Introduction
The AccuGrade ® System is designed for earthmoving equipment in the construction application. The system can be used with a wide variety of sensors in order to provide conventional control or 3D machine control.
Safety
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Do not operate or work on this machine unless you have read and understand the instructions and warnings in the Operation and Maintenance Manuals. Failure to follow the instructions or heed the warnings could result in injury or death. Contact your Caterpillar dealer for replacement manuals. Proper care is your responsibility. |
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This warning label is located on the electric masts. The warning label is placed to the rear of the masts at eye level.
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| Illustration 1 | g01069921 |
Warning decal that is located on the electric masts | |
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To prevent possible personal injury during installation and removal of the laser receivers, lower the mast to the minimum height and use an approved access system to reach the mounting locations of the laser receivers at the top of the mast. Do not climb on the blade. |
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Once the system is placed in automatic mode, blade movement may occur. Ensure that all personnel are clear of the blade before you place the system in automatic mode. Personal injury or death from crushing could occur. |
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Do not operate this system unless you are fully trained on this equipment. To avoid injury, the machines park brake must be engaged prior to starting the calibration. Maintain adequate clearance from people and objects as the blade may move abruptly during automatic hydraulic valve calibration. |
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This warning label is located on the tripod. The label is placed in a location on each leg of the tripod in order to be easily seen.
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| Illustration 2 | g01073304 |
Warning decal that is located on the legs of the laser transmitter | |
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Movement of the transmitter could cause unexpected blade movement. Death or serious injury could occur. Turn off the transmitter before you move the transmitter or before you adjust the transmitter. |
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Safety (Laser)
The IEC and the United States Government Center of Devices for Radiology Health (CDRH) has classified this laser as a Class II laser product. The maximum radiant power output of this laser is less than 5 milliwatts.
Refer to the operator's manual of the laser transmitter for installation and operating instructions.
The laser that is supplied with the AccuGrade - Laser System complies with all applicable portions of "Title 21" of the "Code of Federal Regulations, Department of Health and Human Services, Food and Drug Administration, Federal Register, Volume 50, Number 161, 20August 1985".
This laser complies with "OSHA Standards Act, Section 1518.54" for use without eye protection. Eye protection is not required or recommended. The following safety rules should be observed:
- Never look into a laser beam or point the beam into the eyes of other people. Set the laser at a height that prevents the beam from flashing directly into people's eyes.
- Do not remove any warning signs from the laser.
- Use of this product by personnel that are not trained on this product may result in exposure to hazardous laser light.
- If initial service requires the removal of the outer protective cover, removal of the cover must be performed by trained personnel.
Crushing Prevention and Cutting Prevention
Support the equipment properly when you work beneath the equipment. Do not depend on the hydraulic cylinders to hold up the equipment. An attachment can fall if a control is moved, or if a hydraulic line breaks.
Unless you are instructed otherwise, never attempt adjustments while the machine is moving. Also, never attempt adjustments while the engine is running.
Whenever there are attachment control linkages, the clearance in the linkage area will increase or the clearance in the linkage area will decrease with movement of the attachment. Stay clear of all rotating and moving parts.
Keep objects away from moving fan blades. The fan blade will throw objects or cut objects. Do not use a kinked wire cable or a frayed wire cable.
Wear gloves when you handle wire cable. When you strike a retainer pin with force, the retainer pin can fly out. The loose retainer pin can injure personnel. Make sure that the area is clear of people when you strike a retainer pin.
In order to avoid injury to your eyes, Wear protective glasses when you strike a retainer pin.
Chips or other debris can fly off objects when you strike the objects. Make sure that no one can be injured by flying debris before striking any object.
Operation
Clear all personnel from the machine and from the area.
Clear all obstacles from the machine's path. Beware of hazards (wires, ditches, etc).
Be sure that all windows are clean.
Secure the doors and the windows in the open position or in the shut position.
Adjust the rear mirrors (if equipped) for the best visibility close to the machine.
Make sure that the horn, the travel alarm (if equipped), and all other warning devices are working properly.
Fasten the seat belt securely.
Warm up the engine and the hydraulic oil before operating the machine.
Only operate the machine while you are in a seat. The seat belt must be fastened while you operate the machine. Only operate the controls while the engine is running.
While you operate the machine slowly in an open area, check for proper operation of all controls and all protective devices. Before you move the machine, you must make sure that no one will be endangered.
Do not allow riders on the machine unless the machine has the following equipment:
- Additional seat
- Additional seat belt
- Rollover Protective Structure (ROPS)
Note any needed repairs during machine operation. Report any needed repairs.
Avoid any conditions that can lead to tipping the machine. The machine can tip when you work on hills, on banks and on slopes. Also, the machine can tip when you cross ditches, ridges or other unexpected obstructions.
