Design Of Legged Robots Research Articles

Shock Absorption for Legged Locomotion through Magnetorheological Leg-Stiffness Control

The objective of this study was to evaluate the performance of a magnetorheological-fluid-based variable stiffness actuator leg under high impact forces through optimal tuning and control of stiffness and damping properties. To achieve this, drop testing experiments were conducted with the leg at various drop heights and payload masses. The results showed that while lower stiffness and higher damping can lead to lower impact forces and greater energy dissipation, respectively, optimal control can also protect the leg from deflecting beyond its functional range. Comparison with a rigid leg with higher damping showed a 57.5% reduction in impact force, while a more compliant leg with lower damping results in a 61.4% reduction. These findings demonstrate the importance of considering both stiffness and damping in the design of legged robots for high impact force resistance. This simultaneously highlights the efficacy of the proposed magnetorheological-fluid-based leg design for this purpose.

Modeling and simulation for designing a line walking chameleon-like legged robot

Legged robots have been developed to move on uneven terrains. They can move smoother and step over obstacles easily, and they are more versatile in various environmental scenarios. These features make them desirable for maintenance and/or search-and-rescue tasks where mobility is restricted on these complex terrains. A problem arises when legged robots are required to walk on the top of narrow support, e.g. thin beams or tubes. In this work, we present the design of a line walking legged robot for narrowed support. To achieve this goal, we get inspiration from the chameleon locomotion. From these observations, we simulate the robot, design an intelligent control strategy for self-balancing and walking, and we implement a robot prototype. The experimental results show that the balance controller provides a tilt angle of 2.24±2.21∘, while the robot walks in a straight line with a maximum offset of 3.0 cm and with a walking velocity of 0.2 cm/s. Our results demonstrate that the robot can move on narrowed support lines. We anticipate that the design of legged robots inspired by the chameleon locomotion might open wider possibilities for rescue and maintenance missions.

Bioinspired Legged Robot Design via Blended Physical and Virtual Impedance Control

In order to approach the performance of biological locomotion in legged robots, better integration between body design and control is required. In that respect, understanding the mechanics and control of human locomotion will help us build legged robots with comparable efficient performance. From another perspective, developing bioinspired robots can also improve our understanding of human locomotion. In this work, we create a bioinspired robot with a blended physical and virtual impedance control to configure the robot’s mechatronic setup. We consider human neural control and musculoskeletal system a blueprint for a hopping robot. The hybrid electric-pneumatic actuator (EPA) presents an artificial copy of this biological system to implement the blended control. By defining efficacy as a metric that encompasses both performance and efficiency, we demonstrate that incorporating a simple force-based control besides constant pressure pneumatic artificial muscles (PAM) alone can increase the efficiency up to 21% in simulations and 7% in experiments with the 2-segmented EPA-hopper robot. Also, we show that with proper adjustment of the force-based controller and the PAMs, efficacy can be further increased to 41%. Finally, experimental results with the 3-segmented EPA-hopper robot and comparisons with human hopping confirm the extendability of the proposed methods to more complex robots.

BirdBot achieves energy-efficient gait with minimal control using avian-inspired leg clutching.

Designers of legged robots are challenged with creating mechanisms that allow energy-efficient locomotion with robust and minimalistic control. Sources of high energy costs in legged robots include the rapid loading and high forces required to support the robot's mass during stance and the rapid cycling of the leg's state between stance and swing phases. Here, we demonstrate an avian-inspired robot leg design, BirdBot, that challenges the reliance on rapid feedback control for joint coordination and replaces active control with intrinsic, mechanical coupling, reminiscent of a self-engaging and disengaging clutch. A spring tendon network rapidly switches the leg's slack segments into a loadable state at touchdown, distributes load among joints, enables rapid disengagement at toe-off through elastically stored energy, and coordinates swing leg flexion. A bistable joint mediates the spring tendon network's disengagement at the end of stance, powered by stance phase leg angle progression. We show reduced knee-flexing torque to a 10th of what is required for a nonclutching, parallel-elastic leg design with the same kinematics, whereas spring-based compliance extends the leg in stance phase. These mechanisms enable bipedal locomotion with four robot actuators under feedforward control, with high energy efficiency. The robot offers a physical model demonstration of an avian-inspired, multiarticular elastic coupling mechanism that can achieve self-stable, robust, and economic legged locomotion with simple control and no sensory feedback. The proposed design is scalable, allowing the design of large legged robots. BirdBot demonstrates a mechanism for self-engaging and disengaging parallel elastic legs that are contact-triggered by the foot's own lever-arm action.

