IFPE Paper 2.2 Global Navigation Satellite Systems (GNSS) technologies for Off-Highway Agricultural Vehicles: The Benefits of using Stateof-Art Mobile Hydraulics Technology Leroy O. Garciano, Ricky Anderson, Jan Henrik Reese Danfoss Power Solutions ABSTRACT Global Navigation Satellite Systems (GNSS) based technology has revolutionized production agriculture on a site specific basis otherwise known as Precision Farming (PF). Precision Farming practices implies the application of chemical inputs at the right amount, at the right location, and at the right time. GNSS based PF technologies such as hands-off precision steering, variable rate application, active control of implement; data acquisition and crop management are some of the applications. These technologies deliver unprecedented levels of reliability and accuracy (e.g., signal availability at any time, sub-inch guidance accuracy, etc.) to offhighway agricultural vehicles. Original Equipment Manufacturers (OEM) offer a broad spectrum of GNSS technology based solutions that are cost-effective. implement follows the desired A-B line or guidance path. Implement guidance provide benefits when 1) operating in fields that have steep slopes or rolling terrain where the implement tends to slip downhill; 2) driving curved paths which can occur when farming around terraces or on contours; 3) due to lateral forces, an implement does not directly track behind the tractor. In some cases, implement guidance can be a benefit when several implements are pulled in tandem to ensure they all remain on the same path. Figure 1 shows some of the typical GNSS technology equipped vehicles for precision farming. Engineered mobile hydraulics and electronic products benefits GNSS equipped agricultural off-highway vehicles where state-of-art hydraulic solutions at the component or system levels are available. This tight system integration leads to: (1) Optimal space claim; (2) Minimize parasitic energy losses because components are designed to work together efficiently; (3) Ability to perform multiple work functions simultaneously with more precision and accuracy; and, (4) electro-hydraulic control systems and software compliant hardware components which enable tweaking mobile hydraulics machine performance on the fly to change performance characteristics. State-of-art hydrostatic auto guidance steering technologies solutions not only increases productivity and reduce operator fatigue, but also insure safety compliance. INTRODUCTION A GNSS based agricultural vehicle guidance system is one of the most adopted technologies by growers. Guidance systems continue to evolve, improving field performance and providing capabilities beyond solely guidance. One enhancement has been the development of GNSS-based implement guidance which insures the Fig.1 GNSS based technology used in Precision Farming In Fig. 1(a) a sprayer for applying liquid fertilizer and chemicals; when the sprayer is equipped with vehicle guidance and variable rate application (VRA) technology, the following advantages are possible: - human fatigue factor is minimized due to hands-off guidance extending work hours and leading to increased productivity; - cost of agricultural input is minimized by reducing overlap and over-application (e.g., previously applied areas will not be sprayed, or amount of applied chemicals per acre could be set); in addition, VRA
automatically shuts-off at end-of-rows of the field, while maintaining speed, reducing wastage of inputs and extending work hours; Figure 1(b) shows a spreader for variable rate application of fertilizers; 1(c) precise on-the-go planting of seeds to minimize double application on headlands and point rows for improve crop stands leading to significant savings on seed costs; and, 1(d) a GNSS guided vehicle for application of anhydrous ammonia. GNSS based technologies records information, such as the amount of agricultural and chemical inputs applied; during the application of these inputs, the overlaps and skips are minimized; with GNSS displays capable of recording amount of inputs applied leads to information on the spatial distribution of agricultural inputs in the fields; during harvest season, spatial crop yield recorded is also possible for some of these machines; thus, a spatial yield map variability can be generated that could identify low and high yielding areas. This information leads to a variable rate application of agricultural inputs that could potentially enhance yield for the next growing season. OTHER APPLICATIONS Other applications where GNSS based technologies are applied include farm drainage solution to better manage the water for those types of fields such as dry-lands and fields having poor drainage (ponding in the middle of the field, etc.). Water drainage helps minimize chemical runoff that go to