A pick-to-light system puts a light and a display at each location and tells the operator which location and how many. It is accurate at the pick, and that accuracy is only worth something if the container the parts go into carries an identifier that survives to the next step. Where the container labelling is weaker than the pick system, errors appear downstream and get blamed on picking.
The container is the record of the pick
Once parts are in a container, the container is the only thing that says what the pick was for – which order, which batch, which destination. A pick-to-light system knows, but the knowledge lives in the system and not on the box. Where the box carries a matching identifier, the two can be reconciled at any point. Where it does not, the reconciliation has to happen by position or by memory, and both fail.
Identifier has to survive the route
From the pick face the container goes onto a cart, onto a conveyor, into a consolidation area and into a vehicle. Every one of those is an abrasion opportunity. A label that is legible at the pick face and unreadable at consolidation is a system with a gap in it, and the gap is usually discovered when a container arrives somewhere with no readable identification. Durability matters more here than at almost any other point in the container’s life.
Placement for both people and readers
An operator needs to see the identifier when placing parts, which means on the front or the top. A fixed reader needs it in its field, which is usually on a side. Those are not the same face, and the resolution is either two identifiers or one identifier on a face that serves both – usually a wrap-around or a position on an upper side wall. Where only one is used, one of the two users is straining.
Reusable identifiers and the changeover problem
A container identifier that belongs to the trip rather than to the container has to change every trip, which means either a writable surface or a replaceable label. A writable surface – a card holder, a sleeve, a wipe-clean panel – is the standard solution and it is worth designing into the container. A replaceable label works and generates waste and a re-labelling step at every trip.
Colour as a secondary channel
Colour coding containers by destination or by order type is fast to read at a distance and needs no power. It is also coarse – a handful of categories at most – and it fades. Where colour is used, it should be a secondary channel confirming what the identifier says, not the primary one, and the colours need to stay distinguishable after a year of use.
What to check before installing
Whether the container identifier is readable at every point the container passes, whether it survives the route, and whether it can be changed when the trip changes. Three questions. Where all three are yes, the pick system’s accuracy carries through. Where any is no, the container is the weak link and the system’s accuracy stops at the pick face. The general durability question is in label wear and read rates.
Reconciliation at consolidation
Where several containers are consolidated into one shipment, the identifiers have to be read together and matched to the order. A container whose identifier cannot be read at that moment becomes a manual reconciliation, and manual reconciliation is where the errors are. Reading the containers at the point of consolidation, before they are combined, is the cheapest control available and it depends entirely on the container label surviving that far.