Troubleshooting

Common issues when integrating Struckig in PLC projects.

TrajectoryState.Error right after start

Likely causes:

• negative or zero limits where positive limits are required
• inconsistent vector size for configured DoFs
• impossible target state for active constraints

What to check:

• all Max* limits are sensible and positive
• each array has exactly dofs entries
• current and target state values are in consistent units
• inspect ErrorCode() in addition to ErrorMessage()

Zero limits conflict errors

Likely causes:

• one or more axes use zero acceleration or jerk limits while target states still require constrained motion
• synchronization forces coupling with another DoF that cannot satisfy zero-limit constraints

What to check:

• avoid mixing zero limits with aggressive target velocity/acceleration requests
• test with SynchronizationType.None to isolate per-axis feasibility
• reintroduce synchronization after each axis is individually valid

Motion looks too slow or too fast

Likely causes:

• cycletime does not match actual task period
• unit mismatch (mm vs m, deg vs rad)

What to check:

• task period in TwinCAT and cycletime are equal
• velocity, acceleration, jerk are scaled to your position unit

Never reaches Idle

Likely causes:

• target is overwritten each cycle by other logic
• external sequence logic modifies Current* continuously

What to check:

• write targets at state boundaries, not continuously
• avoid changing CurrentPosition/Velocity/Acceleration during active segments unless intentional
• verify whether target velocity or target acceleration is intentionally non-zero

Axis movement is jerky

Likely causes:

• jerk limits too high for mechanics
• output updates are not applied every cycle
• drive interpolation mode mismatch

What to check:

• reduce MaxJerk and test again
• ensure cyclic setpoint mapping runs unconditionally
• validate axis mode and interpolation settings
• consider DiscretizationType.Discrete for cycle-aligned durations

Unexpected path shape in multi-axis motion

Likely causes:

• synchronization mode does not match path intent
• constraints differ strongly between axes

What to check:

• try SynchronizationType.Phase for geometric path consistency
• align relative limits between axes where possible
• avoid partial per-DoF overrides unless required

Validation passes, but runtime still errors

Likely causes:

• parameters changed between ValidateInput and otg() call
• external logic writes NaN or invalid numbers during runtime

What to check:

• keep setpoint update and otg() call in the same deterministic code region
• guard external writes and sanitize values
• log parameter snapshots on transition edges

Diagnostic workflow

1. log State and ErrorMessage() when errors occur
2. log current and target vectors at segment entry
3. verify cycle time, units, and limit ranges
4. reduce complexity to a 1-axis move, then scale back up