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Estimating the reduction in sortation productivity due to congestion caused by addition of robots in a given area is one of the most challenging problem while designing an robotic sortation system. Offcourse, simulation can provide the answer but in a world where feasibility checks are to be provided to the customers in a blink of an eye, guesstimating the unknowns like traffic factors becomes the need of the day.
Accurately guesstimating traffic factor in robotics sortation system helps to understand two things, that are if,
The solution is even feasible? (can we achieve required sorts per hour in a given area? Or congestion due to number of robots will not let us achieve the target ever?)
The estimated number of robots required will be close to actual robots required based on simulation and pilot projects.
Calculating productivity of an robot,
Calculating productivity of an robot,
This is function of four activities, pickup + travel to sort point + sort + travel back to induction point.
~90 % of time robots spend is on travelling. They perform best when they travel unobstructed in a straight path with minimum turns. However with a fixed area and many robots working around, optimizing the travelling path unobstructed is challenging feat for any Fleet Management System (FMS). Hence, guesstimating the number of times an robot will be obstructed by another robot becomes important to understand the loss of productivity with every added robot in the system.
Path length per robot (Identifying degree of congestion in a layout)
Path length per robot (Identifying degree of congestion in a layout)
Robots run on bar codes with certain pitch. The pitch depends on the make of the robot. Let's say the pitch is 0.5 meter. That means if an sort area is 10x10m (LxW). There will be a total path of 10x10=100/0.5=200M length. Thus, based on productivity of an unobstructed robot there are 100 robots required in given 100M2 of area then, every robot gets 200/100= 2M per robot.
If, total travel path (travel to sort point + return back to induction point) per sort for an robot is greater than 10M then the chances of getting obstructed by another robot increases. More time robot gets obstructed those many times it slows down, waits and then accelerates to reach full speed. So real loss of productivity occurs due to frequent stopping and frequent acceleration and deacceleration.
If total travel path = path length per robot, then this is the sweet spot at which in ideal conditions, robots to provide max productivity. This is denoted by critcal point in the graph. At any point above this critical point means we are giving extra area than required and point below critical point means area is insufficient for robots to work at full potential and more will be the obstruction.
Other key points that will affect the congestion which are not covered in this article and readers are encouraged to share there thoughts on how to cover these while calculating productivity per robot.
Distance between induction points
Intersection between X and Y direction paths
Anything else?
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