Freedom.

Although global movement abnormalities in the lower extremity poststroke have been studied, the expression of specific motor impairments such as weakness and abnormal muscle and joint torque coupling patterns have received less attention. We characterized changes in strength, muscle coactivation and associated joint torque couples in the paretic and nonparetic extremity of 15 participants with chronic poststroke hemiparesis (age 59.6 ± 15.2 years) compared with 8 age-matched controls. Participants performed isometric maximum torques in hip abduction, adduction, flexion and extension, knee flexion and extension, ankle dorsi- and plantarflexion and submaximal torques in hip extension and ankle plantarflexion. Surface electromyograms (EMGs) of 10 lower extremity muscles were measured. Relative weakness (paretic extremity compared with the nonparetic extremity) was measured in poststroke participants. Differences in EMGs and joint torques associated with maximum voluntary torques were tested using linear mixed effects models. Results indicate significant poststroke torque weakness in all degrees of freedom except hip extension and adduction, adductor coactivation during extensor tasks, in addition to synergistic muscle coactivation patterns. This was more pronounced in the paretic extremity compared with the nonparetic extremity and with controls. Results also indicated significant interjoint torque couples during maximum and submaximal hip extension in both extremities of poststroke participants and in controls only during maximal hip extension. Additionally, significant interjoint torque couples were identified only in the paretic extremity during ankle plantarflexion. A better understanding of these motor impairments is expected to lead to more effective interventions for poststroke gait and posture.

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Do Arm Postures Vary With the Speed of Reaching?

Journal of Neurophysiology ◽

10.1152/jn.1999.81.5.2582 ◽

1999 ◽

Vol 81 (5) ◽

pp. 2582-2586 ◽

Cited By ~ 65

Author(s):

Kiisa C. Nishikawa ◽

Sara T. Murray ◽

Martha Flanders

Keyword(s):

Degrees Of Freedom ◽

Three Dimensional ◽

Optimal Solution ◽

Reaching Movements ◽

Total Force ◽

Joint Torques ◽

Dynamic Factors ◽

Human Arm ◽

Wide Range ◽

Dynamic Forces

Do arm postures vary with the speed of reaching? For reaching movements in one plane, the hand has been observed to follow a similar path regardless of speed. Recent work on the control of more complex reaching movements raises the question of whether a similar “speed invariance” also holds for the additional degrees of freedom. Therefore we examined human arm movements involving initial and final hand locations distributed throughout the three-dimensional (3D) workspace of the arm. Despite this added complexity, arm kinematics (summarized by the spatial orientation of the “plane of the arm” and the 3D curvature of the hand path) changed very little for movements performed over a wide range of speeds. If the total force (dynamic + quasistatic) had been optimized by the control system (e.g., as in a minimization of the change in joint torques or the change in muscular forces), the optimal solution would change with speed; slow movements would reflect the minimal antigravity torques, whereas fast movements would be more strongly influenced by dynamic factors. The speed-invariant postures observed in this study are instead consistent with a hypothesized optimization of only the dynamic forces.

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Impedance Model-Based Optimal Regulation on Force and Position of Bimanual Robots to Hold an Object

Complexity ◽

10.1155/2020/3561807 ◽

2020 ◽

Vol 2020 ◽

pp. 1-13

Author(s):

Darong Huang ◽

Hong Zhan ◽

Chenguang Yang

Keyword(s):

Degrees Of Freedom ◽

Target Position ◽

Internal Force ◽

Robot System ◽

Joint Torques ◽

Impedance Model ◽

Generalized Momentum ◽

Optimal Target ◽

End Effectors ◽

Bimanual Robot

Bimanual robots have been studied for decades and regulation on internal force of the being held object by two manipulators becomes a research interest in recent years. In this paper, based on impedance model, a method to obtain the optimal target position for bimanual robots to hold an object is proposed. We introduce a cost function combining the errors of the force and the position and manage to minimize its value to gain the optimal coordinates for the robot end effectors (EE). To implement this method, two necessary algorithms are presented, which are the closed-loop inverse kinematics (CLIK) method to work out joint positions from desired EE pose and the generalized-momentum-based external force observer to measure the subjected force acting on the EE so as to properly compensate for the joint torques. To verify the effectiveness, practicality, and adaptivity of the proposed scheme, in the simulation, a bimanual robot system with three degrees of freedom (DOF) in every manipulator was constructed and employed to hold an object, where the results are satisfactory.

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Design and analysis of a tendon-based MRI-compatible surgery robot for transperineal prostate needle placement

Proceedings of the Institution of Mechanical Engineers Part C Journal of Mechanical Engineering Science ◽

10.1177/0954406214533783 ◽

2014 ◽

Vol 229 (2) ◽

pp. 335-348 ◽

Cited By ~ 1

Author(s):

Shan Jiang ◽

Fude Sun ◽

Jiansheng Dai ◽

Jun Liu ◽

Zhiyong Yang

Keyword(s):

Magnetic Resonance Imaging ◽

Magnetic Resonance ◽

Degrees Of Freedom ◽

Virtual Work ◽

Inverse Kinematic ◽

Surgical Robot ◽

Resonance Imaging ◽

Joint Torques ◽

Reachable Workspace ◽

6 Degrees Of Freedom

Tendon-based transmission has significant advantages in the development of a surgical robot, which is fully magnetic resonance imaging compatible and can work dexterously in the very limited space inside magnetic resonance imaging core. According to the requirements of magnetic resonance imaging compatibility, a novel 6 degrees of freedom tendon-based surgical robot composed of three independent modules is developed in this paper. After a brief introduction to the robot, the direct and inverse kinematic equations are deduced by applying the concept of screw displacements, and the reachable workspace of the robot is calculated. As to the static force analysis, we apply the principle of virtual work to derive a transmission between the equivalent joint torques and the tendon forces. By the use of the pseudoinverse technique, a systematic method is developed for the resolution of redundant tendon forces.

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Comparison of Sprinting With and Without Running-Specific Prostheses Using Optimal Control Techniques

Robotica ◽

10.1017/s0263574719000936 ◽

2019 ◽

Vol 37 (12) ◽

pp. 2176-2194 ◽

Cited By ~ 2

Author(s):

Anna Lena Emonds ◽

Johannes Funken ◽

Wolfgang Potthast ◽

Katja Mombaur

Keyword(s):

Optimal Control ◽

Degrees Of Freedom ◽

Sagittal Plane ◽

Reference Group ◽

Optimality Criteria ◽

Mechanical Work ◽

Step Frequency ◽

Joint Torques ◽

Linear Spring ◽

Multi Body

SummaryThe purpose of our study was to get deeper insights into sprinting with and without running-specific prostheses and to perform a comparison of the two by combining analysis of known motion capture data with mathematical modeling and optimal control problem (OCP) findings. We established rigid multi-body system models with 14 bodies and 16 degrees of freedom in the sagittal plane for one unilateral transtibial amputee and three non-amputee sprinters. The internal joints are powered by torque actuators except for the passive prosthetic ankle joint which is equipped with a linear spring–damper system. For each model, the dynamics of one sprinting trial was reconstructed by solving a multiphase least squares OCP with discontinuities and constraints. We compared the motions of the amputee athlete and the non-amputee reference group by computing characteristic criteria such as the contribution of joint torques, the absolute mechanical work, step frequency and length, among others. By comparing the amputee athlete with the non-amputee athletes, we found reduced activity in the joints of the prosthetic limb, but increased torques and absolute mechanical work in the arms. We also compared the recorded motions to synthesized motions using different optimality criteria and found that the recorded motions are still far from the optimal solutions for both amputee and non-amputee sprinting.

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Estimation of Metabolical Costs for Human Locomotion

Volume 6: 5th International Conference on Multibody Systems, Nonlinear Dynamics, and Control, Parts A, B, and C ◽

10.1115/detc2005-84229 ◽

2005 ◽

Cited By ~ 3

Author(s):

Werner Schiehlen ◽

Marko Ackermann

Keyword(s):

