A non-standard line is judged on the machine, but it is delivered through the points where machines meet other machines. The frame, the fixture and the program can all be excellent, and the line still fails on the day it is switched on next to the upstream feeder, because nobody agreed who owns the conveyor flange, who writes the diverter command, which signals pass to the factory control room, or who signs the terminal that carries the emergency stop chain.
Reviewing the interface requirements of non-standard automation equipment before metal is cut removes that risk at the only stage where it is cheap to fix: the drawing and list stage. A requirement in this sense is a written statement that someone must be able to test, so each question below asks for a statement of that kind. The review follows the order in which interfaces actually appear in a build package, from boundary sheets and fixtures to records, spares and the signature on the acceptance sheet.
Why the interface list decides the schedule
Standard machines are bought against a catalogue; a custom line is bought against an agreement that someone else has to honour later. Every point where the new cell touches an existing process is a promise made twice: the mechanical promise of alignment and load, the electrical promise of signals and power, and the procedural promise of who changes what when the process recipe moves.
When those promises are written down as requirements, with an owner and a test attached, the build runs quietly. When they are assumed, they surface in commissioning, in the week when the plant has already stopped an old line and the cell cannot be released. The review below is a sequence of questions to put to a drawing package, a supplier scope, or your own engineering team, with the failure mode stated next to each question so the answer can be challenged.
Start with the boundary drawing, not the machine drawing
Ask for a single line that separates the new equipment from everything already in the building, drawn on one sheet in the same scale as the layout. Everywhere that line crosses something, there is an interface to review. If the only drawings available show the machine alone, the interface conversation has not started.
The boundary sheet should show hand-off points, power terminals, air connection, network entry, floor footprint, door and maintenance access, and the direction of material flow in and out. Every crossing needs an owner, a method of attachment and a state at the moment of transfer: temperature, orientation, cleanliness, data attached or not attached.
A useful test is to read the boundary sheet aloud with the people who will run the line. If they cannot say what arrives, in what condition, from which neighbour, and what leaves for the next neighbour, the boundary is a drawing exercise rather than a working document.
Product, fixture and carrier requirements
The first interface is the part itself. Confirm the datum surfaces the line may touch, which surfaces must not be touched, and the tolerance band of the incoming part as it arrives, not as it appears on the ideal drawing. A fixture designed around the nominal part will reject parts from the real supplier.
Ask what happens to the part between stations. If a carrier, pallet or nest travels with the product, the carrier becomes an interface: its locating features, its wear life, its cleanliness, and whether the downstream cell accepts it. A carrier that is convenient for one station and unusable at the next turns into a transfer mechanism nobody budgeted for.
Then think about changeover. Parts change. Confirm how many part families the fixtures must accept, what is changed by hand, what is changed by a tool, and what requires a drawing change. A fixture arrangement that cannot be revised quickly becomes the constraint on every future product revision.
Transfer hand-off between cells
A hand-off is a negotiation expressed in metal. Review the geometry: height, orientation, grippable area, clear envelope at the moment of grasp, and the reach the transfer device has. Review the timing: how long a part may wait, whether a neighbour may be starved, and what a full outfeed does to the upstream station.
Review the signal exchange that accompanies the part. Does the receiving cell announce readiness, does the sending cell announce presence, and which side decides the moment of release? Where the two cells come from different suppliers, an unnamed handshake is the usual cause of a stalled line, because each vendor believes the other owns it.
Confirm the reject route. A line that can detect a bad part but has nowhere to put it will either mix the part back into good flow or stop the whole line while an operator decides. Decide the reject rule, the reject location and the record that follows the reject before commissioning.
Control system, PLC and HMI boundaries
Ask which controller is the master of the cell and which neighbours merely respond. Then ask for the signal list in writing: every input, every output, the direction, the voltage or protocol, the meaning of a held contact, and the behaviour of the cell when a neighbour disappears from the network mid-cycle.
The HMI is also an interface, because it is how operators negotiate with the machine. Review which alarms the operator may clear, which require a supervisor, which require maintenance, and whether the wording of an alarm tells the operator where to look. Review the language of the HMI against the crew who will use it at shift change.
Then review recipe ownership. If the process parameters live in the machine and also in a factory database, ask which copy wins, who may change them, and whether a change is stamped with a time and a person. Uncontrolled recipe drift is invisible until a quality problem is traced back to it.
Electrical, utility and panel terminals
Electrical review is mostly a question of terminals. Agree where factory power ends and machine power begins, which side supplies protection and isolation, and which terminal block each cable lands on. Confirm the panel layout is serviceable: spare capacity, labelled ends, and a wire list that a local electrician can read.
