Interaction Torque Research Articles

The role of intersegmental dynamics in coordination of the forelimb joints during unperturbed and perturbed skilled locomotion.

Joint coordination during locomotion and how this coordination changes in response to perturbations remains poorly understood. We investigated coordination among forelimb joints during the swing phase of skilled locomotion in the cat. While cats walked on a horizontal ladder, one of the cross-pieces moved before the cat reached it, requiring the cat to alter step size. Direction and timing of the cross-piece displacement were manipulated. We found that the paw was transported in space through body translation and shoulder and elbow rotations, whereas the wrist provided paw orientation required to step on cross-pieces. Kinetic analysis revealed a consistent joint control pattern in all conditions. Although passive interaction and gravitational torques were the main sources of shoulder and elbow motions for most of the movement time, shoulder muscle torque influenced movement of the entire limb at the end of the swing phase, accelerating the shoulder and causing interaction torque that determined elbow motion. At the wrist, muscle and passive torques predominantly compensated for each other. In all perturbed conditions, although all joints and the body slightly contributed to changes in the step length throughout the entire movement, the major adjustment was produced by the shoulder at the movement end. We conclude that joint coordination during the swing phase is produced mainly passively, by exploiting gravity and the limb's intersegmental dynamics, which may simplify the neural control of locomotion. The use of shoulder musculature at the movement end enables flexible responses to environmental disturbances. NEW & NOTEWORTHY This is the first study to investigate joint control during the swing phase of skilled, accuracy-dependent locomotion in the cat and how this control is altered to adapt to known and unexpected perturbations. We demonstrate that a pattern of joint control that exploits gravitational and interaction torques is used in all conditions and that movement modifications are produced mainly by shoulder muscle torque during the last portion of the movement.

Development and Pilot Testing of a Novel Electromechanical Device to Measure Wrist Rigidity in Parkinson's Disease.

Quantitative assessment of the muscle tone is important when studying patients with neurological disorders such as Parkinson's disease (PD). For the assessment of therapeutic progress, quantitative and objective outcome measures are needed. This article presents a novel electromechanical device to monitor the quantitative rigidity of the wrist joint against passive movement. The novel device is equipped with an electrical motor to move the wrist joint in a flexion-extension manner with different velocity profiles. The accuracy of the device was measured in terms of position, velocity and torque accuracy. The feasibility of the measurement procedure was tested in a pilot study with four PD patients and 12 healthy controls (HC), at velocities of 10 °/s,50 °/s, and 100 °/s. {The position and velocity of the developed device were (0.005 ± 0.105)° and (0.734 ±0.276) °/s, unloaded, and (0.003 ± 0.113) ° and (0.013 ± 0.038) °/s, loaded with a relaxed arm, respectively. The torque accuracy was (15.029 ± 2.235) mNm. The comparison of the median rigidity between the PD patients and HC showed significant differences at all tested velocities, during both flexion and extension movements. This device proved to have sufficient accuracy and sensitivity to precisely measure the interaction torque at the wrist joint and to differentiate PD rigidity from normal muscle tone. The device, thus provides a quantitative and objective measure of rigidity in PD.

Control of redundant pointing movements involving the wrist and forearm.

The musculoskeletal system can move in more ways than are strictly necessary, allowing many tasks to be accomplished with a variety of limb configurations. Why some configurations are preferred has been a focus of motor control research, but most studies have focused on shoulder-elbow or whole arm movements. This study focuses on movements involving forearm pronation-supination (PS), wrist flexion-extension (FE), and wrist radial-ulnar deviation (RUD) and elucidates how these three degrees of freedom (DOF) combine to perform the common task of pointing, which only requires two DOF. Although pointing is more sensitive to FE and RUD than to PS and could be easily accomplished with FE and RUD alone, subjects tend to involve a small amount of PS. However, why we choose this behavior has been unknown and is the focus of this paper. With the use of a second-order model with lumped parameters, we tested a number of plausible control strategies involving minimization of work, potential energy, torque, and path length. None of these control schemes robustly predicted the observed behavior. However, an alternative control scheme, hypothesized to control the DOF that were most important to the task (FE and RUD) and ignore the less important DOF (PS), matched the observed behavior well. In particular, the behavior observed in PS appears to be a mechanical side effect caused by unopposed interaction torques. We conclude that moderately sized pointing movements involving the wrist and forearm are controlled by ignoring forearm rotation even though this strategy does not robustly minimize work, potential energy, torque, or path length. NEW & NOTEWORTHY Many activities require us to point our hands in a given direction using wrist and forearm rotations. Although there are infinitely many ways to do this, we tend to follow a stereotyped pattern. Why we choose this pattern has been unknown and is the focus of this paper. After testing a variety of hypotheses, we conclude that the pattern results from a simplifying strategy in which we focus on wrist rotations and ignore forearm rotation.

