Commissioning Flags & Safe Forcing Rules for Roll Forming PLC Systems — How to Do It Properly

Introduction — Why Commissioning Flags and Safe Forcing Are Necessary

Commissioning a roll forming machine requires testing the PLC program before every sensor and mechanical system is fully operational. During early startup, many components may not yet be installed or connected.

Examples include:

punch cylinders not yet connected
shear sensors not installed
stacker system incomplete
servo systems still being tuned.

To allow the PLC program to run while systems are incomplete, engineers sometimes force inputs or bypass certain conditions temporarily.

However, forcing signals incorrectly can cause dangerous machine behavior, including:

unexpected motion
incorrect sequence transitions
hidden faults.

For this reason, professional PLC programs include commissioning flags and strict rules for safe forcing during machine startup.

These tools allow engineers to test the machine while maintaining control and safety.

What Commissioning Flags Are

A commissioning flag is a PLC variable that temporarily changes machine behavior during startup.

When commissioning mode is active, certain interlocks or checks may be bypassed or simulated.

For example:

Normal operation requires:

ShearHomeSensor = TRUE

During commissioning, the program may allow:

CommissioningMode = TRUE → bypass shear home check.

This allows engineers to test other machine functions even if the shear sensors are not yet installed.

Why Commissioning Flags Are Better Than Direct Forcing

Many PLC software tools allow engineers to force inputs directly.

However, forcing signals manually can create several problems:

forced inputs may remain active accidentally
forced signals are not visible to operators
forced states may bypass critical safety logic.

Using commissioning flags inside the PLC program is much safer because:

the program explicitly handles the bypass logic
the status is visible on the HMI
the behavior is controlled and predictable.

Types of Commissioning Flags

Several commissioning flags may be used in roll forming machines.

Common examples include:

Simulation Mode

Allows sensors such as strip detection or encoder signals to be simulated.

Mechanical Test Mode

Allows individual machine components to be tested without running the full production sequence.

Interlock Bypass Mode

Temporarily bypasses certain machine interlocks.

Motion Test Mode

Allows servo or drive systems to be tested independently.

Each mode should have clearly defined behavior.

Implementing a Commissioning Mode

A commissioning mode should be controlled by a dedicated PLC variable such as:

CommissioningMode

When this flag is active, specific program sections modify their behavior.

Example logic concept:

IF CommissioningMode = TRUE
THEN IgnoreShearHomeCheck.

However, safety circuits should never be bypassed in software.

HMI Indication of Commissioning Mode

Operators must always know when the machine is running in commissioning mode.

The HMI should display a clear message such as:

Commissioning Mode Active

This prevents accidental production while the machine is still in testing mode.

Visual indicators such as yellow status bars or warning messages are commonly used.

What Inputs May Be Safely Simulated

During commissioning, certain signals may be simulated.

Examples include:

strip presence sensors
encoder counts
stacker panel detection
punch cycle confirmation.

Simulating these signals allows engineers to test PLC sequences without material.

Inputs That Must Never Be Forced

Some signals must never be bypassed for safety reasons.

These include:

emergency stop signals
safety relay outputs
safety guard interlocks
safety light curtain signals.

Safety systems should always operate independently of PLC logic.

Forcing Outputs During Commissioning

Occasionally engineers may need to force outputs to test machine components.

Examples include:

activating hydraulic valves
testing motor drives
triggering punch solenoids.

Forcing outputs should only occur under controlled conditions.

Before forcing an output, engineers must ensure that the machine area is safe.

Safe Forcing Procedure

When forcing signals during commissioning, engineers should follow a strict procedure.

Step 1 — Verify Machine Safety

Ensure no personnel are near moving components.

Step 2 — Identify the Signal Clearly

Confirm the correct PLC tag or output.

Step 3 — Activate the Force Temporarily

Apply the forced signal only long enough to perform the test.

Step 4 — Remove the Force Immediately

After testing, remove the forced state.

Step 5 — Document the Test

Record what was tested and why.

Following this process reduces the risk of unintended machine behavior.

Avoiding Hidden Forces

One of the biggest dangers during commissioning is leaving signals forced unintentionally.

This can cause unexpected machine behavior later.

To avoid this problem:

always review the PLC force list
remove all forces before production
include a PLC check that prevents machine start if forces remain active.

Some PLC programs include a diagnostic signal such as:

ForceActiveDetected.

This signal blocks machine startup until all forces are cleared.

Commissioning Flags for Mechanical Testing

Engineers often need to test individual machine components without running the entire sequence.

Commissioning flags may allow:

testing the shear without material
running the stacker independently
jogging servo axes.

These modes isolate machine subsystems and simplify troubleshooting.

Testing Motion Systems Safely

Servo and drive systems require special care during commissioning.

Before forcing motion commands, engineers should verify:

mechanical clearances
correct direction of motion
emergency stop functionality.

Slow speed tests should be used initially.

This minimizes risk if unexpected movement occurs.

Using Timeouts During Commissioning

PLC programs should still include timeout protection even when commissioning flags are active.

Example:

If the PLC commands a shear movement but the simulated sensor does not respond, the program should generate a timeout alarm.

This helps detect programming errors early.

Logging Commissioning Activity

It is good practice to log commissioning actions.

Examples include:

activation of commissioning mode
forced outputs
bypassed interlocks.

Logging helps engineers review the commissioning process and identify potential issues.

Commissioning Checklist

Before transitioning from commissioning to production, engineers should verify several points.

Typical checklist includes:

1 disable commissioning mode
2 remove all forced inputs and outputs
3 verify safety systems
4 test full machine sequence with material
5 confirm normal machine operation.

Only after these steps should the machine enter production.

Risks of Improper Forcing

Improper forcing can cause serious problems.

Examples include:

unexpected machine movement
incomplete PLC sequences
hidden faults during production.

For this reason, forcing should only be performed by trained engineers.

Benefits of Commissioning Flags

When implemented correctly, commissioning flags provide several advantages.

These include:

faster machine startup
safer testing of machine functions
easier troubleshooting during installation
reduced risk of programming errors.

For large roll forming machines with complex automation systems, commissioning flags are essential tools.

FAQ — Commissioning Flags and Forcing

What is a commissioning flag in a PLC program?

A commissioning flag is a variable that modifies machine behavior during startup to allow testing before full installation is complete.

Why should engineers avoid forcing signals directly?

Direct forcing can hide problems and may remain active unintentionally, causing unsafe machine behavior.

Can safety signals be bypassed during commissioning?

No. Safety systems such as emergency stops and guard interlocks must never be bypassed in software.

How can engineers detect active forced signals?

Many PLC systems provide a force list or diagnostic signals that indicate when forcing is active.

Why should commissioning mode be visible on the HMI?

Operators must know when the machine is in testing mode to avoid accidental production.

What should be done before production begins?

Commissioning mode should be disabled, all forced signals removed, and full machine tests completed with real material.