Swing Foot Research Articles

The Neuro-Mechanical Processes That Underlie Goal-Directed Medio-Lateral APA during Gait Initiation.

Gait initiation (GI) involves passing from bipedal to unipedal stance. It requires a rapid movement of the center of foot pressure (CoP) towards the future swing foot and of the center of mass (CoM) in the direction of the stance foot prior to the incoming step. This anticipatory postural adjustment (APA) allows disengaging the swing leg from the ground and establishing favorable conditions for stepping. This study aimed to describe the neuro-mechanical process that underlies the goal-directed medio-lateral (ML) APA. We hypothesized that controlled knee flexion of the stance leg contributes to the initial ML displacement of the CoP and to the calibration of the first step. Fourteen subjects initiated gait starting from three different initial stance widths of 15 cm (Small), 30 cm (Medium), and 45 cm (Large). Optoelectronic, force platform and electromyogram (EMG) measurements were performed. During APA, soleus activity diminished bilaterally, while tibialis anterior (TA) activity increased, more so in the stance leg than in the swing leg, and to a larger extent with increasing initial stance width. Knee flexion of the stance leg was observed during APA and correlated with the ML CoP displacement towards the swing leg. ML CoP and CoM displacements during APA increased with increasing stance width. The activity of stance-leg TA was correlated with the degree of knee flexion. Swing-leg tensor fasciae latae (TFL) was also active during APA. Across subjects, when stance-leg tibialis activity was low, TFL activity was large and vice versa. The modulation of the ML CoP position during APA allowed the gravity-driven torque to place the CoM just lateral to the stance foot during step execution. Accordingly, the gravity-driven torque, the ML CoM velocity during step execution, and the step width at foot contact (FC) were lower in the Small and greater in the Large condition. Consequently, the position of the stepping foot at FC remained close to the sagittal plane in all three conditions. Conclusively, coordinated activation of hip abductors and ankle dorsiflexors during APA displaces the CoP towards the swing leg, and sets the contact position for the swing foot.

Evidence of impaired neuromuscular responses in the support leg to a destabilizing swing phase perturbation in hemiparetic gait.

The neuromuscular mechanisms that underlie post-stroke impairment in reactive balance control during gait are not fully understood. Previous research has described altered muscle activations in the paretic leg in response to postural perturbations from static positions. Additionally, attenuation of interlimb reflexes after stroke has been reported. Our goal was to characterize post-stroke changes to neuromuscular responses in the stance leg following a swing phase perturbation during gait. We hypothesized that, following a trip, altered timing, sequence, and magnitudes of perturbation-induced activations would emerge in the paretic and nonparetic support legs of stroke survivors compared to healthy control subjects. The swing foot was interrupted, while subjects walked on a treadmill. In healthy subjects, a sequence of perturbation-induced activations emerged in the contralateral stance leg with mean onset latencies of 87–147 ms. The earliest latencies occurred in the hamstrings and hip abductor and adductors. The hamstrings, the adductor magnus, and the gastrocnemius dominated the relative balance of perturbation-induced activations. The sequence and balance of activations were largely preserved after stroke. However, onset latencies were significantly delayed across most muscles in both paretic and nonparetic stance legs. The shortest latencies observed suggest the involvement of interlimb reflexes with supraspinal pathways. The preservation of the sequence and balance of activations may point to a centrally programmed postural response that is preserved after stroke, while post-stroke delays may suggest longer transmission times for interlimb reflexes.

