Passive Walking Research Articles

Painlevé paradox and dynamic self-locking during passive walking of bipedal robot

When analyzing the passive walking of bipedal robot using the traditional methods, it usually assumes the contact foot and the slope maintain stick state. However, in the actual stable walking, the sliding contact caused by structural vibration is inevitable. Some special configuration of bipedal robot can result in dynamic self-locking or “jam” at the sliding contact if the coefficient of friction (COF) is sufficiently large; this has been termed, Painlevé paradox in rigid body dynamics. The objective of this paper is to propose a rigid body dynamic combined with Linear Complementary Problem to calculate the occurrence conditions of Painlevé paradox, and develop a completely flexible body model (CFBM) to analyze its bouncing motion induced by dynamic self-locking during passive walking of bipedal robots. The structural deformation field and inertial field of CFBM are discretized by finite element method. The contact forces and transient waves propagating in the CFBM are calculated. In the range of configurations and COF where Painlevé paradox occurs, analysis based on rigid body dynamics gives results indicating that either there are multiple solutions or the solution doesn't exist; analysis using CFBM finds that the bouncing motion will cause walking unstable and the normal contact force increases abruptly. In addition, increasing structural compliance will decrease the critical COF of dynamic self-locking roughly by 46%.

Development and Clinical Evaluation of a Posterior Active Walker for Disabled Children

This paper presents a novel posterior active walker designed for disabled children. The active walker adapts an existing posterior passive walker by motorising its back wheels and propelling them in accordance with intention of walking gait of the user. The gait intention of the user is determined from the position of user’s trunk with respect to the walker frame using an array of sensors. The principle of working of the active walker is explained in this paper. A mathematical model for the active walker is developed and the same has been simulated for a control algorithm developed, which controls the walker in different possible conditions to achieve a comfortable and efficient propulsion. The simulation results present performance of the active walker. The walker has been practically implemented and the details of the same have been presented. The experimental functional evaluation of the walker has been done in the lab which matches the simulation result. Later the developed walker was assessed for its ability to track the user. Three healthy children are made to walk with the active walker on different surfaces and the test results show that the walker is able to effectively track the children. The developed walker was subjected to clinical evaluation which involved ten disabled children who were prescribed use of walker. Clinical study involved relative evaluation of effectiveness of passive and the active walkers. It was concluded from the clinical trials that the use of the developed active walker significantly reduces the energy spent by the user compared to the conventional passive walker.

An Improved Method for Estimating the Domain of Attraction of Passive Biped Walker

An indicator of a passive biped walker’s global stability is its domain of attraction, which is usually estimated by the simple cell mapping method. It needs to calculate a large number of cells’ Poincare mapping result in the estimating process. However, the Poincare mapping is usually computationally expensive and time-consuming due to the complex dynamical equation of the passive biped walker. How to estimate the domain of attraction efficiently and reliably is a problem to be solved. Based on the simple cell mapping method, an improved method is proposed to solve it. The proposed method uses the multiple iteration algorithm to calculate a stable domain of attraction and effectively decreases the total number of Poincare mappings. Through the simulation of the simplest passive biped walker, the improved method can obtain the same domain of attraction as that calculated using the simple cell mapping method and reduce calculation time significantly. Furthermore, this improved method not only proposes a way of rapid estimating the domain of attraction, but also provides a feasible tool for selecting the domain of interest and its discretization level.

