Pick and Place Machine Maintenance Schedule

A placement machine is a set of mechanical axes, a set of feeders and a vision system, and each of them drifts. Maintenance is the schedule that keeps the drift inside the tolerance the placement accuracy depends on, and the schedule is set from the drift rate rather than from a manufacturer interval alone.

What Drifts and How Fast

The nozzles wear at the tip and lose their grip, the feeders index slightly further or less far with each pull, the belt tension changes and the vision system collects dust. Each has its own rate and each is found by a different check.

The machine calibration holds better than the consumables, which is why the consumables are the first place to look when placement degrades. Our placement capability notes describe how the accuracy is measured.

Nozzle Care and Its Check

The nozzle picks a part by vacuum and it loses the part when the tip is worn, chipped or partly blocked. A blocked nozzle picks the part at an angle and places it with an offset that varies between placements.

The check is a vacuum reading per nozzle and an inspection of the tip under magnification. Both are quick and both are worth doing on a schedule rather than after a defect.

Feeder Maintenance

A feeder is a mechanism with a spring and a ratchet, and it feeds a pitch that is smaller than the human eye can judge. The wear shows as a part that is picked slightly off centre and placed with an offset in one direction only.

The check is the pick position on the vision system, and the indicator is a drift in one direction across many placements. Our first pass yield notes describe how the resulting defect pattern appears.

The vision system aligns the part and checks it, and its accuracy depends on the lens, the lighting and the cleanliness of both. A dusty lens produces a placement offset that is constant and a change in the lighting produces one that varies with the part.

The check is a calibration target placed on the table and measured, and the lighting is verified with the same target. Both are simple and both are often omitted from a maintenance schedule.

The belt tension changes the position of the board rail and therefore the position of every placement. The rails move when the conveyor width is changed, and the reference is the machine coordinate system rather than the rail itself.

The check is a placement on a target board at the start of a run after any width change. Our board quality notes describe how the result is judged.

The schedule is a compromise between the cost of a maintenance stop and the cost of the defects that a drifting machine produces. Both are measurable, and the schedule belongs with the data rather than with a preference.

The pattern that works is short frequent checks on the consumables and longer scheduled work on the axes, with the results recorded so that the interval can be adjusted. Our floor zoning notes describe how the line is arranged around those stops.

The record is the vacuum reading per nozzle, the pick position per feeder and the calibration result. Those three describe the state of the machine well enough to predict the next drift.

The trend of vacuum readings predicts a nozzle replacement, and the trend of the pick position predicts a feeder service. Both are cheaper than the defect that follows them.

Checks Before Release

The environment around the process, including temperature, humidity and cleanliness, sets limits on what the process can hold. A result that cannot be reproduced is not a result, and reproducibility should be demonstrated rather than assumed.

The tooling, the material and the profile form one system, and a change to any of them should be assessed against the other two before it is released. Handling between operations is part of the process, and the damage it causes is often attributed to the operation that preceded it.

A change that is not recorded is a change that cannot be explained when the result moves, which is why the record is part of the process. The checks that matter are the ones performed on the product rather than on a sample kept for the purpose, because a coupon that travels with the panel is the only evidence about that panel.

Where an operation cannot be verified afterwards, it has to be controlled during the operation, and that control has to be visible in the record. Consumables have a life measured in cycles, and the replacement point should come from the measurement rather than from a failure.

The sequence of operations is part of the specification, because a different order produces a different result from the same steps.

Verification and Records

Where a process is at the edge of its capability, the margin should be bought deliberately rather than discovered during production. Where two operations share a tolerance, the allocation between them should be explicit rather than left to whichever is measured first.

Where a requirement can be measured, it should be measured at the point of manufacture and recorded against the board or the lot it applies to. A measurement taken at the wrong point of the process describes the wrong thing, however carefully it is made.

Does a machine calibration replace feeder maintenance? No. The calibration describes the axes and the feeder is a separate mechanism with its own drift.

How often should nozzles be replaced? On the trend of the vacuum readings and the tip inspection rather than on a fixed count.

What does gopcba provide for machine maintenance? We provide a schedule built from measured drift rather than from default intervals, vacuum readings and pick positions recorded per nozzle and feeder, vision calibration verified with a target, a placement check after every rail width change, and trends that predict the replacement.

Points to Confirm at First Article

A parameter that is set once and never re verified drifts, and the drift is usually discovered by a defect rather than by the record. Where the process window is narrow, the measurement resolution has to be better than the window, or the data cannot distinguish a good part from a marginal one.