Swing Leg Research Articles

Prediction of Lower Limb Kinetics and Kinematics during Walking by a Single IMU on the Lower Back Using Machine Learning.

Recent studies have reported the application of artificial neural network (ANN) techniques on data of inertial measurement units (IMUs) to predict ground reaction forces (GRFs), which could serve as quantitative indicators of sports performance or rehabilitation. The number of IMUs and their measurement locations are often determined heuristically, and the rationale underlying the selection of these parameter values is not discussed. Using the dynamic relationship between the center of mass (CoM), the GRFs and joint kinetics, we propose the CoM as a single measurement location with which to predict the dynamic data of the lower limbs, using an ANN. Data from seven subjects walking on a treadmill at various speeds were collected from a single IMU worn near the sacrum. The data was segmented by step and numerically processed for integration. Six segment angles of the stance and swing leg, three joint torques, and two GRFs were estimated from the kinematics of the CoM measured from a single IMU sensor, with fair accuracy. These results indicate the importance of the CoM as a dynamic determinant of multi-segment kinetics during walking. The tradeoff between data quantity and wearable convenience can be solved by utilizing a machine learning algorithm based on the dynamic characteristics of human walking.

Characterizing healthy knee symmetry using the finite helical axis and muscle power during open and closed chain tasks

Understanding healthy joint movement and muscle control, and injurious alterations, is important to determine musculoskeletal contributions to post-injury joint instabilities or altered dynamic joint function. The contralateral limb is often used as a point of reference to determine the effects of knee joint injury. However, it is currently difficult to interpret within subject variability between limbs as this is not well established in the healthy population. There is a continuing need to characterize healthy knee joint mechanics and neuromuscular control to determine the degree of symmetry within healthy individuals. The current study quantified limb symmetry in healthy individuals using the finite helical axis with a unique reference position (rFHA) and electromyography (EMG) approaches, for a closed-chain single leg squat (SLS) and an open-chain seated leg swing. Muscle power and FHA translation, orientation and dispersion were similar between limbs. However, the FHA was located significantly more anterior in the dominant limb relative to the contralateral during both tasks. These between-limb differences in FHA location could be attributed to differences in joint geometry and strength between limbs. This finding provides evidence that healthy knees have asymmetries which have implications for selection of control limbs in studies comparing conditions within and between individuals. Differences identified in dynamic joint function between tasks suggest that the SLS is useful for revealing joint asymmetries due to altered muscular control strategies, while the swing task is expected to highlight asymmetries in joint motion due to altered knee structures following injury.

Optimal Control of a Differentially Flat Two-Dimensional Spring-Loaded Inverted Pendulum Model

This letter considers the optimal control problem of an extended spring-loaded inverted pendulum (SLIP) model with two additional actuators for active leg length and hip torque modulation. These additional features arise naturally in practice, allowing for consideration of swing leg kinematics during flight and active control over stance dynamics. On the other hand, nonlinearity and the hybrid nature of the overall SLIP dynamics introduce challenges in the analysis and control of the model. In this letter, we first show that the stance dynamics of the considered SLIP model are differentially flat, which has a strong implication regarding controllability of the stance dynamics. Leveraging this powerful property, a tractable optimal control strategy is developed. This strategy enables online solution while also treating the hybrid nature of the SLIP dynamics. Together with the optimal control strategy, the extended SLIP model grants active disturbance rejection capability at any point during the gait. Performance of the proposed control strategy is demonstrated via numerical tests and shows significant advantage over existing methods.

Whole-Body Motion Planning for a Six-Legged Robot Walking on Rugged Terrain

Whole-body motion planning is a key ability for legged robots, which allows for the generation of terrain adaptive behaviors and thereby improved mobility in complex environment. To this end, this paper addresses the issue of terrain geometry based whole-body motion planning for a six-legged robot over a rugged terrain. The whole-body planning is decomposed into two sub-tasks: leg support and swing. For leg support planning, the target pose of the robot torso in a walking step is first found by maximizing the stability margin at the moment of support-swing transition and matching the orientation of the support polygon formed by target footholds. Then, the torso and thereby the leg support trajectories are generated using cubic spline interpolation and transferred into joint space through inverse kinematics. In terms of leg swing planning, the trajectories in a walking step are generated by solving an optimal problem that satisfies three constraints and a bioinspired objective function. The proposed whole-body motion planning strategies are implemented with a simulation and a real-world six-legged robot, and the results show that stable and collision-free motions can be produced for the robot over rugged terrains.

