Week TechVideo, 2011 #16 - Moving Targets

Likely you remember the first video from the LEGO FlexPicker, developed by Shep.

Shep is a mechanical engineer fascinated by this type of robots and since then he didn't stop doing improvements and expanding his model, making it running faster and smoother.

Finally this culminated into a 10ft (3m) long workcell, with four autonomous delta robots, capable of picking and placing colored blocks at a rate of 48 per minute. Each robot can handle 12 blocks per minute, meaning it can move one every 5 seconds!
The blocks constitute moving targets, fed by two conveyor belts moving at 100 inches (2,5m) per minute, which makes them not trivial to catch and sort.
There is a light/color sensor on each conveyor, which determines the blocks color and position into a chronological array. With this information and some mathematical operations, it is possible to calculate precisely the blocks position at each moment, and where the robots should pick each block.

The precise kinematics for the movements of the robots are dynamically calculated using detailed formulas that convert the Cartesian coordinates (x,y,z) of the location of the brick into the angles of the servo motors (theta1, theta2 and theta3) from each delta robot and vice versa. This is the heart and soul of the robots.

As the robot moves around, each motor speed is adjusted relative to the other motors speed in a manner that all three motors arrive at their target position at the same time. This makes all the movements very smooth and the robot doesn’t shake too much. The motor speeds are also adjusted so that the robot moves as fast as possible.

Since the blocks on the conveyors are always moving, the robot actually moves to a position where the block will be, rather than where the block actually is.


It looks complex. Right!?
A LEGO Technic and MINDSTORMS masterpiece, I'd say...

Here's the recipe, if you want to build yours...

• 6 LEGO NXT bricks
• 15 LEGO NXT servomotors
• 6 LEGO NXT touch sensors
• 6 LEGO legacy touch sensors
• 2 HiTechnic touch multiplexers
• 2 HiTechnic sensor multiplexers
• 4 HiTechnic IRLinks
• 5 LEGO light sensors
• 2 LEGO color sensor
• 1 mindsensors pressure sensor
• 4 LEGO PF M-motors
• 3 LEGO PF XL-motors
• 4 LEGO PF IR receivers
• 4 LEGO PF LED
• 1 LEGO PF switches
• 1 LEGO Train 9V speed regulator

For an extensive description about this work by Shep, visit the Tinkernology blog.