Steer-by-wire Control System Using GPS for Articulated Vehicles

Global positioning system (GPS) and embedded computing technology offer new automation opportunities in mobile equipment applications. GPS signals are widely used in direction guidance of cars, ships and airplanes. Construction, mining and agricultural equipment industries stand to benefit from the application of GPS in various control functions. Using GPS and digital embedded control technology, many motion control functions such as motion planning and motion execution can be automated. Automated control of various machine functions without operator (human) involvement brings the embedded control technology closer to autonomous operation capability. Many of these machines require an expert operator who must deal with steering, throttle, and multi-axis tool motion control tasks at the same time, while being very careful in the rather hazardous work environment. It is, therefore, desirable to be able to operate these machines without the operator, that is autonomously, and remove the operator from the dangerous work environment. Autonomous steering of a motor grader is studied in this paper. The system automates the process of generating the desired motion path for a given field operation, and then using GPS signals for its position measurement, it controls the steering system to follow the planned path. This concept can then be integrated with automatic throttle, transmission, brake and tool control sub-systems to achieve completely autonomous mobile machine operation. The system design details of the by-wire-steering system are discussed in hardware and software components. Simulation and tests results on a motor grader are presented. Path tracking accuracy of the by-wire steering system using carrier phase differential GPS (CP-DGPS) position signal was less than 10 cm consistently in our tests using a motor grader.

Keywords: GPS, DGPS, CP-DGPS, By-wire-steering, steer-by-wire, electrohydraulics, pump, cylinder, valve, ECM (electronic control module), articulated machine, motor grader, autonomous mobile machines.