Joint Torque Profiles Research Articles

Human-Exoskeleton Coupling Simulation for Lifting Tasks with Shoulder, Spine, and Knee-Joint Powered Exoskeletons.

In this study, we introduce a two-dimensional (2D) human skeletal model coupled with knee, spine, and shoulder exoskeletons. The primary purpose of this model is to predict the optimal lifting motion and provide torque support from the exoskeleton through the utilization of inverse dynamics optimization. The kinematics and dynamics of the human model are expressed using the Denavit-Hartenberg (DH) representation. The lifting optimization formulation integrates the electromechanical dynamics of the DC motors in the exoskeletons of the knee, spine, and shoulder. The design variables for this study include human joint angle profiles and exoskeleton motor current profiles. The optimization objective is to minimize the squared normalized human joint torques, subject to physical and task-specific lifting constraints. We solve this optimization problem using the gradient-based optimizer SNOPT. Our results include a comparison of predicted human joint angle profiles, joint torque profiles, and ground reaction force (GRF) profiles between lifting tasks with and without exoskeleton assistance. We also explore various combinations of exoskeletons for the knee, spine, and shoulder. By resolving the lifting optimization problems, we designed the optimal torques for the exoskeletons located at the knee, spine, and shoulder. It was found that the support from the exoskeletons substantially lowers the torque levels in human joints. Additionally, we conducted experiments only on the knee exoskeleton. Experimental data indicated that using the knee exoskeleton decreases the muscle activation peaks by 35.00%, 10.03%, 22.12%, 30.14%, 16.77%, and 25.71% for muscles of the erector spinae, latissimus dorsi, vastus medialis, vastus lateralis, rectus femoris, and biceps femoris, respectively.

Design, Control, and Validation of a Polycentric Hybrid Knee Prosthesis

This paper presents a novel polycentric hybrid knee prosthesis (PHKP) by enabling a multi-bar linkage to work for high-torque activities in active mode and for low-torque activities in passive mode. The mode transition is implemented by a servo-controlled telescopic slide rails. Distinguished from the single-axis hybrid knee prostheses, the PHKP Knee provides geometric stability in stance and notably increases toe clearance in swing by using an optimally designed instantaneous center of rotation (ICR) trajectory. In active mode, the PHKP Knee provides high transmission ratio and continuous peak torque offering sufficient support for torque-demanding activities. Impedance control was employed to regulate joint torque as a response to knee motion in the active mode. It was found that due to the inherent geometric stability of the polycentric mechanism in stance, the damping coefficient of the controller can be tuned much smoother than the single-axis knees leading to more compliant and comfortable interactions among the wearer, the prosthesis and the ground. The stair ascent tests showed that the joint angle and torque profiles of the PHKP Knee are similar to those of the able-bodied by demonstrating a step-over-step pattern with a peak angle of 73 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\deg$</tex-math></inline-formula> and a maximum torque of 0.92 Nm/Kg.

Electromyography-driven model-based estimation of ankle torque and stiffness during dynamic joint rotations in perturbed and unperturbed conditions

The simultaneous modulation of joint torque and stiffness enables humans to perform large repertoires of movements, while versatilely adapting to external mechanical demands. Multi-muscle force control is key for joint torque and stiffness modulation. However, the inability to directly measure muscle force in the intact moving human prevents understanding how muscle force causally links to joint torque and stiffness. Joint stiffness is predominantly estimated via joint perturbation-based experiments in combination with system identification techniques. However, these techniques provide joint-level stiffness estimations with no causal link to the underlying muscle forces. Moreover, the need for joint perturbations limits the generalizability and applicability to study natural movements. Here, we present an electromyography (EMG)-driven musculoskeletal modeling framework that can be calibrated to match reference joint torque and stiffness profiles simultaneously via a multi-term objective function. EMG-driven models calibrated on <2 s of reference torque and stiffness data could blindly estimate reference profiles across 100 s of data not used for calibration. Model calibrations using an objective function comprising torque and stiffness terms always provided less feasible solutions than an objective function comprising solely a torque term, thereby reducing the space of feasible muscle–tendon parameters. Results also showed the proposed framework’s ability to estimate joint stiffness in unperturbed conditions, while capturing differences against stiffness profiles derived during perturbed conditions. The proposed framework may provide new ways for studying causal relationships between muscle force and joint torque and stiffness during movements in interaction with the environment, with broad implications across biomechanics, rehabilitation and robotics.

