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.
