Malan, NT, Van Der Merwe, JS, Huisman, HW, Kruger, A, Eloff, FC, Pretorius, PJ & Laubscher, PJ 1992, 'A comparison of cardiovascular reactivity of rural blacks, urban blacks and whites', Stress Medicine, vol. 8, no. 4, pp. 241-246.
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AbstractUrbanization is a worldwide phenomenon and is most often accompanied by an increased prevalence of western‐type diseases like hypertension. The higher cardiovascular reactivity (CVR) of black people compared to white people during passive coping stressors has often been linked to their greater vulnerability to hypertension. Blacks, however, display a lower CVR than whites during active coping stressors. In this study it was found that urban blacks show a higher CVR than whites during a passive coping stressor and a lower CVR than whites during an active coping stressor. However, rural blacks consistently show much higher CVR than either whites or urban blacks during both active and passive coping stressors. It seems that CVR is not only a function of the type of stressor applied but can be altered significantly by environmental factors like those experienced during urbanization.
Mukherjee, S & Waldron, KJ 1992, 'An Exact Optimization of Interaction Forces in Three-Fingered Manipulation', Journal of Mechanical Design, vol. 114, no. 1, pp. 48-54.
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Manipulation with three fingers in frictional contact is known to be an underspecified problem. The minimum norm solution, also referred to as the equilibrating solution field, can be modified by superimposing a linear combination of the resulting null solutions, called the interaction force field. The modification proposed here, applicable to the three-dimensional problem, minimizes the maximum value of the friction angle at the points of contract. A grasp of maximum possible stability under a set of contact and loading conditions is hence achieved.
MURTHY, V & WALDRON, KJ 1992, 'POSITION KINEMATICS OF THE GENERALIZED LOBSTER ARM AND ITS SERIES-PARALLEL DUAL', JOURNAL OF MECHANICAL DESIGN, vol. 114, no. 3, pp. 406-413.
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The generalized lobster arm is a six revolute open kinematic chain with 3 consecutive intersecting pairs of axes. A new solution of the inverse position kinematics problem of this arm which takes advantage of its specific geometry is presented. A compari
Husain, M & Waldron, KJ 1970, 'Direct position kinematics of the 3-1-1-1 Stewart platforms', American Society of Mechanical Engineers, Design Engineering Division (Publication) DE, pp. 89-97.
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In this work, a closed form solution of the direct position kinematics problem of a special class of Stewart Platform is presented. This class of mechanisms has a general feature that the top platform is connected to the six limbs at four locations. Three limbs connect at one location and the remaining limbs connect to the top platform singly at three separate locations. The base platform is connected at six different locations as is the case in the general platform. This particular class of mechanism is termed as 3-1-1-1 mechanism in this paper. It has been shown that there are a maximum of sixteen real assembly configurations for the direct position kinematics problem. This has been verified using a geometric argument also. The numerical example solved in this paper demonstrates that it is possible to obtain a set of solutions which are all real.
Nanua, P & Waldron, KJ 1970, 'Instability and chaos in quadruped gallop', American Society of Mechanical Engineers, Design Engineering Division (Publication) DE, pp. 599-604.
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A dynamic model for the two dimensional quadruped has been developed. The main body is modelled as a rigid bar and each leg consists of a constant stiffness spring, a viscous damper and a force actuator. Based on symmetry principles, a controller has been devised that will enable the quadruped to gallop at constant speed. The controller consists of two parts: an energy controller which will apply the required amount of force through the legs, and the speed controller that will control the forward speed by appropriately placing the legs. It will be shown that the body pitch need not be explicitly controlled. The stability of this controller will be examined using Poincare maps. Stable systems show either periodic or quasi-periodic response. This system also exhibits chaotic behavior and chaotic response leads to instability. The stability of the system with changes in the initial conditions, as well as variations in the system parameters, will also be examined. It will be shown that the system is stable for a range of leg stiffnesses. Outside this range, the system shows chaotic behavior.
Venkataraman, SC, Kinzel, GL & Waldron, KJ 1970, 'Optimal synthesis of four-bar linkages for four-position rigid-body guidance with selective tolerance specifications', American Society of Mechanical Engineers, Design Engineering Division (Publication) DE, pp. 651-659.
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In practical rigid-body guidance problems, very often one or more of the design positions need not be generated exactly. Further, extreme accuracy at the design positions is somewhat pointless considering the inherent limitations in linkage manufacturing processes. This emphasizes the requirement of synthesis techniques to be able to handle tolerance specifications on the nominal design positions. A favorable offshoot of the tolerance incorporation would be the accompanying increase in the solution space of the synthesis problem thereby yielding better linkage solutions.
Waldron, KJ 1970, 'Actively controlled mobility systems', TENCON'92 - Technology Enabling Tomorrow, TENCON'92 - Technology Enabling Tomorrow, IEEE, pp. 332-336.
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© 1992 IEEE. The author discusses the coordination problem which arises in vehicles with large numbers of independently actuated joints designed to operate in unknown terrain. Coordination requires a considerable amount of sensor data. Some of this may be available from sensors required by other machine systems. Other necessary data mandates installation of sensor systems which would not otherwise be required. Much of the technology discussed is based on the adaptive suspension vehicle legged vehicle. An important application area for this technology is in planetary rover vehicles. A number of the diverse designs under study are reviewed with regard to their coordination requirements.
Xianghua Wu & Dissanayake, MWMG 1970, 'A Generalized Classification And Coding System For Computer Aided Process Planning', IEEE International Workshop on Emerging Technologies and Factory Automation,, IEEE International Workshop on Emerging Technologies and Factory Automation,, IEEE, pp. 156-160.
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© 1992 IEEE. Most previous studies on computer aided process planning (CAPP) have shown that conventional group technology (GT) based classification and coding systems do not contain sufficient component information for producing an effective and flexible CAPP system. In this paper we present a generalized classification and coding system which combines GT codes, feature-based codes and specification data bases. The proposed coding system is based on a relational data structure. Information not amenable to coding is stored in data bases. The proposed technique retains all component information necessary for CAPP, which may be easily retrieved using a decoding process. A detailed example to illustrate the proposed method is also presented.
