Method for improving the position precision of a hydraulic robot arm: dual virtual spring–damper controller

Recently, control approaches for a hydraulic robot in the field of robotics have attracted considerable attention owing to their high power-to-weight ratio. Many studies on behavior and control exploiting the advantages of hydraulic robots have been pursued. Application to hydraulically actuated systems, however, is not straightforward due to the nonlinear internal dynamics of the actuators. This paper presents a relatively simple method to improve the position precision of a hydraulic robot arm. We propose a simple control method concept based on a virtual spring–damper (VSD) controller, which enables the robot to realize a desired position. The main advantage of the VSD control is its simple calculation method, which eliminates the need to solve the Jacobian pseudo-inverse or ill-posed inverse kinematics. In this study, experiments were conducted to identify the problems in previous study results and evaluated the applicability of VSD control to the hydraulic robot arm. A relatively simple method was proposed to solve these problems and to verify improvements in the position precision. The proposed method is the dual VSD controller in which an additional VSD model is applied to the elbow, in addition to the conventional VSD model connected to the wrist. The effectiveness of the proposed control scheme is demonstrated in experimentation with the hydraulic robot arm.     

Verification of the peak time approach for detection of step initiation using the UTRCEXO

We were able to detect the step initiation for the Unmanned Technology Research Center Exoskeleton before visible movements occurred during the peak time approach. Detection of the step initiation is important for the rapid onset of assistance with the exoskeleton operator’s movement. Many previous studies have attempted to detect the step initiation more rapidly using the precedence walking assistance mechanism with electromyography, or the shadow walking assistance mechanism with the heel-off or toe-off time. In this paper, we detect the step initiation and implement the precedence walking assistance mechanism using the peak time approach. In particular, we detect the vertical ground reaction forces before visible movements occur, which is more reliable, simpler and faster than the previous approaches. We also present insole-type force sensing resistors based on the peak time approach that are used in force plates that can be applied to the Unmanned Technology Research Center Exoskeleton to detect similar events, such as the ground reaction force events, and the step initiation. With the insole-type force sensing resistors, the Unmanned Technology Research Center Exoskeleton can not only detect step initiation before visible movements occur, but can also implement the precedence walking assistance mechanism for step initiation without using any bio-signals.     

A SLIP-based Robot Leg for Decoupled Spring-like Behavior: Design and Evaluation

International Journal of Control, Automation and Systems - We present a spring loaded inverted pendulum (SLIP) based robot leg to enable decoupled swing motion and spring-like behavior. The two...