CEO interview: Robot wireless charging for industrial automation
A startup in Israel has developed a unique wireless charging system to keep robots moving in automated factories.
Prof Mor Peretz, co-founder and CEO of CaPow, talks to Nick Flaherty at eeNews Europe about the technology, what it means for the lifetime of battery systems, automated ground vehicles (AGVs) and even humanoid robots.
The technology is set to receive CE certification in Europe for use on the factory floor in the next few months.
“What CaPow is addressing is the operational efficiency of everything related to autonomous automation that is ramping up rapidly,” said Peretz, who is professor of electronics and energy management at Ben Gurion University.
“These autonomous factories rely heavily on robots and these in turn rely on batteries, from lithium ion to lead acid, but the primary cause of inefficiencies is from energy, or the lack of it. The work to charge ratio is 3:1 to 5:1 so we provide power in motion and en route,” he said.
Painting charging plates
So CaPow places an electrode on the floor, or on shelves, that can charge the robots as it passes. These electrodes can be thin sheets of copper or aluminium or even conductive ink.
“This is capacitive power rather than inductive so we don’t have coils,” he said, “Our antennas are sheets of conductive foil or even conductive paint in any form, wide and short, rectangle on the floor, on shelves, wherever it is needed. “We have an algorithmic tool that places the antenna in strategic places where the robots converge or visit for a sip of power. Most of the time its quite simple – the robots queue up for loading, or use a highway through the factory.”
“The secret source is we support is very wide freedom of positioning, misalignments, and this is where the trick is.”
This is not opportunistic charging, in place where the robots linger.
“Our charging is not opportunistic, we eliminate this from the equation as the robots never deviate from the route with enough robots to make it worthwhile,” he says.
“Our power level is 500W. Its not huge and is lower than other alternatives, We chose this as we don’t need to compensate for peak power but average power. The small robots consume 50 to 200W so ten seconds of a 500W source provides 10x of what they need and we found this suitable for the majority of applications.”
Battery health
There are significant advantages for the lifetime of the battery pack.
“We allow customer to keep their batteries to extend the lifetime. Many years of research shows you hurt the battery when you do full cycles,” he said. “The way that CaPow works is to trickle charge around the sweet spot, eg 60 to 70% and the battery never overcharges and this extends the lifetime of a pack by at least 3x.”
The wireless charging circuits can also highlight issues with the battery cells. “We already have customers that installed our system which told them particular cells were draining much faster and informing them, to avoid the danger zone.”
CaPow can also eliminate the batteries with supercapacitor powerpack replacement that holds the power for the time that the robot moves between the interval charging. This has come from the experience of working with the AGV makers who have to service and ship lithium ion battery cells around the world as part of a logistics chain. “Lithium safety is no joke in terms of the complexity to address especially in harsh environments,” said Peretz.
“We already have a few customers where the corporate logistics do not want to ship lithium batteries and store them and definitely don’t want to recycle them.”
Energy transfer
All of this comes from RF energy transfer technique originally developed at Ben Gurion University.
“We took RF energy transfer with ideas from the radio world,” said Pertez. “In a similar way a radio searches for a channel and stays tuned, even if you are driving around. CaPow searches for the best energy channel and we adapt the system parameters so that it looks to the optimum power transfer.”
The electronics tunes out the variations in the medium. “Our system monitors the change in the capacitance and varies the system parameters to tune to the different capacitance.” The idea is the control bandwidth can support motion, up to 10m/s in products, although in the lab we have supported much larger speeds.”
The system operates at a single fixed frequency in the lower MHz range, including the common 6.78MHz. An adaptive lock in circuit tunes the link.
“A basic resonance system has current voltage phase signals that align at optimum points of transfer so we take all these measurements and vary the system parameters so its always coupled, with a variable inductance which we had to invent.”
This very deliberately means there is no out of band communications system such as Bluetooth or WiFI as this is difficult to certify, he says.
The transmitter and receiver are self sustaining, sensing the current, voltage and phase and tunes onto the best coupling modes on their own. “If you can vary the source impedance you can match the load characteristics, and you can do the same at the load, and we showed that this converges to a maximum power point,” said Peretz.
“Our end to end efficiency is over 75% all the way to weakest coupling, and the best coupling efficiency is 87%. The link capacity is 98% efficient up to 10cm vertical, and on up to 50% of the receiver size for the full power zone. We have demonstrations of over a metre, the problem is the certification for these types of links.”
Certification is a significant issue for this type of system.
“One of the challenges was that there were no reference products on capacitive wireless power but we created a set of additional tests to make sure we never radiate or pollute the electric field. This is something we put a lot of energy into, understanding the sources of the radiation, even going into the soft switching of the circuits, the ringing, the damping, locking down parts of the non-broadcasting systems in their own faraday cages, so its not only the power electronics, but the RF, analog and digital.”
The system has been pre-complied with the FCC regulations in the US where it is running pilots and the company expects to finalise full CE certification by June for the end of this year. “For target markets in Europe you need CE to even run pilots and we have several design partners in Europe running pilots in the US.”
Humanoid robots
The next step will be providing wireless charging for more mobile robots where the weight and size of the batteries really limits the performance. “Humanoid robots will definitely be the next growing market to achieve fully autonomous warehouses,” said Peretz. These could be powered through their feet using this system. “We did a demo with a robot dog patrolling a line, so we figured out a better way to charge them.”
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