Recently Delta Computer System designed a six degree of freedom platform to display at trade shows. The platform was designed at Delta by Paul Huumala using SolidWorks. The top and bottom platform were manufactured externally but then assembled at Delta. The cylinders are very small with internal analog position feedback. The servo valves are small Star servo valves. The machine was assembled just a few days before being sent to a show in California. The program uses three tasks. There is a main supervisor task, task 2, that calls sub programs, task 1, to run a bit and then a new sub program is executed. When all the sub programs are executed the program loops around to the first sub program. These programs generate X, Y, Z, Yaw, Pitch, using 6 virtual axes. As the 6 virtual axes move from on position to another they update their target positions.
Normally the X, Y, Z, Yaw, Pitch and Roll are generated by an external simulator program such as a flight simulator, car simulator or even a amusement park simulator. In our case we had to use task 2 and tasks 1 to generate X, Y, Z, Yaw, Pitch and Roll.
Task 0 converts the X, Y, Z, Yaw, Pitch and Roll to cylinder positions. This requires rotating and offsetting vectors to find the coordinates of where the 6 cylinders connects to the top platform. Task 0 also calculates the velocity and acceleration at these end positions. The RMC then executes 6 Advanced Time Move command to generate a 5th order polynomial so the motion will be be smooth as it moves through each point. This means there can be no discontinuity in the velocity and acceleration at each point.
Below is a link to a video that shows our six degree of freedom platform in action.
Keywords:
- 6DOF
- Stewart Platform
- Hexapod
- Gough-Stewart Platform