Detecting Missing Parts After Assembly

A missing part is "what should have been done was not done" (the part is not in place, the process step was not performed); a wrong part is "it was done, but done wrong" (reversed part, wrong model, wrong orientation). The first checks existence, while the second also has to judge attribute and orientation, which makes the acceptance criteria design more complex.

At process steps where the acceptance criteria are clear and imaging is stable, visual inspection can take on 100% inspection and is more consistent than manual labour. However, for process steps whose criteria are hard to quantify or that require tactile or auditory judgement, it is still recommended to keep manual labour or switch to other sensing methods — there is no need to force vision to solve every problem.

It depends on whether the process steps are completed at the same position and at the same moment. For several process steps completed in sequence at the same station, one camera can image them at different times; process steps distributed across different stations need their own acquisition points. The core constraint is Whether the result features can be captured after each process step is completed.

Make "model" a dimension of the inspection solution (recipe): when the model changes, switch to the corresponding inspection regions and acceptance criteria templates. The switch can be done automatically by a model signal from the PLC, or selected by the operator in the interface.

The value of missing-part inspection lies not only in "sorting out defective parts" but also in exposing process problems: if missing parts occur repeatedly at a certain process step, the problem may lie in upstream equipment or material supply, and the inspection data itself is a troubleshooting clue. When interlocking with the PLC, we recommend distinguishing two signals, "single defective part" and "consecutive defective parts": the former only needs rejection, while the latter should trigger a line stop or alarm to prevent the same problem from continuing to produce output.

In multi-process scenarios, arranging the inspection sequence in physical assembly order is the most intuitive and makes problems easiest to locate: if the criteria for a process step are not met, the site immediately knows which station to return to. Note that the same position may have several legitimate visual manifestations. For example, press-fit seating may show up as consistent height, or as a correctly positioned press mark. The criterion should be the one that is most stable and least affected by illumination and batch variation, not the one that looks the most precise.

View the object characteristics, acceptance criteria and optical considerations for each object; it covers 8 common object types including screw presence/absence inspection, spring presence/absence inspection, clip presence/absence inspection and seal ring presence/absence inspection.

What visual inspection replaces is repetitive visual judgement, not manual labor for everything. The typical division of labor is: vision performs part-by-part full inspection and judgement, while people handle re-judgement of borderline samples, changeovers and exceptions, and maintenance of the optics and tooling. How many people are actually involved depends on the degree of automation and the re-judgement strategy.

Please provide the assembly flow chart (process sequence) and photos of the results at each process step; our engineers will judge process step by process step which elements are suitable for vision verification.