Material depositing robot arm for arc welding: Structure & driving mechanism
This thesis presents the research work on the design and modeling of a 3-DoF robot arm as part of the 6-DoF arc welding robot called Robotums RA-01 developed at Centre of Materials & Minerals, Universiti Malaysia Sabah. A 3-DoF robot arm has been designed with the ability to interface with a for...
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| Format: | Thesis |
| Language: | English |
| Published: |
2008
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| Subjects: | |
| Online Access: | https://eprints.ums.edu.my/id/eprint/6428/1/mt0000000157.pdf |
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| Summary: | This thesis presents the research work on the design and modeling of a 3-DoF robot arm as part of the 6-DoF arc welding robot called Robotums RA-01 developed at Centre of Materials & Minerals, Universiti Malaysia Sabah. A 3-DoF robot arm has been designed with the ability to interface with a forearm mechanism developed by Chua (2007) to form a complete 6-DoF arc-welding robot with a maximum reachable distance of 1,300mm and a handling payload of 6kg at the wrist center. As well as designing of the robot-arm mechanics and structure, and the driving system design fundamentals. The robot kinematics model has been developed to serve as the fundamental mechanics of the robot-arm system. Modified Denavit-Hartenberg frame assignment is introduced to resolve the complexity of the skeleton structure frame assignment with a final reference coordinate frame been fixed, which leads to the forward and inverse kinematics model formulation. Each joint of the designed robot arm is given a degree of freedom by attaching a joint driving system using servomotors and harmonics drive partnership. The joint driving systems are designed based on the criteria to meet acceleration and manipulation of the robot arm structures and inertia masses achieving the 6kg payload at the wrist center point. Prediction of harmonic drive safety functional life span of the shortest period of 8 years is achieved at 1st joint driving system before failure is anticipated. The robot arm 3-D virtual prototype linkage structures are designed through SolidWorks to meet the design requirement of a maximum deflection value of 0.257mm and an equivalent stiffness of 295717.5 N/mm for 6kg payload acting at the wrist center has also been achieved. The main linkage structures design involved the theoretical model, and the iteration or numerical via CAD with CAE verification has been introduced. For analyzing the theoretical dynamic behavior of the robot arm, a dynamic model of the arm has been developed based on the Lagrange approach. An ideal theoretical dynamic model, neglects on the frictional force terms are simulated in the development of inverse dynamic solutions of the joint torques. A close-to real life dynamic simulation or 3-D motion numerical analysis has also been performed through CosmosMotion CAE application tool for comparison and verification of the results with the theoretical model. The linear trajectory simulation of the GMAW robot-arm wrist center Cartesian position error range of 0.00mm to 0.35mm is achieved at 400 mm/min for standard gas metal welding operation, which permitted tolerance variation position between the arc and joint gap not to exceed more than +0.5 mm. Therefore, the designed GMAW robot-arm has successfully met the requirement of gas metal arc welding operation. |
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