Improved estimation of torque between a surgical instrument and environment in multi-DOF motion

Wires and pulleys drive instruments attached to a surgical robot. Driving torque of the surgical instrument is measured to estimate the interaction torque between the instrument tip and organ tissues. Friction occurring in the pulleys during torque transmission, however, induces estimation error. Coupling effect in the transmission structure also needs to be resolved for accurate estimation during multidegree- of-freedom motion. This paper proposes a method to reduce the estimation error by employing friction model in the multi-degreeof- freedom motion. The friction model is empirically developed based on analysis of the coupling effect and the characteristics of the driving mechanism. Experiments with right-grip motion in the multi-DOF show that the estimation error is reduced to 7.70 %.

Numerical and experimental study of a double physical pendulum with magnetic interaction

Chaotic and regular behavior of the system consisting of a double physical pendulum with two repulsive permanent magnets is studied. We are focused on mathematical modelling, numerical simulations, experimental measurements and in particular on a novel magnetic interaction modelling. System parameters are identified by matching the output signals from experiments and numerical solutions to the developed mathematical model governed by a strongly non-linear set of two second order ODEs including the friction and the magnetic interaction torques. Considered system shows chaotic and periodic dynamics. Few chaotic zones have been detected numerically and confirmed experimentally. Scenarios of transition from regular to chaotic motion and vice versa, as well as the bifurcation diagrams are illustrated and discussed. Good agreement between the numerical simulation and experimental measurement is achieved.

Neural Networks Enhanced Adaptive Admittance Control of Optimized Robot-Environment Interaction.

In this paper, an admittance adaptation method has been developed for robots to interact with unknown environments. The environment to be interacted with is modeled as a linear system. In the presence of the unknown dynamics of environments, an observer in robot joint space is employed to estimate the interaction torque, and admittance control is adopted to regulate the robot behavior at interaction points. An adaptive neural controller using the radial basis function is employed to guarantee trajectory tracking. A cost function that defines the interaction performance of torque regulation and trajectory tracking is minimized by admittance adaptation. To verify the proposed method, simulation studies on a robot manipulator are conducted.

Adaptive Admittance Control for an Ankle Exoskeleton Using an EMG-Driven Musculoskeletal Model.

Various rehabilitation robots have been employed to recover the motor function of stroke patients. To improve the effect of rehabilitation, robots should promote patient participation and provide compliant assistance. This paper proposes an adaptive admittance control scheme (AACS) consisting of an admittance filter, inner position controller, and electromyography (EMG)-driven musculoskeletal model (EDMM). The admittance filter generates the subject's intended motion according to the joint torque estimated by the EDMM. The inner position controller tracks the intended motion, and its parameters are adjusted according to the estimated joint stiffness. Eight healthy subjects were instructed to wear the ankle exoskeleton robot, and they completed a series of sinusoidal tracking tasks involving ankle dorsiflexion and plantarflexion. The robot was controlled by the AACS and a non-adaptive admittance control scheme (NAACS) at four fixed parameter levels. The tracking performance was evaluated using the jerk value, position error, interaction torque, and EMG levels of the tibialis anterior (TA) and gastrocnemius (GAS). For the NAACS, the jerk value and position error increased with the parameter levels, and the interaction torque and EMG levels of the TA tended to decrease. In contrast, the AACS could maintain a moderate jerk value, position error, interaction torque, and TA EMG level. These results demonstrate that the AACS achieves a good tradeoff between accurate tracking and compliant assistance because it can produce a real-time response to stiffness changes in the ankle joint. The AACS can alleviate the conflict between accurate tracking and compliant assistance and has potential for application in robot-assisted rehabilitation.

Interaction Forces and Torques between Two Perpendicular Magnetic Tubes

Cylinders, tubes, cuboids, etc. are basic magnet shapes used in permanent magnet machines. The relative positions between magnets include parallel, perpendicular, or inclined. The force and torque between two cuboid magnets of almost any status and two cylindrical magnets with paralleled axes have been solved. Using the theory of magnetic charges and magnetic Coulomb’s law, this study derives a mathematical model for interaction forces and torques between two perpendicular magnetic tubes in three dimensions. Using this model, the effects of tube relative positions on the interaction forces and torques is analyzed by numerical calculation. The model can also express interaction forces and torques between a magnetic tube and magnetic cylinder or between two magnetic cylinders when the inner radius of one magnetic tube is zero or the radii of both tubes are zero. This study provides the theoretical background for magnetic tube and cylinder applications, such as magnetic drive or control across space in mechanical, medical treatment, chemical industry, food production, aerospace, etc.

BIO-BASED SUPERVISORY CONTROL OF A LOWER EXOSKELETON FOR STANCE PHASE

This paper presents a newly supervisory impedance control strategy of a wearable lower limb exoskeleton in stance phase intended to enhance human performance and support load-carrying using biomechanical analysis. In order to control the coupled human-robot system, the impedance control strategy, previously developed by the authors for swing phase, has been herein expanded up to the stance phase by regulating the desired impedance between the exoskeleton and a wearer's limb according to a specific motion speed. The effect of human behaviours on the change of impedance parameters across variable walking speeds in the stance phase is adopted to design the fuzzy rules for the control strategy. The control performance of the designed exoskeleton is evaluated on a bench-testing over different ranges of walking speeds (about 0.3 m/s to 1.2 m/s). Experimental results show that the resulting interaction torque, the human-exoskeleton tracking error, and electrical power consumption are significantly reduced as compared to a traditional impedance control, especially in the stance phase. Besides that, an average of 72.3 % of the load was transferred to the ground by the exoskeleton during the stance phase of walking. The developed control strategy on the lower exoskeleton has the potential to increase comfort and adaptation to users during daily use.

Comparison of Human-Robot Interaction Torque Estimation Methods in a Wrist Rehabilitation Exoskeleton

In this paper, experimental implementation and comparative accuracy evaluation of five methods for estimation of human-robot interaction torques are presented. These methods vary from the simplest case of using solely commanded motor torques, to partial consideration of the robot dynamics, to advanced methods considering full robot dynamics such as inverse dynamics (ID) and nonlinear disturbance observer (NDO) based algorithms. Dynamic and friction models of the exoskeleton were developed and their parameters were identified using an evolutionary optimization algorithm to ensure high parameter accuracy. When used with accurate model parameters, ID method led to 20 to 22% average error, while NDO method generated 12 to 18% average error, as evaluated in experiments with a force sensor. These values compare to average error values of up to 132% for using motor torques only, and between 25 to 69% when partial dynamics were used. A sensitivity analysis of the ID and NDO methods to inaccuracies in model parameter estimations revealed considerable sensitivity of these advanced methods to model parameter variations. A summary is provided for the typical estimation accuracy levels that can be expected of these methods and discuss the limitations and considerations that should be taken into account for their use.

An Apparatus to Measure Wheel–Soil Interactions on Sandy Terrains

Wheeled mobile robots (WMR) have been deployed in Mars/Lunar exploration, military missions, and geological investigations, and they must handle rough and deformable terrains. The dynamics at the wheel–soil interface, including the wheel–terrain contact angle, wheel sinkage, and wheel–soil interaction forces and torque, are major factors in the entrapment of NASA SPIRIT MER and the subsequent mission failure. This paper presents an experimental apparatus that is developed to measure the wheel–terrain contact angle, wheel sinkage, and wheel–soil interaction forces and torque in real time to improve our understanding of the WMR mobility on soft and deformable terrains. A method for wheel sinkage evaluation is presented based on measuring the wheel–terrain contact angle. The wheel–soil interaction forces and torque are measured by installing a force/torque sensor along the axle of the apparatus. The proposed approach is implemented on a testbed, and the experimental results are used to evaluate it; they demonstrate the reliable detection of the wheel–terrain contact angle, wheel sinkage, and wheel–soil interaction forces and torque. Moreover, based on the measured wheel–terrain contact angle, the relative errors in the predicted wheel–soil interaction forces and torque are less than 8% compared with the experimental data.

