Design of spherical wrist and trajectory solution for robotic arc welding application

Chua , Bih Lii (2007) Design of spherical wrist and trajectory solution for robotic arc welding application. Masters thesis, Universiti Malaysia Sabah.

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Abstract

This thesis centred on designing a three degree-of-freedom (3-DOF) spherical wrist subassembly. This wrist subassembly was integrated with a concurrent 3-DOF arm subassembly project to form a complete arc welding robot assembly capable of handling 6 kilogram payload called Robotums RA-01 in the Universiti Malaysia Sabah (UMS). This was done by first determining the design goal via a design framework that had been laid out to allow design independency in which all required information for design is shared for easing the concurrent works and promoting the reuse of design with different configurations in the future. The functional kinematic structure for the Robotums RA-01 , which has the similar robot configuration to other typical arc welding robots, and the mechanism in the wrist subassembly were formed and analysed. The torch tip position and orientation was mapped from and to the corresponding robot joint angles via the forward and inverse kinematic respectively with the aid of 4x4 transformation matrix. The kinematics model was implemented and verified by a double number precision program with the negligible computational error of less than 5.0 x 10-13 degree for the joint-toCartesian- to-joint space transformations using joint angles input in degree unit. The wrist orientation error increases when joint angle 6 was approaching zero from absolute one degree, but still acceptable for arc welding application. Besides, the wrist singularity occurred due to the joint angle 6 was investigated computationally. Meanwhile, the wrist kinematics analysis was performed by using the fundamental circuit and coaxiality condition to reveal the relationship between the actuator and joint space parameters. The concept of fundamental circuit was extended to cater for ready-made drive reduction unit by introduction of the' equivalent fundamental circuit. Besides, the static analysis for the wrist mechanism was performed using virtual work method to determine the torque relationship between the joints and the actuators, Then, iterative selection of transmission drive ratio for harmonic drives, timing belts and miter gears as well as actuators was exercised to meet the torque and speed requirement before the functional kinematic structure of the wrist subassembly can be transformed into a virtual CAD solid model using SolidWorks 2005 that details the transmission elements with all the necessary bearings, seals and mountings and includes a standard mechanical plate interface, wire feeder mounting points and cable bending space in between the upper arm links. Several critical parts in the wrist subassembly were ensured not to be failed under normal loadings using CosmosWorks 2005 and by manual calculations. With the weight and moment of inertia of the transmission elements being computed by the CAD program, the selection of actuators was validated at the end of the wrist subassembly design process. Finally, this thesis proposed an arc welding trajectory planning algorithm for stationed typical 6-DOF industrial robot configuration that capable to generate the torch frame automatically for a specified straight trajectory and extendable for arc or circular trajectory with correlation to the torch speed, height and angles without collision. These torch frames were interpolated along the Cartesian path and the robot joints trajectory were planned using cubic polynomial interpolation scheme.

Item Type:Thesis (Masters)
Uncontrolled Keywords:3-DOF, wrist, arc welding robot, torch frame, Cartesian path, robot joints trajectory, cubic polynomial interpolation scheme
Subjects:T Technology > TJ Mechanical engineering and machinery
Divisions:SCHOOL > School of Engineering and Information Technology
ID Code:7530
Deposited By:IR Admin
Deposited On:18 Nov 2013 11:00
Last Modified:18 Nov 2013 11:00

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