Joint Degrees Of Freedom Research Articles

Hardware Impairments Aware Transceiver for Full-Duplex Massive MIMO Relaying

This paper studies the massive MIMO full-duplex relaying (MM-FDR), where multiple source-destination pairs communicate simultaneously with the help of a common full-duplex relay equipped with very large antenna arrays. Different from the traditional MM-FDR protocol, a general model where sources/destinations are allowed to equip with multiple antennas is considered. In contrast to the conventional MIMO system, massive MIMO must be built with low-cost components which are prone to hardware impairments. In this paper, the effect of hardware impairments is taken into consideration, and is modeled using transmit/receive distortion noises. We propose a low complexity hardware impairments aware transceiver scheme (named as HIA scheme) to mitigate the distortion noises by exploiting the statistical knowledge of channels and antenna arrays at sources and destinations. A joint degree of freedom and power optimization algorithm is presented to further optimize the spectral efficiency of HIA based MM-FDR. The results show that the HIA scheme can mitigate the "ceiling effect" appears in traditional MM-FDR protocol, if the numbers of antennas at sources and destinations can scale with that at the relay.

Effect of six degrees of freedom knee kinematics on ligament length and moment arm in an intact knee model.

Biomechanics studies can help improve athletic performance. However, the biomechanics of knee joint ligament length changes and moment arms over six degrees of freedom (DOF) have yet to be established. To construct a knee model to investigate the length and moment arm changes of the anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial collateral ligament (MCL), and lateral collateral ligament (LCL). Six DOF joint modeling and analysis were performed using specialized modeling software. The length of all ligaments varied with tibiofemoral flexion angle, contributed to joint motion, and restrained the joint in different positions. The ACL, MCL, and LCL lengths decreased, the PCL increased, the posterior tibial translation increased, the MCL moment arm increased, and the LCL moment arm decreased between 0° and 90°. The primary ligament restraints were the PCL (0° to 30°), MCL (30° to 60°), and PCL (60° to 90°). The restraining function of each ligament during motion can be modeled based on changes in ligament lengths during tibial translations and rotations during flexion. Understanding the correlations between ligament lengths and moment arm changes over a wide range of motion will help improve our understanding of joint kinematics and may be useful for the diagnosis and treatment of sports injury.

Models of Postural Control: Shared Variance in Joint and COM Motions.

This paper investigated the organization of the postural control system in human upright stance. To this aim the shared variance between joint and 3D total body center of mass (COM) motions was analyzed using multivariate canonical correlation analysis (CCA). The CCA was performed as a function of established models of postural control that varied in their joint degrees of freedom (DOF), namely, an inverted pendulum ankle model (2DOF), ankle-hip model (4DOF), ankle-knee-hip model (5DOF), and ankle-knee-hip-neck model (7DOF). Healthy young adults performed various postural tasks (two-leg and one-leg quiet stances, voluntary AP and ML sway) on a foam and rigid surface of support. Based on CCA model selection procedures, the amount of shared variance between joint and 3D COM motions and the cross-loading patterns we provide direct evidence of the contribution of multi-DOF postural control mechanisms to human balance. The direct model fitting of CCA showed that incrementing the DOFs in the model through to 7DOF was associated with progressively enhanced shared variance with COM motion. In the 7DOF model, the first canonical function revealed more active involvement of all joints during more challenging one leg stances and dynamic posture tasks. Furthermore, the shared variance was enhanced during the dynamic posture conditions, consistent with a reduction of dimension. This set of outcomes shows directly the degeneracy of multivariate joint regulation in postural control that is influenced by stance and surface of support conditions.