MEASUREMENT, PREDICTION AND VALIDATION OF HUMAN GAIT TORQUE FOR LOWER LIMB ASSISTIVE DEVICES

The lower limb rehabilitation process requires external control inputs based on joint kinematics and kinetics to its actuator for generating the motion of a robotic assistive device. This paper describes the procedures for measuring, predicting and validating the joint kinematics and kinetics of human gait for the lower limb exoskeleton. The high-speed multi-camera-based video system associated with passive optical markers and a force plate sensor is used to measure the gait data. The lower limb joint torques have also been predicted using three different machine learning regression models, viz. Decision Tree (DT), Gaussian Process Regression (GPR) and Support Vector Machine (SVM). The analysis is further validated with the geometry-based analytical method. Three lower limb joint torques have been predicted by utilizing gait period, joint angle, joint velocity and joint acceleration as the predictors. The lowest average 10-fold cross-validation Root Mean Square Error (RMSE) using the DT model between measured and predicted torques have been recorded for the ankle, knee and hip joint as 1.9521, 1.5527 and 1.5684[Formula: see text]Nm, respectively. This study enhances the field of medical rehabilitation by providing the required knowledge of human gait kinematics/kinetics and predicting the joint torque profile without any force sensor.

Model-Based Design and Optimization of Passive Shoulder Exoskeletons

Abstract To physically assist workers in reducing musculoskeletal strain or to develop motor skills for patients with neuromuscular disabilities, recent research has focused on exoskeletons. Designing exoskeletons is challenging due to the complex human geometric structure, the human-exoskeleton wrench interaction, the kinematic constraints, and the selection of power source characteristics. This study concentrates on modeling a 3D multibody upper-limb human-exoskeleton, developing a procedure of analyzing optimal assistive torque profiles, and optimizing the passive mechanism features for desired tasks. The optimization objective is minimizing the human joint torques. Differential-algebraic equations (DAEs) of motion have been generated and solved to simulate the complex closed-loop multibody dynamics. Three different tasks have been considered, which are common in industrial environments: object manipulation, over-head work, and static pointing. The resulting assistive exoskeleton's elevation joint torque profile decreases the specific task's human shoulder torque in computer simulations. The exoskeleton is not versatile or optimal for different dynamic tasks since the passive mechanism produces a specific torque for a given elevation angle. We concluded that designing a fully passive exoskeleton for a wide range of dynamic applications is impossible.

Exoskeleton Active Walking Assistance Control Framework Based on Frequency Adaptive Dynamics Movement Primitives.

This paper introduces a novel exoskeleton active walking assistance control framework based on frequency adaptive dynamics movement primitives (FADMPs). The FADMPs proposed in this paper is an online learning and prediction algorithm which is able to online estimate the fundamental frequency of human joint trajectory, learn the shape of joint trajectory and predict the future joint trajectory during walking. The proposed active walking assistance control framework based on FADMPs is a model-based controller which relies on the human joint torque estimation. The assistance torque provided by exoskeleton is estimated by human lower limb inverse dynamics model which is sensitive to the noise in the joint motion trajectory. To estimate a smooth joint torque profile, the joint motion trajectory must be filtered first by a lowpass filter. However, lowpass filter will introduce an inevitable phase delay in the filtered trajectory. Both simulations and experiments in this paper show that the phase delay has a significant effect on the performance of exoskeleton active assistance. The active assistant control framework based on FADMPs aims at improving the performance of active assistance control by compensating the phase delay. Both simulations and experiments on active walking assistance control show that the performance of active assistance control can be further improved when the phase delay in the filtered trajectory is compensated by FADMPs.

