May 21, 2017

[2.70] Seek and Geek #12: Flower-transplanter Robot

This flower transplanter robot (TTA PackPlanter 2230) is really cool. How does it repeatably pick up tiny fragile flowershoots without crushing them?

robot picking up plants
The end effector of these pneumatic picker-uppers consists of a shovel-shaped set of needles. The gripper takes advantage of the increased density of the plant's rootball (relative to the rest of the soil) so that compressive force is tuned just enough to hold onto the plant and not crush the roots.

The gripper has to overcome adhesive forces (wall of the tray or soil sticking to the seedling) as well as gravity. The end effector has three needles, so each needle needs to handle

$F sin \alpha = G/3 + A/3 - F_{friction} cos \alpha$

where $F_{friction} = \mu \cdot \frac{G+A}{3(\mu cos \alpha + sin \alpha)}$

$\alpha$ being needle angle, $A$ being adhesion force, $\mu$ being the coefficient of friction. 

A pansy plug weighs approximately 20g, and the coefficient of friction can be assumed similar to snow ~0.2. Adhesion force between water and plastic is estimated to be 4N, and gripper force is estimated to be 5N.
The tradeoff between plug forces and friction sets $\alpha$ to be somewhere around 10$^\circ$. 

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