A Stewart Platform six-axis milling machine development.
Thesis DisciplineMechanical Engineering
Degree GrantorUniversity of Canterbury
Degree NameMaster of Engineering
This manuscript describes the development of an experimental NC milling machine having control over all the 6 bodily degrees of freedom of movement. The mechanism used is called a Stewart Platform. These mechanisms have a platform connected to a base by 6 variable length "legs". The Stewart Platform is considered to have good potential as a rigid 5 axis milling machine having a simpler structure than conventional machines. Platform motion is achieved by pre-calculated movements of 6 stepper motors which actuate leg mounted lead screws. These movements are controlled using microcomputer controlled electronic hardware. The development of the system progressed along several paths among which were: path synthesis methods in six dimensions, stepper motors, simultaneous open-loop control of 6 data manipulation and storage structures in software to execute the control strategies, and the development of the existing positioning machine for milling operations. The system was successfully developed to enable machining of rigid urethane foam blocks in 5 useful degrees of freedom. The envelope of movement was restricted to +/- 100mm translations and +/- 30 degree rotations. Accuracy of movement was beyond that detectable using foam. Suggestions are made for further developments, particularly for improving the machine's envelope of movement and method of actuation.