Sizing a manipulator correctly: payload, reach, takt time

A 60-kilogram part does not need a 60-kilogram unit. The gripper weighs too – a vacuum gripper for cartons eight to fifteen kilograms, a mechanical form gripper with a rotary axis easily twice that. Add adapters, exchange plates and anything permanently mounted. Payload therefore always means the total at the tool interface. We quote our payloads including the tool for exactly this reason – anyone quoting without it is selling a figure never reached in service.

At the base of a pillar-mounted unit a bending moment arises from load times reach. 125 kilograms at 3.4 metres gives roughly 4.2 kilonewton metres – regardless of how sturdy the unit itself is, that moment has to go into the floor. Anchoring is therefore part of the design: bolted, anchored or on a ballasted base plate. Calculating anchor forces on site means calculating too late.

Reach is almost always specified for the typical movement and needed for the rare one. The exchange container stands two metres further back once a day; the pallet is approached from the other side towards the end of the shift. Size for the most distant point that actually occurs in service – not for the one drawn on the sketch. Extending later means a new unit.

Twenty movements per shift and twenty per hour are two different machines. Frequency determines drive sizing, duty cycle, maintenance interval – and whether pick-up time is an issue at all. At high frequency every second in gripping counts for more than every second in lifting; then the choice falls on a combined control that merges travelling and lifting into one element.

Coolant, scale, flour dust, cleaning foam, solvents, radiant heat, cold store temperatures, an ATEX zone – each of these changes the version. It rarely affects the structure but almost always seals, hoses, coating and sensors. These details belong in the enquiry, not in the commissioning.

Industrial floor is not the same as industrial floor. Screed on insulation, a raised floor, a freshly renovated coating, a duct just below the surface – all of this decides whether anchoring is allowed. Where drilling is not possible we use a ballasted mobile base plate; the ballast weight in turn follows from payload and reach. A circle that only closes if you walk it before ordering.

First: forgetting the gripper weight – the unit is too small and retrofitting costs more than the right size would have. Second: sizing for the typical rather than the least favourable point – the unit cannot reach the task on three days a month. Third: underestimating pick-up time – the unit is technically correct and still goes unused because lifting by hand is faster. All three arise at the desk and can be avoided with an hour at the workstation.