When a six-axis robot is fixed to the floor, its working envelope is limited by arm reach, so one machine often serves a single station. As workpieces grow larger or need to move between several machines, adding a seventh axis or a floor-mounted gantry track is the most cost-effective way to extend the robot along the shop floor.
Three configurations are common. A floor-mounted seventh axis places the robot on a carriage that travels in a straight line; it is simple and economical. An overhead gantry track suspends the robot from a beam, keeping floor space and aisles clear, which suits shops where parts are lifted from above. A truss-type travel axis mounts the robot on a high gantry, combining long span with clearance underneath.
Structurally, a travel axis consists of foundation rails, rack-and-pinion drive, carriage, cable carrier and protective covers. Long-stroke systems place high demands on the foundation: straightness and parallelism of the rail mounting surfaces must be held to a few hundredths of a millimetre per metre, otherwise the carriage will creep and rumble. Grout the base, provide levelling shims and finish with fine adjustment after installation.
Accuracy is the decisive indicator. Repeatability is typically plus or minus 0.05 to 0.1 mm, and long strokes bring rack accumulation error and thermal growth into play. Dual servo drives with anti-backlash pinions and closed-loop linear encoders are common practice; for welding and grinding paths, laser tracking or robot calibration compensates the axis error.
Speed and synchronisation set the cycle time. Travel speed is usually one to two metres per second, and the acceleration profile must match robot motion to avoid end-effector vibration at start and stop. The controller must support synchronous or coordinated motion between the external axis and the robot, planning travel ahead so that moving overlaps with welding or handling.
Size the axis on total payload: robot, end effector, workpiece and cables, with a safety margin. Confirm stroke, mounting style, floor load capacity and aisle width at the same time. In dusty or spatter-heavy cells, add covers and wiper plates, and prefer centralised lubrication to cut manual maintenance.
In practice, seventh axes and gantry tracks serve welding, grinding, painting, handling and machine tending where several stations share one robot. One robot covering three or four machines raises utilisation markedly, and for large workpieces in wind power, construction machinery and steel structures the floor-travel solution is close to standard.
Extending a robot from a fixed station to a whole line is exactly what a seventh axis or gantry track delivers, flexibly and economically. Stroke, accuracy, synchronisation and protection must all match for the system to run reliably. Truman designs and delivers robot seventh axes and gantry tracks based on your workpiece size and shop layout.
