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BATTERIES & CHARGERS
HOW TO PROCURE 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. How do they affect the choice of chemistry, cell, and battery pack design? Owen McNally, Alexander Battery Technologies, investigates...
fficiency, maximisation of throughput, safety and operating cost reduction are the watchwords of today’s smart, digitalised factories and warehouses. To meet these business objectives, industrial companies are automating ever more processes, and deploying more robotic devices, particularly various types of mobile robots. These include devices such as automated guided vehicles (AGVs) used in materials handling and other applications, automated mobile robots (AMRs) for last-mile deliveries (see Figure 1), and frame climbers in automated warehouses. One of the advantages of mobile robots in comparison to their human counterparts is the ability to continue working 24 hours a day without the need for breaks. But this calls for a portable battery power system that can maintain a continuous output, without running out of charge, or failing prematurely because of a fault or breakdown.
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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 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. So, what is the latest best practice for battery pack specification, and what are the key considerations that mobile robot OEMs should be taking into account today when specifying the cell type, pack design, and quality criteria?
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SPECIFYING A BATTERY PACK: BALANCING THE TECHNICAL TRADE-OFFS The proliferation of lithium chemistries, and of the components such as battery charge controller ICs that support lithium battery packs, mean that a robot OEM can be faced with a complex set of trade-offs to consider. Cell chemistries such as 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
Cycle life
Nominal output voltage Maximum charge rate
The decision about the best set of trade-offs needs to 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, a requirement that would generally call for the use of NMC cells. On the other hand, in a large mobile lifting platform capable of shifting loads of as much as 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 – more than 2,000 cycles,
compared to as few as 500-600 cycles in some NMC implementations. LFP cells also operate safely at much higher temperatures than NMC, easing the design requirement for thermal dissipation, 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. In this case, the cells in the pack need to be able to withstand many charge cycles, and to withstand fast charging so that they are available for use quickly after removal from an AGV in a discharged state. A reputable battery pack manufacturer will be able to provide detailed guidance about the these and every other performance attribute of each lithium chemistry, and to advise on the best choice for the OEM’s mobile robot application.
Spring 2024 UKManufacturing
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