Chapter 18 - Neurophysiology of gait

Beyond the classic clinical description, recent studies have quantitatively evaluated gait and balance dysfunction in cerebellar ataxias by means of modern motion analysis systems. These systems have the aim of clearly and quantitatively describing the differences, with respect to healthy subjects, in kinematic, kinetic, and surface electromyography variables, establishing the basis for a rehabilitation strategy and assessing its efficacy. The main findings which characterize the gait pattern of cerebellar patients are: increased step width, reduced ankle joint range of motion with increased coactivation of the antagonist muscles, and increased stride-to-stride variability. Whereas the former is a compensatory strategy adopted by patients to keep the center of mass within the base of support, the latter indicates the inability of patients to maintain dynamic balance through a regular walking pattern and may reflect the primary deficit directly related to cerebellar dysfunction and the consequent lack of muscle coordination during walking. Moreover, during the course of the disease, with the progressive loss of walking autonomy, step length, and lower-limb joint range of motion are drastically reduced. As to the joint coordination defect, abnormal intralimb joint coordination during walking, in terms of both joint kinematics and interaction torques, has been reported in several studies. Furthermore, patients with cerebellar ataxia show a poor intersegmental coordination, with a chaotic coordinative behavior between trunk and hip, leading to increased upper-body oscillations that affect gait performance and stability, sustaining a vicious circle that transforms the upper body into a generator of perturbations. The use of motion analysis laboratories allows a deeper segmental and global characterization of walking impairment in these patients and can shed light on the nature of both the primary specific gait disorder and compensatory mechanisms. Such deeper understanding might reasonably represent a valid prerequisite for establishing better-targeted rehabilitation strategies.

Cooperative Control for A Hybrid Rehabilitation System Combining Functional Electrical Stimulation and Robotic Exoskeleton.

Functional electrical stimulation (FES) and robotic exoskeletons are two important technologies widely used for physical rehabilitation of paraplegic patients. We developed a hybrid rehabilitation system (FEXO Knee) that combined FES and an exoskeleton for swinging movement control of human knee joints. This study proposed a novel cooperative control strategy, which could realize arbitrary distribution of torque generated by FES and exoskeleton, and guarantee harmonic movements. The cooperative control adopted feedfoward control for FES and feedback control for exoskeleton. A parameter regulator was designed to update key parameters in real time to coordinate FES controller and exoskeleton controller. Two muscle groups (quadriceps and hamstrings) were stimulated to generate active torque for knee joint in synchronization with torque compensation from exoskeleton. The knee joint angle and the interactive torque between exoskeleton and shank were used as feedback signals for the control system. Central pattern generator (CPG) was adopted that acted as a phase predictor to deal with phase confliction of motor patterns, and realized synchronization between the two different bodies (shank and exoskeleton). Experimental evaluation of the hybrid FES-exoskeleton system was conducted on five healthy subjects and four paraplegic patients. Experimental results and statistical analysis showed good control performance of the cooperative control on torque distribution, trajectory tracking, and phase synchronization.

The effect of multiple segment interaction dynamics on elbow valgus load during baseball pitching

Elbow valgus load generated in baseball pitching is a risk factor for throwing-related injuries. However, an induced acceleration analysis establishing the cause–effect relationship between elbow valgus load and causal joint kinematics is lacking. The purpose of this study was to identify the underlying mechanism of how the elbow valgus load is generated by muscular and non-muscular interactive torque effects. The throwing motions of five fastball pitches from 16 male collegiate baseball pitchers were measured by a three-dimensional motion capture system. The induced acceleration analysis developed in this study was used to separate the elbow valgus stress of the throwers into causal muscular and interactive torque components. The results showed that the shoulder internal rotation torque-induced component was greatest, accounting for 73.0% of the valgus-related contribution, while the other joint components in the muscular and interactive torque components were relatively smaller. This implied that the elbow valgus stress was highly influenced by the internal rotation torque effect, while the motion-dependent effect due to the trunk and shoulder kinematics was not influential. In conclusion, to reduce the risk of injury, pitchers should acquire proper coordination without excessive shoulder internal rotation action.

