Woosub Lee

Characterization and Properties of P(VdF-HFP)-Based Fibrous Polymer Electrolyte Membrane Prepared by Electrospinning

Microporous fibrous membranes were prepared from poly(vinylidenefluoride-co-hexafluoropropylene) P(VdF-HFP) solutions in an acetone/N,N-dimethylacetamide mixture using the electrospinning method. Varying the P(VdF-HFP) polymer concentration in electrospinning can easily control the pore size and the porosity of the electrospun fibrous membranes (ES-FMs). The usefulness of the ES-FMs as a matrix of polymer electrolyte for a lithium-ion polymer battery with high performance was evaluated. Electrospun fibrous polymer electrolyte membranes (ES-FPEMs) showed excellent electrochemical properties of ionic conductivity, higher than 1 X 10 - 3 S/cm at room temperature, and the electrochemical stability window, up to 4.5 V vs. Li + /Li. At a C/2 rate, the prototype cell using the ES-FPEM showed a good charge/discharge property, with little capacity fade under constant current and constant voltage conditions at 20 and 60°C.

A Robot Joint With Variable Stiffness Using Leaf Springs

Interaction with humans is inevitable for service robots, which results in safety being one of the most important factors in designing the robots. Compliant component is an answer to the safety issue at the cost of performance degradation. In order to reduce the performance degradation, manipulators equipped with variable stiffness have been studied by many researchers. This paper presents a variable stiffness joint (VSJ) designed for a robot manipulator, as well as a control scheme to control the stiffness and position of the VSJ. Compliance is generated by leaf springs and two actuators are used to control the position and stiffness of the joint using four-bar linkages. Two actuators in parallel configuration are connected to the spring. Changing the effective length of the spring results in a change in stiffness. The position of the joint is controlled via two actuators rotating at the same speed in the same direction. A nonlinear controller is used to control the VSJ, and a singular perturbation model is adopted to prove the stability of the closed-loop system. Experiments are conducted to show that the position and stiffness are controlled independent of each other, and having less stiffness at the joint helps in making an unexpected collision with an object safer.

Electrochemical and Spectroscopic Properties of Electrospun PAN-Based Fibrous Polymer Electrolytes

Microporous fibrous polymer electrolytes were prepared by immersing electrospun poly(acrylonitrile) (PAN)-based fibrous membranes into lithium salt-based electrolytes. They showed high ionic conductivities of up to 1.0 X 10 - 3 S/cm at 20°C, and sufficient electrochemical stabilities of up to 4.5 V. Their ion conduction depended on the physicochemical properties of the lithium salt-based electrolytes trapped in pores, as well as on the interactions among the Li + ion, the carbonate, and the PAN. From the Fourier transform-Raman data, lithium ion transport was mainly achieved by the lithium salt-based electrolytes in pores via the interaction between the Li + ion and the C=O group of carbonate molecules, and was also affected by the PAN through the interaction between the Li + ion and the C≡N groups of PAN. Their electrochemical stabilities were enhanced by the swelling of the electrospun PAN nanofibers because of the dipolar interaction between the C≡N groups of PAN and the C=O groups of carbonate in the lithium salt-based electrolytes. Prototype cells using electrospun PAN-based fibrous polymer electrolytes thus showed different cyclic performances, according to the composition of the lithium salt-based electrolytes. The prototype cell with 1 M LiPF 6 -ethylene carbonate/dimethyl carbonate (1/1) showed the highest discharge capacity and the most stable cyclic performance among them.

Design of a robot joint with variable stiffness

A robot joint with a variable stiffness unit is presented. The variable stiffness unit (VSU) is composed of a motor, two rings that consist of arc-shaped magnets separated by spacers, and a linear guide to change the cross-sectional area of the two rings. Angular displacement between two rings causes the magnets to generate torque, which acts as a nonlinear spring. The stiffness of the joint is varied via changing the overlapping area of the magnets. The VS J exhibits nearly zero stiffness, which enables robot manipulator to be harmless to humans at a wide range of operating speed. Connected to a joint motor in series, the stiffness by the VSU and the position of the joint are controlled independently by two motors. The torque generated by the magnets is analyzed. Using dynamics of the joint, feedback linearization method is adopted to control the VSJ. In addition to feedback linearization, an integral controller is augmented in order to reduce the effect of model uncertainty and disturbances.

A variable stiffness joint using leaf springs for robot manipulators

Safety of a manipulator designed to be used at home requires different approach than industrial robots, where safety is achieved mainly by decreasing the interaction with humans. Robots for applications at home, however, require frequent interaction with humans. Introducing compliant component gives the answer to the safety issue at the cost of performance degradation. In order to reduce the performance degradation, manipulators equipped with variable stiffness have been studied by many researchers. This paper presents a variable stiffness joint(VSJ) designed for a robot manipulator. The stiffness is generated by leaf springs and two actuators are used to control the position and stiffness of the joint. Changing the effective length of the spring results in change in stiffness. The position of the joint is controlled via rotating two actuators at the same speed in the same direction. The stiffness is controlled when the two actuators rotate in the different speed. Experiments are conducted to show that the position and stiffness are controlled independent with each other and having less stiffness at the joint helps in making unexpected collision with object safer.

