Basic
20 min

Weld Cell Cycle

weldingclampsequencingfaultsafety

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Weld Cell Cycle scenario preview

Briefing

A welding cell fixture clamps a part, triggers a spot-weld, releases the clamp, and signals cycle complete. An E-stop or any mid-cycle clamp anomaly (clamp neither extended nor retracted within a timeout) latches a fault. The pallet must also be present before clamping begins.

Objectives

  • Sequence: PART_IN_FIXTURE → CLAMP_EXTEND → wait CLAMP_EXTENDED_LS → WELD_START → wait WELD_COMPLETE → CLAMP_RETRACT → wait CLAMP_RETRACTED_LS → pulse CYCLE_COMPLETE_LAMP
  • ESTOP or clamp timeout latches FAULT_LAMP and halts the cell
  • FAULT_LAMP clears only when ESTOP is de-asserted and the cell is reset
  • PALLET_PRESENT must be true before any clamping begins

Hints

  • Use a STEP INT (0=IDLE, 1=CLAMP_EXT, 2=WELDING, 3=CLAMP_RET, 4=DONE)
  • Add a TON (2s) for clamp travel timeout — if CLAMP_EXTENDED_LS / CLAMP_RETRACTED_LS not reached, set fault
  • ESTOP: S= FAULT_BIT on any ESTOP edge, R= only when ESTOP cleared and no clamp anomaly
  • CYCLE_COMPLETE_LAMP: single-scan pulse in step 4, then return to IDLE

I/O Table

Inputs

PART_IN_FIXTURE

Part sensor in fixture

BOOL · %I0.0

CLAMP_EXTENDED_LS

Clamp fully extended limit switch

BOOL · %I0.1

CLAMP_RETRACTED_LS

Clamp fully retracted limit switch

BOOL · %I0.2

WELD_COMPLETE

Weld controller cycle done signal

BOOL · %I0.3

ESTOP

Emergency stop (asserted when hit)

BOOL · %I0.4

PALLET_PRESENT

Pallet present in cell

BOOL · %I0.5

Outputs

CLAMP_EXTEND

Clamp extend solenoid

BOOL · %Q0.0

CLAMP_RETRACT

Clamp retract solenoid

BOOL · %Q0.1

WELD_START

Weld start trigger output

BOOL · %Q0.2

CYCLE_COMPLETE_LAMP

Cycle complete indicator lamp

BOOL · %Q0.3

FAULT_LAMP

Fault indicator lamp

BOOL · %Q0.4

Your program will be tested against:

All test cases run automatically when you submit. Assertions are hidden until you pass.

  1. #1Full weld cycle completes successfully

    Physics drives all limit switches; CYCLE_COMPLETE_LAMP pulses at end

  2. #2CLAMP_EXTEND fires when PART_IN_FIXTURE is asserted

    With part in fixture and pallet present, clamp extend solenoid energises

  3. #3ESTOP during weld cycle latches FAULT_LAMP

    E-stop halts the cell and latches the fault indicator

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Runnable simulator field guide

Weld-cell PLC cycle scenario: test checklist

Direct answer

The learner can require safe entry conditions, prove fixture and part state, exchange bounded ready and complete signals and recover without automatic hazardous motion.

Written for automation learners modeling a weld-cell handshake without exposure to real arc, motion or hazardous energy.

a guarded compact manufacturing cell with conveyor, sensors, pneumatic handling and a labeling station used for repeatable sequence training while studying guarded weld-cell states, fixture proof, robot handshake and recoverable cycle control
System map / 02

NODE 01observable

Scenario setup

Cell safe state, guard and safety status, part present, fixture clamp, robot ready, cycle request, weld complete, quality result, unload and reset policy.

NODE 02observable

I/O and state map

Operator load through part and clamp proof, controller handshake, robot cycle, weld result, release, unload and return-to-ready evidence.

NODE 03observable

Normal run

One correctly loaded part completes the declared handshake while entry demand or lost permissive prevents further hazardous sequence.

NODE 04observable

Boundary run

Part missing, double part, clamp not made, robot not ready, handshake stuck, cycle timeout, weld fault, quality fail, stop, restart and manual recovery.

NODE 05observable

Injected fault

A safety-status, part, fixture, handshake, robot, weld, quality, timeout or recovery mismatch.

NODE 06observable

Target check

The production cell validated by qualified robotics, welding, safety and process specialists under applicable standards.

Answer surface / 07

What signals should a PLC exchange with a weld robot?

Use a documented handshake separating cell permission, robot ready, cycle request, in-cycle, complete, fault and reset, with independent safety functions outside standard control logic.

How should a weld cell recover after a stopped cycle?

First establish actual robot, fixture and part state, then follow an approved bounded recovery path that cannot silently resume hazardous motion.