Figure 1. TSD's TruPath is an integrated auto-guidance system aimed at the agricultural machinery market, bringing together hydraulics and GPS-based positioning control.

Figure 2. Wheel position is monitored by a Sauer-Danfoss SASA wheel-position sensor to provide feedback to the system.

If the wheel marks in this farm field look so perfect that's hard to imagine an operator being so accurate, you're right. Auto-steering — combining GPS technologies from Topcon and specialized hydraulics from Sauer-Danfoss — allow fields like this one to be sprayed with fertilizer. With GPS positioning, there is no overlap — everything is properly spaced.


"You're going to see, in the next five years, tractors and machinery operating on the farm that have no drivers. Agriculture will be the first robotically controlled industry in the world. We're doing some of that today in the mining industry, a little bit in hazardous areas in construction industries, but the first mass market of that technology will be the agriculture industry," says Ray O'Connor, president of Topcon Positioning Systems, Livermore, Calif. And he should know — Topcon is one of the leading suppliers of the technologies required to make that prediction come true.

The technology O'Connor is relying on to steer those robotic tractors and combines is a combination of satellitebased global positioning (GPS) data and intelligent computer systems put to work via a sophisticated hydraulic system to control steering and other functions. Generically, the technology is called GPS Auto-Guidance, and is marketed under the trade name TruPath by TSD Integrated Controls, a joint venture between Topcon and Sauer-Danfoss.

As close as a centimeter
Here's how the systems work today. The TSD TruPath receiver, Figure 1, processes satellite data to resolve position with repeatable accuracies as close as 1 cm. In addition to the capability of receiving satellite signals, the unit is also equipped with inertial sensors to determine the attitude and acceleration of the vehicle and a microprocessor to plan paths for the vehicle — whether it be straight, curved, or otherwise. The receiver is also equipped with two CAN ports for communication with vehicle sub-systems, most specifically the hydraulics for steering control/feedback to display to the machine operator.

Steering control of the vehicle is a job in itself. The steering system communicates among components via a steering CANbus connecting pieces such as a Sauer-Danfoss PVED-CL actuator and steering valve, as well as other possible sensors, to execute closed loop steering control of the vehicle.

A second CAN communication port is designed to use the ISObus 11783 protocol to interface with a display screen to communicate and receive commands from the equipment operator. These displays can be as simple as a push button display or as complex as a color touch screen computer running an embedded Windows XP operating system. Currently, TSD can offer a range of displays with the TruPath steering systems, ranging from a simple virtual terminal to a high functionality dedicated display, such as the Topcon X20 computer.

The X20 uses specialized software coupled, with the data from the GPS, to create layers of data and information that can form a database known as a Geographic Information System (GIS). The GIS contains both information on work to be performed and data recorded from sensors about work that was performed with the time, location, and specifics on what happened where.

The X20 can replace existing rate controllers for liquid, granular, or injection control systems. Combining the capabilities of these units into a single console removes clutter from the cab and simplifies the operator's task. In addition, the X20 provides the enhanced functionality of automated section control (ASC) with capability to control up to 30 individual or grouped boom sections.

The end result, as Albert Zahalka, vice president of mobile electronics for Sauer-Danfoss sees it, "We can now control the machine all the way from the GPS signal to where the wheels meet the road." In practical terms, that vision translates into a tractor or a combine that literally drives itself, guided by signals from outer space, and controlled by a computer brain. Or, at least that's the goal. Today's reality, though, is just a little more down to earth.

Data from above
One of the advantages Topcon GPS systems offer is the ability to use data from both the 24 U.S. GPS satellites and 17 Russian GLONASS satellites. That means the receiver is virtually always in sight of enough satellites to provide centimeter-accurate positioning. That's not true of other receiver systems, that are limited to either GPS or GLONASS signals, but can't use both. It's one of the reasons why TruPath-equipped tractors and combines can be used around the clock virtually anywhere in the world.

Position data from the Topcon system is combined with GIS data stored in the onboard X20 computer to determine the vehicle's present position on the ground. Inputs from inertial sensors are used to fine-tune this information to accommodate the bumps and shocks inevitably encountered in off-road operation.

All this information is processed by the TSD TruPath receiver to produce control signals delivered via CAN-bus for the Sauer-Danfoss PVED-CL hydraulic steering controller. The PVED-CL controller is mounted on an electrohydraulic proportional control valve that regulate oil flow to the steering cylinders. Wheel position is monitored by a Sauer-Danfoss SASA wheel-position sensor, Figure 2, with feedback directly to the valve. In addition, sensors mounted in the steering cylinders (or externally on the steering cylinders) provide feedback regarding wheel position as they turn during vehicle operation.

"This is an adaptation of the Sauer-Danfoss hydraulic steering system in use on hundreds of thousands of vehicles around the world," explained Michael Gomes, TSD integrated controls' product manager. "We've replaced the driver's eyes and hands with GPS signals and GIS information communicated directly to the PVED-CL steering controller. But, other than that the system really is pretty conventional.

"Think of the EHPS valve as a combination hydraulic flow amplifier that's actuated by a hydraulic steering unit, and a proportional valve actuated by an electric signal all in a single casting. Both functions are available all of the time, but for safety reasons the hydraulic steering unit has priority.

"Unless it's actuated by the operator moving the steering wheel, though, the system runs in steer by wire mode. So, unless the operator manually overrides the system, the onboard TruPath receiver provides the signals to the PVED-CL steering controller that actuates the EHPS valve to guide the vehicle.

"And, of course, the hydraulic system also powers and controls most of the other functions of the tractor or combine as well," continued Gomes. "Using five channels of control signals from the X20, the tractor can selectively apply granulars, liquids, pre-emergence herbicides, and inject anhydrous ammonia — all at independently variable rates from data layers on a GIS map."

What's next?
The TruPath system will soon be available for OEM installation, and will be offered on tractors built by several European and North American suppliers. As the installed base grows, and users develop confidence in the system, it may be only a matter of time until the breakthrough to a driverless application happens.

Zahalka sees this as a natural outgrowth of a larger trend. "I believe we will, in many cases, eliminate the operator and, in every case, have more control capability."

Why robotic tractors?
Before looking at how it will be done, it's worthwhile to ask why anyone would want a robot tractor in the first place. The answer is summed up in another emerging technology, precision agriculture.

Precision agriculture is all about maximizing production while minimizing inputs. One way to do that is to accomplish tasks such as tilling, seeding, and fertilizer application in the most efficient way possible. As equipment gets bigger and wider, that means calculating the most efficient path with a computer and then making sure the vehicle follows it exactly with a GPS Auto-Guidance system.

In practical terms, where a manually steered tractor and an experienced driver might hold pass-to-pass overlap to 20%, a TruPath-equipped tractor reduces that to 3% or less. Since the time spent re-tilling the overlap, and the seed and fertilizer deposited on it the second time around are all essentially wasted, the economics are obvious.

The benefits don't stop there, though. Because the operator doesn't need to steer the vehicle, he or she is able to handle other tasks, like controlling modern variable rate fertilizer application systems to further optimize inputs.

The tractor also can operate at higher speed because human reaction time is no longer the determining factor in avoiding a collision. And, because it's not necessary to be able to see what's ahead, a robotically operated tractor can operate in total darkness as efficiently as it does in broad daylight — extending the workday as long as necessary to get the job done during peak times.

"The next step will be to add vision and other sensors that add value to the machine beyond the capabilities of a person and with the possibility to preserve the safety of human life," said Ivan Di Federico, general manager of TSD Integrated Controls.