Robust Control of Semi-passive Biped Dynamic Locomotion based on a Discrete Control Lyapunov Function

SUMMARYThis paper focuses on robust control of a simplest passive model, which is established on a DCLF (discrete control Lyapunov function) -based control system, and presents gait transition method based on the study of purely passive walker. Firstly, the DCLF is introduced to stabilize walking process between steps exponentially by modulating the length of next step. Next, the swing leg trajectory from mid-stance position to foot-strike can be planned. Then the control law is calculated to resist external disturbance. Besides, an impulse is added just before foot-strike to realize a periodic walking pattern on flat or uphill ground. With walking terrain varying, the robot can transit to an adaptive walking gait in a few steps. With different push or pull disturbances acting on hip joint and the robot gait transiting on a continuously slope-changing downhill, the effectiveness of the presented DCLF-based method is verified using simulation experiments. The ability to walk on a changing environment is also presented by simulation results. The insights of this paper can help to develop a robust control method and adaptive walking of dynamic passive locomotion robots.

A stepping gait trajectory design based on hip height variation of swing leg for the balance of lower extremity exoskeleton

PurposeLower extremity exoskeletons have drawn much attention recently due to their potential ability to help the stroke and spinal cord injury patients to regain the ability of walking. However, the balance of the human-exoskeleton system (HES) remains a big challenge. Usually, patients use crutches to keep balance when they wear exoskeleton. However, the balance depends greatly on the patient's balance ability and will be inevitably poor occasionally, which often causes the landing in advance of HES. The purpose of this paper is to propose a real-time stepping gait trajectory planning method based on the hip height variation of the swing leg to solve the problem.Design/methodology/approachThe hip height of the swing leg was analyzed and measured. The simulation with MATLAB and the experimental test with the prototype of the proposed gait were conducted to verify its feasibility.FindingsWith the proposed method, HES can achieve successful step even when the balance kept by crutches is poor.Research limitations/implicationsInstead of actively avoiding the poor balance due to the instability caused by gravity, the method just modifies the stepping gait passively to avoid the landing in advance when the poor balance appears. In addition, it may not work well when the balance is too poor. Moreover, the proposed gait is just used in the initial stage of rehabilitation training. Besides, the step length of the gait must be limited for comfort.Originality/valueA real-time stepping gait trajectory planning method based on the hip height variation of the swing leg is first proposed and its feasibility to avoid the landing in advance when the balance kept by the crutches is poor has been preliminary verified.

Research on Improved Pedestrian Dead Reckoning Algorithms

In view of user's requirements of high performance, easy operation and low cost with indoor location, data acquisition software based on Android platform utilize sensors built-in cellphone is used to study the pedestrian dead reckoning (PDR). Step detection and step length estimation are carried out by collecting leg swing angle while walking, and the classical step length estimation algorithm is improved. At the same time, the improved heuristic drift elimination algorithm is used to calculate the direction. Finally, the experiment results show that the PDR technology can better satisfy the requirements of indoor pedestrian positioning, and as for the low-cost multi-sensor. compared with the existing algorithm, the improved algorithm with higher positional accuracy.

What happens before the first step? A New Approach to Quantifying Gait Initiation Using a Wearable Sensor

BackgroundWalking is a volitional behavior that requires planning and initiation before a step is observed. Following a signal to begin walking, studies of gait initiation in specialized labs have identified three phases that occur during the transition from a standing position via anticipatory postural adjustment (APA) to the first step. Routine instrumented gait testing outside of the laboratory setting focuses on gait execution and does not include gait initiation measures. Research questionCan a single IMU sensor be used for performing gait initiation evaluations outside the lab? MethodsWe recorded walking in young (N = 41) and older (N = 26) adults using an instrumented gait mat while they were wearing a 3D accelerometer on their lower back. Subjects were instructed to begin walking following an auditory signal. An algorithm was developed to extract the following measures from the acceleration signal: gait initiation time, measured from the start of the auditory cue to begin walking and ends at the heel-strike of the swing leg, time-to-APA (reaction time), APA duration and swing time (execution of the first step). ResultsIntraclass correlation coefficient analysis showed good to excellent agreement between gait initiation metrics obtained with the gait mat and the wearable sensor (mean 0.88, range [0.75-0.96]). Except for swing time, all measures were longer in the older subjects, compared to the young adults (p < 0.01). SignificanceExtracting gait initiation measures from routine instrumented gait testing may facilitate studies that can better determine the extent to which impaired gait planning and execution contribute to mobility impairments.

