Fabrication, bonding, assembly, and testing of metal-based microchannel devices

Microsystem technologies are believed to be an important part of the contemporary technological foundation and are becoming a commercially significant specialty area in manufacturing. The design and fabrication of microscale engineering structures has the potential of generating revolutionary changes in many products over a wide range of industrial sectors. Metal-based microchannel heat exchangers (MHEs) promise high heat transfer coefficients together with mechanical robustness, and are of interest for a wide range of applications. Fabrication technologies capable of creating high-aspect-ratio microscale structures (HARMSs) in metals such as Cu at low cost and high throughput are of particular interest. Likewise, simple and reliable bonding and assembly techniques are critical for building functional metal-based microfluidic devices. This dissertation focuses on various aspects of fabrication, bonding, assembly, and testing of metal-based microdevices. In chapter 1, existing techniques for fabricating metal-based HARMSs are reviewed briefly and compared with each other. A new technique for fabricating metal-based HARMSs, high temperature compression molding, is introduced. Two related issues, bonding and assembly of metal-based HARMSs and testing of assembled metal-based microdevices are discussed respectively. In chapters 2-6, Cu- and Al- based HARMSs were successfully bonded using Al or Sn thin foil intermediate layers and co-deposited Al-Ge thin film intermediate layers, respectively. Quantitative evaluation of bond strengths was carried out as a function of various bonding parameters. Tensile bond strengths are shown to be ~30MPa for bonded Cu pieces and to exceed 75MPa, reaching as high as 165MPa, for boned Al pieces. Detailed characterizations of the micro-/nano- scale structure of buried bonding interfaces were conducted to rationalize results of mechanical testing. Chapters 7&8 talk about systematic experimentation of fabrication, bonding, and testing of Cu- and Al- based MHEs, and detailed results and discussion on flow and heat transfer performance of these MHEs under two different testing configurations, constant heat flux and constant wall temperature. The results show the increase of surface roughness in the replicated microchannels can cause significant improvements to microchannel heat exchanger performance. Finally, chapter 9 summarizes this dissertation research with main results and achievements. Future work is also discussed in this chapter

Bovine PrPC directly interacts with αB-crystalline

AbstractWe used a bovine brain cDNA library to perform a yeast two-hybrid assay with bovine mature PrPC as bait. The screening result showed that αB-crystalline interacted with PrPC. The interaction was further evaluated both in vivo and in vitro with different methods, such as immunofluorescent colocalization, native polyacrylamide-gel electrophoresis, and IAsys biosensor assays. The results suggested that αB-crystalline may have the ability to refold denatured prion proteins, and provided first evidence that αB-crystalline is directly associated with prion protein

A Bioinspired Gait Transition Model for a Hexapod Robot

Inspired by the analysis of the ant locomotion observed by the high-speed camera, an ant-like gait transition model for the hexapod robot is proposed in this paper. The model which consists of the central neural system (CNS), neural network (NN), and central pattern generators (CPGs) can produce the rhythmic signals for different gaits and can realize the transition of these gait automatically and smoothly according to the change of terrain. The proposed model suggests the neural mechanisms of the ant gait transition and can improve the environmental adaptability of the hexapod robot. The numerical simulation and corresponding physical experiment are implemented in this paper to verify the proposed method

A Novel Cam-Based Variable Stiffness Actuator: Pitch Curve Synthetic Approach for Reconfiguration Design

Variable stiffness actuators (VSA) have attracted much attention because of their potential for human-like interaction behaviors. This paper devotes to improving the VSA’s versatility. VSA with different characteristics can be obtained by shape reconfiguration of its internal driving cams. The proposed VSA mainly includes a variable stiffness module and a cam-based driven module. A common node connects the two modules. It is placed in the common grooves of the dual cams. Kinematically, the radial position of the node can be changed for stiffness adjustment by cam differential motion. Mechanically, the driven force on this node can be resolved into two orthogonal directions by cam groove, one for stiffness adjustment and another for position balance., The paper establishes the analytical relationship between the pressure angle of the cam pitch curve, stiffness adjustment speed and accuracy, and load distribution. Furtherly, the pitch curve synthetic approach for VSA reconfiguration is provided. A special cam shape with a favorable load distribution is proposed to verify the method. The correctness of the design was effectively proved by experiments in the virtual model and physical prototype

Design and Experiment Evaluation of Load Distribution on the Dual Motors in Cam-Based Variable Stiffness Actuator with Helping Mode

