Xizhe Zang

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.

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.

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.

Design of a biped robot actuated by pneumatic artificial muscles

High compliant legs are essential for the efficient versatile locomotion and shock absorbency of humans. This study proposes a biped robot actuated by pneumatic artificial muscles to mimic human locomotion. On the basis of the musculoskeletal architecture of human lower limbs, each leg of the biped robot is modeled as a system of three segments, namely, hip joint, knee joint, and ankle joint, and eleven muscles, including both monoarticular and biarticular muscles. Each rotational joint is driven by a pair of antagonistic muscles, enabling joint compliance to be tuned by operating the pressure inside the muscles. Biarticular muscles play an important role in transferring power between joints. Walking simulations verify that biarticular muscles contribute to joint compliance and can absorb impact energy when the robot makes an impact upon ground contact.

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.

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.

Towards MOOCs and Their Role in Engineering Education

Massive Open Online Courses (MOOCs) are the latest installment in the field of distance education. This paper discusses the pros and cons of MOOCs in the educational systems with a special emphasis on the engineering education. Since 2012, more and more universities have been joining MOOC revolution and the number of online courses has considerably increased over time. Engineering MOOCs are also increasing. Due to their access to large audience, massive online courses have been expanding their horizon of admission to engineering education at all levels and improving the in-campus learning.

The analysis on period doubling gait and chaotic gait of the compass-gait biped model

The passive dynamic walking model, which can only depend on the gravity and its own inertia, presents stable, high-efficient, natural periodic gait on a slight slope. The stable periodic gait of the robot has a delicate balance of energy conversion, which makes the gait adjust itself as the parameters of the model change. In our work, the cell mapping method is combined with Newton-Raphson iteration to obtain the limit cycle of the periodic gait in the model, the track stability of the limit cycle is analyzed, and the eigenvalues change rule of Poincaré Jacobi matrix is deduced. The influence of changing parameters on the gait is analyzed and discussed by simulations on the model with different sets of parameters. The result suggests that, the location of the center of leg mass too high or too low, foot radius increase or decrease, the slope or moment of inertia increase, will lead to the occurrence of bifurcation of the gait period and chaos; while the way the gait enters chaos from period doubling bifurcation, which results from different parameters change, obeys the law all the period doubling bifurcation share, that is, it has the same Feigenbaum constant. Furthermore, the dynamic features of the robot at the entrance of the chaos are obtained by the rule of the period doubling bifurcation of the gait; meanwhile, it can be found by the analysis of the gait features in the chaos area that there is also certain periodic law in the chaotic gait.

Are MOOCs Advancing as Predicted by IEEE CS 2022 Report

Few trends in education in the last century match the sudden onset of Massive Open Online Courses (MOOCs). The modern MOOC movement started in late 2011, when the first standard MOOC was launched. In few years, MOOCs have received immense coverage in media, academia and industry. MOOCs have established one of the key facts that education is no longer a privilege but a basic right. Students can learn any imaginable subject from the worlds top professors and industry experts. Massive online courses have also increased interest in online learning. Current online learning is a classic disruptive innovation as it is economical and of high quality. The main aim of this paper is to analyze the state of the art in MOOCs since the IEEE CS Report 2022 was made public.