Linear Gantry and Truss Robot Systems

Motionwell Automation designs and builds linear gantry and truss robot systems in Singapore, and this page is about the machine rather than the job it does: what the structure is, how the series steps, and what has to be settled before anyone can size a beam. Our own linear gantry series runs a compact three-axis aluminium extrusion frame at 5 to 20 kg payload with pneumatic multi-finger grippers, a welded steel single beam at 50 to 200 kg with 10 to 30 m of X-axis travel, and a double beam carrying 200 to 1,000 kg and above across spans beyond 20 m. The X axis runs on rack and pinion, the beam is built in sections, and the single-beam and double-beam builds can carry one or two independent Z columns. On a row of machine tools, one gantry services more than ten machines. Machines are designed, assembled and tested at our Woodlands Link facility, and the company has delivered more than 150 special purpose machines since 2014 under ISO 9001:2015 and bizSAFE Level 3.

Where we stand, said plainly before you read further. We do not manufacture robot arms, servo drives, linear guides or rack. We buy those and design the gantry around them: the frame, the beam, the carriages, the Z columns, the tooling interface, the cable management, the guarding and the controls. We therefore have no reason to sell a beam where an arm is the right machine, and a section at the end is devoted to when a gantry is the wrong purchase.

This page covers what Cartesian kinematics buys structurally, how the three series step together, when a second beam becomes necessary, why deflection over span usually sets the beam instead of the motor, what two Z heads change, drive choice over long X travel, aluminium against welded steel, and how a machine whose working envelope is overhead gets guarded. The application of tending machines with a gantry, including the arithmetic for how many machines one beam can hold, is on our machine tending automation page and is not repeated here. If you already have a part weight, a span and a ceiling height, skip ahead and talk to an engineer.

What Does Cartesian Kinematics Buy You Structurally?

A different load path, and everything else follows from it. In a gantry the payload is carried by a beam supported at its ends and grounded through columns into the floor or the building steel. In an articulated arm every newton of payload is a moment carried through each joint in turn, back into the base casting.

Three consequences of that table are why a gantry gets chosen at all.

Distance is cheap on a beam. Adding travel adds beam, rail and rack, not a moment arm, so the payload at the far end of a long run is the payload at the near end. On an arm, reach and payload trade against each other continuously, which is why extending an arm usually means moving up a class or putting it on a track.

Orientation is what you give up. Three linear axes deliver the part in the orientation the gripper picked it up in. Where a part must enter a fixture at an angle, no amount of travel substitutes for a wrist. A rotary axis can be added at the Z column, but at that point you are buying articulation on a Cartesian frame and the comparison deserves to be reopened.

Which of the Three Series Fits Your Payload and Span?

Payload, span and beam construction step together rather than independently. You do not get 200 kg on an aluminium extrusion frame, and you do not need a welded double beam to move a light tray between assembly stations. The boundaries below are structural.

Traverse speed moves the other way as the machine gets bigger: 1.5 m/s on the compact frame, 1.2 m/s on the steel single beam, 1.0 m/s on the double beam. On any long axis the binding limit is usually what it costs to stop the moving mass without exciting the structure, rather than the torque available at the drive.

Two cautions before a row of that table gets read as a specification.

Repeatability is not placement accuracy. ±0.2 mm describes how tightly the machine returns to a taught point, not whether the part seats, which is decided by how well it was located before the pick, by gripper repeatability, by debris on a locating face and by fixture wear. Where a part cannot be located mechanically, a camera measures its position before each pick and the controller corrects the move, as set out on our machine vision inspection page.

The gap between the compact and single-beam classes is real. There is a step in construction between a bolted aluminium frame and a welded steel one, and an application landing between the two gets engineered rather than picked off the list. Say so early, because it changes the frame rather than the drive sizing.

The compact class also appears where nothing heavy is handled at all. On the semi-automatic electronic test machines we build, an XYZ three-axis gantry frame carries the test head down onto the product over a linear guided worktable, which is how a small Cartesian frame delivers a controlled vertical press with a repeatable approach.

When Is a Second Beam Structurally Necessary?

When the span, the payload or the number of Z carriages puts more into one beam than one beam should carry. That is a stiffness and torsion question, not a payload rating.

The torsion row decides more than people expect, because it is not on the payload rating. A single beam carries the Z column and its load hanging to one side of the beam’s own centre, so it bends and twists at once, and the twist reaches the tool as a lateral error that grows with Z extension. Deepening the section helps the bending far more than the torsion. Bridging between two beams changes the mechanism: the pair resists that twist as a couple, which is far stiffer per kilogram of steel than winning it on one section.