Avoid operating the machine across the slope. When possible, operate the machine up the slopes and down the slopes.
Maintain control of the machine.
Do not overload the machine beyond the machine capacity.
Be sure that the hitches and the towing devices are adequate.
Never straddle a wire cable. Never allow other personnel to straddle a wire cable.
Before you maneuver the machine, make sure that no personnel are between the machine and the trailing equipment.
Always keep the Rollover Protective Structure (ROPS) installed during machine operation.
Conventional Systems
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| Illustration 3 | g01506777 |
Conventional systems provide elevation or slope control. Conventional elevation systems continually measure the offset between a reference surface and the cutting edge of the machine. This measured offset is compared against a design offset that has been entered into the system. If the measured offsets and the design offsets differ, the AccuGrade System drives the cutting edge of the machine upward or downward until the offsets match. Elevation sensors, such as a Sonic Tracer, provide elevation control.
Conventional slope control systems use sensors that are mounted on the machine in order to measure the cross slope of the cutting edge of the machine. This measured cross slope is compared against a design cross slope that was entered into the system. If the measured cross slope and design cross slope differ, one side of the blade is raised or lowered until the cross slopes match.
Conventional systems do not provide a horizontal position. So, the following items are not used in a conventional system: design files, background maps and avoidance zones.
Laser
Laser Grading
Setup and operation is easy with the AccuGrade System. An off-board tripod mounted laser transmitter emits a thin beam of light that rotates 360 degrees. This creates a grade reference over the work area. Grade information is transferred to the machine via the laser beam.
A digital laser receiver, mounted on an electric telescopic mast above the cutting edge of the machine, detects the elevation of the laser beam. Then, the information is sent to the display.
The AccuGrade System is available with a single mast system or a dual mast system. The single mast system and the dual mast system both provide single dimensional (elevation) control. For example, a flat plane or a single sloped plane. The dual mast system provides two-dimensional control. For example, a sloped plane with cross slope (elevation and tilt).
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| Illustration 4 | g01046037 |
The display informs the operator of the position of the that is relative to grade. The Display indicates the cut or the fill requirements of the work area.
An automated blade control feature allows the operator to automatically control the lift function (single mast system) or both the lift and tilt (dual mast system) functions by placing the cutting edge to the precise elevation needed for fine grading.
The AccuGrade Laser system provides valve drive signals for automatic blade control. The valve automatically raises or lowers the cutting edge based on the correction signals to maintain elevation for precise grade control and optimum productivity.
Unique control functions allow the system to be user configured to suit operator preference and specific job site requirements.
Applications
The AccuGrade Laser System is designed for fine grading of sites with flat, single or dual slope surfaces.
3D Systems
3D Systems use sensors that can measure horizontal position and vertical position. The resulting X,Y, Z coordinates are compared against a design that was loaded into the system. The system sends corrections to the hydraulic valves for the machine in order to drive the cutting edge of the machine to grade. The system uses either a Advanced Tracking System (ATS) robotic total station or Global Positioning System (GPS) receivers as the 3D sensor.
The idea behind the AccuGrade System is very simple. Computers and design software produce accurate 3D models of project designs. In the past, these models stayed in the office with the engineer. The engineer gave information to the surveyor. The surveyor then put stakes in the ground in order to guide the machine operators.
With the AccuGrade System, the 3D model comes into the field as a design surface. By adding GPS, you can accurately determine the position of the blade on your machine in both horizontal direction and the vertical direction on the design surface. The cut or the fill that is to be applied to the design surface can then be computed on the machine in order to provide guidance for the machine.
When all of the hardware is installed on the machine you need to configure the AccuGrade System. You can configure all system components with the Display. The Display is the onboard computer. The default settings support most of the conditions, but the settings can be changed as required. Items that need to be configured in order to make the AccuGrade System work properly include the following items:
- GPS Receiver Configuration (Site Coordinates)
- Light Bar Configurations
- Radio Network Or Frequency
- Machine Settings
- Units Of Measurement
- Machine Dimension Information
- Pitch Sensor Calibration
- Valve Calibration
- Operator Configuration
At the start of any new project or work area the site calibration, and the design are required. GPS data is needed in order to position the blade. GPS signals are received through the GPS Receivers. At the same time, base station data is received through the data radio and sent to the left hand GPS Receiver. The GPS data from each GPS Receiver on the blade is combined with the slope information in the Display to produce a blade position and blade cross slope. The system uses the design in conjunction with the GPS information in order to compute the cut or the fill at the blade tips in respect to the design. The design can be in the form of a DTM (TIN or Grid), road, level or sloping surface. The Display has a color LCD that has brightness control in order to allow the operator to see the LCD in both day light and at night. Information on the screen is available in the following views:
- Plan
- Cross section
- Profile
- Text
The operator will be able to switch between these views at any time. The Display uses the GPS positions and the machine dimensions in order to compute the position of each blade tip. The Display compares the blade tips to the design elevation to calculate the cut or fill needed to be on-grade. The cut or fill data is also displayed on light bars, which act as another visual indication to the operator. When horizontal alignments are defined, the center light bar provides left and right guidance to the selected alignment.