외력의 상호작용과 용접 로봇 매니퓰레이터의 모션 생성을 위한 동역학 정식화 및 최적화 알고리즘

This paper studies the modeling and simulation method of a robot manipulator with external force interaction. We analyze a welding robot manipulator that is used for building box girders in an offshore plant. The robot platform has six degrees of freedom and all rotational joints. To build a mechanical structure of the robot manipulator, the DH (Denavit-Hartenberg) method is used, and the equations of motion driven by the Lagrange’s formulation with external force are implemented. The external force interacting with the robot platform is modeled as a mass-spring-damper system. The joint angle profiles of the robot manipulator parameterized with B-spline function approximation are the variables of optimization. The objective function is the summation of joint torque squares, and it is equally weighted for each joint. For constraints, joint angle limits; joint torque limits; collision avoidance; continuity condition; and the position, velocity, and orientation of end effector are imposed. Using the optimization-based modeling and simulation method, we can obtain all information related to the joint space, such as joint angle profiles, joint velocity profiles, and joint torque profiles under the external force interaction condition.

Optimal control of joint torques using direct collocation to maximize ball carry distance in a golf swing

Forward dynamics golf swing simulations are important to gain insight into how a golfer should swing a particular club and which design improvements should be considered by golf club manufacturers. A new method of optimizing a four degree-of-freedom (DoF) biomechanical golfer model swinging a flexible shaft with a rigid clubhead was developed using a direct orthogonal collocation approach. The kinematic and kinetic results of the simulation confirm previous findings on optimal joint angle trajectories, shaft deflection patterns, and joint torque profiles in a golf swing. This optimization approach is a promising development in biomechanics research, and future work will implement this method in three-dimensional swing models that have been shown to have higher robustness and fidelity.

Exoskeleton Online Learning and Estimation of Human Walking Intention Based on Dynamical Movement Primitives

Human walking intention estimation is a critical step for the active assistance control of lower limb exoskeleton, because the purpose of active assistance control is human motion assistance rather than human motion tracking. Complying with human walking intention is the basic requirement of human walking assistance. Hence, the human walking intention must be estimated first to ensure the exoskeleton will not impede human motion. Actually, estimating human walking intention is to estimate human joint torque during walking. In order to estimate a smooth personalized human joint torque profile, an online learning and prediction algorithm of human joint trajectory and joint torque is proposed in this article. The algorithm is based on the dynamical movement primitives model which is used for online learning and predicting human joint trajectory which is substituted into the human dynamics model to estimate the human joint torque. The results of human walking experiments demonstrate that the proposed algorithm can not only predict a smooth human joint trajectory and joint torque profile in real time but also compensate the phase delay caused by sensor signal filtering. Hence, the proposed algorithm is suitable for the active walking assistance control of exoskeleton.

Characteristics of lower limb force exertion during diving motions by collegiate male soccer goalkeepers

ABSTRACTIntroduction: Diving is a high-intensity movement with a determining effect on the soccer game. So, the aim of this study was to evaluate the effects of distance and height on lower limb kinetics and ground reaction force (GRF) during a diving motion of soccer goalkeepers. Methods:The analysis was based on whole-body three-dimensional motion capture (250 Hz) with GRFs recorded using force plates (1000 Hz). Lower limb joint torque and power profile were computed using standard inverse dynamics equations. Results: Significant effects of both dive distance and ball height were identified based on the magnitude and orientation of the GRF vector for the ball-side leg (BS leg) and on the magnitude of the GRF vector for the contralateral-side leg (CS leg). Overall, flexion torques were negligible, with significant contributions of the hip and ankle to extension torques and power. Of note, the BS leg provided an important negative (braking) power, which increased as a function of increasing ball distance and height. Conclusion: From these results, spatial parameters of the goalkeeper's diving motion appear to affect the kinetics of the BS leg.