Three signals that the second beam has stopped being optional: the span has to grow but the ceiling will not allow a deeper section; two Z columns have to work the same run and one beam does not give enough carriage length to keep them apart; or the machine needs a walkway, which has to sit on something. Where a single beam still wins it wins clearly, and a row of machine tools inside the 50 to 200 kg band with column positions along one side is what it was drawn for.

Why Does Deflection Over Span, Not the Motor, Usually Set the Beam?

Because those are two different sizing problems and only one of them is easy. Motor sizing is a torque calculation: inertia, friction, acceleration, duty. Beam sizing is a stiffness calculation, and stiffness is a set of decisions about section, span and column spacing that you can still influence at concept review and nobody can change after fabrication.

For a beam carrying a load between supports, deflection scales with the cube of the span and inversely with the second moment of area of the section. Doubling the unsupported span is therefore roughly a factor of eight in droop at the same section, and the recovery comes from section depth or another column, not from a bigger drive. A quotation that answers a longer span with a larger motor is answering the wrong question.

Static droop is only the visible half. The moving half usually costs the cycle:

The beam is a spring and the carriage is a mass. Every stop excites an oscillation, and until it decays the Z column cannot descend into a fixture with any confidence, so settle time joins the cycle whether or not it appears on a timing chart. A deeper section raises the natural frequency and shortens the settle. A faster drive shortens the move and lengthens it.

Worst case is not the end of travel. For a simply supported beam the worst deflection is near mid-span, not at the columns, and with two Z carriages it is both of them near mid-span at once. Ask for the deflection figure at that position, with the tool loaded, not as a single headline number.

Thermal length is a long-travel problem. A steel structure tens of metres long grows and shrinks with shop floor temperature. If the machine homes at one end and works at the other, that growth lands in the placement error at the far end, which is one reason to reference against a datum near the work.

Deflection under load is the honest acceptance test. The figure worth writing into a specification is placement measured at the far end of the envelope with the tool loaded, because that is where compliance in the tool, deflection in the structure and inertia in the moving mass appear together. The same discipline applied to tooling is on our end of arm tooling page.

The series repeatability figures step from ±0.1 to ±0.2 to ±0.3 mm for exactly this reason. The machines are not built to a worse standard as they get bigger; they get longer, heavier and more flexible, and the achievable figure follows the structure.

What Do Two Z Heads on One Beam Actually Change?

Mechanically, they turn one carriage into two independent lifting mechanisms on the same beam, each with its own gripper set. On the dual Z-axis builds each column carries a pair of pneumatic grippers, so the head handles four workpieces at once: one column lifts finished parts out while the other lowers blanks in, and load and unload happen in one visit instead of two.

What that buys is visits. Load and unload happen in one visit instead of two, so across a row of machines a dual-Z head halves the number of visits the gantry has to make, and it is the visits rather than the reach that limit how many machines one gantry can hold. How that gain translates into machines served is worked through in the cycle-time arithmetic on our machine tending automation page.

What the second head costs on the structure side is less often discussed:

Mass on the beam, always. Both columns and both gripper sets ride the beam on every move, working or not, and that mass sits permanently in the deflection case, the settle time and the drive sizing.

Carriage length. Two carriages need enough beam to sit on without colliding, and enough length at each end for both to reach the same station. On a shorter single beam that is sometimes why the answer comes back as one head.

A collision envelope that is enforced, not assumed. Two independently driven carriages on one rail is a machine that can drive into itself. That constraint belongs in the motion controller as a hard limit checked at commissioning, not in a comment in the program.

Two of everything else. Two Z drives, two sets of tooling, and twice the air and signals to route along the full travel, so the cable carrier and its fill get sized alongside the tooling rather than after it.

What Drives the X Axis Over Ten to Thirty Metres?

Long travel eliminates most of the options before anyone gets to preference. Here is what survives and why.

That is why the X axis in our gantry series runs on rack and pinion, why the Y axis uses a ball screw or a timing belt depending on the class, and why the Z runs on precision linear guides. (In the drive table, change the ball screw row to: ‘Excellent stiffness and resolution on short precision axes, and one of the two options our series specifies on Y’.), and why the Z runs on precision linear guides. The same reasoning shapes the related products: the low-profile seventh-axis track drives ground-grade rack and pinion from a servo motor and planetary gearbox, and the dual-rail truss manipulators drive theirs through a common pivot shaft on V-groove roller guides rather than recirculating ball guides, because a roller on a V edge sheds the debris a ball guide would ingest.

