When a factory asks a supplier for a machine that does not exist in any catalogue, the project usually fails long before the first drawing. Not because the idea is wrong, but because the request reached the builder as a sentence: “we need something that can do this, at our speed, on our line.” What engineering teams actually need to document is everything that was assumed when that sentence was written.
Start with the process, not the machine
Before anyone talks about frames, motors or vision systems, write down how the work is done today. The current manual or semi-automatic process is the only reference you will have for cycle time, defect rate and labour input, and it is what the new cell has to beat.
- The task broken into steps as it is performed now, including handling, waiting and rework — not just the value-adding action.
- Who performs it, how often, in which shift pattern, and what the operator has to decide rather than merely repeat.
- Measured takt and available window per unit, together with changeover time between products.
- Where the process currently fails: which step produces rejects, which one limits throughput, which one causes the complaints.
If this baseline is missing, a custom machine can be delivered exactly to specification and still fail the business case, because nobody recorded what “better” was supposed to mean.
Describe the part, and every variation of it
Non-standard automation almost always lives or dies on part variability. A requirement document that says “handle our 400 mm panel” is not enough. For each product family the machine must touch, record the dimensional envelope with tolerances, the material and surface condition, how the part is presented (orientation, nesting, fixtures, incoming packaging) and how much the incoming state can drift between suppliers and batches.
Then state the product mix explicitly: which variants run on the same cell, which changeover is acceptable, and whether new variants will appear within the machine's lifetime. This is the point at which a one-off machine turns into a platform. If a second product family is likely, say so now — fixturing, vision fields and recipe handling are cheap to design for on paper and expensive to retrofit later.
Turn outcomes into acceptance conditions
Vendors quote against what they can prove on a test run, so each requirement needs a condition that both sides can check at a defined moment. Phrase the requirement as an observable result plus the method of measuring it.
| Requirement type | Weak wording | Verifiable wording |
| Throughput | Fast enough for our line | Cycle time per unit measured over a continuous production window agreed with the supplier |
| Quality | No damage to the part | Reject cause list defined up front; pass/fail criteria for each, judged on parts from an agreed incoming batch |
| Availability | Reliable | Permitted stoppage time per shift, plus a list of consumables and their expected replacement intervals |
| Flexibility | Adjustable | Named variants and the changeover steps an operator may perform, with the target changeover duration |
| Safety | Compliant | Applicable market and standards for the installation site, and who signs off guarding and interlocks |
Anything that cannot be written this way is not yet a requirement; it is a wish, and it will be resolved later at whoever's expense is least prepared.
Document the boundary conditions of the site
A large share of custom-equipment arguments are not about the machine but about the interface it was never told to meet. Put the installation constraints in the same document as the function:
- Available floor area, entry doors, loading dock, and whether the cell must fit an existing line layout or a new building.
- Electrical supply, compressed air, water and drainage available at that position — voltage, phase, flow, and whether the equipment can add a load at all. Battery-operated and fixed-supply machines solve this problem very differently, and the choice belongs in the requirement, not in the quotation.
- Ambient conditions: temperature range, dust, moisture, washdown, hazardous or hygienic zones.
- Who operates and who maintains the equipment, their shift pattern, and what local skills and spare parts are realistically available.
Cleaning, surface preparation and other “support” tasks inside a plant show the same pattern. A PowerDe cleaning equipment line, for example, is split between driving-style mobile units for garages and narrow parking areas, hand-pushed units, and fixed 220 V machines — precisely because mobility, power source and working position are site constraints, not performance preferences. The same logic applies to any custom cell: state the boundary first.
Put the change process on paper with the requirement
Custom projects change; the risk is uncontrolled change. Agree in writing, before the build starts, how an added feature is raised, priced and accepted, who has authority to accept it, and how already-verified functions are re-verified afterwards. Add the same clarity to data and interfaces: which signals the machine must expose to your MES or line controller, who writes the recipe logic, and which documents (spare-part list, wiring diagrams, parameter backup, operator manual) must arrive with the equipment.
Include the questions nobody has answered yet as an open-points list rather than leaving them silent. An explicit open item that both sides have to close is a manageable risk; an assumption neither side wrote down becomes a dispute.
Where supplier engineering services fit
Sometimes the team asking for the machine cannot produce this document alone, because the process itself has not been defined. That is a normal situation and it is exactly what supplier-side engineering work is for. Non-standard automation equipment developed together with an engineering partner usually starts from a joint process study rather than a purchase order.
If your team is short of capacity in the middle of a project, staged support is worth asking about directly: hardware testing to confirm a process before it is committed to a cell, and integrated engineering team services when you need design and validation capability alongside your own engineers rather than a black-box delivery. For the cleaning side of factory maintenance, our Fixed Steam Cleaning Machine PowerDe HW02 shows how a documented duty — vehicle exterior, interior and engine-compartment work at stations and parking facilities — translates into published parameters such as heating power, steam temperature and tank capacity.
A practical sequence for the requirement document
- Baseline of the current process, with measured cycle time and known failure points.
- Part and variant description, including incoming condition and tolerance for drift.
- Functional requirements, each tied to a measurable acceptance condition.
- Site and utility boundary conditions, plus operating and maintenance responsibilities.
- Change control, deliverable documents, and the open-points list.
Write in English or in the language of the people who will build and maintain the machine, and keep the numbers you are unsure of on the open list instead of in the specification. If you are preparing this kind of document for a cell you have not built before, send it to us as it stands — gaps included. Reviewing an incomplete requirement is far cheaper for both sides than rebuilding a machine that met the words and missed the process.