Muscle-Tendon Unit Parameter Estimation of a Hill-Type Musculoskeletal Model Based on Experimentally Obtained Subject-Specific Torque Profiles.

The aim of this study was to generate a subject-specific musculoskeletal muscle model, based on isometric and isovelocity measurements of the whole lower extremity. A two-step optimization procedure is presented for optimizing the muscle-tendon parameters (MTPs) for isometric and isovelocity joint torque profiles. A significant improvement in the prediction of joint torque profiles for both the solely isometric and a combined isometric and dynamic method of optimization when compared to the standard scaling method of the AnyBody Modeling System (AMS) was observed. Depending on the specific purpose of the model, it may be worth considering whether the isometric-only would be sufficient, or the additional dynamic data are required for the combined approach.

Squat Vertical Jump of a 3DOF Robot Leg over an Inclined Plane: Analysis with Joint Torque Profile Approximation

This work shows an analysis of the movement of a robot with an articulated leg (without a toe) of 3 degrees of freedom (3DOF) when performing a squat vertical jump over an inclined plane. We propose two different approaches to model this problem. The first method estimates the ankle position and foot orientation at the landing time, using the non-zero angular momentum and the plane tilt angle; thus, the foot orientation can be corrected during the time in the air, which achieves greater contact area when the robot land. The second method adjusts the relative position of the CoM (Center of Mass) to the horizontal axis in order to infer the joint torque profile in different tilt angles of the plane. Matlab simulation results show that, the ankle is the most affected joint whereas the plane tilts with the same jump pattern. Having a range of inclination values of ± &#960;/18, the torque variation changes from 35.82% to 2.59%, which proves the efficiency of the evaluated cases.

Infant intralimb coordination and torque production: Influence of prematurity

The purpose of this study is to investigate changes in leg joint coordination, intersegmental dynamics, and their relation in infants born preterm (PT) during the first months of life. Kicking actions were analyzed of 11 infants born PT at 6 and 15-weeks corrected age (CA) using three-dimensional kinematics and kinetics; results were compared to the kicking actions of 10 infants born full-term (FT). Both groups changed from a predominately in-phase coordination at 6-weeks CA to a less in-phase coordination at 15-weeks CA, however, at 6-weeks CA, infants born PT demonstrated less in-phase coordination of their ankle joints with their hip and knee joints. Between groups and across ages, both groups demonstrated consistent net and partitioned joint torque profiles, however, at 6-weeks CA infants born PT demonstrated more complex patterns of torque components. In both groups, less in-phase hip-knee coordination was associated with reduced active knee muscle torque and increased passive knee torques, however, passive knee torques had a greater influence on the kicks of infants born PT at 6-weeks CA. At 6-weeks CA, infants born PT, compared to FT, generated kicks with less in-phase hip-knee coordination, hip excursion, hip angular velocity, and hip muscle torque impulse. By 15-weeks CA, differences resolved in all variables except hip muscle torque impulse. These results highlight a different trajectory of leg joint coordination and torque production for infants born PT compared to FT.

Toward goal-oriented robotic gait training: The effect of gait speed and stride length on lower extremity joint torques.