Walking With Arm Swinging and Pelvis Rotation Generated With the Relative Angular Acceleration

A natural-looking arm swinging in biped locomotion can be generated by appropriately controlling the quantities derived from the momentum equilibrium principle such as the rate of change of the relative angular momentum or the relative angular acceleration (RAA). The arm swinging compensates completely the undesirable yaw moment generated by the swing leg. The RAA control input can also be used to control the angular excursion of the pelvis that contributes to the compensation of the yaw moment, either in a passive or in an active way. It is shown that by varying the intensities of the arm swinging and the pelvis rotation, human-like gaits can be easily generated. The yaw-moment compensation strategies are implemented with a recently developed walking controller that distributes the body wrench with the so-called virtual repellent point (VRP) generalized inverse (VRP-GI). This controller is time-efficient since iterative computations are avoided. The performance of the controller in dynamic walking with arm swinging and passive/active pelvis rotation is confirmed via simulations.

Mechanical–electrical–pneumatic systematic design exploration of hexapod robot experimental prototype

Aiming at the problem of the detect and rescue in the coal mine with the leaking vas, a type of pneumatic hexapod explored robot which uses a high pressure nitrogen cylinder as the power producer is designed. The leg mechanism is designed with three degrees of freedom, the straight line walking and turning gaits are planned, which are testified by the virtual prototype. The control loop of the cylinder is designed with the magnetic valve with three positions and five paths. The air bottle, the reducing valve, the general follow control part (GFC) the magnetic valve with three positions and five paths, the cylinder are selected and the air supply loop of the hole machine is designed, the 3D model of the hole machine is built which is used to confirm the installing form of the hole body. The experimental prototype is obtained at last. The power supply and control circuits of the magnetic valves are designed, the control series is written on the Arduino single chip. The experiment of the leg swing of the robot on the stage is proceeded which verifies the correctness of the design.

High-speed locomotion in the Saharan silver ant, Cataglyphis bombycina

The diurnal thermophilic Saharan silver ant, Cataglyphis bombycina, is the fastest of the North African Cataglyphis desert ant species. These highly mobile ants endure the extreme temperatures of their sand dune environment with outstanding behavioural, physiological and morphological adaptations. Surprisingly, C. bombycina has comparatively shorter legs than its well-studied sister species Cataglyphis fortis from salt pan habitats. This holds despite the somewhat hotter surface temperatures and the more yielding sand substrate. Here, we report that C. bombycina employs a different strategy in reaching high running speeds, outperforming the fastest known runs of the longer-legged C. fortis ants. Video analysis across a broad range of locomotor speeds revealed several differences to C. fortis Shorter leg lengths are compensated for by high stride frequencies, ranging beyond 40 Hz. This is mainly achieved by a combination of short stance phases (down to 7 ms) and fast leg swing movements (up to 1400 mm s-1). The legs of one tripod group exhibit almost perfect synchrony in the timings of their lift-offs and touch-downs, and good tripod coordination is present over the entire walking speed range (tripod coordination strength values around 0.8). This near synchrony in leg movement may facilitate locomotion across the yielding sand dune substrate.

Kinematics of Maximal Speed Sprinting With Different Running Speed, Leg Length, and Step Characteristics.

This study aimed to provide multiple regression equations taking into account differences in running speed, leg length, and step characteristics to predict kinematics of maximal speed sprinting. Seventy-nine male sprinters performed a maximal effort 60-m sprint, during which they were videoed through the section from the 40- to 50-m mark. From the video images, leg kinematic variables were obtained and used as dependent variables for multiple linear regression equation with predictors of running speed, leg length, step frequency, and swing/support ratio. Multiple regression equations to predict leg kinematics of maximal speed sprinting were successfully obtained. For swing leg kinematics, a significant regression model was obtained to predict thigh angle at the contralateral foot strike, maximal knee flexion and thigh lift angular velocities, and maximal leg backward swing velocity (adjusted R2 = 0.194–0.378, medium to large effect). For support leg kinematics, a significant regression model was obtained to predict knee flexion and extension angular displacements, maximal knee extension velocity, maximal leg backward swing angular velocity, and the other 13 kinematic variables (adjusted R2 = 0.134–0.757, medium to large effect). Based on the results, at a given leg length, faster maximal speed sprinting will be accompanied with greater thigh angle at the contralateral foot strike, greater maximal leg backward swing velocity during the swing phase, and smaller knee extension range during the support phase. Longer-legged sprinters will accomplish the same running speed with a greater thigh angle at contralateral foot strike, greater knee flexion range, and smaller maximal leg backward swing velocity during the support phase. At a given running speed and leg length, higher step frequencies will be achieved with a greater thigh angle at contralateral foot strike and smaller knee flexion and extension ranges during the support phase. At a given running speed, leg length and step frequency, a greater swing/support ratio will be accompanied with a greater thigh angle at contralateral foot strike and smaller knee extension angular displacement and velocity during the support phase. The regression equations obtained in this study will be useful for sprinters when trying to improve their maximal speed sprinting motion.

