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The Micromuscle


By Nanook - Posted on 21 October 2010

The Micromuscle

INTRODUCTION:

The Micromuscle is an intelligent, fluidic actuator that provides strong actuation forces in a centimeter sized package. The micromuscle combines five important elements in a single package: a bellows, control valves, extension sensor, pressure sensor and microcomputer. A diagram for a typical device is shown here:

The bellows acts as a pneumatic or hydraulic cylinder. The use of high pressure fluid produces very fast and powerful actuation forces. But being a bellows, instead of a conventional hydraulic cylinder, it has no sliding seal. This means no friction and no leakage!

Built into the end of the bellows is a set of microelectromechanical (MEMS) control valves. These regulate the flow of fluid between the pressure and drain ports and the bellows. Having the control valves right on the actuator provides a major advantage of allowing many actuators to be operated from a single pair of fluid lines. This becomes a very strong advantage when the number of actuators is hundreds or thousands.

The extension sensor is typically a micro strain gage attached to the bellows. This provides information about how far the bellows is extended.

The pressure sensor measures the pressure in the bellows and infers the force being applied by the bellows to the exterior environment.

The microcomputer provides local control of the micromuscle.

The extension sensor, pressure sensor and microcomputer along with the local control valves act as a very intelligent local actuator system. This means the micromuscle can be given simple commands that produce quite complex control responses.

For example, one command might be “move muscle to 50% open”. In that case, the controller would open the pressure valve and monitor the bellows extension until the 50% point is reached. Additional commands might be “hold 50% open” or “hold constant pressure”. The microcomputer would then adjust the valves continuously to hold the 50% point, or hold constant force or some other complicated control function. Another example might be a command to, “move finger until an obstruction is sensed and report back”. In this case, the computer would move the finger at a predetermined rate until a predetermined pressure increase was measured. It would then stop moving the finger and report back its extension. Because the microcomputer can send as well as receive signals, micromuscles can talk to a central brain or even each other to share information.

The following figure shows a possible application. In the figure, two micromuscles are used to move the line of gaze of an eye, replacing diseased muscles. In this application, the microcomputer in the micromuscle would accept control signals directly from the human nerves that normally control eye positioning. The patient would learn to control eye position through therapy, but in normal use, would not even be aware of the artificial muscle control. (The electrical and fluidic lines are not shown. Remote battery and pressure pump are also not shown.)

The device was called the micromuscle because its three external interfaces mimic a human muscle. It has a mechanical actuator which mimics muscle fiber; it has a pressure and drain line which can be thought of as artery and vein; and it has electrical control analogous to nerves.

Because of the simplicity of the bellows as the actuator and now, the availability of MEMS devices, the micromuscle can be made quite small and inexpensive.

What are the main advantages of this device? Before the micromuscle was invented, there were many very large actuators, such as motors and hydraulics. There were also very small devices, such as MEMS micro motors. But there weren’t any strong actuators in the size range from about 1mm to 4cm. This is a critical size range for automation and robotics. The micromuscle was invented to solve this problem.

POSSIBLE APPLICATIONS:

The micromuscle, because of its combination of properties, can become the enabling technology for a number of major technical advances:

• In medicine, a whole range of intelligent orthotic devices could be built to replace diseased human muscle. These are not practical now because the available actuators are too big.
• In robotics, the micromuscle is the first device that will allow the development of truly human scale, non-tethered, anthropomorphic robots.
• The advantages for space and military applications are great. Small size is critical. But the ability of the muscle to control itself adds great intelligence. The bellows offers high reliability and low maintenance.
• In automation, the cost of production machines could be greatly reduced. The micromuscle, ultimately a $20 item, would replace a servo motor and controller, typically $200 per actuator.
• For household appliances, low cost actuators would be a major missing link to achieve total voice control. An example would be intelligent curtains that adjust to follow the sun.
• For tools, size and cost could be reduced while performance and reliability increase. An example would be intelligent “third hands” that hold and move material being worked on.

STATE OF DEVELOPMENT: The concept is patented, but has never been built. All of its elements are commercially available, even in miniature size. There is quite a bit of work needed to launch a commercial product here. On the other hand, lab devices could be built fairly easily and the resulting prototypes used to build robots for experimental applications and groups like NASA and DARPA.

The Micromuscle is protected by U.S. Patent 5,697,285 December 1997 and is available for license. For more information contact Nanook {{at}} A3society.org