Passive dynamics refers to the dynamical behavior of

actuator An actuator is a component of a machine that is responsible for moving and controlling a mechanism or system, for example by opening a valve. In simple terms, it is a "mover". An actuator requires a control device (controlled by control signal) a ...

robot A robot is a machine—especially one programmable by a computer—capable of carrying out a complex series of actions automatically. A robot can be guided by an external control device, or the control may be embedded within. Robots may be ...

s, or

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s when not drawing energy from a supply (e.g.,

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fuel A fuel is any material that can be made to react with other substances so that it releases energy as thermal energy or to be used for work. The concept was originally applied solely to those materials capable of releasing chemical energy bu ...

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). Depending on the application, considering or altering the passive dynamics of a powered system can have drastic effects on performance, particularly energy economy,

stability Stability may refer to: Mathematics * Stability theory, the study of the stability of solutions to differential equations and dynamical systems ** Asymptotic stability ** Linear stability ** Lyapunov stability ** Orbital stability ** Structural st ...

, and task bandwidth. Devices using no power source are considered "passive", and their behavior is fully described by their passive dynamics. In some fields of robotics (

legged robot Legged robots are a type of mobile robot which use articulated limbs, such as leg mechanisms, to provide locomotion. They are more versatile than wheeled robots and can traverse many different terrains, though these advantages require increased ...

ics in particular), design and more relaxed control of passive dynamics has become a complementary (or even alternative) approach to joint-positioning control methods developed through the 20th century. Additionally, the passive dynamics of animals have been of interest to biomechanists and integrative biologists, as these dynamics often underlie biological motions and couple with neuromechanical control. Particularly relevant fields for investigating and engineering passive dynamics include legged locomotion and

manipulation Manipulation may refer to: * Manipulation (psychology) - the action of manipulating someone in a clever or unscrupulous way * Crowd manipulation - use of crowd psychology to direct the behavior of a crowd toward a specific action ::*Internet mani ...

History

The term and its principles were developed by Tad McGeer in the late 1980s. While at

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Burnaby Burnaby is a city in the Lower Mainland region of British Columbia, Canada. Located in the centre of the Burrard Peninsula, it neighbours the City of Vancouver to the west, the District of North Vancouver across the confluence of the Burrard ...

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, McGeer showed that a human-like frame can walk itself down a slope without requiring muscles or motors. Unlike traditional robots, which expend energy by using motors to control every motion, McGeer's early passive-dynamic machines relied only on gravity and the natural swinging of their limbs to move forward down a slope.

Models

The original model for passive dynamics is based on human and animal leg motions. Completely actuated systems, such as the legs of the

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robot, are not very efficient because each joint has a motor and control assembly. Human-like gaits are far more efficient because movement is sustained by the natural swing of the legs instead of motors placed at each joint. Passive dynamic walker

Tad McGeer's 1990 paper "Passive Walking with Knees" provides an excellent overview on the advantages of knees for walking legs. He clearly demonstrates that knees have many practical advantages for walking systems. Knees, according to McGeer, solve the problem of feet colliding with the ground when the leg swings forward, and also offers more stability in some settings. Passive dynamics is a valuable addition to the field of controls because it approaches the control of a system as a combination of mechanical and electrical elements. While control methods have always been based on the mechanical actions (physics) of a system, passive dynamics utilizes the discovery of morphological computation. Morphological computation is the ability of the mechanical system to accomplish control functions.

Applying passive dynamics

Adding actuation to passive dynamic walkers result in highly efficient robotic walkers. Such walkers can be implemented at lower mass and use less energy because they walk effectively with only a couple of motors. This combination results in a superior "specific cost of transport". Energy efficiency in level-ground transport is quantified in terms of the dimensionless "specific cost of transport", which is the amount of energy required to carry a unit weight a unit distance. Passive dynamic walkers such as the

Cornell Cornell University is a private statutory land-grant research university based in Ithaca, New York. It is a member of the Ivy League. Founded in 1865 by Ezra Cornell and Andrew Dickson White, Cornell was founded with the intention to teac ...

Efficient Biped have the same specific cost of transport as humans, 0.20. Not incidentally, passive dynamic walkers have human-like gaits. By comparison, Honda's biped ASIMO, which does not utilize the passive dynamics of its own limbs, has a specific cost of transport of 3.23. The current distance record for walking robots, 65.17 km, is held by the passive dynamics based Cornell Ranger. Passive dynamics have recently found a role in the design and control of

prosthetics In medicine, a prosthesis (plural: prostheses; from grc, πρόσθεσις, prósthesis, addition, application, attachment), or a prosthetic implant, is an artificial device that replaces a missing body part, which may be lost through trau ...

. Since passive dynamics provides the mathematical models of efficient motion, it is an appropriate avenue to develop efficient limbs that require less energy for amputees. Andrew Hansen, Steven Gard and others have done extensive research in developing better foot prosthetics by utilizing passive dynamics. Passive walking biped robots exhibit different kinds of

chaotic Chaotic was originally a Danish trading card game. It expanded to an online game in America which then became a television program based on the game. The program was able to be seen on 4Kids TV (Fox affiliates, nationwide), Jetix, The CW4Kids ...

behaviors e.g.,

bifurcation Bifurcation or bifurcated may refer to: Science and technology * Bifurcation theory, the study of sudden changes in dynamical systems ** Bifurcation, of an incompressible flow, modeled by squeeze mapping the fluid flow * River bifurcation, the f ...

intermittency In dynamical systems, intermittency is the irregular alternation of phases of apparently periodic and chaotic dynamics ( Pomeau–Manneville dynamics), or different forms of chaotic dynamics (crisis-induced intermittency). Pomeau and Mannev ...

and

crisis A crisis ( : crises; : critical) is either any event or period that will (or might) lead to an unstable and dangerous situation affecting an individual, group, or all of society. Crises are negative changes in the human or environmental affair ...

References

Bibliography

* * * * and *{{cite journal , author=Chandana Paul , title = Morphology and Computation , journal = Proceedings of the International Conference on the Simulation of Adaptive Behaviour , year = 2004 , pages = 33–38

External links

Cornell Biorobotics and Locomotion Lab
— videos and papers on passive dynamic walkers, including McGeer's originals, the Cornell Efficient Walker, and the Cornell Ranger
Droid Logic
— simulations of passive dynamic walkers and runners created using

evolutionary robotics Evolutionary robotics is an embodied approach to Artificial Intelligence (AI) in which robots are automatically designed using Darwinian principles of natural selection. The design of a robot, or a subsystem of a robot such as a neural controller, ...