Rough Terrain Negotiable Mobile Platform with Passively Adaptive Double-Tracks and Its Application to Rescue Missions

This paper presents design and integration of the ROBHAZ-DT3, which is a newly developed mobile robot system with chained double-track mechanisms. A passive adaptation mechanism equipped between the front and rear body enables the ROBHAZ-DT3 to have good adaptability to uneven terrains including stairs. The passive adaptation mechanism reduces energy consumption when moving on uneven terrain as well as its simplicity in design and remote control, since no actuator is necessary for adaptation. Starting from this novel design, dynamic analysis and simulation were conducted to verify the mobility of the double-track mechanism and to obtain significant design parameters such as a suitable track size and an allowable attack angle. Based on this novel mobile platform, a rescue version of the ROBHAZ-DT3 with appropriate sensors and a semi-autonomous mapping and localization algorithm is developed to participate in the RoboCup2004 US-Open: Urban Search and Rescue Competition. From the various experiments in the realistic rescue arena, we can verify that the ROBHAZ-DT3 is reliable in travelling rugged terrain and the proposed mapping and localization algorithm are effective in the unstructured environment with uneven ground.

ROBHAZ-DT3: teleoperated mobile platform with passively adaptive double-track for hazardous environment applications

In this paper, design and integration of the ROBHAZ-DT3 are introduced which is a newly developed mobile robot system with double tracks. It is designed to curry out military and civilian missions in various hazardous environments. The rotational passive adaptation mechanism equipped between the front and rear body enables the ROBHAZ-DT3 to have good adaptability to uneven terrain including stairways. The passive adaptation mechanism reduces energy consumption in moving on uneven terrain as well as it offers simplicity in design and teleoperation. Based on this new design concept, dynamic simulation was conducted to determine the significant parameters such as optimal track size and allowable attack angle. Also dynamic effects in vehicle turning are investigated to assess proper load torque. The ROBHAZ-DT3 system developed was successfully experimented in stair climbing case.

Mechanical analysis for crack-free release of chemical-vapor-deposited diamond wafers

Chemical-vapor-deposited (CVD) diamond thick films for electronic applications must be released without cracks from the substrate as freestanding wafers. In this study, the mechanism of cracking in the CVD films was investigated experimentally and theoretically. Experimental observations showed that cracks initiated at the edge of the diamond wafer and then propagated towards the center. Finite-element analysis (FEA) reveals that, during cooling, compressive thermal stresses concentrate at the thick films edge and additional tensile stress acts circumferentially. This was verified by the experimental analysis of diamond films deposited on Si, Mo and W substrates. Observations on low interfacial adhesion and crack-free film on the W substrate indicated that, in addition to the high thermal stress, low interfacial adhesion plays an important role in cracking. Thus, film cracking depends on the fracture strength of the film and its relative magnitude with respect to interfacial adhesion. Methods of crack suppression were suggested on the basis of this cracking mechanism: increase of film thickness and minimization of the substrates CTE and interfacial adhesion. The analysis was confirmed by successful suppression of cracking by application of a low-adhesion interlayer prior to deposition of diamond film.

Spring-Clutch: A safe torque limiter based on a spring and CAM mechanism with the ability to reinitialize its position

Service robots are anticipated to be used in unstructured areas such as homes, hospitals, and public areas in the near future. However, safety issues need to be addressed before this can occur. In particular, robot manipulators that handle objects by physical contact run the risk of colliding with people or objects. Thus, it is important to prevent collisions that could injure people and damage robot manipulators. In this study, a safe joint mechanism is developed to ensure the safe use of a manipulator. This mechanism, termed ‘Spring-Clutch,’ is a simple passive mechanism that consists of a coil spring and a CAM mechanism. When a torque is applied that is less than a threshold value, Spring-Clutch functions as a rigid joint between the input and the output. However, when an applied torque exceeds the threshold, angular displacement occurs between the input and output to reduce the collision force. If the applied torque is removed, Spring-Clutch immediately returns to its nominal position without the need for additional operations. This paper describes the design principles and performance of Spring-Clutch, and discusses the possibility of its practical use as a joint mechanism for safe manipulation.

Intrinsic stress in chemical vapor deposited diamond films: An analytical model for the plastic deformation of the Si substrate

The intrinsic stress in diamond film deposited on a Si substrate is difficult to measure because high-temperature deposition induces plastic deformation in the Si and so renders useless an elastic solution. In this study, an analytical model is proposed to estimate intrinsic stress using a substrate-curvature technique and considering the plastic deformation of substrate. The stress distribution of the as-deposited film is affected not only by the intrinsic stress of the film but also by the bending and plastic deformation of the substrate. In this model, the distribution is formulated, based on elastic/plastic plate-bending theory, in terms of substrate curvatures, intrinsic stress in the film, and yield stress of the substrate. The intrinsic stress of the film together with the yield stress of the substrate can be obtained from experimentally measured substrate curvatures by solving two equilibrium equations and a moment-relaxation equation describing the film removal. Diamond films were deposited by mi...