Knee dynamo taps 'people power'

[Guest guest]

Knee dynamo taps 'people power'

By Fildes - Science and technology reporter, BBC News

http://news.bbc.co.uk/2/hi/technology/7226968.stm

A stroll around the park may soon be enough to charge the raft of

batteries needed in today's power-hungry gadgets. US and Canadian

scientists have built a novel device that effortlessly harvests

energy from human movements.

The adapted knee brace, outlined in the journal Science, can generate

enough energy to power a mobile phone for 30 minutes from one minute

of walking.

The first people to benefit could be amputees who are being fitted

with increasingly sophisticated prosthetics.

" All of the new developments in prosthetics require large power

budgets, " Dr Weber of the University of Pittsburgh, and one

of the authors of the paper, told BBC News.

" You need power to run your neural interface; you need it to run your

powered joint, and so on.

" Getting that power is going to be really important. "

The new device generates power by a process known as " generative

braking " , analogous to the braking systems found in hybrid-electric

cars such as the Toyota Prius.

" Walking is a lot like stop-and-go driving, " explained Dr Max Donelan

of Simon Fraser University in Burnaby, Canada, lead author of the

paper.

" Within each stride muscles are continuously accelerating and

decelerating the body.

Hybrid electric cars take advantage of stop-and-go driving using so-

called " regenerative braking " where the energy normally dissipated as

heat is used to drive a generator.

" We have essentially applied the same principle to walking. "

Using a series of gears, the knee brace assists the hamstring in

slowing the body just before the foot hits the ground, whilst

simultaneously generating electricity.

Sensors on the device switch the generator off for the remainder of

each step.

In this way, the device puts less strain on the wearer than if it was

constantly producing energy.

Tests of the 1.6kg device produced an average of 5 watts of

electricity from a slow walk.

" We also explored ways of generating more electricity and found that

we can get as much as 13 watts from walking, " said Dr Donelan.

" 13 watts is enough to power about 30 minutes of talk time on a

typical mobile phone from just one minute of walking. "

However, to generate this amount of power the generator had to be

constantly switched on, which required more effort from the wearer.

The knee brace is the latest development in a field known as " energy

harvesting " .

The field seeks to develop devices and mechanisms to recover

otherwise-wasted energy and convert it into useful electrical energy.

" We're pretty effective batteries, " Dr Donelan told BBC News. " In our

fat we store the equivalent of about a 1,000kg battery. "

Tapping this power source is not a new idea and has been exploited in

everyday devices such as wind-up radios and self-winding watches.

The US defence research agency Darpa has a long-standing project to

tap energy from " heel-strike " generators implanted in soldier's boots

and powered through the pumping motion of a footstep.

And in 2005, US scientists showed off an energy-harvesting backpack

which used a suspended load to convert movement into electrical

energy.

However, heel-strike devices generate relatively little energy whilst

people using the backpack have to bear the burden of carrying the

bag.

" It requires a relatively heavy load - around 38kg - to get a

substantial amount of power, " said Dr Donelan.

Simulations showed that a soldier carrying the pack and walking at a

relatively brisk pace could generate around 7.4 watts of power. " It's

about the same amount of power as [the knee braces] produce, " said Dr

Donelan.

The team believes the new device could have many uses.

" I think the early adopters will be people whose lives depend on

portable power, " he told BBC News.

" On the medical front, portable power is used by those who have

amputated limbs to charge their powered prosthetic limbs, " he said.

However, Dr Art Kuo at the University of Michigan does not believe it

will be simply a case of strapping the device on to an existing

prosthetic.

" It would probably involve building a new [prosthetic] knee that uses

some existing ideas and then also tries to harvest energy using these

principles, " he said.

The team also hope the device could be useful for people who have

suffered a stroke or spinal chord injury who wear an " exoskeleton " to

help them move.

" The current and future emphasis is on powered exoskeletons, " said Dr

Donelan.

Soldiers may also benefit from wearing the knee brace to power the

multitude of devices they now carry ,such as night vision goggles and

GPS.

" They treat batteries like they treat food and water - they are so

essential to what they do, " he said.

Dr Donelan has now set up a spin-out company to exploit the

technology and believes it will eventually be possible to develop a

small device that can be fitted internally across different joints.

However, in the short term he has his sights set on a light weight,

slim-line version of the knee brace.