Robot-assisted gait training is becoming increasingly common to support recovery of walking function after neurological injury. How to formulate controllers capable of promoting desired features in gait, i.e. goals, is complicated by the limited understanding of the human response to robotic input. A possible method to formulate controllers for goal-oriented gait training is based on the analysis of the joint torques applied by healthy subjects to modulate such goals. The objective of this work is to understand how sagittal plane joint torque is affected by two important gait parameters: gait speed (GS) and stride length (SL). We here present the results obtained from healthy subjects walking on a treadmill at different speeds, and asked to modulate stride length via visual feedback. Via principal component analysis, we extracted the global effects of the two factors on the peak-to-peak amplitude of joint torques. Next, we used a torque pulse approximation analysis to determine optimal timing and amplitude of torque pulses that approximate the SL-specific difference in joint torque profiles measured at different values of GS. Our results show a strong effect of GS on the torque profiles in all joints considered. In contrast, SL mostly affects the torque produced at the knee joint at early and late stance, with smaller effects on the hip and ankle joints. Our analysis generated a set of torque assistance profiles that will be experimentally tested using gait training robots.

Adaptive Control of Exoskeleton Robots for Periodic Assistive Behaviours Based on EMG Feedback Minimisation.

In this paper we propose an exoskeleton control method for adaptive learning of assistive joint torque profiles in periodic tasks. We use human muscle activity as feedback to adapt the assistive joint torque behaviour in a way that the muscle activity is minimised. The user can then relax while the exoskeleton takes over the task execution. If the task is altered and the existing assistive behaviour becomes inadequate, the exoskeleton gradually adapts to the new task execution so that the increased muscle activity caused by the new desired task can be reduced. The advantage of the proposed method is that it does not require biomechanical or dynamical models. Our proposed learning system uses Dynamical Movement Primitives (DMPs) as a trajectory generator and parameters of DMPs are modulated using Locally Weighted Regression. Then, the learning system is combined with adaptive oscillators that determine the phase and frequency of motion according to measured Electromyography (EMG) signals. We tested the method with real robot experiments where subjects wearing an elbow exoskeleton had to move an object of an unknown mass according to a predefined reference motion. We further evaluated the proposed approach on a whole-arm exoskeleton to show that it is able to adaptively derive assistive torques even for multiple-joint motion.

A Novel Joint Design for Robotic Hands With Humanlike Nonlinear Compliance

Robotic hands are typically too rigid to react against unexpected impacts and disturbances in order to prevent damage. Human hands have great versatility and robustness due, in part, to the passive compliance at the hand joints. In this paper, we present a novel design for joint with passive compliance that is inspired by biomechanical properties of the human hands. The design consists of a compliant material and a set of pulleys that rotate and stretch the material as the joint rotates. We created six different compliant materials, and we optimized the joint design to match the desired humanlike compliance. We present two design features that allow for the tuning of the joint torque profile, namely, a pretension mechanism to increase pretension of the compliant material, and a design of varying pulley configuration. We built a prototype for the new joint by using additive manufacturing to fabricate the design components and built a test-bed with a force sensor and a servo motor. Experimental results show that the joint exhibits a nonlinear, double exponential joint compliance with all six compliant materials. The design feature involving variable pulley configurations is effective in adjusting the slope of joint torque during the joint rotation while the pretension mechanism showed only a limited effect on increasing the torque amplitude. Overall, with its small size, light weight, low friction, and humanlike joint compliance, the presented joint design is ready for implementation in robotic hands.

Leg mechanics contribute to establishing swing phase trajectories during memory-guided stepping movements in walking cats: a computational analysis.

When quadrupeds stop walking after stepping over a barrier with their forelegs, the memory of barrier height and location is retained for many minutes. This memory is subsequently used to guide hind leg movements over the barrier when walking is resumed. The upslope of the initial trajectory of hind leg paw movements is strongly dependent on the initial location of the paw relative to the barrier. In this study, we have attempted to determine whether mechanical factors contribute significantly in establishing the slope of the paw trajectories by creating a four-link biomechanical model of a cat hind leg and driving this model with a variety of joint-torque profiles, including average torques for a range of initial paw positions relative to the barrier. Torque profiles for individual steps were determined by an inverse dynamic analysis of leg movements in three normal cats. Our study demonstrates that limb mechanics can contribute to establishing the dependency of trajectory slope on the initial position of the paw relative to the barrier. However, an additional contribution of neuronal motor commands was indicated by the fact that the simulated slopes of paw trajectories were significantly less than the observed slopes. A neuronal contribution to the modification of paw trajectories was also revealed by our observations that both the magnitudes of knee flexor muscle EMG bursts and the initial knee flexion torques depended on initial paw position. Previous studies have shown that a shift in paw position prior to stepping over a barrier changes the paw trajectory to be appropriate for the new paw position. Our data indicate that both mechanical and neuronal factors contribute to this updating process, and that any shift in leg position during the delay period modifies the working memory of barrier location.

