Young Hun Lee

Exploration and reconstruction of unknown object by active touch of robot hand

This paper proposes a method of exploring the global shape of an unknown object using information on local geometric features. In the first, we introduce a rolling and sliding motion of a fingertip with a force/torque sensor to estimate an unknown local curvature. Also, a recognition algorithm for local geometry using normal curvature equations is presented, which are composed of principal curvatures and principal direction. Finally, to reconstruct the global shape of the object, we propose an interpolation method using principal curvatures at contact points. The proposed method is verified using a hand-arm system consisting of an industrial robot arm and an anthropomorphic robot hand with a 6-axis force/torque sensor. The effectiveness of the proposed method is experimentally validated for different type of objects.

Semiconducting/insulating polymer blends with dual phase separation for organic field-effect transistors

In this study, diketopyrrolopyrrole (DPP)-based semiconducting polymers with alkyl chain spacers of different lengths (C24 and C29) were used to compare the effects of crystalline nature in semiconducting polymer on the phase-separation and electrical properties of DPP-based semiconducting polymer/poly(methyl methacrylate) (PMMA) blends. Hierarchical structures containing ultrathin-film (bottom) and hairy rods (top) of DPP-based semiconducting polymers formed on the substrates due to the combined effects of the self-stratification and Marangoni-instability during the phase-separation of polymer blends. In particular, 24-DPP-TVT/PMMA blend film formed-fewer and bigger semiconductor rods, because of coarsening of 24-DPP-TVT phase during solvent evaporation. In contrast, highly crystalline nature of 29-DPP-TVT prevented the coarsening of the 29-DPP-TVT rods, thereby resulted in densely packed semiconductor rods. According to the crystalline natures in DPP-based semiconducting polymers, 29-DPP-TVT phase in 29-DPP-TVT/PMMA blend exhibited lower angular spread in molecular orientation compared to 24-DPP-TVT phase in 24-DPP-TVT/PMMA blend. Accordingly, 29-DPP-TVT/PMMA field-effect transistors (FETs) exhibited significantly higher electrical properties than those of 24-DPP-TVT/PMMA FETs. In addition, field-effect mobility of 29-DPP-TVT/PMMA FETs is comparable to those of homo 29-DPP-TVT FETs, whereas the partial passivation effect lowers turn-on voltage of 29-DPP-TVT/PMMA FETs. This study that utilized dual phase-separation would provide possible guidelines for the selection of semiconducting polymer for the use of semiconducting/insulating polymer blends in FETs.

Design of anthropomorphic robot hand with IMC joints

This paper presents a novel anthropomorphic robot hand with IMC joints. IMC joints are applied to robot hand to grasp various objects regardless of the size and get large overlapped workspace between thumb and other fingers, which allow all the fingertips to be located on a single spot in a wide range. Desinged IMC joints of robot hand are always rotated with 1:1 ratio by mechanical constraint using passive tendon. Actuation module consists of miniature BLDC motor and ballscrew drives two IMC joints with a single motor. To evaluate the advantages of robot hand with IMC joints, grasping experiments are performed.

Design of backdrivable soft robotic finger mechanism

This paper presents a new joint actuation mechanism, called Active DIP-PIP (ADP) joint, for robotic finger. The mechanism consists of a pair of moveable pulleys and springs to generate both linked and adjustable motion. While the set of DIP (Distal-Interphalangeal) and PIP (Proximal-Interphalangeal) joint shows coupled movement in free space, it moves adaptively when it contacts with an object. The torsion springs attached on each joints ensure 1:1 ratio movement while finger is moving freely and produce additional joint torque while grasping an object. In addition, actuation module composed of miniature BLDC motor and ball screw allows each joint to be back drivable.

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.

Sampling-based path planning with goal oriented sampling

Path planning in complicated environments is a time consuming and computationally expensive task. Especially in high-dimensional configuration spaces with complex obstacles, searching for a proper path while avoiding collisions is still challenging. This paper presents an improved sampling-based algorithm, called the Goal Oriented sampling method (GO sampling) that quickly generates an initial solution overcoming these problems. GO sampling extends the sampling method of the Rapidly-exploring Random Tree (RRT) algorithm. GO sampling is able to identify the initial solution in a shorter time than that of the RRT algorithm and shows significant improvement in computational efficiency. The algorithm is evaluated with simulations in 2D and 3D space.

Computation of minimum contact forces of multifingered robot hand with soft fingertips

In the human hand, the softness of a fingertip plays a significant role on stable grasping and dexterous manipulation. This paper presents a method of computing minimum grasp forces of a multi-fingered hand with soft fingertips. In the first, we built up a simple linear contact model of a soft fingertip. Then, based on Pontryagin’s principle, the problem of minimizing contact forces for realizing the stable grasping was formulated and the forces were computed. Finally, the experiments were carried out using a multifingered robot hand, called “Allegro Hand” with hard fingertips and soft ones, and the effectiveness of the proposed method was validated.