Biped Locomotion by Reduced Ankle Power

Power reduction in the ankle joints of a biped robot is considered inthis paper. Ankles of human beings have small torque and are veryflexible within a certain range of motion (very stiff near and beyondthis range). This characteristic makes foot landing soft and gives agood contact between its sole and the ground. This feature can beimplemented in a biped robot by using a small actuator for the anklejoints. A small actuator consumes less energy and reduces the weightof the leg. With less power in the ankle joints, robot walkingbecomes more difficult to control. This problem can be solved byproviding a feedback control mechanism as presented in this paper. Thecontrol mechanism uses the motion of the body and the swinging leg toeliminate instability caused by the weak ankle. Two locomotionexamples, standing and walking, were investigated respectively toshow the validity of the proposed control scheme. In standing, thecontrol input is the displacement of the ankle joint of thesupporting leg. The control mechanism decides the bending angle ofthe body and the position of the swinging leg. For walking, only thebending angle of the body is used to avoid the discontinuity of thecontrol input. Experimental results are presented to show theeffectiveness of the control mechanism.     

A lower bound for the mixed μ problem

The mixed μ problem has been shown to be NP hard so that exact analysis appears intractable. Our goal then is to exploit the problem structure so as to develop a polynomial time algorithm that approximates μ and usually gives good answers. To this end it is shown that μ is equivalent to a real eigenvalue maximization problem, and a power algorithm is developed to tackle this problem. The algorithm not only provides a lower bound for μ but has the property that μ is (almost) always an equilibrium point of the algorithm     

Taking the load off: investigations of how adaptive cruise control affects mental workload

It has been posited that Adaptive Cruise Control (ACC) represents a new generation of vehicle automation, in that it has the potential to relieve drivers of mental as well as physical workload. The results of previous research however, have raised some confusing issues about the specific effects of Adaptive Cruise Control (ACC) on driver mental workload (MWL)--some studies report reduced MWL compared to manual driving, while others find no effect. Two hypotheses are proposed in an attempt to explain these discrepancies: (a) that any potential MWL reductions due to ACC could be masked by the overriding influence of steering demand; or (b) that the tasks designed in some experiments do not exploit the adaptive nature of the ACC system, therefore precluding any potential benefits. Two related experiments were designed to test these hypotheses. It was found that the main reason for the discrepant findings was the nature of the driving task chosen--constant-speed tasks do not realise the mental workload benefits of ACC. Future researchers using ACC devices are advised to use variable-speed tasks to ensure that all aspects of device functionality are covered.     

In search of online pedagogical models: investigating a paradigm change in teaching through the School for All community

Following a preliminary evaluation of the Web‐mediated School for All in 2002, this study further examines the online teacher role and explores the possible pedagogical models in this Web‐based informal lifelong learning context through a long‐term innovative e‐learning project over a 2‐year period. The author documents the educational rationale, reviews related literature on Web‐based instructional design, and presents longitudinal in‐depth study results based on empirical data collected from the four Web‐course contests held over 2 years from the perspective of outstanding online teachers. Significantly, three categories of six Web‐based pedagogical models induced from this research project are presented, and the rationale for how and why teachers would prefer to use certain teaching models is discussed. In addition, the characteristics of the outstanding online teachers and issues inherent in this alternative mode of a Web‐based informal educational setting are discussed. Finally, more research issues, questions, and possibilities for future research work are raised or identified for further study.     

MMA/MPEOMA copolymers as coating materials for improved blood compatibility: protein adsorption study

Surface-induced thrombosis remains one of the main problems in the development of blood-contacting devices. When a foreign surface comes in contact with blood, the initial blood response is adsorption of blood proteins, followed by platelet adhesion and activation, leading to thrombus formation. A particularly effective polymer for the prevention of protein adsorption and platelet adhesion appears to be polyethylene oxide (PEO). In this study, water-insoluble copolymers of methyl methacrylate (MMA) and methoxy PEO monomethacrylates (MPEOMA) with different PEO molecular weights (200, 400, and 1000) and monomer composition were synthesized and characterized by gel permeation chromatography and ¹H-nuclear magnetic resonance spectroscopy. The synthesized copolymers were coated on glass slides by a spin coating method to prepare PEO-rich surfaces as blood-compatible surfaces. The surface properties of the copolymers and their interaction with blood proteins (albumin, γ-globulin, fibrinogen, and plasma proteins) were investigated by the measurement of water contact angles and by electron spectroscopy for chemical analysis, respectively. It was observed that the protein adsorption on the copolymer surfaces decreased with increasing PEO molecular weight and MPEOMA content in the copolymers. The copolymers with long PEO chains in MPEOMA (MMA/MPEO₀₀₀MA copolymers) were effective in preventing protein adsorption, even though their MPEOMA content was less than the copolymers with shorter PEO chains. © 1999 Kluwer Academic Publishers     