Degrees Of Freedom ◽

Inverse Dynamics ◽

Sagittal Plane ◽

Human Locomotion ◽

Human Gait ◽

Joint Torques ◽

Gait Quality ◽

Analysis Laboratory ◽

Muscle Models

Metabolical energy is the chemical energy consumed by skeletal muscles to generate force. This quantity is useful to understand the comfort of human gait and to evaluate, in terms of effort required, the performance of devices or therapies designed to improve gait quality of persons presenting gait disorders. Firstly, this paper presents the frequently used estimations of energy expenditure based lonely on joint torques and mechanical costs obtained by inverse dynamics of passive and active walking devices. Secondly, a more advanced approach is discussed consisting of modeling the musculoskeletal system with Hill-type phenomenological muscle models and computing the metabolical expenditure adopting expressions recently proposed in the literature. As an example a musculoskeletal model of the lower limb in the sagittal plane consisting of thigh, shank and foot with three degrees of freedom and actuated by eight muscles is considered. This model is used to estimate metabolical costs for known normal gait kinematical data obtained in a gait analysis laboratory.

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Optimization-Based Digital Human Dynamics: Santos™ Walking Backwards

Volume 8: 31st Mechanisms and Robotics Conference, Parts A and B ◽

10.1115/detc2007-35616 ◽

2007 ◽

Cited By ~ 1

Author(s):

Hyun Jung Kwon ◽

Yujiang Xiang ◽

Salam Rahmatalla ◽

R. Timothy Marler ◽

Karim Abdel-Malek ◽

...

Keyword(s):

Degrees Of Freedom ◽

Optimization Problem ◽

Joint Angle ◽

Spline Interpolation ◽

Performance Measure ◽

Degree Of Freedom ◽

Human Model ◽

Entire Body ◽

Joint Torques ◽

Digital Human

An objective of this study is to simulate the backward walking motion of a full-body digital human model. The model consists of 55 degree of freedom – 6 degrees of freedom for global translation and rotation and 49 degrees of freedom representing the kinematics of the entire body. The resultant action of all the muscles at a joint is represented by the torque for each degree of freedom. The torques and angles at a joint are treated as unknowns in the optimization problem. The B-spline interpolation is used to represent the time histories of the joint angles and the well-established robotics formulation of the Denavit-Hartenberg method is used for kinematics analysis of the mechanical system. The recursive Lagrangian formulation is used to develop the equations of motion, and was chosen because of its known computational efficiency. The backwards walking problem is formulated as a nonlinear optimization problem. The control points of the B-splines for the joint angle profiles are treated as the design variables. For the performance measure, total dynamic effort that is represented as the integral of the sum of the squares of all the joint torques is minimized using a sequential quadratic programming algorithm. The solution is simulated in the Santos™ environment. Results of the optimization problem are the torque and joint angle profiles. The torques at the key joints and the ground reaction forces are compared to those for the forward walk in order to study the differences between the two walking patterns. Simulation results are approximately validated with the experimental data which is motion captured in the VSR Lab at the University of Iowa.

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Kinematic and Kinetic Constraints on Arm, Trunk, and Leg Segments in Target-Reaching Movements

Journal of Neurophysiology ◽

10.1152/jn.00582.2004 ◽

2005 ◽

Vol 93 (1) ◽

pp. 352-364 ◽

Cited By ~ 54

Author(s):

James S. Thomas ◽

Daniel M. Corcos ◽

Ziaul Hasan

Keyword(s):

Degrees Of Freedom ◽

Neural Control ◽

Time Course ◽

Sagittal Plane ◽

Principal Component ◽

Joint Torque ◽

Trunk Flexion ◽

Joint Torques ◽

Joint Task ◽

Task Conditions

We studied target reaching tasks involving not only the arms but also the trunk and legs, which necessitated some trunk flexion. Such tasks can be successfully completed using an infinite number of combinations of segment motions due to the inherent kinematic redundancy with the excessive degrees of freedom (DOFs). Sagittal plane motions of six segments (shank, thigh, pelvis, trunk, humerus, and forearm) and dynamic torques of six joints (ankle, knee, hip, lumbar, shoulder, and elbow) were analyzed separately by principal component (PC) analyses to determine if there was a commonality among the shapes of the respective waveforms. Additionally, PC analyses were used to probe for constraining relationships among the 1) relative magnitudes of segment excursions and 2) the peak-to-peak dynamic joint torques. In summary, at the kinematic level, the tasks are simplified by the use of a single common waveform for all segment excursions with 89.9% variance accounted for (VAF), but with less fixed relationships among the relative scaling of the magnitude of segment excursions (62.2% VAF). However, at the kinetic level, the time course of the dynamic joint torques are not well captured by a single waveform (72.7% VAF), but the tasks are simplified by relatively fixed relationships among the scaling of dynamic joint torque magnitudes across task conditions (94.7% VAF). Taken together, these results indicate that, while the effective DOFs in a multi-joint task are reduced differently at the kinematic and kinetic levels, they both contribute to simplifying the neural control of these tasks.

