When something went wrong, basic trouble-shooting skills could usually determine the problem. A simple replacement often got the machine back into operation.
Those days are long gone. The carburetor has been replaced by electronically controlled fuel injection systems. Alternators tie into complex electrical systems. Hydraulic valves now operate by changes in electric current instead of a pushrod. When problems occur, trained mechanics with specialized testing devices must be called in to determine the cause.
Technology has leaped ahead of our ability to understand machine components and how they operate. The rapid advancement of technology puts many contractors in a dilemma. Should I or shouldn’t I? The choices aren’t as simple as they were in the old days. It’s hard to make an informed purchase decision and be confident that an investment in technology will pay off when you don’t quite understand how things work.
Taking a few minutes to learn the basic concepts of equipment automation can raise your comfort level with technology and help you understand your options.
Two Types of Machine Control Systems
There are two types of machine control systems. Indicate systems provide visual guidance to the operator in the cab so that he can determine the position of the cutting edge in relation to the design grade. The operator still controls the blade but doesn’t need to interpret grade stakes to perform his work. Automatic systems control the cutting edge to match the design surface without the need for operator intervention.
For the average contractor, indicate systems are a cost-effective way to get started with machine control. Hydraulic valves and connections can be added at a later time when fully automatic performance is desired. Many larger contractors use a combination of systems. For bulk earthmoving tasks—scrapers and large dozers—indicate systems provide grade information and allow the operator to move at a relatively fast pace. After the mass grading is completed, smaller dozers and motor graders running fully automatic systems are used to bring area within specified tolerances.
The basic principles of equipment automation are not difficult to understand if we group components according to their function.
How They Work—The Machine Interface
The first group, called the machine interface, includes the components that physically move different parts of earthmoving and grading equipment. Hydraulic cylinders are used for these tasks. The piston of the cylinder is connected to the part by a mechanical linkage. Multiple cylinders are used when the part, such as a blade, needs to be rotated through horizontal and vertical angles, as well as moved up and down.
Moving the heavy mass of a dozer or motor grader blade would be impractical with mechanical linkages. But pumping a non-compressible fluid into a small cylinder under high pressure creates a mechanical force many times greater. Thus heavy machine components can be positioned quickly and accurately with hydraulics.
Hydraulic oil is the perfect non-compressible fluid for operating cylinders. It can be easily routed to many different locations on a machine through flexible lines. By placing a valve in line, the flow of hydraulic fluid can be regulated to control the motion of the cylinder. Modern hydraulic valves are very sophisticated and are capable of very precise operation—provided the fluid flowing through them is stable and free of contamination.
Valves need some type of input to operate. Linkages from control levers in the machine cab can control valves through a direct mechanical connection. Valves can also be operated with an electric current, similar to the way a servo operates.
The hydraulic components that operate a modern machine are installed as part of the manufacturing process. After the machine leaves the assembly line, automated grade control systems can be added by installing additional valves and manifold assemblies. These components, designed specifically for particular machine models, are tied into the parent hydraulic system.
The Operator Interface
The second group of components is known as the operator interface. On an indicate system, a display in the cab of the machine provides the operator with lighted dots or arrows. These indicate when the blade is above, below, or on grade.
On an automatic system, the control box serves as the primary operations center for a machine control system. It is connected to valves located at remote locations on the machine by cables. Switches, located on the machine’s control levers, enable the operator to change from manual to automatic mode without taking his hands off the controls.
An onboard computer and operating software in the control box process information from input devices and send signals to control the hydraulic valves. Advanced control boxes, like Topcon’s 9168, have a touch-screen display that provides visual information to the operator and enables him to set and adjust system functions. The operator can choose between plan view, section view, and profile view—or choose a slit-screen option that allows up to three views simultaneously.
Sensors
The third group of components is sensors—devices that provide positioning input to the control box. There are three different kinds of sensor commonly used for machine control applications.
A sonic sensor measures distance with sound waves, controlling grade from an existing physical feature—a road surface, a concrete curb, or a stringline. A transducer in the bottom of the sensor generates sound pulses and listens for return echoes. It then sends position information to the control box for elevation adjustments to the moldboard. Sonic sensors are generally used to cut or place material with asphalt pavers, milling machines, trimmers, and motor graders.
