• Linear Gantries
  

  Gantries extend robotic working envelopes beyond the reach of wall-mounted tracks and add additional axes. (Photo 3.)

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  Gantries extend the envelope of the robot beyond the reach of a wall-mounted track by suspending the robot overhead and adding additional axes. (See Photo 3.)

  The Y-axis of travel allows a wider part to be accessed by providing motion perpendicular to the length of travel. A vertical Z-axis allows a robot to reach deeper into part cavities. With the addition of gantry axes, a shorter-reach robot can be used to reduce the weight requirement for the gantry drives. Gantries with shorter axes can be supported from one side on a single rail. Larger span gantries utilize a bridge structure with supports on each side. Driving a bridge gantry requires special robot controller software to synchronize the motion of two independent motors to position each leg of the gantry.

  Gantries can add a great deal of expense to a robot system, but they are one of the few ways to process very large parts.

  A part positioner normally is combined with a gantry to turn the part for robot access. Most robots feature software to allow the coordination of all axes — the robot, the base, and the positioner — to achieve long continuous welds or circumferential welds in a single pass.

  A sufficient Z-axis stroke can allow the robot to weld the inside truck bodies, containers or other box-like parts while a longer Y-axis could allow the robot to work on the outside surfaces. Of course, the longer the spans, the larger the required supporting structure and the higher the cost.

  Long cable length and cable management become an issue the longer the stroke of the robot transporter.

  For gantry systems, it is not uncommon to mount the robot controller and process equipment to the gantry structure so that only primary power is supplied the length of the track, and so that the robot and process cables are limited to the Y- and Z-axis stokes.

  The other concern for a gantry system is overhead clearance, particularly for systems that use the Z-axis stroke.

  Large parts normally require overhead cranes to load and unload. Users can add interlocks between the robot gantry and overhead crane to keep the crane out of the gantry area while the robot is operating or while the Z-stroke extends up in the air.

• Multiple floor track configurations
  

  Floor tracks on either side of a large part can be relatively inexpensive, and can enhance productivity. (Photo 4.)

  Using two floor tracks on either side of a large part may be less expensive than a using a single robot on an overhead gantry, and the multiple arcs provided by the dual track configuration can enhance productivity. (See Photo 4.)

• Radial Gantries

  Radial gantries provide one of the most economical overhead robot transporter solutions. (See Photo 5.)

  
  
  

A rotary base is less expensive than a linear axis, but it has a fixed boom length.

Radial gantries can provide an economical overhead robot transporter solution. (Photo 5.)

However, a single robot mounted on a two-meter to three-meter boom can expand its working volume by nearly 10 times.

Robots can be wall-mounted or ceiling-mounted on the end of the gantry boom. Wall-mounted robots provide a deeper envelope, allowing robots to reach into part cavities or access vertical surfaces, such as the outside of a box.

Ceiling-mounted robots provide a wide, flat envelope that is suited to processing flat panels such as mower decks or truck sides. Care needs to be taken with ceiling-mounted robots that wire feeders or cables do not hang down below the arm so they do not contact or snag the part or fixturing.

As with linear gantries, part positioners usually are combined with radial gantries to improve their flexibility. However, the orientation of the positioner in the workcell affects the robot's access to the part.

Locating a headstock/tailstock positioner perpendicular to the boom allows the robot to process longer parts using the length of the boom to move the robot closer to the headstock or tailstock.

The width of the part is limited to the reach of the robot — nearly double the reach for ceiling-mounted robots — and part depth that can be accessed is limited. If the headstock/tailstock positioner is located so it is in line with the gantry boom, then the boom can be pivoted to either side of the positioner to allow the robot to access the part from each side, providing more depth.