Development of Fuzzy Logic Controllers for Controlling Bipedal Robot Locomotion on Uneven Terrains with IMU Feedbacks

Locomotion controller is an important and essential aspect for bipedal robots. Typically, a Linear Inverted Pendulum Model (LIPM) is a mathematical approach to generate the Center of Mass (CoM) trajectory of a bipedal robot. By combining the swing foot trajectory, the omni-directional walking command is capable of generating joint angle control commands in terms of Inverse Kinematics (IK). To improve bipedal locomotion stability on uneven terrain situations, an Inertia Measurement Unit (IMU) was desired to place on the robot's chest was used to measure the body's tilt posture on uneven terrains. The robot body's tilt posture provided an indication of locomotion stability. The body's tilt posture information was further evaluated with a Fuzzy Logic Controller (FLC) to generate appropriate offset angles to be applied on the corresponding joints so that the body's tilt posture can be adjusted accordingly to meet a stable situation. Finally, a kid-size bipedal robot, named Huro Evolution JR, was used as the experiment platform. The proposed FLC can be applicable to the terrain conditions of maximum 25° slope in Double Support Phased (DSP) stand cases. With the walking cases, the FLC is capable of walking on maximum 12° slope, 1 cm stair height and the combined terrain situation well. In the future, the Center of Pressure (CoP) information will be accompanied with the IMU information to further improved the locomotion stability in a high dynamic environment.

Terrain-Blind Humanoid Walking Based on a 3-D Actuated Dual-SLIP Model

While a number of controllers exist for dynamic humanoid walking over known uneven terrain, the ability to negotiate moderate changes in ground height without environment perception is still lacking. Such capability would mitigate problems caused by inaccurate sensing and reduce online terrain-dependent computational requirements. This letter proposes a 1-step terrain adaptation strategy for humanoid walking based on the 3-D actuated Dual-SLIP model. A flexible gait to negotiate unknown terrain is synthesized from a series of consistent gait adaptations acquired from off -line optimization with this simple model. Being open-loop prior to touchdown, the strategy requires no perception of the terrain. Also, the resultant terrain-robust swing foot trajectory exhibits human-like characteristics such as leg retraction and extension near the end of the swing phase. Through a task-space control framework, the model-derived gait is embedded into the high-DoF ATLAS humanoid model. In the final result, a “blindfolded” ATLAS model reliably walks over randomly generated uneven terrain (with per-step height changes of up to 5% of the leg length) at a constant midstance speed.

Research on Optimization Walking Robot Gait Planning Based on Human Bionics

This paper had analyzed the degree of freedom robot and then simulates the robots and humans similar to the lower limbs, to establish sports model of the robot. The analysis robot has 10 degrees of freedom, in which one leg has five degrees of freedom, namely, a degree of freedom of the knee, hip ankle is assigned two degrees of freedom. Depending on the needs of the kinematic model is divided into forward motion model and lateral movement model. Link by representatives’ form various parts of the robot to simplify the model. Through the establishment of the geometry and the Cartesian coordinate system, analyze the relationship between the joint angle and joint use mathematical functions to represent the correspondence between swing foot and between each joint. By Zero Moment Point (ZMP) stability analysis, to ensure the stability of humanoid robot, obtained center of gravity and zero moment point formula, thus proving humanoid robot walking stability. Using of spline interpolation and polynomial fitting method for solving the hip, the equations of motion of the ankle joint, the knee. By setting the parameters, the use of MATLAB simulation software to obtain motion curve of each joint and humanoid robot designed to simulate obtain humanoid robot gait simulation video.

Anticipatory postural adjustments are unaffected by age and are not absent in patients with the freezing of gait phenomenon

In bipedal gait, the initiation of the first step is preceded by a complex sequence of movements which shift the centre of mass of the body towards the stance foot to allow for a step of the swing foot. These anticipatory postural adjustments (APAs) have been investigated in order to elucidate movement strategies in healthy and diseased persons. We studied the influence of several external parameters (age, type of step initiation) on APAs and investigated whether Parkinsonian patients may have different APAs. As a result, we found that externally elicited steps were preceded by faster and larger APAs than self-timed steps. Parkinsonian patients without the freezing of gait (FOG) phenomenon showed overall slightly reduced APAs but did not clearly differ from patients with FOG. Multiple APAs were seen in up to 25% of the steps of the patients and in a much lower percentage of the steps of control subjects. The results indicate that APAs are significantly influenced by the timing of a step, i.e. are larger in externally elicited steps. The patients showed an overall preserved APA pattern but slowed movements and amplitude, indicating that increased bradykinesia due to progressive illness is a plausible explanation for these findings. The freezing phenomenon is not explained by a general absence or massive reduction in APA measures.

