Development of cable-assisted robotic system for machining
Date
2023-01-10
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Abstract
Nowadays, industrial robots are the synonym for automation and efficiency, and have developed a strong presence in the manufacturing industry. The main application of industrial robots is widely known as handling, assembly, and welding, while the interest in employing industrial ro-bots as machine tools is rising in many manufacturing sectors. Compared with conventional CNC machine tools, industrial robots are advantageous in terms of easy integration, ample workspace, and cost saving. These unique advantages motivate the industry to replace CNC machine tools with industrial robots. However, among various sources of errors, their low structural rigidity is the most significant challenge, hindering the application of the robot in machining tasks and de-grading the machining quality.Herein, this study seeks to propose an innovative robotic configuration named cable-assisted ro-botic system (CARS) to solve the structural stiffness problem of industrial robots. The concept of CARS is explained in this study, and its prototype is built up with customized cable-winches based on servo motors and a serial industrial robot. The design of the mechanical structure, elec-trical circuit, and multi-platform control program are detailed to provide guidelines for duplica-tion. The performance of the implemented PID controller is examined under different conditions.The theoretical foundation is also provided, and the feasibility of CARS is evaluated in this study. The kinematic model of CARS is derived from the closed-loop kinematic chains. CARS's dynamic model is derived based on the rigid-link-flexible-joint multibody dynamic model of ro-bot and cable's elongation dynamic equations to account for elastic effects. Dynamic analyses are performed to compare the dynamics of the CARS prototype and the serial industrial robot. Along the most flexible direction, the static stiffness is improved by approximately 92% in the CARS prototype, and its dynamic stiffness is almost doubled. In order to construct the numeri-cal dynamic model of CARS, the inertia parameters of the KR6 industrial robot are identified via the least-square method, followed by fitting elastic parameters to modal measurements from ex-perimental modal analysis and measuring cable elongation stiffness. The constructed model is then transformed into the form of frequency-response function and validated with the experi-mental modal measurements. A novel configuration optimization framework is proposed in this study, targeting providing design guidelines and evolving dynamics towards desired perfor-mance. A case study of the optimization framework is presented based on the acquired dynamic model of CARS, where the effectiveness of the optimization framework is verified, and the dy-namic stiffness with the optimal configuration improves by 42% compared with the original con-figuration’s dynamic stiffness. Lastly, a series of machining tests are conducted to evaluate the CARS prototype's improvement in chatter resistance. The proposed CARS system will be appli-cable to robotic machining applications and intends to improve the accuracy and finish quality of applications such as milling, drilling, grinding, etc.
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Keywords
industrial robot, hybrid robot, cable-assisted robotic system, dynamic modelling, parameter identifictaion
Citation
Wang, Z. (2023). Development of cable-assisted robotic system for machining (Master thesis). University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca .