Human tongues, elephant trunks, octopus legs, and prehensile monkey tails are examples of organic tentacles that have the ability to manipulate. Tentacles are a special class of manipulator quite different from the familiar jointed arm. A tentacle is flexible over its entire length, is usually able to retract or elongate, and is often capable of a prehensile grip. A tentacle can be better than a jointed arm at manipulation tasks requiring extreme dexterity, a soft wrapping grasp, compliant contact with the environment, or compact stowage .
The KSI Tentacle TM manipulatorKinetic Sciences Inc. (KSI) has developed and patented a robotic tentacle that mimics the motions and exceeds the extension capabilities of organic tentacles (see Plate 1). The KSI Tentacle TM manipulator is powered by a hybrid combination of pneumatic pressure and electric motors (Immega, 1994). The Tentacle TM can extend to more than five times its contracted length, with independently controlled bending and compliance in one or more regions .
How it worksThe Tentacle's articulated body is a pneumatic structure comprising one or two patented KSI bellows actuators (Immega, 1993). These bellows are more extensible than conventional bellows, and can extend, contract, and bend in any direction. Plate 2 shows representative configurations achievable with two contiguous bellows.Compressed air inside a bellows causes extension and controls compliance -the higher the internal pressure, the stiffer or less compliant the bellows becomes. This compliance prevents physical damage should the Tentacle TM collide with objects in its workspace. The air, supplied by an external compressor and controlled by a servo loop, is metered in and out as required to maintain a designated pressure as the Tentacle TM moves. Three stainless steel tendons run alongside each bellows to control contraction and bending. (Thus, a two-stage Tentacle TM requires six tendons.) Each tendon is dispensed by a KSI self-tending servo winch -a proprietary actuator that reliably servos long lengths of cable, even without tension in the cable. Each 423
