International Journal of Robotics
Volume:2 Issue: 1, Winter-Spring 2011

In this paper, stability analysis of walking gaits and robustness analysis are developed for a five-link and four-actuator biped robot. Stability conditions are derived by studying unactuated dynamics and using the Poincaré map associated with periodic walking gaits. A stable gait is designed by an optimization process satisfying physical constraints and stability conditions. Also, considering underactuation problem, a time-invariant control law is designed to track the stable motion of biped. Validation of proposed approach is achieved by numerical simulations. Moreover, the robustness of motion on the uneven surfaces and elastic contact model are investigated.

In this paper the design of a biped robot actuated with Shape Memory Alloy (SMA) springs with minimum degrees of freedom is presented. SMA springs are a class of smart materials that are known for their high power to mass and volume ratios. It was shown that utilizing spring type of SMAs have many advantages as large deformation, smooth motion, silent and clean movement compared to ordinary type of actuators. In this work a Biped robot actuated through SMA springs with four DOFs is modeled and designed. Walking trajectory is generated validating the Zero Moment Point (ZMP) Criteria and the number of DOFs is modified accordingly. To verify the design, a complete model of the biped actuated with SMA is modeled through computer simulation in MATLAB and Visual Nastaran. Finally to validate the results, a prototype is manufactured and tested. Experimental results showed reasonable agreement with simulation results.

This work intends to deal with the optimal kinematic synthesis problem of Tricept parallel manipulator. Observing that cuboid workspaces are desirable for most machines, we use the concept of effective inscribed cuboid workspace, which reflects requirements on the workspace shape, volume and quality, simultaneously. The effectiveness of a workspace is characterized by the dexterity of the manipulator all over its workspace. Tricept has a complex degree of freedom, i.e. both rotational and translational DoF, therefore its performance indices depend on the singular values of the dimensional in-homogeneous Jacobian. Here, we divide the Jacobian entries by units of length, thereby producing a new Jacobian that is dimensionally homogeneous. By multiplying the associated entries of the twist array to the same length, we made this array homogeneous as well. This implies some sort of tradeoff between position and orientation components of the twist array. An optimal design problem, including constraints on actuated and passive joint limits, is then formulated. This problem is a constrained nonlinear optimization problem. Therefore, Genetic Algorithm toolbox of Matlab is adopted to solve the problem.

The main objective of this paper is to study the Euclidean displacement of a 5-DOF parallel mechanism performing three translation and two independent rotations with identical limb structures-recently revealed by performing the type synthesis-in a higher dimensional projective space, rather than relying on classical recipes, such as Cartesian coordinates and Euler angles. In this paper, Study's kinematic mapping is considered which maps the displacements of three-dimensional Euclidean space to points on a quadric, called Study quadric, in a seven-dimensional projective space, P7. The main focus of this contribution is to lay down the essential features of algebraic geometry for our kinematics purposes, where, as case study, a 5-DOF parallel mechanism with identical limb structures is considered. The forward kinematic problem is reviewed and the kinematic mapping is introduced for both general and first-order kinematics, i.e., velocity, which provides some insight into the better understanding of the kinematic behaviour of the mechanisms under study in some particular configurations for the rotation of the platform and also the constant-position workspace.

This paper presents a Gaussian radial basis function neural network based on sliding mode control for trajectory tracking and vibration control of a flexible joint manipulator. To study the effectiveness of the controllers, designed controller is developed for tip angular position control of a flexible joint manipulator. The adaptation laws of designed controller are obtained based on sliding mode control methodology without calculating the Jacobian of the flexible joint system. Also in this study, the anti-control is applied to reduce the deflection angle of flexible joint system. To achieve this goal, the chaos dynamic must be created in the flexible joint system. So, the flexible joint system has been synchronized to chaotic gyroscope system. In this study, control and anti-control concepts are applied to achieve the high quality performance of flexible joint system. It is tried to design a controller which is capable to satisfy the control and anti- control aims. The performances of the proposed control are examined in terms of input tracking capability, level of vibration reduction and time response specifications. Finally, the efficacy of the proposed method is validated through experimentation on QUANSER’s flexible-joint manipulator.

This paper employs nonlinear disturbance observer (NDO) for robust trajectory-free Nonlinear Model Predictive Control (NMPC) of biped robots. The NDO is used to reject the additive disturbances caused by parameter uncertainties, unmodeled dynamics, joints friction, and external slow-varying forces acting on the biped robots. In contrary to the slow-varying disturbances, handling sudden pushing disturbances acting on the biped robots is much more complicated and using the NDO doesn’t guarantee the biped walking stability. In order to reject these kinds of disturbances, the motion controller must be able to make suitable decisions for quick changing of the gait length or the walking speed. However, the gait length change is not possible while tracking fixed predefined joint trajectories. Hence, in this paper the NMPC is designed in such a way that it has the ability to change the gait length appropriately. In addition, some schemes will be proposed to reduce the computation time of the NMPC. Simulating results show good performance of the proposed method in trajectory-free walking of biped robots as well as disturbance rejection.

The large amount of computation necessary for obtaining time optimal solution for moving a manipulator on specified path has made it impossible to introduce an on line time optimal control algorithm. Most of this computational burden is due to calculation of switching points. In this paper a learning algorithm is proposed for finding the switching points. The method, which can be used for both serial and parallel manipulators, is based on a two-switch algorithm with three segments of moving with maximum acceleration, constant velocity and maximum deceleration along the path. The learning algorithm is aimed at decreasing the length of constant velocity segment in each step of learning process. The algorithm is applied to find the near minimum time solution of a parallel manipulator along a specified path. The results prove versatility of the algorithm both in tracking accuracy and short training process.