OBSERVATIONS ON THE DESIGN OF DISTRIBUTED ARMATURE WINDING BY POLY PHASE SYMMETRISATION

ABSTRACT

The generalised process of designing distributed poly-phase armature windings by the technique of symmetrization offers special advantages in developing dedicated machines for operation with non-sinusoidal supplies.

Principles of symmetrization have been reviewed with special reference to 3-phase windings and important rules governing the applications of the process have been enumerated, both with reference to single-speed balanced and unbalanced windings as well as multi-speed windings.

Although such special windings in general, have wider harmonic spectra compared to standard designs, a judicious selection of symmetrised windings can, in fact prove beneficial in specific cases. The paper attempts to lay down the procedure for systematic design of 3-phase symmetrised windings.     

Effect of anodization on corrosion behaviour and biocompatibility of Cp-titanium in simulated body fluid

The objective of this investigation is to study the effectiveness of anodized surface of commercial purity titanium (Cp-Ti) on its corrosion behaviour in simulated body fluid (SBF) and proliferation of osteoblast cells on it, to assess its potentiality as a process of surface modification in enhancing corrosion resistance and osseointegration of dental implants. Highly ordered nano-porous oxide layer, with nano-sized pores, is developed on the surface of Cp-Ti through electrochemical anodization in the electrolyte of aqueous solution of 0·5% HF at 15 V for 30 min at 24 °C. The nano-porous feature of the anodized surface is characterized by field-emission scanning electron microscope (FESEM). Pores of some anodized samples are sealed by exposing the anodized surface in boiling water. Corrosion behaviour of the anodized specimen is studied in Ringer’s solution at 30 ± 2 °C, using electrochemical impedance and cyclic polarization technique. Biocompatibility of the anodized surface is accessed using MG63 osteoblast cells. Both corrosion as well as pitting resistance of Cp-Ti in simulated body fluid are found to be highest in the anodized and sealed condition and followed in decreasing order by those of anodized and unanodized ones. Significantly higher MG63 osteoblast cell proliferations are found on the anodized surface than that on the unanodized one. Anodized Cp-Ti develops nano-size surface pores, like that of natural bone. It enhances corrosion and pitting resistance and also the process of osteoblast cell proliferation on Cp-Ti.     

Trajectory control of a PUMA robot arm by inversion and servocompensation

Based on invertibility and functional reproducibility, an approach to the control of the PUMA arm with six rotational degrees of freedom is presented. The control system has two important features: (i) the ability for fast, precise trajectory tracking; and (ii) robustness to uncertainty in the system, such as variable payload, inertia, etc. The control law derived using invertibility gives decoupled, independently controlled responses in each joint angle using torquers. For robustness, a first-order servocompensator is designed for each decoupled inner loop driven by the joint angle error. For smooth joint angle responses, a command generator is constructed that produces the reference trajectories to be tracked. Simulation results are presented to show that rapid, accurate trajectory following is achieved in the closed-loop system in spite of large payload uncertainty.     

The estimation of atmospheric corrections to one-channel (11 μ m) data from the AVHRR; simulation using AVHRR/ 2

It has been established that the sea-surface brightness temperatures Tb₄ in the 11 μ m channel and T_b4in the 12 μ m channel of the Advanced Very High Resolution Radiometer (AVHRR/ 2) are linearly related to a good degree of accuracy, i.e. T_b5= α+ β T_b4 Using AVHRR/ 2 data for various dates and from different parts of the world's oceans, the parameters a and 0 have been determined. The above relation may then be used for simulating T_b5 for those cases for which only Tb4 is available (e.g. for the AVHRR on TIROS-N, NOAA-6, NOAA-8, etc.). The brightness temperature TM and pseudo-brightness temperature T_b5 then enable one to use the split-window technique for estimating atmospherically-corrected sea-surface temperatures (SSTs) from the 11μ m channel data alone. Such an atmospheric correction technique should be a possibility because the 11μ m channel of the AVHRR on the various satellites in question are almost identical

This technique has been used with two split-window algorithms for correcting the data from the 11μ m channel of the AVHRR instrument on the TIROS-N satellite obtained off south-western Portugal. One of the algorithms gives ‘ skin’ temperatures and the other algorithm gives bulk temperatures. The resulting SSTs for twelve dates from 15 June 1979 to 14 June 1980 have been compared with sea-surface (skin) temperatures which were obtained with airborne radiometer data obtained on the same dates.     

HEAT TRANSFER IN MULTIPHASE CONTACTORS

A procedure for the prediction of wall-bed heat transfer coefficient for bubble columns and gas-solid fluidized beds is developed on the basis of hydrodynamic behavior of these contactors. A comparison between the predicted and experimental values of heat transfer coefficient over a wide range of design and operating variables is presented. An attempt is made to analyze the occurrence of maxima in heat transfer coefficient with respect to gas velocity in the case of fluidized beds. A procedure for the calculation of the optimum superficial gas velocity is outlined.