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Mission 68 · Pro PLC programming exercise

Let the cartons through

Mute the light curtain for cartons, in order and for a short time, and stop for anything else.

Let a carton through the light curtain by muting it, but only when the muting eyes see it in the right order with the conveyor running. Stop the robot and conveyor for any other break in the curtain.

Training only. This is not a certified safety system. On a real machine these rules run in a safety relay or a safety PLC, designed and validated to ISO 13849-1 or IEC 62061.

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The 3D robot safety cell this mission runs on Pro mission
Test replay

Cartons pass muted

Test 1 of 5
Set by the testChecked by the testStep 19 of 19 · 2 s
Level
Expert
Time
About 50 min
Reward
+600 XP
Rig
3D robot safety cell
Siemens editors
Ladder (LAD), SCL
Rockwell editors
Ladder, Structured Text
Beckhoff editors
Structured Text
Course stage
34. Safety lab 3: how to stop, and what to let through
Automatic tests

What the tests check

  1. A carton that makes MuteA then MuteB passes the curtain without a stop, with MuteLamp ON.
  2. Muting ends when the carton has cleared the curtain.
  3. A person breaking the curtain stops the robot and conveyor at once.
  4. Eyes made in the wrong order, or with the conveyor stopped, do not mute.
  5. Muting ends after 4 s; a carton still in the curtain then stops the cell.
  1. Try it Use the buttons below the model and watch the rig respond.
  2. Test solution Every check runs on your code in one press.
  3. Replay If one fails, step through it one scan at a time to see why.
Why it matters

Where you’d see this on site

Pallet and carton conveyors into robot cells and wrappers use muting. The eyes are placed so a person walking in cannot make them in order.

A curtain that stopped for every carton would stop the line all day, and people would bypass it. Muting done badly is worse: a curtain that is muted when a person walks in protects no one.

Where you'd find thisKeep people out while the arm moves, and prove it every time

A robot stacks cartons inside a fence. A gate lets a fitter in, a light curtain lets the cartons in, and an emergency stop sits outside. Two contactors in a row cut the robot's power, so one that sticks cannot keep it running.

  1. InfeedCartons through the curtain
  2. PickRobot takes the carton
  3. GuardStop, reset, restartYou are here
  4. PalletSix cartons, then change
On a real site: places, parts and safety
  • Robot palletising and packing cells
  • Machine tending: robots loading presses and machine tools
  • Any guarded machine with a door, a curtain or an E-stop

Training only: this rig is not a certified safety system. Real safety functions run in safety relays or a safety PLC, designed and validated to ISO 13849-1 or IEC 62061.

IEC 60204-1 sets out stop categories 0, 1 and 2 and how an emergency stop must behave. Which category a machine uses comes from its risk assessment.

The sizes, timings and cutaways are teaching choices, not a drawing of any one real installation.

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