Yanhe Zhu

Bifurcations and chaos in passive dynamic walking

Irrespective of achieving certain success in comprehending Passive Dynamic Walking (PDW) phenomena from a viewpoint of the chaotic dynamics and bifurcation scenarios, a lot of questions still need to be answered. This paper provides an overview of the previous literature on the chaotic behavior of passive dynamic biped robots. A review of a broad spectrum of chaotic phenomena found in PDW in the past is presented for better understanding of the chaos detection and controlling methods. This paper also indicates that the bulk of literature on PDW robots is focused on locomotion on slope, but there is a thriving trend towards bipedal walking in more challenging environments. The chaos research in Passive Dynamic Walking (PDW) is covered in the reviewed literature.An account of chaos control techniques in PDW bipeds is presented. This area certainly necessitates further investigation.The need of new mathematical methods is emphasized so that PDW bipeds can be studied analytically.Potential research directions have been identified.

A new self-reconfigurable modular robotic system UBot: Multi-mode locomotion and self-reconfiguration

In the paper, a concept of novel self-reconfigurable robotic system made of the autonomous robotic modules has been reviewed. Each robotic module is made of simple structure and few degrees of freedom; however, a group of the modules is able to change its connective configuration by changing their local connections and has functionality of robotic system which is capable of generating complicated motions and accomplishing a large variety of tasks, such as: transportation, exploration, inspection, construction and in-situ resource utilization. Multimode locomotion and self-reconfiguration are the basic and essential abilities for the self-reconfigurable robotic system. Based on this concept, a new self-reconfiguration system, UBot robotic system that combines the advantages from the chain-based and lattice-based robots has been proposed. Each UBot module which is cubic structure based on universal joint has two rotational DOF and four connecting surfaces that can connect to or disconnect from adjacent modules. The smart structure and the reliable connecting mechanism of the modules make the robot flexible enough to complete multimode locomotion and self-reconfiguration. This paper demonstrates the design philosophy of the UBot module and a solution for multimode motions and self-reconfiguration using the UBot system. The system can complete motion in the modes of quadruped, chain and loop configuration. Besides, the system can deform from one mode to the other though self-reconfiguration. All the proposed methods have been verified though simulations and real hardware experiments.

Applications of Chaotic Dynamics in Robotics

This article presents a summary of applications of chaos and fractals in robotics. Firstly, basic concepts of deterministic chaos and fractals are discussed. Then, fundamental tools of chaos theory used for identifying and quantifying chaotic dynamics will be shared. Principal applications of chaos and fractal structures in robotics research, such as chaotic mobile robots, chaotic behaviour exhibited by mobile robots interacting with the environment, chaotic optimization algorithms, chaotic dynamics in bipedal locomotion and fractal mechanisms in modular robots will be presented. A brief survey is reported and an analysis of the reviewed publications is also presented.

BP neural network tuned PID controller for position tracking of a pneumatic artificial muscle

BACKGROUND Although Pneumatic Artificial Muscle (PAM) has a promising future in rehabilitation robots, its difficult to realize accurate position control due to its highly nonlinear properties. OBJECTIVE This paper deals with position control of PAM. METHODS To describe the hysteresis inside PAM, a polynomial based phenomenological function is developed. Based on the phenomenological model for PAM and analysis of pressure dynamics within PAM, an adaptive cascade controller is proposed. Both outer loop and inner loop employ BP Neural Network tuned PID algorithm. The outer loop is to handle high nonlinearities and unmodeled dynamics of PAM, while the inner loop is responsible for nonlinearities caused by pressure dynamics. RESULTS Experimental results show high tracking accuracy as compared with a convention PID controller. CONCLUSION The proposed controller is effective in improving performance of PAM and will be implemented in a rehabilitation robot.

