Uncrewed Systems Technology 043 l Auve Tech Iseauto taxi l Charging focus l Advanced Navigation Hydrus l UGVs insight l MVVS 116 l Windracers ULTRA l CES 2022 show report l ECUs focus I Distant Imagery

42 has been trained to recognise different charging ports in images and to determine their precise position and orientation. The system has been tested with autonomous delivery trucks developed by Einride, and the developers are already working on a next generation of charging robot that will deliver charging power of 1 MW. Wireless charging For wireless charging, the biggest issues are power levels, reliability and the alignment of the wireless coils. One approach to give more flexibility in positioning for UAVs or industrial systems is smart inductive coupling between coils. This uses comms data embedded in the power link, known as in-band comms, to constantly tune the frequency of the power in each coil with a millisecond resolution. This link, typically with a data rate of 100 kbit/s, is used to keep the two coils at the optimum resonance frequency regardless of how the position of the coils changes. With an antenna gap of 20-25 cm, this supports an alignment tolerance of 10- 15 cm and still provides 90% efficiency for the power transfer across the gap. This approach also tolerates changes in alignment, supporting an angular difference of up to 30 º between the coils. If the conditions change, autocalibration redefines the optimum point for resonance, working across a 100-300 kHz range. This is currently used for 300 and 600 W systems for UAVs, although there are plans for 1, 3 and 9 kW charging systems for industrial forklifts. Fleet charging One challenge for UGVs in industrial environments is that there can be many different types of vehicle in use. A programmable battery charger coupled with wireless charging loops can allow an operator to use different types of UGV with different types of batteries. This requires a comms system that allows for any of the onboard chargers to communicate with the wireless charging station, along with back-end software that can provide the appropriate profile for each UGV. The sweet spot for these industrial UGVs is 300 W. This allows them to charge up for 10 minutes between tasks to keep the battery topped up. The challenge of positioning is key. A UGV needs tolerance if it is repeatedly trying to dock at a given position, so operating anywhere in a 5 cm diameter zone gives maximum charging power. Higher power is also possible with wireless systems. For example, multiple 300 W systems can be cascaded together, but the limit is more of a physical one if the coils are side by side. This can lead to new topologies, with perhaps a number of receivers and transmitters operating independently, for example on three sides in a garage to charge three receivers on a vehicle. In outdoor environments, UGVs are often exposed to dust, dirt, debris and moisture. Electrical components subjected to these are particularly susceptible to corrosion and mechanical failure, resulting in unreliable charging. Fully sealed wireless power kits increase the reliability of UGVs in those environments. Such systems are also being developed to power unmanned rovers on the Moon, protecting them from the effects of the dust. Chargers also need to adapt to different models of charging. It could be beneficial to charge a particular robot’s battery as quickly as possible during working hours to minimise downtime. Overnight, however, it is typically better for the battery’s long-term health to charge more slowly. Wireless charging also avoids the need for precise alignment, with up to 5 cm of antenna air gap or misalignment being tolerated while still delivering full power and efficiency. Different UGVs use different battery chemistries, voltages and charging rates. That means customers who operate fleets of them frequently have a patchwork of non-interoperable battery April/May 2022 | Unmanned Systems Technology Shown here is an automated system for charging vehicles using existing CCS charging connectors and cables (Courtesy of Siemens Technology) This 300 W wireless charging system for commercial robotics supports power transfer over up to 150 mm between receiver and transmitter (Courtesy of Powermat Technologies)