Running birds reveal secrets for legged robot design.

Recapitulating avian locomotion opens the door for simple and economical control of legged robots without sensory feedback systems.

Four Legged Guará Robot: From Inspiration to Implementation

Design of legged robots is still an open problem with several implementation challenges and there is little material available to guide new designs. Moreover, usually the actuator sets of the robot are heavy and bulky and are placed near the joints, which increases the weight and inertia of the legs and consequently results in instability, slower movement and high energy consumption. This paper presents the design, modeling, and control of the Guara, a sixteen-degree-of-freedom (DOF) legged robot, covering all stages of development of a quadruped robot, including experiments with a prototype. The system is composed by four legs, each one with 4 DOF. To reduce the leg’s weight and inertia, here we present a design concept for the legs where the actuators are positioned on the robot platform and timing belt transmissions are used to drive the joints. Moreover, the design of the legs mimics the human leg by presenting the knees faced forward and its locomotion pattern mimics the quadruped wave gait. With this configuration, the robot is able to walk on straight lines or free curved paths. The control system of the robot consists of a high-level state machine and a lower level PID position controller. The electronics are embedded over a flat platform coupled to the legs. The kinematics of the robot was studied and an integrated environment was provided for walking simulation, adjustment, and diagnosis of operation. The experimental results are focused on the kinematics of the legs and the stability of the robot and show a good agreement between the designed and executed movements. This paper is presented as a framework that can be generalized to other systems and can be a useful reference for the design of other legged robots.

Experimental verification of the characteristic behaviors in passive dynamic walking

It is well known that passive dynamic walking shows chaotic behavior owing to changes in the environment. In addition, when the environment changes continuously during walking, passive dynamic walking shows “adaptive behaviors” in which the stride angle changes itself in an attempt to keep walking. These behaviors are very interesting and useful for the legged robot design. However, the studies on passive dynamic walking are preceded only by numerical simulations. For this reason, it is very important to confirm, by actual experiments, whether these characteristic behaviors appear. In this paper, we verify the existence of these behaviors by several actual experiments.

Legged robot design and Van der Pol oscillator based control approach

Legged robot design and Van der Pol oscillator based control approach

Legged robot design and Van der Pol oscillator based control approach

Legged robot design and Van der Pol oscillator based control approach

Legged robot design applying the connections among the different dynamical systems

Legged robot design applying the connections among the different dynamical systems

Design, Modelling and Validation of Hydraulic Servo Actuator With Passive Compliance for Legged Robots

The hydraulic driven legged robots walking on the ground always encounter impact forces due to the contacts between feet and ground. Aiming to reduce the impact forces, a novel passive compliance method is proposed by adding a miniature hydraulic accumulator to the piston chamber of the hydraulic actuator. And the overflow valve and the check valve are newly equipped to prevent overpressure operation and suction. The accumulator as an elastic component is used to reduce the increment of piston chamber pressure due to the impact forces. To demonstrate the effectiveness of the proposed actuator, a dynamic and hydraulic co-simulation platform for a single actuator is built. Both simulation and experiment results show that the new actuator has better passive compliant characteristics while ensuring rather high position servo precision. Under the control of the low bandwidth hydraulic servo valve, the impact forces are reduced by 30% within the scope of the study. The modeling methodology and experimental details give effective references for the legged robot design.

Compliant Locomotion

This article describes benefits of model-based approach in developing humanoids and presents experimental results as well. Regardless of the chosen actuation strategy, the design of humanoid locomotion controllers is greatly complicated by the underactuated and nonlinear nature of the associated multibody dynamics. Drawing inspiration from biology, researchers have begun to incorporate passive mechanical compliance into the design of legged robots, often by adding spring elements in series with the robot’s actuators. First introduced by the MIT Leg Laboratory, series elastic actuators (SEAs) have been shown to improve the fidelity and stability of closed-loop force controllers while simultaneously increasing shock tolerance. The chapter shows an example SEA utilized in the design of THOR, a compliant humanoid robot developed at Virginia Tech. Despite new advancements, several challenges remain before humanoids can be fielded in real-world applications that require a high degree of mobility. Model-based control approaches could greatly benefit from techniques found in the robust and adaptive control literature. The field is also interested in moving towards more efficient, human-like locomotion using biologically-inspired control strategies.

