Energy efficient robots of the future could be able to continuously inspect structures like dykes, without requiring constant access to electrical charging stations, thanks to Dutch mechanical engineering expertise.
Robots are used to inspect the condition of dykes and other sea defence structures. With current artificial intelligence and control technologies, it is possible for a group of robots to work in a team in a highly autonomous way to undertake these difficult and time consuming tasks.
However, these robots have to move around these massive structures, perform tests, and communicate the results for extended periods of time, making energy use a major hurdle.
Recognising that it would be impractical to introduce charging stations, Douwe Dresscher, a researcher at the University of Twente in the Netherlands, focused on making the robots as “energy-autonomous” as possible.
He introduced a smart gearbox for the robot, drastically reducing the energy consumption. The gear box, a modern version of the variomatic used in Dutch DAF vehicles, uses two metal hemisphere instead of a belt drive.
Dresscher had to first decide on the best way for the robot to move about on the dyke: using wheels, caterpillar tracks, or legs. While wheels are energy efficient on even surfaces, wet and muddy slopes erode their performance.
Tracks, while more powerful, risk damaging the structures when they turn, and are also inefficient. Walking robots perform best, when equipped with four to six legs. However, they also consume a lot of energy.
According to Dresscher, the high energy consumption of legged robots can be traced to the electric motors. Motors perform best at high revolution speeds and low torques. But walking movements are dependent on low revolution speeds and high torques.
He found that if the motors are accompanied by a mechanism that stores energy not electrically but mechanically, their level of energy efficiency improves, while the mechanical energy can also be improved.
In the system he engineered, a spring stores the mechanical energy, and a gear box takes care of the optimum transmission. Two half-turning half-hemispheres, constantly in contact, experience angular changes when the torque changes, resulting in the relative radius changing.
The difference in effective radiuses determines the transfer ratio and the best mechanical load. The electromotors join in, only to compensate for mechanical losses. By doing so, they can work within the high rev, low torque regime.
According to Dresscher, the robots can be made smaller and even more autonomous by integrating energy harvesting capabilities, so they can derive energy from solar, wind and biomass sources when moving, in order to power their sensing and communication capabilities.
While Dresscher’s powertrain is specifically designed for dyke inspection robots of the future, it could also be applied to existing robots and robotic arms to improve their energy efficiency.
[The Dual-Hemi continuosly variable transmission. Photo: University of Twente]
Transport and infrastructure will be a major topic of discussion at the Australian Engineering Conference 2016 in Brisbane on November 23-25.