This simple scenario is the reason why more and more contractors are implementing machine control systems on earthmoving and grading equipment—scrapers, dozers, and motor graders. Investment in these systems is returning unprecedented levels of productivity, accuracy, and control. Labor costs for layout and grade checking are dramatically reduced. Contractors are finishing jobs ahead of schedule and overcoming weather delays instead of asking for time extensions.
Machine control systems are here to stay. In many ways, we are just at the beginning of a new frontier where automated machines will easily accomplish many of the goals that contractors have striven to achieve for years—accuracy, efficiency, and productivity. To better understand the impact these will have, let's take a look at some basic information about how they operate.
The Basics of Machine Control Systems
Machine control systems are extremely complex and are evolving rapidly. This discussion will deal primarily with systems that use hydraulics to position the cutting edges of earthmoving and grading equipment in order to match a design grade. Understanding these complex systems is best accomplished by dividing the components and functions into three generalized groups:
Machine Interface
Operator Interface
Sensors and input devices
The Machine Interface
Let's start at the machine interface and work backward. The cutting edge of any machine is positioned by mechanical links to the pistons of hydraulic cylinders. These cylinders move the blade up and down, and rotate it through horizontal and vertical angles. Simple enough.
Hydraulic systems also multiply force. Moving the heavy mass of a dozer or motor grader blade would be highly impractical with mechanical devices. 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.
The motion of hydraulic cylinders is determined by the amount and speed of fluid—hydraulic oil—flowing into and out of them. Valves are used to regulate the flow. Hydraulic valves have become very sophisticated, and are capable of very precise operation—provided the fluid flowing through them is stable and free of contamination.
To operate, the valve needs some type of input. Valves can be operated in two different ways. 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.
When an automated control system is added to a machine, valve and manifold assemblies, specially designed for the particular model, are tied into the hydraulic system. The valves are also connected electrically to a control box.
The Operator Interface
The control box is the operator's interface, as well as the primary control center for the system. Cables connect it to valves and sensors. Advanced control boxes, the heart of any system, often have voice prompts or a touch screen display that provide information to the operator and enable him to set and adjust system functions. Typically, the operator can choose between plan view, section view, and profile view—or choose a split-screen option that allows up to three views simultaneously.
Control boxes also contain onboard computers and operating software that process information from input devices and send signals to control the hydraulic valves. In the case of machine control systems that use satellite positioning information, digital design files created from the project's grading plan are also needed. The processing and integration of these two information sources enables positioning of the cutting edge to match the design grade.
Switches are located on the levers used to operate the machine. These allow the operator to go from manual to automatic without taking his hands off the controls.
Sensors and Input Devices
The term sensor covers many different devices that provide input to the control box.
The sensor provides signals to the control box. There are several sensors that can be used for different applications. A sonic sensor measures distance with sound waves, controlling grade from a physical reference—curb, stringline, or existing road surface. It provides information to the control box for elevation adjustments to the moldboard. A transducer in the bottom of the sensor generates sound pulses and listens for return echoes. Sonic sensors are generally used to cut or place material with asphalt pavers, milling machines, trimmers, and motor graders.
Simple laser systems use a machine-mounted sensor and a laser transmitter mounted on a tripod. A rotating laser will provide elevation information in a uniform plane. These systems can "indicate," as opposed to "automatic," providing visual signals to the operator to raise or lower the cutting edge to match the planned grade. They can also provide automatic control by adding hydraulic valves. Laser control systems have been widely used for many years to fine grade areas like building pads and athletic field surfaces with minimal slope. Range limitations are the major drawbacks of these systems.
A laser signal can also be used to transmit three-dimensional information. Some total stations are designed to provide three-dimensional positioning information to a machine control system. where that data 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 is the ultimate input device. To understand how it works, think of a GPS survey system with the rover mounted on the machine. Satellites send positioning data to the GPS antenna/receiver combination at the base station, located at a known stationary point on the site. Positioning data is 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. The machine's three-dimensional location on the site is accurately determined.
Position data is processed by control box software and compared to the design grade at that specific location. The design grade information comes from data files loaded into the control box on a compact flash card. The control box updates positioning data ten times per second and send signals to the hydraulic valves. The blade is automatically positioned for elevation and slope.
Other sensors are needed to inform the control box of certain machine conditions. A blade slope sensor is used for dozer applications. On motor graders, a rotation sensor is located at the rotation swivel. These sensors can work together to enable the rotation of a grader blade while maintaining cross-slope. A mainfall sensor mounts on the mainframe 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.
Topcon's 3D-GPS+ machine control systems accurately control the cutting edge in all conditions by comparing the cutting edge elevation to design elevation and computing design cross-slope based on the machines orientation and location.
Indicate systems provide visual guidance for machine operators. They are not connected to the hydraulic system—the operator must control the cutting edge. These systems are a cost-effective way for contractors to get started with GPS. Hydraulic valves can be added at a later time to enable automated control of the cutting edge. Indicate-only systems are typically used on bulk earth-moving machines—scrapers and large dozers.
Greater GPS Accuracy
GPS accuracy is variable depending on the number of available satellites, their distribution in the sky, and other factors. This variable accuracy is acceptable when working to plus or minus one-tenth foot, but cannot be considered reliable when higher precision is required.
One augmentation to the vertical component, developed by Topcon, uses a laser level and can be added to a Topcon system. It is available for both machine control systems and survey rovers. Other manufacturers offer similar solutions.
Benefits of Machine Control
Machine control systems produce substantial increases in earthwork productivity. The cutting edge is controlled automatically, allowing the operator to concentrate on steering and make the most efficient use of machine motion.
