Yoon Haeng Lee

Development of Wall Climbing Robot System by Using Impeller Type Adhesion Mechanism

In this paper, we present a wall climbing robot system, called “LARVA”, developed for visual inspection of structures with flat surfaces. The robot has two differential driving wheels with a suspension and an adhesion mechanism. The adhesion mechanism is composed of an impeller and two–layered suction seals. It is designed to provide sufficient adhesion force and be controlled so that the robot can move freely on various wall surfaces. The static and aerodynamic modeling of the adhesion mechanism is given and the analysis of the adhesion mechanism, air leakage, and inner flow are carried out to be useful for the design as well as the control. Finally, the performances of the robot are experimentally verified on several kinds of walls and its feasibility is validated.

Central pattern generator based reflexive control of quadruped walking robots using a recurrent neural network

This paper presents a novel Central Pattern Generator (CPG) model for controlling quadruped walking robots. The improvement of this model focuses on generating any desired waveforms along with accurate online modulation. In detail, a well-analyzed Recurrent Neural Network is used as the oscillators to generate simple harmonic periodic signals that exhibit limit cycle effects. Then, an approximate Fourier series is employed to transform those mentioned simple signals into arbitrary desired outputs under the phase constraints of several primary quadruped gaits. With comprehensive closed-form equations, the model also allows the user to modulate the waveform, the frequency and the phase constraint of the outputs online by directly setting the inner parameters without the need for any manual tuning. In addition, an associated controller is designed using leg coordination Cartesian position as the control state space based on which stiffness control is performed at sub-controller level. In addition, several reflex modules are embedded to transform the feedback of all sensors into the CPG space. This helps the CPG recognize external disturbances and utilize inner limit cycle effect to stabilize the robot motion. Finally, experiments with a real quadruped robot named AiDIN III performing several dynamic trotting tasks on several unknown natural terrains are presented to validate the effectiveness of the proposed CPG model and controller.

Biologically inspired gait transition control for a quadruped walking robot

The gait transition of a quadruped walking robot is the switching of gait with non-periodic gait sequences between the periodic ones such as from walk to trot or trot to walk etc. It is very much important because the robot should change its gait depending upon the moving speed to enhance the efficiency of locomotion. In this paper, we present a quasi-static gait transition control method for a quadruped walking robot. It is based on the observation on the locomotion behaviors of quadruped animals, which show a sudden and discrete changes of gait patterns depending on the speed. The method predefines gait transition patterns, and gait sequences are determined according to the current and desired leg postures. It can be useful because the applicable to any type of walking controller. In this study, we implement the proposed method on a self-contained quadruped walking robot, called Artificial Digitigrade for Natural Environment Version III (AiDIN-III), and its effectiveness is experimentally validated.

A gait transition algorithm based on hybrid walking gait for a quadruped walking robot

This paper presents a quasi-dynamic gait, called Hybrid Walking Gait, and a new gait transition algorithm for a quadruped walking robot. The Hybrid Walking gait reduces the steps of a generic walking gait with primitive foot trajectory generation using some of parameters easily defined. It shows great improvements over existing ones in terms of higher mobility, less complexity to define the motion, and smooth body movements that affect to the stability of the robot. The Gait Transition pattern generated with the Hybrid Walking Gait guarantees stability as good as that of a traditional walking gait and high mobility such as the dynamic trot gait. We perform experiments with a quadruped robot called “Artificial Digitigrade for Natural Environments Version III”, and validate the effectiveness of our proposed gait patterns over several types of terrains.

Hybrid quadruped bounding with a passive compliant spine and asymmetric segmented body

Most legged animals exploit flexible body and supporting muscles to produce power for dynamic behaviors which results in fast locomotion and additional mobility. Previous works have focused on the symmetric flexible body with massless legs associated to the body. However, body bending in animals during running happens prior to the rear side instead of the middle point of body. Therefore, a quadruped model with a passive spinal joint, asymmetric segmented body, actuated hip joints and legs is introduced. By using a numerical return map, a periodic bounding locomotion of the model is found with optimal sets of initial conditions and proper system parameters. Moreover, this paper investigates the effects of spine flexibility in segmented body on quadrupedal bounding gait. The results show that asymmetric segmented body has bigger spine oscillation, shorter stride period and smaller cost of transport, which helps the robot run more efficiently.

Quadruped bounding with a passive compliant spine

This paper investigates the effects of spine flexibility on quadruped running with a bounding gait. A quadruped model with a passive, flexible, segmented body, actuated hip joints and legs is introduced. By using a numerical return map, a periodic bounding locomotion of the model has been found, with an optimal set of initial conditions and proper system parameters.

Effects of spinal joint on quadrupedal bounding

This paper studies the effects of a spinal joint on quadrupedal running with a bounding gait. Both models have the actuated hips and legs with masses and inertias. In this work, we used the numerical return map to find periodic locomotion of both models then, by comparing the performance of an articulated-body quadruped to a rigid-body one, we observed that the presence of spinal joint helps the robot increase the stride length and clearly affect the locomotion efficiency.

Stable running with a two-segment compliant leg

This research presents a two-segment compliant leg model for understanding fast running locomotion of animals and extending to quadruped robot later. We introduce an approach toward a full understanding of the model by investigating the energy of the system and constructing a set of data, called Limit Cycle Set. The set is computed via optimization procedures and includes all the configurations of the model that contribute to its periodic, stable running locomotion. By introducing the creative design of the configurations, the two-segment compliant model is sufficiently general to be extended to other similar two-segment leg models. Along with the computation, we investigate the system stability and discover that it is possible to achieve stability of a compliant leg in real environments with a simple control strategy. The stable motion is successfully validated in real experiments.

Biologically inspired robotic leg for high-speed running

Low speed and low energy efficiency are intrinsic issues to be tackled in the study of legged robots. To cope with these problems, this paper presents a bio-inspired design methodology and its implementation on the compliant robotic leg. The proposed robotic leg achieves excellent performances for the high-speed running with low inertia, high energy reusability and large workspace. Moreover, its joint design has great benefits of large passive deflection angle, and linear stiffness. According to our study, the error between the calculated and the measured stiffness curve of the unidirectional compliant joint mechanism is less than 2% and the joint stiffness can be handled as a constant number. To validate the idea, we demonstrate the robotic leg periodically jumps in the vertical direction, and stores the 18 % of its initial potential energy.

Design of variable compliance joint mechanism for legged robots

This paper presents a compliant joint mechanism design, called Compliant Ellipsoid Joint (CEJ). The CEJ consists the two main elements which are plate spring and ellipsoid shape. The force range of this joint mechanism can be easily set by the plate spring and the ellipsoid surface parameters. In the first, we modelled the CEJ and propose a mathematical analysis to tune the force range. The performance of CEJ is verified by experimental validation and the average error between calculated and measured angle along the external load is 1.03 degree (at E=210 GPa).