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Picture a busy DC, with manually operated forklifts, people, and pallets in constant motion. At the same time, the stationary equipment they interact with, such as conveyors and palletizers, is industriously whirring away. Together, they are performing something akin to a carefully choreographed ballet.

Now add driverless forklifts to the mix. Shuttling along without a human operator on board, they may look like they’re operating independently, but they’re not. They’re actually in constant contact with other equipment and software, making sure they perform their part in the dance at the right moment. Without that ability to communicate, the forklifts—and other warehouse operations—could come to a standstill.

Who, exactly, are driverless forklifts “talking” to, what information are they sharing, and how does that exchange happen? We asked automation experts to explain. They also shared tips on ensuring successful communication between automated lift trucks and other equipment and software.

TWO-WAY COMMUNICATION

Lift trucks that do their jobs without a human operator on board cannot “speak” directly to each other. “As it stands now, there is no peer-to-peer communication or interaction on a forklift-to-forklift basis,” notes David Griffin, chief sales officer for Seegrid, a developer of autonomous lift trucks and AMRs (autonomous mobile robots). There is, however, interaction between forklifts via a centralized fleet manager system (also referred to as a traffic management system or an automation server). This “overarching conductor of the automated system” assigns tasks to each forklift, controls the route the trucks will follow, and manages traffic flow, says Nick McClurg, a sales engineer at forklift maker Hyster Co.

The forklifts communicate with many kinds of material handling equipment, such as robotic palletizers and depalletizers, stretch wrappers, conveyors, automated storage and retrieval systems (AS/RS), and dock equipment. That communication must be bidirectional, says Michael Marcum, senior director of autonomous vehicles at systems integrator Bastian Solutions, a Toyota Automated Solutions company that also makes robotic forklifts. Much of the exchange consists of messages that indicate status—whether or not the two pieces of equipment involved are ready to conduct a transaction. For example, if a forklift will be delivering a pallet to a stretch wrapper, then the wrapper has to tell that forklift, via the fleet manager system, that the load position is empty and the forklift is allowed to set a payload there, Marcum explains. After a pallet has been wrapped, the stretch wrapper will call for a pickup via the fleet manager. Once the forklift picks up the wrapped pallet, it must confirm to the stretch wrapper that it has departed; without that signal, the wrapper cannot receive its next load.

If a truck is not ready for an assigned task, it signals that status to the fleet manager, and the task will be reassigned to another nearby vehicle, says Jayce Nelson, sales manager, North America, for Kion Group’s Linde Automated Solutions, a specialist in automated forklifts and software. When the assigned forklift is ready to approach, say, the end of a conveyor to pick up a load, it uses its vision systems, such as 3D cameras, to align itself with the equipment.

With their control software, robotic forklifts also have the ability to communicate with other warehouse equipment, like fire-detection systems and automated rollup doors. “If a device is capable of sending or receiving electrical signals, then the vehicle can interact with that device via the automation host software,” McClurg says. Even a piece of mechanical equipment could be outfitted with sensors that help it interact with automated forklifts, according to Brian Markison, director of sales for Rocrich AGV Solutions, a joint venture of Mitsubishi Logisnext’s Rocla and Jungheinrich units that specializes in automated guided vehicles.

The capability to communicate with different types of devices enhances warehouse safety, Griffin says, because it enables automated forklifts to talk to safety equipment like pedestrian warning lights and intersection gates. And since the robots constantly transmit their location, the traffic control system can identify developing problems and prevent them. For example, the system will stop an autonomous forklift from entering an intersection that’s occupied by another lift truck. Once the other truck has moved on, the system will give the approaching forklift the “all clear,” he says.

Hardware isn’t the only thing driverless forklifts can talk to; they also are in continual dialogue with various types of software. “Most commercial warehouse software programs today have the capability for two-way communication, and most can be integrated with automated lift truck fleet management software,” observes John Wilkins, a sales engineer for Yale Lift Truck Technologies. The most common are warehouse management systems (WMS) and warehouse control systems (WCS); others include enterprise resource planning (ERP) software, fleet management and telematics systems, and transportation management (TMS) and order management (OMS) systems.

As for how that might work, Rocrich’s Markison gives the example of a WMS sending an order to move a pallet from one location to another. The order typically will include start and completion time, and some indication of the move’s priority. “That order can then be taken into the fleet manager, which will appropriately queue up the tasks that need to be done,” he explains. The forklift must also report completed missions back to the WMS.

HOW TO TALK TO A FORKLIFT

Communication between robotic forklifts and warehouse equipment and software happens in a number of ways. Which method is deployed depends on the equipment and software involved as well as the tasks to be carried out. Each installation is unique in some way, but there are some commonly used approaches.

Some communication protocols are more widely used than others. Examples of those in widespread use include modbus, a serial communication protocol that governs an initiating and a responding device, and CANbus (Controller Area Network), a real-time communication protocol that transmits data to networked industrial controls.

