Papers by Masoumeh Safartoobi
To simulate the complex human walking motion accurately, a suitable biped model has to be propose... more To simulate the complex human walking motion accurately, a suitable biped model has to be proposed that can significantly translate the compliance of biological structures. In this way, the simplest passive walking model is often used as a standard benchmark for making the bipedal locomotion so natural and energy-efficient. This work is devoted to a presentation of the application of internal damping mechanism to the mathematical description of the simplest passive walking model with flexible legs. This feature can be taken into account by using the viscoelastic legs, which are constituted by the Kelvin–Voigt rheological model. Then, the update of the impulsive hybrid nonlinear dynamics of the simplest passive walker is obtained based on the Euler–Bernoulli’s beam theory and using a combination of Lagrange mechanics and the assumed mode method, along with the precise boundary conditions. The main goal of this study is to develop a numerical procedure based on the new definition of t...
Gait cycles of passive walking biped robot model with flexible legs
Mechanism and Machine Theory, 2021
Abstract Passive dynamic walking of bipeds exhibits a new concept of robot locomotion that is wel... more Abstract Passive dynamic walking of bipeds exhibits a new concept of robot locomotion that is well- known for its success in human mimicry. Many efforts have been devoted in the literature to implement flexible and anthropomorphic passive bipeds. However, utilization of flexible characteristics of elastic structures has not been considered yet. This paper presents a modified simplest passive walking model with flexible legs which are a pair of elastic beams with small deflections instead of usual rigid links. The main contributions of this paper lie in modeling the impulsive hybrid dynamics of the flexible passive biped and applying a numerical technique based on finite difference formula to seek for appropriate initial conditions of walking gait cycles. Extended Hamilton's principle and assumed mode method along with Euler–Bernoulli's beam theory and updated transition rules at impact are used to derive the mathematical model of this biped. Numerical simulations reveal non-periodic patterns of motion for small slope angles due to vibrations of elastic legs. It is also shown that the period-one gait cycles with quicker steps can be generated on slower slopes for different values of elasticity and damping coefficients compared to the rigid model.
Determination of the initial conditions by solving boundary value problem method for period-one walking of a passive biped walking robots
Robotica, 2015
SUMMARYWith regard to the small basin of attraction of the passive limit cycles, it is important ... more SUMMARYWith regard to the small basin of attraction of the passive limit cycles, it is important to start from a proper initial condition for stable walking. The present study investigates the passive dynamic behaviors of two-dimensional bipedal walkers of a compass gait model with different foot shapes. In order to find proper initial conditions for stable and unstable period-one gait limit cycles, a method based on solving the nonlinear equations of motion is presented as a boundary value problem (BVP). An initial guess is required to solve the related BVP that is obtained by solving an initial value problem (IVP). For parametric analysis purposes, a continuation method is applied. Simulation results reveal two, period-one gait cycles and the effects of parameters variation for all models.
Finite difference method to find period-one gait cycles of simple passive walkers
Communications in Nonlinear Science and Numerical Simulation, 2015
ABSTRACT Passive dynamic walking refers to a class of bipedal robots that can walk down an inclin... more ABSTRACT Passive dynamic walking refers to a class of bipedal robots that can walk down an incline with no actuation or control input. These bipeds are sensitive to initial conditions due to their style of walking. According to small basin of attraction of passive limit cycles, it is important to start with an initial condition in the basin of attraction of stable walking (limit cycle). This paper presents a study of the simplest passive walker with point and curved feet. A new approach is proposed to find proper initial conditions for a pair of stable and unstable period-one gait limit cycles. This methodology is based on finite difference method which can solve the nonlinear differential equations of motion on a discrete time. Also, to investigate the physical configurations of the walkers and the environmental influence such as the slope angle, the parameter analysis is applied. Numerical simulations reveal the performance of the presented method in finding two stable and unstable gait patterns.
International Journal of Engineering, Transactions B: Applications, 2014
The simple passive dynamic walker can walk down a shallow downhill slope with no external control... more The simple passive dynamic walker can walk down a shallow downhill slope with no external control or energy input. Nevertheless, the period-one gait stability is only possible over a very narrow range of slopes. Since the passive gaits are extremely sensitive to slope angles, it is important to use a control strategy in order to achieve a wide range of stable walking. The computed torque method is proposed here to produce stable period-one gait cycles for different slopes. In this present method, the unstable walking gait is stabilized by a stable period-one gait pattern on a small specific slope. The proposed approach is illustrated by the simplest passive walkers with point and curved feet. Simulation results reveal the usefulness of this control method for improvement in stability properties of the models.
Finite difference method to find period-one gait cycles of simple passive walkers
Communications in Nonlinear Science and Numerical Simulation, 2015
ABSTRACT Passive dynamic walking refers to a class of bipedal robots that can walk down an inclin... more ABSTRACT Passive dynamic walking refers to a class of bipedal robots that can walk down an incline with no actuation or control input. These bipeds are sensitive to initial conditions due to their style of walking. According to small basin of attraction of passive limit cycles, it is important to start with an initial condition in the basin of attraction of stable walking (limit cycle). This paper presents a study of the simplest passive walker with point and curved feet. A new approach is proposed to find proper initial conditions for a pair of stable and unstable period-one gait limit cycles. This methodology is based on finite difference method which can solve the nonlinear differential equations of motion on a discrete time. Also, to investigate the physical configurations of the walkers and the environmental influence such as the slope angle, the parameter analysis is applied. Numerical simulations reveal the performance of the presented method in finding two stable and unstable gait patterns.
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Papers by Masoumeh Safartoobi