J Electr Eng Technol.2016; 11(5): 1433-1440 ISSN(Print) 1975-0102 http://dx.doi.org/10.5370/JEET.2016.11.5.1433 ISSN(Online) 2093-7423 Simple Walking Strategies for Hydraulically Driven Quadruped Robot over Uneven Terrain Jungsan Cho*, Jin Tak Kim*, Jungyoung Kim**, Sangdeok Park* and Kab Il Kim† Abstract – 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. Keywords: Jinpoong, Walking robot, Hydraulic quadruped robot, Balance control 1. Introduction robots with electric motors are the robot developed by Hirose et al. [3], Sony’s AIBO [4], and Little Dog [5]. In The most promising aspect of quadruped robots is that combination with high position gain control and kinematic they can easily adapt to and walk over uneven terrain, planning, these robots demonstrated statically and quasi- such as that found in mountainous areas, owing to their statically stable walking gaits. One approach to achieving structural similarity to quadruped animals. This advantage stable walking is to use springs in combination with can be leveraged for applications such as entering collapsed electric motors. Examples of this approach are the structures and providing military transportation. To quadruped robots Tekken [6], KOLT [7], and Cheetah [8]. accomplish such tasks, the range over which a quadruped These quadruped robots are able to perform bounding and robot can operate must be expanded to include uneven trotting on flat ground. terrain, such as that found in mountainous areas, and Significant examples of quadruped robots with hydraulic stability in walking on uneven terrain must be achieved. actuators are BigDog [9] and HyQ [10]. Boston Dynamics Dynamic locomotion of quadruped robots has been has demonstrated an advanced level of performance on investigated using a variety of approaches [1]. However, uneven terrain with their BigDog, AlphaDog, and Wild Cat several major problems associated with dynamic locomotion robots. BigDog was stabilized by applying torque to the of quadruped robots need to be resolved. One of the hip joint during the stance phase. The torque applied was major problems is the need to design mechanical systems computed as a function of the body pitch and roll angles that are able to deliver the energy needed to sustain and rates by a proportional-derivative (PD) controller. The dynamic locomotion during intermittent periods of foot Italian Institute of Technology (IIT) has demonstrated the contact. When this need is considered together with the practicality of a hydraulic robot with their HyQ design. needs for acceptable energy efficiency and an acceptable HyQ utilizes a floating-base inverse dynamics-based weight, the demands placed on the actuation systems of a feed-forward servo control algorithm to ensure that quadruped robot are difficult to fulfill. position tracking is achieved with low PD control gains. Stabilization and control of dynamic locomotion are also All of these robots operate using a walking stabilization significant problems. Successful control strategies are based algorithm that is based on the application of torque to on the observations of Raibert [2], who demonstrated the control the joints. While this type of algorithm is quite importance of two essential ingredients: control of the body useful, we think that a better approach would be one that through the hip stance and foot placement control for combines balance control with force control. balance recovery. Hydraulic actuation offers the advantages of substantial The driving system consists of electric motors and power, a wide range of speed, small size, and low weight hydraulic motors. Significant examples of quadruped [11]. Because of these advantages, hydraulic actuation is often used in robots that lift heavy loads. Jinpoong (shown † Corresponding Author: Dept. of Electrical Engineering, Myong Ji in Fig. 1) is a hydraulically operated quadruped robot University, Korea. ([email protected]) that is powered by an engine. Jinpoong was developed * Robotics R&D Group, Korea Institute of Industrial Technology, Korea. ({chojs, jintagi, sdpark}@kitech.re.kr) for military transportation applications [12-14]. ** Dept. of Intelligent Robot Engineering, University of Science & This study was conducted to develop a method for Technology, Korea. ([email protected]) ensuring the stability of a hydraulic robot system as it Received: November 27, 2014; Accepted: March 7, 2016 1433 Copyright ⓒ The Korean Institute of Electrical Engineers This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/ licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Simple Walking Strategies for Hydraulically