The rotation axis of human knee joint varies according to knee flexion angles. That is, human knee movement is spatial with dominant flexional rotation. Knee joints of most lower-limb exoskeletons were, however, realized with a simple revolute pair for design simplicity. Wearing the knee joint with a simple revolute pair constrains inevitably natural parasitic motion of human knee joint. Rigid constraints imposed due to the simple knee joint lowers wearability and comfortability. In addition, it may act as potential risks to harm the knee joint structure of the wearer. The concept of polycentric knee is a well-known approach to mimic the variation of knee rotation center. Polycentric knees, however, realize only the planar trace of projected points of rotation axis. That is, parasitic knee rotations of varus and internal rotation occuring naturally during knee flexion cannot be realized by polycentric knees. In order to resolve this, a novel spherical knee joint of exoskeleton is introduced in this paper to realize knee spherical movements. For the design, change in instantaneous rotation axes during knee flexion is formulated to a spherical trace as a function of knee flexion angles. A spherical four-bar linkage is suggested to realize the axis trajectory, not the point trace. A method to find instantaneous rotation axis and rotation matrix of coupler link is derived, when the angle of input link is given. Using the kinematic relations, kinematic parameters of the mechanism are optimized to minimize angle difference between the instantaneous axis of coupler and the required axis of knee rotation. Finally, based on the synthesized kinematic parameters, a prototype design was introduced in this paper.

Numerous attempts have been made to reduce metabolic energy while running with the help of assistive devices. A majority of studies on the assistive devices have focused on the assisting torque in the sagittal plane. In the case of running, however, the abduction torque in the frontal plane at the hip joint is greater than the flexion/extension torque in the sagittal plane. During running, as does an elastic body, the abduction torque and the motion of the hip joint have a linear relationship, but are opposite in direction. It is expected that the hip abduction torque can be assisted with a simple passive method by using an elastic body that reflects the movement characteristics of the hip joint. In this study, therefore, a system to assist hip abduction torque using a leaf spring was proposed with a prototype testing. While running with the assist system proposed, the leaf spring aids the abduction torque on the stance phase, and the torque is not generated due to the passive revolute joint on the swing phase. The joint angle is changed with respective to the rotation in the flexion/extension direction to prevent discomfort torque during swing phase and to increase the duration of the torque action during stance phase. A preliminary test was conducted on one subject using the prototype of the hip joint abduction torque assistive device. The participant with the assistive device reduced metabolic energy by 5% compared to the case without abduction torque assist while running at 2.5m/s. In order to increase the amount of metabolic reduction, the device shall be supplemented by system mass reduction and hip joint position optimization.

In this paper, we present KULEX-hand, a novel underactuated hand exoskeleton for grasping power assistance for patients having a partially paralyzed hand or the elderly with weakened muscle strength. This mechanism consists of an underactuated finger for grasp motion generation, a spherical four-bar linkage for power transmission, and a passive thumb link with a flexure hinge structure. Based on the natural closing motion of the human index finger, the motion generation linkage was synthesized as a planar five-bar in which two input links were coupled with a four-bar linkage. Therefore, after contact occurs on the proximal link, the synthesized linkage can mimic the grasping motion of the human middle and distal phalanges. The kinetoelastic relation of the underactuated finger was derived using the theory of screws. Based on this relation, guidelines were proposed for selecting the springs for achieving a stable pinch grasp. A prototype was designed, and the naturalness of motion was evaluated from an experiment with five subjects.

In this paper, a novel three-DOF ankle mechanism is introduced. A lower-limb exoskeleton is developed by our research group to strengthen wearer's muscle power in military missions. Owing to the tough operational condition, each module of the exoskeleton should be carefully designed for safety and to reduce the sense of fatigue of the wearer. To this end, it is desirable for the ankle module to be lightweight and compact and to have a remote center of rotation which is closely located to the rotation center of the wearer's ankle. In order to satisfy these design considerations, the proposed ankle mechanism consists of the parallel connection of a spherical five-bar linkage and an RSU (revolute-spherical-universal)- serial chain. The spherical five-bar linkage realizes two-DOF ankle rotations of inversion/eversion and internal/external rotation, and the RSU-serial chain controls the ankle dorsiflexion/plantar flexion. The forward and inverse kinematics are derived, and instantaneous kinematics as well as force relations are analyzed by deriving the screw-based Jacobian and the reciprocal Jacobian. Finally, based on the gait data obtained from a normal subject with 4km/h of walking speed and 45kg of backpack load, the initial version of it is designed as a fully passive-type mechanism with a torsional spring. It is shown from a simulation that 42% reduction of the wearer's ankle peak torque is expected by using the proposed ankle exoskeleton.

In this paper, a novel concept of two-degree-of-freedom (2-DOF) compliant forceps is suggested for the measure of pulling and grasp forces at the tip of surgical instrument for minimally invasive surgery robot. For the design of the compliant forceps, the required compliance characteristics are first defined using a simple spring model with one linear and one torsional springs. This model may be directly realized as the compliant forceps. However, for the compact realization of the mechanism, we synthesize the spring model with two torsional springs that has equivalent compliance characteristics to the linear-torsional spring model. Then, each of the synthesized torsional springs is realized physically by means of a flexure hinge. From this design approach, direct measurement of the pulling and grasp forces is possible at the forceps, and measuring sensitivity can be adjusted in the synthesis process. The validity of the design is evaluated by finite element analysis. Further, from the measured values of bending strains of two flexure hinges, a method to compute the decoupled pulling and grasp forces is presented via the theory of screws. Finally, force-sensing performance of the proposed compliant forceps is verified from the experiments of the prototype using some weights and load cells.

This paper presents a method of determining exact solutions to kinestatic analyses of lower mobility manipulators by means of the reciprocal Jacobian. The existence and uniqueness of the reciprocal Jacobian are shown, which enables the complete kinestatic analyses of both serial and fully parallel manipulators in a unified way, as well as the derivation of the constraints on the end-effector twist and wrench.