Pallet Wrapper Stops Mid-Cycle
Where in the cycle the machine stops is the single most useful piece of information. A stop at the same point every time points to a specific system - sensor, interlock, drive, or program. A stop that varies points somewhere else entirely.
Common symptoms
Before checking anything, note the exact point where the machine stops - which part of the wrap sequence, what the display shows, and whether the stop is consistent or random.
Stops at the same point in the cycle every time
A consistent stop location is the clearest diagnostic signal. The machine is waiting for something that isn't happening - a sensor confirmation, a drive acknowledgement, or a sequence step completing. The display alarm code, if there is one, will usually name the cause.
Stops with no alarm showing
A stop with no alarm or code on the display suggests a safety interlock has opened - a guard that's moved slightly, a mat that's been activated, or an e-stop that's not fully reset. Safety stops are by design silent on some machines to avoid bypassing them.
Stops during the final wraps or cut sequence
A stop late in the cycle - during the top wraps, the film cut, or the cycle-complete step - often points to the cut mechanism or a film sensor. The machine may be detecting that the film hasn't been cut correctly and stopping rather than completing.
Stops when the load is heavy or the turntable accelerates
A stop that correlates with load weight or speed suggests the drive is overload-tripping. The stop point varies because it depends on the load - the drive faults when the torque demand exceeds its threshold, which can happen at different points in the cycle.
Stops after a film break
If the machine stops following a film break, it may be a film break sensor detecting the break and halting the cycle correctly - as designed. If this is happening more frequently, the underlying issue is the film breaks, not the stops.
Stops at random points with no pattern
Stops that don't follow a pattern - different points each time, different loads, no consistent alarm - often point to an intermittent electrical fault. Loose connections, a failing sensor, or a signal that's cutting out under vibration are typical causes.
Typical causes
Safety interlock triggered
Guards, access gates, safety mats and e-stops all halt the cycle immediately if activated. A guard that vibrates slightly open, a mat that's been stepped on, or an e-stop that hasn't been fully reset will all cause mid-cycle stops. These stops are intentional - the machine is working as designed.
Drive overload or fault
Turntable or carriage drives that trip on overload will halt the cycle. The inverter logs the fault - overcurrent, overtemperature, or communication loss are the most common codes. Resetting without reading the code loses the diagnosis. Repeated overload trips suggest a mechanical or load issue that isn't going away.
Sensor fault or misalignment
Position sensors, film break detectors, and load height sensors all feed into the control sequence. A sensor that gives an unexpected signal - or no signal at all - can halt the cycle at the point where the PLC is waiting for that confirmation. Sensors are often the cause of consistent stop-point faults.
Program or timing fault
A program step with a timeout that's too short, or a sequence that's waiting for a condition that never completes, will halt the cycle at a specific point. This can appear after a software update, after parameters have been adjusted, or if a component has slowed slightly and is no longer completing its step within the allowed time.
What to check first
Don't reset and retry before recording where the stop happened and what the display showed. That information is what makes the diagnosis quick.
Record exactly where in the cycle the stop happens
Note the wrap stage - bottom wraps, mid-cycle, top wraps, cut sequence - and what the display shows when it stops. If there's an alarm code, write it down before resetting. Run the cycle again and let it fault in the same place if needed. This record is the starting point for any diagnosis.
Walk every safety system
Check every e-stop button is fully released and reset. Check all guard doors are fully closed and latched. Check any safety mats are clear. A guard that's fractionally open or an e-stop that's not fully twisted back out will cause a clean mid-cycle stop with no drive fault code.
Check drive fault codes on the inverter
Go to the inverter display directly - not just the machine panel - and check the fault history. Inverters log fault codes even when the machine panel shows nothing. An overload, overtemperature or communication fault code on the inverter tells you the drive stopped it, not a safety system.
Run three cycles and map the stop pattern
Run three consecutive cycles with the same load. If the stop happens at the same point each time, the cause is consistent - a sensor, a sequence step, a drive trip at a specific torque point. If the stop varies, the fault is intermittent - likely electrical or a load-related variable. The pattern tells you which direction to investigate.
If any of these apply, don't wait
- The machine stops at the same point on every cycle and you can't identify what's causing it
- The drive is showing an overload or fault code that keeps returning after reset
- Stops are random with no pattern and you suspect an intermittent electrical fault
- The machine stopped during a cycle and now won't restart even after a full reset
A consistent stop-point fault that doesn't respond to the checks above needs sensor or control system investigation. An intermittent fault that varies in location is often harder to catch - an engineer may need to observe the machine running to identify the cause.