Can an assembly machine detect defective products during assembly and then reject them?

I. Quick Answer

Yes, modern assembly machines can detect defective products during the assembly process and automatically reject them without stopping the production line. This is a standard feature in advanced automated assembly systems.

II. How It Works

StepAction
1Parts are fed into the assembly machine (e.g., via a vibratory bowl feeder).
2Inspection stations are placed at key points in the assembly sequence (e.g., after part insertion, after fastening, after final assembly).
3Sensors or vision systems check each product for defects.
4If a product passes inspection, it continues to the next station.
5If a product fails inspection, the machine triggers a reject mechanism (air blast, pusher, diverter) to remove the defective part from the line.
6The defective part is collected in a reject bin for later analysis or rework.

III. Common Defect Detection Methods

MethodWhat It DetectsNotes
Vision system (camera + software)Missing parts, incorrect orientation, surface defects, scratches, wrong color, misalignment, foreign objectsMost flexible method; can detect many types of defects in one station.
Torque sensorInsufficient or excessive fastening torque (screws, bolts)Monitors screwdriving or press‑fit operations.
Force / pressure sensorInsufficient insertion force, missing components, press‑fit depthDetects abnormal resistance during insertion.
Presence sensor (photoelectric, inductive, or fiber optic)Missing components or partsSimple and fast but limited to presence/absence only.
Leak tester (pressure or vacuum)Leaks in sealed or fluid‑containing productsUsed in automotive, medical, and pneumatic applications.
Electrical testContinuity, resistance, short circuitsUsed for electronic or wired assemblies.
Dimension gauge (laser or mechanical)Out‑of‑tolerance dimensionsVerifies critical dimensions (e.g., height, width, diameter).
Weight check (checkweigher)Missing components or materialDetects missing screws, seals, or liquids.

IV. Rejection Mechanisms

MechanismHow It WorksSuitable For
Air blast nozzleBlows the defective product off the conveyor or trackSmall, lightweight parts
Pusher / solenoid plungerPushes the product sideways into a reject chuteMost products; reliable and simple
Diverter gate / flipperRedirects the product to a reject conveyorProducts on conveyors; can handle heavier items
Robotic pick‑and‑place rejectRobot picks the defective item and places it into a reject binFlexible reject handling for many product types
Drop‑out / trapdoorA trapdoor opens, allowing the part to fall into a reject binGravity‑fed systems; parts that can fall freely

V. Reject Handling Workflow Example

text
Assembly → Inspection (vision + torque) → If PASS → Continue to next station
                                       → If FAIL → Air blast or pusher removes the part → Part goes to reject bin

VI. Important Considerations

FactorRecommendation
Inspection positionPlace inspection stations after each critical operation to catch defects early.
Reject delay timeProgram a small delay to allow the defective part to reach the reject mechanism.
Data loggingRecord reject count and defect type for quality analysis (helps identify recurring issues).
Operator alertSound an alarm or show a message on the HMI when a high reject rate is detected.
Reject binProvide a clearly marked bin with separate compartments for different defect types.
Rework loopFor some parts, include a manual rework station near the reject bin for minor defects.

VII. Summary Table

Inspection TypeDefects DetectedReject MethodTypical Cycle Time
VisionMissing parts, orientation, scratches, misalignmentAir blast or pusher0.1–0.5 seconds
TorqueUnder‑torqued or over‑torqued fastenersPusher or diverter0.3–0.8 seconds
ForceInsufficient insertion depthPusher or diverter0.3–0.6 seconds
PresenceMissing componentsAir blast or pusher0.05–0.1 seconds
Leak testAir/fluid leaksPusher or diverter1–5 seconds
Electrical testShorts, open circuits, wrong resistancePusher or diverter0.5–2 seconds
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