Development and testing of a passive Walking Assist Exoskeleton

The ability to walk is perhaps the most common indicator of mobility and independence. Regrettably, a large portion of the population is experiencing a loss in mobility due to aging and/or chronic health conditions. There is thus an urgent need to develop systems that would help preserve mobility for individuals in need. One promising solution to this growing problem is Walking Assist Exoskeletons. Current devices mostly rely on powered systems to provide walk assist by applying complementary torques about lower limb joints. Whereas these exoskeletons have achieved technological breakthroughs, they are not without limitations. In response, developments of passive alternatives are now emerging and have demonstrated the potential for simple, cost-effective devices. Aligned with this progress, the following study proposes the development of a passive exoskeleton that enhances mobility during stance and walking. This is achieved through an unpowered seat mechanism that produces an upward force on the pelvis of the user. Two analytical models are developed to predict its behavior, by evaluating the effect of increasing the stiffness of the mechanism, as well as predicting device kinematics and its resulting assistance throughout a gait cycle. A human-scale proof of concept prototype was fabricated and tested using motion capture equipment and load cells. The results validated the proposed design, which provided an upward stance force between 9.41% and 26.18% of body weight for six levels of spring stiffness. The exoskeleton also provided an upward peak walking force between 14.02% and 27.52% of body weight for five levels of spring stiffness.

Deep Reinforcement Learning on Passive Walking in Real Environment

Deep Reinforcement Learning on Passive Walking in Real Environment

Effect of foot shape and ankle stiffness on gait in a planar passive biped walker

Effect of foot shape and ankle stiffness on gait in a planar passive biped walker

Development of 2D Kneed Passive Walker for Robot Education

Development of 2D Kneed Passive Walker for Robot Education

Gait of Passive Walking Mechanism by bi-articular Muscle of Thigh

Gait of Passive Walking Mechanism by bi-articular Muscle of Thigh

University Students’ Inquiry Activities Related to the Creation of Quadrupedal Passive Walking Paper Toys

University Students’ Inquiry Activities Related to the Creation of Quadrupedal Passive Walking Paper Toys

Highly efficient walking perovskite solar cells based on thermomechanical polymer films

Inspired by heliotropism in nature, a passive walking perovskite solar cell is constructed as a prototype actuator with an advanced structure.

Active Passive Nature of Assistive Wearable Gait Augment Suit for Enhanced Mobility

In this paper we discuss the active and passive nature of the assistive wearable gait augment suit (AWGAS). AWGAS is a soft, wearable, lightweight, and assists walking gait by reducing muscle activation during walking. It augments walking by reducing the muscle activation of the posterior and anterior muscles of the lower limb. The suit uses pneumatic gel muscles (PGM), foot sensors for gait detection, and pneumatic valves to control the air pressure. The assistive force is provided using the motion in loop feedforward control loop using foot sensors in shoes. PGMs are actuated with the help of pneumatic valves and portable air tanks. The elastic nature of the PGM allows AWGAS to assist walking in the absence of the air supply which makes AWGAS both active and passive walking assist suit. To evaluate the active and passive nature of the AWGAS, we experimented to measure surface EMG (sEMG) of the lower limb muscles. sEMG was recorded for unassisted walking, i.e., without the suit, passive assisted walking, i.e., wearing the suit with no air supply and active assisted walking, i.e., wearing the suit with air supply set at 60 kPa. The results shows reduction in the muscle activity for both passive and active assisted walking as compared to unassisted walking. The pilot trials of the AWGAS were conducted in collaboration with local farmers in the Hiroshima prefecture in Japan where feedback received is complementing the results obtained during the experiments.

Self-Synchronization and Self-Stabilization of Walking Gaits Modeled by the Three-Dimensional LIP Model

The linear inverted pendulum model is often used to study walking gaits, but the transition from one step to the following step is often neglected, whereas it is really important for the walking stability. This letter studies different landing positions of the swing foot, and different conditions to switch the stance leg, based on time or on the configuration of the robot. It is shown that self-synchronization of the motion in sagittal and frontal planes is dependent on different switching conditions. Neither self-synchronization nor self-stabilization is observed when the stance leg switching is based on time or when both the step length and width are fixed. On the other hand, self-synchronization can be obtained when the switching condition of the stance leg is based on a linear combination of the positions of the center of mass (CoM) along the sagittal and frontal axes. Moreover, self-stabilization can be obtained when the velocity of the CoM in the sagittal plane is taken into account. Index Terms-Humanoid and bipedal locomotion, passive walking , dynamic stability.

Exercise intervention alleviates nerve injury by the suppression of inflammatory mediator expression via the TLR4/NF-κB signaling pathway.