Digit mechanics in relation to endpoint compliance during precision pinch

This study investigates the mechanics of the thumb and index finger in relation to compliant endpoint forces during precision pinch. The objective was to gain insight into how individuals modulate motor output at the digit endpoints and joints according to compliance-related sensory feedback across the digits. Thirteen able-bodied subjects performed precision pinch upon elastic resistance bands of a customized apparatus instrumented with six degree-of-freedom load-cells. Compliance levels were discretely adjusted according to the number of bands connected. Subjects were provided visual feedback to control the rate of force application. Fifteen repetitions of low-to-moderate force (<20N) pinches were analyzed at each of five compliance levels, during which force and motion data were collected. Joint angles and moments normalized by pinch force magnitude were computed. Second-order polynomials were used to characterize joint mechanics as a function of compliance. The joint degrees-of-freedom (DOFs) at the finger showed greater dependence on compliance for angular position while the thumb joint DOFs demonstrated greater dependence for normalized joint moment. The digits also adjusted coordination of their endpoint forces according to compliance. Overall, the finger may be altering its position to increase load to the joints of the thumb with changing compliance. These findings describe naturally emergent changes in digit mechanics for compliant precision pinch, which involves motor execution in response to endpoint sensory feedback. Identifying and understanding these motor patterns may provide theoretical basis for restoring and rehabilitating sensorimotor pathologies of the hand.

A-24 関節トルクの発揮様式を考慮した野球打撃動作の動力学的分析(バットスイング)

The purpose of this study was to quantify the contribution of the whole-body joint torques to the generation of evaluation values during baseball batting motion, such as bat head speed and angular motion of the lower trunk in consideration of the joint torque generating mode. The whole-body segments and bat were modeled as a system of sixteen-rigid linked segments, and constraint axes of the elbow, wrist, knee and ankle joints were modeled with anatomical constraint equations in order to consider the degree of freedom (DOF) of the joint. Each hand was considered to be connected with the bat through zero DOF joint. The equation of motion with respect to the whole-body and bat was obtained by considering modelling errors, such as, residual joint force and moment, and fluctuation of segment's length. The dynamic contributions of the joint moments, motion dependent term and gravity term to the bat head speed and angular motion of the lower trunk were derived from the equation of motion for the system. Furthermore, the joint torque was divided into two components, such as eccentric torque component, which shows negative sign of its torque power, and concentric torque component, which shows positive sign of its torque power. The results obtained in this study showed that 1) motion dependent term was the great contributor to the generation of bat head speed and 2) major contributors to the generation of the bat head speed, such as concentric components of knob-side shoulder abduction torque and torso joint rotational torque were quantified by considering main generating factor of motion dependent term.

Tolerance analysis by polytopes: Taking into account degrees of freedom with cap half-spaces

To determine the relative position of any two surfaces in a system, one approach is to use operations (Minkowski sum and intersection) on sets of constraints. These constraints are made compliant with half-spaces of Rn where each set of half-spaces defines an operand polyhedron. These operands are generally unbounded due to the inclusion of degrees of invariance for surfaces and degrees of freedom for joints defining theoretically unlimited displacements. To solve operations on operands, Minkowski sums in particular, “cap” half-spaces are added to each polyhedron to make it compliant with a polytope which is by definition a bounded polyhedron. The difficulty of this method lies in controlling the influence of these additional half-spaces on the topology of polytopes calculated by sum or intersection. This is necessary to validate the geometric tolerances that ensure the compliance of a mechanical system in terms of functional requirements.

Adaptive postural control for joint immobilization during multitask performance.