On the motor, a long gantry axis is servo territory with an absolute encoder. The encoder removes the homing routine, holds position through a power loss and supports dual-motor gantry sync, which keeps the two ends of a bridge on a double beam from racking against each other. Where an axis has no positioning requirement, an induction motor and a VFD is the cheaper right answer, and our gantry builds use servo or VFD drive depending on what the axis has to do. The full trade is in our note on choosing between servo and stepper drives.

Cable management is not a detail on a long axis. A truss manipulator with 12 metres of Y-axis travel has to deliver air and signals to a tool that never stops moving, so we use igus cable carriers with continuous-flex cable rated for the travel, and the bend radius gets respected.

Should the Frame Be Aluminium Extrusion or Welded Steel?

The payload class mostly decides this, and the environment decides the finish. It is not an open choice at every size.

The environment is the second filter, and our material selection across machine types runs the same way: mild steel or aluminium extrusion for general industrial work, anodised 6061-T6 aluminium with a hard anodise for electronics and cleanroom builds, and stainless for GMP and food-contact machines. Anything sliding, rolling, meshing or flexing sheds particles as it wears, so a gantry inside a classified zone gets its mechanism enclosed or moved below the product plane rather than cleaned more often.

One honest note on aluminium. One honest note on aluminium. Extrusion is specified on the compact class as a lightweight frame, and it is not a route to the same stiffness. Holding 200 kg over a long span on extrusion means adding so much section that the argument has already been lost.

How Do You Guard a Machine Whose Working Envelope Is Overhead?

From the risk assessment, and with the recognition that a perimeter fence answers only part of the question. Start from an ISO 12100 risk assessment and let it drive the design. The robot and the integrated system are covered by ISO 10218-1:2025 and ISO 10218-2, with each safety function carrying a required performance level under ISO 13849-1:2023, calculated and validated rather than asserted. The 2025 edition of ISO 10218-1 references the 2023 edition of ISO 13849-1, so a design documented against the older edition will need its performance level calculations restated when the machine is reassessed.

The ordinary guarding standards still set the physical design. ISO 13857 fixes safety distances for reaching over, under, around and through openings, which sets mesh aperture against standoff. ISO 13855 governs scanner and light curtain positioning, with the minimum distance coming from the approach speed constant, taken as 2,000 mm/s up to 500 mm and 1,600 mm/s beyond, plus measured stopping performance. ISO 14119 covers interlocking devices and how hard each is to defeat.

Four things are specific to a machine working above head height.

The travel path crosses things a fence does not. A perimeter guard controls who walks in at floor level. It does nothing about a load travelling over an aisle, a walkway or a workstation somebody stands at. Settle the route at layout stage, either keeping the loaded path off the areas people occupy or containing what is underneath it. That decision is nearly free before the columns are placed.

Grip has to survive losing its utilities. The design question is whether loss of air or power releases the load. A mechanically retained grip, a design that fails closed, or containment under the path are the answers. A perimeter guard is not one.

The maintenance route is part of the machine. The double beam builds carry a maintenance walkway with safety railing and an access ladder, which is an access route at height on your machine and needs its own assessment, its own lockout point and a defined way of getting somebody down again. It is also why a walkway is a specification item rather than an extra: retrofitting one onto a beam that was not designed for it is not a small job.

Stopping performance is measured, not assumed. A long axis moving at 1.0 to 1.5 m/s with hundreds of kilograms on it has run-down behaviour that has to be measured on the built machine before any scanner distance calculated to ISO 13855 can be confirmed.

Singapore does not require CE marking, but the Workplace Safety and Health Act requires dangerous parts of machinery to be securely fenced, and machines incorporating lifting equipment must be certified by an approved authorised examiner before use, which is a live question on a gantry rather than a formality. We deliver the physical scope that follows: guard fencing and interlocked access doors, safety laser scanners, safety-rated stop circuits, LVD and CE testing, and MOM lifting certification, as set out on our machine safety and CE marking page. We do not issue CE certificates and we are not a notified body.

What Has to Be Specified Before a Gantry Can Be Sized?

Four things decide the structure, and none of them is the drive.

