A 1300 mm reach cobot cannot normally build an 1800 mm pallet unaided because its usable vertical envelope must cover the stack, pallet, box height, gripper depth and approach clearance.
Why robot reach does not equal pallet stack height
Published reach measures the maximum distance from the cobot base axis to its wrist centre. It does not describe a rectangular working envelope or guarantee the wrist orientation required for palletising.
A floor-mounted cobot loses usable height because its shoulder starts near floor level and its links cannot remain fully extended through every joint configuration. The EOAT also places the gripping face below the wrist centre. A vacuum gripper with 250 mm of depth reduces the available height at the top layer by approximately the same dimension.
The top placement position includes the pallet height, completed stack height and a vertical approach distance. A 150 mm pallet carrying an 1800 mm product stack, with a 250 mm gripper and 100 mm approach, requires the system to control a gripping face above 2050 mm.
Joint limits, singularities and collision zones reduce the practical envelope further. Offline reach studies and physical trials establish whether every pick, approach, place and retreat pose remains achievable.
How a vertical lifting column works
A vertical lifting column moves the complete cobot base up and down on a guided linear carriage. Servo-driven ball screws, toothed belts and rack systems provide programmable motion over a defined stroke.
The column becomes an external axis when the palletising controller coordinates its position with the robot programme. Some systems reposition between pallet layers, while synchronised systems move during the robot cycle.
Layer-based repositioning is simpler because the column stops before the cobot executes the placement path. Continuous coordinated motion reduces dead time but requires compatible control software, motion limits and safety functions.
Common palletising column strokes range from 800 to 1600 mm. The selected stroke must cover the vertical difference between the lowest valid pick or place pose and the highest valid pose, plus clearance at both ends.
Stack height and indicative lifting stroke
The values below assume a 150 mm pallet, 250 mm-deep EOAT, 100 mm vertical approach and a cobot installation that provides 1050 mm of usable unaided vertical travel at the gripping face. They are initial sizing figures rather than substitutes for a reach simulation.
| Product stack height | Required gripping-face height | Indicative minimum stroke | Practical selected stroke |
|---|---|---|---|
| 1200 mm | 1700 mm | 650 mm | 800 mm |
| 1400 mm | 1900 mm | 850 mm | 1000 mm |
| 1600 mm | 2100 mm | 1050 mm | 1200 mm |
| 1800 mm | 2300 mm | 1250 mm | 1400 mm |
| 2000 mm | 2500 mm | 1450 mm | 1600 mm |
A reach model must also test the lowest layer. Excessive elevation can make the lower pallet corners unreachable or force the wrist into a joint limit.
Lift speed and palletising cycle time
Commercial cobot lifting columns commonly operate between 100 and 500 mm/s, although rated speed depends on stroke, moving mass and drive design. Acceleration and settling time often affect cycle time more than maximum speed over short moves.
A 300 mm layer transition at 250 mm/s takes 1.2 seconds before acceleration, deceleration and confirmation delays. Moving the column once per layer adds less time than repositioning it for every case.
Cycle modelling must separate robot travel, gripper actuation, product release and external-axis movement. The palletising cycle time calculation also includes conveyor presentation and pallet exchange delays.
Column movement during cobot travel can shorten the cycle where the controller supports coordinated motion. The risk assessment must evaluate the combined speed and kinetic energy of both mechanisms.
Payload derating and structural loading
The column carries more than the product payload. Its moving load includes the cobot, base plate, EOAT, product, dress pack and any valve manifold mounted on the arm.
A cobot rated for 20 kg still follows its own payload and centre-of-gravity limits when mounted on a lifting column. A 5 kg gripper leaves 15 kg nominal product capacity before accounting for hoses, fittings and offset mass.
The column rating must cover the complete moving assembly under acceleration. Bending moment also matters because an extended cobot creates an overturning load at the carriage and column base.
Manufacturers specify allowable axial load, moment load, duty cycle and speed as separate values. Floor fixings and the supporting slab require calculations based on dynamic loading rather than static mass alone.
Column, horizontal rail or fixed pedestal
A fixed pedestal raises the cobot base without adding a powered axis. It has the lowest mechanical complexity, but one fixed height rarely covers both a low infeed and an 1800 mm stack.
A vertical column suits one or two pallet positions where height is the main reach constraint. Its compact footprint preserves floor space around the palletising cell.
A horizontal rail moves the cobot between pallet stations, conveyors or multiple machines. Rail travel increases the accessible floor area but does not solve top-layer reach unless the base height and robot geometry already cover the stack.
Some cells combine a raised pedestal with a horizontal seventh axis. The cobot palletising solutions layout must balance reach, throughput, pallet exchange and guarding before selecting the mechanism.