An admittance controller based on assistive torque estimation for a rehabilitation leg exoskeleton

A rehabilitation exoskeleton leg was constructed for gait training, and a method for exoskeleton leg swing control based on admittance model was studied. The man–machine interaction torque, the inertia compensator torque, and the exoskeleton’s assistive torque act as the inputs to the admittance control system for realizing the effective assistance to the wearer. The exoskeleton’s assistive torque is generated by estimating net torque exerted by the muscle based on adaptive frequency oscillator. A variable swing frequency experiment for simulating physical rehabilitation exercise was implemented. The results show that the inertia compensator adjusting the compensation varies with the swing frequency. The control system provides effective assistance to the wearer. The coordinated control experiment of hip and knee joints was also implemented. The results show that the interaction forces are all controlled in a reasonable and small range, and there is a good coordination between the hip joint and knee joint during swing motion.

Reliability and concurrent validity of spatiotemporal stride characteristics measured with an ankle-worn sensor among older individuals

BackgroundWearable inertial sensors have been shown to provide valid mean gait characteristics assessments, however, assessment of variability is less convincingly established. Research questionWhat level of concurrent validity, and session-to-session reliability does an ankle-worn inertial measurement unit (IMU)-based gait assessment with a novel angular velocity-based gait event detection algorithm have among older adults? MethodsTwenty seven (women N = 17) participants volunteered (age 74.4 (SD 4.3) years, body mass 74.5 (12.0) kg, height 165.9 (9.9) cm). Right leg stance, swing, and stride duration and stride length, and stride velocity were concurrently assessed with motion capture and with an IMU from a 3 min self-paced walk up and back a 14 m track repeated twice a week apart. Gait variability was assessed as the SD of all of the registered strides. ResultsSignificant difference was observed between methods for many of the mean stride characteristics and stride variability (all p < 0.05), fair to excellent agreement was observed for mean values of all of the five stride characteristics evaluated (intra-class correlation coefficient [ICC] from 0.43 to 1.00). However, poor agreement was observed for the SD of all of the evaluated stride characteristics (ICC from -0.25 to 0.00). Both methods indicated excellent session to session reliability for all of the five stride characteristics evaluated (ICC from 0.84 to 0.98, CV%RMS from 1.6% to 3.6%), whereas the variability characteristics exhibited poor to good reliability (ICC from 0.0 to 0.69, CV%RMS from 18.0% to 34.4%). SignificanceExcellent concurrent validity and reliability was observed for mean spatiotemporal stride characteristics, however, gait variability exhibited poor concurrent validity and reliability. Although IMUs and the presented algorithm could be used to assess mean spatiotemporal stride characteristics among older individuals, either a more reliable gait event detection algorithm or alternative analytical approaches should be used for gait variability.

Delayed Output Feedback Control for Gait Assistance With a Robotic Hip Exoskeleton

In this paper, we propose a new and simple control strategy for gait assistance with a hip exoskeleton robot. This controller is based on the time delayed, self-feedback known for stabilizing oscillatory systems under certain conditions. In this controller, there are no separate estimators for the gait phase nor the environment, yet the controller can be generalized to operate under various walking conditions (e.g., stair and ramp walking). We first define a state variable representing the current leg's movement with hip joint angles. A simple assistance control can be described in closed-loop form with the delayed state feedback. By assigning the appropriate time-delay and self-feedback gain, we can generate assistive torques stably under the interaction between human and exoskeleton. The controller provides immediate and smooth assistance to user movement by reflecting the change of leg motion at every control period. The proposed joint-angle-based delayed-feedback assistance controller can operate under various walking speeds and environmental changes (e.g., stairs and ramps) without the need for additional sensors, computational processing, and parameter adjustment. Using a simple leg swing model, we perform a stability analysis under a simplified condition to provide insights into the effects of the time-delayed feedback in oscillatory systems. Then, we experimentally validate the efficacy of the proposed assistance controller by measuring the metabolic energy expenditure for level treadmill walking. We also test and analyze the generated assistive torques and power under the different walking conditions to show the generalizability of the controller.

Control of mediolateral gait stability: center of pressure control strategies.