A study on an up-milling rock crushing tool operation of an underwater tracked vehicle

In this article, we develop the analysis of a new underwater tracked vehicle with rock crushing tool, working under the water. To design the capacity of the underwater tracked vehicle actuator and the rock crushing tool actuator, we analyze the interaction forces and torque between the rock and the rock crushing tool. Since experiments on the underwater tracked vehicle with a rock crushing tool are very difficult, costly, time-consuming, we first perform a mathematical modeling of the underwater tracked vehicle with the rock crushing tool. We analyze the mechanics of the underwater tracked vehicle system that is affected by the forces and moments of the underwater rock crushing, where the force and torque on the rock crushing tool are based on the analysis of the mechanics of an individual cutter tool. We derive a mathematical expression for the forces and moments of the combined system on the underwater tracked vehicle and the rock crushing tool for rock crushing. For this, we study the parameters that affect the mechanics of the underwater tracked vehicle system with the rock crushing tool. To apply the rock crushing tool to underwater rock excavation, we also study the hydrostatic effects to the combined underwater tracked vehicle system with the rock crushing tool. To design the capacity of the actuator of the developing underwater tracked vehicle and the rock crushing tool, we analyze the required tractive or down thrust forces, and the torque to the rotor carriage caused by the cutting system. In addition, we analyze the energy and the power for the rock crushing tool actuator related to the tool characteristics. To support the validity of the analyses, we use the derived equations to perform a number of numerical simulations.

Robust Adaptive Sliding Mode Admittance Control of Exoskeleton Rehabilitation Robots

A nonlinear robust adaptive sliding mode admittance controller is proposed for exoskeleton rehabilitation robots. The proposed controller has robustness against uncertainties of dynamic parameters using an adaptation law. Furthermore, an adaptive Sliding Mode Control (SMC) scheme is employed in the control law to provide robustness against disturbances (non-parametric uncertainties) with unknown bounds. For this purpose, another adaptation law is defined for the variation of the SMC gain. The proposed scheme is augmented with an admittance control method to provide compliance for the patient during interaction with the rehabilitation robot. The stability of the proposed controller and the tracking performance of the system are proven using the Lyapunov stability theorem. To verify the effectiveness of the proposed control method, some simulations are conducted for a nonlinear lower-limb exoskeleton robot interacting with a patient leg via some braces. Based on the obtained results, the controller is able to provide a flexibility for the patient and appropriately respond to his/her non-compliant interaction torques. Moreover, the proposed controller significantly reduces the chattering of the input torques in comparison with a previous adaptive control method with a constant SMC gain, while it maintains a similar tracking performance.

Contribution of interaction torques during dart throwing: Differences between novices and experts

We examined if experts and novices show different utilization of the torque components impulses during dart throwing. Participants threw darts continuously at a dartboard aiming for the centre (target bull’s eye). The upper-limb joint torque impulses were obtained through inverse dynamics with anthropometric and motion capture data as input. Depending on the joint degree of freedom (DOF) and movement phase (acceleration and follow-through), three main strategies of net torque (NET) impulse generation through joint muscle (MUS) and interaction (INT) torque impulses were highlighted. Firstly, our results showed that the elbow flexion–extension DOF leads the movement according to the joint leading hypothesis. Then, considering the acceleration phase, the analysis revealed differences in torque impulse decomposition between expert and novices. For the glenohumeral (GH) joint abduction–adduction and for wrist flexion, the INT torque impulse contributed positively to NET joint torque impulse in the group of experts unlike novices. This allowed to lower the necessary MUS torque impulse at these DOFs. Also, GH axial rotation was actively controlled by muscle torque impulse in the group of experts. During the follow-through, the experts used the INT torque impulse more proficiently than novices to break the elbow extension. The comparison between experts and novices through inverse dynamics document the link between the exploitation of interaction torques impulses and expertise in dart throwing for which the main objective is precision rather than velocity.