Motor abundance is an essential feature of adaptive control. The range of joint combinations enabled by motor abundance provides the body with the necessary freedom to adopt different positions, configurations, and movements that allow for exploratory postural behavior. This study investigated the adaptation of postural control to joint immobilization during multi-task performance. Twelve healthy volunteers (6 males and 6 females; 21–29 yr) without any known neurological deficits, musculoskeletal conditions, or balance disorders participated in this study. The participants executed a targeting task, alone or combined with a ball-balancing task, while standing with free or restricted joint motions. The effects of joint configuration variability on center of mass (COM) stability were examined using uncontrolled manifold (UCM) analysis. The UCM method separates joint variability into two components: the first is consistent with the use of motor abundance, which does not affect COM position (VUCM); the second leads to COM position variability (VORT). The analysis showed that joints were coordinated such that their variability had a minimal effect on COM position. However, the component of joint variability that reflects the use of motor abundance to stabilize COM (VUCM) was significant decreased when the participants performed the combined task with immobilized joints. The component of joint variability that leads to COM variability (VORT) tended to increase with a reduction in joint degrees of freedom. The results suggested that joint immobilization increases the difficulty of stabilizing COM when multiple tasks are performed simultaneously. These findings are important for developing rehabilitation approaches for patients with limited joint movements.

Indirectly self-adaptive underactuated robot hand with block-linkage mechanisms

A novel indirectly self-adaptive (ISA) underactuated hand with block-linkage mechanism is developed in this paper. There are two basic requirements for design of a humanoid robot hand. Firstly, regarding the function of the hand, the hand should be able to stably grasp common objects with different shapes and sizes. Secondly, regarding the structure of the hand, the hand should be similar to a human hand in its appearance and joint degrees of freedom (DOFs). The ISA Hand reaches the balance point in meeting both of requirements. The ISA Hand has 5 fingers, 14 joint DOFs and only 5 motors. There are nine ISA joints in the ISA Hand. All fingers are similar in structure. The thumb has two joints, one in which is the ISA joint. Four fingers in the ISA hand have three joints, two in which are the ISA joint. The reacting force from objects in grasping process can be used to drive the ISA joint. The architecture, grasping process and force analysis of the ISA finger are given in detail. Experimental results show that the ISA Hand can grasp different objects stably.

Change of a motor synergy for dampening hand vibration depending on a task difficulty.

The present study investigated the relationship between the number of usable degrees of freedom (DOFs) and joint coordination during a human-dampening hand vibration task. Participants stood on a platform generating an anterior-posterior directional oscillation and held a water-filled cup. Their usable DOFs were changed under the following conditions of limb constraint: (1) no constraint; (2) ankle constrained; and (3) ankle-knee constrained. Kinematic whole-body data were recorded using a three-dimensional position measurement system. The jerk of each body part was evaluated as an index of oscillation intensity. To quantify joint coordination, an uncontrolled manifold (UCM) analysis was applied and the variance of joints related to hand jerk divided into two components: a UCM component that did not affect hand jerk and an orthogonal (ORT) component that directly affected hand jerk. The results showed that hand jerk when the task used a cup filled with water was significantly smaller than when a cup containing stones was used, regardless of limb constraint condition. Thus, participants dampened their hand vibration utilizing usable joint DOFs. According to UCM analysis, increasing the oscillation velocity and the decrease in usable DOFs by the limb constraints led to an increase of total variance of the joints and the UCM component, indicating that a synergy-dampening hand vibration was enhanced. These results show that the variance of usable joint DOFs is more fitted to the UCM subspace when the joints are varied by increasing the velocity and limb constraints and suggest that humans adopt enhanced synergies to achieve more difficult tasks.

A weighted cost function to deal with the muscle force sharing problem in injured subjects: A single case study

The human body is an over-actuated multi-body system, as each joint degree of freedom can be controlled by more than one muscle. Solving the force-sharing problem (i.e. finding out how the resultant joint torque is shared among the muscles actuating that joint) calls for an optimization process where a cost function, representing the strategy followed by the central nervous system to activate muscles, is minimized. The main contribution of the present study has been the particular formulation of that cost function for the case of the pathological gait of a single subject suffering from anterior cruciate ligament rupture. Our hypothesis was that the central nervous system does not weight equally the muscles when trying to compensate for a lower limb injury during gait (in contrast to what is the usual practice for healthy gait where all muscles are weighted equally). This hypothesis is supported by the fact that muscle activity in injured individuals differs from that of healthy subjects. Different functions were tested until we finally came out with a cost function that was consistent with experimental electromyography measurements and inverse dynamics results for a subject suffering this particular pathology.

