FEATURE Automated warehousing
Procuring the right battery pack for mobile industrial robots
Long cycle life, high energy density and resistance to shock and vibration are common requirements in AGVs and other types of mobile robots. How do they affect the choice of chemistry, cell and battery pack design? asks Owen McNally, Alexander Battery Technologies
E
fficiency, maximal throughputs, safety and lower operating costs are key requirements in today’s smart, digitalised factories and
warehouses. To meet these objectives, industrial companies are automating even more processes and use robotic devices, particularly mobile robots such as automated guided vehicles (AGVs), automated mobile robots (AMRs) and frame climbers in automated warehouses. These systems’ popularity is due to their ability to work 24 hours a day without stopping, which in turn calls for portable battery power systems to maintain their continuous operation, without running out of charge, or failing prematurely because of a fault. This highlights the importance of specifying a mobile robot’s battery pack the right way. In nearly all cases, a mobile robot will require a custom battery pack, to meet the application’s requirements for capacity, size, durability and ruggedness, peak power output, cycle life, temperature tolerance and more. This means that choosing the right custom battery pack manufacturer is also a critical decision.
Lithium-based batteries have become the most common choice for new industrial batteries today, because of their high energy density and capacity, giving much longer run-time between charges than any other battery chemistry. In fact, many types of lithium chemistries may be used in battery cells, and the technology and production of battery cells and packs is constantly advancing, giving OEMs the benefit of improved specifications year-on-year.
Specifying a battery pack The proliferation of lithium chemistries and components like battery controller ICs means that a robot OEM can face a complex set of trade-offs. Cell chemistries like NMC (lithium nickel manganese cobalt oxide), LFP (lithium
24 February 2024 | Automation
iron phosphate), LTO (lithium titanate), LMO (lithium manganese oxide) and LCO (lithium cobalt oxide) vary on a range of parameters: • Energy density, affecting the size and weight of the battery pack; • Maximum peak power output; • Maximum safe operating temperature and susceptibility to thermal runaway; • Cycle life;
• Nominal output voltage; • Maximum charge rate. The decision about the best set of trade-offs must be made on an application-by-application basis. For instance, in a small AGV or AMR carrying light loads, the battery pack will typically make up a large proportion of the total robot’s weight and take up a large space relative to the robot’s enclosure: here, high energy density is a key requirement, to produce the smallest and lightest possible battery, which generally calls for NMC cells. On the other hand, in a large mobile lifting platform capable of shifting loads to 1,000kg, the battery pack will make a negligible contribution to total size and
weight. Here, energy density is of little importance, so the platform OEM could instead choose LFP cells: their energy density is at least one-third less than that of NMC, but cycle life is much longer – over 2,000 cycles, compared to 500-600 in some NMC implementations. LFP cells also operate more safely at much higher temperatures than NMC, easing the design requirement for thermal dissipation, thermal monitoring and safety circuits. Cycle life and charge time are crucial parameters for many mobile robots: AGVs in a smart warehouse, for instance, might work 24/7 all year round. A typical configuration uses a removable battery pack, allowing the AGV to return to a charging point for the removal of a discharged pack and its replacement by a newly-charged one. In this case, packs are continually cycling through the charge/discharge process. Here, the cells in the pack must withstand many charge cycles and fast charging, to be available immediately after removal from a discharged AGV. A reputable battery pack manufacturer
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