A driverless forklift’s interface with other equipment could be something electromechanical, such as a photo-eye sensor, says Jeff Kuss, product manager–automated solutions at forklift maker and intralogistics specialist The Raymond Corp. A sensor at the end of a conveyor, for instance, could detect the presence of a pallet. That triggers the sensor to create an electrical signal that it sends to a programmable logic controller (PLC). The PLC receives the electrical signal as a digital input and then transmits a message, via ethernet, to the server that controls the automated vehicles. Finally, the server sends the instructions over Wi-Fi to the closest available forklift to “pick up the pallet and take it to Location X.” (Some facilities use Bluetooth or cellular transmission instead of Wi-Fi.) Data that identify loads and trigger a task can also be acquired through IoT (internet of things) platforms, RFID (radio-frequency identification) systems, and barcode scanning.

Another option, Bastian’s Marcum says, is to use infrared-based optic couplers that share bits (binary digits, the smallest units of digital information) as inputs and outputs. When the forklift gets within a certain distance of another piece of equipment, “the two devices can talk to each other, similar to the way a TV remote works,” he explains.

Usually, though, software is a critical intermediary between driverless forklifts and other equipment. It can be complicated. In the case of a WMS, McClurg says, his company’s approach is to send a text or JavaScript Object Notation (JSON) file to the WMS; in exchange, the WMS sends a file to a folder on the localized network that can be accessed by the automation host software. The fleet manager reads the file and executes it. Once the task has been completed, a message is sent to another folder. The WMS opens it, reads it, and, based on its contents, either closes out the order or sends additional instructions.

To ensure that interfacing software programs understand the messages they receive from each other, it’s often necessary to create an application programming interface (API). An API is a comparatively simple type of middleware—or software layer—that acts as a translator, facilitating communication by reformatting messages so they will be intelligible to the receiver. In essence, they are “setting ground rules in terms of what information is passing back and forth and what it means,” Markison explains.

In some cases, more complex middleware may be needed. According to Brice Bucher, senior manager of products at software developer and systems integrator Flexware Innovation, APIs have limitations. In a presentation at the Autonomous Mobile Robotics & Logistics Conference 2024, Bucher noted that APIs don’t address data transformation, protocol conversion, or business logic integration. When each system has different data formats or requires specific protocols, middleware bridges those gaps, he said. Middleware also ensures that data moves between systems without delay, he said. For example, if an AGV completes a task, middleware can instantly trigger updates across systems, so that WMS, ERP, and other systems are aligned in real time.

CAN WE TALK?

Raymond’s Kuss notes that each communication integration will be unique in some way. That’s partly because automated forklift vendors and suppliers of fleet manager systems have proprietary interfaces. On top of that, software with some degree of customization, such as a WMS, may require modifications to the fleet manager system, he explains. What’s more, adds his colleague John Rosenberger, director, iWarehouse Gateway & Global Telematics, “even if we know the format for efficient data transfer, the content of the messages may differ depending on the forklift manufacturer, or it can be different by functionality.”

Mixed fleets with forklifts from different manufacturers present a particular challenge. Seegrid’s Griffin notes that it’s common for facilities to use robots from multiple vendors. Generally, he says, each automated solution has its own proprietary fleet manager software that understands where all units under its purview are and controls their movements. When robots of different brands cannot be confined to separate areas, it’s important that their fleet managers have the ability to communicate, so they can do things like open and close intersections where different types of robots cross paths.

While it is possible for dissimilar fleet managers to talk to each other, that’s easier said than done. “Those systems inherently are not interoperable,” Nelson says. “The need to share information like coordinates, current status, past assignments, and prioritization makes it difficult to assign travel paths.” In addition, if the forklifts are unable to communicate location information and what they are doing, that can lead to deadlock, where the vehicles simply stop—what Yale’s Wilkinson calls “the classic situation: a staring contest between two autonomous vehicles from different OEMs, neither one capable of blinking or losing.”

A solution for some facilities is third-party fleet manager software that’s designed to work in multiple brands of autonomous forklifts; examples include those offered by independent developers such as Kollmorgen, BlueBotics, Navitech Systems, and Flexware Innovation. In fact, some forklift OEMs partner with these and other providers instead of developing their own fleet managers. This opens the way for a fleet to potentially buy different robots utilizing the same control and navigation system, which will reduce complexity to some degree, Marcum says.

Communications with driverless forklifts may become simpler in the near future. VDA 5050, an open-source protocol for communication between AGVs and fleet manager systems, is currently in development. Coordinated by two German industry organizations, one for auto manufacturers and the other for material handling and intralogistics, this universal protocol promises to allow “any mobile robot, regardless of brand, [to] be seamlessly integrated into existing operations,” wrote Alfredo Pastor Tella, who runs the Europe-based AGV Network website, in a LinkedIn post. Pastor Tella wrote that Kollmorgen will introduce VDA 5050 into its robot control software in 2025, but other industry observers have noted that because the protocol’s roots are in European manufacturing and there are still technical issues to be worked out, it may be a few years before it takes hold in the forklift world. When it does, conversations with autonomous forklift fleets will likely become much less complicated to hold.

For more on introducing robotic forklifts in the warehouse, see “How to get your DC ready for driverless forklifts” in DCV’s October 2023 issue.