An improved OpenSim gait model with multiple degrees of freedom knee joint and knee ligaments

Musculoskeletal models are widely used to investigate joint kinematics and predict muscle force during gait. However, the knee is usually simplified as a one degree of freedom joint and knee ligaments are neglected. The aim of this study was to develop an OpenSim gait model with enhanced knee structures. The knee joint in this study included three rotations and three translations. The three knee rotations and mediolateral translation were independent, with proximodistal and anteroposterior translations occurring as a function of knee flexion/extension. Ten elastic elements described the geometrical and mechanical properties of the anterior and posterior cruciate ligaments (ACL and PCL), and the medial and lateral collateral ligaments (MCL and LCL). The three independent knee rotations were evaluated using OpenSim to observe ligament function. The results showed that the anterior and posterior bundles of ACL and PCL (aACL, pACL and aPCL, pPCL) intersected during knee flexion. The aACL and pACL mainly provided force during knee flexion and adduction, respectively. The aPCL was slack throughout the range of three knee rotations; however, the pPCL was utilised for knee abduction and internal rotation. The LCL was employed for knee adduction and rotation, but was slack beyond 20° of knee flexion. The MCL bundles were mainly used during knee adduction and external rotation. All these results suggest that the functions of knee ligaments in this model approximated the behaviour of the physical knee and the enhanced knee structures can improve the ability to investigate knee joint biomechanics during various gait activities.

Improving Inverse Dynamics Accuracy in a Planar Walking Model Based on Stable Reference Point

Physiologically and biomechanically, the human body represents a complicated system with an abundance of degrees of freedom (DOF). When developing mathematical representations of the body, a researcher has to decide on how many of those DOF to include in the model. Though accuracy can be enhanced at the cost of complexity by including more DOF, their necessity must be rigorously examined. In this study a planar seven-segment human body walking model with single DOF joints was developed. A reference point was added to the model to track the body’s global position while moving. Due to the kinematic instability of the pelvis, the top of the head was selected as the reference point, which also assimilates the vestibular sensor position. Inverse dynamics methods were used to formulate and solve the equations of motion based on Newton-Euler formulae. The torques and ground reaction forces generated by the planar model during a regular gait cycle were compared with similar results from a more complex three-dimensional OpenSim model with muscles, which resulted in correlation errors in the range of 0.9–0.98. The close comparison between the two torque outputs supports the use of planar models in gait studies.

Fuzzy PID-controlled SMA actuator for a two DOF joint

Shape memory alloy (SMA) actuator is a potential advanced component for servo-system of aerospace vehicles and aircrafts. This paper presents a joint with two degrees of freedom (DOF) and a mobility range close to ±60° when driven by SMA tripe wires. The fuzzy potential-integral-derivative (PID)-controlled actuator drive was designed using antagonistic SMA triple wires, and the resistance feedback signal made a closed loop. Experiments showed with the driving responding frequency increasing, the overstress is becoming harder to be avoided at the position under maximum friction force. Furthermore, the hysteresis gap between the heating and cooling paths of the strain-to-resistance curve expanded under this condition. It is considered a fuzzy logic control as a solution, and the curves of the wires were then modeled by fitting polynomials, such that the measured resistance was used directly to determine the control signal. Accurate control was demonstrated through the step response, and the experimental results showed that under the fuzzy PID-control program, the mean absolute error (MAE) of the rotation angle was about 3.147°. Also, the investigation of the external interference to the system proved the controllable maximum output.