Thin‐walled closed box beam element for static and dynamic analysis

A new displacement‐based finite element is developed for thin‐walled box beams. Unlike the existing elements, dealing with either static problems alone or dynamic problems only with the additional consideration of warping, the present element is useful for both static and dynamic analyses with the consideration of coupled deformation of torsion, warping and distortion. We propose to use a statically admissible in‐plane displacement field for the element stiffness matrix and a kinematically compatible displacement field for the mass matrix so that the present element is useful for a wide range of beam width‐to‐height ratios. The axial variation of cross‐sectional deformation measures is approximated by C⁰ continuous interpolation functions. Numerical examples are considered to confirm the validity of the present element. Copyright © 1999 John Wiley & Sons, Ltd.     

Rule-based personalized comparison shopping including delivery cost

Comparison shopping allows customers to reduce time and effort when searching for product information and prices. However, traditional comparison sites mainly compare product prices without using precise information on delivery cost. To overcome this limitation, we adopted a rule-based comparison shopping framework using the eXtensible Rule Markup Language (XRML) architecture, which computes the exact personalized delivery cost at comparison sites. The prototype ConsiderD, which was developed for this purpose, computes the exact delivery costs considering the shipping rules, destination, delivery speed, and shipping rates. The XRML architecture effectively maintains the consistency of formal rules with the original Web pages. To demonstrate the performance of rule-based comparisons, we conducted an experiment on the purchase of books based on real-world data from five leading online bookstores. This experiment shows that rule-based comparison can significantly outperform data-based comparison in terms of the total cost of product and delivery. We also found that the comparison of delivery cost is very important because the variance of delivery cost can be as big as the variance of book prices itself.     

Efficient parameterisation of nonlinear system models: a comment on Nöel and Schoukens (2018)

Abstract

Nöel, J. P., & Schoukens, J. [2018. Grey-box state-space identification of nonlinear mechanical vibrations. International Journal of Control, 91, 1–22] discuss a methodology for the discrete-time state-space identification of nonlinear systems and apply this to experimental data from the well known Silverbox nonlinear circuit, producing a model characterised by 13 parameters. This model explains the data very well but the parameter estimates are not well defined in the optimisation results, with the very large confidence bounds suggesting that the model is over-parameterised. This comment shows that this is indeed the case and that the data can be explained equally well by an alternative continuous-time, State-Dependent Parameter (SDP) transfer function model with only 6 parameters, the estimates of which are well defined with very tight confidence bounds. The comment also raises questions about how the model form for nonlinear systems such as the Silverbox should be identified and suggests that the Data-Based Mechanistic (DBM) approach to modelling has some advantages in this regard.     

A Robust Control Approach for Hydraulic Excavators Using <Emphasis Type="Italic">μ</Emphasis>-synthesis

In this work, a robust control is applied to the automation of a hydraulic excavator. Hydraulic excavators exhibit complex nonlinear behavior due to the inherent nonlinearity of the hydraulic servo system. Furthermore, the hydraulic excavator is subject to large disturbance forces during interaction with the environment. As a result, conventional feedback control techniques, such as a proportional-integral-derivative (PID) control, fail to provide consistent performance over the whole operation region of the excavator. Especially, when phase-offset errors vary between joints, undesirable motions are generated in the workspace, which evidently degrades the overall performance of the controller. With this in mind, we apply a robust control approach to the autonomous hydraulic excavators. By handling the nonlinearities and disturbances as uncertainties within the joint dynamics, a robust controller is designed by means of μ-synthesis that guarantees robust stability and performance within the given uncertainty bounds. Furthermore, by adopting a common model reference for each joint, we seek to increase the overall performance of tracking the digging trajectory in the workspace. Experimental results of the robust controller conducted on an industrial 21-ton class hydraulic excavator are presented.