Peat Moss Harvesting
NREC developed an add-on perception system for automating peat moss harvesting and integrated it onto a team of three computer-controlled tractors developed by John Deere. These autonomous tractors were used in harvesting operations in a peat bog.
Peat moss is commonly used in gardening and plant growing. It is an accumulated, partially decayed plant material that is found in bogs. An active peat bog is divided into smaller, rectangular fields that are surrounded by drainage ditches on three sides. When the top layer of peat is dry, the fields are ready to be harvested. Harvesting is done daily, weather permitting.
Peat is harvested with tractor-pulled vacuum harvesters. The vacuum harvesters suck up the top layer of dry peat as they’re pulled across a peat field. When the harvester is full, its operator dumps the harvested peat onto storage piles. The stored peat is later hauled away to be processed and packaged. Peat bogs are located in remote areas, where there are often shortages of qualified operators. This provides an incentive to automate the harvesting process.
Detecting Peat Storage Piles
Before it can dump the harvested peat onto a storage pile, the robot needs to find the edge of the pile. However, it cannot rely on GPS because the storage piles change shape, size and location as harvested peat is added to them. To locate the edges of storage piles, the perception system finds contiguous areas of high slope in the sensed 3D ground surface. A probabilistic spatial model of the ground surface generates smoothed estimates of ground height and handles sensor noise.
Although peat fields are generally free of obstacles, the harvesters must detect the presence of obstacles such as people, other harvesters and other vehicles to ensure safe unmanned operation. To detect different types of objects, the perception system uses a combination of algorithms that make use of 3D ladar data to find dense regions, tall objects and hot regions above the ground surface.
Ditch locations are mapped with GPS. However, as an added safety precaution, they are also detected by the perception system. The perception system searches for ditch shapes in the smoothed estimate of ground height.