Modeling, Simulation and Control of the Walking of Biped Robotic Devices, Part II: Rectilinear Walking

This is the second part of a three-part paper. It extends to the free walking results of a previous work on postural equilibrium of a lower limb exoskeleton for rehabilitation exercises. A classical approach has been adopted to design gait (zero moment point (ZMP), linearized inverted pendulum theory, inverse kinematics obtained through the pseudo-inverse of Jacobian matrices). While several ideas exploited here can be found in other papers of the literature, e.g., whole-body coordination, our contribution is the simplicity of the whole control approach that originates logically from a common root. (1) The approximation of the unilateral foot/feet-ground contacts with non-holonomic constraints leads naturally to a modeling and control design that implements a two-phase switching system. The approach is facilitated by Kane’s method and tools as described in Part I. (2) The Jacobian matrix is used to transfer from the Cartesian to the joint space a greater number of variables for redundancy than the degrees of freedom (DOF). We call it the extended Jacobian matrix. Redundancy and the prioritization of postural tasks is approached with weighted least squares. The singularity of the kinematics when knees are fully extended is solved very simply by fake knee joint velocities. (3) Compliance with the contact and accommodation of the swing foot on an uneven ground, when switching from single to double stance, and the transfer of weight from one foot to the other in double stance are approached by exploiting force/torque expressions returned from the constraints. (4) In the center of gravity (COG)/ZMP loop for equilibrium, an extended estimator, based on the linearized inverted pendulum, is adopted to cope with external force disturbances and unmodeled dynamics. Part II treats rectilinear walking, while Part III discusses turning while walking.

Compliant Biped Walking on Uneven Terrain with Point Feet

In this paper, we aim to realize compliant biped walking on uneven terrain with point feet. A control system is designed for a 5-link planar biped walker. According to the role that each leg plays, the control system is decomposed into two parts: the swing leg control and the support leg control. The trajectory of the swing foot is generated in real-time to regulate the walking speed. By considering the reaction torque of the swing leg's hip joint as disturbance, a sliding model controller is implemented at the support leg's hip joint to control the torso's posture angle. In order to make sure the landing foot does not rebound after impact, the vertical contact force control is set as the internal loop of the hip's height control. In simulation, the control system is tested on a virtual 5-link planar biped walker in Matlab. Finally, stable biped walking is realized on uneven terrain with roughness up to 2cm.

Age effects on the control of dynamic balance during step adjustments under temporal constraints

This study investigated the age effects on the control of dynamic balance during step adjustments under temporal constraints. Fifteen young adults and 14 older adults avoided a virtual white planar obstacle by lengthening or shortening their steps under free or constrained conditions. In the anterior–posterior direction, older adults demonstrated significantly decreased center of mass velocity at the swing foot contact under temporal constraints. Additionally, the distances between the ‘extrapolated center of mass’ position and base of support at the swing foot contact were greater in older adults than young adults. In the mediolateral direction, center of mass displacement was significantly increased in older adults compared with young adults. Consequently, older adults showed a significantly increased step width at the swing foot contact in the constraint condition. Overall, these data suggest that older adults demonstrate a conservative strategy to maintain anterior–posterior stability. By contrast, although older adults are able to modulate their step width to maintain mediolateral dynamic balance, age-related changes in mediolateral balance control under temporal constraints may increase the risk of falls in the lateral direction during obstacle negotiation.

