By the EVST Applications Engineering Team · Last updated 1 June 2026 · Reviewed by EVST motion-systems engineering
A robot ground rail — also called a seventh axis, linear track or travel axis — moves an industrial robot along a straight line so one robot can reach and serve several machines or stations instead of standing fixed at one. It expands the working envelope, enables a one-track-multi-machine layout, and cuts the robot count for a given line. This guide covers the load and length that decide a rail, the one-track-multi-machine economics, and how EVST sizes a travel axis — for welding, machine tending and handling.
Key takeaways
- A ground rail adds a 7th axis so one robot covers several stations along a line, rather than buying a robot per station.
- EVST standard rails come in W500 / W650 / W800 frames rated for 500 / 1000 / 2000 kg, spliced in whole-metre sections from 3 to 6 m, with travel speed ≥20 m/min.
- Work stations can sit on both sides of the track; a handling robot can share the same rail to relay tasks.
- It pays when stations are spread along a line and a fixed robot would otherwise idle or be duplicated.
- The industrial robot and cell run guarded to ISO 10218.
This article is for integrators, production managers and plant owners extending robot reach along a line. It covers ground rails (and references sky rails and trusses); it does not cover AGV/AMR transport between separate cells.
What a ground rail (7th axis) actually does
A standard six-axis robot has a fixed working radius. A ground rail mounts the robot on a servo-driven linear track so the whole robot travels along a straight path, adding a seventh coordinated axis. The robot and rail move as one system, so a single arm can pick, weld or tend at multiple positions spread along a line — work that a fixed robot could not reach without duplicating the robot.
According to the International Federation of Robotics’ World Robotics reports, handling and welding — the two jobs that most often run on a travel axis — are among the largest industrial-robot application categories, because extending reach along a line is one of the cheapest ways to raise a cell’s coverage.
When a ground rail pays off — and when it doesn’t
EVST scopes a travel axis with what our engineers call the Coverage-First method: map where the work actually sits along the line before specifying the robot, because the rail length and load follow from the station layout, not from the arm’s spec sheet. Use this frame:
| Choose a ground rail when… | Reconsider when… |
|---|---|
| Work stations are spread along a line | All work sits inside one fixed radius |
| A fixed robot would idle between stations | The single station already saturates the robot |
| You’d otherwise buy a robot per station | The line is short and duplication is cheap |
| Both sides of an aisle need serving | Floor space for a floor track is unavailable (consider a sky rail) |
| Long or large workpieces exceed arm reach | Multi-directional XYZ travel is needed (consider a truss) |
One-track-multi-machine: the core economics
The headline benefit is the one-track-multi-machine layout: a single robot rides the rail to serve several machines or stations in sequence, so you buy one robot instead of one per station. EVST rails allow work stations on both sides of the track, so one robot serves left and right in turn; a handling robot can share the same rail to relay welding and transfer, packing the cycle tighter. The result is fewer robots and a lower automation cost per station — the rail itself is far cheaper than an additional robot.
EVST ground-rail specifications
| Item | EVST spec |
|---|---|
| Load classes | W500 = 500 kg · W650 = 1000 kg · W800 = 2000 kg |
| Splicing | Whole-metre sections, 3–6 m (extend to required travel) |
| Travel speed | ≥20 m/min |
| Control | Robot–rail coordinated as a 7th external axis |
| Stations | Both sides of the track; optional handling-robot relay |
| Structure | Cast or welded body; four cover types (organ / sheet-metal / flower-plate / armoured) |
These are EVST’s own product figures, not generic estimates. Crucially, EVST machine-bases every metal structural part through an annealing process so the rail stays dimensionally stable over years of high-precision travel — a step low-cost makers skip to cut cost — and sizes the motor and reducer to prevent the vibration that wrecks accuracy and lifespan.
How a rail cell is built
A travel-axis cell has the robot and gripper/torch, the rail and its drive (servo motor + precision reducer + rack-and-pinion), the station layout along the track, and the coordinated control that sequences the stations. Two engineering details decide whether it holds up: the drive sizing (under-sized motor/reducer causes the shudder that degrades repeatability) and the structural stability (annealed, QC-checked frames hold flatness over the rail length). In practice the failure mode we see most is a cheap rail that shudders or warps within months; EVST addresses this with annealing, three QC gates (hole-position accuracy, flatness, smooth no-noise travel) and correct drive sizing.
Where it applies across industries
- Steel structures and heavy fabrication — welding long beams and frames a fixed robot can’t span.
- Automotive and battery lines — tending and handling across machines, lithium drying-line transfer.
- Machining shops — one robot riding the rail to load several CNC machines.
One rail concept maps onto all three because the problem — work spread along a line beyond one robot’s reach — is the same. Looking ahead, IFR data shows handling and tending growing as plants extend lines and unattended running, which makes shared-rail layouts more decisive, not less.
FAQ
What is a robot 7th axis / ground rail? A servo-driven linear track that moves the whole robot along a straight line, adding a coordinated seventh axis so one robot can serve several positions along a line.
How many machines can one rail-mounted robot serve? As many as fit within the rail’s travel and cycle overlap; with stations on both sides and a shared handling robot, one rail commonly replaces several fixed robots.
What load and length does EVST offer? W500/W650/W800 frames at 500/1000/2000 kg, spliced in whole-metre 3–6 m sections to the required travel, at ≥20 m/min.
Why do some rails shudder or wear out? Usually an under-sized motor/reducer or steel that skipped annealing; EVST sizes the drive correctly and anneals every structural part, with three QC gates before shipping.
Ground rail, sky rail or truss — which? Ground rail for floor-level single-direction travel; sky rail to save floor space overhead; truss for multi-directional XYZ travel. See our rail-vs-truss guide.
Bringing it into your plant
A robot ground rail turns a fixed arm into one that covers a whole line — one track, many machines — cutting robot count and automation cost per station. The decision hinges on where the work sits along the line, not on the robot brand. EVST designs travel-axis cells with the Coverage-First method and builds its own rails — annealed, QC-gated, correctly driven — see our guides to extending robot reach with a rail, sky rails and welding with positioners, or talk to EVST about a one-track-multi-machine layout.
About the author — The EVST Applications Engineering Team designs and manufactures robot ground rails, sky rails, trusses and welding positioners, and integrates them into welding, tending and handling cells across steel-structure, automotive and machining industries. The team scopes a travel axis around measured station layout, load and travel — using the Coverage-First method above — and machine-bases every rail through annealing with three QC gates. Reviewed by EVST motion-systems engineering for technical accuracy; figures are EVST product specifications, sized per project. Corrections: see the Last Updated date.