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A host–parasite structural analysis of industrial robots

International Journal of Advanced Robotic Systems ◽

10.1177/1729881420954043 ◽

2020 ◽

Vol 17 (5) ◽

pp. 172988142095404

Author(s):

Wei Wei ◽

Ganwei Cai ◽

Junjie Gong ◽

Caixia Ban

Keyword(s):

Degrees Of Freedom ◽

Optimization Method ◽

Industrial Robots ◽

Joint Torques ◽

Maximum Deformation ◽

Overall Performance ◽

Representation Method ◽

Branched Chains ◽

Host Parasite ◽

Positive Factor

Most driving torques in serial industrial robots are used to overcome the weight of the robot. Although actuators account for a large proportion of the total mass of a robot, they have yet to become a positive factor that enables the robot to achieve gravity balance. This study presents a host–parasite structure to reconstruct the distribution of actuators and achieve gravity balance in robots. First, based on the characteristics of tree–rattan mechanisms, a method for calculating the degrees of freedom and a symbolic representation method for the distribution of branched chains are formulated for host–parasite mechanisms. Second, a configuration analysis and optimization method for host–parasite structure-based robots and a robot prototype are presented. Finally, four host–parasite mechanisms/robots (A, B, C, and D) are compared. The results are as follows. If more parasitic branched chains are added to the yz plane, the loads along axes 2 and 3 become more balanced, which significantly increases the stiffnesses of the mechanism in the y- and z-directions ( Ky and Kz, respectively). If the additional branched chains are closer to the site of maximum deformation, the stiffness of the mechanism in the z-direction ( Kz) increases more significantly. Of the four mechanisms, mechanism D has the best overall performance. The joint torques of mechanism D along axes 2 and 3 are lower than those of mechanism A by 99.78% and 99.18%, respectively. In addition, Kx, Ky, and Kz of mechanism D are 100.56%, 336.19%, and 385.02% of those of mechanism A, respectively. Moreover, the first-order natural frequency of mechanism D is 135.94% of that of mechanism A. Host–parasitic structure is conducive to improving the performance of industrial robots.

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A Comparison of Continuum and Lumped-Mass Models for Hyper-Redundant Manipulator Mechanics

14th Biennial Conference on Mechanical Vibration and Noise: Vibrations and Dynamics of Robotic and Multibody Structures ◽

10.1115/detc1993-0137 ◽

1993 ◽

Author(s):

Gregory S. Chirikjian

Keyword(s):

Continuum Model ◽

Degrees Of Freedom ◽

Point Of View ◽

Redundant Manipulators ◽

Redundant Manipulator ◽

Lumped Mass ◽

Mass Model ◽

Joint Torques ◽

Lumped Mass Model ◽

The Continuum

Abstract The most efficient methods for representing dynamics in the literature require serial computations which are proportional to the number of manipulator degrees-of-freedom. Furthermore, these methods are not fully parallelizable. For ‘hyper-redundant’ manipulators, which may have tens, hundreds, or thousands of actuators, these formulations preclude real time implementation. This paper therefore looks at the mechanics of hyper-redundant manipulators from the point of view of an approximation to an ‘infinite degree-of-freedom’ (or continuum) problem. The dynamics for this infinite dimensional case is developed. The approximate dynamics of actual hyper-redundant manipulators is then reduced to a problem which is O(1) in the number of serial computations, i.e., the algorithm is O(n) in the total number of computations, but these computations are completely parallelizable. This is achieved by ‘projecting’ the dynamics of the continuum model onto the actual robotic structure. The results are compared with a lumped mass model of a particular hyper-redundant manipulator. It is found that the continuum model can be used to generate joint torques to within ten percent of values computed from the lumped mass model.

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