Switching contact task control in hydraulic actuators: Stability analysis and experimental evaluation

A switching contact task control for hydraulic actuators is proposed. The controller is built upon three individually designed control laws for three phases of motion: (1) position regulation in free space, (2) impact suppression and stable transition from free to constrained motion and (3) force regulation in sustained‐contact motion. The position and force control schemes are capable of asymptotic set‐point regulation in the presence of actuator friction and without the complexity of sliding mode or adaptive control techniques. The intermediate impact control scheme is included for the first time to dampen the undesirable impacts and dissipate the impact energy that could potentially drive the whole system unstable. The solution concept and the stability of the complete switching control system are analyzed rigorously using the Filippov's solution concept and the concept of Lyapunov exponents. Both computer simulations and experiments are carried out to demonstrate the efficacy of the designed switching control law. Copyright © 2009 John Wiley & Sons, Ltd.     

Honeycomb Wachspress finite elements for structural topology optimization

Traditionally, standard Lagrangian-type finite elements, such as linear quads and triangles, have been the elements of choice in the field of topology optimization. However, finite element meshes with these conventional elements exhibit the well-known “checkerboard” pathology in the iterative solution of topology optimization problems. A feasible alternative to eliminate such long-standing problem consists of using hexagonal (honeycomb) elements with Wachspress-type shape functions. The features of the hexagonal mesh include two-node connections (i.e. two elements are either not connected or connected by two nodes), and three edge-based symmetry lines per element. In contrast, quads can display one-node connections, which can lead to checkerboard; and only have two edge-based symmetry lines. In addition, Wachspress rational shape functions satisfy the partition of unity condition and lead to conforming finite element approximations. We explore the Wachspress-type hexagonal elements and present their implementation using three approaches for topology optimization: element-based, continuous approximation of material distribution, and minimum length-scale through projection functions. Examples are presented that demonstrate the advantages of the proposed element in achieving checkerboard-free solutions and avoiding spurious fine-scale patterns from the design optimization process.     

大型绘画中丙烯材料应用与优越性表现

丙烯画材是目前在壁画、架上绘画等大型绘画作品中使用广泛的新型绘画材料,为了更好地认识并发挥丙烯的材料优势,本文就丙烯材料画特性及其在大型绘画创作和绘制型壁画中的实际应用与表现进行初步的研究和探讨。     

从茶具材质发展谈产品设计专业的材料教学

现今的产品设计材料教学,很大程度上仅仅局限在对材料本身的讲授,而没有把材料置于设计中,将材料的设计表现意义传达出来,这种对材料片面性的理解势必影响学生在设计中对材料的充分使用。本文就以茶具为例,透过茶具材质的发展来探讨材料对于设计的深层意义,并且提出在产品设计的材料教学中,应该在设计的大前提之下对材料知识进行全面的讲授与科学的分析。     

设计素描中材质感的表现在时装画中的应用

本文介绍了设计素描的概念和研究要素,指出设计素描中材质感的表现形式——线和明暗,并从时装面料和服饰配件两方面阐述了线和明暗在时装画中的应用,为我们认识、理解和感悟设计素描在服装设计中的作用提供了切入点。     

Iterative control approach to high-speed force-distance curve measurement using AFM: time-dependent response of PDMS example

Force-distance curve measurements using atomic force microscope (AFM) has been widely used in a broad range of areas. However, currently force-curve measurements are hampered the its low speed of AFM. In this article, a novel inversion-based iterative control technique is proposed to dramatically increase the speed of force-curve measurements. Experimental results are presented to show that by using the proposed control technique, the speed of force-curve measurements can be increased by over 80 times--with no loss of spatial resolution--on a commercial AFM platform and with a standard cantilever. High-speed force curve measurements using this control technique are utilized to quantitatively study the time-dependent elastic modulus of poly(dimethylsiloxane) (PDMS). The force-curves employ a broad spectrum of push-in (load) rates, spanning two-order differences. The elastic modulus measured at low-speed compares well with the value obtained from dynamic mechanical analysis (DMA) test, and the value of the elastic modulus increases as the push-in rate increases, signifying that a faster external deformation rate transitions the viscoelastic response of PDMS from that of a rubbery material toward a glassy one.     

新型水温控制系统的设计与实现

针对磁滞伸缩材料在应用中对温度的要求,设计了基于逻辑规则控制算法的水温控制系统。该系统根据设定温度与实测温度形成的偏差及偏差变化率,按照一定的规则调节PWM脉冲的占空比大小,从而调节了加热设备的输出功率。实际测试表明,系统超调量小,上升时间快,控制精度达到了0．1℃。     

潜艇推进器模型参考模糊自适应PID控制方法研究

本文主要介绍了模型参考模糊自适应PID控制在潜艇推进液压伺服系统中的应用。潜艇推进液压伺服系统因随外界环境的变化而变化,因此常规PID控制无法满足要求,本文采用模型参考模糊自适应PID控制对其进行控制,并对控制结果进行仿真分析,通过与传统PID控制进行比较从而得出该控制方法可以有效抑制负载干扰和参数扰动,具有很强的鲁棒性。     

Harmonic potential in media of inhomogeneous hydraulic conductivity

The hydraulic conductivityK of inhomogeneous isotropic saturated stable porous media is computed from the observed or known piezometric head for the special case of harmonic potentials when the streamlines and the iso-K lines are orthogonal to the isopiestic or equipotential surfaces.     

含泥砂河流水轮机增容改造的探讨─刘家峡2~＃水轮机增容改造

本文简要叙述了刘家峡电厂水轮机增容改造中的水力研究、结构设计、中间试验、材料选择以及制造工艺等方面内容,并探讨了减轻泥砂磨蚀的措施。该水轮机的增容改造经验对含泥砂河流水轮机的设计与改造是有益的。