Walking Algorithm of Humanoid Robot on Uneven Terrain with Terrain Estimation

Humanoid robots are expected to achieve stable walking on uneven terrains. In this paper, a control algorithm for humanoid robots walking on previously unknown terrains with terrain estimation is proposed, which requires only minimum modification to the original walking gait. The swing foot trajectory is redesigned to ensure that the foot lands at the desired horizontal positions under various terrain height. A compliant terrain adaptation method is applied to the landing foot to achieve a firm contact with the ground. Then a terrain estimation method that takes into account the deformations of the linkages is applied, providing the target for the following correction and adjustment. The algorithm was validated through walking experiments on uneven terrains with the full-size humanoid robot Kong.

A free gait generation method for quadruped robots over rough terrains containing forbidden areas

Planning a robust gait is one of the most basic aspects to enable a quadruped robot to walk stably on rough terrains. In this paper, we focus on the scenario where a quadruped robot travelling on the rough terrains containing forbidden areas, and a free gait generation method for quadruped robot is proposed. Under the assumption that a set of the positions which can be selected as the foothold is given, the quadruped robot can select the swing foot sequence and choose the best foothold for the swing foot automatically. A body sway motion is included into the motion planning of the free gait to enlarge the stability margin of the robot. With the aid of the sway motion, the stability margin of the robot is no less than the minimum stability margin during the whole walking process. In order to guarantee the locomotion continuity of the quadruped robot, a COG trajectory which has continuous velocity and acceleration profiles is automatically generated. Moreover, the locomotion speed of the robot is improved by ensuring the kinematic margin of the selected swing foot to be zero just before this foot lift-off the ground. With the free gait generation method proposed in this paper, the robot can autonomously navigate through rough terrains as soon as possible on the condition that the robot has enough stability margin. The simulation results show the correctness and effectiveness of the proposed method.

P57. Validation of gait analysis with inertial sensors

Inertial sensors are electric circuits which measure acceleration and rotational velocity. This information is needed to determine the 3-D position of a body in space. With the help of those sensors gait can be recorded. The method was validated by a motion-capture system. We examined twelve healthy young men. Sensors were attached at the thigh as well as at the lower leg on each side. One sensor consisted of one gyroscope and two accelerometers. With the help of an integrated Kalman Filter it was possible to calculate the position of all 4 leg segments in the sagittal plane. Specific pattern of gyroscopic and accelerometric data helped defining moments of terminal contact (toe-off) and initial contact (heel strike). These events were validated by a pressure-sensitive inserted sole. To reconstruct the position of the swing foot, forward kinematics were used, i.e. the stance foot was taken a pivotal point and the position of the leg segments was computed with reference to that point so it was possible to calculate step length and step velocity. We compared this data with data synchronously obtained from a motion capture system while subjects walked on a treadmill. Comparison of the time of initial and terminal contact obtained by inertial sensors and pressure sensitive soles resulted in very small deviations within the range of data resolution. Correlation between segment angles measured with inertial sensors and motion capture system was above r = 0.9. Correlation between step length measured by these two systems was above r > 0.8 and could be increased by a calibration of the inertial-sensors system by a defined gait distance. Gait analysis with inertial sensors is less expensive than with conventional methods and allows for the assessment of gait in more natural environments. The actual disadvantage of less precision is compensated in future with better sensors and software.

An Interactive Treadmill Under a Novel Control Scheme for Simulating Overground Walking by Reducing Anomalous Force

Since the purpose of treadmill-based locomotor training is to transfer lower extremity coordinative skill to overground walking (OW), it needs to simulate OW as closely as possible for optimal skill transfer. Typical treadmill walking at a preset constant speed is different from realistic overground walking because it is less engaging and more automatic. As a remedy for the limitation, this paper investigates a novel treadmill control scheme that allows users to change walking speed freely. It further simulates natural walking by reducing anomalous force (AF) due to acceleration of the treadmill belt. Adding an attenuator in the scheme effectively diminishes the AF when changing walking speed. The proposed scheme, which requires real-time measurement of pelvic and swing foot motion, was developed for a treadmill with a typical belt length (1.5m). A clinical test was conducted with nine healthy subjects in order to quantitatively evaluate the proposed scheme by comparing it with the two existing control schemes in the literature.

Can toe-ground footwear margin alter swing-foot ground clearance?

