Zhenhua Cai

Computer-Aided Robot Trajectory Auto-generation Strategy in Thermal Spraying

This paper is concerned with a new methodology which is designed to auto-generate the robotic trajectory for thermal spraying process. Based on it, a software package named Thermal Spray Toolkit is developed and integrated in the main frame of off-line programming software RobotStudio™ (Product of ABB Company, Sweden). This toolkit implements the robotic trajectory planning in an interactive manner between RobotStudio™ and the finite element analysis software (FES). It allows rearranging the imported node index created on the surface of workpiece by FES and in turn generating the thermal spraying needed robot trajectories. Several parameters in thermal spraying, such as scanning step and torch-substrate relative velocity which have major influence on the coating deposition, are considered in the trajectory generation process. Experiment is carried out to check the reliability of the generated robot trajectory.

Kinematic Optimization of Robot Trajectories for Thermal Spray Coating Application

Industrial robots are widely used in the field of thermal spray nowadays. Due to their characteristics of high-accuracy and programmable flexibility, spraying on complex geometrical workpieces can be realized in the equipped spray room. However, in some cases, the robots cannot guarantee the process parameters defined by the robot movement, such as the scanning trajectory, spray angle, relative speed between the torch and the substrate, etc., which have distinct influences on heat and mass transfer during the generation of any thermally sprayed coatings. In this study, an investigation on the robot kinematics was proposed to find the rules of motion in a common case. The results showed that the motion behavior of each axis of robot permits to identify the motion problems in the trajectory. This approach allows to optimize the robot trajectory generation in a limited working envelop. It also minimizes the influence of robot performance to achieve a more constant relative scanning speed which is represented as a key parameter in thermal spraying.

A Global Approach to the Optimal Trajectory Based on an Improved Ant Colony Algorithm for Cold Spray

Abstract This paper is concerned with finding a global approach to obtain the shortest complete coverage trajectory on complex surfaces for cold spray applications. A slicing algorithm is employed to decompose the free-form complex surface into several small pieces of simple topological type. The problem of finding the optimal arrangement of the pieces is translated into a generalized traveling salesman problem (GTSP). Owing to its high searching capability and convergence performance, an improved ant colony algorithm is then used to solve the GTSP. Through off-line simulation, a robot trajectory is generated based on the optimized result. The approach is applied to coat real components with a complex surface by using the cold spray system with copper as the spraying material.

A Robot Trajectory Optimization Approach for Thermal Barrier Coatings Used for Free-Form Components

This paper is concerned with a robot trajectory optimization approach for thermal barrier coatings. As the requirements of high reproducibility of complex workpieces increase, an optimal thermal spraying trajectory should not only guarantee an accurate control of spray parameters defined by users (e.g., scanning speed, spray distance, scanning step, etc.) to achieve coating thickness homogeneity but also help to homogenize the heat transfer distribution on the coating surface. A mesh-based trajectory generation approach is introduced in this work to generate path curves on a free-form component. Then, two types of meander trajectories are generated by performing a different connection method. Additionally, this paper presents a research approach for introducing the heat transfer analysis into the trajectory planning process. Combining heat transfer analysis with trajectory planning overcomes the defects of traditional trajectory planning methods (e.g., local over-heating), which helps form the uniform temperature field by optimizing the time sequence of path curves. The influence of two different robot trajectories on the process of heat transfer is estimated by coupled FEM models which demonstrates the effectiveness of the presented optimization approach.

A wavelet transform based power allocation strategy for lithium battery and ultra capacitor hybrid vehicular power system

Hybridization of battery with other energy storage devices, such as Ultra-Capacitors (UC) are often equipped in vehicular applications, therefore a well-designed Energy Management Strategy (EMS) is necessary for it can be effective for power sharing between the lithium battery and UC. This paper puts forward a wavelet transform based power allocation strategy for the EMS of Hybrid Electrical Vehicles (HEV). The original power demand signal is decomposed by wavelet transform into high frequency and low frequency components, and then the decomposed power demands are allotted to the lithium battery and UC respectively according to their output characteristics. The developed strategy is validated by a typical HEV model in ADVISOR, the experiment result shows that the wavelet transform based power allocation strategy can dramatically improve the efficiency of the overall system, which helps minimizing the waste of energy and enhancing the transient performance of HEV.

Mesh-based trajectories generation strategy and thermal distribution analysis in thermal spraying

The strategy of robot trajectory generation is still an experience issue in industry applications. This paper introduces a mesh-based method to generate different patterns of trajectory for thermal spraying applications. In this method, the appropriate mesh is generated on the coating surface of model in CATIA, the mesh information including the node index, position and orientation is then imported into an off-line programming software RobotStudioTM (Product of ABB Company, Swiss) by a secondary development user interface. In the environment of RobotStudioTM, robot targets are generated according to the mesh information and user-defined robot relative parameters. The different trajectory patterns formed by varied execution order of robot targets are simulated in RobotStudioTM. By analyzing the real time speed of Tool Center Point (TCP), the most appropriate trajectory can be determined. Finally, the recorded TCP speed is considered as the displacement of thermal source in ANSYS, the thermal distribution of the workpiece during the thermal spray process is analyzed accordingly in this article.

A robot trajectory sample algorithm for optimizing thermal spraying torch velocity on the complex surface

During the process of thermal spray applications, the spray torch is usually driven by the robot, and its movements are in turns controlled by robot trajectories. The increasing requirements of coating productivity lead to the objectivity of generating robot trajectories on the complex surface. However, when the spray torch moves in a constant given torch velocity, the large curvature change of the coating surface will cause the sudden transition of one or several robot axes and thus lead to the undulation of torch velocity. This study aims at introducing a new trajectory point sample algorithm for optimizing the robot trajectory, and thus leads to desired torch velocity. Thermal distribution analysis of the thermal spray process is carried out to check the reliability of the optimization algorithm and the optimized robot trajectory.