Robotic limbs that are controlled by electrostatic brakes rather than many motors could lead to a new generation of lightweight robots that use around 90 per cent less power than existing designs.
Robots usually have one or more motors for every joint to control its movement, but at the University of Washington in Seattle and his colleagues have created simple brakes that enable joints to be frozen or released in precise combinations so that a single motor can power a limb with as many as 10 joints.
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Each electrostatic brake is made of two thin sheets of metal separated by an insulating layer. When no voltage is applied across the sheets, they move freely over each other, but when a current is present there is an electrostatic attraction between the plates which clamps them tightly together so that friction stops movement.
Lancaster says that by carefully controlling which joints are braked, a single motor can be used to move a robot limb to any position. Unlike a limb that requires multiple motors, an electrostatic limb may have to be more selective about the precise movements it makes to achieve a given position. It may also take longer to get into position as it brakes certain joints, runs the motor and repeats the process to make additional movements. But while it lacks the direct and decisive motion of a heavily motorised robot, it has the advantage of allowing a much cheaper, lighter and more energy efficient design.
Each brake requires just tens of microamps of current to operate, although the voltage can be as high as 1000 volts. When one of the brakes is charged, it acts like a capacitor and essentially requires very little additional power in order to retain its braking force for long periods of time.
Lancaster says that each brake uses around 1000 times less power than a comparably powerful motor would, so a robot arm with 10 joints and one motor uses around 90 per cent less power than a traditional design.
But he concedes that electrostatic brakes are 鈥渘owhere near鈥� ready to use in commercial robots yet, and that although the concept has been proven, the engineering will have to be made more reliable for real-world operation.
鈥淏uilding and designing these electrostatic brakes, as well as integrating them into joints, it鈥檚 a very new thing,鈥� he says. 鈥淥ne of the challenges we鈥檝e been working on is the strength of the brake. It鈥檚 highly dependent on the thickness of this insulating layer. But you can imagine that if you try to use thinner materials, they鈥檙e less mechanically robust.鈥�
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