tributaries mitigating non-point source pollution commonly attributed to production agriculture. In this regard, the benefits include: improves crop yields by controlling ponding optimizing root depth maximizing planting density minimizing nutrient loss improves water infiltration rate into the soil VEHICLE GUIDANCE OPTIONS As previously stated, vehicle guidance is one of the most adopted technologies for GNSS based guidance systems by growers. Two options for vehicle guidance are: Assisted-Steer Guidance Auto-Guidance Assisted Steer Vehicle Guidance System Solution (aftermarket solution) T2 Terrain Compensation Technology Friction Pad Fast install & wide range of platforms Recommended WAAS System Fig.2 An entry level assisted steer vehicle guidance solution. 2 Platform Kit to Adapt to Steering Column Torque Motor Fig. 3 A typical assisted-steer vehicle guidance solution. The main components are: 1- GPS receiver; 2 display; 3 guidance controller; 4 - torque motor. An entry level assisted-steer system shown in Fig. 2 is an economical guidance solution without involving the hydraulics of the vehicle. It can be installed in more than 500 OEM vehicle models including most tractors and other machines such as a windrower, etc. This assisted steer system can be installed in a vehicle in less than 30 minutes. Unlike other assisted steer systems, Fig. 3 is portable and can be switched between different vehicles or cross-banded, i.e., can be installed on different tractor brands. It is popular among growers because it is simple as well as cost effective product. The assisted steer in Fig. 4 integrates the torque motor on the steering column. It is a mid-range steering accuracy which means better precision guidance than the one shown in Fig. 2 & 3, and offers in-between step to autopilot performance. It is also composed of a torque motor installed directly below the steering wheel (that latches to the spline of the steering rod) and has an inertial guidance made up of three accelerometers. In Fig. 2, the guidance controller is a gyro-box that has two accelerometers (T2) for inertial guidance while in Fig. 4 the controller is called an IMU and has three accelerometers (T3) for inertial guidance which means better accuracy in being able to follow the guidance path. 1 3 4 Figures 2 & 3 show steer-assisted guidance solutions with all components installed inside the cab. The steer assisted system is shown in Fig. 2. The components are a torque motor mounted onto the steering shaft, a friction wheel pad that steers the wheel providing hands-free steering operation of the wheel (Fig. 3).
T3 Enhance Terrain Compensation Technology Immediately adjusts vehicle steering to compensate for rough terrain or slopes and hillsides Sleek, Clean Design Motor integrated into the steering column provides clear access to all instrument panels and no decrease in leg room in cab. Higher Torque Better steering of vehicles with more rigid power steering systems, such as floaters. Fast-Reacting Motor Allows system to quickly get the vehicle online and stay there Compatible Steering Options Steering system installation Preserves the use of the vehicle s original steering Wheel and telescopic functionality Greater Flexibility Electric steering motor allows for unrestricted manual steering when assisted steering is not engaged. Fig. 4 A mid-range accuracy assisted-steer guidance solution. The advantages of the mid-range assisted steer solution are: Torque developed is 30% higher Three accelerometers insure more guidance accuracy in following the A-B line In both assisted steer systems, safety of operation of the vehicle is transferred to the operator by disengaging the assisted steered-wheel by manually moving the steering wheel from side-to-side. accomplished. The displays are capable of operating in nightmode for better visibility at night, thus extending productivity. In addition, feature mapping and record keeping capabilities are possible. In an example, if a prescription map is loaded into the display to vary the amounts of agricultural inputs to match the needs of specific areas in the fields, the display reads the data and sends the rate information to the application controller. This is called variable rate application (VRA). Together with the assisted-steer or auto guidance technologies, more precise, productive and profitable farming is accomplished. Some of these displays support: wireless data transfer between the field and office; offer touch screen technology and work with assisted steer and auto guidance; the integrated GNSS receiver supports both GPS and GLONASS satellite constellations for submeter RTK level accuracy; work in different guidance patterns to best fit the layout and contour of your fields; and, feature mapping and record keeping capabilities GPS/GNSS Displays Generating