Fishbone diagram · Two fault investigations
Misroute Investigation
Do not rush to replace people or machines. Let test results show where to intervene.
Suspicion on the night shift
The day batch had no errors; the night batch did. Do not blame people yet: their environments differed too. Deliver at least 10 correct parcels per batch, no misroutes, and evidence for the repair.
The letter on each box is its intended exit; ! marks a misrouted parcel.
Displayed setup: Night shift · Paper labels · Humid · Fast · Close · Single channel
First see which explanations fit the handover records, then choose category checks that distinguish them.
View misrouted parcel numbers and actual exits
Parcel 3: expected A, actual B; Parcel 6: expected B, actual A; Parcel 9: expected A, actual B; Parcel 12: expected B, actual A
Handover records · Correlation is not yet a cause
Production repair · Budget 0 / 3
The test bench does not change production automatically. Select repairs to install, then run acceptance. You can revise the plan and test it again.
Production starts from fixed conditions: night shift, paper labels, humid, fast, close spacing and a single-channel scanner. Selected repairs override the relevant conditions.
Before acceptance, you need a comparison that changes only the chosen repair's condition and eliminates misroutes. Compare handover records with new tests if useful.
Investigation bench · Checks remaining: 2
One category check compares two setups; an individual test adds evidence. With only two checks, you cannot inspect all four categories. First see which explanations remain indistinguishable, then choose. Undo to replan.
Cause framework · Remaining explanations: 3
These are working hypotheses supplied for this case, not every possible cause. Rule one out only when a result contradicts its prediction. Categorization alone does not prove causality.
View excluded explanations and evidence
Paper labels alone cause misroutes: inconsistent with record 1.
Fast speed alone causes misroutes: inconsistent with record 1.
Close spacing alone causes misroutes: inconsistent with record 1.
A single channel alone causes misroutes: inconsistent with record 1.
Fast speed and close spacing interact, regardless of scanner: inconsistent with record 1.
Fast speed, close spacing and a single channel interact: inconsistent with record 1.
Add an individual test
You can also set conditions freely. If several change together, success alone cannot identify the cause.
Compared with record 2: 0 conditions changed.
View sorting floor ↑Cause framework · Candidates are not conclusions
A category check may cross two categories. Existing single-variable comparisons appear under their corresponding branches below; you need not tick off every item.
Does night-shift operation cause misroutes?
UntestedIs the label material reliable under the current conditions?
UntestedDid humidity change the sorting result?
UntestedDoes slowing down remove errors? At what cost?
UntestedDoes spacing affect scanning and sorting?
UntestedDoes a dual-channel scanner restore reliable sorting?
Untested