Eliminating operator interpretation of grades has other advantages. Consider a typical bluetopping job where hubs are set at 50-foot intervals. The operator can clearly see that he is "on grade" at the bluetop, but he must carry that grade between these points. In many instances this intermediate area will end up with grade inconsistencies—the grade will not be continuous. In large surface areas, like building pads, it can result in material overruns. On highways and roads, the deviations can cause the repetitive bump-bump-bump syndrome.
Design grade is achieved the first time, eliminating the time and expense of reworking areas. Operator fatigue is reduced. Job site safety is improved. Fewer people are required to work close to machine operations because the need for layout crews and grade checkers is reduced.
Machine control systems facilitate the grading of complex curves and slopes. Current trends in stormwater design are creating detention basins with convoluted edges and transitioning slopes. In short, there are a lot of things happening in a relatively small area. These areas are difficult to stake for machine grading. For the contractor who is responsible for layout, this is a significant labor savings.
Surface File Preparation
GPS machine control systems cannot provide automatic grade control without reference to information about the planned design. This information is supplied in the form of surface data files that are prepared on a computer and transferred to a compact flash card. The card is loaded to a special slot on the control box.
"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 program and create a surface file. While this TIN file may be great for visualizing a 3D 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 two-foot intervals. There may be a contour two feet away from the actual toe of the slope on a relatively flat surface, and another contour of higher value three 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.
If this file is placed in a control box, the machine has no idea regarding the transition between the contours created in the TIN. To make the file useful, a breakline at the toe of the slope must be added. This breakline signals the machine control system that there is a distinct edge between the flat and sloped surfaces. Breaklines are crucial.
Surface files for machine control use must also be checked for erroneous z values. These values may be negative, zero, or inconsistent with the other points along the contour. These types of inconsistencies in digital data can be caused by CAD drafting errors or file corruption. Leaving these uncorrected will cause a grading machine to run erratically when it encounters these areas. Electronic files provided by engineers are not meant to be surfaces that can be installed in a machine or rover. These surfaces were most likely generated for calculating dirt quantities early in the design phase. Chances are the design on the paper plans is different from the surface that is in the CAD file.
Software programs developed for office PCs can expedite the creation of surface files for machine control applications. Topcon's Office 3D will open an AutoCad drawing file and allow the user to evaluate the surface. The program also features a machine simulator. With this feature, the computer operator can steer a model of a grading machine across the planned surface, viewing it three dimensionally. Irregularities can be observed and corrected before the file is exported to a flash card and loaded to the control box.
Future Developments in Machine Control
We are only at the edge of a new frontier created by machine control systems. 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 provides 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 after-market 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 for 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.
The diagram (right) shows how the CAN bus provides information for cutting edge (elevation) control, propulsion, and steering. Many new advances in machine control are being made by means of the two interconnections. New model grading machines use the propulsion interface to perfectly manage load, power, and speed. Steering systems for agricultural tractors enable the perfect alignment of field passes, providing precise, economical distribution of fertilizer and crop management chemicals.
Today, technology is created by specialists. Developing new technologies is of little value unless they can be applied to products that put them to use. Manufacturers may have the resources to develop core technologies needed for their products, but frequently rely on specialists for related systems and components.
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 original equipment manufacturers (OEM) like 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 Intergrated Controls. The company name sums up their unique services—a single-source combining 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.
The Surveyor and Machine Control
It's true—machine control systems reduce the need for construction staking and layout by surveyors. You can't hide from the facts. But the widespread use of these systems also offers new opportunities to surveyors.
Historically, surveyors have been the "keepers" of construction staking and layout data. They have provided an invaluable service to contractors—obtaining design plans, identifying and calculating the points required to establish feature locations and elevations, and putting them on the ground at the job site.
Surveyors have the capabilities to follow a similar process for 3D pro-jects. They can provide job site control, prepare machine control files, and certify finished grade. Surveyors have the dual knowledge of both office and field operations as they relate to design and construction. Surveyors are familiar with the operation of CAD programs and field software. A change in methodology and specific training will complete the equation.
Surveyors use point data to define and set grades for earthwork operations. Machine control systems operate with surface data. Thinking along this path, the surveyor's objective is to comprehend the intent of a grading plan and produce a surface that reflects that intent and enables the smooth operation of a machine. The addition of breaklines, interpretation of contour and spot elevations to ensure positive drainage flow, and error checking are part of that process.
Training in surface file preparation can be obtained from a number of sources. TakeOff Professionals (TOPS), located in Peoria, Arizona, specializes in data file preparation for site work contractors. It is frequently more cost effective and reliable to engage their services than to add a skilled person to the contractor's staff. TOPS will also provide targeted consulting with other professionals at a reasonable cost to fill gaps in knowledge and technique. Most manufacturers offer training in the use of their software.
There is a definite need for precise surface file preparation. Most small to mid-sized contractors do not have personnel on staff with the necessary technical knowledge to perform the tasks involved. These are the same companies that relied on surveyors for staking and layout services.
When you take an overall perspective of the many services that a surveying firm can offer, and the new opportunities that surface file preparation provides, the only real loss is time spent on fieldwork. For most surveying firms, construction staking has been a marginally profitable service. It's labor intensive, requires travel, and is subject to weather variations. And when stakes get knocked out at the job site, everyone wants you back on the job—immediately. The exciting world of machine control may provide the surveyor the opportunity to return to his traditional role of expert in analysis.
本文转自：China Industry News