Actuators for exoskeleton robots comprise various types such as electric, hydraulic, and pneumatic and it is necessary to apply the correct actuator according to the purpose. Most exoskeleton robots mainly use electric actuators, and some special-purpose robots, such as for heavy-load transport requiring large force, use hydraulic actuators. In this paper, friction of the actuation module consisting of a harmonic drive and a brushless DC motor is measured through experiments. And the friction characteristics of the actuation module are analyzed. The harmonic drive transmission system has various advantages, but it also has hysteresis and nonlinear friction characteristics. The friction compensation control of the actuation module enables precise control of the exoskeleton robot, and improves the robot’s performance. Appropriate friction model selection and design affects friction compensation performance. In this study, static and dynamic friction models are designed and analyzed based on the friction data of the actuation module.

This study presented a mechanism overview of a novel modular knee exoskeleton, ACE-Knee, and the analysis of the design requirements by observing human knee-motion characteristics. The ACE-Knee exoskeleton consists of 1) base frame at waist, 2) a 3-DOF (degrees of freedom) passive spherical hip, and 3) a knee driving mechanism. The passive hip is designed based on a 3R spherical serial chain such that it has RCM (remote center of motion) capability. For designing a compact and efficient knee driving mechanism, it is realized by two crank-slider linkages where two sliders are coupled with a linear spring. The proposed kinematic structure enables the driving concept of the passive support by the linear spring and the active following by an actuator. In order to setup design requirements, gait experiments were performed for level walking and ascending/descending stairs. From the analysis of experimental results, unique motion and quasi-stiffness characteristics of human knee were identified.

To maintain communication quality of a mobile satellite antenna system without disconnection, the satellite tracking technique is required. There are two major tracking methods called step tracking and monopulse tracking, which utilize satellite signals as a tracking feedback. The monopulse tracking method provides fast and accurate tracking performance, whereas it can be used only in limited small regions near the satellite’s direction. In the case of step tracking method, it can be applied in relatively large regions. However, this method also has a limitation, in that it cannot provide fast and accurate tracking performance near the satellite direction. In this paper, a hybrid tracking method composed of step tracking mode and monopulse tracking mode is proposed. The proposed tracking method can present accurate tracking performance near the satellite direction as well as be applied in relatively large regions.

The weight of an antenna system pointing satellite on the mobile platform is restricted by the weight limit of the mobile platform. The maximum power of the actuator driving the antenna system is thus limited because a high power actuator needs a heavier weight. Thus, a drive system is designed to have a low torque requirement by reducing the gravitational torque depending on gravity or acceleration of the mobile platform, including vibration, shock, and accelerated motion. To reduce the gravitational torque, the mathematical model of the gravitational torque is preferentially obtained. However, the method to directly estimate the mathematical model in an antenna system has not previously been reported. In this paper, a method is proposed to estimate the gravitational torque as a mathematical model in the antenna system. Additionally, a method is also proposed to calculate the optimal weight of the balancing weight to compensate for the gravitational torque.