Jungsan Cho

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.

Simple Walking Strategies for Hydraulically Driven Quadruped Robot over Uneven Terrain

Jinpoong is a quadruped walking robot developed by the Korea Institute of Industrial Technology. Jinpoong was developed for use in surveillance, reconnaissance, transportation, and guidance tasks in atypical environments such as those encountered after a disaster. To perform these tasks successfully, the robot must be able to walk stably over uneven terrain. The aim of this study was to develop a method for absorbing the impacts experienced by the robot while walking and a method for resisting external forces applied to the side (sagittal plane) of the robot so that it can walk stably. We demonstrate the efficacy of the methods developed through experiments.

Dynamic walking of JINPOONG on the uneven terrain

The Quadruped walking robot “JINPOONG” is developed to be able to walk in the field which is use to detection, surveillance, reconnaissance, security, and assistance. It can move, carry the luggage of 60kg or more and walk at the uneven terrain such as gravel road and slope of 15 degrees or more. By adjusting the length of the leg caused by the ground reaction force and body posture balance control to the sagittal and lateral plane it is possible to walk stably on the uneven terrain. In this paper, we describe a method for the stable walk on the uneven terrain of JINPOONG and show experimental results about varied terrain.

Design of quaternion controller based on Virtual Spring-Damper hypothesis for hydraulic manipulator

Systems that implement robot joints by using servo valve-controlled hydraulic actuators are known to be difficult to control because hydraulic systems are highly nonlinear. Although this problem is tough to solve, these systems continue to be of interest because their hydraulic manipulators have a high power-to-weight ratio, which can be used for a variety of tasks. In order to enable a hydraulic manipulator to perform these tasks, the position and orientation of its end-effector must be controlled. We have designed Virtual Spring-Damper (VSD) hypothesis based quaternion controller to control the orientation of a hydraulic manipulator end-effector. VSD hypothesis is a relatively simple calculation method that uses virtual force and joint damping to move the end-position of a robot arm to the desired position (control point). We extended VSD hypothesis for orientation control and connected 2 additional VSD models to the wrist and thumb in order to control the orientation of an end-effector with 3 degrees of freedom (DoF). We have proposed a quaternion controller to determine control points used as input for each VSD model. We have also designed VSD controller to calculate the control input of joints; this input is used for the movement to each control point. In order to verify the performance of the proposed control method, we present the results of experiments performed on a hydraulic manipulator with 7 DoF.

JINPOONG, posture control for the external force

The quadruped walking robot “JINPOONG” is developed to be able to walk in the field which is used to detection, surveillance, reconnaissance, security, and assistance. It can move, carry the luggage of 60kg or more and walk at the uneven terrain such as gravel road and slope of 15 degrees or more. To the legged robot walking stable, when an external force is applied to the body, the posture control is necessary to maintain stability. In this paper, we describe a method for the stabilization posture of JINPOONG and show experimental results about the external force.

Development of engine speed control system for power supply of the robot

JINPOONG, a walking robot using hydraulic pressure, requires a power source to operate the power-pack. Therefore, power was supplied to JINPOONG by using an engine that has high power per unit engine weight. Hydraulic pump requires a constant rotating speed in order to supply stable hydraulic pressure because the pressure and flow rate changes according to rotating speed. This study proposes a way to maintain relatively stable rotating speed of engine with irregular and fluctuating load.

Design and Implementation of the Cable Rod Hydraulic Actuator for Robotic Revolute Joints

This paper presents a cable-driven hydraulic actuator named Cable Rod Hydraulic Actuator (CRHA). The cable actuating system is attractive for designing a compact joint in robotic applications since it can be installed remotely from the joint. Recently, cable rods have been used in pneumatic area for inertia reduction. However, designing cable rods in hydraulics is challenging because it is difficult to achieve flexibility and endurance simultaneously under high pressure conditions. In this paper, the cable rod, which consists of a cable and jacket, is proposed to meet both requirements. To design the CRHA, we determined the design parameters, such as cylinder size, and selected the cable rod’s material by friction and leakage test. Finally, comparisons experiments about step and frequency responses with conventional hydraulic actuators were performed to assess feasibility for robotic joints, and the results show that the proposed system has good bandwidth and fast response as robotic joints.

Leg mechanism design for SLIP model of hydraulic quadruped robot

The Spring Loaded Inverted Pendulum (SLIP) describes the dynamic walking of humans and animals in a simplified manner. However, realizing such movements by means of a combination of typical articulated legs and linear actuators has some limitations. This paper proposes a leg mechanism that accurately reflects the SLIP based on its mechanical constitution. The SLIP design based leg is able to do decoupled swing motion and extension motion. Also this study has focused on improving the straightness of extension motion.

Design and implementation of electronic governor system for 2 stroke engine

JINPOONG, a walking robot using hydraulic pressure, requires a power source to operate the power-pack. Therefore, power was supplied to JINPOONG by using an engine that has high power per unit engine weight. Hydraulic pump requires a constant rotating speed in order to supply stable hydraulic pressure because the pressure and flow rate changes according to rotating speed. This study proposes a way to maintain relatively stable rotating speed of engine with irregular and fluctuating load.