1. Heaviest part, plus the tool. Gripper body, fingers, manifold, valves and cabling come out of the payload before the part gets any, and the centre of mass matters as much as the total.
2. The envelope in three numbers, measured to the extremes actually reached, including the top of the tallest stack and the depth of the deepest fixture.
3. Where columns can land, and what is already overhead. Column positions are a floor constraint rather than a machine one, and crane, ducting, sprinkler heads and roof trusses change concepts more often than anything else on this list.
4. Placement tolerance and where it is measured. A tolerance at the far end of the envelope with the tool loaded is a specification. A single repeatability figure is a datasheet line. Duty, environment and the interface list decide what it costs to build rather than what shape it is, and they belong in the same enquiry.

Lead time runs 16 to 24 weeks from concept approval to factory acceptance testing on a standard build, and 24 to 32 weeks where cleanroom compatibility or full validation documentation applies. Design, fabrication, assembly and testing happen at Woodlands Link with an in-house design team of eight, so a Singapore buyer attends the factory acceptance test instead of flying to it. How a build of this shape is scoped and commissioned is in our special purpose machine design guide.

On cost we will be specific about direction rather than price. For a row of machine tools served by one overhead gantry, capital and fenced cell area come out materially below deploying several six-axis arms for the same job, because you buy one motion system instead of several and fence one perimeter instead of several. Read that with its framing intact: it compares against several arms covering a run of stations rather than against one arm. It reverses as soon as the work stops being in a line.

When Is a Gantry the Wrong Machine?

This is the section that decides whether the rest of the page is worth trusting.

The work is not in a line. A beam pays for itself by serving stations along its length. Machines on both sides of an aisle, a scattered layout or two stations at right angles all push the answer back towards arms, and no amount of travel fixes a layout that is not linear.

The part has to arrive at an angle. Three linear axes present the part as the gripper holds it. If a fixture, a chuck or an assembly needs approach angles, the wrist is the machine, and the alternative worth pricing is a six-axis arm on a linear track rather than a gantry with axes bolted onto it. That is a product we build: the low-profile seventh-axis track holds ±0.05 mm repeat positioning on ground rack and pinion within 100 mm of overall height, so it costs little of the arm’s usable working height and needs no pit.

The building will not take it. Insufficient headroom, an existing crane on the same run, a roof that cannot be loaded, or a floor with nowhere to put a column foot. These are found by looking at the space, and finding them late is expensive.

The job is one station with a light part. A compact gantry frame is more machine than a single pick-and-place needs, and a small arm or a collaborative cell is usually cheaper and quicker to redeploy. That comparison is worked through on our cobot versus industrial robot page.

The parts arrive heaped. Our delivered picking is from fixtured, taught or vision-corrected positions, and we have not delivered a random bin picking cell. If your parts genuinely arrive in a bin, treat it as its own project, and check first whether tray or magazine presentation upstream is cheaper than perception downstream.

Two standing exclusions while we are being direct. We do not take on production welding cells, and we do not manufacture robots: we design and build the gantry, the tooling and the controls, and integrate arms across FANUC, ABB, KUKA, Yaskawa, Yamaha and JAKA platforms, as set out on our robot integration services page. Where a standard machine covers your application at a lower price than anything we would build, we will say so. The delivered gantry work in context sits on our warehouse and intralogistics page.

Frequently Asked Questions

What is the difference between a gantry robot and a truss robot?

Usually nothing structural. Both names describe a Cartesian machine: three linear axes at right angles, carried on a fixed frame rather than cantilevered from a base like an articulated arm. Truss robot is the name used where the X beam spans between columns as a bridge over a row of machines, while linear gantry and Cartesian robot are used more broadly. What actually changes between builds is the beam construction, the span, the payload class and the number of Z columns on the beam, not the label on the quotation.

What payload and span can a linear gantry cover?

Our series covers 5 to 20 kg on a compact three-axis aluminium extrusion frame, 50 to 200 kg on a welded steel single beam with 10 to 30 m of X-axis travel, and 200 to 1,000 kg and above on a double beam across spans beyond 20 m. Payload on its own does not size the machine. What sets the beam is the load held at the worst position in the envelope, which is the Z column extended near mid-span, plus the deflection you are willing to accept there and the settling time you are willing to spend waiting for it to stop moving.

How do you guard a gantry robot that works overhead?

From the risk assessment, and with the awareness that a floor-level fence answers only half of it. Perimeter guarding is sized by ISO 13857 for reaching over, under, around and through, and any scanner or light curtain distance is calculated to ISO 13855 rather than chosen. What a fence does not address is a load carried above people, so the travel path over aisles and workstations, the behaviour of the grip on loss of air or power, and access to any maintenance walkway on the beam all have to be settled in the design. In Singapore, machines incorporating lifting equipment also need certification by an approved authorised examiner before use.