Spinal cord injury (SCI) may cause changes that have damaging effects on sensation and functionality. However, methods for the significant amelioration of SCI-reduced nerve injury are lacking. Previous studies have indicated that reasonable and effective exercise may promote the recovery of injured nerves. Therefore, the aim of the present study was to investigate the ability of exercise to improve recovery following SCI and the underlying mechanism. A rat model was used to evaluate the effects of two different periods of exercise intervention on recovery following SCI. The exercise intervention comprised 15 or 30 min/day passive walking for 30 days. ELISA measurements were used to analysis the plasma levels of inflammatory cytokines. Reverse transcription-quantitative polymerase chain reaction and western blot analyses were performed to examine the levels of proteins and mRNAs associated with nuclear factor (NF)-κB-related signaling. In addition, histological examination and immunostaining were used to evaluate the neural injury and associated indicators. The results indicated that severe SCI induced a peripheral inflammatory response and increased the expression of inflammatory cytokines. In addition, the SCI-induced nerve injury was associated with increased glial fibrillary acidic protein (GFAP) expression and the upregulation of Toll-like receptor 4 (TLR4)/NF-κB signaling, which may further aggravate the inflammatory responses induced by SCI. However, the exercise intervention decreased SCI-induced GFAP expression and reduced the activation of the TLR4/NF-κB signaling pathway compared with that of SCI model rats that did not exercise. Furthermore, the exercise intervention inhibited the release of inflammatory cytokines into the serum. These results indicate that exercise treatment reduces inflammation and glial activation, and may be beneficial to recovery following SCI.

Online visual cues can compensate for deficits in cutaneous feedback from the dorsal ankle joint for the trailing limb but not the leading limb during obstacle crossing.

Precise control of the ankle is required to safely clear the ground during walking. Skin input contributes to proprioception about the ankle joint, during both passive movements and level walking. How skin might contribute to proprioceptive control of the ankle during a more complex functional task such as obstacle avoidance is unknown. The purpose of this study was to investigate skin contribution from the dorsum of the ankle joint to safely cross an obstacle, and examine the interaction between vision and skin. It was hypothesized that the lead and trail limbs would be influenced primarily by visual information and skin cues, respectively. Eleven healthy adults crossed an obstacle with either (1) intact sensory input (control) (2) reduced skin input using a topical anesthetic (anesthesia), (3) reduced visual input of the lower half of the visual field (partial vision) or (4) simultaneous reduction of skin and vision (paired). Kinematic measures of phase-dependent changes during these conditions were examined while subjects crossed the obstacle with their anesthetised foot as either the leading or trailing limb. Interestingly, lead limb toe trajectory was significantly affected both by deficits in visual and skin input, although the joint angle strategies differed across these sensory conditions. Subjects increased lead hip flexion with partial vision but increased hip roll with skin anesthesia relative to control. In contrast, trail limb toe trajectory was affected only by visual sensory loss. Overall visual feedback and skin input from the ankle dorsum differentially affect lead and trail limb kinematics to successfully cross an obstacle. Interestingly, it appears vision is not entirely able to compensate for reduced skin input during obstacle crossing.

Analyzing Bifurcation, Stability and Chaos for a Passive Walking Biped Model with a Sole Foot

Human walking is an action with low energy consumption. Passive walking models (PWMs) can present this intrinsic characteristic. Simplicity in the biped helps to decrease the energy loss of the system. On the other hand, sufficient parts should be considered to increase the similarity of the model’s behavior to the original action. In this paper, the dynamic model for passive walking biped with unidirectional fixed flat soles of the feet is presented, which consists of two inverted pendulums with L-shaped bodies. This model can capture the effects of sole foot in walking. By adding the sole foot, the number of phases of a gait increases to two. The nonlinear dynamic models for each phase and the transition rules are determined, and the stable and unstable periodic motions are calculated. The stability situations are obtained for different conditions of walking. Finally, the bifurcation diagrams are presented for studying the effects of the sole foot. Poincaré section, Lyapunov exponents, and bifurcation diagrams are used to analyze stability and chaotic behavior. Simulation results indicate that the sole foot has such a significant impression on the dynamic behavior of the system that it should be considered in the simple PWMs.