Finite Element Analysis of the Mechanical Structure in Portable Exoskeleton Based on DOF Coupling

Since the posture of portable exoskeleton is consistent with human motion and each joint degree of freedom is same, on the basis of DOF coupling in portable exoskeleton, the finite element analysis of the mechanical structure in portable exoskeleton has been calculated. According to the anthropomorphic mechanism design method, the universal joint structure has been used to meet the requirements of degrees of freedom in the mechanical structure of the exoskeleton; using the Hydraulic cylinder to simulate the contraction or stretch of human muscle, and the three-dimensional model of the exoskeleton mechanical systems has been created with the Solidworks software; selecting Human CAD software and setting the parameters of the movement of the human body model, the variations of the various joints can be obtained; using the Parasolid as the standard format for data transfer between the two software Solidworks and ANSYS, the finite element analysis model was established, and according to the principle of coupling, the three translational DOF and two rotating DOF was coupled, besides through both legs vertical standing, one knee kneeling, and one leg vertical standing three conditions, the exoskeleton strength was analyzed. The simulation results show that under the three conditions, a concentrated stress all has been found in the exoskeleton structure, besides the concentrated stresses all have been obtained in the cross-section changing site or the junction of the two components, which stress values exceeded the allowable stress values of the aluminum alloy material, so the suggestions for improvement of the structure are put forward in the article; at the same time, the simulation results provide a numerical basis for the optimization of the portable exoskeleton structure.

Motor Variability but Functional Specificity: The Case of a C4 Tetraplegic Mouth Calligrapher

This study examined the movement coordination in an exceptional tetraplegic individual who has practiced Japanese calligraphy with a mouth-held brush for over 25 years to reach master level. In the experiment, the calligrapher wrote the same Chinese character on a sheet of ink paper multiple times. The uncontrolled manifold analysis revealed the forms of covariation among joint degrees of freedom so as to keep the brush pressure, brush angle, and upright head posture invariant over different realizations of the task while allowing for joint configuration fluctuations that do not affect these task variables. The fact that the 3 task variables were simultaneously controlled further suggested that the acquisition of the skill was not only a matter of learning to control each of the task variables but also a matter of learning to nest different layers of activities that control the multiple functional relationships to the environment in such a way as not to be dysfunctional for one layer to another.

A Musculoskeletal Modeling Approach for Estimating Anterior Cruciate Ligament Strains and Knee Anterior–Posterior Shear Forces in Stop-Jumps Performed by Young Recreational Female Athletes

The central goal of this study was to contribute to the advancements being made in determining the underlying causes of anterior cruciate ligament (ACL) injuries. ACL injuries are frequently incurred by recreational and professional young female athletes during non-contact impact activities in sports like volleyball and basketball. This musculoskeletal-neuromuscular study investigated stop-jumps and factors related to ACL injury like knee valgus and internal-external moment loads, knee anterior-posterior (AP) shear forces, ACL strains and internal forces. Motion capture data was obtained from the landing phase of stop-jumps performed by eleven young recreational female athletes and electromyography (EMG) data collected from quadriceps, hamstring and gastrocnimius muscles which were then compared to numerically estimated activations. Numerical simulation tools used were Inverse Kinematics, Computed Muscle Control and Forward Dynamics and the knee modeled as a six degree of freedom joint. Results showed averaged peak strains of 12.2±4.1% in the right and 11.9±3.0% in the left ACL. Averaged peak knee AP shear forces were 482.3±65.7N for the right and 430.0±52.4N for the left knees, approximately equal to 0.7-0.8 times body weight across both knees. A lack of symmetry was observed between the knees for valgus angles (p<0.04), valgus moments (p<0.001) and muscle activations (p<0.001), all of which can be detrimental to ACL stability during impact activities. Comparisons between recorded EMG data and estimated muscle activations show the relation between electrical signal and muscle depolarization. In summary, this study outlines a musculoskeletal simulation approach that provides numerical estimations for a number of variables associated with ACL injuries in female athletes performing stop-jumps.

