Separate the initiating event from the machines that stopped afterwards, then use product, sensor, controls and quality evidence to correct the real constraint safely.
1. Make the line safe before investigating
Do not reach into moving equipment, bypass safeguards or clear a blockage while the line can restart. Follow the site’s safe stop, isolation and access procedure, including stored energy. The HSE provides general guidance on safe maintenance and isolation; the actual method must be defined by a competent site-specific assessment.
Once the condition is safe, preserve evidence before resetting everything. Note the first alarm, product position, sensor state, component level and what the operator observed.
2. Classify the line condition correctly
A stopped machine may be healthy but starved by its upstream process or blocked by its downstream process. Distinguishing these conditions prevents unnecessary adjustment of the machine that merely reported the consequence.
| Condition | What it means | First evidence to inspect |
|---|---|---|
| Starved | The machine is ready but does not receive product or components | Upstream release, feeder level, transfer sensor and product spacing |
| Blocked | The machine cannot discharge or release the next pack | Downstream permission, buffer level, reject area and transfer obstruction |
| Faulted | A machine or interface condition prevents operation | First alarm, interlock, utility, actuator and safety status |
| Quality hold | The process runs or cycles but packs are not accepted | Inspection result, reject reason, component or product condition |
| Manual hold | An operator or external system has intentionally paused production | HMI mode, production order, line-clearance or approval state |
3. Capture the first cause and the propagation path
Use synchronised timestamps where possible and identify the first event that changed the line state. A blocked downstream machine may make several upstream modules report blockage; those secondary messages should not be counted as independent causes.
- First alarm or state change
- Machine and physical location
- Product or component present at each relevant sensor
- Selected format and recipe
- Utility and network status
- Operator action before and after the event
- Whether the event repeats with the same format, batch or condition
4. Inspect product handling before changing software
Many repeated line stops begin with product presentation. Check container stability, guide pressure, conveyor speed changes, dead plates, curves, merges, queue pressure and sensor sight lines. Component tolerances, static, contamination or damaged packaging can make a previously stable transfer unreliable.
Compare a good pack with a failed pack and observe the transfer at normal production conditions. A slow manual test can hide effects caused by queue pressure, vibration or spacing.
5. Check feeders and replenishment as part of the line
Closure, label, carton or container feeders can create intermittent starvation before they show an empty alarm. Review hopper level, orientation, recirculation, jam detection, refill method and the way component variation affects the feed path.
Record whether the issue follows a component batch, storage condition or operator replenishment event. Do not compensate for poor component quality by repeatedly widening machine settings without a controlled decision.
6. Verify sensors, handshakes and state logic
Check that sensors see the product consistently and that their physical position still matches the format. Review debounce or delay settings only against the approved controls design. At machine boundaries, confirm ready, blocked, starved and fault signals in both directions.
The controls architecture guide explains how to define interface signals and first-cause logic before commissioning.
| Symptom | Possible evidence path | Avoid |
|---|---|---|
| Random container gaps | Feeder release, conveyor slip, sensor trace and upstream stop history | Increasing line speed without finding the missing supply |
| Repeated transfer jam | Pack dimensions, guide setting, speed ratio, queue pressure and transition condition | Removing guides or protection to create temporary clearance |
| Unconfirmed reject | Detection, reject actuator, confirmation sensor, bin status and pack path | Disabling reject confirmation to keep production running |
| Multiple simultaneous alarms | Timestamp order, initiating machine and propagation logic | Treating every secondary alarm as a separate root cause |
| Fault after changeover | Recipe match, change parts, component version and first-off record | Changing several settings at once without recording them |
7. Recover in a controlled way
Before restart, decide what happens to product already inside the line. Packs may need to complete, be rejected, be quarantined or be manually verified. Clear the initiating condition, restore guards and utilities, confirm the correct mode and use the approved reset route.
After restart, watch the line beyond the first successful cycle. Confirm that buffers, counts, reject systems and downstream handling have returned to their normal state.
8. Turn repeated faults into an improvement plan
Group events by first cause, format, product, component batch and operating condition. Prioritise frequent or high-impact causes, then verify that the corrective action changes the evidence. The action may be mechanical, controls, component quality, maintenance, training or line balance.
Use the line balancing and OEE guide to define loss categories and the retrofit and upgrade page when the existing design is the constraint.