Compliant walking model with a curvy foot reflecting the position of ankle on reproducing the ankle torque profile

Compliant walking model served as a theoretical framework because of the generation of kinetic information of human walking. Moreover, as Whittington applied a curvy foot to the compliant walking model, the exaggerated ratio of the vertical ground reaction force (GRF) to the horizontal GRF and the fixed center of pressure during the single stance phase have been solved. However, giving meaning to the stiffness of the compliant leg became difficult because of the exaggerated height of the foot and the shortened leg length. Moreover, joint torque was not compared with the ankle torque because the joint position is different from the ankle position. Thus, in this study, we modified the compliant walking model with a curvy foot that reflects the configuration of the human leg and examined whether the modified compliant walking model with a curvy foot could represent human walking. We reflected the configuration of the human leg to the model by shortening the height of the curvy foot, lengthening the compliant leg length, and shifting the joint position similar to the ankle position. To confirm the feasibility of the modified model and to examine the effect of shifting the joint position, we compared the simulation data with the experimental data: the GRF obtained with the force plate and the ankle torque obtained with the inverse dynamics through kinematic data. Thus, the modified model can reproduce the symmetric M-shape of the GRF but not the asymmetric shape of the model. Furthermore, the modified model can also produce the joint torque profile similar to the ankle torque profile. In conclusion, considering the human leg configuration can provide us with information about human walking.

Dynamic Optimization of Human Running With Analytical Gradients

The optimization-based dynamic prediction of 3D human running motion is studied in this paper. A predictive dynamics method is used to formulate the running problem, and normal running is formulated as a symmetric and cyclic motion. Recursive Lagrangian dynamics with analytical gradients for all the constraints and objective function are incorporated in the optimization process. The dynamic effort is used as the performance measure, and the impulse at the foot strike is also included in the performance measure. The joint angle profiles and joint torque profiles are calculated for the full-body human model, and the ground reaction force (GRF) is determined. Several cause-and-effect cases are studied, and the formulation for upper-body yawing motion is proposed and simulated. Simulation results from this methodology show good correlation with experimental data obtained from human subjects and the existing literature.

Design and characterization of a biologically inspired quasi-passive prosthetic ankle-foot.

By design, commonly worn energy storage and release (ESR) prosthetic feet cannot provide biologically realistic ankle joint torque and angle profiles during walking. Additionally, their anthropomorphic, cantilever architecture causes their mechanical stiffness to decrease throughout the stance phase of walking, opposing the known trend of the biological ankle. In this study, the design of a quasi-passive pneumatic ankle-foot prosthesis is detailed that is able to replicate the biological ankle's torque and angle profiles during walking. The prosthetic ankle is comprised of a pneumatic piston, bending spring and solenoid valve. The mechanical properties of the pneumatic ankle prosthesis are characterized using a materials testing machine and the properties are compared to those from a common, passive ESR prosthetic foot. The characterization spanned a range of ankle equilibrium pressures and testing locations beneath the foot, analogous to the location of center of pressure within the stance phase of walking. The pneumatic ankle prosthesis was shown to provide biologically appropriate trends and magnitudes of torque, angle and stiffness behavior, when compared to the passive ESR prosthetic foot. Future work will focus on the development of a control system for the quasi-passive device and clinical testing of the pneumatic ankle to demonstrate efficacy.