Mukherjee, S. & Waldron, K. 1992, 'An Exact Optimization Of Interaction Forces In 3-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
Murthy, V. & Waldron, K. 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
Nair, S.S., Singh, R., Waldron, K.J. & Vohnout, V.J. 1992, 'Power system of a multi-legged walking robot', Robotics and Autonomous Systems, vol. 9, no. 3, pp. 149-163.
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The power system of a legged vehicle is considerably more complex than the one used by a conventional land vehicle because of the wide range of power demands and the coordination and stability issues due to the large number of degrees of freedom. This paper is concerned with the conceptual and physical characteristics of the power system of a rough terrain, six-legged, walking vehicle. Modelling techniques and detailed analytical and simulation models are developed for the vehicle power system consisting of the prime mover, energy storage system, mechanical drives, hydraulic actuation systems and the associated control systems. Dynamics of the various subsystem and their interactions have been studied for control and optimization purposes. Validation of the models is provided by several experiments performed on a prototype leg and the vehicle. © 1992.
Bawab, S., Kinzel, G.L. & Waldron, K.J. 1992, 'Rectified synthesis of coupler-driven four-bar mechanisms for four-position motion generation', American Society of Mechanical Engineers, Design Engineering Division (Publication) DE, pp. 147-155.
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A rectified synthesis procedure for designing coupler-driven four-bar mechanisms to pass a moving lamina through four precision positions is developed. The procedure includes the elimination of circuit, branch and order defects. This is achieved with the aid of Roberts' linkage. The procedure has been implemented in the interactive synthesis package RECSYN.
Husain, M. & Waldron, K.J. 1992, '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.
Husain, M. & Waldron, K.J. 1992, 'Position kinematics of a mixed mechanism', American Society of Mechanical Engineers, Design Engineering Division (Publication) DE, pp. 41-47.
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Although robotics has traditionally focused on the serial chain structures typical of industrial robots, fully parallel structures such as the Stewart Platform have also found considerable industrial use. Actively coordinated mechanisms which have combinations of serial and parallel characteristics have been practically employed, and can be expected to become more important in the future. There has been very little study of the kinematic and static characteristics of these mechanisms which have been combinations of the characteristics of fully serial and fully parallel structures. This work addresses the direct and inverse position kinematics of such a hybrid mechanism with combination of serial and parallel structure which has multiple, actively controlled actuators. While not the most general possible configuration, this particular case does include many important features of the general mechanism, and the solution obtained gives useful insight for developing a general theory of forward and inverse kinematics which will be equally applicable to serial, parallel and combination structures. Such a theory is necessary for rational design of hardware and software for such systems.
Nanua, P. & Waldron, K.J. 1992, '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.
Song, S.M., Lu, F.H., Chen, N.X. & Waldron, K.J. 1992, 'Determination of the shortest crank in four position synthesis: a numerical apporach', American Society of Mechanical Engineers, Design Engineering Division (Publication) DE, pp. 315-321.
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The shortest crank of a four position synthesis can be determined by solving a statically determinate five-bar structure and a set of seven nonlinear equations have been proposed for this purpose. In this paper a numerical method which can directly solve the shortest crank is presented. It is found that a direct implementation of the original seven equations has two problems: many spurious solutions and poor numerical stability. And the spurious solutions are of the following two types: solutions with incorrect signs of angles and solutions with incorrect geometry. In order to solve the problems, a set of ten equations is developed and parameter perturbation method is applied. Furthermore, a set of eight equations is developed for better numerical stability. Both the ten and eight equations can eliminate the spurious solutions with incorrect geometry. Yet the spurious solutions with incorrect signs of angles can only be rectified after convergence. An automatic search algorithm is included to automatically search the shortest crank in the solution space. Many examples are given to illustrate this numerical approach.
Sreenivasan, S.V. & Waldron, K.J. 1992, 'Drift-free navigation system for a mobile robotic vehicle operating on unstructured terrain', American Society of Mechanical Engineers, Design Engineering Division (Publication) DE, pp. 413-422.
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The orientation and the angular rates of the body of a robotic vehicle are required for guidance and control of the vehicle. In the current robotic systems these quantities are obtained by the use of inertial sensing systems. Inertial sensing systems involve drift errors which can be significant even after the vehicle has traversed only short distances on the terrain. A different approach is suggested here which guarantees accurate, drift-free sensing of the angular position and rates of the vehicle body. A camera system consisting of two cameras in fixed relationship to one another is made to continuously track two stationary objects. The camera system is mounted on the vehicle body through an actuated three degree of freedom joint. The angular positions and rates of these joints can be used to evaluate the angular positions and rates of the vehicle body. An approximate estimate of the position of the vehicle on the terrain can also be obtained from the sensing system. This can serve as primary system for estimating the vehicle position, or as a backup to a more accurate scheme for obtaining the position of the vehicle on the terrain.
Srikrishna, P. & Waldron, K.J. 1992, 'Unified analysis and implementation of four multiply separated position synthesis of four-bar linkages', American Society of Mechanical Engineers, Design Engineering Division (Publication) DE, pp. 301-308.
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The objective of this paper is to derive analytically the circle-point and center-point curve equations for the synthesis of four-bar linkages for rigid body guidance through four multiply separated design positions. A unified approach is evolved to deal with the different combinations of four finitely and infinitesimally separated design position, namely the PP-P-P, PP-PP and PPP-P cases. The design procedure incorporates the rectification procedures developed by Waldron (1977) to eliminate the branch and order problems and is implemented in the interactive synthesis package RECSYN.
Venkataraman, S.C., Kinzel, G.L. & Waldron, K.J. 1992, '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.