Experimental Investigations on the Contour Generation of a Reconfigurable Stewart Platform

Reconfiguration of Stewart platform for varying tasks accentuates the importance for determination of optimum geometry catering to the specified task. The authors in their earlier work (Satheesh et al., 2008) have indicated the non availability of an efficient holistic methodology for determining the optimum geometry. Further, they have proposed a solution using the variable geometry approach through the formulation of dimensionless parameters in combination with generic parameters like configuration and joint vector. The methodology proposed provides an approach to develop a complete set of design tool for any new reconfigurable Stewart platform for two identified applications viz., contour generation and vibration isolation. This paper details the experimental investigations carried out to validate the analytical results obtained on a developed Stewart platform test rig and error analysis is performed for contour generation. The experimental natural frequency of the developed Stewart platform has also been obtained.

Kinematics and Dynamics Modeling of a New 4-DOF Cable-Driven Parallel Manipulator

This paper addresses the kinematics and dynamics modeling of a 4-DOF cable-driven parallel manipulator with new architecture and a typical Computed Torque Method (CTM) controller is developed for dynamic model in SimMechanics. The novelty of kinematic architecture and the closed loop formulation is presented. The workspace model of mechanism’s dynamic is obtained in an efficient and compact form by means of natural orthogonal complement (NOC) method which leads to the elimination of the nonworking kinematic-constraint wrenches and also to the derivation of the minimum number of equations. To verify the dynamic model and analyze the dynamical properties of novel 4-DOF cable-driven parallel manipulator, a typical CTM control scheme in joint-space is designed for dynamic model in SimMechanics.

Random Weighting Estimation of One-Sided Confidence Intervals in Discrete Distributions

This paper presents a new random weighting method for estimation of one-sided confidence intervals in discrete distributions. It establishes random weighting estimations for the Wald and Score intervals. Based on this, a theorem of coverage probability is rigorously proved by using the Edgeworth expansion for random weighting estimation of the Wald interval. Experimental results demonstrate that the proposed random weighting method can effectively estimate one-sided confidence intervals, and the estimation accuracy is much higher than that of the bootstrap method.

Computation of the Output Torque, Power and Work of the Driving Motor for a Redundant Parallel Manipulator

Inverse dynamic analysis of the 8-PSS redundant parallel manipulator is carried out in the exhaustive decoupled way. The required output of the torque, the power and the work of the driving motor are achieved. The whole actuating torque is divided into four terms which are caused by the acceleration, the velocity, the gravity, and the external force. It is also decoupled into the components contributed by the moving platform, the strut, the slider, the lead screw, the motor rotor-coupler, and the external force. The required powers contributed by the component of torque caused by the acceleration term, the velocity term, the gravity term, the external force term, and the powers contributed by the moving platform, the strut, the slider, the lead screw, and the motor rotor-coupler are computed respectively. For a prescribed trajectory, the required output work generated by the ith driving motor is obtained by the presented numerical integration method. Simulation for the computation of the driving motor’s output torque, power and work is illustrated.

Optimal Robot Path Planning with Cellular Neural Network

This paper presents a new methodology based on neural dynamics for optimal robot path planning by drawing an analogy between cellular neural network (CNN) and path planning of mobile robots. The target activity is treated as an energy source injected into the neural system and is propagated through the local connectivity of cells in the state space by neural dynamics. By formulating the local connectivity of cells as the local interaction of harmonic functions, an improved CNN model is established to propagate the target activity within the state space in the manner of physical heat conduction, which guarantees that the target and obstacles remain at the peak and the bottom of the activity landscape of the neural network. The proposed methodology cannot only generate real-time, smooth, optimal, and collision-free paths without any prior knowledge of the dynamic environment, but it can also easily respond to the real-time changes in dynamic environments. Further, the proposed methodology is parameter-independent and has an appropriate physical meaning.

Which is Better?

Natural multiped gaits are believed to evolve from countless generations of natural selection. However, do they also prove to be better choices for walking machines? This paper compares two surefooted gaits, one natural and the other artificial, for six-legged animals or robots. In these gaits four legs are used to support the body, enabling greater stability and tolerance for faults. A standardized hexapod model was carefully examined as it moved in arbitrary directions. The study also introduced a new factor in addition to the traditional stability margin criterion to evaluate the equilibrium of such gaits. Contrary to the common belief that natural gaits would always provide better stability during locomotion, these results show that the artificial gait is superior to the natural gait when moving transversely in precarious conditions.

Dynamic Modeling, Simulation and Velocity Control of Rocker-Bogie Rover for Space Exploration

Wheeled mobile rovers are being used in various missions for planetary surface exploration. In this paper a six-wheeled rover with rocker-bogie structure has been analyzed for planar case. The detailed kinematic model of the rover was built and the dynamic model was derived based on bond graph. The simulation studies were performed for obstacle climbing capability of the rover. It was observed from the study that rover can pass through plane surface, inclined surface, and inclined ditch without any control on the actuators of the rover. However, it fails to cross a vertical ditch so a velocity controller was designed. It consists of a proportional integral (PI) controller and reduced model of the rover. It is found from simulation and animation studies that with the proposed velocity controller the rover is able to cross the vertical ditch.

Parallel Architecture Manipulators for Use in Masticatory Studies

There is considerable scientific and commercial interest in understanding the mechanics of mastication. In this paper, the authors develop quantitative engineering tools to enable this process by: (i) designing a general purpose mastication simulator test-bed based on parallel architecture manipulator, capable of producing the requisite motions and forces; and (ii) validating this simulator with a range of test-foods, undergoing various mastication cycles under controlled and monitored circumstances. Such an implementation provides a test bed to quantitatively characterize the mastication based on “chewability index”. Due to the inherent advantages of locating actuators at the base (ground) in terms of actuator efforts and structural rigidity as well as benefits of using prismatic sliders compared to revolute actuators, the 6-P-U-S system was chosen. A detailed symbolic kinematic analysis was then conducted. For the practical implementation of the test-bed, the analytical Jacobian was examined for singularities and the design was adapted to ensure singularity free operation. A comprehensive parametric study was undertaken to obtain optimal design parameters for desired workspace and end effector forces. Experiments captured jaw motion trajectories using the high speed motion capture system which served as an input to the hardware-in-the-loop simulator platform.

Kinematic Isotropic Configuration of Spatial Cable-Driven Parallel Robots

In this paper, the authors study the kinematic isotropic configuration of spatial cable-driven parallel robots by means of four different methods, namely, (i) symbolic method, (ii) geometric workspace, (iii) numerical workspace and global tension index (GTI), and (iv) numerical approach. The authors apply the mentioned techniques to two types of spatial cable-driven parallel manipulators to obtain their isotropic postures. These are a 6-6 cable-suspended parallel robot and a novel restricted three-degree-of-freedom cable-driven parallel robot. Eventually, the results of isotropic conditions of both cable robots are compared to show their applications.

High Performance Control of Stewart Platform Manipulator Using Sliding Mode Control with Synchronization Error

This paper presents the design and analysis of a high performance robust controller for the Stewart platform manipulator. The controller is a variable structure controller that uses a linear sliding surface which is designed to drive both tracking and synchronization errors to zero. In the controller the model based equivalent control part of the sliding mode controller is computed in task space and the discontinuous switching controller part is computed in joint space and hence it is a hybrid of the two approaches. The hybrid implementation helps to reduce computation time and to achieve high performance in task space without the need to measure or estimate 6DOF task space positions. Effect of actuator friction, backlash and parameter variation due to loading have been studied and simulation results confirmed that the controller is robust and achieves better tracking accuracy than other types of sliding mode controllers and simple PID controller.