Engineering · PLC · Project 15 of 15 · Conveyors and doors · Level 3

Roller door with safety beam

Open, close and stop a roller door. If something breaks the beam while closing, the door reverses.

Learning model only. This page teaches the program logic. A real machine needs a proper control panel with an isolator, fuses, motor protection and a hard-wired emergency stop. Mains and motor wiring is for qualified electricians. A PLC output never drives a motor directly.

You will learn

Limit switches stop the door at each end and the safety beam adds a reversing action. Up and down rungs block each other so the motor is never told to go both ways.

How it works

Press OPEN. The door rises to the top limit and stops.
Press CLOSE. The door lowers to the bottom.
Flip Obstacle while it closes: the door stops, reverses to the top, then waits.

In real life

Garage doors, warehouse shutters, factory gates.

Inputs, outputs and addresses

The same signals on seven PLC brands. Inputs and outputs are numbered in order; check your own hardware and software, because addresses depend on the model and module position.

Name	What it is	Type	Siemens S7-1200	Allen-Bradley CompactLogix	Mitsubishi iQ-F FX5U	Delta DVP / AS	Omron CP2E	Schneider M241	Inovance H5U
OPEN	OPEN button	Input	`%I0.0`	`Local:1:I.Data.0`	`X0`	`X0`	`0.00`	`%IX0.0`	`X0`
CLOSE	CLOSE button	Input	`%I0.1`	`Local:1:I.Data.1`	`X1`	`X1`	`0.01`	`%IX0.1`	`X1`
STOP	STOP button (N.C.)	Input	`%I0.2`	`Local:1:I.Data.2`	`X2`	`X2`	`0.02`	`%IX0.2`	`X2`
BEAM	Safety beam (ON when clear)	Input	`%I0.3`	`Local:1:I.Data.3`	`X3`	`X3`	`0.03`	`%IX0.3`	`X3`
TOP	Top limit switch	Input	`%I0.4`	`Local:1:I.Data.4`	`X4`	`X4`	`0.04`	`%IX0.4`	`X4`
BOT	Bottom limit switch	Input	`%I0.5`	`Local:1:I.Data.5`	`X5`	`X5`	`0.05`	`%IX0.5`	`X5`
UP	Motor up	Output	`%Q0.0`	`Local:2:O.Data.0`	`Y0`	`Y0`	`100.00`	`%QX0.0`	`Y0`
DN	Motor down	Output	`%Q0.1`	`Local:2:O.Data.1`	`Y1`	`Y1`	`100.01`	`%QX0.1`	`Y1`

Ladder diagram (shown for Siemens, live state)

Green wires carry power in the moment captured below. Switch the brand and the language in the simulator.

Structured text, Siemens SCL

(* Siemens S7-1200, CPU 1214C DC/DC/DC - TIA Portal - SCL *)
(* Rung 1: Beam broken while closing sets reverse *)
IF "DN" AND NOT "BEAM" THEN "REV" := TRUE; END_IF;
(* Rung 2: Reverse ends at the top *)
IF "TOP" THEN "REV" := FALSE; END_IF;
(* Rung 3: Door up *)
"UP" := ("OPEN" OR "REV" OR "UP") AND "STOP" AND NOT "TOP" AND NOT "DN";
(* Rung 4: Door down *)
"DN" := ("CLOSE" OR "DN") AND "STOP" AND NOT "BOT" AND NOT "UP" AND "BEAM" AND NOT "REV";

Structured text, Allen-Bradley

(* Allen-Bradley CompactLogix 5069 (L306ER) - Studio 5000 Logix Designer - Structured Text *)
(* Rung 1: Beam broken while closing sets reverse *)
IF DN AND NOT BEAM THEN REV := TRUE; END_IF;
(* Rung 2: Reverse ends at the top *)
IF TOP THEN REV := FALSE; END_IF;
(* Rung 3: Door up *)
UP := (OPEN OR REV OR UP) AND STOP AND NOT TOP AND NOT DN;
(* Rung 4: Door down *)
DN := (CLOSE OR DN) AND STOP AND NOT BOT AND NOT UP AND BEAM AND NOT REV;

Try this

Press STOP mid-travel.
Try OPEN and CLOSE together.

Parts to buy

The links open a search on each store, so you see what is in stock today. Check the model, voltage and price before you order.

#	Item	Buy / compare
1	PLC	Amazon.in · IndiaMART · Robu.in
2	Two limit switches	Amazon.in · IndiaMART · Robu.in
3	Safety photo-eye	Amazon.in · IndiaMART · Robu.in
4	Reversing contactors	Amazon.in · IndiaMART · Robu.in

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This is a learning tool. It teaches the logic, not the exact keystrokes of each vendor’s software. Check the manual of your own PLC.