This paper presents a novel cam-based variable stiffness actuator (VSA). It significantly differs from its counterparts in that the external load distributes on its two motors with a small difference. It is a feasible method to improve VSA’s output power, especially in compact joints, such as rehabilitation devices. The stiffness adjustment involves a spring-balanced crank-slider mechanism with a variable-length base frame. Its tunable node is the common node for force decomposition, synthesis, stiffness adjustment, and position control by setting it at the common groove of two differential variable-pitch cams. The paper establishes analytical expressions among the pressure angle of the cam pitch curve, load distribution, and its crucial design indexes and constraints. Based on this, the pitch curve synthesis method is put forward to optimize the load distribution. In addition, a reasonable tradeoff can be easily made by locally adjusting the cam pressure angle. So, the dual motors can work against the output load together in the same direction with a close amount. In the fabricated prototype, current stratification caused by the unstable friction direction has been observed. The estimation results of motor frictionless current matched the designed load distribution behavior

Design and Experiment Evaluation of Load Distribution on the Dual Motors in Cam-Based Variable Stiffness Actuator with Helping Mode

This paper presents a novel cam-based variable stiffness actuator (VSA). It significantly differs from its counterparts in that the external load distributes on its two motors with a small difference. It is a feasible method to improve VSA’s output power, especially in compact joints, such as rehabilitation devices. The stiffness adjustment involves a spring-balanced crank-slider mechanism with a variable-length base frame. Its tunable node is the common node for force decomposition, synthesis, stiffness adjustment, and position control by setting it at the common groove of two differential variable-pitch cams. The paper establishes analytical expressions among the pressure angle of the cam pitch curve, load distribution, and its crucial design indexes and constraints. Based on this, the pitch curve synthesis method is put forward to optimize the load distribution. In addition, a reasonable tradeoff can be easily made by locally adjusting the cam pressure angle. So, the dual motors can work against the output load together in the same direction with a close amount. In the fabricated prototype, current stratification caused by the unstable friction direction has been observed. The estimation results of motor frictionless current matched the designed load distribution behavior

Distributed H∞ and H2 Time-Varying Formation Tracking Control for Linear Multi-Agent Systems with Directed Topologies

In this paper, the H∞ and H2 time-varying formation tracking problems for multi-agent systems with directed topologies in the presence of external disturbances are investigated. The followers need to achieve the desired time-varying formation during movement and simultaneously track the state trajectory generated by the leader. First, a distributed consensus protocol based on the local state information of neighbors of the agents for solving H∞ and H2 time-varying formation tracking problems are proposed without utilizing global information about the entire agents. The conditions to achieve H∞ and H2 time-varying formation tracking in the presence of external disturbances are suggested respectively. Then, to determine the parameters of the designed protocol which satisfy suitable conditions, algorithms for H∞ and H2 time-varying formation tracking in the form of pseudo-code are presented, respectively. Furthermore, the proofs of the proposed theorems are derived by utilizing algebraic graph theory and Lyapunov analysis theory tools to demonstrate the closed-loop stability of the system in the presence of external disturbances. Finally, the usefulness and effectiveness of the approaches proposed are demonstrated by numerical simulation examples

Distributed <i>H</i>_∞ and <i>H</i>₂ Time-Varying Formation Tracking Control for Linear Multi-Agent Systems with Directed Topologies

In this paper, the H∞ and H2 time-varying formation tracking problems for multi-agent systems with directed topologies in the presence of external disturbances are investigated. The followers need to achieve the desired time-varying formation during movement and simultaneously track the state trajectory generated by the leader. First, a distributed consensus protocol based on the local state information of neighbors of the agents for solving H∞ and H2 time-varying formation tracking problems are proposed without utilizing global information about the entire agents. The conditions to achieve H∞ and H2 time-varying formation tracking in the presence of external disturbances are suggested respectively. Then, to determine the parameters of the designed protocol which satisfy suitable conditions, algorithms for H∞ and H2 time-varying formation tracking in the form of pseudo-code are presented, respectively. Furthermore, the proofs of the proposed theorems are derived by utilizing algebraic graph theory and Lyapunov analysis theory tools to demonstrate the closed-loop stability of the system in the presence of external disturbances. Finally, the usefulness and effectiveness of the approaches proposed are demonstrated by numerical simulation examples

Preparation and Performance Enhancements of Low-Heat-Releasing Polyurethane Grouting Materials with Epoxy Resin and Water Glass

Polyurethane (PU) grouting materials possess excellent fluidity and strong injectability. However, the high heat release during the reaction process restricts its application. In this study, with the addition of water glass (WG), a prepolymer was prepared by epoxy resin reacted with isocyanate to form modified polyurethane. The effects of epoxy resin and water glass on the compressive properties, expansion rate, structure of the cell, and maximum reaction temperature of the grouting materials were also investigated. The results showed that the cell size of modified PU was smaller and more regular, the maximum reaction temperature of the modified PU was reduced to 89 °C, and the compressive strength and expansion rate went up to 0.27 MPa and 57, respectively. This investigation will expand the application of PU grouting materials in underground engineering