ATS System
With an Advanced Tracking Sensor (ATS) System, a prism and a radio are attached to the machine. The prism is mounted on a mast above the cutting edge of the machine. The ATS robotic total station can be set up over a known point on site. The ATS robotic station can also be set up on an unknown point. The position of an unknown point can be determined by methods such as resection. The position of the point must be determined before you start using the ATS for machine control.
The ATS tracks the machine as it moves. Then, the ATS broadcasts the position of the machine to the AccuGrade System via one of the following radios: TC900C/CR900C and TC2400/CR2400. An ATS System is usually combined with a Cross Slope System in order to provide guidance across the entire cutting edge of the machine.
If the MT900 machine target is used with a SPSx30 total station, a 2400 MHz radio is required.
The Global Positioning System (GPS)
With a GPS system, one or two GPS receivers are attached to the machine. With single GPS systems, the receiver is mounted on one of the masts that is located above the cutting edge of the machine at either end of the blade. With a dual GPS system, the GPS receivers are mounted on masts that are located above both ends of the cutting edge of the machine.
GPS receives data from a system of satellites that orbit the earth twice a day at very high altitudes. The orbit radius is approximately 26600 km (16528 miles). GPS was set up by the government of the United States. GPS provides precise timing and positioning anywhere on earth, 24 hours per day with no charge to users.
Newer GPS receivers will be able to also receive data from the Global Navigation Satellite System (GLONASS). GLONASS consists of 21 satellites in 3 orbital planes, with 3 on-orbit spares. The three orbital planes are separated 120 degrees, and the satellites within the same orbit plane by 45 degrees. Each satellite completes an orbit in approximately 11 hours 15 minutes. This allows more GPS satellites to used to for the solution.
In very general terms, a GPS receiver computes a position based on radio signals received from several different satellites. The satellites have highly reliable clocks, so the timing of these satellite signals is known very accurately. The GPS receiver calculates the relative distance to each of the satellites. This calculation is based on the travel time of the signal and the speed of light (speed of the signal). The receiver then uses these distances in order to calculate the receiver's location on earth.
As a broadcast only radio system, GPS supports an unlimited number of users. The broadcast frequencies penetrate clouds, rain, and snow. GPS can also accurately guide operations in fog or dust as well as at night. There are different levels of precision and accuracy available from GPS. These levels depend on the GPS receivers and the methods that you use.
The four basic levels of position accuracy (1 sigma) that are available in real time (that is, instantaneously) from GPS are as follows:
- Autonomous, 10 m (30 ft) to 15 m (50 ft)
- SBAS, 1.0 m (3.3 ft) to 2.0 m (6.6 ft)
- DGPS, 0.3 m (1.0 ft) to 1.0 m (3.0 ft)
- RTK (Float), 0.2 m (0.7 ft) to 1.0 m (3.0 ft)
- RTK (Fixed), .02 m (.07 ft) to .03 m (.10 ft)
Illustration 5 shows the GPS accuracy levels.
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| Illustration 5 | g01374212 |
GPS accuracy levels (1) Autonomous (2) DGPS (3) RTK Fixed (4) RTK Float (5) SBAS | |
The method that is used for machine grade control in construction is the same as that used by surveyors for stakeout in construction. The method is called Real-Time Kinematic (RTK), GPS.
In order to produce RTK positions two GPS receivers are required. One receiver is known as the GPS base station and is fixed in one place. The other GPS receiver is known as the rover. This receiver can be stationary or mobile.
The base station communicates to the rover ('s) through a wireless data link using a data radio. Illustration 6 shows this setup.
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| Illustration 6 | g01507075 |
GPS and the AccuGrade® System (1) GPS satellites (2) GPS base station and data radio (3) Repeater radio (optional) (4) Machine equipped with the AccuGrade System | |
Both GPS receivers make observations (measurements) of the GPS signals at the same time. The base station broadcasts the observed information together with the location and other information across the data radio link to the rover. The rover then combines the data from the base station together with its own data in order to compute a very accurate position relative to the base station.
A single base station can support an unlimited number of rovers, provided the rovers are within about 20 km (12.4 miles) of the base station. Normally, the range of the data radio link is the more limiting factor. You can use radio repeaters in order to extend the radio coverage.
