Sensors and Controllers for Primary Drivers and Soil Engaging Implements

Real-time control is becoming an integral part of modern machine systems for efficient agricultural production. Maintaining consistently high quality agricultural production in the face of growing labor shortages is a challenge (Kisu, 1985). Providing a work place for laborers that meets increasingly rigorous safety requirements and environmental constraints is likewise a challenge (Grisso, et al. 1988). More appropriate energy management and soil compaction management have also motivated real-time control applications. Appropriate sensing and control systems can reduce labor requirements, function in difficult environments, and allow vehicles to adapt to varying chemical and physical soil states. Labor shortages and unfriendly environmental constraints coupled with the reality of spatial variability within agricultural production areas readily explain the move towards real-time control of agricultural equipment. A machine system in the context of this chapter is any combination of driving and driven elements that exerts force upon or is resisted by the soil. Machine systems include primary movers such as tractors, wide span vehicles, and other devices that provide propulsion for soil contacting implements. Self-propelled and dependent implements are also included in this definition. The scope of the following review is mainly limited to those primary driver functions that involve soil contact. In the case of implements, the review goes somewhat beyond soil contact to include other functions such as chemical spraying because these control objectives could conceivably be readily transferred to soil engaging systems. Sensing and control systems currently used in the rapid characterization of machine state and soil variables are reviewed, with primary emphasis toward the soil state and secondary interest toward the machine state. Sensing systems with potential for inclusion in future machine systems are also reviewed. Since mapping is a relevant concern of what is now commonly referred to as site-specific field management or precision farming, sensing systems for mapping various soil state indicators are also discussed. For both control and mapping, sensing systems capable of on-the-go measurement are of major interest. The overall control objective in farming systems is to provide an adequate supply of food and fiber while maintaining profitability and sustainability. Much remains to be learned about the deterministic aspects of generic farming systems. A reasonably rigorous statement of the objective functions incorporating the prediction of physical and chemical soil properties is still beyond our grasp. How to handle stochastic (or chaotic) aspects of agricultural production in field environments is also a major challenge. This review will be confined to more immediate sensing and control objectives such as machine speed, draft, and energy management. Implement controllers are also reviewed. These immediate control objectives directly impact profitability and can indirectly and directly impact sustainability.