The boom length is fixed, so the robot can only access parts limited in length to approximately twice the robot's reach. Booms can easily be moved out of the way to improve overhead crane access for loading and unloading large parts.

It is not possible to use multiple carriages with radial gantries, but it is possible to combine multiple gantries in the same work cell. (See Photo 6)

Combining multiple gantries enlarges the part envelope that can be reached, and adds multiple arcs.

Similarly, radial gantries do not lend themselves to in-line processing.

However, two work stations can be are located on either side of the base, 180 degrees apart to expand the work envelope, and limiting devices can be integrated into the boom axis to interlock the booms, to provide safeguarding for either work station and to prevent overhead crane intrusion into the active workstation. Also, smaller robots can be mounted to a radial gantry to enhance their reach at a reduced cost.

Radial gantries also can be scaled up to include large extended-reach robots.

Because a radial gantry supports the robot as a cantilevered load, it must be rigid and have a solid foundation.

Special foundation requirements, ballast or base plates may be needed to counteract the forces of a moving robot at the end of the boom.

Utilities normally are routed through the interior of the boom, and an assist feeder for welding wire can be mounted to the wire drum at the base of the structure. Process equipment, such as nozzle cleaners, may be mounted on the boom in proximity to the robot.

Radial gantries often are used in applications in which short, intermittent welds or processing is done across the part, while linear tracks often are applied to applications that require long, continuous weld seams.

While coordinated motion between the robot, boom, and positioner is possible to achieve continuous welds, it is more common to “park” the boom in a stationary position and move the robot to weld joints within its reach.

Summary

In summary, the dimensions of the part usually dictate the method of transporting the robot.

In some cases, two radial gantries or floor tracks might be more economical than a single multi-axis gantry solution.

Using extended-reach robots on a single-axis transporter is less expensive than multi-axis transporter solutions.

If multiple robots are used in the same workspace, then programming and safeguarding for them must be addressed. It is most cost-effective to perform as much welding as possible on subassemblies in smaller cells, and limit the welding time of bigger components in large workcells to maximize their throughput.

If you would like to contact Chris Anderson, call him at 937.847.3216 or e-mail chris.anderson@motoman.com.