Wearable inertial sensors have been shown to provide valid mean gait characteristics assessments, however, assessment of variability is less convincingly established.What level of concurrent validity, and session-to-session reliability does an ankle-worn inertial measurement unit (IMU)-based gait assessment with a novel angular velocity-based gait event detection algorithm have among older adults?Twenty seven (women N = 17) participants volunteered (age 74.4 (SD 4.3) years, body mass 74.5 (12.0) kg, height 165.9 (9.9) cm). Right leg stance, swing, and stride duration and stride length, and stride velocity were concurrently assessed with motion capture and with an IMU from a 3 min self-paced walk up and back a 14 m track repeated twice a week apart. Gait variability was assessed as the SD of all of the registered strides.Significant difference was observed between methods for many of the mean stride characteristics and stride variability (all p < 0.05), fair to excellent agreement was observed for mean values of all of the five stride characteristics evaluated (intra-class correlation coefficient [ICC] from 0.43 to 1.00). However, poor agreement was observed for the SD of all of the evaluated stride characteristics (ICC from -0.25 to 0.00). Both methods indicated excellent session to session reliability for all of the five stride characteristics evaluated (ICC from 0.84 to 0.98, CV%RMS from 1.6% to 3.6%), whereas the variability characteristics exhibited poor to good reliability (ICC from 0.0 to 0.69, CV%RMS from 18.0% to 34.4%).Excellent concurrent validity and reliability was observed for mean spatiotemporal stride characteristics, however, gait variability exhibited poor concurrent validity and reliability. Although IMUs and the presented algorithm could be used to assess mean spatiotemporal stride characteristics among older individuals, either a more reliable gait event detection algorithm or alternative analytical approaches should be used for gait variability.

Movement history alters kinematics of leg swing in spastic cerebral palsy

Movement history alters kinematics of leg swing in spastic cerebral palsy

Aging effects on the mechanical energy transfer through the lower extremity joints during the swing phase of level walking

Age-related changes of gait performance have been evidenced by the altered kinetic coordination of the lower extremity. However, a systematic approach to explore the gait control in terms of the mechanical energy transfer across multiple segments throughout the gait phases is still not well documented. Ten healthy elderly and ten young adults were asked to walk along a 10-meter walkway at the self-selected and fast walking speeds. The visualized energy flow model of the swing leg was established and the factor analysis was then applied to extract the high-dimensional energy flow characteristics of the swing leg. The results showed that the young adults have similar energy flow characteristics of the swing leg for both fast and self-selected walking speeds, while the elderly showed an opposite energy flow pattern especially at the fast walking speed. The hip power and the knee power were also found to mainly correspond to the swing acceleration and deceleration, respectively. This study demonstrated a valuable tool to explore the change of the gait characteristics in the elderly and could help to facilitate the understanding of the neuromuscular adaptation due to aging.

Improving Kinematic Flexibility and Walking Performance of a Six-legged Robot by Rationally Designing Leg Morphology

This paper explores the design of leg morphology in a six-legged robot. Inspired by nature, where animals have different leg morphology, we examined how the difference in leg morphology influences behaviors of the robot. To this end, a systematic search was conducted by scanning over the parameter space consisting of default angles of leg joints of the six-legged robot, with two main objectives: to maximize the kinematic flexibility and walking performance of the robot. Results show that (1) to have a high kinematic flexibility with both the torso and swing legs, the femur segment should tilt downwards by 5°–10° and the tibia segment should be vertically downwards or with a slight inward tilt; (2) to achieve relatively energy-efficient and steady walking, the tibia segment should be approximately vertically downwards, with the femur segment tilting upwards to lower the torso height. The results of this study suggest that behaviors of legged robots can be passively enhanced by careful mechanical design choices, thereby leading to more competent legged machines.

Anti-Slip Gait Planning for a Humanoid Robot in Fast Walking

Humanoid robots are expected to have broad applications due to their biped mobility and human-like shape. To increase the walking speed, it is necessary to increase the power for driving the joints of legs. However, the resulting mass increasing of the legs leads to a rotational slip when a robot is walking fast. In this paper, a 3D three-mass model is proposed, in which both the trunk and thighs are regarded as an inverted pendulum, and the shanks and feet are considered as mass-points under no constraints with the trunk. Then based on the model, a friction constraint method is proposed to plan the trajectory of the swing leg in order to achieve the fastest walking speed without any rotational slip. Furthermore, the compensation for zero-moment point (ZMP) is calculated based on the 3D three-mass model, and the hip trajectory is obtained based on the compensated ZMP trajectory by using the preview control method, thus improving the robot’s overall ZMP follow-up effect. This planning method involves simple calculations but reliable results. Finally, simulations confirm that the rotational slip is avoided while stable and fast walking is realized, with free joints of the waist and arms, which then could be planned for other tasks.