ATS Control Systems on Dozers: Precision Grading Without Satellites

[MikePhua]

Introduction: Bridging the Gap Between GPS and Laser Control
In environments where satellite signals are unreliable—such as dense forests, underpasses, or urban canyons—traditional GPS-based machine control systems fall short. Enter ATS (Advanced Tracking Sensor) control systems, which use robotic total stations to deliver 3D grading precision without relying on satellites. This article explores the implementation of ATS systems on Caterpillar dozers, particularly the D6T LGP, and compares their performance to GPS and laser-based alternatives.
What Is ATS Control?
ATS (also referred to as UTS or Universal Total Station control) is a 3D machine guidance system that uses a robotic total station to track a prism mounted on the dozer. Unlike GPS, which triangulates position from satellites, ATS relies on line-of-sight communication between the total station and the machine.
Key components include:

• Robotic Total Station: Mounted on a tripod, it continuously tracks the machine’s prism.
  
• Machine-Mounted Prism: Typically placed on a power mast at the center of the blade.
  
• Onboard Computer: Receives positional data and compares it to the loaded 3D design.
  
• Radio Link: Transmits data between the total station and the machine.
  

Advantages of ATS Over GPS and Laser Systems

• Satellite Independence: Ideal for forested areas, tunnels, or urban zones with poor GPS coverage.
  
• High Accuracy: Down to ±3 mm, suitable for fine grading and rail construction.
  
• 3D Capability: Supports complex designs with changing slopes, curves, and crossfalls.
  

Field Application: Railroad Grading in Denmark
A Caterpillar D6T LGP equipped with ATS was deployed on a railroad project requiring precise grading with no physical stakes. The terrain included:

• Curves up to 35 degrees
  
• Mainfall gradients between 0.9% and 1.5%
  
• Crossfall of 4%
  
• Frequent changes in slope every 30–40 meters
  

GPS was unusable due to tree cover, and laser control proved inefficient—requiring repositioning every 10 meters. ATS provided continuous 3D control, dramatically improving grading speed and accuracy.
Technical Parameters and Setup Recommendations

• Total Station Range: 600–800 meters diameter
  
• Accuracy: ±3 mm horizontal and vertical
  
• Power Mast Type: EM400 or equivalent
  
• Setup Time: 15–30 minutes for calibration and lock-on
  
• Battery Life: Total station operates on rechargeable batteries; status monitored via onboard display
  

Installation and Calibration Process

1. Tripod Setup: Position total station with clear line-of-sight to work area.
   
2. Calibration: Use handheld survey prism to measure three known points.
   
3. Machine Lock-On: Define a “search window” for the total station to reacquire the prism if signal is lost.
   
4. 3D Design Upload: Load digital grading plan into the machine’s control unit.
   
5. Operation: The system continuously calculates cut/fill values and adjusts blade position.
   

Operator Feedback and Performance Insights
Operators reported:

• Seamless tracking even when dump trucks temporarily blocked the line of sight
  
• Automatic reacquisition of signal within 2–3 seconds
  
• Blade control remained stable even during material dumping and elevation changes
  

One operator graded 700 meters of stone with ±1 cm tolerance in just 10 hours—an impressive feat given the complexity of the terrain.
Limitations and Considerations

• Station Relocation: Must be moved every 800 meters, unlike GPS systems with 8 km range
  
• Line-of-Sight Dependency: Obstructions can temporarily interrupt tracking
  
• Initial Setup Complexity: Requires survey knowledge for calibration
  

Comparative Insight: ATS vs. GPS vs. Laser

• GPS Systems
  • Pros: Long range, minimal setup
    
  • Cons: Useless under canopy or structures
    
• Laser Systems
  • Pros: Simple and affordable
    
  • Cons: Limited to 2D grading; frequent repositioning
    
• ATS Systems
  

• Pros: High accuracy, 3D capability, satellite-free
  
• Cons: Shorter range, requires survey setup
  

Case Study: ATS on a Freeway Project
A Trimble-equipped grader used ATS under multi-lane underpasses where GPS failed. While the system worked well for short passes, it struggled with long turns and frequent obstructions. Manual resetting was often required. However, newer ATS systems have improved tracking algorithms and reacquisition speed, addressing many of these issues.
Conclusion: Precision Without Satellites
ATS control systems offer a powerful alternative to GPS and laser grading, especially in environments where satellite signals are blocked. With high accuracy and full 3D capability, they are ideal for complex grading tasks like railroads, urban infrastructure, and forestry roads. While setup and range limitations exist, the benefits in precision and reliability make ATS a valuable tool in the modern earthmoving arsenal.
Final Advice
If your jobsite challenges GPS coverage or demands fine grading in obstructed areas, consider investing in ATS technology. Partner with experienced surveyors for setup, and ensure your crew is trained in calibration and troubleshooting. With the right preparation, ATS can turn a difficult grading job into a showcase of precision and efficiency.