Xin Luo

Mechanism Design and Gait Experiment of an Amphibian Robotic Turtle

In this paper we describe the design of a new bio-inspired amphibian robot with high environmental adaptability. The robot, called MiniTurtle-I, can transform terrestrial and aquatic locomotion configurations through a new variable topology mechanism (Leg-Flipper). Based on the modular design philosophy, four rotatory joint modules (Joints I–IV) constitute a Leg-Flipper module. Variable topology structure transformation of Leg-Flipper by actuation redundancy enables the robot to achieve a variety of locomotion. Our motivation is to provide another solution to achieve amphibious movement both easily and efficiently. A prototype of MiniTurtle-I is built to exam the configuration transformations. Terrestrial, aquatic and semiaquatic gait experiments are performed to verify the locomotion functions of the MiniTurtle-I.

Design of an eccentric paddle locomotion mechanism for amphibious robots

In this paper we present a novel eccentric paddle mechanism (ePaddle) for amphibious robots that can work in terrestrial, aquatic and semi-aquatic environments and perform wheeled, legged and paddling locomotion gaits. The concept of the ePaddle mechanism is discussed firstly and followed by its forward and inverse kinematic models. The ePaddle mechanism brings remarkable locomotion ability to a robot working in complex amphibious environments that are hazardous to most of existing robots. Three terrestrial gaits and two aquatic gaits are introduced in this paper. The prototype design of the ePaddle mechanism is introduced and the terrestrial trafficability analysis shows that the ePaddle-based robot is highly capable of overcoming steps and ditches. Finally, the prototype of an ePaddle module is simulated with a legged walking gait, and the proposed locomotion ability as well as its kinematic models are verified by the simulation results.

Hybrid control for SLIP-based robots running on unknown rough terrain

Rapid and efficient dynamic stability control has been one of the important motivations in legged robot research, especially for legged robots running at high speed and/or on rough terrain. This paper presents a feasible control strategy, named Hybrid Feedback Control (HFC), for running systems based on the spring-loaded inverted pendulum principle (SLIP). The HFC strategy, which comprises two modules (i.e., touchdown angle control and energy compensation), predicts and regulates touchdown angle of the current cycle and need-to-complement energy input of the next cycle through hybrid feedback of flying apex state. This strategy can significantly reduce the computational complexity and enable the system to quickly converge to its control target, meeting the requirements of real-time control. Simulation experiments on various terrains were conducted to verify the adaptability of our HFC strategy. Results of these simulation experiments show that the approach herein can realize the periodical stability control of SLIP systems on different terrain conditions quickly and effectively.

Virtual constraint based control of bounding gait of quadruped robots

This paper presents a control approach for bounding gait of quadruped robots by applying the concept of Virtual Con-straints (VCs). A VC is a relative motion relation between two related joints imposed to the robots in terms of a specified gait, which can drive the robot to run with desired gait. To determine VCs for highly dynamic bounding gait, the limit cycle motions of the passive dynamic model of bounding gait are analyzed. The leg length and hip/shoulder angle trajectories corresponding to the limit cycles are parameterized by leg angles using 4 th-order polynomials. In order to track the calculated periodic motions, the polynomials are imposed on the robot as virtual motion constraints by a high-level state machine controller. A bounding speed feedback strategy is introduced to stabilize the robot running speed and enhance the stability. The control approach was applied to a newly designed lightweight bioinspired quadruped robot, AgiDog. The experimental results demonstrate that the robot can bound at a frequency up to 5 Hz and bound at a maximum speed of 1.2 m⊙s-1 in sagittal plane with a Froude number approximating to 1.

Judgment and adjustment of tipping instability for hexapod robots

Real-time response to tipping is essential for a hexapod robot to avoid damaging itself and load when it walks on rough terrains. In this paper, a criterion is proposed combining ZMP and FASM for the judgment of the stability of walking hexapod robots, and an analytical method is applied to determine the reachable workspace of its adjusted-leg and to choose footholds to restore stability based on the principle of maximizing force arm. Taking the case of a hexapod robots sideline tipping on a slope terrain as an example, the simulation results verify the effectiveness of the proposed method.

A control strategy for SLIP-based locomotion under lateral impact in 3D space

Lateral impact disturbances upon a legged running locomotion can result in the generation of an unexpected lateral velocity, consequently cause the deviation of the locomotion from its original direction of movement, even falling down to destroy the system. Dealing with the influence of lateral impact disturbances greatly increases the complexity of control in 3D space. Inspired by biomechanical studies, this paper constructs a control strategy based on the spring-loaded inverted pendulum principle (SLIP) for legged locomotion under lateral impact disturbances. This strategy, named 3D-HFC, is composed of three core modules: touchdown angle control, body attitude angle control and energy compensation. The first module regulates the forward/lateral running velocities such that lateral velocity recovers to zero after impact, the second maintains the body posture without being influenced by external forces, and the third compensates energy loss to ensure a desired hopping height. These three parts operate commonly to achieve the APEX state variables converging to the desired value in each running cycle, so as for the system to keep stable periodic motion. The simulations of running systems bearing different force impacts are conducted to verify the effectiveness of the 3D-HFC strategy, indicating that the proposed approach can reject impact disturbances effectively.

Design and analysis of a bionic quadruped robot

In this article, design of bionic quadruped, mainly focusing on leg design, is given and force analysis of the mechanism is calculated and simulated. To better improve the design, force on sole and torque on joints should be diminished to increase the mobility and capacity of the robot. Therefore, a design method based on biomechanics and bionic control strategy is proposed for this quadruped robotic system considering compliance. This design method, including mainly mechanical compliance element and control compliance element, can decrease the contact force and torque of both hip and knee joints. This first prototype of leg design is aimed to achieve a general concept about optimizing force and torque of robot leg and prepares for further experiments on complex terrain condition.

Study on multi-legged walking robot in Huazhong University of Science & Technology

This paper introduces the research on multi-legged walking robot in Huazhong University of Science & Technology (HUST) over the past ten years. We have been committed to improving the performance of multi-legged walking robots such as versatility, easiness in controllability, intelligence level and excellent environmental adaptability, as well as making them assist human beings to finish some tasks. Our works are divided into four parts in detail: the basic theory, mechanism design, control and simulation systems, and prototype models. The problems we have encountered and the corresponding solutions are discussed in each section. Our aim is to make the multi-legged walking robot have a better performance and complete various tasks independently in the complex environment. Moreover, the development planning of the multi-legged walking robot in the future is discussed.