A Simplified Approach to Realize Cellular Automata for UBot Modular Self-Reconfigurable Robots

Abstract—Like cellular systems—Modular Self-Reconfigurable Robots (MSRR)—accomplish certain tasks through coordination of numerous independent modules. At the center of Cellular Automation (CA) is the sliding cube model (SCM) that is a mainstay supporting theoretical developments. Motion constraints of physical modules limit the application of CA method in real robotic systems. This paper proposes a new strategy for implementing CA on MSRR—which is a synergy of CA rules and modular design. Firstly, using the geometric expression of CA rules for SCM, a 2-DOF cube-shaped MSRR module (UBot system) is proposed, which lays the foundation for implementation of unified and highly effective modular locomotion criteria. Secondly, cellular rules are arranged according to the locomotion property of UBot module, and distributed control algorithm is designed for the robot to explore unknown environments. Simulations results verified this approach with reconfiguration locomotion of UBot robots in diverse unfamiliar environments. Hardware experiment with 16 modules also indicates the physical feasibility of the method.

On the impact of MOOCs on engineering education

From the early 90s, online education has been continually reshaping the notion of open learning. Massive Open Online Courses (MOOCs) have generated a paradigm shift in online education by presenting free high-quality education to anyone, anywhere with Internet access. Since 2012, MOOCs got attention of the universities, media and entrepreneurs. These online courses may change the world by 2022. This paper discusses major elements of MOOCs that can influence teaching and learning in engineering. It also explores the promise of online education in improving standard in-class engineering education.

Study of bifurcation and chaos in DC-DC boost converter using discrete-time map

This paper aims to present an investigation of bifurcation and chaos in a DC-DC boost converter using a discrete-time map. For a discrete-time (iterative) map of the converter, the time series plot and the bifurcation diagram were drawn. Both these nonlinear analysis tools confirmed that this power electronics circuit exhibits bifurcation patterns and chaotic dynamics. It is also demonstrated that discrete-time modeling approach is valuable in analyzing chaotic behavior. A brief literature review is also reported.

Introducing Undergraduate Electrical Engineering Students to Chaotic Dynamics: Computer Simulations with Logistic Map and Buck Converter

In current undergraduate electrical engineering, the emphasis on linear systems develops a way of thinking that dismisses nonlinear dynamics as spurious oscillations. The linear systems approach oversimplifies the dynamics of nonlinear systems. This paper helps students understand chaotic behavior using simulations of a continuous-time circuit, DC-DC buck converter and a discrete-time system - logistic map. The undergraduate students and teachers can recognize the educational value of chaotic phenomena from them. Practicing engineers will also have more insight of nonlinear circuits and systems by having an exposure to chaotic dynamics.

One Nonlinear PID Control to Improve the Control Performance of a Manipulator Actuated by a Pneumatic Muscle Actuator

Braided pneumatic muscle actuator shows highly nonlinear properties between displacements and forces, which are caused by nonlinearity of pneumatic system and nonlinearity of its geometric construction. In this paper, a new model based on Bouc-Wen differential equation is proposed to describe the hysteretic behavior caused by its structure. The hysteretic loop between contractile force and displacement is dissolved into linear component and hysteretic component. Relationship between pressure within muscle actuator and parameters of the proposed model is discussed. A single degree of freedom manipulator actuated by PMA is designed. On the basis of the proposed model, a novel cascade position controller is designed. Single neuron adaptive PID algorithm is adopted to cope with the nonlinearity and model uncertainties of the manipulator. The outer loop of the controller is to handle position tracking problem and the inner loop is to control pressure. The controller is applied to the manipulator and experiments are conducted. Results demonstrate the effectiveness of the proposed controller.

Design and evaluation of a parallel-series elastic actuator for lower limb exoskeletons

This paper presented a novel compliant actuator used for lower limb exoskeletons. The compliant joint consists of a series elastic actuator (SEA) and parallel elastic (PE) unit. SEA has various advantages as the actuator of assistive exoskeletons, such as low output impedance, impact absorption, precise force control and high stability. We designed and fabricated a novel SEA as the primary joint actuator which is compact, adjustable and low-cost. Meanwhile an additional elastic unit is installed in parallel with the SEA to improve energy utilization by storing and releasing energy during motion cycles. An adaptive stable controller is designed to realize the joint following motion to a virtual limb. The algorithm can identify and compensate the undetermined contact stiffness between the joint output and the virtual limb. Finally, the performance of the actuator is evaluated through motion tracking and energy-conservation experiments. Preliminary results indicate the validity of the design and imply its potential usage in lower limb exoskeletons.