Falls are an important healthcare concern in the older population and tripping is the primary cause. Greater swing foot-ground clearance is functional for tripping prevention. Trips frequently occur due to the lowest part of the shoe contacting the walking surface. Shoe design effects on swing foot-ground clearance are, therefore, important considerations. When a shoe is placed on a flat surface, there usually is small vertical margin (VM) between the walking surface and the minimum toe point (MTP). The current study examined the effects of VM on swing foot-ground clearance at a critical gait cycle event, minimum foot clearance (MFC). 3D coordinates of the swing foot (i.e. MTP and heel) were obtained during the swing phase. MTP represented the swing foot-ground clearance and various MTPs were modelled based on a range of VMs. The sagittal orientation of the toe and heel relative to the walking surface was also considered to evaluate effects of VM and swing foot angle on foot-ground clearance. Greater VM increased the swing foot-ground clearance. At MFC, for example, 0.09cm increase was estimated for every 0.1cm VM. Foot angle throughout the swing phase was typically −30° and 70°. Increasing swing ankle dorsiflexion can maximise VM, which is effective for tripping prevention. Further research will be needed to determine the maximum thresholds of VM to be safely incorporated into a shoe.

Effects of temporal constraints on medio-lateral stability when negotiating obstacles

If an obstacle suddenly appears during walking, either the crossing step can be lengthened or the precrossing step shortened to avoid the obstacle. We investigated the effects of temporal constraints on dynamic stability during step adjustments. Twelve healthy young adults avoided a virtual white planar obstacle by lengthening or shortening their steps under free or constrained conditions. When constrained, participants had only one step to avoid the obstacle. The results indicated that center of mass (COM) displacement in the mediolateral (ML) direction and the COM velocity toward the swing-leg side during the crossing step were significantly increased in the long-constraint compared with the long-free condition. Consequently, the extrapolated COM (XcoM) position at the swing foot contact was also located further toward the swing-leg side. However, the distances between the XcoM and base of support (BOS) at the swing foot contact in the ML direction was unchanged because of greater lateral foot placement. In the anteriorposterior (AP) direction, temporal constraints led to greater AP COM displacement. The XcoM–BOS distance in the AP direction was unchanged in the long-constraint condition because of greater step length. However, the value became negative in the short-constraint condition, violating the conditions for dynamic stability, because step length adjustments were obstructed by the spatial constraints of the obstacles. These results suggest that temporal constraints affect postural stability in the AP and ML directions during step adjustments. AP and ML stability at swing foot contact are maintained through adjustments of step length and lateral foot placement, respectively.

Prefrontal, posterior parietal and sensorimotor network activity underlying speed control during walking.

Accumulating evidence suggests cortical circuits may contribute to control of human locomotion. Here, noninvasive electroencephalography (EEG) recorded from able-bodied volunteers during a novel treadmill walking paradigm was used to assess neural correlates of walking. A systematic processing method, including a recently developed subspace reconstruction algorithm, reduced movement-related EEG artifact prior to independent component analysis and dipole source localization. We quantified cortical activity while participants tracked slow and fast target speeds across two treadmill conditions: an active mode that adjusted belt speed based on user movements and a passive mode reflecting a typical treadmill. Our results reveal frequency specific, multi-focal task related changes in cortical oscillations elicited by active walking. Low γ band power, localized to the prefrontal and posterior parietal cortices, was significantly increased during double support and early swing phases, critical points in the gait cycle since the active controller adjusted speed based on pelvis position and swing foot velocity. These phasic γ band synchronizations provide evidence that prefrontal and posterior parietal networks, previously implicated in visuo-spatial and somotosensory integration, are engaged to enhance lower limb control during gait. Sustained μ and β band desynchronization within sensorimotor cortex, a neural correlate for movement, was observed during walking thereby validating our methods for isolating cortical activity. Our results also demonstrate the utility of EEG recorded during locomotion for probing the multi-regional cortical networks which underpin its execution. For example, the cortical network engagement elicited by the active treadmill suggests that it may enhance neuroplasticity for more effective motor training.

