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Merlin launch innovative and unique range of servo controlled "air muscles" to provide full position control for challenging motion control applications Plymouth UK, 9th December 2003: Merlin Actuators, the Plymouth UK based pioneer of robotics technology announce the launch of their Humaniform [TM] range of servo controlled air muscle actuators with closed loop position control (patents pending). This breakthrough provides both lower cost and simpler installation over traditional rotary and linear servo motor based solutions, will replace pneumatic cylinders and is available with a range of interfaces to suit a majority of machine control technologies.
Whilst air muscles have been available for simple, fixed length applications for many years, Merlin are the first company to launch a standard range of servo controlled actuators complete with their own patented LEX optical position sensors and SMART proportional valves. Such closed loop position control ensures that the target position is reached, even if external load or other factors change. By adapting the air muscle in this way, applications previously restricted to servo motors with their inherent high cost and complexity are now possible.
The basic air muscle construction combines a high durability rubber inner tube surrounded by a tough braided mesh. The muscle is mounted and secured by clamp blocks at each end. As air is introduced into the muscle via standard 4mm push-fit connectors, the braid expands radially and contracts axially causing the muscle to shorten in length.
Merlin have taken this basic concept and added a feedback sensor, proportional valves and a choice of three control systems to realise position control. Position feedback is provided by Merlin's patented LEX optical sensor which has been designed for standalone applications as an LVDT replacement system. The LEX sensor is robust yet light and compact with fully integrated on-board position processing and is intrinsically immune to electromagnetic fields. The Merlin SMART valves are fully proportional micro-miniature air valves using their latest SMART material technology and in combination with the control system, provide consistent positioning accuracy and repeatability over a wide rangeof applied air pressure.
Three different control interfaces are available, the 'Servo', the 'ASCII' and the 'Voltage', all of which use the same Merlin developed system components. The Servo Interface is designed to be a plug in replacement for a standard rotary or linear servo motor. It includes onboard control electronics and motion control software and is similar in concept to an integrated or intelligent servo drive. The ASCII Interface is driven from an ASCII input command interface where a simple 2-byte code allows muscles to be addressed on a bus, and driven to maintain a required length. The Voltage Interface is driven from a reference voltage level input. This interface is ideal for automation type applications where a machine control system such as a PLC is used or could be used with any manufacturers' motion controller with a command reference voltage and encoder feedback. CANBus and other fieldbus control options are in development.
The new Humaniform [TM] range of precision air muscles is available in standard lengths of 20, 30, 40 and 50cm and typically contract by 30% of their length with a pressure rating of 4 Bar (5 Bar maximum). They have a 12mm minimum diameter and a 25mm contracted diameter and deliver peak forces in excess of 200N. Muscles become increasingly powerful with diameter, and force/weight ratio's in excess of 800:1 are achievable. By designing the complete system using its own technology, Merlin can maintain positional accuracy and repeatability to 3% of travel length. The Humaniform [TM] muscles are inherently self-damping when contracting and their flexible construction allows cushioning when extending.
Muscles produce their peak force output at maximum extension, and only consume power when changing length making them energy efficient for many applications. For maximum contraction muscles should be installed in a taut position and it is usual to design them into applications where they form the prime mover in a lever system and work against a spring return force or have muscle pairs working against each other.
Typical applications for this exciting new range of products will include robotics, animatronics and automation systems where their low cost and compact design combined with flexible installation possibilities will challenge designers to consider their use to replace traditional pneumatic cylinder, servo and stepper motor driven systems.
Merlin Actuators is a division of Merlin Systems Corp. Ltd which was formed August 1998 by Dr Mark Norman. Situated at the highly successful Tamar Science Park in Plymouth UK where a small but expanding team of enthusiastic robotics engineers has enabled MA to become the leading innovator in artificial muscle and robotics design.
Don't see much future for humanoids, dogoids or bird-oids, might be used as an alternative to a chain hoist and in some kinds of manipulators that are used for lifting moderately heavy things like automobile engines, transmissions and the like.
Pneumatic actuation is basically inefficient because the air that is compressed to do work via cylinder, rotary actuator or bladder is released to the atmosphere, rather than being recycled as is the case with relatively incompressible oil, hydraulic fluid, or in some cases water. For some applications, two air muscles would be required, one to retract an articulated arm and one to extend it.
My opinion is that something called piezohydraulics will overtake anything the Merlin guys develop as soon as piezopumps can deliver a bit more pressure and flow than they do now. Piezopumps wouldn't need to be large central things like the pumps on garbage trucks for example, Instead, each smart cylinder or rotary actuator could have its own vibrating piezopump with a couple of piezovalves that functioned as intake or exhaust valves for instant reversal of hydraulic flow. This would eliminate the need for a lot of plumbing that would be replaced by wires, or perhaps wireless control of the UHF type used for communicating with moving locomotives.
I saw some air muscles in action a few years ago, and I think their possible applications are fairly limited. The main problem is that whatever robot you install them on has to carry around its own compressor, or a bulky compressed air tank. Anyone who has ever gone scuba diving knows how heavy and cumbersome compressed air tanks can be and how quickly they run out. Half an hour and its game over.
There may possibly be industrial applications for this sort of technology, but I've worked in industrial automation for a long time and there has been a consistent trend of old pneumatic and hydrolic controls being replaced by electric servos. If I told some of the guys at work that I wanted to use a new type of actuator with a 3% repeatability they would just laugh.
I think the use of air tanks, pumps and compressors is the wrong way to look at this, what if there was a way to generate pressure with some type of chemical reaction.
- - generate pressure with some type of chemical reaction that is safe, controllable, cheap, eternally sustainable and non polluting, you will be richer than Bill Gates! Be careful though, previous attempts to do this have caused acid rain, holes in the ozone layer, and global warming that might turn a lot of coastal areas into WaterWorld before it is through.
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