A Laboratory Study of Force-Cognitive Excavation

Excavation is characterized by the development of unmodelled forces between the bucket and the soil; the subsurface conditions are generally uncertain, and the development of these forces is only revealed during the very act of disturbing the medium. A human operator typically exerts control to keep such forces within limits created by the combined constraints of equipment, geometry, and task. This research effort developed and tested a supervisory control approach of discrete adjustments to the digging trajectory in response to forces encountered during excavation-essentially constructing a device which can dig by feel. A laboratory manipulator was configured with four actuated degrees of freedom to approximate a backhoe. The motion sequence is represented symbolically as swing-sweep-scoop-raise-swing-dump, with the sweep-scoop-raise motions comprising the actual digging trajectory. Simple rules for supervisory control were programmed and tested in laboratory studies of sand excavation, and were effective in adjusting the digging actions to maintain forces within the target envelope.