Laser sensors don’t require continuous reference to physical objects. A rotating laser transmitter sends elevation control information in a uniform plane that provides 360-degree coverage. Laser-indicate systems are a popular starting point for contractors needing grade control. Hydraulic valves can be added at a later date for automatic control. Laser control systems have been widely used for many years to fine grade areas like building pads and athletic field surfaces with minimal slope. The major drawback is limited horizontal and vertical range.
A laser signal can also be used to transmit three-dimensional information. Topcon’s GRT-2000 robotic auto-tracking total station is designed to provide three-dimensional positioning information to a machine control system. The total station unit includes a fan-beam laser capable of communicating digital control data. An LS-2000 receiver, mounted on the machine, receives elevation, design cross-slope, and steering information. This information is sent to the control box, where it is forwarded to hydraulic valves. This system is widely used on motor graders. It can even be used to automate a concrete curb machine, eliminating the need for a stringline.
GPS—The Ultimate Sensor
Global positioning systems can also provide input for machine control systems. In reality, GPS is just another sensor. The term “GPS” is widely used as a general classification for products using satellite positioning technology. However, GPS implies a specific satellite system launched, maintained, and operated by the United States government.
A group of satellites belonging to a specific system is referred to as a “constellation.” The US GPS constellation, with 24 operational satellites, is not the only constellation in existence today. Russia operates and maintains another constellation—GLONASS. This constellation currently has 17 satellites in operation and will have 24 when fully deployed. In January 2006, the European Space Agency launched test satellites as the first step in the implementation of a third satellite constellation—Galileo. When complete, Galileo is planned for 27 operational satellites. When all three constellations are fully deployed and operable, a total of 75 satellites will be available for positioning tasks.
Satellite positioning products used for machine control systems need a minimum of five satellites to operate. Currently, devices that track only the GPS constellation have access to 24 satellites. Some satellites will not be available to positioning devices due to their orbital positions around the earth. Structures and trees may block access to other satellites. When these conditions occur, it is sometimes impossible to access the minimum number required for system operation. The result is downtime and loss of productivity.
Topcon, a leading manufacturer of products for land surveying and construction applications, has made two major advances in satellite positioning technology: Its exclusive GPS+ technology provides access to both GPS and GLONASS constellations, raising the number of available satellites to 45. GPS+ has proven successful in virtually eliminating downtime due to insufficient satellite access. It also provides a significant increase in accuracy—more reference points establish a position with greater precision.
To provide improved positioning performance from the future Galileo constellation, the company recently developed the G3 chip. This groundbreaking technology is capable of tracking all signals and codes from these new satellites, as well as those from existing GPS and GLONASS satellites and any future satellites. The G3 chip is also 75% smaller than existing processors and uses less power. Products using G3 technology will be more compact and have longer battery life for extended hours of operation.
Typical global positioning systems used in machine control systems achieve accuracies in the range of one-tenth of a foot. But GPS accuracy is variable depending on the number of available satellites, their distribution in the sky, and obstructions on the job site. This variable accuracy is acceptable for general site areas but cannot be considered for fine grading areas such as building pads or athletic fields.
How GPS Controls Machines
Satellites send positioning data to a GPS antenna/receiver base station. The base is located at a known stationary point on the site. At the same time, positioning data are also sent to the “rover” on the machine—a rugged GPS antenna mounted to a shock-absorbing, vibration-damping pole and a receiver box mounted in a secure location. The stationary base and mobile rover work together to provide RTK (real-time kinematic) position information and accurately determine the machine’s three-dimensional location on the site.
Software in the control box processes these position data and compares them to the design grade at that specific location. Data files, loaded in the control box on a compact flash card, provide the design grade information.
The control box updates positioning data 10 times per second and sends signals to the hydraulic valves. The blade is automatically positioned for elevation and slope.
It takes more than just satellite signals and design files to make a machine control system work. On dozers, a blade sensor is needed. On motor graders, a sensor is located at the rotation swivel to track the angular position of the blade. The rotation sensor enables the system to maintain the cross-slope of the grader blade while it is turned. A mainfall sensor mounts on the frame of a grader and provides slope measurement in the direction of machine travel. It also serves as a junction box for other sensors and hydraulic valves.
Surface File Preparation
When a machine control system uses satellite positioning as a position sensor, it also needs information about proposed grades. This information is supplied in the form of surface data files that are prepared on a computer and transferred to the control box on a compact flash card. The processing and integration of these two information sources enables positioning of the cutting edge to match the design grade.
