The Case for Coordinated Cellular Robotics

Feb. 13, 2007
This type of conveyorless manufacturing eliminates virtually all of the non-value added time.
Robotics has become a necessity in both high production and high precision manufacturing operations. Despite the maturity of robots in the workplace, numerous challenges continue for factory floor managers; a key challenge is utilization and continuous improvement directives. To address this problem, new robotic configurations are emerging that lend themselves, at the very least, to greater efficiency. The technology—known as Coordinated Cellular Robotics (CCR) involves conveyorless cells that employ robots capable of working cooperatively and simultaneously on a work piece.

Many discrete manufacturing processes incur between 15 percent and 20 percent transportation time for work-in-process (WIP), which adds no value. Even in the automotive industry, where the emphasis is on efficiency and utilization, it is widely recognized that the robots are standing idle for too long while they wait for parts to come down the conveyor. One solution to this problem is to eliminate the conveyors. Conveyors can be a constraint in manufacturing, and in some cases, in fact, are regarded as a sworn enemy of continuous flow. By their very nature, conveyors are fixed, unable to present multiple perspectives of the WIP, and are subject to stop-and-go cycles. 

CCR can enable a factory to be designed with no conveyor lines; instead, clusters of robots are all working together to create the finished parts. The parts are always in a state of motion, no longer handcuffed to a conveyor and the go, stop, work, go cycle. In combination, operations are being performed on the WIP by other robots as the parts are in motion. Cooperative robots in a cell are tracking the WIP as it is being translated and rotated, resulting in continuous material flow. Robots hold the parts for each other while one, two or even three robots perform operations on the pieces simultaneously. The ability of a robot to rotate, raise and lower a piece, combined with the holding robot’s ability to position the work piece in between two or three process robots adds to the efficiency of the process. Known as process relative motion, this is the idea of working on the piece as it progresses down the line. This type of conveyorless manufacturing eliminates virtually all of the non-value added time, because the work piece is never in a state of rest as it would be if it were riding down a conveyor between operations. Furthermore, the system is more flexible because the line is not constrained by any hard automation.

Unsurpassed flexibility

As soon as a manufacturer wants to mix part types, the challenge is to identify flexible solutions that are cost effective and efficient. Robots are highly flexible—capable of reaching virtually every possible location within a defined envelope—but compared to hard automation, are relatively slower. However, when flexible manufacturing is the driving force, robots cannot be surpassed. Robots efficiently perform tool changes and can be reprogrammed for new applications. Advances in both simulation software and offline programming have made this possible. All of these advantages add up to a line that is capable of part type mixing with no difficulty. Furthermore, robots are faster, more reliable and less expensive than in the past.

Daimler Chrysler is among the most well known users of Coordinated Cellular Robotics. The company is currently using an ABB system in its Belvidere, Ill., plant, and has plans to use 50 to 60 Kuka cooperating robots in its new body facility, which will be operational in 2007. In addition, both BMW and the Volkswagen Group are using the technology. The most common uses of coordinated robotics is arc/spot welding and also load sharing, with two robots lifting one heavy piece together.          

Stefan G. Surpitski,