Quote:
Originally Posted by JesseK
What about your 'pincher' requires so much power? Does it do more than pinch? What does it pinch?
Do you have any limit switches anywhere on your robot?
Do you guys powdercoat your stock, and then drill into it?
|
1) Cans, totes, robots, people, etc. Two motors are dedicated to the 'pinching' function, the other two power the rollers on the pincher.
2) Nope. We've done a fair amount of control theory work and implementation this year. It's been a great experience for our students to be exposed to even more practices that are fairly common in the controls industry.
All of our rezeroing, minimum and maximum positions are determined by using a combination of position gathered using a quadrature encoder and monitoring output current and output voltage.
For example, we'd limit the upper end of our elevator travel based on an estimated position and then we'd calculate how much power is going into the elevator to prevent a motor stall condition.
After profiling the current draw, we determined that it requires a little bit of logic to figure out if we're indeed stalling the gearbox, or lifting a bunch of totes.
We'd also rezero our elevator when it returns to its minimum position. Essentially, we'd allow for the elevator to run past the minimum position. Once we've detected that we're not moving anymore, the position is past the minimum position (our elevator has a spring loaded return cable), and current has trended upward, we can safely say that we're at the minimum position. We'd then allow the elevator to back drive itself via the spring to its natural state where we'd then reset the encoder.
Finally, we're using a quad encoder on our pincher gearbox along with two different PIDs. One PID handles position control so that our drivers can quickly acquire game pieces. Once the game piece is kinda-sorta in our possession, we'd switch to a current based PID.
This ensures that we'd be placing almost an equal amount of force on what ever we decide to grab. This configuration works on game pieces in any orientation. Cans fallen over, Cans upside down, totes from the wide side, totes from the long side, totes that are upside down, you name it.
3) We do not powdercoat our stock and do post machining. It just happened to be on that part, we kind of forgot a few holes. Careful measurements and some patience later along with a handheld drill, we'd have some pretty precise holes.