Biomechanical effect of increasing or decreasing degrees of freedom for surgery of trapeziometacarpal joint arthritis: A simulation study

Osteoarthritis of the trapeziometacarpal (TMC) joint can be treated by arthrodesis and arthroplasty, which potentially decreases or increases the degrees of freedom (DoF) of the joint, respectively. The aim of our study was to bring novel biomechanical insights into these joint surgery procedures by investigating the influence of DoF at the TMC joint on muscle and joint forces in the thumb. A musculoskeletal model of the thumb was developed to equilibrate a 1 N external force in various directions while the thumb assumed key and pulp pinch postures. Muscle and joint forces were computed with an optimization method. In comparison to that of the 2-DoF (intact joint) condition, muscle forces slightly decreased in the 0-DoF (arthrodesis) condition, but drastically increased in the 3-DoF (arthroplasty) condition. TMC joint forces in the 3-DoF condition were 12 times larger than the 2-DoF joint. This study contributes to a further understanding of the biomechanics of the intact and surgically repaired TMC joint and addresses the biomechanical consequences of changing a joint's DoF by surgery.

Knee and hip joint forces – sensitivity to the degrees of freedom classification at the knee

Previous research has demonstrated that the number of degrees of freedom (DOF) modelled at a given joint affects the antagonistic muscle activity predicted by inverse dynamics optimization techniques. This higher level of muscle activity in turn results in greater joint contact forces. For instance, modelling the knee as a 3 DOF joint has been shown to result in higher hip and knee joint forces commensurate with a higher level of muscular activity than when the knee is modelled with 1 DOF. In this study, a previously described musculoskeletal model of the lower limb was used to evaluate the sensitivity of the knee and hip joint contact forces to the DOF at the knee during vertical jumping in both a 1 and a 3 DOF knee model. The 3 DOF knee was found to predict higher tibiofemoral and hip joint contact forces and lower patellofemoral joint contact forces. The magnitude of the difference in hip contact force was at least as significant as that found in previous research exploring the effect of subject-specific hip geometry on hip contact force. This study therefore demonstrates a key sensitivity of knee and hip joint contact force calculations to the DOF at the knee. Finally, it is argued that the results of this study highlight an important physiological question with practical implications for the loading of the structures of the knee; that is, the relative interaction of muscular, ligamentous, and articular structures in creating moment equilibrium at the knee.

Mechanism State Matrices for Planar Reconfigurable Mechanisms

This paper introduces mechanism state matrices as a novel way to represent the topological characteristics of planar reconfigurable mechanisms. As part of this new approach, these matrices will be used as an analysis tool to automatically determine the degrees of freedom (DOFs) of planar mechanisms that only contain one DOF joint. The DOF at each state can be combined with a mechanism state matrix to form an augmented mechanism state matrix. A series of examples will be used to illustrate the proposed concept.

Movement Optimization of a Redundant Serial Robot for High-Quality Pipe Cutting

The subject of this research concerns an innovative serial robot developed to introduce the laser ray technology in the on-line pipes cutting in a continuous process of production. The presence of different cutting constraints and the necessity of avoiding any robot collisions suggested the insertion of a redundant degree of freedom allowing infinite inverse kinematics solutions for the motion planning as well as for the movement optimization. The inverse kinematics requires to evaluate the pseudo-inverse matrix of the kinematical system in several trajectory points while the optimization is performed with an opportune weighting variable assigned for each joint degree of freedom. The supervision of the machine dynamic behavior is obtained through the change of these weights during the motion. As a consequence, a suitable multi-objective genetic algorithm (MOGA) has been adopted to reduce vibration effects and to improve the quality of the robot motion with optimal motion profiles. In comparison with the traditional cutting techniques, the proposed one allows, as a result of the optimal motion of the robot, an increased quality improvement and a reduced cutting cycle time. Premised a brief description of the technological context, this paper presents the kinematical analysis of the machine and its optimization with the implemented MOGA. The proposed algorithm has been implemented on a working laser pipe cutting machine and exhibits a behavior really similar to the forecasted one.