Yeongtae Jung

Kinematic Analysis of a 5-DOF Upper-Limb Exoskeleton With a Tilted and Vertically Translating Shoulder Joint

In this paper, an upper-limb exoskeleton with a tilted and vertically movable shoulder joint is proposed. By analyzing the biomechanics of the shoulder, the upper limb for the shoulder and the elbow was approximated to five degrees of freedom (DOFs) by including the vertical translation of the glenohumeral joint of the shoulder, in addition to the 3 DOFs of the shoulder and 1 DOF of the elbow, which are conventionally used to analyze the motion of the shoulder. The shoulder joint was tilted to avoid singularity problems in the workspace, i.e., by tilting the shoulder joint, the singularity position was placed outside of the normal range of motion. This configuration was analyzed using forward and inverse kinematics methods. Because the shoulder elevation affects all of the joint angles, the angles were calculated by applying an inverse kinematics method in an iterative manner. The performance of the proposed upper-limb exoskeleton and analysis methods was verified by simulations and experiments.

Kinematic analysis of a 5 DOF upper-limb exoskeleton with a tilted and vertically translating shoulder joint

In this paper, an upper-limb exoskeleton with a tilted and vertically movable shoulder joint is proposed. By analyzing the biomechanics of the shoulder, the motion of the upper limb is approximated by including one degree of freedom (DOF), namely vertical translation of the glenohumeral joint, in addition to the three DOFs that are conventionally employed to analyze the motion of the shoulder. Also, the shoulder joint is tilted to avoid singularity problems in the workspace; by tilting the shoulder joint, the singularity position was placed outside of the normal range of motion. This configuration was analyzed using forward and inverse kinematics methods. Because the shoulder elevation affects all the joint angles, the angles were calculated by applying an inverse kinematics method in an iterative manner. The performance of the proposed upper-limb exoskeleton and analysis methods have been verified by simulations.

A tele-operation interface with a motion capture system and a haptic glove

Tele-operation systems have been developed to perform tasks in extreme environments which cannot be easily accessed by human. However, non-intuitive control interfaces using only a keyboard or a joystick and wireless communication issues have prohibited the wide application of the tele-operation systems. In this work, an intuitive operation interface using inertial measurement units (IMUs) and a haptic glove was proposed to control a six degrees of freedom (DOFs) robot arm in remote place. Using the measured joint angles by the IMUs, the wrist position of the human arm was obtained by forward kinematics, which was used to calculate the robot joint angles by inverse kinematics. Considering workspace of the robot and human arms, robot joint angles were selected from many feasible solutions by the inverse kinematics. Also, the robot hand was controlled by the measured finger joint angles from the haptic glove, which also delivered vibration to the fingers according to the grasp force of the robot hand. As a tele-communication method, the 3GPP (3rd Generation Partnership Project) Long Term Evolution (LTE) network and a virtual private network (VPN) were utilized. The performance of the proposed system was verified by experiments.

Simulation analysis on friction compensation of a double tendon-sheath actuation system

A tendon-sheath system has been researched for human-robot interaction systems because of its simple and light tendon routing mechanism. Since the tendons contact with the inner surface of sheaths in a tendon-sheath system, many undesirable phenomena appear due to the friction between them. Force transmission models and feedforward friction compensation methods have been developed for precise force transmission; however, those methods are not applicable with varying sheath curvatures. In this paper, a double-tendon sheath actuation system with a sheath routing method that enables feedforward torque control in a varying sheath curvatures is introduced. A feedforward friction compensation law was developed by analyzing the system, and was verified by a simulation.

Performance verification of a kinematic prototype 5-DOF upper-limb exoskeleton with a tilted and vertically translating shoulder joint

In this paper, the performance of the 5-DOF upper-limb exoskeleton with a tilted and vertically translating shoulder joint, which was proposed in our previous work, is verified by simulations and experiments. In this design, one vertical prismatic joint was added for the vertical translation of the shoulder, and the shoulder joint was tilted to avoid the singularity problem. Based on the kinematic analysis in our previous work, the manipulability analysis was performed to determine the tilting angles and to check whether the singularity problem was appropriately addressed by the proposed design. The natural motion enabled by the added vertical translation was experimentally verified. For the experiments, an unactuated prototype of the proposed exoskeleton system was designed and manufactured. The experiment was focused on the decrease of the load on users shoulder with a vertically translating shoulder joint. The three axis forces at the shoulder joint were compared with those of conventional upper-limb exoskeleton whose shoulder joint was fixed. The simulation and experimental results show that the proposed upper-limb exoskeleton design is suitable for supporting natural motions of the upper-limb.

Torque control of a double tendon-sheath actuation mechanism in varying sheath configuration

Tendon-sheath actuation mechanism has been researched due to its extremely simple and light cable routing structure. However, the slide-based force transmission mechanism causes friction, which disturbs precise force control. To overcome such disadvantage, friction compensation algorithms in tendon-sheath actuation systems have been studied. However, the torque control of double tendon-sheath mechanism has not been achieved yet without a torque feedback. In this research, a double-tendon sheath actuation mechanism with series elastic elements and tight sheath routing method is introduced to achieve feedforward torque control. The performance of proposed mechanism is verified with experiments.

InterActive and intuitiVe control interfAce for a Tele-operAted Robot (AVATAR) system

Tele-operation systems have been developed to perform tasks in extreme environments that cannot be accessed easily by humans. However, non-intuitive control interfaces, low immersive feeling, and wireless communication issues have prevented the wide application of such tele-operation systems. In this study, an intuitive and interactive control interface using inertial measurement units (IMUs), a wearable sensing glove, and a head-mounted display (HMD) is proposed to control a tele-operated robot in a remote place. Using user information measured from the wearable interface, the desired joint angles of the robot are derived by a kinematic analysis of the robot. Also, the measured visual information and the torque of the robot hand are transmitted to the user as visual feedback on the HMD and vibrational feedback to the users fingertips, respectively. A semi-autonomous control strategy, referred to as shared control, was developed to overcome dimensional differences between the user and the robot, and to reduce the users workload. As telecommunication methods, a long-term evolution (LTE) and a virtual private network (VPN) are used. The performance of the proposed system was verified by experiments.

A Six-Legged Walking Robot Inspired by Insect Locomotion

In this paper, a six-legged walking robot inspired by insect locomotion is discussed. To implement the walking pattern of insects, four-bar linkage based structure is proposed and its performance is analyzed by kinematic simulation. Two servomotors are applied to left and right sides of the robot, which allows smooth turns and a natural walking pattern by the phase difference between two motors. The main structure of the robot is manufactured by a rapid prototyping method with polypropylene material, and a micro camera is installed for real-time video transmission to show its potential applications.