FEATURE Robotics


Procuring the right battery pack for a mobile industrial robot


Long cycle life, high energy density and resistance to shock and vibration are common requirements in AGVs and other types of mobile robots. Owen McNally, Alexander Battery Technologies explains


ability to work 24 hours a day, without stopping. To do so, they require portable battery power systems that can maintain a continuous output, without running out of charge, or failing prematurely because of a fault or breakdown. 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 other factors. This means that choosing the right battery manufacturer is also a critical decision.


O


Lithium-based batteries are 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. The proliferation of lithium chemistries and accompanying components like controller ICs means that a robot OEM can face a complex set of trade-offs to work with. Cell chemistries like NMC (lithium nickel manganese cobalt oxide), LFP (lithium 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;


22 July/August 2024 | Automation


ne of the advantages of mobile robots in comparison to their human counterparts is the


Battery pack


• Cycle life;


• Nominal output voltage; • Maximum charge rate. The decision about the best set of trade-offs must be made based on the application. 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 footprint relative to its enclosure. Here, high energy density is a key requirement, to produce the smallest and lightest possible battery, which generally calls for using NMC cells. On the other hand, in a large mobile lifting platform capable of shifting loads of up to 1,000kg, the battery pack will make a negligible contribution to the robot’s 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 NMCs, but cycle life is much longer – over 2,000 cycles, compared to 500-600 cycles for some NMC implementations. LFP cells also operate safely at much higher temperatures than NMC ones, easing the design requirement for thermal dissipation and thermal monitoring, and safety circuitry.


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 pack. In this case, packs are continually cycling through the charge/discharge process. Cells in the pack must withstand many charge cycles and fast charging so they can be available quickly after removal from an AGV in a discharged state.


For the era of mobile robotics The advance of digitalised and smart manufacturing and warehousing practices is leading to a rapid increase in the number and range of mobile robots for industrial settings.


The battery power supply must be


as reliable as any other component of a mobile robot. The guidance discussed here shows how careful attention to cell and battery specification, design and production, and the choice of a dependable pack manufacturer can ensure reliable and predictable performance for the life of the robot.


automationmagazine.co.uk


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