Input-dependent stability of joint torque control of tendon-drivenrobot hands

The input-dependent stability observed during torque control experiments using the first joint of the Darmstadt-HAND is discussed. Friction and compliance existing in tendon-sheath drive systems introduce a hysteresis nonlinearity between the joint torque output and the actuator displacement. Although this transmission characteristic is close to the well-known backlash behavior of the gears situated between a motor and a load shift, this hysteresis loop exhibits input-dependent characteristics in the backlash region of the transmission system, with springlike behavior within a portion of the backlash region. Experiments confirmed that there is a close relationship between the input-dependent backlash characteristics and the input-dependent stability. Based on these experiments, the authors describe the transmission characteristic using a simple model and explore the system stability using sinusoidal-input-describing-functions (SIDF). A nondimensional stability-criterion-map that successfully predicts the experimental results is presented     

Effect of addition of saccharose on gelation of aqueous poly(vinyl alcohol) solutions

The properties of poly(vinyl alcohol) (PVA) hydrogels containing saccharose were examined. The effect of the addition of saccharose to atactic PVA (α-PVA) gels on their melting temperatures was larger than that for syndiotacticity-rich PVA (s-PVA) gels and the melting temperature was above 100°C for α-PVA gels with saccharose contents of 60 wt %. However, the fusion enthalpy (ΔH) of the α-PVA gels was at most 100 kJ/mol. The release of solvent (water/saccharose) from gels in air decreased with an increase in the saccharose content and the equilibrium was achieved after standing for 20 days for the α-PVA and s-PVA gels with saccharose contents above 40 and 20 wt %, respectively. © 1995 John Wiley & Sons, Inc.     

Study on thermal-hydraulic behavior during molten material and coolant interaction

In a core disruptive accident (CDA) of a Fast Breeder Reactor, the post accident heat removal (PAHR) is crucial for the accident mitigation. The molten core material should be solidified in the sodium coolant in the reactor vessel. The material, being fragmented while solidification and forming debris bed, will be cooled in the coolant.

In the experiment, molten material jet is injected into water to experimentally obtain the visualized information of the fragmentation and boiling phenomena during PAHR in CDA. The experiment shows that the break up of the molten material into fine fragments is observed at the front, side and middle part of the jet during very short time interval. The distributed particle behavior of the molten material jet is observed with high-speed video camera. And the visual data is analyzed with Particle Imaging Velocimetry (PIV).

The experimental results are compared with the existing theories. Consequently, the marginal wavelength on the surface of a water jet is close to the value estimated based on the Rayleigh–Taylor instability. Moreover, the fragmented droplet diameter obtained from the interaction of molten material and water is close to the value estimated based on the Kelvin–Helmholtz instability.     

Frequency responses of spherically contoured rectangular AT-cut quartz crystal resonators fabricated by fixed abrasive method

Frequency responses of spherically contoured rectangular AT-cut quartz crystal resonators fabricated by fixed abrasive method have been analyzed experimentally. Not only the required mode, but also many spurious modes can exist on rectangular AT-cut plates. Empirically, in order to eliminate the spurious modes and to achieve high stable and reliable quartz crystal resonators, quartz crystal blanks have been polished into lens-like shape (spherically contoured shape). The spherically contoured blanks have a drastic effect on the decoupling of modes by restricting the vibrating area of the plate within its central region (energy trapping effect). However, a long process time is necessary to fabricate the quartz blanks into spherically contoured shape. In our previous works, a fixed abrasive method has been introduced as a new rotary barrel finishing method for finishing the spherically contoured blanks. In this paper, the frequency responses and the shape of the spherically contoured resonators fabricated with different process times have been presented and discussed. As a result, resonators with very little spurious at 15 MHz within 2 MHz bandwidth have been successfully fabricated.     

Structural and surface property changes of macadamia nut-shell char upon activation and high temperature treatment

Structural and surface property changes of macadamia nut-shell (MNS) char upon activation and high temperature treatment (HTT) were studied by high-resolution nitrogen adsorption, diffuse reflectance infra-red Fourier transform spectroscopy, X-ray photoelectron spectroscopy, and temperature-programmed desorption. It is found that activation of MNS char can be divided into the low extent activation which may involve the reactions of internal oxygen-containing groups and leads to the formation of comparatively uniform micropores, and the high extent activation which induces reactions between carbon and activating gas and produces a large amount of micropores. The surface functional groups (SFGs) basically increase with the increase of activation extent, but high extent activation preferentially increases the amount of -C-O and -CO. HTT in air for a short time at a high temperature (1173 K) greatly increases the micropore volume and the amounts of SFGs. By appropriately choosing the activation and HTT conditions, it is possible to control both the textural structure and the type and amounts of SFG.     

“In Situ” Observation of Smelting Reduction and Carburization of Iron Ore with Carbonaceous Materials by Laser Scanning Microscope

It is a very valuable key technology to accelerate the rates of smelting reduction of iron ore and the succeeding carburization at low temperatures for lower energy consumption in the iron‐making process. It is well known that the smelting reduction and carburization are very complicated phenomena, but the mechanism has not yet been brought into daylight. It is considered that the molten iron oxide containing slag among carbonaceous materials and reduced iron is strongly concerned in the phenomena. Thereupon, an experimental model is made in the present work, and “in situ” observation was made on the smelting reduction and carburization phenomena at iron‐making temperatures by a laserscanning microscope. The mechanism of the phenomena is discussed based on the observed results and concentration profiles of carbon in quenched iron samples.     

Influences of cellular components and redox potential of liquid concentrated culture of Lactobacillus bulgaricus on acid-producing activity and viability

Acid-producing activity and viability of the liquid concentrated culture of Lactobacillus bulgaricus 1067 were markedly improved only when the cells were grown in a medium supplemented with Span 80 and then stored with .1% sodium ascorbate after addition of bubbling N2 into the culture. Oleic acid content of the cells increased from 17 to 38% to 39 to 54%, and the endothermic transition of the cell lipids shifted to a lower temperature when growth medium was supplemented with Span 80. During storage, the cells grown in the medium supplemented with Span 80 consumed a larger amount of lactose than those grown without Span 80. Also, the former cells had more ATP than the latter after storage at 5 degrees C for 14 d. Permeability of the cells for lactose might be improved by increased oleic acid content of the cellular components in which care the lactose incorporated into the cells would be utilized as the energy source during storage.