Legged Robot design applying the behavior of Passive Dynamic Walking

Legged Robot design applying the behavior of Passive Dynamic Walking

2A1-H08 受動的動歩行の性質を利用した脚ロボットの設計と評価(受動歩行ロボット(1))

2A1-H08 受動的動歩行の性質を利用した脚ロボットの設計と評価(受動歩行ロボット(1))

Design of fuzzy algorithms locomotion for six legged walking robot

One of the most relevant topics in the design of legged robots is to perform movements. The aim of this article is to present a set of algorithms that allow a six-legged walking robot to achieve the mobility of its different legs among irregular or no established actions, this gait is known as: free locomotion. The development of these algorithms using fuzzy logic allows the system to have a redundant behavior. The algorithms evaluation is performed by simulating the locomotion process of the robot. Key words: Walking robot, free locomotion, margin stability, fuzzy logic, adaptive algorithm, predictive algorithm.

Mass Distribution Effects on Dynamic Performance of a Cable-Driven Hexapod

This paper illustrates the use of dynamic performance analysis in the design of legged robots, specifically hexapods. This is accomplished by comparing the dynamic performance of a cable-driven hexapod to that of a more conventional design in which the actuators are mounted at the joints. By integrating the actuators into the torso and through the use of cable transmission, the mass and inertias of the legs are reduced in order to attain high accelerations and backdrivability. The dynamic performance described herein is bounded by the actuator torque limits and the no-slip condition at the ground contact points. The result is a description of how well each hexapod can accelerate its torso without causing slippage at the ground contact points.

Digital compass as heading sensor for hexapod robot

A growing research in biomimetic legged robot design challenges today's theory path planning and motion control. For many reasons a biomimetic robot requires a heading sensor onboard for better path following and steering. We propose a use of a digital compass as low-cost sensor. However, cheap versions of that sensor are extremely sensitive to inclination that occurs due to locomotion, resulting in incorrect measurements. This paper presents a modeling procedure of a digital compass performance with respect to altered roll and pitch angles. With information from an additional accelerometer as tilt sensor that reads roll and pitch angles of the robot the model improves the compass readings making it insensitive to altered tilt. The fusion of the modeling and a compass-accelerometer setup is experimentally verified.

Construction of a Hexapod Robot with Cockroach Kinematics Benefits both Robotics and Biology

Any device that moves by actuating several multi-segmented legs must solve fundamental problems in mechanics and control regardless of whether that device is made out of living tissue or metal. With this in mind, we believe that advances can be made both in the design of legged robots and in understanding how legged animals locomote by working on these issues in tandem. This basic philosophy has led us to build a hexapod robot with kinematics that are remarkably similar to those of the death head cockroach Blaberus discoidalis . This eff ort has required us to make detailed neurobiological and kinematic observations of cockroaches walking on a treadmill and climbing over barriers. The data acquired in this way were then input to our dynamic simulation tool to determine mechanically accurate parameters for the design of the robot. The resulting vehicle captures the cockroach kinematics so well that issues that are being addressed in controlling it are providing important notions regarding the neural control of locomotion in the animal. Thus, the project has led to benefits in both directions. Biological data inspired the initial design of the robot, while engineering eff orts in control are inspiring further neurobiological experiments in animal locomotion.

A simple legged locomotion gait model

Significant advances have been occurred over the past two decades in issues related to the mechanical design of legged robots and the coordination and control of legs during locomotion. The performance of current legged robots, however, remains far below even their most simple counterparts in the biological world. Naturally, this has lead to a search by researchers for biologically motivated principles of design and control which might lead to improved performance and robustness. In this paper, the role of central pattern generators (CPGs) in locomotion is studied. In contrast with previous approaches, we suggest the use of a single pattern generator whose output is connected to motor neurons (servo controllers) through neural pathways (cables) that generate the time delays characteristic of various gaits. A mathematical model for such a scheme is developed and a simple algorithm for encoding the characteristic gaits of bipeds, quadrupeds and hexapeds is presented. The paper concludes with a description of ongoing experimental work on a hexaped robot.

A biologically consistent model of legged locomotion gaits

Significant advances have occurred over the past two decades in issues related to the mechanical design of legged robots and the coordination and control of legs during locomotion. The performance of current legged robots, however, remains far below even simplest counterparts in the biological world. Naturally, this has led to a search by researchers for biologically motivated approaches to the design and control of legged robots in order to improve their performance and robustness. In this paper the use of central pattern generators (CPGs) will be examined for the control of locomotion. In doing so, a biologically consistent mathematical model that has the ability to emulate arbitrary gaits is developed. A simple algorithm for encoding the characteristic gaits of bipeds, quadrupeds and hexapeds is presented. The paper concludes with a brief description of a locomotion control architecture for actually realizing leg movements that correspond to various gaits.