THE NIST ROBOCRANE

The Robot Systems Division of the National Institute of Standards and Technology (NIST) has been experimenting for several years with new co ncepts for robot cranes. These concepts utilize the basic idea of the Stewart platform parallel link manipulator. The unique feature of the NIST approach is to use cables as the parallel links and to use winche s as the actuators. As long as the cables are all in tension, the load is kinematically constrained and the cables resist perturbing forces and moments with equal stiffness to both positive and negative loads. The result is that the suspended load is constrained with a mechanical stiffness determined by the elasticity of the cables, the suspended w eight, and the geometry of the mechanism. Based on these concepts, a r evolutionary new type of robot crane, the NIST ROBOCRANE, has been dev eloped that can control the position, velocity, and force of tools and heavy machinery in all six degrees of freedom (x, y, z, roll, pitch, and yaw). Depending on what is suspended from its work platform, the R OBOCRANE can perform a variety of tasks. Examples are: cutting, excava ting and grading, shaping and finishing, lifting, and positioning. A 6 -m version of the ROBOCRANE has been built and critical performance ch aracteristics analyzed.