AGVs, AMRs, and Conveyors: Automated Product Transport Applications
What type or mixture of technologies fit your operation?
When you need to move loads—pallets, totes, cartons or other items—through a facility without manual involvement, the options fall into three broad categories: AMRs (automated mobile robots), AGVs (automated guided vehicles) and conveyor systems. Each of these methods has its advantages, and all can be integrated to work with each other.
What are your operational needs?
Before automating any solution, you should collect significant data and build a full case analysis. What’s happening with product flow within your operation, before and after the load is moved? Finding the right solution starts with data and a clear understanding of the business case. When it comes to moving products efficiently, many types of material handling technology can work, so it’s important to compare alternatives.
The load, its weight and its characteristics
What are you moving, how is it shaped and what does it weigh? Material handling applications usually begin with a thorough load profile.
- AGVs can handle heavier, bulkier loads than AMRs. For pallets, heavy containers and larger payloads, the solution is usually between conveyors, AGVs and manual methods.
- While some limited range of AMRs can pick and place pallets on and off racks, AGVs are much better suited to the task. Driverless forklift AGVs are a common and proven technology for that type of operation.
- Conveyors can handle the broadest range of loads and types, but offer the least flexibility. If the load is large, bulky and heavy, but always moves from point to point, conveyors are at their best. Consider a large manufactured unit moving through a line of assembly technicians. Conveyors have been doing that for decades.
- AGVs can load and unload pallets into and out of trucks; conveyors can’t always do that. Extendable conveyors reach deep inside trailers, but that function is usually for hand stacking of smaller loads.
- AMRs tend to work best in areas where the tasks and pathways change. They’re usually used for order fulfillment of relatively lighter, more unitized loads. Think of delivering containers to stationary order pickers, or taking away finished packages from a zone. AMRs are built for higher accuracy and flexible control.
Navigation and pathway factors
The way these technologies interact with your operation, floor space and infrastructure creates important distinctions. When it comes to the way the load travels through a facility, the “between” of point-to-point transport is important to know and understand.
- AGVs are less rigid than conveyors, but require you to design and program paths for them to follow. They have the same wired-in safety sensors and collision avoidance as AMRs, but cannot navigate except on their defined pathways. Depending on the situation and type of AGV, you can change these paths over time as business needs evolve. AGVs are ideal for repeatable, consistent workflows.
- Conveyors transport loads fast to multiple destinations, but only to those defined areas. If you’ve built a pallet on the conveyor and it travels between workstations, this works well in a dedicated line, with the least flexible travel path. Changing this path requires a new layout and installation. If you are utilizing a pick module, conveyors can easily integrate with it at all levels, where vehicles are usually not suitable for multi-level applications.
- AMRs don’t require pre-plotted paths—they can navigate most anywhere in your facility. They adapt to the situation on any given day and have safety sensors that allow them to avoid obstructions like pallet stacks, trash or parked forklifts. Their onboard processing and vision systems ensure that they’re the most flexible option. If your environment is dynamic, like a busy shipping or staging area where things are always in flux, AMRs may be the right choice.
Applications and operational needs
Labor needs
One of the most compelling questions when comparing these systems are labor needs. Do you need more people with conveyors vs. a vehicle? Clear-cut answers probably won’t exist until you have a more detailed application concept and a thorough analysis. In theory, a pick & pass conveyor system with dedicated slotting may need more people, but that isn’t always the case. This is a question to resolve in the early stages of an automation project – maybe the most important question.
Throughput and speed
Conveyors flow continuously (or stop only when they don’t need to flow) and can move more, faster than either AMRs or AGVs. They rely on consistent and predictable product demand, and are simply faster than the alternatives. AGVs, which also travel a pre-planned pathway, can typically flow products faster than robots. However, throughput isn’t why you deploy mobile robotics. You do that for flexibility. AMRs aren’t as fast as AGVs and conveyors, but they can also find their way around obstacles. When there is an obstruction, the AMR will circumvent it and move to its destination, where the AGV sits idle until the obstruction is removed.
