No abstract

Delta parallel robot is widely used in the manufacturing process of food, medicine, electronics and military industries, which is a highly nonlinear system with strongly uncertain dynamics. Therefore, there are many difficulties in the controller design of delta robot. Based on the simplified dynamic model, a nonlinear PD+ controller with nonlinear disturbance observer is proposed for Delta parallel robot in this article, which can realize high-precision trajectory tracking in high-speed and high-acceleration motion. Then, the asymptotic stability of the closed-loop system’s equilibrium point is proven by utilizing Lyapunov techniques and LaSalle’s invariance theorem. It is obvious that the proposed controller is significantly less dependent on the accuracy of the dynamic model. Besides, a disturbance observer based on the generalized momentum is constructed, which can effectively observe and compensate the disturbances. What’s more, the constructed disturbance observer avoids the calculation of the inverse of inertia matrix, which will greatly improve the response speed of the controller. The simulation results show that the proposed controller can assure better trajectory tracking accuracy in high-speed and high-acceleration motion. And the disturbance observer can effectively estimate the disturbance. The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article:This work was supported by the National Natural Science Foundation of China (grant number51474320).

Parallel kinematic machines have been applied in aerospace and automotive manufacturing due to their potentials in high speed and high accuracy. However, there exists coupling in parallel kinematic machines, which makes dynamic analysis, rigidity enhancement, and control very complicated. In this article, coupling characteristics of a 5-degree-of-freedom (5-dof) hybrid manipulator are analyzed based on a local index and a global index. First, velocity analysis as well as acceleration analysis of the robot is conducted to provide essential information for dynamic modeling. Then the dynamic model is built based on the principle of virtual work. Whereas the mass matrix is off-diagonal, a local coupling index as well as a global index is defined, based on which coupling characteristics of the robot are analyzed. Results show that distributions of coupling indices are symmetric due to its structural features. And dimensional parameters, structural parameters, as well as mass parameters have a large influence on the system’s coupling characteristics. Research conducted in the article is of great help in optimal design and control. Meanwhile, the method proposed in the article can be applied to other types of parallel kinematic machines or hybrid manipulators.