" That's about 18 months away, so it's not science fiction far in the

future stuff, " he said.

A stroll around the park may soon be enough to charge the raft of

batteries needed in today's power-hungry gadgets.

US and Canadian scientists have built a novel device that

effortlessly harvests energy from human movements.

The adapted knee brace, outlined in the journal Science, can generate

enough energy to power a mobile phone for 30 minutes from one minute

of walking.

The first people to benefit could be amputees who are being fitted

with increasingly sophisticated prosthetics.

" All of the new developments in prosthetics require large power

budgets, " Dr Weber of the University of Pittsburgh, and one

of the authors of the paper, told BBC News.

" You need power to run your neural interface; you need it to run your

powered joint, and so on.

" Getting that power is going to be really important. "

The new device generates power by a process known as " generative

braking " , analogous to the braking systems found in hybrid-electric

cars such as the Toyota Prius.

" Walking is a lot like stop-and-go driving, " explained Dr Max Donelan

of Simon Fraser University in Burnaby, Canada, lead author of the

paper.

" Within each stride muscles are continuously accelerating and

decelerating the body.

Hybrid electric cars take advantage of stop-and-go driving using so-

called " regenerative braking " where the energy normally dissipated as

heat is used to drive a generator.

" We have essentially applied the same principle to walking. "

Using a series of gears, the knee brace assists the hamstring in

slowing the body just before the foot hits the ground, whilst

simultaneously generating electricity.

Sensors on the device switch the generator off for the remainder of

each step.

In this way, the device puts less strain on the wearer than if it was

constantly producing energy.

Tests of the 1.6kg device produced an average of 5 watts of

electricity from a slow walk.

" We also explored ways of generating more electricity and found that

we can get as much as 13 watts from walking, " said Dr Donelan.

" 13 watts is enough to power about 30 minutes of talk time on a

typical mobile phone from just one minute of walking. "

However, to generate this amount of power the generator had to be

constantly switched on, which required more effort from the wearer.

Battery pack

The knee brace is the latest development in a field known as " energy

harvesting " .

The field seeks to develop devices and mechanisms to recover

otherwise-wasted energy and convert it into useful electrical energy.

" We're pretty effective batteries, " Dr Donelan told BBC News. " In our

fat we store the equivalent of about a 1,000kg battery. "

Tapping this power source is not a new idea and has been exploited in

everyday devices such as wind-up radios and self-winding watches.

The US defence research agency Darpa has a long-standing project to

tap energy from " heel-strike " generators implanted in soldier's boots

and powered through the pumping motion of a footstep.

And in 2005, US scientists showed off an energy-harvesting backpack

which used a suspended load to convert movement into electrical

energy.

However, heel-strike devices generate relatively little energy whilst

people using the backpack have to bear the burden of carrying the

bag.

" It requires a relatively heavy load - around 38kg - to get a

substantial amount of power, " said Dr Donelan.

Simulations showed that a soldier carrying the pack and walking at a

relatively brisk pace could generate around 7.4 watts of power. " It's

about the same amount of power as [the knee braces] produce, " said Dr

Donelan.

The team believes the new device could have many uses.

" I think the early adopters will be people whose lives depend on

portable power, " he told BBC News.

" On the medical front, portable power is used by those who have

amputated limbs to charge their powered prosthetic limbs, " he said.

However, Dr Art Kuo at the University of Michigan does not believe it

will be simply a case of strapping the device on to an existing

prosthetic.

" It would probably involve building a new [prosthetic] knee that uses

some existing ideas and then also tries to harvest energy using these

principles, " he said.

The team also hope the device could be useful for people who have

suffered a stroke or spinal chord injury who wear an " exoskeleton " to

help them move.

" The current and future emphasis is on powered exoskeletons, " said Dr

Donelan.

Soldiers may also benefit from wearing the knee brace to power the

multitude of devices they now carry ,such as night vision goggles and

GPS.

" They treat batteries like they treat food and water - they are so

essential to what they do, " he said.

Dr Donelan has now set up a spin-out company to exploit the

technology and believes it will eventually be possible to develop a

small device that can be fitted internally across different joints.

However, in the short term he has his sights set on a light weight,

slim-line version of the knee brace.

" That's about 18 months away, so it's not science fiction far in the

future stuff, " he said.