an A-B line guidance pattern is a simple task with a GPS/GNSS display (Fig. 5). It is accomplished by marking a point-a when the vehicle is stationary (at engine idle condition) and then the vehicle is moved forward until point-b icon appears on the display. When this reference line is set, straight lines are automatically generated parallel from the A-B line equally spaced based on other required input parameters such as vehicle and implement measurements (i.e., swath-width wheel-base, degree of aggressiveness in following the A-B line, etc.), and desired amount of overlap (Fig. 6). a) b) Fig. 6 Vehicle parameters, swath width, over-lap, and aggressiveness to follow the A-B line are some of the inputs into the GPS/GNSS display. Typical Guidance Path Designs c) d) Fig. 5 Various GPS/GNSS displays from several original equipment manufacturers. Depending on the level of accuracy of the GNSS displays, precision farming activities such as planting, spraying, spreading and strip-till can be controlled that means no skips and minimum overlaps are Different guidance patterns that best fit to the layout and contour of a particular field are shown in Fig. 7. In headlands, straight swaths automatically generate a straight line pattern, however by setting the heading direction between 0 to 360 (increments of 1 degree) or by indicating North, South, East, West, an A-B line is automatically generated, and parallel lines are generated with the other required parameters. In identical curves, every swath is parallel to the first guidance line map new A and B point to set a curved guidance line, and when the vehicle turns, the next swath is automatically selected.
GPS/GNSS receiver Corrected Position Uncorrected Position f Roll Angle Fig. 7 Typical guidance pattern designs. (a) Headland (b) identical curve (c) A+ Pattern (d) Multi-headlands (e) free-form (f) adaptive curve GUIDANCE CONTROLLERS Terrain Compensation When vehicles are operating on rolling, undulating or uneven terrain conditions, it tends to be off-position from the desired trajectory, and to get back to its desired path takes some time. Three orientations which can cause errors in GPS/GNSS positions are shown in Figure 8. Pitch motion is the oscillation between the front and rear; roll motion is a side-to-side oscillation when looking at the front or rear of vehicle; and, yaw motion is the heading or turning oscillation to the left or right. If the guidance system has terrain compensation (TC), then it automatically corrects the GPS/GNSS position calculation to the centerline of the machine (Fig. 9). Inertial sensors are commonly used by manufacturers to measure the potential changes in machine orientation and then utilize this data to compensate or correct GPS/GNSS positions. The actual sensing mechanism could include accelerometers, gyroscopes or a combination of both types of sensors. At times, multiple GPS/GNSS receivers may serve as input for TC technology. Fig.8 Three types of vehicle orientations that can generate GPS/GNSS receiver position errors: 1) Pitch 2) Roll and, (c) Yaw oscillations. Fig. 9 Roll motion corrected position of a vehicle. Accelerometers (1, 2, or 3 D) will determine the angle of incline, while gyroscopes measure the speed that the angle changes caused by oscillations. Simply, these sensors measure the grade of the slope and how quick the grade changes. The important aspect is that a guidance system with TC capabilities such as a guidance or navigation controller will automatically adjust for orientation (1, 2 or 3 D compensation depending on the system (Table 1) to the correct GPS/GNSS positions while maintaining the reported accuracy by the manufacturer. For older systems or those not having TC, operators will observe and manually compensate for errors in the GPS/GNSS positions. HYDROSTATIC AUTO GUIDANCE SOLUTION (FACTORY/AFTERMARKET AND STATE OF ART GUIDANCE SOLUTION) The auto guidance solution is accomplished via hydrostatic steering where there is no mechanical link between the steering column and the steered wheels. These are replaced with hydraulic hoses between the steering unit and steering cylinder and electro-hydraulic valves. In hydrostatic steering, as the wheel is turned, the steering valve meters out an oil volume proportional to the rate of rotation of the steering wheel. The volume is directed to the appropriate side of the steering cylinder, while simultaneously the displaced oil is directed to tank. In an electro-hydraulic (EH) steer system, steering control is realized for an auto guidance system of an agricultural vehicle. One of the advantages of EH steer system is power density, flexible and efficient means of power transfer, and electronic control. AFTERMARKET AUTO GUIDANCE SOLUTION An example of an aftermarket auto guidance vehicle solution is shown in Fig. 10.
