Mechatronics modeling and vibration analysis of a 2-DOF parallel manipulator in a 5-DOF hybrid machine tool

Efficient and precise processing of large-scale parts is an uprising problem in industry. In this paper, a method to polish large-scale wind turbine blades using hybrid mobile robots is proposed. The robot combines an automated guided vehicle (AGV), a 2-DoF 3-parallelogram hybrid module and a 1T2R parallel module. This paper focuses on the design of the 1T2R parallel mechanism. In order to realize flexible A/B axis rotational capacity and efficient transmission of driving units, two 1T2R parallel mechanisms actuated by ball screw drives are derived under the guidance of a type synthesis approach based on Grassmann line geometry and a line-graph method. Under the description of Tilt and Torsion (T&T) angles, kinematics (especially the parasitic motion) of the proposed mechanisms is investigated. To carry out the dimension synthesis, performance evaluation indices including good transmission and constraint workspace, maximum orientation capacity, global transmission and constraint index and global average parasitic motion are defined. The performance atlases are plotted in the parameter design space. By comparing the parasitic motion and the motion/force transmission and constraint performance of the two mechanisms, 3-RCU mechanism is identified to develop the parallel module and its kinematic optimization is carried out. The CAD model with a set of optimal parameters is presented. The work in this paper lays the foundation for the development of the hybrid mobile robot, and the configuration design and parameter optimization in this paper can be further applied to the design of other parallel mechanisms.

Design of the parallel mechanism for a hybrid mobile robot in wind turbine blades polishing

To obtain higher performance for hybrid robots subject to nonlinear dynamics and friction, feedforward compensations have been ubiquitously utilized in the industrial robotic field to attenuate these disturbances. However, due to the complex friction model and the coupling and time-varying dynamic of hybrid robots, there is no effective approach to realize accurate feedforward compensations in industrial control systems. This paper investigated an accurate dynamic modeling and control parameters design method to address these issues all at once. Taking the friction of each joint into account, the accurate dynamic model of the hybrid robot is developed and verified by experiments. With the accurate dynamic model, an exact control parameter design method is proposed based on the mapping relationship between the dynamic model and the feedforward compensations. Additionally, the control system designed by the method proposed in this paper is compared with the one tuned by an experienced engineer. Particularly, the robot's position and motion accuracy are also tested by a third-party inspection agency. The experimental and test results show that the position and velocity accuracy of the robot is improved significantly when the control system is designed by using the method proposed in this paper, which proves the effectiveness of the proposed method.

Accurate dynamic modeling and control parameters design of an industrial hybrid spray-painting robot

Grinding marks and traces, as well as the over- and under-cutting phenomenon are the severe challenges in robotic abrasive belt grinding of turbine blades and it greatly limits the further application of robotic machining technology in the thin-walled blade fields. In the paper, an active force control method consisting of force/positon and PI/PD controller based on six-dimensional force/torque sensor is introduced to eliminate the grinding marks and traces, and a passive force control method including PID controller based on one-dimensional force sensor is proposed to reduce the over- and under-cutting phenomenon in robotic machining system. Then the Kalman filter information fusion methodology is adopted to combine the active and passive force control methods which could improve the controlled force accuracy and efficiency, as well as avoid the control interference. Finally both the test workpiece and turbine blade are employed to examine and verify the reliability and practicality of the proposed hybrid force control method by achieving the desired surface quality and higher profile precision.

Hybrid active/passive force control strategy for grinding marks suppression and profile accuracy enhancement in robotic belt grinding of turbine blade

The Hessian matrix, one of the most pivotal parts in a robotic system's acceleration model, is a prerequisite for dynamic modeling and control of parallel robots. Aimed at providing a straightforward and effective way for modeling, design, and control of parallel robots, a new approach to formulate the Hessian matrix using the finite and instantaneous screw theory is presented in this paper. The new approach is generalizable in that it can be used to formulate the Hessian matrix of any parallel robot in a simple and concise manner. It also provides a theoretical foundation for the dynamic control of industrial robotic systems with parallel structures. The new approach is verified through comparison with the traditional exponential matrix method. The Exechon parallel robot and a hybrid serial-parallel robot are used as examples to further detail the procedures of this approach. The acceleration model formulated in this paper is closely related with the topological and parametric models, resulting in a unified mathematical framework for modeling and control of parallel robots.

An Approach to Formulate the Hessian Matrix for Dynamic Control of Parallel Robots

The paper deals with the workspace and dynamic performance evaluation of the PRR-PRR parallel manipulator in spray-painting equipment. Functional workspace of planar fully parallel robots is often limited because of interference among their mechanical components. The proposed 3-DOF planar parallel manipulator with two kinematic chains connecting the moving platform to the base can reduce interference while still maintaining 3 DOFs. Based on the kinematics, four working modes are analyzed and singularity is studied. The workspace is investigated and the inverse dynamics is formulated using the virtual work principle. The dynamic performance evaluation indices are designed on the basis of maximum and minimum magnitude of acceleration vector of the moving platform produced by a unit actuated force. The index not only can evaluate the accelerating performance of a manipulator, but also can reflect the isotropy of accelerating performance. Workspace and dynamic performances of the four working modes are compared and the optimal working mode for the painting of a large object with conical surface is determined. HighlightsFour working modes are analyzed and the optimal mode for painting a long rocket fairing with conical surface is determined.Dynamic performance indices are designed on the basis of acceleration vector of the moving platform produced by a unit actuated force.The index not only can evaluate the accelerating performance, but also can reflect the isotropy of accelerating performance.

Liping Wang

Papers

Workspace and dynamic performance evaluation of the parallel manipulators in a spray-painting equipment