­ Industrial robots unplugged

 A worldwide shortage of labour has seen an increase on the take up of robots for industrial use. It is really unsurprising, since today’s robots are much more sophisticated than previous generations, allowing them to take on more complex roles. At the same time, their costs have dropped, making them much more affordable to businesses. Originally, in the workplace at least, robots were static, performing repetitive tasks on production lines. That has now changed. Mobile robots were first introduced to perform simple tasks and usually followed set routes that were marked on the floor or on signs on walls. Now, robots can be fully autonomous, scanning their own surroundings, plotting the best route to their destination and at the same time, constantly scanning to avoid humans and any other obstructions on their path. However, like any non-static device powered by electricity, charging provides a challenge, especially for larger facilities with hundreds of mobile robots.

Up until now, getting an autonomous robot to the charging dock and charging has proven difficult. The robot has to know that it is time to charge, find a dock that is unoccupied and align perfectly to the connector. Wireless charging has been tried, but requires the robot to be in exactly the correct spot or the charger would either not charge at all, or would charge very slowly. Now there is a wireless charging solution that provides industrial robot users with a bit of leeway on position, and it is mainly thanks to GaN technology that it is possible. Seattle-based WiBotic has developed a wireless charging system that can quickly charge robots that are up to 5cm in any direction from the ideal position at full power.

The solution consists of transmitters that use any AC or DC voltage source to generate a high frequency wireless power signal which is then fed to an antenna which generates both electrical and magnetic fields. The positioning of the antenna is flexible, to allow it to operate both vertically and horizontally, making it easier for robots to dock. WiBotic’s onboard chargers then collect the signal through a receiver antenna and convert it back into a usable DC voltage. The onboard charger is a fully programmable battery charger that can be configured for a wide variety of battery designs. Output voltage and current are also programmable to help optimize charging and ensure the batteries have the longest possible working lifetime.

Charging hardware is only half of the story. Coordinating charging for autonomous fleets requires tremendous coordination between the robots and charging stations. WiBotic Commander is a software package for fleet-wide charging configuration and monitoring. It can be connected to other fleet management software at the facility or an implemented on premise as an IoT installation, allowing the owners of the robots to see the battery status and location and status of all charging stations. Monitoring charge status and station availability can increase fleet uptime by allowing robots with aging batteries to be redeployed to “easier” roles in the facility.

The key to the new wireless charging solution is GaN technology, which is much more efficient and allows faster power switching. WiBotic CEO Ben Waters explains, “The big challenges to building a wireless network for robotic charging have been heat, compliance, and efficiency. You take DC to the charging station from a power supply, and then convert that to RF to send across the wireless link, and then you've got to rectify from RF back to DC on the robot side. In our system that can mean 300 watts of power, which even at 90% efficiency is still 30 watts of heat dissipation in a small area. We utilize GaN FETs when we switch from DC to RF and RF to DC. GaN FETs have much lower junction capacitance compared to MOSFETs and therefore, at the RF frequencies we operate, dissipate much less heat. The challenge with Gan FETs is that they generally are a more sensitive in terms of how you control their gates. We had to really spend a lot of time optimizing that when we transitioned from MOSFETs”.

WiBotic has recently formed a partnership with ResGreen Group to wirelessly charge ResGreen’s LilBuddy Autonomous Mobile Robots (AMRs). Wireless charging capabilities allow the LilBuddy vehicles to charge efficiently and frequently without the worry of worn-out charging contacts or the need for precise navigation to charging stations. One wireless station can also charge a wide variety of vehicles with different battery types, sizes and configurations that require different voltages and charging rates. ResGreen is also planning to add WiBotic’s wireless charging capabilities to its larger PullBuddy Automatic Guided Vehicles (AGVs) in the near future.