CAN Bus GPS/GNSS Antenna integrated compact design (as well as the work function) and offers the OEM the capability for auto guidance (Fig. 12). Display with Integrated GPS Microcontroller Electro-Hydraulic Valve Wheel angle sensor AutoSense TM Steering Sensor Navigation controller Steering unit Display Fig. 10 An aftermarket auto-pilot vehicle guidance solution. The components are: GPS/GNSS antenna, display, EH valve, autosense steering sensor, navigation controller. Steering wheel sensor Proportional Valve group (PVG) GNSS Receiver In the aftermarket auto guidance vehicle solution, platform kits are available that include component hardware such as a hydraulic valve, controller, autosense steering sensor, and cable kits which are available to a wide range of tractors and other agricultural machines (older and newer machines). FACTORY INSTALLED AUTO GUIDANCE SOLUTION Factory installed auto guidance solutions have a steer valve integrated into the steer wheel of a vehicle, whereas, an aftermarket has an EH valve kit, therefore, a factory installed system offers a more seamless integration of the steer unit technology into the machine. Shuttle valve Auxiliary pump (Open circuit pump) to Work function Fig.12 Typical mobile hydraulics technology for auto guidance solution illustrating tight system integration of the steer unit and work function capabilities with software compliant components. An integrated EH valve in the hydraulic steering unit leads to a compact design where external valving is not needed. The integrated design enhances flexibility, and the single piece casting optimizes space claim. In addition, hardware components are software compliant which means tweaking performance is available on the fly to change steer characteristics for optimal performance and for safety compliance. Selectable reactive and non-reactive steering Fig. 11 Factory installed accu-guide guidance technology solution. STATE-OF-ART MOBILE HYDROSTATIC STEERING TECHNOLOGY FOR AUTO GUIDANCE SOLUTIONS There are auto guidance solutions that are an integration of several technologies from several vendors. Whereas the single-source supplier combines the steer unit (orbitrol) and electrohydraulic valve into an Whether driving on-or off-road conditions, selectable options such as reactive and non-reactive steering mode ensures that the vehicle will steer with a firm, automotive feel when needed e.g., to automatically return to center. With two steering modes, it also enables reaction steering on vehicles with an auto-steering function. Furthermore, a second generation reaction technology, RM (Reaction Motoring) significantly improves the return to center performance. On many vehicles, steering geometry creates a force that wants to re-center the wheels causing a delta pressure over the cylinder; restrictions in the integrated rotary valve set (spool-sleeve) will determine how quickly the wheels will re-center (Fig. 13). New machining of the valve set significantly reduced pressure drop and allowing the cylinder to re-center much quicker. It is
available in Load Sensing, and makes it easy to feel feedback when driving on-road conditions significantly improving operator comfort and vehicle performance. Improved Reaction Steering Unit L Flow restrictions Fig. 13 A steer unit design with improved reaction response A Safe-State Steer Technology Fig. 14 shows a state-of-art steer unit technology system with functional safety features (Category 3 architecture) that complies with revised safety legislation and new standards (e.g., ISO 25119). This steer unit technology offers a defined safe state. In the event of an electronic or hydraulic system malfunction, this option, activated by an external watchdog controller, can isolate the electrohydraulic (EH) section of the steering valve in order to protect the steering system. Another safety feature ensures that, in electrohydraulic steering (non-reactive) mode, the steering ports from the steer unit will not be blocked. This is achieved with an extra connection from the hydrostatic steering unit to the cylinder. In contrast to other systems, this keeps the steering wheel fully operational and the driver in complete control. This improves the safety performance of an auto guidance machine. R Reaction Mode RM Steering unit Spool/sleeve set Gear wheel set