Stability and agility: biped running over varied and unknown terrain

We tackle the problem of a biped running over varied and unknown terrain. Running is a necessary skill for a biped moving fast, but it increases the challenge of dynamic balance, especially when a biped is running on varied terrain without terrain information (due to the difficulty and cost of obtaining the terrain information in a timely manner). To address this issue, a new dynamic indicator called the sustainable running criterion is developed. The main idea is to sustain a running motion without falling by maintaining the system states within a running-feasible set, instead of running on a periodic limit cycle gait in the traditional way. To meet the precondition of the criterion, the angular moment about the center of gravity (COG) is restrained close to zero at the end of the stance phase. Then to ensure a small state jump at touchdown on the unknown terrain, the velocity of the swing foot is restrained within a specific range at the end of the flight phase. Finally, the position and velocity of the COG are driven into the running-feasible set. A five-link biped with underactuated point foot is considered in simulations. It is able to run over upward and downward terrain with a height difference of 0.15 m, which shows the effectiveness of our control scheme.

Time-To-Contact Analysis of Gait Stability in the Swing Phase of Walking in People With Multiple Sclerosis.

This study investigated timing and coordination during the swing phase of swing leg, body center of mass (CoM) and head during walking people with multiple sclerosis (MS; n = 19) and controls (n = 19). The MS group showed differences in swing phase timing at all speeds. At imposed but not preferred speeds, the MS group had less time to prepare for entry into the unstable equilibrium, as the CoM entered this phase of swing earlier. Time-to-contact coupling, quantifying the coordination between the CoM and the swing foot, was not different between groups. The projection of head motion on the ground occurred earlier after toe-off and was positioned closer to the body in the MS group, illustrating increased reliance on visual exproprioception in which vision of the body in relation to the surface of support is established. Finally, prospective control, linking head movements to the swing foot time-to-contact and next step landing area, was impaired in the MS group at higher gait speeds.

Optimization‐based Full Body Control for the DARPA Robotics Challenge

We describe our full body humanoid control approach developed for the simulation phase of the DARPA Robotics Challenge (DRC), as well as the modifications made for the DARPA Robotics Challenge Trials. We worked with the Boston Dynamics Atlas robot. Our approach was initially targeted at walking, and it consisted of two levels of optimization: a high‐level trajectory optimizer that reasons about center of mass and swing foot trajectories, and a low‐level controller that tracks those trajectories by solving floating base full body inverse dynamics using quadratic programming. This controller is capable of walking on rough terrain, and it also achieves long footsteps, fast walking speeds, and heel‐strike and toe‐off in simulation. During development of these and other whole body tasks on the physical robot, we introduced an additional optimization component in the low‐level controller, namely an inverse kinematics controller. Modeling and torque measurement errors and hardware features of the Atlas robot led us to this three‐part approach, which was applied to three tasks in the DRC Trials in December 2013.

Modeling and Finite-Time Walking Control of a Biped Robot with Feet

This paper addresses the problem of modeling and controlling a planar biped robot with six degrees of freedom, which are generated by the interaction of seven links including feet. The biped is modeled as a hybrid dynamical system with a fully actuated single-support phase and an instantaneous double-support phase. The mathematical modeling is detailed in the first part of the paper. In the second part, we present the synthesis of a controller based on virtual constraints, which are codified in an output function that allows defining a local diffeomorphism to linearize the robot dynamics. Finite-time convergence of the output to the origin ensures a collision between the swing foot and the ground with an appropriate configuration for the robot to give a step forward. The components of the output track adequate references that encode a walking pattern. Finite-time convergence of the tracking errors is enforced by using second-order sliding mode control. The main contribution of the paper is an evaluation and comparison of discontinuous and continuous sliding mode control in the presence of parametric uncertainty and external disturbances. The robot model and the synthesized controller are evaluated through numerical simulations.