“Surface file” is a commonly used name for a DTM (digital terrain model). The DTM is a representation of an actual three-dimensional surface. It is created as a TIN (triangulated irregular network)—a mesh of flat triangles with sides of varying length. When creating the TIN surface, the computer program looks at entities that contain x, y, and z position information. These are generally contours on a grading plan because it is the current convention for expressing a grading concept. Point data and spot elevations should also be included in the file.
Anyone can click on a command in a CAD (computer-aided design) program and create a surface file. While this TIN file may be great for visualizing a three-dimensional surface, it does not have enough information to be useful for machine control operation. When a TIN surface is created, areas between contours are averaged. Take a toe-of-slope situation with contours at 2-foot intervals. There may be a contour 2 feet away from the actual toe of the slope on a relatively flat surface and another contour of higher value 3 feet up the slope face. The TIN surface will directly connect the two contours, ignoring the point where the slope actually begins because there is no defined z value at that location.
Proper surface file preparation is one of the biggest challenges to the proper performance of satellite positioning machine control systems. Many contractors have experienced erratic operation of a machine and suspected faulty components. Later they discover that the problem was an improperly prepared surface file.
Not every contractor has an experienced “GPS manager” on staff who is skilled in computer programs and understands how earthmoving/grading machines operate. Training existing staff members in proper file preparation is one option. Local dealers may provide this type of training. Outsourcing file preparation to a specialist like Take-Off Professionals of Peoria, AZ, can be a cost-effective and reliable alternative to in-house data management.
Machine Control Systems of the Future
We are only at the edge of a new frontier created by machine control systems. The CAN bus is the route machine control systems will follow in the future. A CAN (controlled area network) provides data communication between hardware components and sensors. This data network operates through an electrical bus—a group of wires with multiple termination nodes that provide a common connection within the machine. The CAN bus is the power distribution and communication infrastructure of modern grading and earthmoving equipment.
Since the CAN bus is already incorporated into the machine right at the assembly line, it is the perfect connection to integrate machine control systems. Instead of adding components as aftermarket options, CAN bus systems are being designed to provide connections for GPS control boxes, receivers, and antennas.
John Deere’s recent development of the Autoblade system provides these connections. The standard in-cab display provides graphical information to the operator, reporting essential details of systems operation—such as oil pressure, battery condition, and transmission oil temperature. At the push of a button, the display changes to show the typical screen views of the GPS machine control system. The operator can easily switch between the two as needed.
Five years ago, two companies joined their fields of expertise to develop new machine control solutions for a wide variety of applications. Sauer-Danfoss was in the business of developing and designing electro-hydraulic operating systems for off-highway equipment. Its primary customers were such original equipment manufacturers as Caterpillar and Gomaco. Topcon was developing and manufacturing machine control systems based on laser, sonic, and satellite positioning technologies. Its primary customers were after-market purchasers, specifically contractors.
A joint venture agreement between the two companies created TSD Integrated Controls. The name sums up the services that this unique company offers—a single-source solution for off-highway applications integrating mobile hydraulic controls with optional positioning controls and tracking systems. Through TSD, Sauer-Danfoss’ state-of-the-art hydraulic systems are combined with the most advanced positioning technologies from Topcon and offered to any and all equipment manufacturers for incorporation into their machines.
TSD is continually developing new concepts and products that will further revolutionize machine control. Upcoming developments include concrete/asphalt paving machines guided by satellite positioning; two-way communication systems between office and job site; and agricultural steering systems.
Take Advantage of the Benefits
Machine control systems produce substantial increases in earthwork productivity—an average of 50% or more depending on site conditions and skill of the contractor. Jobs can be started when crews are ready without waiting for layout and grade staking by others. Design grade is achieved on the first machine pass, and costly reworking of areas is eliminated.
Difficult areas with transitioning slopes and complex curves, such as detention basins, can be graded easily without stakes. And the bottom line—profit—rises accordingly. The fact is technology will continue to move ahead. More and more products with advanced features will become available. The contractor who hesitates to invest in these products because of lack of understanding will end up behind the competition. There’s no question that you, as a contractor, will embrace technology. The only question is when.
Richard Rybka, an applications journalist with Topcon, has 30 years’ experience in site engineering, land development, and construction.
GEC
- May/June 2006 |