Costs: acquisition, implementation and operational
Because they require more infrastructure, AGVs can be more expensive than AMRs. AGVs can move heavier load capacities and have the ability to raise and lower loads to storage positions. They’re more complex to implement, but simpler to operate since they are more task-oriented. Due to expensive onboard computing and sensors, AMRs can cost more per unit, but require less infrastructure. Conveyors are the least flexible transport option, but tend to be simpler to operate and less expensive.
Energy, maintenance and operational costs
AMRs, Conveyors and AGVs require various maintenance, energy and repair levels. These ongoing costs pose a critical factor.
AMRs require little in terms of basic infrastructure; they do require charging and maintenance. Some AMR companies operate on subscription models that allow you to add robots for the peak seasons and scale back when you need to transport less. This may cost more than owning the robots, but also let you scale as needed with little investment. AMRs require more IT and controls infrastructure than conveyors or AGVs. They require standard maintenance, cleaning and inspections along with software updates.
Modern conveyors can idle so they don’t needlessly consume energy. Conveyors don’t require more maintenance than mobile vehicles, but maintenance is more critical for them. If a single AGV or AMR is offline, these systems can still move product, but a faulty conveyor zone can bottle up a sortation line or even an entire operation. For that reason, maintenance and spare parts inventories are more important for conveyors than for independent vehicles. Conveyors present the fewest issues in terms of software and controls.
Read more: Conveyors and The Total Cost of OwnershipÂ
AGVs are heavier than AMRs, and can require more involved maintenance of their mechanical components and guidance systems. They tend to operate in manufacturing areas where airborne debris might be more common. Their guidance systems can also require repairs and inspections. However, they aren’t as software-reliant as AMRs due to their relative simplicity.
The difference depends on operational needs and applications
Conveyors
Conveyor systems deliver the fastest throughput and can work with other automation technologies to ensure end-to-end automation that reduces the need for human interaction with the load as it moves to its destination. This is typically in a pick & pass system. They can pair with scanners, packaging systems, sortation, scales and other equipment that helps ensure quality and boost flow rates. Conveyors occupy more fixed warehouse space and offer the least flexibility compared to the alternatives. They often work in conjunction with AGVs and AMRs when the flow of goods begins or ends its process. Conveyors can provide storage buffering where vehicles usually cannot.
- Conveyor systems are harder to scale up compared to AMRs and AGVs.
- Conveyors have much faster throughput applications with a purposeful design and fixed stop/start points.
- Conveyors are more difficult to relocate if business needs change.
- Conveyors are less expensive to purchase than AMRs or AGVs, but may have more extensive maintenance costs.
Automated guided vehicles
AGVs are reliable and fast. They are deployed more frequently in manufacturing than AMRs due to more consistent processes and less need to evolve based on SKU counts and operational disruptions. They’re ideal for truck loading and unloading full pallets, which they can transport from trailer to rack and vice-versa without human interactions. AGVs are the choice for repeatable work in predictable circumstances where conveyor systems cannot fulfill the need, or where faster changes may be needed. Both conveyors and AMRs can currently handle bulkier and heavier loads than popular AMRs, but that will change over time.
In many respects, the case for AGVs and AMRs are similar, but never identical. Both are “shelf to person” or “shelf to position” concepts, rather than the goods-to-person concept in a pick & pass conveyor application.
Autonomous mobile robots
Due to their adaptability and flexible options, AMRs are used more frequently in distribution and order fulfillment.
- They can circumvent obstructions the way a human operator might.
- Consider functions where people push carts as candidates for AMRs.
- AMRs are easier to scale for brownfield operations than conveyors, since you can deploy AMRs in stages. This can make them more flexible than either conveyor systems or AGVs.
- They are the most expensive implementation and IT infrastructure concept for goods-to-person picking.
Which works best? This depends on load, operational objectives and industry: “what does it cost to transport a given range of products, and how much interaction is required by people or machinery in the process?” That’s the true, long-term cost of transport. Implementation plays a large role in answering this question. Remember that it’s entirely possible to mix all three of these methods in the same facility or operation, depending on the needs of an area.
Download the Cisco-Eagle guide to order picking
When it comes to picking orders, you have many options: equipment types, methods, technologies and more. Download our guide to order picking to read tips and articles from our expert employee-owners. You’ll find practical examples of ways to cope with ergonomics, slow movers, various picking systems and much more.
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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.