Many objects going through manufacturing processes are inherently flat and rectangular. And yet these two characteristics are becoming less necessary as pre-requisites in today's factory. Consider a circuit board. It meets the "flat and rectangular" requirement to a respectable degree. And for the last two or even three decades the conveyor handling of circuit boards has been commonplace. Today, with sophisticated vision systems (sophisticated in that complex vision algorithms are given "handles" that render them far less complicated to implement), height measurement systems, and other tools, it becomes reasonable to pass parts by a robot via flat-belt conveyor so that adhesives, greases, or gaskets can be applied no matter the orientation of the part, short of the part being upside down.
With any conveyor application some consideration needs to be given to handshaking. Typically in a conveyor system a part passes by or through a robotic work zone. Preceding process equipment is considered the "upstream" hardware and the equipment that follows a given zone is considered the "downstream" hardware. A very basic communications protocol was developed by the Surface Mount Equipment Manufacturers Association (SMEMA). It specifies a downstream output (Board Available) and a downstream input (Machine ready). The upstream output was the inverse of the downstream. Now, machine-to-machine and machine-to-factory communication protocols are highly refined, efficient systems that fully leverage factory floor information technology.