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Comparing AGV Navigation Methods

Evaluating the ways navigation affects costs, safety, maintenance, product flow and more

AGV Systems Inquiry

AGVs in a variety of configurations - unit style, driverless forklift.

The type of AGV and the way it navigates are two huge considerations in any automated material transport project. Vehicle type dictates functionality, interface and payload factors, but navigation is critical to overall performance. After all, AGVs travel; that’s their primary role. The way they do wind their way through rack aisles, across dock areas, near work cells, around conveyors and throughout the warehouse can make or break a project. The options range from simple methods like tape guidance to highly-automated laser and contour systems.

AGVs must know their position to effectively navigate, and that is done in two ways: relative or absolute.

  • Absolute positioning is basically as described: the AGV is aware of its place on a precise map of the facility.
  • Relative positioning is calculated based on a reference point.

What are the factors for AGV navigation?

How do these systems compare on the major factors?

  • Budget – more AGVs means lower cost per vehicle.
  • Safety – how the AGV responds to its environment, walkways and aisles.
  • Implementation costs – setup, programming, software, charging stations.
  • Ongoing costs – maintenance, energy consumption.
  • Flexibility – how rigid is the navigation scheme?
  • Interfaces – with various infrastructures; the options are nearly infinite.
  • Size and scope – how long are the pathways? How complex?
  • Scalability – is it easy to add more vehicles when needed?
  • Plant environment – are there issues with the floor? Is airborne debris present?

 

“When you evaluate automated guided vehicle navigation methods, take a hard look at the environment in which the vehicles will operate, the safety features needed for its surroundings, and the level of precision you need for the task or the flexibility for future expansion.”  – Scott Matlock, North American General Manager-Logistics and Automation, Muratec Machinery USA

Laser-guided navigation: nothing to install on the floor and plenty of flexibility

AGV with laser guidance navigation.

With laser-guided navigation, you install reflectors along the AGV’s pathway to guide it.

Advantages

  • This is a precise navigational system, useful for a variety of automated systems in manufacturing and material handling.
  • You don’t need to install tape, wire or other floor-based infrastructure.
  • Laser-guided systems are one of the most precise and accurate AGV navigation schemes.
  • This is a very flexible and configurable method since there is no floor infrastructure needed. Reflectors can be installed and removed with relative ease for reprogrammable pathway designs.
  • Laser guidance may be more economical than other methods.

Limitations

  • Smoke, airborne debris and reflections from other sources may impact the AGV if not specified for the environment.
  • These systems may have a more limited range than alternatives. This is something to consider in the design phase.
  • AGVs guided by lasers may require more maintenance, as they must be precisely calibrated to their pathways to ensure proper tracking and functionality.

Contour or “natural” navigational systems: complex systems free of navigation infrastructure

AGV with contour style navigation.

Contour-guided AGVs are complex to implement but have excellent flexibility free of reflectors, tape or other installed infrastructure. This technique is often used for driverless forklift applications and can be costlier than other methods.

Advantages

  • Allows for fast and easy pathway changes. You can change routes without any infrastructure alterations.
  • AGVs with contour/natural navigation maneuver with a high degree of accuracy. They are extremely precise.
  • Contour systems excel at detecting and avoiding collisions. They’re strong in applications where they must interact with floor workers, forklifts, other AGVs and industrial traffic of all types. They can tie into overhead doors, traffic gates and other systems.
  • Because they don’t require navigational infrastructure like reflectors or tape, natural and contour systems can be more cost-effective.
  • Contour systems are very scalable for plant expansions and system changes. They work in small or large-scale operations.

Limitations

  • Like laser reflective systems, contour-guided AGVs can be sensitive to their environment. Airborne dust and debris or smoke can interfere with sensors in some cases.
  • AGVs with contour navigation are more complex and require more programming compared to other navigation methods.
  • Like laser-reflective systems, natural/contour AGVs can be more maintenance intensive.
  • Contour systems may be a shorter range than more infrastructure-intensive designs.
  • Because they are reading their environment as they navigate, contour systems may move slower than some alternative navigational alternatives.
  • Also due to complexity, contour systems may have higher initial costs.

For some applications, even with their cost and complexity, contour systems are the right choice due to their flexibility and ability to navigate in more situations.

Above: automated forklift style AGV video. This AGV can be guided by inductive wire, painted lines, magnetic tape, magnetic spot, QR code, contour or laser systems.


Simultaneous localization and mapping (SLAM) navigation: excellent for dynamic applications, but highly complex

These systems rely on sensors and software to calculate the AGV’s position while simultaneously mapping the environment. In SLAM systems, the AGV creates a map on the fly and compares it to what its sensors see in operation. Advantages: SLAM lets AGVs to navigate autonomously without the need for a pre-defined path, wires, reflectors or tape. The vehicles can navigate obstacles and are extremely flexible. SLAM navigation also allows AGVs to detect and avoid obstacles in real time. Limitations: SLAM systems require an extensive IT infrastructure and significant computing power. In some cases, the map created can be affected by sensor noise, which complicates navigation and applications in complex, variable or lower-light environments.


Inductive wire guidance: durable, economical and precise

AGV automated guided vehicle with inductive navigation.

Wire-guided systems rely on wires embedded into your floor. These wires communicate with the AGV with radio signals.

