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Sheet 420 · Automation

Conveyor sorting line

A small production line from a university project: a conveyor belt, a metal sensor and pistons, run by ladder logic on a Siemens PLC, sending parts down different paths by colour and material.

What it is

Part on the beltSensors read itmetal or not, and itscolourPLC programladder logic picks themodePistons route ita different path percolour and materialPart on the beltSensors read itmetal or not, and its colourPLC programladder logic picks the modePistons route ita different path per colour and material
FIG. 1How a part gets sorted. One part, one pass. My notes do not record how many paths the line had, so the drawing shows one.
Source: My interview notes, 1 Nov 2026

A small production line I made for a university project. Parts ride a conveyor belt past a metal sensor, and pistons send each one down a different path. The line changed mode depending on a part's colour and material.

The controller is a Siemens PLC from the SIMATIC S7 family. I wrote its program in ladder logic, and I also built the line around it: the belt, the sensor and the pistons.

What happened

Ladder logic is the classic language of factory controllers. It is drawn like an old relay wiring diagram: each rung has conditions on the left and an output on the right, and the controller scans every rung, top to bottom, over and over. A sorting line maps onto it almost word for word. A rung reads like "if this sensor is on and the line is in this mode, fire that piston".

It belongs with the other physical things I have made, from my own circus props to the lightboard studios. I like picturing something in my head and then making it real.

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