From a 3D Passive Biped Walker to a 3D Passivity-Based Controlled Robot

Asymptotically stable control of biped robots, especially based on reproducing passive periodic motions, have become of interest nowadays. In this paper, firstly, a three-dimensional (3D) stable passive biped walker which is a compass gait one with flat feet, compliant ankles and particular arrangement of moments of inertia has been presented. Then, a passivity-based control of the related biped robot based on elaborating 3D form of potential energy shaping method has been applied. In other words, by adding minimal actuations to the aforementioned passive walker, its passive periodic gait that belongs to a particular slope has been reproduced on any arbitrary surface such as the level ground. Simulation results support the effectiveness of the proposed approach.

Verification of Transport of Moai Statues by Passive Walking Theory

Verification of Transport of Moai Statues by Passive Walking Theory

Passivity-Based Control with a Generalized Energy Storage Function for Robust Walking of Biped Robots.

This paper offers a novel generalization of a passivity-based, energy tracking controller for robust bipedal walking. Past work has shown that a biped limit cycle with a known, constant mechanical energy can be made robust to uneven terrains and disturbances by actively driving energy to that reference. However, the assumption of a known, constant mechanical energy has limited application of this passivity-based method to simple toy models (often passive walkers). The method presented in this paper allows the passivity-based controller to be used in combination with an arbitrary inner-loop control that creates a limit cycle with a constant generalized system energy. We also show that the proposed control method accommodates arbitrary degrees of underactuation. Simulations on a 7-link biped model demonstrate that the proposed control scheme enlarges the basin of attraction, increases the convergence rate to the limit cycle, and improves robustness to ground slopes.

The simple chaotic model of passive dynamic walking

Recent findings on the dynamical analysis of human locomotion characteristics such as stride length signal have shown that this process is intrinsically a chaotic behavior. The passive walking has been defined as walking down a shallow slope without using any muscular contraction as an active controller. Based on this definition, some knee-less models have been proposed to present the simplest possible models of human gait. To maintain stability, these simple passive models are compelled to show a wide range of different dynamics from order to chaos. Unfortunately, based on simplifications, for many years the cyclic period-one behavior of these models has been considered as the only stable response. This assumption is not in line with the findings about the nature of walking. Thus, this paper proposes a novel model to demonstrate that the knee-less passive dynamic models also have the ability to model the chaotic behavior of human locomotion with some modifications. The presented novel model can show chaotic behavior as a stable and acceptable answer using a chaotic function in heel-strike condition. The represented chaotic model is also able to simulate different types of motor deficits such as Parkinson’s disease only by manipulating the value of chaotic parameter. Our model has extensively examined in complexity and chaotic behavior using different analytical methods such as fractal dimension, bifurcation and largest Lyapunov exponent, and it was compared with conventional passive models and the stride signal of healthy subjects and Parkinson patients.

The effects of ground compliance on flexible planar passive biped dynamic walking

Passive biped dynamic walking exhibits humanoid gait. Many efforts have been made to implement a flexible and anthropomorphic passive model. However, the couple of flexible passive walker on compliant ground has not been well studied yet. The objective of this paper was to develop multibody dynamics for flexible passive walker on compliant ground, in which the nonlinear spring-damper contact model was used both in normal and tangential directions to represent ground compliance. Inspired by elastic mechanisms in human locomotion, hip stiffness and damping were incorporated in the proposed flexible passive walker. Different from traditional impactmomentum method, one unified set of continuous dynamics based on continuous force method was developed to describe the entire passive walking gait on compliant ground, including the real double support phase. Through numerical simulations, stable period-one gait and double support phase were gained. After investigating the effects of contact parameters on step length, period and velocity, it was found that larger contact stiffness and smaller contact damping lead to a higher step velocity gait. The adjustment of hip stiffness could be used to improve the versatility of the flexible walker on varying compliant grounds.