Steering wheel Fig. 14 State-of-art of GNSS steer technology system Category 3 safety-integrity level 2 (SIL 2) CONCLUSION Global Navigation Satellite Systems (GNSS) based technologies have revolutionized production agriculture. Robust precision farming solutions such as water management in the agricultural fields enhances planting density thus, increasing yields; and variable rate application minimizing agricultural inputs are some of the benefits. In conjunction with assisted steer or auto guidance technologies, hands-off precision farming leads to enhanced productivity such as the ability to perform multiple work functions with more precision and accuracy. With state-of-art mobile hydrostatic steer system technology an integrated steer system design enhances flexibility and optimizes space claim. Furthermore, this state-of-art technology has safety features that are in compliance with ISO 13849 and ISO 25119. ACKNOWLEDGMENTS The author wishes to acknowledge CNH and Trimble Navigation Limited on the use of some of their presentation materials. REFERENCES 1. CNH Industrial (www.cnhindustrial.com) 2. Danfoss technical information brochure. 2013. Document No.520L0502. 3. http://powersolutions.danfoss.com/stellent/groups/publicati ons/documents/product_literature/11059881.pdf 4. Trimble Navigation Limited (www.trimble.com) 5. Wikipedia.org CONTACT Leroy O. Garciano is a Systems & Application Engineer for Danfoss Power Solution at the Ames, Iowa location. He has BS degree in Mechanical Engineering at the University of San Carlos, Philippines. He obtained his MS/PhD degrees in Bio-Engineering resources at Iwate University, Japan. Prior to joining Danfoss, he worked in Japan at the Tokyo University of Agriculture and Technology; in the US at the Univ. of California, Davis; and in North Dakota. His research and industry experiences include vehicle dynamics; development of commercially-off-the-shelf (COTS) sensor devices for soil dynamics research; 3D Discrete Element Modeling (DEM) of a cutting tool in soil; multispectral and hyperspectral technologies for crop yield prediction; and precision agriculture technologies for assisted-steer and auto guidance for agricultural machineries. His published peer-reviewed papers are in the areas of vehicle dynamics, multispectral and hyperspectral, as well as in soil dynamics research. He is conversational in the
Japanese language. Garciano may be contacted at lgarciano@danfoss.com. Ricky Anderson is a Sales Development Manager for Danfoss Power Solutions at the Ames, Iowa Location, responsible for steering product in the Americas. He has a BS in Mechanical Engineering from Iowa State University, Ames, Iowa. He has 25 years of experience in product design, manufacturing and quality engineering as well as 7 years in technical sales and marketing. Jan Henrik Reese is a Sales Development Manager Danfoss Power Solutions ApS, Denmark, Work Function Division, Business Unit Steering. He holds a bachelor degree in Export Engineering from the University of Southern Denmark. He is involved with steering system integration with original equipment manufacturers (OEMs) and distribution customers on a global level. This includes agricultural, construction, material handling, turf care and many other applications utilizing mobile hydraulics technologies. DEFINITIONS, ACRONYMS, ABBREVIATIONS GLONASS Global'naya Navigatsionnaya Sputnikovaya Sistema is the Russian Federation Global Navigation Satellite System. GNSS Global Navigation Satellite System. It is a term used for the entire constellation of space-based navigation that comprises of orbiting satellite vehicles (SV s) and their ground control and monitoring stations. GPS Global Positioning Satellite which is maintained by the U.S. government. Non-reaction steer unit - With non-reaction steering units there is no corresponding movement of the steering wheel when the driver is not steering the vehicle. Reaction steer unit any external forces acting on the steered wheels result in a corresponding movement of the steering wheel when the driver is not steering the vehicle. RTK Real-Time Kinematics is a technique used to enhance the precision of position data derived from satellite based positioning systems. The RTK solution has a higher position accuracy of <2.5 cm (I-inch) passto-pass and year-to-year.