Ig Mo Koo

Development of Soft-Actuator-Based Wearable Tactile Display

As a major human sensory function, the implementation of the tactile sensation for the human-machine interface has been one of the core research interests for long time. In this paper, an innovative tactile display device based on the soft actuator technology is presented. Using electroactive polymer for the construction of the tactile display device, it can provide stimulation on the human skin without any additional electromechanical transmission. Softness and flexibility of the device structure, ease of fabrication, possibility for miniaturization, and low cost for mass production are the representative benefits of the presented device. Especially, the device application is open to many different purposes since the flexible structure offers the excellent adaptability to any contour of the human body. To prove its feasibility, a wearable device that can fit to the distal part of the human finger is presented and its performance is evaluated, experimentally.

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.

Development of wall climbing robotic system for inspection purpose

In this paper, we introduce a wall climbing robotic system for visual inspection of man-made structures. The adhesion mechanism of our system consists of an impeller and two-layer suction seals which provide sufficient adhesion forces for supporting the robot body on the non-smooth vertical wall and horizontal ceiling by generating pressure difference between the inside of the pressure chamber and the ambient environment. A comprehensive study is performed on the dynamic fluid modeling of the adhesion mechanism and the adhesion force is controlled by adjusting the pressure inside of the chamber. In addition, stable differential-driving locomotion on non-smooth surface are achieved by adapting a suspension mechanism for each wheel. A wall climbing robot, called LARVA, is successfully developed and its effectiveness of locomotion is verified with experiments on non-smooth vertical wall and horizontal ceiling surface.

Improving traversability of quadruped walking robots using body movement in 3D rough terrains

This paper presents a study on improving the traversability of a quadruped walking robot in 3D rough terrains. The key idea is to exploit body movement of the robot. The position and orientation of the robot are systematically adjusted and the possibility of finding a valid foothold for the next swing is maximized, which makes the robot have more chances to overcome the rough terrains. In addition, a foothold search algorithm that provides the valid foothold while maintaining a high traversability of the robot, is investigated and a gait selection algorithm is developed to help the robot avoid deadlock situations. To explain the algorithms, new concepts such as reachable area, stable area, potential search direction, and complementary kinematic margin are introduced, and the effectiveness of the algorithms is validated via simulations and experiments.

Fabrication and characterization of linear motion dielectric elastomer actuators

This paper presents a new artificial muscle actuator produced from dielectric elastomer, called Tube-Spring Actuator(TSA). The new actuator construction includes two steps: the first part is a cylindrical actuator manufactured with dielectric elastomer and the second is a compressed spring inserted inside the tube. An inner spring is used to maximize the axial deformation while constraining the radial one. This unique design enables linear actuation with the largest strain of active length up to 14% without any additional means. As a result this actuator was applied to a robot hand. This study lays the foundation for the future work on dielectric polymer actuator.

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.

Body Workspace of Quadruped Walking Robot and its Applicability in Legged Locomotion.

This paper discusses on determination of the workspace of the body of a quadruped walking robot, called “body workspace”, and its applicability in legged locomotion. The body workspace represents the set of all valid body configurations for a next step by considering three constraints of a body position: existence of the inverse kinematic solutions, reach-ability of the next swing leg to the next desired foothold, and static equilibrium of the robot when the next swing leg is lifted. The space contains all the body positions that ensure the existence of inverse kinematic solutions, is calculated in the first. Then, a subspace inside the determined space that allows the robot to reach the next desired foothold is analyzed. Finally, the workspace is obtained by excluding all the positions inside the subspace that do not ensure the equilibrium of the robot when the next swing leg is lifted. Therefore, the workspace shows all possible solutions for choosing the next body configuration of a given static walking problem. It is significant in improving the robot’s performances since moving body takes an intrinsic role in static walking, besides swinging a leg. The algorithm runs fast in real-time because it is a pure geometric method. The body workspace of a quadruped walking robot is visualized to help the understanding of the algorithm. In addition, applications of using the body workspace in improving the robot’s ability are presented to show potential applicability of the workspace.

Sensing and control of quadruped walking and climbing robot over complex environment

In this paper, we propose a method of sensing outdoor environments for a walking and climbing robot. The proposed method ensures the realtime perception of the surface geometry by integrating a range and a gyroscope with a novel arrangement of the sensors. In addition, a gait planning algorithm based on the sensing method is presented. The algorithm runs fast since it is simple, and the rich information from the sensing system helps the robot overcome the real environment, even an extremely complex one. The sensing system is implemented in a quadruped walking robot, called MRWALLSPECT IV and its effectiveness is proved experimentally.

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.