Pallet Wrapper Film Carriage Not Moving
A carriage that won't move is usually a drive fault, a mechanical obstruction on the mast, or a limit switch that isn't clearing. Whether it won't move at all or moves only in one direction determines where to start.
Common symptoms
Note where the carriage is when the fault occurs, whether it moves at all, and whether the machine shows an alarm. That combination narrows the cause quickly.
Carriage doesn't move at all on cycle start
No movement from the carriage when a cycle starts - with the turntable running normally - suggests the carriage drive isn't receiving a run signal or has tripped. Check for a fault code on the carriage drive inverter, which may be separate from the main machine display.
Carriage moves up but won't come back down
Movement in one direction only points to either a limit switch that isn't clearing at the top of travel, or a directional fault in the drive. If the carriage reaches the top and stops without descending, check whether the upper limit switch is activating correctly or is stuck.
Carriage stops at the same height every cycle
A consistent stop height that isn't the normal reversal point suggests an obstruction, a limit switch at that position, or a drive that's tripping at that point in the travel. Check for anything on the mast at that height - debris, a cable that's fouling, or a guide roller that's become misaligned.
Carriage moves jerkily or inconsistently
Jerky movement suggests mechanical drag on the mast - a guide roller, a belt or chain component, or debris that's creating intermittent resistance. It can also indicate a drive that's hunting due to a feedback fault.
Manual carriage movement works but auto doesn't
If the carriage can be moved in manual or jog mode but won't travel in auto, the drive and mechanism are functional. The issue is in the control sequence - a sensor the PLC is waiting for, a sequence condition that isn't being met, or a program step that's blocking carriage travel.
Drive fault code showing on the inverter
A fault code on the carriage drive inverter tells you what stopped it. Overcurrent and overload codes suggest mechanical drag or an obstruction. Encoder or feedback faults suggest a position sensing issue. Communication faults suggest the control signal to the drive has been lost.
Typical causes
Carriage drive motor or inverter fault
The carriage is driven by its own motor and inverter, usually separate from the turntable drive. A drive trip - overcurrent, overtemperature, encoder fault - will stop carriage movement and log a code. The code needs to be read from the inverter directly, not just the machine panel.
Obstruction or mechanical drag on the mast
Film tails, cable drag, debris on the guide rails, or a guide roller that has worn or shifted can all create enough resistance to trip the drive or prevent movement. The mast and guide system should be clear and lubricated as part of routine maintenance - neglect here is a common cause of carriage faults.
Limit switch fault or misalignment
Upper and lower limit switches tell the control system where the carriage is and prevent it from overrunning. A limit switch that's stuck in the active position will prevent travel in that direction. A switch that's drifted out of alignment may not activate correctly at the travel limits, causing the machine to behave unexpectedly.
Belt, chain or drive component wear
The carriage is typically driven by a belt or chain running the length of the mast. A worn, stretched or damaged drive component can slip or fail to transmit motion to the carriage even when the motor is running. Gradual wear produces increasing hesitation before outright failure.
What to check first
Check the carriage drive inverter for fault codes before anything else - it logs what stopped the carriage and is the fastest route to a diagnosis.
Check the carriage drive inverter for fault codes
Go directly to the carriage drive inverter - not just the machine control panel - and check for logged fault codes. Record any code before resetting. An overload or overcurrent code suggests mechanical drag. An encoder or feedback fault suggests a position sensing issue. A comms fault suggests the signal from the PLC has been lost.
Inspect the mast and guide rails for obstruction
With the machine isolated, visually inspect the full length of the mast and guide rails. Look for film tails that have wrapped around any component, debris on the rails, or any cable that's caught or kinked. Try moving the carriage manually by hand - you should be able to feel any drag or resistance.
Try manual or jog mode
If the machine has a manual or jog function for the carriage, try commanding upward and downward movement independently. If it moves in manual but not in auto, the drive is functional and the control sequence is the issue. If it won't move in manual either, the fault is in the drive, mechanism, or power supply to the carriage circuit.
Check limit switch positions
With the machine isolated, locate the upper and lower limit switches on the mast. Check that neither is visibly damaged, stuck, or so far out of alignment that it can't activate correctly when the carriage reaches its travel limits. A limit switch that's permanently active will prevent carriage movement in that direction.
If any of these apply, don't wait
- The carriage drive is showing a fault code that returns after reset
- The carriage won't move in manual mode even with no visible obstruction
- The mast or guide rails show visible damage or component wear
- The carriage moves in one direction only and you can't identify the blocking condition
A drive that keeps overload-tripping without a clear mechanical cause needs inverter investigation. Running the carriage repeatedly against a fault condition risks motor and gearbox damage that's more expensive to repair than the original fault.