Selecting the external axis
Start with the highest gripping-face pose and the lowest pick or place pose. Add approach distances, EOAT depth, box dimensions and pallet tolerances to both positions.
Check every pallet corner because the furthest horizontal pose often occurs at the top outside corner. Verify the payload and centre of gravity for the heaviest product rather than the average case.
Specify stroke, usable speed, acceleration, repeatability, duty cycle, holding brake and ingress protection. Confirm that loss of power cannot allow the carriage to descend under gravity.
The final design requires a three-dimensional reach study using the selected cobot, EOAT and pallet pattern. Pallet pattern software defines layer geometry, but the integrator validates the resulting robot poses and joint limits.
Safety implications of adding a powered axis
A lifting column or rail changes the palletiser from a cobot-only installation into an integrated robot application with an additional powered hazard. BS EN ISO 10218 treats the complete robot system, including external axes, EOAT, conveyors and control functions, as the subject of system-level risk reduction.
The risk assessment identifies crushing, shearing, impact, trapping and gravity-drop hazards throughout the full stroke. A moving carriage creates pinch points at guides, covers, base plates and surrounding structures.
Collaborative operation is not established by the cobot label. The complete application requires validation of separation distances, speed and separation monitoring, safety-rated stop functions or power and force limiting according to the selected collaborative method.
A vertical axis can store gravitational potential energy when raised. A holding brake, mechanically secure drive arrangement or secondary restraint prevents uncontrolled descent after power loss or component failure.
Safety scanners, interlocked guarding or pressure-sensitive devices often protect pallet access and column movement. Muting and reset logic must prevent automatic restart while an operator remains inside the safeguarded space.
The technical file records the risk assessment, safety-related control performance, stopping measurements, drawings and validation results. PUWER duties apply to workplace use, while UKCA or CE marking follows the applicable supply route and current legislation for the completed machine.
Dress pack and cabling for a moving cobot base
A lifting column changes cable routing because power, communications, pneumatic lines and vacuum hoses travel with the carriage. Unsupported loops snag on the column, pallet load or robot joints.
An energy chain provides controlled bend radius and separates power cables from signal wiring where required. The chain length must accommodate full stroke without tension at either travel limit.
The robot dress pack also moves through six arm joints while the base changes height. Routing requires service loops at the base and wrist, strain relief at fixed transitions and clearance from sharp edges.
Vacuum hose diameter affects evacuation time and pressure loss. The vacuum gripper selection guide covers flow, cup area and product leakage alongside hose routing.
Cable carriers, hoses and valve blocks add moving mass to the column. Include them in payload, bending moment and duty-cycle calculations.
Commissioning checks for the seventh axis
Commissioning starts with mechanical end stops, software limits and homing repeatability. The column must retain a known safe state after an emergency stop, power interruption or encoder fault.
Test every pallet corner at the lowest and highest layers with the production EOAT and maximum case mass. Record joint positions, clearance, cable movement and cycle time during those tests.
Validate stopping performance at the maximum permitted column speed and moving load. Repeat measurements after changes to payload, speed, tooling or safety scanner fields.
Inspect fixings, guides, drive components and the energy chain at the manufacturer-defined intervals. Maintenance access must not require personnel to work beneath an unsupported raised carriage.
Frequently asked questions
Is a lifting column always required for an 1800 mm stack?
No. A long-reach cobot on a correctly sized pedestal can cover some 1800 mm stacks where the infeed height, pallet footprint, EOAT depth and joint geometry align. A reach simulation determines the result for the specified cell.
Is a lifting column the seventh axis?
Yes, when the controller commands the column as an additional programmable robot axis. A separately controlled lift that only indexes between fixed heights is still an external powered mechanism, even when the robot controller does not coordinate its trajectory.
Does the seventh axis reduce cobot payload?
The column does not change the cobot manufacturer's wrist payload rating. EOAT mass, dress-pack mass and centre-of-gravity offset reduce the product mass available within that rating.
Can the column move while the cobot is palletising?
It can when the controller, drive and safety architecture support coordinated motion. The combined trajectory requires collision checking and safety validation across the complete operating envelope.
Is a rail better for two pallets?
A horizontal rail suits separated pallet positions and shared infeed points. A fixed cobot can often serve two adjacent pallets through layout design, while a vertical column addresses stack height rather than horizontal spacing.
How much stroke margin is appropriate?
Specify enough margin for approach clearance, pallet tolerance, product variation and software limits. A design that uses the full mechanical stroke at a production pose leaves no allowance for overtravel prevention or later format changes.