In areas where the 900 MHz band is available, the TC900C or CR900 data radio is recommended. In areas where the 900 MHz band is not available, one of the following radios is recommended:
- TC450 (450 Mhz)
- TC2400 (2.4 Ghz)
Low accuracy corrected GPS (SBAS)
If low accuracy GPS positions are adequate for the required site work, you can use Satellite-Based Augmentation System (SBAS) error corrections. SBAS corrected systems do not require additional site infrastructure.
Satellite-Based Augmentation Systems are free-to-air GPS correction services. SBAS networks consist of ground stations that are set at known positions around the world, and geo-stationary satellites that maintain a fixed position above the Earth. The ground stations receive GPS signals from all GPS satellites in view. The GPS data is then sent to a master control site, which then transmits GPS corrections to the geostationary satellites. These satellites broadcast the information to all SBAS enabled GPS receivers.
The following SBAS networks are currently available:
WAAS - Wide Area Augmentation System (United States)
EGNOS - European Geostationary Navigation Overlay Service (Europe)
MSAS - Multi-Functional Satellite Augmentation System (Japan)
GPS receivers use a GPS receiver configuration file (.cfg) to convert from WGS84 coordinates to the site coordinate system. High accuracy (RTK) GPS systems use a configuration file generated from the site calibration. Inaccuracies in the entered position of the base station for the site calibration will result in a shift of the site coordinate system away from the local circuit coordinate system. When this configuration file is used by a GPS receiver using RTK, the shift is not exposed, as the relative positions of points on the site are still accurately known, and the accuracy of RTK positioning is unaffected. However, if the same configuration file is used by a GPS receiver using SBAS corrections, the shift in the site coordinate system away from the local circuit is exposed, and results in additional positioning errors.
To avoid additional errors, do one of the following:
- Make sure the base station antenna position used for the RTK site calibration is accurate to within about 1 m (3.3 ft). This accuracy can be achieved via traditional surveying methods or long autonomous GPS occupations. Speak to your site surveyor for more information.
- Use a configuration file generated by the AccuGrade Office software using the local circuit coordinate system, instead of the configuration file produced by the site calibration.
GPS Site Calibration
Note: A poor quality GPS site calibration will result in poor quality guidance information from the AccuGrade Grade Control System.
A GPS site calibration is a mathematical relationship between a grid coordinate system (northing, easting, and elevation) of a project and the GPS coordinate system (latitude, longitude, and ellipsoidal height - also known as WGS84 coordinates ).
This relationship is determined by using GPS to measure points with known grid coordinates, and then calculating the calibration parameters.
A surveying or civil engineering company should be employed to establish the control points around a site. Make sure that you locate the control points where they will not be destroyed during construction. Five or more control points located at, or near, the corners and center of the project will normally give good results.
Note: If you employ a GPS surveyor to create the GPS site calibration, make sure that you clearly specify the requirements. Caterpillar recommends that you give them a copy of this section of the manual.
Some survey software can do both a full site calibration and a single point calibration.
A single point calibration cannot provide any guarantee of accuracy as the parameters that define a site calibration will be default values that may have no resemblance to the real values obtained through a full calibration. A single point calibration should only be employed on small sites with no existing control. Caterpillar recommends that you carry out a full site calibration to guarantee the required accuracy all over the site.
When doing a site calibration, pay attention to the following points:
- A minimum of five 3D local grid coordinates (north, east, elevation) and five observed GPS coordinates (latitude, longitude, height) to provide enough redundancy.
- The set of GPS coordinates must be independently obtained from the set of grid coordinates.
- The selected calibration points should be around the perimeter of the site. Do not work outside of the area enclosed by the calibration points, as the calibration is not valid beyond this perimeter.
- When defining the acceptable accuracy limits, the calibration tolerances should not be larger than the accuracy tolerance for the site.
- When measuring points, use a bipod on a staff or a tripod to maintain stability.
- Check the accuracy of the calibration by visiting other control points that were not used in the calibration.
Converting The Site Calibration To A GPS Configuration File
When the site calibration is complete, the site surveyor uses a surveying software package to convert the site calibration data to a calibration file, for example Site.dc.
Once the site calibration file is generated, use AccuGrade Office to convert the calibration to a GPS configuration file which can then be copied to the data card. For information on how to do this, refer to the AccuGrade Office Help file.
The site calibration files are stored in the Display rather than the GPS receiver. For this reason, each time you change site, make sure you update the site calibration files.
To ensure the correct files for each design are in use, do one of the following:
- Make sure there is a valid configuration (.cfg) file for the design in each design folder. When you load the design the associated configuration file is sent to the receiver.
- Use the GPS Receiver Configuration item in the Setup Menu. This sends the site calibration to the GPS receiver and updates the parameters held in the Display.
When a GPS receiver configuration (.cfg) file is sent to a GPS receiver, the system resets the receiver to factory defaults before applying new settings.