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Building industrial robots do not necessarily mean spending lots of money on expensive hardware. Built with fischertechnik (a construction toy originating from Germany) and controlled by an Arduino Mega, this delta robot is a fairly simple machine. Nonetheless, it does not lack speed or precision to fulfill its job: The robot picks items from a conveyor and sorts them by color similarly to industrial pick and place robots.
What are the main challenges of this project?
- Delta robot kinematics
- Motion tracking of items on conveyor
- Vacuum gripping
Unlike simple kinematics such as linear kinematics that are often used in 3D printers, delta robot kinematics are more complicated and not straightforward to understand.To control a delta robot with cartesian coordinates, so-called inverse kinematics is required. I've implemented inverse kinematics for delta robots according to a paper published by Robert L. Williams II: "The Delta Parallel Robot: Kinematics Solutions" Although this seems to be computational expensive, delta kinematics have some good advanteges over other robot kinematics. Firstly, they are astoundingly fast and precise, secondly the have quite a good range of operation. However, vibrations are a serious issue and moving load should be as low as possible.
The following video gives you an intuition of what is possible with delta robots:
Motion tracking The position of every item is captured by a laser light barrier. This lets the robot know when the item has passed a certain position on the conveyor. Furthermore, the conveyor speed is measured by reading a encoder signal. This lets the robot know how fast the item is moving. Given that imformation, the robot's movement can be calculated so that it picks the item at the right time.
Vacuum gripper The items are manipulated by an vacuum gripper. Since I do not have a vacuum pump, I've looked for another solution to this task:
There are two pneumatic cylinders mounted next to each other. The first cylinder is connected to a valve the either lets pressure in or pressure out. The second cylinder is connected to a vacuum cup. When pressure is applied to the first cylinder it extends. As both pistons are mechanically connected to each other, the movement of the first cylinder also force the second cylinder to extend. However, this movement generates a vacuum inside the second cylinder. This vacuum is used for picking the items.