Driven Quadruped Robot over Uneven Terrain Fig. 1. Jinpoong, a hydraulically actuated quadruped robot Fig. 2. Composition of Jinpoong walks over uneven terrain, using a controller that operates the joint actuator located within each of the four legs by based on joint position control. In this paper, we present means of four sub-manifold folds. the results of experiments conducted to verify the efficacy Jinpoong has onboard systems that provide power, of the method developed. We developed a hydraulically actuation, sensing, controls and communications, as shown actuated quadruped robot as shown in Fig. 1 which in Fig. 2. Jinpoong uses a two-stroke, 30-horsepower experiments are walking on the gravelly field, kicked from engine and a swash-plate-type hydraulic pump to provide the side, and mounted by person. In Section 2, we describe power for walking across open terrain. The maximum the configuration of Jinpoong, and in Section 3, we explain hydraulic pressure is 210 bars, and the maximum flow is the walking strategy. The verification tests conducted and 35 lpm. Jinpoong has 16 degrees of freedom (each of the the results obtained are described in Section 4. four legs having four degrees of freedom) for walking over uneven terrain. The height of the robot is 1.2 m, the length is 1.1 m, the width is 0.4 m, and the weight is 120 kg. 2. Hardware Specifications These dimensions were selected on the basis of a typical human being’s height, mobility, speed, and load-carrying Jinpoong uses hydraulic connections to power its capacity. components when walking. These components include the The legs consist of rolling joints for the hips, with rotary body frame, the hydraulic system, the power system, and hydraulic actuators, and pitching joints for the hips, knees, the control system. The body frame was designed to protect and feet, with linear hydraulic actuators. The operating the internal components. A component arrangement was range of the rotational actuator is ±70°, and its output designed to ensure stability during walking. A separate power is 400 Nm at a pressure of 210 bars. The operating structure that could be mounted on the engine through the range of the linear actuator is 54 mm, and its output power lower body was attached to the inner body frame so that is 8000 Nm at 210 bars. The actuators are controlled by the components did not protrude outside the body frame. electronic servo-valves (Star Hydraulics Ltd., UK). All of The walking stability of the robot was improved by the actuators are equipped with potentiometers to measure lowering the center of gravity. their positions. The hydraulic system drives the hydraulic pump that The linear hydraulic actuators are lighter and yet more powers the engine and generates and supplies the oil powerful than rotary actuators and were designed to move pressure required to drive the joint actuator. In view of the quickly despite the robot carrying a payload over rough arrangement of the component modules of the robot, such terrain. The hydraulic actuators are placed on the upper as the leg modules, controller and sensors, engine, and parts of the legs to make the lower parts lighter. muffler, the hydraulic system was designed together with This design allows the overall center of gravity to be the body structure. To ensure smooth movement during closer to the center of the robot, thus improving stability walking and to optimize the space efficiency of the and making the robot less susceptible to the dynamics of a hydraulic components between the hydraulic pumps and swinging leg. Rotary actuators rather than linear actuators manifolds, such as storage tanks, the trajectory and radius are used for the hip joint to optimize the size and shape of of curvature of the hydraulic hose were taken into the platform. The modular design concept employed for the consideration in the design of the hydraulic system. The components such as the controllers also helped to optimize hydraulic system was designed to supply hydraulic fluid to the size and shape of the platform. 1434 │ J Electr Eng Technol.2016; 11(5): 1433-1440 Jungsan Cho, Jin Tak Kim, Jungyoung Kim, Sangdeok Park and Kab Il Kim An inertial measurement unit (HG1700, Honeywell Company, USA) is used to measure body posture and inertia. The control system consists of a power control unit (PCU) to control the engine and hydraulic power, a leg control unit (LCU) to control the action of each joint and leg, a sensor processing unit (SPU) to collect information necessary for walking and navigating, and a behavior control unit (BCU) to control walking and other actions.