robocrane

machine#current_designs: robocrane

RoboCrane

*1
Much work in the field of parallel kinematics has to do with cable-based systems. I will refer to these by the name RoboCrane to differentiate them from hexapods.

RoboCranes have the advantage that a large percentage of the frame volume can be utilized, since the travel of a cable and winch mechanism is higher than that of a ballscrew strut assembly. Cables are also lighter and more easily transported, especially when considering an actuator with hundreds of meters of travel.

RoboCranes are quite easily controlled using EMC, and there are multiple papers written by the original authors on this subject. (see below)

Fig. 1: the hanging platform cannot rotate beyond the point where the center of mass is directly below a joint (or through any kinematic singularity)

While a RoboCrane is capable of being positioned in six degrees of freedom just like a hexapod, its range of rotation is restricted to much less than 90 degrees, since the cables have no compressive strength. This limitation also applies to hexapods, however a hexapod can still function once it has passed through the kinematic singularity because the struts can provide compressive support.

The amount of force a robocrane can exert in any direction is equal to the amount of preload. (verify this) Preload can be accomplished by using redundant cables to tension the structure or by adding weight to the moving platform.

Applications of robocranes include:

• Robotic greenhouse tending
• Contour Crafting, Excavation, and traditional construction
• Material handling, pick-and-place, automated component assembly
• Photography, inspection, and digitizing large objects
• Hedge trimming and ice/snow sculpture

In the next year or so, expect to see some examples on this page of research on the topic of incorporating robocranes into geodesic domes.

Links:
Models of various arrangements to accomplish the robocrane concept.
http://www.isd.mel.nist.gov/projects/robocrane/gantry.html

Alex Joni's 3 cable system, to be used as a plasma cutter XY table with torch height control:
http://dsplabs.utt.ro/~juve/emc/mytoy/