Design and Control of a Quadruped Robot for High Mobility

Abstract

To achieve high mobility on various environments, quadrupedal robots have been studied. High mobility requires five characteristics: force, energy efficiency, speed, stability and versatility. In this thesis, the design and control of quadrupedal robots were studied to have high mobility, considering above characteristics. The thesis is introducing three methods to achieve high mobility for a quadruped robot. Chapter 2 describes about the design of a quadruped robot for high force, speed and energy efficiency. By designing the leg with high torque density motors with the developed motor frame for optimized overhang, a capacity of exerting large force and fast speed leg was designed and developed. Furthermore, an advanced adaptive robust position tracking controller was developed and implemented to the robot, to assure high accuracy even in the fast speed gait and exerting high forces such as adding heavy loads or rapid change between the stance and swing phase. The developed robot was tested on both the simulation and experiments. The proposed design of the robot could exert a high force; it can lift the payload up to 200 kg. In addition, the developed robot could perform dynamic gaits of trotting and bounding, which is only available at medium-high speed. By adding spring in series to the leg with the proposed joint locking mechanism, energy could be saved from the negative work of the ground, and then released by our intention via controlling the robot hip. The proposed mechanism was tested on both the simulations and the experiments. It was found that the joint locking mechanism absorbs maximum 25 % of the energy from the impact. Furthermore, the joint locking mechanism also showed robustness to the varying locomotion speed in open loop control. Chapter 3 aimed to design a robust gait stabilizing controller which can be applied to wide range of the speed and gait types. The basic idea of the proposed controller is to control the body pitch angle through controlling the contact time of the leg with the ground. If the contact time changes, the body pitch angle of the robot changes, which was given to the model of the system. Based on the model, stability of the proposed algorithm was mathematically verified, and tested on the simulation environment. The developed gait controller showed high robustness on wide range of the locomotion speed, and the various gait types compared to the conventional gait controllers. Chapter 4 describes the development of the design of a robotic foot to enhance gait stability and versatility. Although a robust gait stabilizing controller was developed in Chapter 3, the developed algorithm needs impact force to stabilize the body. Therefore, during the standing posture, stabilizing effect is vulnerable. Instead of adding another controller, in Chapter 4, embedding the hardware intelligence of stability was studied. Inspired from the human foot, tensegrity-based design using proprioceptive artificial tendons showed high adaptability on various ground inclination angles and obstacles. In addition, using embedded proprioceptive tendons, ground information including ground inclination angles and the ground reaction force could be measured. The research contents in this thesis produce a guideline of designing and controlling quadruped robots to achieve five components of mobility: high force, energy efficiency, speed, stability and versatility. Through the outcomes of this research, quadruped robots can step toward to the robot which can finally be utilized in various fields in our daily lives.