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82 console. If a carrier is no longer operational, they can geofence a section of the terminal via the user interface to force other carriers to keep their distance. This helps prevent further issues, and potentially enables a clear path for repair technicians to approach the carrier. The supervisor could also take remote control of the problematic carrier (if it is still operable) and manually drive it to a servicing area. To reduce the rate of such issues, a laser rangefinder is installed in front of each outermost wheel for autonomous obstacle detection. If workers or objects are detected on the path ahead, the carrier can slow to a halt. “A standard Sick Lidar with about 20- 30 m of range is installed on each of the four corners of each machine,” Alho notes. “While we want and encourage a controlled environment, with no people or objects inside the spaces where the carriers work, wind could blow down a container stack or shake goods out of their containers – anything can happen – so the Lidars are really important for that. “Furthermore, the Lidars help a lot when the carriers need to park accurately over containers before picking them up, by giving the angle and speed of approach to a high resolution.” Once a straddle carrier has positioned itself over its assigned container, it will lower its spreader tool for grasping the container’s top rail (using a winch system driven by two induction motors), before hoisting it up at a rate of 15 m/minute for a 50 t load. The top speed of the carriers is 30 kph; unloaded, they can reach this from 0 kph in 24 seconds. Traction power is supplied by four induction motors installed on the topside of the horizontal beam on each side, directly above the driving wheels – the four central wheels – with the motors’ driveshafts connecting directly to wheel hub gears. Refuelling and charging The standard diesel tank holds 1000 litres of fuel, and the carriers use 15-20 litres/ hour. Thus the standard diesel-electric autonomous carrier can operate for two days at a time between refuelling and servicing cycles, running non-stop every hour of the day on its engines. “We have smaller engines for the hybrid-power versions,” Alho says. “Since power supply is controlled by the battery, we’ll use an engine that is the most cost-effective, and to charge the battery we’ll just run it at whatever speed gives the end-user the most efficient specific fuel consumption – a small engine is perfectly fine for that. “And no matter what the powertrain architecture is, the driving speeds, lifting speeds and lifting weight capacities all tend to stay the same. The choice of power system really comes down to what kinds of infrastructure and operations a terminal operator wants to have.” Naturally, the hybrid-electric carriers can run their engines whenever needed to recharge their batteries. For the fully electric versions, an automated pantograph system is used to enable opportunity charging, without the need for manpower. Having preprogrammed the location December/January 2021 | Unmanned Systems Technology The Kalmar One’s software automatically determines and dispatches the AutoStrads’ work orders via wi-fi, although human technicians can make manual adjustments if necessary Automated charging of the AutoStrads’ batteries is via pantograph poles, with several minutes of charging typically enabling another hour of operation