Control Engineering

Paul Grayson

Any color
February 8, 2008

Picture by Trimble Precision Agriculture 

TRACTORS OF ANY COLOR
While Case-IH Tractor Company suggested I call the makers of their self-driving system, Trimble, directly, Trimble was quick to point out that their AgGPS Autopilot System can be installed on most any make and model (designated by color) of tractor which has power steering.  The people I spoke to at Trimble were also quick to point out that their tractor driving systems require a person in the cab at all times.  That they have monitors to make sure that the driver is awake, alert, and in the cab or the tractor will shut down.  The driver must not touch anything in the cab when it is in "auto" or that will kick it back into "manual" operation.   They have full featured retrofit kits available for $25,000.  Another $12,000 will buy a base station that allows Real Time Correction Broadcast (RTK) correction signal which allows control of tire position +/- 1 inch.  This is an amazing difference from just a few years ago.  Prices have dropped to one third of what they were and accuracy has gone up by about a power of 10 for mobile applications.

Jeff Moore at Farm Depot, an agricultural machinery guidance systems dealer, mentioned that his systems also can be used with community or state based GPS correction signal systems.   In Michigan it is CORS at http://www.mdotcors.org/ .  This eliminates the need for having your own RTK base station or subscribing to a signal service to get the +/- 1" accuracy.  

STEERING SYSTEM EXAMPLE
As an example of a GPS referenced automatic guide path following steering systems that are in wide production, Trimble's LeaAnn McNabb has provided these great pictures of the parts used in the Trimble system.  The software in this system leads the operator through the process of creating the guide path for each field, then follows it.   There are several options for creating the guide path that are intuitive for farmers who have driven tractors.  Guide paths in the past were only good for short periods of time because of signal drift but now can be stored for each field and reused year after year, greatly improving productivity.


STEERING VALVE
The hydraulic steering valve receives electrical signals from the AgGPS NavController II and converts them to precise hydraulic steering movements to keep the vehicle on path. 


DISPLAY / USER INTERFACE
The AgGPS FieldManager™ display has a large touch screen, built in software for GPS guidance, automated steering controls, multiple field pattern options, and record-keeping.  The guide path is located in this unit that travels with the vehicle rather than residing at some central location as in factory AGV's.
 


STEERING SENSOR
AgGPS AutoSense™ provides a highly accurate measure of wheel angle without the use of moving parts and sends that information to the AgGPS NavController II.   In the dirt and mud environment that agricultural tractors operate in, no moving parts is a good idea.
 

RECEIVERS
AgGPS 252 Receiver with AgGPS 900 Radio provide multiple options for GPS corrections including WAAS, OmniSTAR, and RTK  provides +/-1 inch pass-to-pass, year-to-year accuracy using RTK corrections.  In the case of tractor operation in the Traverse City, MI area we are hoping to use the state wide correction signal provided by Michigan MDOT CORS.  

NAV CONTROLLER
AgGPS NAVController II uses data from the GPS receiver and internal sensors, and sends precise instructions to the steering control valve.  T3™ technology continually corrects for roll, pitch, and yaw by using state of the art 6-axis solid state inertial sensors to give a true on-ground position.   This single integrated unit represents a great simplification over how things were done in the past. 


 
CORRECTION SIGNAL
GPS, GLONASS and RTK Base Station combines a GPS receiver and RTK broadcast radio.  Setting up an RTK  base station to produce your own correction signal is only necessary if you are not going to use one of the correction signal sources and need the +/- 1" accuracy.   Without correction the position accuracy is about +/- 8".

2007 DARPA URBAN CHALLENGE VIDEOS
http://search.msn.com/video/results.aspx?q=darpa%20urban%20challenge&FORM=BVRE
--and others--
http://search.msn.com/video/results.aspx?q=driverless&FORM=BVRE

GO ROBOTS !

Posted by Paul Grayson on February 8, 2008 | Comments (0)