Advantages

  • Because the wiring system is embedded, it won’t be harmed by foot or industrial traffic. This reduces maintenance concerns and makes these systems very durable for repetitive, heavy operation.
  • Because the wire system communicates with the AGV via radio, environmental interference (smoke, steam, airborne dust) is much less of a concern.
  • Wire-guided vehicles are extremely precise. They follow their designed pathways with exacting tolerance. For heavily-repeated sequences, this is a superior guidance system. This is often found in heavy manufacturing and many material handling interfaces, such as delivering product to or from a conveyor or AS/RS system.
  • From a cost perspective, wire-guided systems are very competitive from both an implementation cost and maintenance viewpoint. You’ll need much less “runway” from an IT and logic-building integration standpoint.

Limitations

  • Flexibility is more limited as pathway changes involve the removal and addition of embedded wires. By no means is this impossible or highly difficult, but does involve infrastructure changes that must be dealt with when your operation or application requires pathway changes.
  • AGVs can only navigate where wire is installed. Adding new zones requires wire embedding.
  • Because wiring must be installed, these systems may be less scalable compared to more free-form navigations. There is only so much wire network for more AGVs to travel.
  • Wire-guided systems cannot avoid obstacles at all. They’re safe (they will stop when something is in the way) but they must wait until the obstruction is removed.
  • All areas where the AGV operates must be able to accommodate the wire system, meaning that certain parts of a plant may be excluded from its operational zone. Sloping or uneven terrain may pose challenges for wire systems.

Overall, you trade flexibility for precise simplicity and easy maintenance with wire-guided systems.

AGV navigation flexibility: listed least to most flexible

  1. Inductive wire
  2. Painted line
  3. Magnetic tape
  4. Magnetic spot
  5. QR code
  6. Contour
  7. Laser

Vision guidance: dynamic and real-time “pathless” navigation

Vision-guided AGVs use stereoscopic cameras to “see” the environment in three dimensions. Advantages: Vision guidance allows AGVs to travel “path-free,” with limitless routes throughout a facility, ideal for complex intra-facility transportation and materials movement. Limitations: Complexity and reliance on onboard computing power.


Magnetic tape guidance systems: easy installation and simplicity and low maintenance requirements

AGV automated guided vehicle with magnetic tape navigation.

This system uses magnetic tape applied to the floor to guide the AGV. This is perhaps the simplest, lowest cost and lowest infrastructure load of any AGV navigation alternative.

Advantages

  • Perhaps the most economical navigation system to implement and maintain. The low cost of this method makes it a frequent favorite.
  • Like wire systems, tape guidance is well-suited to high-volume, repetitive operations. AGVs will follow the tape pathways with precision and complete accuracy.
  • Tape-guided AGVs are easier to install than wire systems and can be reconfigured moved, expanded or altered faster due to the relative ease of adding new routes with tape.
  • These are very cost-effective systems, with relatively little IT infrastructure compared to laser and contour systems.
  • Tape can be applied to a broad variety of surfaces to guide AGVs, allowing them to travel almost anywhere. They can traverse tight spaces and operate in very large facilities, between departments and functions with ease.
  • Safety is boiled in because floor tape is easily visible and apparent to pedestrians. You know if you are in the pathway when there is tape on the floor. Like all AGVs, tape-guided ones have built-in safety sensors and measures, but the extra visual cue of floor tape can prevent loitering by pedestrians or accidental obstructions like placing a pallet in the way.

Limitations

  • While tape applications are durable, they are more vulnerable to damage from traffic or machinery than embedded wire or systems that require no applied wire or tape.
  • Like wire systems, tape systems have scalability limits based on the “runway” of taped areas. Adding more vehicles to the same area for faster throughput may be limited.
  • You’ll have to keep your magnetic tape pathway system maintained and clear of obstacles.

Magnet spot/inertial guidance systems are an alternative to tape guidance that use magnets as beacons. These systems are less common and more flexible than tape applications.


What is the best navigation method for you?

The answer to this question almost always comes back to a combination of application, location, situation, environment and budget.

AGV navigation should consider existing infrastructure, both physical and information technology. What will the AGV do — deliver to a dock? Load a rack? Pick up from a palletizer or conveyor line? Where will it travel, and what does it do with its payload? Scalability also plays a part: some of the systems described above are much easier to scale than others, while those less scalable systems are ideal for repetitive, constant, higher throughput tasks.

Integration with your existing systems is critical. AGV navigation system should be compatible with the existing layout and equipment in your facility. 

Budget is always important. What works within your budget and ROI standards?

Safety is always a factor: how will your layout, people and processes interact with the AGV? The way it navigates is critical to safety considerations. Technical support and maintenance are also important. What kind of maintenance regimen does a particular navigation method require, and how does that work in your operation?

Ultimately, AGVs are a highly efficient method for material transport, and can fit the needs of more operations than ever, but a critical evaluation of your processes and situation will help you make the right decision for your operation’s requirements.

More resources


Scott Stone is Cisco-Eagle's Vice President of Marketing with more than thirty years of experience in material handling, warehousing and industrial operations. His work is published in multiple industry journals an websites on a variety of warehousing topics. He writes about automation, warehousing, safety, manufacturing and other areas of concern for industrial operations and those who operate them.

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