Tracking control of time-varying knee exoskeleton disturbed by interaction torque

Knee exoskeletons have been increasingly applied as assistive devices to help lower-extremity impaired people to make their knee joints move through providing external movement compensation. Tracking control of knee exoskeletons guided by human intentions often encounters time-varying (time-dependent) issues and the disturbance interaction torque, which may dramatically put an influence up on their dynamic behaviors. Inertial and viscous parameters of knee exoskeletons can be estimated to be time-varying due to unexpected mechanical vibrations and contact interactions. Moreover, the interaction torque produced from knee joint of wearers has an evident disturbance effect on regular motions of knee exoskeleton. All of these points can increase difficultly of accurate control of knee exoskeletons to follow desired joint angle trajectories. This paper proposes a novel control strategy for controlling knee exoskeleton with time-varying inertial and viscous coefficients disturbed by interaction torque. Such designed controller is able to make the tracking error of joint angle of knee exoskeletons exponentially converge to zero. Meanwhile, the proposed approach is robust to guarantee the tracking error bounded when the interaction torque exists. Illustrative simulation and experiment results are presented to show efficiency of the proposed controller. Additionally, comparisons with gradient dynamic (GD) approach and other methods are also presented to demonstrate efficiency and superiority of the proposed control strategy for tracking joint angle of knee exoskeleton.

Energy distribution mechanism and open-kinetic-chain characteristics of the upper body system in female volleyball spiking

The aim of this study was to investigate the energy distribution mechanism in volleyball spike movement by assessing the individual contributions of muscular torque and interactive torques of the upper body including gyroscopic, centripetal force, and Coriolis force effects. The spiking movements of seven female collegiate volleyball players were recorded using a three-dimensional motion capture system and an induced power analysis using a link system with 18 degrees of freedom joints to decompose the system’s mechanical energy into causal torque- and force-dependent components. The kinetic energy output of the striking hand at ball impact was 28% (40.7 J) of the system kinetic energy. The decrease in system kinetic energy (−91.3 J) during the early period resulted from the energy absorption mechanism associated with an external joint force component. The energy transfer mechanism, which occurred in the later period, was attributed to a centripetal force effect. Although proximal-to-distal sequential joint rotations were observed in the participants, the quantified data that were calculated using the induced power analysis did not completely agree with the effective energy transfer pattern. These findings indicate that open-kinetic-chain movement–specific task in volleyball spiking likely affected the energy flow characteristics. From the view of energy flow perspective, this study suggests that the volleyball spike movement might have inefficient movement characteristics.

Impedance control of a cable-driven SEA with mixed H2/H∞ synthesis

PurposeThis paper aims to present an impedance control method with mixed H2/H∞ synthesis and relaxed passivity for a cable-driven series elastic actuator to be applied for physical human–robot interaction.Design/methodology/approachTo shape the system’s impedance to match a desired dynamic model, the impedance control problem was reformulated into an impedance matching structure. The desired competing performance requirements as well as constraints from the physical system can be characterized with weighting functions for respective signals. Considering the frequency properties of human movements, the passivity constraint for stable human–robot interaction, which is required on the entire frequency spectrum and may bring conservative solutions, has been relaxed in such a way that it only restrains the low frequency band. Thus, impedance control became a mixed H2/H∞ synthesis problem, and a dynamic output feedback controller can be obtained.FindingsThe proposed impedance control strategy has been tested for various desired impedance with both simulation and experiments on the cable-driven series elastic actuator platform. The actual interaction torque tracked well the desired torque within the desired norm bounds, and the control input was regulated below the motor velocity limit. The closed loop system can guarantee relaxed passivity at low frequency. Both simulation and experimental results have validated the feasibility and efficacy of the proposed method.Originality/valueThis impedance control strategy with mixed H2/H∞ synthesis and relaxed passivity provides a novel, effective and less conservative method for physical human–robot interaction control.