two-DOF Parallel Research Articles

Control of a two-DOF parallel robot with unknown parameters using a novel robust adaptive approach

Model-based methods lose their performance in confronting with model uncertainties and disturbances. Accordingly, some degrees of adaptation to the involved conditions are required. In this paper, a novel robust adaptive scheme is proposed which guarantees the simultaneous identification and control of a system in the presence of external disturbances. Thereafter, the suggested algorithm is implemented on a 2-DOf spherical parallel robot as a stabilizer device. By identifying unknown parameters of Jacobian matrix, the relative identification error is obtained as 0.0207. Applying external excitations to the base, the ratio of end-effector to base orientation is acquired as 0.091, demonstrating proper stabilization in comparison with other two well-known methods. The proposed structure also reveals a reliable performance in tracking desired paths for the end-effector Euler angles.

On a Two-DoF Parallel and Orthogonal Variable-Stiffness Actuator: An Innovative Kinematic Architecture

Variable-Stiffness Actuators are continuously increasing in importance due to their characteristics that can be beneficial in various applications. It is undisputed that several one-degree-of-freedom (DoF) solutions have been developed thus far. The aim of this work is to introduce an original two-DoF planar variable-stiffness mechanism, characterized by an orthogonal arrangement of the actuation units to favor the isotropy. This device combines the concepts forming the basis of a one-DoF agonist-antagonist variable-stiffness mechanism and the rigid planar parallel and orthogonal kinematic one. In this paper, the kinematics and the operation principles are set out in detail, together with the analysis of the mechanism stiffness.

Dynamic modeling of a two-DoF rotational parallel robot with changeable rotational axes

Because of the outstanding capabilities to realize flexible orientations, the specific category of rotational parallel robots with changeable rotational axes have a wide application in design of bionic eyes, dexterous wrists, tracking and pointing devices. A two-DoF parallel robot in this category called Helix is studied in this paper. Employing a finite and instantaneous screw based method, dynamic modeling and analysis of Helix robot is presented, which provides a theoretical foundation for performance design and dynamic control. Firstly, concept description and inverse kinematics of Helix robot is given, which is the prerequisite for dynamic modeling and analysis. Secondly, twist and wrench based velocity, force and acceleration analysis of this robot is carried out, resulting in the Jacobian and Hessian matrices which are obtained through directly differentiating the finite screw based topological model. Then, using these matrices, its dynamic equation is formulated considering the gravity of each component. Finally, the obtained dynamic model of Helix robot is verified through comparing the simulation results in ADAMS and Matlab software. The finite and instantaneous screw based method used in this paper is a generic one which is suitable for dynamic modeling of different serial and parallel robots.

2 자유도 병렬 메니퓰레이터의 동적 모델링

In this paper, two-DOF parallel manipulator has the sliders which execute a linear reciprocating motion depending on parallel guides and the end-effector which can be adjusted arbitrarily. To investigate the dynamic characteristics of the manipulator, the dynamic performance index is used. The index is able to be obtained by the relation between the Jacobian matrix and the inertia matrix. The kinematic and the dynamic analysis find these matrices. Also, the dynamic model of the manipulator is derived from the Lagrange formula. This model represents complicated nonlinear equations of motion. With the simulation results of the dynamic characteristic of the manipulator, we find that the dynamic performance index is based on the selection of the ranges for the continuous movement of the manipulator and the dynamic model derived can be used to the control algorithm development of the manipulator.