An exciting new research area in the field of fluid power is miniaturised hydraulics, or mesofluidics.
This is the application of millimetre to centimetre sized hydraulics to problems that require substantial amounts of power to be generated and applied in a limited space. Hydraulics offers power and strength in a light package, and researchers at Oak Ridge National Laboratory (ORNL) in the USA have shrunk that technology down by orders of magnitude.
Mesofluidic actuators range from a few millimetres to centimetres in size and use pressurised fluid for the motive force, with flow rates from less than one ml/sec to 10 ml/sec. Mesofluidic technology provides high force density, low friction, direct drive and high mechanical bandwidth. It can utilise a variety of working fluids ranging from oil to water or saline solution.
The researchers have developed an artificial finger powered by mesofluidics. A unique feature is that all the control valves and other equipment required to operate the finger are small enough to fit inside the finger. Despite their miniature size, the hydraulics in the finger provide over 10 kg of pinch force – twice that generated by a human finger. This is a big improvement on existing prostheses, which are typically powered by electric motors. “The amount of force you can generate with an electric motor is an order of magnitude lower than what you can do with hydraulics, so prostheses are quite a bit heavier than those powered by mesofluidics, and they also get really hot, so temperature is a problem,” says senior researcher, Lonnie Love.
Two key innovations contributed to the group’s progress. The first is a small but powerful hydraulic pump. About 16 cm&$179; in volume, it operates at 1300 kPa and generates about 30 watts of hydraulic power. The other is the miniature high performance valve that controls motion in the system. “We cannot buy control valves off the shelf that provide this level of performance at this small scale,” says Love. “Because no one makes the kind of high pressure, low flow valves needed for mesofluidic applications, we were forced to make them ourselves.”
The flow control valves can be combined in a multistage design to greatly amplify their flow rates and have some additional benefits: low cost of construction; zero internal leakage flows due to the poppet style of the valve, which is very energy efficient; low electrical power required to modulate the hydraulic source; and the ability of valves to be combined to allow individual control of each flow port, allowing regeneration of hydraulic energy.
The design of a hydraulic finger led to the group’s current efforts to design and control a mesofluidic hand. In addition to the obvious prosthetic applications, the ORNL team believes the hand also could serve as a remotely controlled device used for disposing of explosives.
Love’s team is also designing a glove with a mesofluidic exoskeleton that will be linked to a remote hydraulic hand with force feedback. They hope to enable the position of each finger joint to be measured and transmitted to the remote hand. Similarly, the exoskeleton would be able to measure the forces occurring remotely and use mesofluidics to provide force feedback, so the user can feel what the remote hand is doing.
The enabling technologies developed by Love and his colleagues are leading to a broader understanding that ‘wearable’ robotics, lightweight devices worn like braces to provide extra strength to a weak joint, can be applied in a number of areas. The team is currently working on a meso-fluidic elbow which can curl 30 kg – a feat most human elbows could not accomplish.
Love is enthusiastic about the future of this line of research. “Our initial discoveries have opened up a variety of opportunities,” he says. “There are many potential applications where the primary energy source is limited and fine motion control is required. Our challenge now is to find even more unique applications.”
For more information visit http://motioncontrol.co.za/+mesofluidics
© Technews Publishing (Pty) Ltd | All Rights Reserved
printer friendly version