Utilities are where custom cells embarrass teams. Compressed air needs a regulated pressure band, filtration quality, a shut-off, and a drain route. Water, if used at all, needs supply and dump arrangements, plus a plan for what happens when it is absent. Heating and extraction need to be checked against the building, not only against the machine.
Cleaning or surface preparation stations add their own boundary conditions, because process media may leave the cell. Where an application combines customized steam cleaning equipment with an automated transfer cell, drainage, humidity and residue belong on the same interface list. A transfer mechanism that works in a dry cell may not work in the same place once a process medium is present.
Data, traceability and record exchange
Ask what the cell must record, and for whom. Some records exist for the operator, some for process engineering, some for a customer audit, and some for the maintenance team. Each audience wants different granularity, retention and access, and each has to be designed rather than promised.
Then ask how a record is attached to a product. Where a part carries no identity, traceability means time plus station plus recipe, and that is enough for many processes. Where a part carries a code, review who reads it, when it is read, and what happens if the read fails.
Agree the exchange format and the boundary of responsibility for it. Whether the cell hands records to a plant database, a historian or a file share, confirm who maps the field names, who handles a gap in the exchange, and who can prove the exchange worked over a full production week.
Safety, guarding and machine-level interlocks
Review who is inside the risk zone during normal running, during a jam, during cleaning, and during a changeover. Guarding follows from that list, not the other way round. Ask what the machine does when a guard opens, when an operator reaches in, and when the line is in a slow jog mode.
Interlock boundaries matter most between cells. If a person opens a gate in one cell, what happens in the neighbour? Ask for a written stop-zone map, an emergency stop chain with its elements named, and a reset rule that an operator can follow without guessing.
Confirm that the safety design and the production design are reviewed together. A stop chain that clears every fault but restarts a half finished transfer has created a different hazard in the name of the first one.
Feed, environment and consumable routes
Feed and presentation are interfaces too. Confirm how parts arrive: bulk, nested, oriented, or already on a carrier. A supplier who assumes oriented parts and a plant that supplies bulk parts will design two different machines on the same purchase order.
Confirm the environment around the cell: ambient temperature band, dust, humidity, vibration from neighbours, and light level for the inspection station. Where a downstream station performs inspection or measurement, an upstream station that generates vapour, mist or residue is an interface problem long before it is a cleaning problem.
Ask where consumables enter and where waste leaves. Filter elements, media, tips and wear parts need a route that does not cross a clean product path and does not require a person to climb into the machine.
Supplier scope and documentation interfaces
With more than one vendor in the cell, the interface list is a contract document. For each crossing, name the party that provides the cable, the party that provides the connector, the party that writes the program, and the party that tests the exchange. Unnamed crossings are paid for twice later.
Documentation is an interface with the future. Ask what a new engineer needs to run the cell in two years: mechanical drawings that match the built machine, electrical drawings that match the panel, a program backup with a change log, a spare parts list with the parts actually fitted, and the parameter sheet that was used at acceptance.
Ask when documents are issued and how revisions are marked. Drawings that describe the machine as designed rather than as built create a maintenance trap the first time someone opens a cover.
Commissioning, acceptance and handover
The last interface is between the build team and the operating team, and it is reviewed as a schedule. Confirm what must be true before integration begins, what is tested at the cell level, what is tested with neighbours attached, and what runs for a sustained period before release.
For each interface crossing on the boundary sheet, ask for a witnessed result: the transfer was made, the signal was proven, the alarm was seen, the record appeared in the plant system. A signed interface list is worth more than a signed machine list, because the machine list is not where the risk lives.
Close the review with the people who will own the line. Ask them to walk the boundary sheet once more, in the order a shift would meet it: start, stop, jam, changeover, cleaning, and end of shift. A handover is complete when that walk produces no new questions.
A practical sequence for the review
Run the review in one meeting with the boundary sheet printed, and let each crossing be answered by name. Confirm the part interface, the transfer hand-off, the control and HMI boundary, the utility terminals, the record exchange, the safety chain, the documentation set, and the witnessed tests. Where an answer is not ready, write down who owes the answer and by when.
Where the line is part of a wider plan, the same questions apply at a larger scale, because automated production line solutions are assembled from cells whose boundaries were agreed one at a time. Where a process step is a cleaning or surface preparation task rather than an assembly task, bring the media, drainage and residue questions into the same meeting, since those boundaries cross both scopes.
For a first pass, a short list is enough: boundary crossings, owners, states, and the witnessed test for each. When that list exists and has been challenged by the people who will run the equipment, interface risk has moved from commissioning week to a quiet afternoon in the design office, which is exactly where it belongs.
